Acoustic impact of seismic research surveys on marine mammals in the Southern Ocean - Geophysical contributions to a risk assessment study

• Main Author: Breitzke, Monika
• Format: Conference Object
• Language: unknown
• Published: 2009
• Subjects: Alfred Wegener Institute; Antarc*; Antarctic; Southern Ocean; Weddell Sea
• Online Access: https://epic.awi.de/id/eprint/19711/; https://hdl.handle.net/10013/epic.31581

According to the Protocol on Environmental Protection to the Antarctic Treaty seismic surveys in the Southern Ocean south of 60°S are exclusively dedicated to academic research. To assess the potential risk of such research surveys posed on marine mammals a risk assessment study was prepared by the Alfred-Wegener-Institute for Polar and Marine Research (AWI), Bremerhaven. The geophysical contributions to this risk assessment study focus on 3 topics: (1) regional and seasonal distribution of seismic surveys, (2) in-situ calibration of air gun configurations used by R/V Polarstern, (3) modeling sound propagation of single shots and cumulative effects of multiple shots along a seismic line.The studies on the regional and seasonal distribution of seismic surveys are based on the Seismic Data Library System for Cooperative Research (SDLS). They indicate that seismic research surveys conducted by the AWI focused on two areas: the Weddell Sea and the Amundsen/Bellinghausen Sea. Histograms of the Julian days and water depths covered by these surveys indicate that maximum activities occurred from January to March, and most lines were collected either in shallow waters of 200 to 600 m depth or in deep waters of 3000 to 4000 m depth. An in-situ calibration of the air gun configurations used by R/V Polarstern was conducted in the Herdlefjord, Norway in October 2003. The objective was to study the spatial distribution of the sound pressure levels emitted by the different air gun configurations, to describe their frequency content, and to derive nominal source levels and mitigation radii for different thresholds. The analysis of the recorded data shows that back-calculated zero-to-peak source levels range from 224 to 240 dB re 1 µPa @ 1 m for a single GI gun (0.7/1.7 l) to an 8 VLF gun array (24 l). Mitigation radii derived from the sound exposure levels (SEL) of single shots vary between 50 and 300 m for a 183 dB SEL threshold. For sound propagation modeling a 2.5D finite-difference code provided by T. Bohlen (TU ...