Palaeoceanographic conditions and palaeoproductivity changes from the sub-Antarctic island South Georgia since the late deglacial, using marine micropalaeontology and geochemistry

This thesis presents a high-resolution multiproxy reconstruction of palaeoceanographic conditions and palaeoproductivity on the South Georgia shelf spanning the late deglacial through the Holocene. South Georgia lies within the path of the Antarctic Circumpolar Current (ACC) and the Southern Hemisphere Westerly Winds (SWW), south of the current position of the Antarctic Polar Front and encircled by the Southern ACC Front (SACCF). South Georgia is one of the few locations in the sub-Antarctic where it is possible to compare both terrestrial and marine records. Two sediment cores (GC666 and GC673) from the north-eastern shelf were analysed to reconstruct changes in oceanography, productivity, and glacial activity. Core GC666, recovered from the mid-shelf off Royal Bay, spans ca. 15.3 cal. kyr BP to present, while core GC673, from Cumberland Bay fjord, covers ca. 9.5 cal. kyr BP to present. Multiproxy methods include benthic foraminiferal and diatom assemblage analysis, XRF elemental analysis, and alkenone-derived sea-surface temperatures (SST). The base of GC666 contains laminated sediments (ca. 15.2 to 14.7 cal. kyr BP) interpreted as seasonal alternations between Chaetoceros-dominated biogenic laminae formed during the spring/early summer melt, and terrigenous laminae deposited from late summer glacial outwash and ice-rafted debris. This depositional setting is consistent with a calving-bay re-entrant formed during rapid deglacial ice retreat, supporting the interpretation that South Georgia reached the shelf edge in places during the Last Glacial Maximum. Warming during the late Pleistocene caused ice sheet retreat, though this was briefly reversed during the Antarctic Cold Reversal, when sea-ice associated diatoms increased and tidewater glaciers expanded. The Holocene climate evolution seems to show three phases. Early Holocene SST cooling between 10 and 8.2 cal. kyr BP is attributed to Antarctic meltwater input and the poleward migration of the SWW. This was followed by warming during the remainder of the early Holocene and during the mid Holocene climatic optimum (ca. 6.5 to 4.2 cal. kyr BP) with warmer SSTs and lower productivity resulting from greatly reduced glacial outwash-derived iron. The late Holocene Neoglacial (from ca. 4.2 cal. kyr BP) is characterised by cooling, increased sedimentation, and renewed productivity, consistent with Neoglacial advances. Cooler temperatures caused a northward migration of the SWW towards South Georgia, increasing precipitation rates and replenishing glaciers.<p></p>

Author dc:creator

• Jack Thomas Rhodes Wilkin (21052412)

• Micropalaeontology
• Palaeoclimatology
• South Georgia
• Diatoms
• XRF
• Foraminferia
• Alkenones
• Marine Geology
• Holocene
• Quaternary
• South Westerly Winds
• Climate Dynamics
• Productivity

Statement dc:rights

• All rights reserved
• Open Access after 2027-08-02

Identifier

10779/exe.31220797.v1

OAI identifier oai:identifier

oai:figshare.com:article/31220797