Seasonal Variability of the Oceanic Circulation in the Gulf of San Jorge, Argentina

Section: G01 G04 G05 G06 G07 G09 G10 G11 G12 G13 G14 G15 G16 Sf15mentioning

confidence: 75%

Light Absorption by Phytoplankton, Non-Algal Particles, and Dissolved Organic Matter in San Jorge Gulf in Summer

Williams¹,

Larouche²,

Dogliotti³

et al. 2018

“…The general circulation in the SJG is seasonally variable, exhibiting two distinct patterns, austral summer and winter modes (Matano and Palma, 2018, in this issue). The summer mode, which reflects annual mean patterns, is characterized by a cyclonic gyre that is bound to the west by coastal currents and to the east by the Patagonia Current (PC, Matano et al, 2018, in this issue). The PC is composed mainly of low-salinity, subantarctic waters from the Strait of Magellan (Brandhorst and Castello, 1971).…”

Section: Regional Settingmentioning

confidence: 99%

“…The PC is composed mainly of low-salinity, subantarctic waters from the Strait of Magellan (Brandhorst and Castello, 1971). According to Matano and Palma (2018, in this issue), the summer mode is characterized by maximum intrusion of the PC into the gulf, and the cyclonic gyres weaken significantly during the winter mode. Strong winter mode westerlies generate two anticyclonic subgyres, the larger of which is situated in the southwestern gulf and characterized by a southward-flowing coastal current (Matano and Palma, 2018, in this issue).…”

Section: Regional Settingmentioning

confidence: 99%

“…According to Matano and Palma (2018, in this issue), the summer mode is characterized by maximum intrusion of the PC into the gulf, and the cyclonic gyres weaken significantly during the winter mode. Strong winter mode westerlies generate two anticyclonic subgyres, the larger of which is situated in the southwestern gulf and characterized by a southward-flowing coastal current (Matano and Palma, 2018, in this issue). The surface circulation pattern suggests that winds, heat fluxes, the topographic depression in the central part of the gulf, and the seasonal development of tidal fronts control hydrodynamics in the area (Krock et al, 2015;Matano and Palma, 2018, in this issue).…”

Section: Regional Settingmentioning

confidence: 99%

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Distribution of Modern Dinoflagellate Cyst Assemblages in Surface Sediments of San Jorge Gulf (Patagonia, Argentina)

Faye¹,

Rochon²,

St‐Onge³

2018

INTRODUCTION The Southwest Atlantic is an area of high primary productivity, where upwellings and oceanic fronts control the intensity of organic production (Gregg et al., 2005; Rivas et al., 2006). Along the Argentinian coasts, dinoflagellates and diatoms dominate the primary production (e.g., Lutz and Carreto, 1991; Segura et al., 2013; Krock et al., 2015). These microorganisms represent the bottom link in the food web and are essential for marine ecosystems. Dinoflagellates are unicellular biflagellate organisms that thrive in both freshwater and marine environments. They display a wide range of morphologies, live in a variety of habitats (Evitt, 1985; Taylor et al., 2008), and are found at all latitudes, though they are particularly abundant in coastal waters (Zonneveld et al., 2013). Most dinoflagellates are autotrophic and/or mixotrophic (50%), but some are either heterotrophic, parasitic, or ABSTRACT. The presence of upwelling systems and oceanic fronts makes the Southwest Atlantic Ocean a region of high primary productivity. These same conditions are present in San Jorge Gulf (SJG) along the southern Argentinian coast, where dinoflagellates and diatoms dominate primary production. The distribution of these microorganisms, including the cysts produced by some dinoflagellates during their life cycles, is controlled in marine environments by oceanographic parameters that include salinity, surface water temperature, ice cover duration, and productivity. The objective of this study is to document the modern distribution of dinoflagellate cyst assemblages in surface sediments so that the environmental preferences of each taxon can be inferred and used to reconstruct paleoenvironmental conditions. The dinoflagellate cyst (dinocyst) assemblages of 52 surface samples collected in 2014 aboard R/V Coriolis II in the SJG were described and compared to surface oceanographic conditions and grain size data. The results indicate dinocyst concentrations vary between 64 cysts g-1 and 45,848 cysts g-1 dry sediment, with Spiniferites ramosus and Operculodinium centrocarpum the dominant species, accompanied by Spiniferites mirabilis, Dubridinium sp., cysts of Polykrikos kofoidii, and cysts of Brigantedinium simplex, Brigantedinium auranteum, and Brigantedinium spp. We have defined two spatial domains based on the distribution of dinocysts in and near the SJG: northern/southern-central gulf and offshore domains. We found an increase in dinocyst concentrations along a north-south gradient in the SJG and minimum concentrations at offshore sites. In addition, multivariate analyses reveal the relationships among the relative abundances of dinocysts, fine grain size data (<63 μm; silts and clays), and primary productivity, as well as offshore upwelling, which appear to control most of the distribution of dinocysts.

“…Traditionally, the stratified region is considered a two-layer system where optimal light and nutrient conditions occur only in the transition zone between the mixed and stratified regions (Le Fevre, 1987). An alternative model has been proposed in which the stratified region operates like a three-layer system (surface, bottom, and middle layers), where horizontal subsurface intrusions of water rich in nutrients may occur, causing subsurface chlorophyll-a maxima (Richardson et al, 2000;Matano and Palma, 2018, in this issue).…”

Section: Introductionmentioning

confidence: 99%

High-Frequency Frontal Displacements South of San Jorge Gulf During a Tidal Cycle Near Spring and Neap Phases: Biological Implications Between Tidal States

Carbajal¹,

Rivas²,

Chavanne³

2018

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 advection by cross-frontal tidal currents. The frontal position was also modified by baroclinic instabilities that significantly distort the front. Measurements reveal intrusions of lowsalinity, 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.