Changes in ocean chemistry show how sea level affects global carbon cycle

New analysis of strontium isotopes reveals how the global carbon cycle has responded to changes in climate and sea level through geologic time




A new analysis of strontium isotopes in marine sediments has enabled scientists to reconstruct fluctuations in ocean chemistry related to changing climate conditions over the past 35 million years.

The results, published March 26 in Science, provide new insights into the inner workings of the global carbon cycle and, in particular, the processes by which carbon is removed from the environment through the deposition of carbonates.

“Strontium is very similar to calcium, so it gets incorporated into the calcium carbonate shells of marine organisms,” explained lead author Adina Paytan, research professor in the Institute of Marine Sciences at UC Santa Cruz.

Paytan and her coauthors looked at the ratios of different isotopes of strontium, including radiogenic isotopes (produced by radioactive decay) and stable isotopes, which provide complementary information about geochemical processes. They found that the stable isotope ratio of strontium in the ocean has changed considerably over the past 35 million years, and it is still changing today, implying large changes in seawater strontium concentration.

“It’s not in a steady state, so what’s coming into the ocean and what’s leaving don’t match,” Paytan said. “The strontium composition of seawater changes depending on how and where carbonates are deposited, and that is influenced by changes in sea level and climate.”

The fluctuations in strontium isotope ratios analyzed in this study reflect the combined effect of shifts in the global balance of geologic processes including weathering of rocks on land, hydrothermal activity, and the formation of carbonate sediments in both deep-sea and shallow, nearshore marine environments.

Carbonate deposition in the open ocean comes from marine plankton like coccolithophores and foraminifera, which build their shells of the calcium carbonate mineral calcite. In shallow water on the continental shelves, hard corals are more abundant, and they build their skeletons of a different mineral of calcium carbonate, aragonite, which incorporates more strontium than calcite does.

“When corals form, they remove strontium, and when they are exposed, this strontium washes out and goes back into the ocean,” Paytan said. “With changes in sea level, more or less of the continental shelf where corals grow is exposed, so that impacts the strontium composition of seawater.”

Carbonate deposition also feeds back into the climate system, because the ocean absorbs carbon dioxide from the atmosphere, and carbonate deposition on geological timescales removes carbon from the system. The global carbon cycle and atmospheric carbon dioxide are tightly coupled to climate change, both in the long-term and during the recurring ups and downs of recent ice age cycles.

“The new type of information we can read from the stable strontium isotopes now allows us to take a close look at the business end of the global carbon cycle, when carbon is removed from the environment and laid down into marine carbonate beds,” said coauthor Mathis Hain, assistant professor of Earth and planetary sciences at UCSC.

“These findings throw open a new window to let us see how the global carbon cycle adjusted to sea level and climate change through geologic time,” he added. “We will need these insights in guiding our response to our current climate emergency and to mitigate the worst effects of ocean acidification.”

The researchers were able to reconstruct a robust and detailed record of strontium isotope variations in seawater based on an analysis of marine barite extracted from deep-sea sediment cores.

“Records like this are critical to understanding how our earth operates over geologic times,” said coauthor Elizabeth Griffith at Ohio State University. “Our international team worked together to both create this unique record and explain its significance through mathematical modeling, so we can reconstruct changes in the past when the climate conditions were different. The hope is to gain insight into how our blue planet might operate in the future.”


In addition to Paytan, Hain, and Griffith, the coauthors of the paper include Anton Eisenhauer and Klaus Wallmann at the GEOMAR Helmholtz Center for Ocean Research in Germany, and Andrew Ridgwell at UC Riverside. This work was supported by the National Science Foundation.

From EurekAlert!

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A C Osborn
March 27, 2021 2:33 am

Undersea Volcanoes.

March 27, 2021 2:43 am

Adjusted… to sea level

Well it is the adjustocene after all

March 27, 2021 3:01 am

And could it be, the rise of CO2 in the atmosphere since direct measurements started have nothing what so ever to do with man, something like this going on, something we have not figured out as of now. How do you explain the lack of response in measurements of Co2 on Mauna Loa from Covid 19, none.

Ron Long
March 27, 2021 3:12 am

It took them a while to get around to the focus of their research, but the phrases “…current climate emergency…ocean acidification.” appears in the fourth paragraph from the end. Meanwhile they generate some useful data, however their understanding of the carbonate deposition and transformation process might be a little sketchy. Most sea creatures that build exoskeletons from calcium carbonate generate the mineral aragonite. The poorly formed crystal structure of aragonite allow a lot of ion substitution, like strontium and barium. As the aragonite is buried it quickly re-crystallizes to calcite, whose crystal structure is much more ordered than aragonite, and the mis-match ions, like strontium and barium, are expelled. The expelled ions form minerals like strontionite and barite, both common in buried sea floor sediments. During this process the barium and strontium may be expelled from the compacting sediments and form syngenetic deposits of strontionite, celestite, and barite. All of this process would include isotope fractionation, so they need to be careful what they are sampling.

Joel O’Bryan
Reply to  Ron Long
March 27, 2021 7:08 am

translation: They are creating the illusion of knowledge using OPM.

Robert W Turner
Reply to  Ron Long
March 27, 2021 7:25 am

They are also sampling “deep sea” which makes it sound like they are well below the CCD.

H. D. Hoese
Reply to  Ron Long
March 27, 2021 11:39 am

I’m looking at an antique (1957) table showing Sr/Ca ratios from Pacific and Key West cores that range from 0.60 to 13.00 from various corals, sand, forams, mollusks, calcite, aragonite, dolomite, often higher at the surface, but also some high at depths, didn’t make much sense then. Extensive bibliography back to 1888 including barite (1928), always have to check if this century paper authors knew their literature. Some do, too many don’t.

Reply to  Ron Long
March 27, 2021 10:31 pm

but the phrases “…current climate emergency…ocean acidification.” appears in the fourth paragraph from the end

Just reading the abstract, my impression is that phrase may just be a stock answer to a press officers question.

I could be wrong, but this seems like a genuine effort to understand how and why the composition of seawater changes over millennium.

March 27, 2021 3:17 am

Some ocean water chemistry:
The stability of subducted glaucophane with the Earth’s secular cooling
The blueschist to eclogite transition is one of the major geochemical–metamorphic processes typifying the subduction zone, which releases fluids triggering earthquakes and arc volcanism. Although glaucophane is an index hydrous mineral for the blueschist facies, its stability at mantle depths in diverse subduction regimes of contemporary and early Earth has not been experimentally determined. Here, we show that the maximum depth of glaucophane stability increases with decreasing thermal gradients of the subduction system. Along cold subduction geotherm, glaucophane remains stable down ca. 240 km depth, whereas it dehydrates and breaks down at as shallow as ca. 40 km depth under warm subduction geotherm or the Proterozoic tectonic setting. Our results imply that secular cooling of the Earth has extended the stability of glaucophane and consequently enabled the transportation of water into deeper interior of the Earth, suppressing arc magmatism, volcanism, and seismic activities along subduction zones.

Reply to  Krishna Gans
March 27, 2021 5:04 am

I’m aware, they don’t write about climate cooling 😀

Joel O’Bryan
Reply to  Krishna Gans
March 27, 2021 7:24 am

The slow steady sequestration of carbon over geologic time is indeed the largest threat to the biosphere. The near starvation levels of CO2 during ice ages and the evolution of C4 plants are testament to this carbon crisis, which humanity is temporarily delaying by burning fossil fuels.
A large bolid strike of Earth is only a distant threat compared to carbon starvation.

Last edited 1 year ago by Joel O’Bryan
Eric Vieira
March 27, 2021 3:46 am

As soon as the words “to mitigate the worst effects of ocean acidification” came up, I stopped reading the article…

Reply to  Eric Vieira
March 27, 2021 4:25 am

So did I. If the authors are unaware of the buffering effects of carbonate and hydrogencarbonate ions in sea water, they really should not be publishing articles on geochemistry.

Reply to  Graemethecat
March 27, 2021 4:34 am

You have to wonder how they would go about describing [water] hardness, alkalinity etc

I doubt they’re even aware

Joel O’Bryan
Reply to  Graemethecat
March 27, 2021 7:27 am

“It Is Difficult to Get a Man to Understand Something When His Salary Depends Upon His Not Understanding It“
– Upton Sinclair

Reply to  Joel O’Bryan
March 27, 2021 7:54 pm

Thank you for that Joel. I was going to have to look that up tomorrow as I found out last week that I was doing a project with an EU group that turned out to be an instantaneous clown show. My colleague doesn’t understand it. This will do more than help.

Robert W Turner
Reply to  Graemethecat
March 27, 2021 7:30 am

I’d like to ask them to explain how inorganic CaCO3 production continues (oolites and whitings) despite the meme of ocean acidification.

Reply to  Robert W Turner
March 27, 2021 10:45 am

Ask them how it is that bivalves with calcium carbonate shells live and thrive in fresh waters with pH less than 8 or even 7.

March 27, 2021 4:03 am

In addition to Paytan, Hain, and Griffith, the coauthors of the paper include Anton Eisenhauer and Klaus Wallmann at the GEOMAR Helmholtz Center for Ocean Research in Germany, and Andrew Ridgwell at UC Riverside. This work was supported by the National Science Foundation.

Richard Brown
March 27, 2021 4:41 am

They haven’t proved Co2 is raising sea levels, just that corals and bivalves are adapting to fluctuations in various chemical elements. As for ‘ocean acidification’……🙄

March 27, 2021 5:51 am

Do they account for changes in the Strontium source? I did not see in the article that they did so. It seems quite likely that the rocks which were weathered 30M years ago for example did not contain the same concentration of Strontium as those weathered 10M years ago. Likewise the weathering rate – soft rocks vs. hard rocks and such. It does not seem reasonable to me that variations in the concentration and isotope ratio of deposited Strontium can be ascribed to climate without first understanding the source term.

March 27, 2021 6:06 am

NASA claims 97% of all “active” climate scientists agree ….with NASA. Maybe one forensic bio-climatologist disagrees, see?

Robert W Turner
March 27, 2021 7:22 am

Coral debris might make up the majority of carbonate sediment in a few select places right near reefs, but forams dominate the vast majority of shells in the carbonate factories. Mollusks and carbonate algae also make up a significant portion of carbonate sediments. By no means are corals the dominant sediment supply in near shore environments in general.

Also, this press release said absolutely nothing novel. They are coring deep sea barite to determine a Sr record, okay, that’s probably going to depend on carbonate sediments delivered to the deep ocean from continental shelves more than anything else.

March 27, 2021 2:44 pm

“our current climate emergency”

now that the pandemic’s over, it’s time for a new emergency to give gov’t more power over us

Last edited 1 year ago by TallDave
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