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 transition zone of the Canary Current upwelling region

Eddies and other mesoscale oceanic processes, such as fronts, can enhance biological production in the ocean, according to several open-ocean studies. The effect is thought to be particularly pronounced in low-nutrient environments, where mesoscale processes increase the net upward flux of limiting nutrients. However, eddies have been suggested to suppress production in the highly productive eastern boundary upwelling systems. Here, we examine the relationship between satellite-derived estimates of net primary production, of upwelling strength, and of eddy-kinetic energy--a measure of the intensity of mesoscale activity--in the four most productive eastern boundary upwelling systems. We show that high levels of eddy activity tend to be associated with low levels of biological production, indicative of a suppressive effect. Simulations using eddy-resolving models of two of these upwelling systems support the suggestion that eddies suppress production, and show that the downward export of organic matter is also reduced. According to these simulations, the reduction in production and export results from an eddy-induced transport of nutrients from the nearshore environment to the open ocean. Eddies might have a similar effect on marine productivity in other oceanic systems that are characterized by intense eddy activity, such as the Southern Ocean.

Eddy-induced reduction of biological production in eastern boundary upwelling systems

http://digital.csic.es/bitstream/10261/49073/1/CanC_review_PiO2009.pdf

Sub-regional ecosystem variability in the Canary Current upwelling

INTRODUCTION. A HISTORICAL OVERVIEW OF NITROGEN STUDY IN THE SEA. Determination of Nitrogenous Compounds in the Sea. Biological Transformation of Nitrogen. Stoichiometric Model of Organic-Matter Mineralization. Natural 15N Abundance. THE NITROGEN CYCLE. PHYSICO-CHEMICAL PROPERTIES OF NITROGEN. PROPERTIES OF THE NITROGEN ATOM AND BONDING. THERMODYNAMIC FUNCTIONS OF NITROGEN. BIOGEOCHEMICAL SKETCH OF NITROGEN. NITROGEN ISOTOPES. GENESIS OF ISOTOPES OF LIGHT ELEMENTS. ISOTOPE ABUNDANCE AND FRACTIONATION. ISOTOPIC EXCHANGE REACTIONS. KINETIC ISOTOPE EFFECTS. OVERALL ISOTOPIC FRACTIONATION. One-Step Reaction. Unidirectional Two-Step Reaction at Steady State. Two-Step Reaction with a Reversible First Step at a Steady State. Three-Step Reactions. Multistep Reactions. ISOTOPIC EXCHANGE EQUILIBRIA OF NITROGEN. NITROGEN KINETIC ISOTOPE EFFECTS DURING NITRATE REDUCTION. Chemical Systems. Biological Systems. ISOTOPE FRACTIONATION IN BRANCHED REACTIONS AND ITS ECOLOGICAL SIGNIFICANCE. ISOTOPE MASS BALANCE IN MARINE ECOSYSTEMS. Two-Source Model. Three-Source Model. COMPONENTS, SYSTEMS, AND PROCESSES. NITROGENOUS COMPOUNDS IN THE SEA: ABUNDANCE, SOURCES, AND SINK. PHYSICAL FACTORS. Water Movement and Mixing of Water. Solar Radiation. Effects of Temperature and Pressure on Chemical and Biochemical Reactions. Nitrogen Supply by River Runoff and Precipitation. CHEMICAL FACTORS. Chemical Behavior of Nitrogenous Compounds in the Sea. Hydrogen Ion Concentration. Oxidation-Reduction Potential. BIOCHEMICAL PROCESSES. Nitrogen Uptake and Assimilation. Mineralization. Nitrification. Nitrate Respiration and Denitrification. N2 Fixation. ABUNDANCE AND DISTRIBUTION OF NITROGEN IN THE SEA AND THEIR PHYSICAL, CHEMICAL, AND BIOCHEMICAL REGULATION. ROLES OF THE OCEAN IN THE GLOBAL NITROGEN CYCLE. The Buildup of the Biogeochemical Cycle. Nitrogen Inventories. Nitrogen Budgets. DISSOLVED NITROGEN GAS. Atmospheric Pressure. Occlusion of Air Bubbles. Effect of Mixing of Different Water Masses. Biological Effects. AMMONIUM, NITRITE, AND NITRATE. Distribution of Ammonium. Distribution of Nitrite. Distribution of Nitrate. NITROUS OXIDE. UREA. OTHER NITROGENOUS COMPOUNDS IN A WATER COLUMN. NITROGEN UPTAKE BY PHYTOPLANKTON. MECHANISM OF FORMATION OF THE PRIMARY NITRITE MAXIMUM. Nitrification in the Sea. Nitrite Production from Nitrate by Microalgae. Nitrite Assimilation. Formation of Primary Nitrite Maximum. NITROGEN DYNAMICS IN VARIOUS OCEANIC SYSTEMS. HIGH LATITUDINAL AREAS RICH IN NITRATE. OLIGOTROPHIC AREAS. Kuroshio Area. Anticyclonic Gyre Off Shikoku. SUBTROPICAL AND TROPICAL AREAS WITH SUPPLY OF NITRATE. Upwelling Region. Regional Upwelling. SEA AREAS WHERE NITROGEN FIXATION OCCURS. Trichodesmium Ecosystems. Local Ecosystems Characterized by N2 Fixation. SUBSURFACE ECOSYSTEMS. Decomposition of Organic Matter in the Subsurface Water. Nitrogen Diagenesis in Sediments. SEA AREAS WHERE DENITRIFICATION OCCURS. Denitrification in the Subsurface Water. Marine Sediments. NEAR SHORE AND ESTUARINE SYSTEMS. Flooded Soil Ecosystems. Tokyo Bay. VARIATION OF 15N/14N IN NITROGEN CYCLING AND ITS SIGNIFICANCE IN MARINE ENVIRONMENTS. ISOTOPE FRACTIONATION IN THE NITROGEN CYCLE. Isotope Exchange Reactions. Fractionation in Biological Metabolic Processes. DISTRIBUTION OF 15N IN NATURE. General Patterns of 15N Distribution. 15N in Antarctica. 15N Abundance and the Biogeochemical Cycle. INTEGRATED NITROGEN ISOTOPE FRACTIONATION IN ECOSYSTEMS. Enrichment of 15N in a Feeding Process. d15N-d13C Relationship. MARINE ECOSYSTEMS. Phytoplankton and Particulate Organic Matter. The Area Characterized by N2 Fixation. Isotope Biogeochemistry of the Antarctic Ecosystem. Dentrification in the Marine Aquatic System as Investigated Based on 15N Abundance Data. 15N and 13C Abundance in River, Estuarine, and Coastal Areas. Seabird Rookeries. The Deep-Sea World. Animal Behavior. FUTURE STUDIES ON NITROGEN DYNAMICS. HUMAN IMPINGEMENT ON THE NITROGEN CYCLE IN MARINE SYSTEMS. Long-Term Effects. Short-Term Effects. A NEW PARADIGM. Isotope Biogeochemistry. From Components to Systems. REFERENCES. INDEX.

Nitrogen in the sea : forms, abundances, and rate processes

Coupling between the open ocean and the coastal upwelling region off northwest Africa: water recirculation and offshore pumping of organic matter

Variability in plankton community structure, metabolism, and vertical carbon fluxes along an upwelling filament (Cape Juby, NW Africa)

Exchange of carbon by an upwelling filament off Cape Ghir (NW Africa)

Seamounts are considered to be "hotspots" of marine life but, their role in oceans primary productivity is still under discussion. We have studied the microbial community structure and biomass of the epipelagic zone (0-150 m) at two northeast Atlantic seamounts (Seine and Sedlo) and compared those with the surrounding ocean. Results from two cruises to Sedlo and three to Seine are presented. Main results show large temporal and spatial microbial community variability on both seamounts. Both Seine and Sedlo heterotrophic community (abundance and biomass) dominate during winter and summer months, representing 75% (Sedlo, July) to 86% (Seine, November) of the total plankton biomass. In Seine, during springtime the contribution to total plankton biomass is similar (47% autotrophic and 53% heterotrophic). Both seamounts present an autotrophic community structure dominated by small cells (nano and picophytoplankton). It is also during spring that a relatively important contribution (26%) of large cells to total autotrophic biomass is found. In some cases, a "seamount effect" is observed on Seine and Sedlo microbial community structure and biomass. In Seine this is only observed during spring through enhancement of large autotrophic cells at the summit and seamount stations. In Sedlo, and despite the observed low biomasses, some clear peaks of picoplankton at the summit or at stations within the seamount area are also observed during summer. Our results suggest that the dominance of heterotrophs is presumably related to the trapping effect of organic matter by seamounts. Nevertheless, the complex circulation around both seamounts with the presence of different sources of mesoscale variability (e.g. presence of meddies, intrusion of African upwelling water) may have contributed to the different patterns of distribution, abundances and also changes observed in the microbial community.

/pdf/is-there-a-seamount-effect-on-microbial-community-structure-2albcxrb6z.pdf

Alicia Ojeda

Papers

Variability in plankton community structure, metabolism, and vertical carbon fluxes along an upwelling filament (Cape Juby, NW Africa)

Exchange of carbon by an upwelling filament off Cape Ghir (NW Africa)

Is there a seamount effect on microbial community structure and biomass? The case study of Seine and Sedlo seamounts (northeast Atlantic).

Mesozooplankton metabolism and its effect on chlorophyll and primary production in slope waters of the Canary Islands