Changes in Holocene climate and the intensity of Southern Hemisphere Westerly Winds based on a high-resolution palynological record from sub-Antarctic South Georgia

Sub-Antarctic South Georgia is a key region for studying climate variability in the Southern Hemisphere, because of its position at the core of the Southern Hemisphere Westerly Wind belt and between the Antarctic Circumpolar Current and the Polar Frontal Zone. Here, we present a 5.8-m long high-resolution pollen record from Fan Lake on Annenkov Island dominated by local sub-polar vegetation, with Acaena and Poaceae being present throughout the last 7000 years. Palynological and sedimentological analyses revealed a warm late Holocene ‘climate optimum’ between 3790 and 2750 cal. yr BP, which was followed by a gradual transition to cool and wet conditions. This cooling was interrupted by slightly warmer environmental conditions between 1670 and 710 cal. yr BP that partly overlap with the Northern Hemisphere ‘Medieval Climate Anomaly’. Increases in non-native and long-distance pollen grains transported from South America (e.g. Nothofagus, Podocarpus) indicate that stronger Southern Hemisphere Westerly Winds over South Georgia possibly occurred during some ‘colder’ phases of the late Holocene, most notably between c. 2210 and 1670 cal. yr BP and after 710 cal. yr BP

A new quantitative approach to identify reworking in Eocene to Miocene pollen records from offshore Antarctica using red fluorescence and digital imaging

Antarctic palaeoclimate evolution and vegetation history after the formation of a continent-scale cryosphere at the Eocene-Oligocene boundary, 33.9 million years ago, has remained a matter of controversy. In particular, the reconstruction of terrestrial climate and vegetation has been strongly hampered by uncertainties in unambiguously identifying non-reworked as opposed to reworked sporomorphs that have been transported into Antarctic marine sedimentary records by waxing and waning ice sheets. Whereas reworked sporomorph grains over longer non-successive geological timescales are easily identifiable within younger sporomorph assemblages (e.g. Permian sporomorphs in Pliocene sediments), distinguishing non-reworked from reworked material in palynological assemblages over successive geological time periods (e.g. Eocene sporomorphs in Oligocene sediments) has remained problematic. This study presents a new quantitative approach to identifying non-reworked pollen assemblages in marine sediment cores from circum-Antarctic waters. We measured the fluorescence colour signature, including red, green, and blue fluorescence; brightness; intensity; and saturation values of selected pollen and spore taxa from Eocene, Oligocene, and Miocene sediments from the Wilkes Land margin Site U1356 (East Antarctica) recovered during Integrated Ocean Drilling Program (IODP) Expedition 318. Our study identified statistically significant differences in red-fluorescence values of non-reworked sporomorph taxa against age. We conclude that red fluorescence is a reliable parameter for identifying the presence of non-reworked pollen and spores in Antarctic marine sediment records from the circum-Antarctic realm that are influenced by glaciation and extensive reworking. Our study provides a new tool to accurately reconstruct Cenozoic terrestrial climate change on Antarctica using fossil pollen and spores.This study was funded by the Faculty of Engineering and Environment Research Studentship from Northumbria University. The samples used for this research were provided by the Integrated Ocean Drilling Program (IODP). Ulrich Salzmann acknowledges funding received from the Natural Environment Research Council (NERC grant NE/H000984/1). Francesca Sangiorgi thanks the Netherlands Organisation for Scientific Research (NWO) for NNPP Polar 866.10.110. Peter K. Bijl acknowledges the Dutch National Organisation for Scientific Research(NWO)for VENI grant no. 863.13.002. Carlota Escutia thanks the MINECO for scientific research grant CTM2014-60451-C2-1-P. Jörg Pross acknowledges support through the German Science Foundation (DFG; grant PR 651/10). We would finally like to thank the anonymous reviewer and Michael Hannah for their useful comments, which helped us to further improve this paper

Paleoceanography and ice sheet variability offshore Wilkes Land, Antarctica - Part 1: Insights from late Oligocene astronomically paced contourite sedimentation

Antarctic ice sheet and Southern Ocean paleoceanographic configurations during the late Oligocene are not well resolved. They are however important to understand the influence of high-latitude Southern Hemisphere feedbacks on global climate under CO scenarios (between 400 and 750 ppm) projected by the IPCC for this century, assuming unabated CO emissions. Sediments recovered by the Integrated Ocean Drilling Program (IODP) at Site U1356, offshore of the Wilkes Land margin in East Antarctica, provide an opportunity to study ice sheet and paleoceanographic configurations during the late Oligocene (26-25 Ma). Our study, based on a combination of sediment facies analysis, magnetic susceptibility, density, and X-ray fluorescence geochemical data, shows that glacial and interglacial sediments are continuously reworked by bottom currents, with maximum velocities occurring during the interglacial periods. Glacial sediments record poorly ventilated, low-oxygenation bottom water conditions, interpreted as resulting from a northward shift of westerly winds and surface oceanic fronts. Interglacial sediments record more oxygenated and ventilated bottom water conditions and strong current velocities, which suggests enhanced mixing of the water masses as a result of a southward shift of the polar front. Intervals with preserved carbonated nannofossils within some of the interglacial facies are interpreted as forming under warmer paleoclimatic conditions when less corrosive warmer northern component water (e.g., North Atlantic sourced deep water) had a greater influence on the site. Spectral analysis on the late Oligocene sediment interval shows that the glacial-interglacial cyclicity and related displacements of the Southern Ocean frontal systems between 26 and 25Ma were forced mainly by obliquity. The paucity of iceberg-rafted debris (IRD) throughout the studied interval contrasts with earlier Oligocene and post-Miocene Climate Optimum sections from Site U1356 and with late Oligocene strata from the Ross Sea, which contain IRD and evidence for coastal glaciers and sea ice. These observations, supported by elevated sea surface paleotemperatures, the absence of sea ice, and reconstructions of fossil pollen between 26 and 25 Ma at Site U1356, suggest that open-ocean water conditions prevailed. Combined, this evidence suggests that glaciers or ice caps likely occupied the topographic highs and lowlands of the now marine Wilkes Subglacial Basin (WSB). Unlike today, the continental shelf was not overdeepened and thus ice sheets in the WSB were likely land-based, and marine-based ice sheet expansion was likely limited to coastal regions.This research used samples and data provided by the Integrated Ocean Drilling Program, now the International Ocean Discovery Program (IODP). We thank thestaff onboard IODP Exp. 318 and at the Gulf Coast, the Bremen, and the Kochi IODP core repositories for assistance in core handling and shipping. We thank Vera Lukies (MARUM) for technical support with XRF core scanning and Shizu Yanagimoto (KOCHI) fortechnical supportwith CT scans.We alsothank theconstructive comments of an anonymous reviewer and Steven Pekar that have helped to improve this paper. Funding for this research is provided by the Spanish Ministerio de Economía y Competitividad (grants CTM 2011-24079 and CTM2014-60451-C2-1-P), co-funded by the European Union through FEDER funds. Ulrich Salzmann thanks the Deutsche Forschungsgemeinschaft (DFG) (RO 1113/6). Peter K. Bijl, Francesca Sangiorgi, and Julian D. Hartman acknowledge funding through the NWO polar programme grant no 866.10.110. Peter K. Bijl acknowledges funding through NWO-VENI grant no 863.13.002. Ulrich Salzmann acknowledges funding received from the Natural Environment Research Council (NERC grant NE/H000984/1)

Paleoceanography and ice sheet variability offshore Wilkes Land, Antarctica - Part 1 : Insights from late Oligocene astronomically paced contourite sedimentation

Antarctic ice sheet and Southern Ocean paleoceanographic configurations during the late Oligocene are not well resolved. They are however important to understand the influence of high-latitude Southern Hemisphere feedbacks on global climate under CO2 scenarios (between 400 and 750 ppm) projected by the IPCC for this century, assuming unabated CO2 emissions. Sediments recovered by the Integrated Ocean Drilling Program (IODP) at Site U1356, offshore of the Wilkes Land margin in East Antarctica, provide an opportunity to study ice sheet and paleoceanographic configurations during the late Oligocene (26-25 Ma). Our study, based on a combination of sediment facies analysis, magnetic susceptibility, density, and X-ray fluorescence geochemical data, shows that glacial and interglacial sediments are continuously reworked by bottom currents, with maximum velocities occurring during the interglacial periods. Glacial sediments record poorly ventilated, low-oxygenation bottom water conditions, interpreted as resulting from a northward shift of westerly winds and surface oceanic fronts. Interglacial sediments record more oxygenated and ventilated bottom water conditions and strong current velocities, which suggests enhanced mixing of the water masses as a result of a southward shift of the polar front. Intervals with preserved carbonated nannofossils within some of the interglacial facies are interpreted as forming under warmer paleoclimatic conditions when less corrosive warmer northern component water (e.g., North Atlantic sourced deep water) had a greater influence on the site. Spectral analysis on the late Oligocene sediment interval shows that the glacial-interglacial cyclicity and related displacements of the Southern Ocean frontal systems between 26 and 25Ma were forced mainly by obliquity. The paucity of iceberg-rafted debris (IRD) throughout the studied interval contrasts with earlier Oligocene and post-Miocene Climate Optimum sections from Site U1356 and with late Oligocene strata from the Ross Sea, which contain IRD and evidence for coastal glaciers and sea ice. These observations, supported by elevated sea surface paleotemperatures, the absence of sea ice, and reconstructions of fossil pollen between 26 and 25 Ma at Site U1356, suggest that open-ocean water conditions prevailed. Combined, this evidence suggests that glaciers or ice caps likely occupied the topographic highs and lowlands of the now marine Wilkes Subglacial Basin (WSB). Unlike today, the continental shelf was not overdeepened and thus ice sheets in the WSB were likely land-based, and marine-based ice sheet expansion was likely limited to coastal regions

Paleoceanography and ice sheet variability offshore Wilkes Land, Antarctica - Part 1 : Insights from late Oligocene astronomically paced contourite sedimentation

Antarctic ice sheet and Southern Ocean paleoceanographic configurations during the late Oligocene are not well resolved. They are however important to understand the influence of high-latitude Southern Hemisphere feedbacks on global climate under CO2 scenarios (between 400 and 750 ppm) projected by the IPCC for this century, assuming unabated CO2 emissions. Sediments recovered by the Integrated Ocean Drilling Program (IODP) at Site U1356, offshore of the Wilkes Land margin in East Antarctica, provide an opportunity to study ice sheet and paleoceanographic configurations during the late Oligocene (26-25 Ma). Our study, based on a combination of sediment facies analysis, magnetic susceptibility, density, and X-ray fluorescence geochemical data, shows that glacial and interglacial sediments are continuously reworked by bottom currents, with maximum velocities occurring during the interglacial periods. Glacial sediments record poorly ventilated, low-oxygenation bottom water conditions, interpreted as resulting from a northward shift of westerly winds and surface oceanic fronts. Interglacial sediments record more oxygenated and ventilated bottom water conditions and strong current velocities, which suggests enhanced mixing of the water masses as a result of a southward shift of the polar front. Intervals with preserved carbonated nannofossils within some of the interglacial facies are interpreted as forming under warmer paleoclimatic conditions when less corrosive warmer northern component water (e.g., North Atlantic sourced deep water) had a greater influence on the site. Spectral analysis on the late Oligocene sediment interval shows that the glacial-interglacial cyclicity and related displacements of the Southern Ocean frontal systems between 26 and 25Ma were forced mainly by obliquity. The paucity of iceberg-rafted debris (IRD) throughout the studied interval contrasts with earlier Oligocene and post-Miocene Climate Optimum sections from Site U1356 and with late Oligocene strata from the Ross Sea, which contain IRD and evidence for coastal glaciers and sea ice. These observations, supported by elevated sea surface paleotemperatures, the absence of sea ice, and reconstructions of fossil pollen between 26 and 25 Ma at Site U1356, suggest that open-ocean water conditions prevailed. Combined, this evidence suggests that glaciers or ice caps likely occupied the topographic highs and lowlands of the now marine Wilkes Subglacial Basin (WSB). Unlike today, the continental shelf was not overdeepened and thus ice sheets in the WSB were likely land-based, and marine-based ice sheet expansion was likely limited to coastal regions

Late Oligocene XRF scanner data from IODP Site 318-U1356 Willkes Land Margin, Antarctica

Antarctic ice sheet and Southern Ocean paleoceanographic configurations during the late Oligocene are not well resolved. They are however important to understand the influence of high-latitude Southern Hemisphere feedbacks on global climate under CO2 scenarios (between 400 and 750 ppm) projected by the IPCC for this century, assuming unabated CO2 emissions. Sediments recovered by the Integrated Ocean Drilling Program (IODP) at Site U1356, offshore of the Wilkes Land margin in East Antarctica, provide an opportunity to study ice sheet and paleoceanographic configurations during the late Oligocene (26-25 Ma). Our study, based on a combination of sediment facies analysis, magnetic susceptibility, density, and X-Ray Fluorescence geochemical data, shows that glacial and interglacial sediments are continuously reworked by bottom-currents, with maximum velocities occurring during the interglacial periods. Glacial sediments record poorly ventilated, low-oxygenation bottom water conditions, interpreted to result from a northward shift of westerly winds and surface oceanic fronts. Interglacial sediments record more oxygenated and ventilated bottom water conditions and strong current velocities, which suggests enhanced mixing of the water masses as a result of a southward shift of the Polar Front. Intervals with preserved carbonated nannofossils within some of the interglacial facies are interpreted to form under warmer paleoclimatic conditions when less corrosive warmer northern component water (e.g. North Atlantic sourced deep water) had a greater influence on the Site. Spectral analysis on the late Oligocene sediment interval show that the glacial-interglacial cyclicity and related displacements of the Southern Ocean frontal systems between 26-25 Ma were forced mainly by obliquity. The paucity of iceberg rafted debris (IRD) throughout the studied interval contrasts with earlier Oligocene and post-Miocene Climate Optimum sections from Site U1356 and with late Oligocene strata from the Ross Sea, which contain IRD and evidence for coastal glaciers and sea ice. These observations, supported by elevated sea surface paleotemperatures, the absence of sea-ice, and reconstructions of fossil pollen between 26 and 25 Ma at Site U1356, suggest that open ocean water conditions prevailed. Combined, these evidences suggest that glaciers or ice caps likely occupied the topographic highs and lowlands of the now marine Wilkes Subglacial Basin (WSB). Unlike today, the continental shelf was not over-deepened and thus ice sheets in the WSB were likely land-based and marine-based ice sheet expansion was likely limited to coastal regions