No evidence for extreme, long term warming in early Pliocene sediments of the Southern ocean

During the past similar to 10 years there has been considerable debate with respect to the response of the Antarctic ice sheets to early Pliocene warmth. Interpretations generally fall into one of three categories; (1) there was a major drawdown of the East Antarctic Ice Sheet (EAIS), (2) drawdown of EAIS was relatively small; (3) EAIS was largely unaffected by early Pliocene warmth. Here, this question is approached by using biogenic opal and carbonate in deep-sea sediments as proxy for paleoceanographic change. During the present day, these measures are largely dictated by the position of the Antarctic Polar Front (APF) with biogenic carbonate exhibiting an increase north of the APF and biogenic opal increasing to the south, That the carbonate/opal transition zone is a reliable feature in deep-sea sediments is evidenced by the fact that it is recorded north of its present position during the Last Glacial Maximum (LGM) and to the south of it during oxygen isotope stage 11, a warmer than present interglacial. When these proxies are applied to Southern Ocean sediments, high frequency glacial/interglacial changes are seen in the Pliocene and early Pleistocene. What appears to be a major glacial is recorded at about 4.5 Myrs B.P. Three, short duration carbonate highs (up to 18%), suggesting a southward movement of APF, occur at discrete intervals between about 4.6-4.8 Myrs B.P. However, these disappear or become reduced in amplitude toward the continent. Such data do not support any appreciable warming of surface waters near the Antarctic continent; neither does it support any claims of high (circa 20 degrees C) sea-level air temperatures over the EAIS. It is concluded that there is no evidence for significant drawdown of EAIS during early Pliocene warmth.