SEASonality of the DRAKE Passage pelagic ecosystem

Project Description
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The Southern Ocean exerts a strong influence on global climate through
the circulation of the Circumpolar Current and the seasonal shift of
the sea-ice cover. While currently there are many different ways of
assessing the intensity of phenomena associated with Climatic Change
(ozone depletion, increase of temperature, CO2 and UV radiation),
there is no single tool for measuring the indirect effects of these
alterations, most of which are critical to the functioning of
ecosystems. In the marine environment, changes in thermal gradients
modify the global oceanic circulation pattern, thus bringing
unpredictable consequences to the structure of communities, trophic
relationships and biogeochemical cycling. The geographic distribution
and abundance of plankton stem from a combination of factors that
include the interaction between the life cycle of species, oceanic
circulation, formation of eddies, the behaviour of frontal systems
(e.g., advance and retreat of the sea-ice cover), and the abundance of
vertebrate predators (fish, birds and marine mammals). Any alteration,
natural and/or anthropogenic (e.g., fisheries), in the intensity of
predation leads to a change in the structure of trophic webs, thus
affecting biodiversity, concentration of key Antarctic species,
nutrient loading and carbon fluxes to the deep-sea, often resulting in
the general unbalance of the ecosystem. In order to examine within an
integral framework this conjunction of factors, the present project
will focus on the seasonality of one of the most peculiar areas of the
Southern Ocean: the Drake Passage, a key open-ocean choke point for
the Antarctic Circumpolar Current. The pronounced continental
constriction between South America and the Antarctic Peninsula causes
the northern deflection of the ACC and, jointly with the ENSO cycles,
influences directly the Southwestern Atlantic in terms of
oceanographic-atmospheric and biological processes. Drake Bioseas is
intended to achieve a first step towards the understanding of these
processes by covering aspects that range from the assessment of
air-sea interactions to geochronological surveys of the sea bottom,
and from organisms living in the pelagic realm to benthic communities
and micro-paleonthological indicators, emphasising in the
Magellan-Antarctic regions and the Atlantic-Pacific
connections. Specific richness, population density, biomass and
geographic distribution, shifts in community structure and
biogeography, oxidative stress biomarkers and antioxidant defenses
will be examined for bacteria, protozoa, planktonic algae, meso-and
macrozooplankton, sea birds and marine mammals. Antarctic and
subantarctic fishes will be examined only as to their systematic
(morphological and molecular) and oxidative stress; this will allow
elucidating the patterns of distribution of key species, migration
processes and physiological responses to environmental
changes. Special attention will be paid to dormant stages of
microscopic organisms (non active bacteria, auxospore formation,
cysts, resting propagules) as well as to factors controlling the
timing of activation. The role of species within the trophic web will
be evaluated, taking into consideration a wide spectrum of topics,
including fluctuations in the nutritional mode of unicellular
organisms, diet composition, energy content, interspecific food
overlapping in top predators, etc. Previous information from land,
coastal and open ocean communities, provided from scientists involved
in the project and by official and private institutions dedicated to
fisheries, will constitute the tools for comparisons of past and
current conditions. Such objectives make Drake Bioseas directly link
to CCAMLR, EBA SCAR and CAML projects. This will be the first time in
which a multidisciplinary and integrated approach is made on waters of
the Drake Passage and its surroundings, emphasizing on the seasonal
and inter-annual dynamics (2007-2008) of marine communities in natural
boundaries such as Subantarctic vs. Antarctic, neritic vs. oceanic,
Pacific vs. Atlantic, summer vs. winter, low- vs. mid-latitude
environments, and on trophic relationships (areas/seasons/years of
dominance of net phytoplanktonic cells vs. DOM-based microbial food
web, and of crustacean vs. gelatinous zooplankton) and the magnitude
of ecosystem fluctuations due to frontal behaviour (Subantarctic
Front, Polar Front, Ice-Edge, winter conjunction of Polar and Ice
fronts). Manipulative experimental work (productivity, grazing,
physiological responses) on board will be carried out to complement in
situ studies. Besides its scientific goals, the priorities of this
endeavour embrace the legacy of an Experimental Research Centre for
multidisciplinary studies on cold-water organisms, and an Argentine
icebreaker reconditioned for scientific purposes. These legacies are
expected to significantly contribute to the formation of a new
generation of "bio-seas" scientists.