Abstract
AbstractTerrigenous dissolved organic matter (tDOM) carried by rivers represents an important carbon flux to the coastal ocean, which is thought to be increasing globally. Because tDOM is rich in light‐absorbent chromophoric dissolved organic matter (CDOM), it may also reduce the amount of sunlight available in coastal ecosystems. Despite its biogeochemical and ecological significance, there are few long‐term records of tDOM, hindering our understanding of its drivers and dynamics. Corals incorporate terrestrial humic acids, an important constituent of CDOM, resulting in luminescent bands that have been previously linked to rainfall and run‐off. We show that luminescence green‐to‐blue (G/B) ratios in a coral core growing in waters affected by peatland run‐off correlate strongly with remote sensing‐derived CDOM absorption. The 24‐year monthly resolution reconstructed record shows that rainfall controls land‐to‐ocean tDOM flux from this protected peatland catchment, and suggests an additional impact by solar radiation, which degrades tDOM at sea.
Highlights
The flux of terrigenous dissolved organic carbon from land to sea is quantitatively significant in the global carbon cycle, but the fate of tDOC in the ocean remains poorly known (Ciais et al, 2014; Cole et al, 2007)
Because Terrigenous dissolved organic matter (tDOM) is rich in lightabsorbent chromophoric dissolved organic matter (CDOM), it may reduce the amount of sunlight available in coastal ecosystems
TDOC is rich in chromophoric dissolved organic matter (CDOM), which is the fraction of dissolved organic matter
Summary
The flux of terrigenous dissolved organic carbon (tDOC) from land to sea is quantitatively significant in the global carbon cycle, but the fate of tDOC in the ocean remains poorly known (Ciais et al, 2014; Cole et al, 2007). CDOM plays an important role in aquatic ecosystems by absorbing sunlight and reducing its transmission through the water column (Kowalczuk et al, 2005; Mascarenhas et al, 2017). This is partly beneficial for aquatic life: photodegradation can release nutrients from refractory organic compounds (Bushaw et al, 1996), while absorption of ultraviolet radiation protects biota (Dunne & Brown, 1996; Pienitz & Vincent, 2000). Light absorption by CDOM reduces the availability of light for primary producers, which affects benthic ecosystems such as seagrass meadows, kelp forests, and coral reefs (Gattuso et al, 2006; Jones, 1998)
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