@article{DietzeMangelsdorfAndreevetal.2020, author = {Dietze, Elisabeth and Mangelsdorf, Kai and Andreev, Andrei and Karger, Cornelia and Schreuder, Laura T. and Hopmans, Ellen C. and Rach, Oliver and Sachse, Dirk and Wennrich, Volker and Herzschuh, Ulrike}, title = {Relationships between low-temperature fires, climate and vegetation during three late glacials and interglacials of the last 430 kyr in northeastern Siberia reconstructed from monosaccharide anhydrides in Lake El'gygytgyn sediments}, series = {Climate of the Past}, volume = {16}, journal = {Climate of the Past}, number = {2}, publisher = {Copernicus Publications}, address = {G{\"o}ttingen}, issn = {1814-9332}, doi = {10.5194/cp-16-799-2020}, pages = {788 -- 818}, year = {2020}, abstract = {Landscapes in high northern latitudes are assumed to be highly sensitive to future global change, but the rates and long-term trajectories of changes are rather uncertain. In the boreal zone, fires are an important factor in climate-vegetation interactions and biogeochemical cycles. Fire regimes are characterized by small, frequent, low-intensity fires within summergreen boreal forests dominated by larch, whereas evergreen boreal forests dominated by spruce and pine burn large areas less frequently but at higher intensities. Here, we explore the potential of the monosaccharide anhydrides (MA) levoglucosan, mannosan and galactosan to serve as proxies of low-intensity biomass burning in glacial-to-interglacial lake sediments from the high northern latitudes. We use sediments from Lake El'gygytgyn (cores PG 1351 and ICDP 5011-1), located in the far north-east of Russia, and study glacial and interglacial samples of the last 430 kyr (marine isotope stages 5e, 6, 7e, 8, 11c and 12) that had different climate and biome configurations. Combined with pollen and non-pollen palynomorph records from the same samples, we assess how far the modern relationships between fire, climate and vegetation persisted during the past, on orbital to centennial timescales. We find that MAs attached to particulates were well-preserved in up to 430 kyr old sediments with higher influxes from low-intensity biomass burning in interglacials compared to glacials. MA influxes significantly increase when summergreen boreal forest spreads closer to the lake, whereas they decrease when tundra-steppe environments and, especially, Sphagnum peatlands spread. This suggests that low-temperature fires are a typical characteristic of Siberian larch forests also on long timescales. The results also suggest that low-intensity fires would be reduced by vegetation shifts towards very dry environments due to reduced biomass availability, as well as by shifts towards peatlands, which limits fuel dryness. In addition, we observed very low MA ratios, which we interpret as high contributions of galactosan and mannosan from biomass sources other than those currently monitored, such as the moss-lichen mats in the understorey of the summergreen boreal forest. Overall, sedimentary MAs can provide a powerful proxy for fire regime reconstructions and extend our knowledge of long-term natural fire-climate-vegetation feedbacks in the high northern latitudes.}, language = {en} } @article{VogeliNajmanvanderBeeketal.2017, author = {Vogeli, Natalie and Najman, Yani and van der Beek, Pieter A. and Huyghe, Pascale and Wynn, Peter M. and Govin, Gwladys and van der Veen, Iris and Sachse, Dirk}, title = {Lateral variations in vegetation in the Himalaya since the Miocene and implications for climate evolution}, series = {Earth \& planetary science letters}, volume = {471}, journal = {Earth \& planetary science letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0012-821X}, doi = {10.1016/j.epsl.2017.04.037}, pages = {1 -- 9}, year = {2017}, abstract = {The Himalaya has a major influence on global and regional climate, in particular on the Asian monsoon system. The foreland basin of the Himalaya contains a record of tectonics and paleoclimate since the Miocene. Previous work on the evolution of vegetation and climate has focused on the central and western Himalaya, where a shift from C3 to C4 vegetation has been observed at similar to 7 Ma and linked to increased seasonality, but the climatic evolution of the eastern part of the orogen is less well understood. In order to track vegetation as a marker of monsoon intensity and seasonality, we analyzed delta C-13 and 8180 values of soil carbonate and associated delta C-13 values of bulk organic carbon from previously dated sedimentary sections exposing the syn-orogenic detrital Dharamsala and Siwalik Groups in the west, and, for the first time, the Siwalik Group in the east of the Himalayan foreland basin. Sedimentary records span from 20 to 1 Myr in the west (Joginder Nagar, Jawalamukhi, and Haripur Kolar sections) and from 13 to 1 Myr in the east (Kameng section), respectively. The presence of soil carbonate in the west and its absence in the east is a first indication of long-term lateral climatic variation, as soil carbonate requires seasonally arid conditions to develop. delta C-13 values in soil carbonate show a shift from around -10 parts per thousand to -2 parts per thousand at similar to 7 Ma in the west, which is confirmed by delta C-13 analyses on bulk organic carbon that show a shift from around -23 parts per thousand to -19 parts per thousand at the same time. Such a shift in isotopic values is likely to be associated with a change from C3 to C4 vegetation. In contrast, delta C-13 values of bulk organic carbon remain at 23 parts per thousand o in the east. Thus, our data show that the current east -west variation in climate was established at similar to 7 Ma. We propose that the regional change towards a more seasonal climate in the west is linked to a decrease of the influence of the Westerlies, delivering less winter precipitation to the western Himalaya, while the east remained annually humid due to its proximity to the monsoonal moisture source. (C) 2017 Elsevier B.V. All rights reserved.}, language = {en} } @article{RepaschScheingrossHoviusetal.2022, author = {Repasch, Marisa and Scheingross, Joel S. and Hovius, Niels and Vieth-Hillebrand, Andrea and Mueller, Carsten W. and H{\"o}schen, Carmen and Szupiany, Ricardo N. and Sachse, Dirk}, title = {River organic carbon fluxes modulated by hydrodynamic sorting of particulate organic matter}, series = {Geophysical research letters}, volume = {49}, journal = {Geophysical research letters}, number = {3}, publisher = {American Geophysical Union}, address = {Washington}, issn = {0094-8276}, doi = {10.1029/2021GL096343}, pages = {11}, year = {2022}, abstract = {Rivers regulate the global carbon cycle by transferring particulate organic carbon (POC) from terrestrial landscapes to marine sedimentary basins, but the processes controlling the amount and composition of fluvially exported POC are poorly understood. We propose that hydrodynamic sorting processes modify POC fluxes during fluvial transit. We test this hypothesis by studying POC transported along a similar to 1,200 km reach of the Rio Bermejo, Argentina. Nanoscale secondary ion mass spectrometry revealed that POC was either fine, mineral-associated organic matter, or coarse discrete organic particles. Mineral-associated POC is more resistant to oxidation and has a lower particle settling velocity than discrete POC. Consequently, hydraulic sorting and downstream fining amplify the proportion of fine, mineral-associated POC from similar to 55\% to similar to 78\% over 1,220 km of downstream transit. This suggests that mineral-associated POC has a greater probability of export and preservation in marine basins than plant detritus, which may be oxidized to CO2 during transit.}, language = {en} }