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|Title:||Sensitivity analysis of CDOM spectral slope in artificialand natural samples: an application in the central easternMediterranean Basin||Authors:||Luca, Bracchini
Arduino Massimo, Dattilo
Loiselle, Steven Arthur
|Keywords:||CDOM; UV; Spectroscopy; Absorption; Spectral Slope; Mediterranean Basin||Issue Date:||2010||Project:||None||Journal:||AQUATIC SCIENCES||Abstract:||
In the past two decades, optical properties ofchromophoric dissolved organic matter (CDOM) in marineenvironments have been extensively studied. Many of thesestudies report CDOM properties for the offshore environmentwhere this complex mixture of optically activecompounds is strongly diluted. Nevertheless, autochthonousand allochthonous sources have been identified andsinks related to photodegradation and bacterial activityhave been demonstrated. The calculation of the spectralslope of the CDOM absorption curve has been proven to beuseful and is often reported. However, a rigorous uncertaintyanalysis of the slope calculation is rarely reported. Inthis paper, we propose a method to evaluate the uncertaintyof CDOM spectral slope calculated between 270 and400 nm, using both naturally sampled and artificial solutions.We use these results to study the ultra-oligotrophicwaters of the Mediterranean Sea (central eastern basin),where little is known about CDOM spatial distribution. Weshow that dilutions of both artificial and natural samplesproduce a Gaussian distribution of spectral slopes, indicating that consistent values may be determined, with atypical uncertainty of ±0.0004 nm-1 when absorption at300 nm was greater then 0.1 m-1 (0.1 m pathlength).Comparing the distribution of spectral slopes from centraleastern basin samples to a Gaussian distribution, we showdifferences between measurements that were significantlydifferent. These values allow us to distinguish possiblesources (algal derived CDOM), sinks (e.g. photo-bleaching)at different depths. We propose a subdivision ofCDOM compounds into refractory and semilabile/refractorypools and evaluate the CDOM spectral slope of algalderived CDOM released at or near deep chlorophyllmaximum.
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