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The hydrological cycle in the Arctic is composed of three branches: atmosphere, land and ocean. Figure 15.1 schematically shows the estimated annual rate of transport in cubic kilometer per year carried by the individual branches. Bold numbers are observational estimates taken from Aagaard and Carmack (1989), Carmack (2000) and Woodgate and Aagaard (2005), while other numbers are taken from freshwater budget analysis of several century long climate model simulations: (a) ECHAM5/MPIOM under pre-industrial conditions and (b) Bergen Climate Model (BCM) present-day control experiment. These numbers should be treated with caution because of the large uncertainties involved in various observational estimates and the realism of the relatively coarse resolution climate models in representing the hydrological process and the complicated geometry of the narrow straits. The choice of a reference salinity used to calculate freshwater content in the ocean can also introduce discrepancies in ocean transport and storage changes, although a common reference of 34.8 psu is adopted here. It is clear that significant differences exist between modelled and observational estimates as well as among different models at the present stage. It is, however, useful to show the relative importance of each individual component in the overall hydrological budget. Nonetheless, both models and observations agree on the leading terms of contribution. [ABSTRACT FROM AUTHOR]

The Atlantic Meridional Overturning Circulation (AMOC) is part of a global redistribution system in the ocean that carries vast amounts of mass, heat, and freshwater. Within the AMOC, water mass transformations in the Nordic Seas (NS) and the overflows across the Greenland-Scotland Ridge (GSR) contribute significantly to the overturning mass transport. The deep NS are separated by the GSR from direct exchange with the subpolar North Atlantic. Two deeper passages, Denmark Strait (DS, sill depth 630 m) and Faroe Bank Channel (FBC, sill depth 840 m), constrain the deep outflow. The outflow transports are assumed to be governed by hydraulic control (Whitehead 1989, 1998). According to the circulation scheme by Dickson and Brown (1994), there is an overflow of 2.9 Sv (1 Sv = 1 Sverdrup = 106 m3 s-1) through DS, 1.7 Sv through FBC and another 1 Sv from flow across the Iceland%Faroe Ridge (IFR). To the south of the GSR, the overflows sink to depth and then spread along the topography, eventually merging to form a deep boundary current in the western Irminger Sea. During the descent, the dense bottom water flow doubles its volume by entrainment of ambient waters (e.g. Price and Baringer 1994) so that there is a deep water transport of 13.3 Sv once the boundary current reaches Cape Farvel (Dickson and Brown 1994). Thus the overflows and the overflow-related part of the AMOC account for more than 70% of the maximum total overturning, which is estimated from observations to be about 18 Sv (e.g. Macdonald 1998). [ABSTRACT FROM AUTHOR]

The Arctic plays an important role in the climate system. The sea ice controls most of the heat, momentum and matter transfers in the ice-covered Arctic regions. Furthermore, melting and freezing of sea ice have a considerable impact on the ocean stratification. Only a small fraction of the salt is included in the sea ice during freezing processes while the majority is released to the underlying ocean layer. The density of the seawater is increased, which may lead to a destabilization of the ocean stratification. In contrast, melting of sea ice represents a freshwater input into the ocean. The density is reduced and the ocean stratification stabilized. It is of great importance for the ocean where sea ice is freezing and melting. The formation area is not necessarily the same as the melting area. The transport of ice along with the associated freshwater and negative latent heat plays a critical role in the climate system. [ABSTRACT FROM AUTHOR]