Westberry, Toby: Oregon State University (Project Lead)
Project Funding:
2014 - 2016
NRA: 2013 NASA: The Science of Terra and Aqua
Funded by NASA
Abstract:
Phytoplankton net primary production (NPP) is the main conduit through which atmospheric CO2 enters the complex maze of organic carbon transformation pathways in marine ecosystems and ultimately creates the export flux of carbon to depth (i.e., the 'biological pump'). MODIS Aqua ocean products have now reached the status of climate- quality data and present greater opportunities for an advanced understanding of NPP than earlier ocean color sensors (CZCS, SeaWiFS) or the follow-on VIIRS sensor. The research proposed here uses the advanced observational capabilities of the MODIS Aqua and Terra sensors to establish a next-generation approach for assessing global ocean productivity that addresses key physiological- and ecological attributes of the plankton, thereby yielding improved understanding of surface ocean carbon flow and a foundation for realizing both NASA's broad ocean science objectives and specific goals for upcoming ocean missions. The current research project encompasses the complete set of MODIS ocean ecosystem properties to first constrain global ocean NPP, and then address a specific science issue: the partitioning of newly formed organic carbon into new phytoplankton biomass versus transfer to other trophic levels. Employment of MODIS ocean color data as the primary tool for this investigation makes this project responsive to component 2.1 'Science Data Analysis' of NASA solicitation NNH13ZDA001N-TERAQ (The Science of Terra and Aqua). However, the importance of this investigation reaches beyond the analysis of MODIS data alone, as it will also establish a foundation for advanced NPP modeling envisioned for future NASA ocean missions, in particular the PACE mission.
The assessment and monitoring of global ocean NPP has always been recognized as a key objective in oceanographic research and it has been a primary motivation behind NASA's sustained ocean color record. Prior to satellite observations, the paucity of relevant field observations was the primary source of uncertainty in global NPP assessments. With the launch of CZCS and SeaWiFS uncertainties in NPP assessments became dominated by the challenge of converting standing stocks of chlorophyll into rates of carbon fixation. With MODIS observations and recent advances in ocean color data analyses, it is now possible to combine information on phytoplankton carbon biomass (C), pigment absorption, chlorophyll fluorescence quantum yields, and phytoplankton size fractions to address the NPP assessment problem with a more sophisticated approach. This research project focuses on 4 key developmental activities:

1. Physiological assessments based on absorption:carbon ratios, rather than Chl:C 2. Correction for iron-stress effects by employing MODIS fluorescence quantum yield data
3. Chlorophyll-independent partitioning of production among phytoplankton size groups
4. Growth irradiance assessments using alternative mixed layer depth criteria
Following model development, we will quantify uncertainties in NPP estimates to identify specific issues for refinement. We will then focus our science analysis comparisons of NPP and net population growth rates to evaluate spatio-temporal changes in production-loss balances and their links to environmental forcings.
Publications:
Silsbe, G. M., Behrenfeld, M. J., Halsey, K. H., Milligan, A. J., Westberry, T. K. 2016. The CAFE model: A net production model for global ocean phytoplankton. Global Biogeochemical Cycles. 30(12), 1756-1777. DOI: 10.1002/2016GB005521
More details may be found in the following project profile(s):
