ECOLE DOCTORALE DES SCIENCES DE L

ECOLE DOCTORALE DES SCIENCES DE L’ENVIRONNEMENT
D'ILE DE France N° 129
Proposition de sujet de thèse pour la rentrée 2016
Nom du Laboratoire d’accueil :
LOCEAN
N° UMR :
Nom du Directeur du laboratoire : Anne-Marie Lézine
Adresse : UPMC, 4 pl. Jussieu
Equipe d’accueil : SURF
Nom du co-directeur Responsable (HDR) :G. Reverdin
Nom du co-directeur :
Téléphone :
0144272342
Téléphone :
Mail : [email protected]
Mail :
7657
(notice that this work will be done in close cooperation with Giovanni Aloisi (LOCEAN) and Jean-Baptiste
Sallée, who will be co-advisers)
• Titre de la thèse : contribution au bilan d’eau douce de l’océan austral par utilisation
des isotopologues de l’eau
• Sujet proposé (2 pages maximum) :
Surface salinity in the near-surface Antarctic sector of the Austral Ocean has diminished in many sectors in
the last twenty years. This is particularly strong near the west Antarctic Peninsula (Meredith et al., 2015), but
has also been observed in the Australian Antarctic Basin north of the Adélie Land from summer surveys
(Morrow and Kestenare, 2014). Contributions to this decrease vary depending on the sector and the period
investigated. It includes increased precipitation, contribution of increased glacial melt, but also processes
associated with sea ice formation, export (transport) and melt. Processes of ocean-glacial ice interaction
might be very different depending on local shelf conditions. In particular, in west Antarctica, glacial melt
water is often associated with intrusions of warm circumpolar water on the shelf and further interaction with
the ice shelves. In region of dense shelf water production such as in the Ross Sea or some regions of the East
Antarctic Shelf, further interaction with the locally formed dense products are expected which involve
additional dependency to regional air-sea exchanges and sea ice distribution. These different contributions
can be traced in sea water isotopologs in addition to salinity and temperature, and estimates of air-sea fluxes
and sea ice cover/formation and melt rates.
Antarctic sea ice cover has been waning and then increasing on average over the last forty years of satellite
observations. This overall tendency however underlies strong regional contracts, with regions such as the
Antarctic Peninsula being characterized by a rapid sea ice retreat. Peak ice concentration has been happening
in many sectors as recently as 2014. Although there are meteorological/atmospheric climate reasons for that
(changes in winter cooling, wind driven transport or mixing), changes in surface salinity and thus in upper
ocean stratification have also been invoked. There is also evidence of long-term changes in newly formed
(and exported) deep water. How this deep water forms and entrains the excess freshening of the surface or
shelf waters has very important climate consequences.
This thesis will focus on samples and records of sea water isotopes (δD and δ18O of water) from different
cruises, taking place mostly in late 2016 and early 2017 as tracers of the hydrological cycle in two sectors of
the Antarctic Austral Ocean. The thesis will have two focuses:
1- Analysis of water column properties and water masses with focus on the sources of freshwater and
interaction with glacial melt, meteoric water and sea ice processes. This will be done in the two
contrasted sectors of the eastern Weddell Sea and the Adélie Land investigated during different
cruises. In these two sectors, earlier cruise data will be also searched for and compared to the recent
data to provide reference material.
2- Analysis of surface properties in the different sectors of Antarctica that will be sampled with focus on
the freshwater budget. This will involve analyzing and estimating the evaporative exchanges and
possible precipitation properties, as well as the meteorology and sea surface properties during the
different cruises (this work will be done in collaboration with other groups).
Most of the material (T, S, isotopologs of sea water, additional information on meteorology, evaporation and
precipitation) will originate from two cruises. The Wapiti cruise (PI Jean-Baptiste Sallée) will take place in
late 2016 in the Weddell Sea (transit from/to Punta Arenas) with a large number of CTD stations allowing
water collection, and continuous surface sampling of oxygen isotopes. In addition, during the cruise, it is
likely that water vapor isotopic measurements will also be available to constrain evaporative exchanges
(rainfall or snowfall water will also be collected) (in collaboration with Marion Benetti, Univ. Iceland,
Reykjavik). The second main source of data will be from the ACE circum-Antarctica cruise planed in late
2016-early 2017 with particular focus on water column sampling proposed in the Adélie Land sector. Some
samples are also available in the Adelie Land sector in the last decade. Measuring surface sea water isotope
composition is also proposed throughout the ACE cruise by another group, with whom we collaborate (H-C.
Steen-Larsen, UCPH, Kopenhagen). In addition, measuring atmospheric isotopologs (and rainfall samples) is
proposed by two groups, which should help constrain evaporative processes. Water samples will also be
collected from other ships of opportunity in the Drake Passage sector and in the southern Atlantic and Indian
oceans.
Note: most sea water samples will be analyzed at LOCEAN by PICARRO CRDS, possibly without previous
distillation. The accuracy of this approach is currently tested at LOCEAN, as well as the comparison with
mass-spectrometer approaches with CO2 equilibration, to check further the differences found between the
different approaches. We also expect that the work will involve cooperation with colleagues in Iceland and
Denmark.
References:
Meredith, M., et al., 2015: The freshwater system west of the Antarctic Peninsula: spatial and temporal
changes. J. Climate, 26, 1669-1684. Morrow, R., and E. Kestenare, 2014 : Nineteen-year changes in surface
salinity in the Southern Ocean south of Australia. J. Mar. sys., 129, 472-483.
• Type de Financements prévu autre que ED 129 :
Pas de co-financement de la bourse de these.
Par ailleurs, les frais de fonctionnement inhérents à la thèse seront pris en charge en partie sur le projet
Wapiti, ainsi que sur des projets nationaux à déposer ultérieurement. Un soutien limité est disponible pour
des missions sur l’Islande en 2016 et 2017.
• Encadrement :
. Liste des autres doctorants que vous encadrés au 1er janvier 2016 toutes ED confondues ? (Nom, Université
d’inscription, type de financement, date de soutenance envisagée)
Gilles Reverdin :
Co-direction avec Jacqueline Boutin de Anna Sommer (soutenance prévue 10/2016) (ED129)
Co-direction avec Guillaume Charria et Xavier Capet de Ozge Yelekci (soutenance prévue le 12/2016)
(ED129)
Marie-Noëlle Houssais :
Direction d’Antoine Martin (soutenance prévue : printemps 2016) (ED129)