Based on observations during the 5th Chinese Arctic expedition in 2012, the property and distribution of water masses were identified and the evolution of cooling convection was studied. In the upper layer, from the warm and salty Atlantic waters, which mainly lie on the east, westerly to the cold and fresh Greenland upper waters, the temperature and the salinity decreases were about 8 ℃ and 0.4 psu respectively. As for the intermediate and deep waters, water properties were more homogeneous and stable. Along with the depth deepening, there existed the Arctic Intermediate Water, the Basin Deep Water, the Arctic Deep Water and the Basin Bottom Water in all the three deep basins. In the center of the Greenland Basin, the potential temperature was about -0.97 ℃ at depth 3 500 m, which was nearly 0.3 ℃ warmer compared to the value -1.30 ℃ observed in 1970s, implying a heat increase in the deep layer. Under a simplified hypothesis only concerning the surface cooling to erode the seasonal pycnocline, now a total heat loss of about 0.9×10⁹~1.2×10⁹ J/m² was needed for the upper ocean of the Greenland Sea. This process may take at least two months and thus leaves less time for the following deepreaching convection. At present, the Nordic seas are becoming a heat reservoir on the northern hemisphere and impacts of such change on the Arctic climate are worthy of further study.