Joana Angélica Guimarães da Luz

Chlorophyll a and nutrient distribution around seamounts and islands of the tropical south-western Atlantic

Data collected on two large-scale surveys around the seamounts and islands off north-eastern Brazil during 1997 and 1998 provided information on the distribution of Chlorophyll a and inorganic nutrients. During both surveys, the concentrations of Chlorophyll a and nutrients were highly patchy. The highest measurement of Chlorophyll a was 3.91 µg L–1 during 1997. A wide range of nutrient concentrations were found, from undetectable values to a maximum of 17.52 µm L–1 (Si), 1.37 µm L–1 (PO4), 10.02 µm L–1 (NO3) and 0.72 µm L–1 (NO2). In 1998, concentrations of Chlorophyll a and nutrients (nitrite and nitrate) were far more uniform, with Chlorophyll a concentrations lower and phosphate concentrations generally higher than in 1997. Topography–flow interaction on thermohaline structures was observed around Saint Peter and Saint Paul Archipelago and in the Fernando de Noronha Chain, creating a patchy pattern around the island and seamounts. Nutrients exhibited an inverse linear relationship with temperature and salinity and an exponential decay relationship with Chlorophyll a.

Approximate up-scaling of geo-spatial variables applied to deep foundation design

We present a series of simple approximate methods for up-scaling the cumulative distribution function of spatially correlated variables by using an effective number n e of independent variables. Methods are based on the property of distribution permanence of the gamma and inverse Gaussian distributions under averaging, bootstrap sampling and expansions about the normal and gamma distributions. A stochastic simulation study is used to validate each method, and simple parameters are defined to identify respective ranges of applicability. A practical example is presented where core sample rock strength data are up-scaled to shaft size for probabilistic (risk-based) deep foundation design. Supplemental material is available online.

Relationship between spatial distribution of chaetognaths and hydrographic conditions around seamounts and islands of the tropical southwestern Atlantic

Relationship between spatial distribution of chaetognaths and hydrographic conditions around seamounts and islands off Northeastern Brazil were analyzed from 133 oceanographic stations during the months of January - April of 1997 and April - July of 1998. Oblique zooplankton tows, using 50 cm diameter Bongo nets with 500µm mesh with a flowmeter to determine the filtered volume, were carried out to a maximum of 200m depth. The Superficial Equatorial Water, which had a salinity > 36 PSU and temperature > 20°C, occupied the top 80 to 200m depth. Below this water mass was the South Atlantic Central Water with salinity ranging from 34.5 to 36 PSU and temperature from 6 to 20°C. The community of chaetognaths showed six species: Pterosagitta draco, Flaccisagitta enflata, Flaccisagitta hexaptera, Pseudosagitta lyra, Serratosagitta serratodentata, and Sagitta helenae. Of these species, F. enflata was the most abundant (32.05% in 1997 and 42.18% in 1998) and the most frequent (87.88% in 1997 and 95% in 1998) during both periods. A mesopelagic specie was identified (P. lyra). This specie was more abundant in 1997 (3.42%), when the upwelling was more intense. P. lyra occurred in 22% of the samples during 1997. The abundance of F. enflata, an epiplanktonic species, increased, associated with greater water-column stability.