Search

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2006.09.002 Byline: C.G. Castro, M. Nieto-Cid, X.A. Alvarez-Salgado, F.F. Perez Keywords: Water masses; Remineralization; Nutrients; Dissolved organic matter; Mesopelagic zone; Northeast Atlantic Ocean; European ocean margin Abstract: The short-time-scale variability of the remineralization patterns in the domain of Eastern North Atlantic Central Waters (ENACW) off the NW Iberian Peninsula is studied based on biogeochemical data (oxygen, nutrient salts, total alkalinity, pH, dissolved organic matter and fluorescence of dissolved humic substances) collected weekly between May 2001 and April 2002. The temporal variability of inorganic variables points to an intensification of remineralization during the summer and autumn, with an increase of nutrients, total inorganic carbon and fluorescence and a decrease of oxygen. During the subsequent winter mixing, there is a biogeochemical reset of the system, with lower nutrients, total inorganic carbon and fluorescence and higher oxygen. In contrast to inorganic variables, the levels of dissolved organic matter in the ENACW seem to respond to short-term events probably associated with fast sinking particles, where solubilisation of organic matter prevails over remineralization. Applying a previously published stoichiometric model, we observed a vertical fractionation of organic-matter remineralization. Although there is a preferential remineralization of proteins and P compounds in the entire domain of ENACW, the percentage was higher in the upper ENACW (I80% for the upper ENACW and 63% for the lower. Likewise, the redissolution of calcareous structures contributes about 6% and 13% to the carbon regenerated in the upper and lower layers of ENACW, respectively. Author Affiliation: CSIC, Instituto de Investigacions MariA[+ or -]as, Eduardo Cabello 6, 36208 Vigo, Spain Article History: Received 15 July 2005; Revised 29 August 2006; Accepted 5 September 2006

The continental shelf and the coastal transition zone were described in chemical and biological points of view. The influence of these structures on the shelf regime and their biological consequences were also investigated. Chemical and biological similarities of the two structures suggests that the eddy was an isolated and aged parcel of water originating from the poleward flow.

The costal upwelling system of Ria de Vigo (NW Spain) was monitored during 10 d period to study onset development and decay of winter bloom of Skeletonema costatum which is a common feature there. It is observed that under winter thermal inversion condition onset occurred at upwelling favorable 1/2 week period followed by subsequent 1/2 week of development of bloom followed by down welling which forced the decay of bloom in the next 1/2 week period.

This work aimed to study how mussel culture of Mytilus galloprovincialis Lmk modulates the natural sedimentation rates through the water column as key controlling factor of the potential organic load reaching the bottom sediments. To achieve this objective, seston, feces production and natural sedimentation dynamics were characterized during 4 seasonal campaigns at two mussel rafts and at a reference station not affected by the mussel culture in the Ría de Ares–Betanzos (NW Iberian Peninsula). Our results showed that seston content are below the pseudofeces threshold (< 4 mg L − 1 ) with inorganic contents ranging between maximum values of 76 ± 4% in winter and minimum values of 6 ± 4% in spring. These seasonal variations controlled the feces (biodeposits) production by mussels (11–221 mg ind − 1 d − 1 ) that increased with seston content, in particular under winter stormy conditions, when intense continental runoff and resuspension processes represented an important source of non-digestive inorganic particles for mussels. Natural sedimentation fluxes recorded by means of sediment traps under the rafts (84–536 g m − 2 d − 1 ) seasonally varied with mussel biodeposition being 6–7 folds the rates at the reference site. This fact corroborates that mussel feeding activity throughout the production of feces increased natural sedimentation rates in the Ría de Ares–Betanzos. However, the relatively energetic water column conditions and the potentially high degradation rates of feces in the culture area reduced up to 55–90% the biodeposits' organic carbon potentially arriving at the seafloor. This indicates that in highly hydrodynamic environments the impact derived from shellfish culture may be reduced, attenuating a possible impact on the benthic communities. [ABSTRACT FROM AUTHOR]

Data collected in February, 2003, along the upper continental slope of western North America between Monterey Bay, California (37°N, 122°W), and Cabo San Lucas, Mexico (23°N, 118°W), document, for the first time, the alongshore distribution of total organic carbon (TOC). Highest TOC concentrations (>70 µM) were observed for waters above the nitracline and associated with both California Current and southern surface waters. The northward advection of tropical waters in the California Undercurrent did not have any discernible impact on TOC distributions. An estimate of the average rate at which TOC in surface waters was exported offshore by Ekman transport in February 2003 was 1.73 × 103 kg C yr−1 for each meter of coastline. The offshore flux estimate is thought to be conservative with respect to the annual mean offshore flux because the offshore Ekman transport and primary production increase in late spring and early summer and the contribution of upwelling filaments has not been considered. Analysis of TOC contributions to pelagic respiration suggested that TOC accounted for 45% of the oxygen decrease in southern oxic waters. In California Current and oxygen minimum zone waters, TOC did not contribute to pelagic respiration. [ABSTRACT FROM AUTHOR]

Abstract: Long-term variability of the biogeochemical properties during the formation of central waters in the Eastern North Atlantic were analyzed between 42–47°N and 10–20°W from the dataset gathered during the Galicia VII (GVII) and C. Darwin 58/59 (CD58/59) cruises. These cruises that showed important changes in the thermohaline properties and the nutrient abundance of the upper layers were carried out under contrasting conditions of the North Atlantic Oscillation (NAO) index. The different climate forcing led a meridional shift of the transition zone between the formation regions of subpolar and subtropical Eastern North Atlantic Central Water (ENACWp and ENACWt, respectively). This displacement conditioned the presence of each ENACW in the study region and so the thermohaline and biogeochemical properties. The effect of the observed variability at decadal scale on the air–sea CO2 gradient (ΔfCO2) and exchange (F CO2) was analyzed using 1D model approach throughout 11 weekly-steps that simulated the development of a spring bloom during the shoaling of the mixed layer. The outputs of the model showed an intensification of the ocean CO2 uptake due to higher biological CO2 drawdown, during positive NAO conditions and its weakening under negative NAO influence. [ABSTRACT FROM AUTHOR]

Abstract: The Bay of Biscay is part of the North Atlantic Ocean, the most important sink of CO2, and a subduction zone of mode waters that favours the entry of carbon to the ocean interior. To investigate the seasonal and interannual variability of CO2 uptake, continuous underway measurements of the partial pressure of CO2 at sea surface were performed along a commercial route between Vigo (Spain) and St. Nazaire (France). An unattended measuring system of CO2 fugacity (fCO2), with meteorological station, and temperature, salinity, oxygen and fluorescence sensors, was installed on board of ships of opportunity (RO-RO L’Audace and RO-RO Surprise). The dataset collected between December 2002 and December 2004 reported a significant interannual variability; mainly for the winter season. The noticeable increase of fCO2 sw during the winter mixing period of 2004 was associated to biogeochemical differences related to nutrient ratios, phytoplankton activity and atmospheric CO2 uptake. Dividing the seasonal cycle into three periods, prebloom (October–February), bloom (March–May) and postbloom (June–September), the fCO2 sw for the entire seasonal cycle was correctly predicted by empirical relationships with an error lower than 10μatm in spite of the high interannual variability. The fCO2 sw variability at seasonal scale was mainly controlled by processes of synthesis and remineralization of organic matter during prebloom and bloom periods whereas SST was the key parameter during postbloom period. The surface waters of the Bay of Biscay showed a clear role as atmospheric CO2 sink ranging from −2.7±2.8 (±0.3) to −0.08±0.41 (±0.04)molCm−2 yr−1 (mean±standard deviation (±error)) throughout each complete period although CO2 release to atmosphere was also observed during short episodes of summer. Using the regular wind speed sources of CO2 fluxes estimation ranged from −1.3±1.7 (±0.1) to −2.4±2.7 (±0.1)molCm−2 yr−1 at annual scale, exceeding the sink capacity of the nearby regions of the North Atlantic Ocean. [Copyright &y& Elsevier]

Abstract: We analyse the 30 October, 2004, X1.2/SF solar event that occurred in AR 10691 (N13 W18) at around 11:44UT. Observations at 212 and 405GHz of the Solar Submillimeter Telescope (SST), with high time resolution (5ms), show an intense impulsive burst followed by a long-lasting thermal phase. EUV images from the Extreme Ultraviolet Imaging Telescope (SOHO/EIT) are used to identify the possible emitting sources. Data from the Radio Solar Telescope Network (RSTN) complement our spectral observations below 15GHz. During the impulsive phase the turnover frequency is above 15.4GHz. The long-lasting phase is analysed in terms of thermal emission and compared with GOES observations. From the ratio between the two GOES soft X-ray bands, we derive the temperature and emission measure, which is used to estimate the free-free submillimeter flux density. Good temporal agreement is found between the estimated and observed profiles, however the former is larger than the latter. [Copyright &y& Elsevier]

Abstract: Since the installation of the Solar Submillimeter Telescope (SST) in 1999 in the Complejo Astronómico El Leoncito (CASLEO, Argentina), the almost unexplored solar emissions at frequencies >100 GHz started to reveal new insights about thermal and non-thermal processes in active regions. SST operates at the frequencies of 212 and 405 GHz providing the unique opportunity to distinguish and investigate emission mechanisms. We present a review of the most relevant findings obtained. An statistical study made with observations of a selected sample of active regions shows that their flux density spectra increase with frequency. Rapid brightenings (pulses) are always observed both at 212 and 405 GHz in association to solar flares lasting for some tens to hundreds of milliseconds. They are well correlated between the two frequencies and have flux spectra either flat or increasing with frequency. The flux of submillimeter wave pulses remain within the same order of magnitude for different bursts, ranging typically 100–300 s.f.u. at 212 GHz and 500–1000 s.f.u. at 405 GHz. The time evolution of the pulse occurrence rate usually reproduces the time profile of the X-rays/γ-rays emission, and the bulk emission at submillimeter waves, when the latter is observable. There are examples of good correlation between individual pulses at submillimeter waves and hard X-rays/γ-rays. Submillimeter pulses are not restricted to flare events, but appear to be a general phenomenon that occurs over active regions as well. The starting time of the rapid submillimeter wave pulses is coincident or precedes the projected launch time of the coronal mass ejections. SST observations of the November 4, 2003 large flare revealed a new and yet unknown spectral component with intensities increasing towards even higher frequencies, appearing along with, but separated from the well-known microwave component. [Copyright &y& Elsevier]

Presents a study which explored the chemical fields in the Eastern Bellingshausen Sea, Gerlache and Bransfield Straits for nutrients, apparent oxygen utilization and total inorganic carbon during the FRUELA program surveys in 1995 and 1996. Materials and methods; Results; Discussion.

Presents a study which reported the findings of oceanographic surveys on the Bransfield Strait and Gerlache Strait in the Antarctic Peninsula in December 1995 and January 1996. Materials and methods; Results; Discussion.

The hydrodynamics of the bottom boundary layer (BBL) in the Ría de Vigo (NW Iberian Peninsula) are studied for the first time, identifying their possible forcing factors and filling a previous lack of knowledge about the coastal upwelling system of NW Iberian Peninsula. For tackling this subject, high resolution time series of bottom currents by means of a downwards looking Acoustic Doppler Current Profiler (3m above the bottom) were recorded in the inner part of the Ría de Vigo covering the four seasons of the climate year 2004–2005. Our results point to a coupling among bottom residual currents, shelf winds and runoff supporting previous works not directly focused on BBL. Most of the time, 64.5%, 75.4% and 61.6% for residual, tidal and total currents respectively, the bottom currents respond to a logarithmic profile being possible to apply the law of the wall and estimate shear stress. Shear stress variability is controlled by the frequency of wind reversals and modulated by runoff and thermal stratification. Rapid shifts of wind direction favors the generation of shear stress. Intense summer stratification or strong winter mixing of the water column reduces shear stress levels. Runoff by increasing the variability of the velocity pulse direction can favor the development of shear stress. Bottom shear stress reaches levels that are strong enough (~5% of the time in autumn) to re-suspend fine cohesive sediments. This fact comes out to support previous biogeochemistry studies suggesting the occurrence of intense resuspension processes during the autumn season. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps. The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365mgm−2 d−1, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (Cphyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546mgm−2 d−1 and 22mgchl a m−2 d−1, respectively) and minimum values during winter (22mgm−2 d−1 and 0.1mgchl a m−2 d−1, respectively). The contribution of Cphyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of Cphyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, Cphyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal Cphyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension. [Copyright &y& Elsevier]

Abstract: The influence of suspended mussel culture on the benthic–pelagic coupling was evaluated in the Ría de Vigo, in the coastal upwelling system of the NW Iberian Peninsula, during the month of July 2004. Measurements of water column properties were carried out at three stations in the Ría de Vigo: under a mussel raft (1), and at two reference sites in the main channel (2) and in the inner part (3) of the Ría. Dissolved nutrients, dissolved oxygen and inorganic carbon benthic fluxes were measured by means of a benthic chamber at stations 1 and 3. Sediment traps were deployed at 6 locations to estimate vertical fluxes. The water column structure at the three study stations was very similar, characterized by upwelling conditions during the second week of July and a posterior stratification showing a strong thermocline, with a depth fluctuation mainly modulated by the shelf wind regime. Vertical POC fluxes underneath the mussel raft (3gCm− 2 d−1) were 3 times higher than those obtained between rafts and 10 times higher than in the main channel reference site. Dissolved oxygen, ammonium, silicate and phosphate benthic fluxes were significantly higher under the raft than at the inner Ría reference site. A 1D carbon budget showed the importance of benthic metabolism under the raft (2.3±0.8gCm−2 d−1), being higher than the organic carbon produced at the photic layer (0.7±0.3gCm−2 d−1), as a result of higher organic loading compared to the inner Ría reference site. The results show for the first time the important role that suspended mussel cultures play in the benthic–pelagic coupling in this coastal upwelling ecosystem. [Copyright &y& Elsevier]

Repeated hydrobiological surveys over the period 1988–2002 perpendicular to the central California coast indicate strong coupling between physical circulation and biological production. An equatorward-flowing jet about 100–200 km from shore marked the inshore edge of the California Current (CC). This “CC Jet” had its highest velocities during late winter and spring. The jet divided inshore, biologically productive waters from offshore, low-production waters. Mean flow in the inshore waters is poleward. However, this flow is interrupted in late spring and summer by a surface-enhanced, equatorward-flowing, coastal upwelling jet. The upwelling jet coincides with maxima of nutrients, chlorophyll-a and primary production. Annual variability in the inshore zone is related to (1) vertical pycnocline movements associated with geostrophic adjustments to accelerations of the California Current system, and (2) coastal upwelling. In offshore waters, the annual cycle accounted for a small fraction of the variability, indicating the dominance of eddies and meanders in this zone (J. Geophys. Res. 92 (1987) 12 947). The offshore regime was mesotrophic to oligotrophic, with a subsurface chlorophyll-a maximum above the nutricline. Considerable subduction may occur under the California Current jet and be an important process in the export of biogenic material to the deep sea. [Copyright &y& Elsevier]

Over the past decades, as a consequence of human activity, there was an increase in nutrient inputs to the ocean and they are expected to enhance even more in the future. Coastal areas, accounting for a significant proportion of marine primary productivity, are the most vulnerable zones to anthropogenic impacts. The response of phytoplankton communities to an increase in organic and inorganic nutrients levels from natural allochthonous sources was assessed in microcosm experiments conducted in a coastal system affected by intermittent upwelling events (Ría de Vigo, NW Iberia). Three nutrient addition experiments were performed in spring, summer and autumn, when surface water was supplemented with 5 and 10% of atmospheric and riverine matter. Pico-, nano- and microphytoplankton abundances, chlorophyll a concentration (Chl a ) and primary production rates (PP) were measured and compared with those in the control seawater sample (without additions) after 48 h of incubation. Simultaneous experiments with controlled additions of inorganic and organic nutrients were also performed in order to describe the limiting nutrient for phytoplankton growth at each experiment. The composition of the matter inputs and the structure of the phytoplankton communities determined the type of response observed. Phytoplankton responses varied among seasons, being positively correlated with dissolved inorganic nitrogen (DIN) concentrations. As expected, the phytoplankton responses to external nutrient inputs were stronger under low nutrient levels (summer) than when phytoplankton was already growing in nutrient replete conditions (spring). Null and negative responses to the natural inputs were observed in autumn, which suggests that the oceanic phytoplankton advected to this coastal system during downwelling events could be occasionally inhibited by these nutrient inputs. In a future global change scenario, characterized by enhanced nutrient inputs from riverine and atmospheric origin, the response of phytoplankton communities will strongly depend on the concentration and chemical composition of these inputs and on the structure of phytoplankton communities able to respond to them. [ABSTRACT FROM AUTHOR]

To better understand sources and transport of particulate material in the NW Iberian coastal upwelling system, a mooring line dotted with an automated PPS 4/3 sediment trap was deployed off Cape Silleiro at the base of the photic zone. The samples were collected from November 2008 through June 2012 over sampling periods of 4–12 days. Our study represents the first automated sediment trap database for the NW Iberian margin. The magnitude and composition of the settling material showed strong seasonal variability with the highest fluxes during the poleward and winter mixing periods (averages of 12.9±9.6 g m −2 d −1 and 5.6±5.6 g m −2 d −1 respectively), and comparatively lower fluxes (3.6±4.1 g m −2 d −1 ) for the upwelling season. Intensive deposition events registered during poleward and winter mixing periods were dominated by the lithogenic fraction (80±3%). They were associated to high energy wave-driven resuspension processes, due to the occurrence of south-westerly storms, and intense riverine inputs of terrestrial material from Minho and Douro rivers. On the other hand, during the spring - summer upwelling season, the share of biogenic compounds (organic matter, calcium carbonate (CaCO3), biogenic silica (bSiO2)) to downward fluxes was higher, reflecting an increase in pelagic sedimentation due to the seasonal intensification of primary production and negligible river inputs and wave-driven resuspended material. Otherwise, the large variations of biogenic settling particles were mainly modulated by upwelling intensity, which by means of upwelling filaments ultimately controlled the offshore transport of the organic carbon fixed by primary producers towards the adjacent ocean. Based on the average downward flux of organic carbon (212 mg C m −2 d −1 ) and considering an average primary production of 1013 mg C m −2 d −1 from literature, we estimated that about 21% of the fixed carbon is vertically exported during the upwelling season. [ABSTRACT FROM AUTHOR]