Our Common Future Under Climate Change

International Scientific Conference 7-10 JULY 2015 Paris, France

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Wednesday 8 July - 16:30-18:00 UNESCO Bonvin - ROOM XIV

1110 - Observing the changing ocean climate

Parallel Session

Lead Convener(s): A. Fischer (Intergovernmental Oceanographic Commission of UNESCO, Paris, France)

Convener(s): B. Dewitte (IRD, Toulouse Cedex 9, France), V. Garçon (CNRS, Toulouse Cedex 9, France), P.Y. Le Traon (MERCATOR OCEAN, Brest, France), A. Melet (CNES/LEGOS, Toulouse, France)

16:30

Climate and Ocean: past, current and future changes and variability - a challenge for observations, models and assessment

M. Visbeck (GEOMAR & Kiel University, Kiel, Germany)

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Climate and Ocean: past, current and future changes and variability - a challenge for observations, models and assessment

M. Visbeck (1)
(1) GEOMAR & Kiel University, Kiel, Germany

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The ocean covers more than 70 % of the surface of our planet and plays a key role in supporting life on earth. It hosts the most diverse and important ecosystems, and contributes to global and regional elemental cycling. The ocean regulates our climate, and through climate, habitats are shaped that allowed humans to thrive and develop our societies. The marine system provides us with natural resources such as food, materials, substances, and energy. Furthermore, the oceans and the regional seas are essential for international trade, recreational and cultural activities.

 

A growing world population with increasing levels of affluence has had a noticeable impact on the environment causing ‘global change’. In the area of climate in particular increasing levels of greenhouse gas emissions have altered the planetary heat balanced and caused changes in both global and regional climate.

 

The Intergovernmental Panel for Climate Change (IPCC) most recent assessment reminds us that: “The ocean’s heat capacity is about 1,000 times larger than that of the atmosphere, and the oceans net heat uptake since 1960 is around 20 times greater than that of the atmosphere.”  About 90% of this extra heat has been stored in the ocean.  The ocean plays a crucial role in climate change, in particular in variations on seasonal to decadal time scales. One example is sea level: the addition of heat and freshwater flux from the melting glaciers and ice sheets have cause the sea level to rise. The latest IPCC gives a best estimate rate for 1961 to 2003 as 1.8 ± 0.5 mm yr–1. However, the regional differences are large and the interplay between natural climate and ocean variability and change remains a challenge for assessments.

 

Finally the IPCC addresses the adequacy of ocean observing systems: “Many ocean observations are poorly sampled in space and time, and regional distributions often are quite heterogeneous. Furthermore, the observational records only cover a relatively short period of time (e.g., the 1950s to the present). Many of the observed changes have significant decadal variability associated with them, and in some cases decadal variability and/or poor sampling may prevent detection of long-term trends. When time series of oceanic parameters are considered, linear trends are often computed in order to quantify the observed long-term changes; however, this does not imply that the original signal is best represented by a linear increase in time.” Thus this provides an opportunity for the global ocean observing community to rise to the challenge and deliver a fit-for-purpose more integrated, more cost effective and more sustained ocean observing system.

 

16:45

How do we observe and model the changing ocean physics, biogeochemistry, and ecosystems?

N. Pinardi (University of Bologna, Bologna, Italy)

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How do we observe and model the changing ocean physics, biogeochemistry, and ecosystems?

N. Pinardi (1)
(1) University of Bologna, Department of Physics and Astronomy, Bologna, Italy

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The oceans play a crucial role as a climate regulator, and changing ocean physics, biogeochemistry, and biology have direct impact on human well-being through hazards and ecosystem services changes.

Long-term, globally-coordinated, and high-quality sustained ocean observations are required to understand and model the role of the ocean in the earth’s climate, to monitor ocean change, and to provide initial conditions to predict the evolution of climate on scales including seasonal, decadal, and centennial. Building on national efforts, these observations are internationally coordinated through the Global Ocean Observing System and the Joint WMO-IOC Technical Commission for Oceanography and Marine Meteorology, building on the processes of a common Framework for Ocean Observing devised and adopted by the ocean observing community.

Observations and models combine to provide the best possible estimates of the present and future state of the ocean. These observations and forecasts inform decision-making about coastal protection, the marine economy, long-term changes in patterns of drought and flood, and the human consequences linked to climate change. Our confidence in the observations and models has increased over time, even as some key critical knowledge gaps remain.

17:00

Introduction to a panel of contributed short talks on ocean observing challenges, gaps and recommendations - covering different ocean regions and regimes, in situ and satellite observations, sustainability issues, and the link between sustained ocean observations and modeling for climate research, projections, and services.

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Introduction to a panel of contributed short talks on ocean observing challenges, gaps and recommendations - covering different ocean regions and regimes, in situ and satellite observations, sustainability issues, and the link between sustained ocean observations and modeling for climate research, projections, and services.
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17:02

Pacific western boundary currents and their roles in climate

17:02 Pacific western boundary currents and their roles in climate D. Hu, (Institute of Oceanology, CAS, Qingdao, China), L. Wu, (Qingdao Collaborative Innovation Center of Marine Science and Technology, OUC, Qingdao, China), W. Cai (CSIRO, Melbourne, Australia), G. A. Sen (The University of New South Wales, Sydney, Australia), A. Ganachaud (IRD/LEGOS, Toulouse, France), B. Qiu, (University of Hawaii at Manoa, Honolulu, United States of America), A. Gordon, (Lamont-Doherty Earth Observatory, New York, United States of America), X. Lin, (Qingdao Collaborative Innovation Center of Marine Science and Technology, OUC, Qingdao, China), Z. Chen, (Qingdao Collaborative Innovation Center of Marine Science and Technology, OUC, Qingdao, China), S. Hu, (Institute of Oceanology, CAS, Qingdao, China), G. Wang, (CSIRO, Melbourne, Australia), Q. Wang, (Institute of Oceanology, CAS, Qingdao, China), J. Sprintall, (Scripps Institution of Oceanography, La Jolla, United States of America), T. Qu, (SOEST, University of Hawaii, Honolulu, United States of America), Y. Kashino, (Japan Agency for Marine- Earth Science and Technology (JAMSTEC), Kanagawa, Japan), F. Wang, (Institute of Oceanology, CAS, Qingdao, China), W. Kessler, (NOAA, Seattle, United States of America), A. Melet (CNES/LEGOS, Toulouse, France)

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Pacific western boundary currents and their roles in climate

A. Ganachaud (1) ; D. Hu, (2) ; L. Wu, (3) ; W. Cai (4) ; GA. Sen (5) ; B. Qiu, (6) ; A. Gordon, (7) ; X. Lin, (3) ; Z. Chen, (3) ; S. Hu, (2) ; G. Wang, (8) ; Q. Wang, (2) ; J. Sprintall, (9) ; T. Qu, (10) ; Y. Kashino, (11) ; F. Wang, (2) ; W. Kessler, (12) ; A. Melet (13)
(1) IRD/LEGOS, Toulouse, France; (2) Institute of Oceanology, CAS, Key laboratory of ocean circulation and waves, Qingdao, China; (3) Qingdao Collaborative Innovation Center of Marine Science and Technology, OUC, Physical oceanography laboratory, Qingdao, China; (4) CSIRO, Melbourne, Australia; (5) The University of New South Wales, Australian research council (arc) centre of excellence for climate system science, Sydney, Australia; (6) University of Hawaii at Manoa, Department of oceanography, Honolulu, United States of America; (7) Lamont-Doherty Earth Observatory, Earth institute at columbia university, New York, United States of America; (8) CSIRO, Marine and atmospheric research, Melbourne, Australia; (9) Scripps Institution of Oceanography, La Jolla, United States of America; (10) SOEST, University of Hawaii, Iprc, department of oceanography, Honolulu, United States of America; (11) Japan Agency for Marine- Earth Science and Technology (JAMSTEC), Center for earth information science and technology, Kanagawa, Japan; (12) NOAA, Pacific marine environmental laboratory, Seattle, United States of America; (13) CNES/LEGOS, Toulouse, France

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Pacific Ocean western boundary currents and the interlinked equatorial Pacific circulation system were among the first to be explored by pioneering oceanographers. The widely accepted but poorly quantified importance of these currents - in processes such as the El Niño-Southern Oscillation, Pacific Decadal Oscillation and Indonesian Throughflow - has triggered renewed interest, with ongoing efforts seeking to understand the heat and mass balances of the equatorial Pacific, and possible changes associated with greenhouse-induced climate change. Only a concerted international effort through WCRP/CLIVAR will close the observational, theoretical and technical gaps currently limiting a robust answer to these elusive questions. This work will present a review of the boundary current characteristics, variations and their effects on local and remote climate, as well as their future projections. 

17:09

Preliminary results from the international South Atlantic Meridional Overturning Circulation (SAMOC) Initiative

S. Speich (Ecolne normale superieure, paris, France), S. Garzoli (NOAA, Miami, United States of America), A. Piola (Servicio de Hidrografia Naval, Buenos Aires, Argentina), E. Campos (Universidade de Sao Paolo, Sao Paolo, Brazil)

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Preliminary results from the international South Atlantic Meridional Overturning Circulation (SAMOC) Initiative

S. Speich (1) ; S. Garzoli (2) ; A. Piola (3) ; E. Campos (4)
(1) Ecolne normale superieure, Departement de geosciences, paris, France; (2) NOAA, Aoml - phod, Miami, United States of America; (3) Servicio de Hidrografia Naval, Buenos Aires, Argentina; (4) Universidade de Sao Paolo, Instituto oceanográfico, Sao Paolo, Brazil

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Within the MOC, the South Atlantic Ocean plays a key role as a nexus for water masses formed elsewhere and en-route to remote regions of the global ocean. Because of this important interbasin exchanges, the South Atlantic Ocean is the only major ocean basin that transports heat from the pole towards the equator. However, the South Atlantic is not merely a passive conduit for remotely formed water masses. Indeed, within this basin water masses are significantly altered by local air-sea interactions and diapycnal/isopycnal fluxes, particularly in regions of intense mesoscale activity and steep topography. These contributions have been shown to have a crucial role in the strength of the MOC in paleoceanographic and modelling studies.

The monitoring of the North Atlantic portion of the MOC has been ongoing for a decade now through the RAPID/MOCHA/WBTS program as well as other national and international initiatives. They all provide a scope for understanding the MOC variability in that region. Given the complex, multibasin nature of the MOC, achieving a more complete understanding of its behaviour and changes requires a more comprehensive observing system, one that extends across neighbouring ocean basins as the one we are developing for the South Atlantic within the CLIVAR SAMOC initiative.

In this presentation, we will discuss the preliminary results on estimates of the daily MOC strength at 35°S during a ~20 month long pilot array of mooring as well as model outputs and Argo data. The MOC variability show to be as large as that at 26N, with both eastern and western boundary flows contributing equally to the variance.

The full array was re-established in the fall of 2013 in collaboration with France, Brazil, Argentina and South Africa.

17:16

Exceptional 20th-Century slowdown in Atlantic Ocean overturning circulation

S. Rahmstorf (Potsdam Institute for Climate Impact Research, Potsdam, Germany), J. Box, (Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark), G. Feulner, (Potsdam Institute for Climate Impact Research, Potsdam, Germany), M. Mann, (Pennsylvania State University, University Park, United States of America), A. Robinson, (Universidad Complutense de Madrid, Madrid, Spain), S. Rutherford, (Roger Williams University, Bristol, United States of America), E. Schaffernicht, (Potsdam Institute for Climate Impact Research, Potsdam, Germany)

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Exceptional 20th-Century slowdown in Atlantic Ocean overturning circulation

S. Rahmstorf (1) ; J. Box, (2) ; G. Feulner, (1) ; M. Mann, (3) ; A. Robinson, (4) ; S. Rutherford, (5) ; E. Schaffernicht, (1)
(1) Potsdam Institute for Climate Impact Research, Potsdam, Germany; (2) Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark; (3) Pennsylvania State University, University Park, United States of America; (4) Universidad Complutense de Madrid, Madrid, Spain; (5) Roger Williams University, Bristol, United States of America

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Possible changes in Atlantic meridional overturning circulation (AMOC) provide a key source of uncertainty regarding future climate change. Maps of temperature trends over the twentieth century show a conspicuous region of cooling in the northern Atlantic. Here we present multiple lines of evidence suggesting that this cooling may be due to a reduction in the AMOC over the twentieth century and particularly after 1970. Since 1990 the AMOC seems to have partly recovered. This time evolution is consistently suggested by an AMOC index based on sea surface temperatures, by the hemispheric temperature difference, by coral-based proxies and by oceanic measurements. We discuss a possible contribution of the melting of the Greenland Ice Sheet to the slowdown. Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event in the past millennium (p>0.99). Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC.

Reference: Rahmstorf et al, Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation, Nature Climate Change (in the press)

17:23

Variability of the Meridional Overturning Circulation observed since 1993 across the A25-OVIDE section in the North Atlantic subpolar gyre, and its impact on the CO2 physical pump

P. Lherminier (Ifremer, PLOUZANE, France), H. Mercier (CNRS, PLOUZANE, France), N. Daniault, (Université de Bretagne Occidentale, BREST, France), F. F. Perez, (Instituto Investigaciones Marinas (CSIC), VIGO, Spain), P. Zunino, (Ifremer, PLOUZANE, France), M. I. García-Ibáñez (Instituto Investigaciones Marinas (CSIC), VIGO, Spain), A. Sarafanov, (P.P. Shirshov Institute of Oceanology, Moscow, Russia), F. Gaillard (Ifremer, PLOUZANE, France), P. Morin (IPEV, PLOUZANE, France), A. F. Rios (Instituto Investigaciones Marinas (CSIC), VIGO, Spain), D. Desbruyères (National Oceanography Centre, Southampton, United Kingdom), A. Falina (P.P. Shirshov Institute of Oceanology, Moscow, Russia), B. Ferron (CNRS, PLOUZANE, France), T. Huck (CNRS, Brest, France), V. Thierry (Ifremer, PLOUZANE, France)

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Variability of the Meridional Overturning Circulation observed since 1993 across the A25-OVIDE section in the North Atlantic subpolar gyre, and its impact on the CO2 physical pump

P. Lherminier (1) ; N. Daniault, (2) ; FF. Perez, (3) ; P. Zunino, (1) ; H. Mercier (4) ; A. Sarafanov, (5) ; F. Gaillard (1) ; P. Morin (6) ; AF. Rios (3) ; D. Desbruyères (7) ; A. Falina (5) ; B. Ferron (4) ; T. Huck (8) ; V. Thierry (1) ; MI. García-Ibáñez (3)
(1) Ifremer, Laboratoire de Physique des Océans, PLOUZANE, France; (2) Université de Bretagne Occidentale, Laboratoire de physique des océans, BREST, France; (3) Instituto Investigaciones Marinas (CSIC), Departamento de oceanografia, VIGO, Spain; (4) CNRS, Laboratoire de physique des océans, PLOUZANE, France; (5) P.P. Shirshov Institute of Oceanology, Moscow, Russia; (6) IPEV, Scientific direction, PLOUZANE, France; (7) National Oceanography Centre, Southampton, United Kingdom; (8) CNRS, Laboratoire de physique des océans, Brest, France

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The meridional overturning circulation (MOC) transports heat from the subtropics to high latitudes and hence plays an important role in the Earth’s climate. A region crucial for the MOC is the northern North Atlantic and the adjacent Nordic Seas, where waters transported northwards in the MOC upper limb progressively cool, gain density and eventually sink into the southward flowing lower limb. Here we will discuss the variability of the subpolar gyre circulation, the MOC and heat transport as quantified from a joint analysis of hydrographic and velocity data from eight repeats of the Greenland to Portugal OVIDE section (1997–2014), satellite altimetry and ARGO float measurements. For each repeat of the OVIDE section, the full-depth absolute circulation and transports were assessed using an inverse model constrained by ship-mounted Acoustic Doppler Current Profiler data and by an overall mass balance. The obtained circulation patterns revealed remarkable transport changes in the whole water column and evidenced large variations (up to 50% of the lowest value) in the magnitude of the MOC computed in density coordinates (MOCσ). The extent and timescales of the MOCσ variability in 1993–2014 were then evaluated using a monthly MOCσ index built upon altimetry and ARGO data at the OVIDE section location. The MOCσ index, validated by the good agreement with the estimates from repeat hydrographic surveys, shows a large variability on monthly to decadal time scales, with an inter-annual variability from less than 15 Sv to about 25 Sv (1 Sv = 1,000,000 m3s-1). The heat transport estimated from the repeated hydrographic OVIDE sections varies between 0.29 and 0.70 ± 0.05 PW and is linearly related to the MOCσ intensity.

The uptake of atmospheric carbon dioxide in the subpolar North Atlantic Ocean declined rapidly between 1990 and 2006. This reduction in CO2 uptake was related to warming at the sea surface, which—according to model simulations—coincided with a reduction in the Atlantic MOC. Here, we use the observed oceanic transport of volume, heat and carbon dioxide to track the CO2 uptake in the subtropical and subpolar regions of the North Atlantic Ocean over the past two decades. We separate anthropogenic carbon—derived from human activities—from natural carbon by assuming that the latter corresponds to a pre-industrial atmosphere, whereas the remaining is anthropogenic. We find that the uptake of anthropogenic carbon dioxide occurred almost exclusively in the subtropical gyre. In contrast, natural carbon dioxide uptake—which results from natural Earth system processes—dominated in the subpolar gyre. We attribute the weakening of contemporary carbon dioxide uptake between 1997 and 2006 in the subpolar North Atlantic to a reduction in the natural component. We show that the slowdown of the MOC was largely responsible for the reduction in carbon uptake, through a reduction of oceanic heat loss to the atmosphere, and for the concomitant decline in anthropogenic carbon dioxide storage in subpolar waters. To understand the mechanisms controlling the variability of the transport of anthropogenic carbon (Tcant) across the subpolar gyre, we decomposed it according to the net, the diapycnal and the isopycnal circulation. The diapycnal component is found to be the main driver of the Tcant variability. From this analysis, we propose a simplified estimator for the variability of Tcant based on the intensity of the MOCσ and on the difference of anthropogenic carbon dioxide concentration between the upper and lower limb of the MOCσ (ΔCant). This estimator shows a good consistency with the diapycnal component of Tcant, and helps to disentangle the effect of the variability of both the circulation and the Cant increase on the Tcant variability. We find that ΔCant keeps increasing over the past decade, and it is very likely that the continuous Cant increase in the water masses will cause an increase in Tcant across the subpolar North Atlantic Ocean at long timescale. Nevertheless, at the timescale analyzed here (1997–2010), the MOCσ controls the Tcant variability, blurring any Tcant trend.

17:30

Oxygen Minimum Zone (OMZ) dynamics in the context of the ocean deoxygenation: the case off Peru from the AMOP «Activities of research dedicated to the Minimum of Oxygen in the eastern Pacific» project

A. Paulmier (LEGOS, TOULOUSE, France), M. Bretagnon (LEGOS, Toulouse, France), B. Dewitte (LEGOS, Toulouse, France), V. Garçon (CNRS, Toulouse Cedex 9, France), C. Maes (IRD-CNRS-Ifremer-UBO, Plouzane, France), F. Campos (UNAC, CALLAO, Peru), F.-G. Augusto (UPCH, LIMA, Peru), K. Mosquera (IGP, LIMA, Peru), O. Vergara (LEGOS, Toulouse, France), C. Barus (LEGOS, Toulouse, France), L. Coppola (OOV, VILLEFRANCHE/S/MER, France), O. Depretz-De-Gesincourt (Parc Instrumental DT-INSU/CNRS, PLOUZANE, France), E. Garcia-Robledo (University of Aahrus, AAHRUS, Denmark), J. Grelet (US IMAGO, PLOUZANE, France), S. Illig (LEGOS, Toulouse, France), I. Montes (IGP, LIMA, Peru), N. Leblond (CNRS, Villefranche sur mer, France), A. Oschlies (GEOMAR, Kiel, Germany), J. Quispe (IMARPE, CALLAO, Peru), J. Sudre (LEGOS, Toulouse, France)

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Oxygen Minimum Zone (OMZ) dynamics in the context of the ocean deoxygenation: the case off Peru from the AMOP «Activities of research dedicated to the Minimum of Oxygen in the eastern Pacific» project

A. Paulmier (1) ; M. Bretagnon (2) ; B. Dewitte (2) ; V. Garçon (3) ; C. Maes (4) ; F. Campos (5) ; FG. Augusto (6) ; K. Mosquera (7) ; O. Vergara (2) ; C. Barus (2) ; L. Coppola (8) ; O. Depretz-De-Gesincourt (9) ; E. Garcia-Robledo (10) ; J. Grelet (11) ; S. Illig (2) ; I. Montes (7) ; N. Leblond (12) ; A. Oschlies (13) ; J. Quispe (14) ; J. Sudre (2)
(1) LEGOS, SYSCO2 team, TOULOUSE, France; (2) LEGOS, Toulouse, France; (3) CNRS, LEGOS, Toulouse Cedex 9, France; (4) IRD-CNRS-Ifremer-UBO, Laboratoire de physique des océans, Plouzane, France; (5) UNAC, CALLAO, Peru; (6) UPCH, LIMA, Peru; (7) IGP, LIMA, Peru; (8) OOV, VILLEFRANCHE/S/MER, France; (9) Parc Instrumental DT-INSU/CNRS, PLOUZANE, France; (10) University of Aahrus, AAHRUS, Denmark; (11) US IMAGO, PLOUZANE, France; (12) CNRS, Lov, Villefranche sur mer, France; (13) GEOMAR, Kiel, Germany; (14) IMARPE, CALLAO, Peru

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Oxygen Minimum Zones (OMZs), defined as suboxic (O2<20 µmol/L) subsurface layer and mainly associated with Eastern Boundary Upwelling Systems (EBUS), would contract and expand during cold and warming periods, respectively. In the current context of the ocean deoxygenation, OMZs are known to play a key-role on the evolution of climate (greenhouse gases) and on the ecosystems and fisheries (nitrogen loss, respiratory barrier, sulfidic events) at both local and global scales. The objective of the AMOP project (“Activities of research dedicated to the Minimum of Oxygen in the eastern Pacific”) is to provide an estimate of physical and biological processes contributing to the O2 budget off Peru. The central hypothesis is that the physical and biogeochemical O2 contribution to the OMZ maintaining and variability depends on the characteristics of the different OMZ layers, where the oxycline behaves as an engine of an intense but intermittent biogeochemical and ecosystem activity. The project is focused in one of the most intense and shallow OMZs associated with the most productive upwelling system (10 % of the world fisheries), the Peruvian OMZ. The trans-disciplinary approach is based on a cruise that took place in  January-February 2014 off Peru and that consisted in 8 fixed stations (~54 h) on 3 transects at 7°S, 12°S and 14°S with the RV Atalante. The cruise also benefited from experimental development (instrumentation, sensors: argo-floats experiments; drifting lines; a trimaran dedicated to ocean-atmosphere exchanges; nanomolar O2 measurements). AMOP has also led to the deployment of the first long term (2013-2014) subsurface mooring off Peru providing unprecedented information of the OMZ variability at diurnal to intraseasonal timescales, and invaluable data for the validation of a high resolution regional ocean-atmosphere-biogeochemistry coupled modeling platform under development within the project. This French-Peruvian-German project involving 5 other countries (~90 participants) is viewed as one of the main pilot projects of the SOLAS Mid Term Strategy Initiative on OMZ-EBUS. In this presentation, preliminary results of the project will be presented both on observations and modeling, illustrating current challenges for the investigation of OMZ dynamics in Eastern Boundary current systems.

17:37

Discussion and Q&A session

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Discussion and Q&A session
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17:52

Summary and adoption of synthesis recommendations

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Summary and adoption of synthesis recommendations
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