Thanks, that's a very good observation, and interesting question; it does seem somewhat unusual and levels were super high, indeed. We don't know, but the data we have do provide some hints so I will speculate! :)
Our monthly SPOT cruise that month was on January 11th, 2011 and we observed somewhat elevated chlorophyll, ~2 µg/L versus ~20 µg/L for the 8 day average from MODIS. I suspect that the large bloom suggested by MODIS happened after our cruise. Generally, the water column is well-mixed during our Southern Californian "winter" months, down to at least 20 m but more typically between 30-40 m. However, this particular month, for some reason, perhaps unseasonably warm air and calm seas, the mixed layer depth was only about 12.5 m (so most of the plankton stay mixed within the well-lit waters longer) and nutrients were 2-4x higher than usual for that time of year (January is already one of the higher months). Couple that with what appears to be warming air temperatures (~6C, January 10th-15th, https://www.wunderground.com/personal-weather-station/dashboard? ID=KCACATAL2#history/tgraphs/s20110101/e20110131/mmonth , which which seems to correspond to clear skies (from UV index at LAX ftp://ftp.cpc.ncep.noaa.gov/long/uv/cities ) and relatively calm seas (not shown), and perhaps you have a recipe for a bloom!
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