Peter H. Wiebe delivers a lecture

Dr. Peter H. Wiebe, Scientist Emeritus, at the Woods Hole Oceanographic Institute, will give a lecture on North Atlantic High Latitude Acoustic Backscattering on November 10. The lecture will begin at 12:30 pm at Skúlagata 4, 1st floor.

Abstract:

During a SI_ARCTIC cruise aboard the RV Helmer Hanssen west and north of Svalbard in August-September 2014, acoustic data for distribution and abundance estimation of zooplankton and fish were collected with calibrated EK60 echo sounder systems at the acoustic frequencies 18, 38, and 120 kHz. Plankton, miconekton, and fish contributions to the backscattering at 38 kHz were determined by the frequency response, thresholding techniques, and corroborating plankton and trawl data. Typically, there was strong patchy scattering between the surface and about 50 m throughout the area consisting of a range of weak acoustic scatterers like copepods, krill, and amphipods in addition to 0-group fish that were particularly abundant west of the Spitsbergen Archipelago. Off-shelf there was strong deep scattering layer (DSL) between 300 and 500 m containing a range of larger longer lived organisms (mesopelagic fish, shrimps, and various plankton) with a standing biomass likely less variable than for the epipelagial over time. In eastern Fram Strait, the DSL was dominated by fish close to the shelf/slope break that were associated with Warm Atlantic Water moving north towards the Arctic Ocean, but switched to dominance by the plankton/micronekton further offshore. The northward bound organisms in the DSL that have a more southern origin diminished in abundance and taxonomic richness while being transported into the Arctic habitat north of Svalbard. The documented patterns and structures, particularly the DSL and its constituents, will be an important reference point for understanding and quantifying future changes in the pelagic ecosystem of the Arctic Ocean.