Climate Change in the Arctic - The Changing Arctic Environment: The Arctic Messenger - page 262

mer, most of the energy input to the near-surface atmosphere is from advec-
tion of air masses from lower latitudes and from the ocean. If you wish to
warm the Arctic, the best thing to do is to melt off the sea ice and let the ex-
posed ocean warm the atmosphere and evaporate moisture to form clouds.
Once there is a cloud layer, it will trap the energy below.
For those who would like to learn more about the mechanisms of Arctic amplification (par-
ticularly with respect to the loss of sea ice and ocean atmosphere interaction), a good place
to start would be the papers by Deser and colleagues (2010), Ghatak and Miller (2013),
Overland, Wood and Wang (2011), Screen and Simmonds (2010) and Serreze and Barry
(2011).
Thereisonemoreconsequenceofmeltingseaicethatweshouldconsider.Thesurface
of the Arctic Ocean is becoming much less saline. This is a result of a number of responses
to climate warming, including the melting of sea ice (remember that when water freezes,
it expels its salt content) and the delivery to the ocean of more meltwater from snow, gla-
ciers, ice sheets, ice caps and permafrost. The low-salinity water also has a low density.
Consequently, it floats at the top of the Arctic marine water column and has become known
as Arctic Ocean freshwater . The subsurface density difference that results (called the halo-
cline ) inhibits vertical mixing. Surface waters therefore spend more time exposed to the
sun. Because warm water has a lower density than cold water, we now have another mech-
anism that creates a density difference (called the thermocline ), which also restricts vertic-
al mixing. The depth at which the density differences caused by temperature and salinity
combine is called the pycnocline .
The Arctic Ocean freshwater tends to be concentrated by anticyclonic wind forcing
(due to the Coriolis effect) in the Beaufort Gyre of the Canada Basin, which has accumu-
lated more than 5,000 cubic kilometres of freshwater between 2003 and 2012. 12 The full
implications of this increasing accumulation of Arctic Ocean freshwater are poorly under-
stood, but we will consider some later in relation to ocean acidification. At this point, we
will just note that the resultant strong density stratification of the water column restricts