Search

The relationship between phytoplankton abundances and wind forcing in upwelling systems involves a number of processes that make the relationship nonlinear in nature. In particular, although upwelling-favorable winds tend to provide nutrients for phytoplankton growth, they can also induce export of both biomass and nutrients to the open ocean through Ekman and eddy-induced transport, or dilution of populations through vertical mixing, which negatively impacts increase in biomass. These processes are essentially nonlinear and can interact antagonistically or synergistically on the overall coastal accumulation of biomass. Consequently, producers and consumers tend to decline above a certain wind threshold despite input of nutrient-enriched water. We have observed this phenomenon in an embayment off Central Chile (30°S), where almost 10 years (2000-2009) of microphytoplankton data were analyzed together with environmental variables and wind phenology. Our findings showed that abundance, species diversity and evenness of diatoms and dinoflagellates all increased post-2005 when the mean of the alongshore surface wind stress reached a maximum threshold value of 0.026 N m-2, observed at the decadal temporal variability scale. The increased abundances of diatoms and dinoflagellates post-2005 was associated with the changing phase of the Pacific Decadal Oscillation (PDO) from positive (warm) to negative (cold) phases, which was also associated with a decrease in the intra-seasonal wind activity. Both abundance and diversity of the microphytoplankton community peaked during the post-2005 period whereas higher abundances and frequency of harmful algal blooms (e.g. Pseudo-nitzschia australis) were observed prior to 2005. We suggest that the low-frequency (decadal) variations of mean wind stress during a transition phase of the PDO combined with the reduction in intra-seasonal (periods shorter than 2 months) wind variability after 2005 provided an "optimal environmental window" for the ecosystem. [ABSTRACT FROM AUTHOR]

The monsoon is the primary force behind the upper‐layer circulation system and regulates eddy activity in the South China Sea (SCS). Using satellite observations and a state‐of‐the‐art oceanic reanalysis, this study examines transferring processes of eddy kinetic energy (EKE) during the SCS Summer Monsoon (SCSSM) onset (20th May on average). The SCSSM onset transforms surface winds from easterly to southwesterly, increasing EKE in the southwestern SCS by surface wind work. Despite the persistent energy input from wind work, EKE growth ceases during the first 20 days after SCSSM onset. An EKE budget analysis suggests that most energy input dissipates in the mixed layer due to the high wind speed, which explains the EKE stagnation. Additionally, eddy‐mean flow interactions transfer kinetic energy from eddies to mean flows during the SCSSM onset. The Vietnam coastal upwelling system provides available potential energy to EKE on the offshore side through buoyancy work. Our study reveals energy‐transferring processes from the summer monsoon to eddy activity and dissipation in the SCS, with implications for understanding multiscale dynamic evolutions during the monsoon transition. Plain Language Summary: The South China Sea (SCS) has received much attention for its unique ocean dynamics impacted by monsoons. While the SCS monsoon is known to modulate the seasonal variation in SCS circulation, the effects of the intraseasonal monsoon oscillations on the oceanic eddy activity remain unclear. Generally, ocean circulation and eddy activity get stronger when surface winds strengthen. However, this study reports a stagnation of eddy kinetic energy (EKE) after the SCS summer monsoon onset in the southern SCS despite the persistent energy input from the surface winds. EKE budget results show that high‐speed wind changes the current structure and greatly intensifies ocean dissipation. This study provides a new perspective on ocean energy‐transferring processes under the SCS monsoon transition and will benefit ocean circulation modeling and prediction in the future. Key Points: Eddy kinetic energy (EKE) growth stagnates for 20 days in eastern Vietnam after the South China Sea Summer Monsoon onsetDissipation due to the high wind speed explains the EKE stagnation as a dominant energy sinkThe formation of the upwelling system changes the energy transfer process and modulates the eddy‐mean flow interaction [ABSTRACT FROM AUTHOR]

The relationship between phytoplankton abundances and wind forcing in upwelling systems involves a number of processes that make the relationship nonlinear in nature. In particular, although upwelling-favorable winds tend to provide nutrients for phytoplankton growth, they can also induce export of both biomass and nutrients to the open ocean through Ekman and eddy-induced transport, or dilution of populations through vertical mixing, which negatively impacts increase in biomass. These processes are essentially nonlinear and can interact antagonistically or synergistically on the overall coastal accumulation of biomass. Consequently, producers and consumers tend to decline above a certain wind threshold despite input of nutrient-enriched water. We have observed this phenomenon in an embayment off Central Chile (30°S), where almost 10 years (2000-2009) of microphytoplankton data were analyzed together with environmental variables and wind phenology. Our findings showed that abundance, species diversity and evenness of diatoms and dinoflagellates all increased post-2005 when the mean of the alongshore surface wind stress reached a maximum threshold value of 0.026 N m-2, observed at the decadal temporal variability scale. The increased abundances of diatoms and dinoflagellates post-2005 was associated with the changing phase of the Pacific Decadal Oscillation (PDO) from positive (warm) to negative (cold) phases, which was also associated with a decrease in the intra-seasonal wind activity. Both abundance and diversity of the microphytoplankton community peaked during the post-2005 period whereas higher abundances and frequency of harmful algal blooms (e.g. Pseudo-nitzschia australis) were observed prior to 2005. We suggest that the low-frequency (decadal) variations of mean wind stress during a transition phase of the PDO combined with the reduction in intra-seasonal (periods shorter than 2 months) wind variability after 2005 provided an “optimal environmental window” for the ecosystem.

The Galician shelf (northwestern Iberian Peninsula) is a highly dynamic area with an important multi-species fisheries industry that exploits resources from several habitats, characterized by being not only highly diverse, rich, and productive but also seasonally and interannually variable. Early life stages of different species are distributed throughout the year, with fluctuating abundances and community composition. Likewise, the influence of environmental factors and processes on larval production and survival remains unknown. Sampling was carried out in July 2012, and all the larvae obtained were identified to establish the specific composition of the community in a summer upwelling scenario. The results show no zonation in the species distribution, a consequence of the mixing effects of the upwelling and eddies, with high diversity but low abundance, which render in a slight predominance of a few species. Due to the dependence of planktonic populations on upwelling events, which was not highly pronounced in 2012, we cannot conclude that this was a typical conformation of the Galician summer larval fish community, but it is a first approach to comprehend the community composition.

Global warming has been causing severe impacts on marine ecosystems, a notorious one being shifts in the geographical ranges of species. The north-western coast of the Iberian Peninsula is an especially interesting zone to study distributional shifts as it has a strong latitudinal thermal gradient, is influenced by the Canary upwelling system (which partially cancels coastal warming) and holds some of the most diverse macroalgae communities in Europe. Notably, it is within this region that many cold-water species, common in northern Europe, have their southernmost distribution refuge. Recent studies hypothesize that the environmental conditions may be nonetheless changing and already threatening this biodiversity hotspot. The main goal of this study was to carry out a fine-scale assessment of the distributional limits of several macroalgae in North-western Iberia, as well as identify possible population and range shifts using historical data (2001-2005) as reference. In addition, non-indigenous species were also surveyed. We also assessed if the regions of (i) Galicia, (ii) Northern Portugal, and (iii) Central Portugal displayed distinctive characters regarding macroalgae composition and abundance. We identified an increase in abundance of some non-indigenous macroalgae as well as a decrease in the abundance of some cold-water species. In the most severe cases, cold-water species were extirpated along hundreds of km. The compounded effect of the decrease in the abundance of cold-water species and the increase in the abundance of non-indigenous species is leading to the homogenization of macroalgae communities in north-western Iberia.

The Galician shelf (northwestern Iberian Peninsula) is a highly dynamic area with an important multi-species fisheries industry that exploits resources from several habitats, characterized by being not only highly diverse, rich, and productive but also seasonally and interannually variable. Early life stages of different species are distributed throughout the year, with fluctuating abundances and community composition. Likewise, the influence of environmental factors and processes on larval production and survival remains unknown. Sampling was carried out in July 2012, and all the larvae obtained were identified to establish the specific composition of the community in a summer upwelling scenario. The results show no zonation in the species distribution, a consequence of the mixing effects of the upwelling and eddies, with high diversity but low abundance, which render in a slight predominance of a few species. Due to the dependence of planktonic populations on upwelling events, which was not highly pronounced in 2012, we cannot conclude that this was a typical conformation of the Galician summer larval fish community, but it is a first approach to comprehend the community composition. [ABSTRACT FROM AUTHOR]

Predicting changes in the abundance and distribution of small pelagic fish species in response to anthropogenic climate forcing is of paramount importance due to the ecological and socioeconomic importance of these species, especially in eastern boundary current upwelling regions. Coastal upwelling systems are notorious for the wide range of spatial (from local to basin) and temporal (from days to decades) scales influencing their physical and biogeochemical environments and, thus, forage fish habitat. Bridging those scales can be achieved by using high-resolution regional models that integrate global climate forcing downscaled from coarser resolution earth system models. Here, “end-to-end” projections for 21st century sardine population dynamics and catch in the California Current system (CCS) are generated by coupling three dynamically downscaled earth system model solutions to an individual-based fish model and an agent-based fishing fleet model. Simulated sardine population biomass during 2000–2100 exhibits primarily low-frequency (decadal) variability, and a progressive poleward shift driven by thermal habitat preference. The magnitude of poleward displacement varies noticeably under lower and higher warming conditions (500 and 800 km, respectively). Following the redistribution of the sardine population, catch is projected to increase by 50–70% in the northern CCS and decrease by 30–70% in the southern and central CCS. However, the late-century increase in sardine abundance (and hence, catch) in the northern CCS exhibits a large ensemble spread and is not statistically identical across the three downscaled projections. Overall, the results illustrate the benefit of using dynamical downscaling from multiple earth system models as input to high-resolution regional end-to-end (“physics to fish”) models for projecting population responses of higher trophic organisms to global climate change.

Thermosediminibacter oceani (Lee et al. 2006) is the type species of the genus Thermosediminibacter in the family Thermoanaerobacteraceae. The anaerobic, barophilic, chemoorganotrophic thermophile is characterized by straight to curved Gram-negative rods. The strain described in this study was isolated from a core sample of deep sea sediments of the Peruvian high productivity upwelling system. This is the first completed genome sequence of a member of the genus Thermosediminibacter and the seventh genome sequence in the family Thermoanaerobacteraceae. The 2,280,035 bp long genome with its 2,285 protein-coding and 63 RNA genes is a part of the Genomic Encyclopedia of Bacteria and Archaea project.

This study presents novel results about ocean-atmosphere CO 2 exchanges based upon novel direct in situ measurements of turbulent fluxes using the eddy covariance (EC) methodology. This study was carried out on the Southeast coast of Brazil and the adjacent open ocean during two days of the austral winter of 2015, on board the RV Vital de Oliveira. This is the first time that the EC technique was used in this region for CO 2 flux studies. The results presented illustrate contrasting magnitudes of CO 2 fluxes measured on the open sea region (1.22 ± 2.08 μmol m−2 s−1), the Brazil Current (−2.92 ± 1.25 μmol m−2 s−1) and the coastal region (−3.11 ± 1.67 μmol m−2 s−1). The main cause of negative CO 2 fluxes, indicating a mean CO 2 sink behavior of this region, is due to the occurrence of the coastal upwelling phenomenon and the atmospheric conditions. We found that lower atmosphere local modulation due to sea surface temperature (SST) variations along the study region combined with the large-scale atmospheric synoptic conditions contributed to the flux behavior. • First CO 2 fluxes measured in Southwestern Atlantic Ocean using Eddy Covariance method. • Interaction between distinct atmospheric spatio-temporal scales (large scale x local SST modulation) affects the CO 2 fluxes. • Atmospheric parameters have high dependence on the sea surface temperature. • Physical processes on sea-air interface shows great influence on CO 2 fluxes direction. • The open ocean area and the upwelling region have opposite sign of CO 2 fluxes. [ABSTRACT FROM AUTHOR]

Abstract The spatial and temporal variability of upwelling events occurring offshore northern Colombia (southern Caribbean Sea) on seasonal and intraseasonal time scales is analysed in detail for the period 01/1993–12/2015 using high-resolution oceanic and atmospheric reanalysis products. Different methods are applied that together allowed us to identify the upwelling and relaxation events observed in this area and to explain the main dynamic processes that occur within the annual cycle. In this region, the wind impulse directly determines the intensity and occurrence of upwelling. This upward motion can be full, with a clear surface signal during the months of intense northeast winds, or it can be partial during the rainy season, when winds weaken, and cold subsurface waters do not rise to the sea surface. There is evidence of onshore geostrophic flow affecting the Ekman dynamics when the wind impulse is low during the peak of the rainy season. Short-term atmospheric perturbations that interrupt the upwelling process for several days in La Guajira were characterised. On occasions, cold fronts associated with the intrusion of winds from the north (Nortes), and warm fronts associated with air masses coming from the eastern tropical Pacific, induce a favourable downwelling condition in the upper layer off La Guajira. During these short relaxation periods, the mixed layer is warm, and the relatively cold subsurface isotherms are located at greater depths due to the onshore transport of surface waters. Highlights • We examined active/quiescent upwelling events in the La Guajira system at different scales. • High-resolution oceanic and atmospheric reanalysis were used in the three-dimensional analysis of upwelling. • Several indices were applied to identify the evolution of each upwelling event. • We provide further insights towards understanding the local mechanisms interrupting upwelling. [ABSTRACT FROM AUTHOR]

Highlights • Onshore recruitment is not correlated across the different larval behaviours. • Diel vertical migration increases recruitment, but also mean dispersal distance. • DVM effect on recruitment is of lesser importance than timing larvae are released. • Small changes in PLDs are of higher importance than DVM effect on recruitment. • DVM magnify the differences in spatial patterns of recruitment across PLDs. Abstract Several empirical plankton studies and realistic numerical models of the coastal ocean have clearly shown the dramatic effects that larval behaviour and coastal topography can have on effective alongshore dispersal, population connectivity, successful recruitment and cross-shore distribution of the larval stages of benthic coastal invertebrates and fish. All these are essentially distinct and ecologically important aspects of the dispersal process, but which are correlated to a greater or lesser extent through the interaction of larval attributes (e.g., behaviour, pelagic larval duration, PLD) and specific velocity fields of a region of the ocean. Vertical positioning in the water column and ontogenetic and diel vertical migration (DVM) have been identified as the most efficient behavioural mechanisms that can modulate larval transport in the ocean, especially in stratified, baroclinic water columns such as those typically found in upwelling ecosystems. The large seasonal variability in circulation within most upwelling ecosystems is therefore expected to deeply influence all aspects of the larval dispersal process, but it has been less researched. Here, we use a realistic representation of velocity fields across a section of the Humboldt Current Upwelling Ecosystem (HCUE) to evaluate the relative effects of variation in PLD, geographic position, DVM and the timing of larval release on successful onshore recruitment, alongshore dispersal distances, cross-shore retention and persistence of recruitment spatial patterns. Our results show that an increase in pelagic larval duration exponentially increase larval waste, consequently reducing onshore recruitment, regardless of whether larvae perform DVM or not during their development. For any given larval duration, season of the year and location along the shore (topography) had the largest effects on recruitment variability, explaining over 8.49% and over 11.47% of the temporal and spatial variation, respectively. In contrast, while DVM had a highly consistent positive effect on recruitment along the shore, PLD's and seasons, it only explained about 3% of recruitment variability. Thus, while performing DVM appears to be a safe strategy to increase recruitment, selective forces for such behaviour maybe weak when only oceanic transport is considered. Neither season of the year, nor larval behaviour altered the broad spatial pattern of recruitment across the study region. Pelagic larval durations of over 20 days did not significantly alter this spatial pattern either, suggesting the existence of persistent sources and sinks for benthic populations across the region, although the connectivity matrices must be examined in more detail. Interestingly, in the section of the HCUE, the DVM behaviour led to significantly higher mean dispersal distances along the shore during the upwelling season, as compared to passively advected particles. Such a behavioural effect on dispersal distances have all but disappeared when larvae were released in winter time. These results demonstrate that onshore recruitment, dispersal and connectivity among populations are not correlated across the different larval behaviours, as it has often been implied in the literature and that timing of peak larval release must receive more attention within the HCUE. Results also illustrate the importance of examining fundamental questions of the dispersal process, distance, recruitment, retention, connectivity, in different regions of the world's costal ocean. [ABSTRACT FROM AUTHOR]

Over the past decades, as a consequence of human activity, there was an increase in nutrient inputs to the ocean and they are expected to enhance even more in the future. Coastal areas, accounting for a significant proportion of marine primary productivity, are the most vulnerable zones to anthropogenic impacts. The response of phytoplankton communities to an increase in organic and inorganic nutrients levels from natural allochthonous sources was assessed in microcosm experiments conducted in a coastal system affected by intermittent upwelling events (Ría de Vigo, NW Iberia). Three nutrient addition experiments were performed in spring, summer and autumn, when surface water was supplemented with 5 and 10% of atmospheric and riverine matter. Pico-, nano- and microphytoplankton abundances, chlorophyll a concentration (Chl a ) and primary production rates (PP) were measured and compared with those in the control seawater sample (without additions) after 48 h of incubation. Simultaneous experiments with controlled additions of inorganic and organic nutrients were also performed in order to describe the limiting nutrient for phytoplankton growth at each experiment. The composition of the matter inputs and the structure of the phytoplankton communities determined the type of response observed. Phytoplankton responses varied among seasons, being positively correlated with dissolved inorganic nitrogen (DIN) concentrations. As expected, the phytoplankton responses to external nutrient inputs were stronger under low nutrient levels (summer) than when phytoplankton was already growing in nutrient replete conditions (spring). Null and negative responses to the natural inputs were observed in autumn, which suggests that the oceanic phytoplankton advected to this coastal system during downwelling events could be occasionally inhibited by these nutrient inputs. In a future global change scenario, characterized by enhanced nutrient inputs from riverine and atmospheric origin, the response of phytoplankton communities will strongly depend on the concentration and chemical composition of these inputs and on the structure of phytoplankton communities able to respond to them. [ABSTRACT FROM AUTHOR]

Despite a growing interest in common octopus for aquaculture, massive mortalities during the planktonic paralarval stage still hamper production. Prior to die-off during rearing trials for paralarvae, it could be observed that the food-capturing paralarvae tended to be carried downward in a current induced by the aeration system, eventually depositing the animals on the tank bottom. The aim of this study was to investigate the effect of upwelling water-flow, that might support paralarval swimming and floating, on paralarval survival and growth. A new artificial upwelling rearing system using a strong downward flow in the center to the bottom of the tank was developed. The effects of the new system in combination with supplying natural zooplankton (mainly decapod crustacean zoeae) or Artemia were evaluated using three different broods hatched from three mothers (broods A, B, and C). As food items for zooplankton, n-3 highly unsaturated fatty acid (n-3 HUFA)-fortified rotifers and digestible microalgae Nannochloropsis oculata were supplemented. The hatchling dry weight was significantly different among broods, showing heavier weight in order of broods A > C > B. Use of the upwelling rearing system significantly improved the rate of paralarval survival as compared with using the standard system, and paralarval growth was significantly faster when reared in the upwelling system with zooplankton supplementation. Paralarvae in the upwelling + zooplankton group kept high survival rates over 80% until 18 days after hatching (DAH). The survival rate of the tank of brood A could achieve 80.8% at 20 DAH, however, those of broods B and C dropped to 8.2% and 54.4% at 20 DAH, respectively, presumably due to combined effect of small hatchling size and insufficient food supply. The octopuses of broods A and C reached benthic stage by 25 and 23 DAH, with survival rates of 51.0% and 45.3%, respectively. The overall results suggest that an inadequate water-flow environment in combination with poor food quality and quantity are major causes of paralarval mortality of the common octopus. For culturing paralarvae, the combined use of an upwelling rearing system and supplying decapod crustacean zoeae supplemented with n-3 HUFA fortified rotifers and digestible N. oculata was recommended. [ABSTRACT FROM AUTHOR]

Zoea larvae of decapod crustaceans are considered to be the best prey organisms for culturing paralarvae of merobenthic octopuses. Because paralarvae consume many zoeae until settling as juveniles, a reliable method is required to rear a large number of zoeae at a high stocking density while maintaining their nutrition at a level to meet the demands of octopus paralarvae. However, when rearing zoeae, "sinking-death syndrome" (where many zoeae are deposited on the bottom of the rearing tanks) results in high mortality. In Experiment 1, to reduce larval deposition and lower the mortality, an upwelling system was installed and tested for its effectiveness in rearing a high stocking density of Portunus trituberculatus zoeae at low mortality. The effect of different supply densities of Artemia on growth and morphology of zoeae was also investigated to evaluate the nutrient sufficiency of zoeae under intensive rearing conditions. In Experiment 2, Octopus sinensis paralarvae were reared for 15 d, supplied with either early-stage zoeae or late-stage (long-term reared) zoeae, to examine the dietary effect of intensively reared zoeae on paralarval survival and growth. In Experiment 1, the proportion of zoeae sinking to the bottom was significantly reduced by using the upwelling system, and the survival rate of zoeae was higher in tanks with an upwelling system at a high stocking density of zoeae (500 individuals L−1) compared to those without. Larger body size and faster morphogenesis of larvae were obtained at the final (fourth) zoeal stage when zoeae were supplied with Artemia at high density compared with those supplied at low density. Composition of docosahexaenoic acid (DHA) in intensively-reared final-stage zoeae (10 d old) was maintained at a similar level to that in first-stage zoeae (1 d old) by supplying a high density of Artemia enriched with DHA. In Experiment 2, a higher survival rate and heavier body weight of paralarvae were obtained in the group supplied mainly with late-stage zoeae compared to that with early-stage zoeae. Because the supply of zoeae was adjusted to the same dry weight for both groups, it is concluded that supplying large-sized zoeae increases the efficiency of prey capture and nutrient absorption by the paralarvae. These results suggest that a combination of the use of an upwelling system and a high-density supply of enriched Artemia is effective for intensive rearing of zoeae, achieving reduced facility costs and more efficient production of high-quality prey for rearing octopus paralarvae. • Use of upwelling system improved survival of swimming crab zoeae reared at a high stocking density. • Nutritional status of zoeae was maintained by supplying DHA-fortified Artemia at a high density. • Supply of late-stage large zoeae achieved high survival and growth rates of octopus paralarvae. • Intensive rearing of zoeae can achieve secure supply of high-quality prey for paralarval rearing. [ABSTRACT FROM AUTHOR]

• An algorithm for detecting mesoscale fronts from the multiscale oceans is proposed. • The method combines objective sliding-window thresholds and morphological operations. • It has the merits of low sensitivity to gradient fields and identifying more fronts. • A global frontal occurrence map from 39-year SST images is obtained using the method. • Some known persistent fronts hard to be detected before are identified on the map. Mesoscale ocean fronts play a significant role in marine fisheries, ecosystems, and climate change, and a front detection algorithm appropriate for satellite Earth observation use is a fundamental tool to observe and monitor long-term frontal activities. Since various ecological processes usually work on different spatiotemporal scales, it is vital to separate the fronts at different scales from the multiscale oceans to better study their scale-specific biophysical processes. A sliding-window-threshold algorithm (SWTA) is thus developed to extract the mesoscale frontal zones and lines from the multiscale frontal information existing in the high-resolution satellite images, which employs the sliding-window thresholds to sift for the candidate frontal pixels and a set of morphological operations to then generate more continuous frontal zones and lines. Compared with the two commonly used gradient and population-based algorithms, statistical analysis indicates that a great majority of fronts identified by the existing algorithms are detected by the use of a SWTA, while the SWTA detects more fronts that were ignored by them. Visual and statistical analyses, together with some known fronts, suggest that SWTA seems to be as insensitive to gradient variations as the population-based algorithms are and they have the same merits as the gradient-based algorithms in the ability to identify coastal or complex fronts. The application, based on 14,245 SST images from 1982 to 2020, shows the global distribution patterns of frontal occurrence and intensity, with some well-known persistent fronts reappearing in the extensions of the western boundary currents and Antarctic circumpolar currents that are not clearly defined in the global probability maps generated with the previous algorithms. In addition, similar seasonal variations in the frontal occurrence are found in the five western boundary current/extension areas and the four eastern upwelling systems, reaching a peak intensity during the warm season and a minimum intensity during the cold season. The information on the mesoscale fronts detected by SWTA would be potentially useful for better understanding of the ecological and climatic effects of front dynamics and in the predicting of the distribution of fish species and other marine organisms in a changing climate. [ABSTRACT FROM AUTHOR]

Purpose: The accumulation of trace elements in sediments from highly productive continental margins may depend on the affinity of these elements for organic matter and their degrees of further incorporation into pyrite (FeS). We tested the hypothesis that the relative contributions of these geochemical phases play a substantial role as trace element (As, Cd, Cr, Cu, Mn, Ni, and Zn) sinks in the highly bioturbated sediments from the tropical upwelling system off Cabo Frio, southeastern Brazil. Materials and methods: Four sediment cores sampled across the Cabo Frio continental shelf were submitted to a sequential extraction procedure performed to separate three different operationally defined fractions, i.e., the geochemical phases soluble in 1 M HCl (considered as the 'reactive' fraction), concentrated HSO (considered as the organic matter-bound phase), and concentrated HNO (considered as the pyrite-bound phase). The trace metal incorporation into pyrite was assessed by estimating the degree of trace metal pyritization (DTMP), while the pyrite sulfur stable isotope signatures ( δ S) were used as proxies for sulfur redox cycling intensity. Results and discussion: Relative contributions of trace element fixation by organic matter and pyrite were positively correlated for Mn, Cr, and Ni on one hand, and negative correlated for Cu, on the other hand. The positive correlations imply in synergistic roles of these geochemical phases in determining the trace elements sedimentary sinks, while the negative relationship found for Cu reflects differences in the predominant retention mechanisms along with sediment burial. The δ3S signatures were negatively correlated with DTMP values of As, Cd, and Mn, suggesting a diminishing effect of the sulfur redox cycling on trace elements pyritization. These δ S signatures were not correlated with DTMP values of Cr, Cu, and Ni, which were dominantly associated with the high organic matter contents found in this upwelling system. Conclusions: The role of pelagic organic matter scavenging of metals and later fueling of benthic microbial sulfate reduction and pyrite accumulation were evidenced as highly variable across the Cabo Frio shelf sediments. Differences in the organic matter accumulation in response to upwelling-enhanced primary productivity and in the intensity of bioturbation-driven sulfur redox cycling help to explain the spatial variability in the biogeochemical processes affecting the sedimentary trace metal sinks. [ABSTRACT FROM AUTHOR]

Protoceratium reticulatum is considered a potential toxic dinoflagellate. This paper describes a high-frequency monitoring study performed at Chipana Bay (northern Chile), sampling over 48 hours in a near-bottom shallow coastal area to quantify the biochemical features of a red tide dominated by this microscopic algae. This area belongs to the Humboldt Current upwelling system, and is considered highly productive for artisanal fisheries. Total chlorophyll a, total lipids, particulate organic carbon and nitrogen, fatty acids and major phytoplankton group concentration (i.e. dinoflagellates, diatoms, ciliates and cysts) were studied in 7-hour intervals in February 2007. Our results indicate a high concentration of potential available food in the form of lipids ranging from 50 to 300 μg L-1 for benthic suspension feeders, i.e. bivalves. The dominance of P. reticulatum (60-80% of the total cell concentration per litre, ranging from 55x103 to 384x103 cells L-1) can be considered as a possible interference for harvesting in this productive area, although the toxicity of this algae was not proved in the present study. The main dinoflagellate fatty acid markers [18:0, 18:4(n-3), 20:5(n-3), and 22:6(n-3)] showed high proportions (%) during the short time cycle and in at least two cases [the 18:4 (n-3) and 22:6 (n-3) fatty acids] a highly significant relationship with dinoflagellate concentration (cells L-1). The topographical and benthic structure (mainly kelp forest) of the zone helps to retain particles and nutrients that may in part explain the high productivity and food availability, but the presence of recurrent red tides in this coastal area—if they prove to be toxic—is argued to be a major problem for local fisheries.

Entre junio de 2002 y abril de 2003 se midió el contenido de cadmio total y disuelto entre la superficie y los 100 m de profundidad, en dos estaciones localizadas en la bahía Mejillones del Sur. El rango de cadmio total y cadmio disuelto en las aguas de esta bahía fue 0,41-10,7 y 0,08-1,61 nM, respectivamente, durante el período de muestreo. Los resultados fueron correlacionados con la estructura físico-química de la columna de agua al momento del muestreo, de manera de estudiar los patrones de variabilidad estacional de este metal en este sistema de surgencia. Las condiciones oceanográficas imperantes durante este período correspondieron a un año normal (no-El Niño). Las masas de agua presentes en la bahía correspondieron a agua subantártica, subtropical y ecuatorial subsuperficial, con diferentes grados de mezcla y estratificación durante el período de estudio. Los perfiles de cadmio presentaron una distribución vertical clásica de un micronutriente. Sin embargo estos perfiles presentaron leves diferencias que pueden ser atribuidas a la condición de mezcla de las masas de agua al interior de la bahía. Un análisis multivariado de los parámetros registrados indicó que la variación temporal de cadmio en las aguas superficiales está asociada a las fluctuaciones de la clorofila a y la temperatura. Esto sugiere que, a escala estacional, la producción de biomasa fitoplanctónica sería el principal factor que controla la distribución de cadmio en esta bahía. Por otro lado, a pesar de que el cadmio es un metal redox sensitivo no se encontró un efecto significativo de la disponibilidad de oxígeno sobre el comportamiento de este metal, de manera que la condición micróxica de las aguas de fondo de la bahía no sería un factor preponderante en el flujo de cadmio hacia los sedimentos. La razón Cd/PO4 encontrada en Mejillones es similar a la reportada en otras zonas costeras de Chile. Los bajos valores y la tendencia temporal observada en esta razón pueden ser explicados ya sea por una mayor eficiencia en la remoción de PO4 que de Cadmio en las aguas superficiales o una mayor remineralización de cadmio en las aguas subsuperficialesTotal and dissolved cadmium were measured from surface to 100 m water depth, between June 2002 and April 2003, in Mejillones bay. Total and dissolved cadmium range concentration was 0.41-10.7 and 0.08-1.61 nM, respectively. Cadmium profiles and water structure were used to study seasonal variability patterns of this metal in this upwelling system. Oceanographic conditions during this period correspond to a normal (non-El Niño) year. Water masses present in this bay correspond to subantartic superficial water, subtropical superficial water and Equatorial subsuperficial water with different degree of mixture and stratification during sampling period. Cadmium profiles showed a classic nutrient-type distribution. Whereas some differences in this profiles could be attributed to a water masses mixing condition into the bay. Multivariate analysis indicates that temporal cadmium variations were associated with chlorophyll-a concentration and temperature fluctuation, indicating that, at this temporal resolution, phytoplanktonic biomass production is the principal factor controlling cadmium concentration in surface waters of Mejillones bay. By other hand, in spite of cadmium being a redox-sensitive metal, any significant influence of dissolved oxygen on this metal were founded, thus microxic condition of bottom water of Mejillones bay is not the principal factor that promotes cadmium flux to the sediments. Cd/PO4 ratio is in agreement with normal values reported for the Chilean coast, and its low values, compared with the northeast Pacific coast, can be explained either by the fact that PO4 is more efficiently removed than cadmium from the surface layer, or that cadmium remineralization is occurring much faster than in the case of PO4

In this study, we obtained concentrations and abundance ratios of long-chain alkenones and glycerol dialkyl glycerol tetraethers (GDGTs) in a one-year time-series of sinking particles collected with a sediment trap moored from December 2001 to November 2002 at 2200 m water depth south of Java in the eastern Indian Ocean. We investigate the seasonality of alkenone and GDGT fluxes as well as the potential habitat depth of the Thaumarchaeota producing the GDGTs entrained in sinking particles. The alkenone flux shows a pronounced seasonality and ranges from 1 µg m −2 d −1 to 35 µg m −2 d −1 . The highest alkenone flux is observed in late September during the Southeast monsoon, coincident with high total organic carbon fluxes as well as high net primary productivity. Flux-weighted mean temperature for the high flux period using the alkenone-based sea-surface temperature (SST) index U 37 K ′ is 26.7 °C, which is similar to satellite-derived Southeast (SE) monsoon SST (26.4 °C). The GDGT flux displays a weaker seasonality than that of the alkenones. It is elevated during the SE monsoon period compared to the Northwest (NW) monsoon and intermonsoon periods (approximately 2.5 times), which is probably related to seasonal variation of the abundance of Thaumarchaeota, or to enhanced export of GDGTs by aggregation with sinking phytoplankton detritus. Flux-weighted mean temperature inferred from the GDGT-based TEX 86 H index is 26.2 °C, which is 1.8 °C lower than mean annual (ma) SST but similar to SE monsoon SST. As the time series of TEX 86 H temperature estimates, however, does not record a strong seasonal amplitude, we infer that TEX 86 H reflects ma upper thermocline temperature at approximately 50 m water depth. [ABSTRACT FROM AUTHOR]

We synthesise and update results from the suite of biophysical, larval-dispersal models developed in the Benguela Current ecosystem. Biophysical models of larval dispersal use outputs of physical hydrodynamic models as inputs to individual-based models in which biological processes acting during the larval life are included. In the Benguela, such models were first applied to simulate the dispersal of anchovyEngraulis encrasicolusand sardineSardinops sagaxichthyoplankton, and more recently of the early life stages of chokka-squidLoligo reynaudiiand Cape hakesMerlucciusspp. We identify how the models have helped advance understanding of key processes for these species. We then discuss which aspects of the early life of marine species in the Benguela Current ecosystem are still not well understood and could benefit from new modelling studies. [ABSTRACT FROM AUTHOR]

Western boundary upwelling systems such as those found in the southeastern Brazilian margin (SBM) are promoted by special atmospheric and oceanographic interactions with topography of the coastline. In order to investigate the evolution of the upwelling system in SBM over the past 110 kyr, the abundance of Globigerina bulloides (a planktonic foraminiferal species typically associated with upwelling waters) from two marine cores was combined with estimates of upper water thermal structure derived from Modern Analog Technique based on planktonic foraminifera. High abundances (up to 35%) of large specimens of G. bulloides (≥ 250 μm) associated with cooling subsurface waters reveal the occurrence of an intense coastal upwelling system between 110 kyr and 88 kyr. Changes in coastline orientation due to lower sea level stand (20–70 m lower than today) and a longer season of vigorous Brazil Current (BC) and prevailing northeasterly winds maintained permanently the cold and nutrient-rich South Atlantic Central Waters (SACW) over the shelf promoting the strongest upwelling system of the Brazilian coast over the past 110 kyr. At 88 kyr, a sharp reduction of 14% in abundance of G. bulloides and a 2.6 °C warming of the water column indicates an abrupt weakening of the coastal upwelling, probably caused by a disturbance in SACW formation. During the last glaciation, longer current winter-like conditions of prevailing southwesterly winds and a weakened Brazil Current suppressed the upwelling system in SBM. At this time, constant and relatively high abundance of G. bulloides (up to 10%) suggest that the coastal upwelling was restricted to a short period of months year-round, when the BC and northeasterly winds were relatively vigorous despite the glacial context. The predominance of warm and oligotrophic Tropical Waters due to the shutdown of coastal upwelling in northern SBM was inferred for the last 20 kyr. Despite vigorous northeasterly winds and BC strength, high sea level stand during the Holocene submersed the Abrolhos Bank (AB) leading to a new coastline configuration. Presently, the interaction between the AB and the BC generated a new oceanographic feature in SBM, the Vitória Eddy, with very limited efficiency in producing a strong upwelling such as the one recorded in the past. [ABSTRACT FROM AUTHOR]

Highlights: [•] We assess changes in the southern Humboldt over the last century using food web models. [•] Fishing is the main predator in the system in the more recent state. [•] The biomass of most target species and top predators decreases in recent models. [•] Groups with small sized individuals having short life spans and at low trophic levels dominate in recent models. [•] The system is more susceptible to external forcing and negative ecological interactions than historically. [Copyright &y& Elsevier]

The present study uses a suite of coupled physical-biogeochemical model simulations at 1/3°, 1/10°, and 1/30° to assess the impact of horizontal resolution on air-sea CO2 fluxes in the California Current System (CCS), a relevant issue for downscaling between coarser resolution global climate models and higher resolution regional models. The results demonstrate that horizontal resolution is important to reproduce the sharp transition between near-shore outgassing and offshore absorption, as well as to resolve regions of enhanced near-shore outgassing in the lee of capes. The width of the outgassing region is overestimated when horizontal resolution is not eddy resolving (i.e., 1/3°) but becomes more dependent on shelf topography for eddy-resolving simulations (i.e., 1/10° and 1/30°). Enhanced near-shore outgassing is associated with a local increase in wind-driven upwelling in the lee of capes (i.e., expansion fans), meaning that sufficient horizontal resolution is needed both in the ocean circulation model and in the wind field forcing the model. From a global carbon budget perspective, the model indicates that biological production generates sufficient absorption within a few hundred kilometers of the coast to offset near-shore outgassing, which is consistent with the notion that midlatitude eastern boundary current upwelling systems act both as a sink and source for atmospheric CO2. Based on the 1/30° solution, the CCS between 35 and 45 N and out to 600 km offshore is a net carbon sink of approximately 6 TgC yr−1, with the 1/10° solution underestimating this value by less than 10% and the 1/3° solution by a factor of 3. [ABSTRACT FROM AUTHOR]

The oceanographic conditions in the north Pacific have shifted to a colder period, Pacific sardine (Sardinops sagax) biomass has declined precipitously in the California Current, the international sardine fishery is collapsing, and mackerel (Trachurus symmetricus and Scomber japonicus) are thriving. This situation occurred in the mid-1900s, but indices of current oceanographic conditions and the results of our acoustic-trawl surveys indicate it likely is recurring now, perhaps with similar socioeconomic and ecological consequences. Also alarming is the repetition of the fishery's response to a declining sardine stock—progressively higher exploitation rates targeting the oldest, largest, and most fecund fish. Furthermore, our data indicate the recent reproductive condition of sardine is poor, and their productivity is below modeled estimates used to derive the current fishery-exploitation rates. Consequently, the sardine population has been reduced to two cohorts that are unlikely to produce an appreciable new cohort. Thus, a near-term recovery of this important stock is unlikely, depending on the return of warmer oceanographic conditions, reduced pressure from mackerel species, and perhaps the adoption of a more precautionary strategy for managing the residual sardine population. [ABSTRACT FROM AUTHOR]

Abstract: The distribution and composition of phytoplankton assemblages were studied in the Nazaré submarine canyon, during an upwelling event, using high-performance liquid chromatography (HPLC) pigment analysis, complemented by microscopic qualitative observations. High chlorophyll a (Chl a) concentrations were recorded in the canyon head, near the coast, where values greater than 4μgL−1 were observed. In contrast, Chl a was relatively low in offshore regions, with values below 0.5μgL−1. The most abundant accessory pigments were fucoxanthin, peridinin, diadinoxanthin and 19′-hexanoyloxyfucoxanthin. Pigment data information was analyzed using the CHEMTAX software to estimate the contribution of different taxonomic groups to total Chl a. North of the canyon head, an area with high concentration of peridinin-containing dinoflagellates was identified (with presence of chain-forming toxic dinoflagellates). The presence of these organisms was associated with mixed water columns and phosphate values lower than the ones south of the canyon head, where a dominance of diatoms was recorded. The rest of the study region showed a dominance of prymnesiophytes and a significant contribution of cyanobacteria at oceanic stations. This study demonstrates the usefulness of using pigment analysis to study spatial distribution of phytoplankton groups in relation to a complex physical environment. [Copyright &y& Elsevier]

The article discusses a study on the ecological factors that influence the net ecosystem metabolism based on the functional relationship between phytoplankton size structure, heterotrophic prokaryote production, nutrients and net ecosystem metabolism at the coastal upwelling sites Chipana and Mejillones off Chile in 2005, 2006 and 2007. Conductivity, temperature and depth (CTD) vertical profiles were used to characterize seasonal changes in winds and the physical environment. The estimated sea surface temperature difference is 4°Celsius (C) between austral winter and summer. Results showed that the carbon export is increased by the heightened dominance of large phytoplankton cells. Wind stress drives the synoptic-scale shifts in the upwelling that affect the microbial community.

Abstract: Blooms of Dinophysis spp. associated with lipophilic shellfish toxin outbreaks are common in Northwestern Iberia waters from spring to autumn. Blooms of Dinophysis acuta are very seasonal (late summer-early autumn); they start earlier in Northern Portuguese waters during the upwelling season, and reach their maximum values in the Galician Rías during downwelling events at the end of the upwelling season. There is controversy about whether sudden increases in cell concentrations in the rías result from cross-shelf transport of populations previously established in adjacent shelf waters, or are due to longshore transport that brings populations located off Portugal to the North. In 2005, record concentrations of D. acuta were observed in Portuguese waters (14×104 cellL−1) off Aveiro in early September, while concentrations off the Galician coast were very moderate (102–103 cellL−1). During the autumn transition from upwelling- to downwelling-favourable winds, D. acuta declined abruptly off Portugal while the annual maximum (up to 22×103 cellL−1) was found in the Galician Rías. A new approach was used that combined physical observations (SST, current measurements); weekly observations from monitoring programmes in Galicia and Portugal; weekly division rate (μ min ) estimates of D. acuta in Ría de Vigo, together with monthly transects and additional ad hoc sampling in the Ría. During August and early September, division rates were high in Ría de Vigo but concentrations were low, whereas higher SST values in Portugal (a proxy for thermal stratification) seemed to promote the build up of high densities of D. acuta. During the last week of October and the first week of November, populations declined, whereas in Galicia, maximum concentrations were reached while division rate estimates were almost zero. Results presented here confirm that increased numbers in the Galician Rías are not due to intrinsic growth but to physically driven accumulation; a simple cell concentration budget calculated during the accumulation period suggests that the high net growth observed during downwelling, in the absence of cellular division, must be due to cells imported by longshore transport. [Copyright &y& Elsevier]

Abstract: High-resolution records of organic and inorganic geochemical proxies document environmental changes during Oceanic Anoxic Event 1b for the Albian upwelling system at DSDP Site 545 Mazagan Plateau off NW Africa. Sea surface temperature estimates based on TEX86 analyses show an abrupt rise by ~3 °C concurrent with a more than 2-fold increase in accumulation rates for organic carbon and siliciclastic sediment components. Geochemical grain-size indicators (Si/Al and Zr/Al) indicate the influx of overall finer grained sediment during the event. Our data suggest that the warming phase associated with OAE 1b resulted in an attenuation of the NE trade wind system and a weakening of local upwelling conditions. Higher amounts of precipitation over NW Africa and an associated higher continental run off may have supplied nutrients to the eastern North Atlantic and fostered the production of organic matter and black shale deposition. [Copyright &y& Elsevier]

Abstract: Water was collected from the Sagres station (SW Portugal) in September 2002, at a site adjacent to the upwelling centre of Cabo São Vicente, during relaxation of upwelling conditions. Surface and depth samples were enriched with inorganic nutrients in order to evaluate their relative influence on the microalgal assemblage. Small-scale, short-term bioassays involved separate in vitro additions of nitrogen and phosphorus. Enrichments with nitrogen led to a general increase of primary production, suggesting nitrogen as the primary potential nutrient limiting microalgal growth during this period, as well as altering the relative microplanktonic composition in favour of diatoms. [Copyright &y& Elsevier]

The vertical and temporal dynamics of total picoplankton, heterotrophic nanoflagellates and ciliates were monitored monthly from May 2002 to April 2003, along with environmental parameters, in Lake Faro, a meromictic coastal basin characterized by a permanently anoxic monimolimnion and sulfide-rich bottom waters. A two-layer discrimination was delineated in the water column of the lake, based on the correlations between environmental and biological descriptors and on the ciliated protozoa community composition. The latter showed a clear zonation pattern along the water column with two main recognizable facies: a superficial and a deep one. Choreotrichida and Strombidiida dominated the upper facies nearly throughout the study period, while Tintinnida were only found in summer months. The mixotrophic cyclotrichid Myrionecta rubra was also frequently observed in the upper facies. Typical of the deep facies was the occurrence of Pleuronematida ( Cyclidium sp.) and of flagellates of the order Cryptomonadida ( Chilomonas sp.), which were the main potential picoplankton grazers during a summer bloom of photosynthetic sulfur bacteria. Sporadic inputs of Levantine Intermediate Waters (LIW) from the upwelling system of the Straits of Messina, although limited to the mixolimnion, clearly affected the physical and chemical environment, as well as the microbial biomass and the ciliated protozoa assemblage composition, all along the water column of the lake, suggesting that meromictic basins, although strongly stratified, may experience perturbation effects from the surface down to the bottom, with important consequences on their biogeochemical cycles and on their ecology. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of dissolved gases (O2, N2O), nutrients (NO3 −, NO2 −, PO4 3−), and oceanographic variables were performed off northern Chile (∼21°S) between March 2000 and July 2004, in order to characterize the existing oxygen minimum zone (OMZ) and identify processes involved in N2O cycling. Both N2O and NO3 − displayed sharp, shallow peaks with concentrations of up to 124nM (1370% saturation) and 26μM, respectively, in association with a strong oxycline that impinges on the euphotic zone. NO2 − accumulation below the oxycline''s base reached up to 9μM. The vertical distribution of physical and chemical parameters and the existing relationships between apparent oxygen utilization (AOU), apparent N2O production (ΔN2O), and NO3 − revealed three main layers within the upper OMZ. The first layer, or the upper part of the oxycline, is located between the base of the mixed layer and the mid-point of the oxycline (around σt =25.5kgm−3). There the O2 declines from ∼250 to ∼50μM, and strong (but opposing) O2 and NO3 − gradients and their associated AOU–ΔN2O and AOU–NO3 − relationships indicate that nitrification produces N2O and NO3 − in the presence of light. The second layer, or lower part of the oxycline, represents the upper OMZ boundary and is located between the middle and the base of the oxycline (25.9<σt <26.1kgm−3). In this layer NO3 − reduction begins at O2 levels ranging from ∼50 to ∼11μM and accumulation of 41–68% of the ΔN2O pool occurs. The accumulation of N2O (but not of NO2 − or NH4 +) and the observed AOU–ΔN2O and AOU–NO3 − relationships (which are opposite to those of the overlying first layer) suggest that a coupling between nitrification and NO3 − reduction is involved in N2O cycling in this second layer. The third layer is the OMZ core, where the O2 concentration remains constant (O2<11μM). It coincides with σt >26.2kgm−3, which is typical of Equatorial Subsurface Water (ESSW). In this layer, N2O and NO3 − continue to decrease, but a large NO2 − accumulation is observed. Considering all the data, a biogeochemical model for the upper OMZ off northern of Chile is proposed, in which nitrification and denitrification differentially mediate N2O cycling in each layer. [Copyright &y& Elsevier]