A LONG RECORD OF FORAMINIFERA HELPS RESOLVE QUATERNARY WESTERN ARCTIC STRATIGRAPHY

Foraminifers found in sediment cores from the Northwind Ridge, north of Alaska, yield valuable information regarding the Quaternary history of water inputs and ice cover in the western Arctic Ocean. One core, taken from the northern end of the Northwind Ridge is unique in that formainifera and other calcareous microfossils are preserved beyond estimated Marine Isotope State (MIS) 11, where other Arctic records are virtually barren of biogenic calcite. This record is estimated to extend to the Mid-Pleistocene Transition (MPT), a time of global deep-ocean faunal turnover linked to a shift in global glaciation cyclicity and intensity culminating at MIS 16. Here we present initial stratigraphic results based on benthic and planktonic foraminifera population counts in Northwind Ridge cores. Benthic assemblages below estimated MIS 16 include extinct species and foraminifera that are rare or absent from other Quaternary Arctic records. Notably, the abundance of Epistominella exigua and Eponides weddelensis indicates persistent seasonal phytodetrital pulses, which can only occur in the absence of perennial ice cover near the sea-ice margin. On the other hand, foraminiferal fauna characteristic of the modern, perennially ice covered Arctic Ocean appear above the estimated MIS16 transition. A comprehensive examination of the foraminiferal assemblages in this record combined with other Northwind Ridge records, which are stratigraphically shorter but of higher resolution, will help reconstruct sea-ice and hydrographic conditions in the western Arctic Ocean as well as the history of arctic North American glaciations.