Virginia Maria Tavano Garcia

Empirical and semi‐analytical chlorophyll algorithms in the south‐western Atlantic coastal region (25–40°S and 60–45°W)

Global ocean colour algorithms, used to extract chlorophyll concentration in the ocean surface, normally overestimate pigment values in coastal regions, due to optical interference of water components. The objective of the present investigation was to test the performance of both empirical (SeaWiFS OC4v4) and semi‐analytical (GSM01 and CARDER) algorithms in the south‐western Atlantic. In situ pigment and optical data have been collected in waters influenced by continental discharge from La Plata River and Patos Lagoon. The data was used to develop a regional version of the empirical SeaWiFS OC2v4 algorithm (termed OC2‐LP). The relative percentage difference (RPD) between in situ and algorithm‐derived chlorophyll was 11% in the regional version as compared to the global OC4v4 (RPD = 27%). The GSM01 and CARDER showed RPD of 14% and 31%, respectively. We have also tested the accuracy of the four algorithms (OC4v4, OC2‐LP, GSM01 and CARDER) on SeaWiFS images taken over two cruise periods in the study region (winter of 2003 and summer of 2004). A seasonal difference was observed, where both OC4v4 and OC2‐LP overestimate chlorophyll in summer at a higher magnitude than in winter, and the GSM01 algorithm showed a marked underestimation of chlorophyll in winter. The CARDER model showed a good performance both in winter and summer, when applied to satellite‐retrieved radiances. Our results show that the use of semi‐analytical models does not improve significantly the accuracy of chlorophyll retrievals in coastal areas when not properly tuned with regional inherent optical properties measurements.

Phytoplankton community during a coccolithophorid bloom in the Patagonian Shelf: microscopic and high-performance liquid chromatography pigment analyses

We describe the phytoplankton community and biomass during a summer coccolithophorid bloom sampled over the Patagonian shelf (48.5°S–50.5°S). Those phytoplankton species can contribute to the flux of calcium carbonate out of surface waters. Results from both microscope and high-performance liquid chromatography (HPLC) analysis are shown to complement information on the phytoplankton community. From CHEMTAX analysis of HPLC data, the most important organisms and groups identified were the coccolithophorid Emiliania huxleyi , the haptophyte Phaeocystis antarctica , dinoflagellates, diatoms, cryptophytes, prasinophytes and cyanobacteria. Phytoplankton microscope counts were converted into phytoplankton group-specific biovolume estimates. Although some microscope-identified taxa could not be determined by CHEMTAX, e.g. the autotrophic ciliate Myrionecta rubra , cluster analyses from both techniques showed similar results for the main groups. Both Emiliania huxleyi cell concentration and biomass, and the pigment 19′-hexanoyloxyfucoxanthin were the most important biological features during the sampling period. At surface, nitrate was moderately high (0.2–4.2 µM) in coccolithophorid-dominated samples, whereas phosphate ( E. huxleyi . Competition and probably differential grazing could also promote a coccolithophorid outgrowth over other photoautotrophs during the summer season in the Patagonian shelf.

Potential source regions of biogenic aerosol number concentration apportioning at King George Island, Antarctic Peninsula

Abstract Nowadays it is well accepted that background aerosols in the boundary layer over remote oceans are of marine origin and not aged continental. Particularly in the Atlantic sector of the Southern Ocean at least four main important regions exhibit significant ocean primary productivity. They are the Bellingshausen–Amundsen Sea, the Weddell Sea, the southern Argentinean shelf and the southern Chilean coast. In this work, we have combined ground-based continuous atmospheric sampling of aerosol number concentration (ANC), over-sea dimethyl sulphide (DMS) measurements, chlorophyll a (chl a) concentration provided by Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite images, in situ meteorological data and monthly regional NCEP-NCAR re-analysis wind fields in order to investigate the relative contribution of each of the above regions to the apportionment of the ANC at King George Island (KGI), South Shetland Islands. Our results suggest that, at least during the period from September 1998–December 1999, the southern Argentinean shelf acted as the main contributor to the ANC measured in KGI.

Influência da temperatura, salinidade e luz sobre o crescimento do dinoflagelado Alexandrium tamarense (dinoflagellata, dinophyceae) da plataforma continental adjacente ao estuário da Lagoa dos Patos

The dinoflagellate Alexandrium tamarense (Lebour) Balech potentially produces saxitoxins which can be accumulated through the food web and cause a serious disease called PSP (Paralytic Shellfish Poisoning) in higher-level consumers, including humans, birds and mammals. There were obtained 13 strains through cysts germination and motile cells isolation that were kept in culture, under constant conditions of temperature (20°C), light intensity (ca. 350 μmol.m-2.s-1), salinity (31) and nutrients (f/2 medium without silicate), until the experiments were carried out. Assays were performed to determine optimal environmental conditions for growth, after acclimation to respective test conditions. Although relatively high growth rates (0.3 div.day-1) were found under a wide range of temperature (7 to 25°C), light intensity (over 80 μmol.m-2.s-1) and salinity (7 to 32), highest growth rates up to 0.7 div day-1 were measured under restricted ranges of temperature (15 to 20°C), light intensity (above 150 μmol.m-2. s-1) and salinity (26 and 31). These growth rates are among the highest reported for Alexandrium tamarense under laboratory conditions and represent a potentiality for high cell concentrations during fast growth in the southern Brazilian coastal waters.