IODP Expedition 323—Pliocene and Pleistocene Paleoceanographic Changes in the Bering Sea

Abstract

High-resolution paleoceanography of the Plio-Pleistocene is important in understanding climate forcing mechanisms and the associated environmental changes. This is particularly true in high-latitude marginal seas such as the Bering Sea, which has been very sensitive to changes in global climate during interglacial and glacial or Milankovitch time scales. This is due to significant changes in water circulation, land-ocean interaction, and sea-ice formation. With the aim to reveal the climate and oceanographic history of the Bering Sea over the past 5 Ma, Integrated Ocean Drilling Program (IODP) Expedition 323 cored a total of 5741 meters of sediment (97.4% recovery) at seven sites covering three different areas: Umnak Plateau, Bowers Ridge, and the Bering slope region. Four deep holes range from 600 m to 745 m spanning in age from 1.9 Ma to 5 Ma. The water depths (819 m to 3173 m) allow characterization of past vertical water mass distribution such as the oxygen minimum zone (OMZ). The results highlight three key points. (1) The first is an understanding of long-term evolution of surface-water mass distribution during the past 5 Ma including past sea-ice distribution and warm and less eutrophic subarctic Pacific water mass entry into the Bering Sea. (2) We characterized relatively stagnant intermediate water mass distribution imprinted as laminated sediment intervals that have been ubiquitously encountered. Today, the OMZ impinges upon the sediments at ~700-1600 m water depths. In the past, the OMZ appears to have occurred mainly during interglacial periods. Changes in low oxygen-tolerant benthic foraminiferal faunas clearly concur with this observation. (3) We also characterized significant changes between glacial episode of terrigenous sedimentary supply and interglacial episode of diatom flux.

Clay mineral stratigraphy during the last 2.4Ma at IODP Exp. 323 Site U1343 in the Bering Sea

“…Oxygen isotopes were measured at~0.6 m intervals (~2 kyr resolution) and 4 m intervals (~10 kyr resolution) for intervals above and below 365 m CCSF, respectively. The age model is consistent with biostratigraphic data and paleomagnetic isochron ages reported in Takahashi et al (2011). The sample interval of the upper (0-170 m CCSF) part corresponds to 0-600 ka, and the lower part (365-780 m CCSF) to 1250-2400 ka.…”

“…Triangles represent oxygen stratigraphic control points (adopted fromAsahi et al, 2014). Closed circles and squares represent biostratigraphic datums and paleomagnetic isochron ages, respectively, as reported inTakahashi et al (2011). LO: last occurrence and LCO: last common occurrence.…”

Repeated pulses of vertical methane flux recorded in glacial sediments from the southeast Bering Sea

“…The Bering Sea is a subpolar marginal basin with very productive surface waters and high delivery of organic carbon to sediments, especially along the Bering Slope [ Springer et al , 1996]. Evidence for biogenic sedimentary methane in the Bering Sea was first noted in the early days of ocean drilling [ Claypool et al , 1973; Scholl et al , 1973], and more recently, gassy sediments and shallow sulfate‐methane transition zones (6–10 mbsf) were observed during coring of the Umnak Plateau and Bering Slope regions during Leg 323 of the Integrated Ocean Drilling Program [ Takahashi et al , 2011].…”

The connection between natural gas hydrate and bottom‐simulating reflectors

“…Majumdar,majumdar.19@osu such as in the Nankai Trough [Tsuji et al, 2009] and the Bering Sea in the northern Pacific Ocean [Takahashi et al, 2011]. Majumdar,majumdar.19@osu such as in the Nankai Trough [Tsuji et al, 2009] and the Bering Sea in the northern Pacific Ocean [Takahashi et al, 2011].…”