Decadal changes in the CaCO3 saturation state along 179°E in the Pacific Ocean

Abstract

To assess degrees of ocean acidification, we mainly investigated decadal changes in the saturation state of seawater with respect to aragonite (Ωarg), which is a more vulnerable mineral form of CaCO3, along the 179°E meridian (WOCE P14N) in the Pacific Ocean. We found a maximum decrease of Ωarg of −0.48 (−0.034 a−1) at 200–300 dbar (isopycnal surfaces of 24.0–25.8 kg m−3) at 20°N. Between 1993 and 2007, the saturation horizon rose by 17 dbar (1.2 dbar a−1) at latitudes 10°N–50°N. Although ΔΩarg mostly reflected changes in normalized dissolved inorganic carbon (ΔnCT), it was larger than could be explained by anthropogenic CO2 storage alone. Decomposition of ΔnCT revealed that ΔΩargwas enhanced by approximately 50% by a non‐anthropogenic CO2 contribution represented by changes in apparent oxygen utilization. Our results suggest that ocean acidification can be temporarily accelerated by temporal changes in oceanic conditions.