Climate Variability (PAL LTER)

The annual advance and retreat of pack ice, a characteristic feature of
polar marine environments, affects a significant fraction of the Southern
Ocean as well as vast areas of the Arctic Ocean and Bering Sea.  In these
polar environments, pack ice provides marine habitats that are clearly
distinct from those of the open-water (Smith, 1990; Murphy et al., 1988)
and where microbial communities are abundant.  Annual pack ice may also be
the major physical determinant of temporal/spatial changes in the structure
and function of polar biota (Ainley et al. 1986; Fraser and Ainley 1986;
Smith 1990).  Thus 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 (Smith et al., 1988) to breeding
success in seabirds.

In addition predictions suggest that the effects of global change (climate
warming, ozone depletion) will be more pronounced and thus detectable
earlier in Antarctica than in mid-latitudes (Manabe and Stouffer, 1979).  A
primary goal for the Palmer LTER is to monitor the ecological effects of
changes in sea-ice extent and thickness, study the processes underlying
these effects and build interactive models in an effort to predict the
impacts of global warming and attendant changes in the annual cycle of pack
ice on Antarctic biota.  Thus the effects of climate variability on the
Antarctic marine ecosystem are a major research focus for the Palmer LTER. 
Past and present climate variability is documented by:  (1)  data on ice
cover from microwave remote sensing, with data on a coarse scale of 30 km
from 1973, and the potential for finer scale 1 km data from 1991; (2)
automatic weather stations installed at several locations, both near Palmer
Station (installed 1991), and on Hugo Island 65 km to the west (to be
installed January  1995); and (3) historical data from several marine
stations in the region, including Palmer Station (from 1989) and the
British Antarctic Survey Stations, Faraday 40 km south (from 1946) and
Rothera 400 km south (from 1981).

ICE
In the region around Palmer Station the maximum extent of pack ice west of
the Antarctic Peninsula varies widely, from near zero to halfway across
Drake Passage (Quetin and Ross, 1991), and shows some evidence of being on
a 6 to 8 year cycle (Stammerjohn, 1993).  Data obtained with satellite
microwave sensors suggests that there is an alternation between consecutive
high ice years (1979-1982 and 1986-1987) followed by consecutive low ice
years (1983-1985 and 1988-1989) (Fig.4.4 in Stammerjohn (1993)). 
Documenting the impact of this cycle on the marine ecosystem, and
identifying the processes involved are major objectives of the Palmer LTER.
 The current hypotheses state that one major predator/prey combination
(Adelie penguins and antarctic krill) have better survivorship and
reproductive success in years with greater ice cover, and another (south
polar skuas and antarctic silverfish) benefit during years of lesser cover.
 Estimates of total annual primary production also vary by 50% depending on
the extent of winter ice cover (Smith et al., 1988).  Thus accurate
estimates of the extent of winter ice, both historically and in the future,
are essential.

Fig. 4.4:  Contour plot of LTER annual cycles for years 1979-1991. 
Contours are labelled with ice coverages in km2.

BIBLIOGRAPHY

Ainley, D. G., W. R. Fraser, C. W. Sullivan, J. J. Torres, T. L. Hopkins
and W. O. Smith.  1986.  Antarctic mesopelagic micronekton:  Evidence from
seabirds that pack ice affects community structure.  Science 232: 847-849.
Fraser, W. R. and D. G. Ainley.  1986. Ice edges and seabird occurrence in
Antarctica.  BioScience 36: 258-263.
Manabe, S. and R. J. Stouffer.  1979.  A CO2-climate sensitivity study with
a mathematical model of the global climate.  Nature 282: 491-492.
Murphy, E. J., D. J. Morris, J. L. Watkins, and J. Priddle.  1988.  Scales
of interaction between antarctic krill and the environment, in Antarctic
Ocean and Resources Variability, E. Sahrhage, (ed).  pp.  120-130.  Berlin:
Springer-Verlag.
Quetin, L. B., and R. M. Ross.  1991.  Behavioral and physiological
characteristics of the Antarctic krill, Euphausia superba.  Amer. Zool. 31:
49-63.
Smith, W. O., Jr., N. K. Keene, and J. C. Comiso.  1988.  Interannual
variability in estimated primary production of the Antarctic marginal ice
zone, in Antarctic Ocean and Resources Variability, E. Sahrhage, (ed).  pp.
 131-139.  Berlin: Springer-Verlag.
Smith, W. O., Jr.  1990.  Polar Oceanography.  Academic Press, Inc., San
Diego.  760 pp.
Stammerjohn, S.  1993.  Spatial and temporal variability in Southern Ocean
sea ice coverage.  MS Thesis.  University of California, Santa Barbara,
California.  111 p.