Sea-bird affinities for ocean and ice boundaries in the Antarctic

Abstract

More sea birds were observed near the Ross Sea continental slope and near ice than over the adjacent continental shelf, deep ocean and ice-free regions. Bird concentrations near the continental margin occurred above the subsurface Antarctic Slope Front, defined by increased horizontal gradients in water temperature, salinity, density, chemistry, color and transparency. A convergence between easterly and westerly currents near the continental shelf break may accumulate plankton and other positively buoyant material from oceanic gyres to the north and south. Some sea-bird prey are believed to have life cycles adapted to the continental margin regime of upwelling deep water and sinking shelf water. Order-of-magnitude changes in bird abundance over relatively small distances indicate the importance of hydrographic and cryographic features to sea-bird distributions in the Southern Ocean.