Steve L. Forman

Freshwater and Atlantic water inflows to the deep northern Barents and Kara seas since ca 13 14C ka:: foraminifera and stable isotopes

Foraminiferal stable isotopes and assemblages from Franz Victoria and St. Anna troughs provide a valuable record of freshwater and Atlantic Water flows to the northern Barents and Kara seas from deglaciation to present. The d 18 O and d 13 C of planktonic Neogloboquadrina pachyderma (s) and benthic Elphidium excavatum were up to1.4 % lower than present at ca 13, 11.5, and 10 14 C ka (global sea-level corrected), mostly reflecting substantial freshwater inputs coincident with glacial–marine sediment deposition. Cassidulina teretis exceeded 40% of benthic foraminifera ca 13 and 10 14 C ka, indicating subsurface penetrations of Atlantic Water. The transition to postglacial marine conditions is marked by a � 1% rise in foraminiferal d 18 O and a sharp fall in % C. teretis soon after 10 14 C ka. These changes imply reduced inputs of freshwater and Atlantic Water. Subsequent isotopic and foraminiferal assemblage variations reflect changing Atlantic Water conditions ‘‘upstream’’ in the Nordic Seas and shifts between the warm Fram Strait and cold Barents Sea branches of Atlantic Water. We hypothesize that glacial-isostatically induced deepening by up to � 150 m influenced Atlantic Water inflows to the northern Barents Sea during deglaciation and the Holocene. Thus, effects of isostatic recovery have to be factored into paleoceanographic reconstructions. # 2001 Elsevier Science Ltd. All rights reserved.

Environmental changes on Yugorski Peninsula, Kara Sea, Russia, during the last 12,800 radiocarbon years

Abstract New pollen and radiocarbon data from an 8.6-m coastal section, Cape Shpindler (69°43′N; 62°48′E), Yugorski Peninsula, document the latest Pleistocene and Holocene environmental history of this low Arctic region. Twelve AMS 14 C dates indicate that the deposits accumulated since about 13,000 until 2000 radiocarbon years BP. A thermokarst lake formed ca. 13,000–12,800 years BP, when scarce arctic tundra vegetation dominated the area. By 12,500 years BP, a shallow lake existed at the site, and Arctic tundra with Poaceae, Cyperaceae, Salix , Saxifraga , and Artemisia dominated nearby vegetation. Climate was colder than today. Betula nana became dominant during the Early Preboreal period about 9500 years BP, responding to a warm event, which was one of the warmest during the Holocene. Decline in B. nana and Salix after 9500 years BP reflects a brief event of Preboreal cooling. A subsequent increase in Betula and Alnus fruticosa pollen percentages reflects amelioration of environmental conditions at the end of Preboreal period (ca. 9300 years BP). A decline in arboreal taxa later, with a dramatic increase in herb taxa, reflects a short cold event at about 9200 years BP. The pollen data reflect a northward movement of tree birch, peaking at the middle Boreal period, around 8500 years BP. Open Betula forest existed on the Kara Sea coast of the Yugorski Peninsula during the Atlantic period (8000–4500 years BP), indicating that climate was significantly warmer than today. Deteriorating climate around the Atlantic–Subboreal boundary (ca. 4500 years BP) is recorded by a decline in Betula percentages. Sedimentation slowed at the site, and processes of denudation and/or soil formation started at the beginning of the Subatlantic period, when vegetation cover on Yugorski Peninsula shifted to near-modern assemblages.