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Soutenance

Pascaline Bourgain (LOCEAN)

Titre : The upper Arctic Ocean variability at a time of rapid Arctic climate change

Date et heure : Le 17-02-2012 à 10h00

Type : thèse

Université qui délivre le diplôme : UPMC

Lieu : UPMC, 4 place Jussieu, Paris 5e, Bâtiment Esclangon, Amphi Durand
Membres du jury :

Mr Claude Frankignoul
Mr Bert Rudels (rapporteur)
Mme Cecilie Mauritzen (rapporteur)
Mr Gilles Garric (examinateur)
Mr Jean Claude Gascard (directeur de thèse)

Résumé :

The Arctic climate underwent strong modications over the past decades, with a drastic sea ice extent decrease of about 10% per decade. Thanks to a data base gathering more than 18000 observations collected in the entire deep basin of the Arctic Ocean since 1997, we focused on the interannual variability of the upper ocean, particularly on what could potentially contribute to a heat flux from the ocean toward sea ice. For this purpose, the recent evolution of warm water masses from the Atlantic or the Pacific, as well as vertical stratication, are at the heart of the debate.

 

The subsurface Summer Pacific Water warmed up since the late 1990s in agreement with observations collected in the Bering Strait [Woodgate et al.,2010]. Notably, a particularly warm flux entered the Arctic Ocean in 2004 was documented all along its propagation in the Canadian basin. These analyses suggest a possible influence of the subsurface waters on the sea ice evolution in the Arctic region. At depth, observations confirm the propagation of warm Atlantic water pulses, in particular a warm anomaly of 0.8°C detected for the first time in 2004 by Polyakov et al. [2005] West of Svalbard. Nevertheless, on a relatively short time period (11 years), we did not find evidence for any gradual warming trend of this water mass as suggested by Polyakov et al. [2010].

 

The double diffusion process which occurs sometimes in the thermocline, seems to be a widespread phenomenon in the entire deep basin. The vertical heat fluxes transmitted through the interfaces between two mixed layers increased since the 1980s, notably because of the "supersteps" appearance, characterized by a strong temperature increase at the interface between two mixed layers.

 

Above the thermocline, the halocline remained relatively robust over the past decade. Its stratication intensified in 2007-2008 in the Canadian basin due to a freshwater content increase probably in response to the atmospheric forcing. As a consequence, the warm Atlantic waters remained insulated from the surface waters and did not contribute to the changes observed at the surface over this period.

Contact :
Pascaline Bourgain
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