We demonstrate for the first time the detectability of mid-latitude Rossby
waves in global ocean colour data from the Japanese Ocean Colour and Temper
ature Scanner (OCTS) and U.S. Sea-viewing Wide Field-of-view Sensor (SeaWiF
S) radiometers. By producing longitude-time plots of the merged OCTS and Se
aWiFS datasets we observe at some latitudes westward propagating signals. T
heir signature is much weaker than the annual phytoplankton cycle but can b
e highlighted by filtering the plots. The main propagating speed is estimat
ed with the Radon Transform and increases equatorward, as expected for Ross
by waves. A comparison with both speeds derived from altimeter data and the
zonal mean of the speed predicted by a recent theory of Rossby wave propag
ation shows a broad agreement. We conclude that Rossby waves are sometimes
observable in the ocean colour field and thus have some effects on biology,
and we suggest two simple hypotheses for the underlying interaction mechan
ism.