DETERMINATION OF PHYTOPLANKTON ABSORPTION-COEFFICIENT IN NATURAL SEAWATER SAMPLES - EVIDENCE OF A UNIQUE EQUATION TO CORRECT THE PATHLENGTHAMPLIFICATION ON GLASS-FIBER FILTERS
B. Arbones et al., DETERMINATION OF PHYTOPLANKTON ABSORPTION-COEFFICIENT IN NATURAL SEAWATER SAMPLES - EVIDENCE OF A UNIQUE EQUATION TO CORRECT THE PATHLENGTHAMPLIFICATION ON GLASS-FIBER FILTERS, Marine ecology. Progress series, 137(1-3), 1996, pp. 293-304
Estimations of the spectral absorption coefficients of phytoplankton i
n the sea, based on the spectrum of absorption of particles retained o
n a filter, require a correction for pathlength amplification in the g
lass fibre filter (beta factor). The relationship between the optical
density in suspension and 'on filter' is misleading due to the hystere
sis effect. This effect is reduced on eliminating the absorption due t
o non-pigmentary material, minimising the dependency of the beta facto
r on wavelength. A general quadratic equation, ODsus(lambda) = 0.38 OD
filter(lambda) + 0.42 ODfilter2(lambda) (r(2) = 0.97, n = 15600), was
obtained on comparing 52 pairs of spectra of 9 marine phytoplankton sp
ecies. The algorithm was validated against natural samples, obtaining
a 1% average error. Comparisons between Cleveland & Weidemann's equati
on (1993, Limnol Oceanogr 38:1321-1327) and the equation obtained in t
his study provided a 2% average difference, suggesting that a unique e
quation can be useful in determining the phytoplankton absorption coef
ficient in seawater samples. We compared the absorption coefficients o
btained by spectra reconstructed from the pigment content in seawater
samples with those obtained with spectra on GF/F filters and beta-corr
ected. Our results indicate that the spectra-reconstructed approach is
only suitable when the sample consists of small quasi-spherical cells
. For coastal-upwelling samples which are mainly composed of large cel
ls the approach overestimates the package effect.