Physical and Chemical Characteristics of Ogac Lake, a Landlocked Fiord on Baffin Island

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Abstract
Ogac Lake is the small (148 ha) landlocked head of a fiord with 3 distinct basins. It receives highest spring tides (maximal range 12 m, as high as 1.2 m above lake level) monthly during the open-water season through a narrow entrance. The predictable inflows displaced about 1/4 of the lake''s volume in 1957. The lake is meromictic, fresh at the surface and 28%o salinity at depth. Some 55 kg/m2 salt lost in surface outflow in summer was more than restored by the tides by the end of 1957. Deep salinities did not change between 1951 and 1962. Vertical attenuation of light is adequately accounted for by chlorophyll alone. The lake is much warmer than the nearby sea. Temperature inversions are caused by cold tidal water and perpetuated by vertical stability. The gross annual heat budget in 1957 was 22,000 cal/cm2, about the same as in the nearby sea, but higher than in a freshwater lake. Heating from below a few m to 30 m can be accounted for by radiation alone. About 20% of radiation reaching the bottom subsequently appeared as heat in the water immediately overlying the bottom, thus implying restricted horizontal transfer. O was absent below 25-32.5 m, which may approximate the compensation level in this and similar lakes. O dif-ferences between basins are partly controlled by morphometry. Distinct oxygen minima in 1957 were associated with temperature minima and caused by concentrations of zooplankton. Vertical distribution of pH parallels that of O. Specific alkalinities seem slightly higher than in normal seawater. Phosphate showed a distinct and stable minimum just above the anoxic layer and was as high as 14.3 [mu]g-at/liter within that layer. Nitrate was relatively low and maximal just above the anoxic layer. Although nutrient levels seemed partly related to morphometry in the 3 basins, no evidence of nutrient enrichment of bottom water was found in late summer. The tides contribute negligible nutrients to the lake. The character of Ogac Lake compared with similar lakes derives from the great tidal amplitude and narrow connection with the sea, as well as from its small size and sheltered setting.

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