North Pacific Water’s Larger Potential Sink Capacity for Absorbing Anthropogenic CO₂ and the Processes Recovering It

Abstract

The potential sink capacity of water for absorbing atmospheric CO₂ has been defined. The capacity is the amount of CO₂ absorbable when all the nutrients contained are transformed to organic matter. The Pacific Deep Water should have an excess potential sink capacity relative to the Atlantic Deep Water due to the gas exchange not consuming nutrients in the Antarctic Ocean in winter and the dissolution of CaCO₃ in the deep Pacific. Although the capacity has not yet been exactly estimated because of the lack of accurate and worldwide data of all the oceanic carbon components, the fact that the concentration of CO₂ equilibrated with the North Pacific Deep Water of null AOU is somewhat lower than that of the pre-industrial atmosphere may be caused by excess potential sink capacity. The total carbonate content corrected for phosphate and alkalinity clearly shows an invasion of anthropogenic CO₂ into the North Pacific Intermediate Water. The ¹³C data depict the warm surface water having absorbed much anthropogenic CO₂, while its total CO₂ profile indicates inversely a small net loss by warming of the water. This means the warm water can absorb much CO₂ when it is cooled. Thus, the more the upwelling water in the eastern and equatorial Pacific, the greater the amount of CO₂ absorbed in the high-latitudes. Four processes are raised and discussed for realizing the large potential sink capacity and the absorption of much anthropogenic CO₂ in the North Pacific. These seem to be overlooked or underestimated by the present modelers giving smaller values for the oceanic uptake of CO₂. They are (1) the formation of the North Pacific Intermediate Water in the northwestern North Pacific occupying the layer down to about 1000 m with a residence time of a few tens to one hundred years, (2) the continental shelf system making the dense water which contains more total carbonate and supplying it to the subsurface layer of the open ocean, (3) the gas exchange process in the high-latitudes where the gas transfer velocity, being accelerated by bubbles, is larger than that accepted at present by the majority of scientists in this field, and (4) the abundant silica controlling the ecosystem by producing larger particles sinking into the abyss with higher speeds and larger organic-C/carbonate-C ratios in the western North Pacific. All these processes indicate the peculiar and important role of the North Pacific, especially its western part, in the oceanic uptake of anthropogenic CO₂.