Late glacial to Holocene climatic and oceanographic record of sediment facies from the South Scotia Sea off the northern Antarctic Peninsula

Abstract

Two gravity cores were collected from the South Scotia Sea located off the northern Antarctic Peninsula during the 2002/2003 Korea Antarctic Research Program (KARP) expedition to determine the late Quaternary climatic and oceanographic history. Reassessment of previous sedimentological, geochemical and micropaleontological analyses combined with established age model of AMS 14C dates represent the reliable record of late Pleistocene climatic/oceanographic change for the Scotia Sea region of Antarctica. During the Last Glacial Maximum (LGM), the South Scotia Sea received large amounts of sorted terrigenous sediments and some of the reworked diatom fossils emplaced by bottom currents from an extensively glaciated Weddell Sea continental margin. Drifting icebergs calved from the glacial fronts have dispersed glacial dropstones throughout the study area. The bottom current deposits during the glacial phase comprise two lithologic units: (1) bioturbated gravelly sandy mud (Facies 1), formed by sluggish bottom current caused by reduced dense-water production originated from the ice sheet on the Weddell Shelf, (2) indistinctly layered diatomaceous mud as shown by total organic carbon (TOC) highs in the Facies 1, deposited by sporadic bottom currents caused by intensified sea–ice formation in polynya during the glacial stage. The LGM is characterized by greater and longer sea–ice coverage and a restricted Weddell/Scotia summer communication, as evidenced by a relative decrease in percentage Thalssiosira antarctica and Chaetoceros resting spores, which are more abundant close to the Weddell Ice Shelf. Deglaciation (about 13,000–9000 14C yr BP) in the South Scotia Sea was characterized by increasing TOC, diatom abundance, and decreasing magnetic susceptibility and sand contents up core. At this time, subglacial meltwater streams began to emanate from the Weddell Ice Sheet with peak of ice rafting. Sediment-laden turbid plumes from melting glacier and deglaciated Weddell Shelf have probably been joined into the realm of contour currents, Weddell Gyre circulation, ultimately forming indistinctly laminated gravelly mud (Facies 2) in the South Scotia Sea. These currents probably resulted from water exchange between the Weddell Ice Shelf and Circumpolar Warm Deep Water during the retreating phase of the last glaciation. The deglaciation was probably followed by a period of open-marine conditions with variable extent of sea ice (variable TOC content). Between about 9000 and 3000 14C yr BP, bottom water production occasionally appears to have diminished or ceased due to the disintegration of some of the Weddell Ice Shelf, and biogenic input became increased forming bioturbated diatomaceous mud and ooze (Facies 3). The climatic amelioration could have restored the Weddell/Scotia communication during the summer, as evidenced by a relative increase of T. antarctica and C. resting spore in Facies 3. At the onset of Neoglacial (about 3000 14C yr BP), a decrease in TOC and diatom abundance, and an increase of sand content reflect the formation of more extensive and seasonally persistent multiyear sea ice. The Weddell Ice Shelf advanced with increased sea–ice coverage at this time, and as a result, bottom water might play a role in transporting terrigenous sediments and reworked fossil diatoms into the South Scotia Sea, forming diatomaceous sandy mud (Facies 4). During this time, it is possible that the Weddell/Scotia communication would have been partly restricted, as evidenced by a reduction of the numbers of T. antarctica and C. resting spores. Our results indicate environmental variability throughout the late Quaternary that was consistent across most portions of the maritime Antarctic Peninsula. In addition, the timing of climatic transitions correlates with the Northern Hemisphere, indicating the possibility of coherent climatic variability during the late Quaternary, at least for the higher latitudes.