Geoscience Reference
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Plate 3. (left) Present-day temperature at 400 m: blue shading (orange coloring) characterizes temperatures below (above)
CO
2
triple-point temperature indicating CO
2
clathrate stability (instability). The temperature data are taken from the work
of Levitus [1994]; cyan contours indicate the triple-point temperature at 400 m depth. (right) LGM temperature at 400 m;
coloring same as left. The LGM temperature data are obtained by subtracting an LGM temperature anomaly estimate from
the Levitus [1994] temperature climatology. The LGM temperature anomaly estimate is obtained by averaging the
difference between LGM and present-day simulations obtained from two climate models: (1) the LOVECLIM climate
model [Timmermann et al., 2009] and (2) the CCSM3 model [Otto-Bliesner et al., 2006].
solubility into a colder glacial ocean would account for only
a small, ~30 ppm, portion of the total 80 ppm decrease in
glacial atmospheric concentrations. Higher salinities in the
glacial ocean, as well would have offset the effects of en-
hanced solubility. Carbonate chemistry and shifting carbon-
ate deposition have also been considered as influences on the
atmospheric CO
2
variability during glacials [Ainsworth et
al., 2004; Archer and Maier-Reimer, 1994; Brigault et al.,
1998; Broecker, 1982, 2009b; Broecker and Clark, 2003;
Marchitto et al., 2005]. For this mechanism to explain the
recurrent ~80
100 ppm drops in atmospheric CO
2
during
glacials, decreased carbonate deposition in the oceans would
have to be invoked. The deep-sea carbonate record itself
does not provide a clear indication that this factor was the
primary in
-
uence on glacial/interglacial CO
2
variability, al-
though it very likely contributed to the variability [Broecker
and Clark,2001;Farrell and Prell, 1989]. Furthermore,
while shallow water carbonate deposition was reduced dur-
ing glacials, the deglacial increase in deposition on the con-
tinental shelves and at shallow carbonate reefs did not occur
until after sea level had risen and, therefore, well after atmo-
spheric CO
2
had begun to increase.
Considerable research has focused on mechanisms to en-
hance carbon transfer into the ocean
s interior during glacials
via biological processes termed the
“
biological pump.
”
The
Southern Ocean has received most attention because macro-
nutrients are not fully utilized there. If biological sequestration
of carbon was increased within the Southern Ocean during
glacials, it could have enhanced transfer of CO
2
from the
atmosphere into the ocean interior [Adkins et al., 2002; Ito and
Follows, 2005; Keeling and Stephens, 2001a, 2001b; Masson-
Delmotte et al., 2005; Rozanski et al., 1992; Sarmiento and
Toggweiler, 1984; Siegenthaler and Wenk, 1984; Sigman et al.,
2010; Stephens and Keeling, 2000; Toggweiler and Sarmiento,
1985]. It is also possible, although debated, that weakening or
equatorward displacement of westerly winds over the Southern
Ocean during glacials reduced Ekman pumping and upwelling
of carbon-rich waters to the surface during glaciation
'
Plate 4. Timing of Southern Ocean temperature (black) and sea ice
(red) change during the last glacial termination in relation to the
austral spring insolation at 70°S (W m
2
, blue). The Southern
Ocean SST index is obtained by averaging over the spline-interpo-
lated SST records from MD88-770 MD97-2120, RC11-120; the sea
ice proxy is derived from the sea salt sodium
flux in the EPICA
Dronning Maud Land (EDML) ice core and plotted on common
EDML1/EDC3 time scale.
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