Johan EtourneauEcole Pratique des Hautes Etudes | EPHE · UMR EPOC
Johan Etourneau
PhD
About
56
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Introduction
Additional affiliations
May 2010 - February 2014
January 2006 - July 2009
Publications
Publications (56)
Antarctic sea ice plays a critical role in the Earth system, influencing energy, heat and freshwater fluxes, air–sea gas exchange, ice shelf dynamics, ocean circulation, nutrient cycling, marine productivity and global carbon cycling. However, accurate simulation of recent sea-ice changes remains challenging and, therefore, projecting future sea-ic...
Antarctic sea ice plays a critical role in the Earth system, influencing energy, heat, and freshwater fluxes, air-sea gas exchange, ice shelf dynamics, ocean circulation, nutrient cycling, marine productivity, and global carbon cycling. However, accurate simulation of recent sea-ice changes remains challenging, and therefore projecting future sea-i...
Reconstructions of ocean primary productivity (PP) help to explain past and present biogeochemical cycles and climate changes in the oceans. We document PP variations over the last 50 kyr in a currently oligotrophic subtropical region, the Gulf of Cadiz. Data combine refined results from previous investigations on dinocyst assemblages, alkenones, a...
The role and climatic impact of the opening of the Drake Passage
and how it affected both marine and terrestrial environments across the
Eocene–Oligocene transition (EOT ∼34 Ma) period remains
poorly understood. Here we present new terrestrial palynomorph data compared
with recently compiled lipid biomarker (n-alkane) data from Ocean Drilling
Progr...
Molecular proxies, also named organic biomarkers, have increasingly been used over the last decades in both marine and continental environments to track past climate variability at several timescales. Marine and terrestrial living organisms synthetize organic compounds, in particular some lipids that are exported to lake and deep ocean sediments wh...
The vigorous eastward flow of the Antarctic Circumpolar Current (ACC) connects all major ocean basins and plays a prominent role in the transport of heat, carbon and nutrients around the globe. However, the establishment of a deep circumpolar flow, similar to the present-day ACC, remains controversial thereby obscuring our understanding of its clim...
The Antarctic coastal zone is an area of high primary productivity,
particularly within coastal polynyas, where large phytoplankton blooms and
drawdown of CO2 occur. Reconstruction of historical primary
productivity changes and the associated driving factors could provide
baseline insights on the role of these areas as sinks for atmospheric
CO2, es...
Antarctic sea-ice extent, primary productivity and ocean circulation represent interconnected systems that form important components of the global carbon cycle. Subdecadal to centennial-scale variability can influence the characteristics and interactions of these systems, but observational records are too short to evaluate the impacts of this varia...
The role and climatic impact of the opening of the Drake Passage and how it affected both marine and terrestrial environments across the Eocene-Oligocene Transition (EOT ~ 34 Ma) period remains poorly understood. Here we present new terrestrial palynomorph data compared with recently compiled lipid biomarker (n-alkane) data from Ocean Drilling Prog...
The scarcity of paleo-records from the Antarctic Peninsular region of the Southern Ocean hinders our understanding of the timing of the opening of Drake Passage, specifically in the region of the South Orkney Microcontinent (SOM) and Powell Basin, between the Scotia and Antarctic plates. At Ocean Drilling Program (ODP) Hole 696B, SOM sediments reco...
Antarctic sea ice has paradoxically become more extensive over the past four decades despite a warming climate. The regional expression of this trend has been linked to changes in vertical redistribution of ocean heat and large-scale wind-field shifts. However, the short length of modern observations has hindered attempts to attribute this trend to...
Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large-cavity ice shelves is not included in current Earth System models and may be a d...
Abstract. The Antarctic coastal zone is an area of high primary productivity, particularly within coastal polynyas where large phytoplankton blooms and drawdown of CO<sub>2</sub> occur. Reconstruction of historical primary productivity changes, and the associated driving factors, could provide baseline insights on the role of these areas as sinks f...
Abstract. Over recent decades Antarctic sea-ice extent has increased, alongside widespread ice shelf thinning and freshening of waters along the Antarctic margin. In contrast, Earth system models generally simulate a decrease in sea ice. Circulation of water masses beneath large cavity ice shelves is not included in current models and may be a driv...
Dramatic changes in sea ice have been observed in both poles in recent decades. However, the observational period for sea ice is short, and the climate models tasked with predicting future change in sea ice struggle to capture the current Antarctic trends. Paleoclimate archives, from marine sedimentary records and coastal Antarctic ice cores, provi...
The emergence of high-amplitude, low-frequency glacial-interglacial cycles during the mid-Pleistocene climate transition (MPT; 800–1,200 ka) is associated with global cooling. In the eastern equatorial Pacific, sea surface temperatures cooled, and the upwelling-induced cold tongue expanded significantly during the MPT. Here we use sedimentary recor...
Recent paleoclimatic studies suggest that changes in the tropical rainbelt across the Atlantic Ocean during the past two millennia are linked to a latitudinal shift of the Intertropical Convergence Zone (ITCZ) driven by the Northern Hemisphere (NH) climate. However, little is known regarding other potential drivers that can affect tropical Atlantic...
Recent paleoclimatic studies suggest that changes in the tropical rainbelt across the Atlantic Ocean during the past two millennia are linked to a latitudinal shift of the Intertropical Convergence Zone (ITCZ) driven by the Northern Hemisphere (NH) climate. However, little is known regarding other potential drivers that can affect tropical Atlantic...
The recent thinning and retreat of Antarctic ice shelves has been attributed to both atmosphere and ocean warming. However, the lack of continuous, multi-year direct observations as well as limitations of climate and ice shelf models prevent a precise assessment on how
the ocean forcing affects the fluctuations of a grounded and floating ice cap. H...
This study presents new high resolution sedimentary δ¹⁵N records from piston cores collected within and outside the present-day eastern south Pacific oxygen minimum zone along a latitudinal transect from 3.5°S to 15°S. Radiocarbon dating of foraminifera and organic matter show that the cores cover the Holocene and the last deglaciation with high se...
In this study, we present a unique high-resolution Holocene record of oceanographic and climatic change based on analyses of diatom assemblages combined with biomarker data from a sediment core collected from the Vega Drift, eastern Antarctic Peninsula (EAP). These data add to the climate framework already established by high-resolution marine sedi...
In this study, we present a unique high-resolution Holocene record of oceanographic and climatic change based on analyses of diatom assemblages combined with biomarker data from a sediment core collected from the Vega Drift, eastern Antarctic Peninsula (EAP). These data add to the climate framework already established by high-resolution marine sedi...
Upwelling within the highly productive Benguela current off the Namibian coast began in, and intensified throughout, the Neogene epoch. Model simulations indicate its development was intimately connected to evolving topography and mountain uplift in Africa.
Suitable paleoenvironmental records in semi-arid areas are rare due to the paucity of
water systems, such a lake or swamps. This is particularly true in the northeastern
Brazil (NEB), where extremely low annual precipitations are mostly governed by the
seasonal migration of the Intertropical Convergence Zone (ITCZ). In this ongoing study,
we will p...
As compared to the late Pleistocene, Alkenone-based sea surface temperature (SST) in the Benguela region revealed relatively warm and stable SST recorded between ~3.5 and 2.0 Ma, and coincide with a period of increasing biological productivity as revealed by increasing deposition of biogenic opal. We assess how the hydrological patterns recorded in...
The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pl...
The West Antarctic ice sheet is particularly sensitive to global warming
and its evolution and impact on global climate over the next few decades
remains difficult to predict. In this context, investigating past sea
ice conditions around Antarctica is of primary importance. Here, we
document changes in sea ice presence, upper water column temperatu...
Over much of the ocean’s surface, productivity and growth are limited by a scarcity of bioavailable nitrogen. Sedimentary δ15N records spanning the last deglaciation suggest marked shifts in the nitrogen cycle during this time, but the quantification of these changes has been hindered by the complexity of nitrogen isotope cycling. Here we present a...
The TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon
atoms, Schouten et al., 2002) paleothermometer was proposed based on the
relative distribution of thaumarchaeotal lipids, i.e. isoprenoid
glycerol dibiphytanyl glycerol tetraethers (GDGTs), and has been
increasingly used to reconstruct past sea surface temperatures (SSTs).
However,...
The largest increase in export production in the eastern Pacific of the
last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of
major climatic and oceanographic reorganization in the region. Here, we
investigate the causes of this event using reconstructions of export
production, nutrient supply and oceanic conditions across the
Pl...
Antarctic sea ice impacts on the ocean-atmosphere heat and gas fluxes, the formation of deep and intermediate waters, the nutrient distribution and primary productivity, the so-called ‘biological carbon pump’, one of the most active in the global ocean. In this study, we explore the link between sea ice dynamic, biological production and nutrient c...
The West Antarctic ice sheet is particularly sensitive to global warming and its evolution and impact on global climate over the next few decades remains difficult to predict. In this context, investigating past sea ice conditions around Antarctica is of primary importance. Here, we document changes in sea ice presence, upper water column temperatu...
The West Antarctic ice sheet is particularly sensitive to global warming and its evolution and impact on global climate over the next few decades remains difficult to predict. In this context, investigating past sea ice conditions around Antarctica is of primary importance. Here, we document changes in sea ice presence, upper water column temperatu...
The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pl...
The global late Pliocene/early Pleistocene cooling (~3.0-2.0 million
years ago, Ma) concurred with extremely high diatom and biogenic opal
production in most of the major coastal upwelling regions. This
phenomenon was particularly pronounced in the Benguela Upwelling System
(BUS), off Namibia, where it is known as the Matuyama Diatom Maximum
(MDM)....
The global late Pliocene/early Pleistocene cooling (~3.0–2.0 million years ago, Ma) concurred with extremely high diatom and biogenic opal production in most of the major coastal upwelling regions. This phenomenon was particularly pronounced in the Benguela Upwelling System (BUS), off Namibia, where it is known as the Matuyama Diatom Maximum (MDM)....
Future climate change is predicted to significantly impact ocean
circulation and, potentially, to reduce ocean oxygenation.
Paradoxically, the transition from the warm Pliocene, often held as an
analog for a future, warmer Earth, to the cool Pleistocene appears to
accompany a decrease in intermediate water oxygenation. The
Plio-Pleistocene cooling...
Ce projet vise à développer de nouveaux marqueurs pour explorer le lien entre la glace de mer et les écosystèmes marins polaires. Un ensemble de molécules de type isoprénoïdes hautement ramifiés (HBIs) est en effet synthétisé par certaines diatomées. Alors que certaines espèces de diatomées associées à la glace de mer produisent un HBI di-insaturé...
When comparing new sea surface temperature (SST) records between the western and eastern equatorial Pacific spanning the last 3.2 Ma, we found that the zonal temperature gradient over the entire tropical Pacific irreversibly increased by 3 to 4 °C from 2.2 to 2.0 Ma. Here, we suggest a pronounced increase in atmospheric circulation from a weak to a...
No abstract available.
doi:10.2204/iodp.sd.9.11.2010
The warm Pliocene epoch (5–3 million years ago) is often cited as a good analog for the near future climate because of its striking resemblance to the predictions of the “Intergovernmental Panel on Climate Change” for the next decades. Indeed, relative to today, during the Pliocene epoch, surface temperatures were 3–4°C warmer, sea level was about...
When comparing new sea surface temperature (SST) records between the western and eastern equatorial Pacific spanning the last 3.2 Ma, we found that the zonal temperature gradient over the entire tropical Pacific irreversibly increased by 3 to 4 °C from 2.2 to 2.0 Ma. Here, we suggest a pronounced increase in atmospheric circulation from a weak to a...
In this study we present combined high-resolution records of sea surface temperature (SST), phytoplankton productivity, and nutrient cycling in the Benguela Upwelling System (BUS) for the past 3.5 Ma. The SST record provided evidence that upwelling activity off Namibia mainly intensified ca. 2.4-2.0 Ma ago in response to the cooling of the Southern...
In this study we present combined high-resolution records of sea surface temperature (SST), phytoplankton productivity, and nutrient cycling in the Benguela Upwelling System (BUS) for the past 3.5 Ma. The SST record provided evidence that upwelling activity off Namibia mainly intensified ca. 2.4-2.0 Ma ago in response to the cooling of the Southern...
Most high-southern latitude records of carbon and nitrogen isotopic ratios and elemental ratios are from the Antarctic and Polar Front zones, thus hindering a comprehensive view of nutrient cycling in the Southern Ocean. We present, for the first time, two records from the Subantarctic Zone and the southern Subtropical Zone of the Indian Ocean. The...
Projects
Project (1)
The PHC-STAR MEDKO project between EPOC (EPHE, University of Bordeaux, France) and Hanyang University (South Korea) aims to document and understand the response of the Mediterranean and Eastern Seas to the abrupt climate changes of the last glacial period. Two cores are being analyzed: one from the Gulf of Cadiz (Mediterranean region, core MD99-3339) and one from the Eastern Sea (core ES14 GC01). The analysis of alkenones, branched tetraethers lipids (GDGT) and the resulting computed index TEX86 will provide a robust reconstruction of regional oceanic parameters (sea surface and subsurface temperatures), while pollen, n-alkanes (wax lipids) and their associated carbon isotopes (δ13C), GDGT-BIT86 index as well as trace elements composition will give insights into atmospheric climate changes (vegetation and precipitation).
