Accueil > Actualités > Séminaires > Séminaire de Jeff SEVERINGHAUS (LSCE)


Titre : Noble gases in ice cores as paleo-indicators of local and mean ocean temperature
Nom du conférencier : Jeff Severinghaus
Son affiliation : Scripps Institution of Oceanography, Univ. Calif. San Diego07
Laboratoire organisateur : LSCE
Date et heure : 08-07-2010 11h00
Lieu : LSCE-Orme, Bât. 701, Pte 17C, CEA Saclay - Orme des Merisiers
Résumé :

Krypton and xenon are water-soluble gases whose solubility in seawater is temperature-dependent, making the oceanic inventory of these gases sensitive to changes in mean ocean temperature.

Because the total number of Kr and Xe atoms in the ocean-atmosphere system is constant for practical purposes, a change in oceanic inventory causes an opposite change in atmospheric inventory. Reconstruction of past atmospheric noble gas abundance from trapped air in bubbles in glacial ice has recently become possible with sufficient precision to reveal changes in mean ocean temperature at the level of 1 ˚C or so. Corrections for gravitational and thermal fractionation in the firn layer on top of the ice sheet must be made, using nitrogen (N2), argon, and krypton isotopes.

The Last Glacial Maximum shows an ocean cooling of about 3 ˚C as expected from studies of deep ocean temperature using benthic foram 18O and pore waters. As a byproduct of the gas isotope measurement, local temperature change at the ice core site is also obtained via the thermal diffusion gas thermometer. This enables trace gas measurements to be compared with local and mean-ocean temperature, all registered on the same ice core timescale with nil relative age uncertainty. Initial results suggest a 2 ˚C warming of the mean ocean between 18 and 15 ka, a time when atmospheric CO2 rose strongly.