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  • 1. Divine, D. V.
    et al.
    Sjolte, J.
    Isaksson, E.
    Meijer, H. A. J.
    van de Wal, R. S. W.
    Martma, T.
    Pohjola, V.
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Godtliebsen, F.
    Modelling the regional climate and isotopic composition of Svalbard precipitation using REMOiso: a comparison with available GNIP and ice core data2011In: Hydrological Processes, ISSN 0885-6087, E-ISSN 1099-1085, Vol. 25, no 24, 3748-3759 p.Article in journal (Refereed)
    Abstract [en]

    Simulations of a regional (approx. 50 km resolution) circulation model REMOiso with embedded stable water isotope module covering the period 1958-2001 are compared with the two instrumental climate and four isotope series (d18O) from western Svalbard. We examine the data from ice cores drilled on Svalbard ice caps in 1997 (Lomonosovfonna, 1250 m asl) and 2005 (Holtedahlfonna, 1150 m asl) and the GNIP series from Ny-angstrom lesund and Isfjord Radio. The surface air temperature (SAT) and precipitation data from Longyearbyen and Ny-angstrom lesund are used to assess the skill of the model in reproducing the local climate. The model successfully captures the climate variations on the daily to multidecadal times scales although it tends to systematically underestimate the winter SAT. Analysis suggests that REMOiso performs better at simulating isotope compositions of precipitation in the winter than summer. The simulated and measured Holtedahlfonna d18O series agree reasonably well, whereas no significant correlation has been observed between the modelled and measured Lomonosovfonna ice core isotopic series. It is shown that sporadic nature as well as variability in the amount inherent in precipitation process potentially limits the accuracy of the past SAT reconstruction from the ice core data. This effect in the study area is, however, diminished by the role of other factors controlling d18O in precipitation, most likely sea ice extent, which is directly related with the SAT anomalies.

  • 2. Edwards, Thomas W. D.
    et al.
    Hammarlund, Dan
    Newton, Brandi W.
    Sjolte, Jesper
    Linderson, Hans
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Amour, Natalie A. St.
    Bailey, Joscelyn N. -L.
    Nilsson, Anders L.
    Seasonal variability in Northern Hemisphere atmospheric circulation during the Medieval Climate Anomaly and the Little Ice Age2017In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 165, 102-110 p.Article in journal (Refereed)
    Abstract [en]

    Here we report new reconstructions of winter temperature and summer moisture during the past millennium in southeastern Sweden, based on stable-isotope data from a composite tree-ring sequence, that further enhances our knowledge and understanding of seasonal climate variability in the Northern Hemisphere over the past millennium. Key features of these new climate proxy records include evidence for distinctive fluctuations in winter temperature in SE Sweden, superimposed upon the general pattern of cooling between the so-called Medieval Climate Anomaly (MCA) of the early millennium and the Little Ice Age (LIA) of the late millennium, as well as evidence for sustained summer wetness during the MCA, followed by drier and less variable conditions during the LIA. We also explore these new records within a circumpolar spatial context by employing self-organizing map analysis of meteorological reanalysis data to identify potential modern analogues of mid-tropospheric synoptic circulation types in the Northern Hemisphere extratropics that can reconcile varying seasonal climate states during the MCA and LIA in SE Sweden with less variable conditions in southwestern Canada, as portrayed by paleoclimate records developed in the same manner in an earlier study.

  • 3. Insel, Nadja
    et al.
    Poulsen, Christopher J.
    Ehlers, Todd A.
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Response of meteoric delta O-18 to surface uplift - Implications for Cenozoic Andean Plateau growth2012In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 317, 262-272 p.Article in journal (Refereed)
    Abstract [en]

    The timing and magnitude of surface uplift provide important constraints on geodynamic models of orogen formation. Oxygen isotope (delta O-18) and mass-47 isotopolog (Delta(47)) compositions from terrestrial carbonate sediments have been used with modern isotope and temperature lapse rates to infer past surface elevations of the Andes. However, these paleoaltimeny interpretations are contentious because variations in the oxygen isotope composition in meteoric water (delta O-18(p)) are caused by changes in elevation (orographic) and regional climate. Here, we use a limited-domain isotope-tracking general circulation model to simulate changes in delta O-18(p) and isotopic lapse rates in response to Andean surface uplift, and to re-evaluate delta O-18 and Delta(47) changes in late Miocene carbonates previously associated with rapid Andean growth. Results indicate that Andean surface uplift leads to changes in low-level atmospheric circulation and an increase in precipitation along the eastem Andean flank which influences isotopic source and amount effects. Simulated changes in Andean delta O-18(p) are not systematic with an increase in surface elevation, but are instead a function of orographic thresholds that abruptly change regional climate. A delta O-18(p) decrease of >5%. over the central Andes and an increase in isotopic lapse rates (up to 0.8%. km(-1)) coincide with Andean surface uplift from 75 to 100% of modem elevation. These changes in the isotopic signature could account for the entire 3-4%. delta O-18 depletion in late Miocene carbonate nodules, and suggest an Andean paleoelevation of similar to 3000 m (75% of modem elevations) before 10 Ma.

  • 4. Insel, Nadja
    et al.
    Poulsen, Christopher J.
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Ehlers, Todd A.
    Climate controls on Andean precipitation delta O-18 interannual variability2013In: Journal of Geophysical Research: Atmospheres, ISSN 2169-897X, Vol. 118, no 17, 9721-9742 p.Article in journal (Refereed)
    Abstract [en]

    The stable oxygen isotopic composition of precipitation (O-18(p)) is used as a proxy for modern and past atmospheric, biologic, and surface processes. Although the physical processes that fractionate O-18 in vapor are known, regional controls of O-18(p) are not well understood. Here we present results from a limited-domain general circulation model (REMOiso) to quantify regional controls on modern (1976-1999) interannual and spatial variations of O-18(p) across four Andean domains spanning 50 degrees latitude. Results are compared to observed O-18(p) from meteorological stations. Simulated annual amount-weighted mean O-18(p) ranges between -4 and -7 (0-5 degrees S), -8 and -20 (14 degrees S-26 degrees S), -4 and -8.5 (30 degrees S-35 degrees S), and -7 to -10 (45 degrees S-50 degrees S). Relationships between climate and O-18(p) on interannual timescale vary along the Andes and are tied to changes in precipitation and large-scale dynamics. In the northern Andes, interannual variations in O-18(p) are mainly associated with precipitation amounts driven by low-latitude sea surface temperature and Amazon Basin conditions. In the north central Andes, O-18(p) correlates with precipitation amount and wind trajectory, which is related to the position of the Bolivian High. In the south central Andes, O-18(p) variability is mainly influenced by precipitation amounts that are controlled by the position and strength of the westerlies. In the southern Andes, interannual O-18(p) variability is linked to the intensification and weakening of the South Pacific High. The regional climate-O-18(p) relationships are discussed in the context of pre-Quaternary sedimentary O-18 proxy records.

  • 5.
    Muschitiello, Francesco
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Schwark, L.
    Wohlfarth, Barbara
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Hammarlund, D.
    New evidence of Holocene atmospheric circulation dynamics based on lake sediments from southern Sweden: a link to the Siberian High2013In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 77, 113-124 p.Article in journal (Refereed)
    Abstract [en]

    Oxygen (delta O-18) and carbon (delta C-13) isotope records of calcitic carbonate components (Chara sp. algal encrustations and Bithynia tentaculata gastropod opercula) from a lake-sediment succession on the Baltic Sea island of Gotland, south-eastern Sweden, have been obtained to investigate regional climate dynamics during the Holocene. The hydrological sensitivity of the small lake, particularly in terms of spring snowmelt contribution to the local water budget, provides a means of tracing past changes in the influence of snow-bearing easterly winds across the Baltic Sea Proper, which signifies the wintertime strength of the Siberian High. Repeated episodic depletions in O-18 at the centennial scale correlate with events of increased potassium concentration in the GISP2 ice-core record from Greenland, which indicates a coupling to large-scale fluctuations in atmospheric circulation patterns. A corresponding correlation with simultaneous depletions in C-13 suggests repeated responses of the local lake hydrology to snow-rich winters through decreasing water residence time, perhaps augmented by methanogenesis due to prolonged ice-cover seasons under the influence of an expanding Siberian High. Frequency analysis of the isotopic records reveals well-defined fluctuations at quasi-500-520-, 670-, 830- and 1430-yr periodicities, and a gradually stronger impact of Polar air outbreaks across the southern Baltic Sea region with time after ca 6000 cal. BP.

  • 6. Risi, Camille
    et al.
    Noone, David
    Worden, John
    Frankenberg, Christian
    Stiller, Gabriele
    Kiefer, Michael
    Funke, Bernd
    Walker, Kaley
    Bernath, Peter
    Schneider, Matthias
    Bony, Sandrine
    Lee, Jeonghoon
    Brown, Derek
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopic observations: 2. Using isotopic diagnostics to understand the mid and upper tropospheric moist bias in the tropics and subtropics2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, D05304- p.Article in journal (Refereed)
    Abstract [en]

    Evaluating the representation of processes controlling tropical and subtropical tropospheric relative humidity (RH) in atmospheric general circulation models (GCMs) is crucial to assess the credibility of predicted climate changes. GCMs have long exhibited a moist bias in the tropical and subtropical mid and upper troposphere, which could be due to the mis-representation of cloud processes or of the large-scale circulation, or to excessive diffusion during water vapor transport. The goal of this study is to use observations of the water vapor isotopic ratio to understand the cause of this bias. We compare the three-dimensional distribution of the water vapor isotopic ratio measured from space and ground to that simulated by several versions of the isotopic GCM LMDZ. We show that the combined evaluation of RH and of the water vapor isotopic composition makes it possible to discriminate the most likely cause of RH biases. Models characterized either by an excessive vertical diffusion, an excessive convective detrainment or an underestimated in situ cloud condensation will all produce a moist bias in the free troposphere. However, only an excessive vertical diffusion can lead to a reversed seasonality of the free tropospheric isotopic composition in the subtropics compared to observations. Comparing seven isotopic GCMs suggests that the moist bias found in many GCMs in the mid and upper troposphere most frequently results from an excessive diffusion during vertical water vapor transport. This study demonstrates the added value of water vapor isotopic measurements for interpreting shortcomings in the simulation of RH by climate models.

  • 7. Risi, Camille
    et al.
    Noone, David
    Worden, John
    Frankenberg, Christian
    Stiller, Gabriele
    Kiefer, Michael
    Funke, Bernd
    Walker, Kaley
    Bernath, Peter
    Schneider, Matthias
    Wunch, Debra
    Sherlock, Vanessa
    Deutscher, Nicholas
    Griffith, David
    Wennberg, Paul O.
    Strong, Kimberly
    Smale, Dan
    Mahieu, Emmanuel
    Barthlott, Sabine
    Hase, Frank
    Garcia, Omaira
    Notholt, Justus
    Warneke, Thorsten
    Toon, Geoffrey
    Sayres, David
    Bony, Sandrine
    Lee, Jeonghoon
    Brown, Derek
    Uemura, Ryu
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopologues: 1. Comparison between models and observations2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, D05303- p.Article in journal (Refereed)
    Abstract [en]

    The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in atmospheric general circulation models (GCMs). We analyze a large number of isotopic data sets (four satellite, sixteen ground-based remote-sensing, five surface in situ and three aircraft data sets) that are sensitive to different altitudes throughout the free troposphere. Despite significant differences between data sets, we identify some observed HDO/H2O characteristics that are robust across data sets and that can be used to evaluate models. We evaluate the isotopic GCM LMDZ, accounting for the effects of spatiotemporal sampling and instrument sensitivity. We find that LMDZ reproduces the spatial patterns in the lower and mid troposphere remarkably well. However, it underestimates the amplitude of seasonal variations in isotopic composition at all levels in the subtropics and in midlatitudes, and this bias is consistent across all data sets. LMDZ also underestimates the observed meridional isotopic gradient and the contrast between dry and convective tropical regions compared to satellite data sets. Comparison with six other isotope-enabled GCMs from the SWING2 project shows that biases exhibited by LMDZ are common to all models. The SWING2 GCMs show a very large spread in isotopic behavior that is not obviously related to that of humidity, suggesting water vapor isotopic measurements could be used to expose model shortcomings. In a companion paper, the isotopic differences between models are interpreted in terms of biases in the representation of processes controlling humidity.

  • 8. Sjolte, J.
    et al.
    Hoffmann, G.
    Johnsen, S. J.
    Vinther, B. M.
    Masson-Delmotte, V.
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Modeling the water isotopes in Greenland precipitation 1959-2001 with the meso-scale model REMO-iso2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, D18105- p.Article in journal (Refereed)
    Abstract [en]

    Ice core studies have proved the delta(18)O in Greenland precipitation to be correlated to the phase of the North Atlantic Oscillation (NAO). This subject has also been investigated in modeling studies. However, these studies have either had severe biases in the delta(18)O levels, or have not been designed to be compared directly with observations. In this study we nudge a meso-scale climate model fitted with stable water isotope diagnostics (REMO-iso) to follow the actual weather patterns for the period 1959-2001. We evaluate this simulation using meteorological observations from stations along the Greenland coast, and delta(18)O from several Greenland ice core stacks and Global Network In Precipitation (GNIP) data from Greenland, Iceland and Svalbard. The REMO-iso output explains up to 40% of the interannual delta(18)O variability observed in ice cores, which is comparable to the model performance for precipitation. In terms of reproducing the observed variability the global model, ECHAM4-iso performs on the same level as REMO-iso. However, REMO-iso has smaller biases in delta(18)O and improved representation of the observed spatial delta(18)O-temperature slope compared to ECHAM4-iso. Analysis of the main modes of winter variability of delta(18)O shows a coherent signal in Central and Western Greenland similar to results from ice cores. The NAO explains 20% of the leading delta(18)O pattern. Based on the model output we suggest that methods to reconstruct the NAO from Greenland ice cores employ both delta(18)O and accumulation records.

  • 9.
    Sturm, Christophe
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Noone, David
    University of Colorado.
    Comprehensive dynamical models of global and regional isotope distribution2009In: Isoscapes: Understanding movement, pattern, and process on Earth through isotope mapping / [ed] West, J.B.; Bowen, G.J.; Dawson, T.E.; Tu, K.P., Springer, 2009, 1, Chap 10- p.Chapter in book (Other academic)
  • 10.
    Sturm, Christophe
    et al.
    Stockholm University, Faculty of Science, Department of Geology and Geochemistry.
    Zhang, Qiong
    Stockholm University, Faculty of Science, Department of Meteorology .
    Noone, David
    University of Colorado.
    An introduction to stable water isotopes in climate models: benefits of forward proxy modelling for paleoclimatology2010In: Climate of the past, ISSN 1814-9332, Vol. 6, 115-129 p.Article in journal (Refereed)
    Abstract [en]

    Stable water isotopes have been measured in a wide range of climate archives, with the purpose of reconstructing regional climate variations. Yet the common assumption that the isotopic signal is a direct indicator of temperature proves to be misleading under certain circumstances, since its relationship with temperature also depends on e.g. atmospheric circulation and precipitation seasonality. The present article introduces the principles, benefits and caveats of using climate models with embedded water isotopes as a support for the interpretation of isotopic climate archives. A short overview of the limitations of empirical calibrations of isotopic proxy records is presented, with emphasis on the physical processes that infirm its underlying hypotheses. The simulation of climate and its associated isotopic signal, despite difficulties related to downscaling and intrinsic atmospheric variability, can provide a "transfer function" between the isotopic signal and the considered climate variable. The multi-proxy data can then be combined with model output to produce a physically consistent climate reconstruction and its confidence interval. A sensitivity study with the isotope-enabled global circulation model CAM3iso under idealised present-day, pre-industrial and mid-Holocene is presented to illustrate the impact of a changing climate on the isotope-temperature relationship.

  • 11. Yao, T.
    et al.
    Masson-Delmotte, V.
    Gao, J.
    Yu, W.
    Yang, X.
    Risi, C.
    Sturm, Christophe
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Werner, M.
    Zhao, H.
    He, Y.
    Ren, W.
    Tian, L.
    Shi, C.
    Hou, S.
    A review of climatic controls on δ18O in precipitation over the Tibetan Plateau: Observations and simulations2013In: Reviews of geophysics, ISSN 8755-1209, E-ISSN 1944-9208, Vol. 51, no 4, 2012RG000427- p.Article in journal (Refereed)
    Abstract [en]

    The stable oxygen isotope ratio (δ18O) in precipitation is an integrated tracer of atmospheric processes worldwide. Since the 1990s, an intensive effort has been dedicated to studying precipitation isotopic composition at more than 20 stations in the Tibetan Plateau (TP) located at the convergence of air masses between the westerlies and Indian monsoon. In this paper, we establish a database of precipitation δ18O and use different models to evaluate the climatic controls of precipitation δ18O over the TP. The spatial and temporal patterns of precipitation δ18O and their relationships with temperature and precipitation reveal three distinct domains, respectively associated with the influence of the westerlies (northern TP), Indian monsoon (southern TP), and transition in between. Precipitation δ18O in the monsoon domain experiences an abrupt decrease in May and most depletion in August, attributable to the shifting moisture origin between Bay of Bengal (BOB) and southern Indian Ocean. High-resolution atmospheric models capture the spatial and temporal patterns of precipitation δ18O and their relationships with moisture transport from the westerlies and Indian monsoon. Only in the westerlies domain are atmospheric models able to represent the relationships between climate and precipitation δ18O. More significant temperature effect exists when either the westerlies or Indian monsoon is the sole dominant atmospheric process. The observed and simulated altitude-δ18O relationships strongly depend on the season and the domain (Indian monsoon or westerlies). Our results have crucial implications for the interpretation of paleoclimate records and for the application of atmospheric simulations to quantifying paleoclimate and paleo-elevation changes.

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