Changes in Watermass Properties Between the North Pole and Ellesmere Island After the 2007 Summer Sea Ice Retreat

One component of the Arctic Observing Network is the Switchyard project, which occupies a line of stations between the North Pole and the northern tip of Ellesmere Island each spring using Twin Otter aircraft. CTD measurements and water samples are collected using a modular rosette that is lowered through a 12-inch diameter hole in the sea ice from the aircraft and additional CTD-only stations are taken from helicopters as well as Twin Otters. This program is closely coordinated with the NPEO program, which surveys other regions by aircraft and between the two programs, the section has been occupied annually since 2003. Here results from 2006-2009 bracketing the large sea ice melt back during the summer of 2007 are reported.

Between the spring of 2006 and 2007, there was a slight freshening of the halocline along entire section, except at the North Pole, with the greatest freshening of about 0.5 psu in the upper halocline at the southern end of the section; this freshening was generally accompanied by a slight cooling. There was a strong freshening in the mixed layer, which generally extended to 50 m, between 2007 and 2008, except at the North Pole, which remained essentially constant. The freshening was strongest in the middle and southern end of the section and reached values of 1.5 psu. In the upper halocline at the southern end of the section, there was an increase in salinity of 0.5 psu. Freshening in the mixed layer occurred along the entire section between 2008 and 2009, but it was greatest at the North Pole where it reached a value of 2 psu. The average thickness of the freshwater along the section increased from 10.5 m in spring 2006 to 14.2 m in spring 2009. The basic structure in the oxygen and nutrient distribution changed little during this time. There was a strong oxygen minimum and nutrient maximum extending northward from Ellesmere Island at about 100 m depth and a deeper less intense oxygen minimum and nutrient maximum along the southern and central part of the section. These data and oxygen isotope data are now being worked up and will be used to calculate the fractions of Atlantic water, Pacific water, sea ice melt and meteoric freshwater along the section, which will also be presented.