Determination of apparent quantum yield spectra of DMS photo-degradation in an in situ iron-induced Northeast Pacific Ocean bloom (original) (raw)
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Limnology and Oceanography, 2002
Quantum yield spectra for the photochemical formation of biologically labile photoproducts from dissolved organic matter (DOM) have not been available previously, although they would greatly facilitate attempts to model photoproduct formation rates across latitudinal, seasonal, and depth-related changes in spectral irradiance. Apparent quantum yield spectra were calculated for two coastal environments from the southeastern United States using postirradiation bacterial respiration as a measure of total labile photoproduct formation and a cutoff filter method to model spectral dependence. As has been the case for previously studied classes of DOM photoproducts (i.e., dissolved inorganic carbon, CO, and H 2 O 2 ), ultraviolet (UV)-B irradiance was significantly more efficient at forming labile photoproducts (i.e., compounds readily assimilated by marine bacterioplankton) than UV-A and visible irradiance. Calculations of DOM photoproduct formation in southeastern U.S. coastal surface waters indicate a formation ratio for biologically labile photoproducts : CO of 13 : 1. The slope of a natural log plot of the apparent quantum yield spectrum obtained for biologically labile photoproducts was similar to that for CO (0.028 nm Ϫ1 vs. 0.034 nm Ϫ1 ). Modeled kinetic rates therefore indicate that the production ratio of these photoproduct classes is approximately maintained despite variations in the solar spectrum that occur with depth in a water column or distance from shore. Application of the apparent quantum yield to coastal regions worldwide predicts an annual formation rate of biologically labile photoproducts in coastal waters of 206 ϫ 10 12 g C.
Rate and apparent quantum yield of photodissolution of sedimentary organic matter
Limnology and Oceanography, 2012
We quantified rates of photochemical dissolution (photodissolution) of organic carbon in coastal Louisiana suspended sediments, conducting experiments under well-defined conditions of irradiance and temperature. Optical properties of the suspended sediments were characterized and used in a radiative transfer model to compute irradiances within turbid suspensions. Photodissolution rate increased with temperature (T), with activation energy of 32 6 7 kJ mol 21 , which implicates indirect (non-photochemical) steps in the net reaction. In most samples, dissolved organic carbon (DOC) concentration increased approximately linearly with time over the first 4 h of irradiation under broadband simulated sunlight, after higher rates in the initial hour of irradiation. Four-hour rates ranged from 2.3 mmol DOC m 23 s 21 to 3.2 mmol DOC m 23 s 21 , but showed no relation to sample origin within the study area, organic carbon or reducible iron content, or mass-specific absorption coefficient. First-hour rates were higher-from 3.5 mmol DOC m 23 s 21 to 7.8 mmol DOC m 23 s 21-and correlated well with sediment reducible iron (itself often associated with organic matter). The spectral apparent quantum yield (AQY) for photodissolution was computed by fitting DOC photoproduction rates under different spectral irradiance distributions to corresponding rates of light absorption by particles. The photodissolution AQY magnitude is similar to most published dissolved-phase AQY spectra for dissolved inorganic carbon photoproduction, which suggests that in turbid coastal waters where particles dominate light absorption, DOC photoproduction from particles exceeds photooxidation of DOC.
Biogeosciences Discussions, 2015
In order to assess the production of biologically labile photoproducts (BLPs) from non-labile riverine dissolved organic carbon (DOC), we collected water samples from ten major rivers, removed labile DOC and mixed the residual non-labile DOC with artificial seawater for microbial and photochemical experiments. Bacteria grew on non-labile DOC with a growth efficiency of 11.5% (mean; range from 3.6 to 15.3%). Simulated solar radiation transformed a part of non-labile DOC into BLPs, which stimulated bacterial respiration and production, but did not change bacterial growth efficiency (BGE) compared to the non-irradiated dark controls. In the irradiated water samples, the amount of BLPs stimulating bacterial production depended on the photochemical bleaching of chromophoric dissolved organic matter (CDOM). The apparent quantum yields for BLPs supporting bacterial production ranged from 9.5 to 76 (mean 39) (μmol C mol photons<sup>−1</sup>) at 330 nm. The corresponding values f...
Water research, 2015
Chromophoric dissolved organic matter (CDOM) in surface waters is a photochemical source of several transient species such as CDOM triplet states ((3)CDOM*), singlet oxygen ((1)O2) and the hydroxyl radical (OH). By irradiation of lake water samples, it is shown here that the quantum yields for the formation of these transients by CDOM vary depending on the irradiation wavelength range, in the order UVB > UVA > blue. A possible explanation is that radiation at longer wavelengths is preferentially absorbed by the larger CDOM fractions, which show lesser photoactivity compared to smaller CDOM moieties. The quantum yield variations in different spectral ranges were definitely more marked for (3)CDOM* and OH compared to (1)O2. The decrease of the quantum yields with increasing wavelength has important implications for the photochemistry of surface waters, because long-wavelength radiation penetrates deeper in water columns compared to short-wavelength radiation. The average steady-...
Limnology and Oceanography, 2000
We measured photochemical mineralization of dissolved organic carbon in a humic lake in situ. At a depth of 1 cm, solar radiation mineralized 19 mmol C m Ϫ3 d Ϫ1 . The rate of mineralization decreased with increasing depth with an attenuation coefficient of 23 m Ϫ1 . Consequently, most photochemical mineralization in the water column (0.99 mmol C m Ϫ2 d Ϫ1 ) took place in the top 10 cm. The rate of photochemical mineralization was also modeled as a product of three spectra: (1) scalar photon flux density, (2) the apparent quantum yield ( ), and (3) the absorption of chromophoric dissolved organic matter. We described the spectrum for apparent quantum yield as ϭ c ϫ 10 Ϫ d , where c (dimensionless) and d (nm Ϫ1 ) are positive constants. Mathematical optimization for the best fit between the measured and the modeled photochemical mineralization resulted in of 7.52 ϫ 10 Ϫ0.0122 . The based on the measurements in situ agreed with determined in a laboratory at 320, 355, and 390 nm. Using the determined , we calculated that UV-B contributed 9%, UV-A 68%, and visible light 23% to the photochemical mineralization. Half of total photochemical mineralization was due to wavelengths Ͻ360 nm. Our method for the determination of is applicable in situ, improves the prediction of photochemical reaction rates in surface waters, and offers an alternative to the determination of quantum yields at discrete wavelengths. helsinki.fi).
Journal of Geophysical Research, 1995
The quantum yield •b of photosynthesis (mol C (mol photons) -1) was calculated at six depths for the waters of the Marine Light-Mixed Layer (MLML) cruise of May 1991. As there were photosynthetically available radiation (PAR) but no spectral irradiance measurements for the primary production incubations, three ways are presented here for the calculation of the absorbed photons (AP) by phytoplankton for the purpose of calculating •b. The first is based on a simple, nonspectral model; the second is based on a nonlinear regression using measured PAR values with depth; and the third is derived through remote sensing measurements. We show that the results of •b calculated using the nonlinear regression method and those using remote sensing are in good agreement with each other, and are consistent with the reported values of other studies. In deep waters, however, the simple nonspectral model may cause quantum yield values much higher than theoretically possible.
Increases in the longwave photobleaching of chromophoric dissolved organic matter in coastal waters
Limnology and Oceanography, 2009
Salinity effects on the photobleaching of chromophoric dissolved organic matter (CDOM) due to coastal mixing were investigated through a comparative study of surrogate and surface-water CDOM. Suwannee River humic acid (SRHA) and ultrafiltered river dissolved organic matter (UDOM) added to mixtures of river and seawater permeates (,1 kDa) that varied in salinity from 0 to 33 to mimic coastal mixing. Surface-water CDOM was collected from the Chesapeake Bay in January, June, and September 2002. Shortwave CDOM absorption loss (e.g., 280 nm) did not change with salinity; however, longwave CDOM absorption loss (e.g., 440 nm) often decreased by 10% to 40% with salinity. Apparent quantum yields for average absorption loss from 280 to 550 nm (Q avg ) increased with salinity for both surrogate and surface-water CDOM, providing evidence for an effect of salinity independent of light absorption among different samples. Further, hydrogen peroxide photoproduction from UDOM increased from 15 to 368 nmol L 21 h 21 with salinity, even though pH values were circumneutral. A kinetic model demonstrated that, at circumneutral pH and iron concentrations expected for the Chesapeake Bay, photo-Fenton chemistry could not explain the increase in hydrogen peroxide production quantum yields (Q hp ) with salinity. Using Q avg for the SRHA and UDOM surrogates, a model of the change in surface-water CDOM photoreactivity in the Chesapeake Bay as a function of salinity suggested additional CDOM inputs for the lower Chesapeake Bay. Because estuarine mixing increases photobleaching of longwave CDOM absorption, the modeling of absorption coefficients above 400 nm may underestimate dissolved organic matter in coastal waters. 1 Corresponding author (chris_osburn@ncsu.edu).
Marine Ecology Progress Series, 1993
The Watercolors field study quantified time and space variability in the quantum yield for carbon fixation (4) within the Southern California Bight, USA. (SCB) for 3 wk during summer 1988. The highly variable waters of the Bight allow a diverse spatial gradient in optical properties and phytoplankton community structure to b e sampled on a single transect. Therefore this dataset provides a stringent test to any enip~rical model attempting to predict biological parameters. The data were used to determine whether observed var~ability in C$ could be empirically explained by independent param e t e r (~) routinely measured at sea (e.g. nitrate, temperature, light, accessory pigmentation). Most of the phytoplankton communities sampled were light-limited and thus operating at a maximum quantum yield (4,,,). In situ d,,,, values were rout~nely 2-to 10-fold lower than the theoretical upper limit of 0.125 m01 C pEin-', varied more than 10-fold over the time and space scales of the study, did not routinely increase with decreasing hght levels, and showed no correlation with any single or set of environmental variables measured. These findlngs challenge existing assumptions regarding in situ behavior of 4 as presented in many bio-optlcal models of primary production. The unpredictable behavior of 6 was shown to result largely from variable correspondence between environmental parameters and the photosynthetic components of the quantum yield calculations, namely the photosynthesis-irradiance parameters P,,,,,, a and I,. The significance of these findings for bio-optical modeling of @ a n d primary productivity are d~scussed.