Océanographie | EPFL Graph Search

vignette|La Thalassa, navire océanographique français appartenant à Genavir, notamment pour le compte de l’Ifremer, en rade de Brest en 2016 L’océanographie (du grec , « Océan », dieu de la mer et « écrire ») est une discipline scientifique, faisant partie des sciences de la Terre, consacrée à l'étude des mers et des océans. Un premier congrès en 1871 et l'expédition Challenger accomplie entre 1872 et 1876 concrétisent la naissance de cette discipline et en popularisent rapidement le nom et les premières avancées auprès du public amateur. Le terme océanographe, désignant les chercheurs de cette science, apparaît en France en 1881. Les océanographes étudient un très grand nombre d'aspects des océans et des mers, incluant la tectonique des plaques, les grands cycles biogéochimiques, les courants océaniques ou encore les organismes et les écosystèmes marins ou encore les liens entre océans et modifications climatiques. Ces domaines variés reflètent la multitude de disciplines que les

Estimates of the temperature flux-temperature gradient relation above a sea floor

Andrea Cimatoribus

The relation between the flux of temperature (or buoyancy), the vertical temperature gradient and the height above the bottom is investigated in an oceanographic context, using high-resolution temperature measurements. The model for the evolution of a stratified layer by Balmforth el at. (J. Fluid Mech., vol. 355, 1998, pp. 329-358) is reviewed and adapted to the case of a turbulent flow above a wall. Model predictions are compared with the average observational estimates of the flux, exploiting a flux estimation method proposed by Winters & D'Asaro (1. Fluid Merit., vol. 317, 1996, pp. 179-193). This estimation method enables the disentanglement of the dependence of the average flux on the height above the bottom and on the background temperature gradient. The classical N-shaped flux gradient relation is found in the observations. The model and the observations show similar qualitative behaviour, despite the strong simplifications used in the model. The results shed light on the modulation of the temperature flux by the presence of the boundary, and support the idea of a turbulent flux following a mixing-length argument in a stratified flow. Furthermore, the results support the use of Thorpe scales close to a boundary, if sufficient averaging is performed, suggesting that the Thorpe scales are affected by the boundary in a similar way to the mixing length.

Cambridge University Press2016

Recent warming in Greenland in a long-term instrumental (1881-2012) climatic context: I. Evaluation of surface air temperature records

Konrad Steffen

We present an updated analysis of monthly means of daily mean, minimum and maximum surface air temperature (SAT) data from Greenland coastal weather stations and from a long-running site on the Greenland ice sheet, and analyse these data for evidence of climate change, especially focusing on the last 20 years but using the whole periods of available records (some since 1873). We demonstrate very strong recent warming along the west coast of Greenland, especially during winter (locally > 10 degrees C since 1991), and rather weaker warming on the east Greenland coast, which is influenced by different oceanographic/sea-ice and meteorological synoptic forcing conditions to the rest of Greenland. Coastal Greenland seasonal mean SAT trends were generally 2-6 degrees C, strongest in winter (5.7 degrees C) and least in summer and autumn (both 2.2 degrees C), during 1981-2011/12. Since 2001 Greenland mean coastal SAT increased significantly by 2.9 degrees C in winter and 0.8 degrees C in summer but decreased insignificantly by 1.1 degrees C in autumn and 0.2 degrees C in spring, during a period when there was little net change (

Iop Publishing Ltd2012

Community-Level Responses to Iron Availability in Open Ocean Plankton Ecosystems

Anna Carratala Ripolles

Predicting responses of plankton to variations in essential nutrients is hampered by limited in situ measurements, a poor understanding of community composition, and the lack of reference gene catalogs for key taxa. Iron is a key driver of plankton dynamics and, therefore, of global biogeochemical cycles and climate. To assess the impact of iron availability on plankton communities, we explored the comprehensive bio-oceanographic and bio-omics data sets from Tara Oceans in the context of the iron products from two state-of-the-art global scale biogeochemical models. We obtained novel information about adaptation and acclimation toward iron in a range of phytoplankton, including picocyanobacteria and diatoms, and identified whole subcommunities covarying with iron. Many of the observed global patterns were recapitulated in the Marquesas archipelago, where frequent plankton blooms are believed to be caused by natural iron fertilization, although they are not captured in large-scale biogeochemical models. This work provides a proof of concept that integrative analyses, spanning from genes to ecosystems and viruses to zooplankton, can disentangle the complexity of plankton communities and can lead to more accurate formulations of resource bioavailability in biogeochemical models, thus improving our understanding of plankton resilience in a changing environment. Plain Language Summary Marine phytoplankton require iron for their growth and proliferation. According to John Martin's iron hypothesis, fertilizing the ocean with iron could dramatically increase photosynthetic activity, thus representing a biological means to counteract global warming. However, while there is a constantly growing knowledge of how iron is distributed in the ocean and about its role in cellular processes in marine photosynthetic groups such as diatoms and cyanobacteria, less is known about how iron availability shapes plankton communities and how they respond to it. In the present work, we exploited recently published Tara Oceans data sets to address these questions. We first defined specific subcommunities of co-occurring organisms that co-vary with iron availability in the oceans. We then identified specific patterns of adaptation and acclimation to iron in different groups of phytoplankton. Finally, we validated our global results at local scale, specifically in the Marquesas archipelago, where recurrent phytoplankton blooms arc believed to be a result of iron fertilization. By integrating global data with a localized response, we provide a framework for understanding the resilience of plankton ecosystems in a changing environment.

AMER GEOPHYSICAL UNION2019

Community-Level Responses to Iron Availability in Open Ocean Plankton Ecosystems

Anna Carratala Ripolles

AMER GEOPHYSICAL UNION2019