Africa's climate became progressively drier and more variable in the last few million years (e.g., deMenocal, 2004). Of particular interest, is a shift to drier and more variable conditions in the Olorgesailie Formation (Kenya) between 500 and 300 thousand years ago (ka) in which Potts et al. (2018) observed a turnover of ~85% of large-body mammalian fauna to smaller-body related taxa, suggesting that the shift was an evolutionary response to better adapt to the changing climate. However, a hiatus in the Olorgesailie record means that the cause of this faunal shift is still an outstanding question. Here, we analyze Lake Malawi drill core MAL 05–1 (~11ºS, 34ºE) to investigate if a specific climatic event stands out as a possible driver of the dramatic change observed in the East African mammal community. We use organic geochemical proxies including branched glycerol diaklyl glycerol tetraethers (GDGTs), leaf wax carbon and deuterium isotopic records to develop high-resolution temperature, vegetation, and precipitation records, respectively, between 600 and 200 ka. Results show a dramatic and abrupt temperature increase of ~6°C occurring in less than 3000 years during Glacial Termination V, which is the Marine Isotope Stage (MIS) 12 to MIS 11 transition at ~430 ka. Notably, this deglacial warming coincides with enriched leaf wax deuterium isotopic values suggesting a shift to more arid conditions in interglacial MIS 11 than in glacial MIS 12. Results also show another abrupt warming period in which temperature increased ~9°C around MIS 7 (~240 ka). We propose that the major warming and drying during Termination V in East Africa represents a significant abrupt change in the climate of eastern Africa and was a likely driver of the major faunal turnover noted in the Olorgesailie Basin.

Fjords contain a significant quantity of sediments deposited in coastal zones over the last ~100,000 years. Studies of Northern Hemisphere fjords have shown that a large part of the high concentration of sedimentary organic matter (OMsed) is terrestrial in origin (OMterr), composed of a modern detrital fraction and an old mineral-associated fraction (OMfossil). These results suggest that fjords are disproportionately responsible, on a per area basis, for the burial of organic matter in coastal zones. This study, after a rigorous examination of CuO and GDGT biomarker methods used to quantify terrestrial organic matter in coastal environments, demonstrated this hypothesis in a Southern Hemisphere fjord system, Fiordland, New Zealand. CuO analysis of Doubtful Sound surface sediments indicated a large contribution of vascular plant material to fjord sediments. The BIT Index correlated strongly with both delta13C and C/N values in Doubtful Sound surface sediments, indicated that it may accurately trace the relative proportions of marine and soil organic matter (OMsoil) in Fiordland. However, a detailed analysis of the conversion of the BIT Index to quantitative estimates of terrestrial (soil) organic matter revealed that these values are overestimates. Reconstructions of the BIT Index and tetraethers in cores from two locations on the Louisiana continental shelf demonstrated the influence of the crenarchaeol term on BIT Index-based terrestrial organic matter estimates. The differences in the applicability of the BIT Index to these two coastal environments was most likely due to large seasonal changes in productivity on the Louisiana Continental Shelf as well as higher marine relative to terrestrial inputs. Six cores were reconstructed for contributions from marine OM (OMmar), OMfossil, and OMterrestrial representing the last ~500 years of sedimentation. Spatial variations were larger than temporal variations, owing to negligible development and deforestation in the region. OMterr was the dominant fraction in all but one core, and OMfossil inputs were significant. Additionally, source reconstructions from a variety of biomarkers indicated that Landslides deliver large volumes of detrital organic matter to fjord sediments. These results confirm that fjords bury quantitatively significant volumes of organic carbon on a global scale.

The Arctic Region is currently experiencing an amplified warming if compared to the rest of the world. The soils in this region store approximately half of the global soil organic carbon (OC), mainly locked in the permanently-frozen ground (permafrost). This carbon sink is sensitive to global warming meaning that the predicted warming will likely increase the thaw-release of this ‘old’ carbon. However, what happens to this remobilized OC once it is transported to the Arctic Ocean, including the potential conversion to greenhouse gasses causing a positive feedback to climate warming, remains unclear. In this work, we further investigate the fate of terrestrial derived OC (terrOC) in the Eurasian Arctic Region. The key findings of this work are: • Glycerol dialkyl glycerol tetraethers (GDGTs) and bacteriohopanepolyols (BHPs) are present in marine sediments of the Eurasian Arctic Region and the associated Branched and Isoprenoidal tetraether (BIT) and Rsoil indices can be used to trace terrOC in marine realm. However, a slight modification in the Rsoil index is suggested (R’soil). • Analyses indicate that the behaviour of BIT is largely controlled by a marine GDGT contribution while the R’soil index is mainly controlled by the removal of soil marker BHPs. Although both indices suggest a non-conservative behavior for the terrOC, this leads to differences in the estimations for the percentage terrOC present. A multi-proxy approach is essential since the use of a single-proxy approach can lead to over/under estimation.• Comparison of BIT and 13Csoc indices across the East Siberian Shelf indicates that the BIT index is possibly reflecting a predominantly fluvial input while 13Csoc represents a mixed fluvial and coastal erosion input.• The macromolecular terrOC composition varies along a west-east Eurasian Arctic climosequence and is mainly controlled by the river runoff of surface derived terrOC and wetland coverage (sphagnum vs. higher plants) but is not affected by the presence/absence of continuous permafrost. • The phenols/(phenols+pyridines) ratio was suggested as a proxy to trace terrOC at the macromolecular level along the Kolyma River-East Siberian Sea transect. The results indicate a non-conservative behavior of the macromolecular terrOC comparable to the bulk of the terrOC.All molecular analyses/based proxies used showed that the remobilized terrOC in the Eurasian Arctic region behaves non-conservatively potentially causing a positive feedback to global climate change.