Uncertainties regarding ocean biogeochemical cycling exert significant influence on the response of the ocean carbon cycle to climate change at regional scales
Abstract
A key component of the response of the ocean carbon cycle is the process of net primary production (NPP), which fuels upper ocean ecosystems and sets the upper limit on interior ocean carbon sequestration via the biological carbon pump. By playing a first order role in regulating NPP over large areas of the ocean, the micronutrient iron is a crucial component of how ocean NPP responds to climate change, especially at regional scales. However, the cycling of iron in the ocean is distinct from the major nutrients nitrate and phosphate and significant uncertainties remain regarding the representation of the internal cycling linked to biological activity and scavenging. Here we use the state-of-the-art ocean biogeochemical model PISCES to explore how the ocean iron cycle evolves to shape ocean NPP over the coming century under the RCP8.5 scenario. There is a clear mosaic in the response of the upper ocean iron cycle to climate change, driven by regional variations in resource limitation and the sign of projected changes in NPP. Via additional experiments, we find that relatively minor structural and parameter uncertainties associated with poorly understood components of the ocean iron cycle can strongly affect regional NPP projections, despite models performing similarly over the historical period. In particular, projections of NPP change in the tropical Pacific Ocean and, to a lesser extent, the Southern Ocean, are strongly sensitivity to assumptions about the biological iron uptake and the iron stoichiometry of organic material. We found that the magnitude and sign of projected NPP changes may be dampened, amplified or even reversed depending on the assumptions varied. These results are important as they affect regional projections of carbon cycling by ocean microbes and may act to regulate the vulnerability of low latitude fisheries. Better understanding of the internal cycling of iron and its representation in global ocean models would reduce uncertainties associated with projections of NPP and the biological carbon pump at regional scales.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B53K2541T
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 1622 Earth system modeling;
- GLOBAL CHANGE;
- 4815 Ecosystems;
- structure;
- dynamics;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL