The relationship between Suspended Particulate Matter and Turbidity at a mooring station in a coastal environment: consequences for satellite-derived products

Type Article
Date 2017-07
Language English
Author(s) Jafar-Sidik Madihah1, 2, Gohin Francis3, Bowers David2, Howarth John4, Hull Tom5
Affiliation(s) 1 : Univ Malaysia Sabah, Borneo Marine Res Inst, Kota Kinabalu 88450, Sabah, Malaysia.
2 : Bangor Univ, Sch Ocean Sci, Anglesey, Wales.
3 : IFREMER, Ctr Ifremer Brest, Dyneco Pelagos, BP 70, F-29280 Plouzane, France.
4 : Natl Oceanog Ctr, Joseph Proudman Bldg, Liverpool, Merseyside, England.
5 : Cefas, Lowestoft, Suffolk, England.
Source Oceanologia (0078-3234) (Polish Acad Sciences Inst Oceanology), 2017-07 , Vol. 59 , N. 3 , P. 365-378
DOI 10.1016/j.oceano.2017.04.003
WOS© Times Cited 23
Keyword(s) Turbidity, Suspended matter, MODIS, Irish Sea

From a data set of observations of Suspended Particulate Matter (SPM) concentration, Turbidity in Formazin Turbity Unit (FTU) and fluorescence-derived chlorophyll-a at a mooring station in Liverpool Bay, in the Irish Sea, we investigate the seasonal variation of the SPM:Turbidity ratio. This ratio changes from a value of around 1 in winter (minimum in January–February) to 2 in summer (maximum in May–June). This seasonal change can be understood in terms of the cycle of turbulence and of the phytoplankton population that affects the nature, shape and size of the particles responsible for the Turbidity. The data suggest a direct effect of phytoplankton on the SPM:Turbidity ratio during the spring bloom occurring in April and May and a delayed effect, likely due to aggregation of particles, in July and August. Based on the hypothesis that only SPM concentration varies, but not the mass-specific backscattering coefficient of particles bbp*, semi-analytical algorithms aiming at retrieving SPM from satellite radiance ignore the seasonal variability of bbp* which is likely to be inversely correlated to the SPM:Turbidity ratio. A simple sinusoidal modulation of the relationship between Turbidity and SPM with time helps to correct this effect at the location of the mooring. Without applying a seasonal modulation to bbp*, there is an underestimation of SPM in summer by the Ifremer semi-analytical algorithm (Gohin et al., 2015) we tested despite the good relationship observed between the backscattering coefficient and Turbidity.

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