*NEWS*MELTING ICE DILUTES NORTHERN SEAS

[Anonymous]

Melting ice dilutes northern seas
Freshwater
pouring into northern oceans is slowly turning high-latitude waters
less salty.Shrinking ice sheets and melting glaciers are partly
responsible for the freshening effect, a review in the journal Science
has confirmed.If salinity levels continue to drop, dramatic changes to
the North Atlantic currents could occur.But more work is needed to be
sure that rising global temperatures are to blame, say the authors.”For
the last 50 years, oceanographers have been cruising seas at northern
latitudes taking vertical profiles of salinity, and they have observed
gradual declines,” said lead author Bruce Peterson, of the Marine
Biological Laboratory, Woods Hole, US.”The salt water, although still
very salty, is getting fresher.”

Warm shallows, cold depths
The
volume of fresh water is a good match for the amount which rivers,
precipitation, sea-ice melt and glacier melt are producing. Run-off
from these sources must be creating the dilution effect, the
researchers conclude.The measurements are taken from the Nordic seas
and Atlantic Sub-polar Basins.Cold water from the Arctic is usually
exchanged for warm water from the tropics in a self-propelling cycle.In
the north, the warm water arriving via surface currents sinks and flows
back to warmer climes through the deep ocean. Because fresher water is
less dense, it does not sink so far as salty water would at the same
temperature.If the trend continues, the changes to this current system
may be significant. “It is expected that the North Atlantic circulation
will slow down,” said Professor Peterson.

Global warming or not?
But
how likely is the trend to continue? It is not yet possible to be sure
to what extent global warming can be blamed for the changes, say the
authors.Fluctuating salinity could potentially result from a normal
periodical weather pattern known as the North Atlantic Oscillation
index. If this index is high, seas in the north are less salty than
average Until 1995, the changes were in line with what would be
expected under the climatic conditions; but when the index changed
recently, becoming low or neutral, the proportion of fresh water did
not go down accordingly in some places.So the greater bulk of fresh
water running into the sea is probably – at least in part – due to
rising global temperatures. “I suspect parts of it are due to global
warming. It’s a difficult quandary,” said Professor Peterson.If salt
levels continue to decline, and currents change, the implications for
aquatic ecosystems would be dramatic.”The organisms in the oceans are
affected by the distribution of sea ice, and by temperatures and
salinity fields, and all of these would change,” the author
explained.”Changes in these currents would have tremendous impact for
fisheries and other species important to man.” 

[Author]

August 30, 2006 at 11:57 AM