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EMB Future Science Brief N°7 outlines the current state of our knowledge on the sources of anthropogenic sounds and the effects of noise on marine organisms. Moreover, it provides an overview of the measures that have been taken to address the issue of underwater noise. In order to develop proportionate mitigation strategies and effective regulation, we have to advance our knowledge about the effects of anthropogenic noise on marine organisms and their ecosystems.

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Understanding the regional and seasonal distribution of seismic research surveys in the Southern Ocean is essential for assessing their acoustic impact on the marine environment. An analysis of the navigation data and cruise table in the Seismic Data Library System for Cooperative Research (SDLS) shows that a fairly extensive network of seismic lines is now available for the Southern Ocean. However, line spacing ranges from tens to hundreds of kilometres, and some almost unsurveyed areas still exist. The seasonal distribution of the seismic profile lengths shows periods with increased survey activity between 1976/77 and 2001/02, but only moderate levels of activity between 2002/03 and 2010/11. The corresponding line spacing is large, and lines are widely distributed over the Southern Ocean. None of the eight Antarctic regions considered here have experienced seismic survey activity during all summer seasons in the last 35 years. Instead, periods with survey activity are interspersed by periods with no survey activity. The average survey length ranges from ~2600 km/season off the Antarctic Peninsula to ~260 km/season off Enderby Land. Compared to the industrial seismic exploration off Norway the acoustic impact of the seismic research activity in the Southern Ocean is at least ~150 times lower.

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New high-resolution bathymetric and sub-bottom profiler data collected in the Southern Mozambique Channel along a grid of 16 parallel, non-overlapping lines show a large variety of bedforms which were formed by strong bottom currents. They are classified into four main microtopographic zones and several sub-zones and divide the study area into regions with (1) smooth seafloor, (2) undulating bedforms, (3) seamounts and islands, and (4) the Zambezi Channel. A smooth seafloor occurs on the Mozambican continental slope together with downslope mass-wasting processes, north and south of Bassas da India, on the eastern levee of the Zambezi Channel and in the Zambezi cone. Undulating bedforms of some kilometres wavelength and several tens of metres height cover most of the southern, central and northeastern study area. The most spectacular bedforms are numerous, closely spaced, giant erosional scours of up to ~450 m depth, more than ~20 km length and ~3 - 7 km width in the southwestern part of the study area. Here, northward flowing Antarctic Bottom Water (AABW) is topographically blocked to the north and deflected towards the east due to the shallowing bathymetry of the Mozambique Channel. SW-NE trending undulating bedforms aligned parallel to the deflected AABW and interpreted as small contourite mounds allow to trace the AABW flow path eastwards. An ~100 km long W-E trending channel indicates the northernmost extension of the AABW. NW-SE oriented undulating bedforms in the west, hummocky bedforms in the east and arcuate, cross-cutting features in-between reflect a completely different current regime in the central study area. Comparisons with LADCP sections show, that the western part lies in the range of deep-reaching anticyclonic Mozambique Channel eddies (MCEs), so that the undulating bedforms are again considered to be small contourite mounds aligned parallel to a part of the swirl. The cross-cutting features in the middle mark the eastern boundary of the MCE, where

New high-resolution bathymetric and sub-bottom profiler data collected in the Southern Mozambique Channel along a grid of 16 parallel, non-overlapping lines show a large variety of bedforms which were formed by strong bottom currents. They are visually classified into four main microtopographic zones and several sub-zones which divide the study area into regions with (1) smooth seafloor, (2) undulating bedforms, (3) seamounts and islands, and (4) the Zambezi Channel. A smooth seafloor occurs on the Mozambican continental slope together with downslope mass-wasting processes, north and south of Bassas da India, on the eastern levee of the Zambezi Channel and in the Zambezi cone. Undulating bedforms of some kilometres wavelength and several tens of metres height cover most of the southern, central and northeastern study area. The most spectacular bedforms are numerous, closely spaced, giant erosional scours of up to ~450 m depth, more than ~20 km length and ~3 - 7 km width in the southwestern part of the study area. Here, northward flowing Antarctic Bottom Water (AABW) is topographically blocked to the north and deflected towards the east due to the shallowing bathymetry of the Mozambique Channel. SW-NE trending undulating bedforms aligned parallel to the deflected AABW and interpreted as small contourite mounds allow to trace the AABW flow path eastwards. An ~100 km long W-E trending channel indicates the northernmost extension of the AABW. NW-SE oriented undulating bedforms in the west, hummocky bedforms in the east and arcuate, cross-cutting features in-between reflect a completely different current regime in the central study area. Comparisons with LADCP sections show, that the western part lies in the range of deep-reaching anticyclonic Mozambique Channel eddies (MCEs), so that the undulating bedforms are again considered to be small contourite mounds aligned parallel to a part of the swirl. The cross-cutting features in the middle mark the eastern boundary of the

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The Mozambique Channel (MC) plays an important role in the exchange of water masses between Indian and Atlantic Ocean. During R/V SONNE cruise SO-183 16 lines of multibeam sonar and sub-bottom profiler data were collected in the southern MC. They show a highly variable microtopography on the seafloor. Four main microtopographic zones and several sub-zones have visually been identified. The main zones consider the overall morphology and divide the study area into regions with smooth seafloor, wavy bedforms, seamounts and islands, and the Zambezi Channel. The sub-zones take the reflection pattern and the shape, size and orientation of the bedforms into account. A smooth seafloor occurs on the Mozambican continental slope, north and south of Bassas da India, on the eastern Zambezi Channnel levee and in the Zambezi cone. Wavy bedforms cover the SW, central and NE areas. The most spectacular features are large erosional scours in the SW area. They lie in a region, where the northward flowing Antarctic Bottom Water (AABW) is deflected towards the east due to the shallowing of the MC. Farther eastwards SW-NE trending wavy bedforms are obviously aligned parallel to the deflected AABW and are therefore interpreted as contourite mounds. A W-E trending channel indicates the northernmost extension of the AABW. NW-SE oriented wavy bedforms in the west, hummocky bedforms in the east and arcuate, cross-cutting features in-between reflect a different current regime in the central area. Comparisons with LADCP measurements show, that the western part lies in the range of deep-reaching eddies, so that the wavy bedforms again seem to be contourite mounds aligned parallel to a part of the swirl. The cross-cutting features mark the eastern boundary of the eddy, where a northbound flow direction prevails. The origin of arcuate bedforms and depressions in the NE area is not clear. Deep-reaching eddies which interact with the topography of Bassas da India and the Zambezi Channel may contrib

During the past two years, the AWI prepared a comprehensive, strategic assessment of the risk posed to marine mammals by the use of airguns for scientific, geophysical research in the Southern Ocean around Antarctica [Boebel et al., 2009]. This strategic risk assessment focuses not only on a single activity (e.g. a specific expedition) as a risk assessment would, but more generally considers the use of research air-guns in this region’s typical environmental context, which show little variation from year to year. The study aims at distinguishing between aspects of analysis (based on scientific knowledge and numerical calculations) and evaluation (based on a set of risk criteria and associated thresholds). The term assess-ment is used to describe the overall process, involving both analysis and evaluation.

The Mozambique Basin and Mozambique Channel are one of the key areas in the Southwest Indian Ocean, where ocean currents are considered to generate a highly variable microtopography on the sea floor. The Antarctic Bottom Water (AABW) and the North Atlantic Deep Water (NADW) flowing northward along the southeast African margin and returning southward along the west Madagascan margin are the dominant bottom currents. The Mozambique Current (MC) flowing southward along the southeast African margin, the East Madagascar Current (EMC) surrounding the southern tip of Madagascar and the southward flowing Agulhas Current (AC) formed by the confluence of the former two currents off southeast Africa are the dominant surface currents. Pronounced eddies traveling southward through the Mozambique Channel additionally contribute to the surface circulation.During the R/V Sonne cruise SO-183 a rectangular grid (500 km x 700 km) of high-resolution multibeam sonar and parametric subbottom profiler data was collected in the Southern Mozambique Channel, which allows to study both the orientation and lateral extension of the current-controlled submarine bedforms and the shallow acoustic subsurface structures. Generally, this data set illustrates, that factors such as the large-scale morphology, the sediment supply from southeast Africa and Madagascar, the sediment transport and sorting via the Zambesi Channel and external forces like the Coriolis force play an important role in the generation, distribution, shape and size of the submarine bedforms. Based on the multibeam bathymetry several microtopographic zones ranging from a flat sea floor over large- and small-scale sinusoidal bedforms to rough, irregular, erosional features are defined to classify the study area. An additional inspection of the subbottom profiler data allows a further detailed description and subdivision of the microtopographic zones. For instance, both the northwestern and the southeastern part of the study area are

In 2008/9, the AWI prepared a comprehensive, strategic assessment of the risk posed to marine mammals by the use of airguns for geophysical research in the Antarctic Treaty area. Operational and environmental conditions of all seismic expeditions of the past 22 years are evaluated, to obtain a set of 4 representative environmental scenarios. For each of these scenarios, acoustic fields (SPL and SEL) were calculated by numerical (finite difference 2.5 D full waveform) modelling for 6 airgun characteristics, resulting in a total of 24 different acoustic scenarios. The current state of ecological knowledge, as relevant to this risk assessment, was compiled for 20 species to which this ocean region represents an important habitat. As specific noise exposure criteria for the Antarctic Treaty Area have not been specified yet, possible hazards and corresponding numerical and qualitative evaluation criteria were extracted on the basis of available, published information. Finally, by applying these criteria to the modelled acoustic fields, critical exposure zones were calculated and incorporated in the development of a set of dedicated mitigation measures to minimize possible risks. The talk will present concepts, methods and results of this study along with controversial issues that unavoidable are part of such studies.

During the past two years, the AWI prepared a comprehensive, strategic assessment of the risk posed to marine mammals by the use of airguns for scientific, geophysical research in the Southern Ocean around Antarctica. The study attempts distinguishing between aspects of analysis (based on scientific knowledge and numerical calculations) and evaluation (based on a set of risk criteria and associated thresholds). The term assessment is used to describe the overall process, involving both analysis and evaluation. The analytical part commences with a synopsis of environmental (oceanographic and bathymetric) and operational characteristics from all seismic expeditions conducted in the Antarctic by the AWI. This resulted in a set of 4 basic environmental scenarios, which, combined with a set of 6 airgun configurations, were used to calculate single shot acoustic fields (SPL and SEL) by numerical (finite difference 2.5 D full waveform) modelling for a realistic ocean of 10x10 km dimension, resulting in a total of 24 different acoustic scenarios [Breitzke and Bohlen, 2010]. The current state of ecological knowledge was compiled for the 14 cetacean and 6 pinniped species to which the Antarctic represents an important habitat. Ecological and physiological information such as dive cycles and hearing curves are subsequently used to guide estimations of cumulative exposure levels and to develop mitigation measures. The identification of hazards including associated evaluation criteria and threshold levels provides the critical link between the sound propagation analysis and the risk evaluation. As currently no legally binding set of numerical threshold levels exists for this ocean region, we conducted a literature review of the pertinent literature. Three different risk categories were identified, for which a set of evaluation criteria was extracted from primarily three recent overview articles: (1) Southall et al., [2007], which provides numerical thresholds for the risk of dir

Modelling sound propagation in the ocean is an essential tool to assess the potential risk of air-gun shots on marine mammals. Based on a 2.5D finite-difference code (Bohlen, 2002) a full waveform modelling approach is presented, which determines both sound exposure levels of single shots and cumulative sound exposure levels of multiple shots fired along a seismic line. Point source approximations of compact air-gun clusters typically deployed by R/V Polarstern in polar regions are used as sound sources. Marine mammals are simulated as static receivers.Applications to deep (3000 m) and shallow (400 m) water models including constant and depth-dependent sound velocity profiles of the Amundsen/Bellingshausen and the Weddell Sea show dipole-like directivities in case of single shots and tubular cumulative sound exposure level fields beneath the seismic line in case of multiple shots. Compared to a semi-infinite model an incorporation of sea floor reflections enhances the seismically induced noise levels close to the sea surface. Refraction due to sound velocity gradients and sound channelling in near-surface ducts are evident, but affect only low to moderate levels. Hence, exposure zone radii derived for different hearing thresholds are almost independent of the sound velocity structure. With decreasing thresholds radii increase according to a spherical 20 log10 r law in case of single shots and according to a cylindrical 10 log10 r law in case of multiple shots. A doubling of the shot interval diminishes the cumulative sound exposure levels by -3 dB and halves the radii. The ocean bottom properties only slightly affect the radii in shallow waters, if the normal incidence reflection coefficient exceeds 0.2.A detailed description of this modelling study can be found in Breitzke & Bohlen (2010). It is a contribution to a risk assessment on the impact of seismic research surveys on marine mammals in the Antarctic Treaty area (Boebel et al., 2009) prepared by the Alfred-We

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-differ

The SDLS, established by Antarctic geoscientists in 1991, provides access to Antarctic multichannel seismic (MCS) data at SDLS library branches and via the WWW to facilitate and promote multifaceted research. Of the existing 332,000 km of Antarctic MCS data, 197,000 km are openly available, 31,000 km are being prepared, and 40,000 km are promised to achieve the goal of all due data being submitted to the library during IPY. The SDLS is currently used in several new ways that help manage biodiversity, protect the Antarctic environment and decipher paleoenvironments. Examples include: * Bioregionalisation study for CCAMLR to map geomorphic units of the seafloor and identify areas of Vulnerable Marine Ecosystems, such as cold seeps, seamounts, and others;* Minimizing anthropogenic noise in the marine environment by historic study of surveying and avoiding repeated annual surveys, and by modeling of acoustic wave propagation in the Southern Ocean to estimate and minimize the effect of seismic surveys if any on marine mammals; and * Regional compilations of seismic data by Cenozoic Circum-Antarctic Stratigraphy Project (CASP) to create paleobathymetry maps of the Southern Ocean.The SDLS is a valued science-support group whose continued successes rely on proactive support by the science community.

According to the Protocol on Environmental Protection to the Antarctic Treaty seismic surveys in the Southern Ocean south of $60\deg$S are exclusively dedicated to academic research. The seismic surveys conducted by the Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany during the last 20 years focussed on two areas: The Wedell 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. To assess the potential risk of future seismic research surveys on marine mammal populations an acoustic wave propagation modeling study is conducted for the Weddell and the Amundsen/Bellinghausen Sea. A viscoelastic 2.5D finite-difference code is used, which allows to simulate the spherical amplitude decay of point sources correctly. A sinusoidal wavelet of 50 Hz dominant frequency serves as source wavelet. Based on CTD measurements, sediment core samplings and sediment echosounder recordings two horizontally-layered, range-independent generic input models are established for the Wedell and the Amundsen/Bellinghausen Sea, one for shallow (400 m) and one for deep water (3000 m). They indicate that the vertical structure of the water masses is characterized by a 100 m thick, cold, low sound velocity layer ($\sim$1440 - 1450 m/s), centered in 100 m depth. In the austral summer it is overlain by a warmer, 50 m thick surface layer with slightly higher sound velocities ($\sim$1447 - 1453 m/s). Beneath the low-velocity layer sound velocities increase rapidly to $\sim$1450 - 1460 m/s in 200 m depth, and smoothly to $\sim$1530 m/s in 4700 m depth. The sea floor is mainly covered with soft fine-grained clayey or silty sediments, so that P- and S-wave velocities of 1600 and 200 m/s and a wet bulk density of 1450 kg/m${3}$ are assumed.

According to the Protocol on Environmental Protection to the Antarctic Treaty, adopted 1991, seismic surveys in the Southern Ocean south of 60°S are exclusively dedicated to academic research. The seismic surveys conducted by the Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany during the last 20 years focussed on two areas: The Wedell Sea (60°W - 0°W) and the Amundsen/Bellinghausen Sea (120°W - 60°W). Histograms of the Julian days and water depths covered by these surveys indicate that maximum activities occurred in January and February, and most lines were collected either in shallow waters of 400 - 500 m depth or in deep waters of 2500 - 4500 m depth. To assess the potential risk of future seismic research on marine mammal populations an acoustic wave propagation modeling study is conducted for the Wedell and the Amundsen/Bellinghausen Sea. A 2.5D finite-difference code is used. It allows to simulate the spherical amplitude decay of point sources correctly, considers P- and S-wave velocities at the sea floor and provides snapshots of the wavefield at any spatial and temporal resolution. As source signals notional signatures of GI-, G- and Bolt guns, computed by the NUCLEUS software (PGS) are used. Based on CTD measurements, sediment core samplings and sediment echosounder recordings two horizontally-layered, range-independent generic models are established for the Wedell and the Amundsen/Bellinghausen Sea, one for shallow (500 m) and one for deep water (3000 m). They indicate that the vertical structure of the water masses is characterized by a 100 m thick, cold, low sound velocity layer (~1440 - 1450 m/s), centered in 100 m depth. In the austral summer it is overlain by a warmer, 50 m thick surface layer with slightly higher sound velocities (~1447 - 1453 m/s). Beneath the low-velocity layer sound velocities increase rapidly to ~1450 - 1460 m/s in 200 m depth, and smoothly to ~1530 m/s in 4700 m depth. The sea floor is mainly covered