Coral Skeletal Luminescence Records Changes in Terrestrial Chromophoric Dissolved Organic Matter in Tropical Coastal Waters

Abstract

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). In some regions, a potentially large fraction of this tDOC flux can be oxidized to CO 2 through photodegradation and biodegradation processes, contributing to coastal ocean acidification and ultimately degassing to the atmosphere (Fichot et al., 2014;Semiletov et al., 2016;Ward et al., 2017). Moreover, tDOC is rich in chromophoric dissolved organic matter (CDOM), which is the fraction of dissolved organic matter

Rising dissolved organic carbon concentrations in coastal waters of northwestern Borneo related to tropical peatland conversion

“…S2 to S6). Riverine DOC fluxes and CDOM absorption in coastal waters in the region are highest during the northeast monsoon ( 42 , 43 ), reflecting the importance of rainfall in driving tDOC flux from tropical peatlands ( 24 ). The seasonal patterns in our data thus further support our conclusion that peat-draining rivers are a key source of DOC to the coastal waters.…”

“…Additional support for the accuracy of our remote sensing analysis is provided by an independent analysis in which we compared our satellite-derived time series of CDOM concentration for a 3 km × 3 km location in the west of our study region (centered on 1.914°N 109.741°E) to a record of relative variation in terrestrial humic acid concentration recorded as luminescent growth bands in a core of a massive Porites sp. coral collected from an adjacent coral reef ( 43 ). Such luminescent bands are caused by the inclusion of terrestrial humic acids, which are a key component of CDOM, from ambient seawater into the coral skeleton and can accurately reconstruct river discharge ( 84 , 85 ).…”

“…Such luminescent bands are caused by the inclusion of terrestrial humic acids, which are a key component of CDOM, from ambient seawater into the coral skeleton and can accurately reconstruct river discharge ( 84 , 85 ). The analysis shows that monthly average coral luminescence intensity is strongly correlated with average monthly satellite-derived CDOM concentration throughout the 12-year period of overlap between coral growth and the satellite record ( r 2 = 0.57, P < 0.001) ( 43 ). This shows that our remote sensing model returns accurate estimates of seasonal and interannual variability in CDOM throughout the remote sensing time series.…”

Environmental records from coral skeletons: A decade of novel insights and innovation

“…First, as reviewed by Saha et al (2016) there has been rapid expansion and refinement of proxies for upwelling (Grottoli et al, 2013;LaVigne et al, 2010LaVigne et al, , 2016Watanabe et al, 2017), runoff/river discharge (Brenner et al, 2017;Chen et al, 2020;Grove et al, 2012;Kaushal et al, 2020Kaushal et al, , 2021LaVigne et al, 2016;Maina et al, 2012;Saha et al, 2018), and/or sediment flux on to the reef (Carriquiry & Horta-Puga, 2010;Fleitmann et al, 2007;Ito et al, 2020;Mallela et al, 2013;Prouty et al, 2010;Tanzil et al, 2019) from elements with nutrient-like profiles in the water column (Ba/Ca, P/Ca, Y/Ca, Cd/Ca, δ 13 C) and from skeletal luminescence. For example, while Ba/Ca proxy has been widely applied for some time, the interpretation of these records has varied greatly among sites.…”

“…Finally, a robust, reproducible luminescence signal has been identified among cores within a watershed due to the conservative behavior of humic acids in seawater, particularly when separated from the density-related signal (Grove et al, 2010(Grove et al, , 2012. Furthermore, the strong link between skeletal luminescence, humic acid abundance, and light-absorbent (chromophoric) dissolved organic matter suggests that luminescence records may provide insights into terrestrial carbon fluxes and their impact on coastal productivity (Kaushal et al, 2020(Kaushal et al, , 2021. Luminescence records are also non-destructive and may be less susceptible to non-climatic, low-frequency (red) noise characteristic of other geochemical proxies (Loope, Thompson, Cole, & Overpeck, 2020).…”