A Circum‐Antarctic Plankton Isoscape: Carbon Export Potential Across the Summertime Southern Ocean

作者：Luca Stirnimann, Thomas G. Bornman, Heather J. Forrer, Joshua Mirkin, Thomas Ryan‐Keogh, Raquel Flynn, Rosemary A. Dorrington, Hans M. Verheye, Sarah E. Fawcett · 发表于：Global Biogeochemical Cycles · 年份：2024 · DOI：10.1029/2023gb007808 · 被引用次数：12 · 研究领域：Marine and coastal ecosystems、Isotope Analysis in Ecology、Marine Biology and Ecology Research

Abstract The Southern Ocean accounts for ∼30% of the ocean's CO 2 sink, partly due to its biological pump that transfers surface‐produced organic carbon to deeper waters. To estimate large‐scale Southern Ocean carbon export potential and characterize its drivers, we measured the carbon and nitrogen isotope ratios of surface suspended particulate matter (δ 13 C SPM , δ 15 N SPM ) for samples collected in summer 2016/2017 during the Antarctic Circumnavigation Expedition (364 stations). Concurrent measurements of phytoplankton community composition revealed the dominance of large diatoms in the Antarctic and nano‐phytoplankton (mainly haptophytes) in open Subantarctic waters. As expected, δ 13 C SPM was strongly dependent on pCO 2 , with local deviations in this relationship explained by phytoplankton community dynamics. δ 15 N SPM reflected the nitrogen sources consumed by phytoplankton, with higher inferred nitrate (versus recycled ammonium) dependence generally coinciding with higher micro‐phytoplankton abundances. Using δ 15 N SPM and a two‐endmember isotope mixing model, we quantified the extent of nitrate‐ versus ammonium‐supported growth, which yields a measure of carbon export potential. We estimate that across the Southern Ocean, 41 ± 29% of the surface‐produced organic carbon was potentially exported below the seasonal mixed layer during the growth season, with maximum export potential (50%–99%) occurring in the Antarctic Circumpolar Current's southern Boundary Zone an...