No abstract

No abstract

Core NWR 5 from Northwind Ridge in the westem Arctic Ocean contains a climatic record that extends back for over 1 •11ion years. Dark brown beds with abundant planktonic fomminifers represent interglacial conditions, whereas glacial and transitional conditions are represented by lithologies barren or nearly barren of planktonic foraminifers. We conclude that seven, and possibly all nine, interglacials of the Brunhes magnetic chronozone (the last 780,000 years) are represented in NWR 5. For about the last 800,000 years, the western Arctic Ocean apparently had a permanent, thick ice cover and was unable to support significant populations of planktonic foraminifers except during major interglacials when seasonally open and highproductivity surface waters occurred at least along the basin margins. Our results support previous interpretations that climate variations in the Arctic are in phase with glacial/interglacial cycles observed in other proxy records of the Brunhes. INTRODUCWION The Arctic Ocean is a key component of the Earth's climate system, but the paleoceanographic and paleoclimate record of the Arctic is still poorly •own and controversial. Documenting the late Neogene histo :ry of the Aretic •e• has -been hampered by a lack of suitable marine records. In This paper is not subject to U.S. copyright. Published in 1993 by the American Geophysical Union. Paper number 93PA00146. general, only short piston and gravity cores are available, and most cores from topographic highs in the central and western Arctic recovered sedimentary sections with extremely slow average accumulation rates (about 1 to 2 mm/1000 yr ). Age and environmental interpretations derived from -these cores are complicated by the low resolution of the records. In 1988, the U.S. Coast Guard Icebreaker Polar Star recovered a series of cores from Northwind Ridge, a prominent bathymetric feature extending from the Chukchi Sea continental slope into the Canada Basin of the western Arctic Ocean (Figure 1). Integrated lithostratigraphic, paleomagnetic, and paleontologic analysis of the relatively expanded Pleistocene section recovered in NWR 5 (average accumulation rate >4 rmm/1000 yr ) reveals a more detailed, albeit still condensed, paleoclimate record for the western Arctic Ocean that provides improved information on the features and timing of Arctic Pleistocene paleoceanographic changes over the last 800,000 years. LITHOSTRATIGRAPHY The section recovered in NWR 5 consists of prom•ent •rk brown foraminifer-rich, muddy beds that altemate with gray, olive gray, or tan strata. The distribution of the sand-size fraction (0.•2-2.00 ram), comp•son with published unit des•ptions of Clark et al. [ 1980], which are bas• on T-3 cores from the central Amemsia Basin, and •scussions and examination of b•VR 5 with D. Clark CLlniversity of Wisconsin, private communications, 1992) were used to identify standard Arctic Iithostratigraphic units M through I in NWR 5. A sum.mary of the units is presented below and in

No abstract

No abstract

No abstract

A workshop was held at Pajaro Dunes, Watsonville, CA in January, 1991 as part of the USGS Climate Change Program to organize and coordinate a project to correlate marine and terrestrial paleoclimatic records from the western U.S. and eastern North Pacific Ocean. The focus of the project is to develop detailed, high-resolution paleoclimatic records of the last 130,000 years, with as many climate proxy variables as possible, and a time resolution of 1,000 years or less. The workshop convened a group of experts from the USGS and the academic community (participants are listed in Appendix I) to: prioritize potential sites to obtain long sediment cores in the western U.S. and the eastern North Pacific Ocean, identify the preferred methods and equipment for coring the proposed terrestrial and marine sites. discuss the logistics of sample treatment and archival and development of a database. review and discuss the best stratigraphic correlation and dating techniques to apply to these cores. This report outlines the organization and objectives of the project and summarizes the consensus of the workshop on the above four topics.

Beds of the Glenns Ferry Formation (Pliocene to early Pleistocene) form the Chalk Hills about 23 km (14 mi) west of Nampa, Idaho, near the site of abandoned Froman Ferry on the Snake River. With one noteworthy exception, the beds there contain vertebrate fossils typical of late Blancan (Blancan V; ~2.6 Ma -~1.9 Ma) land mammal age assemblages found elsewhere in the formation. The noteworthy exception is the co-occurrence ofPhenacomys gryci , an immigrant microtine rodent and indicator species for Irvingtonian time (~1.9 Ma -0.9 Ma) in the coterminous United States. Paleomagnetic samples were collected from twelve horizons in an attempt to refine age control by identifying the Olduvai Normal Polarity Subchron (~1.87 Ma -~1.67 Ma) which is associated with the Blancan-Irvingtonian boundary. Sampled horizons were sufficiently close that, if present, an Olduvai zone could reasonably be expected to be identified at two or three of the horizons. Paleomagnetic samples from 11 of the 12 horizons are clearly of stable, reversed paleomagnetic polarity. Although characteristic reversed polarity directions could not be isolated by alternating field demagnetization from samples of the lowest horizon, changes in direction and intensity of magnetization during treatment indicate that they carry weak, but stable components of reversed polarity that are obscured by present field normal polarity overprints. Thus, we interpret all sampled horizons to be of primary reversed polarity, and do not recognize an Olduvai Normal Polarity Subchronozone in the section. If the section spans any part of Olduvai time, the zone is anomalously thin or missing.