IPY-1098-PACIFIC-ANTARCTIC INFLUENCE ON THE ATLANTIC SIDE OF THE MAGELLAN STRAIT: LONG TERM MONITORING OF PATAGONIAN MICROBIAL COMMUNITIES AT CA. 52�S. (PAMPA)

PROYECTO ARGENTINO MULTIDISCIPLINARIO

Multidisciplinary, international efforts have led to a fair knowledge of
microbial communities (pico-, nano- and microplankton) as to their structure,
abundance, and processes involved in the global carbon cycle. Advanced,
exhaustive studies on this field have been encouraged in many different sectors
of the World Ocean, including those of difficult access such as the Antarctic.
Curiously, for a few geographic areas adjacent to the latter region and under
its strong, direct influence, studies of this kind are only in their initial
stages. Such is the case of the Argentine shelf, which is characterized both
by being one of the widest in the world and by its high diversity of marine
ecosystems. In terms of dynamic processes (removal of CO2 from the atmosphere
through photosynthesis, nutrient recycling, coupling of phytoplanktonic and
bacterioplanktonic production, food web interactions, transport of species by
currents), this lack of knowledge prevents from establishing links and
comparisons with adjacent oceanic regions (e.g., Southern Ocean, SE Pacific),
as well as from constructing ecosystem models aimed to predict the patterns of
carbon flux, among other limitations. Previous results from latitudinal
transects extending from the Argentine shelf to the Southern Ocean during
austral summer revealed that South Patagonian waters (mainly those along the
coast of the Santa Cruz Province) favor the development of an extremely rich
pseudo-estuarine ecosystem hosting high microbial and heterotrophic biomass.
These waters are under the influence of (1) nutrient-enriched Circumpolar
waters, (2) a tongue of low-salinity, subantarctic waters proceeding from the
Strait of Magellan (the most important choke point between the Atlantic and
Pacific) and the Cape Horn Current, and extending northward up to 47�S, (3)
frontal processes, and (4) human impact due to exploitation of living and
non-living resources. Moreover, while the Atlantic side of the Magellan Strait
exhibits the world's second largest tidal ranges, the Pacific end receives the
direct effect from glacial continental ice melting during summer.

Given the implications of this particular sector in local carbon fluxes, marine
fisheries and Global Change, further critical questions arise: Is the
Pacific-Atlantic link a potential catalyst of microbial activity on the
Atlantic side of the Magellan Strait? Which are the environmental factors
causing and regulating such high productivity levels? Is this phenomenon
permanent, occasional or seasonal? To what degree do these unexpectedly high
heterotrophic biomass contribute to the local carbon flux and to Global Change?
Which are the relationships between food-web structure, organic matter fluxes
and climatic variability (e.g., ENSO)? What is the magnitude and fate of
primary and secondary production in this area and how will it change as global
temperature increases and atmospheric ozone becomes further depleted? These
important questions need to be answered in the forthcoming years in order to
understand both the dynamics of this unique environment and the connections
between Polar and mid-latitude ecosystems (for instance, how and to what extent
"open-ocean" Drake Passage waters impact on this environment, and how this
impact compares with that caused by the "protected" chokepoint of the Magellan
Strait, directly influenced by the ENSO cycles). As a starting point for this
ample research field, the present project intends to initiate a long-term
monitoring of microscopic communities and their role in biogeochemical cycles
through a Time Series Station in neritic Patagonian waters (ca. 52�S). Such a
station will be the core of in situ and experimental studies on seasonal and
inter-annual variability of the local microbial community structure, cell size
and abundance, key species and functional groups, red tides, alternation
between bacterioplankton and net phytoplankton dominance, etc. Data will be
analyzed in relation to the main physico-chemical and geological constraints of
the sector (temperature and salinity fluctuations, wind, turbulence, local
tidal ranges, re-suspension processes, land-coast and plankton-benthos-sediment
interactions, quality, origin and concentration of DOM and POM, organic and
inorganic nutrients, DO, pH, chlorophyll, among others) as well as to
meso-scale phenomena such as ENSO (actual and past conditions). This approach
is expected to help in the understanding of coastal ecosystem responses to
natural and anthropogenic changes and to promote the development of disciplines
such as Aquatic Microbial Ecology and Marine Biogeochemistry in the young
generation of scientists.