Small particles and carbon export in the ocean
Chin-Chang Hung and Gwo-Ching Gong
Institute of Marine Environmental Chemistry and Ecology,
National Taiwan Ocean University,
Keelung, 20224, Taiwan, Republic of China
Abstract
The rare large particles (>50 m) are believed to be responsible for the majority of
the carbon export in the surface ocean, but the size spectrum of the sinking material
(collected via sediment traps) in the ocean is still poorly documented and understood. We
analyzed the carbon content and 234Th activity on size-fractionated (1-10, 10-50, 50-150,
and >150 m) sinking particles in marginal seas, upwelling region and oligotrophic ocean.
Within the POC pool (>1 m), the 1-10 m fraction had the largest share of POC
(21-63%), followed by the 10-50 m (21-44%), the 50-150 m (8-26%), and the >150
m (5-25%). The distribution pattern of 234Th on size-fractionated sinking particles was
similar to that of POC and small particles (<50 m) had the largest share (73-94%) of
234
Th. We perform that small particles (1-10 and 10-50 m) likely represent the majority
of sinking particles in terms of carbon and 234Th contents in the surface ocean. The results
suggest that small sinking particles dominating carbon flux in the surface ocean are
beyond current dogma of biological oceanography. Most importantly, our results also
show that the previous 234Th-derived carbon export, based on POC/234Th ratios on large
filtered particles (>50 m) times 234Th flux, may be significantly biased because plenty of
filtered large particles (formed by small particles) may be breakup during sequential
filtration process.