The Annual Oceanographic Cycle at Igloolik in the Canadian Arctic. 1. The Zooplankton and Physical and Chemical Observations

Abstract

Materials used were collected September 1955 to September 1956 near Igloolik, northwest Foxe Basin, in the Canadian arctic. A single station, about one mile from shore and 52 m deep, was occupied 27 times during the year. It is in a region of net flow of arctic water from Fury and Hecla Strait, whose strong current probably brings ever-changing hydrographic conditions and plankton populations to the station area. Sea ice formed in early November, and had thickened to about 152 cm by early May. Melting then began and continued until the station was free of fast ice soon after mid-July. Water temperatures varied only 3.55 °C at all depths during the year, and only 0.07° from November until May. The coldest record was −1.75° at 50 m in April and May, the warmest 1.80° at the surface in early September. Salinities varied from a maximum of 32.59‰ in early May to less than 1.68‰ at the surface in mid-July. A thin layer of brackish water, probably not exceeding 2 m in depth, was developed at the surface during the ice-melting period from late June until early August. Dissolved oxygen content varied from 9.52 ml/1 in early July to 4.08 ml/l in early September. The maximum saturation recorded was 110.3% at 10 m on July 15. Dissolved inorganic phosphate rose from near zero in February to a maximum of 1.5 μg-at/l in mid-June, then declined until autumn.Zooplankton volume (from the coarse net) was greatest in late September (4.85 ml per 50-m haul), least in mid-April (0.15 ml). Among identifiable material, copepods were volumetically the largest group. Twenty-eight species were identified, the most numerous forms being copepods (Pseudocalanus minutus, Calanus finmarchicus, C. hyperboreus, Oithona similis), chaetognaths (Sagitta elegans), cirriped larvae, medusae (Halitholus cirratus) and larvaceans (Fritillaria borealis). Several of the more abundant species provide life-history information. All the plankton species had previously been collected in the arctic, and all are circumpolar (one possible exception).Propagation times of primarily herbivorous plankters coincide with the abundance of their phytoplankton food, and the numerical cycle of these individuals during the year shows a restricted period of maximum numbers during the time of reproduction (summer) followed by gradual decline until late winter. In contrast, the primarily carnivorous plankters show relatively slight numerical variation throughout the year, and no concentrated period of reproduction. These species reproduce at various times of the year, many of them during winter. A rough estimate of the Igloolik yearly mean standing crop of zooplankton (without correction for straining efficiency of the No. 6xxx net) is 0.10 ml/m3 or 5.2 ml/m2 of surface area; the maximum observed was 0.50 ml/m3. Another arctic coastal locality, in Greenland, had similar figures; coastal boreal stations have mean crops 4 to 8 times as great (volume basis) or 2 to 9 times as great (surface area basis).