Late Holocene cool climate episodes, recorded on Lake Bonney, an Antarctic amplifier lake

Abstract

Chemical, stable isotope and natural abundance radionuclide analysis of cores taken through sediments below Lake Bonney, Taylor Valley, Antarctica, show evidence of multiple episodes of flooding by meltwaters from Taylor Glacier and desiccation to brines sufficiently concentrated to produce ice free conditions. The last three identified desiccation events date 1550 ± 40, 800 ± 100 and 450 ± 160 yr B.P. and match the last three periods of sustained cooling identified by isotope changes in the Taylor Dome ice core. Similar cooling events have been identified by other authors elsewhere in Antarctica.

The desiccation events have produced dramatic changes in the sediment character of Lake Bonney East Lobe, but show little impact in the West Lobe. In East Lobe halite, hydrohalite, gypsum, and aragonite are precipitated and extreme isotopic enrichment of carbon (up to 813C of +12.0%0) occurred as aragonite was forced from solution by rapid freezing of the brine over winter. Reflooding events were often associated with algal blooms and resulted in radical changes in the 180/1 60 ratio in the water column.

It is speculated that Taylor Glacier retreated to expose a 250 m deep subglacial depression during the last glacial maximum allowing Glacial Lake Washburn to extend westwards to perhaps Cavendish Rocks. The reduced Taylor Glacier enabled Taylor Dome to lower causing deposition of more 180 enriched ice than would otherwise have been expected. Taylor Glacier and Taylor Dome have continued to advance throughout the Holocene.