New perspectives on Beringian Quaternary paleogeography, stratigraphy, and glacial history

Aspects of the paleogeography, stratigraphy, and glacial history of Beringia have been greatly revised over the past 15}20 yr. Access to North East Russia, in particular, has provided the opportunity to evaluate the Beringia landscape as a contiguous subcontinent during the Quaternary. For the "rst time, new research has made clearer the connection between tectonic forces and the submergence of the Bering Strait during the middle Pliocene. Revisions in the regional stratigraphy of glacial and interglacial deposits in northwest Alaska and northeast Russia provide a new foundation for assessing the causes for di!erences in glacial ice extent through time. The consensus of all "eld workers veri"es that glacial ice throughout most of Beringia was of very limited extent during the last glacial maximum. The onset of regional glaciation during the waning stages of the last interglaciation is clearly out of phase with glaciation at lower latitudes. Despite the lack of much glacial activity during the early Holocene, Alaska contains a rich record of late Holocene glacial response to Neoglacial cooling. Changes in the Holocene environment of Beringia likely had a profound a!ect on early inhabitants. The curiosity-driven vision and spirit of both David Hopkins and the late Troy Pewe have had a profound in#uence on Arctic paleoenvironmental research. ( 2000 Elsevier Science Ltd. All rights reserved. Quaternary science has always progressed incrementally as new research, techniques, and proxies emerge as standard tools for understanding environmental change. Such incremental progress also requires periodic review and synthesis in order to redirect new questions being asked in Earth system science. Throughout his career David Hopkins has provided the impetus for creative thought on the Quaternary history of Beringia and has actively participated in continually questioning our collective knowledge of marine and terrestrial archives of climate change. As a subcontinent the geography of Beringia has been repeatedly bifurcated by periodic #ooding of the broad Chukchi/Bering continental shelf. The notion that both Alaska and northeast Russia possessed comparable Quaternary histories propelled Hopkins' (cf. Hopkins et al., 1965) research e!orts as he sought opportunities for collaboration with Russian scientists through the 1960s, 1970s and 1980s. The Beringian workshop held in September of 1997 provided the most recent forum for scientists from many countries to share their knowledge of the Great Land Bridge. As a complement to the paleoecological research summary of Elias (2001), here is summarized a perspective on the remaining collection of 15 papers (Fig. 1) along the themes of paleogeography, stratigraphy, and glacial/interglacial climate change. In detail these papers address several broad research issues including: (1) the biogeography and timing of the "rst submergence of Bering Strait; (2) long-term glacial/interglacial paleoclimate, especially the chronology and glacial ice extent of the Last Glacial Maximum (LGM); (3) the nature and stratigraphy of the Last Interglacial; (4) growing evidence for the so-called out-of-phase glaciations in Beringia; (5) the signi"cance and extent of loess and `yedomaa sediment archives; and (6) Lateglacial/Holocene paleogeography and climate. The purpose of this paper is to summarize the new "ndings presented at the 1997 workshop in view of both past research and new paradigms in our global understanding of the ocean, atmosphere, geosphere system. 1. First submergence of Bering Strait The submergence of the Bering Strait has for many years been placed in the context of oceanic gateways 0277-3791/01/$ see front matter ( 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 7 3 7 9 1 ( 0 0 ) 0 0 1 3 4 7 Fig. 1. Approximate location across Beringia of stratigraphic and paleogeographic studies documented in this volume. (A) Marincovich, Jr., L., and Gladenkov, A.Y., 2001; (B) Kaufman, D.S., Manley, W.F., Forman, S.L., and Layer, P.W., 2001; (C) Manley, W.F., Kaufman D.S., and Briner: J.P., 2001; (D) Hamilton, T.D., 2001; (E) Heiser, P.A., and Roush, J.J., 2001; (F) Glushkova, O.Y., 2001; (G) Brigham-Grette, J., Hopkins, D.M., Benson, S.L., Heiser, P.A., Ivanov, V.F., Basilyan, A., and Pushkar, V., 2001; (H) Felzer, B., 2001; (I) Calkin, P.E., Wiles, G.C., Gregory, C., and Barclay, D.J., 2001; (J) Khim, B.K., Krantz, D.E., and Brigham-Grette, J., 2001; (K) Berger, G.W., and PeH weH , T.L., 2001; (L) BegeH t, J.E., 2001; (M) Jordan, J.W., 2001; (N) Mason, O.K., Bowers, P.M., Hopkins, D.M., 2001; Guthrie, R.D., 2001, not listed as it pertains to all of Beringia. leading to full communication between the North Paci"c and North Atlantic via the Arctic Ocean (Durham and MacNeil, 1967; Einarsson et al., 1967; Vermeij, 1991). The "rst strong temporal evidence for submergence came not from Beringia, but rather from Iceland with the poststrait arrival of boreal Paci"c mollusks in the basal Serripes Zone of the Tjornes sequence (Einarsson et al., 1967). Dated by newly emerging paleomagnetic techniques and K/Ar dating of interbedded basalt #ows, submergence of the Bering Strait was placed at slightly more than ca. 3.3 My and supported by the arrival of Atlantic endemic mollusks, especially Astarte in deposits of the Beringian transgression as "rst de"ned by Hopkins, 1959, 1967b; Hopkins et al., 1965. Kennett (1982) went so far as to implicate the nearly simultaneous emergence of the Isthmus of Panama and submergence of the Bering Strait as critical elements in Pliocene cooling of the Northern Hemisphere. This view persisted for more than a decade until Gladenkov et al. (1991) presented new evidence from Karaginsky Island o! the Kamchatka Peninsula for the arrival of Atlantic mollusk endemics as early as 4.0}4.2 My, based on diatom biostratigraphy and "ssion-track ages. The discovery of a similar fauna in a bore hole o!shore of Nome (Kaufman, 1992) concurred with placing the initial submergence earlier in time than the Beringian I transgression at Nome and earlier than the correlative Colvillian transgression on the Alaskan north slope (BrighamGrette and Carter, 1992). New work by Marincovich and Gladenkov (1999, 2001), however, outlines new evidence for initial submergence as early as 4.8}5.5 My based on the occurrence of Arctic}Atlantic Astarte in the Bear Mountain Formation on the Alaskan Peninsula. The age of these deposits is founded on diatom biostratigraphic zones and is the focus on ongoing work. Moreover, new geochronologic evidence 16 J. Brigham-Grette / Quaternary Science Reviews 20 (2001) 15}24