Circum-Antarctic Coastal Environmental Changes and Climate Feedbacks During the Mid-Holocene

Paul Arthur Berkman (Byrd Polar Research Center, Ohio State University, Columbus, OH 43210; ph 614-292-3670; fax 614-292-4697; Internet: PAUL+@osu.edu); [David H. Bromwich] (Byrd Polar Research Center, Ohio State University, Columbus, OH 43210; ph 614-292-6692; fax 614-292-4697; Internet: bromwich.1@osu.edu); [Lonnie G. Thompson] (Byrd Polar Research Center, Ohio State University, Columbus, OH 43210; ph 614-292-6531; fax 614-292-4697; Internet: thompson.3@osu.edu)

The mid-Holocene was a dynamic period of global climate change. Cores from Peruvian glaciers and hermatypic corals in the tropical Pacific Ocean region indicate that global temperatures were 1-2 oC warmer 7000 to 5000 BP than today. Lake levels associated with monsoon circulations also were decreasing during this period. Together, these data indicate that there were marked changes in the zonal evaporation-precipitation profile during the mid-Holocene. The purpose of this presentation is to assess whether these ocean-atmosphere phenomena in the tropics could have been connected to circum-Antarctic coastal environmental changes which also occurred during the mid-Holocene.

In the circum-Antarctic coastal zone, several independent datasets indicated that there were marked coastal environmental changes around the continent during the mid-Holocene. Along the Victoria Land Coast in the Ross Sea, penguins which require access to open water have continuously occupied rookeries near the present Drygalski Ice Tongue for the last 6000 years. Considering that the Drygalski Ice Tongue is the primary forcing factor for the Terra Nova Bay polynya, these data suggest there has been a persistent polynya operating in the Ross Sea since the mid-Holocene. Presence of this polynya, which has been estimated to influence more than 20% of the sea-ice production in the Ross Sea today, would have influenced the higher abundances of sea-ice diatoms in Ross Sea sediments after 6000 BP. Moreover, deposition of marine mollusc assemblages from low-energy coastal environments (which are another indicator of sea-ice coverage) began in the Ross Sea, along the East Antarctic coastline and in the Antarctic Peninsula region from 7000 to 5000 BP. These sea-ice changes were contemporaneous with the abrupt increases in methanesulfonic acid concentrations in the Taylor Dome ice core and the outlet glacier advances around Antarctica during the mid-Holocene.

These cryospheric changes around Antarctica during the mid-Holocene may have been influenced by extratropical transport of water vapor. Similar to the period before the Last Glacial Maximum, when there was increased surface-water stratification south of the Polar Front, expanded sea-ice coverage around Antarctica could have reduced the CO2 'leak' from the Southern Ocean and influenced global cooling. Decreasing CO2 concentrations since the mid-Holocene have indeed been identified from the ice core at Dome C in Antarctica. It is suggested that this tropical-high latitude feedback has influenced the dynamics of the climate system and global temperatures at least since the mid-Holocene.