Abstract
Hadal trenches act as depocenters for organic material, although
pathways for hadal 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
provinces of different net primary productivity in the surface ocean –
from the eutrophic Atacama and Kuril-Kamchatka trenches, and the
mesotrophic Kermadec Trench, to the oligotrophic Mariana Trench. The
study is based on the distributions of
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 continuous downslope focusing of material towards the
interior of the trenches. The estimated accumulation rates of organic
carbon 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 and accumulation rates during periods of steady
deposition was not mirrored by surface ocean productivity, but appeared
confounded by local bathymetry. Seismic driven mass wasting events
markedly enhanced the accumulation of sediment and organic carbon by
factors from 20 to 400. Thus, hadal trenches are important sites for
deposition and sequestration of organic carbon in the deep-sea partly
due to intensified downslope focusing of material but mainly due to
mass-wasting events.