Physical and chemical changes in the ocean over basin-wide zones and decadal or longer time-scales: perspectives on current and future conditions - Ocean Sustainability in the 21st Century - page 108

altered stratification, increased acidification and, in the sub-Arctic Pacific, increased hyp-
oxia.
An understanding of the changes in the Arctic Ocean requires consideration of its
coupling to the global ocean and the sub-Arctic Pacific and Atlantic in particular. These
areas are characterized by a salinity dominated stratification which influences all processes
associated with horizontal and vertical fluxes (Carmack, 2007 ). Global ocean stratification
is largely driven by the hydrological cycle, with evaporation in the warm oceans and con-
densationinthecold.RelativelycolderandfresherwatersfromthePacificflownorthwards
into the Arctic Ocean, through the Bering Strait, with a higher sea level on the Pacific side,
overflowing the warmer and saltier Arctic water, with additional inflows from the contin-
ental rivers supporting the stratification required for the formation of sea ice. The combin-
ation of sea ice formation and fresh water run-off generates buoyancy changes. Thus the
buoyancy forcing of the coastal circulation becomes very important in regulating vertical
mixing. The fresh water loop is closed with the export of sea ice and low salinity waters
through the Fram Strait and the Canadian Arctic Archipelago into the convective gyre re-
gions of the Greenland, Iceland, Norwegian, Irminger, and Labrador Seas (Carmack and
McLaughlin 2011 ) .
HistoricalrecordsofthestorageoffreshwaterintheArcticshowstrongmulti-decadal
variability over the past century (Proshutinsky et al ., 2009 ) . In some parts of the region
the freshwater inputs may be changed by human activities, including river deviations, dam-
ming, and hydroelectric power generation. This may influence the coastal water circulation
in combination with natural changes in the freshwater cycle. The significance may be re-
flected, although it cannot be proven, in the Great Salinity Anomaly in the North Atlantic
during the 1980s, which changed the rate of deep water formation there for several years
(Royer and Stabeno, 1998 ) .
This phenomenon may be coupled with the strong negative anomalies of the NAO in
the period 1955-1965. A weakening of the westerlies associated with the relatively high
Icelandic pressure(lowNAO),favourednortherlytoeasterly windswithadvection ofpolar
water towards the Iceland-Greenland region (e.g. Voituriez, 2003 ) . The low density water,