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 109

forming a vast lens not mixing easily with the underlying layers, was carried by prevailing
currents along Greenland into the Labrador Sea and on into the North Atlantic (Voituriez,
2003 ) .
The analysis of Carmack and McLaughlin ( 2011 ) concludes with a summary of the
changes which have potential biological consequences. Ocean temperature has measurably
increased in parts of the Arctic Basin. This is partly associated with local warming due to
the decreased albedo, but also includes water of Atlantic origin. The salinity-driven strati-
ficationintheupperlayersofhigh-latitude oceansisincreasingduetothecombinedeffects
of an accelerated hydrological cycle and increasing ice melting during the summer season.
A major result of this is a possible decrease in transfer of nutrients into the productive eu-
photic zone, resulting in a decrease in primary production. The freshening of the Arctic
Ocean also leads to a change in phytoplankton species, with the smallest cells dominating
the larger ones (Li et al. , 2009 ). This may have strong consequences for the food web if
it persists. A 'tipping point' may be reached if the combined effects of warming and in-
creased stratification support food webs that favour low energy predators like jellyfish.
The changes in stratification are different between the Eurasian and the North Amer-
ican Canadian parts of the Arctic (Carmack and Melling, 2011 ) . On the Eurasian side the
stratification and vertical stability are decreased, possibly allowing an increased heat flow
upwards from the intermediate warmer water of Atlantic origin. On the Canadian side the
stratification is increased, associated with the inflowing low salinity water fromthe Pacific.
Decreasing ice cover extent, thickness, and duration are basic features of changes in
the Arctic. The observations of the 2007-2008 IPY showed record breaking minimal sea
ice extent (Carmack et al. , 2010 ). The changes include earlier melting and delayed freeze-
up in some parts, for example, the Canada Basin. Consequences include increased ice mo-
tion in response to wind forcing and increased potential for transfer of nutrients to the shelf
areas, when the ice retreats beyond the shelf break. An unexpected consequence of the in-
creased sea ice melt is its effect on the carbonate chemistry and related decrease in pH and
increase in acidification in parts of the Canada Basin. The low alkalinity sea ice melt water
tends to decrease the saturation state of calcium carbonate (Yamamoto-Kawai et al. , 2009 ) .