Low-latitude mesopelagic nutrient recycling controls productivity and export

Keith B. Rodgers (), Olivier Aumont (), Katsuya Toyama, Laure Resplandy, Masao Ishii, Toshiya Nakano, Daisuke Sasano, Daniele Bianchi and Ryohei Yamaguchi
Additional contact information
Keith B. Rodgers: Tohoku University
Olivier Aumont: LOCEAN/IPSL
Katsuya Toyama: Japan Meteorological Agency
Laure Resplandy: Department of Geosciences
Masao Ishii: Japan Meteorological Agency
Toshiya Nakano: NPO Nagasaki Marine Industry Cluster Promotion Association
Daisuke Sasano: Japan Meteorological Agency
Daniele Bianchi: Los Angeles
Ryohei Yamaguchi: Japan Agency for Marine-Earth Science and Technology

Nature, 2024, vol. 632, issue 8026, 802-807

Abstract: Abstract Low-latitude (LL) oceans account for up to half of global net primary production and export1–5. It has been argued that the Southern Ocean dominates LL primary production and export6, with implications for the response of global primary production and export to climate change7. Here we applied observational analyses and sensitivity studies to an individual model to show, instead, that 72% of LL primary production and 55% of export is controlled by local mesopelagic macronutrient cycling. A total of 34% of the LL export is sustained by preformed macronutrients supplied from the Southern Ocean via a deeper overturning cell, with a shallow preformed northward supply, crossing 30° S through subpolar and thermocline water masses, sustaining only 7% of the LL export. Analyses of five Coupled Model Intercomparison Project Phase 6 (CMIP6) models, run under both high-emissions low-mitigation (shared socioeconomic pathway (SSP5-8.5)) and low-emissions high-mitigation (SSP1-2.6) climate scenarios for 1850–2300, revealed significant across-model disparities in their projections of not only the amplitude, but also the sign, of LL primary production. Under the stronger SSP5-8.5 forcing, with more substantial upper-ocean warming, the CMIP6 models that account for temperature-dependent remineralization promoted enhanced LL mesopelagic nutrient retention under warming, with this providing a first-order contribution to stabilizing or increasing, rather than decreasing, LL production under high emissions and low mitigation. This underscores the importance of a mechanistic understanding of mesopelagic remineralization and its sensitivity to ocean warming for predicting future ecosystem changes.

Date: 2024
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DOI: 10.1038/s41586-024-07779-1

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