Publications

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2017
Hamme, RC, Emerson SR, Severinghaus JP, Long MC, Yashayaev I.  2017.  Using noble gas measurements to derive air-sea process information and predict physical gas saturations. Geophysical Research Letters. 44:9901-9909.   10.1002/2017gl075123   AbstractWebsite

Dissolved gas distributions are important because they influence oceanic habitats and Earth's climate, yet competing controls by biology and physics make gas distributions challenging to predict. Bubble-mediated gas exchange, temperature change, and varying atmospheric pressure all push gases away from equilibrium. Here we use new noble gas measurements from the Labrador Sea to demonstrate a technique to quantify physical processes. Our analysis shows that water-mass formation can be represented by a quasi steady state in which bubble fluxes and cooling push gases away from equilibrium balanced by diffusive gas exchange forcing gases toward equilibrium. We quantify the rates of these physical processes from our measurements, allowing direct comparison to gas exchange parameterizations, and predict the physically driven saturation of other gases. This technique produces predictions that reasonably match N-2/Ar observations and demonstrates that physical processes should force SF6 to be approximate to 6% more supersaturated than CFC-11 and CFC-12, impacting ventilation age calculations. Plain Language Summary Gases dissolved in the ocean are important because they influence oceanic habitats and Earth's climate. Physics and biology combine to control the amounts of gases like carbon dioxide, oxygen, and nitrogen in the ocean. Our research seeks to disentangle and quantify the competing effects of physics and biology on dissolved gases. We present very precise measurements of dissolved noble gas concentrations (neon, argon, and krypton) in the Labrador Sea, one of the few places on Earth where the surface and deep ocean communicate with each other. Because noble gases have no biological function, responding only to physical processes in the ocean, we use these measurements to discover the amounts of physical processes that affect gases during the winter at this site, like rapid cooling of the water or bubbles injected by breaking waves. From these amounts of physical processes, we calculate the concentrations of nitrogen and chlorofluorocarbons if only physical processes affected these gases. Our work will allow oceanographers to better estimate the rate that bioavailable nutrients are being removed from the ocean (a process that biologically creates nitrogen gas) and to better determine how the ocean moves from observations of changing chlorofluorocarbons in the ocean.

1999
Severinghaus, JP, Brook EJ.  1999.  Abrupt climate change at the end of the last glacial period inferred from trapped air in polar ice. Science. 286:930-934.   10.1126/science.286.5441.930   AbstractWebsite

The last glacial period was terminated by an abrupt warming event in the North Atlantic similar to 15,000 years before the present, and warming events of similar age have been reported from Low Latitudes. Understanding the mechanism of this termination requires that the precise relative timing of abrupt climate warming in the tropics versus the North Atlantic be known. Nitrogen and argon isotopes in trapped air in Greenland ice show that the Greenland Summit warmed 9 +/- 3 degrees C over a period of several decades, beginning 14,672 years ago. Atmospheric methane concentrations rose abruptly over a similar to 50-year period and began their increase 20 to 30 years after the onset of the abrupt Greenland warming. These data suggest that tropical climate became warmer or wetter (or both) similar to 20 to 80 years after the onset of Greenland warming, supporting a North Atlantic rather than a tropical trigger for the climate event.

1998
Severinghaus, JP, Sowers T, Brook EJ, Alley RB, Bender ML.  1998.  Timing of abrupt climate change at the end of the Younger Dryas interval from thermally fractionated gases in polar ice. Nature. 391:141-146.   10.1038/34346   AbstractWebsite

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 degrees C colder than today.