Phytoplankton: a negative feedback?

There are several potential negative feedbacks out there that I still haven't properly researched and written about, such as ocean snow effect, river discharge, salinity, inversion, clouds, ice drift (I know, some of them turn out to actually be positive feedbacks), but lately it occured to me that an increase in algal blooms might actually pull out more CO2 from the atmosphere and thus in a sense be a negative feedback. I didn't think any more of it, as I'm prone to do.

This week, however, there has been a wave of reports in the media about a research result from last year's IceScape mission (here, here, here, here, here, and many more). Contrary to what was thought, phytoplankton is also growing under the ice. With Arctic sea ice thinning ever more, it is expected that algal activity will also increase. The news articles are based on this research paper by Arrigo et al., that is due for publication in Science next week.

Here's a video explaining the whole thing (h/t Climatecrocks):

 

All those articles basically say the same thing (I think, didn't read them all), except for this one from The Capitol Column that caught my eye: NASA: Increase in CO2 could indirectly lessen effects of global warming. Because of the title I was expecting to read something about CO2, but apparently the take-away message had to be:

While the results of the study are likely alarming for climate scientists, the team noted that the presence of the plants could ultimately lead to a thriving fishing industry and additional benefits.

However, in some of the other articles, such as this one in the Christian Science Monitor, there was a tiny speck of info regarding CO2:

The scientists said the discovery also may have major implications for the global carbon cycle and the ocean’s energy balance, and they may need to revise their understanding of the ecology of the Arctic and the region’s role in the Earth system.

This phenomenon has many implications, as most developments in the Arctic do, for ecosystems, marine life and fisheries. But what will the effects of the increase in phytoplankton under the ice be for the ice itself, for the Arctic as a whole, for CO2 uptake, for ocean acidity, for oxygen availability (there will be more nutrient-rich river discharge because of melting permafrost)?

I honestly don't have a clue, but would love to read anything that readers know about this subject. It might come in handy if I ever do come around to writing that piece on negative feedbacks.

Comments

[Aaron Lewis]

Where does this bio-mass go in the fall, when it gets dark? It may die, and be converted to methane. This may resolve the question regarding the source of Arctic methane detected at sea ice cracks. We may have an ecosystem in the Arctic that takes CO2 out of the atmosphere and converts it to methane. I do not think that is in the IPCC models.

[Peter Ellis]

Dead biomass generally sinks and thus buries the carbon, thus acting as a net CO2 sink. This has happened before, back when the Arctic was open ocean: in fact it's thought to be one of the mechanisms that brought temperatures down during the Eocene and initiated planetary glaciation.

http://en.wikipedia.org/wiki/Azolla_event

However, it's worth pointing out that this is a [i]very slow[/i] process. In the long term, extra Arctic phytoplankton may help draw down some of our emissions. In the short term, it's negligible. To get a ballpark estimate of the effect of CO2 drawdown by plants, look at the Mauna Loa CO2 data.
http://en.wikipedia.org/wiki/File:Mauna_Loa_Carbon_Dioxide.png

See the little wiggles in it? That's the aggregate effect of [i]every deciduous plant in the Northern Hemisphere growing its leaves[/i]. A little extra phytoplankton won't budge that.

In fact, over the short term I'd suspect it of being a significant positive feedback via albedo effects. By definition, plankton absorbs more of the Sun's energy than water alone would. It's how plants [i]work[/i] - absorbing sunlight is what they do! Unless the biomass production process is 100% energy efficient (and it can't be), then some of the absorbed energy will be converted into heat. That will vastly outweigh the minute effects of extra CO2 drawdown.

Over millions of years, then sure, all means of fossilising carbon are useful - rebuilding the coal and oil we've burned. But we don't exactly have that time to hand.

[Peter Ellis]

http://www.agu.org/pubs/crossref/2002/2001JD000562.shtml

Albedo effect of phytoplankton is an extra net absorption of ~0.25W/m^2 averaged across the globe (or possibly just the oceans, don't have access to the full text). Heavy concentrations can absorb up to an extra 1.5 W/m^2.

[Neven]

Thanks for the info, Peter!

[R. Gates]

This is a very interesting discovery, but I am skeptical about it being a negative feedback. Much like the discovery recently that trees were expanding faster than expected into warmer climates in Siberia, and this absorbing more sunlight in the region than tundra, I suspect that phytoplankton might do much the same in the ocean. True, there is more CO2 being released in both cases, but the net short-term I suspect will be a positive feedback to warming. On balance, the eventual open ocean in the summer and more trees in the formerly open Arctic tundra will only serve to continue the warming of the Arctic...and then of course, we must think of all that CO2 and methane being released from the melting permafrost on land and clathrates under the warming ocean.

[R. Gates]

Of course I meant to say "more CO2 being absorbed" in both cases.

[idunno]

Hi Neven,

I remember reading a very long time ago about plankton which can actually grow within the ice itself, and survives at temps down to as low as -20 C, as it produces some kind of natural anti-freeze.

I would guess that a bloom of these wee beasties would be very significant.

[Aaron Lewis]

Peter, just because the dead algae sink to the bottom of the ocean does not mean the carbon compounds are not available to methanogenic bacteria.

[Ned Ward]

Peter, thanks for the link to the paper on the albedo effect of phytoplankton. I look forward to reading it ... but my initial reaction is surprise.

It's true that phytoplankton have lower reflectance at short wavelengths, but above 520 nm or so, they actually increase the reflectance of water. So I wouldn't have thought there'd be much overall effect on albedo.

I also don't think that any CO2 feedback from polar phytoplankton would be very large. We're not exactly talking about another azolla event here....

[Hank Roberts]

http://www.agu.org/pubs/crossref/2005/2004GL020778.shtml

Bio-optical feedbacks among phytoplankton, upper ocean physics and sea-ice in a global model

and much, much else. This has been a big deal for a long time. For most plankton (other than larval forms), lifetime in the ocean is a few days to at most a few weeks, so both the turnover and the selection for fitness under the immediate conditions -- which species increase and which decrease -- change very rapidly.

Back before the 2007 arctic sea ice low point, when Dr. Bitz wrote a guest post at RC about the theoretical possibility of such sudden changes, I recall I asked and she said her colleagues studying what lives around the Arctic and northern oceans were watching this stuff very carefully.

[Wayne Kernochan]

@Neven: I would be very cautious about taking what Capitol Column says at face value. It reads like a US denier site (note the right-wing Republican coverage and some of the other assertions in the article). - w

[Account Deleted]

"presence of the plants could ultimately lead to a thriving fishing industry and additional benefits."

I would also take this with a grain of salt - yes it is one possible outcome, but the blooms could also have a detrimental effect - it will depend on which species benefit the most from the new conditions, how these condition effect interactions among the arctic ocean communities, etc. Some commentators like to play up the CO2 is a plant food and increases in CO2 will be beneficial idea. The problem is ecosystem don't always responsed the way we would like/predict
A good non-arctic example of this is the paper by Oliver Phillips (http://eprints.whiterose.ac.uk/76/1/phillipsol1.pdf)

[Timothy Chase]

Wayne Kernochan wrote, "I would be very cautious about taking what Capitol Column says at face value. It reads like a US denier site (note the right-wing Republican coverage and some of the other assertions in the article)."

A couple of examples from the article might help.

One that really stood out for me was the final closing sentence, "The results of the study could further complicate the international response to the threat poised by global warming, which has divided both the scientific community and the policy makers worldwide." The scientific community isn't that divided. There is a strong, evidence-based expert consensus.

However, more revealing is the following statement that I found in the third paragraph, "The team of scientists suggest that the large quantities of phytoplankton, recently discovered growing under sea ice, could pull in large amounts of the greenhouse gas, possibly curtailing any potential consequences of global warming." Possibly curtailing any potential consequence?

Nothing quoted by the author suggests anything of the sort, and the simple fact that carbon dioxide levels have been steadily increasing over the past several decades strongly argues against it. Furthermore, one would certainly expect some of the carbon dioxide that gets consumed by the phytoplankton to return as methane when the phytoplankton dies and undergoes organic decay in the absence of oxygen.

On a 20 year horizon, molecule per molecule, methane is 72 times as powerful a greenhouse gas as carbon dioxide, on a 100 year horizon 25 times as powerful, and on a 500 year horizon 7.6 times. (See IPCC Fourth Assessment Report, Table 2.14, Chapter 2, p. 212) It seems rather debatable whether the drawdown of carbon dioxide by the phytoplankton would itself constitute any sort of negative feedback, at least on any time horizon we might be considering.

[Bob Wallace]

Some more info from another source...

"Apparently, phytoplankton begins to grow beneath the Arctic ice in the late spring, as soon as there is ample light for photosynthesis.

After a couple of weeks, the ice disappears and what is left is a remnant population of phytoplankton from that earlier under-ice bloom.

The reason that relatively little phytoplankton is later seen in open waters is because most of the available nutrients were already consumed by their under-ice brethren.

http://www.mnn.com/earth-matters/wilderness-resources/stories/arctic-sea-ice-explorers-find-massive-bright-green-micros

[Wayne Kernochan]

@Timothy Chase: thanks very much for the sleuthing. Yes, those were the quotes I meant.

I'd add with regard to phytoplankton turning into methane: late last year, iirc, there was an extensive discussion of "blooms" with regard to their ultimate effect on methane. Off the top of my head, scientific examination of "clathrate methane emissions don't bubble to the top, they feed blooms" concluded that, yes, those blooms would live a short time, and then emit comparable amounts of methane as they die -- which would, in turn, come to the top, although not as bubbles. Also, some of it would rise as carbon dioxide -- and because it would cause a local imbalance in carbon between ocean and atmosphere, that would likewise rise into the atmosphere. In other words, both a faster (methane) and slower/longer-lived (carbon dioxide) poison.

[Twemoran]

Wayne
Do you have links referring to methane feeding 'blooms'. I have an idea that some of the blue ice we are seeing is clear ice with methane fed growth on the bottom. I'm sure I recall an article that spoke of the methane/algae connection but have been unable to locate it.

Thanks
Terry

[Bob Wallace]

This newly discovered bloom is possibly carbon/methane neutral.

There seems to be a limited amount of nutrients available. Early, under the ice blooms seem to be using them up resulting in less growth later in the season.

From a NPR interview with Kevin Arrigo, professor of environmental earth systems science at Stanford University...

" You know, there's a certain amount of food that gets produced in places like the Chukchi Sea and there's a limited amount of nutrients, and so there's only so much to go around.

There's a lot of animals that feed off the bottom. And most of the stuff that's going to be produced under the ice is probably going to sink to the bottom. So, things like walruses and gray whales, they feed off of things at the bottom and they'll probably do really well.

Other animals that feed more in the water - seabirds that eat small fish - they may actually do worse under this situation, because more of the food is going to be going to the bottom feeders, as opposed to them"

http://www.npr.org/2012/06/12/154872704/thinner-arctic-ice-sparks-massive-algae-bloom

[Seke Rob]

Why would phytoplankton fare better in the Arctic Ocean with the ice being off over ever greater acreage over ever longer periods?

http://colli239.fts.educ.msu.edu/2010/07/29/40-decline-in-phytoplankton-of-oceans-in-last-100-years/

Stronger ocean currents as developing over the past 50 years will most likely, aside from greater heat transport into the Arctic, also transport in more tripe... after all, dead polar bears are disposed of as toxic waste by the Inuit... top of the food chain. To know that phytoplankton is the most major oxygen maker on the planet, a 40% reduction is... No worries, there will be enough left to breath for a long time, be it 7 billion now or 9-10 billion by 2050.