The extraterrestrial dust flux: size distribution and mass contribution estimates inferred from the Transantarctic Mountain (TAM) micrometeorite collection

This study explores the long-duration (0.8-2.3Ma), time-averaged
micrometeorite flux (mass and size distribution) reaching Earth, as
recorded by the Transantarctic Mountain (TAM) micrometeorite collection.
We investigate a single sediment trap (TAM65), performing an exhaustive
recovery and characterization effort and identifying 1643 micrometeorites
(between 100-2000μm). Approximately 7% of particles are unmelted or
scoriaceous, of which 75% are fine-grained. Among cosmic spherules, 95.6%
are silicate-dominated S-types, and further subdivided into porphyritic
(16.9%), barred olivine (19.9%), cryptocrystalline (51.6%) and vitreous
(7.5%). Our (rank)-size distribution is fit against a power law with a
slope of -3.9 (R2=0.98) over the size range 200-700μm. However, the
distribution is also bimodal, with peaks centered at ~145μm and ~250μm.
Remarkably similar peak positions are observed in the Larkman Nunatak
data. These observations suggest that the micrometeorite flux is composed
of multiple dust sources with distinct size distributions. In terms of
mass, the TAM65 trap contains 1.77g of extraterrestrial dust in 15kg of
sediment (<5mm). Upscaling to a global annual estimate gives 1,555
(±753) t/yr – consistent with previous micrometeorite abundance estimates
and almost identical to the previous South Pole Water Well flux estimate
(~1,600 t/yr) and potentially suggesting minimal variation in the
background cosmic dust flux over the Quaternary. The greatest uncertainty
in our mass flux calculation is the accumulation window. A minimum age
(0.8Ma) is robustly inferred from the presence of Australasian
microtektites, while the upper age (~2.3Ma) is loosely constrained based
on 10Be exposure dating of glacial surfaces at Roberts Butte (6km from our
sample site).