Dynamical connections between large marine ecosystems of austral South America based on numerical simulations

The Humboldt Large Marine Ecosystem (HLME) and Patagonian Large Marine Ecosystem (PLME) are the two largest marine ecosystems in the Southern Hemisphere and are respectively located along the Pacific and Atlantic coasts of southern South America. This work investigates the exchange between these two LMEs and its seasonal and interannual variability by employing numerical model results and offline particle-tracking algorithms. Our analysis suggests a general poleward transport on the southern region of the HLME, a well-defined flux from the Pacific to the Atlantic, and equatorward transport on the PLME.Lagrangian simulations show that the majority of the southern PS waters originate from the upper layer in the southeast South Pacific (<200 m), mainly from the southern Chile and Cape Horn shelves. The exchange takes place through the Le Maire Strait, Magellan Strait, and the shelf break. These inflows amount to a net northeastward transport of 0.88 Sv at 51∘ S in the southern PLME. The transport across the Magellan Strait is small (0.1 Sv), but due to its relatively low salinity it greatly impacts the density and surface circulation of the coastal waters of the southern PLME. The water masses flowing into the Malvinas Embayment eventually reach the PLME through the Malvinas Shelf and occupy the outer part of the shelf. The seasonal and interannual variability of the transport are also addressed. On the southern PLME, the interannual variability of the shelf exchange is partly explained by the large-scale wind variability, which in turn is partly associated with the Southern Annular Mode (SAM) index (r=0.52).Fil: Guihou, Karen. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Piola, Alberto Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias de la Atmósfera y los Océanos; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; 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: Chidichimo, María Paz. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval. Departamento Oceanografía; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Franco-Argentino sobre Estudios del Clima y sus Impactos; Argentin

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

Circulation, Vol. 7, No. 3

Fall 2000 issue of CCPO Circulation featuring article Worldwide Coastal Ocean Research at CCPOhttps://digitalcommons.odu.edu/ccpo_circulation/1026/thumbnail.jp

Impact du changement climatique sur la circulation océanique dans les systèmes d'upwelling de bord Est de l'hémisphère Sud

Parmi les océans du monde, les Systèmes d'Upwelling de Bord Est (EBUS, de l'anglais "Eastern Boundary Upwelling Systems") présentent un intérêt particulier car ils relient les bassins océaniques tropicaux aux latitudes moyennes et sont donc soumis à de fortes fluctuations associées à la fois à la variabilité naturelle du climat et au forçage anthropique. Comprendre comment le réchauffement climatique modifie la circulation océanique et les écosystèmes marins dans les EBUS reste un défi scientifique en raison de la complexité des processus en jeu. La génération actuelle de modèles couplés de circulation générale souffre encore des limitations associées à la non prise en compte de manière réaliste de certains aspects de la dynamique des upwellings côtiers et de la circulation à méso-échelle. Dans cette thèse, nous avons étudié les processus de formation du pattern de changement climatique et de la variabilité naturelle dans le Pacifique Sud-Est (SEP, de l'anglais "South East Pacific") sur la base de simulations numériques de dernière génération mises à disposition de la communauté pour étudier le changement climatique en présence de la variabilité climatique interne. Ces ressources incluent le CESM Large Ensemble (CESM-LENS) modèle réalisé par le NCAR aux Etats Unis et des simulations à long terme du climat mondial résolvant la méso-échelle réalisées au Centre IBS Center for Climate Physics (ICCP) en Corée du sud. En supposant un quasi-équilibre entre le forçage radiatif externe et les processus de couche de mélange de la circulation de l'océan de surface, il est possible d'identifier les processus océaniques et atmosphériques responsables de la tendance de la température de surface de la mer (SST, de l'anglais "Sea Surface température") sur la période 2006-2100. Nous montrons tout d'abord que la localisation latitudinale du réchauffement minimum de la SST dans le SEP s'écarte significativement de celle prédite par la théorie pour laquelle le refroidissement évaporatif maximum est contrôlé par le pattern de chaleur latente climatologique (précipitations moyennes). Le bilan de chaleur des simulations CESM-LENS révèle que l'advection océanique est responsable du pattern de réchauffement de type El Niño dans la région équatoriale et le long des côtes du Pérou et du Chili. Le centre de la zone de réchauffement minimum est principalement déterminé par le refroidissement relatif du flux de chaleur latente et le rayonnement solaire, partiellement compensé par l'advection méridienne de l'océan. Les détails de la tendance au réchauffement le long des côtes du Pérou et du Chili résultent également d'un équilibre entre l'advection induite à la fois par le changement des courants d'Ekman et la compensation géostrophique. Les résultats révèlent également que le pattern de changement climatique de la SST a une projection significative sur les modes de variabilité naturelle dans le SEP, ce qui suggère qu'il peut être compensé par la variabilité naturelle. Dans une suite de simulations de modèles à haute résolution, nous étudions la téléconnection océanique d'ENSO (de l'anglais "El Niño Southern Oscillation") le long des côtes du Pérou et du Chili sur le flux turbulent, considéré ici comme une source de variabilité naturelle dans le SEP. Nous avons montré en particulier que l'ENSO peut alimenter l'énergie de la circulation à des échelles de temps décennales le long des côtes du Pérou et du Chili en modulant les instabilités du système de courants côtiers. Globalement, la thèse illustre la complexité des processus associés à la téléconnection équatoriale dans le SEP à différentes échelles de temps, qui ne sont pas encore accessibles à partir du système d'observations actuel trop court.Among the world oceans, the Eastern Boundary Upwelling Systems (EBUS) are of particular interest because they connect the tropical ocean basins with the mid-latitudes and so are subject to large fluctuations associated with both the natural climate variability and the anthropogenic forcing. Understanding how global warming will modify the oceanic circulation and the marine ecosystems in the EBUS remains a scientific challenge due to the complex of processes at play. Current generation of Coupled General Circulation Models (CGCMs) still suffers limitations associated to not resolving realistically some aspects of the coastal upwelling dynamics and mesoscale circulation. Still they remain powerful tools to better understand the formation of climate change patterns in a key region of the world for the Earth's radiation budget. In this thesis, we have investigated processes of formation of the climate change pattern and of natural variability in the EBUS of the South Hemisphere, with particular emphasis in the South Eastern Pacific (SEP). We take advantage on latest generation resources to the community for studying climate change in the presence of internal climate variability, including the CESM Large Ensemble performed by NCAR and meso-scale-resolving global climate long-term simulations performed at the IBS Center for Climate Physics. Assuming quasi-equilibrium between the radiative external forcing and mixed layer and upper-ocean processes, oceanic and atmospheric processes responsible for the SST trend over the period 2006-2100 are derived. It is first shown that the latitudinal location of the minimum warming in the SEP deviates significantly from that predicted by theory for which maximum evaporative cooling is controlled by the pattern of mean climatological latent heat/precipitation. The explicit heat budget of the CESM-LE simulations reveals that advection forms the El Niño-like warming pattern in the equatorial region and along the coast of Peru and Chile, while the minimum warming center is mostly determined by the relative cooling of both latent heat and solar radiation, partly compensated by meridional advection. Details in the warming trend along the coast of Peru and Chile are also shown to result from a balance between advection induced by both change in Ekman currents and geostrophic compensation. The results also reveal that the SST climate change pattern has a significant projection on the patterns of natural variability in the SEP (i.e. El Niño and the South Pacific Meridional Mode), suggesting that it can be off-set by natural variability. In a suite of high-resolution model simulations we investigate the ENSO oceanic teleconnection along the coast of Peru and Chile on the turbulent flow, considered here as a source of natural variability in the SEP. It is shown in particular that ENSO can fuel energy in the circulation at decadal timescales along the coast of Peru and Chile through modulating instabilities in the coastal current system. Overall, the thesis illustrates the complex of processes associated to the equatorial teleconnection in the SEP at different timescales, which are not yet accessible from the current too-short observing system

Circulation of the Western Antarctic Peninsula: Implications for Biological Production

The western Antarctic Peninsula (wAP) continental shelf is characterized by large persistent populations of Antarctic krill ( Enphausia superba) and by regions of enhanced concentrations of marine mammals and other predators (hot spots). This study focused on understanding the role of ocean circulation in providing retention/connectivity of wAP Antarctic krill populations and in maintaining biological hot spot regions. Numerical Lagrangian particle tracking simulations obtained from the Regional Ocean Modeling System (ROMS) configured for the wAP region provided quantitative estimates of retention, immigration and emigration from the wAP continental shelf. Additional simulations with a one-dimensional temperature-dependent growth model for krill embryos and early larval stages allowed mapping of the Lagrangian trajectories into krill developmental stages. The simulated particle trajectories showed preferred sites for across-shelf transport, with Marguerite Trough being a primary pathway for movement into Marguerite Bay, Crystal Sound, and the inner shelf regions. Residence times for the biological hot spots were 18 to 27 days for Alexander Island and Crystal Sound and almost 35 days for Laubeuf Fjord (biological hot spot regions). Particles released in the Bellingshausen Sea (remote source) were transported to the wAP shelf with a time scale consistent with the time required for Antarctic krill embryos to develop into larvae (120 days). The trajectories of floats released along the wAP shelf inside the 500-in isobath (local source) showed retention times on the order of 3 months and low connectivity among different release sites on the mid to inner shelf, suggesting that local reproduction and development can be important contributors to wAP Antarctic krill populations. Successful completion of the descent-ascent cycle of Antarctic krill embryo-larvae occurred along the outer shelf and in shelf regions where bottom depths were greater than 500 m. Estimated residence times in these areas were 20–30 days, which suggests that krill spawned in the mid and inner shelf are retained in these regions through development to the first feeding stage (calyptopis I). These results suggest that wAP Antarctic krill populations along the outer and mid shelf may be dependent on inputs from upstream sources. Maintenance of populations confined to the inner shelf regions may be dependent on local processes. Simulated trajectories obtained for projected future environmental conditions suggested that the circulation would enhance advection of krill larvae to the shelf but that recruitment and reproduction may be altered, thereby impeding survival of Antarctic krill