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Minimal Antarctic sea ice during the Pliocene

¹ Department of Geology, University of Nebraska, Lincoln, Nebraska 68588-0340, USA, and Institute of Antarctic and Southern Ocean Studies, University of Tasmania, Hobart, Tasmania 7005, Australia
² School of Mathematics and Physics, University of Tasmania, Hobart, Tasmania 7005, Australia
³ Earth Sciences Department, University of California, Santa Cruz, California 95064, USA

Antarctic sea-ice concentration at Ocean Drilling Program Sites 1165 (64.380°S, 67.219°E) and 1166 (67.696°S, 74.787°E) was lower than today through much of the Pliocene. The low sea-ice concentration is evident from the proportion of the diatom Eucampia antarctica with intercalary valves (Eucampia index). This sea-ice proxy was calibrated by using modern diatom data obtained from core-top samples and winter sea-ice concentration data (September average through 1979–1987). The modern relationship is expressed as a binomial generalized linear model (modern sea-ice model). This model was applied to the Pliocene Eucampia index within a 95% tolerance interval (obtained from bootstrap estimates). The results indicate that reduced winter sea-ice concentrations persisted through much of the Pliocene and at times were 78% and 61% relatively less concentrated than today at Sites 1165 and 1166, respectively.

Key Words: Eucampia antarctica • diatom • sea ice • Pliocene • Southern Ocean • Ocean Drilling Program Leg 188 • Antarctica