Description and Mechanisms of the Mid-Year Upwelling in the Southern Caribbean Sea from Remote Sensing and Local Data

The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June–August, when local coastal wind intensities weaken. Using synoptic satellite measurements and in situ data, this mid-year upwelling was characterized in terms of surface and subsurface temperature structures, and its mechanisms were explored. The mid-year upwelling lasts 6–9 weeks with satellite sea surface temperature (SST) ~1–2° C warmer than the primary upwelling. Three possible upwelling mechanisms were analyzed: cross-shore Ekman transport (csET) due to alongshore winds, wind curl (Ekman pumping/suction) due to wind spatial gradients, and dynamic uplift caused by variations in the strength/position of the Caribbean Current. These parameters were derived from satellite wind and altimeter observations. The principal and the mid-year upwelling were driven primarily by csET (78–86%). However, SST had similar or better correlations with the Ekman pumping/suction integrated up to 100 km offshore (WE100) than with csET, possibly due to its influence on the isopycnal depth of the source waters for the coastal upwelling. The mid-year upwelling was not caused by dynamic uplift but it might have been enhanced by the seasonal intensification of the Caribbean Current during that period

On the spatial and temporal variability of upwelling in the southern Caribbean Sea and its influence on the ecology of phytoplankton and of the Spanish sardine (Sardinella aurita)

The Southern Caribbean Sea experiences a strong upwelling process along the coast from about 61°W to 75.5°W and 10-13°N. In this dissertation three aspects of this upwelling system are examined: (A) A mid-year secondary upwelling that was previously observed in the southeastern Caribbean Sea between June-July, when land based stations show a decrease in wind speed. The presence and effects of this upwelling along the whole southern Caribbean upwelling system were evaluated, as well as the relative forcing contribution of alongshore winds (Ekman Transport, ET) and wind-curl (Ekman Pumping, EP). (B) Stronger upwelling occurs in two particular regions, namely the eastern (63-65°W) and western (70-73°W) upwelling areas. However, the eastern area has higher fish biomass than the western area (78% and 18%, respectively, of the total small pelagic biomass of the southern Caribbean upwelling system). The upwelling dynamics along the southern Caribbean margin was studied to understand those regional variations on fish biomass. (C) The most important fishery in the eastern upwelling area off Venezuela is the Spanish sardine (Sardinella aurita). The sardine artisanal fishery is protected and only takes place up to ~10 km offshore. The effects of the upwelling cycle on the spatial distribution of S. aurita were studied. The main sources of data were satellite observations of sea surface temperature (SST), chlorophyll-a (Chl) and wind (ET and EP), in situ observations from the CARIACO Ocean Time-Series program, sardine biomass from 8 hydroacoustics surveys (1995-1998), and temperature profiles from the World Ocean Atlas 2005 used to calculate the depth of the Subtropical Underwater core (traced by the 22°C isotherm). The most important results of the study were as follows: (A) The entire upwelling system has a mid-year upwelling event between June-August, besides the primary upwelling process of December-April. This secondary event is short-lived (~5 weeks) and ~1.5°C warmer than the primary upwelling. Together, both upwelling events lead to about 8 months of cooler waters (-3, averaged from the coast to 100 km offshore) in the region. Satellite nearshore wind (~25 km offshore) remained high in the eastern upwelling area (\u3e 6 m s-1) and had a maximum in the western area (~10 m s-1) producing high offshore ET during the mid-year upwelling (vertical transport of 2.4 - 3.8 m3 s-1 per meter of coastline, for the eastern and western areas, respectively). Total coastal upwelling transport was mainly caused by ET (~90%). However, at a regional scale, there was intensification of the wind curl during June as well; as a result open-sea upwelling due to EP causes isopycnal shoaling of deeper waters enhancing the coastal upwelling. (B) The eastern and western upwelling areas had upwelling favorable winds all year round. Minimum / maximum offshore ET (from weekly climatologies) were 1.52 / 4.36 m3 s-1 per meter, for the western upwelling area; and 1.23 / 2.63 m3 s-1 per meter, for the eastern area. The eastern and western upwelling areas showed important variations in their upwelling dynamics. Annual averages in the eastern area showed moderate wind speeds (6.12 m s-1), shallow 22°C isotherm (85 m), cool SSTs (25.24°C), and phytoplankton biomass of 1.65 mg m-3. The western area has on average stronger wind speeds (8.23 m s-1) but a deeper 22°C isotherm (115 m), leading to slightly warmer SSTs (25.53°C) and slightly lower phytoplankton biomass (1.15 mg m-3). We hypothesize that the factors that most inhibits fish production in the western upwelling area are the high level of wind-induced turbulence and the strong offshore ET. (C) Hydroacoustics values of Sardinella aurita biomass (sAsardine) and the number of small pelagics schools collected in the eastern upwelling region off northeast Venezuela were compared with environmental variables (satellite products of SST, SST gradients, and Chl -for the last two cruises-) and spatial variables (distance to upwelling foci and longitude-latitude). These data were examined using Generalized Additive Models. During the strongest upwelling season (February-March) sAsardine was widely distributed in the cooler, Chl rich upwelling plumes over the wide (~70km) continental shelf. During the weakest upwelling season (September-October) sAsardine was collocated with the higher Chl (1-3 mg m-3) found within the first 10 km from the upwelling foci; this increases Spanish sardine availability (and possibly the catchability) for the artisanal fishery. These results imply that during prolonged periods of weak upwelling the environmentally stressed (due to food scarceness) Spanish sardine population would be closer to the coast and more available to the fishery, which could easily turn into overfishing. After two consecutive years of weak upwelling (2004-2005) Spanish sardine fishery crashed and as of 2011 has not recovered to previous yield; however during 2004 a historical capture peak occurred. We hypothesize that this Spanish sardine collapse was caused by a combination of sustained stressful environmental conditions and of overfishing, due to the increased catchability of the stock caused by aggregation of the fish in the cooler coastal upwelling cells during the anomalous warm upwelling season

On the spatial and temporal variability of upwelling in the southern Caribbean Sea and its influence on the ecology of phytoplankton and of the Spanish sardine (Sardinella aurita)

The Southern Caribbean Sea experiences a strong upwelling process along the coast from about 61°W to 75.5°W and 10-13°N. In this dissertation three aspects of this upwelling system are examined: (A) A mid-year secondary upwelling that was previously observed in the southeastern Caribbean Sea between June-July, when land based stations show a decrease in wind speed. The presence and effects of this upwelling along the whole southern Caribbean upwelling system were evaluated, as well as the relative forcing contribution of alongshore winds (Ekman Transport, ET) and wind-curl (Ekman Pumping, EP). (B) Stronger upwelling occurs in two particular regions, namely the eastern (63-65°W) and western (70-73°W) upwelling areas. However, the eastern area has higher fish biomass than the western area (78% and 18%, respectively, of the total small pelagic biomass of the southern Caribbean upwelling system). The upwelling dynamics along the southern Caribbean margin was studied to understand those regional variations on fish biomass. (C) The most important fishery in the eastern upwelling area off Venezuela is the Spanish sardine (Sardinella aurita). The sardine artisanal fishery is protected and only takes place up to ~10 km offshore. The effects of the upwelling cycle on the spatial distribution of S. aurita were studied. The main sources of data were satellite observations of sea surface temperature (SST), chlorophyll-a (Chl) and wind (ET and EP), in situ observations from the CARIACO Ocean Time-Series program, sardine biomass from 8 hydroacoustics surveys (1995-1998), and temperature profiles from the World Ocean Atlas 2005 used to calculate the depth of the Subtropical Underwater core (traced by the 22°C isotherm). The most important results of the study were as follows: (A) The entire upwelling system has a mid-year upwelling event between June-August, besides the primary upwelling process of December-April. This secondary event is short-lived (~5 weeks) and ~1.5°C warmer than the primary upwelling. Together, both upwelling events lead to about 8 months of cooler waters (-3, averaged from the coast to 100 km offshore) in the region. Satellite nearshore wind (~25 km offshore) remained high in the eastern upwelling area (\u3e 6 m s-1) and had a maximum in the western area (~10 m s-1) producing high offshore ET during the mid-year upwelling (vertical transport of 2.4 - 3.8 m3 s-1 per meter of coastline, for the eastern and western areas, respectively). Total coastal upwelling transport was mainly caused by ET (~90%). However, at a regional scale, there was intensification of the wind curl during June as well; as a result open-sea upwelling due to EP causes isopycnal shoaling of deeper waters enhancing the coastal upwelling. (B) The eastern and western upwelling areas had upwelling favorable winds all year round. Minimum / maximum offshore ET (from weekly climatologies) were 1.52 / 4.36 m3 s-1 per meter, for the western upwelling area; and 1.23 / 2.63 m3 s-1 per meter, for the eastern area. The eastern and western upwelling areas showed important variations in their upwelling dynamics. Annual averages in the eastern area showed moderate wind speeds (6.12 m s-1), shallow 22°C isotherm (85 m), cool SSTs (25.24°C), and phytoplankton biomass of 1.65 mg m-3. The western area has on average stronger wind speeds (8.23 m s-1) but a deeper 22°C isotherm (115 m), leading to slightly warmer SSTs (25.53°C) and slightly lower phytoplankton biomass (1.15 mg m-3). We hypothesize that the factors that most inhibits fish production in the western upwelling area are the high level of wind-induced turbulence and the strong offshore ET. (C) Hydroacoustics values of Sardinella aurita biomass (sAsardine) and the number of small pelagics schools collected in the eastern upwelling region off northeast Venezuela were compared with environmental variables (satellite products of SST, SST gradients, and Chl -for the last two cruises-) and spatial variables (distance to upwelling foci and longitude-latitude). These data were examined using Generalized Additive Models. During the strongest upwelling season (February-March) sAsardine was widely distributed in the cooler, Chl rich upwelling plumes over the wide (~70km) continental shelf. During the weakest upwelling season (September-October) sAsardine was collocated with the higher Chl (1-3 mg m-3) found within the first 10 km from the upwelling foci; this increases Spanish sardine availability (and possibly the catchability) for the artisanal fishery. These results imply that during prolonged periods of weak upwelling the environmentally stressed (due to food scarceness) Spanish sardine population would be closer to the coast and more available to the fishery, which could easily turn into overfishing. After two consecutive years of weak upwelling (2004-2005) Spanish sardine fishery crashed and as of 2011 has not recovered to previous yield; however during 2004 a historical capture peak occurred. We hypothesize that this Spanish sardine collapse was caused by a combination of sustained stressful environmental conditions and of overfishing, due to the increased catchability of the stock caused by aggregation of the fish in the cooler coastal upwelling cells during the anomalous warm upwelling season

The Southern Caribbean Upwelling System: Sea Surface Temperature, Wind Forcing and Chlorophyll Concentration Patterns

Sixteen years of sea surface temperature (SST, 1994-2009) were used to characterize the southern Caribbean upwelling system. This system extends from 61-75.5°W and 10-12.5°N, with 21 upwelling foci clustered in seven groups differentiated by their SST cycles. Two of those groups had the strongest coastal upwelling: the \u27eastern area\u27 (63-65°W) and the \u27western area\u27 (70-73°W). The literature reports that the eastern and western upwelling areas hold 78% and 18% of the small pelagic biomass within the upwelling system, respectively. We looked into variations of the upwelling dynamics in those areas using seasonal cycles of satellite SST, chlorophyll-a (Chl) and sea-wind, as well as climatological hydrographic data from the World Ocean Atlas. Comparing their annual averages, the eastern area featured the lowest SST (25.24°C) and the highest Chl (1.65mgm -3 ); it has moderate wind intensity (6.12ms -1 ) and shallower 22°C isotherm (85m). The western area had stronger winds (8.23ms -1 ) but deeper 22°C isotherm (115m), slightly higher SST (25.53°C) and moderate Chl (1.15mgm -3 ). The upwelling in the eastern area was more prolonged than in the western area (SST \u3c26°C during 8.5 and 6.9 months, respectively). According to the \u27optimal environmental window\u27 theory, small clupeoid recruitment is a dome-shaped function of the upwelling intensity, turbulence and SST, with an optimum wind speed around 5-6ms -1 . The eastern upwelling area wind speed is close to this optimum value. The western upwelling area shows much higher wind speed that causes high level of turbulence and strong offshore transport that could hinder small pelagics recruitment in that area

Description and Mechanisms of the Mid-Year Upwelling in the Southern Caribbean Sea from Remote Sensing and Local Data

The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June–August, when local coastal wind intensities weaken. Using synoptic satellite measurements and in situ data, this mid-year upwelling was characterized in terms of surface and subsurface temperature structures, and its mechanisms were explored. The mid-year upwelling lasts 6–9 weeks with satellite sea surface temperature (SST) ~1–2° C warmer than the primary upwelling. Three possible upwelling mechanisms were analyzed: cross-shore Ekman transport (csET) due to alongshore winds, wind curl (Ekman pumping/suction) due to wind spatial gradients, and dynamic uplift caused by variations in the strength/position of the Caribbean Current. These parameters were derived from satellite wind and altimeter observations. The principal and the mid-year upwelling were driven primarily by csET (78–86%). However, SST had similar or better correlations with the Ekman pumping/suction integrated up to 100 km offshore (WE100) than with csET, possibly due to its influence on the isopycnal depth of the source waters for the coastal upwelling. The mid-year upwelling was not caused by dynamic uplift but it might have been enhanced by the seasonal intensification of the Caribbean Current during that period

Description and Mechanisms of the Mid-Year Upwelling in the Southern Caribbean Sea from Remote Sensing and Local Data

The southern Caribbean Sea experiences strong coastal upwelling between December and April due to the seasonal strengthening of the trade winds. A second upwelling was recently detected in the southeastern Caribbean during June–August, when local coastal wind intensities weaken. Using synoptic satellite measurements and in situ data, this mid-year upwelling was characterized in terms of surface and subsurface temperature structures, and its mechanisms were explored. The mid-year upwelling lasts 6–9 weeks with satellite sea surface temperature (SST) ~1–2° C warmer than the primary upwelling. Three possible upwelling mechanisms were analyzed: cross-shore Ekman transport (csET) due to alongshore winds, wind curl (Ekman pumping/suction) due to wind spatial gradients, and dynamic uplift caused by variations in the strength/position of the Caribbean Current. These parameters were derived from satellite wind and altimeter observations. The principal and the mid-year upwelling were driven primarily by csET (78–86%). However, SST had similar or better correlations with the Ekman pumping/suction integrated up to 100 km offshore (WE100) than with csET, possibly due to its influence on the isopycnal depth of the source waters for the coastal upwelling. The mid-year upwelling was not caused by dynamic uplift but it might have been enhanced by the seasonal intensification of the Caribbean Current during that period

Vertical Structure and trends in CO2 at the CARIACO Ocean Time Series Station: 1995-2017

Abstract: Changes in the vertical structure of pH (total proton scale at 25 °C or pHT), total alkalinity, total CO2 (TCO2), and partial pressure of CO2 (pCO2) were examined at the CARIACO Ocean Time Series station (10º30’N, 64º40’W) from December 1995 to January 2017. Long-term trends were studied in the three water masses present in the Cariaco Basin: the surface layer (SL, located between 0-100 m depth), the Subtropical Underwater (SUW, with minimum depths between the surface and 105 m and maximums between 30-165 m depending on the season) and the deep water (DW, with minimum depths between 175-380 m to the bottom). The seasonal detrended TCO2 normalized to a constant salinity (nTCO2) showed a positive trend 2.23 ± 0.43 µmol kg-1 yr-1 in the SL, associated with an increase in pCO2 (3.06 ± 0.42 µatm yr-1) and a decrease in pH (-0.0028 ± 0.0004 pH yr-1). SUW and DW also exhibited increasing trends nTCO2 (1.82 ± 0.42 and 4.46 ± 0.32 µmol kg-1 yr-1, respectively). Between 2002 and 2017, an increase of 67 µmol kg-1 of TCO2 was observed below 300 m at the CARIACO station. Overall, acidification trends were observed at the Cariaco station from the surface to the bottom, with an average of ~ -0.003 ± 0.0004 pH units per year. Air-sea CO2 flux calculations showed an average net evasion of CO2 from the sea to the air of 0.6 ± 2.2 mol C m-2 yr-1 for the period of observation.   Estructura vertical y tendencias en el CO2 en la estación Serie de Tiempo CARIACO: 1995-2017 Resumen: Se examinaron cambios en la estructura vertical del pH (escala total de protones a 25 °C o pHT), la alcalinidad total, el CO2 total (TCO2) y la presión parcial de CO2 (pCO2) en la estación oceanográfica serie de tiempo CARIACO (10º30'N, 64º40'O) desde diciembre de 1995 hasta enero de 2017. Se estudiaron las tendencias a largo plazo en las tres masas de agua presentes en la cuenca de Cariaco: la capa superficial (SL, ubicada entre 0-100 m), la Subtropical (SUW, con profundidades mínimas entre la superficie y 105 m y máximas entre 30-165 m dependiendo de la temporada), y las aguas profundas (DW, con profundidades mínimas entre 175-380 m hasta el fondo). El TCO2 desestacionalizado y normalizado a una salinidad constante (nTCO2) mostró una tendencia positiva de 2,23 ± 0,43 μmol kg-1 año-1 en la capa SL, relacionada con un aumento en pCO2 (3.06 ± 0.42 μatm año-1) y una disminución del pH (-0.0028 ± 0.0004 pH año-1). SUW y DW también mostraron tendencias crecientes en nTCO2 (1,82 ± 0,42 y 4,46 ± 0,32 μmol kg-1 año-1, respectivamente). Entre 2002 y 2017, se observó un aumento de 67 μmol kg-1 de TCO2 por debajo de 300 m en la estación CARIACO. En general, se observaron tendencias de acidificación en la estación Cariaco desde la superficie hasta el fondo, con un promedio de ~ -0.003 ± 0.0004 unidades de pH por año. Los cálculos del flujo de CO2 entre el aire y el océano mostraron una evasión neta promedio de CO2 desde el mar al aire de 0.6 ± 2.2 mol C m-2 año-1 durante el período de observación

Water Temperature, Salinity, and Other Parameters from CTD Taken from the Research Vessel Hermano Gines at the CARIACO Ocean Time-Series Location in the Southeastern Caribbean Sea (Cariaco Basin) from 1995-11-08 to 2017-01-17

his dataset contains Water temperature, salinity, and other parameters from CTD taken from the research vessel Hermano Gines at the CARIACO Ocean Time-Series location in the Southeastern Caribbean Sea (Cariaco Basin) from 1995-11-08 to 2017-01-17. The CARIACO Ocean Time-Series project has been studying the relationship between surface primary production (carbon fixation rates by photosynthesis of planktonic algae), regional hydrography, physical forcing variables (such as the wind), and the settling flux of particulate organic carbon in the Cariaco Basin. This tectonic depression, located on the continental shelf of eastern Venezuela, shows marked seasonal and interannual variation in hydrography and primary production, with a seasonal wind-induced coastal upwelling. Below about 250 m, the Cariaco Basin waters are permanently anoxic. This CTD data set is part of the core variables collected monthly at the time-series station. Each CTD profile has a depth resolution of 1 meter up to 1300 meters, and it is a composite of 4 casts completed during a 24-hour period. Missing or not-collected data are denoted by -9999. Data are in CSV format

Seasonal factors affecting sea turtle nesting in the Southeastern Caribbean Sea (Gulf of Paria, Venezuela)

The nesting characteristics (number of nests and eggs, time of year, nesting initiation, and nesting length) of leatherback (Dermochelys coriacea) and hawksbill (Eretmochelys imbricata) sea turtles of the southern Caribbean Sea (specifically in the Gulf of Paria in Venezuela), were examined in association with weekly precipitation averages and number of rainy days per week during the period between 2009 and 2018. We hypothesized about the influence of rainfall intensity and patterns as the main abiotic factor for sea turtle nesting. On average, leatherbacks preferred nesting during the drier season of each year (March, April, and May), while hawksbills nested during the rainy season (June to September). For both species, we found few significant correlations between the number of nests or clutch size (number of eggs per nest) and weekly averages of seasonal precipitation rates in the region. Average hawksbill clutch sizes were not correlated with average precipitation rates but were positively correlated with the number of rainy days per week (r=0.66, P≤0.05). Average hawksbill clutch sizes decreased each year on average (-3.3 eggs/year, r=-0.88, P≤0.001), which coincided with a negative long-term trend in the number of rainy days (-0.11 rainy days/week, r=-0.69, P≤0.05). During the study period, nesting activities for both leatherback and hawksbills started progressively later (0.9 and 0.6 weeks/year, respectively p≤0.05) and were shorter (-0.9 and -0.8 weeks /year, P≤0.1 and P≤0.05, respectively)

Seasonal factors affecting sea turtle nesting in the Southeastern Caribbean Sea (Gulf of Paria, Venezuela)

The nesting characteristics (number of nests and eggs, time of year, nesting initiation, and nesting length) of leatherback (Dermochelys coriacea) and hawksbill (Eretmochelys imbricata) sea turtles of the southern Caribbean Sea (specifically in the Gulf of Paria in Venezuela), were examined in association with weekly precipitation averages and number of rainy days per week during the period between 2009 and 2018. We hypothesized about the influence of rainfall intensity and patterns as the main abiotic factor for sea turtle nesting. On average, leatherbacks preferred nesting during the drier season of each year (March, April, and May), while hawksbills nested during the rainy season (June to September). For both species, we found few significant correlations between the number of nests or clutch size (number of eggs per nest) and weekly averages of seasonal precipitation rates in the region. Average hawksbill clutch sizes were not correlated with average precipitation rates but were positively correlated with the number of rainy days per week (r=0.66, P≤0.05). Average hawksbill clutch sizes decreased each year on average (-3.3 eggs/year, r=-0.88, P≤0.001), which coincided with a negative long-term trend in the number of rainy days (-0.11 rainy days/week, r=-0.69, P≤0.05). During the study period, nesting activities for both leatherback and hawksbills started progressively later (0.9 and 0.6 weeks/year, respectively p≤0.05) and were shorter (-0.9 and -0.8 weeks /year, P≤0.1 and P≤0.05, respectively)