Publication Date:
2022-05-25
Description:
Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 244 (2019): 502-521, doi:10.1016/j.gca.2018.09.034.
Description:
Relatively little is known about the amount of time that lapses between the
photosynthetic fixation of carbon by vascular land plants and its incorporation into the
marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have
important implications for the carbon cycle. Vascular plant carbon may encounter
multiple potential intermediate storage pools and transport trajectories, and the age of
vascular plant carbon accumulating in marine sediments will reflect these different predepositional
histories. Here, we examine down-core 14C profiles of higher plant leaf waxderived
fatty acids isolated from high fidelity sedimentary sequences spanning the socalled
“bomb-spike”, and encompassing a ca. 60-degree latitudinal gradient from tropical
(Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to
constrain integrated vascular plant carbon storage/transport times (“residence times”).
Using a modeling framework, we find that, in addition to a "young" (conditionally
defined as 〈 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the
fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the
environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old
pool of 28 ky (±9.4, standard deviation), indicating extensive pre-aging in permafrost
soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger,
7.9 (±5.0) and 2.4 (±0.50) to 3.2 (±0.54) ky, respectively, indicating less protracted
storage in terrestrial reservoirs. The "young" pool showed clear annual contributions for
Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool,
respectively), likely reflecting episodic transport of OC from steep hillside slopes
surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta,
respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay
of OC inflow, potentially related to transport time to the offshore basin. Modeling results
also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30
years of age), pointing to the presence of an intermediate reservoir.
Overall, these results show that a significant fraction of vascular plant C
undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine
sediments. The age distribution, reflecting both storage and transport times, likely
depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the
degree of soil buildup and preservation. We show that catchment-specific carbon
residence times across landscapes can vary by an order of magnitude, with important
implications both for carbon cycle studies and for the interpretation of molecular
terrestrial paleoclimate records preserved in sedimentary sequences.
Description:
Financial support was provided by a Schlanger Ocean
Drilling Graduate Fellowship (NJD), an EPA STAR Graduate Fellowship (NJD), a Dutch
NWO Veni grant #825.10.022 (JEV), US NSF grants #OCE-0137005 (TIE and KAH),
#OCE-052626800 (TIE), #OCE-0961980 (ERMD), and #EAR-0447323 (ERMD and
JRS), a Swiss SNF grant #200021_140850 (TIE), a Swedish Research Council grant
#2013-05204 (MS), as well as the Stanley Watson Chair for Excellence in Oceanography
at WHOI (TIE) and the WHOI Arctic Research Initiative (TIE and LG).
Keywords:
Terrestrial carbon
;
Organic matter
;
Radiocarbon
;
Leaf waxes
;
Sediment
;
Residence time
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
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