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Alvarez M.,Spanish Institute of Oceanography | Brea S.,IIM CSIC | Mercier H.,French Research Institute for Exploitation of the Sea | Alvarez-Salgado X.A.,IIM CSIC
Progress in Oceanography | Year: 2014

This is the first of two manuscripts dealing with the circulation, mixing, ventilation and organic matter mineralization of the South Atlantic Ocean (SAO). The present work quantifies the complex mixing of water masses in the SAO using a constrained, least-squares regression, Optimum MultiParameter (OMP) analysis. The OMP based on temperature, salinity, silicate and the conservative parameter NO, was applied on two World Ocean Circulation (WOCE) lines, A17 and A14, in the western and eastern SAO, respectively. The constrained OMP sensitivity to sources of error in the end-member characteristics, measured parameters, equation weights and oxygen to nitrogen mineralization ratio (RN) was carefully assessed using perturbation tests. Perturbation of RN was the only test that changed significantly the mixing proportions although by less than 5%. The constrained OMP method allowed defining the realm and identifying the core-of-flow of each water mass to study its circulation, the evolution of its chemical composition and, eventually, to separate the contribution of physical and biogeochemical processes. Relevant specific outputs of this first manuscript are: (1) north of the South Equatorial Current, the silicate maximum is primarily composed of Antarctic Intermediate Water (AAIW) rather than Circumpolar Deep Water (CDW); (2) the two degree discontinuity (TDD) experiences a dramatic meridional change of water masses composition, being dominated by North Atlantic Deep Water (NADW) north of the Vema Channel and by CDW southwards; (3) the 50% proportion horizon of Weddell Sea Deep Water (WDSW), with a θ of -0.3°C at the entry of the SAO, defines the upper limit of the WSDW realm more properly than the classical isopycnals of 46.04 or 46.06 σ4, where the proportion of WSDW is around 75%. © 2014 Elsevier Ltd. Source


Radovic J.R.,CSIC - Institute of Environmental Assessment And Water Research | Rial D.,IIM CSIC | Lyons B.P.,CEFAS - Center for Environment, Fisheries and Aquaculture Science | Harman C.,Norwegian Institute for Water Research | And 5 more authors.
Journal of Environmental Management | Year: 2012

Oil and chemical spills in the marine environment are an issue of growing concern. Oil exploration and exploitation is moving from the continental shelf to deeper waters, and to northern latitudes where the risk of an oil spill is potentially greater and may affect pristine ecosystems. Moreover, a growing number of chemical products are transported by sea and maritime incidents of hazardous and noxious substances (HNS) are expected to increase. Consequently, it seems timely to review all of the experience gained from past spills to be able to cope with appropriate response and mitigation strategies to combat future incidents. Accordingly, this overview is focused on the dissemination of the most successful approaches to both detect and assess accidental releases using chemical as well as biological approaches for spills of either oil or HNS in the marine environment. Aerial surveillance, sampling techniques for water, suspended particles, sediments and biota are reviewed. Early warning bioassays and biomarkers to assess spills are also presented. Finally, research needs and gaps in knowledge are discussed. © 2012 Elsevier Ltd. Source


Alvarez-Salgado X.A.,IIM CSIC | Alvarez M.,Spanish Institute of Oceanography | Brea S.,IIM CSIC | Memery L.,LEMAR | Messias M.J.,UEA
Progress in Oceanography | Year: 2014

The variability of nitrate (N), phosphate (P), silicate (Si) and Apparent Oxygen Utilization (AOU) due to water mass mixing was objectively separated from the variability due to mineralization of biogenic materials in the western and eastern South Atlantic Ocean on basis of the constrained Optimum MultiParameter (OMP) analysis implemented in the companion manuscript. Using a consensus linear regression model, AOU/N/P/Si mineralization ratios and the corresponding oxygen utilisation rates (OURs) were obtained for the realm of each water mass defined after the OMP analysis. Combining these results with a stoichiometric model, the organic carbon to nitrogen (C/N) ratios and the biochemical composition (carbohydrates+lipids, proteins and phosphorus compounds) of the mineralized material, were derived. The vertical variability of the AOU/N, AOU/P and AOU/C mineralization ratios pointed to a significant fractionation during the mineralization of sinking organic matter. This fractionation was confirmed by preferential consumption of organic phosphorous compounds and proteins in shallower levels, which produced an increase of the C/N ratio of the mineralised materials of 0.5±0.2molCmolN-1 every 1000dbar. OURs in the twilight zone decreased quadratically with the C/N molar ratio of the mineralised material and exponentially with pressure (p, in 103dbar) according to the following regression equation: Ln (OUR)=6.2(±1.2)-2.0(±0.7)*Ln (C/N)-0.6(±0.2)*p (r2=0.87, p<0.006, n=8). This variability in the rates and stoichiometric ratios of the biogenic material mineralization compromises our capacity to predict the ocean biogeochemistry response to global change, including the CO2 uptake and storage and the corresponding feedback mechanisms. © 2014 Elsevier Ltd. Source


Martinez-Garcia S.,University of Vigo | Martinez-Garcia S.,Linnaeus University | Arbones B.,IIM CSIC | Garcia-Martin E.E.,University of Vigo | And 7 more authors.
Estuarine, Coastal and Shelf Science | Year: 2015

The impact of rain water collected at marine, urban and rural sites on coastal phytoplankton biomass, primary production and community composition as well as the effect on microbial plankton metabolism was studied in 3 microcosm experiments conducted under contrasting spring, autumn and winter conditions. The measured responses were highly variable. Rainwater additions increased chlorophyll a (Chl a) concentration (5-68% difference between rainwater treatments relative to the control) in all experiments and reduced or stimulated primary production (PP) depending on the treatment and the experiment (from-10 to+169% relative to the control). Autotrophic stimulation was highest in spring, probably related to the low initial natural nutrient concentrations. Under winter nutrient replete conditions, rainwater inputs changed the phytoplankton community although this change did not promote increases in primary production. Enhancement of net autotrophy (increase of net oxygen production up to 227%) after rainwater inputs were only found during the period of low nutrient availability. Inputs of dissolved organic nitrogen (DON) explained a large fraction of the variability in the response of PP, Chl a, community respiration (CR) and net community production (NCP). Our results suggest that differences in the initial environmental conditions (i.e. nutrient availability), rainwater composition and the ability of the present autotrophic communities to utilize the new nutrients result in substantial changes in the microbial responses and associated biologically-mediated carbon fluxes. As atmospheric nutrient inputs into coastal oceans are increasing rapidly, our results help to understand the effects of different inputs on the metabolism of distinct microbial communities. © 2014 Elsevier Ltd. Source

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