On eddy polarity distribution in the southwestern Atlantic

Eddies in the southwestern Atlantic were detected from more than 18 years of satellite altimetry data using a modified version of the Okubo–Weiss method. The spatial distribution and polarity of eddies were examined. A larger concentration of cyclonic (anticyclonic) eddies was found on the left (right) side when looking downstream on some of the largest current systems in the region, such as the South Atlantic Current, the anticyclonic circulation associated with the Zapiola Drift (ZD) and the northern branch of the Antarctic Circumpolar Current. In the region isolated by the anticyclonic Zapiola Current, 91% of eddies were cyclonic. The observed distribution of eddies is in agreement with the generation of eddies from meanders of the above-mentioned currents: cyclonic (anticyclonic) eddies might detach from a meander of the current on the left (right) side when looking downstream on the current. Furthermore, in the ZD area, the bottom topography plays a key role in determining the trajectory of eddies: the anticyclonic current associated with the ZD meanders and eventually generates a cyclonic eddy that enters the ZD region only across the northeastern border, where the gradient of potential vorticity is lower. Finally, average surface chlorophyll-a concentration inside cyclonic and anticyclonic eddies shows that the former have higher chlorophyll-a values. Thus, on average, the classical eddy-pumping theory explains the difference in chlorophyll-a concentration within eddies in the southwestern Atlantic.Fil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmosfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmosfera; ArgentinaFil: Provost, Christine. Universite Pierre et Marie Curie; Franci

A variational method for inverting hydrographic data

We present a new method for estimating the three-dimensional field of geostrophic velocity from hydrographic station data. Very simply, we ask for the smoothest velocity field (in the sense of an arbitrarily defined norm) which is consistent with the data and with selected approximate dynamical constraints to within prescribed misfits, which, we will argue, should never be zero. The misfits represent errors in the data and in the approximate dynamical constraints. By varying the misfits relatively to one another, we explore the full envelope of physically plausible estimates of the average geostrophic flow. We illustrate the method by application to hydrographic measurements in the Labrador Sea

Satellite Altimetry and Current-Meter Velocities in the Malvinas Current at 41°S: Comparisons and Modes of Variations

Three year long current-meter arrays were deployed in the Malvinas Current at 418S below a satellite altimeter track at about 10 years intervals. Surface geostrophic velocities (SGV) derived from satel- lite altimetric data are compared with the in situ velocities at the upper current meter (􏰁300 m). Multisatel- lite gridded SGV compare better with in situ observations than along-track SGV. In spite of the proximity of the moorings to the complex Brazil-Malvinas Confluence (BMC) region, satellite SGV are significantly corre- lated with the 20 day low-passed in situ velocities (0.85 for along-isobaths velocities, 0.8 for cross-isobaths velocities). The recent in situ measurement period (2014?2015) stands out in the altimetry record with a long-lasting (4 months) high level of eddy kinetic energy at the mooring site and a southernmost location of the Subantarctic Front (SAF). The first two modes of variations of sea level anomaly (SLA) over the BMC remarkably match the first two modes of the low-passed in situ velocities. The first mode is associated with a latitudinal migration of the SAF, and the second with a longitudinal displacement of the Brazil Current overshoot. The two modes dominate the 24 year long record of SLA in the BMC, with energy peaks at the annual and semiannual periods for the first mode and at 3?5 months for the second mode. The SLA over the Southwest Atlantic was regressed onto the two confluence modes of SLA variations and showed remarkable standing wave train like structures in the Argentine Basin.Fil: Ferrari, Ramiro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Artana, Camila Indira. Universite de Paris VI; FranciaFil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Provost, Christine. Universite de Paris VI; Franci

Silicate determination in sea water: toward a reagentless electrochemical method

ilicate has been determined in sea water by four different electrochemical methods based on the detection of the silicomolybdic complex formed in acidic media by the reaction between silicate and molybdenum salts. The first two methods are based on the addition of molybdate and protons in a seawater sample in an electrochemical cell. Cyclic voltammetry presents two reduction and two oxidation peaks giving four values of the concentration and therefore increasing the precision. Then chronoamperometry is performed on an electrode held at a constant potential. A semi-autonomous method has been developed based on the electrochemical anodic oxidation of molybdenum, the complexation of the oxidation product with silicate and the detection of the complex by cyclic voltammetry. This method is tested and compared with the classical colorimetric one during ANT XXIII/3 cruise across Drake Passage (January–February 2006). The detection limit is 1 μM and the deviation between both methods is less than 3% for concentrations higher than 10 μM. Finally a complete reagentless method with a precision of 2.6% is described based on the simultaneous formation of the molybdenum salt and protons in a divided electrochemical cell. This latter method should be very useful for developing a reagentless sensor suitable for long term in situ deployments on oceanic biogeochemical observatories

Spring and winter water mass composition in the Brazil-Malvinas Confluence

Hydrographic data of the Confluence 1 cruise collected during austral spring (November 1988) have been analyzed to estimate relative mixing proportions of the various water masses of the Brazil-Malvinas Confluence region using a multiparameter analysis. Seven source water types (SWT) are identified in this region, and all are retained for the analysis: Thermocline Water (TW), Subantarctic Surface Water (SASW), Antarctic Intermediate Water (AAIW), Upper Circumpolar Deep Water (UCDW), North Atlantic Deep Water (NADW), Lower Circumpolar Deep Water (LCDW) and Weddell Sea Deep Water (WSDW). Tracers selected are temperature, salinity, dissolved oxygen and nutrients. Mixing proportions are quantified and plotted along five zonal sections at 35.4, 36.5, 37.9, 41 and 41.6S. The solution obtained during the springtime cruise is consistent with the wintertime (September 1989) data set (Maamaatuaiahutapu et al., 1992): both show the large local recirculation of AAIW and the separation of NADW from the coast south of the thermocline front. However, noticeable changes in water mass mixing proportions can be detected between the winter of 1989 and the preceding spring. The seasonal change for the upper layers of TW and SASW is related to temporal and spatial fluctuations of the thermohaline front. The marked differences in SWT proportions between the two seasons occur at the same location for TW, SASW and AAIW; suggesting that the upper waters have a large impact on the AAIW movement. The deep waters undergo great spatial changes between the two cruises. The variation of the deep convergence position (revealed by the variation of spatial occupancy of the CDW and NADW) seems influenced by the movement of the thermocline front

Idéations suicidaires du personnel de la santé pendant la pandémie de COVID-19 : une évaluation écologique momentanée

Introduction: The COVID-19 pandemic had an impact on the psychological health of healthcare workers (HCWs). Cross-sectional studies report suicidal ideation in this population during this period, but no longitudinal study has examined the evolution of these ideas over time. Objectives: To assess the evolution of suicidal ideation of HCWs during the first two waves of the COVID-19 pandemic among Quebec (Canada) HCWs and to identify the risk factors involved. Methods: A longitudinal study among Quebec (Canada) HCWs using ecological momentary assessment was conducted between May 8, 2020, and March 31, 2021 (corresponding to the second half of the first wave to the end of the second). Participants (n=865) answered weekly questions related to anxiety (GAD-7), depression (PHQ-9), suicidal ideation (PHQ-9 Q.9), exposure to COVID-19, exposure to COVID-19-related deaths, their infection status and that of their co-workers and loved ones, as well as the amount of time they spent consuming news related to COVID-19. Results: Proportion of suicidal ideation increased from May to June 2020 (second half of the first wave) peaking at 18% before declining up to March 2021. Anxiety and depression symptoms severity increased those ideations as well as having a colleague confirmed positive to COVID-19. Social support does not appear to be a protective factor for suicidal ideation. Suicidal thoughts are associated with media consumption and appear to be mediated by the presence of clinical distress expressed as depressive or anxiety states. Discussion and conclusion: Media consumption in a pandemic context is associated with anxiety and depression, the more severe states of which may express suicidal ideation. Without inferring causality relationship, it seems advisable for HCWs to limit their media exposure during a disaster such as a pandemic.Introduction : La pandémie de COVID-19 a eu un impact sur la santé psychologique des travailleurs de la santé (TS). Des études transversales rapportent la présence d’idées suicidaires chez cette population pendant cette période, mais aucune étude longitudinale n’a examiné l’évolution de ces idées dans le temps. Objectifs : Évaluer l’évolution des idées suicidaires des TS au cours des deux premières vagues de la pandémie de COVID-19 au Québec (Canada) et identifier les facteurs de risque impliqués. Méthodes : Une étude longitudinale, utilisant l’évaluation écologique momentanée, a été menée entre le 8 mai 2020 et le 31 mars 2021 (correspondant à la période entre la moitié de la 1re vague à la fin de la seconde) auprès des TS québécois. Les participants (n=865) ont répondu de façon hebdomadaire à des questions relatives à l’anxiété (GAD-7), à la dépression (PHQ-9), aux idées suicidaires (PHQ-9 Q.9), à l’exposition à la COVID-19, à l’exposition aux décès liés à la COVID-19, à leur statut infectieux et à celui de leurs collègues et de leurs proches, ainsi qu’au temps passé à consommer des nouvelles liées à la COVID-19. Résultats : La proportion d’idées suicidaires a augmenté de mai à juin 2020 (deuxième moitié de la première vague) atteignant un pic à 18% avant de diminuer par la suite jusqu’en mars 2021. La gravité des symptômes d’anxiété et de dépression était corrélée positivement avec les idéations suicidaires, tout comme le fait d’avoir un collègue infecté à la COVID-19. Le soutien social ne semble pas être un facteur protecteur des idées suicidaires. Les idées suicidaires sont corrélées à la consommation de médias et un effet médiateur est observé par la présence d’une détresse clinique exprimée par des états dépressifs ou anxieux. Discussion et conclusion : La consommation de médias dans un contexte de pandémie est associée à de l’anxiété et à de la dépression, dont les états les plus graves peuvent exprimer des idées suicidaires. Sans inférer un lien de causalité, il semble recommandé aux travailleurs de la santé de limiter leur exposition aux médias lors d’une catastrophe telle qu’une pandémie

Atlantic Water Circulation and Properties Northwest of Svalbard During Anomalous Southerly Winds

Atlantic Water (AW), the main source of heat and salt for the Arctic Ocean, undergoes large transformations (cooling and freshening) north of Svalbard as it flows near the surface above the Yermak Plateau (YP). In September 2017, a SeaExplorer ocean glider deployed in the West Spitsbergen Current (WSC) and recovered north of Svalbard documented the circulation and properties of the AW crossing the YP. The glider sampled the different branches of the AW flowing into the Arctic around the YP: the WSC, the Svalbard Branch (SB), the Yermak Pass Branch, and the Yermak Branch. Unusual southerly winds prevailed in summer 2017 impacting AW circulation in the region. Cold and fresh lenses of shelf-origin waters detached from the slope in the WSC to reach their density level below the core of the AW. This resulted in cooling and freshening of the AW inflow from below. The eastward current associated with the SB was found to be weak at its usual location above the 400 m isobath, likely the result of the adjustment of the flow influenced by anomalous southerly wind conditions.publishedVersio

Atlantic Water Modification North of Svalbard in the Mercator Physical System From 2007 to 2020

The Atlantic Water (AW) inflow through Fram Strait, largest oceanic heat source to the Arctic Ocean, undergoes substantial modifications in the Western Nansen Basin (WNB). Evaluation of the Mercator system in the WNB, using 1,500 independent temperature‐salinity profiles and five years of mooring data, highlighted its performance in representing realistic AW inflow and hydrographic properties. In particular, favorable comparisons with mooring time‐series documenting deep winter mixed layers and changes in AW properties led us to examine winter conditions in the WNB over the 2007–2020 period. The model helped describe the interannual variations of winter mixed layers and documented several processes at stake in modifying AW beyond winter convection: trough outflows and lateral exchange through vigorous eddies. Recently modified AW, either via local convection or trough outflows, were identified as homogeneous layers of low buoyancy frequency. Over the 2007–2020 period, two winters stood out with extreme deep mixed layers in areas that used to be ice‐covered: 2017/18 over the northern Yermak Plateau‐Sofia Deep; 2012/13 on the continental slope northeast of Svalbard with the coldest and freshest modified AW of the 12‐year time series. The northern Yermak Plateau‐Sofia Deep and continental slope areas became “Marginal Convection Zones” in 2011 with, from then on, occasionally ice‐free conditions, 50‐m‐ocean temperatures always above 0 °C and highly variable mixed layer depths and ocean‐to‐atmosphere heat fluxes. In the WNB where observations require considerable efforts and resources, the Mercator system proved to be a good tool to assess Atlantic Water modifications in winter