Timescales of ventilation and consumption of oxygen and fixed nitrogen in the eastern tropical South Pacific oxygen deficient zone from transient tracers

Details

• Journal Title:
  Deep Sea Research Part I: Oceanographic Research Papers
• Personal Author:
  Sonnerup, Rolf E. ; Chang, Bonnie X. ; Warner, Mark J. ; Mordy, Calvin W.
• NOAA Program & Office:
  PMEL (Pacific Marine Environmental Laboratory) ; OAR (Oceanic and Atmospheric Research)
• Description:
  The anthropogenic trace gases chlorofluorocarbon (CFC)-12 and sulfur hexafluoride (SF6) were measured during 2013 in the eastern tropical South Pacific Ocean (ETSP) offshore Chile and Peru (12°-22°S, 70°-86°W). Since the WOCE P21 line along ~17°S in 1993, the CFC-12 penetration depth increased from ~550 m to ~800 m. In 2013, CFC-12 had penetrated through the bottom of the oxygen deficient zone (ODZ, where oxygen (O2) < 4.5 μmol kg−1) at all stations, indicating that a portion of waters in this ODZ are ventilated on timescales < 60 years. Isopycnal trends in pSF6 and pCFC-12 ages versus AOU indicated oxygen utilization rates of 11.2 ± 4.7 μmol kg−1 yr−1 just above the ODZ (90–130 m) and 1.0 ± 0.5 μmol kg−1 yr−1 beneath the ODZ (400–700 m). Isopycnal trends in pSF6 ages and nutrients implied fixed N-loss rates of 0.6 ± 0.4 μmol kg−1 yr−1 at the top of the ODZ (~120 m). The pSF6 and pCFC-12 ages were significantly younger than mean ages estimated from one-dimensional transit time distributions, which were difficult to constrain using the SF6 and CFC-12 tracer combination. Despite the fact that tracer concentrations tend to underestimate mean ages, and thus overestimate nutrient regeneration/consumption rates, N-loss rates were undetectable (<0.5 μmol kg−1 yr−1) within the ODZ itself (~175–400 m). When integrated over depth, the oxygen and nitrogen consumption rates determined above and below the ODZ implied total organic carbon (C) remineralization rates on the order of 0.6 ± 0.1 mol C m−2 yr−1. These low C-export rates, and the decadal ventilation timescale of this ODZ, support a body of work suggesting that the ODZ may be sustained by inputs of high-tracer, low-oxygen waters from the adjacent Peru-Chile coastal upwelling system rather than by organic matter oxidation occurring locally.
• Keywords:
  Aquatic Science Oceanography
• Source:
  Deep Sea Research Part I: Oceanographic Research Papers, 151, 103080
• DOI:
  https://doi.org/10.1016/j.dsr.2019.103080
• ISSN:
  0967-0637
• Format:
  PDF
• Publisher:
  Elsevier BV
• Document Type:
  Journal Article
• Rights Information:
  Accepted Manuscript
• Compliance:
  Library
• Main Document Checksum:
  urn:sha-512:1bb7cc697420f2bc55190ba7f23410fc59904fd6aa392ae1709c2a408eb7910a5afbcca5bfbc69702d4134bab3a6e54170cb77a93bc9fb7e47a6a3e37592c9f2
• Download URL:
  https://repository.library.noaa.gov/view/noaa/63852/noaa_63852_DS1.pdf
• File Type:
  [PDF - 1.75 MB ]