Authigenic Nd isotope record of North Pacific Intermediate Water formation and boundary exchange on the Bering Slope

作者：Jang Kwangchul; Huh Youngsook; Han Yeongcheol

来源：Quaternary Science Reviews, 2017, 156: 150-163.

DOI：10.1016/j.quascirev.2016.11.032

• Neodymium
• NPIW
• Bering Sea
• Authigenic
• Brine
• Ventilation
• Seesaw

The Bering Sea is a potential location for the formation of the North Pacific Intermediate Water (NPIW), which drives the global ocean circulation as a counterpart to the North Atlantic Deep Water (NADW). To evaluate the NPIW-NADW seesaw hypothesis, we reconstructed the long-term variation of the bottom water Nd isotopic composition at site U1345 on the Bering Slope by extracting authigenic Fe-Mn oxyhydroxide from bulk sediments. We examined six different extractions in order to ensure that authentic seawater composition is recovered. For Bering Slope sediments whose typical carbonate content is less than 5% (average 2%), the most reliable results are obtained if the decarbonation step is omitted and a low reagent-to-sediment ratio is adopted.
The reconstructed authigenic epsilon(Nd) record for the last 520 kyr exhibits large temporal variations depending on whether the NPIW formation or the boundary exchange process is dominant. Periods of radiogenic eNd can be attributed to NPIW formation triggered by brine rejection, as evidenced by the difference in delta O-18 of benthic foraminifera between sites (Delta delta O-18(bf)), high % sea-ice related diatoms, and low abundance of Bulimina aff Exilis (low-oxygen deep fauna). Diminished supply of unradiogenic Nd from boundary exchange seems to intensify these radiogenic peaks. On the other hand, the unradiogenic eNd intervals can be attributed to stagnant bottom water conditions, as can be deduced from the Delta delta O-18(bf) values, low % sea-ice related diatoms, abundant B. aff Exilis, and laminations. When there is no NPIW formation, the continental margin sediments are exposed to boundary exchange for a longer period of time, leading to release of unradiogenic Nd. The mid-MIS 6 and mid-MIS 5 are exceptions in that NPIW formation occurred yet the eNd compositions are unradiogenic. NPIW formation and cold climate (closed Bering Strait) are not always correlated. Comparison against epsilon(Nd) records of the South Atlantic suggests only an ambiguous NPIW-NADW seesaw for the last 200 kyr.

• 出版日期2017-1-15
• 单位中国极地研究中心