Ice core data - Ice Ages and Interglacials: Measurements, Interpretation, and Models - page 159

ecient mechanism for mixing CO 2 deep into the ocean interior. The return flow
of deep water to the surface occurs primarily in the Southern Ocean representing a
net reflux of carbon to the atmosphere. Thus, the Southern Ocean plays a pivotal
role in controlling the overall e ciency of oceans' physical carbon pump. Any
model to explain the GICC must provide scenarios for these oceanic processes.
A number of interesting new ideas regarding GICC, which are unfortunately
beyond the scope of

this topic, can be found at www.atmos.umd.edu/ cabo/

METO658A/dlove.ppt
Lisiecki (2010) presented an extensive review of estimates of variability of CO 2
concentration over the past 800,000 years. It was found that benthic d 13 C data
provide a good record of deep-ocean carbon storage and, thus, atmospheric
pCO 2 . This study found that the difference between d 13 C data in the deep Pacific
and intermediate North Atlantic provided a good correlation with CO 2 levels
recorded in Antarctic ice cores.
Sigman et al. (2010) asserted:

the cause of the pCO 2 variation must be resolved if we are to understand
its place in the causal succession that produces glacial cycles

'' ...

. The ocean is the
largest reservoir of CO 2 that equilibrates with the atmosphere on the thousand-
year timescale of glacial/interglacial changes in pCO 2 , so the ocean must drive
these changes. CO 2 was more soluble in the colder ice-age ocean, which
should have lowered pCO 2 by 30 ppm, but much of this appears to have been
countered by other ocean changes (in salinity and volume) and a contraction in
the terrestrial biosphere. The most promising explanations for the bulk of the
pCO 2 decrease involve ocean biogeochemistry and its interaction with the
ocean's physical circulation.''

...

Sigman et al. (2010) concluded:

''Global climate and the atmospheric partial pressure of carbon dioxide
(pCO 2 ) are correlated over recent glacial cycles, with lower pCO 2 during ice
ages, but the causes of the pCO 2 changes are unknown. The modern Southern
Ocean releases deeply sequestered CO 2 to the atmosphere. Growing evidence
suggests that the Southern Ocean CO 2 'leak' was stemmed during ice ages,
increasing ocean CO 2 storage. Such a change would also have made the global
ocean more alkaline, driving additional ocean CO 2 uptake. This explanation for
lower ice-age pCO 2 , if correct, has much to teach us about the controls on current
ocean processes.''

Bouttes et al. (2011b) employed a model ''of intermediate complexity'' to
investigate the causes of the increase in pCO 2 following the LGM. They included
the following factors: (1) fertilization of marine biology by iron deposited from the
dusty atmosphere; (2) extension of the Antarctic ice sheet past continental shelves,
thus forming sea ice over deep ocean and allowing brines left over from sea ice
formation to sink to the deep ocean; and (3) stratification of the ocean due to