Scientists at the Cooperative Institute for Marine Resources Studies (CIMRS) are investigating sounds generated by icebergs in the Southern Ocean and their potential to affect marine animals and ecosystems. While the steady increase in global shipping traffic has been identified as a primary cause of rising ocean noise level, the disintegration of large icebergs was found to be another significant noise source that influences the soundscape of the southern hemisphere.
Two icebergs, B15a and C19a, collectively larger than Connecticut, calved off the Ross Ice Shelf in early 2000s and drifted eastward to the warmer South Pacific Ocean in late 2007. For the next 1.5 years, while these icebergs were rapidly melting, they affected water circulation and marine ecosystem in their vicinity.
From 2008 to early 2009, the disintegration of B15a and C19a continuously projected loud low frequency sounds into the water column. The sounds propagated efficiently to lower latitudes, thus influencing the soundscape of the entire South Pacific basin. The icebergs’ sounds were recorded at Juan Fernandez Island (34oS, 79oW) by hydrophones maintained by Comprehensive Nuclear-Test-Ban Treaty Organization. The sounds also propagated across the equator (~10,000 km) and were recorded at 8oN, 110oW by a hydrophone maintained by NOAA Pacific Marine Environmental Laboratory (PMEL) and CIMRS. The noise level was ~7 dB and ~3 dB higher than baseline years, respectively. The icebergs’ sounds dominated frequency ranges below 100 Hz in which marine mammals, such as baleen whales, vocalize for communication, navigation and forage behaviors.
Some large icebergs have lifespans over a decade. This study shows that icebergs the size of B15a and C19a can generate a considerable amount of sound energy, which can propagate across ocean basins, influencing the ocean acoustic environment and potentially marine mammals' acoustic behaviors for the duration of the iceberg’s disintegration.
The study meets NOAA PMEL’s goals of (a) to acquire long-term data sets of the global ocean acoustics environment and (b) to identify and assess acoustic impacts from human activities and natural processes on the marine environment.
Contact: Haru Matsumoto, Oregon State University CIMRS Assistant Professor, Research, firstname.lastname@example.org