Friday, February 13, 2009

carbon pumps and other assorted goodies

Hi all,

First, seems like my entry on my talk a few days ago sounded a little
downbeat. It wasn't meant to be -- just trying to reflect on how to
do it better next time -- all the feedback I've gotten since then
suggests that people were involved and are excited about it.

Next, weather. Calm as possible today. Very glassy water, scattered
with just very small chunks of sea ice and cluttered with medium and
large tabular icebergs. Can't really remember a day like this on the
two Antarctic cruises I've been on now. Very cool for photos: all
the ice reflects in the water below, you can see ledges beneath bergs
deep underwater, and there is just a very thin layer of forming sea
ice at the surface. The wake from the ship is really the only
disturbance to what would be a totally tranquil scene. Unfortunately
we wouldn't be able to experience it without a 300 foot ship tearing
up the picture.

Now, the plan. Exciting news this morning. Because of the light sea
ice, we're able to head back to the Getz ice shelf, which we had to
pass by a few weeks ago due to stormy seas, as referred to in the
weekly report. So Southward we steam! Still competing in the
pingpong tournament, but working my way through the losers' bracket.
It's a long way to the title from where I stand.

Finally, the carbon stuff. Got an interesting comment a while ago
from Roy aka Dad about how the oceans work with respect to Carbon
"One highlighted the fact that the deep ocean is kind of a kidney for
CO2 (absorbs it and flushes it out of the atmosphere), but with a
super-long cycle it just can't keep up."

This is true, but it's really only one part of the story. I'll
elaborate in a very brief way here which doesn't do this topic
justice. But I'm not a very fast typer, so:

Oceans can be looked at as having two parts -- the surface, which is
exposed to the atmosphere and which can exchange gases, heat, and
freshwater (through evaporation and precipitation), and the deep,
which only very slowly exchanges with the surface. Deep oceans
"sequester" carbon because they hold way more than they would if they
were in equilibrium with the atmosphere. The only way for this to
happen is for carbon to move from parts of the ocean that have less
to those that have more. In order to make this work, we need "pumps"
-- processes which allow us to move carbon in the opposite direction
as the difference between the surface and deep (like moving water
uphill!) The two most important are referred to as the solubility
and biological pump. The solubility pump is put into action by the
sinking of cold water near the poles. Since CO2 is more soluble in
cold water than warm, and these cold water fill most of the ocean's
volume, more CO2 is locked up at depth than at the surface. The
biological pump works because phytoplankton use CO2 near the surface
of the ocean to grow (photosynthesis). They die/are eaten/decompose
and eventually sink. But as they sink, they are "remineralized" into
forms of dissolved CO2 by bacteria and other organisms. If they
break down below the level where the atmosphere interacts, the carbon
is trapped in the deeper water. Over the 1000's of years it takes
for some parts of the ocean to get back to the surface, accumulated
dead stuff can take a lot of carbon out of the air.

So the net effect of these pumps is to remove CO2 and they WILL
operate to bring down concentrations of CO2 in the atmosphere if
given enough time (1000's of years). But if we make our model a
little more complicated and look at what happens in different places
near the poles, we see both sources and sinks of carbon. In fact,
where we're traveling, there is a significant amount of upwelling
water (this is the "warm" stuff, CDW) which vents a large amount of
CO2 to the surface. Like a malfunctioning kidney (a very apt
metaphor, coming from me), the ocean may shift it's absorbtion/
venting balance if it is perturbed. More "stuff" may be left in the
bloodstream. Since the amount of CO2 in the atmosphere is so small
relative to the amount in the ocean, even a small change in these
pumps (e.g. changes in the temperature of the water, changes in
locations and strength of winds, dominant phytoplankton species) may
exert a strong (positive or negative) effect on atmospheric CO2.

Enough science for now. Will you be my valentine?


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