Extreme value distributions describe interannual variability in the
North Atlantic spring bloom
Abstract
The North Atlantic spring bloom depends on a confluence of environmental
factors that drive transient periods of exponential phytoplankton growth
and interannual variability in bloom magnitude. We analyze interannual
bloom variability in the North Atlantic via extreme value theory where
the Generalized Extreme Value Distribution (GEVD) is fitted spatially to
annual maxima of satellite-measured surface chlorophyll. We find
excellent agreement between the observed distribution of interannual
bloom maxima and those predicted from the GEVD. The spatial distribution
of fitted GEVD parameters closely follows basin bathymetry where the
largest extremes and heaviest distribution tails are found on the
continental shelves and slopes. Trend analyses suggest weak evidence for
changes in GEVD parameters, despite regional trends in mean chlorophyll
levels and sea surface temperature. These results provide a framework to
quantify interannual bloom variability and call for further work
examining how extreme blooms propagate through food webs and contribute
to carbon export.