  The Southern Ocean (in the region 60-180$^\circ$E) south of the Indian Ocean,
Australia, and the West Pacific is noted for the frequent occurrence and
severity of its storms. These storms give rise to high-amplitude secondary
microseisms from sources, including the deep ocean regions, and primary
microseisms where the swells impinge on submarine topographic features. A
better understanding of the varying microseism wavefield enables improvements
to seismic imaging and development of proxy observables to complement sparse in
situ wave observations and hindcast models of the global ocean wave climate. We
analyze 12-26 years of seismic data from 11 seismic stations either on the East
Antarctic coast or sited in the Indian Ocean, Australia, and New Zealand. The
power spectral density of the seismic wavefield is calculated to explore how
the time-changing microseism intensity varies with (i) sea ice coverage
surrounding Antarctica and (ii) the Southern Annular Mode (SAM) climate index.
Variations in sea ice extent are found to be the dominant control on the
microseism intensity at Antarctic stations, which exhibit a seasonal pattern
phase-shifted by 4-5 months compared to stations in other continents. Peaks in
extremal intensity at East Antarctic stations occur in March-April, with the
highest peaks for secondary microseisms occurring during negative SAM events.
This relationship between microseism intensity and the SAM index is opposite to
that observed on the Antarctic Peninsula. This work informs the complexity of
microseism amplitudes in the Southern Hemisphere and assists ongoing
interdisciplinary investigations of interannual variability and long-term
trends.
