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  • 51. Li, Wei
    et al.
    Ciais, Philippe
    Peng, Shushi
    Yue, Chao
    Wang, Yilong
    Thurner, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Saatchi, Sassan S.
    Arneth, Almut
    Avitabile, Valerio
    Carvalhais, Nuno
    Harper, Anna B.
    Kato, Etsushi
    Koven, Charles
    Liu, Yi Y.
    Nabel, Julia E. M. S.
    Pan, Yude
    Pongratz, Julia
    Poulter, Benjamin
    Pugh, Thomas A. M.
    Santoro, Maurizio
    Sitch, Stephen
    Stocker, Benjamin D.
    Viovy, Nicolas
    Wiltshire, Andy
    Yousefpour, Rasoul
    Zaehle, Soenke
    Land-use and land-cover change carbon emissions between 1901 and 2012 constrained by biomass observations2017Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, nr 22, s. 5053-5067Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The use of dynamic global vegetation models (DGVMs) to estimate CO2 emissions from land-use and land-cover change (LULCC) offers a new window to account for spatial and temporal details of emissions and for ecosystem processes affected by LULCC. One drawback of LULCC emissions from DGVMs, however, is lack of observation constraint. Here, we propose a new method of using satellite-and inventory-based biomass observations to constrain historical cumulative LULCC emissions (E-LUC(c)) from an ensemble of nine DGVMs based on emerging relationships between simulated vegetation biomass and E-LUC(c). This method is applicable on the global and regional scale. The original DGVM estimates of E-LUC(c) range from 94 to 273 PgC during 1901-2012. After constraining by current biomass observations, we derive a best estimate of 155 +/- 50 PgC (1 sigma Gaussian error). The constrained LULCC emissions are higher than prior DGVM values in tropical regions but significantly lower in North America. Our emergent constraint approach independently verifies the median model estimate by biomass observations, giving support to the use of this estimate in carbon budget assessments. The uncertainty in the constrained Ec LUC is still relatively large because of the uncertainty in the biomass observations, and thus reduced uncertainty in addition to increased accuracy in biomass observations in the future will help improve the constraint. This constraint method can also be applied to evaluate the impact of land-based mitigation activities.

  • 52. Lidman, F.
    et al.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Laudon, H.
    Landscape control of uranium and thorium in boreal streams - spatiotemporal variability and the role of wetlands2012Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 9, nr 11, s. 4773-4785Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The concentrations of uranium and thorium in ten partly nested streams in the boreal forest region were monitored over a two-year period. The investigated catchments ranged from small headwaters (0.1 km(2)) up to a fourth-order stream (67 km(2)). Considerable spatiotemporal variations were observed, with little or no correlation between streams. The fluxes of both uranium and thorium varied substantially between the subcatchments, ranging from 1.7 to 30 g km(-2) a(-1) for uranium and from 3.2 to 24 g km(-2) a(-1) for thorium. Airborne gamma spectrometry was used to measure the concentrations of uranium and thorium in surface soils throughout the catchment, suggesting that the concentrations of uranium and thorium in mineral soils are similar throughout the catchment. The fluxes of uranium and thorium were compared to a wide range of parameters characterising the investigated catchments and the chemistry of the stream water, e. g. soil concentrations of these elements, pH, TOC (total organic carbon), Al, Si and hydrogen carbonate, but it was concluded that the spatial variabilities in the fluxes of both uranium and thorium mainly were controlled by wetlands. The results indicate that there is a predictable and systematic accumulation of both uranium and thorium in boreal wetlands that is large enough to control the transport of these elements. On the landscape scale approximately 65-80% of uranium and 55-65% of thorium entering a wetland were estimated to be retained in the peat. Overall, accumulation in mires and other types of wetlands was estimated to decrease the fluxes of uranium and thorium from the boreal forest landscape by 30-40%, indicating that wetlands play an important role for the biogeochemical cycling of uranium and thorium in the boreal forest landscape. The atmospheric deposition of uranium and thorium was also quantified, and its contribution to boreal streams was found to be low compared to weathering.

  • 53. Mahecha, Miguel D.
    et al.
    Gans, Fabian
    Sippel, Sebastian
    Donges, Jonathan F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre. Potsdam Institute for Climate Impact Research, Germany.
    Kaminski, Thomas
    Metzger, Stefan
    Migliavacca, Mirco
    Papale, Dario
    Rammig, Anja
    Zscheischler, Jakob
    Detecting impacts of extreme events with ecological in situ monitoring networks2017Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, nr 18, s. 4255-4277Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Extreme hydrometeorological conditions typically impact ecophysiological processes on land. Satellite-based observations of the terrestrial biosphere provide an important reference for detecting and describing the spatiotemporal development of such events. However, in-depth investigations of ecological processes during extreme events require additional in situ observations. The question is whether the density of existing ecological in situ networks is sufficient for analysing the impact of extreme events, and what are expected event detection rates of ecological in situ networks of a given size. To assess these issues, we build a baseline of extreme reductions in the fraction of absorbed photosynthetically active radiation (FAPAR), identified by a new event detection method tailored to identify extremes of regional relevance. We then investigate the event detection success rates of hypothetical networks of varying sizes. Our results show that large extremes can be reliably detected with relatively small networks, but also reveal a linear decay of detection probabilities towards smaller extreme events in log-log space. For instance, networks with approximate to 100 randomly placed sites in Europe yield a >= 90% chance of detecting the eight largest (typically very large) extreme events; but only a >= 50% chance of capturing the 39 largest events. These findings are consistent with probability-theoretic considerations, but the slopes of the decay rates deviate due to temporal autocorrelation and the exact implementation of the extreme event detection algorithm. Using the examples of AmeriFlux and NEON, we then investigate to what degree ecological in situ networks can capture extreme events of a given size. Consistent with our theoretical considerations, we find that today's systematically designed networks (i.e. NEON) reliably detect the largest extremes, but that the extreme event detection rates are not higher than would be achieved by randomly designed networks. Spatio-temporal expansions of ecological in situ monitoring networks should carefully consider the size distribution characteristics of extreme events if the aim is also to monitor the impacts of such events in the terrestrial biosphere.

  • 54. Miller, Clint M.
    et al.
    Dickens, Gerald R.
    Jakobsson, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Johansson, Carina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Koshurnikov, Andrey
    O'Regan, Matt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Muschitiello, Francesco
    Stranne, Christian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Pore water geochemistry along continental slopes north of the East Siberian Sea: inference of low methane concentrations2017Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, nr 12, s. 2929-2953Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Continental slopes north of the East Siberian Sea potentially hold large amounts of methane (CH4/in sediments as gas hydrate and free gas. Although release of this CH4 to the ocean and atmosphere has become a topic of discussion, the region remains sparingly explored. Here we present pore water chemistry results from 32 sediment cores taken during Leg 2 of the 2014 joint Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) expedition. The cores come from depth transects across the slope and rise extending between the Mendeleev and the Lomonosov ridges, north of Wrangel Island and the New Siberian Islands, respectively. Upward CH4 flux towards the seafloor, as inferred from profiles of dissolved sulfate (SO42-), alkalinity, and the delta C-13 of dissolved inorganic carbon (DIC), is negligible at all stations east of 143 degrees E longitude. In the upper 8m of these cores, downward SO42- flux never exceeds 6.2 mol m(-2) kyr(-1), the upward alkalinity flux never exceeds 6.8 mol m(-2) kyr(-1), and delta C-13 composition of DIC (delta C-13-DIC) only moderately decreases with depth (3.6% m 1 on average). Moreover, upon addition of Zn acetate to pore water samples, ZnS did not precipitate, indicating a lack of dissolved H2S. Phosphate, ammonium, and metal profiles reveal that metal oxide reduction by organic carbon dominates the geochemical environment and supports very low organic carbon turnover rates. A single core on the Lomonosov Ridge differs, as diffusive fluxes for SO42- and alkalinity were 13.9 and 11.3 mol m(-2) kyr(-1), respectively, the delta C-13-DIC gradient was 5.6% m(-1), and Mn2+ reduction terminated within 1.3 m of the seafloor. These are among the first pore water results generated from this vast climatically sensitive region, and they imply that abundant CH4, including gas hydrates, do not characterize the East Siberian Sea slope or rise along the investigated depth transects. This contradicts previous modeling and discussions, which due to the lack of data are almost entirely based on assumption.

  • 55. Ohlendieck, U.
    et al.
    Gundersen, K.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    Meyerhoefer, M.
    Fritsche, P.
    Nachtigall, K.
    Bergmann, B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Botaniska institutionen.
    The significance of nitrogen fixation to new production during early summer in the Baltic Sea2007Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 4, nr 1, s. 63-73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rates of dinitrogen (N-2) fixation and primary production were measured during two 9 day transect cruises in the Baltic proper in June-July of 1998 and 1999. Assuming that the early phase of the bloom of cyanobacteria lasted a month, total rates of N-2 fixation contributed 15 mmol N m(-2) (1998) and 33 mmol N m(-2) (1999) to new production (sensu Dugdale and Goering, 1967). This constitutes 12-26% more new N than other annual estimates (mid July-mid October) from the same region. The between-station variability observed in both total N-2 fixation and primary productivity greatly emphasizes the need for multiple stations and seasonal sampling strategies in biogeochemical studies of the Baltic Sea. The majority of new N from N-2 fixation was contributed by filamentous cyanobacteria. On average, cyanobacterial cells > 20 mu m were able to supply a major part of their N requirements for growth by N-2 fixation in both 1998 (73%) and 1999 (81%). The between-station variability was high however, and ranged from 28-150% of N needed to meet the rate of C incorporation by primary production. The molar C: N rate incorporation ratio (C:N-RATE) in filamentous cyanobacterial cells was variable (range 7-28) and the average almost twice as high as the Redfield ratio (6.6) in both years. Since the molar C: N mass ratio (C:N-MASS) in filamentous cyanobacterial cells was generally lower than C: NRATE at a number of stations, we suggest that the diazotrophs incorporated excess C on a short term basis (carbohydrate ballasting and buoyancy regulation), released nitrogen or utilized other regenerated sources of N nutrients. Measured rates of total N-2 fixation contributed only a minor fraction of 13% (range 4-24) in 1998 and 18% (range 2-45) in 1999 to the amount of N needed for the community primary production. An average of 9 and 15% of total N-2 fixation was found in cells < 5 mu m. Since cells < 5 mu m did not show any detectable rates of N-2 fixation, the N-15-enrichment could be attributed to regenerated incorporation of dissolved organic N (DON) and ammonium generated from larger diazotroph cyanobacteria. Therefore, N excretion from filamentous cyanobacteria may significantly contribute to the pool of regenerated nutrients used by the non-diazotroph community in summer. Higher average concentrations of regenerated N (ammonium) coincided with higher rates of N-2 fixation found during the 1999 transect and a higher level of N-15-enrichment in cells < 5 mu m. A variable but significant fraction of total N-2 fixation (1-10%) could be attributed to diazotrophy in cells between 5-20 mu m.

  • 56. Petrescu, A. M. R.
    et al.
    van Huissteden, J.
    Jackowicz-Korczynski, M.
    Yurova, A.
    Christensen, T. R.
    Crill, Patric M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Bäckstrand, Kristina
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Maximov, T. C.
    Modelling CH4 emissions from arctic wetlands: effects of hydrological parameterization2008Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 5, nr 1, s. 111-121Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study compares the CH4 fluxes from two arctic wetland sites of different annual temperatures during 2004 to 2006. The PEATLAND-VU model was used to simulate the emissions. The CH4 module of PEATLAND-VU is based on the Walter-Heimann model. The first site is located in northeast Siberia, Indigirka lowlands, Kytalyk reserve (70 degrees N, 147 degrees E) in a continuous permafrost region with mean annual temperatures of -14.3 degrees C. The other site is Stordalen mire in the eastern part of Lake Tornetrask (68 degrees N, 19 degrees E) ten kilometres east of Abisko, northern Sweden. It is located in a discontinuous permafrost region. Stordalen has a sub arctic climate with a mean annual temperature of -0.7 degrees C. Model input consisted of observed temperature, precipitation and snow cover data. In all cases, modelled CH4 emissions show a direct correlation between variations in water table and soil temperature variations. The differences in CH4 emissions between the two sites are caused by different climate, hydrology, soil physical properties, vegetation type and NPP. For Kytalyk the simulated CH4 fluxes show similar trends during the growing season, having average values for 2004 to 2006 between 1.29-2.09 mg CH4 m(-2) hr(-1). At Stordalen the simulated fluxes show a slightly lower average value for the same years (3.52 mg CH4 m(-2) hr(-1)) than the observed 4.7 mg CH4 m(-2) hr(-1). The effect of the longer growing season at Stordalen is simulated correctly. Our study shows that modelling of arctic CH4 fluxes is improved by adding a relatively simple hydrological model that simulates the water table position from generic weather data. Our results support the generalization in literature that CH4 fluxes in northern wetland are regulated more tightly by water table than temperature. Furthermore, parameter uncertainty at site level in wetland CH4 process models is an important factor in large scale modelling of CH4 fluxes.

  • 57. Pirk, Norbert
    et al.
    Mastepanov, Mikhail
    Parmentier, Frans-Jan W.
    Lund, Magnus
    Crill, Patrick
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Christensen, Torben R.
    Calculations of automatic chamber flux measurements of methane and carbon dioxide using short time series of concentrations2016Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, nr 4, s. 903-912Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The closed chamber technique is widely used to measure the exchange of methane (CH4) and carbon dioxide (CO2) from terrestrial ecosystems. There is, however, large uncertainty about which model should be used to calculate the gas flux from the measured gas concentrations. Due to experimental uncertainties the simple linear regression model (first-order polynomial) is often applied, even though theoretical considerations of the technique suggest the application of other, curvilinear models. High-resolution automatic chamber systems which sample gas concentrations several hundred times per flux measurement make it possible to resolve the curvilinear behavior and study the information imposed by the natural variability of the temporal concentration changes. We used more than 50 000 such flux measurements of CH4 and CO2 from five field sites located in peat-forming wetlands ranging from 56 to 78 degrees N to quantify the typical differences between flux estimates of different models. In addition, we aimed to assess the curvilinearity of the concentration time series and test the general applicability of curvilinear models. Despite significant episodic differences between the calculated flux estimates, the overall differences are generally found to be smaller than the local flux variability on the plot scale. The curvilinear behavior of the gas concentrations within the chamber is strongly influenced by wind-driven chamber leakage, and less so by changing gas concentration gradients in the soil during chamber closure. Such physical processes affect both gas species equally, which makes it possible to isolate biochemical processes affecting the gases differently, such as photosynthesis limitation by chamber headspace CO2 concentrations under high levels of incoming solar radiation. We assess the possibility to exploit this effect for a partitioning of the net CO2 flux into photosynthesis and ecosystem respiration as an example of how high-resolution automatic chamber measurements could be used for purposes beyond the estimation of the net gas flux. This shows that while linear and curvilinear calculation schemes can provide similar net fluxes, only curvilinear models open additional possibilities for high-resolution automatic chamber measurements.

  • 58.
    Porada, Philipp
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Pöschl, Ulrich
    Kleidon, Axel
    Beer, Christian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Weber, Bettina
    Estimating global nitrous oxide emissions by lichens and bryophytes with a process-based productivity model2017Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, nr 6, s. 1593-1602Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nitrous oxide is a strong greenhouse gas and atmospheric ozone-depleting agent which is largely emitted by soils. Recently, lichens and bryophytes have also been shown to release significant amounts of nitrous oxide. This finding relies on ecosystem-scale estimates of net primary productivity of lichens and bryophytes, which are converted to nitrous oxide emissions by empirical relationships between productivity and respiration, as well as between respiration and nitrous oxide release. Here we obtain an alternative estimate of nitrous oxide emissions which is based on a global process-based non-vascular vegetation model of lichens and bryophytes. The model quantifies photosynthesis and respiration of lichens and bryophytes directly as a function of environmental conditions, such as light and temperature. Nitrous oxide emissions are then derived from simulated respiration assuming a fixed relationship between the two fluxes. This approach yields a global estimate of 0.27 (0.19-0.35) (TgN(2)O) year(-1) released by lichens and bryophytes. This is lower than previous estimates but corresponds to about 50% of the atmospheric deposition of nitrous oxide into the oceans or 25% of the atmospheric deposition on land. Uncertainty in our simulated estimate results from large variation in emission rates due to both physiological differences between species and spatial heterogeneity of climatic conditions. To constrain our predictions, combined online gas exchange measurements of respiration and nitrous oxide emissions may be helpful.

  • 59. Rammig, A.
    et al.
    Wiedermann, M.
    Donges, Jonathan F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre. Potsdam Institute for Climate Impact Research, Germany.
    Babst, F.
    von Bloh, W.
    Frank, D.
    Thonicke, K.
    Mahecha, M. D.
    Coincidences of climate extremes and anomalous vegetation responses: comparing tree ring patterns to simulated productivity2015Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, nr 2, s. 373-385Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate extremes can trigger exceptional responses in terrestrial ecosystems, for instance by altering growth or mortality rates. Such effects are often manifested in reductions in net primary productivity (NPP). Investigating a Europe-wide network of annual radial tree growth records confirms this pattern: we find that 28% of tree ring width (TRW) indices are below two standard deviations in years in which extremely low precipitation, high temperatures or the combination of both noticeably affect tree growth. Based on these findings, we investigate possibilities for detecting climate-driven patterns in long-term TRW data to evaluate state-of-the-art dynamic vegetation models such as the Lund-Potsdam-Jena dynamic global vegetation model for managed land (LPJmL). The major problem in this context is that LPJmL simulates NPP but not explicitly the radial tree growth, and we need to develop a generic method to allow for a comparison between simulated and observed response patterns. We propose an analysis scheme that quantifies the coincidence rate of climate extremes with some biotic responses (here TRW or simulated NPP). We find a relative reduction of 34% in simulated NPP during precipitation, temperature and combined extremes. This reduction is comparable to the TRW response patterns, but the model responds much more sensitively to drought stress. We identify 10 extreme years during the 20th century during which both model and measurements indicate high coincidence rates across Europe. However, we detect substantial regional differences in simulated and observed responses to climatic extreme events. One explanation for this discrepancy could be the tendency of tree ring data to originate from climatically stressed sites. The difference between model and observed data is amplified by the fact that dynamic vegetation models are designed to simulate mean ecosystem responses on landscape or regional scales. We find that both simulation results and measurements display carry-over effects from climate anomalies during the previous year. We conclude that radial tree growth chronologies provide a suitable basis for generic model benchmarks. The broad application of coincidence analysis in generic model benchmarks along with an increased availability of representative long-term measurements and improved process-based models will refine projections of the long-term carbon balance in terrestrial ecosystems.

  • 60.
    Salvadó, Joan A.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Tesi, Tommaso
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi. CNR-National Research Council of Italy, ISMAR-Marine Sciences Institute, Italy..
    Sundbom, Marcus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Karlsson, Emma
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Kruså, Martin
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Semiletov, Igor P.
    Panova, Elena
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Contrasting composition of terrigenous organic matter in the dissolved, particulate and sedimentary organic carbon pools on the outer East Siberian Arctic Shelf2016Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, nr 22, s. 6121-6138Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fluvial discharge and coastal erosion of the permafrost-dominated East Siberian Arctic delivers large quantities of terrigenous organic carbon (Terr-OC) to marine waters. The composition and fate of the remobilized Terr-OC needs to be better constrained as it impacts the potential for a climate-carbon feedback. In the present study, the bulk isotope (delta C-13 and Delta C-14) and macromolecular (lignin-derived phenols) composition of the cross-shelf exported organic carbon (OC) in different marine pools is evaluated. For this purpose, as part of the SWERUS-C3 expedition (July-September 2014), sediment organic carbon (SOC) as well as water column (from surface and near-bottom seawater) dissolved organic carbon (DOC) and particulate organic carbon (POC) samples were collected along the outer shelves of the Kara Sea, Laptev Sea and East Siberian Sea. The results show that the Lena River and the DOC may have a preferential role in the transport of Terr-OC to the outer shelf. DOC concentrations (740-3600 mu g L-1) were 1 order of magnitude higher than POC (20-360 mu g L-1), with higher concentrations towards the Lena River plume. The delta C-13 signatures in the three carbon pools varied from -23.9 +/- 1.9 parts per thousand in the SOC, 26.1 +/- 1.2 parts per thousand in the DOC and 27.1 +/- 1.9 parts per thousand in the POC. The Delta C-14 values ranged between 395 +/- 83 (SOC), 226 +/- 92 (DOC) and 113 +/- 122 parts per thousand(POC). These stable and radiocarbon isotopes were also different between the Laptev Sea and the East Siberian Sea. Both DOC and POC showed a depleted and younger trend off the Lena River plume. Further, the Pacific inflow and the sea-ice coverage, which works as a barrier preventing the input of young DOC and POC, seem to have a strong influence in these carbon pools, presenting older and more enriched delta C-13 signatures under the sea-ice extent. Lignin phenols exhibited higher OC-normalized concentrations in the SOC (0.10-2.34 mg g(-1) OC) and DOC (0.08-2.40 mg g(-1) OC) than in the POC (0.03-1.14 mg g(-1) OC). The good relationship between lignin and Delta C-14 signatures in the DOC suggests that a significant fraction of the outer-shelf DOC comes from young Terr-OC. By contrast, the slightly negative correlation between lignin phenols and Delta C-14 signatures in POC, with higher lignin concentrations in older POC from near-bottom waters, may reflect the off-shelf transport of OC from remobilized permafrost in the nepheloid layer. Syringyl/vanillyl and cinnamyl/vannillyl phenol ratios presented distinct clustering between DOC, POC and SOC, implying that those pools may be carrying different Terr-OC of partially different origin. Moreover, 3,5-dihydroxybenzoic acid to vanillyl phenol ratios and p-coumaric acid to ferulic acid ratios, used as a diagenetic indicators, enhanced in POC and SOC, suggesting more degradation within these pools. Overall, the key contrast between enhanced lignin yields both in the youngest DOC and the oldest POC samples reflects a significant decoupling of terrestrial OC sources and pathways.

  • 61. Sapart, Célia J.
    et al.
    Shakhova, Natalia
    Semiletov, Igor
    Jansen, Joachim
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Utrecht University, the Netherlands.
    Szidat, Sönke
    Kosmach, Denis
    Dudarev, Oleg
    van der Veen, Carina
    Egger, Matthias
    Sergienko, Valentine
    Salyuk, Anatoly
    Tumskoy, Vladimir
    Tison, Jean-Louis
    Röckmann, Thomas
    The origin of methane in the East Siberian Arctic Shelf unraveled with triple isotope analysis2017Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, nr 9, s. 2283-2292Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Arctic Ocean, especially the East Siberian Arctic Shelf (ESAS), has been proposed as a significant source of methane that might play an increasingly important role in the future. However, the underlying processes of formation, removal and transport associated with such emissions are to date strongly debated. CH4 concentration and triple isotope composition were analyzed on gas extracted from sediment and water sampled at numerous locations on the shallow ESAS from 2007 to 2013. We find high concentrations (up to 500 µM) of CH4 in the pore water of the partially thawed subsea permafrost of this region. For all sediment cores, both hydrogen and carbon isotope data reveal the predominant occurrence of CH4 that is not of thermogenic origin as it has long been thought, but resultant from microbial CH4 formation. At some locations, meltwater from buried meteoric ice and/or old organic matter preserved in the subsea permafrost were used as sub-strates. Radiocarbon data demonstrate that the CH4 present in the ESAS sediment is of Pleistocene age or older, but a small contribution of highly C-14-enriched CH4, from unknown origin, prohibits precise age determination for one sediment core and in the water column. Our sediment data suggest that at locations where bubble plumes have been observed, CH4 can escape anaerobic oxidation in the surface sediment.

  • 62.
    Sawicka, Joanna E.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Jorgensen, B. B.
    Bruchert, Volker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Temperature characteristics of bacterial sulfate reduction in continental shelf and slope sediments2012Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 9, nr 8, s. 3425-3435Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The temperature responses of sulfate-reducing microbial communities were used as community temperature characteristics for their in situ temperature adaptation, their origin, and dispersal in the deep sea. Sediments were collected from a suite of coastal, continental shelf, and slope sediments from the southwest and southeast Atlantic and permanently cold Arctic fjords from water depths ranging from the intertidal zone to 4327 m. In situ temperatures ranged from 8 A degrees C on the shelf to -1 A degrees C in the Arctic. Temperature characteristics of the active sulfate-reducing community were determined in short-term incubations with S-35-sulfate in a temperature gradient block spanning a temperature range from 0 to 40 A degrees C. An optimum temperature (T-opt) between 27 A degrees C and 30 A degrees C for the South Atlantic shelf sediments and for the intertidal flat sediment from Svalbard was indicative of a psychrotolerant/mesophilic sulfate-reducing community, whereas T-opt < 20 A degrees C in South Atlantic slope and Arctic shelf sediments suggested a predominantly psychrophilic community. High sulfate reduction rates (20-50%) at in situ temperatures compared to those at T-opt further support this interpretation and point to the importance of the ambient temperature regime for regulating the short-term temperature response of sulfate-reducing communities. A number of cold (< 4 A degrees C) continental slope sediments showed broad temperature optima reaching as high as 30 A degrees C, suggesting the additional presence of apparently mesophilic sulfate-reducing bacteria. Since the temperature characteristics of these mesophiles do not fit with the permanently cold deep-sea environment, we suggest that these mesophilic microorganisms are of allochthonous origin and transported to this site. It is likely that they were deposited along with the mass-flow movement of warmer shelf-derived sediment. These data therefore suggest that temperature response profiles of bacterial carbon mineralization processes can be used as community temperature characteristics, and that mixing of bacterial communities originating from diverse locations carrying different temperature characteristics needs to be taken into account to explain temperature response profiles of bacterial carbon mineralization processes in sediments.

  • 63.
    Sawicka, Joanna E.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Brüchert, Volker
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Annual variability and regulation of methane and sulfate fluxes in Baltic Sea estuarine sediments2017Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, nr 2, s. 325-339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Marine methane emissions originate largely from near-shore coastal systems, but emission estimates are often not based on temporally well-resolved data or sufficient understanding of the variability of methane consumption and production processes in the underlying sediment. The objectives of our investigation were to explore the effects of seasonal temperature, changes in benthic oxygen concentration, and historical eutrophication on sediment methane concentrations and benthic fluxes at two type localities for open-water coastal versus eutrophic, estuarine sediment in the Baltic Sea. Benthic fluxes of methane and oxygen and sediment pore-water concentrations of dissolved sulfate, methane, and S-35-sulfate reduction rates were obtained over a 12-month period from April 2012 to April 2013. Benthic methane fluxes varied by factors of 5 and 12 at the offshore coastal site and the eutrophic estuarine station, respectively, ranging from 0.1 mmol m(-2) d(-1) in winter at an open coastal site to 2.6 mmol m(-2) d(-1) in late summer in the inner eutrophic estuary. Total oxygen uptake (TOU) and S-35-sulfate reduction rates (SRRs) correlated with methane fluxes showing low rates in the winter and high rates in the summer. The highest pore-water methane concentrations also varied by factors of 6 and 10 over the sampling period with the lowest values in the winter and highest values in late summerearly autumn. The highest pore-water methane concentrations were 5.7 mM a few centimeters below the sediment surface, but they never exceeded the in situ saturation concentration. Of the total sulfate reduction, 21-24% was coupled to anaerobic methane oxidation, lowering methane concentrations below the sediment surface far below the saturation concentration. The data imply that bubble emission likely plays no or only a minor role in methane emissions in these sediments. The changes in pore-water methane concentrations over the observation period were too large to be explained by temporal changes in methane formation and methane oxidation rates due to temperature alone. Additional factors such as regional and local hydrostatic pressure changes and coastal submarine groundwater flow may also affect the vertical and lateral transport of methane.

  • 64. Schneider-Zapp, K.
    et al.
    Salter, Matt E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Mann, P. J.
    Upstill-Goddard, R. C.
    Technical Note: Comparison of storage strategies of sea surface microlayer samples2013Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 10, nr 7, s. 4927-4936Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The sea surface microlayer (SML) is an important biogeochemical system whose physico-chemical analysis often necessitates some degree of sample storage. However, many SML components degrade with time so the development of optimal storage protocols is paramount. We here briefly review some commonly used treatment and storage protocols. Using freshwater and saline SML samples from a river estuary, we investigated temporal changes in surfactant activity (SA) and the absorbance and fluorescence of chromophoric dissolved organic matter (CDOM) over four weeks, following selected sample treatment and storage protocols. Some variability in the effectiveness of individual protocols most likely reflects sample provenance. None of the various protocols examined performed any better than dark storage at 4 degrees C without pre-treatment. We therefore recommend storing samples refrigerated in the dark.

  • 65. Semiletov, I. P.
    et al.
    Pipko, I. I.
    Shakhova, N. E.
    Dudarev, O. V.
    Pugach, S. P.
    Charkin, A. N.
    McRoy, C. P.
    Kosmach, D.
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Carbon transport by the Lena River from its headwaters to the Arctic Ocean, with emphasis on fluvial input of terrestrial particulate organic carbon vs. carbon transport by coastal erosion2011Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, nr 9, s. 2407-2426Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Lena River integrates biogeochemical signals from its vast drainage basin, and the integrated signal reaches far out over the Arctic Ocean. Transformation of riverine organic carbon (OC) into mineral carbon, and mineral carbon into the organic form in the Lena River watershed, can be considered to be quasi-steady-state processes. An increase in Lena discharge exerts opposite effects on total organic (TOC) and total inorganic (TCO(2)) carbon: TOC concentration increases, while TCO(2) concentration decreases. Significant inter-annual variability in mean values of TCO(2), TOC, and their sum (total carbon, TC) has been found. This variability is determined by changes in land hydrology which cause differences in the Lena River discharge. There is a negative correlation in the Lena River between TC in September and its mean discharge in August; a time shift of about one month is required for water to travel from Yakutsk to the Laptev Sea. Total carbon entering the sea with the Lena discharge is estimated to be almost 10 Tg C yr(-1). The annual Lena River discharge of particulate organic carbon (POC) can be as high as 0.38 Tg (moderate to high estimate). If we instead accept Lisytsin's (1994) statement that 85-95% of total particulate matter (PM) (and POC) precipitates on the marginal filter, then only about 0.03-0.04 Tg of Lena River POC reaches the Laptev Sea. The Lena's POC export would then be two orders of magnitude less than the annual input of eroded terrestrial carbon onto the shelf of the Laptev and East Siberian seas, which is estimated to be about 4 Tg. Observations support the hypothesis of a dominant role for coastal erosion (Semiletov, 1999a, b) in East Siberian Arctic Shelf (ESAS) sedimentation and the dynamics of the carbon/carbonate system. The Lena River is characterized by relatively high concentrations of the primary greenhouse gases, dissolved carbon dioxide (CO(2)) and methane (CH(4)). During all seasons the river is supersaturated in CO(2) compared to the atmosphere, by up to 1.5-2 fold in summer, and 4-5 fold in winter. This results in a significant CO(2) supersaturation in the adjacent coastal sea. Localized areas of dissolved CH(4) along the Lena River and in the Lena delta channels may reach 100 nM, but the CH(4) concentration decreases to 5-20nM towards the sea, which suggests that riverborne export of CH(4) plays but a minor role in determining the ESAS CH(4) budget in coastal waters. Instead, the seabed appears to be the source that provides most of the CH(4) to the Arctic Ocean.

  • 66. Siegmund, Jonatan F.
    et al.
    Wiedermann, Marc
    Donges, Jonathan F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholm Resilience Centre. Potsdam Institute for Climate Impact Research, Germany.
    Donner, Reik V.
    Impact of temperature and precipitation extremes on the flowering dates of four German wildlife shrub species2016Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, nr 19, s. 5541-5555Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ongoing climate change is known to cause an increase in the frequency and amplitude of local temperature and precipitation extremes in many regions of the Earth. While gradual changes in the climatological conditions have already been shown to strongly influence plant flowering dates, the question arises if and how extremes specifically impact the timing of this important phenological phase. Studying this question calls for the application of statistical methods that are tailored to the specific properties of event time series. Here, we employ event coincidence analysis, a novel statistical tool that allows assessing whether or not two types of events exhibit similar sequences of occurrences in order to systematically quantify simultaneities between meteorological extremes and the timing of the flowering of four shrub species across Germany. Our study confirms previous findings of experimental studies by highlighting the impact of early spring temperatures on the flowering of the investigated plants. However, previous studies solely based on correlation analysis do not allow deriving explicit estimates of the strength of such interdependencies without further assumptions, a gap that is closed by our analysis. In addition to direct impacts of extremely warm and cold spring temperatures, our analysis reveals statistically significant indications of an influence of temperature extremes in the autumn preceding the flowering.

  • 67.
    Siewert, Matthias B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för naturgeografi. Umeå University, Sweden.
    High-resolution digital mapping of soil organic carbon in permafrost terrain using machine learning: a case study in a sub-Arctic peatland environment2018Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, nr 6, s. 1663-1682Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Soil organic carbon (SOC) stored in northern peatlands and permafrost-affected soils are key components in the global carbon cycle. This article quantifies SOC stocks in a sub-Arctic mountainous peatland environment in the discontinuous permafrost zone in Abisko, northern Sweden. Four machine-learning techniques are evaluated for SOC quantification: multiple linear regression, artificial neural networks, support vector machine and random forest. The random forest model performed best and was used to predict SOC for several depth increments at a spatial resolution of 1 m (1 x 1 m). A high-resolution (1 m) land cover classification generated for this study is the most relevant predictive variable. The landscape mean SOC storage (0-150 cm) is estimated to be 8.3 +/- 8.0 kg C m(-2) and the SOC stored in the top meter (0-100 cm) to be 7.7 +/- 6.2 kg C m(-2). The predictive modeling highlights the relative importance of wetland areas and in particular peat plateaus for the landscape's SOC storage. The total SOC was also predicted at reduced spatial resolutions of 2, 10, 30, 100, 250 and 1000 m and shows a significant drop in land cover class detail and a tendency to underestimate the SOC at resolutions > 30 m. This is associated with the occurrence of many small-scale wetlands forming local hot-spots of SOC storage that are omitted at coarse resolutions. Sharp transitions in SOC storage associated with land cover and permafrost distribution are the most challenging methodological aspect. However, in this study, at local, regional and circum-Arctic scales, the main factor limiting robust SOC mapping efforts is the scarcity of soil pedon data from across the entire environmental space. For the Abisko region, past SOC and permafrost dynamics indicate that most of the SOC is barely 2000 years old and very dynamic. Future research needs to investigate the geomorphic response of permafrost degradation and the fate of SOC across all landscape compartments in post-permafrost landscapes.

  • 68. Sparkes, R. B.
    et al.
    Selver, A. Dogrul
    Bischoff, J.
    Talbot, H. M.
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Semiletov, I. P.
    Dudarev, O. V.
    van Dongen, B. E.
    GDGT distributions on the East Siberian Arctic Shelf: implications for organic carbon export, burial and degradation2015Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 12, nr 12, s. 3753-3768Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Siberian permafrost contains a globally significant pool of organic carbon (OC) that is vulnerable to enhanced warming and subsequent release into the contemporary carbon cycle. OC release by both fluvial and coastal erosion has been reported in the region, but the behaviour of this material in the Arctic Ocean is insufficiently understood. The balance between OC deposition and degradation on the East Siberian Arctic Shelf (ESAS) influences the climate-carbon cycle feedback in this area. In this study we couple measurements of glycerol dialkyl glycerol tetraethers (GDGTs) with bulk geochemical observations to improve knowledge of the sources of OC to the ESAS, the behaviour of specific biomarkers on the shelf and the balance between delivery and removal of different carbon pools. Branched GDGT (brGDGT) concentrations were highest close to river mouths, yet low in 'ice complex' permafrost deposits, supporting recent observations that brGDGTs are mostly delivered by fluvial erosion, and may be a tracer for this in complex sedimentary environments. BrGDGT concentrations and the branched and isoprenoidal tetraether (BIT) index reduced quickly offshore, demonstrating a rapid reduction in river influence. Stable carbon isotope ratios changed at a different rate to the BIT index, suggesting not only that OC on the shelf is sourced from fluvial erosion but also that erosion of coastal sediments delivers substantial quantities of OC to the Arctic Ocean. A model of OC export from fluvial, coastal and marine sources is able to recreate the biomarker and bulk observations and provide estimates for the influence of fluvial and coastal OC across the whole shelf. The model shows that coastal erosion delivers 43 % of the OC and 87 % of the mineral sediment to the ESAS, but that rivers deliver 72 % of brGDGTs, indicating that brGDGTs can be used as a proxy for river-derived sediment.

  • 69. Spungin, Dina
    et al.
    Belkin, Natalia
    Foster, Rachel A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Stenegren, Marcus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Caputo, Andrea
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Pujo-Pay, Mireille
    Leblond, Nathalie
    Dupouy, Cecile
    Bonnet, Sophie
    Berman-Frank, Ilana
    Programmed cell death in diazotrophs and the fate of organic matter in the western tropical South Pacific Ocean during the OUTPACE cruise2018Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, nr 12, s. 3893-3908Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fate of diazotroph (N-2 fixers) derived carbon (C) and nitrogen (N) and their contribution to vertical export of C and N in the western tropical South Pacific Ocean was studied during OUTPACE (Oligotrophy to UlTra-oligotrophy PACific Experiment). Our specific objective during OUTPACE was to determine whether autocatalytic programmed cell death (PCD), occurring in some diazotrophs, is an important mechanism affecting diazotroph mortality and a factor regulating the vertical flux of organic matter and, thus, the fate of the blooms. We sampled at three long duration (LD) stations of 5 days each (LDA, LDB and LDC) where drifting sediment traps were deployed at 150, 325 and 500m depth. LDA and LDB were characterized by high chlorophyll a (Chl a) concentrations (0.2-0.6 mu g L-1) and dominated by dense biomass of the filamentous cyanobacterium Trichodesmium as well as UCYN-B and diatom-diazotroph associations (Rhizosolenia with Richelia-detected by microscopy and het-1 nifH copies). Station LDC was located at an ultra-oligotrophic area of the South Pacific gyre with extremely low Chl a concentration (similar to 0.02 mu g L-1) with limited biomass of diazotrophs predominantly the unicellular UCYN-B. Our measurements of biomass from LDA and LDB yielded high activities of caspase-like and metacaspase proteases that are indicative of PCD in Trichodesmium and other phytoplankton. Metacaspase activity, reported here for the first time from oceanic populations, was highest at the surface of both LDA and LDB, where we also obtained high concentrations of transparent exopolymeric particles (TEP). TEP were negatively correlated with dissolved inorganic phosphorus and positively coupled to both the dissolved and particulate organic carbon pools. Our results reflect the increase in TEP production under nutrient stress and its role as a source of sticky carbon facilitating aggregation and rapid vertical sinking. Evidence for bloom decline was observed at both LDA and LDB. However, the physiological status and rates of decline of the blooms differed between the stations, influencing the amount of accumulated diazotrophic organic matter and mass flux observed in the traps during our experimental time frame. At LDA sediment traps contained the greatest export of particulate matter and significant numbers of both intact and decaying Trichodesmium, UCYN-B and het-1 compared to LDB where the bloom decline began only 2 days prior to leaving the station and to LDC where no evidence for bloom or bloom decline was seen. Substantiating previous findings from laboratory cultures linking PCD to carbon export in Trichodesmium, our results from OUTPACE indicate that nutrient limitation may induce PCD in high biomass blooms such as displayed by Trichodesmium or diatom-diazotroph associations. Furthermore, PCD combined with high TEP production will tend to facilitate cellular aggregation and bloom termination and will expedite vertical flux to depth.

  • 70.
    Stenegren, Marcus
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Caputo, Andrea
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Berg, Carlo
    Bonnet, Sophie
    Foster, Rachel A.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Distribution and drivers of symbiotic and free-living diazotrophic cyanobacteria in the western tropical South Pacific2018Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, nr 5, s. 1559-1578Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The abundance and distribution of cyanobacterial diazotrophs were quantified in two regions (Melanesian archipelago, MA; and subtropical gyre, SG) of the western tropical South Pacific using nifH quantitative polymerase chain reaction (qPCR) assays. UCYN-A1 and A2 host populations were quantified using 18S rRNA qPCR assays including one newly developed assay. All phylotypes were detected in the upper photic zone (0-50 m), with higher abundances in the MA region. Trichodesmium and UCYN-B dominated and ranged from 2.18 x 10(2) to 9.41 x 10(6) and 1.10 x 10(2) to 2.78 x 10(6) nifH copies L-1, respectively. Het-1 (symbiont of Rhizosolenia diatoms) was the next most abundant (1.40 x 10(1)-1.74 x 10(5) nifH copies L-1) and co-occurred with het-2 and het-3. UCYN-A1 and A2 were the least abundant diazotrophs and were below detection (bd) in 63 and 79, respectively, of 120 samples. In addition, in up to 39% of samples in which UCYN-A1 and A2 were detected, their respective hosts were bd. Pairwise comparisons of the nifH abundances and various environmental parameters supported two groups: a deep-dwelling group (45 m) comprised of UCYN-A1 and A2 and a surface group (0-15 m) comprised of Trichodesmium, het-1 and het-2. Temperature and photosynthetically active radiation were positively correlated with the surface group, while UCYN-A1 and A2 were positively correlated with depth, salinity, and oxygen. Similarly, in a meta-analysis of 11 external datasets, all diazotrophs, except UCYN-A were correlated with temperature. Combined, our results indicate that conditions favoring the UCYN-A symbiosis differ from those of diatom diazotroph associations and free-living cyanobacterial diazotrophs.

  • 71.
    Sun, Xiaole
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Andersson, Per
    Naturhistoriska riksmuseet, Laboratoriet för isotopgeologi.
    Humborg, Christoph
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM). Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute.
    Gustafsson, Bo
    Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute.
    Conley, Daniel J.
    Lunds universitet.
    Crill, Patrick
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Mörth, Carl-Magnus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper. Stockholms universitet, Stockholm Resilience Centre, Baltic Nest Institute.
    Climate Dependent Diatom Production is Preserved in Biogenic Si Isotope Signatures2011Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 8, nr 11, s. 3491-3499Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The aim of this study was to reconstruct diatom production in the subarctic northern tip of the Baltic Sea, Bothnian Bay, based on down-core analysis of Si isotopes in biogenic silica (BSi). Dating of the sediment showed that the samples covered the period 1820 to 2000. The sediment core record can be divided into two periods, an unperturbed period from 1820 to 1950 and a second period affected by human activities (from 1950 to 2000). This has been observed elsewhere in the Baltic Sea. The shift in the sediment core record after 1950 is likely caused by large scale damming of rivers. Diatom production was inferred from the Si isotope composition which ranged between δ30Si −0.18‰ and +0.58‰ in BSi, and assuming fractionation patterns due to the Raleigh distillation, the production was shown to be correlated with air and water temperature, which in turn were correlated with the mixed layer (ML) depth. The sedimentary record showed that the deeper ML depth observed in colder years resulted in less production of diatoms. Pelagic investigations in the 1990's have clearly shown that diatom production in the Baltic Sea is controlled by the ML depth. Especially after cold winters and deep water mixing, diatom production was limited and dissolved silicate (DSi) concentrations were not depleted in the water column after the spring bloom. Our method corroborates these findings and offers a new method to estimate diatom production over much longer periods of time in diatom dominated aquatic systems, i.e. a large part of the world's ocean and coastal seas.

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  • 72. Sundqvist, E.
    et al.
    Vestin, P.
    Crill, Patrick
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Persson, T.
    Lindroth, A.
    Short-term effects of thinning, clear-cutting and stump harvesting on methane exchange in a boreal forest2014Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, nr 21, s. 6095-6105Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Forest management practices can alter soil conditions, affecting the consumption and production processes that control soil methane (CH4) exchange. We studied the short-term effects of thinning, clear-cutting and stump harvesting on the CH4 exchange between soil and atmosphere at a boreal forest site in central Sweden, using an undisturbed plot as the control. Chambers in combination with a high-precision laser gas analyser were used for continuous measurements. Both the undisturbed plot and the thinned plot were net sinks of CH4, whereas the clear-cut plot and the stump harvested plot were net CH4 sources. The CH4 uptake at the thinned plot was reduced in comparison to the undisturbed plot. The shift from sink to source at the clear-cut and stump harvested plots was probably due to a rise in the water table and an increase in soil moisture, leading to lower gas diffusivity and more reduced conditions, which favour CH4 production by archea. Reduced evapotranspiration after harvesting leads to wetter soils, decreased CH4 consumption and increased CH4 production, and should be accounted for in the CH4 budget of managed forests.

  • 73. Upstill-Goddard, Robert C.
    et al.
    Salter, Matthew E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi.
    Mann, Paul J.
    Barnes, Jonathan
    Poulsen, John
    Dinga, Bienvenu
    Fiske, Gregory J.
    Holmes, Robert M.
    The riverine source of CH4 and N2O from the Republic of Congo, western Congo Basin2017Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 14, nr 9, s. 2267-2281Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We discuss concentrations of dissolved CH4, N2O, O-2, NO(3)(-)and NH4-, and emission fluxes of CH4 and N2O for river sites in the western Congo Basin, Republic of Congo (ROC). Savannah, swamp forest and tropical forest samples were collected from the Congo main stem and seven of its tributaries during November 2010 (41 samples; wet season) and August 2011 (25 samples; dry season; CH4 and N2O only). Dissolved inorganic nitrogen (DIN: NH4- + NO3-; wet season) was dominated by NO3- (63 +/- 19% of DIN). Total DIN concentrations (1.545.3 mu mol L-1) were consistent with the near absence of agricultural, domestic and industrial sources for all three land types. Dissolved O-2 (wet season) was mostly undersaturated in swamp forest (36 +/- 29 %) and tropical forest (77 +/- 36 %) rivers but predominantly supersaturated in savannah rivers (100 +/- 17 %). The dissolved concentrations of CH4 and N2O were within the range of values reported earlier for sub-Saharan African rivers. Dissolved CH4 was found to be supersaturated (11.2-9553 nmol L-1; 440-354 444 %), whereas N2O ranged from strong undersaturation to supersaturation (3.2-20.6 nmol L-1; 47-205 %). Evidently, rivers of the ROC are persistent local sources of CH4 and can be minor sources or sinks for N2O. During the dry season the mean and range of CH4 and N2O concentrations were quite similar for the three land types. Wet and dry season mean concentrations and ranges were not significant for N2O for any land type or for CH4 in savannah rivers. The latter observation is consistent with seasonal buffering of river discharge by an underlying sandstone aquifer. Significantly higher wet season CH4 concentrations in swamp and forest rivers suggest that CH4 can be derived from floating macrophytes during flooding and/or enhanced methanogenesis in adjacent flooded soils. Swamp rivers also exhibited both low (47 %) and high (205 %) N2O saturation but wet season values were overall significantly lower than in either tropical forest or savannah rivers, which were always supersaturated (103-266 %) and for which the overall means and ranges of N2O were not significantly different. In swamp and forest rivers O-2 saturation co-varied inversely with CH4 saturation (log %) and positively with % N2O. A significant positive correlation between N2O and O-2 saturation in swamp rivers was coincident with strong N2O and O-2 undersaturation, indicating N2O consumption during denitrification in the sediments. In savannah rivers persistent N2O supersaturation and a negative correlation between N2O and O-2 suggest N2O production mainly by nitrification. This is consistent with a stronger correlation between N2O and NH4+ than between N2O and NO3-. Our ranges of values for CH4 and N2O emission fluxes (33-48 705 mu mol CH4 m(-2) d(-1); 1-67 mu mol N(2)Om(2)(-) d(-1)) are within the ranges previously estimated for sub-Saharan African rivers but they include uncertainties deriving from our use of basin-wide values for CH4 and N2O gas transfer velocities. Even so, because we did not account for any contribution from ebullition, which is quite likely for CH4 (at least 20 %), we consider our emission fluxes for CH4 to be conservative.

  • 74. Van Oijen, M.
    et al.
    Balkovi, J.
    Beer, Christian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM). Max Planck Society, Germany.
    Cameron, D. R.
    Ciais, P.
    Cramer, W.
    Kato, T.
    Kuhnert, M.
    Martin, R.
    Myneni, R.
    Rammig, A.
    Rolinski, S.
    Soussana, J. -F
    Thonicke, K.
    Van der Velde, M.
    Xu, L.
    Impact of droughts on the carbon cycle in European vegetation: a probabilistic risk analysis using six vegetation models2014Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 11, nr 22, s. 6357-6375Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We analyse how climate change may alter risks posed by droughts to carbon fluxes in European ecosystems. The approach follows a recently proposed framework for risk analysis based on probability theory. In this approach, risk is quantified as the product of hazard probability and ecosystem vulnerability. The probability of a drought hazard is calculated here from the Standardized Precipitation-Evapotranspiration Index (SPEI). Vulnerability is calculated from the response to drought simulated by process-based vegetation models. We use six different models: three for generic vegetation (JSBACH, LPJmL, ORCHIDEE) and three for specific ecosystems (Scots pine forests: BASFOR; winter wheat fields: EPIC; grasslands: PASIM). The periods 1971-2000 and 2071-2100 are compared. Climate data are based on gridded observations and on output from the regional climate model REMO using the SRES A1B scenario. The risk analysis is carried out for similar to 18 000 grid cells of 0.25 x 0.25 degrees across Europe. For each grid cell, drought vulnerability and risk are quantified for five seasonal variables: net primary and ecosystem productivity (NPP, NEP), heterotrophic respiration (Rh), soil water content and evapotranspiration. In this analysis, climate change leads to increased drought risks for net primary productivity in the Mediterranean area: five of the models estimate that risk will exceed 15 %. The risks increase mainly because of greater drought probability; ecosystem vulnerability will increase to a lesser extent. Because NPP will be affected more than Rh, future carbon sequestration (NEP) will also be at risk predominantly in southern Europe, with risks exceeding 0.25 g Cm-2 d(-1) according to most models, amounting to reductions in carbon sequestration of 20 to 80 %.

  • 75. Vehmaa, Anu
    et al.
    Almen, Anna-Karin
    Brutemark, Andreas
    Paul, Allanah
    Riebesell, Ulf
    Furuhagen, Sara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för miljövetenskap och analytisk kemi. Swedish Chemical Agency, Sweden.
    Engstrom-Ost, Jonna
    Ocean acidification challenges copepod phenotypic plasticity2016Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, nr 22, s. 6171-6182Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ocean acidification is challenging phenotypic plasticity of individuals and populations. Calanoid copepods (zooplankton) are shown to be fairly plastic against altered pH conditions, and laboratory studies indicate that transgenerational effects are one mechanism behind this plasticity. We studied phenotypic plasticity of the copepod Acartia sp. in the course of a pelagic, large-volume mesocosm study that was conducted to investigate ecosystem and biogeochemical responses to ocean acidification. We measured copepod egg production rate, egg-hatching success, adult female size and adult female antioxidant capacity (ORAC) as a function of acidification (fCO(2) similar to 365-1231 mu atm) and as a function of quantity and quality of their diet. We used an egg transplant experiment to reveal whether transgenerational effects can alleviate the possible negative effects of ocean acidification on offspring development. We found significant negative effects of ocean acidification on adult female size. In addition, we found signs of a possible threshold at high fCO(2), above which adaptive maternal effects cannot alleviate the negative effects of acidification on egg-hatching and nauplii development. We did not find support for the hypothesis that insufficient food quantity (total particulate carbon <55 mu m) or quality (C : N) weakens the transgenerational effects. However, females with high-ORAC-produced eggs with high hatching success. Overall, these results indicate that Acartia sp. could be affected by projected near-future CO2 levels.

  • 76. Viktorsson, L.
    et al.
    Ekeroth, Nils
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Nilsson, M.
    Kononets, M.
    Hall, P. O. J.
    Phosphorus recycling in sediments of the central Baltic Sea2013Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 10, nr 6, s. 3901-3916Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Benthic fluxes of phosphorus (P) were measured in situ in the Eastern Gotland Basin (EGB), central Baltic Sea, using benthic landers. A total of 40 flux measurements of dissolved inorganic P (DIP) on 13 stations at water depths ranging 30-210 m and under different oxygen regimes were carried out on three cruises during three consecutive years (2008-2010) in August-September. Our study is the first to report in situ DIP fluxes in the Baltic proper, and it provides the most comprehensive dataset of benthic fluxes of DIP and dissolved organic P (DOP) in the Baltic proper existing to date. DIP fluxes increased with increasing water depth and with decreasing bottom water oxygen concentration. Average DIP fluxes were calculated for oxic bottom water conditions (-0.003+/-0.040 mmol m(-2) d(-1)), hypoxic conditions (0.027+/-0.067 mmol m(-2) d(-1)) and anoxic conditions (0.376+/-0.214 mmol m(-2) d(-1)). The mean DIP flux at anoxic bottoms was higher than previous estimates based on ex situ measurements of pore water gradients. The DIP flux was positively correlated with the organic carbon inventory of sediment, and the benthic flux of dissolved inorganic carbon (DIC) at anoxic stations, but these variables were uncorrelated at oxic stations. The positive correlation between DIP and DIC fluxes suggests that the benthic DIP efflux from anoxic bottoms in the Baltic Proper is mainly controlled by rates of deposition and degradation of organic matter. The flux from anoxic sediment was very P rich in relation to both C and nitrogen (N). The average C : P ratio in fluxes at anoxic accumulation bottoms was 69+/-15, which is well below the Redfield C : P ratio of 106 : 1. At oxic stations, however, the C : P flux ratio was much higher than the Redfield ratio, consistent with well-known P retention mechanisms associated with iron and bacteria in oxidised sediment. Using a benthic mass balance approach, a burial efficiency estimate of 0.2-12% was calculated for the anoxic part of the EGB, which suggests that anoxic Baltic sediments are very efficient in recycling deposited P. Based on the measured fluxes and the average areal extent of anoxic bottoms during years 1999-2006, an internal DIP load of 152 k ton yr(-1) was calculated. This is almost 9 times higher than the average external total phosphorus (TP) supply to the Baltic proper during the same period. This comparison clearly highlights the dominance of internally regenerated P as a DIP source in the Baltic Sea.

  • 77. Virtanen, Elina A.
    et al.
    Norkko, Alf
    Stockholms universitet, Naturvetenskapliga fakulteten, Stockholms universitets Östersjöcentrum. University of Helsinki, Finland.
    Nyström Sandman, Antonia
    Viitasalo, Markku
    Identifying areas prone to coastal hypoxia - the role of topography2019Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 16, nr 16, s. 3183-3195Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hypoxia is an increasing problem in marine ecosystems around the world. While major advances have been made in our understanding of the drivers of hypoxia, challenges remain in describing oxygen dynamics in coastal regions. The complexity of many coastal areas and lack of detailed in situ data have hindered the development of models describing oxygen dynamics at a sufficient spatial resolution for efficient management actions to take place. It is well known that the enclosed nature of seafloors and reduced water mixing facilitates hypoxia formation, but the degree to which topography contributes to hypoxia formation and small-scale variability of coastal hypoxia has not been previously quantified. We developed simple proxies of seafloor heterogeneity and modeled oxygen deficiency in complex coastal areas in the northern Baltic Sea. According to our models, topographical parameters alone explained similar to 80 % of hypoxia occurrences. The models also revealed that less than 25 % of the studied seascapes were prone to hypoxia during late summer (August-September). However, large variation existed in the spatial and temporal patterns of hypoxia, as certain areas were prone to occasional severe hypoxia (O-2 < 2 mg L-1), while others were more susceptible to recurrent moderate hypoxia (O-2 < 4.6 mg L-1). Areas identified as problematic in our study were characterized by low exposure to wave forcing, high topographic shelter from surrounding areas and isolation from the open sea, all contributing to longer water residence times in seabed depressions. Deviations from this topographical background are probably caused by strong currents or high nutrient loading, thus improving or worsening oxygen status, respectively. In some areas, connectivity with adjacent deeper basins may also influence coastal oxygen dynamics. Developed models could boost the performance of biogeochemical models, aid developing nutrient abatement measures and pinpoint areas where management actions are most urgently needed.

  • 78.
    Vonk, Jorien E.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Sanchez-Garcia, Laura
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Semiletov, I.
    Dudarev, O.
    Eglinton, T.
    Andersson, August
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Gustafsson, Örjan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för tillämpad miljövetenskap (ITM).
    Molecular and radiocarbon constraints on sources and degradation of terrestrial organic carbon along the Kolyma paleoriver transect, East Siberian Sea2010Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, nr 10, s. 3153-3166Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate warming in northeastern Siberia may induce thaw-mobilization of the organic carbon (OC) now held in permafrost. This study investigated the composition of terrestrial OC exported to Arctic coastal waters to both obtain a natural integration of terrestrial permafrost OC release and to further understand the fate of released carbon in the extensive Siberian Shelf Seas. Application of a variety of elemental, molecular and isotopic (delta C-13 and Delta C-14) analyses of both surface water suspended particulate matter and underlying surface sediments along a 500 km transect from Kolyma River mouth to the mid-shelf of the East Siberian Sea yielded information on the sources, degradation status and transport processes of thaw-mobilized soil OC. A three end-member dual-carbon-isotopic mixing model was applied to deduce the relative contributions from riverine, coastal erosion and marine sources. The mixing model was solved numerically using Monte Carlo simulations to obtain a fair representation of the uncertainties of both end-member composition and the end results. Riverine OC contributions to sediment OC decrease with increasing distance offshore (35 +/- 15 to 13 +/- 9%), whereas coastal erosion OC exhibits a constantly high contribution (51 +/- 11 to 60 +/- 12%) and marine OC increases offshore (9 +/- 7 to 36 +/- 10%). We attribute the remarkably strong imprint of OC from coastal erosion, extending up to similar to 500 km from the coast, to efficient offshoreward transport in these shallow waters presumably through both the benthic boundary layer and ice-rafting. There are also indications of simultaneous selective preservation of erosion OC compared to riverine OC. Molecular degradation proxies and radiocarbon contents indicated a degraded but young (Delta C-14 ca. -60% or ca. 500 C-14 years) terrestrial OC pool in surface water particulate matter, underlain by a less degraded but old (Delta C-14 ca. -500% or ca. 5500 C-14 years) terrestrial OC pool in bottom sediments. We suggest that the terrestrial OC fraction in surface water particulate matter is mainly derived from surface soil and recent vegetation fluvially released as buoyant organic-rich aggregates (e. g., humics), which are subjected to extensive processing during coastal transport. In contrast, terrestrial OC in the underlying sediments is postulated to originate predominantly from erosion of mineral-rich Pleistocene coasts (i.e., yedoma) and inland mineral soils. Sorptive association of this organic matter with mineral particles protects the OC from remineralization and also promotes rapid settling (ballasting) of the OC. Our findings corroborate recent studies by indicating that different Arctic surface soil OC pools exhibit distinguishing susceptibilities to degradation in coastal waters. Consequently, the general postulation of a positive feedback to global warming from degradation of permafrost carbon may be both attenuated (by reburial of one portion) and geographically displaced (degradation of released terrestrial permafrost OC far out over the Arctic shelf seas).

  • 79.
    Walve, Jakob
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Sandberg, Maria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Larsson, Ulf
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och botanik.
    Lännergren, Christer
    A Baltic Sea estuary as a phosphorus source and sink after drastic load reduction: seasonal and long-term mass balances for the Stockholm inner archipelago for 1968-20152018Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, nr 9, s. 3003-3025Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Internal phosphorus (P) loading from sediments, controlled by hypoxia, is often assumed to hamper the recovery of lakes and coastal areas from eutrophication. In the early 1970s, the external P load to the inner archipelago of Stockholm, Sweden (Baltic Sea), was drastically reduced by improved sewage treatment, but the internal P loading and its controlling factors have been poorly quantified. We use two slightly different four-layer box models to calculate the area's seasonal and annual P balance (input-export) and the internal P exchange with sediments in 1968-2015. For 1020 years after the main P load reduction, there was a negative P balance, small in comparison to the external load, and probably due to release from legacy sediment P storage. Later, the stabilized, near-neutral P balance indicates no remaining internal loading from legacy P, but P retention is low, despite improved oxygen conditions. Seasonally, sediments are a P sink in spring and a P source in summer and autumn. Most of the deep-water P release from sediments in summer-autumn appears to be derived from the settled spring bloom and is exported to outer areas during winter. Oxygen consumption and P release in the deep water are generally tightly coupled, indicating limited iron control of P release. However, enhanced P release in years of deep-water hypoxia suggests some contribution from redox-sensitive P pools. Increasing deep-water temperatures that stimulate oxygen consumption rates in early summer have counteracted the effect of lowered organic matter sedimentation on oxygen concentrations. Since the P turnover time is short and legacy P small, measures to bind P in Stockholm inner archipelago sediments would primarily accumulate recent P inputs, imported from the Baltic Sea and from Lake Mälaren.

  • 80.
    Yamoah, Kweku Afrifa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Callac, Nolwenn
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chi Fru, Ernest
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Wohlfarth, Barbara
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Wiech, Alan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    Chabangbor, Akkaneewut
    Smittenberg, Rienk H.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för geologiska vetenskaper.
    A 150-year record of phytoplankton 1 community succession controlled by hydroclimatic variability in a tropical lake2016Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 13, nr 13, s. 3971-3980Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Climate and human-induced environmental change promotes biological regime shifts between alternate stable states, with implications for ecosystem resilience, function and services. While this has been shown for recent microbial communities, the long-term response of microbial communities has not been investigated in detail. This study investigated the decadal variations in phytoplankton communities in a ~150 year long sedimentary archive of Lake Nong Thale Prong (NTP), southern Thailand using a combi nation of DNA and lipid biomarkers techniques. Reconstructed drier climate from ~1857-1916 Common Era (CE) coincided with oligotrophic lake water conditions and dominance of the green algae Botryococcus braunii, producing characteristic botryococcene lipids. A change to higher silica (Si) input ~1916 CE, which was related to increased rainfall concurs with an abrupt takeover by diatom blooms lasting for 50 years. Since the 1970s more eutrophic conditions prevailed, which was likely caused by increased levels of anthropogenic phosphate (P), aided by increased lake stratification caused by somewhat dryer conditions. The eutrophic conditions led to increased primary productivity consisting again of a Botryococcus sp., though this time not producing the botryococcene lipids. Moreover, Cyanobacteria became dominant. Our results indicate that a combined DNA and lipid biomarker approach provides an efficient way to allow tracking centennial-scale hydroclimate and anthropogenic feedback processes in lake ecosystems.

  • 81. Zhang, J.
    et al.
    Gilbert, D.
    Gooday, A. J.
    Levin, L.
    Naqvi, S. W. A.
    Middelburg, J. J.
    Scranton, M.
    Ekau, W.
    Pena, A.
    Dewitte, B.
    Oguz, T.
    Monteiro, P. M. S.
    Urban, E.
    Rabalais, N. N.
    Ittekkot, V.
    Kemp, W. M.
    Ulloa, O.
    Elmgren, Ragnar
    Stockholms universitet, Naturvetenskapliga fakulteten, Systemekologiska institutionen.
    Escobar-Briones, E.
    Van der Plas, A. K.
    Natural and human-induced hypoxia and consequences for coastal areas: synthesis and future development2010Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 7, nr 5, s. 1443-1467Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hypoxia has become a world-wide phenomenon in the global coastal ocean and causes a deterioration of the structure and function of ecosystems. Based on the collective contributions of members of SCOR Working Group #128, the present study provides an overview of the major aspects of coastal hypoxia in different biogeochemical provinces, including estuaries, coastal waters, upwelling areas, fjords and semi-enclosed basins, with various external forcings, ecosystem responses, feedbacks and potential impact on the sustainability of the fishery and economics. The obvious external forcings include freshwater runoff and other factors contributing to stratification, organic matter and nutrient loadings, as well as exchange between coastal and open ocean water masses. Their different interactions set up mechanisms that drive the system towards hypoxia. Coastal systems also vary in their relative susceptibility to hypoxia depending on their physical and geographic settings. It is understood that coastal hypoxia has a profound impact on the sustainability of ecosystems, which can be seen, for example, by the change in the food-web structure and system function; other influences include compression and loss of habitat, as well as changes in organism life cycles and reproduction. In most cases, the ecosystem responds to the low dissolved oxygen in non-linear ways with pronounced feedbacks to other compartments of the Earth System, including those that affect human society. Our knowledge and previous experiences illustrate that there is a need to develop new observational tools and models to support integrated research of biogeochemical dynamics and ecosystem behavior that will improve confidence in remediation management strategies for coastal hypoxia.

  • 82.
    Ödalen, Malin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Nycander, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Oliver, Kevin I. C.
    Brodeau, Laurent
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). Barcelona Supercomputer Center, Spain.
    Ridgwell, Andy
    The influence of the ocean circulation state on ocean carbon storage and CO2 drawdown potential in an Earth system model2018Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 15, nr 5, s. 1367-1393Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During the four most recent glacial cycles, atmospheric CO2 during glacial maxima has been lowered by about 90-100 ppm with respect to interglacials. There is widespread consensus that most of this carbon was partitioned in the ocean. It is, however, still debated which processes were dominant in achieving this increased carbon storage. In this paper, we use an Earth system model of intermediate complexity to explore the sensitivity of ocean carbon storage to ocean circulation state. We carry out a set of simulations in which we run the model to pre-industrial equilibrium, but in which we achieve different states of ocean circulation by changing forcing parameters such as wind stress, ocean diffusivity and atmospheric heat diffusivity. As a consequence, the ensemble members also have different ocean carbon reservoirs, global ocean average temperatures, biological pump efficiencies and conditions for air-sea CO2 disequilibrium. We analyse changes in total ocean carbon storage and separate it into contributions by the solubility pump, the biological pump and the CO2 disequilibrium component. We also relate these contributions to differences in the strength of the ocean overturning circulation. Depending on which ocean forcing parameter is tuned, the origin of the change in carbon storage is different. When wind stress or ocean diapycnal diffusivity is changed, the response of the biological pump gives the most important effect on ocean carbon storage, whereas when atmospheric heat diffusivity or ocean isopycnal diffusivity is changed, the solubility pump and the disequilibrium component are also important and sometimes dominant. Despite this complexity, we obtain a negative linear relationship between total ocean carbon and the combined strength of the northern and southern overturning cells. This relationship is robust to different reservoirs dominating the response to different forcing mechanisms. Finally, we conduct a drawdown experiment in which we investigate the capacity for increased carbon storage by artificially maximising the efficiency of the biological pump in our ensemble members. We conclude that different initial states for an ocean model result in different capacities for ocean carbon storage due to differences in the ocean circulation state and the origin of the carbon in the initial ocean carbon reservoir. This could explain why it is difficult to achieve comparable responses of the ocean carbon pumps in model intercomparison studies in which the initial states vary between models. We show that this effect of the initial state is quantifiable. The drawdown experiment highlights the importance of the strength of the biological pump in the control state for model studies of increased biological efficiency.

  • 83.
    Ödalen, Malin
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU). University of Arizona, USA.
    Nycander, Jonas
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Ridgwell, Andy
    Oliver, Kevin I. C.
    Peterson, Carlye D.
    Nilsson, Johan
    Stockholms universitet, Naturvetenskapliga fakulteten, Meteorologiska institutionen (MISU).
    Variable C∕P composition of organic production and its effect on ocean carbon storage in glacial-like model simulations2020Ingår i: Biogeosciences, ISSN 1726-4170, E-ISSN 1726-4189, Vol. 17, nr 8, s. 2219-2244Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During the four most recent glacial maxima, atmospheric CO2 has been lowered by about 90–100 ppm with respect to interglacial concentrations. It is likely that most of the atmospheric CO2 deficit was stored in the ocean. Changes in the biological pump, which are related to the efficiency of the biological carbon uptake in the surface ocean and/or of the export of organic carbon to the deep ocean, have been proposed as a key mechanism for the increased glacial oceanic CO2 storage. The biological pump is strongly constrained by the amount of available surface nutrients. In models, it is generally assumed that the ratio between elemental nutrients, such as phosphorus, and carbon (C∕P ratio) in organic material is fixed according to the classical Redfield ratio. The constant Redfield ratio appears to approximately hold when averaged over basin scales, but observations document highly variable C∕P ratios on regional scales and between species. If the C∕P ratio increases when phosphate availability is scarce, as observations suggest, this has the potential to further increase glacial oceanic CO2 storage in response to changes in surface nutrient distributions. In the present study, we perform a sensitivity study to test how a phosphate-concentration-dependent C∕P ratio influences the oceanic CO2 storage in an Earth system model of intermediate complexity (cGENIE). We carry out simulations of glacial-like changes in albedo, radiative forcing, wind-forced circulation, remineralization depth of organic matter, and mineral dust deposition. Specifically, we compare model versions with the classical constant Redfield ratio and an observationally motivated variable C∕P ratio, in which the carbon uptake increases with decreasing phosphate concentration. While a flexible C∕P ratio does not impact the model's ability to simulate benthic δ13C patterns seen in observational data, our results indicate that, in production of organic matter, flexible C∕P can further increase the oceanic storage of CO2 in glacial model simulations. Past and future changes in the C∕P ratio thus have implications for correctly projecting changes in oceanic carbon storage in glacial-to-interglacial transitions as well as in the present context of increasing atmospheric CO2 concentrations.

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