Fine-scale spatial and interannual cadmium isotope variability in the subarctic northeast Pacific

• Published in: Earth and Planetary Science Letters
• Main Authors: Janssen, D. J., Abouchami, W., Galer, S. J. G., Cullen, J. T.
• Other Authors: Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), ANR-10-LABX-0023,UnivEarthS,Earth - Planets - Universe: observation, modeling, transfer(2010), ANR-11-IDEX-0005,USPC,Université Sorbonne Paris Cité(2011)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2017
• Subjects: cadmium isotopes; northeast Pacific; GEOTRACES; biogeochemical cycles; low oxygen; [SDU]Sciences of the Universe [physics]; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Pacific; Southern Ocean; Subarctic
• Online Access: https://insu.hal.science/insu-03748846; https://doi.org/10.1016/j.epsl.2017.04.048

International audience We present dissolved cadmium (Cd) concentrations, [Cd], and stable isotope compositions, ɛ 112 / 110 Cd, in high-resolution depth profiles from five stations along the Line P transect in the subarctic northeast Pacific Ocean. In addition to profiles collected in 2012, subsurface isopycnal samples and surface samples were collected in 2013 and 2014 respectively, providing both temporal and spatial coverage. Surface waters are characterized by Cd depletion relative to phosphate ( 4 3- PO) compared to deepwater 4 -3 Cd:PO, and high inferred remineralization ratios in the nutricline (0.45nmolμmol -1 ) are observed, consistent with Cd enrichment relative to phosphorus (P) in surface-derived biogenic particles. The correlation between Cd and 4 3- PO weakens at depths where oxygen is highly depleted as shown by local minima in dissolved [Cd] and the tracer Cd * . The decoupling, which is driven by a deficit of Cd relative to 4 3- PO, appears consistent with the recent hypothesis of dissolved Cd removal in oxygen-depleted regions by insoluble metal sulfide formation. Dissolved ɛ 112 / 110 Cd indicates a biologically driven fractionation in surface waters with more positive (heavy) values in the upper water column and lower (light) values in deeper waters. The highest ɛ 112 / 110 Cd observed in our sample set (5.19 ± 0.23) is comparable to observations from the Southern Ocean but is significantly lighter than maximum reported surface values from the subtropical North Pacific of ɛ 112 / 110 Cd ≥ 15. A global compilation of low [Cd] surface water shows similar differences in maximum ɛ 112 / 110 Cd. A surface water intercalibration should be prioritized to help determine if these differences at low [Cd] reflect true physical or biological variability or are due to analytical artefacts. Surface samples from the 2012 sampling campaign fit a closed-system Rayleigh fractionation model; however, surface waters sampled in 2014 had much lower [Cd] with relatively constant ɛ 112 / 110 Cd that cannot be ...