By OCAdmin in Research highlights on

Shou-En Tsao, Chun-Mao Tseng^*

Since the industrial revolution, the level of atmospheric carbon dioxide (CO₂) has increased by ~50% due to human activities in the past centuries which accelerated global change and a warming threat to the earth. Meanwhile, the ocean has absorbed around 30% of the emitted anthropogenic carbon through the air-sea exchange and has played a major buffering role in slowing down the accumulation of atmospheric CO₂ and mitigating climate change. The uptake of CO₂ has led to ocean acidification, referring to the decline of pH through the years, which enhances CaCO₃ dissolution and poses a threat to marine life. Thus, understanding the long-term changes in ocean carbonate chemistry under anthropogenic influence is greatly important.

In this study, we explored the trends of seawater acidification and the increased partial pressure of carbon dioxide (pCO₂) in the western boundary current of East Asia by analyzing nine-year carbonate data sampled during 2010-2018 along Kuroshio Current near East China Sea (ECS) by the Japan Meteorological Agency. Professor Tseng’s lab group found trends of surface seawater pCO₂ at 3.70±0.57 µatm year^-1 and pH at -0.0033±0.0009 unit year^-1_, which were significantly greater than the expected rates from CO₂ air-sea equilibrium and those reported from other oceanic time-series studies. We assessed potential drivers, processes, fluxes, and implications of CO₂ cycling in the Kuroshio under climate change. A much faster effect of temperature increase on the rapid rates of pCO₂ increase and acidification under a sustained supply of dissolved inorganic carbon (DIC) was first identified and then CO₂ flux declined significantly by ~50% (~-0.8 to -0.4 mole C m^-2 y^-1) over the Kuroshio study region estimated. If this trend continued and the atmospheric CO₂ continued to increase at its current rate, the faster-warming Kuroshio regions could potentially become a CO₂ source from a sink status and eventual loss of oceanic CO₂ uptake under climate change near future ca. 2030-2040.

In summary, this study explored the effects of seawater warming and sustained DIC supply on the CO2 uptake and acidification along the Kuroshio Current in the ECS. Other “warming hotspots” of the global ocean located along western boundary currents with a continuous DIC supply should exhibit similarly accelerated acidification and pCO₂ rise, which could lead to a significant reduction in ocean CO₂ uptake. It is eventually of great significance to prevent marine pollution by reducing carbon release to maintain the health of the earth.

Web link：https://www.sciencedirect.com/science/article/pii/S0025326X22011535

Conceptual illustration of effects of ocean warming and possible DIC sources on CO₂ increase and acidification in the Kuroshio seawater of the East China Sea