The physical limnology of a permanently ice‐covered and chemically stratified Antarctic lake using high resolution spatial data from an autonomous underwater vehicle

Abstract

We used an Environmentally Non-Disturbing Under-ice Robotic ANtarctic Explorer to make measurements of conductivity and temperature in Lake Bonney, a chemically stratified, permanently ice-covered Antarctic lake that abuts Taylor Glacier, an outlet glacier from the Polar Plateau. The lake is divided into two lobesEast Lobe Bonney (ELB) and West Lobe Bonney (WLB), each with unique temperature and salinity profiles. Most of our data were collected in November 2009 from WLB to examine the influence of the Taylor Glacier on the structure of the water column. Temperatures adjacent to the glacier face between 20 m and 22 m were 38C colder than in the rest of WLB, due to latent heat transfer associated with melting of the submerged glacier face and inflow of cold brines that originate beneath the glacier. Melting of the glacier face into the salinity gradient below the chemocline generates a series of nearly horizontal intrusions into WLB that were previously documented in profiles measured with 3 cm vertical resolution in 1990-1991. WLB and ELB are connected by a narrow channel through which water can be exchanged over a shallow sill that controls the position of the chemocline in WLB. A complex exchange flow appears to exist through the narrows, driven by horizontal density gradients and melting at the glacier face. Superimposed on the exchange is a net westto-east flow generated by the higher volume of meltwater inflows to WLB. Both of these processes can be expected to be enhanced in the future as more meltwater is produced.

Microbial diversity of an Antarctic subglacial community and high‐resolution replicate sampling inform hydrological connectivity in a polar desert

“…For example, slight changes in oxygen concentration may play a role, WLB has a strong redoxycline with oxygen rapidly decreasing from ~48 mg O 2 /L at 15 m to 0 by 25 m depth (http://mcm.lter.org). However, the depth at which EMB is predicted to enter WLB at 17–25 m (Spigel et al ., ) is hypoxic to suboxic which is consistent with measurements made at the Blood Falls discharge (Mikucki et al, ). A third possible scenario is that the till below Taylor Glacier that separates WLB and the subglacial aquifer may serve as a physical filter, retaining microorganisms (which can range from ~0.5 to 2 μm in size), while solutes continuously percolate into WLB through Darcian flow (Rebata‐Landa and Santamarina, ).…”

“…Blood Falls directly discharges into the surface waters of its proglacial lake, Lake Bonney, and very likely discharges below the glacier snout directly into deeper later waters (Mikucki et al, ; Spigel et al, ); yet the diversity data presented here suggests a more complicated relationship between these waters. Cluster analyses clearly indicate that the geochemistry between EMB and the deeper waters of WLB are very similar (Fig.…”

“…These two studies suggest a second, direct transport along the glacier base into the lake, with subglacial brine entering WLB at a depth between 17 and 25 m. This depth correlates with where the Taylor Glacier snout protrudes into the lake and is also where the density of EMB and the WLB water column would equilibrate (Spigel et al, ). Water column conductivity, temperature (Spigel et al, ) and iron (Mikucki et al, ) measurements support these models. If this subsurface connection exists, and EMB enters the lake at the glacier base into geochemically similar waters, brine may still experience selective pressure from some as of yet unmeasured biogeochemical parameter.…”

Prediction of Ice‐Free Conditions for a Perennially Ice‐Covered Antarctic Lake

“…The high heat capacity of the water column, in conjunction with high deep water salinity in chemically stratified lakes, allows for the development of thermal maxima at depth (Obryk, Doran, Hicks, et al, ; Vincent et al, ). Deep (~>20 m) perennially ice‐covered lakes are often highly stratified, with dense and deep hypersaline waters (Chinn, ; Spigel et al, ; Spigel & Priscu, ). The high salinity of the deep water column in Lake Bonney and other chemically stratified lakes inhibits seasonal mixing of the water column, with temperature having little to no influence on density‐induced water mixing (Chinn, ; Spigel et al, ; Spigel & Priscu, ).…”

“…Deep (~>20 m) perennially ice-covered lakes are often highly stratified, with dense and deep hypersaline waters (Chinn, 1993;Spigel et al, 2018;Spigel & Priscu, 1998). The high salinity of the deep water column in Lake Bonney and other chemically stratified lakes inhibits seasonal mixing of the water column, with temperature having little to no influence on density-induced water mixing (Chinn, 1993;Spigel et al, 2018;Spigel & Priscu, 1998).…”