Possible Sea Ice Impacts on Oceanic Deep Convection 
Claire L. Parkinson 
NASA/Goddard Space Flight Center 
Greenbelt, MD 20771 
Many regions of the world ocean known or suspected to have deep convection are sea-ice 
covered for at least a portion of the annual cycle (Fig. 1). As this suggests that sea ice might 
have some impact on generating or maintaining this phenomenon, several mechanisms by which sea 
ice could exert an influence are presented in the following paragraphs. 
Sea ice formation could be a direct causal factor in deep convection by providing the sur- 
face density increase necessary to initiate the convective overturning (Fig. 2). As sea ice 
forms, either by ice accretion or by in situ ice formation in open water or in lead areas bet- 
ween ice floes, salt is rejected to the underlying water. This increases the water salinity, 
thereby increasing water density in the mixed layer under the ice. A sufficient increase in den- 
sity will lead to mixing with deeper waters, and perhaps to deep convection or even bottom 
water formation. Observations are needed to establish whether this -process is actually 
occurring; it is most likely in regions with extensive ice formation and a relatively unstable 
oceanic density structure. 
In regions and periods with deep convection just seaward of the ice edge, the presence of 
the ice, rather than its formation, could contribute by intensifying the ocean/atmosphere 
contrast. Specifically, air flowing off the Greenland or Antarctic ice caps, already cold and 
dry, is further cooled radiatively as it flows over the adjacent sea ice, so that the temperature 
contrast between ocean and atmosphere is even greater once the air reaches open water either 
in a polynya or beyond the ice edge (Fig. 3). The large resulting heat and evaporative fluxes 
from ocean to atmosphere decrease ocean temperatures and increase ocean salinities. Both of 
these adjustments increase surface water densities, and, with sufficient density increase, can 
lead to mixing with deep waters and perhaps to deep convection and even bottom water formation. 
In this case sea ice has an indirect role, contributing to the creation of the atmospheric con- 
ditions which allow the fundamental ocean/atmosphere mechanism to operate. 
NORTH POLAR REGION SOUTH POLAR REGION 
yore en 
- 
s 
¢ 
4 
4% 
em eremeoen a? 
— ICE EDGE MARCH 5-7, 1974 
—— ICE EDGE SEPTEMBER 16-18, 1974 
@® REGIONS OF DEEP CONVECTION 
Fig. 1. The approximate seasonal range of the ice edge location in both the north and south 
polar regions, plus the approximate locations of oceanic deep convection. The ice edge is 
determined from the Electrically Scanning Microwave Radiometer on board NASA's Nimbus 5 
Satellite, using the 193 K brightness temperature contour, while the locations of deep convection 
are approximated from Killworth (1983; Figs. 2 and 10). 
