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Meridional geostrophic velocity derived from conductivity, temperature, and depth from CTD casts in the upper 300 m depth water column for the (a) northern and (b) southern transects of the PHYTO‐FRONT cruise. Positive (negative) velocity values represent a northward (southward) flow. The geostrophic velocity was computed from the geopotential anomaly relative to the sea surface. The thick black line represents the zero velocity contour, and the gray lines correspond to isopycnals; dots as in Figure 1.
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Mesoscale and submesoscale processes that contribute to localized increases in nutrients in the sunlit layer can stimulate phytoplankton growth and community changes, but the mechanisms involved remain sparsely documented with in situ data in the case of Eastern Boundary Upwelling Systems (EBUSs) and of most ocean regions. The role of diapycnal mix...
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... Further north (St. 1), the nutrient depletion evidenced by lower nitrate and phosphate availability in February, and high concentration of Chl-a is related to the higher abundance of the diatom P. pseudodelicatissima, which has been reported to essentially require these nutrients for growth (Anabalón et al., 2016;Corredor-Acosta et al., 2020), largely provided by the ESSW and SSAW water masses (Silva et al., 2009;Llanillo et al., 2012). ...
Changes in phytoplankton composition and abundance are controlled by multiple factors, including physical forcing and nutrient stoichiometry. This study seeks to assess the interplay between the environmental and biogeochemical conditions in shaping the phytoplankton community structure in open ocean waters off western Patagonia. For this purpose, we used biological, hydrographic, and chemical data measured aboard the R/V Mirai during the austral summer of 2017, combined with remote sensing and reanalysis products. Although no first-order predictive relationships were found between the environmental and biological data, the results showed a latitudinal gradient of the phytoplankton structure, favoring maximum abundances of diatoms (∼10x10⁴ cells L⁻¹) in the northern area (∼43-48°S) characterized by high stratification and freshwater content. The high diatom abundances of Thalassiosira spp., Chaetoceros spp., Pseudo-nitzschia cf. australis and Pseudo-nitzschia cf. pseudodelicatissima taxa in this area results in a nutrient content decreases (nitrate < 9 μmol kg⁻¹, phosphate < 0.9 μmol kg⁻¹, silicic acid < 1.5 μmol kg⁻¹), and low N:Si (<8) and N:P (<10) ratios. Nonetheless, the total dinoflagellates abundance was equal to or higher than those of diatoms (∼10.2x10⁴ cells L⁻¹) throughout most of the sampling region. Specifically, maximum abundances (∼6.3x10⁴ cells L⁻¹) of Karenia spp. were found in the north under the freshwater influence from the Gulf of Penas, where the highest ammonium:nitrate ratio (∼4 to 11.5) was recorded. In contrast, high dinoflagellate abundances of Azadinium spp. were found in the south (∼48-55°S), where an increase of nutrient content (nitrate ∼12μmol kg⁻¹, phosphate ∼1 μmol kg⁻¹, ammonium ∼0.4 μmol kg⁻¹), and high N:Si and N:P ratios (∼35 and ∼12) were observed. This study highlights a major presence of potentially toxic phytoplankton species in the oceanic zone off northern Patagonia under conditions of strong latitudinal and cross-shore gradients in nutrient content and salinity, related to the interplay between oceanic water masses and freshwater input.
... The presence and dynamic evolution of ocean fronts can influence the biogeochemical and physical properties of the surrounding ocean areas by altering material and energy transport (Corredor-Acosta et al. 2020;Siegelman et al. 2020;Nicholson et al. 2022;Song et al. 2022;Zhou and Cheng 2022). Therefore, the exploration of ocean fronts holds significant implications for various fields, including marine ecology, oceanic climatology, marine fisheries, and maritime military operations (Pattiaratchi et al. 2022;Prants 2022;Salim et al. 2023). ...
... Similarly, Su et al. (2020) and colleagues utilized high-resolution ocean models to demonstrate the pivotal role of ocean fronts in influencing the global ocean's heat absorption through heat transfer mechanisms. Furthermore, Corredor-Acosta and his research team have shown that ocean fronts significantly enhance nutrient concentrations within the ocean's euphotic layer, thereby fostering phytoplankton growth and affecting community dynamics (Corredor-Acosta et al. 2020). Nevertheless, it is worth noting that in eastern boundary upwelling systems and various other ocean regions, the underlying mechanisms are not fully understood owing to the absence of in situ observational data (Jian et al. 2019Wang et al. 2021b;Luo et al. 2022Luo et al. , 2023. ...
This paper proposes an ocean front database and a method for its construction tailored for studying the dynamic evolution of ocean fronts. Ocean fronts play a crucial role in the interactions between the ocean and atmosphere, affecting the transfer of heat and matter in the ocean. In recent years, research on ocean fronts has emerged as a significant and rapidly evolving area within oceanography. With the development of ocean remote sensing technology, the amount of available ocean remote sensing data has been increasing. However, the potential of this expanding volume of ocean front data remains largely untapped. The lag in data processing technology has hindered research progress in understanding ocean fronts despite the growing amount of data available. To bridge this gap, this paper proposes an ocean front dynamic evolution database along with a method for its construction to further promote research into the variations and interactions of ocean fronts. This is especially relevant for studies utilizing deep learning to explore the dynamic evolution of ocean fronts. Specifically, the proposed database is designed to capture the variation processes of ocean front enhancement and attenuation, as well as the interactions during ocean front splitting and merging. The proposed database construction method allows for the segmentation and extraction of specific ocean fronts of interest from ocean front images. The proposed method is beneficial for analyzing the dynamic evolution between multiple ocean fronts on the same timeline.
... Most studies conducted in the North Atlantic have not included calculations of nutrient fluxes immediately below the mixed layer using direct microstructure observations nor in highly turbulent environments such as frontal systems. The values reported for frontal systems in other EBUS range from 5.2 (mmol m -2 d -1 ) in the California Current EBUS to 19.11 (mmol m -2 d -1 ) in the Chilean EBUS (Hales et al., 2005;Hales et al., 2009;Li et al., 2012;Corredor-Acosta et al., 2020). The latter values agree with our maxima of 8.34 (mmol m -2 d -1 ) for station 42 (group-F) and average of 1.35 (mmol m -2 d -1 ) for all stations influenced by the upwelling filament front. ...
The filaments of the African Eastern Boundary Upwelling System (EBUS) are responsible for feeding nutrients to the oligotrophic waters of the northeastern Atlantic. However, turbulent mixing associated with nutrient uplift in filaments is poorly documented and has been mainly evaluated numerically. Using microstructure profiler measurements, we detected enhanced turbulent kinetic energy dissipation rates (ε) within the Cape Ghir upwelling filament. In contrast to previous studies, this enhancement was not related to symmetrical instabilities induced by down-front winds but to an increase in vertical current shear at the base of the mixed layer ( h ρ ). In order to quantify the impact of vertical shear and the influence of the active mixing layer depth ( h ε ) in the filament, a simple one-dimensional (1D) turbulent entrainment approach was used. We found that the effect of turbulent enhancement, together with the isopycnal morphology of the filament front, drove the formation of local positive entrainment zones ( Δ h = h ε − h ρ ), as h ε was deeper than h ρ . This provided suitable conditions for the entrainment of cold, nutrient-rich waters from below the filament pycnocline and the upward transport of biophysical properties to the upper boundary layer of the front. We also found that diapycnal nutrient fluxes in stations influenced by the filament (1.35 mmol m⁻² d⁻¹) were two orders of magnitude higher than those of stations not affected by the filament front (0.02 mmol m⁻² d⁻¹). Despite their importance, the effects of vertical shear and h ε have often been neglected in entrainment parameterizations. Thus, a modified entrainment parameterization was adapted to include vertical shear and observed ε, which are overestimated by existing parameterizations. To account for the possible role of internal waves in the generation of vertical shear, we considered internal wave scaling to parameterize the observed dissipation. Using this adapted parameterization, the average entrainment velocities were six times (6 m d⁻¹) higher than those obtained with the classic parameterization (1 m d⁻¹).
... Accordingly, the physical advection can potentially favor the lateral transport of organic C and N produced, mostly by diatoms, at the upwelling zone (Corredor-Acosta et al., 2020;Morales et al., 2010). The more diverse feeding behavior over the Atacama Trench (i.e., a broader niche), along with a deeper mixed layer and the greater biomass of large-sized zooplankton, will then contribute to sustain the metabolic demands in the deep ocean. ...
The highly productive upwelling zone in the Southeast Pacific provides inputs of C and N to the oceanic deep-water system via lateral transport, although the quality of this organic matter, the organisms being transported, and the controlling mechanisms are unclear. Here, we assessed whether the taxonomic and trophic structure of zooplankton over more oceanic offshore waters differ from that of zooplankton located in the upwelling zone, along with the characterization of the oceanographic processes and variables associated with the lateral transport. For this, epipelagic, mesopelagic, and bathypelagic zooplankton along with oceanographic variables and particulate organic matter (POM) were analyzed at the upwelling zone and adjacent oceanic stations off Central Chile (27–33°S), some of which were located over the Atacama trench, during September 2016. The community structure of size-fractioned zooplankton (<200 μm, 200–500 μm, 500–1000 μm, 1000–2000 μm, and >2000 μm size classes) was assessed by an automated method, along with the analysis of the isotopic niche computed from their δ¹⁵N and δ¹³C. The isotope signatures of POM indicated that diatoms contributed mostly to production of new organic C, being the main food source for small-sized zooplankton in coastal waters. The zooplankton community structure differed between the upwelling and oceanic areas, but their isotopic signature showed a large overlap (78%). Satellite-derived geostrophic flow and the depth of the mixed layer appeared as the main factors explaining the homogeneity in the isotopic and biogeochemical signatures of zooplankton between the upwelling zone and offshore waters. Cross-shelf advection is thus suggested as a key process promoting zooplankton export to the deep-water ecosystem, including the ultra-deep Atacama Trench.
... Diapycnal mixing has been shown to be a dominant component of the vertical velocity in submesoscales fronts and filaments by destroying the thermal wind and driving intense ASC in the upper layers (Estrada-Allis et al., 2019). Thus, intensification of diapycnal mixing may enhance vertical transport of nutrients (Arcos-Pulido et al., 2014;Corredor-Acosta et al., 2020;Tsutsumi et al., 2020) as well as upwelling/downwelling of phytoplankton communities from sub-surface layers into the euphotic zone and vice versa. These physical cells act to restore the geostrophy by means of restratification in a process known as frontogenesis (Hoskins and Bretherton, 1972;Hoskins, 1982;Capet et al., 2008;McWilliams, 2016). ...
... In all cases, nutrient intrusions were associated with isopleths doming driven by front-associated upwelling, where positive (upward) w GL and F NOx near the MLD occurred. Though small, the upward fluxes are consistent with other observations in areas of intense mesoscale and submesoscale activity (Arcos-Pulido et al., 2014;Corredor-Acosta et al., 2020). The overlapping of positive w GL with F NOx suggests that diapycnal mixing is acting as an important contributor to the vertical velocity (Ponte et al., 2013) and may be associated with submesoscale process (Estrada-Allis et al., 2019). ...
... The growing accumulation of plastic litter in the marine environment poses an unattended environmental threat to islands, as they become increasingly exposed to pollution of which they have very little control (e.g., Baztan et al., 2014;Monteiro et al., 2018;Pham et al., 2020;Pieper et al., 2020). Its impacts are extensive and can be felt on highly vulnerable socio-economic sectors of which islands depend on, such as tourism, fisheries and shipping industries (Rodríguez et al., 2020). Beach clean-ups are often the only possible remediation measure for the removal of stranded plastic debris from local coastlines, representing an enormous cost to local organizations and governments (Burt et al., 2020;Rodríguez et al., 2020). ...
... Due to the chaotic nature of energy transfer from large eddy currents to small ones, a created turbulent cell is assumed homogeneous, isotropic, with constant n generally different from the refractive indices of other cells. Furthermore, inspired by the isotherm map acquired by satellite reported in [28] and their corresponding eddy currents, in this paper, the boundary of surrounding cells is modeled by a random sequence of convex or concave hemispheres. It is also assumed that radii (R) of hemispheres are randomly selected within an acceptable range to mimic the arbitrary shape of surrounding cells. ...
Recently, compared with acoustic and radio methods, underwater optical wireless communications has been considered as a high-speed and high-bandwidth transmitting method at a lower cost. Absorption, scattering, and optical turbulence are three destructive phenomena that affect the performance of underwater optical communication systems. In this work, we use computer simulations to mimic the statistical behavior of underwater media employing the Monte Carlo method. Our simulation results for optical turbulence are in good agreement with the lognormal probability density function, which describes weak turbulence well, and they deviate as the turbulence moves away from weak. By considering the combined effect of absorption, scattering, and turbulence (AST) phenomena, we obtain the underwater channel’s impulse response (IR). We demonstrate that there is no noticeable difference between the mean of ensemble IRs of the AST channel and the IR of the channel when turbulence is not taken into account. Moreover, our results predict that tripling the coastal link length from 10 to 30 m increases the average variance of sample IRs of the AST channel from their ensemble average by more than five times.
... Diapycnal mixing has been shown to be a dominant component of the vertical velocity in submesoscales fronts and filaments by destroying the thermal wind and driving intense ASC in the upper layers (Estrada-Allis et al., 2019). Thus, intensification of diapycnal mixing may enhance vertical transport of nutrients (Arcos-Pulido et al., 2014;Corredor-Acosta et al., 2020;Tsutsumi et al., 2020) as well as upwelling/downwelling of phytoplankton communities from sub-surface layers into the euphotic zone and vice versa. These physical cells act to restore the geostrophy by means of restratification in a process known as frontogenesis (Hoskins and Bretherton, 1972;Hoskins, 1982;Capet et al., 2008;McWilliams, 2016). ...
... In all cases, nutrient intrusions were associated with isopleths doming driven by front-associated upwelling, where positive (upward) w GL and F NOx near the MLD occurred. Though small, the upward fluxes are consistent with other observations in areas of intense mesoscale and submesoscale activity (Arcos-Pulido et al., 2014;Corredor-Acosta et al., 2020). The overlapping of positive w GL with F NOx suggests that diapycnal mixing is acting as an important contributor to the vertical velocity (Ponte et al., 2013) and may be associated with submesoscale process (Estrada-Allis et al., 2019). ...
The distribution and variability of phytoplankton in the upper layers of the ocean are highly correlated with physical processes at different time and spatial scales. Model simulations have shown that submesoscale features play a pivotal role on plankton distribution, metabolism and carbon fluxes. However, there is a lack of observational studies that provide evidence for the complexity of short-term phytoplankton distribution and variability inferred from theoretical and modeling approaches. In the present study, the development and decay of a submesoscale front south of Gran Canaria Island is tracked at scales not considered in regular oceanographic samplings in order to analyze the picoplankton response to short-term variability. Likewise, the contribution of each scale of variability to the total variance of the picophytoplankton community has been quantified. We observe statistically different picophytoplankton assemblages across stations closer than 5 km, and between time periods shorter than 24 h, which were related to high physical spatiotemporal variability. Our results suggest that both temporal and spatial variability may equally contribute to the total variance of picoplankton community in the mixed layer, while time is the principal contributor to total variance in the deep chlorophyll maximum (DCM).
... Figure 12 shows the diffusivity for surface and type 2 releases at the two resolutions from the fourth day after the particle release, once the diffusivity has stabilized. The SP run is characterized by nearly an order of magnitude greater spreading in both cases, with k z approximately 1.4 × 10 −3 m 2 s −1 and 9.6 × 10 −4 m 2 s −1 for surface and type 2 particles, respectively, in agreement with the indirect estimates from in situ sampling of nutrient fluxes in the upper 100 m of the water column off Concepción, Chile presented in Corredor-Acosta et al. (2020). The system is neither unbounded nor homogeneous, and the model uses the KPP parameterization, therefore interpreting the relative dispersion slope in terms of turbulent theories is not possible. ...
Submesoscale circulations influence momentum, buoyancy and transport of biological tracers and pollutants within the upper turbulent layer. How much and how far into the water column this influence extends remain open questions in most of the global ocean. This work evaluates the behavior of neutrally buoyant particles advected in simulations of the northern Gulf of Mexico by analyzing the trajectories of Lagrangian particles released multiple times at the ocean surface and below the mixed layer. The relative role of meso- and submesoscale dynamics is quantified by comparing results in submesoscale permitting and mesoscale resolving simulations. Submesoscale circulations are responsible for greater vertical transport across fixed depth ranges and also across the mixed layer, both into it and away from it, in all seasons. The significance of the submesoscale-induced transport, however, is far greater in winter. In this season, a kernel density estimation and a detailed vertical mixing analysis are performed. It is found that in the large mesoscale Loop Current eddy, upwelling into the mixed layer is the major contributor to the vertical fluxes, despite its clockwise circulation. This is opposite to the behavior simulated in the mesoscale resolving case. In the “submesoscale soup,” away from the large mesoscale structures such as the Loop Current and its detached eddies, upwelling into the mixed layer is distributed more uniformly than downwelling motions from the surface across the base of the mixed layer. Maps of vertical diffusivity indicate that there is an order of magnitude difference among simulations. In the submesoscale permitting case values are distributed around 10–3 m² s–1 in the upper water column in winter, in agreement with recent indirect estimates off the Chilean coast. Diffusivities are greater in the eastern portion of the Gulf, where the submesoscale circulations are more intense due to sustained density gradients supplied by the warmer and saltier Loop Current.
With the general objective of evaluating the spatiotemporal distribution of plankton under different environmental conditions, governed by physical processes, on the inner shelf off Ubatuba (SP), Brazil, considering more detailed vertical and spatial resolutions, three independent studies were carried out. These studies are presented throughout this thesis in the form of scientific articles, in chapters II to IV. In chapter II, the occurrence of thin layers of phytoplankton and their temporal evolution were investigated over two days of observations in February/2019. Chapter III analyzed seasonal (winter/summer) and short-term variation (hours) in the plankton abundance and distribution and their relationship with hydrodynamic conditions, based on observations carried out in July/2018 and January/2019. In chapter IV the influence of environmental conditions on the abundance and vertical and horizontal distributions of the Synechococcus, Prochlorococcus, picoeukaryotes, and nanoeukaryotes populations was evaluated, comparing different scenarios obtained in December/2018 and January/2019. Overall, the data collection relied on field observation techniques at fixed and spatial stations, continuous high-resolution profilings with optical and acoustic sensors, in addition to discrete sample collection for analysis in laboratory. The abundance of the main plankton groups, from autotrophic microorganisms to mesozooplankton, was estimated using an in situ imaging system and flow cytometry (pico-nanoplankton). The general results suggest that the wind is the primary forcing of the variability in the plankton abundance and vertical and horizontal distribution in the coastal zone of Ubatuba, driving submesoscale phenomena related to the intrusion and retreat of the South Atlantic Central Water along the inner shelf and vertical mixing processes in events of change in the wind pattern, especially when associated with frontal systems. The present thesis makes an original contribution to the knowledge about the influence of physical processes on plankton distribution in high spatio-temporal resolution in a subtropical coastal ecosystem.
