Project Funding: 2014 - 2017

NRA: 2013 NASA: Terra and Aqua: Algorithms--Existing Data Products   

Funded by NASA

Abstract:
I propose to maintain the algorithm for particulate inorganic carbon (PIC; otherwise known as calcium carbonate). To date, the PIC algorithm has been based on an ever- increasing, but still relatively small, set of field measurements (small as compared to the chlorophyll a validation data set, which contains ~350X more data simply because more investigators have sampled it over the years and chlorophyll analyses are cheaper to run). The merged two-band/three-band algorithm is fundamentally a Case I algorithm; that is, it is designed for areas where suspended sediments,river-born sediments or colored dissolved organic matter do not significantly impact ocean optical properties. The PIC algorithm accounts for 78% of the variance in field-measured PIC and the standard error  of PIC determinations (compared to shipboard validation data) is +/-0.08mmol m^-3, comparable to the PIC concentrations found in oligotrophic gyres. But there is still considerable room for improvement in the PIC algorithm. These statistics can only be achieved if the satellite data are binned in space and time (relatively easy to do with satellite data, but this obviously compromises temporal and spatial resolution). In Case I waters, errors in the algorithm result from: (a) the calcite-specific backscattering cross- section attributed to coccolithophores; (b) errors in the chlorophyll-dependent backscattering attributed to phytoplankton; and (c) presence of other scattering minerals, such as biogenic silica from diatom frustules, which do not scatter as intensely as PIC, but nonetheless can contribute significant optical backscattering. I propose to continue evaluating new data sets for PIC (generated from other ongoing studies) in order to revise PIC algorithm coefficients and look-up tables. Regarding the first source of error, I will focus on better defining the backscattering cross-section of calcite coccoliths geographically. Improvements in our estimate of the backscattering cross-section for calcite coccoliths will significantly improve the accuracy of the PIC algorithm. Regarding the second source of error, I will experiment with new algorithms for deriving chlorophyll concentration (e.g., the reflectance differencing algorithm of Hu et al., 2012). This will provide a better derivation of the backscattering associated with chlorophyll- containing phytoplankton, which, in turn, will allow improved estimates of PIC. This work will be in collaboration with Dr. Chuamin Hu (Univ. South Florida). Regarding the third source of error, I will correct for the presence of biogenic silica, which is ubiquitous over the globe and a potentially important light scattering contributor in its own right. Moreover, biogenic silica can now be estimated remotely (Balch et al., 2010). Accounting for this component of the backscattering signal will allow better estimates of PIC backscattering and derivation of PIC concentration. I will compare algorithm implementation for both MODIS Aqua and MODIS Terra satellites and perform full error analyses of the revised algorithm in the interest of providing seamless, climate-quality, PIC data. Although the focus of this proposal is on continuity of the Terra and Aqua PIC product, the algorithm can also be applied to VIIRS imagery. Dr. Howard Gordon (Univ. Miami) will be collaborating on the overall assessment of the revised PIC algorithm. The outcome of this algorithm maintenance work will be an improved PIC product with lower RMS error.

Publications:

Balch, W. M., Bates, N. R., Lam, P. J., Twining, B. S., Rosengard, S. Z., Bowler, B. C., Drapeau, D. T., Garley, R., Lubelczyk, L. C., Mitchell, C., Rauschenberg, S. 2016. Factors regulating the Great Calcite Belt in the Southern Ocean and its biogeochemical significance. Global Biogeochemical Cycles. 30(8), 1124-1144. DOI: 10.1002/2016GB005414 

Balch, W. M., Bowler, B. C., Drapeau, D. T., Lubelczyk, L. C., Lyczkowski, E. 2018. Vertical Distributions of Coccolithophores, PIC, POC, Biogenic Silica, and Chlorophyll a Throughout the Global Ocean. Global Biogeochemical Cycles. 32(1), 2-17. DOI: 10.1002/2016GB005614

Hopkins, J., Balch, W. M. 2018. A New Approach to Estimating Coccolithophore Calcification Rates From Space. Journal of Geophysical Research: Biogeosciences. 123(5), 1447-1459. DOI: 10.1002/2017JG004235

Maranon, E., Balch, W. M., Cermeno, P., Gonzalez, N., Sobrino, C., Fernandez, A., Huete-Ortega, M., Lopez-Sandoval, D. C., Delgado, M., Estrada, M., Alvarez, M., Fernandez-Guallart, E., Pelejero, C. 2016. Coccolithophore calcification is independent of carbonate chemistry in the tropical ocean. Limnology and Oceanography. 61(4), 1345-1357. DOI: 10.1002/lno.10295

More details may be found in the following project profile(s):

• NASA Ocean Biology & Biogeochemistry (OBB) Project Profile