Re: [asa] Southern Ocean Loaded With Carbon Dioxide

From: PvM <pvm.pandas@gmail.com>
Date: Sun May 20 2007 - 14:08:46 EDT

I have not yet gotten access to the Science 2007 paper although I have
located papers which corroborate these findings by others.

First of all a correction to the claim about acidification, in fact
that the surface waters of the antarctic become saturated is negative
potentials for impact on corals.
As to the claims about good news for coral reefs etc, this also seems
to be misplaced 'optimism'

The increased winds mix waters from deeper depths with higher CO2 to
the surface where they become saturated and no further CO2 exchange is
possible. This leads to surface waters becoming even more acidic.

<quote>
The problem is that the extra CO2 from human emissions stays in the
surface ocean and does not get removed to deep waters," said Dr Le
Quere.

"So the problem gets worse, because the biological organisms affected
by ocean acidification live, of course, at the surface where there is
sunlight."
</quote>

To understand the differences between the two papers, one has to
realize that the papers are doing two very different things.

The 2006 paper is first of all quite careful about its predictions

<quote>
Assuming that the magnitude of the wind stress is relatively close to
the observed value (say within 20% or so), then it seems to us that
the location of the westerlies is the single most important factor in
getting the control Southern Ocean simulation correct. Obviously, many
other model errors can impact the Southern Ocean and a careful
analysis must be performed before
a judgment made on the quality of a given model's response to
increasing greenhouse gases is reliable.
</quote>

The 2006 paper, which argues that the reservoir in the antarctic may
be larger than expected, bases their predictions on the fact that the
model better captures the fact that the winds move further south and
accellerate. These stronger winds will stir up more of the ocean
surface, increase mixing. In addition, the wind speed affects the gas
exchange,

however the relationship between exchange and windspeed is quite uncertain

<quote>As discussed by Takahashi et al. [2006], the uncertainty
associated with the pCO2 based flux estimates is mostly caused by
possible sampling biases and uncertainties associated with the gas
transfer velocity. The use of a linear dependence of the gas transfer
velocity on wind
speed, as recently proposed by Krakauer et al. [2006], decreases the
pCO2 based fluxes south of 44 S by only 0.05 Pg C yr −1 . The cubic
dependence of Wanninkhof and McGil lis [1999] increases the uptake
flux substantially to 0.6 Pg C yr −1 . However, Krakauer et al. [2006]
demon-
strated that a cubic dependence on the windspeed is inconsistent with
carbon-13 and carbon-14 constraints, a conclusion supported by the
recent in-situ measurements, which suggest a quadratic dependence [Ho
et al., 2006].
</quote>

The 2007 paper collected available data and used an inverse model
approach to determine the relevant fluxes and observed that the uptake
of CO2 has slowed down significantly.

Amy H. Butler David W.J. Thompson Kevin R. Gurney, Observed
Relationships between the Southern Annular Mode and Atmospheric Carbon
Dioxide

Submitted to Global Biogeochemical Cycles July 2006 Revised March 2007

<quote>The findings in this study thus provide observational support
for possible
feedbacks between the carbon cycle and large-scale climate variability
in the Southern
Hemisphere. Virtually all climate change simulations suggest that
increased atmospheric
CO2 will lead to a poleward shift in the Southern Hemisphere storm
track consistent with
the high-index polarity of the SAM [Kushner et al., 2001; Miller et
al., 2006], and there
is now both modeling [Lovenduski et al., submitted 2007] and
observational (this study)
evidence that the high-index polarity of the SAM, in turn, drives
anomalous fluxes of
CO2 from the high-latitude Southern Ocean to the atmosphere.
Toggweiler et al. [2006]
have suggested such a feedback may have been key in driving past
climate changes.
What such a feedback portends for the climate response to
anthropogenic emission of
CO2 remains to be determined. </quote>

Also the following paper argues

Nicole S. Lovenduski and Nicolas Gruber and Scott C. Doney and Ivan D. Lima
Enhanced CO2 outgassing in the Southern Ocean from a positive phase
of the Southern Annular Mode

<quote>The primary cause of the natural CO2 outgassing is anomalously
high oceanic partial
pressures of CO2 caused by elevated dissolved inorganic carbon (DI C )
concentrations. These anomalies in DI C are primarily a result of the
circulation changes associated with the southward shift and
strengthening of the zonal winds during positive phases of the SAM.
The secular, positive trend in the SAM has led to a reduction in the
rate of increase of the uptake of COby the Southern Ocean over the
past 50 years.
</quote>

This shows once again that relying on actual papers, provides a much
better insight that press releases.

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Received on Sun May 20 14:09:33 2007

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