No abstract

No abstract

Coastal upwelling regions, which are affected by equatorward-wind variability, are among the most productive areas of the oceans. It has been suggested that global warming will lead to a general strengthening of coastal upwelling, with important ecological implications and an impact on fisheries. However, in the case of the Iberian upwelling, the long-term analysis of climatological variables described here reveals a weakening in coastal upwelling. This is linked to a decrease of zonal sea level pressure gradient, and correlated with an observed increase of sea surface temperature and North Atlantic Oscillation. Weakening of coastal upwelling has led to quantifiable modifications of the ecosystem. In outer shelf waters a drop in new production over the last 40 years is likely related to the reduction of sardine landings at local harbors. On the other hand, in inner shelf and Ria waters, the observed weakening of upwelling has slowed down the residual circulation that introduces nutrients to the euphotic layer, and has increased the stability of the water column. The drop in nutrient levels has been compensated by an increase of organic matter remineralization. The phytoplankton community has responded to those environmental trends with an increase in the percentage of dinoflagellates and Pseudonitzschia spp. and a reduction in total diatoms. The former favors the proliferation of harmful algal blooms and reduces the permitted harvesting period for the mussel aquaculture industry. The demise of the sardine fishery and the potential threat to the mussel culture could have serious socio-economic consequences for the region.

No abstract

Daily changes in the concentrations of carbon and nitrogen species were monitored during the course of a Lagrangian drifter experiment in a recurrent upwelling filament south of Cape Finisterre (NW Iberian Upwelling System). A drifting buoy released at the southern edge of the upwelling centre generated by the Cape moved 60km southwestwards from 3 to 7 August 1998. Organic matter in the 50m deep study water mass (average 77±2 µM C) consisted of: 57µM C of dissolved organic matter (DOM) with a C/N molar ratio of 19±2; 6µM C of DOM with a C/N ratio of 9±2, and 14µM C of 50% DOM and 50% suspended organic matter (POM susp ) with a C/N ratio of 6.0±0.4.Net conversion of consumed inorganic salts into accumulated TOM=POM susp +DOM was ෂ40% for nitrogen and ෂ30% for carbon. Since the parcel of water crossed the shelf-edge, these conversion efficiencies are equivalent to net horizontal export-ratio of 0.4 and 0.3 respectively. A second drifter was deployed in the offshore-end of the filament, and was displaced 20km west between 14 and 17 August 1998. Nitrate was exhausted in the surface water and no significant changes were observed in the variables measured during the course of the second experiment. Low C/N ratios (6.5±0.4) and rapid POM susp /DOM inter-conversion in the 20 µM C excess observed in the study volume points to the persistence of the labile materials formed on the shelf during transport to the ocean. Our data demonstrate a) the key role of upwelling filaments in off-shelf export of organic materials and b) the major contribution of DOM to this horizontal export, a previously unaccounted amount.The high nitrogen content of the materials exported make them attractive organic substrates for use by microbial populations in the adjacent oligotrophic ocean. 

No abstract

No abstract

Temperate, transitional and subtropical waters of the remote Azores Front region east of Azores (24-40ºN, 22-32ºW) were sampled during three cruises conducted under increasing stratification conditions (April 1999, May 1997 and August 1998 respectively. Vertical eddy diffusion is 35% and 2% of the spring and summer sinking POC flux, respectively. On the other hand, DOC only contributes 13% to the local oxidation of organic matter in subsurface waters (between the pycnocline and 500m) of the study region.