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Aguirre-Hernandez, E, Gaxiola-Castro G, Najera-Martinez S, Baumgartner T, Kahru M, Mitchell BG.  2004.  Phytoplankton absorption, photosynthetic parameters, and primary production off Baja California: summer and autumn 1998. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 51:799-816.   10.1016/j.dsr2.2004.05.015   AbstractWebsite

To estimate ocean primary production at large space and time scales, it is necessary to use models combined with ocean-color satellite data. Detailed estimates of primary production are typically done at only a few representative stations. To get survey-scale estimates of primary production, one must introduce routinely measured Chlorophyll-a (Chl-a) into models. For best precision, models should be based on accurate parameterizations developed from optical and photosynthesis data collected in the region of interest. To develop regional model parameterizations C-14- bicarbonate was used to estimate in situ primary production and photosynthetic parameters (alpha*, P-m*, and E-k) derived from photosynthesis-irradiance (P-E) experiments from IMECOCAL cruises to the southern California Current during July and October 1998. The P-E experiments were done for samples collected from the 50% surface light depth for which we also determined particle and phytoplankton absorption coefficients (a(p), a(phi), and a(phi)*). Physical data collected during both surveys indicated that the 1997-1998 El Ni (n) over tildeo was abating during the summer of 1998, with a subsequent transition to the typical California Current circulation and coastal upwelling conditions. Phytoplankton chl-a and in situ primary production were elevated at coastal stations for both surveys, with the highest values during summer. Phytoplankton specific absorption coefficients in the blue peak (a(phi)*(440)) ranged from 0.02 to 0.11 m(2) (mg Chl-a)(-1) with largest values in offshore surface waters. In general a(phi)*5 was lower at depth compared to the surface. P-E samples were collected at the 50% light level that was usually in the surface mixed layer. Using alpha* and spectral absorption, we estimated maximum photosynthetic quantum yields (phi(max); mol C/mol quanta). phi(max) values were lowest in offshore surface waters, with a total range of 0.01-0.07. Mean values of phi(max) for July and October were 0.011 and 0.022, respectively. In July P-m* was approximately double and alpha* was about 1.4 times the values for October. Since the P-E samples were generally within the upper mixed layer, these tendencies in the photosynthetic parameters are attributed to deeper mixing of this layer during October when the mean mixed layer for the photosynthesis stations was 35m compared to a mean of 10m in July. Application of a semi-analytical model using mean values of P-E parameters determined at the 50% light depth provided good agreement with C-14 in situ estimates at the discrete 50% light depth and for the water-column integrated primary production. (C) 2004 Elsevier Ltd. All rights reserved.

Schwarz, JN, Kowalczuk P, Kaczmarek S, Cota GF, Mitchell BG, Kahru M, Chavez FP, Cunningham A, McKee D, Gege P, Kishino T, Phinney DA, Raine R.  2002.  Two models for absorption by coloured dissolved organic matter (CDOM). Oceanologia. 44:209-241. AbstractWebsite

The standard exponential model for CDOM absorption has been applied to data from diverse waters. Absorption at 440 nm (a(g)440) ranged between close to zero and 10 m(-1), and the slope of the semilogarithmic absorption spectrum over a minimum range of 400 to 440 nm (s440) ranged between < 0.01 and 0.04 nm(-1). NO relationship was found between a(g)440 or s440 and salinity. Except in the southern Baltic, s440 was found to have abroad distribution (0.0165 +/- 0.0035), suggesting that it should be introduced as an additional variable in bio-optical models when a(g)440 is large. An alternative model for CDOM absorption was applied to available high quality UV-visible absorption spectra from the Wisla river (Poland). This model assumes that, the CDOM absorption spectrum comprises distinct Gaussian absorption bands in the UV, similar to those of benzene. Five bands were fit to the data. The mean central energy of all hands was higher in early summer (E &SIM;7.2, 6.6, 6.4, 6.2 and 5.5 eV or 172, 188, 194, 200 and 226 nm)) than in winter. The higher energy bands were found to decay in both height and width with increasing salinity, while lower energy bands broadened with increasing salinity. 8440 was found to be correlated with shape parameters of the bands centred at 6.4 and 5.5 eV. While the exponential model is convenient for optical modelling and remote sensing applications, these results suggest that the Gaussian model offers a deeper understanding of chemical interactions affecting CDOM molecular structure.

O'Reilly, JE, Maritorena S, Mitchell BG, Siegel DA, Carder KL, Garver SA, Kahru M, McClain C.  1998.  Ocean color chlorophyll algorithms for SeaWiFS. Journal of Geophysical Research-Oceans. 103:24937-24953.   10.1029/98jc02160   AbstractWebsite

A large data set containing coincident in situ chlorophyll and remote sensing reflectance measurements was used to evaluate the accuracy, precision, and suitability of a wide variety of ocean color chlorophyll algorithms for use by SeaWiFS (Sea-viewing Wide Field-of-view Sensor). The radiance-chlorophyll data were assembled from various sources during the SeaWiFS Bio-optical Algorithm Mini-Workshop (SeaBAM) and is composed of 919 stations encompassing chlorophyll concentrations between 0.019 and 32.79 mu g L(-1). Most of the observations are from Case I nonpolar waters, and similar to 20 observations are from more turbid coastal waters. A variety of statistical and graphical criteria were used to evaluate the performances of 2 semianalytic and 15 empirical chlorophyll/pigment algorithms subjected to the SeaBAM data. The empirical algorithms generally performed better than the semianalytic. Cubic polynomial formulations were generally superior to other kinds of equations. Empirical algorithms with increasing complexity (number of coefficients and wavebands), were calibrated to the SeaBAM data, and evaluated to illustrate the relative merits of different formulations. The ocean chlorophyll 2 algorithm (OC2), a modified cubic polynomial (MCP) function which uses Rrs490/Rrs555, well simulates the sigmoidal pattern evident between log-transformed radiance ratios and chlorophyll, and has been chosen as the at-launch SeaWiFS operational chlorophyll a algorithm. Improved performance was obtained using the ocean chlorophyll 4 algorithm (OC4), a four-band (443, 490, 510, 555 nm), maximum band ratio formulation. This maximum band ratio (MBR) is a new approach in empirical ocean color algorithms and has the potential advantage of maintaining the highest possible satellite sensor signal:noise ratio over a 3-orders-of-magnitude range in chlorophyll concentration.