Santiago Hernández-León

Plastic debris in the open ocean

Significance High concentrations of floating plastic debris have been reported in remote areas of the ocean, increasing concern about the accumulation of plastic litter on the ocean surface. Since the introduction of plastic materials in the 1950s, the global production of plastic has increased rapidly and will continue in the coming decades. However, the abundance and the distribution of plastic debris in the open ocean are still unknown, despite evidence of affects on organisms ranging from small invertebrates to whales. In this work, we synthetize data collected across the world to provide a global map and a first-order approximation of the magnitude of the plastic pollution in surface waters of the open ocean. There is a rising concern regarding the accumulation of floating plastic debris in the open ocean. However, the magnitude and the fate of this pollution are still open questions. Using data from the Malaspina 2010 circumnavigation, regional surveys, and previously published reports, we show a worldwide distribution of plastic on the surface of the open ocean, mostly accumulating in the convergence zones of each of the five subtropical gyres with comparable density. However, the global load of plastic on the open ocean surface was estimated to be on the order of tens of thousands of tons, far less than expected. Our observations of the size distribution of floating plastic debris point at important size-selective sinks removing millimeter-sized fragments of floating plastic on a large scale. This sink may involve a combination of fast nano-fragmentation of the microplastic into particles of microns or smaller, their transference to the ocean interior by food webs and ballasting processes, and processes yet to be discovered. Resolving the fate of the missing plastic debris is of fundamental importance to determine the nature and significance of the impacts of plastic pollution in the ocean.

The Transition Zone of the Canary Current Upwelling Region.

Abstract Like all the major upwelling regions, the Canary Current is characterised by intense mesoscale structure in the transition zone between the cool, nutrient-rich waters of the coastal upwelling regime and the warmer, oligotrophic waters of the open ocean. The Canary Island archipelago, which straddles the transition, introduces a second source of variability by perturbing the general southwestward flow of both ocean currents and Trade winds. The combined effects of the flow disturbance and the eddying and meandering of the boundary between upwelled and oceanic waters produce a complex pattern of regional variability. On the basis of historical data and a series of interdisciplinary field studies, the principal features of the region are described. These include a prominent upwelling filament originating near 28°N off the African coast, cyclonic and anti-cyclonic eddies downstream of the archipelago, and warm wake regions protected from the Trade winds by the high volcanic peaks of the islands. The filament is shown to be a recurrent feature, apparently arising from the interaction of a topographically trapped cyclonic eddy with the outer edge of the coastal upwelling zone. Its role in the transport and exchange of biogenic material, including fish larvae, is considered. Strong cyclonic eddies, observed throughout the year, drift slowly southwestward from Gran Canaria. One sampled in late summer was characterised by large vertical isopycnal displacements, apparent surface divergence and strong upwelling, producing a fourfold increase in chlorophyll concentrations over background values. Such intense eddies can be responsible for a major contribution to the vertical flux of nitrogen. The lee region of Gran Canaria is shown to be a location of strong pycnocline deformation resulting from Ekman pumping on the wind shear boundaries, which may contribute to the eddy formation process.

The influence of island-generated eddies on chlorophyll distribution: a study of mesoscale variation around Gran Canaria

This study reports hydrographic and biological observations from three cruises where cyclonic and anticyclonic eddies were observed downstream of Gran Canaria island. Based on field data and remote sensing images (AVHRR and CZCS), two mechanisms associated with island- generated eddies, largely responsible for the formation and distribution of chlorophyll around the Canary Islands, are proposed. First, nutrient pumping and vertical uplifting of the deep chlorophyll maximum by cyclonic eddies might represent important sources of primary production in the oligotrophic waters of the Canary region. Second, eddies are responsible for the horizontal transport and distribution of chlorophyll originating near the islands or off the African coast. Water with high chlorophyll content, resulting from island stirring or local upwelling at the flanks of the islands, is incorporated into cyclonic eddies in their development and subsequently transported downstream. On the other hand, anticyclonic eddies can also entrain water rich in chlorophyll when interacting with the offshore boundary of the African coastal upwelling. This chlorophyll will be advected southward as the eddy drifts. The recurrence of cyclonic and anticyclonic eddies, together with the presence of upwelling filaments throughout the year, must have important biological consequences in the formation and transport of organic matter in the Canary region. 0 1997 Elsevier Science Ltd. All rights reserved

Large mesopelagic fishes biomass and trophic efficiency in the open ocean

With a current estimate of ~1,000 million tons, mesopelagic fishes likely dominate the world total fishes biomass. However, recent acoustic observations show that mesopelagic fishes biomass could be significantly larger than the current estimate. Here we combine modelling and a sensitivity analysis of the acoustic observations from the Malaspina 2010 Circumnavigation Expedition to show that the previous estimate needs to be revised to at least one order of magnitude higher. We show that there is a close relationship between the open ocean fishes biomass and primary production, and that the energy transfer efficiency from phytoplankton to mesopelagic fishes in the open ocean is higher than what is typically assumed. Our results indicate that the role of mesopelagic fishes in oceanic ecosystems and global ocean biogeochemical cycles needs to be revised as they may be respiring ~10% of the primary production in deep waters.

Island-induced eddies in the Canary Islands

Abstract Cyclonic and anticyclonic eddies were observed downstream of Gran Canaria (Canary Islands), an almost circular island of about 50 km diameter, located in the path of the Canary Current. Temperature data were obtained from five AXBT and one CTD surveys carried out during two years (April, May and December, 1989; February, May and June, 1990), and from NOAA AVHRR (Advanced Very High Resolution Radiometer) sea surface temperature (SST) satellite images. The presence of eddies in most of the surveys and in many SST images suggests that they are common mesoscale features in the flow past the island througout the year. In general, eddy diameter is similar to the width of the island, while the vertical extent is from the near-surface layers down to at least 400 m depth. However, vertical sections across the eddies show distinct patterns in their structures which could correspond to different stages of development. Wakes of relatively warm surface water develop in the lee of the island, interacting with the eddies and affecting their upper mixed layer structure. It is hypothesized that eddies are sequentially spun off from the island with a period ranging from several days to two weeks. If this is the case, they could contribute to the high levels of eddy kinetic energy observed recently downstream of the Canarian archipelago from moored current meters.

Zooplankton biomass and indices of feeding and metabolism in island-generated eddies around Gran Canaria

Abstract Zooplankton biomass and indices of grazing (gut fluorescence), respiration (electron transfer system, ETS), ammonia excretion (glutamate dehydrogenase, GDH) and growth (aspartate transcarbamylase, ATC) were studied around the island of Gran Canaria (Canary Islands) during the so-called “late winter bloom”. Four size classes (100–200, 200–500, 500–1000 and >1000 μm) were studied to assess the contribution of each size fraction to the mesoscale plankton distribution around the island. Cyclonic and anticyclonic eddies were observed downstream the island transporting and entraining water rich in chlorophyll. Zooplankton biomass showed a high variability around the island but it was dramatically lower in the core of the cyclonic eddy induced by the island, probably due to the divergent effect produced by the physical structure. A filament of relatively cold-water was also found reaching the island from the upwelling area off northwest Africa. High zooplankton biomass was observed in association with the filament water and in the vicinity of the anticyclonic eddy shed by the island. Specific gut content showed higher values in the boundaries of the cyclonic structures, while ETS and GDH activities where higher windward of the island, in both the cyclonic and anticyclonic eddies depending on the size fraction considered. With the restrictions of using those indices, control of primary production by grazing was 11–22% and up to 41% of the calculated ingestion from the indices of metabolism and growth could be supported by nonpigmented food. Calculated excretion rates could support about 8% of primary production. The low impact of zooplankton on autotrophic production, the low values of the index of growth and the distribution of biomass in relation to the presence of eddies downstream of Gran Canaria suggest that accumulation was the causative mechanism for the presence of high zooplankton biomass leeward of the island.

Accumulation of mesozooplankton in a wake area as a causative mechanism of the “island-mass effect”

Mesozooplankton biomass (as displacement volume and protein content) and electron-transport system (ETS) activity have been studied in the coastal waters around the Canary Islands. Increases in biomass and ETS activity, on a unit volume basis, were observed in the wakes of the islands. The biomass values obtained in the leeward area for Gran Canaria Island were up to ten times higher than those observed for typical oceanic waters around this archipelago. Sampling was performed in May 1986 at the end of the characteristic vertical mixing period in these waters. Relatively strong winds were recorded prior to sampling. Specific ETS activity was higher at the windward stations on the island shelf. This correlates with the observation in a recent study of increased primary production on the shelf area, where turbulence produced by the northerly trade winds has a marked effect. The persistence of this turbulence during a prolonged wind-pulse results in an accumulation of organisms in the wake of the islands due to current dynamics. This process is proposed as being an important causative mechanism of the island-mass effect. Different biomass values were recorded between circular and oblong islands. The latter are oriented towards the current and the northerly trade winds, and display significantly lower biomass values than the former.

Zooplankton biomass and indices of feeding and metabolism in relation to an upwelling filament off northwest Africa

Zooplankton biomass and indices of grazing (gut e uorescence), respiration (electron transfer system activity, ETS) and growth (aspartate transcarbamylase, ATC) were studied in relation to an upwelling e lament off northwest Africa during August 1993. The e lament extended 150 km offshore into the oligotrophic waters. It was generated by a trapped, quasi-permanent cyclonic eddy located between the Canary Islands and the African shelf. High biomass, specie c gut e uorescence and electron transfer system activity in zooplankton were observed along the e lament structure. In contrast, low values of biomass, gut e uorescence, ETS and ATC specie c activities were found in the center of the trapped cyclonic eddy. Assuming a 50% of pigment destruction, the calculated grazing impact of zooplankton on primary production varied between 16 and 97%, a high range compared to other oceanic systems. Ingestion, estimated from indices of metabolism and growth, accounted for 47- 296% of the primary production (assuming an herbivorous feeding). Mesozooplankton trans- ported offshore into the oligotrophic area fule lled their metabolic demands with nonpigmented food as observed from the increase of omnivory from the coastal waters to the open ocean. The progressive decay of grazing and metabolic indices along the e lament suggests that advection, rather than local enrichment processes, is mostly responsible for the high biomass values in this physical structure.

Modification of the electron transport system (ETS) method for routine measurements of respiratory rates of zooplankton

Respiratory Electron Transport System activity (ETS) was determined in cell-free homogenates of mesozooplankton samples. Several assays were run to investigate possible improvements to the ETS method and to reduce sample processing time. The results showed that: (i) liquid nitrogen is a suitable method for preserving ETS activity for up to at least two months; (ii) the processed sample can be stored for up to 90 minutes in an ice-water bath without loss of activity; (iii) a glass-fibre filter, normally used in phytoplankton assays, is not necessary to achieve efficient enzyme extraction; (iv) centrifugation can be done prior to the assay without any significant loss in activity; and (v) the partitioned enzyme activities were different from the overall ETS activity, with NADH- dehydrogenase activity playing the major role (71 %) and succinate dehydrogenase the minor (<5%). The overall precision of the methods was about 10%, and automation of the method is suggested as a means of standardizing the precision...

Biomass and metabolism of zooplankton in the Bransfield Strait (Antarctic Peninsula) during austral spring

Abstract Zooplankton biomass (as dry weight), respiration and ammonia excretion were studied in three different size classes (200–500, 500–1000 and >1000 μm) in the Bransfield Strait during December 1991. Average mesozooplankton biomass was 86.45 ± 56.74 mg · dry weight · m−2, which is in the lower range of the values cited in the literature for polar waters. Higher biomass was observed in the Weddell water. The small size fraction accounted for about 50% of total biomass while the largest one represented 35%. Rather high metabolic rates were found, irrespective of whether the organisms were incubated in the presence of food. No significant differences were observed in mass specific respiration and ammonia excretion rates between different temperatures of incubation (0.2–2.3°C) and between the size classes studied. Because of the very low biomass values observed, the metabolic requirements of mesozooplankton during December represented a small fraction of the primary production.