Challenges of Measuring Abyssal Temperature and Salinity at the Kuroshio Extension Observatory

Details

• Journal Title:
  Journal of Atmospheric and Oceanic Technology
• Personal Author:
  Anderson, Nathan D. ; Donohue, Kathleen A. ; Honda, Makio C. ; Cronin, Meghan F. ; Zhang, Dongxiao
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; PMEL (Pacific Marine Environmental Laboratory) ; CICOES (Cooperative Institute for Climate, Ocean and Ecosystem Studies)
• Description:
  The deep ocean is severely undersampled. Whereas shipboard measurements provide irregular spatial and
  
  temporal records, moored records establish deep ocean high-resolution time series, but only at limited locations. Here,
  
  highlights and challenges of measuring abyssal temperature and salinity on the Kuroshio Extension Observatory (KEO)
  
  mooring (32.38N, 144.68E) from 2013 to 2019 are described. Using alternating SeaBird 37-SMP instruments on annual
  
  deployments, an apparent fresh drift of 0.03–0.06 psu was observed, with each newly deployed sensor returning to historical
  
  norms near 34.685 psu. Recurrent salinity discontinuities were pronounced between the termination of each deployment
  
  and the initiation of the next, yet consistent pre- and postdeployment calibrations suggested the freshening was ‘‘real.’’ Because
  
  abyssal salinities do not vary by 0.03–0.06 psu between deployment locations, the contradictory salinities during mooring
  
  overlap pointed toward a sensor issue that self-corrects prior to postcalibration. A persistent nepheloid layer, unique to KEO
  
  and characterized by murky, sediment-filled water, is likely responsible for sediment accretion in the conductivity cell. As
  
  sediment (or biofouling) increasingly clogs the instrument, salinity drifts toward a fresh bias. During ascent, the cell is flushed,
  
  clearing the clogged instrument. In contrast to salinity, deep ocean temperatures appear to increase from 2013 to 2017 by
  
  0.00598C, whereas a comparison with historical deep temperature measurements does not support a secular temperature
  
  increase in the region. It is suggested that decadal or interannual variability associated with the Kuroshio Extension may have
  
  an imprint on deep temperatures. Recommendations are discussed for future abyssal temperature and salinity measurements.
  
  
• Keywords:
  Deep-sea Temperature Salinity Deep-sea Temperature Bottom Currents/Bottom Water Decadal Variability Eddies North Pacific Ocean Temperature
• Source:
  Journal of Atmospheric and Oceanic Technology, 37(11), 1999-2014
• DOI:
  https://doi.org/10.1175/JTECH-D-19-0153.1
• Document Type:
  Journal Article
• Place as Subject:
  North Pacific Ocean
• Rights Information:
  CC BY
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha-512:6a0f4fc2d7759c70abca68dd5dffc889cb9b4372c71dbeed03155f2f3f5c53df66e12ac381ef5090213e564b661d3534f0d3db84b252cd61e90c2b73d08051ba
• Download URL:
  https://repository.library.noaa.gov/view/noaa/28992/noaa_28992_DS1.pdf
• File Type:
  [PDF - 3.08 MB ]