LAUSR

Two species of the bivalve family Vesicomyidae have recently been sampled in marine sediment cores at a cold methane seepage site on Vestnesa Ridge, located in the eastern Fram Strait at 79°N. The specimens were dated to between 16,400 and 14,800 calibrated YBP and are the northernmost known representatives of the family. Archivesica arctica n. sp., a comparatively small species within the genus, is described for the first time. Isorropodon nyeggaensis has previously been known solely from the area of the type locality on the Norwegian continental margin at 64°N. Both species were, as typical for vesicomyids, living in the sulphiderich reducing habitats occurring at cold seeps. Both the specimens of A. arctica from the Vestnesa Ridge and the specimens reported previously from the Gakkel Ridge north of Russia occurred exclusively in sediments dated to a cold event during the deglaciation named Heinrich event H1, c. 18,000–15,000 YBP. Despite great efforts, sampling of living specimens in modern active methane seeps in the Arctic has not been successful. It appears that not only the availability of hydrogen sulphide, but also the increased bottom-water temperatures, characterizing H1 in the Arctic, restricted the occurrence of vesicomyids to this short time interval.