Beschreibung: Changes in heat transport associated with fluctuations in the strength of the Atlantic meridional overturning circulation (AMOC) are widely considered to affect the position of the Intertropical Convergence Zone (ITCZ), but the temporal immediacy of this teleconnection has to date not been resolved. Based on a high‐resolution marine sediment sequence over the last deglaciation, we provide evidence for a synchronous and near‐linear link between changes in the Atlantic interhemispheric sea surface temperature difference and continental precipitation over northeast Brazil. The tight coupling between AMOC strength, sea surface temperature difference, and precipitation changes over northeast Brazil unambiguously points to a rapid and proportional adjustment of the ITCZ location to past changes in the Atlantic meridional heat transport.

Beschreibung: Understanding the dynamics of warm climate states has gained increasing importance in the face of anthropogenic climate change, and while it is possible to simulate warm interglacial climates, these simulated results cannot be evaluated without the aid of geochemical proxies. One such proxy is δ18O, which allows for inference about both a climate state's hydrology and temperature. We utilize a stable water isotope equipped climate model to simulate three stages during the Last Interglacial (LIG), corresponding to 130, 125, and 120 kyr before present, using forcings for orbital configuration as well as greenhouse gases. We discover heterogeneous responses in the mean δ18O signal to the climate forcing, with large areas of depletion in the LIG δ18O signal over the tropical Atlantic, the Sahel, and the Indian subcontinent, and with enrichment over the Pacific and Arctic Oceans. While we find that the climatology mean relationship between δ18O and temperature remains stable during the LIG, we also discover that this relationship is not spatially consistent. Our results suggest that great care must be taken when comparing δ18O records of different paleoclimate archives with the results of climate models as both the qualitative and quantitative interpretation of δ18O variations as a proxy for past temperature changes may be problematic due to the complexity of the signals.

Beschreibung: All types of applications of stable water isotopes, for example, for the reconstruction of paleotemperatures or for climate model validation, rely on a proper understanding of the mechanisms determining the isotopic composition of water vapor and precipitation. In this study, we use the isotope‐enabled limited‐area model COSMOiso to characterize the impacts of continental evapotranspiration, rainout, and subcloud processes on δD of European water vapor and precipitation. To this end, we first confirm a reliable implementation of the most important isotope fractionation processes in COSMOiso by comparing 5 years of modeled δD values with multiplatform δD observations from Europe (remote sensing observations of the δD of water vapor around 2.6 km above ground level, in situ δD measurements in near‐surface water vapor, and δD precipitation data from the Global Network of Isotopes in Precipitation). Based on six 15 year sensitivity simulations, we then quantify the climatological impacts of the different fractionation processes on the δD values. We find δD of European water vapor and precipitation to be most strongly controlled by rainout. Superimposed to this are the effect of subcloud processes, which especially affects δD in precipitation under warm conditions, and the effect of continental evapotranspiration, which exerts an important control over the δD of near‐surface water vapor. In future studies, the validated COSMOiso model can be employed in a similar way for a comprehensive interpretation of European isotope records from climatologically different time periods.

Beschreibung: The Central Asian Pamir Mountains (Pamirs) are a high‐altitude region sensitive to climatic change, with only few paleoclimatic records available. To examine the glacial‐interglacial hydrological changes in the region, we analyzed the geochemical parameters of a 31‐kyr record from Lake Karakul and performed a set of experiments with climate models to interpret the results. δD values of terrestrial biomarkers showed insolation‐driven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive δD shifts driven by changes in precipitation seasonality were observed at ca. 31–30, 28–26, and 17–14 kyr BP. Multiproxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer evaporation, triggered higher lake levels during those episodes, possibly synchronous to northern hemispheric rapid climate events. We conclude that seasonal changes in precipitation‐evaporation balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant.

Beschreibung: Variations in oxygen isotope ratios (δ18O) measured from modern precipitation and geologic archives provide a promising tool for understanding modern and past climate dynamics and tracking elevation changes over geologic time. In areas of extreme topography, such as the Tibetan Plateau, the interpretation of δ18O has proven challenging. This study investigates the climate controls on temporal (daily and 6 h intervals) and spatial variations in present-day precipitation δ18O (δ18Op) across the Tibetan Plateau using a 30 year record produced from the European Centre/Hamburg ECHAM5-wiso global atmospheric general circulation model (GCM). Results indicate spatial and temporal agreement between model-predicted δ18Op and observations. Large daily δ18Op variations of 25 to +5‰ occur over the Tibetan Plateau throughout the 30 simulation years, along with interannual δ18Op variations of ~2‰. Analysis of extreme daily δ18Op indicates that extreme low values coincide with extreme highs in precipitation amount. During the summer, monsoon vapor transport from the north and southwest of the plateau generally corresponds with high δ18Op, whereas vapor transport from the Indian Ocean corresponds with average to low δ18Op. Thus, vapor source variations are one important cause of the spatial-temporal differences in δ18Op. Comparison of GCM and Rayleigh Distillation Model (RDM)-predicted δ18Op indicates a modest agreement for the Himalaya region (averaged over 86°–94°E), confirming application of the simpler RDM approach for estimating δ18Op lapse rates across Himalaya.

Beschreibung: Aim: We examined three potential enhancements of the stable isotope tech- nique for elucidating migratory connectivity in birds inhabiting poorly studied areas, illustrated for Eurasian cranes (Grus grus) that overwinter in and migrate through Israel. First, we examined the use of oxygen stable isotopes (d18O), sel- dom applied for this purpose. Second, we examined the relationship between ambient water d18O and hydrogen stable isotope (d2H) values derived from various models, to determine the geographical origins of migrants. Third, we introduced the use of probabilistic distribution modelling to refine the assign- ment to origin of migrants lacking detailed distribution maps. Location: Feather samples were collected in the Hula Valley (northern Israel) and across the species breeding range in north Eurasia. Methods: We analysed d18O and d2H in primary and secondary flight feathers using standard mass spectrometry. The maximum entropy (MAXENT) model was used to map the probability surface of potential breeding areas, as a Bayesian prior for assigning Hula Valley cranes to potential breeding grounds. Results: We found that d18O was suitable and informative. The soil water iso- scape performed better for d18O while precipitation isoscape was preferable for d2H. The MAXENT-based probability surface largely refined assignments. Overall, most (〉85%) cranes were assigned to the area west of the Ural Mountains, but for two individuals, most of the assigned area (〉90%) was farther east, suggest- ing, for the first time, that Eurasian cranes may undertake the North Asia–Mid- dle East (and perhaps Africa) migration flyway. Main conclusions: Our results call for broader use of d18O in migratory con- nectivity studies and for application of probabilistic distribution modelling. We also encourage investigation of factors determining d18O and d2H integration into animal tissues. The proposed framework may help improve our under- standing of migratory connectivity of species inhabiting previously unexplored areas and thus contribute to the development of efficient conservation plans.

Beschreibung: The Arctic water cycle is changing dramatically as evidenced by marked shifts in Arctic sea ice conditions, atmospheric processes, and hydrological regimes. Evaporation from the increasingly ice-free Arctic ocean causes moistening of the atmosphere and serves as an unprecedented water source for the Northern Hemisphere. Stable water isotopes (δ18O, δ2H, d-excess) can be used to trace exchange processes between ocean and atmosphere including their potential to feedback into the global climate system. The MOSAiC expedition provided a unique opportunity to collect, analyze, and synthesize discrete samples of the different hydrological compartments in the central Arctic, comprising sea ice, seawater, snow, and melt ponds. Moreover, we present observations of atmospheric humidity, δ18O, δ2H, and d-excess, obtained from a cavity-ring-down spectrometer installed on RV Polarstern and operated continuously during the MOSAiC expedition. By analyzing discrete samples, we found that average seawater δ18O of -1.7±1.95‰ (n=126) conforms to observed and modelled isotopic traits of the Arctic Ocean. Second year ice is relatively depleted compared to first year ice with average δ18O values of -3.1±2.81‰ (n=397) and -0.7±2.28‰ (n=409), respectively. Snow on top of the sea ice (n=303) has the most depleted isotopic signature among all compartments shaping the Arctic water cycle (mean δ18O=-15.3±7.12‰) The atmospheric water vapour dataset reveals a clear seasonal cycle; significant positive correlations are found both with local specific humidity and air temperature. The comparison of synoptic events, characterized by abrupt isotopic fluctuations, with simultaneous observations from land-based Arctic stations indicates a strong influence of sea ice coverage on the isotopic signal. For an in-depth understanding of the isotopic changes, the observations are compared to an isotope-enhanced ECHAM6 atmosphere simulation. The model-data comparison assesses the capability of this state-of-the-art AGCM to capture the first-order evaporation/condensation processes and their seasonal evolution. Our dataset provides a comprehensive description of the present-day isotopic composition of the Arctic water covering a complete seasonal cycle. This will ultimately contribute to resolve the linkages between sea ice, ocean, and atmosphere during critical transitions from frozen ocean to open water conditions.