RE: The Western Interior Seaway (and computers)

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Phil Bigelow
>
> Good point.  There is not much physical evidence (none?) for a Mesozoic
> arctic sea ice sheet, so if there was a WIS dynamo it may have been a
> very weak one.  A sea ice sheet might be a feature that a computer model
> could predict (or eliminate as a possibility).  If it existed, perhaps
> the sea ice
> was only a seasonal feature.

As alluded to in the post I just posted, Cretaceous global circulation seems to 
have been driven more by a warm circumequatorial
current than a cold thermohaline conveyor belt.

> Our current Arctic Ocean sea ice sheet is eroding at an alarmingly rapid
> rate.  How small can it get before the dynamo shuts down?
>
A paper one doesn't have to wait for...

Curry, R. & C. Mauritzen. 2005. Dilution of the Northern North Atlantic Ocean 
in Recent Decades. Science 308:1772-1774.

Abstract
Declining salinities signify that large amounts of fresh water have been added 
to the northern North Atlantic Ocean since the
mid-1960s. We estimate that the Nordic Seas and Subpolar Basins were diluted by 
an extra 19,000 ± 5000 cubic kilometers of
freshwater input between 1965 and 1995. Fully half of that additional fresh 
water?about 10,000 cubic kilometers?infiltrated the
system in the late 1960s at an approximate rate of 2000 cubic kilometers per 
year. Patterns of freshwater accumulation observed in
the Nordic Seas suggest a century time scale to reach freshening thresholds 
critical to that portion of the Atlantic meridional
overturning circulation.

Last two paragraphs:
Of the total 19,000 km3 of additional fresh water that diluted the northern 
Atlantic since the 1960s, only 4000 km3 remained in the
Nordic Seas. Of this latter volume, our analysis indicates that 2500 km3 
accumulated in the layer 200 to 1000 m between 1970 and
1995. This observed rate of net accumulation (100 km3 year?1) integrates 
various dynamical processes controlling the mixing of fresh
water into this layer and provides a basis for estimating future dilution. At 
the observed rate, it would take about a century to
accumulate enough fresh water (e.g., 9000 km3) to substantially affect the 
ocean exchanges across the Greenland-Scotland Ridge, and
nearly two centuries of continuous dilution to stop them. In this context, 
abrupt changes in ocean circulation do not appear
imminent.

Uncertainties remain in assessing the possibility of such disruptions. A 
weakened Atlantic MOC in the 21st century is a feature of
numerous climate simulations of greenhouse warming (5?9, 23?27). The cause is 
similar in all the models: glacial melting, enhanced
precipitation, and continental runoff, which are projected to increase 
freshwater input to the Arctic and sub-Arctic seas (26, 27).
Pooling and sudden release of glacial meltwater, disintegration of shelf ice 
followed by a surge in glacier movement, and
lubrication of the glacier base by increased melting are all possible 
mechanisms that could inject large amounts of fresh water from
Greenland's ice sheet into the upper layers of the Nordic Seas (28). The 
possibility of such events precludes ruling out a
substantial slowing or shutdown of the overflows as a result of greenhouse 
warming.


                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
        Mailing Address:
                Building 237, Room 1117
                College Park, MD  20742

http://www.geol.umd.edu/~tholtz/
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796