Multiscale analysis of geometric planar deformations: application to wild animals electronic tracking and satellite ocean observation data

International audienceThe development of animal tracking technologies (including for instance GPS and ARGOS satellite systems) and the increasing resolution of remote sensing observations call for tools extracting and describing the geometric patterns along a track or within an image over a wide range of spatial scales. Whereas shape analysis has largely been addressed over the last decades, the multiscale analysis of the geometry of opened planar curves has received little attention. We here show that classical multiscale techniques cannot properly address this issue and propose an original wavelet-based scheme. To highlight the generic nature of our multiscale wavelet technique, we report applications to two different observation datasets, namely wild animal movement paths recorded by electronic tags and satellite observations of sea surface geophysical fields

Acoustic Observation of Living Organisms Reveals the Upper Limit of the Oxygen Minimum Zone

Background: Oxygen minimum zones (OMZs) are expanding in the World Ocean as a result of climate change and direct anthropogenic influence. OMZ expansion greatly affects biogeochemical processes and marine life, especially by constraining the vertical habitat of most marine organisms. Currently, monitoring the variability of the upper limit of the OMZs relies on time intensive sampling protocols, causing poor spatial resolution. Methodology/Principal Findings: Using routine underwater acoustic observations of the vertical distribution of marine organisms, we propose a new method that allows determination of the upper limit of the OMZ with a high precision. Applied in the eastern South-Pacific, this original sampling technique provides high-resolution information on the depth of the upper OMZ allowing documentation of mesoscale and submesoscale features (e.g., eddies and filaments) that structure the upper ocean and the marine ecosystems. We also use this information to estimate the habitable volume for the world’s most exploited fish, the Peruvian anchovy (Engraulis ringens). Conclusions/Significance: This opportunistic method could be implemented on any vessel geared with multi-frequency echosounders to perform comprehensive high-resolution monitoring of the upper limit of the OMZ. Our approach is a novel way of studying the impact of physical processes on marine life and extracting valid information about the pelagic habitat an

Anomalías del perfil vertical de temperatura del punto fijo Paita como indicador de la propagación de Ondas Kelvin

La propagación frecuente de ondas Kelvin de hundimiento o “downwelling” atrapadas a la costa, suele caracterizar la ocurrencia de El Niño costero frente al Perú. Estas ondas causan la elevación del nivel del mar y se asocian a la profundización de la estructura vertical sub-superficial de la columna de agua, influenciando en la fertilidad del afloramiento costero. En el presente estudio se describe la variabilidad mensual de la estructura vertical de la columna de agua frente a la costa de Paita-Piura y se comparan con anomalías del nivel del mar frente a Galápagos y en la costa norte del país. Para tal propósito se calculó una climatología con la base de datos histórica de temperatura del punto fijo de Paita, puesta a disposición por el Monterey Bay Aquarium Research Institute (MBARI), para el periodo 1994-2010. Luego de la remoción de datos extremos dudosos, se realizó una interpolación vertical de los datos cada 10 m y una climatología de los datos a frecuencia mensual. La serie de tiempo de anomalía de temperatura muestra una gran consistencia con el arribo de ondas Kelvin a las costa de Sudamérica, por lo cual su monitoreo es de gran utilidad para la alerta temprana de El Niño.p. 6-8Instituto del Mar del Per

Oxygen: A Fundamental Property Regulating Pelagic Ecosystem Structure in the Coastal Southeastern Tropical Pacific

Background: In the southeastern tropical Pacific anchovy (Engraulis ringens) and sardine (Sardinops sagax) abundance have recently fluctuated on multidecadal scales and food and temperature have been proposed as the key parameters explaining these changes. However, ecological and paleoecological studies, and the fact that anchovies and sardines are favored differently in other regions, raise questions about the role of temperature. Here we investigate the role of oxygen in structuring fish populations in the Peruvian upwelling ecosystem that has evolved over anoxic conditions and is one of the world's most productive ecosystems in terms of forage fish. This study is particularly relevant given that the distribution of oxygen in the ocean is changing with uncertain consequences. Methodology/Principal Findings: A comprehensive data set is used to show how oxygen concentration and oxycline depth affect the abundance and distribution of pelagic fish. We show that the effects of oxygen on anchovy and sardine are opposite. Anchovy flourishes under relatively low oxygen conditions while sardine avoid periods/areas with low oxygen concentration and restricted habitat. Oxygen consumption, trophic structure and habitat compression play a fundamental role in fish dynamics in this important ecosystem. Conclusions/Significance: For the ocean off Peru we suggest that a key process, the need to breathe, has been neglected previously. Inclusion of this missing piece allows the development of a comprehensive conceptual model of pelagic fish populations and change in an ocean ecosystem impacted by low oxygen. Should current trends in oxygen in the ocean continue similar effects may be evident in other coastal upwelling ecosystems

Physicochemical Drivers of Zooplankton Seasonal Variability in a West African Lagoon (Nokoué Lagoon, Benin)

This study aimed to investigate the seasonal variation of zooplankton diversity and abundance in the Nokoué Lagoon in southern Benin. Through extensive sampling, a total of 109 zooplanktonic taxa were identified and quantified. The average zooplankton abundance was found to be 60 individuals per liter, with copepods and rotifers being the most dominant groups, comprising 68.1% and 29.1% of the total abundance, respectively. The key factor identified as driving the structure of the zooplanktonic assemblages was salinity, which showed significant seasonal variation. The results revealed that during the high water period, when the lagoon was filled with fresh water, rotifers were dominant, zooplanktonic diversity was highest, and abundances were quite high. Conversely, during the low water period, when the lagoon was characterized by brackish water, diversity was minimal, and abundance decreased slightly. The study also found that some areas of the lagoon showed high abundances independent of salinity levels, suggesting that other factors such as riverine inputs or the presence of acadjas (home-made brush parks used as fish traps) may also have notable effects on the zooplankton community. Overall, the findings of this study provide valuable insights into the functioning of one of the most biologically productive lagoons in West Africa

EDDY CHARACTERISTICS AND TRACER TRANSPORTS FROM TP/ERS ALTIMETRY, IN A REGION OFFSHORE CHILE

Based on 9 years (1993-2001) of Sea Level Anomaly measurements from TP/ERS altimeters, we characterize the mesoscale structures of the eastern South Pacific (10-35°S, 70-100°W). Integral zonal, meridional, and temporal scales of the mesoscale activity are described geographically in the study region. The length scales increase toward the north in agreement with the increase of the Rossby radius, whereas timescales show higher values in the south of the domain. Typical values of (Lx, Ly) are around 50 km at 35°S and 80-90 km at 10°S with elongation in the zonal direction revealing the anisotropic nature of the mesoscale structures. Timescales are in the range 15-45 days. We also estimate a space-varying eddy transfer coefficient K which parameterize the effect of the eddies on the lateral tracer transports. K increases in the regions of high levels of eddy kinetic energy and is in the range of 110(7) to 410(7) cm².s-1. Considering mean climatological property gradients, we show that near the coast, the mesoscale eddies can play an important role on the long term heat and salt budget

Variabilité de la couche superficielle de l'océan austral entre la Tasmanie et l'Antarctique

TOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocSudocFranceF

Mean surface circulation and mesoscale turbulent flow characteristics in the eastern South Pacific from satellite tracked drifters

International audienceCirculation of the eastern South Pacific region (10°-34°S, 70°-100°W) was studied using drifting buoy trajectories from 1979 to 2003. Three different current regimes were highlighted: the South Equatorial Current, flowing westward north of 26°S with surface velocities of 7-8 cm s−1; the South Pacific Current, an eastward current of ∼2 cm s−1 south of 25°-30°S; and the Chile-Peru Current, a northwestward flow of ∼6 cm s−1 found to the east of 82°W and south of 22°S. The velocity variance distribution showed the regional flow to be anisotropic in nature. Maps of eddy kinetic energy obtained from drifter measurements and satellite altimetry data showed similar patterns, with higher energy levels near the South American coast. The Lagrangian time and length scales of the turbulent flow revealed typical values of 5.9 ± 0.6 days and 40.7 ± 5.4 km in the zonal direction and of 3.5 ± 0.4 days and 29 ± 3.4 km in the meridional direction. The estimated diffusivities were (4.9 ± 0.5) × 107 cm2 s−1 and (2.6 ± 0.3) × 107 cm2 s−1 in the eastward and northward directions, respectively. Finally, we estimated the respective role of horizontal advection and lateral diffusion on the mixed layer heat and salt budgets. Near the coast the lateral turbulent fluxes in the surface layer were two times larger than the horizontal transports associated with the large-scale circulation; mean horizontal heat and salt diffusive fluxes were around 25 W m−2 and 50 g m−2 d−1

Surface circulation and fronts of the south Pacific Ocean, east of 120°W

International audienceThe South Pacific surface circulation east of 120°W is studied, using satellite tracked drifters from 1979-2004. The major currents of this region are described such as the Antarctic Circumpolar, the South Pacific, the Chile-Peru and the Cape Horn Currents. We suggest the presence of a branch, exiting from the ACC between 100-120°W, and transporting subantarctic surface water toward lower latitudes. We also show the existence of an anticyclonic recirculation cell north of 35°S. Finally, based on hydrographic sections, we show that in the eastern South Pacific the core of the Subtropical front corresponds to the 14°C isotherm at 150 m depths and to the 2.7 m of dynamic height relative to 3000 m. The Subantarctic front is located by maximum temperature gradients in the range 3-8°C at 100-400 m depth