"Where the Ocean Exhales "—Carbon and the Southern Ocean

If humans are ever forced to do geoengineering the engineering we should do is feed the phytoplankton by fertilizing with iron. And the place we should do it is the Southern Ocean.

And the pace we should do it at is SLOWLY.*

 

From Nautil.us, May 22:

 

The Southern Ocean controls how much carbon is released into the atmosphere—and our warming world is changing it.

When one thinks of Antarctica, one imagines a vast landscape in shades of blinding white, ice and snow stretching as far as the eye can see. But to really consider Antarctica is to consider its water.

The Southern Ocean, which encircles Antarctica, is where the ocean exhales. It is the primary place where the water of the deep oceans rises to the surface, mingles with the atmosphere in a kind of embrace, and then sinks back into the depths. In the course of this exchange, the Southern Ocean both consumes carbon from the atmosphere and releases some of the vast quantities of carbon stored in the deep ocean, the Earth’s largest natural carbon sink. The Southern Ocean therefore controls the global exchange of carbon between ocean and atmosphere, which is vital to regulating global carbon dioxide levels.  But climate change may alter this dynamic.

We spoke to Elisabeth L. Sikes, a marine biogeochemist and paleooceanographer with Rutgers University who has received awards for her research on Antarctica and the Southern Ocean, about why the Southern Ocean is so vital to carbon regulation and how global climate change is influencing its role.

How does the Southern Ocean work as a carbon sink?

It’s both a source and a sink. Phytoplankton in the surface ocean take up CO₂, through photosynthesis. And when they die, their bodies sink to the bottom of the ocean and somebody else eats them. Then that carbon—that they’ve pulled from the atmosphere, turned into organic matter, and sunk—is released back into the deep ocean as CO₂. So that CO₂ is sequestered in the deep ocean. And that process is called the biological pump.

That’s the first step in why the ocean can sequester CO₂. The second step is sort of why it comes back out again.

And how does that happen?

The ocean has deep circulation that’s different from the surface circulation, which is wind-driven. This deep circulation is called thermohaline circulation. The main place this deep water forms is the North Atlantic.

The Gulf Stream delivers very warm, salty water to the North Atlantic. When you chill salty water—which is already dense from the salt—it gets really cold and really dense. And so that North Atlantic deep water travels around the bottom of the ocean. This deep water is cut off from the rest of the ocean, and it’s traveling along, and that biological pump is putting organic matter into it, which turns into CO₂. So now you’re building up all of the CO₂ in the deep ocean.

It’s about winds, and it’s about density.

....MUCH MORE
*from 2021's "Searching for the Dust That Cooled the Planet":
This is why you want to be careful with the geoengineering proposals. Some links after the jump....

*****

One of the reasons we ran Plankton Week last October—no, not as counterprogramming to Shark Week—was to refresh memories of one of the topics of conversation at all the better salons and soirées circa 2007.

Plankton Week: “Give me a half tanker of iron, and I will give you an ice age.”

The headline quote is from oceanographer John Martin during a 1988 lecture at Woods Hole Oceanographic Institution. Here's NASA's Earth Observatory archive page on the statement.

It is a bit of an exaggeration, you may need ten of those Valemax bulk carriers, currently the second largest ships in the world at 400,000 dwt (Euronav's two TI oil tankers at 441,000 dwt are bigger), to make an environmental change but what a change it would be. The orders of magnitude of carbon the iron-fed plankton would sequester are almost mind-boggling:

...Martin gathered the results of the incubation experiments and laid out the evidence in support of the Iron Hypothesis together with some back‐of‐the‐envelope calculations and presented his findings at a Journal Club lecture at Woods Hole Oceanographic Institution in July of 1988. He estimated that using a conservative Fe : C ratio that 300,000 tons of iron in the Southern Ocean induce the growth of phytoplankton that could draw down an estimated two billion tons of carbon dioxide. Then, putting on his best Dr. Strangelove accent, he suggested that “with half a ship load of iron….I could give you an ice age.” The symposium broke up with laughter and everyone retired to the lawn outside the Redfield Building for beers (from Chisholm and Morel, Editors, preface to: What controls phytoplankton production in nutrient‐rich areas of the open sea? Limnology and Oceanography, 36, 8 December 1991). 

As repeated in "John Holland Martin: From Picograms to Petagrams and Copepods to Climate"
—Bulletin of Limnology and Oceanography, Wiley. 25 March 2016

This year's energy-sourced emissions of CO2 should come in at 30.6 gigatonnes ( 30,600,000,000 tonnes) of which a large part will reenter the carbon cycle, becoming plant material etc. but it is the stuff that remains in the atmosphere after the rest is sequestered that is available to feed the plankton.

So, very, very serious business.

Don't try this at home....

*****

....Coming up tomorrow, the Pope, and a Vancouver stock promoter.

Our series thus far:
October 27
Plankton Week: "Metal deposits from Chinese coal plants end up in the Pacific Ocean, research shows"
October 26
"Plankton Bloom Heralded Earth’s Greatest Extinction"

....MUCH MORE

And many, many more. If interested use the 'search blog' box, keyword plankton and Planktos for the saga of the Pope and the stock promoter.
Also whales. Huge benefits.