Paleogeographic and paleoclimatic significance of diatoms from middle Pleistocene marine and glaciomarine deposits on Baldwin Peninsula, northwesternAlaska

A newly revised diatom biostratigraphic scheme for the North Pacific Ocean based on studies of the diatom flora of the Cape Blossom and Hotham Inlet F ormations of Baldwin Peninsula, northwestern Alaska provides new informatio n on the paleoceanography of Kotzebue Sound, Alaska, during middle Pleistoc ene time. Sediments exposed along coastal bluffs of Baldwin Peninsula conta in subarctic North Pacific zonal-index species, including extinct Proboscia barboi, Pr: curvirostris, Actinocyclus ochotensis var. fossilis, Thalassio sira nidulus var. nidulus, Th. jousene, Th. gravida vac fossilis, and Steph anopyxis dimorpha, which are correlated with the middle part of the Probosc ia barboi Zone (0.43-0.36 Ma). Based on the distribution of the zonal diato m species and on changes in the paleoecological structure of the diatom ass emblages (e.g., warm- vs, cold-water assemblages), we conclude that the mar ine deposits of the Cape Blossom Formation and lower Baldwin Silt member of the Hotham Inlet Formation formed under relatively warm, high sea-level co nditions associated with the marine oxygen isotope stage (OIS) 11 transgres sion. Glaciomarine sedimentation (middle and upper Baldwin Silt and Selawik Gravel members of the Hotham Met Formation) initiated during relatively wa rm conditions at the end of the stage 11 transgression and continued into s tage 10. High-latitude glacier growth during a global 'interglacial' period was likely facilitated by warm surface waters on flooded continental shelv es and limited regional sea ice cover. The biostratigraphic record at Baldw in Peninsula provides further evidence that high-latitude ice growth is fav ored by increased moisture supply during warm climatic intervals and inhibi ted by arid conditions during full glacial intervals. (C) 1999 Elsevier Sci ence B.V. All rights reserved.