Mi. Moore et Rc. Murdoch, PHYSICAL AND BIOLOGICAL OBSERVATIONS OF COASTAL SQUIRTS UNDER NONUPWELLING CONDITIONS, J GEO RES-O, 98(C11), 1993, pp. 20043-20061
Offshore-directed plumes of inshore water, marked by a shallow mixed l
ayer, low salinity, and low temperature during winter, were observed s
outh of the Hokitika Canyon on the South Island west coast, New Zealan
d. Hydrographic and satellite observations are presented which show th
at plume time scales were of the order of a few days, and across-shelf
length scales were approximately 50 km. The low-salinity plumes were
found to be associated with the southern edge of an offshore-directed
jet that followed the Hokitika Canyon bathymetry. Decay of the plumes
was rapid and appears to be associated with mixing of plume water into
offshore surface waters. The occurrence of the plumes is nonseasonal,
and they do not appear to be associated with upwelling. Observations
suggest that strong southward flow around the head of the Hokitika Can
yon, perhaps as a consequence of coastal-trapped wave activity, is a p
ossible mechanism for plume formation. Biologically, the plumes were i
mportant because they stabilized the water column and prevented the mi
xing of phytoplankton below the photic zone. Although the plumes were
found to transport productive nearshore waters offshore, the major imp
act of the plumes was to lower total water column chlorophyll a in out
er shelf regions. The relationship between the Hokitika plumes and the
filaments and squirts identified off the Californian coast is discuss
ed, and it is concluded that the plume dynamics resemble those of the
squirts found inshore of the seasonal filaments off California. The re
sults of this study indicate that squirts not only influence biologica
l variability in shelf waters but are important mechanisms for the acr
oss-shelf exchange of coastal and oceanic waters.