Spatiotemporal Chlorophyll-a Dynamics on the Louisiana Continental Shelf Derived from a Dual Satellite Imagery Algorithm

Authors

Chengfeng Le, ORISE Fellow, US EPA Gulf Ecology Division
John C. Lehrter, ORISE Fellow, US EPA Gulf Ecology Division
Chuanmin Hu, University of South FloridaFollow
Michael C. Murrell, ORISE Fellow, US EPA Gulf Ecology Division
Lin Qi, University of South Florida

Document Type

Article

Publication Date

2014

Keywords

phytoplankton biomass, ocean color, Louisiana continental shelf, satellite imagery, algorithm, hypoxia

Digital Object Identifier (DOI)

https://doi.org/10.1002/2014JC010084

Abstract

A monthly time series of remotely sensed chlorophyll-a (Chla_rs) over the Louisiana continental shelf (LCS) was developed and examined for its relationship to river discharge, nitrate concentration, total phosphorus concentration, photosynthetically available radiation (PAR), wind speed, and interannual variation in hypoxic area size. A new algorithm for Chla_rs, tuned separately for clear and turbid waters, was developed using field-observed chlorophyll-a (Chla_obs) collected during 12 cruises from 2002 to 2007. The new algorithm reproduced Chla_obs, with ∼40% and ∼60% uncertainties at satellite pixel level for clear offshore waters and turbid nearshore waters, respectively. The algorithm was then applied to SeaWiFS and MODIS images to calculate long-term (1998–2013) monthly mean Chla_rs estimates at 1 km resolution across the LCS. Correlation and multiple stepwise regression analyses were used to relate the Chla_rs estimates to key environmental drivers expected to influence phytoplankton variability. The Chla_rs time series covaried with river discharge and nutrient concentration, PAR, and wind speed, and there were spatial differences in how these environmental drivers influenced Chla_rs. The main axis of spatial variability occurred in a cross-shelf direction with highest Chla_rs observed on the inner shelf. Both inner (<10 m depth) and middle-shelf (10–50 m depth) Chla_rs were observed to covary with interannual variations in the size of the hypoxic (O₂ < 63 mmol m⁻³) area, and they explained ∼70 and ∼50% variability in interannual hypoxia size, respectively.

Rights Information

Terms of use for work posted in Scholar Commons.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Journal of Geophysical Research: Oceans, v. 119, issue 11, p. 7449-7462

©2014. American Geophysical Union. All Rights Reserved.

Scholar Commons Citation

Le, Chengfeng; Lehrter, John C.; Hu, Chuanmin; Murrell, Michael C.; and Qi, Lin, "Spatiotemporal Chlorophyll-a Dynamics on the Louisiana Continental Shelf Derived from a Dual Satellite Imagery Algorithm" (2014). Marine Science Faculty Publications. 1939.
https://digitalcommons.usf.edu/msc_facpub/1939