In:
Geoscientific Model Development, Copernicus GmbH, Vol. 12, No. 4 ( 2019-04-16), p. 1491-1523
Abstract:
Abstract. The isotopes of carbon (δ13C) and nitrogen
(δ15N) are commonly used proxies for understanding the ocean.
When used in tandem, they provide powerful insight into physical and
biogeochemical processes. Here, we detail the implementation of
δ13C and δ15N in the ocean component of an
Earth system model. We evaluate our simulated δ13C and
δ15N against contemporary measurements, place the model's
performance alongside other isotope-enabled models and document the response
of δ13C and δ15N to changes in ecosystem
functioning. The model combines the Commonwealth Scientific and Industrial
Research Organisation Mark 3L (CSIRO Mk3L) climate system model with the
Carbon of the Ocean, Atmosphere and Land (COAL) biogeochemical model. The
oceanic component of CSIRO Mk3L-COAL has a resolution of 1.6∘
latitude × 2.8∘ longitude and resolves multimillennial
timescales, running at a rate of ∼400 years per day. We show that this
coarse-resolution, computationally efficient model adequately reproduces
water column and core-top δ13C and δ15N
measurements, making it a useful tool for palaeoceanographic research.
Changes to ecosystem function involve varying phytoplankton stoichiometry,
varying CaCO3 production based on calcite saturation state and
varying N2 fixation via iron limitation. We find that large changes
in CaCO3 production have little effect on δ13C and
δ15N, while changes in N2 fixation and phytoplankton
stoichiometry have substantial and complex effects. Interpretations of
palaeoceanographic records are therefore open to multiple lines of
interpretation where multiple processes imprint on the isotopic signature,
such as in the tropics, where denitrification, N2 fixation and
nutrient utilisation influence δ15N. Hence, there is
significant scope for isotope-enabled models to provide more robust
interpretations of the proxy records.
Type of Medium:
Online Resource
ISSN:
1991-9603
DOI:
10.5194/gmd-12-1491-2019
DOI:
10.5194/gmd-12-1491-2019-supplement
Language:
English
Publisher:
Copernicus GmbH
Publication Date:
2019
detail.hit.zdb_id:
2456725-5
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