气候变化领域集成服务门户

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 approximate to 40% and approximate to 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 (O-2<63 mmol m(-3)) area, and they explained approximate to 70 and approximate to 50% variability in interannual hypoxia size, respectively.

Key Points

A new hybrid Chla algorithm was developed Driving factors of phytoplankton dynamics exhibited spatial differences Phytoplankton dynamics had significant relationship with hypoxia variation