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| Titel |
Regional variability in particulate organic matter remineralization depths: an optimization and sensitivity study using a fast Earth system model |
| VerfasserIn |
Jamie Wilson, Stephen Barker, Andy Ridgwell |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250101205
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| Publikation (Nr.) |
 EGU/EGU2015-309.pdf |
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| Zusammenfassung |
| Nutrient distributions and atmospheric CO2 concentrations are sensitive to changes in the
global average depth of particulate organic matter (POM) remineralization in models. Model
optimization studies have used this sensitivity to find global mean remineralization depths
that result in the statistically best fit to tracer observations such as phosphate (PO4). However,
recent global syntheses of sediment trap data have started to suggest the existence of
significant spatial variability in the depth of POM remineralization. A number of hypothetical
mechanisms have been proposed to explain this variability invoking a wide range of
feedbacks on atmospheric CO2. Progress has been hindered by the relatively low
sampling density of sediment trap data. In response to this, we explore whether
there is an optimal set of regionally variable remineralization depths in an Earth
system model that best fits observed PO4 fields and how robust these solutions
are.
We develop a new computationally fast phosphorous-only version of the Earth system model
GENIE using a transport matrix to represent steady-state circulation. The ocean is divided
into 15 biogeochemical biomes within which the remineralization depth is an independent
parameter. Latin hypercube sampling is used to produce an ensemble of runs that efficiently
sample across the range of potential combinations of remineralization depths, producing
probability distributions for each region. Despite sensitivity to the global remineralization
depth, we find that PO4 is actually relatively insensitive to regional changes in
remineralization. An optimal combination of remineralization depths in the Atlantic is found
that predicts deeper remineralization in the low latitudes and shallower at high latitudes,
matching sediment trap observations. Shallow remineralization is also predicted in the North
Pacific. However, remineralization depths in the Southern Ocean, South and Equatorial
Pacific, and Indian Ocean cannot be successfully constrained. We discuss whether these
results reflect underlying mechanisms or alternatively reflect deficiencies in the
modelled ocean circulation. Our results suggest that nutrient observations, such as
PO4, may not be able to distinguish reliably between mechanistic models of the
biological pump. This has important implications for feedbacks on atmospheric
CO2. |
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