IPY-192-SEASONALITY OF THE DRAKE PASSAGE PELAGIC ECOSYSTEM: BIODIVERSITY, FOOD WEBS, ENVIRONMENTAL CHANGE AND HUMAN IMPACT; PRESENT AND PAST (DRAKE BIOSEAS)

Project endorsed at national level by the Argentine Committee for IPY.

PROYECTO ARGENTINO DRAKE BIOSEAS

There is a strong influence of the Southern Ocean on global climate through
the circulation of the Circumpolar Current and the seasonal extent of sea-ice
cover. While there are at present many ways of assessing the intensity of
phenomena associated with the Global Change (ozone depletion, increase of
temperature, CO2 and UV radiation), there is no single tool for measuring the
indirect effects of these changes, most of which are critical to ecosystems. In
aquatic environments, the changes in thermal gradients induce alterations of
the global oceanic circulation pattern, thus bringing unpredictable
consequences to planktonic communities. The geographic distribution and
abundance of plankton result from a combination of factors such as the
interaction between their species life cycles, oceanic circulation, the
behavior of frontal systems (e.g., the advance and retreat of the sea-ice
cover), and concentration of vertebrate predators, such as fish, birds and
marine mammals. Any alteration, natural and/or anthropogenic (fisheries), in
the intensity of predation leads to a change in the structure of the trophic
webs, thus affecting biodiversity, concentration of key Antarctic species, and
carbon fluxes to the deep-sea, often resulting in the general unbalance of the
ecosystem.

In order to examine this conjunction of factors together with natural processes
and human impact within an integral framework, the present project will focus
on the seasonality of one of the most peculiar areas of the Southern Ocean: the
Drake Passage. The pronounced continental constriction between South America
and the Antarctic Peninsula causes a northern deflection of the Antarctic
Circumpolar Current, which strongly influences the Southwestern Atlantic in
terms of oceanographic-atmospheric and biological processes. To understand
these impacts, the study will include the assessment of biogeochemical fluxes
(e.g., nutrients, organic matter- POM, DOM), size-fractionated chlorophyll a
and the most important physico-chemical variables. Specific richness,
population density and geographic distribution of bacteria, protozoa,
planktonic algae, macro- and mesozooplankton, fish, birds and marine mammals
will be examined. The project will also cover the role of all identified
species within the trophic web, and other inter- and intraspecific interactions
in relation to environmental factors, frontal zones and water masses during
summer and winter. Diet composition, energy content and interspecific food
overlap will be estimated for Antarctic birds and seals occupying distinct
ecological niches. Special attention will be paid to the influence of the
winter sea-ice cover advance towards the Polar Front on the trophic web
structure.

ARGENTINA TEAM

Dr. Viviana Alder - Instituto Antartico Argentino, CONICET
Dr. Esteban Barrera-Oro - Instituto Ant�rtico Argentino, CONICET
Lic. Alejandro Carlini - Instituto Ant�rtico Argentino
Dr. Ricardo Casaux - Instituto Ant�rtico Argentino, CONICET
Lic. N�stor Coria - Instituto Ant�rtico Argentino
Bioq. Mar�a M�rquez - Instituto Ant�rtico Argentino, Univ. of Buenos Aires
Dr. Enrique Marschoff - Instituto Ant�rtico Argentino, Univ. of Buenos Aires

The results of the project will provide an integrated qualitative-quantitative
view of the communities and their functioning within the oceanic ecosystems of
the Drake Passage, mainly during winter. The information to be gathered during
the assessment of the spatial-temporal variability along 2007-2008 will be
organized in a database that will serve for the future monitoring of the area.
In order to establish comparisons between past and present conditions, the
scientists involved in this project will contribute with their sets of
historical data (approx. 10-15 years) on biodiversity of distinct communities
from the Drake Passage (plankton) and the west Antarctic Peninsula (fish,
birds, seals).