Cruising for ocean conservation: no exactly a waste of time. Plastic pollution in the oceans

Grabación realizada por Ciencia compartida (Biblioteca Universitaria)

Respiration in the dark ocean

[EN]The dark ocean, the waters below 200 m depth, comprises about 95% of the volume of the ocean, but its contribution to the metabolism of the ocean is poorly quantified. Here we show that the respiration rate of microplankton declines exponentially at a rate of 0.53 km−1 in the dark ocean, and is enhanced at the interface between the mesopelagic and the abyssal layers (1,000–2,000 m). The respiratory CO2 production in the dark ocean, estimated at 20 to 33.3 Gt C yr−1, renders it a major component of the carbon flux in the biosphere.

Active mesopelagic prokaryotes support high respiration in the subtropical northeast Atlantic Ocean

[EN]Here we provide evidence, based on prokaryote metabolic proxies and direct estimates of oxygen consumption, that the mesopelagic prokaryote assemblage in the subtropical Northeast Atlantic is an active one. It supports a high respiration (0.22 ± 0.05 μmol O2 l−1 d−1, corresponding to 68 ± 8 mmol CO2 m−2 d−1), comparable to that of the epipelagic zone during the same period (64–97 mmol C m−2 d−1). Our findings suggest that mesopelagic prokaryotes in the NE subtropical Ocean, as well as in other eastern boundary regions, are important carbon sinks for organic matter advected from the highly productive coastal systems, and would play a key role in the global carbon cycle of the oceans.

Krill as a central node for iron cycling in the Southern Ocean

[EN] In order to establish the potential role of Antarctic krill (Euphausia superba) in the recycling of bioactive elements, we have quantified the release of iron, phosphate, and ammonia by these organisms along the Antarctic Peninsula sector of the Southern Ocean. The experimental results suggested that the presence of krill has a significant impact on ambient iron concentrations, as large amounts of this trace element were released by the krill (22–689 nmol Fe g Dry Weight−1 h−1, equivalent to 0.2 to 4.3 nmol Fe L−1 d−1). Half of this iron release occurred within the first hour of the experiment, and differences in iron and phosphate release rates (3.1 to 14.0 μmol PO43− g DW−1 h−1) seemed to reflect differences in food availability. These results identify krill as a major node in iron cycling in the Southern Ocean, potentially influencing iron residence time in the upper water column of this region.

Role of slowly settling particles in the ocean carbon cycle

[EN] Here we present results from sediment traps that separate particles as a function of their settling velocity, which were moored in the Canary Current region over a 1.5-year period. This study represents the longest time series using “in situ” particle settling velocity traps to date and are unique in providing year-round estimates. We find that, at least during half of the year in subtropical waters (the largest ocean domain), more than 60% of total particulate organic carbon is contained in slowly settling particles (0.7–11 m d−1). Analyses of organic biomarkers reveal that these particles have the same degradation state, or are even fresher than rapidly sinking particles. Thus, if slowly settling particles dominate the exportable carbon pool, most organic matter would be respired in surface waters, acting as a biological source of CO2 susceptible to exchange with the atmosphere. In the context of climate change, if the predicted changes in phytoplankton community structure occur, slowly settling particles would be favored, affecting the strength of the biological pump in the ocean.

Lagrangian evolution of a mid ocean anticyclonic eddy

[EN]The lagrangian evolution of 4 months old anticyclonic intrathermocline eddy of the Canary Eddy Corridor is investigated from the trajectories of 5 satellites tracked drifting buoys. Buoys were drogued below and above the Ekman depth at 15 m and 100 m, respectively. One buoy remained inside the eddy during almost 4 months being thus a long lived coherent feature with a life span of at least 8 months. The eddy consisted in a central core rotating in solid body rotation with a rather constant periodicity of 4 days and in an outer ring rotating much more slowly with periodicities between 8 and 12 days…

New insights into POC dynamics in the subtropical northeast Atlantic Ocean

[EN]The capacity of the ocean to sequester atmospheric carbon (CO2) depends to a large extent on the dynamics of biogenic carbon in the water column. However, most current global and regional estimates of carbon balances are solely based on particles collected with drifting and moored sediment traps. As a consequence, construction of ocean carbon budgets has long been guided by the simplification introduced by sediment traps, which give a 1D vision of the whole picture. In this thesis we have assessed a quantitative analysis of the flux magnitude and the mechanisms of transport of the whole particle spectrum (suspended, slowly-sinking and sinking particles).

Upwelling in the Eastern Subtropical North Atlantic Ocean

[EN]Coastal upwelling in the eastern margin and offshore curl-driven upwelling in the southeastern margin, make the subtropical Northeast Atlantic a region of major primary productivity. When examining a broad zonal area, from the coast to 40_W, we find that the upward transport of nutrients due to offshore curl-driven upwelling becomes the main control on productivity. Nevertheless, despite its relatively small zonal extension of about 100 km, coastal upwelling extends its impact towards the open ocean through offshore Ekman transport and convergence of the meridional flow at Cape Blanc (21_N).

A preview of the ocean acidification’s impact on potential respiratory activity

[EN]The increase in the anthropogenic CO2 released to the atmosphere, induces an increase in the dissolved CO2 in the ocean, causing elevated pCO2 values and a pH decrease. Due to the increasing atmospheric CO2, several on-going research programs are evaluating the impact of acidification on marine organisms, intent to predict their future. In this mesocosm experiment (KOSMOS 14GC), we assessed the effect of different CO2 concentrations on metabolism in microplankton (0.7-50μm size) and in biogenic particles harvested by sediment traps.

Multiscale variability in the North Atlantic Ocean

Programa de doctorado, Oceanografía ; 2004-2006