Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds

Vonk, J. E. et al. (2019) Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds. Geochimica et Cosmochimica Acta, 244, pp. 502-521. (doi: 10.1016/j.gca.2018.09.034)

Abstract

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 pre-depositional histories. Here, we examine down-core 14C profiles of higher plant leaf wax-derived fatty acids isolated from high fidelity sedimentary sequences spanning the so-called “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.

• Item Type: Articles
• Additional Information: 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).
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Mcintyre, Dr Cameron
• Authors: Vonk, J. E., Drenzek, N. J., Hughen, K. A., Stanley, R. H.R., McIntyre, C., Montluçon, D. B., Giosan, L., Southon, J. R., Santos, G. M., Druffel, E. R.M., Andersson, A. A., Sköld, M., and Eglinton, T. I.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Geochimica et Cosmochimica Acta
• Publisher: Elsevier
• ISSN: 0016-7037
• ISSN (Online): 0016-7037
• Published Online: 09 October 2018
• Copyright Holders: Copyright © 2018 Elsevier Ltd.
• First Published: First published in Geochimica et Cosmochimica Acta 244: 502-521
• Publisher Policy: Reproduced in accordance with the publisher copyright policy