Some thoughts on the freezing and melting of sea ice and their effects on the ocean

Abstract

Abstract. The high-latitude freezing and melting cycle can variously result in haline convection, freshwater capping, or freshwater injection into the interior ocean. An example of the latter process is a secondary salinity minimum near 800 m depth within the Arctic Ocean that results from the transformation on the Barents Sea shelf of Atlantic water from the Norwegian Sea and its subsequent intrusion into the Arctic Ocean. About onethird of the freshening on the shelf of that initially saline water appears to result from ice melt, although the actual sea ice flux is small, only about 0.005 Sv. A curious feature of this process is that water distilled at the surface of the Arctic Ocean by freezing ends up at mid-depth in the same ocean. This is a consequence of the ice being exported southward onto the shelf, melted, and then entrained into the northerly Barents Sea throughflow that subsequently sinks into the Arctic Ocean. Prolonged reduction in sea ice in the region and in the concomitant freshwater injection would likely result in a warmer and more saline interior Arctic Ocean below 800 m. Some Thoughts on the Freezing and Melting of Sea Ice and TheirEffects on the Ocean K. Aagaard and R. A. WoodgateIntroduction Evaporation and precipitation rates over the Arctic Ocean are quite low, respectively about 5-10 cm yr -1 and 20-30 cm yr -1 in liquid water equivalent (Barry and Serreze, 2000). The primary cycling of freshwater in the Arctic Ocean is therefore instead accomplished by the freezing and melting of sea ice, for which characteristic rates are about 100 cm yr -1 and 50 cm yr -1 , respectively (Steele and Flato, 2000). If the ice drifts during the long intervals between the phase changes, the result is a net local distillation, since the freezing process expels the majority of the salt in the freezing water into the underlying ocean. This freezing and melting of sea ice, with their accompanying salinity changes, provide buoyancy forcing that is particularly effective in influencing the circulation because of the primary control of density by salinity at the prevailing low temperatures. For example, Holland, Mysak and Oberhuber (1996) concluded that buoyancy forcing is critical to maintaining the mixed layer circulation in the Arctic Ocean. The present note points to the range of buoyancy forcing that is possible in the high-latitude ocean. We begin with an example from the northern North Atlantic extension, viz., the cooling and freshening of the Atlantic water on the Barents shelf. We then place this process in the broader context of interactions between sea ice and the ocean. The intent is to thereby call attention to some appropriate, and even necessary, considerations in modelling the high-latitude ocean, especially in regard to the possible restructuring of ocean properties under altered climatic conditions.

Arctic layer salinity controls heat loss from deep Atlantic layer in seasonally ice‐covered areas of the Barents Sea

“…A simulation also indicated very large interannual variability (from 143 to 1236 km 3 yr À1 ), and this caused substantial variability in annual ice melt and freshwater content that affected the stratification, vertical mixing rates, and heat loss from the Atlantic Water . This finding is in line with Aagaard and Woodgate [2001] who also found that ice import, melting, and freshwater injection into the interior ocean are important processes in the northern Barents Sea.…”

“…With the rapid climatic changes observed in the Arctic as a whole and the more regional warming in the Barents Sea, significant changes are expected in the ocean climate in the northern Barents Sea. Processes in the Barents Sea may, due to the water mass exchange across the northern and eastern boundaries of the Barents Sea, influence the properties of the halocline, the Atlantic Water (AW) and the intermediate water in the Arctic Ocean (e.g., Schauer et al, 1997;Aagard and Woodgate, 2001). Changing physical conditions in the Barents Sea will also have an impact on the Barents Sea ecosystem.…”

The Barents Sea frontal zones and water masses variability (1980–2011)

“…The BS plays an important role in the Northern Hemisphere climate (Smedsrud et al, 2013) by ventilating the Arctic Ocean with the dense Barents Sea Water (Aagaard and Woodgate, 2001;Schauer et al, 2002) and by being a place of high primary productivity . The BS water masses delimited by several fronts are of particular interest.…”

Modification of water masses in the Barents Sea and its coupling to ice dynamics: a model study

“…The modification of the AW taking place in the Barents Sea is therefore of great importance for the ventilation of the Arctic Ocean (Maslowski et al 2004;Schauer et al 2002;Aagaard and Woodgate 2001). AW enters the Barents Sea across the western open boundary, often called the Barents Sea Opening (BSO) (Loeng 1991).…”

“…There is significant modification of the waters in the Barents Sea (Furevik 2001;Gammelsrød et al 2008;Rudels et al 2004;Schauer et al 2002), and ice dynamics plays an important role (Budgell 2005;Kwok et al 2005;Aagaard and Woodgate 2001). AW looses heat due to atmospheric cooling, radiation, and ice melt.…”