Abstract:

Integrated studies over the past 30 years have shown that the carbon absorption capacity of the Southern Ocean has declined significantly since the 1990s. But this weakening trend began to change significantly with an increasing trend after 2002, showing a stronger ability to absorb anthropogenic CO2 in the atmosphere, which will be further enhanced with acidification of the Southern Ocean. Observations show that the decline rate of pH in the Open Southern Ocean of 45°—50°S was 0.0007 per year during 1991–2000, and the Ωarag rose at a rate of 0.015 per year. The decline rate of pH increased to 0.0024 per year during 2001–2011, the Ωarag turned to decline at a rate of 0.017 per year. However, regional differences in ocean acidification among the coastal waters of the Southern Ocean are very large and the interaction of various influencing factors is more complex. For example, the pH and Ωarag in Prydz Bay dropped by approximately 0.11 and 0.30, respectively, from 1994 to 2010. Observations collected in the Weddell Sea from 1973 to 2008 show a decrease in pH on the order of 0.0011 units per year in surface waters associated with a reduction in Ωarag at a rate of 0.002 units per year. Based on the in situ observations and remote sensing inversion parameter methods, important progress has been made in assessing the acidification trend of the Southern Ocean from point-line observations to the overall extent of the sea area. Recently improved model simulation results likewise shown good agreement with the observation results in both magnitude and large-scale spatial patterns. This paper also reviews the acidification trend in the Southern Ocean under different scenarios including RCP 8.5 predicted by the Earth System Model (ESM) and the effects of ocean acidification on the ecosystem of the Southern Ocean. Results show that most of the Southern Ocean will be in an aragonite un-dersaturated state by the end of this century, indicating that the acidification progress of the southern ocean will seriously affect the marine biogeochemical changes and damage the ecosystem of the entire Southern Ocean. Therefore, the study of ocean acidification processes, driving mechanisms and prediction, as well as the evaluation of the ecological effects of this acidification in the Southern Ocean have been seriously placed in front of all mankind.

Key words: ocean acidification, pH, aragonite saturation, remote sensing, model prediction, Antarctica