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Geophysical Research Letters - Highlights for 1 February 2001

January 18, 2001

American Geophysical Union
Geophysical Research Letters
European Highlights of This Issue - 1 February 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. Numerical model of Lake Vostok

Williams ["Application of a three-dimensional numerical model to
Lake Vostok: an Antarctic subglacial lake"] applies an existing 3-D
numerical ice-ocean model to study the circulation beneath the
Antarctic Ice Sheet, specifically at Lake Vostok, and presents
circulation and ice melt/freeze patterns for two scenarios, namely a
depth-constant fluid and a depth-varying one, the flow in each case
being forced by both bottom geothermal fluxes and surface
thermodynamic fluxes. In the depth-constant case, a largely
barotropic flow is produced and in the depth-varying one a
baroclinic flow. The dominant circulation in the model is
horizontal, but there is also a weaker vertical flow, sufficient to
keep the lake well mixed. The author notes that the mixing makes
it unlikely that the water at the top and bottom of the lake have
significantly different geochemical ages.

4. Rising and sinking mantle plumes

Schaeffer and Manga ["Interaction of rising and sinking mantle
plumes"] determine experimentally the frequency of plume
formation in fully developed thermal convection (a plume is
defined here as a volume of either hot or cold fluid released
periodically from thermal boundary layers). They find that the cold
and hot thermal boundary layers, which have a direct temporal
interaction with each other, have different thicknesses and
viscosities. In addition, the plumes are released from these layers
with different frequencies. The authors note that hot plumes might
form either naturally as boundary layer instabilities or indirectly
via the arrival of a cold plume in the lower thermal boundary layer.
Measurements also suggest that cold sinking plumes in the mantle
induce hot rising plumes.

6. Oceanic uptake of anthropogenic carbon

Thomas et al. ["An off-line 3-D model of anthropogenic CO2
uptake by the oceans"] apply an off-line ocean carbon cycle model
to estimate the extent to which the oceans absorb and redistribute
man made carbon dioxide. According to the model, the annual
uptake rate of man made carbon during 1999 is 3.9 Pg C per year
[petagrams of carbon, one petagram being 10^15 grams]. This
study suggests deeper penetration of the carbon and a much greater
uptake than previous studies based on 13C and oceanic pCO2
[partial pressure of CO2].

7. Fall foliage at a price

Historically, most field measurements of biogenic volatile biogenic
compounds (VOCs) have focused on the summer season (maximal
vegetation growth and ambient temperatures, enhanced
photochemical ozone formation). Karl et al. ["High concentrations
of reactive biogenic VOCs at a high altitude site in late autumn"]
show that deciduous forests release large amounts of reactive
VOCs in late autumn. They measure VOCs at a remote site in
Austria during two periods in November-December 1999, and
propose that when the first hard freeze events occur, significant
leaf wounding reactions release high amounts of C5- and C6-
VOCs, which can then impact the local oxidative balance of the
atmosphere.

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

3. Michael Williams, Danish Ctr. for Earth System Science,
Copenhagen, Denmark.

4. Nathanael Schaeffer, Dept. des Sciences de la Matiere, Ecole
Normale Superieure, Lyon, France; Michael Manga, Dept. of
Geological Science, U. Oregon, Eugene, Oregon.

6. Helmuth Thomas, Inst. of Biogeochemistry and Marine
Chemistry, U. Hamburg, Hamburg, Germany; Matthew H.
England, Ctr. for Environmental Modelling and Prediction, the U.
of New South Wales, Sydney, Australia; Venugopalan Ittekkot,
Ctr. for Marine and Tropical Ecology, Bremen, Germany.

7. Thomas Karl, NCAR, Boulder, Colorado; Alfons Jordan,
Werner Lindinger, Inst. fur Ionenphysik, U. Innsbruck,
Technikerstrasse, Innsbruck, Austria; Ray Fall, Dept. of Chemistry
and Biochemistry, U. Colorado, Boulder, Colorado; Paul J. Crutzen,
Max-Planck-Inst. fuer Chemie, Mainz, Germany.


American Geophysical Union (AGU)