Monitoring a Sentinel Species from Satellites: Detecting Emiliania huxleyi in 25 Years of AVHRR Imagery - Satellite-based Applications on Climate Change - page 267

Chapter 18
Monitoring a Sentinel Species from Satellites:
Detecting Emiliania huxleyi

in 25 Years

of AVHRR Imagery

Stephanie Schollaert Uz, Christopher W. Brown, Andrew K. Heidinger,
Tim J. Smyth, and Raghu Murtugudde

Abstract Blooms of the coccolithophore Emiliania huxleyi were detected around
the world from 1982 through 2006 using Advanced Very High Resolution Radio-
meter (AVHRR) remote sensing reflectances. The annually averaged surface area
of these blooms has decreased over the past 25 years in regions where E . huxleyi
blooms are most prevalent - the Bering Sea, the North Atlantic south of Iceland, the
Norwegian and Barents Sea, and the Patagonian Shelf. Though less sensitive than
satellite ocean color sensors, AVHRR offers the longest continuous global dataset
of visible reflectances and has been used previously to identify regional E . huxleyi
blooms. This declining long-term trend in bloom surface area was correlated to warm
sea-surface temperature anomalies. The trend was weakly correlated to increased
mixed-layer depths. There were mixed results when comparing bloom surface area to
climate indices. Previous studies associated individual E . huxleyi blooms to warmer
temperatures and increased stratification. This apparently contrary result may indi-
cate that the dynamics of large-scale changes are different from those of individual,
local blooms. The decreased extent of blooms could also mean that E . huxleyi
respond to additional factors over the long term, such as ocean chemistry.

Keywords Coccolithophore • Emiliania huxleyi • Phytoplankton bloom • SeaWiFS •
AVHRR • Remote sensing reflectance • Stratification • Warming