Pressure‐driven, shoreline currents in a perennially ice‐covered, pro‐glacial lake in Antarctica, identified from a LiCl tracer injected into a pro‐glacial stream

Abstract

Abstract:The distribution of streamwater within ice-covered lakes influences sub-ice currents, biological activity and shoreline morphology. Perennially ice-covered lakes in the McMurdo Dry Valleys, Antarctica, provide an excellent natural laboratory to study hydrologic-limnologic interactions under ice cover. For a 2 h period on 17 December 2012, we injected a lithium chloride tracer into Andersen Creek, a pro-glacial stream flowing into Lake Hoare. Over 4 h, we collected 182 water samples from five stream sites and 15 ice boreholes. Geochemical data showed that interflow travelled West of the stream mouth along the shoreline and did not flow towards the lake interior. The chemistry of water from Andersen Creek was similar to the chemistry of water below shoreline ice. Additional evidence for Westward flow included the morphology of channels on the ice surface, the orientation of ripple marks in lake sediments at the stream mouth and equivalent temperatures between Andersen Creek and water below shoreline ice. Streamwater deflected to the right of the mouth of the stream, in the opposite direction predicted by the Coriolis force. Deflection of interflow was probably caused by the diurnal addition of glacial runoff and stream discharge to the Eastern edge of the lake, which created a strong pressure gradient sloping to the West. This flow directed stream momentum away from the lake interior, minimizing the impact of stream momentum on sub-ice currents. It also transported dissolved nutrients and suspended sediments to the shoreline region instead of the lake interior, potentially affecting biological productivity and bedform development.

Antarctic lake phytoplankton and bacteria from near‐surface waters exhibit high sensitivity to climate‐driven disturbance

“…into perimeter moats which typically lose their ice during most austral summers (Castendyk et al, 2015;McKnight & Andrews, 1993;Priscu et al, 2005;Wharton Jr et al, 1986). Perennial ice covers in these lakes are under threat of switching to seasonal within the next few decades if the region continues to warm (Obryk et al, 2019).…”

Barotropic seiches in a perennially ice‐covered lake, East Antarctica

“…Although the water column does not routinely mix, the presence of tritium and CFC's in the hypolimnion indicates circulation in recent decades (Tyler et al 1998;Dowling et al 2014). A tracer study in December 2012 showed that discharge from Andersen Creek flowed West, parallel to the shoreline, below moat ice, at 2.6 cm s À1 , and generated diel horizontal pressure gradients (Castendyk et al 2015).…”

Dissolved black carbon in Antarctic lakes: Chemical signatures of past and present sources

“…During the summer the edges of the lake ice thaw, creating a moat of open water which typically ranges in width from 1 to 10 m, but can reach widths of almost a kilometer at the shallow eastern ends of LF and ELB during particularly warm, sunny summers [ McKnight and Andrews , ; Castendyk et al ., ]. Due to lateral circulation in the lakes, the streamflow entering the moat area is entrained with water underneath the ice‐cover [ Castendyk et al ., ]. Even during midsummer only 1% of photosynthetically active radiation (PAR) passes through the ice cover [ Howard‐Williams et al ., ].…”

“…Today a perennial ice-cover with a thickness of 3-5 m [Doran et al, 2002] covers most of the surface area of the MDV lakes. During the summer the edges of the lake ice thaw, creating a moat of open water which typically ranges in width from 1 to 10 m, but can reach widths of almost a kilometer at the shallow eastern ends of LF and ELB during particularly warm, sunny summers [McKnight and Andrews, 1993;Castendyk et al, 2014]. Due to lateral circulation in the lakes, the streamflow entering the moat area is entrained with water underneath the ice-cover [Castendyk et al, 2014].…”