Abundance of organic-walled dinoflagellate cysts of sediment core GeoB3603-2

Here, we reconstruct the varying influence of the Agulhas Current (AgC), the South Atlantic Current and the Antarctic Circumpolar Current on the Agulhas Retroflection (AgR) in the eastern South Atlantic Ocean for the last 160,000 years on the basis of the dinoflagellate cysts, pollen and spores present in a sediment core (GeoB 3603-2) from the southeastern Cape Basin offshore South Africa, where the Agulhas Current enters the Atlantic Ocean. Our analyses reveal strong orbital forcing on the heat exchange between the Indian Ocean and the South Atlantic Ocean during the Late Quaternary. Maxima in local productivity appear to be primarily related to a strengthening of the ocean circulation as a result of the high seasonal contrast during precession maxima. During precession minima, seasonal contrast was low and stratified, oligo- to mesotrophic conditions prevailed, notably when these minima coincided with the glacial terminations. The clear presence of periodicities on a sub-Milankovitch scale as well as modulations of the primary frequencies demonstrate that the Agulhas Retroflection furthermore is modulated substantially by complex interactions between the subtropical, 'precession-driven', climate and ocean circulation systems, and the southern, 'obliquity-driven', high latitudes.

(Table 2) Lipid fluxes derived from sediment trap samples

Phytoplankton is a sentinel of marine ecosystem change. Composed by many species with different life-history strategies, it rapidly responds to environment changes. An analysis of the abundance of 54 phytoplankton species in Galicia (NW Spain) between 1989 and 2008 to determine the main components of temporal variability in relation to climate and upwelling showed that most of this variability was stochastic, as seasonality and long term trends contributed to relatively small fractions of the series. In general, trends appeared as non linear, and species clustered in 4 groups according to the trend pattern but there was no defined pattern for diatoms, dinoflagellates or other groups. While, in general, total abundance increased, no clear trend was found for 23 species, 14 species decreased, 4 species increased during the early 1990s, and only 13 species showed a general increase through the series. In contrast, series of local environmental conditions (temperature, stratification, nutrients) and climate-related variables (atmospheric pressure indices, upwelling winds) showed a high fraction of their variability in deterministic seasonality and trends. As a result, each species responded independently to environmental and climate variability, measured by generalized additive models. Most species showed a positive relationship with nutrient concentrations but only a few showed a direct relationship with stratification and upwelling. Climate variables had only measurable effects on some species but no common response emerged. Because its adaptation to frequent disturbances, phytoplankton communities in upwelling ecosystems appear less sensitive to changes in regional climate than other communities characterized by short and well defined productive periods.

Abundancia y distribución vertical de quistes de dinoflagelados (Gonyaulacales y Peridinales) en sedimentos del golfo de Fonseca, departamento de La Unión

Entre los meses de marzo y agosto de 2012 se recolectaron 15 núcleos sedimentarios cercanos a las playas: La Criba, El Barquito y La Cuevita en el extremo Sur del Golfo de Fonseca, departamento de La Unión, para el estudio de quistes de dinoflagelados. Se registró sus abundancias y distribución en los primeros diez centímetros de profundidad en todos los núcleos sedimentario; la técnica de recolecta y la técnica de limpieza de sedimentos se realizó siguiendo la metodología de Matzuoka y Fukuyo (2000). Se observó un total de 178 morfotipos de quistes Gonyaulacales y Peridinales pertenecientes a las familias Goniodomataceae, Protoperidiniaceae respectivamente. Las especies identificadas fueron: Protoperidinium subinerme, Protoperidinium conicoides, Stelladinium robustum, consideradas como especies abundantes; Protoperidinium oblongum, Pyrodinium bahamense y Protoperidinium sp1, consideradas como especies accesorias y Stelladinium reidii como especie accidental. Los núcleos con mayores registros contenían entre 31-40 quistes ml-1, ubicados en la parte Este del sitio de muestreo. El estudio vertical determinó que la abundancia de quistes decaía a medida que aumenta la profundidad de estudio. La granulometría realizada a 5 núcleos de sedimento se caracterizó por la presencia de cuatro tipos de tamaños de grano, arenas de tipo Medias comprendidas entre 0.250- 0.180 mm, arenas Finas entre los 0.125- 0.090 mm y las arenas muy Finas comprendidas entre 0.063-0.020 mm, por último las fracciones menores a 0.020 mm correspondientes a limos y arcillas. De estas fracciones la más abundante en la zona de estudio fue la de arenas finas, mientras que las más escasas corresponden a limos y arcillas.