Late Quaternary environmental history of Taylor Valley, southern Victoria Land, Antarctica, reconstructed by a multidisciplinary study of lake sediments

Abstract

In the unglaciated areas of Antarctica, lake sediments act as archives of the regional environmental and climatic history. In most cases, the records are restricted to the Holocene. Amongst the few exceptions are lakes in the McMurdo Dry Valleys, southern Victoria Land, which are known to have remained mostly ice-free during the Last Glacial Maximum. Within the scope of an U.S.-American-German expedition in austral summer 2002/2003, several sediment cores were recovered from the three major lakes in the Taylor Valley: lakes Fryxell, Hoare, and Bonney. In order to reconstruct the late Quaternary regional environmental and climate history, sedimentological, biogeochemical, mineralogical, and chronological investigations were conducted on the sediment sequences recovered from Lake Hoare (core Lz1020) and East Lake Bonney (core Lz1023) within the scope of this thesis. Sediment cores from Lake Hoare with a maximum length of 2.3 m mainly consist of coarse-grained material and penetrate back into the late Weichselian, when Taylor Valley was occupied by the large proglacial Lake Washburn. This lake was dammed by the advanced Ross Sea ice sheet at the valley outlet and was mainly fed by meltwater of the ice sheet. During the Pleistocene-Holocene transition, enhanced evaporation led to a significant lake level drop of Lake Washburn. The Lake Hoare record additionally shows that in course of this event, Lake Washburn desiccated to a very low level, with subaerial conditions at the coring site of Lz1020. After the final retreat of the Ross Sea ice sheet during the early Holocene, Taylor Valley was occupied by remnants of Lake Washburn. Environmental conditions comparable to those of today, with an advanced Canada Glacier separating lakes Hoare and Fryxell, established during the Mid-Holocene. A 2.7 m long core recovered from East Lake Bonney mainly consists of a halite crust. Variations in the properties of the salt crystals and of clastic components embedded in the salts imply environmental changes over time. New paleoenvironmental insights provided by this record are the evidence for enhanced evaporation in the late Holocene, which led to the precipitation of the more than 2 m thick salt crust. This event was followed by a lake level rise, caused by inflowing meltwaters refilling the basin. As a result of the establishment of a freshwater lense at the top of East Lake Bonney, a perennial ice cover was formed in the recent past. This study shows that the investigated lake sediment records provide crucial information about the late Quaternary environmental history of Taylor Valley, but should be interpreted in context with ice core records, terrestrial, and marine archives for a better understanding of the regional paleoenvironment, and paleoclimate.