Sea ice and ice algae relationships in the Weddell Sea
Holdsworth, G., and R. Holdsworth. 1978. Erebus Glacier Tongue movement. Antarctic Journal of the U.S., 13(4): 61-63, King, C. C. P., and R. C. Bilham. 1973. Strain measurements, instrumentation and technique. Philosophical Transactions of the Royal Society, London, A(274): 209-217. Press, F., A. P. Crary,J. Oliver, and S. Katz. 1951. Air-coupled flexural waves in floating ice. Transactions of the American Geophysical Union, 32: 673-678. Robinson, E. S. 1965. Seismic surface wave dispersion on the antarctic ice cap and adjacent floating ice—A preliminary study. Department of Geophysics, University of Utah, Utah. Special Report 1-34, Wadhams, P. 1973. Attenuation of swell by sea ice.JournalofGeophysical Research, 78(18): 3552-3563.
Sea ice and ice algae relationships in the Weddell Sea S. F. ACKLEY U.
Cold Regions Research and Engineering Laboratory Hanover, New Hampshire 03755 S. TAGUCHI
Hawaii Institute of Marine Biology Kaneohe, Hawaii 96744 K. R BUCK
Department of Oceanography Texas A&M University College Station, Texas 77843
Preliminary findings on ice properties and ice-associated algae were given using data obtained during a 1977 cruise in the Weddell Sea (Ackley, 1977; El-Sayed and Taguchi, 1977). Further analysis of these data indicates that the ice algal community found during that cruise is distinct from others that have been described (for example, the bottom epontic community in the land-fast ice in McMurdo Sound, the surface communities off East Antarctica, and the bottom communities in Arctic pack ice). The surface communities off East Antarctica (Meguro, 1962) depend on a thick snow cover, in excess of one-fourth the ice thickness. These snow loads depress the ice surface to below sea level, causing seawater to infiltrate the bottom few centimeters of snow. Increased light levels and high nutrient concentrations in the snow-seawater mixture enable the growth of ice algae (Meguro, 1962). Bunt (1963) has described extensively the bottom epontic community formation which appears to occur primarily in fast ice regions and depends for its existence on a relatively low level of mechanical disturbance at the bottom ice surface. In moving pack ice, shear between the ice and water probably would be strong enough to disturb this fragile layer. 70
The other bottom ice communities, observed in the Arctic, depend on thermal processes leading to brine migration to the bottom of the sea ice. Coupled with summer light levels, algae growth is enhanced in this nutrient-rich region at the bottom (Meguro et al., 1967). Unlike these other communities, the Weddell pack ice algae is dominantly an interior one, existing not at the surface or bottom but at mid-depth (.65 to 2.15 meters) within the ice. The formation of this community is dependent on the unique thermal and physical setting for Weddell sea pack ice. Brine drainage processes are initiated by summer warming, but are not carried through to completion as in the Arctic. This process causes a redistribution of salinity, maximizing in the middepth regions of the ice and apparently leading to algae production because of the relatively higher nutrient levels at these mid-depths. A qualitative model indicating the relationship between the thermally induced brine migration and subsequent algae growth is given in the figure. In assessing how this primary production contributes to the food chain, we examine how the algae enters the ocean through pack ice breakup processes. The disintegration of pack ice in the Weddell region seems to be dominated by mechanical processes (divergence and wave action) occurring primarily at the ice edge region. "Ice edge region" refers to the pack ice-open ocean boundary and is different from "the edges of the ice," [implying the edges of particular ice floes]. The broken-up ice mixes with the sun-warmed ocean water until completely melted. These processes affect the time and location of release of ice-associated algae into the pelagic system and differ considerably from the thermal disintegration and consequent pulse input of ice algae to the water column observed in the Arctic (Homer, 1976). In the table we use satellite-derived estimates of the ice extent together with the field measurements of sea ice chlorophyll a to estimate the organic carbon input to the water column from the annual ice retreat in the Weddell Sea. As seen in the table, organic material is supplied to the water column over a prolonged period of roughly half the year. Although these are not high values for carbon and chlorophyll typically found in the Antarctic oceanic region, the constant supply of biomass may provide supplemental nutrition to the pelagic grazers. This algae may also be the major contributor for areas where the water column in situ Chlorophyll content and particulate organic carbon (POC) contributions to the water column by retreating sea ice (Weddell Sea, south of 55°S., between 60°W. and 30°E.). Mass of POC input to Sea ice chlorophyll a water column Date extent (million in sea ice' from retreating sq km) (million kg) ice (million kg)a 15 Sept 15 Oct 15 Nov 15 Dec 15Jan 15 Feb 15 Mar 15 Apr
7.75 7.44 825b 7.92
7.15 5.85 2.25 1.25 1.15 1.65
6.86 5.62 2.16 1.20 1.10 1.58
46 128 36 -
asumes area shown in column 2 is 80 percent ice covered and 20 percent open ocean at any given time. bMaximum area of sea ice coverage.
ANTARCTIC JOURNAL
Ackley, S. F., S. Taguchi, and K. R Buck. In press. Primary productivity in the sea ice of the Weddell Region. US. Army Cold Regions Research and Engineering Laboratory. Research Report. Hanover, New Hampshire. Bunt, J . S. 1963. Diatoms of Antarctic sea ice as agents of primary production. Nature, 199: 1255-1257. El-Sayed, S. Z., and S. Taguchi. 1977. Phyto plankton studies in the water column and in the pack ice of the Weddell Sea. Antarctic Journal of the US., 12: 35-37. Homer, R. A. 1976. Sea ice organisms. In: Oceanography and Marine Biology Annual Review, 14 (H. Barnes, ed.). pp. 167-182. Meguro, H. 1962. Plankton ice in the Antarctic Ocean. Antarctic Record, 14: 1192-1199. Meguro, H., K. Ito, and H. Fukushima. 1967. Ice flora (bottom type). A mechanism of primary production in polar seas and the growth of diatoms in sea ice. Arctic, 20: 114-133.
standing crop is low, such as the northern edges of the Weddeli Sea (El-Sayed and Taguchi, 1977) where pack ice breakup would also be relatively high. More details of the work reported here are in press (Ackley, et al). This work was supported by National Science Foundation grants DPP 76-15351 to the U.S. Army Cold Regions Research and Engineering Laboratory and DPP 76-80738 to Texas A&M University.
References
Ac!kiey, S. F. 1977. Sea ice studies in the Weddell Sea region aboard USCGC Burton Island. AntarcticJournal of the US., 11: 172-174.
Sept WINTER
Oct
SPRING
Nov
Dec
1-v SUMMER
Jan
SAL _1.8vC
Feb
Mar WINTER
FALL
SAL -1.8'C Snow Level
Level
Level
Sea Live
-1.B'C
-1.8'C
Winter's Growth of Sea Ice p - F(T,S)
Warming Causes: (1) Increase in porosity
Algae Growth proceeds because of combination
Growth Stops with decrease in light and temperature.
in upper layers (2) Increase in salinity in middle portion
of:
Algae layer taken to new relative depth in floe
from brine rejection (3) Rising Out of water because of decreased density and increased porosity. Rising accelerates steps 1 and 2 by feedback
(1) High nutrients from Brine rejection
by snow loading and sea ice growth in 2nd winter
(2) High light levels relatively near surface in the ice floe (3) Algae spores present but growth cannot
season.
proceed until all other conditions satisfied (4) Sea Ice provides structural medium for colonizing algees to
A model for Ice algae growth In antarctic sea ice.
grow
Physical oceanography Tritium and carbon-14 distributions in McMurdo Sound, 1977 T. L. JACKSON and T. W. LNIcK Department of Chemistry
October 1978
R. L. MICHELandP. M. WILLIAMS Scripps Institution of Oceanography University of California San Diego, California 92093
During the 1977-1978 season at McMurdo Sound, tritium samples were collected with a 5-liter niskin bottle and
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