Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 74 (2010): 6788-6800, doi:10.1016/j.gca.2010.09.001.
Description:
Long-term carbon cycling and climate change are strongly dependent on organic carbon
(OC) burial in marine sediments. Radiocarbon (14C) has been widely used to constrain the
sources, sinks, and processing of sedimentary OC. To elucidate the dominant controls on the
radiocarbon content of total organic carbon (14CTOC) accumulating in surface sediments we
construct a box model that predicts 14CTOC in the sediment mixed layer (measured as fraction
modern, Fm). Our model defines three distinct OC pools (“degradable,” “semi-labile,” and
“refractory”) and assumes that 14CTOC flux to sediments is exclusively derived from surface
ocean primary productivity, and hence follows a “generic” surface ocean dissolved inorganic
carbon (DIC) bomb curve. Model predictions are compared to a set of 75 surface sediment
samples, which span a wide geographic range and reflect diverse water column and depositional
conditions, and for which sedimentation rate and mixed layer depth are well characterized. Our
model overestimates the Fm value for a majority (65%) of these sites, especially at shallow water
depths and for sites characterized by depleted δ13CTOC values. The model is most sensitive to
sedimentation rate and mixed-layer depth. Therefore, slight changes to these parameters can lead
to a match between modeled and measured Fm values at many sites. Because of model
sensitivity, slight changes in sedimentation rate and mixed layer depth can allow predictions to
match measured Fm at many sites. Yet, in some cases, we find that measured Fm values cannot
be simulated without large and unrealistic changes to sedimentation rate and mixed layer depth.
These results point to sources of pre-aged OC to surface sediments and implicate soil-derived
terrestrial OC, reworked marine OC, and/or anthropogenic carbon as important components of
the organic matter present in surface sediments. This approach provides a valuable framework within which to explore controls on sedimentary organic matter composition and carbon burial
over a range of spatial and temporal scales.
Description:
This work was supported
by NSF grants OCE-0526389 (W. Martin), OCE-0851350 and OCE-0402533 (T. Eglinton), as
well as WHOI Senior Scientist Chair and Independent Study Award funds (T. Eglinton).
Keywords:
Radiocarbon
;
C-14
;
Organic carbon
;
Marine sediments
;
Box model
;
Global carbon cycle
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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