Variability of chromophoric organic matter in surface waters of the Atlantic Ocean

Kitidis, Vassilis; Stubbins, Aron; Uher, G; Upstill‐Goddard, Robert C.; Law, Cliff S.; Woodward, E Malcolm S

doi:10.1016/j.dsr2.2006.05.009

Cited by 88 publications

(93 citation statements)

References 45 publications

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“…where a(k 0 ) is the absorption coefficient at a reference wavelength k 0 , and S is the spectral slope parameter (Blough and Green, 1995;Kitidis et al, 2006). In addition, the specific UV absorption coefficient at 300 nm was calculated as…”

Section: Uv-visible Absorbance Spectrometrymentioning

confidence: 99%

Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis–electrodialysis

Koprivnjak

Pfromm

Ingall

et al. 2009

Geochimica et Cosmochimica Acta

101

117

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The coupled reverse osmosis-electrodialysis (RO/ED) method was used to isolate dissolved organic matter (DOM) from 16 seawater samples. The average yield of organic carbon was 75 ± 12%, which is consistently greater than the yields of organic carbon that have been commonly achieved using XAD resins, C 18 adsorbents, and cross-flow ultrafiltration. UV-visible absorbance spectra and molar C/N ratios of isolated samples were consistent with the corresponding properties of DOM in the original seawater samples, indicating that DOM samples can be isolated using the coupled RO/ED method without any bias for/against these two properties. Five of the samples were desalted sufficiently that reliable measurements of their 13 C and 1 H NMR spectra and their Fourier transform ion cyclotron resonance (FTICR) mass spectra could be obtained. The 13 C and 1 H NMR spectra of RO/ED samples differed distinctly from those of samples that have been isolated in much lower yields by other methods. In particular, RO/ED samples contained a relatively lower proportion of carbohydrate carbon and a relatively greater proportion of alkyl carbon than samples that have been isolated using cross-flow ultrafiltration. From the FTICR mass spectra of RO/ED samples, samples from the open ocean contained a much lower proportion of unsaturated compounds and a much higher proportion of fatty acids than coastal samples.

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Section: Uv-visible Absorbance Spectrometrymentioning

confidence: 99%

Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis–electrodialysis

Koprivnjak

Pfromm

Ingall

et al. 2009

Geochimica et Cosmochimica Acta

101

117

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“…However, the co-variation between CDOM and detrital matter is not perfect, as has been noted in the real ocean (e.g. see Bricaud et al, 1981;Kitidis et al, 2006;Morel et al, 2010;Siegel et al, 2005b). In the model output, there is significant scatter around the core linear relationship (Fig.…”

Section: The Role Of Other Optically Important Constituentsmentioning

confidence: 91%

Modelling ocean-colour-derived chlorophyll <i>a</i>

2018

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Abstract. This article provides a proof of concept for using a biogeochemical/ecosystem/optical model with a radiative transfer component as a laboratory to explore aspects of ocean colour. We focus here on the satellite ocean colour chlorophyll a (Chl a) product provided by the often-used blue/green reflectance ratio algorithm. The model produces output that can be compared directly to the real-world ocean colour remotely sensed reflectance. This model output can then be used to produce an ocean colour satellite-like Chl a product using an algorithm linking the blue versus green reflectance similar to that used for the real world. Given that the model includes complete knowledge of the (model) water constituents, optics and reflectance, we can explore uncertainties and their causes in this proxy for Chl a (called "derived Chl a" in this paper). We compare the derived Chl a to the "actual" model Chl a field. In the model we find that the mean absolute bias due to the algorithm is 22 % between derived and actual Chl a. The real-world algorithm is found using concurrent in situ measurement of Chl a and radiometry. We ask whether increased in situ measurements to train the algorithm would improve the algorithm, and find a mixed result. There is a global overall improvement, but at the expense of some regions, especially in lower latitudes where the biases increase. Not surprisingly, we find that regionspecific algorithms provide a significant improvement, at least in the annual mean. However, in the model, we find that no matter how the algorithm coefficients are found there can be a temporal mismatch between the derived Chl a and the actual Chl a. These mismatches stem from temporal decoupling between Chl a and other optically important water constituents (such as coloured dissolved organic matter and detrital matter). The degree of decoupling differs regionally and over time. For example, in many highly seasonal regions, the timing of initiation and peak of the spring bloom in the derived Chl a lags the actual Chl a by days and sometimes weeks. These results indicate that care should also be taken when studying phenology through satellite-derived products of Chl a. This study also reemphasizes that ocean-colourderived Chl a is not the same as the real in situ Chl a. In fact the model derived Chl a compares better to real-world satellite-derived Chl a than the model actual Chl a. Modellers should keep this is mind when evaluating model output with ocean colour Chl a and in particular when assimilating this product. Our goal is to illustrate the use of a numerical laboratory that (a) helps users of ocean colour, particularly modellers, gain further understanding of the products they use and (b) helps the ocean colour community to explore other ocean colour products, their biases and uncertainties, as well as to aid in future algorithm development.

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“…For our irradiation experiments, we used the setup described by Kitidis et al (2011). Irradiated quartz bottles and 1 liter flasks were placed horizontally in a custom-built solar simulator fitted with UV400W (Commercial Lamp Suppliers) and 150 W metal halide (model MHN-TD, Phillips) lamps (Kitidis et al 2011).…”

Section: Methodsmentioning

confidence: 99%

“…0.05). Additional samples for CDOM absorbance were irradiated in custom-made 1 liter quartz flasks (57 mm diameter; Kitidis et al 2011). …”

Section: Methodsmentioning

confidence: 99%

Untitled

2014

Limnology & Oceanography

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We carried out 16 photochemical experiments of filtered surface water in a custom-built solar simulator and concomitant measurements of in vitro gross primary production (GPP) and respiration (R) in the Mauritanian upwelling during a Lagrangian study following three sulfur hexafluoride-labeled patches of upwelled water (P1 to P3). Oxygen photolysis rates were correlated with the absorbance of chromophoric dissolved organic matter (CDOM) at 300 nm, suggesting first-order kinetics with respect to CDOM. An exponential fit was used to calculate the apparent quantum yield (AQY) for oxygen photolysis, giving an average AQY of 0.00053 mmol O 2 (mole photons m 22 s 21 ) 21 at 280 nm and slope of 0.0012 nm 21 . Modeled photochemical oxygen demand (POD) at the surface (3-16 mmol m 23 d 21 ) occasionally exceeded R and was dominated by ultraviolet radiation (71-79%). Euphotic-layer integrated GPP decreased with time during both P-1 and P-3, whereas R remained relatively constant and POD increased during P-1 and decreased during P-3. On Day 4 of P-3, GPP and POD maxima coincided with high CDOM absorbance, suggesting ''new'' CDOM production. Omitting POD may lead to an underestimation of net community production (NCP), both through in vitro and geochemical methods (here by 2-22%). We propose that oxygen-based NCP estimates should be revised upward. For the Mauritanian upwelling, the POD-corrected NCP was strongly correlated with standard NCP with a slope of 1.0066 6 0.0244 and intercept of 46.51 6 13.15 mmol m 22 d 21 .

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Variability of chromophoric organic matter in surface waters of the Atlantic Ocean

Cited by 88 publications

References 45 publications

Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis–electrodialysis

Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis–electrodialysis

Modelling ocean-colour-derived chlorophyll <i>a</i>

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Variability of chromophoric organic matter in surface waters of the Atlantic Ocean

Cited by 88 publications

References 45 publications

Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis–electrodialysis

Chemical and spectroscopic characterization of marine dissolved organic matter isolated using coupled reverse osmosis–electrodialysis

Modelling ocean-colour-derived chlorophyll &lt;i&gt;a&lt;/i&gt;

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Modelling ocean-colour-derived chlorophyll <i>a</i>