Thongchai Thailand

The Jeff Severinghaus Proxy for Mean Global Ocean Temperature

Posted on: September 8, 2019

 

Professor Jeff Severinghaus (photo above) of the Scripps Institution of Oceanography at UC San Diego has proposed a novel proxy for reconstruction of global mean ocean temperature from ratios of noble gases to Nitrogen in ice core air bubbles. This method has the potential of reconstructing ocean temperatures from the last glaciation through the Holocene for greater clarification of the theory of AGW that relies on changes in ocean heat content to explain heat balance anomalies. The Severinghaus methodology is explained most clearly in Melissa Anne Headly’s Doctoral Dissertation (Headley 2008) and her description is reproduced below and indicated graphically above. The full text of the dissertation (248 pages) is available for download in PDF format [LINK] .

Abstract from Headley 2008: Krypton and xenon are highly soluble noble gases. Because they are inert, they do not react biologically or chemically, and therefore can trace purely physical processes. By taking advantage of both the inert nature of these gases and their high solubility, krypton and xenon can be used to reconstruct past ocean temperature variations and summer snow melt frequency. Ocean temperature is a fundamental parameter of the climate system. It plays a vital role in the transport and storage of heat, and may play a role in regulating atmospheric CO₂ , but its past variations are poorly constrained. This is due to the ambiguous nature of the benthic [delta]¹⁸O record in ocean sediments, which reflects both deep water temperature and the [delta]¹⁸O of the water itself (which depends on the extent of ice sheets on land). Recent studies have better constrained localized ocean temperature, but there is still need for global mean ocean temperature reconstructions. Krypton (Kr) and xenon (Xe) are highly soluble and more soluble in colder water. The total amount of Kr and Xe in the atmosphere and ocean together are essentially constant through time, so variations in mean ocean temperature would therefore modulate atmospheric Kr and Xe abundances. Kr and Xe, measured as ratios to nitrogen (N₂), are measured in air bubbles in ice cores to reconstruct atmospheric Kr/N₂ and Xe/N₂ histories, which can then be interpreted in terms of past mean ocean temperature. These Kr/N₂ and Xe/N₂ data and their derived mean ocean temperature (noble gas temperature index, NGTI) reconstructions are presented in Chapters 2 and 3. In Chapter 2, the initial Kr/N₂ data from the LGM indicate that mean ocean temperatures were 2̃.7°C colder at that time, which is consistent with other estimates of local deep ocean temperatures. In Chapter 3, [delta]Kr/N₂ and [delta]Xe/N₂ time series during the last glacial termination and inception are presented. The reconstructed mean ocean temperatures (NGTI’s) are consistent with our earlier measurement and those of other studies. Additionally, these mean ocean temperature reconstructions appear to vary in step with atmospheric CO₂. Because Kr and Xe are highly soluble, they can also be used as an indicator of ice that has melted and refrozen. Visual identification of melt layers is been used as a proxy for exceptionally warm summers temperatures, but this type of melt layer identification becomes difficult as air bubbles form air clathrates at deeper depths. The use of Kr and Xe, measured as ratios to argon (Ar), is examined in Chapter 4. Seasononality may play a role in climate change, so a proxy of summer temperatures may prove to be a powerful constraint on climate change mechanisms that invoke seasonality.

A Bibliography of the use of the Severinghaus methodology in paleo-climatology for the reconstruction of ocean temperatures over time spans that are relevant in the study of AGW is presented below.

Six highlights from these works, listed in numbered paragraphs from #1 to #6, show that the methodology is useful in climate science for reconstruction of climate history at millennial and longer time scales. 

  1. Headley & Severinghaus 2007: The mean δKr/N2 in air bubbles in the Last Glacial Maximum (LGM) was −1.34±0.37% and in the late Holocene it is found to be essentially zero with two different measurements showing +0.07±0.30% and −0.14±0.93%. In the chart above, this difference in Krypton implies a difference of 2.7±0.6°C in mean ocean temperature. This means that the overall warming of ≈10C from the LGM to the late Holocene was mostly on land with the much greater mass of ocean showing a much lower warming of ≈2.7C.
  2. Bauska 2016: The Kr proxy data reveal two intervals of rapid CO2 rise that are plausibly driven by sources from land carbon (at 16.3 and 12.9 ka) and two others that appear fundamentally different and likely reflect a combination of sources (at 14.6 and 11.5 ka).
  3. Kobashi 2010: 1,000 years of central Greenland surface temperature from isotopes of N2 and Ar in air bubbles in an ice core show that northern hemisphere temperature and Greenland temperature changed synchronously and cyclically at two different time scales: 20 years and 40-100 years. This multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.
  4. Ritz 2011: explores the uncertainties of the Severinghaus novel paleoclimatic proxy by implementing krypton, xenon, argon, and N2 into a reduced-complexity climate model. He finds as follows: The uncertainty of the krypton calibration curve due to uncertainties of the ocean saturation concentrations is ±0.3 °C. An additional ±0.3 °C uncertainty must be added for the last deglaciation and up to ±0.4 °C for earlier transitions due to age-scale uncertainties in the sea-level reconstructions.
  5. Cuffey 2016: Used this novel ocean temperature proxy to study the magnitude and timing of Antarctic temperature change through the last deglaciation and found that: deglacial warming was 11.3±1.8C, ≈two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature.
  6. Bereiter 2018: finds that the mean global ocean temperature increased by 2.57 ± 0.24C over the last glacial transition and that the novel reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean. The novel methodology also reveals an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake.

 

 

 

SEVERINGHAUS OCEAN TEMPERATURE BIBLIOGRAPHY

  1. Severinghaus, Jeffrey P., et al. “Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice.” Nature 391.6663 (1998): 141.  Rapid temperature change fractionates gas isotopes in unconsolidated snow, producing a signal that is preserved in trapped air bubbles as the snow forms ice. The fractionation of nitrogen and argon isotopes at the end of the Younger Dryas cold interval, recorded in Greenland ice, demonstrates that warming at this time was abrupt. This warming coincides with the onset of a prominent rise in atmospheric methane concentration, indicating that the climate change was synchronous (within a few decades) over a region of at least hemispheric extent, and providing constraints on previously proposed mechanisms of climate change at this time. The depth of the nitrogen-isotope signal relative to the depth of the climate change recorded in the ice matrix indicates that, during the Younger Dryas, the summit of Greenland was 15 ± 3 °C colder than today.
  2. Caillon, Nicolas, et al. “Timing of atmospheric CO2 and Antarctic temperature changes across Termination III.” Science 299.5613 (2003): 1728-1731.  The analysis of air bubbles from ice cores has yielded a precise record of atmospheric greenhouse gas concentrations, but the timing of changes in these gases with respect to temperature is not accurately known because of uncertainty in the gas age–ice age difference. We have measured the isotopic composition of argon in air bubbles in the Vostok core during Termination III (∼240,000 years before the present). This record most likely reflects the temperature and accumulation change, although the mechanism remains unclear. The sequence of events during Termination III suggests that the CO2 increase lagged Antarctic deglacial warming by 800 ± 200 years and preceded the Northern Hemisphere deglaciation.
  3. Grachev, Alexi M., and Jeffrey P. Severinghaus. “A revised+ 10±4 C magnitude of the abrupt change in Greenland temperature at the Younger Dryas termination using published GISP2 gas isotope data and air thermal diffusion constants.” Quaternary Science Reviews 24.5-6 (2005): 513-519.  We revisit the portion of (Nature 391 (1998) 141) devoted to the abrupt temperature increase reconstruction at the Younger Dryas/Preboreal transition. The original estimate of +5 to +10 °C abrupt warming is revised to +10±4 °C. The gas isotope data from the original work were employed, combined with recently measured precise air thermal diffusion constants (Geochim. Cosmochim. Acta 67 (2003a) 345; J. Phys. Chem. 23A (2003b) 4636). The new constants allow a robust interpretation of the gas isotope signal in terms of temperature change. This was not possible at the time of the original work, when no air constants were available. Three quasi-independent approaches employed in this work all give the same result of a +10 °C warming in several decades or less. The new result provides a firm target for climate models that attempt to predict future climates.
  4. Headly, Melissa A., and Jeffrey P. Severinghaus. “A method to measure Kr/N2 ratios in air bubbles trapped in ice cores and its application in reconstructing past mean ocean temperature.” Journal of Geophysical Research: Atmospheres 112.D19 (2007).  We describe a new method for precise measurement of Kr/N2 ratios in air bubbles trapped in ice cores and the first reconstruction of atmospheric Kr/N2 during the last glacial maximum (LGM) ∼20,000 years ago. After gravitational correction, the Kr/N2 record in ice cores should represent the atmospheric ratio, which in turn should reflect past ocean temperature change due to the dependence of gas solubility on temperature. The increase in krypton inventory in the glacial ocean due to higher gas solubility in colder water causes a decrease in the atmospheric inventory of krypton. Assuming Kr and N2 inventories in the ocean‐atmosphere system are conserved, we use a mass balance model to estimate a mean ocean temperature change between the LGM and today. We measured Kr/N2 in air bubbles in Greenland (GISP2) ice from the late Holocene and LGM, using the present atmosphere as a standard. The late Holocene δKr/N2 means from two sets of measurements are not different from zero (+0.07 ± 0.30‰ and −0.14 ± 0.93‰), as expected from the relatively constant climate of the last millennium. The mean δKr/N2 in air bubbles from the LGM is −1.34 ± 0.37‰. Using the mass balance model, we estimate that the mean temperature change between the LGM ocean and today’s ocean was 2.7 ± 0.6°C. Although this error is large compared to the observed change, this finding is consistent with most previous estimates of LGM deep ocean temperature based on foraminiferal δ18O and sediment pore water δ18O and chlorinity.
  5. Headly, Melissa Anne. Krypton and xenon in air trapped in polar ice cores: paleo-atmospheric measurements for estimating past mean ocean temperature and summer snowmelt frequency. Diss. UC San Diego, 2008. Krypton and xenon are highly soluble noble gases. Because they are inert, they do not react biologically or chemically, and therefore can trace purely physical processes. By taking advantage of both the inert nature of these gases and their high xvi solubilities, krypton and xenon can be used to reconstruct past ocean temperature variations and summer snow melt frequency. Ocean temperature is a fundamental parameter of the climate system. It plays a vital role in the transport and storage of heat, and may play a role in regulating atmospheric CO2, but its past variations are poorly constrained. This is due to the ambiguous nature of the benthic δ18O record in ocean sediments, which reflects both deep water temperature and the δ18O of the water itself (which depends on the extent of ice sheets on land). Recent studies have better constrained localized ocean temperature, but there is still need for global mean ocean temperature reconstructions. Krypton (Kr) and xenon (Xe) are highly soluble and more soluble in colder water. The total amount of Kr and Xe in the atmosphere and ocean together are essentially constant through time, so variations in mean ocean temperature would therefore modulate atmospheric Kr and Xe abundances. Kr and Xe, measured as ratios to nitrogen (N2), are measured in air bubbles in ice cores to reconstruct atmospheric Kr/N2 and Xe/N2 histories, which can then be interpreted in terms of past mean ocean temperature. These Kr/N2 and Xe/N2 data and their derived mean ocean temperature (noble gas temperature index, NGTI) reconstructions are presented in Chapters 2 and 3. In Chapter 2, the initial Kr/N2 data from the LGM indicate that mean ocean temperatures were ~2.7ºC colder at that time, which is consistent with other estimates of local deep ocean temperatures. In Chapter 3, δKr/N2 and δXe/N2 time series during the last glacial termination and inception are presented. The reconstructed mean ocean temperatures (NGTI’s) are consistent with our earlier xvii measurement and those of other studies. Additionally, these mean ocean temperature reconstructions appear to vary in step with atmospheric CO2. Because Kr and Xe are highly soluble, they can also be used as an indicator of ice that has melted and refrozen. Visual identification of melt layers is been used as a proxy for exceptionally warm summers temperatures, but this type of melt layer identification becomes difficult as air bubbles form air clathrates at deeper depths. The use of Kr and Xe, measured as ratios to argon (Ar), is examined in Chapter 4. Seasononality may play a role in climate change, so a proxy of summer temperatures may prove to be a powerful constraint on climate change mechanisms that invoke seasonality.
  6. Kobashi, Takuro, et al. “Persistent multi-decadal Greenland temperature fluctuation through the last millennium.” Climatic Change 100.3-4 (2010): 733-756.  Future Greenland temperature evolution will affect melting of the ice sheet and associated global sea-level change. Therefore, understanding Greenland temperature variability and its relation to global trends is critical. Here, we reconstruct the last 1,000 years of central Greenland surface temperature from isotopes of N2 and Ar in air bubbles in an ice core. This technique provides constraints on decadal to centennial temperature fluctuations. We found that northern hemisphere temperature and Greenland temperature changed synchronously at periods of ~20 years and 40–100 years. This quasi-periodic multi-decadal temperature fluctuation persisted throughout the last millennium, and is likely to continue into the future.
  7. Ritz, Stefan P., Thomas F. Stocker, and Jeffrey P. Severinghaus. “Noble gases as proxies of mean ocean temperature: sensitivity studies using a climate model of reduced complexity.” Quaternary Science Reviews 30.25-26 (2011): 3728-3741. Past global mean ocean temperature may be reconstructed from measurements of atmospheric noble gas concentrations in ice core bubbles. Assuming conservation of noble gases in the atmosphere-ocean system, the total concentration within the ocean mostly depends on solubility which itself is temperature dependent. Therefore, the colder the ocean, the more gas can be dissolved and the less remains in the atmosphere. Here, the characteristics of this novel paleoclimatic proxy are explored by implementing krypton, xenon, argon, and N2 into a reduced-complexity climate model. The relationship between noble gas concentrations and global mean ocean temperature is investigated and their sensitivities to changes in ocean volume, ocean salinity, sea-level pressure and geothermal heat flux are quantified. We conclude that atmospheric noble gas concentrations are suitable proxies of global mean ocean temperature. Changes in ocean volume need to be considered when reconstructing ocean temperatures from noble gases. Calibration curves are provided to translate ice-core measurements of krypton, xenon, and argon into a global mean ocean temperature change. Simulated noble gas-to-nitrogen ratios for the last glacial maximum re δKratm = −1.10‰, δXeatm = −3.25‰, and δAratm = −0.29‰. The uncertainty of the krypton calibration curve due to uncertainties of the ocean saturation concentrations is estimated to be ±0.3 °C. An additional ±0.3 °C uncertainty must be added for the last deglaciation and up to ±0.4 °C for earlier transitions due to age-scale uncertainties in the sea-level reconstructions. Finally, the fingerprint of idealized Dansgaard-Oeschger events in the atmospheric krypton-to-nitrogen ratio is presented. A δKratm change of up to 0.34‰ is simulated for a 2 kyr Dansgaard-Oeschger event, and a change of up to 0.48‰ is simulated for a 4 kyr event. ► With a climate model, noble gases as proxies of mean ocean temperature are tested. ► Past atmospheric noble gas concentrations can be measured in ice cores. ► It is found that noble gases are suitable proxies of global mean ocean temperature. ► The sea-level history must be taken into account in the temperature reconstruction. ► Sea ice has the potential to decouple the noble gas from the temperature signal.
  8. Buizert, Christo, et al. “Greenland temperature response to climate forcing during the last deglaciation.” Science 345.6201 (2014): 1177-1180.  Greenland surface air temperatures changed dramatically during the last deglaciation. The exact amount is unknown, which makes it difficult to understand what caused those changes. Buizert et al. report temperature reconstructions for the period from 19,000 to 10,000 years before the present from three different locations in Greenland and interpret them with a climate model (see the Perspective by Sime). They provide the broad geographic pattern of temperature variability and infer the mechanisms of the changes and their seasonality, which differ in important ways from the traditional view.
  9. Cuffey, Kurt M., et al. “Deglacial temperature history of West Antarctica.” Proceedings of the National Academy of Sciences 113.50 (2016): 14249-14254. The magnitude and timing of Antarctic temperature change through the last deglaciation reveal key aspects of Earth’s climate system. Prior attempts to reconstruct this history relied on isotopic indicators without absolute calibration. To overcome this limitation, we combined isotopic data with measurements of in situ temperatures along a 3.4-km-deep borehole. Deglacial warming in Antarctica was two to three times larger than the contemporaneous global temperature change, quantifying the extent to which feedback processes amplify global changes in polar regions, a key prediction of climate models. Warming progressed earlier in Antarctica than in the Northern Hemisphere but coincident with glacier recession in southern mountain ranges, a manifestation of changing oceanic heat transport, insolation, and atmospheric CO2 that can further test models.  Abstract: The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes’ sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3±1.8C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted.
  10. Bauska, Thomas K., et al. “Carbon isotopes characterize rapid changes in atmospheric carbon dioxide during the last deglaciation.” Proceedings of the National Academy of Sciences 113.13 (2016): 3465-3470.  Antarctic ice cores provide a precise, well-dated history of increasing atmospheric CO2 during the last glacial to interglacial transition. However, the mechanisms that drive the increase remain unclear. Here we reconstruct a key indicator of the sources of atmospheric CO2 by measuring the stable isotopic composition of CO2 in samples spanning the period from 22,000 to 11,000 years ago from Taylor Glacier, Antarctica. Improvements in precision and resolution allow us to fingerprint CO2 sources on the centennial scale. The data reveal two intervals of rapid CO2 rise that are plausibly driven by sources from land carbon (at 16.3 and 12.9 ka) and two others that appear fundamentally different and likely reflect a combination of sources (at 14.6 and 11.5 ka).
  11. Bereiter, Bernhard, et al. “Mean global ocean temperatures during the last glacial transition.” Nature 553.7686 (2018): 39.  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.

1 Response to "The Jeff Severinghaus Proxy for Mean Global Ocean Temperature"

Leave a Reply to uwe.roland.gross Cancel reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: