Guest post by David Middleton
Why bother with Argo floats and ocean heat content? Now the average temperature of the oceans can be instantly calculated by the ratio of noble gasses in the atmosphere…
New Study Identifies Thermometer for Global Ocean
Researchers now able to reconstruct past ocean temperatures
Jan 04, 2018
There is a new way to measure the average temperature of the ocean thanks to researchers at Scripps Institution of Oceanography at the University of California San Diego. In an article published in the Jan. 4, 2018, issue of the journal Nature, geoscientist Jeff Severinghaus and colleagues at Scripps Oceanography and institutions in Switzerland and Japan detailed their ground-breaking approach.
Determining changes in the average temperature of the entire world’s ocean has proven to be a nearly impossible task due to the distribution of different water masses. Each layer of water can have drastically different temperatures, so determining the average over the entirety of the ocean’s surface and depths presents a challenge.
Severinghaus and colleagues were able to bypass these obstacles by determining the value indirectly. Instead of measuring water temperature, they determined the ratio of noble gases in the atmosphere, which are in direct relation to the ocean’s temperature.
“This method is a radically new way to measure change in total ocean heat,” said Severinghaus. “It takes advantage of the fact that the atmosphere is well-mixed, so a single measurement anywhere in the world can give you the answer.”
In the study, the scientists measured values of the noble gases argon, krypton, and xenon in air bubbles captured inside ice in Antarctica. As the oceans warm, krypton and xenon are released into the atmosphere in known quantities. The ratio of these gases in the atmosphere therefore allows for the calculation of average global ocean temperature.
Measurements were taken from ice samples collected during the West Antarctic Ice Sheet (WAIS) Divide coring project, of which Severinghaus is a leader. Over the course of six field seasons in Antarctica, a drill removed ice in cylindrical samples 2.7 meters (just under 9 feet) in length. The final sample was taken at a depth of 3,405 meters (over 11,000 feet) in 2011. This record spans nearly 100,000 years and the age of the layers can be determined to within 50 years. Earth’s atmosphere mixes on a scale of weeks to months, so a measurement of these air bubbles gives what is essentially a global average. For this study, scientists focused on samples 8,000 to 22,000 years old, and collected data in increments averaging 250 years in resolution.
New insights into the glaciation cycles that occurred on Earth long before humans began affecting the temperature of the atmosphere and oceans are now possible using the technique of measuring noble gas quantities. The study determined that the average global ocean temperature at the peak of the most recent ice age was 0.9 ºC (33.6 ºF). The modern ocean’s average temperature is 3.5 ºC (38.3 ºF). The incremental measurements between these data points provide an understanding of the global climate never before possible.
“The reason this study is so exciting is that previous methods of reconstructing ocean heat content have very large age uncertainties, [which] smooths out the more subtle features of the record,” said co-author Sarah Shackleton, a graduate student in the Severinghaus lab at Scripps. “Because WAIS Divide is so well dated, this is the first time that we’ve been able to see these subtle features in the record of the deglaciation. This helps us better understand the processes that control changes in ocean heat content.”
This paper is the result of fifteen years of work for Severinghaus, along with graduate students and postdoctoral scholars in his lab. Discussions with another professor at Scripps, atmospheric scientist Ralph Keeling, brought about the idea. Keeling studies the argon levels in the atmosphere to get a similar record of ocean heat going back a few decades. However, air bubbles trapped in ice don’t preserve argon levels accurately. Severinghaus discovered that xenon and krypton are well preserved in ice cores, which provides the temperature information that can then be used by scientists studying many other aspects of the earth’s oceans and atmosphere over hundreds of thousands of years.
Going forward, the ratios of these same noble gases can be determined from atmospheric samples taken anywhere in the world. For example, a measurement from the Ellen Browning Scripps Memorial Pier in La Jolla represents a global average of ocean temperature. Severinghaus hopes to fine tune the procedure.
“Our precision is about 0.2 ºC (0.4 ºF) now, and the warming of the past 50 years is only about 0.1 ºC,” he said, adding that advanced equipment can provide more precise measurements, allowing scientists to use this technique to track the current warming trend in the world’s oceans.
With this study, Severinghaus and colleagues have shown that measurements of noble gases in the atmosphere provide the historical record long sought by the scientific community, and can be further optimized to gain insights into modern ocean temperature changes as well.
This research was supported by the National Science Foundation (grant numbers 05-38630 and 09-44343), and the Swiss National Science Foundation.
The paper is behind a paywall. Here’s the abstract:
Mean global ocean temperatures during the last glacial transition
Abstract
Little is known about the ocean temperature’s long-term response to climate perturbations owing to limited observations and a lack of robust reconstructions. Although most of the anthropogenic heat added to the climate system has been taken up by the ocean up until now, its role in a century and beyond is uncertain. Here, using noble gases trapped in ice cores, we show that the mean global ocean temperature increased by 2.57 ± 0.24 degrees Celsius over the last glacial transition (20,000 to 10,000 years ago). Our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean, in contrast to the depth-, region-, organism- and season-specific estimates provided by other methods. We find that the mean global ocean temperature is closely correlated with Antarctic temperature and has no lead or lag with atmospheric CO2, thereby confirming the important role of Southern Hemisphere climate in global climate trends. We also reveal an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake.
They assert that this method “has no lead or lag with atmospheric CO2“… which is meaningless because both the new method of estimating temperature and ice-core CO2 are derived from gas bubbles in the ice. Both would lag behind temperature estimates derived from δ18O ratios in the ice crystals. They also assert “unprecedented precision and temporal resolution”… But, they were using WAIS Divide ice cores, which turned out to not be of particularly high precision and temporal resolution. The Law Dome DE08 core has much higher resolution than WAIS Divide. So, “unprecedented” is unwarranted.
Color me skeptical about the claim that the ratio of argon, krypton, and xenon measured anywhere on the planet or in ice core bubbles yields the average temperature of the world’s oceans to within 0.2 ºC.
Their work does seem to have yielded one useful result:
“Our precision is about 0.2 ºC (0.4 ºF) now, and the warming of the past 50 years is only about 0.1 ºC.”
The warming of the past 50 years is equal to half the margin of error of the new global ocean thermometer.
UPDATE: David and I wrote parallel stories, here’s more detail, including graphs from the paper. https://wattsupwiththat.com/2018/01/04/new-study-from-scripps-puts-a-crimp-on-claims-of-recent-rising-ocean-temperatures/
What do the microbes in the ice cores eat?
— Cinaed
https://en.wikipedia.org/wiki/Psychrophile will provide examples
Cinaed,
Depends of the ice temperature and the availability of inclusions. At Vostok with ice average -40ºC, they just survive, without any growth, by repairing their DNA. For that reason they even use CO2 and oxydise traces of ammonia (NH4) to N2O as energy source. If all N2O was from this source, the difference in CO2 level would be less than 0.1 ppmv…
See further item K. in:
http://www.pnas.org/content/101/13/4631.full.pdf
But does this not mean how much heat has been coughed up and out of the oceans? Since ice cores measure change in atmospheric gases, is this reflecting heat discharge or recharge?
Also, does this mean the oceans were overall calmer thus layered up with heat on the top, or mixed with heat not layered up?
Also, does this mean the oceans were overall calmer thus layered up with heat on the top, or mixed with heat not layered up?
So how would one falsify such a method for estimating global sea temperature?
You could falsify the precision by taking hundreds of measurements across the planet at the same time over a period of several years and seeing if they disagree.
There’s no accurate measurement to compare it to. So you can’t falsify the accuracy.
It’s not even wrong.
Peter
Kudos to Mike Jonas, above, for his pinpointing of the most worrying aspect of this paper:
blockquote>Well I think the answer lies in this sentence: “ We find that the mean global ocean temperature … has no lead or lag with atmospheric CO2“.
I did spot this on reading the paper and am surprised that nobody else has replied to Mike’s comment.
That didn’t come out right – my keys are a bit sticky:
I do so wish people wouldn’t move on so quickly to the next article of the day. It’s one of my few beefs with WUWT about having so many to try and keep up with.
Not sure about that. If there is no lag between ocean temperatures and atmosphere composition it is obvious that ocean temperature changes are driving atmospheric changes and not the other way around. We have done the experiment and it takes a lot longer to change the temperature of the ocean than to change the composition of the atmosphere. That sort of kills the argument that CO₂ has been the climate driver of the past.
Precisely what we are seeing now is that ocean temperatures present a very important lag when we change atmospheric composition. The ocean has warmed by only 0.1°C, so that lag is bigger than 50 years.
Which brings us to the question of the temporal resolution. They analyze 10,000s of years. What does it mean no lag? ±50 years? ±200 years?
Javier,
According to the ice cores the lag between surface temperatures and CO2 is 800 +/- 600 years.
As this research looked at total ocean temperatures, the lag still is the same, as the deep ocean turnover is about 800 years.
The noble gases were measured in the gas phase, as good as where CO2 is measured. Thus most of the historical CO2 increase/decrease was induced by the deep oceans…
Great science – maybe they can get a noble price….?
In the lab you measure the partitioning of inert gases between gas and liquid phases using apparatus that keeps the liquid stirred so that one source of uncertainty is minimised..
You can derive reproducible parameters that way.
When you get to oceans, they are not uniformly stirred. If you do not do your partitioning measurements for long enough time, you will not reach an equilibrated experiment so you can’t compare with lab constants. At best, you can make some assumptions about ocean mixing and get some data, but you will never know if it is correct. The assumptions you make about ocean mixing might require a time longer than yours. Geoff.
David wrote: Color me skeptical about the claim that the ratio of argon, krypton, and xenon measured anywhere on the planet or in ice core bubbles yields the average temperature of the world’s oceans to within 0.2 ºC.
Let’s be skeptical for a moment. Do the solubility of a gas vary with temperature? Check. In a simple enclosed system of water and a single gas, can measuring the amount of the gas in the air tell us the temperature of the water? Check. To within 0.2 degC? Possibly. If we make the system more complex and use a mixture of gases, can it still work? Check. Will this gas stay inside air bubble in ice caps? Maybe. CO2 is much larger. Maybe argon diffuses to fast.
The problem is that it takes about 1,000 years for the ocean to mix. Any air bubble being trapped today reflects the AVERAGE temperature of the ocean over the last thousand years. One may be able to measure krypton and xenon accurately enough to report temperature within 0.2 degC, but the time point associated with that temperature is broad and uncertain. This proxy can’t tell us anything useful about anthropogenic climate change because it responds too slowly.
Frank,
There is only a problem with the smallest molecules/atoms at the time of bubble closing. krypton and xenon are large enough, but argon does show some diffusion in firn just before closing. See table 1 in:
http://www.bowdoin.edu/~mbattle/papers_posters_and_talks/Closeoff_fractionation_EPSL.pdf
As that work is also from Severinghaus (and Battle), I suppose that they have taken that into account
Frank, the problem is that you cannot assert that you know the ‘average temperature of the world oceans’ to within a tenth of a degree. Indeed as any metrologist would tell you you probably cannot measure the temperature of a swimming pool with an accuracy of 0.1C, Just because the precision of the maths being used is tenths of a degree does not mean that the results are accurate within a tenth of a degree.
I am amazed that this paper passed peer review.
As Ferdinand and Frank point out one would think that the time for atmosphere/ocean equilibrium would be directly related to the 600-800-year average ocean turnover rate for the water to interface with the surface. This would cause exactly the lag and buffered response as CO2. In fact, if the ice core plots do not match for each type of gas that would be an indication of error or some unknown dynamics. This brings up a question if anyone knows if the CO2 levels in ice cores are normalized the fact that many gasses are fluctating in concentration with ocean temp, not just CO2. Thus the increase in ppm concentration of one gas is not necessarily an absolute increase (partial pressure). It could be that the other gases got diminished by greater absorption in the ocean.
Ron Graf,
The only corrections done are for gravitational enhancement: at a certain depth, there is no exchange anymore with the air at the surface due to wind and pressure changes.
In stagnant air, the heavier molecules and isotopes tend to sink to the bottom of the firn down to just before closing of the pores.
That is compensated for by measuring the 15N/14N ratio change, compared to the current air isotopic composition. The compensation anyway is less than 1% for CO2.
For other changes: all ratio’s are measured in dry air, thus water vapor is excluded. Argon is the largest item present besides nitrogen and oxygen at near 1%. Any changes in ocean temperature will affect the Ar/N2 ratio and the CO2/N2 ratio independent of each other, as per Henry’s law each gas will have its own equilibrium partial pressure independent of all others – even at full vacuum.
Thanks Ferdinand. Yes, Henry’s Law establishes gases that a gas’s partial pressure is based on its concentration inside the medium it’s dissolved in (at equilibrium). But the ppm concentration in that gases partial pressure relative to all the gases combined partial pressures. As global temperature mean changes all the gases increase or decrease in concentration in the ocean while changing their ppm component in air only because their solubility properties vary. If we can accurately measure krypton and xenon, knowing these gases’s solubility are unaffected by plankton concentrations or volcanic activity, they would show a clear baseline for the GMST and dissolved gas lag. If CO2 varies from that baseline one would suspect variation is indicating volcanoes or plankton or surface greening.
http://slideplayer.com/slide/10653988/36/images/16/Dissolved+gases+in+sea+water.jpg
The first time I looked at this, I didn’t read through it thoroughly enough. The second time I found that Middleton did say: “Color me skeptical about the claim that the ratio of argon, krypton, and xenon measured anywhere on the planet or in ice core bubbles yields the average temperature of the world’s oceans to within 0.2 ºC.
Their work does seem to have yielded one useful result:
“Our precision is about 0.2 ºC (0.4 ºF) now, and the warming of the past 50 years is only about 0.1 ºC.”
The warming of the past 50 years is equal to half the margin of error of the new global ocean thermometer.”
It would seem that the standard definition of “precision” would indicate that if the “temperature rise” over the last 50 years was 0.1 C, you CANNOT SAY THAT WITH CERTAINTY, as it is less than your “measurements statistical fluctuation”. I.e., if you had an instrument measuring 0.000000 (forever)…and
it was putting out 0.0000, 0.005, 0.2000, -0.20000 any tabulation of any amount of the data points, which averaged to any value more or less than 0.2 or -0.2 (say a set of 10,000 data points, averaged to 0.05233423 …it would still mean 0.0 !!! I.e., the averaged number would have NO SIGNIFICANCE. But it’s nice to know, that their result has shown with 100% confidence that the change in “ocean temperature” over 50 years is LESS than 0.2 C upward and less than 0.2 C downward. (Another semantic brain twister.)