The figures at the left show real data collected off the US west coast, with the data plotted going down through the top 250 meters of the water column from W (left, offshore), to E (right, next to the coast). The plots show warmer water with higher pH and Ω at the surface and colder water with lower pH and Ω at depth, but also show that the deep waters are brought up towards the surface along the coast. A key point for students to understand is that deep waters have been out of contact with the surface and sunlight, so they have continued to accumulate CO2 as sinking organic matter is respired without the possibility for photosynthesis to remove any of that CO2. This is the reason that deep waters have low pH and Ω.
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