Evidence for an early opening of the Bering Strait

Abstract

The above palaeo¯ux calculations suggest that water-column euxinia could have been achieved even when continued circulation supplied oxygen to deep waters. The trace-metal budget for the studied Pliocene sapropels strongly favours continued circulation during deposition, as this would have provided an extra input of trace metals, required to account for the observed amounts of trace metals in the sapropels. For example, the total amount of nickel sequestered in sapropel i-282 (average of sites 964, 967 and 969), assuming 80% coverage, is 8 3 10 13 g. The water column in a fully stagnant eastern Mediterranean, however, contains only ,2 3 10 12 g Ni (,3%) 13 , and rivers, assuming global average river composition and a present-day discharge, can supply only ,8 3 10 12 g Ni (that is, about 10%) during sapropel formation. Unfortunately, exact river discharges of trace metals during sapropel formation are unknown. A ten-times increase in river water discharge during sapropel formation, however, is highly unrealistic 2,3 . Consequently, it is unlikely that Ni discharge increased to such an extent. Budgets for other trace metals in sapropel i-282 and i-292 yield comparable results 13 . It therefore seems that stagnation of the water column was not as important as generally believed 2,3 . M . MethodsSediment samples (0.5±1 cm resolution) were freeze-dried and ground. Organic-carbon contents (C org ) were determined with an NCS-analyser after carbonate removal with 1M HCl (ref. 13). Sediments were dissolved in HClO 4 ±HNO 3 ±HF; dried residues were dissolved in 1M HCl for analysis with inductively coupled plasma atomic emission spectroscopy (Mo, Ni, V, Ba), Zeeman atomic absorption spectroscopy (Cd), and¯ow-injection analysis system (Se) 13 . Pyritic sulphur (S pyr ) was extracted by Cr(II) reduction 16 . Evolved sulphide was trapped in 1M NaOH and measured polarographically, or trapped as Ag 2 S and measured for sulphur stable-isotope composition (d 34 S pyr ) by combustion isotope ratio monitoring mass spectrometry relative to the V-CDT standard 16 : R 34 S= 32 S, d 34 S pyr ½ 1; 000 3 R pyr =R VÀCDT 2 1. Organic compounds were extracted with methanol/dichloromethane. Elemental sulphur was removed with activated Cu. Apolar fractions were isolated on activated Al 2 O 3 , and analysed by gas chromatography and gas chromatography/ mass spectrometry 30 .

The emergence of modern sea ice cover in the Arctic Ocean

“…37). At this time, the Arctic Ocean was partly isolated, with restricted AAG through-flow 21 , and the Bering Strait still in the initial opening phase [38][39][40][41] . The prevalence of an estuarine circulation in the Arctic Ocean 42,43 , together with a high continental mean annual temperature (MAT) would have restricted the occurrence of sea ice in the Arctic interior.…”

“…Early Pliocene vegetation is characterized by taiga forests with dominant Picea and Pinus 36 . Restricted deep/shallow water exchange through Atlantic-Arctic gateway (HR, Hovgaard Ridge) 21 and Bering Strait (BS) [38][39][40][41] . (Phase 2) Arctic sea ice expanded to its modern summer limits for the first time after B4 Ma.…”

Disentangling the roles of late Miocene palaeogeography and vegetation – Implications for climate sensitivity

“…The geological record provides evidence for an palaeogeographic configuration during the late Miocene that was distinctly different to today including an open Panama Gateway (Duque-Caro, 1990;Keigwin, 1982), an unrestricted Indonesian Seaway (Cane and Molnar, 2001;Edwards, 1975;Kennett et al, 1985;van Andel et al, 1975), a closed Bering Strait (Gladenkov et al, 2002;Marincovich Jr and Gladenkov, 2001;Marincovich and Gladenkov, 1999). On land the palaeorecord suggests major uplift of the Himalayas (Fang et al, 2005;Harrison et al, 1992;Molnar et al, 1993;Rowley and Currie, 2006), the Andes (Garzione et al, 2008;Gregory-Wodzicki, 2002), the North American Rockies (Morgan and Swanberg, 1985), the East African Plateaus (Saggerson and Baker, 1965;Yemane et al, 1985), and the Alps (Kuhlemann, 2007;Spiegel et al, 2001) during the late Miocene.…”

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

“…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 andGladenkov (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.…”

“…The age of these deposits is founded on diatom biostratigraphic zones and is the focus on ongoing work. Moreover, new geochronologic evidence from the Karaginsky Island sequences suggests submergence possibly as early as 5.0}7.0 My (Marincovich and Gladenkov, 2001).…”