Gabriel Rosón

Hydrographic variability off the Rías Baixas (NW Spain) during the upwelling season

During the Galicia X cruise, from May to October 1989 an intensive collection of hydrographic data was carried out at a single station on the shelf off the western coast of Galicia. It allows us to follow the response of the water column to the intermittent equatorward wind stress during the upwelling season. Upwelling events occur with biweekly periodicity, bringing Eastern North Atlantic Water (ENAW) to the subsurface layer at our station. A trend of the thermohaline properties of the upwelled water to increase in time was observed. This seems to be mostly due to the southwestward displacement of the origin of this water mass during the year. Although the saltier and warmer ENAW is less nutrient-rich, nutrient levels increase because of the rapid remineralization of organic matter from the Rias, which takes place in the bottom water on the shelf.

Hydrographic conditions associated with the relaxation of an upwelling event off the Galician coast (NW Spain)

During the GALICIA-XI cruise froIn May 10 to May 14, 1991, the relaxation of a previous strong tipwelling event took place along the Galician coast caused by a shift in the position of the Azores High. The coldest tenperatures and highest nitrate levels were forrod near the coast corresponding to the advection of subsurface waters, particularly of Eastern North Atlantic Water (ENAW). On the basis of thermohaline properties, ENAW of polar (ENAWp) and tropical (ENAWt) origin are distinguished. The highest salinity values found correspond to a saline wedge of ENAW t located off the west coast of Galicia. The relaxation of tipwelling produced a shoreward migration of surface water from oceanic stations which crone into contact with upwelled Eastern North Atlantic Water ti-mn the coastal stations to tbrm a convergence front 28 lan off the coast. Meanwhile, the saline wedge displaced towards both the north and the shore which is thvored by the compression of the tipwelling system to a narrow coastal strip outwardly limited by the convergence zone.

Water masses and distribution of physico-chemical properties in the Western Bransfield Strait and Gerlache Strait during Austral summer 1995/96

In the framework of the FRUELA project, two oceanographic surveys were conducted by R/V Hesperides in the eastern Bellingshausen Sea, western basin of the Bransfield Strait and Gerlache Strait area during December 1995 and January 1996. The main hydrographic structures of the study domain were the Southern Boundary of the ACC and the Bransfield Front. The characteristics and zonation of local water masses are discussed in terms of temperature, salinity, dissolved oxygen, nutrient and inorganic carbon concentrations. Concentration intervals for water mass labelling, on the basis of chemical parameters in addition to the common θ/S-based classification, are defined. Silicate seems to be a very good discriminator for local water masses.

Physical and biogeochemical fluxes and net budgets in the subpolar and temperate North Atlantic

Atransoceanic hydrographic sectionacrossthe North Atlantic Subpolar gyre from Vigo (northwestern Iberian Peninsula) to Cape Farewell (south of Greenland) was sampled in summer 1997 as part of the World Ocean Circulation Experiment program (WOCE A25, 4x cruise). The circulation pattern across the 4x section is diagnosed using inverse methods. The e ow is constrained with measured mass transports at specie c sites, while conserving mass and salt for the region north of the section and forcing the silicate e ux to a reasonable value. The e uxes of physical (heat and freshwater) and chemical (nutrients and oxygen) properties are estimated and decomposed into barotropic, baroclinic and horizontal components. The heat transport amounts to 0.65 6 0.1 PW poleward, with 54% and 45% of the e ux due to the baroclinic (or overturning) and horizontal circulation, respectively. From the salt conservation, an equatorward freshwater transport of 20.4 6 1.5 Sv is estimated, resulting from net precipitation plus runoff over the North Atlantic Ocean north of the section. The Subpolar gyre exports nutrients and oxygen southward toward the Subtropical ocean at rates of 250 6 19, 26 6 2, 226 6 15 and 21992 6 440 kmol s 2 1 for nitrate, phosphate, silicate and oxygen, respectively. The main mechanism responsible for the nutrient transport is the overturning cell, whereas oxygen is mainly transported southward due to the large-scale horizontal circulation. Combining our e uxes with those from the 36N section (Rintoul and Wunsch, 1991) allows us to examine budgets of physical (heat and freshwater) and chemical (nitrogen and oxygen) properties for an enclosed area of the Subpolar and Temperate North Atlantic. The tentative nitrogen budget for the box between the 4x and the 36N sections suggests that the Temperate North Atlantic is exporting

Sea surface carbon dioxide off the Iberian Peninsula (North Eastern Atlantic Ocean)

Abstract The variability in carbon dioxide in the eastern North Atlantic Ocean was analysed during three seasons with differing hydrographical and meteorological conditions that corresponded to upwelling and downwelling. No correlation between surface p CO 2 and chlorophyll was found in spring, although a significant correlation was found in autumn when strong downwelling was observed. The convergence that developed over the slope during strong downwelling, produced different regimes of water column stability on the shelf and created areas of high and low p CO 2 . A positive correlation ( r 2 =0.50; n =33) between surface p CO 2 and chlorophyll occurred during the upwelling season. High p CO 2 is found when the greatest concentration of chlorophyll exists. The uptake of carbon by photosynthetic activity masked the increase in dissolved inorganic carbon concentration at the surface due to the upwelling event. Without this biological input, the increase in p CO 2 during the upwelling would be even higher. Air–sea fluxes of CO 2 were calculated for the three studied seasons. The average CO 2 flux from the atmosphere to the ocean (0.47 mmol m −2 d −1 ) in the eastern margin of North Atlantic was slightly lower than those given in previous studies in the North Atlantic ocean because of the influence of upwelling.

Spatio-temporal variability of Air-Sea fluxes of carbon dioxide and oxygen in the Bransfield and Gerlache Straits during Austral summer 1995-96

The potential of the Bellingshausen Sea, Bransfield and Gerlache Straits as sinks for atmospheric CO2 was investigated by studying the carbon data obtained during FRUELA 95 (December 95-January 96) and FRUELA 96 (January-February 96) cruises. Air-sea exchange of CO2 and its relation to air-sea O2 fluxes, surface chlorophyll concentration, physical structures and other environmental variables were also studied. The processes governing the temporal evolution of total inorganic carbon between the two FRUELA cruises were assessed by means of a carbon budget. During FRUELA 95 the frontal region associated with the Southern Boundary of the Antarctic Circumpolar Current (SbyACC) in the Bellingshausen Sea area presented high undersaturation of surface CO2 content (<200 atm), whereas strong oxygen supersaturation (AOU<-48 mol.kg -1 ). This was accompanied by the development of a diatom bloom. Therefore, this area acted as a strong CO2 sink and oxygen source, -6.56 and 2529 (meanSTD) mmol m 2 d -1 , respectively. However, no phytoplanktonic biomass accumulation was reported for this area

Stoichiometry of the net ecosystem metabolism in a coastal inlet affected by upwelling. The Rı́a de Arousa (NW Spain)

The net uptake of inorganic carbon and nitrogen, phosphate and silicate and the net production of dissolved oxygen and organic carbon, nitrogen and phosphorus have been examined in the Ria de Arousa, a large coastal embayment in the NW Iberian upwelling system. Fluxes and net budgets were estimated with a non-stationary 2-D box model [Roson, G., Alvarez-Salgado, X.A., Perez, F.F., 1997. A non-stationary box-model to determine residual flows in a partially mixed estuary, based on both thermoline properties. Application to the Ria de Arousa (NW Spain). Estuarine, Coastal Shelf Sci., 44, 249–262] and the distributions of the different species acquired twice a week between May and October 1989 [Roson, G., Perez, F.F., Alvarez-Salgado, X.A., Figueiras, F.G., 1995. Variation of both thermohaline and chemical properties in an estuarine upwelling ecosystem: Ria de Arousa: 1. Time Evolution. Estuarine, Coastal Shelf Sci., 41, 195–213]. High N/P and N/Si net uptake ratios of 21 and 3.2 were observed during the upwelling season. The rapid recycling of phosphorus compared to nitrogen and the recurrent succession from pioneer diatoms (Si/N∼1) to red-tide forming species (Si/N=0) following the periodic upwelling pulses are the reasons behind the observed ratios. The molar ratios of dissolved oxygen production to inorganic carbon (−1.48) and nitrogen uptake (−10.2) during the upwelling season agree with the Redfield stoichiometry. On the contrary, net nutrient regeneration occurred with N/P, N/Si and O2/C ratios of 7.4, 1.0 and −1.02 during an intense autumn downwelling event. These low ratios are due to the release of an excess of phosphate, silicate and CO2 from the sediments. Conversely, the production of inorganic nitrogen is associated to the consumption of dissolved oxygen following a Redfield ratio of −10.0. Whereas the C/N ratio of the suspended organic matter produced during the upwelling season and consumed during the autumn downwelling event is 6.3–6.7, the N/P ratio changes from 11 during the upwelling season to 15 during the autumn downwelling. About 1/5 of the dissolved oxygen produced during the upwelling season and consumed during the autumn downwelling is delivered to and came from the atmosphere, respectively. Despite the C/N/P/O2 ratios differ from the Redfield values, the high correlation between nutrient salts consumption and dissolved oxygen production (r2=0.74–0.86) allow to estimate an average net ecosystem production (NEP) from the individual elements. The 3–4 d time-scale variability of the average NEP depends on the 2-week periodicity of upwelling pulses, the heat exchange across the sea surface and the stability of the water column. As much as 70% of the total variability can be explained with a linear combination of these parameters.

Decadal acidification in the water masses of the Atlantic Ocean

Significance We provide the first (to our knowledge) observation-based acidification trends in the water masses of the Atlantic basin over the past two decades and compare them with climate model results. Observations and model output confirm that pH changes in surface layers are dominated by the anthropogenic component. In mode and intermediate waters, the anthropogenic and natural components are of the same order of magnitude and sign. Large changes in the natural component of newly formed mode and intermediate waters are associated with latitudinal shifts of these water masses caused by the Southern Annular Mode in the South Atlantic and by changes in the rates of water mass formation in the North Atlantic. Global ocean acidification is caused primarily by the ocean’s uptake of CO2 as a consequence of increasing atmospheric CO2 levels. We present observations of the oceanic decrease in pH at the basin scale (50°S–36°N) for the Atlantic Ocean over two decades (1993–2013). Changes in pH associated with the uptake of anthropogenic CO2 (ΔpHCant) and with variations caused by biological activity and ocean circulation (ΔpHNat) are evaluated for different water masses. Output from an Institut Pierre Simon Laplace climate model is used to place the results into a longer-term perspective and to elucidate the mechanisms responsible for pH change. The largest decreases in pH (∆pH) were observed in central, mode, and intermediate waters, with a maximum ΔpH value in South Atlantic Central Waters of −0.042 ± 0.003. The ΔpH trended toward zero in deep and bottom waters. Observations and model results show that pH changes generally are dominated by the anthropogenic component, which accounts for rates between −0.0015 and −0.0020/y in the central waters. The anthropogenic and natural components are of the same order of magnitude and reinforce one another in mode and intermediate waters over the time period. Large negative ΔpHNat values observed in mode and intermediate waters are driven primarily by changes in CO2 content and are consistent with (i) a poleward shift of the formation region during the positive phase of the Southern Annular Mode in the South Atlantic and (ii) an increase in the rate of the water mass formation in the North Atlantic.

High spatial resolution Alkalinity and pH measurements by IIM-CSIC group along 24.5°N during the R/V Hesperides WOCE Section A05 cruise (July 14 - August 15, 1992)

Dataset contributed to the Project Carbochange.-- More information in http://hdl.handle.net/10261/93331