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

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. Depthintegrated 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^*