Spatial heterogeneity of the Late Miocene Biogenic Bloom

The late Miocene and early Pliocene is marked by a major
oceanographic and geological event called the Late Miocene Biogenic
Bloom (LMBB). This event is characterized by high accumulation rates of
opals from diatoms and high calcite accumulation rates from calcareous
nannofossils and planktic foraminifera. The LMBB extends over several
million years and is present in the Pacific, Atlantic and Indian Oceans. Two
hypotheses have emerged from the literature to explain this event: a
global increase in the supply of nutrients to ocean basins through chemical
alteration of the continents and/or a major redistribution of nutrients in the
oceans. The objective of this study is to provide a more comprehensive
look at the temporal and geographical aspects of the LMBB. We have
compiled ocean drilling data (ODP-IODP) covering the late Miocene and
early Pliocene. This compilation contains sedimentation rates as well as
CaCO3, opal and terrigenous accumulation rates. After a careful screening
of the database, checking that all data are on the same time scale, we first
work on global trends of sedimentation and biogenic production before
going into more details. For instance, we show that the magnitude of the
Biogenic Bloom strongly varied between the three oceanic basins.
Normalization to a post-LMBB state allows comparison of rates of increase
in CaCO3 accumulation in different geographical areas (grouping several
sites). A very strong LMBB signature is present in oceanic area bordering
the western side of Australia. In the Atlantic Ocean, it is mainly present
near the equator and over South Africa. The LMBB signature is less
pronounced in the Indian Ocean but remains trackable near the northern
coasts of the basin. Moreover, it is also heterogeneous in terms of the
mineralogy produced and deposited in the deep ocean between regions.
For example, in the equatorial eastern Pacific, the LMBB signature is
present in the silica accumulation term but not in carbonates accumulation
one. Outputs from coupled ocean/atmosphere models (IPSL-CM5A2) using
late Miocene paleogeography and integrating a marine biogeochemistry
module (PISCES) have been gathered and will be discussed in regard to
our database.