Estructura comunitaria de foraminíferos bentónicos en relación a factores ambientales en sedimentos marinos someros de la Costa Central del Perú

Universidad Nacional Agraria La Molina. Facultad de Ciencias. Departamento Académico de BiologíaLa presente investigación evaluó la comunidad de foraminíferos bentónicos y su relación con los factores abióticos en ambientes sedimentarios someros de la costa central peruana. Para ello se realizaron mediciones in situ y se tomaron muestras de sedimentos entre octubre y noviembre de 2014 en tres localidades: la zona de Huacho-Salinas, la Bahía de Miraflores y la Bahía de Paracas. La variabilidad espacial de los factores ambientales y los parámetros comunitarios fue evaluada mediante el análisis de Componentes Principales y el análisis Clúster respectivamente, mientras que sus relaciones fueron examinadas mediante correlaciones múltiples y un análisis canónico de Coordenadas Principales. Las propiedades geoquímicas del sustrato variaron ampliamente, mientras que los factores limitantes del agua de fondo variaron moderadamente por estar influenciados por el afloramiento costero. En total se lograron identificar 11 taxones de foraminíferos bentónicos, de los cuales Bolivina costata fue largamente superior en abundancia, seguido por Buliminella elegantissima y Allogromiidae. Las especies calcáreas y pequeñas del orden Rotaliida dominaron la comunidad, aunque los foraminíferos de testa orgánica del orden Allogromiida tuvieron una importante contribución. La densidad comunitaria estuvo concentrada en los dos centímetros más superficiales de los sedimentos. La diversidad, en términos de equidad, se vio favorecida por el contenido orgánico y la temperatura. La estructura comunitaria varió principalmente en relación a las diferencias en las propiedades geoquímicas del sustrato, asociadas a diferencias en el régimen hidrodinámico de los ambientes sedimentarios, y a la temperatura. La especie B. elegantissima adquiere gran relevancia en ambientes someros protegidos que acumulan materia orgánica. La preservación de la tafocenosis calcárea en los sedimentos suele ser mejor bajo regímenes hidrodinámicos moderados e intensos, ya que en regímenes débiles la gran acumulación de materia orgánica hace más probable que se generen condiciones favorables a la disolución de las testas calcáreas en los sedimentos.The community of benthic foraminifera and its relationships with environmental factors were studied in shallow sedimentary environments of Peruvian central coast. For this, in situ measurements were made and sediment samples were taken between October and November of 2014 in three locations: Huacho-Salinas zone, Miraflores Bay and Paracas Bay. Spatial variability of environmental factors and community parameters was assessed by using Principal Components Analysis and Cluster Analysis respectively, while their relationships were examined by using multiple correlations and a Canonical Analysis of Principal Coordinates. Substrate geochemical properties had great variations while bottom waters limiting factors had moderate variations due to the influence of coastal upwelling. At total in the community, 11 benthic foraminiferal taxa were identified, of which Bolivina costata was far superior in abundance, followed by Buliminella elegantissima and Allogromiidae. Small calcareous species from Rotaliida order dominated the community, even though organic-shelled foraminifera from Allogromiida order had an important contribution as well. The density of community was concentrated in the two most superficial centimeters of the sediments. Diversity, as species equitability, was favored by organic matter and temperature. Community structure varied mainly due to differences in substrate geochemical properties, associated to differences in hydrodynamic regimes of sedimentary environments, and to differences in temperature. B. elegantissima appears more relevant in shallow sheltered environments, which accumulate organic matter. The preservation of calcareous taphocenosis in sediments is usually better under intense or moderate hydrodynamic regimes since organic matter accumulation in weak regimes makes conditions favorable to calcareous tests dissolution more likely

Living benthic foraminifera from El Ferrol Bay

The study focused on the assemblage of ‘living’ benthic foraminifera (stained with Rose Bengal) in the surface sediments of El Ferrol Bay (Chimbote, 9°S). Twelve sampling sites were selected at depths ranging from 4.5 to 27 meters in September 2015. Water samples were collected near the seafloor to determine dissolved oxygen (DO), pH, and nutrient (nitrate and phosphate). Sediment samples were analysed for total organic matter (TOM) and the chlorophyll-a to phaeopigment ratio (chl-a/phaeo. Our findings confirm that this bay experiences hypoxic conditions at the seafloor (~2 mL/L) in addition to high dissolved nitrate levels. The assemblage was primarily composed of hyaline calcareous species, a porcelaneous calcareous species, and a soft-shelled foraminiferal species. Densities ranged from moderate to high, with the calcareous species Bolivina costata being the dominant species and B. elegantissima co-dominant in most sites. Based on our analysis, no significant differences were observed between the assemblages of living benthic foraminifera in the inner and outer bay. However, the influence of bottom nitrates on shallow-water foraminiferal species was notable. These results provide a baseline reference for future monitoring and calibration studies

Circulation and stratification drivers during the summer season in the upwelling bay of Paracas (Peru): A modelling study

International audienceThe circulation and stratification in the shallow semi-enclosed bay of Paracas located downstream of the main upwelling cell off the Peruvian coast were studied during the summer season using a regional circulation model and in situ observations. A downscaling strategy based on a series of three embedded grids, from 10 km to 500 m resolution in the bay allows to take into account the influence of remote perturbations on the bay dynamics. Debiased surface winds from a high-resolution regional atmospheric model were used to force the model. The shortwave absorption depth was parameterized using satellite measurements of surface chlorophyll. Sensitivity experiments to the model forcing and parameterizations were performed to investigate the impact of the wind diurnal variability, tidal forcing, freshwater discharge from a nearby river and shortwave absorption depth on the bay stratification. Results show that: debiasing the wind intensity reduced the model cold bias in the bay and increase the stratification; a shallow shortwave absorption depth induced a cooling of the subsurface water, increasing the stratification; freshwater discharge from the Pisco river north of the bay increased slightly the stratification in the bay during days of weak wind. The high sensitivity of the bay stratification to the atmospheric forcing calls for the need to use more realistic wind forcing products. The circulation in the bay under strong (>5.5 m s-1) and weak (-1) winds was also examined. The summer circulation during strong upwelling-favorable wind conditions was characterized by northward surface currents transporting the bay surface waters outward and subsurface currents transporting cold deeper waters into the bay along its western shore. During weak wind conditions, the current is outward in the bottom layer and a surface southward current related to the poleward undercurrent flowing over the continental slope and shelf transported warm waters into the bay, generating a cyclonic circulation in the bay

Circulation and stratification drivers during the summer season in the upwelling bay of Paracas (Peru): A modelling study

International audienceThe circulation and stratification in the shallow semi-enclosed bay of Paracas located downstream of the main upwelling cell off the Peruvian coast were studied during the summer season using a regional circulation model and in situ observations. A downscaling strategy based on a series of three embedded grids, from 10 km to 500 m resolution in the bay allows to take into account the influence of remote perturbations on the bay dynamics. Debiased surface winds from a high-resolution regional atmospheric model were used to force the model. The shortwave absorption depth was parameterized using satellite measurements of surface chlorophyll. Sensitivity experiments to the model forcing and parameterizations were performed to investigate the impact of the wind diurnal variability, tidal forcing, freshwater discharge from a nearby river and shortwave absorption depth on the bay stratification. Results show that: debiasing the wind intensity reduced the model cold bias in the bay and increase the stratification; a shallow shortwave absorption depth induced a cooling of the subsurface water, increasing the stratification; freshwater discharge from the Pisco river north of the bay increased slightly the stratification in the bay during days of weak wind. The high sensitivity of the bay stratification to the atmospheric forcing calls for the need to use more realistic wind forcing products. The circulation in the bay under strong (>5.5 m s-1) and weak (-1) winds was also examined. The summer circulation during strong upwelling-favorable wind conditions was characterized by northward surface currents transporting the bay surface waters outward and subsurface currents transporting cold deeper waters into the bay along its western shore. During weak wind conditions, the current is outward in the bottom layer and a surface southward current related to the poleward undercurrent flowing over the continental slope and shelf transported warm waters into the bay, generating a cyclonic circulation in the bay

Bottom-water hypoxia in the Paracas Bay (Peru, 13.8°S) associated with seasonal and synoptic time scale variability of winds and water stratification

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Characterization of hypoxic events in Paracas bay (Peru, 13.8°S) through intensity and biological effect indexes

International audienceOver the past decade, there has been a significant increase in low oxygen conditions within marine coastal areas, profoundly impacting ecosystem processes and living coastal resources. Coastal bays in highly productive upwelling regions, where hypoxia occurs naturally, are special areas affected by both local and adjacent shelf-related processes. Paracas Bay (13.8°S) is a traditional shellfish fishing and intense farming area highly influenced by one of the most active upwelling centers of the Peruvian coast. Despite the small dimensions of the bay (35 km2), a key feature is its complex physical dynamics and high environmental variability. Recently, important efforts have been made in the study of both the spatial and temporal oxygen concentration variability, nevertheless, information regarding the ecological and biological impact of hypoxic events is still lacking. In this study, the spatial and temporal distribution of hypoxic events was analyzed across Paracas bay at different depths by means of high-frequency hourly dissolved oxygen records collected by data-loggers deployed across the bay during the periods September 2012 – February 2013 and March 2015 – February 2017. To study the ecological impact of hypoxic events, we developed a hypoxia intensity index, while the biological impact was studied through the development of a hypoxia biological effect index using as model species the Peruvian scallop (Argopecten purpuratus). Our results showed that hypoxic events have an intrinsic variability across the bay. The deeper areas of the bay, towards the northwest and center, were characterized by long, intense, and lethal events, while the southeast and southwest, shallower areas, were characterized by shorter events of low intensity and either sublethal or innocuous. We propose that the observed variability is not only related to the large-scale environmental context in which the events occurred, but also to small-scale variability linked to local circulation, biological activity, and sediment biogeochemistry. We expect that our research will be useful not only for scientific purposes, but also for coastal resource management and aquaculture, underlining the importance of developing high-resolution oxygen monitoring systems in coastal bays

Attenuation of wind intensities exacerbates anoxic conditions leading to sulfur plume development off the coast of Peru

The release of vast quantities of sulfide from the sediment into the water column, known as a sulfidic event, has detrimental consequences on fish catches, including downstream effects on other linked element cycles. Despite being frequent occurrences in marine upwelling regions, our understanding of the factors that moderate sulfidic event formation and termination are still rudimentary. Here, we examined the biogeochemical and hydrodynamic conditions that underpinned the formation/termination of one of the largest sulfur plumes to be reported in the Peruvian upwelling zone. Consistent with previous research, we find that the sulfur-rich plume arose during the austral summer when anoxic conditions (i.e., oxygen and nitrate depletion) prevailed in waters overlying the upper shelf. Furthermore, the shelf sediments were organically charged and characterized by low iron-bound sulfur concentrations, further enabling the diffusion of benthic-generated sulfide into the water column. While these biogeochemical conditions provided a predicate to sulfidic event formation, we highlight that attenuations in local wind intensity served as an event trigger. Namely, interruptions in local wind speed constrained upwelling intensity, causing increased stratification over the upper shelf. Moreover, disturbances in local wind patterns likely placed additional constraints on wind-driven mesoscale eddy propagation, with feedback effects on coastal elemental sulfur plume (ESP) formation. We suggest ESP development occurs as a result of a complex interaction of biogeochemistry with regional hydrodynamics