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  • 1.
    Andersson, August
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Deng, Junjun
    Du, Ke
    Zheng, Mei
    Yan, Caiqing
    Sköld, Martin
    Stockholm University, Faculty of Science, Department of Mathematics.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Regionally-Varying Combustion Sources of the January 2013 Severe Haze Events over Eastern China2015In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 49, no 4, p. 2038-2043Article in journal (Refereed)
    Abstract [en]

    Thick haze plagued northeastern China in January 2013, strongly affecting both regional climate and human respiratory health. Here, we present dual carbon isotope constrained (Delta C-14 and delta C-13) source apportionment for combustion-derived black carbon aerosol (BC) for three key hotspot regions (megacities): North China Plain (NCP, Beijing), the Yangtze River Delta (YRD, Shanghai), and the Pearl River Delta (PRD, Guangzhou) for January 2013. BC, here quantified as elemental carbon (EC), is one of the most health-detrimental components of PM2.5 and a strong climate warming agent. The results show that these severe haze events were equally affected (similar to 30%) by biomass combustion in all three regions, whereas the sources of the dominant fossil fuel component was dramatically different between north and south. In the NCP region, coal combustion accounted for 66% (46-74%, 95% C.I.) of the EC, whereas, in the YRD and PRD regions, liquid fossil fuel combustion (e.g., traffic) stood for 46% (18-66%) and 58% (38-68%), respectively. Taken together, these findings suggest the need for a regionally-specific description of BC sources in climate models and regionally-tailored mitigation to combat severe air pollution events in East Asia.

  • 2. Erlandsson, Johan
    et al.
    McQuaid, Christopher D.
    Sköld, Martin
    Stockholm University, Faculty of Science, Department of Mathematics.
    Patchiness and Co-Existence of Indigenous and Invasive Mussels at Small Spatial Scales: The Interaction of Facilitation and Competition2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 11, p. e26958-Article in journal (Refereed)
    Abstract [en]

    Ecological theory predicts that two species with similar requirements will fail to show long-term co-existence in situations where shared resources are limiting, especially at spatial scales that are small relative to the size of the organisms. Two species of intertidal mussels, the indigenous Perna perna and the invasive Mytilus galloprovincialis, form mixed beds on the south coast of South Africa in a situation that has been stable for several generations of these species, even though these populations are often limited by the availability of space. We examined the spatial structure of these species where they coexist at small spatial scales in the absence of apparent environmental heterogeneity at two sites, testing: whether conspecific aggregation of mussels can occur (using spatial Monte-Carlo tests); the degree of patchiness (using Korcak B patchiness exponent), and whether there was a relationship between percent cover and patchiness. We found that under certain circumstances there is non-random conspecific aggregation, but that in other circumstances there may be random distribution (i.e. the two species are mixed), so that spatial patterns are context-dependent. The relative cover of the species differed between sites, and within each site, the species with higher cover showed low Korcak B values (indicating low patchiness, i.e. the existence of fewer, larger patches), while the less abundant species showed the reverse, i.e. high patchiness. This relationship did not hold for either species within sites. We conclude that co-existence between these mussels is possible, even at small spatial scales because each species is an ecological engineer and, while they have been shown to compete for space, this is preceded by initial facilitation. We suggest that a patchy pattern of co-existence is possible because of a balance between direct (competitive) and indirect (facilitative) interactions.

  • 3.
    Jonzén, Niclas
    et al.
    Lund University, Department of Theoretical Ecology.
    Pople, Tony
    Invasive Plants and Animals, Biosecurity Queensland, Department of Primary Industries and Fisheries.
    Knape, Jonas
    Lund University, Department of Theoretical Ecology.
    Sköld, Martin
    Stockholm University, Faculty of Science, Department of Mathematics.
    Stochastic demography and population dynamics in the red kangaroo Macropus rufus2010In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 79, no 1, p. 109-116Article in journal (Refereed)
  • 4.
    Keskitalo, Kirsi
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Tesi, Tommaso
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. CNR-National Research Council of Italy, Italy.
    Bröder, Lisa
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sköld, Martin
    Stockholm University, Faculty of Science, Department of Mathematics.
    Semiletov, Igor P.
    Dudarev, Oleg V.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Sources and characteristics of terrestrial carbon in Holocene-scale sediments of the East Siberian Sea2017In: Climate of the Past, ISSN 1814-9324, E-ISSN 1814-9332, Vol. 13, no 9, p. 1213-1226Article in journal (Refereed)
    Abstract [en]

    Thawing of permafrost carbon (PF-C) due to climate warming can remobilise considerable amounts of terrestrial carbon from its long-term storage to the marine environment. PF-C can be then be buried in sediments or remineralised to CO2 with implications for the carbon-climate feedback. Studying historical sediment records during past natural climate changes can help us to understand the response of permafrost to current climate warming. In this study, two sediment cores collected from the East Siberian Sea were used to study terrestrial organic carbon sources, composition and degradation during the past similar to 9500 cal yrs BP. CuO-derived lignin and cutin products (i.e., compounds solely biosynthesised in terrestrial plants) combined with delta C-13 suggest that there was a higher input of terrestrial organic carbon to the East Siberian Sea between similar to 9500 and 8200 cal yrs BP than in all later periods. This high input was likely caused by marine transgression and permafrost destabilisation in the early Holocene climatic optimum. Based on source apportionment modelling using dual-carbon isotope (Delta C-14, Delta C-13) data, coastal erosion releasing old Pleistocene permafrost carbon was identified as a significant source of organic matter translocated to the East Siberian Sea during the Holocene.

  • 5. Knape, Jonas
    et al.
    Jonzen, Niclas
    Sköld, Martin
    Stockholm University, Faculty of Science, Department of Mathematics.
    On observation distributions for state space models of population survey data2011In: Journal of Animal Ecology, ISSN 0021-8790, E-ISSN 1365-2656, Vol. 80, no 6, p. 1269-1277Article in journal (Refereed)
    Abstract [en]

    1. State space models are starting to replace more simple time series models in analyses of temporal dynamics of populations that are not perfectly censused. By simultaneously modelling both the dynamics and the observations, consistent estimates of population dynamical parameters may be obtained. For many data sets, the distribution of observation errors is unknown and error models typically chosen in an ad-hoc manner. 2. To investigate the influence of the choice of observation error on inferences, we analyse the dynamics of a replicated time series of red kangaroo surveys using a state space model with linear state dynamics. Surveys were performed through aerial counts and Poisson, overdispersed Poisson, normal and log-normal distributions may all be adequate for modelling observation errors for the data. We fit each of these to the data and compare them using AIC. 3. The state space models were fitted with maximum likelihood methods using a recent importance sampling technique that relies on the Kalman filter. The method relaxes the assumption of Gaussian observation errors required by the basic Kalman filter. Matlab code for fitting linear state space models with Poisson observations is provided. 4. The ability of AIC to identify the correct observation model was investigated in a small simulation study. For the parameter values used in the study, without replicated observations, the correct observation distribution could sometimes be identified but model selection was prone to misclassification. On the other hand, when observations were replicated, the correct distribution could typically be identified. 5. Our results illustrate that inferences may differ markedly depending on the observation distributions used, suggesting that choosing an adequate observation model can be critical. Model selection and simulations show that for the models and parameter values in this study, a suitable observation model can typically be identified if observations are replicated. Model selection and replication of observations, therefore, provide a potential solution when the observation distribution is unknown.

  • 6.
    Knape, Jonas
    et al.
    Lund University, Department of Theoretical Ecology.
    Jonzén, Niclas
    Lund University, Department of Theoretical Ecology.
    Sköld, Martin
    Stockholm University, Faculty of Science, Department of Mathematics.
    Kikkawa, Jiro
    McCallum, Hamish
    Individual heterogeneity and senescence in Silvereyes on Heron Island2011In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 92, no 4, p. 813-820Article in journal (Refereed)
    Abstract [en]

    Individual heterogeneity and correlations between life history traits play a fundamental role in life history evolution and population dynamics. Unobserved individual heterogeneity in survival can be a nuisance for estimation of age effects at the individual level by causing bias due to mortality selection. We jointly analyze survival and breeding output from successful breeding attempts in an island population of Silvereyes (Zosterops lateralis chlorocephalus) by fitting models that incorporate age effects and individual heterogeneity via random effects. The number of offspring produced increased with age of parents in their first years of life but then eventually declined with age. A similar pattern was found for the probability of successful breeding. Annual survival declined with age even when individual heterogeneity was not accounted for. The rate of senescence in survival, however, depends on the variance of individual heterogeneity and vice versa; hence, both cannot be simultaneously estimated with precision. Model selection supported individual heterogeneity in breeding performance, but we found no correlation between individual heterogeneity in survival and breeding performance. We argue that individual random effects, unless unambiguously identified, should be treated as statistical nuisance or taken as a starting point in a search for mechanisms rather than given direct biological interpretation.

  • 7.
    Martens, Jannik
    et al.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Wild, Birgit
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Pearce, Christof
    Stockholm University, Faculty of Science, Department of Geological Sciences. Aarhus University, Denmark.
    Tesi, Tommaso
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. National Research Council, Italy.
    Andersson, August
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Bröder, Lisa
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry. Vrije Universiteit Amsterdam, Netherlands,.
    O'Regan, Matt
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Jakobsson, Martin
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sköld, Martin
    Stockholm University, Faculty of Science, Department of Mathematics.
    Gemery, Laura
    Cronin, Thomas M.
    Semiletov, Igor
    Dudarev, Oleg V.
    Gustafsson, Örjan
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Remobilization of Old Permafrost Carbon to Chukchi Sea Sediments During the End of the Last Deglaciation2019In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 33, no 1, p. 2-14Article in journal (Refereed)
    Abstract [en]

    Climate warming is expected to destabilize permafrost carbon (PF-C) by thaw-erosion and deepening of the seasonally thawed active layer and thereby promote PF-C mineralization to CO2 and CH4. A similar PF-C remobilization might have contributed to the increase in atmospheric CO2 during deglacial warming after the last glacial maximum. Using carbon isotopes and terrestrial biomarkers (Delta C-14, delta C-13, and lignin phenols), this study quantifies deposition of terrestrial carbon originating from permafrost in sediments from the Chukchi Sea (core SWERUS-L2-4-PC1). The sediment core reconstructs remobilization of permafrost carbon during the late Allerod warm period starting at 13,000 cal years before present (BP), the Younger Dryas, and the early Holocene warming until 11,000 cal years BP and compares this period with the late Holocene, from 3,650 years BP until present. Dual-carbon-isotope-based source apportionment demonstrates that Ice Complex Deposit-ice- and carbon-rich permafrost from the late Pleistocene (also referred to as Yedoma)-was the dominant source of organic carbon (66 +/- 8%; mean +/- standard deviation) to sediments during the end of the deglaciation, with fluxes more than twice as high (8.0 +/- 4.6 g.m(-2).year(-1)) as in the late Holocene (3.1 +/- 1.0 g.m(-2).year(-1)). These results are consistent with late deglacial PF-C remobilization observed in a Laptev Sea record, yet in contrast with PF-C sources, which at that location were dominated by active layer material from the Lena River watershed. Release of dormant PF-C from erosion of coastal permafrost during the end of the last deglaciation indicates vulnerability of Ice Complex Deposit in response to future warming and sea level changes.

  • 8.
    Sköld, Martin
    et al.
    Stockholm University, Faculty of Science, Department of Mathematics.
    Knape, Jonas
    Bounding reproductive rates in state-space models for animal population dynamics2018In: Ecosphere, ISSN 2150-8925, E-ISSN 2150-8925, Vol. 9, no 5, article id e02215Article in journal (Refereed)
    Abstract [en]

    Time-series models applied in the study of animal population dynamics commonly assume linearity on the log-scale, leading to log-normally distributed rates of increase. While this is often computationally convenient, in particular when performing statistical inference in the presence of observation error, it may lead to unrealistic predictions for animals with a limited reproduction. We introduce a model that includes an explicit bound on the reproductive rate of an individual, and apply this to a population time series of ungulates in Kruger National Park, South Africa. Due to observational error, the year-to-year increases in animal counts occasionally exceeded the maximal reproductive rate of the animals. In such cases, the traditional unbounded model showed a tendency of overfitting data, leading to unrealistic predictions of the underlying population increase. An observed increase above the maximal reproductive rate also provides empirical confirmation that observation error exists. The model with an explicit bound was able to utilize this in order to separate observational error from population process noise, which the traditional unbounded model was unable to do. We conclude that enforcing a strict upper bound on the reproductive rate of an animal population model may lead to more realistic statistical inference than commonly applied log-linear models when an explicit bound on reproductive rate is known. We further conclude that introducing a bound on reproduction can greatly assist in separating observational error and population process noise for slow life histories, or more generally, when the rate of sampling is high compared to reproductive rates.

  • 9. Vonk, Jorien E.
    et al.
    Drenzek, Nicholas J.
    Hughen, Konrad A.
    Stanley, Rachel H. R.
    McIntyre, Cameron
    Montlucon, Daniel B.
    Giosan, Liviu
    Southon, John R.
    Santos, Guaciara M.
    Druffel, Ellen R. M.
    Andersson, August A.
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Sköld, Martin
    Stockholm University, Faculty of Science, Department of Mathematics.
    Eglinton, Timothy I.
    Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds2019In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 244, p. 502-521Article in journal (Refereed)
    Abstract [en]

    Relatively little is known about the amount of time that lapses between the photosynthetic fixation of carbon by vascular land plants and its incorporation into the marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have important implications for the carbon cycle. Vascular plant carbon may encounter multiple potential intermediate storage pools and transport trajectories, and the age of vascular plant carbon accumulating in marine sediments will reflect these different pre-depositional histories. Here, we examine down-core C-14 profiles of higher plant leaf wax-derived fatty acids isolated from high fidelity sedimentary sequences spanning the so-called bomb-spike, and encompassing a ca. 60-degree latitudinal gradient from tropical (Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to constrain integrated vascular plant carbon storage/transport times (residence times). Using a modeling framework, we find that, in addition to a young (conditionally defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old pool of 28 ky (+/- 9.4, standard deviation), indicating extensive pre-aging in permafrost soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger, 7.9 (+/- 5.0) and 2.4 (+/- 0.50) to 3.2 (+/- 0.54) ky, respectively, indicating less protracted storage in terrestrial reservoirs. The young pool showed clear annual contributions for Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool, respectively), likely reflecting episodic transport of OC from steep hillside slopes surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta, respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay of OC inflow, potentially related to transport time to the offshore basin. Modeling results also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30 years of age), pointing to the presence of an intermediate reservoir. Overall, these results show that a significant fraction of vascular plant C undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine sediments. The age distribution, reflecting both storage and transport times, likely depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the degree of soil buildup and preservation. We show that catchment-specific carbon residence times across landscapes can vary by an order of magnitude, with important implications both for carbon cycle studies and for the interpretation of molecular terrestrial paleoclimate records preserved in sedimentary sequences.

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