coral reefs in a more acid ocean, page-2

The high CO2 concentration of 318 mmol L−1 measured
from CTD 13?7 (Figure 2) had a pH of 6.8 ? 0.2.
A pH value of 6.8 corresponds to calculated values of about
9000 ppm CO2 in dry air and a CO2(aq) value of about
320 mmol L−1. Slight reduction of pH in North Sea waters
has been seen where respiration takes place, and annual
cycles of pH vary between 7.8 and 8.4 depending on the
distance to the coast

http://www.eawag.ch/forschung/surf/publikationen/2011/2011_mcginnis.pdf

The ipcc like to focus on peguins, polar bears and coral for impact. How much Co2 is naturally bubbling up globally as bubbles dissolve very rapidly (within meters). How can you model off the unknown as there is very little known about natural CO2 seepage.