JpGU-AGU Joint Meeting 2020

Presentation information

[E] Poster

A (Atmospheric and Hydrospheric Sciences ) » A-OS Ocean Sciences & Ocean Environment

[A-OS24] Exploring new frontiers of oceanic mixing research in the next decade

convener:Toshiyuki Hibiya(Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo), Ichiro Yasuda(Atmosphere and Ocean Research Institute, The University of Tokyo), Lakshmi Kantha(Aerospace Engineering Sciences, University of Colorado, Boulder, Colorado, USA)

[AOS24-P17] Seasonal dynamics of zooplankton at station K2, NW Pacific, reconstructed from archived ADCP data

*Minoru Kitamura1, Motoyo Itho1 (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:zooplankton, acoustic backscattering , western subarctic North Pacific

By using the archived mooring ADCP data, we obtained time-series of acoustic backscattering strength at station K2 (47ºN, 160ºE), the western subarctic North Pacific. In the pelagic water column, main acoustic scatterers are thought to be zooplankton. Actually, many researches showed that the acoustic backscattering strengths have good correlation with zooplankton biomasses in many area of the oceans. In this study, we reconstructed zooplankton dynamics using the acoustic backscattering strength as proxy of zooplankton biomass. ADCPs were moored at 370-400 m in depths at the K2 from 2015 summer to 2018 summer. The echo intensities recorded by ADCPs were converted to acoustic backscattering strength (Sv) in dB according to the following equation (Deines, 1999);

Sv = C + 10log10((Tx+ 273.16) x R2) – LDBM– PDBM+ 2αR +Kc(E –Er)

where C is an empirical constant, Tx is the temperature of the transducer, R is the range along the beam to the scatterers, LDBM is the transmit pulse length, PDBM is the transmit power, α is the absorption coefficient, Kc is a conversion factor for eco intensity from counts to dB, E is the echo intensity in counts, and Er is the reference echo intensity which was taken as the instrument-specific lowest measured value over the mooring period. Although we could not obtain the acoustic data between sea surface and ca 30 m in depth due to side lobe effect of sound, four years time-series of backscattering strengths between 30 and 350 m was successfully collected. In the poster, we will describe seasonal variability and diel change of acoustic backscattering strength at K2. During the summer of 2016, strong current velocity was observed and the moored ADCP sank down to 660 m in depth. We will also discuss zooplankton dynamics during the event.