TITLE:     Palmer LTER: Seasonal changes in the hydrographic structure of the
           upper 100m of the water column
PAGE:      127 of SCAR SIXTH BIOLOGY SYMPOSIUM, Antarctic Communities: Species,
           Structure and Survival 
AUTHOR:    EE Hofmann, CM Lascara, BL Lipphardt, Jr., JM Klinck, DA Smith, RA
           Locarnini, RC Smith
ABSTRACT:  Between November 1991 to September 1993, four multidisciplinary
cruises were conducted in the region west of the Antarctic Peninsula as part
of the Palmer Long-Term Ecological Research (LTER) program.  These cruises
provide an extensive set of temperature and salinity measurements from which
the seasonal changes in the density structure of the upper 100 m of the water
column can be described.  Observations from the austral spring show that the
density structure is relatively uniform to depths of 80 to 100 m (sigma t
of 27.3 to 27.4).  During the austral summer, stratification develops in the 
upper water column as a result of increased solar radiation and icemelt.  At 
this time, temperatures at 100 m increase from - 1.5 degrees C to 1.0 degrees
C.  Coincidently, salinity decreases from 34 psu to 33 psu.  The net result is 
the formation of a seasonal pycnocline that is found at about 20 m or 
shallower.  Beneath the seasonal pycnocline is a region of cold (-1.0 degrees 
C to -1.5 degrees C) water which is the signature of the surface water from 
the previous winter.  The seasonal pycnocline and region of cold water are 
rapidly eroded in the austral fall by increased mixing due to storm activity.
By late May, the density structure is again homogeneous in the upper 80 to 
100 m.  The seasonal change in density structure in the upper 100 m has 
important implications for biological production in the LTER region.