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atmospheric CO
2
(Plate 1) [Jouzel et al., 2007; Luthi et al.,
2008]. Indeed, each glacial/interglacial climate transition
during the past 500 kyr was associated with similar atmo-
spheric CO
2
change. The remarkable similarity in atmospheric
CO
2
variability during the late Pleistocene glacial-interglacial
cycles points to a regulatory mechanism that systematically
limits the range of atmospheric CO
2
change between a gla-
cial and an interglacial climate state. Given the close tempo-
ral relationship between atmospheric CO
2
changes and
temperature variability at high southern latitudes, it appears
the
“
center of action
”
for regulation of atmospheric CO
2
lies at high southern latitudes. But is the Southern Ocean
itself responsible for the uptake and release of CO
2
to and
from the atmosphere, or was the Southern Ocean simply a
conduit through which climate change was communicated to
the deep ocean where CO
2
was stored during glacials and
released during deglaciations?
We set forth a hypothesis wherein the high latitude oceans
act as communicator of orbitally induced climate change
(temperature) to the deep sea. This temperature change stim-
ulates a thermodynamic response at sites in the ocean
where seawater
et al., 2003; Hutnak et al., 2008; Stein and Stein, 1994].
These studies provide insight about the flux of seawater
through the hydrothermal conduits and how this
flux is
in
uenced by temperature differences between cold seawater
that enters a hydrothermal system and the warmer fluids that
emanate at active vents [Fisher et al., 2003; Hutnak et al.,
2008]. If shown to be representative of a wider distribution of
active submarine vent systems throughout the Pacific, these
estimates from the northeast Paci
c imply very high volume
ows, as much as 50 L s
1
at some sites [Walker et al., 2008].
Using heat flow estimates and measurements of dissolved
inorganic carbon (DIC) together with the isotopic composi-
tion (
13
C and
14
C) of DIC from the cold in
ow water and
warm outflow water, Walker et al. [2008] made a compelling
case that hydrothermal systems may sequester signi
δ
Δ
cant
volumes of carbon, both as precipitated carbonate in shallow
crustal rocks and presumably as CO
2
-rich subsurface fluids.
We are drawn to these observations as possible in
uences
on glacial/interglacial CO
2
cycles. We begin by reviewing
some of the previous hypotheses that have been considered
in efforts to explain atmospheric CO
2
variability during the
Pleistocene. In reviewing the previous hypotheses, it is evi-
dent that no single hypothesis can explain all of the phenom-
ena that accompanied glacial/interglacial CO
2
variability,
particularly the marked shifts in surface ocean
flows through hydrothermal conduits and
generates CO
2
and CO
2
-rich fluids that accumulate in sedi-
ments that
flank active volcanic vents. Hydrothermal systems
14
C during
the most recent glacial termination. We then set forth our
reasoning and a physical basis for considering an alternative
mechanism for CO
2
variability.
in the Paci
c act as both a source and sink for carbon. In the
western Pacific, subduction of oceanic crust results in decar-
bonation of the carbonate sediments that produces CO
2
-rich
Δ
fluids and liquid CO
2
[Chivas et al., 1987; de Ronde et al.,
2007; Embley et al., 2006; Inagaki et al., 2006; Lupton et al.,
2006, 2008; Massoth et al., 2007; Resing et al., 2004, 2009].
Recent surveys of these vents highlight accumulations of
liquid CO
2
and CO
2
-rich fluids in sediments that blanket the
2. PREVIOUS HYPOTHESES
During the last glacial termination, the rise in atmospheric
CO
2
began at ~18 kyr B.P. Between 17.5 and 14.5 kyr B.P.,
the concentration of atmospheric CO
2
rose by about 50 ppm.
The source of carbon released to the atmosphere must ac-
count for a 190
flanks of active vent sites [Inagaki et al., 2006]. The
flux of
CO
2
and CO
2
-rich
fluids from sediments at active vent sites
is regulated in part by CO
2
hydrate that can form at the
sediment/water interface where warm, buoyant CO
2
-rich
‰
drop in atmospheric and surface ocean
14
C between ~18 and 14 kyr B.P. (Figure 1) because it
appears that there was no change in the production of cos-
mogenic isotopes at that time [Broecker and Clark, 2010;
Finkel and Nishiizumi, 1997]. Broecker and Clark [2010]
estimated that ~5000 Gt of radiocarbon-dead carbon would
be required to shift the entire ocean and the atmosphere
carbon reservoirs by
flux of CO
2
into the overlying ocean is regulated by diffusion and disso-
lution of CO
2
at the hydrate-sediment/water interface. Today,
the temperature and pressure-dependent hydrate stability
horizon occurs at intermediate water depths below ~700 m
where temperatures are less than 9°C (Plate 2). Many of the
active hydrothermal vents in the Paci
fluids come in contact with cold seawater. The
Δ
c occur at intermediate
depths [Cheminée et al., 1991; Chivas et al., 1987; Hilton et
al., 1998; Inagaki et al., 2006; Lupton et al., 2008; McMurtry
et al., 1993].
Coinciding with the discovery of liquid CO
2
accumula-
tions at active submarine arcs in the Paci
. With this constraint in mind,
the most likely reservoir for sequestration of CO
2
would
seem to be the abyssal ocean [Broecker and Clark, 2010].
Calling upon such a reservoir requires there to be a distinc-
tive isotopic fingerprint in biogenic carbonate that came in
contact with this water mass. Yet after more than 20 years of
research, there is no clear evidence that an abyssal water
mass was isolated from the atmosphere for anomalously
longer periods of time during the last glacial [Broecker and
190
‰
c, there have also
been signi
flow of
seawater and heat exchange at active vents along the axis
and off axis of spreading centers in the eastern Paci
cant advances in the estimates of the
c[Fisher
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