PFysical-chemical oceanography of Arthur Harbor, Anvers Island

may ecplain some of the widely separated frontal positicris reported. Thi research was supported partially by National Sciene Foundation grant GA-41076. Reference

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Gordoi, A. L., H. W. Taylor, and D. T. Georgi. 1974. Antarctic oceanographic zonation. Montreal, McGill Universy, SCOR/SCAR Polar Oceans Conference (May 5 to 1).

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PFysical-chemical oceanography of Arthur Harbor, Anvers Island

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Figure 2. WILLIAM N. KREBS

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Department of Geology University of California Davis, California 95616

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This article reports the preliminary results of physial-chemical oceanographic determinations made in Aihur Harbor, Anvers Island, Antarctic Peninsula, from December 1971 to January 1974 (Krebs, 1973). It represents the combined efforts of the author and Drs. Thomas A. Kauffman and Albert P. Giannini. Some aspects of this study are being continued by the 1974 team at Palmer Station. Support for this research was provided by National Science Foundation grant Gv-3 1162 to the University of California, Davis. Because of the great importance of radiant energy to biological and physical-chemical systems, solar radiation measurements were taken every day at local apparent noon with a portable direct reading pyranometer. Maximum incident solar radiation was attained in January 1973 and the minimum occurred in June 1972 (fig. 1). The slight decline in December 1972 is attributable to a greater number of overcast

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days compared to November 1972. The high albedo from August to November is due to the presence of sea ice. Air temperatures (fig. 2) were recorded from maximum-minimum thermometers that were read every noon. The air temperature graph indicates an austral summer beginning in October and lasting until March or April. The colder winter of 1973 compared to 1972 is reflected in a greater degree of fast ice formation. In 1972, fast ice existed in August, while in 1973 it persisted from early June to midOctober. These yearly differences in sea ice affect both primary and secondary productivity because the sea ice serves as an important habitat for phytoplankton and some marine animals (Andriashev, 1968; Allen, 1971; Krebs, 1973; Lipps et al., 1974). Vertical seawater temperature to depths of 55 meters (175 feet) during the austral summer is more stratified than during, the winter (fig. 3). From January to April 1972, water temperature was coldest at the surface. Low surface salinities indicate that this is attributable to cooling by glacial runoff and brash ice. In addition, low air temperature sometimes chills the surface layers. With the cessation of runoff in April and a continued decrease in air temperature, 219

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surface seawater density increases and mixing commences, thereby promoting a more uniform distribution of temperature with depth. The formation of sea ice further increases surficial seawater density and thus facilitates continued mixing. During the spring, sea ice melts and runoff begins; this causes stratification and reduction of surface water temperature, despite a general warming of the water column. During very warm, calm days, surface water temperature occasionally becomes unusually high. For example, a high of 4.5°C. was recorded at 3 meters (10 feet) on January 4, 1973. Salinities (fig. 4) show a similar pattern. They are stratified during months of high runoff and are more uniform during the austral winter. Surface salinity increases slightly during the formation of sea ice. Phytoplankton exert an important influence upon seawater chemistry. A record was kept, therefore, of phytoplankton standing crop in Arthur Harbor by means of chlorophyll determinations. Prior to June 1972, chlorophyll content is inferred from cell concentrations. Fig. 5 shows three separate phytoplankton blooms during the austral summer. The middle or summer bloom evidently is the largest.

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This pattern resembles that reported by Hart (1942) for his "northern" region of Antarctica. Oxygen concentration correlates well with phytoplankton standing crop. Fig. 6 shows that oxygen concentration during the winter also is homogeneous with depth, and that stratification occurs during the summer. Phytoplankton standing crop and oxygen concentration are directly proportional except during the 1972 fall bloom when respiration from the high concentration 8.60—

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ANTARCTIC JOURNAL

of z oplankton may interfere by reducing oxygen con entrations (Foxton, 1964; Ealey et al., 1956). Car on dioxide concentration (fig. 7) and pH (fig. 8) also are affected by photosynthetic activity. Although carbon dioxide content in seawater is part of a poorly und rstood and complex system (Home, 1969; Riley et a ., 1971), determinations at Arthur Harbor show that it decreases during blooms. This decrease in carbon dioxide produces a concomitant rise in pH. The ways in which changes in seawater properties affe t the ecology and composition of nearshore antarctic marine phytoplankton and, in general, the marne ecosystem, are under study. References Al1e4i, M. B. 1971. High-latitude phytoplankton. Annual Rview of Ecology and Systematics, 2: 261-276.

Tritium and mercury results from Eltanin cruise 51

Andriashev, A. P. 1968. The problem of life community associated with the antarctic fast ice. In: Symposium on Antarctic Oceanography. Santiago, Chile, 1966. 147-155. Ealey, E. H. M., and R. G. Chittleborough. 1956. Plankton, hydrology and marine fouling at Heard Island. Australian National Antarctic Research Expeditions. Interim Reports, 15: 1-81. Foxton, P. 1964. Seasonal variations in the plankton of antarctic waters. In: Biologie Antarctique. Paris, Hermann. 311-318. Hart, T. J . 1942. Phytoplankton periodicity in antarctic surface waters. In: Discovery Reports, 21: 261-356.

Home, R. A. 1969. Marine Chemistry: The Structure of Water and the Chemistry of the Hydrosphere. New York,

John Wiley. 568 p. Krebs, W. N. 1973. Ecology of antarctic marine diatoms. Antarctic Journal of the U.S., VIII(5): 307-309. Lipps, J . H., and W. N. Krebs. 1974. Planktonic foraminifera associated with antarctic sea ice. Journal of Foraminiferal Research, 4(2): 80-85. Riley, J . P., and R. Chester. 1971. Introduction to Marine Chemistry. New York, Academic Press. 465 p.

(1.17 and 0.47 'ru) and in the upper Ross Sea deep water (250 meters) at station 6 (0.94 TU). These results indicate an input of surface waters into deep

P. M. WILLIAMS

Institute of Marine Resources University of California San Diego, California 92037 R. MICHEL Department of Chemistry University of California San Diego, California 92037 H. WEISS

Naval Undersea Center San Diego, California 92132 Seawater, pack ice, and sediment samples collected on USNS Eltanin cruise 51 (February to March 1972) frcm Port Lyttleton, New Zealand, to McMurdo Station, Antarctica, have been analyzed for their tritium and total mercury contents (sampling stations are shown in the figure). Tritium (Tu; one TU is one tritium atom per 1018 hydrogen atoms) was measured in 24 samples collected from the surface to 2,000 meters at stations 3, 4, 6, and 12. High tritium concentrations found in pack ice (5.63 Tu) and in 14-meter (2.15 Tu) and 125-meter (1.03 TU) water samples at station 12 reflect the introduction of tritium from 1971 precipitation on pack ice and subsequent melting of the pack ice and mixing into the antarctic surface water and the Ross Sea winter water. Relatively high tritium concentrations also were found in South Pacific deep water (2,000 meters) at stations 3 and 4 September-October 1974

Stations sampled for tritium and mercury content of seawater, pack ice, and sediments (USNS Eltann cruise 51).

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