COMPARISON OF VERTICAL DISTRIBUTION PATTERNS OF LIVING (STAINED) BENTHIC FORAMINIFERAL ASSEMBLAGES FROM AN ALASKAN MARGIN COLD METHANE SEEP AND THE SURROUNDING SEAFLOOR

In an effort to understand the ecology of deep-sea foraminiferal assemblages at seep and non-seep habitats, living (rose Bengal stained) benthic foraminifera were examined from tube core sediment samples taken by the ROV JASON II from the Aleutian Margin off Unimak Island. Initial comparisons revealed similar vertical distribution patterns of foraminifera (>150µm) between cores taken from a newly discovered cold methane seep (3283 m water depth) and a nearby, non-seep site (3310 m). Agglutinated foraminifera constituted more than 90% of the total foraminiferal assemblage at both sites. Of the agglutinate assemblages at the non-seep site, Reophax had a surface (0-1cm) density maximum and showed density maximum with the top 2 cm at the seep site. Rhabdammina, Recurvoides, and Trochammina had maximum densities at 1.5cm or deeper within the sediment. Relatively little is known about the ecology of deep-sea agglutinated foraminifera, and results from this study provide important information about the ecological preferences of agglutinated species associated with cold methane seeps. Calcareous taxa at these sites also provide ecological insights. Numerous specimens of Cibicides Wuellerstorfi were found attached to pogonophoran tubes associated with the seeps. Of special interest is the occurrence of the calcareous taxon, Elphidium, in the topmost cm at both sites. The presence of this taxon (which is more typically abundant in shallow water), suggests that these deep-water assemblages are influenced by survivors brought in by turbidites. Results from this study will improve our understanding of modern and ancient cold seep ecosystems.