Evidencias do cambio climático na hidrografía e a dinámica das rías e da plataforma galega

16 páginas, 9 figuras, 3 tablas[EN] This study is focused on multidecadal-scale variations of the hydrographic and hydrodynamic features of Rías and shelf waters off Galicia. Water masses take, through their thermohaline characteristics, a footprint of the climatic variability, mainly caused by changes either in the hydrological budget (precipitation, evaporation, runoff), in heat exchange and wind stress. In this study we focus in the evidences of change in the surface and sub-surface water mass characteristics. Regarding surface water masses, a significant warming during the last 45 years has been noticed, at a rate of 0.17 ºC/ decade. This warming was especially intense from the 1970’s, 0.27 ºC/decade. The tendency is opposite in subsurface waters, but it only takes into account data from the last 15 years. Regarding hydrodynamics, because of its strong influence in the renewal time of the Rías and consequently in their living resources, a study of decadal changes in the estuarine circulation of the Rías de Vigo and Arousa has been made. Results showed a progressive decay in the estuarine circulation, which causes an increase of renewal times. On the other hand, indirect evidence of a possible deceleration of the winter Iberian Poleward Current (IPC) are reported. This slow down is partially caused by a decrease in the meridional (N-S) temperature gradient off the Iberian coast. Nevertheless, the fall of the meridional gradient is not clear because it has been inferred from surface waters. On the contrary, IPC seems to be intensified by the increasing southerly autumn winds, although it appears weakened by the decreasing southerly winter winds. Thus, the overall effect of the CIP is still uncertain. Finally, a study of sea level and wave changes on the Galician coast has been made. An increase of (2-2.5 cm/ decade) in the sea level as well as a decrease in the wave height (3 cm/decade) has been reported, but in this last topic results are not significant[GA] Este estudo centrarase en determinar as variacións que ocorren a escalas multidecadais nas características hidrográficas e hidrodinámicas das augas das rías e da plataforma fronte a Galicia. As masas de auga reciben a través das súas características termohalinas unha pegada das alteracións climáticas, principalmente a causa de cambios no balance hidrolóxico (precipitación, evaporación, achegas continentais), do intercambio de calor e da acción do vento. Neste estudo analizaremos as evidencias de cambio nas características das masas de auga superficiais e subsuperficiais. Nas primeiras detectouse quentamento de xeito significativo nos últimos 45 anos a unha taxa media de 0,17 ºC por década, especialmente intenso desde hai 30 anos, 0,27 ºC por década. Nas augas subsuperficiais a tendencia é a inversa, aínda que só se conta con datos dos últimos 15 anos. En canto á hidrodinámica, e pola súa forte implicación nos tempos de renovación da ría e, polo tanto, nos recursos mariños que viven nela, fíxose un estudo sobre os cambios na circulación estuárica das rías de Vigo e Arousa nas últimas décadas. Os resultados amosan un descenso paulatino a longa escala temporal da circulación que causa un aumento dos tempos de renovación. Por outra banda, achéganse evidencias indirectas dunha posible ralentización da corrente invernal cara ao Polo (CIP) causada por un descenso no gradiente meridional (N-S) de temperatura fronte ás costas ibéricas. Non obstante, o descenso do gradiente meridional non está claro, pois induciuse só a partir de datos superficiais. Ademais, a propia CIP amosa estar intensificada pola maior intensidade dos ventos sur no outono e debilitada polo descenso dos ventos do sur no inverno, polo que o efecto global na CIP é aínda incerto. Por último, faise un estudo dos cambios do nivel do mar e da ondada nas costas galegas que amosa un aumento daquel (2-2,5 cm/década) e un descenso desta (3 cm/década), aínda que no caso da ondada os resultados non son concluíntesPeer reviewe

Benthic oxygen fluxes in a coastal upwelling system (Ria de Vigo, NW Iberia) measured by aquatic eddy covariance

Organic carbon mineralization and nutrient cycling in benthic environments are critically important for their biogeochemical functioning, but are poorly understood in coastal up - welling systems. The main objective of this study was to determine benthic oxygen fluxes in a muddy sediment in the Ria de Vigo (NW Iberian coastal upwelling), by applying the aquatic eddy covariance (AEC) technique during 2 campaigns in different seasons (June and October 2017). The main drivers of benthic fluxes were studied and compared among days in each season and between seasons. The 2 campaigns were characterized by an upwelling-relaxation period followed by a downwelling event, the last of which was due to the extratropical cyclone Ophelia in October. The mean (±SD) seasonal benthic oxygen fluxes were not significantly different for the 2 campaigns despite differences in hydrodynamic and biogeochemical conditions (June: -20.9 ± 7.1 mmol m-2d-1vs. October: -26.5 ± 3.1 mmol m-2d-1). Benthic fluxes were controlled by different drivers depending on the season. June was characterized by sinking labile organic material, which enhanced benthic fluxes in the downwelling event, whereas October had a significantly higher bottom velocity that stimulated the benthic fluxes. Finally, a comparison with a large benthic chamber (0.50 m2) was made during October. Despite methodological differences between AEC and chamber measurements, concurrent fluxes agreed within an acceptable margin (AEC:benthic chamber ratio = 0.78 ± 0.13; mean ± SD). Bottle incubations of water sampled from the chamber interior indicated that mineralization could explain this difference. These results show the importance of using non-invasive techniques such as AEC to resolve benthic flux dynamicsPostprin

Description of an experimental set up for the culture of benthic foraminifera in controlled pH conditions

10 páginas, 4 figuras, 1 tabla[EN] Acidification of the oceans is one of the consequences of ongoing increasing atmospheric CO2 concentrations. The effects on organisms that build their shells of calcium carbonate are not sufficiently studied and might be detrimental. Simulating ocean acidification scenarios in the laboratory is a reasonable way to study their response to decreased pH and carbonate ion concentrations. In this study we describe in detail an experimental system to carry out ocean acidification experiments with non-symbiotic benthic foraminifera. We test the performance of the designed experimental set up by running a long-term experiment (90 days) using a potentially suitable benthic foraminiferal species for culturing (Miliolinella spp.). Although foraminifera did not survive the experimental period likely due to ciliates infestation, seawater pH measurement results indicate that the design is suitable for carrying out ocean acidification experiments[ES] La acidificación oceánica es una de las consecuencias del aumento progresivo de la concentración de CO2 en la atmósfera. Los efectos en los organismos que construyen sus conchas con carbonato cálcico no están suficientemente estudiados, pero podrían ser perjudiciales. La simulación en laboratorio de diferentes escenarios de acidificación oceánica es una forma de estudiar la respuesta de esos organismos al descenso de pH y de la concentración del ion carbonato. En este estudio se describe minuciosamente un sistema experimental diseñado para realizar experimentos de acidificación oceánica con foraminíferos bentónicos sin simbiontes. La viabilidad del diseño experimental se ha probado con un experimento de larga duración (90 días) utilizando una especie de foraminífero bentónico potencialmente apta para ser cultivada (Miliolinella spp.). Aunque los foraminíferos no sobrevivieron durante todo el experimento debido a contaminación por ciliados, los resultados de las medidas del pH marino ponen de manifiesto que el diseño es adecuado para llevar a cabo experimentos de acidificación oceánicaThis research leading to these results was supported by the Spanish Ministry of Sciences and Innovation and co-founded by the Fondo Europeo de Desarrollo Regional 2007-2012 (FEDER) through the CATARINA Project (CTM2010-17141/MAR) and GRACCIEPeer reviewe

Decadal acidification in the water masses of the Atlantic Ocean

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 (ΔpH) 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

Tide and wind coupling in a semienclosed bay driven by coastal upwelling

The Ría de Vigo is a semi-enclosed bay in which tidal residual currents are associated with coastal upwelling events. Both upwelling and downwelling favourable winds generate a bidirectional exchange flow with the shelf – a two-layer circulation with surface waters leaving (entering) the ria and a compensating inflow (outflow) through the bottom layer under upwelling (downwelling) conditions. This vertical circulation changes the vertical density structure inside the ria. In the ria, the tide is mainly semidiurnal (M2, S2 and K2), with some energy in the diurnal band (K1). Our velocity observations show that the vertical structure of the tidal currents in the ria do not exhibit a classic barotropic profile with a bottom boundary layer beneath uniform “free-stream” flow as the tidal bottom boundary layer is affected by stratification. This links tidal circulation to the wind-driven residual circulation, since the latter also greatly helps to control the stratification. We quantify this effect by fitting tidal ellipses to observed velocities through the water column. In addition to this indirect coupling through stratification, there is a direct interaction in which velocities in the upper and bottom layers are best correlated with winds while the mid-water velocities are best correlated with tides. These wind-tide interactions are expected to play a key role in the resuspension and transport of nutrients and phytoplankton in the Ria.CTM2012-3515

Geochemical vs. microbial approach to the new production of the coastal upwelling system of the Ría de Vigo (NW Spain)

Symposium GLOBEC–IMBER España, Valencia, 28-30 marzo 2007The fate of the inorganic and organic N trapped in the coastal upwelling system of Ría de Vigo (NW Spain), accumulation/export versus production/ consumption, was studied at the short time–scale (2–4 d) during July 2002. A transient geochemical box model was applied to the measured residual currents and concentrations of inorganic (NT), dissolved (DON) and particulate (PON) organic N to obtain the i) net balance of inputs minus outputs (i – o); ii) the net accumulation (V·dN/dt); and iii) the net ecosystem production (NEP) of NT, DON and PON. The average NEP during July (107 mg N m-2 d-1) indicates an autotrophic metabolism of the ría. About 25% of this material was exported to the shelf and the remaining 75% was transferred to the sediments or promoted to higher trophic levels. Measurements of oxygen production (Pg) and respiration (R) were performed in a single site twice a week at five depths. In addition, microzooplankton grazing and sedimentation rates were measured for first time in the Ría de Vigo. The high grazing rates observed reduces the efficiency of the ría to transfer organic matter directly from phytoplankton to the metazoans Comparison of the metabolic state of the Ría de Vigo derived from these in vitro measurements (Pg, R, grazing and sedimentation) and the in situ geochemical budget shows that they agree in 2 of the 3 study cases. Both methods are complementary and their simultaneous application allows obtaining a better knowledge of coastal upwelling ecosystems functioningN

Oceanographic processes and morphosedimentary products along the Iberian margins: A new multidisciplinary approach

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Radar on RAIA: High frequency radars in the RAIA Observatory

The RADAR ON RAIA project aims to update and extend beyond the Galician border the High Frequency (HF) radar network that has been operating since 2011 in the framework of the RAIA Observatory. The Project is allowing the establishment of a cross-border collaboration beyond the physical infrastructure itself, developing a sharing strategy of maintenance procedures, validation and data processing on both sides of the border, as well as an easy and public access to all the information. In addition, new products are being developed to exploit the potential of the HF radar technology.Peer Reviewe

RADAR ON RAIA: High frequency radars in the RAIA Observatory

9th International Workshop on Marine Technology (MARTECH), virtual, 16-18 June 2021The RADAR ON RAIA project aims to update and extend beyond the Galician border the High Frequency (HF) radar network that has been operating since 2011 in the framework of the RAIA Observatory. The Project is allowing the establishment of a cross-border collaboration beyond the physical infrastructure itself, developing a sharing strategy of maintenance procedures, validation and data processing on both sides of the border, as well as an easy and public access to all the information. In addition, new products are being developed to exploit the potential of the HF radar technologyN