Black Sea hydroclimate and coupled hydrology was strongly controlled by high-latitude glacial climate dynamics

Antje Wegwerth,Helge W Arz,Ilka C Kleinhanns,Birgit Plessen

doi:10.1038/s43247-021-00129-3

Abstract

The Black Sea experienced pronounced millennial-scale changes in temperature and rainfall during the last glacial coinciding with Dansgaard-Oeschger cycles. However, little is known regarding the amount and sources of freshwater reaching this inland basin. Here, we present detailed ostracod δ18O data from the glacial Black Sea showing subdued Dansgaard-Oeschger cyclicity and four prominent longer-term saw-tooth shaped Bond-like cycles. We propose that the δ18Oostracods signature primarily reflects changes in the atmospheric circulation in response to the waxing and waning Eurasian Ice Sheet. The millennial-scale ice sheet variations likely resulted not only in latitudinal migrations of atmospheric frontal systems but also in shifts of dominant moisture sources for the Black Sea. Heavier isotopic precipitation arrived from the North Atlantic-Mediterranean realm during the warmer interstadials and lighter isotopic precipitation from the Eurasian continental interior during the colder stadials. The subdued Dansgaard-Oeschger variability likely reflects an integrated precipitation signal additionally affected by the long mixing times of the large Black Sea volume up to 1,500 years as suggested from hydrologic-isotope-balance modelling.

Highlights

The Black Sea experienced pronounced millennial-scale changes in temperature and rainfall during the last glacial coinciding with Dansgaard-Oeschger cycles
We present a new continuous highresolution δ18O record obtained from benthic ostracod carbonate shells from a well-dated SE Black Sea sediment core in order to investigate the hydrological dynamics in the former Black Sea upper water column and their relation to migrating air mass trajectories subjected to hydroclimate reorganisations
We further will elaborate on why the δ18O record has a significant orbital timescale component and how this is related to the Eurasian Ice Sheet (EIS) dynamics and changes in atmospheric circulation patterns over Eurasia

Summary

Introduction

The Black Sea experienced pronounced millennial-scale changes in temperature and rainfall during the last glacial coinciding with Dansgaard-Oeschger cycles. A simple hydrologic-isotope-balance model will show that the δ18Oostracods pattern reflects an integrated central European precipitation signal with its imprint strongly affected by hydrological activity and mixing times of the large water volume of the Black Sea. A new 87Sr/86Srostracods record obtained from the same sediment core, will serve for estimating changes in the dominant source of riverine supply that might be partially associated with meltwater release from the EIS in turn potentially affecting the δ18O composition of the Black Sea. Today, the Black Sea is a semi-enclosed, brackish basin and represents the largest anoxic water body on Earth[16,17]. Due to the higher input of freshwater by precipitation (P) and riverine runoff (R) compared to the loss of water by evaporation (E), the modern Black Sea has a positive water balance (P + R > E)[17]

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Conclusion