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

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 Formations of Baldwin Peninsula, northwestern Alaska provides new information on the paleoceanography of Kotzebue Sound, Alaska, during middle Pleistocene time. Sediments exposed along coastal bluffs of Baldwin Peninsula contain subarctic North Pacific zonal-index species, including extinct Proboscia barboi, Pr. curvirostris, Actinocyclus ochotensis var. fossilis, Thalassiosira nidulus var. nidulus, Th. jouseae, Th. gravida var. fossilis, and Stephanopyxis dimorpha, which are correlated with the middle part of the Proboscia barboi Zone (0.43–0.36 Ma). Based on the distribution of the zonal diatom species and on changes in the paleoecological structure of the diatom assemblages (e.g., warm- vs. cold-water assemblages), we conclude that the marine deposits of the Cape Blossom Formation and lower Baldwin Silt member of the Hotham Inlet Formation formed under relatively warm, high sea-level conditions associated with the marine oxygen isotope stage (OIS) 11 transgression. Glaciomarine sedimentation (middle and upper Baldwin Silt and Selawik Gravel members of the Hotham Inlet Formation) initiated during relatively warm conditions at the end of the stage 11 transgression and continued into stage 10. High-latitude glacier growth during a global `interglacialʹ period was likely facilitated by warm surface waters on flooded continental shelves and limited regional sea ice cover. The biostratigraphic record at Baldwin Peninsula provides further evidence that high-latitude ice growth is favored by increased moisture supply during warm climatic intervals and inhibited by arid conditions during full glacial intervals.