National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2007

Anthropogenic δ13C changes in the North Pacific Ocean reconstructed using a multiparameter mixing approach (MIX)

Sonnerup, R.E., A.P. McNichol, P.D. Quay, R.H. Gammon, J.L. Bullister, C.L. Sabine, and R.D. Slater

Tellus, 59B, 303–317, doi: 10.1111/j.1600-0889.2007.00250.x (2007)

A multiparameter mixing approach, ‘MIX’, for determining oceanic anthropogenic CO2 was used to reconstruct the industrial-era change in the 13C/12C of dissolved inorganic carbon (δ13C of DIC) along the 1992 165°E WOCE P13N section in the North Pacific Ocean. The back-calculation approach was tested against a known anthropogenic tracer, chlorofluorocarbon-11 (CFC-11), and also by reconstructing an ocean general circulation model’s (OGCM) anthropogenic δ13C change. MIX proved accurate to ±10% against measured CFC-11, but only to ±~25% reconstructing the OGCM’s δ13C change from 1992 model output. The OGCM’s CFC distribution was also poorly reconstructed using MIX, indicating that this test suffers from limitations in the OGCM’s representation of water masses in the ocean. The MIX industrial-era near-surface (200 m) δ13C change reconstructed from the WOCE P13N data ranged from -0.8‰ in the subtropics (15-30°N), to -0.6‰ in the tropics (10°N), and -0.4 to -0.2‰ north of 40°N. Depth-integrated changes along 165°E were -400‰•m to -500‰•m at low latitudes, and were smaller (-200‰•m) north of 40°N. The MIX North Pacific δ13C change is consistent with the global anthropogenic CO2 inventory of 118 ± 17 Pg from ΔC*.

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