An Assessment and Improvement of Satellite Ocean Color Algorithms for the Tropical Pacific Ocean

Abstract

The tropical Pacific Ocean is a globally significant region of climate‐driven biogeochemical variability. Satellite ocean color algorithms have been used for over 20 years, providing a substantial historical record of global ocean chlorophyll‐a variability. Current chlorophyll algorithms perform better in the tropical Pacific than for the globe. Nevertheless, improvements can be made to produce a robust historical record of chlorophyll variability, which is essential to accurately identify ocean‐atmosphere carbon fluxes and long‐term trends in ocean productivity. We use a large in situ chlorophyll database to tune empirical ocean color algorithms to reduce bias in the equatorial Pacific. Traditional band ratio chlorophyll algorithms (OCx) perform adequately but exhibit errors at low chlorophyll concentrations. A new algorithm, the Ocean Color Index (OCI; Hu et al., 2012, https://doi.org/10.1029/2011JC007395), is more effective at calculating low chlorophyll concentrations in the mesotrophic tropical Pacific Ocean. Existing ocean color algorithms underestimate tropical Pacific chlorophyll by 5.8%, 14%, and 2% for three satellite ocean color sensors: SeaWiFS, MODIS‐Aqua, and MERIS. In this paper, we develop regionally tuned sensor‐specific coefficients and blending windows between the OCI to OCx algorithms to reduce systematic biases in the tropical Pacific. We assess cross‐sensor consistency to produce robust 21‐year time series trends. These updated estimates increase chlorophyll concentrations in open water and decrease around island and warm‐pool regions, with implications for our understanding of El Niño‐Southern Oscillation driven carbon fluxes and net primary productivity.

Global Chlorophyll Concentration Distribution and Effects on Bottom Reflectance of Coral Reefs

“…Upon examination of specific oceanic basins, our results align with evidence indicating lower productivity in the central Pacific Ocean compared to other oceanic regions [55][56][57]. Furthermore, our findings in the Equatorial Pacific region are in agreement with previous observations, showing Chl-a concentrations ranging from 0.08 to 0.6 mg•m −3 with low temporal variability [58][59][60]. In contrast, the Indian Ocean and West Pacific exhibit the highest Chl-a concentrations and variability (Chl-a CV).…”

Relationships Between Air‐Sea CO2 Flux and New Production in the Equatorial Pacific

“…This CO 2 flux data was used for comparison with the Landschützer product. The Tropical Pacific Chlorophyll Algorithm (TPCA; Pittman et al., 2019) was accessed from https://researchdata.edu.au/tropical-pacific-chlorophyll-reprocessing-v10/1438905 (downloaded January 2020). Monthly 0.25° wind speeds were obtained for the Cross‐Calibrated Multi‐Platform (CCMP) product Version 2 due to its superior performance in the equatorial Pacific (Chiodi et al., 2019).…”

“…No published decadal new production trends are available for the equatorial Pacific. However chlorophyll, as a proxy for phytoplankton biomass, is a good indicator of both NPP and new production, and has decreased at between 0.33% and 1.30% decade −1 since 2000 (Pittman et al., 2019). The equatorial Pacific Ocean Climate Studies in the 1980s and Joint Global Ocean Flux Study in the 1990s provided a comprehensive database of new production (Aufdenkampe et al., 2001; F. P. Chavez & Barber, 1987; Le Borgne, Feely, & Mackey, 2002; Murray et al., 1994; Quay, 1997).…”

Oceanic primary production trend patterns along coast of Ecuador

“…Compared to other regions of the world, current algorithms for ocean color detection have performed better in the Tropical Pacific Ocean. The MODIS-Aqua algorithms work well, but underestimate low chlorophyll concentration by 10.6% [46]. On the other hand, the current version of MUR (fv04.1) incorporates a multiscale SST data interpolation and fusion technique (including in situ measurements) to correct biases.…”