The Nitrogen Isotopic Composition of Tissue and Shell‐Bound Organic Matter of Planktic Foraminifera in Southern Ocean Surface Waters ...

We present the first nitrogen isotope (δ15N) measurements of planktic foraminifera, paleoceanographically important zooplankton, from the nutrient‐rich waters of the modern Southern Ocean. Foraminifera were collected from net tows in the Subantarctic and Polar Frontal Zones (SAZ and PFZ, respectivel...

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Bibliographic Details
Main Authors: Smart, Sandi M., Fawcett, Sarah E., Ren, Haojia, Schiebel, Ralf, Tompkins, Emily M., Martínez-García, Alfredo, Stirnimann, Luca, Roychoudhury, Alakendra, Haug, Gerald H., Sigman, Daniel M.
Format: Text
Language:English
Published: ETH Zurich 2020
Subjects:
Southern Ocean
Online Access:https://dx.doi.org/10.3929/ethz-b-000456942
http://hdl.handle.net/20.500.11850/456942
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Summary:We present the first nitrogen isotope (δ15N) measurements of planktic foraminifera, paleoceanographically important zooplankton, from the nutrient‐rich waters of the modern Southern Ocean. Foraminifera were collected from net tows in the Subantarctic and Polar Frontal Zones (SAZ and PFZ, respectively) south of Africa during winter 2015 and late summer 2016. In late summer, consistent with preferential uptake of 14N‐nitrate and the progressive, northward depletion of nitrate by phytoplankton across the Southern Ocean, foraminifer tissue and shell‐bound δ15N rise equatorward along with nitrate δ15N. However, foraminifer δ15N is ~3‰ lower than expected for heterotrophs relying on photosynthetic biomass generated directly from nitrate. This discrepancy appears to originate with the particulate organic N (PON) in late‐summer surface waters, the δ15N of which is lowered by ammonium recycling. In winter, when overall productivity and foraminifer production are reduced, foraminifer δ15N is higher (by 4.6 ± 0.8‰ for ... : Geochemistry, Geophysics, Geosystems, 21 (2) ...

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