ALBERT

Description: The subglacial geology in Wilkes Land, East Antarctica is masked by thick ice and remains largely unexplored. Yet the underlying crustal architecture records evidence of repeated supercontinent cycles and provides the geological template for the evolution of the Antarctic Ice Sheet. Sediment eroded from under the ice is ultimately deposited in the ocean, such that marine sediment can be used to characterise the adjacent subglacial geology. We use detrital grain morphology, geochemistry and isotopic data from a kasten core to construct a new marine sediment provenance record for the continental slope of central Wilkes Land, and provide new isotopic signatures from proximal coastal outcrops for comparison. We establish the source rock type, age and provenance, and the associated transport pathways and mechanisms responsible for detrital sediment input from 23.5 ka to present. A principally igneous source is revealed with dominant age populations between c. 1200-1100 Ma and c. 1600-1300 Ma, characteristic of the proximal Banzare, Nuyina and Wilkes Provinces. The detrital geochronology suggests no change in sediment provenance over the last 23.5 ka, despite major ice sheet retreat during this time. A minor c. 700-500 Ma detrital age population unknown from the central Wilkes region was likely transported westward via icebergs to the core site. These findings broadly correspond with earlier interpretations of the subglacial geology and erosion rates at the base of the ice sheet predicted from two ice sheet models, demonstrating the value of sediment provenance studies for uncovering proximal subglacial geology and reconstructing past ice sheet configurations.

Description: Morphometric measurements of Fragilariopsis kerguelensis valves from a two-year time series covering the period from November 2002 to October 2004 collected by a sediment trap at 800m below the ocean surface which was moored near 54° S 140° E in ca. 2300 m water depth, close to the top of the Australia-Antarctica mid-ocean ridge.

Description: Downcore measurements of iceberg-rafted debris (IBRD) flux and biogenic silica concentrations in kasten core IN2017_V01-A042-KC14 from the continental slope of central Wilkes Land, East Antarctica. The IBRD flux was calculated by multiplying the coarse sand fraction by the linear sedimentation rate and the dry bulk density at each depth interval along the core. All of these values are shown. The biogenic silica concentration is shown as a percentage.

Description: Pb-Pb ratios, ages and trace element data from detrital feldspars in kasten core IN2017_V01-A042-KC14 from the continental slope of central Wilkes Land, East Antarctica and in-situ feldspars from coastal basement rocks in East Antarctica (Chick Island and Balaena Islets). All data was obtained using laser ablation-inductively-couple plasma mass spectrometry (LA-ICPMS). All ratios and ages are shown with one standard error.

Description: Diatom assemblages from 228 core-top samples were investigated to determine the modern geographic distributions of 10 major open ocean species or species groups in the Atlantic and Indian sectors of the Southern Ocean. Our study gives a more comprehensive view of the relationships between diatom distribution and environmental pressures than previous studies, as our modern database covers a much wider area, and additionally highlights the relationships with sea ice cover and concentration. The 10 species or species categories can mainly be lumped into three groupings. First, a cool open ocean grouping composed of Rhizosolenia pointed group, Thalassiosira gracilis group and Trichotoxon reinboldii with maximum relative abundances occurring within the maximum winter sea-ice edge. Second, a pelagic open ocean grouping composed of Fragilariopsis kerguelensis, Thalassiosira lentiginosa, Thalassiosira oliverana and Thalassiothrix spp. group with maximum occurrences at the Antarctic Polar Front. Third, a warm open ocean grouping with maximum abundances observed within the Polar Front Zone and composed of the Rhizosolenia rounded group, the Thalassionema nitzschioides var. nitzschioides group and the Thalassionema nitzschioides var. lanceolata. Comparisons of the abovementioned 10 species or species groups with modern February sea-surface temperatures and sea-ice duration and concentration reveal species-specific sedimentary distributions regulated both by sea-surface temperatures and sea ice conditions that support the use of diatom remains to reconstruct past variations of these environmental parameters via qualitative and transfer function approaches.

Description: This paper gives a modern circumscription of Tropical/Subtropical diatoms regarding their relationship with sea-surface temperatures (SST) and sea ice cover. Diatoms from 228 core-top sediment samples collected from the Southern Ocean were studied to determine the geographic distribution of eight major diatom species/taxa preserved in surface sediments generally located north of the Subantarctic Front. The comparison of the relative contribution of diatom species with modern February SST and sea-ice cover reveals species-specific sedimentary distributions regulated both by water temperatures and sea ice conditions. Although selective preservation might have played some role, their presence in surface and downcore sediments from the Southern Ocean are reliable indicators of high SST and poleward transport of waters from the Tropical/Subtropical Atlantic. Our work supports the use of diatom remains to reconstruct past variations of these environmental parameters via qualitative and transfer function approaches.