Beschreibung: Climate in the high latitudes changed massively during the last deglaciation. Temperature rose due to the polar amplification more than twice as much as in the global mean leading predominately to the shrinking of various parts of the cryosphere: decline of northern hem- ispheric (NH) land ice sheets and permafrost thawing, and a reduction in sea ice extent in both hemispheres. It is thus a rather natural choice to also analyse how changes in these polar regions might influence the global carbon cycle and atmospheric CO2. Here we use carbon cy- cle models to analyse two examples of the impact of high latitude climate change on deglacial CO2: (i) changes in the position of the westerly winds in the Southern Ocean during the Last Glacial Maximum (LGM) (based on Völker and Köhler 2013); (ii) Northern Hemisphere permafrost thawing at the onset of the Bølling/Allerød (B/A) around 14.6 ka ago (based on Köhler et al. 2014).

Beschreibung: wo commonly used proxies based on the distribution of glycerol dialkyl glycerol tetraethers (GDGTs) are the TEX86 (TetraEther indeX of 86 carbon atoms) paleothermometer for sea surface temperature reconstructions and the BIT (Branched Isoprenoid Tetraether) index for reconstructing soil organic matter input to the ocean. An initial round-robin study of two sediment extracts, in which 15 laboratories participated, showed relatively consistent TEX86 values (reproducibility ±3–4°C when translated to temperature) but a large spread in BIT measurements (reproducibility ±0.41 on a scale of 0–1). Here we report results of a second round-robin study with 35 laboratories in which three sediments, one sediment extract, and two mixtures of pure, isolated GDGTs were analyzed. The results for TEX86 and BIT index showed improvement compared to the previous round-robin study. The reproducibility, indicating interlaboratory variation, of TEX86 values ranged from 1.3 to 3.0°C when translated to temperature. These results are similar to those of other temperature proxies used in paleoceanography. Comparison of the results obtained from one of the three sediments showed that TEX86 and BIT indices are not significantly affected by interlaboratory differences in sediment extraction techniques. BIT values of the sediments and extracts were at the extremes of the index with values close to 0 or 1, and showed good reproducibility (ranging from 0.013 to 0.042). However, the measured BIT values for the two GDGT mixtures, with known molar ratios of crenarchaeol and branched GDGTs, had intermediate BIT values and showed poor reproducibility and a large overestimation of the “true” (i.e., molar-based) BIT index. The latter is likely due to, among other factors, the higher mass spectrometric response of branched GDGTs compared to crenarchaeol, which also varies among mass spectrometers. Correction for this different mass spectrometric response showed a considerable improvement in the reproducibility of BIT index measurements among laboratories, as well as a substantially improved estimation of molar-based BIT values. This suggests that standard mixtures should be used in order to obtain consistent, and molar-based, BIT values.