Near inertial oscillations at the shelf off northern Patagonia

Quatro séries temporais de correntes obtidas próximas a 43°S sobre a plataforma continental da Patagôn ia, coletadas entre Setembro/1991 e Agosto/1992, foram filtradas com frequências de corte de 0.049 e 0.068 ciclos por hora (cph) para extrair a componente quase inercial. As séries temporais filtradas têm somente uma pequena atenuação de amplitude quando comparadas aos dados originais e a fase não foi alterada. Em dois fundeios costeiros, onde a coluna d’água é fracamente estratificada a energia contida na banda inercial é desprezível. Sobre plataforma externa o pico inercial é largo, e velocidades máximas são > 25 cm s-1. O vetor velocidade horizontal é quase polarizado circularmente (excentricidade de 1.04) e gira em sentido anti-horário com uma freqüência um pouco maior que a freqüência inercial local. A direção de propagação é para 105° relativos ao norte verdadeiro, aproximadamente perpendicular à costa. A correolação complexa entre correntes filtradas nas profundidades de 17 e 67 m tem uma magnitude de 0.83 e uma diferença de fase de 176°, indicando que o fluxo é dominado pelo primeiro modo baroclínico. A taxa entre as amplitudes acima e abaixo da picnoclina é controlada pela profundidade da picnoclina, como previsto por um modelo de duas camadas. O modelo simples de Pollard & Millard (1970), forçado com o vento de Puerto Madryn, reproduziu muitos dos fatores observados das correntes inerciais na camada superficial. A ausência de oscilações inerciais sobre plataforma externa durante o inverno, e a reduzida amplitude costeira durante o período de amostragem, são associadas portanto à reduzida estratificação da coluna de água.Four current time series collected near 43°S on the continental shelf off Patagonia from September 1991 to August 1992 have been band pass filtered with cutoff frequencies of 0.049 and 0.068 cycles per hour (cph) to extract the near-inertial component. The filtered time series have only small amplitude attenuation when compared to the original data and phase is not changed. At two near-shore moorings, where the water column is poorly stratified the energy contained in the inertial band is negligible. At mid-shelf the spectral peak of the inertial band is large and maximum speeds are > 25 cm s-1. The horizontal velocity vector is nearly circularly polarized (eccentricity of 1.04) and rotates counterclockwise with a frequency a few percent greater than the local inertial frequency. The propagation direction is to 105°T, approximately perpendicular to the co ast. The complex correlation between filtered currents at 17 and 67 m depth has a magnitude of 0.83 and a phase difference of 176°, indicating that the flow is dominated by the first baroclinic mode. The ratio between observed amplitudes above and below the pycnocline is controlled by pycnocline depth, as predicted by a two-layer model. The simple model of Pollard and Millard (1970) forced with wind data from Puerto Madryn reproduced many of the observed features of the inertial currents in the surface layer. The lack of inertial oscillations in the mid-shelf during Austral winter and the reduced amplitude near the coast throughout the sampling period, are associated to the reduced stratification of the water column.Fil: Rivas, Andres Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; ArgentinaFil: Piola, Alberto Ricardo. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

High-frequency frontal displacements south of san jorge gulf during a tidal cycle near spring and neap phases biological implications between tidal states

San Jorge Gulf (SJG) is a region of high biological productivity that supports important shrimp (Pleoticus muelleri) and hake (Merluccius hubbsi) fisheries, as well as high marine biodiversity associated, in part, with a tidal front located in the southern part of the gulf. In situ high-resolution cross-frontal measurements were collected using a remotely operated towed vehicle to characterize the three-dimensional structure of the tidal front and to investigate how its position varies during the semidiurnal tidal cycle (high/low) and the spring to neap transition, together with its impact on the distribution of nutrients and chlorophyll-a. Estimates of tidal height and flow velocity derived from a numerical model support the conclusion that frontal displacements mostly result from advec-tion by cross-frontal tidal currents. The frontal position was also modified by baroclinic instabilities that significantly distort the front. Measurements reveal intrusions of low-salinity, nutrient-rich waters from the mixed side into the pycnocline on the stratified side cause a subsurface chlorophyll-a peak near the neap phase. Most prior studies of fronts in the SJG have been limited to their surface manifestations because they were conducted using satellite images. This article aims to contribute to the understanding of the complex southern tidal front dynamics, highlighting that maximum primary productivity occurs in a subsurface layer that is not visible by satellite sensors.Fil: Carbajal, Juan Cruz. Centro Para El Estudio de Sistemas Marinos (cesimar), Conicet-cenpat; ArgentinaFil: Rivas, Andres Lujan. Centro Para El Estudio de Sistemas Marinos (cesimar), Conicet-cenpat; ArgentinaFil: Chavanne, Cédric. Institut Des Sciences de la Mer de Rimouski; Canad

High-frequency frontal displacements south of san jorge gulf during a tidal cycle near spring and neap phases biological implications between tidal states

San Jorge Gulf (SJG) is a region of high biological productivity that supports important shrimp (Pleoticus muelleri) and hake (Merluccius hubbsi) fisheries, as well as high marine biodiversity associated, in part, with a tidal front located in the southern part of the gulf. In situ high-resolution cross-frontal measurements were collected using a remotely operated towed vehicle to characterize the three-dimensional structure of the tidal front and to investigate how its position varies during the semidiurnal tidal cycle (high/low) and the spring to neap transition, together with its impact on the distribution of nutrients and chlorophyll-a. Estimates of tidal height and flow velocity derived from a numerical model support the conclusion that frontal displacements mostly result from advec-tion by cross-frontal tidal currents. The frontal position was also modified by baroclinic instabilities that significantly distort the front. Measurements reveal intrusions of low-salinity, nutrient-rich waters from the mixed side into the pycnocline on the stratified side cause a subsurface chlorophyll-a peak near the neap phase. Most prior studies of fronts in the SJG have been limited to their surface manifestations because they were conducted using satellite images. This article aims to contribute to the understanding of the complex southern tidal front dynamics, highlighting that maximum primary productivity occurs in a subsurface layer that is not visible by satellite sensors.Fil: Carbajal, Juan Cruz. Centro Para El Estudio de Sistemas Marinos (cesimar), Conicet-cenpat; ArgentinaFil: Rivas, Andres Lujan. Centro Para El Estudio de Sistemas Marinos (cesimar), Conicet-cenpat; ArgentinaFil: Chavanne, Cédric. Institut Des Sciences de la Mer de Rimouski; Canad

On the variability of tidal fronts on a macrotidal continental shelf, Northern Patagonia, Argentina

Tidal fronts are associated with the transition between homogeneous and vertically stratified water and characterized by the simultaneous availability of light and nutrients that enhance the growth of marine productivity. We study the variability in the position of two tidal fronts located in Patagonia Argentina: the San Matías and Valdés fronts. The rate of tidal dissipation in these regions is among the highest of the world ocean. The study is based on the analysis of over 1200 satellite derived sea surface temperature images. The results indicate that the mean monthly position of both fronts is strongly linked to the characteristics of the bottom topography. In response to increasing surface heat flux the fronts displace toward shallower areas. Similarly, a slight displacement towards deeper waters is observed when the heat flux decreases. High frequency variability is revealed by the standard deviation around monthly averages. At the mouth of San Matías gulf, the front location variability in the spring-neap cycle is around 10 km, while east of Valdés Peninsula the fortnightly cycle is masked by high frequency fluctuations (~30 km) governed by meanders and meso-scale filaments. A simple conceptual model is proposed that suggests that the mean frontal position is determined by the bottom topography while its seasonal variability is driven by the surface heat flux, and the front intensity is modulated by the spring-neap transition.Fil: Pisoni, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Rivas, Andres Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Universidad Nacional de la Patagonia; ArgentinaFil: Piola, Alberto Ricardo. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Dynamics of Macronutrients in the San Jorge Gulf During Spring and Summer

Following designation of San Jorge Gulf (SJG) as a priority for marine conservation by the Argentine scientific community, it was included in the “Pampa Azul” government initiative. As a contribution to this initiative, we analyzed macronutrient distribution and its relationship to the stratification and primary producer biomass in the water column during austral summer 2014 and spring 2016. In addition, we determined dissolved oxygen, chlorophyll concentrations, and pH. During both seasons in the central and northern gulf, strong stratification separated nutrient-poor, oxygenated surface waters from nutrient-rich, less-oxygenated deep waters. Thermal stratification was correlated to nutrient concentrations. Oxygen decreased up to 60% in bottom waters, although hypoxic conditions were not found. Nitrate limited primary production in surface waters. A tidal front near the gulf’s mouth in the south and wind-forced upwelling in the southwestern coastal zone naturally fertilized the waters. Although there is no information on the precise amount of nutrients each source contributes to the SJG, a shortcut in the path toward resource conservation could be directed through the processes associated with water column stratification because it determines the availability of surface nutrients to primary producers.Fil: Torres, Américo Iadran. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Paparazzo, Flavio Emiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Williams, Gabriela Noemí. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Rivas, Andres Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Solis, Miriam Edith. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Esteves, Jose Luis. Fundación Patagonia Natural, Chubut; Argentin

Quantitative estimation of the influence of surface thermal fronts over chlorophyll concentration at the Patagonian shelf

Eighteen-year (1985–2002) mean monthly SST Pathfinder data with 9 km spatial resolution have been used to estimate surface gradients by finite differences. Then the seasonal climatological means have been calculated from the intensity of these gradients, and surface thermal fronts present in the Patagonian Continental Shelf (PCS) have been located. Moreover, 6 years (1998–2003) of SeaWiFS data with approximately 4 km spatial resolution have been used to estimate monthly composite images of surface chlorophyll concentration, after which seasonal climatological means distributions have been generated. Both seasonal distributions have been analyzed together and by combining the knowledge of oceanographic processes and phytoplankton responses to light and nutrient availability, regions where the presence of a thermal front affects photosynthetic activity have been identified. Subjective criteria have been applied to define eighteen areas where phytoplankton biomass is influenced by the presence of a thermal front. In these areas, the surface chlorophyll (spatial mean and total), its relationship with the surface chlorophyll of the whole region, and the seasonal evolution of this relationship have been calculated. All frontal areas cover less than 15% of the total surface, but they contribute with over 23% of the phytoplankton annual mean biomass. Considered as a group, during summer they show high chlorophyll values very similar to those in spring. During the cold period, when the water column is vertically mixed in practically the whole of PCS, the influence of physical fronts over the biological production is minimum. The frontal zone image remains clearly defined during summer, when approximately 85% of the area will have a determined mean chlorophyll concentration, while the other 15% has a 2.45 times larger value. While three pattern trends have been identified in the frontal areas, only two of them condition the pattern of the group, due to their horizontal extension. © 2006 Elsevier B.V. All rights reserved.–2002) mean monthly SST Pathfinder data with 9 km spatial resolution have been used to estimate surface gradients by finite differences. Then the seasonal climatological means have been calculated from the intensity of these gradients, and surface thermal fronts present in the Patagonian Continental Shelf (PCS) have been located. Moreover, 6 years (1998–2003) of SeaWiFS data with approximately 4 km spatial resolution have been used to estimate monthly composite images of surface chlorophyll concentration, after which seasonal climatological means distributions have been generated. Both seasonal distributions have been analyzed together and by combining the knowledge of oceanographic processes and phytoplankton responses to light and nutrient availability, regions where the presence of a thermal front affects photosynthetic activity have been identified. Subjective criteria have been applied to define eighteen areas where phytoplankton biomass is influenced by the presence of a thermal front. In these areas, the surface chlorophyll (spatial mean and total), its relationship with the surface chlorophyll of the whole region, and the seasonal evolution of this relationship have been calculated. All frontal areas cover less than 15% of the total surface, but they contribute with over 23% of the phytoplankton annual mean biomass. Considered as a group, during summer they show high chlorophyll values very similar to those in spring. During the cold period, when the water column is vertically mixed in practically the whole of PCS, the influence of physical fronts over the biological production is minimum. The frontal zone image remains clearly defined during summer, when approximately 85% of the area will have a determined mean chlorophyll concentration, while the other 15% has a 2.45 times larger value. While three pattern trends have been identified in the frontal areas, only two of them condition the pattern of the group, due to their horizontal extension. © 2006 Elsevier B.V. All rights reserved.–2003) of SeaWiFS data with approximately 4 km spatial resolution have been used to estimate monthly composite images of surface chlorophyll concentration, after which seasonal climatological means distributions have been generated. Both seasonal distributions have been analyzed together and by combining the knowledge of oceanographic processes and phytoplankton responses to light and nutrient availability, regions where the presence of a thermal front affects photosynthetic activity have been identified. Subjective criteria have been applied to define eighteen areas where phytoplankton biomass is influenced by the presence of a thermal front. In these areas, the surface chlorophyll (spatial mean and total), its relationship with the surface chlorophyll of the whole region, and the seasonal evolution of this relationship have been calculated. All frontal areas cover less than 15% of the total surface, but they contribute with over 23% of the phytoplankton annual mean biomass. Considered as a group, during summer they show high chlorophyll values very similar to those in spring. During the cold period, when the water column is vertically mixed in practically the whole of PCS, the influence of physical fronts over the biological production is minimum. The frontal zone image remains clearly defined during summer, when approximately 85% of the area will have a determined mean chlorophyll concentration, while the other 15% has a 2.45 times larger value. While three pattern trends have been identified in the frontal areas, only two of them condition the pattern of the group, due to their horizontal extension. © 2006 Elsevier B.V. All rights reserved. Keywords: Fronts; Patagonian Shelf; Satellite; Physical–biological influencesFronts; Patagonian Shelf; Satellite; Physical–biological influencesFil: Rivas, Andres Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentin

Spatial and temporal variability of satellite-derived sea surface temperature in the southwestern Atlantic Ocean

Mean fields, seasonal cycle, and interannual variability of the Southwestern Atlantic Ocean (SAO) sea surface temperature (SST) distribution are examined during an 18-year (January 1985-December 2002) period by means of monthly composite, around 9 km resolution satellite-derived SST data. Temporal evolution of the mean spatial value shows a very marked annual cycle, certain interannual variability and a weak increasing tendency (∼0.06 °C/decade). Spatial distribution of the mean temporal value shows the influence of the horizontal advection over the SST field. Over 90% of the temporal variability is explained by the annual harmonic, which reaches amplitudes of 7 °C over the shallowest zones. The inclusion of the semiannual harmonic improves the description of the seasonal cycle only in those regions of the domain where warming and cooling cycles show different durations. The strong correlation between the surface heat flux and the SST allows, by means of a single diffusion equation, the prediction of the shelf areas which do not stratify seasonally. The EOF analysis shows three modes (which together explain over 97% of the variance) associated with the stationary value, the amplitude and the phase of the annual harmonic, i.e., with the seasonal cycle. The fourth mode (0.22% of the variance) is the first one to show interannual variability, which is well correlated with the Southern Annular Mode (SAM).Fil: Rivas, Andres Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

Identification, characteristics and seasonal evolution of surface thermal fronts in the Argentinean Continental Shelf

The location and seasonal variability of surface thermal fronts along the Argentinean Continental Shelf (38-55°S) were studied using 18 years (1985-2002) of sea surface temperature (SST) satellite data. Monthly SST gradients were calculated and a threshold was used to identify frontal pixels. Frontal areas were classified into 4 zones according to their seasonal evolution and the main forcings leading to the front's formation were identified for each group. The shelf break front was easily detected due to the large number of frontal pixels in the region and its high mean gradient values. This front showed a marked annual cycle and relatively constant position associated to the bottom slope; it tended to be located where the core of the Malvinas current is closest to the shelf. Tidal fronts also showed a strong annual cycle, being detected in three well-defined regions during spring and summer. Along the coasts of Tierra del Fuego and Santa Cruz, the combination of strong tidal mixing and low-salinity coastal plumes led to semi-annual seasonal cycles of frontal intensity and persistence that showed a relative maximum in winter. A similar behavior (semi-annual) was found at the coast off the Buenos Aires Province. There, the coastal dilution and the bathymetric gradient generated near-coastal fronts that changed direction seasonally. In the northern mid-shelf, a front linked to the intrusion of warm waters formed in the San Matías Gulf was identified during the winter.Fil: Rivas, Andres Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Pisoni, Juan Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentin

The effects of environmental factors on the embryonic survival of the Patagonian squid Loligo gahi

Seawater temperature and salinity are environmental variables that impose physiological limits for the embryonic development of marine invertebrates. For cephalopod species, these limits have rarely been established. This work presents experimental results on the embryonic survival of the Patagonian squid Loligo gahi, which is the last decades' most important loliginid species in terms of volume of commercial catches worldwide, as a function of seawater temperature and salinity. Reference magnitudes of surface seawater temperature and salinity within the area of distribution of the species were explored by analysis of satellite databases and published information. Embryos were incubated under eight constant regimes of temperature within 4–22 °C and four constant salinity regimes within 20–34.33‰ (12 °C). Also, to determine the effects of sudden temperature changes on embryonic survival, embryos were incubated at four variable regimes of temperature, with thermal shifts (6-day long 2-°C magnitude alterations of the incubation temperature) applied both at early and late stages of embryonic development. Embryonic survival was zero in incubations at constant temperature regimes ≤5° and at 22 °C, low at 6 °C, and high within 8–20 °C. A function was fitted by nonlinear regression to relate embryonic survival and mean incubation temperature. Thermal shifts applied in incubations at 20–22–20 °C variable regime of temperature provoked low embryonic survival compared to that observed in incubation at 20 °C constant regime. Embryonic survival was zero in incubations conducted at 20.0‰ and 34.3‰ salinity, and high at 26.4‰ and 32.8‰ salinities.Fil: Cinti, Ana. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Baron, Pedro Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; ArgentinaFil: Rivas, Andres Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentin

Coastal upwelling in the San Jorge Gulf (Southwestern Atlantic) from remote sensing, modelling and hydrographic data

Coastal upwelling is a known mechanism that generates favorable conditions for marine life. In this paper, we evaluate the conditions for the development of coastal upwelling in the San Jorge Gulf, on the west coast of the South Atlantic Ocean. The wind-based upwelling indices were calculated for 4 years (2003–2006) in three coastal regions of the gulf with different orientations. Monthly images of sea surface temperature, chlorophyll-a and wind and numerical simulations were used to analyze upwelling conditions. In addition, results of daily images, numerical simulations with daily forcings and CTD sections in the southwestern region of the gulf during the spring of 2016 and 2017 were described. The upwelling indices clearly highlight the differences between the three regions, linked to the basin geometry. Using an average of daily indices in the southwestern part of the gulf, thirteen upwelling events were detected during the warm season (November to March, 2003–2006). Numerical simulations suggest that the drop in surface temperature generated by an upwelling event in the SW region remains cold for more than a week. The wind pattern and CTD profiles during spring 2016 suggested favorable conditions for coastal upwelling compared to the profiles performed in 2017, in which wind do not appear to be upwelling-favorable.Fil: Pisoni, Juan Pablo. Universidad Nacional de la Patagonia "San Juan Bosco"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Rivas, Andres Lujan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Tonini, Mariano Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales. Universidad Nacional del Comahue. Instituto Andino Patagónico de Tecnologías Biológicas y Geoambientales; Argentin