Casimir de Lavergne

French National Centre for Scientific Research | CNRS · Institut national des sciences de l'univers (INSU)

In 1974, newly available satellite observations unveiled the presence of a giant ice-free area, or polynya, within the Antarctic ice pack of the Weddell Sea, which persisted during the two following winters . Subsequent research showed that deep convective overturning had opened a conduit between the surface and the abyssal ocean, and had maintaine...

In studies of ocean mixing, it is generally assumed that small-scale turbulent overturns lose 15%-20% of their energy in eroding the background stratification. Accumulating evidence that this energy fraction, or mixing efficiency Rf, significantly varies depending on flow properties challenges this assumption, however. Here, the authors examine the...

The abyssal ocean is primarily filled by cold, dense waters formed around Antarctica and collectively referred to as Antarctic Bottom Water (AABW). At steady state, AABW must be consumed in the ocean interior at the same rate it is produced, but how and where this consumption is achieved remains poorly understood. Here, estimates of abyssal water m...

Changes in Pacific tracer reservoirs and transports are thought to be central to the regulation of atmospheric CO 2 on gla-cial-interglacial timescales. However, there are currently two contrasting views of the circulation of the modern Pacific; the classical view sees southern sourced abyssal waters upwelling to about 1.5 km depth before flowing s...

The Southern Hemisphere westerly winds influence deep ocean circulation and carbon storage. While the westerlies are hypothesised to play a key role in regulating atmospheric CO2 over glacial-interglacial cycles, past changes in their position and strength remain poorly constrained. Here, we use a compilation of planktic foraminiferal δ18O from acr...

The world's largest ice shelves are found in the Antarctic Weddell Sea and Ross Sea where complex interactions between the atmosphere, sea ice, ice shelves and ocean transform shelf waters into High Salinity Shelf Water (HSSW) and Ice Shelf Water (ISW), the parent waters of Antarctic Bottom Water (AABW). This process feeds the lower limb of the glo...

The deepest reaches of the ocean are ventilated by sinking of cold and relatively saline seawater around Antarctica. Observations from the Australian sector of the Southern Ocean reveal a decline in sinking and abyssal ventilation, linked to dropping ocean salinity on the Antarctic shelf.

The Southern Ocean greatly contributes to the regulation of the global climate by controlling important heat and carbon exchanges between the atmosphere and the ocean. Rates of climate change on decadal timescales are therefore impacted by oceanic processes taking place in the Southern Ocean, yet too little is known about these processes. Limitatio...

Coastlines in most ocean general circulation models are piecewise constant. Accurate representation of boundary currents along staircase‐like coastlines is a long‐standing issue in ocean modeling. Pioneering work by Adcroft and Marshall (1998, https://doi.org/10.3402/tellusa.v50i1.14514) revealed that artificial indentation of model coastlines, obt...

The ocean's internal pycnocline is a layer of elevated stratification that separates the well‐ventilated upper ocean from the more slowly renewed deep ocean. Despite its pivotal role in organizing ocean circulation, the processes governing the formation of the internal pycnocline remain little understood. Classical theories on pycnocline formation...

Diapycnal mixing shapes the distribution of climatically important tracers, such as heat and carbon, as these are carried by dense water masses in the ocean interior. Here, we analyze a suite of observation‐based estimates of diapycnal mixing to assess its role within the Atlantic Meridional Overturning Circulation (AMOC). The rate of water mass tr...

The world’s largest ice shelves are found in the Antarctic Weddell and Ross Seas where complex interactions between the atmosphere, sea ice, ice shelves and ocean transform shelf waters into High Salinity Shelf Water (HSSW) and Ice Shelf Water (ISW), the parent waters of Antarctic Bottom Water (AABW). This process feeds the lower limb of the global...

Coastlines in most ocean general circulation models are piecewise constant. Accurate representation of boundary currents along staircase-like coastlines is a long-standing issue in ocean modelling. Pioneering work by Adcroft and Marshall (1998) revealed that artificial indentation of model coastlines, obtained by rotating the numerical mesh within...

Irreversible mixing of tracers and momentum in the ocean occurs via diffusion and friction at the scale of molecules. That such molecular processes profoundly influence basin-scale ocean currents is counter-intuitive. Many successful theories of ocean circulation indeed ignore diffusive and frictional processes. Yet oceanographers have long recogni...

Mid-depth North Pacific waters are rich in nutrients and respired carbon accumulated over centuries. The rates and pathways with which these waters exchange with the surface ocean are uncertain, with divergent paradigms of the Pacific overturning: one envisions bottom waters upwelling to 1.5 km depth; the other confines overturning beneath a mid-de...

The Southern Hemisphere westerly winds influence deep ocean circulation and carbon storage. While the westerlies are hypothesised to play a key role in regulating atmospheric CO2 over glacial-interglacial cycles, past changes in their position and strength remain poorly constrained. Here, we use a compilation of planktic foraminiferal delta-18O fro...

The Southern Hemisphere westerly winds strongly influence deep ocean circulation and carbon storage ¹ . While the westerlies are hypothesised to play a key role in regulating atmospheric CO 2 over glacial-interglacial cycles 2–4 , past changes in their position and strength remain poorly constrained 5–7 . Here, we use a compilation of planktic fora...

Ce document synthétise la démarche de réflexion et d'élaboration du vote au sein du LOCEAN visant à réduire l'empreinte carbone de nos activités, de octobre 2018 à septembre 2020.

Turbulent mixing from breaking oceanic internal waves drives a vertical transport of water, heat and other climatically important tracers in the ocean, thereby playing an important role in shaping the circulation and distributions of heat and carbon within the climate system. However, linking internal wave-driven mixing to its impacts on climate po...

Abstract This study presents the global climate model IPSL‐CM6A‐LR developed at Institut Pierre‐Simon Laplace (IPSL) to study natural climate variability and climate response to natural and anthropogenic forcings as part of the sixth phase of the Coupled Model Intercomparison Project (CMIP6). This article describes the different model components, t...

Infographie réalisée en Juillet 2020 pour préparer le vote sur le réduction de l'empreinte carbone de septembre.

Infographic made in July 2020 to prepare the September vote on measures to reduce the carbon footprint

Plain Language Summary When tidal ocean currents flow over bumpy seafloor, they generate internal tidal waves. Internal waves are the subsurface analog of surface waves that break on beaches. Like surface waves, internal tidal waves often become unstable and break into turbulence. This turbulence is a primary cause of mixing between stacked ocean l...

Global three-dimensional maps of turbulence production due to internal tides.

The physical oceanographic environment, water mass characteristics, and distribution in the area adjacent to Larsen C Ice Shelf (LCIS) are investigated using hydrographic data collected during the 2019 Weddell Sea Expedition. The results shed light on the ocean conditions adjacent to a thinning LCIS, on a continental shelf that is a source region f...

Mixing layers near sloped topography in the abyss are thought to play a critical role in the global overturning circulation. Yet the behavior of passive tracers within sloping boundary layer systems has received little attention, despite the extensive use of tracer observations to understand abyssal circulation. Here, we investigate the behavior of...

Horizontal fluxes of heat and other scalar quantities in the ocean are due to correlations between the horizontal velocity and tracer fields. However, the limited spatial resolution of ocean models means that these correlations are not fully resolved using the velocity and temperature evaluated on the model grid, due to the limited spatial resoluti...

Turbulent mixing in the ocean is key to regulate the transport of heat, freshwater and biogeochemical tracers, with strong implications for Earth's climate. In the deep ocean, tides supply much of the mechanical energy required to sustain mixing via the generation of internal waves, known as internal tides, whose fate-the relative importance of the...

Internal tides power much of the observed small-scale turbulence in the ocean interior. To represent mixing induced by this turbulence in ocean climate models, the cascade of internal tide energy to dissipation scales must be understood and mapped. Here, we present a framework for estimating the geography of internal tide energy sinks. The mapping...

Over the past few million years, the Earth descended from the relatively warm and stable climate of the Pliocene into the increasingly dramatic ice age cycles of the Pleistocene. The influences of orbital forcing and atmospheric CO2 on land-based ice sheets have long been considered as the key drivers of the ice ages, but less attention has been pa...

The dataset contains global estimates of barotropic-to-baroclinic tidal energy conversion at 1/30-degree resolution. Three types of estimates are available: 1. Non-modal conversion rates calculated by Falahat et al. (2014) following the method of Nycander (2005). A map for each of the eight most energetic tidal constituents (M2, S2, K1, O1, N2, K...

The dataset consists of global two-dimensional maps of internal tide energy sources and sinks, at half-degree horizontal resolution. Estimated energy sources are provided for the three most energetic tidal constituents: M2, S2 and K1. They are decomposed into vertical normal modes. Units are Watts per square meter. Estimated energy sinks are prov...

The representation of tides in regional ocean simulations of the Amundsen Sea enhances ice-shelf melting, with weakest effects for Pine Island and Thwaites (<+10%) and strongest effects for Dotson, Cosgrove and Abbot (>+30%). Tides increase vertical mixing throughout the water column along the continental shelf break. Diurnal tides induce topograph...

Deep ocean waters hold enormous amounts of carbon, nutrients and heat. Their influence on Earth’s climate depends critically on the pace and pathways of their renewal. Contrary to conventional wisdom, researchers find that these pathways are intimately linked to the shape of the ocean. https://www.thesciencebreaker.com/breaks/earth-space/the-shape...

In situ observations obtained over the last several decades have shown that the intensity of turbulent mixing in the abyssal ocean is enhanced toward the seafloor. Consequently, a new paradigm has emerged whereby dianeutral downwelling dominates in the ocean interior and dianeutral upwelling only occurs within thin bottom boundary layers. This stud...

L'océan profond est un immense réservoir de carbone, de chaleur et de nutriments. Ce réservoir est relié à la surface par un réseau de courants, appelé circulation thermohaline, qui conditionne les variations lentes du climat. Pourtant, les moteurs, la structure et l'intensité de la circulation thermohaline sont encore mal connus. Des bilans de den...

Several processes have been hypothesized to explain the slight overall expansion of Antarctic sea ice over the satellite observation era, including externally forced changes in local winds or in the Southern Ocean’s hydrological cycle, as well as internal climate variability. Here, we show the critical influence of an ocean–sea-ice feedback. Once i...

This gridded product consists of a global (80°S-62°N) climatological estimate of radiocarbon content (∆14C) at half-degree horizontal resolution, provided both on neutral density and depth surfaces. It is based on the GLODAPv2 data compilation (Key et al. 2016, Olsen et al. 2016) and the neutral density (γn; Jackett and McDougall 1997) field of the...

The abyssal ocean is broadly characterized by northward flow of the densest waters and southward flow of less-dense waters above them. Understanding what controls the strength and structure of these interhemispheric flows—referred to as the abyssal overturning circulation—is key to quantifying the ocean’s ability to store carbon and heat on timesca...

Understanding the causes of recent climatic trends and variability in the high-latitude Southern Hemisphere is hampered by a short instrumental record. Here, we analyse recent atmosphere, surface ocean and sea-ice observations in this region and assess their trends in the context of palaeoclimate records and climate model simulations. Over the 36-y...

Antarctic Bottom Water is the most voluminous water mass of the World Ocean, and it feeds the deepest and slowest component of ocean circulation. The processes that govern its lifecycle are therefore key to the ocean's carbon and heat storage capacity on centennial to multi-millennial timescales. This thesis aims at characterizing and quantifying p...

Presentation given at the Meteorological institute of Stockholm University in May 2015.

Presentation prepared for the ”Large-scale climate variability in Antarctica and the Southern Ocean over decades to centuries, and links to extra-polar climate” workshop held in March 2015 in La Jolla, USA.

Presentation prepared for the ”Large-scale climate variability in Antarctica and the Southern Ocean over decades to centuries, and links to extra-polar climate” workshop held in March 2015 in La Jolla, USA.

Presentation prepared for the ”Large-scale climate variability in Antarctica and the Southern Ocean over decades to centuries, and links to extra-polar climate” workshop held in March 2015 in La Jolla, USA.

Ocean Sciences Meeting 2014 poster