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.

2016
Bauska, TK, Baggenstos D, Brook EJ, Mix AC, Marcott SA, Petrenko VV, Schaefer H, Severinghaus JP, Lee JE.  2016.  Carbon isotopes characterize rapid changes in atmospheric carbon dioxide during the last deglaciation. Proceedings of the National Academy of Sciences of the United States of America. 113:3465-3470.   10.1073/pnas.1513868113   AbstractWebsite

An understanding of the mechanisms that control CO2 change during glacial-interglacial cycles remains elusive. Here we help to constrain changing sources with a high-precision, high-resolution deglacial record of the stable isotopic composition of carbon in CO2 (delta C-13-CO2) in air extracted from ice samples from Taylor Glacier, Antarctica. During the initial rise in atmospheric CO2 from 17.6 to 15.5 ka, these data demarcate a decrease in delta C-13-CO2, likely due to a weakened oceanic biological pump. From 15.5 to 11.5 ka, the continued atmospheric CO2 rise of 40 ppm is associated with small changes in delta C-13-CO2, consistent with a nearly equal contribution from a further weakening of the biological pump and rising ocean temperature. These two trends, related to marine sources, are punctuated at 16.3 and 12.9 ka with abrupt, century-scale perturbations in delta C-13-CO2 that suggest rapid oxidation of organic land carbon or enhanced air-sea gas exchange in the Southern Ocean. Additional century-scale increases in atmospheric CO2 coincident with increases in atmospheric CH4 and Northern Hemisphere temperature at the onset of the Bolling (14.6-14.3 ka) and Holocene (11.6-11.4 ka) intervals are associated with small changes in delta C-13-CO2, suggesting a combination of sources that included rising surface ocean temperature.