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Geophysical Research Letters - European Highlights - 1 May 2001

April 18, 2001

American Geophysical Union
Geophysical Research Letters
European Highlights of This Issue - 1 May 2001

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Contents
I. Highlights
II. Authors and their institutions
III. Notes, including ordering information for science writers

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I. Highlights

3. Johnson et al. ["Role of climate feedback on methane and ozone
studied with a coupled ocean-atmosphere-chemistry model"] also
demonstrate the coupling climate change to the evolution of
atmospheric composition. The authors perform two numerical
simulations of future atmospheric chemistry with a coupled
ocean-atmosphere-chemistry model run continuously from 1990 to
2100. The control experiment uses constant greenhouse gases set
at their pre-industrial values, and the second experiment, allowing
greenhouse gases to increase, forces an overall global warming. By
2100 in the climate-change experiment, methane concentrations
are 420 parts per billion (ppb) less than in the control run.
Mid-latitude northern hemisphere ozone concentrations in July for
the mid-troposphere rise from 39 ppb in 1990s to 64 ppb in the
2090s in the control experiment and to only 49 ppb in the climate
change experiment. The authors propose that the direct role of
climate change is a negative feedback on the radiative forcing.

4. Impact of geothermal heating on oceans

A neglected energy source in climate models is the geothermal
heat flux through the sea floor, estimated at 0.05 watts per square
meter on abyssal plains and up to 0.2 watts per square meter on
mid-ocean ridges. Adcroft et al. ["Impact of geothermal heating on
the global ocean circulation"] examine the response of a global
ocean circulation model to a simple representation of the
geothermal heat flux through the sea floor. They compare two
realizations of the model, one forced with this additional, steady
and uniform heat flux of 0.05 watts per square meter. They report
that the addition of the geothermal heat flux leads to deep basin-
scale temperature anomalies on average of about 0.3 degrees
Celsius [0.5 degrees Fahrenheit]. In the Indo-Pacific, where the
existing meridional overturning is enhanced by 25% due to the
flux, the anomalies are as large as 0.5 degrees Celsius [0.9 degrees
Fahrenheit]. For a purely diffusive response (no advection), the
same 0.05 watts per square meter heat flux addition results in a
1.2 degrees Celsius [2.2 degrees Fahrenheit] temperature anomaly at
the ocean bottom.

5. Anthropogenic carbon dioxide storage in Weddell Sea less than
expected

The accurate quantification of the uptake and storage of manmade
carbon dioxide (CO2) by the ocean is a key research topic for the
global carbon cycle. Hoppema et al. ["Direct measurements reveal
insignificant storage of anthropogenic CO2 in the abyssal Weddell
Sea"] investigate the change over a period of about 25 years in
total carbon dioxide (TCO2) and chlorofluorocarbons (CFCs) in
bottom waters near the prime meridian in the Southern Ocean (the
northern Weddell Sea). They find a significant increase in CFC
concentration over the period. The change in TCO2 concentration,
however, is not significant, indicating that the abyssal subpolar
waters in the Southern Ocean are not a significant reservoir of
manmade carbon dioxide. The authors note that the decoupling of
the increase in CFC from that of TCO2 makes it difficult to use
CFCs to estimate uptake of manmade carbon dioxide in this
region.

6. Equatorial thermocline ventilated through subtropics

Hazeleger et al. ["Do tropical cells ventilate the Indo-Pacific
equatorial thermocline?"] study source waters of the Indo-Pacific
equatorial thermocline [layer separating upper level warmer from
deeper colder waters] using a high-resolution global ocean model.
Tropical cells (TCs) and subtropical cells (STCs) both upwell at
the Equator, but downwell at 5 degrees north and 20 degrees north,
respectively. The authors find that the important cells for
transferring mass, heat, and salt to the equatorial thermocline in
the Indo-Pacific Oceans are the STCs. In the modeled mean
circulation, when high-frequency eddy motions and the effect of
sloping isopycnals [of equal density] are taken into account, the
TCs vanish.

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II. Authors referenced in the Highlights (in order of appearance):

3. Collin E. Johnson, William J. Collins, R. G. Derwent, Met.
Office, Hadley Ctr. for Climate Prediction and Research,
Bracknell, United Kingdom; David S. Stevenson, Dept. of
Meteorology, Edinburgh U., Edinburgh, United Kingdom.

4. Alistair Adcroft, Jeffrey R. Scott, MIT, Cambridge,
Massachusetts; Jochem Marotzke, Southampton Oceanography
Ctr., U. Southampton, Southampton, United Kingdom.

5. Mario Hoppema, Wolfgang Roether, U. Bremen, Dept.
Oceanography, Bremen, Germany; Richard G. J. Bellerby,
Geophysical Inst., U. Bergen, Bergen, Norway; Hein J. W. de Baar,
Netherlands Inst. for Sea Research, The Netherlands.

6. Wilco Hazeleger, Pedro de Vries, Geert Jan van Oldenburgh,
Oceanographic Res. Dept., Royal Netherlands Meteorological
Inst., Oceanographic Research Dept., De Bilt, The Netherlands.

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American Geophysical Union (AGU)