Surface nitrate utilization in the Bering sea since 180 kA BP: Insight from sedimentary nitrogen isotopes

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• 关键词：Bering Sea ; Quaternary ; Nitrogen isotopes ; Nitrate utilization
• 刊名：Deep Sea Research Part II: Topical Studies in Oceanography
• 出版年：2016
• 出版时间：March-April 2016
• 年：2016
• 卷：125-126
• 期：Complete
• 页码：163-176
• 全文大小：4721 K

文摘

We present high-resolution records of sedimentary nitrogen (δ¹⁵N_bulk) and carbon isotope ratios (δ¹³C_bulk) from piston core SO201-2-85KL located in the western Bering Sea. The records reflect changes in surface nitrate utilization and terrestrial organic matter contribution in submillennial resolution that span the last 180 kyr. The δ¹⁵N_bulk record is characterized by a minimum during the penultimate interglacial indicating low nitrate utilization (~62–80%) despite the relatively high export production inferred from opal concentrations along with a significant reduction in the terrestrial organic matter fraction (m_terr). This suggests that the consumption of the nitrate pool at our site was incomplete and even more reduced than today (~84%). δ¹⁵N_bulk increases from Marine Isotope Stage (MIS) 5.4 and culminates during the Last Glacial Maximum, which indicates that nitrate utilization in the Bering Sea was raised during cold intervals (MIS 5.4, 5.2, 4) and almost complete during MIS 3 and 2 (~93–100%). This is in agreement with previous hypotheses suggesting that stronger glacial stratification reduced the nutrient supply from the subeuphotic zone, thereby increasing the iron-to-nutrient ratio and therefore the nitrate utilization in the mixed surface layer. Large variations in δ¹⁵N_bulk were also recorded from 180 to 130 ka BP (MIS 6), indicating a potential link to insolation and sea-level forcing and its related feedbacks. Millennial-scale oscillations were observed in δ¹⁵N_bulk and δ¹³C_bulk that might be related to Greenland interstadials.