Journal of Geophysical Research: Biogeosciences
Centre for Marine Ecosystems Research
Australian Research Council. Grant Number: LE170100219
Institute of Environmental Science and Technology. Grant Number: MDM2015-0552
MEXT Japan Society for the Promotion of Science. Grant Number: JP20H02013
ERC Advanced grant, Benthic diagenesis and microbiology of hadal trenches. Grant Number: 669947
Danish National Research Foundation. Grant Number: DNRF145
The Coasts & Oceans Centre of New Zealand's National Institute of Water & Atmospheric Research
The Max Planck Society
Japan Agency for Marine-Earth Science and Technology
ARC Number : LE170100219
Hadal trenches are considered to act as depocenters for organic material, although pathways for the material transport and deposition rates are poorly constrained. Here we assess focusing, deposition and accumulation of material and organic carbon in four hadal trench systems underlying different surface ocean productivities; the eutrophic Atacama and Kuril-Kamchatka trenches, the mesotrophic Kermadec trench and the oligotrophic Mariana Trench. The study is based on the distributions of naturally occurring 210Pbex, 137Cs and total organic carbon from recovered sediment cores and by applying previously quantified benthic mineralization rates. Periods of steady deposition and discreet mass-wasting deposits were identified from the profiles and the latter were associated with historic recorded seismic events in the respective regions. During periods without mass wasting, the estimated focusing factors along trench axes were elevated, suggesting more or less continuous downslope focusing of material toward the interior of the trenches. The estimated organic carbon deposition rates during these periods exhibited extensive site-specific variability, but were generally similar to values encountered at much shallower settings such as continental slopes and margins. Organic carbon deposition rates during periods of steady deposition were not mirrored by surface ocean productivity, but appeared confounded by local bathymetry. The inclusion of deposition mediated by mass-wasting events enhanced the sediment and organic carbon accumulations for the past ∼ 150 years by up to a factor of ∼ 4. Thus, due to intensified downslope material focusing and infrequent mass-wasting events, hadal trenches are important sites for deposition and sequestration of organic carbon in the deep sea.
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