Climate Change During the Pliocene: Interpretations from Site 697, the Jane Basin, Weddell Sea, Antarctica

Recent warming of Earth’s climate has inspired many studies of the polar region in order to better understand how ice-sheets respond to climate change. Oceanic systems play a key role in regulating climate. Surface ocean circulation is driven by wind and deep ocean circulation (thermohaline) by density. Both transport heat and nutrients around the world. This study analyzes changes in grain size and composition of mid and late Pliocene-age sediment (~3.8-2.7 Ma), from the Jane Basin in West Antarctica. The Pliocene was a time when global temperatures were 2.5-4.0 °C warmer, and when carbon dioxide levels were similar to today. Based on changes in both the fine and coarse-fraction sediment (IRD), three distinct intervals were identified in which both the processes and sources of the sediment changed. Interval I extends from ~3.78 to ~3.63 Ma, and was a time when both surface and bottom currents were active and variable, and peak changes in the currents and IRD deposition occurred at similar times. During Interval II, ~3.50-3.30 Ma, both surface and bottom currents continued to active, but were more variable with peak changes offset by about ~15-40 thousand years. Interval III, ~3.30-2.77 Ma, was a time when there was little to no input of IRD, and slower, less variable bottom currents. This data shows that during Intervals I and II, ice sheets produced icebergs that traveled far enough to deposit IRD in the Jane Basin and bottom currents, though variable were strong. However, at the end of Interval II there was a slight decrease in bottom current strength and a much larger decrease in IRD. This change is attributed to an abrupt cooling event. During the late Pliocene, the bottom current activity was lower than in the earlier Pliocene, and IRD deposition decreased, suggesting that fewer icebergs were produced, or that the icebergs did not travel far enough to deposit course sediment into the Jane Basin. Overall, understanding how the Antarctic environment responded to changes in climate allows us to better predict how our climate today will respond to similar conditions from the past. Thus, it is important to use the sedimentary archive as the key to the future.