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  • 1
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    Biome changes and their inferred climatic drivers in northern and eastern continental Asia at selected times since 40 cal ka bp (2018)
    Springer
    In:  Vegetation History and Archaeobotany, 27 (2). pp. 365-379.
    Details
    Publication Date: 2018-12-17
    Description: Recent global warming is pronounced in high-latitude regions (e.g. northern Asia), and will cause the vegetation to change. Future vegetation trends (e.g. the “arctic greening”) will feed back into atmospheric circulation and the global climate system. Understanding the nature and causes of past vegetation changes is important for predicting the composition and distribution of future vegetation communities. Fossil pollen records from 468 sites in northern and eastern Asia were biomised at selected times between 40 cal ka bp and today. Biomes were also simulated using a climate-driven biome model and results from the two approaches compared in order to help understand the mechanisms behind the observed vegetation changes. The consistent biome results inferred by both approaches reveal that long-term and broad-scale vegetation patterns reflect global- to hemispheric-scale climate changes. Forest biomes increase around the beginning of the late deglaciation, become more widespread during the early and middle Holocene, and decrease in the late Holocene in fringe areas of the Asian Summer Monsoon. At the southern and southwestern margins of the taiga, forest increases in the early Holocene and shows notable species succession, which may have been caused by winter warming at ca. 7 cal ka bp. At the northeastern taiga margin (central Yakutia and northeastern Siberia), shrub expansion during the last deglaciation appears to prevent the permafrost from thawing and hinders the northward expansion of evergreen needle-leaved species until ca. 7 cal ka bp. The vegetation-climate disequilibrium during the early Holocene in the taiga-tundra transition zone suggests that projected climate warming will not cause a northward expansion of evergreen needle-leaved species.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00334-017-0653-8
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Atmospheric bridge on orbital time scales (2017)
    Springer
    In:  Theoretical and Applied Climatology, 128 (3-4). pp. 709-718.
    Details
    Publication Date: 2018-12-17
    Description: Large-scale atmospheric patterns are examined on orbital timescales using a climate model which explicitly resolves the atmosphere–ocean–sea ice dynamics. It is shown that, in contrast to boreal summer where the climate mainly follows the local radiative forcing, the boreal winter climate is strongly determined by modulation of circulation modes linked to the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) and the Northern/Southern Annular Modes. We find that during a positive phase of the AO/NAO the convection in the tropical Pacific is below normal. The related atmospheric circulation provides an atmospheric bridge for the precessional forcing inducing a non-uniform temperature anomalies with large amplitudes over the continents. We argue that this is important for mechanisms responsible for multi-millennial climate variability and glacial inception.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1007/s00704-015-1725-2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Holocene Environmental Variability in the Arctic Gateway (2015)
    Springer
    In:  In: Integrated Analysis of Interglacial Climate Dynamics (INTERDYNAMIC). , ed. by Schulz, M. and Paul, A. Springer Briefs in Earth System Sciences . Springer, Berlin, pp. 37-42. ISBN 978-3-319-00692-5
    Details
    Publication Date: 2019-09-23
    Description: Environmental changes in the region connecting the Arctic Ocean and the northern North Atlantic were studied for the last 9,000 years (9 ka) by a combination of proxy-based paleoceanographic reconstructions as well as transient and time-slice simulations with climate models. Today, the area is perennially ice-covered in the west and ice-free in the east. Results show that sea-ice conditions were highly variable on short timescales in the last 9 ka. However, sea-ice proxies reveal an overall eastward movement of the sea-ice margin, in line with a decreasing influence of warm Atlantic Water advected to the Arctic Ocean. These cooling trends were rapidly reversed 100 years ago and replaced by the general warming in the Arctic. Model results show a consistently high freshwater input to the Arctic Ocean during the last 7 ka. The signal is robust against the Holocene cooling trend, however sensitive towards the warming trend of the last century. These results may play a role in the observed Arctic changes.
    Type: Book chapter , NonPeerReviewed
    DOI: 10.1007/978-3-319-00693-2_7
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    OceanRep: Book chapter
  • 4
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    Lessons on Climate Sensitivity From Past Climate Changes (2016)
    Springer
    In:  EPIC3Current Climate Change Reports, Springer, 2(4), pp. 148-158, ISSN: 2198-6061
    Details
    Publication Date: 2019-10-01
    Description: Over the last decade, our understanding of cli- mate sensitivity has improved considerably. The climate system shows variability on many timescales, is subject to non-stationary forcing and it is most likely out of equi- librium with the changes in the radiative forcing. Slow and fast feedbacks complicate the interpretation of geolog- ical records as feedback strengths vary over time. In the geological past, the forcing timescales were different than at present, suggesting that the response may have behaved differently. Do these insights constrain the climate sensitiv- ity relevant for the present day? In this paper, we review the progress made in theoretical understanding of climate sensitivity and on the estimation of climate sensitivity from proxy records. Particular focus lies on the background state dependence of feedback processes and on the impact of tipping points on the climate system. We suggest how to further use palaeo data to advance our understanding of the currently ongoing climate change.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 5
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    Reconciling glacial Antarctic water stable isotopes with ice sheet topography and the isotopic paleothermometer (2018)
    Springer Nature
    In:  EPIC3Nature Communications, Springer Nature, 9(3537), ISSN: 2041-1723
    Details
    Publication Date: 2018-09-17
    Description: Stable water isotope records from Antarctica are key for our understanding of Quaternary climate variations. However, the exact quantitative interpretation of these important climate proxy records in terms of surface temperature, ice sheet height and other climatic changes is still a matter of debate. Here we report results obtained with an atmospheric general circulation model equipped with water isotopes, run at a high-spatial horizontal resolution of one-by-one degree. Comparing different glacial maximum ice sheet reconstructions, a best model data match is achieved for the PMIP3 reconstruction. Reduced West Antarctic elevation changes between 400 and 800 m lead to further improved agreement with ice core data. Our modern and glacial climate simulations support the validity of the isotopic paleothermometer approach based on the use of present-day observations and reveal that a glacial ocean state as displayed in the GLAMAP reconstruction is suitable for capturing the observed glacial isotope changes in Antarctic ice cores.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
    Format: application/pdf
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  • 6
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    Evaluation of Eemian and Holocene Climate Trends: Combining Marine Archives with Climate Modelling (2015)
    Springer
    In:  EPIC3Integrated Analysis of Interglacial Climate Dynamics (INTERDYNAMIC), SpringerBriefs in Earth System Sciences, Germany, Springer, 5 p., pp. 31-35, ISBN: 978-3-319-00693-2
    Details
    Publication Date: 2015-06-05
    Description: In an attempt to assess trends of Holocene sea-surface temperature (SST), two proxies have been compiled and analyzed in light of model simulations. The data reveal contrasting SST trends, depending upon the proxy used to derive Holocene SST history. To reconcile these mismatches between proxies in the estimated Holocene SST trends, it has been proposed that the Holocene evolution of orbitally-driven seasonality of the incoming radiation is the first-order driving mechanism of the observed SST trends. Such hypothesis has been further tested in numerical models of the Earth system with important implications for SST signals ultimately recorded by marine sediment cores. The analysis of model results and alkenone proxy data for the Holocene indicate a similar pattern in temperature change, but the simulated SST trends underestimate the proxy-based SST trends by a factor of two to five. SST trends based on Mg/Ca show no correspondence with model results. We explore whether the consideration of different growing seasons and depth habitats of the planktonic organisms used for temperature reconstruction could lead to a better agreement of model results with alkenone data on a regional scale. We found that invoking shifts in the living season and habitat depth can remove some of the model–data discrepancies in SST trends. Our results indicate that modeled and reconstructed temperature trends are to a large degree only qualitatively comparable, thus providing at present a challenge for the interpretation of proxy data as well as the model sensitivity to orbital forcing.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 7
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    Enhanced North Pacific deep-ocean stratification by stronger intermediate water formation during Heinrich Stadial 1 (2019)
    Springer Nature
    In:  EPIC3Nature Communications, Springer Nature, 10(656), ISSN: 2041-1723
    Details
    Publication Date: 2021-02-16
    Description: The deglacial history of CO2 release from the deep North Pacific remains unresolved. This is due to conflicting indications about subarctic Pacific ventilation changes based on various marine proxies, especially for Heinrich Stadial 1 (HS-1) when a rapid atmospheric CO2 rise occurs. Here, we use a complex Earth System Model to investigate the deglacial North Pacific overturning and its control on ocean stratification. Our results show an enhanced intermediate-to-deep ocean stratification coeval with intensified North Pacific Intermediate Water (NPIW) formation during HS-1, compared to the Last Glacial Maximum. The stronger NPIW formation causes lower salinities and higher temperatures at intermediate depths. By lowering NPIW densities, this enlarges vertical density gradient and thus enhances intermediate-to-deep ocean stratification during HS-1. Physically, this process prevents the North Pacific deep waters from a better communication with the upper oceans, thus prolongs the existing isolation of glacial Pacific abyssal carbons during HS-1.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 8
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    North-West African Hydrologic Changes in the Holocene: A Combined Isotopic Data and Model Approach (2015)
    Springer
    In:  EPIC3Integrated Analysis of Interglacial Climate Dynamics (INTERDYNAMIC), (SpringerBriefs in Earth System Sciences), Heidelberg, Springer, 139 p., pp. 109-114, ISBN: 978-3-319-00692-5, ISSN: 2191-589X
    Details
    Publication Date: 2015-02-04
    Description: To achieve a better understanding of the hydrologic evolution of the North-West (NW) African monsoon system during the Holocene, in particular during inferred abrupt climate changes at the end of the African Humid Period (AHP), we investigated terrigenous plant lipids deposited in marine sediments offshore NW Africa. Changes in rainfall amount were estimated by compound-specific hydrogen isotope (δD) analyses. The spatial gradient of rainfall isotopic compositions is reflected in marine surface sediments. δD changes in plant waxes covering the last 100 years confirm the observed decrease in rainfall during the late twentieth century Sahel drought, and thus can be used for a quantitative calibration of δD and pre- cipitation. δD changes in sedimentary plant waxes show no abrupt change at the end of the AHP suggesting a gradual precipitation decline. These results are supported by Holocene climate simulations using a coupled atmosphere-land surface model, which includes an explicit modeling of isotopic fractionation within the hydrological cycle.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 9
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    Introduction to Modern Fortran for Earth System Sciences (2015)
    Springer
    In:  EPIC3Heidelberg, Springer, 250 p., ISBN: 978-3-642-37008-3
    Details
    Publication Date: 2015-06-05
    Description: This work provides a short "getting started" guide to Fortran 90/95. The main target audience consists of newcomers to the field of numerical computation within Earth system sciences (students, researchers or scientific programmers). Furthermore, readers accustomed to other programming languages may also benefit from this work, by discovering how some programming techniques they are familiar with map to Fortran 95.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Book , peerRev
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  • 10
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    Holocene Environmental Variability in the Arctic Gateway (2015)
    Springer
    In:  EPIC3Integrated Analysis of Interglacial Climate Dynamics (INTERDYNAMIC), Integrated Analysis of Interglacial Climate Dynamics (INTERDYNAMIC), Heidelberg, Springer, pp. 37-42, ISBN: 978-3-319-00692-5, ISSN: 2191-589X
    Details
    Publication Date: 2016-05-13
    Description: Environmental changes in the region connecting the Arctic Ocean and the northern North Atlantic were studied for the last 9,000 years (9 ka) by a combination of proxy-based paleoceanographic reconstructions as well as transient and time-slice simulations with climate models. Today, the area is perennially ice-covered in the west and ice-free in the east. Results show that sea-ice conditions were highly variable on short timescales in the last 9 ka. However, sea-ice proxies reveal an overall eastward movement of the sea-ice margin, in line with a decreasing influence of warm Atlantic Water advected to the Arctic Ocean. These cooling trends were rapidly reversed 100 years ago and replaced by the general warming in the Arctic. Model results show a consistently high freshwater input to the Arctic Ocean during the last 7 ka. The signal is robust against the Holocene cooling trend, however sensitive towards the warming trend of the last century. These results may play a role in the observed Arctic changes.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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