CHANGE AT 85 DEGREES SOUTH: SHACKLETON GLACIER REGION PROGLACIAL LAKES FROM 1960 TO 2020

Over the last two decades, anomalous warming events have drastically altered coastal Antarctic regions. An especially dramatic melt event in the McMurdo Dry Valleys (MDV) (~77°S) during the 2001 to 2002 austral summer resulted in a lake level increase of 0.65 m in Lake Fryxell, which is 600% greater than the 30-year average increase of 0.09 m yr^-1. However, it is generally believed that the Antarctic interior is buffered from regional warming. A prominent exception is Lake Wilson in the Darwin Mountains. Lake Wilson, once believed to be the world’s southern-most lake (80°S), experienced a lake level increase of 25 m from 1975-1993. In this work, we present data from what are now currently believed to be the southern-most Antarctic surface lakes located at Mt. Heekin and Thanksgiving Valley (~85°S) along the Shackleton Glacier in the Transantarctic Mountains. Lake samples were collected in 2018 and analyzed for major ions, nutrients, and water isotopes, and photographs and satellite images were compiled dating back to 1960. The water chemistry from Mt. Heekin was compared to data from 1996 and the areal changes of the lakes were compared to the discharge record of the Onyx River (1969 – 2016), the longest river in Antarctica, and Upland Ponds in the MDV. The dissolved major ion data indicated a freshening of lake water since 1996, likely from increased glacial melt as also illustrated by stable isotopes of water. Additionally, areal increases in lake size did not appear synchronous with warm meltwater events in the MDV before 1996, and were potentially quasi-synchronous afterwards. Our results indicate that despite their southern and inland location, the Shackleton Glacier region lakes have been influenced by meltwater pulses, especially between 2009 and 2018.