Extraterrestrial dust as a source of bioavailable Fe for the ocean productivity

Bioavailable Fe is an essential nutrient for phytoplankton that allows
these organisms to flourish and drawdown atmospheric CO2 affecting global
climatic condition. In marine locales remote from the continents
extraterrestrial (ET) dust provides an important source of Fe and thus
moderates primary productivity. Here we provide the first constraints on
the partitioning of extraterrestrial Fe between seawater and sediments
from observations of the dissolution and alteration of 5228 cosmic
spherules recovered from the deep sea sediments and Antarctica. Of the
~3,000-6,000 t/a ET dust that reaches the Earth surface, ~2–5% material
survives in marine sediments whilst the remainder is liberated into
seawater by dissolution and etching. Both processes contributes
~(3–10)×10-8mol Fe m-2 yr-1. Also, the Fe contribution due to evaporation
of survived particle is estimated to be ~0.2–0.5 t d-1 that is ~10% of Fe
contribution to meteoric smoke. The contribution of Fe from dissolution is
small in comparison to recondensed meteoritic smoke particles. Cosmic
spherules, also indicate that Fe is enhanced in smoke particles compared
to surviving micrometeorites (MMs) by partial evaporation. Whilst smokes
are delivered directly to the photic zone of the ocean, dissolved MMs also
deliver their Fe in those areas. Changes in the ET dust flux vary not only
the amount of Fe by up to three orders of magnitude, but also the
partitioning of Fe between surface and abyssal waters depending on entry
velocity and its effect on evaporation.