  We do a preliminary modelling of the photosynthetic rates of phytoplankton at
the very beginning of the Paleogene, just after the impact of the Chicxulub
asteroid, which decisively contributed to the last known mass extinction of the
Phanerozoic eon. We assume the worst possible scenario from the photobiological
point of view: an already clear atmosphere with no ozone, as the timescale for
soot and dust settling (years) is smaller than that of the full ozone
regeneration (decades). Even in these conditions we show that most
phytoplankton species would have had reasonable potential for photosynthesis in
all the three main optical ocean water types. This modelling could help explain
why the recovery of phytoplankton was relatively rapid after the huge
environmental stress of that asteroid impact. In a more general scope, it also
reminds us of the great resilience of the unicellular biosphere against huge
environmental perturbations.

Earth and Planetary Astrophysics;Atmospheric and Oceanic Physics;Geophysics