Quantifying photodegradation of peatland-derived dissolved organic
carbon in the coastal ocean of Southeast Asia
Abstract
The terrigenous dissolved organic carbon (tDOC) exported from the
peatlands in Southeast Asia appears to be extensively remineralized in
the shelf sea, but the processes that drive this remineralization remain
unclear. Here, we combined incubation experiments and model simulations
to quantify the rate and extent of photodegradation of tDOC in the Sunda
Shelf Sea. Laboratory photodegradation experiments indicate that up to
74% of the peatland tDOC is potentially labile to photochemical
remineralization. Based on our estimated apparent quantum yield for tDOC
remineralization, modeled in-situ solar irradiance, and measured
inherent optical properties of the water column, we simulated peatland
tDOC photoremineralization for two coastal regions of the Sunda Shelf
Sea. These simulation results show that natural solar radiation can
directly remineralize 20±11% of tDOC over 2 years, which corresponds to
the approximate residence time of water in the Sunda Shelf Sea, and that
significant photobleaching of tDOC can occur in coastal waters over
shorter time-scales. We further derived a simplified photochemical decay
constant of 0.008–0.017day-1 for Southeast Asia’s peatland-derived
tDOC, which can be used to parameterize the recently proposed UniDOM
model framework. We conclude that direct photodegradation may be a
greater sink for tDOC in Southeast Asia’s coastal ocean compared to
higher latitudes, although it is insufficient to account for the total
tDOC remineralization observed in the Sunda Shelf Sea.