THE LIMNOLOGY OF LAKE JOYCE, PEARSE VALLEY, ANTARCTICA

The McMurdo Dry Valleys (MDV) region of Antarctica is the largest ice-free area on the continent. This region contains numerous ice-covered lakes and ponds that have been scientifically investigated since the 1960s. With the advent of the McMurdo Dry Valleys Long-Term Ecological Research (MCM-LTER) project in 1993, a number of these lakes have been monitored annually to evaluate how their ecological and biogeochemical properties change with variations in climate forcing. In this presentation we present our data from Lake Joyce (LJ), a closed-basin lake at an elevation of 325m. LJ is dammed by the Taylor Glacier and has the lowest maximum water temperature of the larger MDV lakes. Although LJ is not sampled regularly as part of the MCM-LTER we combine our results from previous investigations since the 1970s. Recent work by Hawes et al. (2011) has shown that the lake has risen 7 meters between 1973-2009. Depth normalized major dissolved constituents have varied little however over this time period, and demonstrate a very steep halocline at 15-20 meters. The Na:Cl, SO₄:Cl and Cl:Br ratios are different than the fresh/brackish, closed-basin lakes at lower elevations in Taylor Valley, suggesting that these salts are probably derived from dissolution of NaCl, Na₂SO₄ and CaSO₄•2H₂O. This result has important implications regarding the origin and past history of the lake. Biologically, previous researchers have observed extensive algal mat structures in the lake, and δ¹³C-DIC values indicate that it is one of the only lakes in MDV demonstrating a strong biological pump. The increased lake level rise has led to the movement of the deep chlorophyll maximum and greatly increased the chlorophyll in the surface waters. Helium isotope concentrations in the deep, more saline waters suggest a residence time or lake “age” that is older than Lakes Fryxell and Hoare in the Taylor Valley. The synthesis of these data clearly points to the idea that LJ is different than the other closed-basin lakes in MDV and its geochemistry and its response to climate variation is closely linked to the Taylor Glacier and possibly the sub-glacial brines beneath it.