Under Landfast Ice

Abstract

The layer of water under landfast ice has unique oceanographic characteristics, as described in this review of recent assessment information for the central Alaskan Beaufort Sea coast. Water circulation is very slow, usually near the lower threshold of current meters. Barometric storms cause infrequent surges of water. The weak thermohaline-driven circulation is the reverse of that in ice-free estuaries. Watertemperatures are always close to the slowly declining freezing point, and salinity gradually increases to high levels in bays because of flushing times of a month or more. Biological processes during the dark third of the year when there is no photosynthesis are dependent primarily on detritus and stored energy. Detritus is decomposed slowly by bacteria, and consumed by epibenthic invertebrates. Invertebrates and their main predators, fish, both reproduce under the ice cover. Food may limit biological activity in late winter, even in nearshore areas. Spring under-ice primary production totals possibly one-third of annual production with production of epontic algae attached to the bottom surface of the ice equalling only 5% of annual production. During breakup, river floods quickly flush under-ice areas; nearshore salinity drops to zero, and the wintertime thermohaline circulation is reversed. Year-to-year physical variations in the habitat cause the populations of three resident animals to vary up to sevenfold, but there are no regular cycles in abundance. Knowledge of these under-ice characteristics is important for understanding the Beaufort Sea coastal ecosystems, even for the relatively short open-water period.

The ecophysiology of under-ice fauna

“…The microdistribution of these crustaceans in the under-ice habitats varies from species to species (Carey 1985). Individuals have been observed living in brine channels (Cross 1982;Newbury 1983) and partially or fully embedded in the ice (Gulliksen 1984). Green & Steele (1975) reported that Gammaraconrhus loricatus was the only amphipod species associated with ice stalactites and may at times be frozen within them.…”

Brine-induced advection of dissolved aromatic hydrocarbons to Arctic bottom waters

“…Newbury (21) has published an excellent review of similar observations made during studies of nearshore waters in areas of the Alaskan Beaufort Sea Stefasson Sound). He also reviewed the nearshore thermohaline circulation required to generate the observed conditions along the Beaufort Sea coast.…”

Hydraulic based sampling equipment for under-ice fauna

“…and in brine channels in the bottom layers of the ice (Cross 1982;Newbury 1983;Gulliksen 1984). These amphipods may vary in size from about 10 to 6Qmm in total length, with Gammarus wilkirzkii being the largest species in the Arctic.…”