Researchers discover a new tool for reconstructing ancient sea ice

BROWN UNIVERSITY

Research News

IMAGE: A COMPOUND THAT WAS NOTORIOUS FOR THROWING OFF RECONSTRUCTIONS OF SEA SURFACE TEMPERATURE TURNS OUT TO BE A GOOD PROXY FOR RECONSTRUCTING PAST SEA ICE, A NEW STUDY FINDS. view more CREDIT: KAREN WANG

PROVIDENCE, R.I. [Brown University] — Sea ice is a critical indicator of changes in the Earth’s climate. A new discovery by Brown University researchers could provide scientists a new way to reconstruct sea ice abundance and distribution information from the ancient past, which could aid in understanding human-induced climate change happening now.

In a study published in Nature Communications, the researchers show that an organic molecule often found in high-latitude ocean sediments, known as tetra-unsaturated alkenone (C37:4), is produced by one or more previously unknown species of ice-dwelling algae. As sea ice concentration ebbs and flows, so do the algae associated with it, as well as the molecules they leave behind.

“We’ve shown that this molecule is a strong proxy for sea ice concentration,” said Karen Wang, a Ph.D. student at Brown and lead author of the research. “Looking at the concentration of this molecule in sediments of different ages could allow us to reconstruct sea ice concentration through time.”

Other types of alkenone molecules have been used for years as proxies for sea surface temperature. At different temperatures, algae that live on the sea surface make differing amounts of alkenones known as C37:2 and C37:3. Scientists can use the ratios between those two molecules found in sea sediments to estimate past temperature. C37:4 — the focus of this new study — had been long considered a bit of problem for temperature measurements. It turns up in sediments taken from closer to the Arctic, throwing off the C37:2/C37:3 ratios.

“That was mostly what the C37:4 alkenone was known for — throwing off the temperature ratios,” said Yongsong Huang, principal investigator of the National Science Foundation-funded project and a professor in Brown’s Department of Earth, Environmental and Planetary Science. “Nobody knew where it came from, or whether it was useful for anything. People had some theories, but no one knew for sure.”

To figure it out, the researchers studied sediment and sea water samples containing C37:4 taken from icy spots around the Arctic. They used advanced DNA sequencing techniques to identify the organisms present in the samples. That work yielded previously unknown species of algae from the order Isochrysidales. The researchers then cultured those new species in the lab and showed that they were indeed the ones that produced an exceptionally high abundance of C37:4.

The next step was to see whether the molecules left behind by these ice-dwelling algae could be used as a reliable sea ice proxy. To do that, the researchers looked at concentrations of C37:4 in sediment cores from several spots in the Arctic Ocean near the present-day sea ice margins. In the recent past, sea ice in these spots is known to have been highly sensitive to regional temperature variation. That work found that the highest concentrations of C37:4 occurred when climate was coldest and ice was at its peak. The highest concentrations dated back to the Younger-Dryas, a period of very cold and icy conditions that occurred around 12,000 years ago. When climate was at its warmest and ice ebbed, C37:4 was sparse, the research found.

“The correlations we found with this new proxy were far stronger than other markers people use,” said Huang, a research fellow at the Institute at Brown for Environment and Society. “No correlation will be perfect because modeling sea ice is a messy process, but this is probably about as strong as you’re going to get.”

And this new proxy has some additional advantages over others, the researchers say. One other method for reconstructing sea ice involves looking for fossil remains of another kind of algae called diatoms. But that method becomes less reliable further back in time because fossil molecules can degrade. Molecules like C37:4 tend to be more robustly preserved, making them potentially better for reconstructions over deep time than other methods.

The researchers plan to further research these new algae species to better understand how they become embedded in sea ice, and how they produce this alkenone compound. The algae appear to live in brine bubbles and channels inside sea ice, but it may also bloom just after the ice melts. Understanding those dynamics will help the researchers to better calibrate C37:4 as a sea ice proxy.

Ultimately, the researchers hope that the new proxy will enable better understanding of sea ice dynamics through time. That information would improve models of past climate, which would make for better predictions of future climate change.

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Other coauthors on the study were Markus Majaneva, Simon Belt, Sian Liao, Joseph Novak, Tyler R. Kartzinel, Timothy Herbert, Nora Richter and Patricia Cabedo-Sanz. The work was supported by the National Science Foundation (EAR-1762431).

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DHR
January 4, 2021 10:21 am

“…which could aid in understanding human-induced climate change happening now.”

How do they know what part of “climate change happening now” is human induced?

Taylor Pohlman
Reply to  DHR
January 4, 2021 10:29 am

I usually ignore statements like this in studies – they are boilerplate required to get past the reviewers. Not much evidence it’s actually believed by all submitters, but they put it anyway as a sop to the faithful…

Reply to  Taylor Pohlman
January 4, 2021 10:59 am

It’s the same thing with ice as a ‘critical indicator’ of climate change. It seems to be a useful indicator of the ebb and flow of floating sea ice, but the only thing ‘critical’ about it is that it shows how sea ice as a proxy for the climate varies widely without any help from man.

2hotel9
Reply to  Taylor Pohlman
January 4, 2021 11:38 am

Statements like this are the indicator that the whole thing is trash.

Gerald Machnee
Reply to  DHR
January 4, 2021 1:42 pm

The usual nonsense. It does not matter what the ancient data shows. It will still be melting “rapidly”

Chris Hanley
Reply to  DHR
January 4, 2021 3:04 pm

Construct a very low resolution proxy graph and stick a much higher resolution version of the GISS record on the end — importantly capturing the most recent strong El Niño — and voila: unprecedented human-caused warming.

Taylor Pohlman
January 4, 2021 10:27 am

OK, this seems like science, at least it’s likely falsifiable, since we have a pretty good idea of the general timing of periods of heavy and light ice coverage. Likely Minoan and Roman periods will show up, and based on Greenland evidence, there should be less of C37:4 during the MWP as well. Conversely, the LIA should be easy to spot. Whether the C37:4 levels can be well correlated to sea ice to make the periods comparable/measurable would be another question, and I’m not sure how that would be done, unless they can get very recent measurements where we have (somewhat) actual ice data.

Rich Davis
Reply to  Taylor Pohlman
January 4, 2021 10:39 am

Any warm periods showing up will surely invalidate this as a proxy, as it would contradict the oft-replicated hockey stick graph?

Richard Page
Reply to  Taylor Pohlman
January 4, 2021 1:08 pm

It all depends on the precision of the proxy measurements. It’s impossible to tell from this article what the shortest period of time that they can measure is. It’s entirely plausible that any fluctuations of less than 500-1000 years might not register. To my mind it might be interesting to read but fairly irrelevant to modern sea ice patterns unless you’re considering the whole interglacial as a single event.

Ron Long
January 4, 2021 10:38 am

OK, there is a little science here. However, sea level reconstruction is easy and straight-forward and shows the partitioning of the water molecule between solid and liquid phases (gas phase inferred) during large climate cycles. The science of Sequence Stratigraphy, thanks to Exxon Research, shows these cyclic changes through nearly 600 million years. Guess what? We’re now in completely normal variance in the inter-glacial cycle of this Ice Age we live in. No anomalous signal detectable against normal, noisy background.

Reply to  Ron Long
January 4, 2021 10:57 am

“sea level reconstruction is easy and straight-forward and shows the partitioning of the water molecule between solid and liquid phases”. This applies to glaciers, not to sea ice.

Ron Long
Reply to  Curious George
January 4, 2021 1:02 pm

Exactly! And?

Pillage Idiot
January 4, 2021 10:52 am

“And this new proxy has some additional advantages over others, the researchers say. One other method for reconstructing sea ice involves looking for fossil remains of another kind of algae called diatoms. But that method becomes less reliable further back in time because fossil molecules can degrade. Molecules like C37:4 tend to be more robustly preserved, making them potentially better for reconstructions over deep time than other methods.”

What?

Diatom skeletons are siliceous and are therefore commonly preserved in sediments and are thus available to make “deep time” reconstructions.

Are they saying that they have discovered preserved C37:4 organic molecules in sediments that are more stable than the siliceous skeletons in those same sediments?

How far back in time have they recovered these preserved organic molecules?

Rory Forbes
January 4, 2021 11:05 am

Yet one more “study” demonstrating expectation bias done by a committee.
Yawn!

Rob_Dawg
January 4, 2021 11:16 am

> Sea ice is a critical indicator of changes in the Earth’s climate.

Who says?

Never mind. Molecules like tetra-unsaturated alkenone (C37:4) are fragile. They don’t survive rationally over the time periods examined.

Yet another case of a climate crisis supposition in search of evidence.

2hotel9
January 4, 2021 11:35 am

This,”which could aid in understanding human-induced climate change happening now.” shoots their whole little grift right in the head.

Philip
January 4, 2021 12:25 pm

A new discovery by Brown University researchers could provide scientists a new way to reconstruct sea ice abundance and distribution information from the ancient past, which could aid in understanding human-induced climate change happening now.

There is really no sense in charting probable sea ice values through time if the obvious goal is to cherry pick timelines and then couch the findings in terms of man as existential threat and earth in climate crisis.
These people are just muddying the water and some future actual scientist, not a propagandist, is going to have to undo it all and start from scratch. Future scientist will be spending a lot of time redoing much of “science” from 1985 or so through to whatever that time is when “science” returns to being a methodology and not a subject made pliable to further a social politic.

Editor
January 4, 2021 1:35 pm

I would like to point out that as atmospheric CO2 levels have increased according to the usual suspects causing alleged warming of the planet. The bulk of this CO2 according to the NOAA by a huge, 60x greater than natural CO2 addition to the atmosphere is by mankind. If this is true how does this graph demonstrate that the during the worldwide lockdown from March of last year, when flights, car usage, heating and lighting in the Northern Hemisphere drastically reduced because it was Spring & Summer, the rate at which CO2 entered the atmosphere according to Mauna Loa Observatory was unchanged? comment image

Stevek
January 4, 2021 1:50 pm

The problem is that this algae that produces the molecule has a population that is likely not just dependent on sea ice, but dependent on other factors both now and in the past. Seems complicated to sort it all out.

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