Ocean Phosphorus Inventory and Ocean Deoxygenation: Large Uncertainties in Future Projections on Millennial Timescales.

Kemena, Tronje Peer , Oschlies, Andreas, Koeve, Wolfgang , Wallmann, Klaus J. G. , Landolfi, Angela and Dale, Andrew W. (2018) Ocean Phosphorus Inventory and Ocean Deoxygenation: Large Uncertainties in Future Projections on Millennial Timescales. Open Access Earth System Dynamics Discussions . pp. 1-28. DOI 10.5194/esd-2018-58.

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Abstract

Previous studies have suggested that weathering and benthic phosphorus (P) fluxes, triggered by climate warming, can increase the oceanic P inventory on millennial time scales, promoting ocean productivity and deoxygenation. In this study, we assessed the major uncertainties in projected P inventories and their imprint on ocean deoxygenation using an Earth system model of intermediate complexity for a business-as-usual carbon dioxide (CO2) emission scenario until year 2300 and subsequent linear decline to zero emissions until year 3000.

Model results suggest a large spread in the simulated oceanic P inventory due to uncertainties in (1) assumptions for weathering parameters, (2) the representation of bathymetry on slopes and shelves in the model bathymetry, (3) the parametrization of benthic P fluxes and (4) the representation of sediment P inventories. Our best estimate for changes in the global ocean P inventory by the year 5000 caused by global warming amounts to +30% compared to pre-industrial levels. Weathering, benthic and anthropogenic fluxes of P contributed +25%, +3% and +2% respectively. The total range of oceanic P inventory changes across all model simulations varied between +2% and +60%. Suboxic volumes were up to 5 times larger than in a model simulation with a constant oceanic P inventory. Considerably large amounts of the additional P left the ocean surface unused by phytoplankton via physical transport processes as preformed P. Nitrogen fixation was not able to adjust the oceanic nitrogen inventory to the increasing P levels or to compensate for the nitrogen loss due to increased denitrification. This is in contrast to palaeo reconstructions of large-scale deoxygenation events.

We suggest that uncertainties in P weathering, nitrogen fixation and benthic P feedbacks need to be reduced to achieve more reliable projections of oceanic deoxygenation on millennial timescales.

Document Type: Article
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BM Biogeochemical Modeling
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > SFB 754 > B1
OceanRep > SFB 754
Refereed: No
Open Access Journal?: Yes
DOI etc.: 10.5194/esd-2018-58
ISSN: 2190-4995
Related URLs:
Projects: SFB754
Date Deposited: 02 Oct 2018 07:20
Last Modified: 02 Oct 2018 08:07
URI: http://oceanrep.geomar.de/id/eprint/44408

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