Project Funding: 2010 - 2013

NRA: 2009 NASA: The Science of Terra and Aqua   

Funded by NASA

Abstract:
The fundamental contribution of the NASA satellite ocean color era has been unprecedented visualization of the ocean biosphere in terms of the ubiquitous plant pigment, chlorophyll. Launched in 2002, MODIS on Aqua continues this tradition, while also providing additional capabilities for ocean color research such as spectral bands specifically designed to look at fluorescence from chlorophyll. Unfortunately, past uncertainty about how to utilize this ability has left of dearth of scientific literature on the topic and has failed to capitalize on one of the major sensor improvements over predecessor missions. A current mission-wide reprocessing of Aqua MODIS ocean data by NASA will remove problems known to exist in the Fluorescence Line Height (FLH) product for the first time and necessitates a re-analysis of FLH-derived quantities. Thus, the overarching goals of this proposal are to re-assess and improve the assumptions required for using Aqua MODIS FLH data and to better understand the environmental forcings responsible for its variability. Recent progress by our research group and others has begun this process, but many details require attention before the richness of FLH-derived information is realized, and further underscores the timeliness of an effort specifically designed to advance our collective understanding of FLH behavior. In our earlier work supported by the 2006 NASA Program entitled Earth System Science Research using Data and Products from Terra, Aqua and ACRIMSAT Satellites (NNH06ZDA001N), we provided an initial framework for working with global FLH data. In that work, a preliminary accounting for the major factors affecting fluorescence quantum yield (φ) revealed tantalizing global patterns which to first order, appeared highly correlated with levels of iron availability. While a potential diagnostic for iron stress from space is exciting, many caveats exist and require attention before a complete picture emerges. For example, why don’t all iron limited regions exhibit a consistent response in φ? Conversely, how do we interpret regions of the ocean that also exhibit enhanced φ, but are not currently thought of as iron limited? There are other environmental factors known to affect φ and which overlay additional variability on its global spatial and temporal patterns. In the work proposed here, we outline a more thorough treatment of mechanisms which exert environmental control on φ variability and describe approaches for their accounting. In particular, we will re-examine FLH and φ variability in the context of changes due to pigment biomass, changes in absorption efficiency, and light driven reductions in φ due to photoprotection (non-photochemical quenching) necessitated by the MODIS reprocessing. A particular focus will be the characterization of phytoplankton photoacclimation and how it can cause differential response in the above relationships with FLH and φ. Once these methodological corrections have been addressed, we will utilize FLH and φ for novel science data analysis. For example, we will explore temporal trends in φ relative to long term and periodic climate trends similar to that which has been done with Chl and its derivative products (e.g., net primary production). We will also use multiple approaches to estimate uncertainties in FLH-derived products as required by the research solicitation. Developments made in the analysis and processing of FLH data will be effectively transferred to the community through a close working relationship with the Ocean Biology Processing Group (OBPG) at NASA, with the ultimate goal of making higher level FLH-derived quantities into future archive products. In the interim, we will provide science test products to the broader science community, and which are distinct from those distributed by NASA OBPG.

2011 NASA Carbon Cycle & Ecosystems Joint Science Workshop Poster(s)

• Retrospective Satellite Ocean Color Analysis of Ocean Iron Fertilization (OIF)   --   (Toby K. Westberry, Michael J. Behrenfeld, Allen J. Milligan, Scott C. Doney)   [abstract]

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

• NASA Ocean Biology & Biogeochemistry (OBB) Project Profile