ABSTRACT: Shelf seas provide valuable ecosystem services, but their productivity and ecological functioning depend critically on sunlight transmitted through the water column. Anthropogenic reductions in underwater light availability are thus a serious threat to coastal habitats. The flux of light-absorbing coloured dissolved organic matter (CDOM) from land to sea may have increased world-wide, but how this has altered the availability and spectral quality of light in shelf seas remains poorly known. We present time-series data from the Sunda Shelf in Southeast Asia, where the monsoon-driven reversal in ocean currents supplies water enriched in CDOM from tropical peatlands for part of the year, resulting in 5- to 10-fold seasonal variation in light absorption by CDOM. We show that this terrigenous CDOM can dominate underwater light absorption at wavelengths up to 500 nm, and shift the underwater irradiance spectrum towards longer wavelengths. The seasonal presence of terrigenous CDOM also reduces the 10% light penetration depth by 1-5 m, or 10-45%. We estimate that on average 0.6 m, or 25%, of this terrigenous CDOM-mediated shoaling might be attributable to the enhanced input of dissolved organic matter following peatland disturbance. The seasonal change in the light environment is correlated with changes in phytoplankton absorption spectra that suggest a photo-acclimation response, and we infer that terrigenous CDOM likely contributes to limiting the depth distribution of photosynthetic corals. The results reveal an ecologically important but largely overlooked impact of human modifications to carbon fluxes that is likely increasingly important in coastal seas.

中文翻译：

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来自热带泥炭地的溶解有机物减少了东南亚新加坡海峡的陆架海光供应

摘要：大陆架海提供了宝贵的生态系统服务，但其生产力和生态功能严重依赖于通过水柱传输的阳光。因此，人为减少水下光线可用性对沿海栖息地构成严重威胁。从陆地到海洋的吸光有色溶解有机物 (CDOM) 的通量可能在全球范围内有所增加，但这如何改变陆架海中光的可用性和光谱质量仍然知之甚少。我们展示了来自东南亚巽他大陆架的时间序列数据，其中季风驱动的洋流逆转在一年中的一部分时间里从热带泥炭地提供富含 CDOM 的水，导致光吸收的季节性变化为 5 到 10 倍通过 CDOM。我们表明，这种陆源 CDOM 可以主导波长高达 500 nm 的水下光吸收，并将水下辐照光谱移向更长的波长。陆源 CDOM 的季节性存在也将 10% 的光穿透深度降低了 1-5 m，即 10-45%。我们估计，平均 0.6 m 或 25% 的这种陆源 CDOM 介导的浅滩可能归因于泥炭地干扰后溶解有机物质的输入增加。光环境的季节性变化与浮游植物吸收光谱的变化相关，表明光适应反应，我们推断陆源 CDOM 可能有助于限制光合珊瑚的深度分布。