LAKE BONNEY NARROWS: OVER A CENTURY OF DATA CREATES THE LONGEST DIRECT RECORD OF ENVIRONMENTAL CHANGE IN ANTARCTICA

Lake Bonney in Taylor Valley, east Antarctica, has two distinct lobes - West Lake Bonney (WLB) and East Lake Bonney (ELB) which are separated by a relatively shallow sill in a narrow channel referred to as the Bonny Narrows. Robert Falcon Scott passed through the Bonney Narrows in 1903 on his first expedition in the area, and made a measurement of the channel’s width of “15 feet” that has been used to estimate lake level at the time in order to extend our lake level record for Lake Bonney to well over 100 years. Using Scott’s measurement, we can calculate that lake level has risen between December 1903 and January 1917 by 18.1 m, an average of 0.16 m/yr. The sill (recently established by divers to be at 49.1 masl) was only 1.25 m deep during Scott’s visit. If we assume a constant rate of lake level rise, the two lobes joined less than a decade prior to Scott making his measurement. Photographs taken by Griffith Taylor’s party on Scott’s second expedition show that there was a dramatic lake level rise between 1903 and 1911 of about 5 m.

The sill in Bonney Narrows is now an important physical control of the geochemistry and ecology of the two lobes. WLB has a hypersaline brine bottom water which is held back from ELB by the sill. The brine is displaced over the sill, by a mechanism referred to as “chemocline leakage”. The brine sinks on the ELB side following a former river channel until if finds it's neutral buoyancy in ELB, about 6 m below the sill depth. The nature and timing of the chemocline leakage is largely unknown. In this presentation, I will review the history of the connectivity between the two lobes of Lake Bonney as indicated by geochemical and physical evidence collected from the lake surface and through recent diving operations.