Observed vs. predicted variability in non-algal suspended particulate matter concentration in the English Channel in relation to tides and waves |
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Authors: | Aurélie Rivier Francis Gohin Philippe Bryère Caroline Petus Nicolas Guillou Georges Chapalain |
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Institution: | (1) IFREMER, Laboratoire d’?cologie p?lagique, DYNECO PELAGOS, BP 70, 29280 Plouzan?, France;(2) Centre d’Etudes Techniques Maritimes et Fluviales (CETMEF), Laboratoire de G?nie C?tier et Environnement (LGCE), 155 rue Pierre Bouguer, Technop?le Brest Iroise BP 5, 29280 Plouzan?, France;(3) ACRI, 40 Quai de la douane, 29200 Brest, France |
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Abstract: | The study of water clarity is essential to understand variability in biological production, particularly in coastal seas.
The spatial and temporal variability of non-algal suspended particulate matter (SPM) in surface waters of the English Channel
was investigated and related to local forcing by means of a large satellite dataset covering the study area with a spatial
resolution of 1.2 km and a daily temporal resolution. This analysed dataset is a time series of non-algal SPM images derived
from MODIS and MERIS remote-sensing reflectance by application of an IFREMER semi-analytical algorithm over the period 2003–2009.
In a first step, the variability of time series of MODIS images was analysed through temporal autocorrelation functions. Then,
non-algal SPM concentrations were assessed in terms of site-specific explanatory variables such as tides, wind-generated surface-gravity
wave amplitudes and chlorophyll-a (Chl-a), based on three statistical models with fitting parameters calibrated on a dataset
of merged MERIS/MODIS images gathered from 2007 to 2009 over the whole English Channel. Correlogram analysis and the first
model highlight the local patterns of the influence of the tide, especially the neap–spring cycle, on non-algal surface SPM.
Its effect is particularly strong in the central and eastern English Channel and in the western coastal areas. The second
model shows that waves prevail as driver at the entrance of the English Channel. The most sophisticated of the three statistical
models, although involving only three explanatory variables—the tide, waves and Chl-a—is able to estimate non-algal surface
SPM with a coefficient of determination reaching 70% at many locations. |
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