摘要
Conductivity, temperature and depth （CTD） data from 1993 2010 are used to study water tempera- ture in the upper Canada Basin. There are four kinds of water temperature structures： The remains of the winter convective mixed layer, the near-surface temperature maximum （NSTM）, the wind-driven mixed layer, and the advected water under sea ice. The NSTM mainly appears within the conductive mixed layer that forms in winter. Solar heating and surface cooling are two basic factors in the formation of the NSTM. The NSTM can also appear in undisturbed open water, as long as there is surface cooling. Water in open water areas may advect beneath the sea ice. The overlying sea ice cools the surface of the advected water, and a temperature maximum could appear similar to the NSTM. The NSTM mostly occurred at depths 10-30 m because of its deepening and strengthening during smnmer, with highest frequency at 20 m. Two clear stages of interannual variation are identified. Before 2003, most NSTMs were observed in marginal ice zones and open waters, so temperature maxima were usually warmer than 0~C. After 2004, most NSTMs occurred in ice-covered areas, with nmch colder temperature maxima. Average depths of the temperature maxima in most years were about 20 m, except for about 16 m in 2007, which was related to the extreme minimum of ice cover. Average temperatures were around 0.8~C to 1.1~C, but increased to around 0.5~C in 2004, 2007 and 2009, corresponding to reduced sea ice. As a no-ice summer in the Arctic is expected, the NSTM will be warmer with sea ice decline. Most energy absorbed by seawater has been transported to sea ice and the atmosphere. The heat near the NSTM is only the remains of total absorption, and the energy stored in the NSTM is not considerable. However, the NSTM is an important sign of the increasing absorption of solar energy in seawater.
Conductivity, temperature and depth （CTD） data from 1993 2010 are used to study water tempera- ture in the upper Canada Basin. There are four kinds of water temperature structures： The remains of the winter convective mixed layer, the near-surface temperature maximum （NSTM）, the wind-driven mixed layer, and the advected water under sea ice. The NSTM mainly appears within the conductive mixed layer that forms in winter. Solar heating and surface cooling are two basic factors in the formation of the NSTM. The NSTM can also appear in undisturbed open water, as long as there is surface cooling. Water in open water areas may advect beneath the sea ice. The overlying sea ice cools the surface of the advected water, and a temperature maximum could appear similar to the NSTM. The NSTM mostly occurred at depths 10-30 m because of its deepening and strengthening during smnmer, with highest frequency at 20 m. Two clear stages of interannual variation are identified. Before 2003, most NSTMs were observed in marginal ice zones and open waters, so temperature maxima were usually warmer than 0~C. After 2004, most NSTMs occurred in ice-covered areas, with nmch colder temperature maxima. Average depths of the temperature maxima in most years were about 20 m, except for about 16 m in 2007, which was related to the extreme minimum of ice cover. Average temperatures were around 0.8~C to 1.1~C, but increased to around 0.5~C in 2004, 2007 and 2009, corresponding to reduced sea ice. As a no-ice summer in the Arctic is expected, the NSTM will be warmer with sea ice decline. Most energy absorbed by seawater has been transported to sea ice and the atmosphere. The heat near the NSTM is only the remains of total absorption, and the energy stored in the NSTM is not considerable. However, the NSTM is an important sign of the increasing absorption of solar energy in seawater.
基金
supported by the Global Change Research Program (Grant no. 2010CB951403)
the National Natural Science Foundation of China (Grant no.40631006)
