Bio-optical anomalies in the world’s oceans: An investigation on the diffuse attenuation coefficients for downward irradiance derived from Biogeochemical Argo float measurements

Organelli, E, Claustre, H, Bricaud, A, Barbieux, M, Uitz, J, D'Ortenzio, F and Dall’Olmo, G 2017 Bio-optical anomalies in the world’s oceans: An investigation on the diffuse attenuation coefficients for downward irradiance derived from Biogeochemical Argo float measurements. Journal of Geophysical Research: Oceans, 122. 3543-3564.

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Identification of oceanic regions characterized by particular optical properties is extremely important for ocean color applications. The departure from globally established bio-optical models (i.e., anomaly) introduces uncertainties in the retrieval of biogeochemical quantities from satellite observations. Thanks to an array of 105 Biogeochemical Argo floats acquiring almost daily downward irradiance measurements at selected wavelengths in the UV and blue region of the spectrum, we reexamined the natural variability of the spectral diffuse attenuation coefficients, Kd(λ), among the world’s oceans and compared them to previously established bio-optical models. The analysis of 2847 measurements of Kd(λ) at 380 and 490 nm, within the first optical depth, provided a classification of the examined regions into three groups. The first one included the Black Sea, a water body characterized by a very high content of coloured dissolved organic matter (CDOM). The second group was essentially composed by the subtropical gyres (Atlantic and Pacific Oceans), with optical properties consistent with previous models (i.e., no anomalies). High latitude (North Atlantic and Southern oceans) and temperate (Mediterranean Sea) seas formed the third group, in which optical properties departed from existing bio-optical models. Annual climatologies of the Kd(380)/Kd(490) ratio evidenced a persistent anomaly in the Mediterranean Sea, that we attributed to a higher-than-average CDOM contribution to total light absorption. In the North Atlantic subpolar gyre, anomalies were observed only in wintertime and were also attributed to high CDOM concentrations. In the Southern Ocean, the anomaly was likely related to high phytoplankton pigment packaging rather than to CDOM.

Item Type: Publication - Article
Additional Information. Not used in RCUK Gateway to Research.: An edited version of this paper was published by AGU. Copyright (2017) American Geophysical Union. Paper featured as a research spotlight for the US Eos magazine. Citation: Stanley, S. (2017), Autonomous floats shed new light on the ocean’s many hues, Eos, 98, Published on 11 May 2017. Marie Sklodowska-Curie Action. Funding provided by PML project REOPTIMIZE “Remineralisation, OPTIcs and Marine partIcle siZE”.
Additional Keywords: Biogeochemical Argo floats, bio-optical anomalies, CDOM, diffuse attenuation coefficient of downward irradiance, global scale
Subjects: Earth Observation - Remote Sensing
Earth Sciences
Marine Sciences
Divisions: Plymouth Marine Laboratory > National Capability categories > National Centre for Earth Observation
Plymouth Marine Laboratory > Science Areas > Earth Observation Science and Applications
Depositing User: Dr E Organelli
Date made live: 04 Jul 2017 13:58
Last Modified: 25 Apr 2020 09:58

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