Flavio E. Paparazzo

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.

Cross-frontal distribution of inorganic nutrients and chlorophyll-a on the Patagonian Continental Shelf of Argentina during summer and fall

Datos oceanograficos recolectados durante 2001-2003 en la Plataforma Continental Patagonica Argentina fueron analizados para estudiar las principales caracteristicas quimicas en esta gran plataforma. Se presenta la variacion de los nutrientes inorganicos y de la clorofila-a a una distancia de 40 a 60 km de la costa. El nitrato es el nutriente limitante en la region y esta negativamente correlacionado con la clorofila-a. Todas las variables presentan variaciones localizadas en verano, las cuales pueden ser relacionadas con los frentes de marea a traves de la comparacion de nuestros datos con el parametro critico de estabilidad de Simpson (50 J m-3). En otono, la concentracion de nutrientes en la plataforma continental fue mas uniforme y generalmente mayor que en verano debido a la disrupcion de dichos frentes.

Incorporación de nitrato por fitoplancton en dos ambientes marinos diferentes de la provincia de Chubut (42°-46°S, Argentina)

Resumen es: La distribucion espacio-temporal de los nutrientes y procesos de produccion primaria son fundamentales para la comprension del funcionamiento de ecosiste...

Surface Macronutrient Dynamics of the Drake Passage and the Argentine Sea

The dynamics of macronutrients on the surface is key for marine life. In this work, we focus on the nitrate, phosphate, and silicate distribution along the Drake Passage and the Argentine Sea. These nutrients have the highest concentration in the south of the Drake Passage because of upwelling of deep waters and inlets of coastal currents. The Antarctic Convergence forms a kind of barrier between water masses, greatly limiting the surface exchange of chemical species to the north. Pacific Ocean waters mixed with surface waters located north of the Polar Front enter the Argentine Sea giving rise to the Patagonian and Malvinas Currents. On their way, primary producers deplete nutrients, and, at a given moment, nitrate reaches limiting concentrations. Two processes locally modify the resulting N-S nutrient gradient: (1) the shelf offshore component receives the contribution of the nutrient-rich Antarctic waters, which move northward along the continental slope through the Malvinas Current; (2) large tidal waves and their interaction with the seabed create seasonal frontal systems that increase the chemical species concentration near the coast. The discharge of the less saline waters of the Magallanes Strait can be observed up to 43°S, but its effect on macronutrients is low. Patagonian rivers present a low flow and seem to make only local contributions. Until now, the fertilization effect of submarine groundwater discharge is unknown and the aeolian dust input is under study. The ice pack coverage in the Drake Passage and the water column stratification in the Argentine Sea govern the seasonal variation. Interannual differences have been associated with ENSO-like events, but information is not enough to draw conclusions. Due to the importance of knowing the nutrient dynamics to understand the biological processes of the region, multidisciplinary studies focusing on this topic should be promoted.

Perspective: Continental Inputs of Matter into Planktonic Ecosystems of the Argentinean Continental Shelf—the Case of Atmospheric Dust

Land-derived dissolved and particulate matter (allochthonous matter) affect pelagic ecosystems by changing factors which include light penetration, nutrient availability, substrate concentration, and in general, biogeochemical cycles in the ocean. In a context of growing anthropogenic impact, this material may not only increase its load but also carry toxic substances. Riverine runoff is the most studied mechanism of particulate matter input from the continent to the sea in the southern region of South America where the continental shelf is widest (e.g., Atlantic Patagonia). However, there are other sources of particulate matter which are not affected by rivers in this semiarid region: aeolian material. Winds in this region (notably the Southern Hemisphere westerlies) are the only way continental aeolian material (atmospheric aerosols or “dust”) can reach not only the shelf but even further onto oceanic HNLC (high nutrient–low chlorophyll) regions of the Atlantic Southern Ocean. This potential impact of Patagonian dust beyond the continental shelf attracts the attention of the global climate community, and at the same time, it opens questions about the potential effects of dust in coastal waters. According to previous work and ongoing studies, deposited particles can have significant impacts in the chemical and biological components in the euphotic zone. However the effects of this airborne material in plankton communities of South America are largely unknown, mostly due to the lack of in situ studies and observations. Since the events of dust mobilization, transport, and deposition are expected to increase (due to climate change) and interact with other global change factors such as warming and more intensive land use, the influence of dust input may become more prominent for coastal and oceanic regions of southern South America in the next decades.