Salvador A. Gaeta

New and regenerated production in the South Atlantic off Brazil

Abstract Rates of assimilation of NH 4 + , NO 3 − and urea were determined at eight oceanic stations in March 1994 and one inshore station in December 1994 in the South Atlantic off Brazil by performing 15 N tracer experiments on microbial populations from two depths (50% and 1% of surface light penetration). Carbon uptake rates were determined by 14 C tracer experiments at the same depths. At each sampling site temperature and salinity profiles were obtained and ambient nutrient and phytoplankton biomass were measured. Concentrations of chlorophyll a were −1 in the oceanic region and varied from 0.12 to 1.41 μg 1 −1 in the inshore region. On average NO 3 − was the main form of nitrogen available for phytoplankton (64–86% of total nitrogen) in oceanic waters, while at the inshore station, NO 3 − represented less than 32% of total nitrogen supply. Nonetheless, primary production was dominated by regenerated production. Uptake of reduced forms of nitrogen represented on average 74% of total nitrogen utilized by phytoplankton in the oceanic region and 96% at the inshore station. In oceanic waters, the mean f -ratio ratio (contribution of new to total production) was 0.16 and 0.30 at subsurface (50% I o and bottom (1% I o ) of the euphotic zone, respectively. At the inshore station the mean f -ratio was 0.05 at the subsurface and 0.10 at the bottom of the euphotic zone. Temperature and salinity measurements showed occasional injections of NO 3 − into the euphotic zone, resulting from the intrusion of the South Atlantic Central Water on the continental shelf. Episodic enrichment of the base of the euphotic zone with NO 3 − enhanced the contribution of new to total production and led to a maximum f -ratio of 0.86 in oceanic waters and 0.26 in coastal waters.

Distribution patterns of epipelagic copepods off Rio de Janeiro (SE Brazil) in summer 1991/1992 and winter 1992

The spatial distribution of copepod populations on the eastern continental shelf off Rio de Janeiro State, Brazil, was analysed in relation to the hydrographic regime in December–January (summer 1991/92) and July (winter 1992). Advection of cold and nutrient-rich South Atlantic Central Water (SACW) onto the shelf was a prevailing circulation mechanism in both seasonal cruises. The SACW occupied a larger proportion of bottom layers in summer as compared to winter, but only in the latter a well-defined upwelling event was recorded off Cape Frio. Two calanoid copepods were representative of shelf areas influenced by SACW intrusions: Calanoides carinatus, which occurred mainly during summer and Ctenocalanus vanus, recorded at high densities in both periods. Paracalanus quasimodo was the dominant copepod at inner- and mid-shelf stations both in summer and winter, followed by Temora spp. and Oncaea spp. These coastal species peaked at the upwelling site. A highly diversified and comparatively less abundant copepod assemblage, dominated by Clausocalanus furcatus and Oithona plumifera, was recorded in outer-shelf stations occupied by the oligotrophic Tropical Waters of the Brazil Current. We conclude that regional and seasonal contrasts in copepod species composition and abundance are controlled to a great extent by the advection and upwelling of the SACW onto the shelf.

Environmental forcing on phytoplankton biomass and primary productivity of the coastal ecosystem in Ubatuba region, southern Brazil

Uma serie temporal de clorofila a e producao primaria obtida em um periodo de 33 dias durante o verao na regiao de Ubatuba, sudeste do Brasil, foi submetida a analise multivariada e harmonica. A Analise de Componentes Principais revelou quatro fatores interpretados como (i) Agua Central do Atlântico Sul; (ii) Sistemas ftontais transientes e chuvas; (iii) Ventos normais a costa; (iv) Ventos paralelos a costa. Estes fatores atuam como forcantes ambientais na determinacao da variabilidade observada na biomassa fitoplanctonica e produtividade primaria. A divisao da serie temporal de acordo com quatro eventos modificadores das caracteristicas fisicoquimicas da regiao mostrou a seguinte variabilidade na producao primaria integrada (g C m,2 dia,l) na camada eufotica: coluna de agua homogenea em processo de estratificacao termica- 0,4O±0, 11; coluna de agua estratificada e chuvas intensas- 1,24±0,28; coluna de agua misturada em fase de estratificacao termica apos intensas chuvas- 0,74:f:0,10; coluna de agua estratificada em fase de processo de mistura- 0,90±0,27; coluna de agua homogenea em fase de estratificao termica apos intensa mistura- 0,63±0,28. A Analise Harmonica revelou dois picos de biomassa significativos- um com periodo de 8,25 dias e outro com periodo de 6,6 dias, contribuindo, respectivamente, com 17 e 32% da variância total da serie. A forcante atmosferica apresentou um periodo caracteristico de 200-264 horas enquanto que a escala de resposta da biomassa fitoplanctonica variou de 144-192 horas e a de produtividade primaria um periodo de 360 horas. Em relacao a biomassa e nitrogenio total, a produtividade primaria apresentou uma defasagem de 96-144 horas.

Satellite estimates of chlorophyll-a concentration in the Brazilian Southeastern continental shelf and slope waters, southwestern Atlantic

Comparisons between in situ measurements of surface chlorophyll-a concentration (CHL) and ocean color remote sensing estimates were conducted in the Brazilian Southeast coast, Southwestern South Atlantic. In situ fluorometric data were acquired in four hydrographic cruises carried out during the austral summer and winter of 2001 and 2002. The satellite estimates of CHL were derived from SeaWiFS data recorded in HRPT mode by INPEs station with a nominal 1.1 km resolution. Four algorithms were used to estimate CHL: two empirical - Ocean Chlorophyll 4 bands (OC4v4), and 2 bands (OC2v4); one semi-analytical - Garver, Siegel, Maritorena (GSM01); and one based on neural network (NN). Comparisons of estimated and measured CHL were done within a temporal window of 12 hours from the in situ sampling time. SeaWiFS algorithms values are 5x5 pixel medians centered on the location of in situ sampling station. For the study area CHL was fairly well estimated by all the SeaWiFS algorithms. OC4 performed better (R2 = 0.71; rms = 0.22) than the other algorithms (OC2, GSM01, and NN). The OC2 algorithm also showed a good performance with R2 = 0.67 and rms = 0.23. The neural network algorithm performed better than the semi-analytical one (R2 = 0.62 and 0.55, respectively), but with a higher rms (0.34 and 0.20, respectively). In general, the OC4, OC2, and NN algorithms showed a tendency for overestimating CHL at higher concentrations and underestimating at lower values. The semi-analytic GSM01 algorithm overestimated only the lower CHL, but underestimated most of the other values.

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.

Variação nictemeral da clorofila α, produção primária do fitoplâncton e fatores ambientais da região de Ubatuba (Lat. 23º30'S Long. 45º06'W)

A series of experiments with natural phytoplankton populations was carried out to study the diel variation of chlrophyll a, primary production and some environmental factors. Samples were collected from surface over a period of 24 hours and always from one fixed station located in Flamengo Inlet, Ubatuba region, southern Brazil The experiments were performed in situ and simulated conditions to verify the patterns of diel cycles of both biotic and abiotic factors. The results obtained showed that diel variations were markedly pronounced mainly in relation to primary production and chlorophyll a. Diel variations of biological factors seems to be due to exogenous and endogenous phenomena.

Satellite estimates of phytoplankton primary production at santos bight, southwestern-south Atlantic: Comparison of algorithms

This study provides a satellite-based estimate of potential primary production in the Brazilian Southeast coast from in situ and Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color data. A non-spectral and vertically homogeneous semi-analytical algorithm and a spectral vertically non-homogeneous numerical algorithm were applied to the satellite ocean color data, which incorporate simultaneously measured in situ photosynthetic parameters. A vertically generalized production model was also tested. The best performing ocean color remote sensing primary productivity algorithm tested agreed with the 14C-based estimates within a factor of 2.

Observações preliminares sobre a toxicidade do γBHC e do cloreto de mercúrio à Artemia salina

Sao apresentados os resultados de bioensaios com larvas de Artemia salinacolocadas em misturas de γBHC e HgCl2, a fim de se compararem os efeitos das mesmas com aqueles obtidos quando essas duas substancias atuam isoladamente. A CL50 para o yBHC foi quase que o dobro do valor para o HgCl2. O efeito da primeira dose foi observado para aproximadamente 16% da populacao (CL16), enquanto que, para o γBHC, o foi em 2,3% da populacao (CL2,3). Assim, as doses subsequentes foram mais efetivas para o HgCl2 que para o γBHC. A dose efetiva 50% (ED50) e mais ou menos igual para o γBHC e para o γBHC + HgCl2, mas em doses altas o YBHC seria mais efetivo, enquanto que em doses baixas a mistura e que o seria.