Temperature, precipitation, and vegetation changes in the Eastern Mediterranean over the last deglaciation and Dansgaard-Oeschger events

Mona Stockhecke,Achim Bechtel,Francien Peterse,Typhaine Guillemot,Carsten J Schubert

doi:10.1016/j.palaeo.2021.110535

Abstract

We here estimate past temperature and hydroclimate variations in eastern Anatolia for marine isotope stages 4 to 1 (MIS4 to MIS1) respectively using branched glycerol dialkyl glycerol tetraethers (brGDGTs) and the hydrogen isotopic composition of n-C29 leaf-wax n-alkanes (δ2Hwax) stored in the sedimentary record of Lake Van (Turkey). Our millennial-scale lipid biomarker records reflect warm and wet conditions during interstadials/interglacials and colder and dryer periods with increased evapotranspiration and aridity during stadials/glacials. The degree of methylation of the 5-methyl brGDGTs (MBT´5me) indicates increasing mean annual air temperatures (MAT) during stadial/interstadial transitions, that characterize Dansgaard-Oeschger events, and during the last glacial termination.Based on the effects of changes in precipitation amount on apparent enrichment factors between the δ2H of the C29n-alkanes and δ2H of precipitation, a total increase in annual precipitation of about 200 mm during transitions from stadials to interstadials, and of 300–350 mm during glacial-interglacial transitions can be determined, in line with previous paleoclimate reconstructions for the Eastern Mediterranean.High sterol concentrations in sediments deposited during warm and humid interstadials reflect increases in lake level, vegetation density and algal blooms, whereas lower values of the branched versus isoprenoid tetraethers ratio (BIT) likely reflects the increased niche of Thaumarchaeota resulting from enhanced windiness and mixing of the water column during colder periods. This quantitative hydroclimate reconstruction from Lake Van (Turkey), as it is optimally situated to respond to North Atlantic climate change via changes in the large-scale wind fields shed light into millennial-scale global climate variability.

Highlights

Information about the magnitude of temperature and precipitation changes during the last glacial termination and within the Holocene, as well as Marine Isotope Stage 3 (MIS3) is scarce for the continental Eastern Mediterranean
The sea surface temperature (SST) of the Black Sea changed with 2–3 ◦C during stadial/interstadial transitions (20–65 kyr BP; Wegwerth et al, 2015) based on the TEX86, a temperature proxy based on changes in the relative abundance of isoprenoid glycerol dialkyl glycerol tetraether (GDGT) membrane lipids produced by temperature-sensitive archaea in the water column (Schouten et al, 2002)
Estimates of temperature and precipitation changes during the last glacial-interglacial transitions in the Eastern Mediterranean have so far primarily been based on paleobotanical data or sea surface tempera tures

Summary

Introduction

Information about the magnitude of temperature and precipitation changes during the last glacial termination and within the Holocene, as well as Marine Isotope Stage 3 (MIS3) is scarce for the continental Eastern Mediterranean. Lake sediments are considered important terrestrial archives of past climate change, especially in areas where other high-resolution records, such as ice cores, are not available. For this reason, the sediments from the endorheic Lake Van (Turkey) were drilled in 2010 within the In ternational Continental Scientific Drilling project (ICDP) Paleovan (Litt and Anselmetti, 2014). The results of high-resolution studies over the last 600 kyr, including sedimentological and bulk geochemical data, pollen counts and isotopic measurements on car bonates, argue for generally cold and dry conditions during glacials, whereas interglacials were warmer and wetter (Kwiecien et al, 2014; Litt et al, 2014; Stockhecke et al, 2014b). The occurrence of deute rium (2H)-enriched C29 n-alkanes and C37 alkenones during MIS4 and MIS2 point towards dry climate conditions in the Lake Van region at this time, which was attributed to a decrease in the regional p/e ratio during this period, and independently supported by a maximum in pore water salinity (Randlett et al, 2017; Tomonaga et al, 2017)

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Conclusion