Ana I. Dogliotti

Distribution and ecology of Pseudo-nitzschia species (Bacillariophyceae) in surface waters of the Weddell Sea (Antarctica)

The distribution of six Pseudo-nitzschia species and their relationship with environmental conditions were studied for the first time in a vast zone of the Weddell Sea (∼61–77°S, Antarctica). Both qualitative and quantitative phytoplankton samples, collected during summer 2004, were examined using light and scanning electron microscopy. Phytoplankton abundance and composition showed great variability along our study area. Diatoms were the most conspicuous phytoplankton group in the northern area while small flagellates were generally dominant in the southern stations. The genus Pseudo-nitzschia was broadly distributed and significantly contributed to total diatom densities. A marked contrast in Pseudo-nitzschia species distribution was observed in three main zones divided by the Weddell Front (WF) and the Antarctic Slope Front (ASF). P. subcurvata and P. turgiduloides were the most abundant species in the neritic Weddell Sea zone, south of the ASF, mainly near the ice-edge in shallower waters and in conditions of long photoperiod. In contrast, P. prolongatoides and P. lineola dominated north of the ASF; the first was associated with deeper and nutrient-rich waters whereas the latter showed a weak relation with environmental variables examined. Finally, P. turgidula and P. heimii were mostly observed in the Weddell–Scotia Confluence Zone in the warmest and far from ice covered waters, north of the WF. A brief morphological Pseudo-nitzschia species description is given in the Appendix, including morphometrics and pictures.

Evaluation of SeaWiFS and MODIS chlorophyll-a products in the Argentinean Patagonian Continental Shelf (38° S-55° S)

Field measurements of surface chlorophyll‐a concentration were used to evaluate for the first time the performance of the standard Moderate Resolution Imaging Spectroradiometer (MODIS) and both standard and regional Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) ocean colour algorithms in the Patagonian Continental Shelf (PCS) between 38° S and 55° S. The results showed that the regional algorithms did not significantly improve the global algorithm estimates. Moreover, the SeaWiFS OC4v4 algorithm, National Aeronautics and Space Administration (NASA) standard chlorophyll product, showed the best performance among all the algorithms examined. Nonetheless, all the global and local algorithms analysed showed uncertainties dependent on chlorophyll concentration. Low chlorophyll‐a concentration values tended to be overestimated and high values tended to be underestimated. A regional analysis within the PCS showed that higher uncertainties are found in the homogeneous side of the tidal fronts present in the PCS, in areas suggested to be optically complex case 2 waters, while a better result (less bias) was obtained in the southern mid‐shelf region. We discuss the probable reasons and provide possible explanations of the regional differences in the performance of the algorithms.

Improved correction methods for field measurements of particulate light backscattering in turbid waters

Monte Carlo simulations are used to compute the uncertainty associated to light backscattering measurements in turbid waters using the ECO-BB (WET Labs) and Hydroscat (HOBI Labs) scattering sensors. ECO-BB measurements provide an accurate estimate of the particulate volume scattering coefficient after correction for absorption along the short instrument pathlength. For Hydroscat measurements, because of a longer photon pathlength, both absorption and scattering effects must be corrected for. As the standard (sigma) correction potentially leads to large errors, an improved correction method is developed then validated using field inherent and apparent optical measurements carried out in turbid estuarine waters. Conclusions are also drawn to guide development of future short pathlength backscattering sensors for turbid waters.

Identification of Bed Forms Through ERS SAR Images in San Matías Gulf, Argentina

Abstract The European Space Agency (ESA) funded two projects in 1991 and 1994 concerning the observation of the Argentine coastal environment with synthetic aperture radar (SAR). Studies were carried out for the periods 1992–1994 and 1994–1997. Several ERS-1/2 satellite SAR images were acquired over the San Matías Gulf in the Patagonian coast during these two periods. SAR is a side-looking imaging radar that operates from either a satellite or an aircraft. The instrument emits a series microwave pulses toward the earth in a direction perpendicular to the flight path. Imagery is constructed from the strength and time delay of the returned signals, which depend primarily on the roughness and dielectric properties of the surface under observation and the distance from the radar. Ocean surface roughness wave-like patterns, imaged as a series of bright and dark linear features by SAR, are persistently observed over the San Matías Gulf mouth region. A total of thirty-three (33) ERS-1/2 SAR images (100 km × 100 km) from 15 different orbits from 1992 to 2000 were analyzed. This series of observations has allowed for a detailed examination of the location, persistence, and the conditions involved in the imaging of the observed wave-like patterns. Very strong tidal currents of the order of 2 m/s characterize the gulf region. The characteristics of recurrent surface patterns in the SAR images indicate that they are caused by the interaction of the tidal currents with bed forms in the bottom topography of the gulf. The location of these bed forms is poorly documented in the available bathymetric charts of the region. The SAR images show the significant potential that satellite radar observations have as a tool for detecting unmapped coastal ocean bottom features, particularly, where bathymetric mapping activities can be extremely difficult, dangerous, or costly.

Remote Sensing of Phytoplankton Blooms in the Continental Shelf and Shelf-Break of Argentina: Spatio-Temporal Changes and Phenology

We studied the spatio-temporal variations of satellite chlorophyll-a (chl-a) and phytoplankton blooms in the continental shelf and shelf-break of the Argentinean patagonic region by means of an 11-years time series of level 3 (L3) MODIS/Aqua chlorophyll products. We aggregated data according to different granularities and estimated climatologies and anomalies. We also studied the phenology of phytoplankton blooms determining bloom starting date and date of maximum concentration. Finally, we estimated and described statistical indexes such as bloom occurrence frequency. The results obtained provide an overview of the evolution and the spatio-temporal variability of chl-a that, in general, and despite its limitations, was complementary and consistent with previous studies based on both satellite and in situ data. This study intended to set the baseline to study algal blooms and their variability in the Argentinian sea, which is valuable information to be included in predictive models related to the occurrence of harmful algal blooms, dynamics of marine system and the effects of global changes over climatic and biogeochemical cycles. In addition, this study also contributes with more up-to-date science data for the future Argentinian and Brazilian SABIA-Mar ocean color mission, which will provide high resolution data (200 m) over the Argentinian coastal zones and continental shelf. Besides the results per se, the relevance of this study is also related to the use of an novel free and open source tool.

The ANTARES observation network

The ANTARES network seeks to understand the variability of the coastal environment on a continental scale and the local, regional, and global factors and processes that effect this change. The focus are coastal zones of South America and the Caribbean Sea. The initial approach includes developing time series of in situ and satellite-based environmental observations in coastal and oceanic regions. The network is constituted by experts that seek to exchange ideas, develop an infrastructure for mutual logistical and knowledge support, and link in situ time series of observations located around the Americas with real-time and historical satellite-derived time series of relevant products. A major objective is to generate information that will be distributed publicly and openly in the service of coastal ocean research, resource management, science-based policy making and education in the Americas. As a first stage, the network has linked oceanographic time series located in Argentina, Brazil, Chile and Venezuela. The group has also developed an online tool to examine satellite data collected with sensors such as NASAs MODIS. Specifically, continental-scale high-resolution (1 km) maps of chlorophyll and of sea surface temperature are generated and served daily over the web according to specifications of users within the ANTARES network. Other satellite-derived variables will be added as support for the network is solidified. ANTARES serves data and offers simple analysis tools that anyone can use with the ultimate goal of improving coastal assessments, management and policies.

Atmospheric correction of SAC-C MMRS imagery for ocean-color applications

An algorithm is presented to correct SAC-C MMRS imagery in the visible for atmospheric and surface effects. These effects are due essentially to gaseous absorption, molecule and aerosol scattering, and Fresnel and whitecap reflection. Aerosol scattering is determined from measurements in the spectral bands centered at 815 and 1,625 nm, where the ocean is assumed to be totally absorbing. The information is then extrapolated to the ocean-color bands, centered at 490, 550, and 660 nm. The algorithms theoretical performance, evaluated for varied geometry, surface conditions, aerosol loading, and mixtures of continental and maritime aerosols, is about ±0.0005 (r.m.s) on the aerosol path reflectance. This accuracy meets the requirements for ocean-color applications, at least in open waters. The algorithm is applied to MMRS imagery acquired off the Valdes Peninsula, Argentina. Compared with SeaWiFS estimates of marine reflectance, the MMRS values are too low and noisy, especially at 660 nm. The discrepancies may be due to non-zero marine reflectance at 815 nm, radiometric calibration errors, and to the large noise in the data (lack of sensitivity in the atmospheric correction bands). The results demonstrate the potential of MMRS for quantitative ocean-color remote sensing in coastal regions of South America.

COMPARISON OF BATHYMETRIC FEATURES DETECTED BY ERS2 SAR AND LANDSAT TM DATA OVER SAN MATÍAS GULF, ARGENTINA

It is well known that Synthetic Aperture Radar (SAR) is capable of imaging bathymetric features by detecting changes in sea surface roughness associated with bathymetry-induced surface current modulations. The high dynamic range of LANDSAT Thematic Mapper (TM) and Enhanced TM+ (ETM+) sensors allow them to observe oceanic surfaces affected by solar specular reflection, or sun glint, without being saturated. This ability allows the imaging of sea surface roughness patterns in the sun glint affected area that are associated with surface current changes such as those produced by bathymetric features. ERS SAR and LANDSAT TM/ETM+ images obtained over the San Matias Gulf, Argentina during similar tidal current conditions are compared and the surface signature generated by the interaction of the tidal current with the bottom topography analyzed. Each type of sensor presents advantages and limitations to the observation of bottom features due to the way each one detects sea surface roughness. Still, when sun glint is present, TM/ETM+ and SAR show similar bathymetric patterns under the same tidal conditions. While both sensors provide consistent information over significant bathymetry features, increased differences in the detection is observed over weaker features

Detecting and Quantifying a Massive Invasion of Floating Aquatic Plants in the Río de la Plata Turbid Waters Using High Spatial Resolution Ocean Color Imagery

Fil: Dogliotti, Ana Ines. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina

The SeaSWIR dataset

The SeaSWIR dataset consists of 137 ASD (Analytical Spectral Devices, Inc.) marine reflectances, 137 total suspended matter (TSM) measurements and 97 turbidity measurements gathered at three turbid estuarine sites (Gironde, La Plata, Scheldt). The dataset is valuable because of the high-quality measurements of the marine reflectance in the Short Wave InfraRed I region (SWIR-I: 1000–1200 nm) and SWIR-II (1200–1300 nm) and because of the wide range of TSM concentrations from 48 up to 1400 mgL−1. The ASD measurements were gathered using a detailed measurement protocol and were subjected to a strict quality control. The SeaSWIR marine reflectance is characterized by low reflectance at short wavelengths (< 450 nm), peak reflectance values between 600 and 720 nm and significant contributions in the near-infrared (NIR) and SWIR-I parts of the spectrum. Comparison of the ASD water reflectance with simultaneously acquired reflectance from a three-radiometer system revealed a correlation of 0.98 for short wavelengths (412, 490 and 555 nm) and 0.93 for long wavelengths (686, 780 and 865 nm). The relationship between TSM and turbidity (for all sites) is linear, with a correlation coefficient of 0.96. The SeaSWIR dataset has been made publicly available (https://doi.org/10.1594/PANGAEA.886287).