ALBERT

Description: 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.

Description: 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 MCE, where a northbound flow direction prevails. The hummocky bedforms in the east may have developed under the influence of seasonally variable cyclonic East Madagascar Current eddies pretending at least two different flow directions. The origin of arcuate bedforms, sediment ridges and circular or elongate depressions in the northeastern study area is not clear. Bottom currents which interact with the topography of the Bassas da India complex and the Zambezi Channel may contribute to their formation. All morphological features are draped with sediments indicating that the present-day current velocities are not strong enough to erode sediments. This agrees with published LADCP bottom-current velocities of 0.1 m/s. Hence, the microtopography must originate from a time when bottom-current velocities were stronger. Assuming a published sedimentation rate of 20 m/Myrs and a drape of at least 50 m thickness the microtopography may have developed during Pliocene times or earlier.

Description: The Ocean presents a cacophony of sounds originating from natural as well as anthropogenic sources. Marine organisms heavily rely on sound to communicate and understand the world around them, and are therefore potentially impacted by anthropogenic sound. However, in developing our Blue Economy and in advancing our knowledge of marine environments and ecosystems, anthropogenic noise is sometimes unavoidable. Understanding the potential effects of anthropogenic noise is therefore integral to addressing this conflict, as it is needed to develop proportionate mitigation strategies and effective regulation. Next to providing an overview of our current knowledge about underwater noise, this publication highlights the priority areas for further research addressing the remaining knowledge gaps about the effects of anthropogenic noise. Furthermore, it points out the relevant actions needed to take in order to ensure ecosystem-based and precautionary legislation.

Description: Challenge 2: Protect and restore ecosystems and biodiversity; Challenge 7: Expand the Global Ocean Observing System.

Description: Published

Description: Refereed