Ross and Quetin: The Antarctic Marine LTER, LTER Network News, Spring 1991

LTER NETWORK NEWS, Spring 1991, Issue 9, cover page and continued on page 5.

PALMER STATION: The Antarctic Marine LTER: An Ecosystem Dominated by Ice

Robin M. Ross and Langdon B. Quetin

Palmer LTER Contribution #01

Palmer Station and the surrounding waters have been chosen as the site of the
first Antarctic LTER.  The smallest of the three U.S. antarctic research
stations managed by NSF, the station is located in a protected harbor on an
island midway down the Antarctic Peninsula, and more than 600 miles from the
tip of South America. LTER research will focus on the pelagic marine ecosystem
and the ecological processes which link the extent of annual pack ice to the
biological dynamics of different trophic levels.  In these polar waters the
annual cycle of ice formation and melting affects about 50% of the open sea.

Because pack ice is postulated to be the major physical determinant of
temporal/spatial changes in the structure and function of polar biota,
interannual cycles and/or trends in the annual extent of pack ice are likely
to have significant effects on all levels of the food web, from total annual
primary production to breeding success in seabirds.  For example, recent
studies suggest a connection between the extent of winter sea ice and the
winter-over survival or reproductive success of the seabirds and their prey.
Both Adelie penguins and antarctic krill, the 35 to 50 mm-long crustacean
which is their favored prey, are positively affected when ice cover is most
extensive.  Conversely, reproductive success in south polar skuas, gull-like
migratory seabirds, appears to be connected to the abundance of one age group
of the antarctic silverfish, which appears to improve with less extensive ice.

SITE Characteristics

The climate is typically maritime Antarctic, with snow and rain common any time
of the year.  The temperature at Palmer Station is relatively mild, averaging
about -10 degrees C in July and 2 degrees C in January.  The extent of sea ice
is highly variable in the region, with particularly severe ice conditions
occurring roughly every seven to 10 years and lasting two to three years
within the last two decades.  The areal extent of ice can vary by 25% between
years.

There are several groups of islands with seabird rookeries between Palmer
Station and Palmer Basin, the only deep basin in the area.  Species studies
under LTER will include the Adelie penguin, which dominates the seabird
assemblage, and south polar skuas.  During the breeding season, they forage in
the upper water column within a 100 km radius of the rookeries, moving
southwest into the Basin and west into the open ocean.  The summer foraging
region and wintering grounds of the seabirds help define the scale of the
region to be investigated.

Overall Objectives

The overall objectives of the Antarctic Marine LTER are: (1) to document
interannual variability in the development and extent of annual pack ice, and
in life-history parameters of primary producers and populations of key species
from different trophic levels; (2) to quantify the processes that underlie
natural variation in these representative populations; (3) to construct models
that link ecosystem processes to physical environmental variables, and that
simulate the spatial/temporal relationships between representative
populations; and (4) to employ such models to predict and validate the impacts
of altered periodicities in the annual extent of pack ice on ecosystem
dynamics.

Approach and Methodology

The general approach capitalizes on populations that are easily accessible
near Palmer Station during a prolonged breeding season, and that sample the
surrounding marine environment.  Beginning in October 1991 (austral spring) a
suite of critical biological and environmental variables will be monitored
continuously on a small spatial scale (adjacent to Palmer Station)
representing the seabird summer foraging area, but a long and recurrent
temporal scale (every year, the entire breeding season).

Satellite imagery will be used to continuously monitor certain environmental
parameters such as sea ice extent and thickness, sea surface temperature, and
potentially color (fluorescence) on larger spatial scales and throughout the
year.  In addition, automatic weather stations at several selected positions
in the regions will continuously monitor atmospheric pressure, wind speed and
direction, and air temperature.  Research at Palmer Station and in the
surrounding nearshore waters will focus on the seabirds, the prey of the
seabirds, primary production and hydrographic characteristics of the water
column.

Processes (reproduction, recruitment) and parameters (food availability) that
are sensitive to environmental change and are important in the structure and
function of the communities will also be monitored.  The inherent interannual
variability in the extent of pack ice allows researchers to "conduct" natural
experiments on the effects of pack ice on the various trophic levels as
parameters and processes are monitored during and after seasons of different
pack ice cover.

The spatial scale of sampling prey distribution, abundance, and physiological
condition, water column properties, primary production estimates, and
hydrographic measurements will be extended during two types of research
cruise: (1) time-series cruises in the late spring; and (2) process-oriented
cruises at critical times in biological cycles.  These process-oriented
cruises are essential for verification of the models of regional processes,
such as primary production, oceanic circulation, and the biological/physical
models of prey abundance.

Robin Ross or Langdon Quetin, Marine Science Institute, University of
California, Santa Barbara, 98106, 805-893-2096, "rRoss@lternet.washington.edu"
or "lQuetin@lternet.washington.edu".