Key biological mechanism is disrupted by ocean acidification

March 14, 2018, University of California - San Diego
Photosynthetic plankton like these Ross Sea diatoms are key players in the global carbon cycle and form the base of marine food webs, but a new study reveals their ability to acquire iron is highly sensitive to ocean acidification. Credit: Jeff McQuaid

A team led by scientists from Scripps Institution of Oceanography at the University of California San Diego and the J. Craig Venter Institute (JCVI) has demonstrated that the excess carbon dioxide added to the atmosphere through the combustion of fossil fuels interferes with the health of phytoplankton which form the base of marine food webs.

Phytoplankton are microscopic plants whose growth in surface waters supports ocean food webs and global marine fisheries. They are also key agents in the long-term removal of carbon dioxide (CO2)

As reported in the March 14 edition of Nature, the team shows that a mechanism widely used by to acquire iron has a requirement for carbonate ions. Rising concentrations of atmospheric CO2 are acidifying the ocean and decreasing carbonate, and the team shows how this loss of carbonate affects the ability of phytoplankton to obtain enough of the nutrient iron for growth. Ocean acidification is poised to decrease the concentration of sea surface carbonate ions 50 percent by the end of this century.

The study, "Carbonate-sensitive phytotransferrin controls high-affinity iron uptake in diatoms," was funded by the National Science Foundation, the Gordon and Betty Moore Foundation, and the U.S. Department of Energy. It reveals an unexpected twist to the theory of how iron controls the growth of phytoplankton. By showing how the loss of seawater carbonate hampers the ability of phytoplankton to grab onto iron, the authors show a direct connection between the effects of ocean acidification and the health of phytoplankton at the base of the marine food chain.

"Ultimately our study reveals the possibility of a 'feedback mechanism' operating in parts of the ocean where iron already constrains the growth of phytoplankton," said Jeff McQuaid, lead author of the study who made the discoveries as a PhD student at Scripps Oceanography. "In these regions, high concentrations of atmospheric CO2 could decrease phytoplankton growth, restricting the ability of the ocean to absorb CO2 and thus leading to ever higher concentrations of CO2 accumulating in the atmosphere."

"Studies investigating the effects of high CO2 on phytoplankton growth have shown mixed results to date. In some cases, certain phytoplankton seem to benefit from high CO2," added Andrew E. Allen, a biologist with a joint appointment at Scripps and JCVI who is senior author and initiator of the study. "Most of these studies, however, have been conducted under high-iron conditions. Our study uncovers a widespread cellular mechanism that suggests high CO2 might be particularly problematic for phytoplankton growth in low-iron regions of the ocean."

Lead author Jeff McQuaid watches an array of pumps designed to test the effects of high CO2 on Ross Sea phytoplankton in Antarctica. Several recent studies have noted that high CO2 has a negative effect on phytoplankton growing in low iron environments like the Southern Ocean Credit: A.E. Allen

One consequence of acidification is a nearly one-for-one reduction in the concentration of carbonate ions for every molecule of CO2 that dissolves in the ocean. The concentration of atmospheric CO2 is predicted to double by the end of this century; thus, the concentration of carbonate ions at the surface of the ocean will nearly halve by the year 2100. While the negative influence of acidification on corals and shellfish is known, this is the first study to reveal a mechanism that affects life which forms the base of most .

This study revises a key concept in oceanography that the growth of phytoplankton in vast areas of the ocean is regulated by the concentration of iron. In ocean regions that are high in dissolved nutrients like nitrogen and phosphorous, iron limitation results in low numbers of phytoplankton relative to amounts of available nutrients. Addition of iron to these areas causes phytoplankton, particularly diatoms, to grow. In the largest of these regions, the Southern Ocean, concentrations of available iron are below one trillionth of a gram per liter, approaching the limit supporting life.

Marine scientists have spent decades investigating how phytoplankton are able to grab such low concentrations of iron from seawater and internalize it.

"Understanding the mechanism of iron uptake is critical to develop meaningful predictions on how phytoplankton may respond to future ocean conditions, but this understanding has been elusive," said Adam Kustka, a trace metal physiologist and project collaborator from Rutgers University.

Clues began to emerge in 2008, when Allen discovered several iron-responsive genes in diatoms that had no known function. That same year, McQuaid was traveling around East Antarctica assisting in a survey of plankton in the Southern Ocean. DNA analysis of those samples revealed that one of Allen's iron genes was not only present in every sample of seawater, but every major phytoplankton group in the Southern Ocean seemed to have a copy.

"This gene, called ISIP2A, was one of the most abundantly transcribed genes in low-iron Southern Ocean, suggesting it had a really important role in the environment," said Allen.

Andrew Allen prepares a sample of phytoplankton filtered from the Ross Sea. In several of the Antarctic marine samples, phytotransferrin was among the most abundant proteins detected. Credit: E. Bertrand

Earlier studies suggested a transferrin-like protein, called phytotransferrin, was at work in the marine environment, but ISIP2A looked nothing like transferrin. It took the development of an entirely new discipline, synthetic biology, to help prove the team's hypothesis that ISIP2A was a type of transferrin. Synthetic biology is the fusion of biology and engineering, and in collaboration with scientists with the Venter Institute, the team developed methods to insert synthetic DNA into a marine diatom. The scientists deleted ISIP2A and replaced it with a synthetic gene for human transferrin, demonstrating that ISIP2A was a type of transferrin.

The team then initiated a study to investigate the evolutionary relationships of transferrin and phytotransferrin. To their surprise, the proteins were functional analogs whose ancient origins extend to the pre-Cambrian period of Earth history, predating the appearance of modern plants and animals.

"The appearance of phytotransferrin some 700 million years ago is consistent with a time in Earth's history marked by massive changes in ocean chemistry, and this ancient evolutionary history helps explain why no one has connected ISIP2A and transferrin," said Miroslav Oborník, a molecular evolutionary biologist from the University of South Bohemia and co-author on the paper.

In transferrin, iron and carbonate bind simultaneously, and neither can bind in the absence of the other. Such synergistic binding is unique among biological interactions. The research team hypothesized that diatom phytotransferrin uses a similar mechanism and that, as a result, reductions in carbonate ion could lead to reduced phytoplankton growth rates.

Using a number of biochemical methods, the researchers were able to independently manipulate pH along with the concentrations of iron and carbonate ion. As they pumped in increasing concentrations of CO2, the team showed that the ability of their diatom to grab onto iron decreased proportionally with the of carbonate ions.

"Since carbonate and iron have to bind simultaneously, as carbonate concentrations drop, phytotransferrin is able to 'see' less iron," said McQuaid. "The total amount of isn't changing - rather the ability to grab onto it changes, and this ultimately influences the growth rate."

Explore further: Iron chemistry matters for ocean carbon uptake

More information: Jeffrey B. McQuaid et al, Carbonate-sensitive phytotransferrin controls high-affinity iron uptake in diatoms, Nature (2018). DOI: 10.1038/nature25982

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howhot3
5 / 5 (8) Mar 14, 2018
Ocean acidification from CO2 rise we get this;
By showing how the loss of seawater carbonate hampers the ability of phytoplankton to grab onto iron, the authors show a direct connection between the effects of ocean acidification and the health of phytoplankton at the base of the marine food chain.

If the thick headed deniers would just get it through their thick skulls. Burning fossil fuels will lead the planet to food shortages, a dead ocean, and a massive extinction event like none ever experienced my modern man.

howhot3
5 / 5 (8) Mar 14, 2018
Well, so true. Physics does span many many fields, from fusion, tech and renewables, to climate, atmospherics and space. I love a good blackhole theory as much as anyone. What I don't get are the thickheaded denier goons that want everyone to ignore problems that are potential planet killers. Are you one of those?
howhot3
5 / 5 (7) Mar 14, 2018
Well, @mack here is an odd fact. The whole planet only contains finite amount of carbon. There is nano amounts being added from space but rarely anything on the scale that earth already contains.
So what we have is very close to a static amount of carbon on the planet. What we have experienced and measured in the last 100 years would be like someone had turned up a huge 40 billion TONS of carbon from the geotherms and put it in the air as CO2. OH WAIT? Isn't that what the combustion of fossil fuel has done in the past 100years or so? Dump about 40 billion tons of carbon in the air via combustion of C+(O2) -> CO2 + energy. Yes it sure has.
howhot3
5 / 5 (7) Mar 14, 2018
And since we are at it, where do you think most of that CO2 goes once released from combustion of Coal, Oil and Natural Gas (+your wimpy liitle volcanoes)? Since 2/3rds out planet is covered in oceans, you can bet that 2/3rds the CO2 pollution for fossil fuels are dump there. Once in water the CO2 goes to H2CO3 which is CARBONIC ACID! Living things don't like living in acid, so they dissolve and die. Whole oceans that feed out planet can be killed. Do you get it now?

howhot3
5 / 5 (7) Mar 14, 2018
Sorry, 40 gigatons of CO2/year from fossil fuels was off the top of my head and was the typical base level CO2 level. From fossil fuel combustion It's actually more closer to 600!
howhot3
5 / 5 (7) Mar 14, 2018
So @mac, you agree then that CO2 is not from "geothermal origin" but has to be from another source. What if, methane isn't enough? What if I show you that methane clathrates are not the cause of our planet's current CO2 levels? Would you then concede that mankind's combustion of fossil fuels is the cause of the planet's newly inflated CO2 levels? CO2 that is acidifying the ocean and er-go slowly killing certain plankton life (er-go food chain).

Parsec
4.5 / 5 (8) Mar 14, 2018
@howhot3 - mack is a troll dude. He is actually an intelligent and reasonably articulate guy who for some odd reason likes to come on these forums and emulate a babbling idiot.
howhot3
5 / 5 (6) Mar 14, 2018
Well there is more in the ocean than just tuna and sailfish @mac. You forgot shrimp, sea bass, cod, lobster and all of the rest my friend. I hope you can find them in a supermarket in 20 years.

Methane clathrates from only in cold and high pressure regions like the very bottom of the ocean, were the are sequestered until warmed or disturbed. It's estimated that there are 1 to 5 x10^15 m^3 of the stuff on the ocean bottom. That is methane that has been absorbed by the ocean (like the CO2 in the article), frozen out and settling on the ocean floor. A processes that has been going on for the life of the planet. What makes methane clathrates so special when it is so freaking obvious CO2 is the cause?

howhot3
5 / 5 (6) Mar 14, 2018
Hi Parsec; I know @mac
likes to come on these forums and emulate a babbling idiot.
. Yeap. It's sad a dumb fuck like him has to waste his time on crap like this. It's the life of a troll.

howhot3
5 / 5 (7) Mar 14, 2018
@mac says;
What if it is? I'm not against fossil fuel replacement, but current strategy of "renewables" doesn't improve it -
. OK cool. Sorry for what I called you earlier. Actually there is only one strategy that can be achieved right in the here-and-now and that is renewables! The one thing that comes to Earth every second is sunlight. The whole of all life, the reason, you, your kids, your pet, you house, your life exists is because of sunlight. All Fossil Fuel is, is just carbon and sunshine sequestered! Stuff burns in Oxygen, and when you burn that sequestered carbon,,, the fossil fuels, all of that carbon-sunshine-hydrogen-thing turns directly into CO2 which in GLOBALLY MASSIVE 600 BILLION TON AMOUNTS WILL cause extinction!

The sun dumps trillions of watts of energy per day on the planet that if harvested and stored would provide more than enough energy to power mankind on earth forever. That is the direction we have to go.
leetennant
5 / 5 (10) Mar 15, 2018
Oh sure, we have a mechanism and modelled outcomes based on that mechanism and real-world observations that fit with the modelled outcomes from that mechanism. But let's not accept the mechanism. No, let's just throw out random 'what ifs' instead. What if it's the unicorns? What if we're all just in the Matrix? What if our head have been invaded by a super-intelligent alien virus that just makes us "believe" the Earth is warming?

Ockhams Razor exists for a reason, you know.
HeloMenelo
5 / 5 (9) Mar 15, 2018
@howhot3 - mack is a troll dude. He is actually an intelligent and reasonably articulate guy who for some odd reason likes to come on these forums and emulate a babbling idiot.

Wwwrong... antigoracle's sockpuppet mackita and his 40 odd other socks(ie still only sorry old he himself) is a complete nut job. In his own mind he thinks he is hitting a banana jacpot while in the real world highlight the idocy of the denier campaigns. A win win for everyone, we just need to sit back and watch how hilariously it unfolds every day :D
leetennant
5 / 5 (4) Mar 15, 2018
What makes methane clathrates so special when it is so freaking obvious CO2 is the cause?
If the global warming would be of geothermal origin, then the clathrates and methane in soil will get release first and oxidized in atmosphere into a carbon dioxide, which would get uptake by oceans back. Such a model also explains the https://i.imgur.com/oVq2M19.gif - whereas greenhouse mechanism would require the opposite.


None of this is true
Da Schneib
5 / 5 (3) Mar 15, 2018
There's a positive feedback loop here. More CO2 => less phytoplankton => more CO2. Phytoplankton are the primary source of oxygen in the atmosphere and the oceans. I see a problem with this, one that will not heal itself quickly. And it's not just a matter of the food we get from the oceans.
barakn
5 / 5 (3) Mar 15, 2018
Wwwrong... antigoracle's sockpuppet mackita and his 40 odd other socks(ie still only sorry old he himself) is a complete nut job. In his own mind he thinks he is hitting a banana jacpot while in the real world highlight the idocy of the denier campaigns. A win win for everyone, we just need to sit back and watch how hilariously it unfolds every day :D - HeloMenelo

Antigoracle doesn't have any sockpuppets, and mackita is the sock of Zephir.
HeloMenelo
5 / 5 (5) Mar 16, 2018
O he does, about 40 of them ;)
humy
5 / 5 (3) Mar 16, 2018
I never saw some alarmist to promote cold fusion and similar technologies - only the "renewables"

mackita

Are you from the flat-Earth society?
Are you seriously implying you would promote the fictitious pseudoscientific "cold fusion" crap instead of "renewables" which we know can exist?
Seriously; was that a joke?
I really hope so else you are even more stupid than I thought.
humy
5 / 5 (2) Mar 16, 2018
If not being "alarmist" means promote the fictitious pseudoscientific "cold fusion" crap and all similar crap instead of real "renewables" then I guess the only sane and reasonable people not way-high on crack are all those that you call "alarmist".

I am not against nuclear power in principle; providing it isn't a factious kind.
humy
5 / 5 (2) Mar 16, 2018
; providing it isn't a factious kind.

Misedit;
"factious" should have been "factitious"

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