Kerguelen Plateau Quaternary–late Pliocene palaeoenvironments: from diatom, silicoflagellate and sedimentological data

Abstract

Gravity cores from the South Kerguelen Plateau contain sections representing two Quaternary intervals: (1) <0.62 Ma and (2) 1.6–1.25 Ma; three Pliocene intervals: (1) 2.2–1.6 Ma, (2) 3.1/3.0–2.64 Ma, (3) 3.2–3.1/3.0 Ma, and at least three disconformities: (1) 0.62 Ma until possibly the Last Glacial Maximum, (2) 2.2–1.6 Ma, and (3) 3.1–2.2 Ma. The disconformities probably formed during intense glacial intervals when the velocity of the Antarctic Circumpolar Current increased. Increased current velocity winnowed away finer biogenic sediment, to create ice rafted debris lags that protected the underlying sediment. Sediment deposition occurred during the less cold climatic intervals. In these deposits, three diatom assemblages were identified by comparison with extant diatoms. The diatom data indicate fluctuating Quaternary open pack-ice and open water conditions. The open pack-ice assemblage differs from modern sea-ice assemblages, and may reflect differences in the sea-ice setting during past colder intervals at latitudes north of the Antarctic Divergence. A silicoflagellate ratio was used to reconstruct Pliocene summer sea-surface temperatures. Two intervals with surface water temperatures warmer than today were identified, during which conditions were 3.0–4.5°C warmer (3.1–2.64 Ma), and 4.5°C warmer (3.2–3.1 Ma) as far south as 62°S. This would have occurred if either the Antarctic Polar Front Zone was ∼1200 km further south, or if the temperature gradient across the associated oceanic fronts would have been significantly lower. The Pliocene intervals contain a large amount of ice rafted debris that may reflect an environment heavily influenced by icebergs due to warmer glacial conditions in Antarctica, with increased sediment discharge and iceberg calving.