Effects of Seasonal and Secular changes in Antarctic Sea Ice on Microseismic Noise

Abstract:

The Earth’s background microseism noise spectrum, observed widely across the Earth is commonly dominated between ~1-30 seconds period by oceanic wave activity that arises when ocean swell is converted to (predominately) Rayleigh waves. Peak power levels in the microseism band at high-latitude stations typically coincide with large-scale extratropical cyclonic winter storm activity. However, due to the seasonal formation of sea ice around the continental shelves of polar regions, oceanic waves are impeded from efficiently exciting seismic energy, and annual peak microseism power thus occurs prior to the midwinter storm peak. We analyze recently collected Polar Earth Observatory (POLENET/A-NET) and Antarctica’s Gamburtsev Province (GAMSEIS) seismic data to characterize the Antarctic microseism signal and its unique seasonality and annual variations in each of three distinct bands: the high-frequency secondary microseism (1-5 s), the secondary microseism (5-10 s) and the primary microseism band (10-20 s). Power in these bands is found to be strongly anti-correlated with sea ice extent. with the shorter period signals being exceptionally sensitive to local conditions. We quantitatively show that the formation of sea ice may be capable of attenuating on-shore microseism power by as much as 90%. Additionally, we note a significant increase in primary microseism power attributable to near coastal Antarctic Peninsula sources during the last twenty years. This increase correlates with regional sea ice loss driven by large-scale wind changes associated with the strengthening of the Southern Annular Mode. Investigation of microseism seasonality, power, and decadal-scale trends in the Antarctic shows promise as a spatially integrated tool for monitoring and interpreting such sea ice strength and extent, metrics through time.