Most of the primary productivity in the ocean comes from phytoplankton,
and is impacted, among other things, by the amount of nutrients
available, as well as by temperature. The Late Miocene and Pliocene were
marked by global aridification, linked to the emergence of the large
deserts, likely increasing the input of dust and thus nutrients into the
ocean. There was also a global decrease in temperature during this
period, linked to a decline in atmospheric CO2 concentration. The
objective of this study is to quantify the impact of dust and pCO2
levels on primary productivity in the oceans under Late Miocene boundary
conditions. New simulations were performed with the coupled
ocean-atmosphere model IPSL-CM5A2 and its marine biogeochemistry
component PISCES with a Late Miocene paleogeography. Our results show
that an increase in dust input produces a quasi-generalized increase in
primary productivity, associated with a decrease in nutrient limitation.
This increase in productivity also leads to nutrient deficits in some
areas. The decrease in pCO2 levels and the associated lower water
temperatures lead to a reduction in primary productivity. This decrease
is mainly due to a reduction in the supply of nutrients resulting from
less intense remineralization. In addition, our results show that change
in carbon export resulting from change in dust input and temperature are
highly heterogeneous spatially. Simulations combined with sedimentary
data suggesting a link between aridification, cooling and the Biogenic
Bloom of the Late Miocene and Pliocene.