Unexpected quasi-independence of coloured dissolved organic matter absorption from chlorophyll-a concentration in the Southern Ocean.
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| Title: | Unexpected quasi-independence of coloured dissolved organic matter absorption from chlorophyll-a concentration in the Southern Ocean. |
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| Authors: | Li, Juan1,2,3 (AUTHOR) juan.li@takuvik.ulaval.ca, Antoine, David1,3 (AUTHOR), Huot, Yannick4 (AUTHOR) |
| Source: | Biogeosciences. 2026, Vol. 23 Issue 9, p3073-3090. 18p. |
| Subject Terms: | *Absorption coefficients, *Chlorophyll in water, *Dissolved organic matter, *Biogeochemical cycles, *Ocean color, *Optical oceanography, *Ocean |
| Geographic Terms: | Antarctic Ocean |
| Abstract: | The absorption coefficient of coloured dissolved organic matter (CDOM), ay , plays a critical role in driving ocean optical properties and thereby light attenuation and light-dependent biogeochemical cycles. In the Southern Ocean (SO), however, ay remains poorly documented because of the scarcity of in situ measurements and the absence of suitable bio-optical models. To address this gap, we derived ay in surface waters from the diffuse attenuation coefficient (Kd) derived from radiometric measurements performed by Biogeochemical-Argo floats. Sensitivity analyses using Monte Carlo simulations indicated that the uncertainty of our estimates is mainly driven by the uncertainty in Kd , and is overall ∼ 18 % for ay at 380 and 412 nm. Our derived ay vs. chlorophyll- a concentration (Chl) relationships for low-latitude waters are consistent with previously published relationships. They, however, diverge in the SO, with a larger relative contribution of ay to the absorption budget for clear waters (Chl < ∼ 0.2 mg m−3) and the opposite for greener waters, leading to a weaker dependence of ay on Chl. Lower-than-expected CDOM absorption mostly happens during the austral summer, suggesting significant photobleaching or lower biologically-mediated production. The relative contributions of CDOM and phytoplankton to the absorption budget are also found to diverge from what bio-optical models predict, with implication for interpretation of satellite ocean colour observations in the SO. [ABSTRACT FROM AUTHOR] |
| Database: | Energy & Power Source |
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| Abstract: | The absorption coefficient of coloured dissolved organic matter (CDOM), ay , plays a critical role in driving ocean optical properties and thereby light attenuation and light-dependent biogeochemical cycles. In the Southern Ocean (SO), however, ay remains poorly documented because of the scarcity of in situ measurements and the absence of suitable bio-optical models. To address this gap, we derived ay in surface waters from the diffuse attenuation coefficient (Kd) derived from radiometric measurements performed by Biogeochemical-Argo floats. Sensitivity analyses using Monte Carlo simulations indicated that the uncertainty of our estimates is mainly driven by the uncertainty in Kd , and is overall ∼ 18 % for ay at 380 and 412 nm. Our derived ay vs. chlorophyll- a concentration (Chl) relationships for low-latitude waters are consistent with previously published relationships. They, however, diverge in the SO, with a larger relative contribution of ay to the absorption budget for clear waters (Chl < ∼ 0.2 mg m−3) and the opposite for greener waters, leading to a weaker dependence of ay on Chl. Lower-than-expected CDOM absorption mostly happens during the austral summer, suggesting significant photobleaching or lower biologically-mediated production. The relative contributions of CDOM and phytoplankton to the absorption budget are also found to diverge from what bio-optical models predict, with implication for interpretation of satellite ocean colour observations in the SO. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 17264170 |
| DOI: | 10.5194/bg-23-3073-2026 |
