THE LIMNOLOGICAL AND SEDIMENTOLOGICAL EFFECTS OF A JÖKULHLAUP DRAINING INTO A MEROMICTIC CANADIAN HIGH ARCTIC LAKE
A jökulhlaup drained between 3.2 x 108 m3 and 5.5 x 108 m3 of water from an ice-dammed lake (IDL) on Ellesmere Island in late July 2003, representing the largest jökulhlaup recorded in the Canadian High Arctic. The jökulhlaup drained into Lake Tuborg, a 42 km2 partially meromictic, annually laminated lake. The IDL (6 km x 1.5 km x 115 m) drained completely by ice-dam flotation via englacial conduits, and created a portal about 900 m from the Lake Tuborg shore. Maximum discharge was likely 3600-5100 m3/s, which caused Lake Tuborg to rise by 7 m in 72 hours.
A physical limnological process study underway in Lake Tuborg at the time of the jökulhlaup yielded valuable details on pre- and post- jökulhlaup limnology and sedimentology.
Lake Tuborg has two basins separated by a shallow sill: the basin closest to jökulhlaup inflow is all fresh water, and the deeper, more distal basin is 25 PSU below 56 m. The sill limited the most erosive underflows to the freshwater basin, but hyperpycnal flows did overtop the sill, and entered the saltwater basin. The jökulhlaup freshened the saltwater layer by about 1.5%. However, the distinctly cold and fresh jökulhlaup water mostly moved along the chemocline, traveling 20 km to the end of the lake. Flows passing along the chemocline turbulently mixed with underlying saltwater. In proximal areas of the meromictic basin, strong interflows and underflows were present; however, sediment at and below the chemocline quickly dropped out of suspension, and strong overflows delivered suspended sediment into the distal areas of the meromictic basin.
Before the jökulhlaup, surface sediments in the freshwater basin were varved, but after the jökulhlaup, sediments were coarse and cross-laminated with fine-grained rip-up clasts. A gravity core from the saltwater side of the sill revealed evidence of a pulsating underflow. However, in the distal portion of the meromictic basin, in 145 m of water, an uninterrupted stratigraphy contains sediments from before and after the jökulhlaup, with a thick, mostly massive, coarser-grained cap. This is an ideal location for an uninterrupted millennial-scale jökulhlaup reconstruction, which is underway using long vibracores.