1Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan
2State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China
3Department of Geography, Durham University, Durham, UK
4Institute of Soil Research, University of Natural Resources and Life Sciences, Vienna, Austria
5Department of Geography, National Taiwan University, Taipei, Taiwan
6Department of Earth Sciences, University of Cambridge, Cambridge, UK
7Institute of Marine Geology and Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan
8School of Physical Sciences, University of California, Irvine, CA, USA
9Geomorphology, GFZ German Research Centre, Telegrafenberg, Potsdam, Germany
Received: 22 Jun 2013 – Discussion started: 17 Jul 2013
Abstract. Geological sequestration of atmospheric carbon dioxide (CO2) can be achieved by the erosion of organic carbon (OC) from the terrestrial biosphere and its burial in long-lived marine sediments. Rivers on mountain islands of Oceania in the western Pacific have very high rates of OC export to the ocean, yet its preservation offshore remains poorly constrained. Here we use the OC content (Corg, %), radiocarbon (Δ 14Corg) and stable isotope (δ13Corg) composition of sediments offshore Taiwan to assess the fate of terrestrial OC, using surface, sub-surface and Holocene sediments. We account for rock-derived OC to assess the preservation of OC eroded from the terrestrial biosphere and the associated CO2 sink during flood discharges (hyperpycnal river plumes) and when river inputs are dispersed more widely (hypopycnal). The Corg, Δ14Corg and δ 13Corg of marine sediment traps and cores indicate that during flood discharges, terrestrial OC can be transferred efficiently down submarine canyons to the deep ocean and accumulates offshore with little evidence for terrestrial OC loss. In marine sediments fed by dispersive river inputs, the Corg, Δ14Corg and δ 13Corg are consistent with mixing of terrestrial OC with marine OC and suggest that efficient preservation of terrestrial OC (>70%) is also associated with hypopycnal delivery. Sub-surface and Holocene sediments indicate that this preservation is long-lived on millennial timescales. Re-burial of rock-derived OC is pervasive. Our findings from Taiwan suggest that erosion and offshore burial of OC from the terrestrial biosphere may sequester >8 TgC yr−1 across Oceania, a significant geological CO2 sink which requires better constraint. We postulate that mountain islands of Oceania provide a strong link between tectonic uplift and the carbon cycle, one moderated by the climatic variability which controls terrestrial OC delivery to the ocean.
Revised: 08 Jan 2014 – Accepted: 06 Feb 2014 – Published: 04 Mar 2014
Kao, S.-J., Hilton, R. G., Selvaraj, K., Dai, M., Zehetner, F., Huang, J.-C., Hsu, S.-C., Sparkes, R., Liu, J. T., Lee, T.-Y., Yang, J.-Y. T., Galy, A., Xu, X., and Hovius, N.: Preservation of terrestrial organic carbon in marine sediments offshore Taiwan: mountain building and atmospheric carbon dioxide sequestration, Earth Surf. Dynam., 2, 127-139, doi:10.5194/esurf-2-127-2014, 2014.