The Arctic Ocean fixed nitrogen cycle in past climates: Insights from foraminifer-bound nitrogen isotopes

• Main Authors: Farmer, Jesse, Sigman, Daniel M, Granger, Julie, Fripiat, François
• Other Authors: AGU Fall meeting (2019: San Francisco)
• Format: Conference Object
• Language: French
• Published: 2019
• Subjects: Sciences de la terre et du cosmos; Arctic; Arctic Ocean; Bering Strait; Pacific; Foraminifera*; Lomonosov Ridge; Sea ice
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/299533

The dramatic loss of summer sea-ice impacts Arctic Ocean biological productivity through poorly understood pathways. While sea-ice loss alleviates light limitation, productivity within the future seasonally ice-free Arctic Ocean will likely be limited by the supply of biologically available (“fixed”) nitrogen. Although the Arctic Ocean has experienced past intervals of reduced sea-ice extent and warmer-than-present conditions, little is known about Arctic Ocean nutrient cycling outside of recent conditions. Here we investigate changes in nitrate supply and utilization in the surface Arctic Ocean over the last 40 kyr using measurements of nitrogen isotopes within the organic matrix of planktic foraminifera (FB-δ15N). Preliminary results show a dramatic, 4‰ FB-δ15N increase in the western Arctic Ocean (Mendeleev Ridge) between 12 and 10 ka, synchronous with postglacial opening of the Bering Strait. We interpret this FB-δ15N increase to reflect the rapid resumption of Pacific water nitrate inflow, with associated influences on shelf denitrification and surface ocean nutrient consumption following Bering Strait opening. A corresponding record from the central Arctic Ocean (Lomonosov Ridge) shows minor FB-δ15N variations since 14 ka, indicating that central Arctic productivity was sustained by Atlantic-sourced nitrate throughout this time. These results suggest that shelf denitrification and surface ocean nitrate consumption in the western Arctic is tightly linked to Pacific water inflow. We will discuss opportunities to apply FB-δ15N to Arctic sediments from past warm climates as potential constraints for the future Arctic Ocean fixed nitrogen cycle. info:eu-repo/semantics/nonPublished