3 Geochemistry: Advances in Low-Temperature and Isotope Geochemistry

Sunday, 4 November 2012
8:00 AM - 12:00 PM
209AB

OXYGEN STABLE ISOTOPES AND CHLORIDE CONCENTRATION IN THE SURFACE WATERS OF TAYLOR VALLEY LAKES, ANTARCTICA, DURING THE PAST 40 YEARS

Paper number: 3-2
Program: Technical Sessions
Time: 8:15 AM – 8:30 AM

Authors

Abstract

The three main lakes of Taylor Valley, a McMurdo Dry Valley of southern Victoria Land, Antarctica, are closed basins, ice-covered, and vary in depth, salinity, and glacial melt water sources. The two Lake Bonney lobes are hypersaline and more than 38 meters deep, Lake Fryxell has brackish bottom waters and is 18 meters deep, and Lake Hoare is fresh water and is 30 meters deep. Since the early 1970s the geochemistry and elemental evolution of the Taylor Valley lakes have been well studied. Stable isotope data from waters of these lakes have been used to interpret the climatic history of this area during the past few thousand years. This study will focus on oxygen isotopes of the near surface waters of the Taylor Valley lakes as related to stream flow, lake levels, and water sources of each basin, and ultimately the impact of recent climate changes on these sensitive systems. The water levels of the lakes are sustained by glacier meltwater inflow and perennial ice-cover sublimation, however the water levels of the Taylor Valley lakes have consistently increasing during the last forty years. Lake Bonney is seven meters higher than it was in 1971, and Lake Hoare and Lake Fryxell are two meters higher than they were in 1971.

For this study oxygen isotope and chloride data for the several meters of water below the ice on each lake are compiled. These data include depth profiles from: Lake Bonney lobes and Lake Fryxell from summer 1972, Lake Fryxell from summer 1991, Lake Hoare from summer 1994, all three lakes from summer 2002, Lake Hoare from summer 2005, and all three lakes from January 2012. The oxygen stable isotope composition of the three lakes differ by lake due to in-stream fractionation within each basin (i.e., enrichment by evaporation) and the glacial source water isotopic signature (i.e., isotopically lighter glacial melt water further inland from Ross Sea and/or from different source areas within a glacier). During the last forty years, the surface waters of the Taylor Valley lakes have become isotopically lighter but the chloride concentration has not decreased from dilution as a result of the drastically increased water levels. In this presentation we address how stream flow during a season influences isotopic and element composition of these lakes, and how the isotopic time series is a response to changing climates and melt regimes.