Ocean Acidification

Abstract

Recent studies suggest that the formation and motion of the North Pacific subtropical mode water (STMW) play an important role in oceanic uptake, transport and storage of anthropogenic CO₂ (C_ANT). However, the variability of STMW acidification rate and its control mechanisms remain unclear. Here we show that the STMW acidification rate during 2005−2020 is about two times of that during 1993−2005, which is due to the cooling-driven enhanced C_ANT accumulation in the formation waters in the recent period. The rapid rates of C_ANT accumulation and acidification are consistently observed in the entire region across 137°−149°E regulated by STMW transport. Moreover, the tracer-based (Δ¹⁴C and δ¹³C) analyses also indicate that the accelerated accumulation of C_ANT could be traced back to the surface formation waters via STMW formation. The vertical and horizontal consistencies imply the memory function of mode waters in retaining the anthropogenic carbon fingerprint during its formation and transport.

Key Points

• The decline rates of pH and Ω_arag in the North Pacific subtropical mode water (STMW) during 2005−2020 are ∼2 times of that during 1993−2005
• The faster STMW acidification is attributed to the accelerated accumulation of anthropogenic CO₂ (C_ANT) in the formation waters
• The rapid rates of C_ANT accumulation and acidification are consistently observed across the 137°−149°E regulated by STMW transport

Li C.-l., Wu Y., Wang X., Feely R. A., Cai W.-J., Han L., Lin X. & Qi D., 2022. Accelerated accumulation of anthropogenic CO₂ drives rapid acidification in the North Pacific subtropical mode water during 1993−2020. Geophysical Research Letters 49: e2022GL101639. doi: 10.1029/2022GL101639. Article.