ABSTRACT: Physical and biological zonation of intertidal flats at Frobisher Bay, N.W.T.

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Abstract

The interaction of biological and physical processes has produced distinct morphological and biological zonation across the intertidal flats at Frobisher Bay, N.W.T. Tidal, ice and wave action appear to be the three dominant processes acting upon the intertidal flats. Tides are semi-diurnal with a mean tidal height of 7.8 m ALLT (above lowest, low tide) and large tides up to 11.6 m ALLT. Exposure indices generated from tidal data reveal two critical heights at 5 and 7.5 m ALLT where the frequency and duration of exposure varies abruptly. Both ebb and flood dominant bedforms are evident. Ebb conditions generate the highest instantaneous velocities over the tidal flats, but average flood tide velocities are higher. Ice action during freezeup and breakup removes and transports sediment, boulders and fauna across the flats, thereby disrupting tidal and wave generated zonation. Sedimentological and morphological characteristics found alongtransects across the tidal flats from high to low tide levels indicate a six-fold zonation based on sediment and boulder distribution, bedforms, drainage patterns and tidal height. The six zones include the upper flat located above 5 m ALLT which is subdivided into beach and finer flat zones. The middle flats area includes three zones: the bouldery flat, very bouldery flat, and boulder ridges, while the lower flat is one unit of graded flat. Evidence from maps and air photographs suggests this classification also applies to other arctic areas having intertidal flats. Floral and faunal communities correspond to the critical tidal heights noted above, so that three biological communities are recognized

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