A Year on the Ice: The SHEBA/JOIS Project

Аннотация

Home is an icebreaker-at least for a few of us frozen into the Arctic Ocean aboard the Canadian Coast Guard ship Des Groseilliers. We are here as an ancillary part of SHEBA (Surface Heat Budget of the Arctic Ocean), the largest project that the United States National Science Foundation has funded in the Arctic to date. Associated with this primary driving force is JOIS (Joint Ocean Ice Study), an integrated science project working on the biology of the Arctic Ocean. ... JOIS has taken advantage of this "ship of opportunity" to measure the carbon flux in and out of the ocean, the plant photosynthesis driving this flux, and the productivity of the food web supported by this production. JOIS is also a collaborative effort, primarily between Canadian and American marine biologists and physical oceanographers. ... We are acquiring the best set of data on the productivity of the Arctic Ocean made to date, .... But there have been some interesting preliminary results. First, the only previous estimates of productivity in this area were made many years ago with cruder techniques, and they indicated a carbon fixation (photosynthesis) rate of 1-5 g C/sq m/yr. But our zooplankton respiration rates require a minimum of 15-20 g C; if we combine them with microbial demand, the requirement must be at least 25-50 g C, or ten ties as much as first thought. Although this is still low compared with, say, the requirement for the east or west coast of Canada, it is not much lower than the production in the seasonal ice zone of Lancaster Sound. Second, there is a persistent, low-salinity surface mixed layer about 35 m thick floating on a remarkably abrupt density gradient, where salinity increases nearly two parts per thousand (ppt) over less than two metres. This layer appears to be a quasi-permanent feature in this region, and it appears not to circulate freely with deeper water even in late winter when salt rejection from new ice growth (on the order of 0.5-0.7 m thick) has increased surface salinity. Third, there is evidence that climate warming has occurred in this part of the Arctic Ocean. When we drove in with the ship, we were surprised that we couldn't find multiyear floes of more than about 1.7 m mean thickness. The low-salinity surface mixed layer discussed above is about 2 ppt fresher than it was 22 years ago. The edge of the pack ice was farther north than usual. It appears that long-term warming is in fact happening. ...