Anthropogenic carbon in the eastern South Pacific Ocean

International audienceWe present results from the BIOSOPE cruise in the eastern South Pacific Ocean. In particular, we present estimates of the anthropogenic carbon CantTrOCA distribution in this area using the TrOCA method recently developed by Touratier and Goyet (2004a, b) and Touratier et al. (2007). We study the distribution of this anthropogenic carbon taking into account of the hydrodynamic characteristics of this region. We then compare these results with earlier estimates in nearby areas of the anthropogenic carbon as well as other anthropogenic tracer (CFC-11). The highest concentrations of CantTrOCA are located around 13° S 132° W and 32° S 91° W, and their concentrations are larger than 80 µmol kg-1 and 70 µmol kg-1, respectively. The lowest concentrations were observed below 800 m depths (=2 µ mol kg-1) and at the Oxygen Minimum Zones (OMZ), mainly around 140° W (-1). The comparison with earlier work in nearby areas provides a general trend and indicates that the results presented here are in general agreement with previous knowledge. This work further improves our understanding on the penetration of anthropogenic carbon in the eastern Pacific Ocean

Design of Sampling Strategy Measurements of Co2/Carbonate Properties

International audienceIn order to study a (terrestrial or oceanic) field area, scientists need first to design a sampling strategy. At first, when nothing is known about this field, there is no other choice than to sample as much as possible wherever it is possible. Then, as something become known about some properties of the field, it becomes possible to use mathematical equations to design a scientifically sound sampling strategy based upon the various constraints (aimed accuracy, number of samples/measurements, etc.), of the study. Based upon available sea-surface salinity and sea-surface temperature data, this work shows a practical and simple way to design a sampling strategy with known accuracy for total CO2 and total alkalinity measurements in sea-surface waters. The results indicate the need to continue to sample the sea-surface waters but with specific designs of sampling strategy to reach the scientific objectives with known maximum error

Determination of discrete sampling locations minimizing both the number of samples and the maximum interpolation error: Application to measurements of carbonate chemistry in surface ocean

Over the past three decades, a variety of programs have conducted extensive measurements of ocean properties at fixed stations throughout the water column, as well as in the surface ocean via oceanographic ships and ships of opportunity. Ships of opportunity were particularly used to determine the air-sea CO2 fluxes from automated measurements of sea-surface temperature, salinity, and CO2 fugacity. These underway measurements, often recorded at a frequency of every minute, generate large data files that need to be quality controlled, stored and analyzed. For practical use these data are often binned by 1° latitude x 1° longitude. Unfortunately, by doing so, there is a consequential loss of accuracy for these data sets. Here, using the original 2010 underway data sets of sea-surface temperature, sea-surface salinity, total alkalinity and total inorganic carbon, along the cruise track from Hobart (Tasmania) to Dumont D'Urville (Antarctica), we show what would had been a more appropriate sampling strategy for each of these properties, maintaining their full measurement accuracy, while improving their interpolation accuracy. Furthermore, this analysis illustrates a general methodology for objectively determining, under suitable conditions, the appropriate locations for each property measurement according to a required accuracy. These results should greatly facilitate future cruise preparation and reduce the cost of measurements, while improving their scientific value

Characterization of ocean biogeochemical processes: a generalized total least-squares estimator of the Redfield ratios

International audienceThe chemical composition of the global ocean is governed by biological, chemical and physical processes. These processes interact with each other so that the concentrations of carbon dioxide, oxygen, nitrate and phosphate vary in constant proportions, referred to as the Redfield ratios. We build here the Generalized Total Least-Squares estimator of these ratios. The interest of our approach is twofold: it respects the hydrological characteristics of the studied areas, and it can be applied identically in any area where enough data are available. The tests performed on the Atlantic Ocean high-light a variability of the Redfield ratios, both with geographical location and with depth. This variability emphasizes the importance of local and accurate estimates of Redfield ratios

Ocean salinity from satellite-derived temperature in the Antarctic Ocean

International audienc

Distribution and inventory of anthropogenic CO₂ in the Southern Ocean: Comparison of three data-based methods

The Southern Ocean is thought to play an important role in the context of global warming and anthropogenic emissions of CO 2 due to its high sensitivity to both climate change and changes in the carbon cycle. Assessing the penetration of anthropogenic CO 2 (C ant) into the Southern Ocean is therefore highly relevant to reduce the uncertainties attached to both the present knowledge of anthropogenic carbon inventories and predictions made by current ocean carbon models. This study compares different databased approaches for estimating the distribution of C ant in the ocean: a recently developed method based on the composite Tracer Combining Oxygen, Inorganic Carbon, and Total Alkalinity (TrOCA) and the ''historical'' back-calculation methods (the so-called DC* and preformed dissolved inorganic carbon methods). Note that the back-calculation technique requires special care when used in the Southern Ocean, where surface oxygen can significantly deviate from equilibrium with the atmosphere. All three methods were applied to data collected at the Indian-Atlantic boundary (WOCE line I6), where significant transient tracer concentrations were observed in deep and bottom waters. North of 50°S, distribution and inventories of C ant are coherent with previous data-based and model estimates, but we found larger storage of C ant south of 50°S as compared to the midlatitude region. In that, our results disagree with most previous estimates and suggest that the global inventory of anthropogenic CO 2 in the Southern Ocean could be much larger than what is currently believed

Plastic strain of cobalt-based hardfacings under friction loading

20th International Wear of Materials Conference (WOM), Toronto, CANADA, APR 12-16, 2015International audienceAeronautic forging dies are subjected to very high loads and temperatures for a long contact time between the pre-heated parts and dies. Cobalt-based hardfacings are commonly deposited on dies and their main wear mechanism is large plastic deformation of the die radii. This paper deals with the wear damage mechanisms of three different cobalt-based hardfacings: Stellite 21 deposited by a MIG process, Stellite 21 and Stellite 6 deposited by a LASER process. The tribological tests are carried out on a high load Ring on Disc tribometer at room temperature. The postmortem investigations are undertaken by SEM observations, micro-hardness measurements as well as by X-ray diffraction analyses. Results show that the increase of the hardness, in order to improve the wear behaviour, can be achieved by a higher carbon content and by a lesser iron dilution that depends on the deposition process. A very important work-hardening, up to 90%, is also observed under sliding conditions and a relationship is established between the increase of the micro-hardness and the plastic strain level. Two different plastic strain mechanisms are observed. For high (MIG) or low (LASER) iron dilution levels, the plastic strain causes respectively a reorientation of grains or a FCC to HCP phase transformation; the latter being associated with a lower friction coefficient

Spatial and temporal variability of the physical, carbonate and CO<SUB>2</SUB> properties in the Southern Ocean surface waters during austral summer (2005-2019)

International audienceIn situ measurements of sea surface temperature (SST), salinity (SSS), Total Alkalinity (AT) and Total Carbon (CT) were obtained during austral summer (mid-February to mid-March) from 2005 to 2019 in the Southern Ocean (SO), along a transect between Hobart, Tasmania and Dumont d'Urville French Antarctic Station. The studied transect is divided in four regions from North to South: the Subtropical Zone (STZ), the Subantarctic Region (SAR), the Antarctic Region (AAR) and the Coastal Antarctic Zone (CAZ). Latitudinal distribution of measured SST, SSS, AT, CT as well as calculated pH, CO2 parameters (seawater fugacity of CO2 (fCO2sw), difference between seawater and atmospheric fCO2 (ΔfCO2), CO2 flux (FCO2)) and satellite-derived Chlorophyll a (Chl-a) are discussed. We show that the variability of physical and carbonate parameters in the STZ and north of the SAR are related to the mesoscale activity. In the CAZ, the freshwater inputs from sea-ice melting strongly impact the variability of all parameters. The comparison between physical and carbonate parameters highlights that AT and CT are directly related to the latitudinal variability of SST and SSS. Study of the CO2 parameters shows that the transect is a sink of CO2 during February and March, with a mean FCO2 of -4.0 ± 2.8 mmol m-2 d-1. The most negative values of FCO2 are found in the STZ and SAR north of 50°S and in the AAR south of 62°S, where biological activity is high. New simple empirical relationships are developed for AT from SST and SSS and for CT using SST, SSS and atmospheric fCO2 (fCO2atm) for the austral summer in the studied area. Using high resolution SSS and SST from the SURVOSTRAL program, trends of AT and CT are determined in the SAR and the AAR from 2005 to 2019. SST, SSS and AT increase over this period in the SAR, which might be explained by the southward migration of the Subtropical Front. In the AAR, no clear trend is detected. CT increases by 1.0 ± 0.2 and 0.8 ± 0.3 μmol kg-1 yr-1 in the SAR and AAR respectively. The trend in the AAR is attributed to the increase in anthropogenic CO2 emissions in the atmosphere while, in the SAR, hydrographic changes also contribute to the increase. Using the coefficient associated with fCO2atm in the equation of CT, we estimate the impact of atmospheric CO2 increase on CT at 1.18 ± 0.14 μmol kg-1 yr-1 and 1.07 ± 0.13 μmol kg-1 yr-1 in the SAR and AAR respectively. Decreases in pH are observed in both regions (-0.0018 ± 0.0001 and -0.0026 ± 0.0003 yr-1 in the SAR and AAR respectively), indicating the sensitivity of surface waters in the area towards the development of ocean acidification processes under rising anthropogenic emissions

Time variability of the north-western Mediterranean Sea pH over 1995–2011

International audienceFactors controlling ocean acidification and its temporal variations were studied over the 1995–2011 period at the Dyfamed site at 10 m depth, in the North Mediterranean Sea. The results indicated a mean annual decrease of 0.003 ± 0.001 pH units on the seawater scale. The seasonal variability was characterized by a pH decrease during springtime and a strong pH increase in late fall. Anthropogenic CO2 (CANT) absorption by the ocean was the key driver of seawater acidification in this region, accounting for about 70% of the observed drop in pH, followed by water temperature (about 30%). The total inorganic carbon (CT) data showed a CT increase of 30.0 ± 1.0 μmol kg−1 per decade. This decadal increase is mainly due to the CANT penetration (43.2 μmol kg−1 per decade) in surface waters, which is mitigated for by relatively small opposing changes in CT due to physical and biological processes

A comparison of Multiple Non-linear regression and neural network techniques for sea surface salinity estimation in the tropical Atlantic ocean based on satellite data

International audienceUsing measurements of Sea Surface Salinity and Sea Surface Temperature in the Western Tropical Atlantic Ocean, from 2003 to 2007 and 2009, we compare two approaches for estimating Sea Surface Salinity : Multiple Non-linear Regression and Multi Layer Perceptron. In the first experiment, we use 18,300 in situ data points to establish the two models, and 503 points for testing their extrapo-lation. In the second experiment, we use 15,668 in situ measurements for establishing the models, and 3,232 data points to test their interpolation. The results show that the Multiple Non-linear Regression is an admissible solution whether it be interpolation or extrapolation. Yet, the Multi Layer Perceptron can be used only for interpolation. Résumé. En utilisant des mesures de Salinité et de Températurè a la surface de la mer, dans l'ouest de l' océan Atlantique tropical, de 2003 a 2007 puis 2009, on compare deux approches pour la prédiction de la Salinité dans l'eau de mer de surface : la Régression Non-linéaire Multiple et le Perceptron Multi Couches. Dans lapremì ere expérience , 18 300 mesures in situ sont utilisées dans la construction des deux mod eles et 503 points pour tester leur extrapolation. Dans ladeuxì eme expérience , 15 668 mesures in situ sont utilisées pour etablir les deux mod eles et 3 232 points pour tester leur interpolation. Les résultats montrent que la Régression Non-linéaire Multiple peut etre appliquéè a la fois pour l'extrapolation et l'interpolation. Cependant, le Perceptron Multi Couches ne peut etre utilisé que pour l'interpolation.En utilisant des mesures de Salinité et de Température à la surface de la mer, dans l’ouest de l’océan Atlantique tropical, de 2003 à 2007 puis 2009, on compare deux approches pour la prédiction de la Salinité dans l’eau de mer de surface : la Régression Non-linéaire Multiple et le Perceptron Multi Couches. Dans la première expérience, 18 300 mesures in situ sont utilisées dans la construction des deux modèles et 503 points pour tester leur extrapolation. Dans la deuxième expérience, 15 668 mesures in situ sont utilisées pour établir les deux modèles et 3 232 points pour tester leur interpolation. Les résultats montrent que la Régression Non-linéaire Multiple peut être appliquée à la fois pour l’extrapolation et l’interpolation. Cependant, le Perceptron Multi Couches ne peut être utilisé que pour l’interpolation