In:
Earth System Dynamics, Copernicus GmbH, Vol. 10, No. 3 ( 2019-09-06), p. 539-553
Abstract:
Abstract. Previous studies have suggested that enhanced weathering and benthic
phosphorus (P) fluxes, triggered by climate warming, can increase the
oceanic P inventory on millennial timescales, 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 the same business-as-usual
carbon dioxide (CO2) emission scenario until the year 2300 and
subsequent linear decline to zero emissions until the year 3000. Our set of
model experiments under the same climate scenarios but differing in their
biogeochemical P parameterizations 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. Considering the weathering
parameters closest to the present day, a limited P reservoir and prescribed
anthropogenic P fluxes, we find a +30 % increase in the total global
ocean P inventory by the year 5000 relative to pre-industrial levels, caused
by global warming. 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. In the model, 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 because low temperatures and iron limitation
inhibited the uptake of the extra P and growth by nitrogen fixers in polar
and lower-latitude regions. 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.
Type of Medium:
Online Resource
ISSN:
2190-4987
DOI:
10.5194/esd-10-539-2019
DOI:
10.5194/esd-10-539-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2578793-7