Uncovering the mystery of the ocean’s “False bottom”

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We will operate scientific echosounders continuously on the circum-Antarctic voyage to map the depth and biomass of acoustic Deep Scattering Layers (DSLs), also sometimes called the “false bottom.” DSLs are ubiquitous features of the world ocean, but data on DSLs in the Southern Ocean are sparse. They comprise communities of fish (lantern fish, myctophids) and zooplankton. Our previous work has revealed pronounced differences in DSL depth and biomass across frontal zones and suggests the possibility of a global DSL biogeography. The ACE cruise will add a Southern Ocean component to that global biogeography.

The daily vertical migrations of animals in DSLs, from deep water in daylight to shallower water to feed at night, make an important contribution to the ‘biological pump’ that moves carbon from the surface to the ocean interior. Fish in DSLs are hunted by diving predators such as elephant seals and king penguins and are also potentially of commercial interest. Data on Southern Ocean DSLs are needed to improve ecosystem-based management and to improve our understanding of biogeochemical cycling and drivers of predator foraging behavior.

To examine associations between the DSL prey-field and predator foraging behavior we will work with biologists tagging elephant seals and penguins on islands along the voyage track. We will analyze the dive depths and duration of predators in the context of DSL depth and biomass: we hypothesize strong correlation.

Principal Investigator (PI)

Andrew Brierley

University of St Andrews, UK

 

Circum-Antarctic distribution of acoustic deep scattering layers, and associated foraging behaviour of deep-diving predators

Principal institution / country

  • Macquarie University (Australia)
  • Sea Mammal Research Unit (UK)
  • Australian Antarctic Division (Australia)
  • British Antarctic Survey (UK)
  • Muséum National d’Histoire Naturelle, (France)
  • Sydney Institute for Marine Science, (Australia)