A RAPIDLY DEPOSITED PENNATE DIATOM OOZE IN UPPER MIOCENE LOWER PLIOCENE SEDIMENT BENEATH THE NORTH PACIFIC POLAR FRONT

Rapidly deposited Thalassionema-Thalassiothrix pennate diatom oozes pr eviously have been described in Upper Miocene-Lower Pliocene sediment beneath the frontal boundary of the eastern equatorial Pacific. Here w e document a new occurrence of Thalassionema-Thalassiothrix ooze in Up per Miocene-Lower Pliocene sediment beneath the frontal boundary of th e subarctic North Pacific. The ooze is a 6 m interval of siliceous sed iment at Ocean Drilling Program (ODP) sites 885/886 that was rapidly d eposited between approximately 5.0 and 5.9 Ma. Bulk sediment in this i nterval may contain greater than 85% pennate diatom tests. There are a lso abundant laminae and pockets that are composed entirely of Thalass ionema and Thalassiothrix diatoms. The presence of a rapidly deposited ooze dominated by pennate diatoms indicates unusual past conditions i n the overlying surface waters. Time coincident deposition of such ooz es at two distinct frontal boundary locations of the Pacific suggests that the unusual surface water conditions were causally linked to larg e-scale oceanographic change. This same oceanographic change most like ly involved (1) addition of nutrients to the ocean, or (2) redistribut ion of nutrients within the ocean. The occurrence and origin of pennat e diatom oozes may be a key component to an integrative understanding of late Neogene paleoceanography and biogeochemical cycling.