Vertical Zooplankton Distribution on Continental Slope off Oregon Coast

Abstract:

The Newport Hydrographic Line Hydrographic and Zooplankton Time Series (NH-Line) has sampled zooplankton biomass biweekly at sites off the coast of Newport, Oregon, for periods beginning in 1961 (Huyer, 2007). The Ocean Observatories Initiative’s Endurance Array Newport Line is located near the NH-Line and has been operational for four years. The three bioacoustic sonar units in this array capture long-term, high temporal-resolution, high depth-resolution measurements of backscatter intensity to show where biomass is located in the water column. Correlation of this relatively new, high-resolution data and the many prior years’ data from the NH-Line Time Series will allow greater understanding of both short-term and long-term biomass trends in the water column. Initial investigation was performed using bioacoustic sonar data from the OOI Regional Cabled Array Oregon Offshore Shallow Profiler Mooring. This mooring includes an upward-looking Kongsberg EK-60 at 200 m depth with transducers at 200 kHz, 120 kHz, and 38 kHz. The data conversion and analysis was performed using a new Python package for Ocean Sonar data analysis, echopype (Lee 2019). This mooring also has a profiler system and data collected with the profiler as it moves up and down through the water column was analyzed in combination with the bioacoustic data. Short time periods of data are considered as examples with the goal of developing an understanding of how physical properties of the water column and bioacoustic measurements are related as well as variation in these measurements throughout the course of a day and seasonally. Comparisons are also made to the NH-Line data in order to verify the ability to make quantitative measurements of biomass.