Geoscience Reference
In-Depth Information
was likely enhanced by the relatively large transport of particularly thick ice from
north of Greenland. Dickson an colleagues (
1988
) estimate the excess freshwater
associated with this event to be about 2,300 km
3
, similar to the mean annual Fram
Strait ice flux. Häkkinen's (
1993
) study also suggests an increased oceanic transport
of fresh anomalies in the East Siberian Sea, moving across the Arctic and entering
the Greenland Sea about four years later. The GSA caused cessation of convection
as recorded at weather station “Bravo” (56°N, 51°W) (Lazier,
1980
). Other lines of
evidence indicate that it was associated with a 30 percent reduction in the strength
of the Gulf Stream system (Greatbatch et al.,
1991
; Ezer, Mellor, and Greatbach,
1995
).
The GSA nevertheless remains somewhat of a puzzle. Vinje's (
2001
) monthly
time series (
Figure 7.17
) shows no obvious indication of a large change in the Fram
Strait flux during the late 1960s. But there were no direct observations of the volume
flux during this time. Additional GSA-like events have been documented by Belkin
et al. (
1998
). They suggest that some of these events have a local source owing to
enhanced ice formation in the Labrador Sea/Baffin Bay areas; whereas others, such
as the GSA of the late 1960s to early 1970s, are remotely forced by enhanced fresh-
water export via either the Fram Strait or through the Canadian Arctic Archipelago.
As reviewed in
Chapter 10
, there is convincing evidence of periods with a much
weaker of altered AMOC during the last glacial cycle, the causes of which are still
incompletely understood.
Focus Questions and Exercises
1) Imagine that a dam was placed across the Bering Strait so that there was no
inflow of ocean waters from the North Pacific. Describe the potential conse-
quences of this change on the salinity contrast between the northern North
Atlantic and northern North Pacific.
2) Imagine a world in which there were no large rivers draining into the Arctic
Ocean. What changes might you expect in the Arctic sea ice regime? On the
salinity of the northern North Atlantic?
3) As the Arctic sea ice cover thins, episodes of sea ice divergence and conver-
gence will tend to become stronger, meaning more leads and more ridging.
Do you agree or disagree? Why?
