Upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary

The upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary is explored using a high resolution ocean model for the last 60 years. Three ocean circulations have been modeled. From North to South, we investigate the dynamics of the Gulf of Alaska (GOA), the California Current System (CCS) and the Humboldt Current System (HCS, also known as the Peru-Chile Current System). The statistics of coastal waters transport are computed using a model passive tracer, which is continuously released at the coast. By looking at the passive tracer concentration distribution, we find that the Pacific Decadal Oscillation modulates the coastal variability of the GOA, the North Pacific Gyre Oscillation controls the upwelling of the CCS, while the El-Niño Southern Oscillation affects the upwelling of Peru and Chile mainly through coastally trapped Kelvin waves. Results also emphasize the key role of the mesoscale eddies in the offshore transport of coastal waters masses. The passive tracer experiments, performed in this study in the GOA, CCS, and HCS, therefore could provide a dynamical framework to understand the dynamics of the upwelling/downwelling and offshore transport of nutrient rich coastal water and to interpret how it responds to atmospheric forcing. This also could reinforce our interpretation (and therefore predictions) in the changes in vertical and offshore advection of other important biogeochemical quantities, essential in understanding ecosystem variability.Ph.D.Committee Chair: Di Lorenzo, Emanuele; Committee Member: Bracco, Annalisa; Committee Member: Curry, Judith A.; Committee Member: Haas, Kevin; Committee Member: Lynch-Stieglitz, Jea

The Burdwood Bank Circulation

A suite of high-resolution numerical simulations characterizes the oceanic circulation in the Burdwood Bank, a shallow seamount located in the northeastern end of the Drake Passage. Model analysis shows energetic upwelling and mixing uplifting deep and benthic waters into the photic layer. Tides and the Antarctic Circumpolar Current are the primary drivers of the bank's circulation. Tidal forcing is the main driver for the entrainment of deep waters into the upper layers of the bank and local wind forcing for the detrainment of these waters into the deep ocean. Passive tracer diagnostics suggest that the dynamical processes triggered by the Burdwood Bank could have a significant impact on local ecosystems and the biogeochemical balance of the southwestern Atlantic region, which is one of the most fertile portions of the Southern Ocean. Model results are robust—they are reproduced in a wide array of model configurations—but there is insufficient observational evidence to corroborate them. Satellite color imagery does not show substantial chlorophyll blooms in this region but it shows strong phytoplankton plumes emanating from the bank. There are several potential explanations for the chlorophyll deficit, including lack of light due to persistent cloud cover, deep mixing layers, fast ocean currents, and the likelihood that blooms, while extant, might not develop on the surface. None of these possibilities can be confirmed at this stage.Fil: Matano, Ricardo P.. State University of Oregon; Estados UnidosFil: Palma, Elbio Daniel. Universidad Nacional del Sur. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Combes, Vincent. State University of Oregon; Estados Unido

Modeling the Offshore Export of Subantarctic Shelf Waters From the Patagonian Shelf

It has been suggested that the Subtropical Shelf Front (STSF) could be a preferential site for the detrainment of Subantarctic Shelf Water (SASW) and related planktonic shelf species onto the open SW Atlantic Ocean. The offshore detrainment of SASW and planktonic shelf species might be an exportation mechanism, affecting the population abundances of fishing resources in Argentina, Uruguay, and Southern Brazil. In this study, we characterize for the first time the 3-D structure of the STSF and the main routes of offshore export of SASW from the Patagonian shelf during austral summer (summer and early fall) and winter (winter and early spring) by using numerical hydrodynamical model results and Lagrangian tracking simulations of neutrally buoyant floats. The transport of SASW toward the open ocean is ~1 Sv (1 Sv = 106 m3/s) during summer and ~0.8 Sv during winter. SASW are exported offshore mainly near the Brazil-Malvinas Confluence region during both seasons. The STSF appears to act as an important retention mechanism for the plankton over the inner and middle shelf mainly during late summer and early fall. Our findings could explain the life cycle of distinct fish species that are distributed in the region, as well as the population abundance variability of such species.Fil: Franco, Barbara Cristie. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; ArgentinaFil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Combes, Vincent. State University of Oregon; Estados UnidosFil: Acha, Eduardo Marcelo. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Saraceno, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentin

Assessing marine heat waves in the Mediterranean Sea: a comparison of fixed and moving baseline methods

The study of marine heat waves as extreme temperature events has a wide range of applications, from a gauge for ecological and socioeconomic impact to a climate change indicator. Various definitions of marine heat waves as extreme sea temperature events exist to account for its broad applicability, with statistical definitions based on percentile based thresholds being widespread in its use. Using satellite and model data of the Mediterranean Sea, we analyze the statistical implications of choosing baseline climatological periods for threshold delineation, which are either fixed in the past or shifted in time. We show that in the context of a warming Mediterranean Sea, using a fixed baseline leads to a saturation of marine heat wave days that compromises the significance of this marine indicator, with 90% of climate models analyzed predicting an average above 189 marine heat wave days per year by 2050 even for the lowest emission scenario. We argue that only with a moving baseline, can we reach a definition for marine heat waves which yield consistently rare extreme events

Subsurface Ocean Warming Hotspots and Potential Impacts on Marine Species: The Southwest South Atlantic Ocean Case Study

In the southwest South Atlantic Ocean (SWAO) strong ocean surface warming hotspots have been observed mainly along the path of the Brazil Current (BC), Brazil-Malvinas Confluence (BMC), and in the Río de la Plata (RdlP). However, there is no knowledge about the signature of ocean hotspots below the surface and the potential effects of ocean warming on marine biota. In this work, we provide initial evidence of how deep the hotspots of the SWAO extend in the water column, in particular at mid-water and bottom layers where two marine species - the green turtle (Chelonia mydas) and the Patagonian scallop (Zygochlamys patagonica) - inhabit. We compare 15 years (2003–2017) of Copernicus Marine Environment Monitoring Service (CMEMS) ARMOR3D high−resolution (1/4°) 3-D temperatures reprocessed from combined satellite and in situ observations with high−resolution (1/12°) Mercator ocean reanalysis. We also use location data of C. mydas and Z. patagonica to discuss the potential impacts of warming on these species in terms of geographic distribution, phenological shifts and thermal tolerance. The potential distribution of C. mydas changes in relation to the sea surface temperature (SST) and the bathymetry. The warming of the whole water column in the RdlP (>0.4°C/decade) and the southward movement of the mean surface isotherms, which likely drove turtle displacements, could enable the opening up of novel optimal thermal habitats and/or a longer seasonal residency for the species. At the BMC, warming is driven by the southward displacement of the BC during the past decades. Ocean model temperature indicates cooling/warming in deep waters along the outer shelf and shelf break regions, which vary according the displacements of the BMC. The expected warming of the waters over the Patagonian scallop largest bed could exceed the thermal tolerance of this species and its survival. Given the lack of long-term monitoring programs to address the impacts of climate change on marine biota in the SWAO, our results provide the first effort to call the attention of stakeholders and decision makers on marine conservation and fishery management to work toward better management strategies in the context of climate change.Fil: Franco, Barbara Cristie. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones del Mar y la Atmósfera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones del Mar y la Atmósfera; Argentina. Instituto Franco-argentino sobre Estudios del Clima y sus Impactos; ArgentinaFil: Combes, Vincent. State University of Oregon; Estados UnidosFil: González Carman, Victoria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Dynamical analysis of the oceanic circulation in the Gulf of San Jorge, Argentina

This study identifies the dynamical mechanisms driving seasonal variations in oceanic circulation and water mass characteristics of the Gulf of San Jorge (GSJ) and its exchanges with the Patagonian Shelf (PS). A suite of process-oriented numerical experiments indicates that GSJ circulation is mainly driven by tidal forcing and modulated by wind forcing and intrusions from the PS. During late spring and summer, stratification decouples the upper and deeper layers of the gulf, leading to a shallow, wind-forced surface circulation and a deeper, density driven, cyclonic geostrophic flow. The subsurface circulation is induced by differential tidal mixing in coastal and deep areas and its intensity is strongly affected by the temporal variability of the atmospheric heat flux, which increases from spring to summer and fades from fall to winter. As stratification weakens, circulation patterns are replaced by wind-driven anticyclonic gyres in the south and an open cyclonic loop in the north. Passive tracer diagnostics show that in summer, surface and subsurface waters from the GSJ northern coast are exported and replaced by waters from the coastal portion of PS currents. The renewal of bottom waters is slower: A small portion upwells in the southwestern coast but most are ventilated by winter convection in the southern region and by intrusions of PS waters in the northern region.Fil: Palma, Elbio Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Matano, Ricardo. State University of Oregon; Estados UnidosFil: Tonini, Mariano Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Centro para el Estudio de Sistemas Marinos; ArgentinaFil: Martos, Patricia. Universidad Nacional de Mar del Plata; Argentina. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Combes, Vincent. State University of Oregon; Estados Unido

A two-way nested simulation of the oceanic circulation in the Southwestern Atlantic

This article presents the results of a high-resolution (1/12°), two-way nested simulation of the oceanic circulation in the southwestern Atlantic region. A comparison between the model results and extant observations indicates that the nested model has skill in reproducing the best-known aspects of the regional circulation, e.g., the volume transport of the ACC, the latitudinal position of the BMC, the shelf break upwelling of Patagonia, and the Zapiola Anticyclone. Sensitivity experiments indicate that the bottom stress parameterization significantly impacts the mean location of the Brazil/Malvinas Confluence and the transport of the Zapiola Anticyclone. The transport of the Brazil Current strengthens during the austral summer and weakens during the austral winter. These variations are driven by the wind stress curl over the southwestern Atlantic. The variations of the transport of the Malvinas Current are out of phase with those of the Brazil Current. Most of the seasonal variability of this current is concentrated in the offshore portion of the jet, the inshore portion has a weak seasonality that modulates the magnitude of the Patagonian shelf break upwelling. Using passive tracers we show that most of the entrainment of deep waters into the shelf occurs in the southernmost portion of the Patagonian shelf and along the inshore boundary of the Brazil Current. Shelf waters are preferentially detrained near the Brazil/Malvinas Confluence. Consistent with previous studies, our simulation also shows that south of ~42°S the Malvinas Current is composed of two jets, which merge near 42°S to form a single jet farther north

Low-frequency variability in the Gulf of Alaska from coarse and eddy-permitting ocean models

[1] An eddy-permitting ocean model of the northeast Pacific is used to examine the ocean adjustment to changing wind forcing in the Gulf of Alaska (GOA) at interannual-to-decadal timescales. It is found that the adjustment of the ocean model in the presence of mesoscale eddies is similar to that obtained with coarse-resolution models. Local Ekman pumping plays a key role in forcing pycnocline depth variability and, to a lesser degree, sea surface height (SSH) variability in the center of the Alaska gyre and in some areas of the eastern and northern GOA. Westward Rossby wave propagation is evident in the SSH field along some latitudes but is less noticeable in the pycnocline depth field. Differences between SSH and pycnocline depth are also found when considering their relationship with the local forcing and leading modes of climate variability in the northeast Pacific. In the central GOA pycnocline depth variations are more clearly related to changes in the local Ekman pumping than SSH. While SSH is marginally correlated with both Pacific Decadal Oscillation (PDO) and North Pacific Gyre Oscillation (NPGO) indices, the pycnocline depth evolution is primarily related to NPGO variability. The intensity of the mesoscale eddy field increases with increasing circulation strength. The eddy field is generally more energetic after the 1976–1977 climate regime shift, when the gyre circulation intensified. In the western basin, where eddies primarily originate from intrinsic instabilities of the flow, variations in eddy kinetic energy are statistically significant correlated with the PDO index, indicating that eddy statistics may be inferred, to some degree, from the characteristics of the large-scale flow

Patterns and Trends in Chlorophyll-a Concentration and Phytoplankton Phenology in the Biogeographical Regions of Southwestern Atlantic

The Southwestern Atlantic Ocean (SWA), is considered one of the most productive areas of the world, with a high abundance of ecologically and economically important fish species. Yet, the biological responses of this complex region to climate variability are still uncertain. Here, using 24 years of satellite-derived Chl-a data, we classified the SWA into 9 spatially coherent regions based on the temporal variability of Chl-a concentration, as revealed by SOM (Self-Organizing Maps) analysis. These biogeographical regions were the basis of a regional trend analysis in phytoplankton biomass, phenological indices, and environmental forcing variations. A general positive trend in phytoplankton concentration was observed, especially in the highly productive areas of the northern shelf-break, where phytoplankton biomass has increased at a rate of up to 0.42 ± 0.04 mg m−3 per decade. Significant positive trends in sea surface temperature were observed in 4 of the 9 regions (0.08–0.26 °C decade−1) and shoaling of the mixing layer depth in 5 of the 9 regions (−1.50 to −3.36 m decade−1). In addition to the generally positive trend in Chl-a, the most conspicuous change in the phytoplankton temporal patterns in the SWA is a delay in the autumn bloom (between 15 ± 3 and 24 ± 6 days decade−1, depending on the region). The observed variations in phytoplankton phenology could be attributed to climate-induced ocean warming and extended stratification period. Our results provided further evidence of the impact of climate change on these highly productive waters.Fil: Delgado, Ana Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Nacional del Sur. Departamento de Geografía y Turismo; ArgentinaFil: Hernández Carrasco, Ismael. Consejo Superior de Investigaciones Científicas. Instituto Mediterráneo de Estudios Avanzados; EspañaFil: Combes, Vincent. Consejo Superior de Investigaciones Científicas. Instituto Mediterráneo de Estudios Avanzados; España. Universitat de Les Illes Balears; EspañaFil: Font Muñoz, Joan. Consejo Superior de Investigaciones Científicas. Instituto Mediterráneo de Estudios Avanzados; EspañaFil: Pratolongo, Paula Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de Geografía y Turismo; ArgentinaFil: Basterretxea, Gotzon. Consejo Superior de Investigaciones Científicas. Instituto Mediterráneo de Estudios Avanzados; Españ

Interannual variability of the subsurface eddy field in the Southeast Pacific

The Southeast Pacific, which encompasses the coasts of Peru and Chile, is one of the world's most productive regions resulting principally from the upwelling of subsurface nutrient-rich waters. Over the satellite altimetry era, there have been numerous evidence that surface mesoscale eddies play an important role in the offshore transport of rich coastal waters, but it has been only recently that few observational/numerical studies have highlighted the importance of the subsurface eddies. The eddy field variability is explored using the results of a high-resolution model experiment from 1979 to 2012. The model results indicate an asymmetry of the surface and subsurface eddy fields. While surface-intensified cyclones are slightly more frequent than anticyclones, the subsurface field is dominated by anticyclones (IntrathermoclineEddies; ITEs), triggered by the instability of the subsurface Peru Chile undercurrent (PCUC). Composite maps are consistent with in situ observations. ITEs are associated with maximum vorticity around 150–200 m depth, warmer and more saline core, characteristic of the equatorial subsurface water from the PCUC. We find that the variability of the ITEs is significantly correlated with the ENSO equatorial signal. During strong El Niño events (e.g., 1982; 1998), we find that while the PCUC transport increases, the volume of coastal waters transported by ITEs however decreases during those periods. We find that the relaxation of the isopycnals along the coast during El Niño events leads to weakened baroclinic instability and to a decrease of the ITEs transport.This is the publisher’s final pdf. The article is copyrighted by American Geophysical Union and published by John Wiley & Sons Inc. It can be found at: http://agupubs.onlinelibrary.wiley.com/agu/jgr/journal/10.1002/%28ISSN%292169-9291