Is this true or are there other factors that could cause Ocean Acidification?
As far as I know, nobody is claiming that ocean acidification will result in the pH going lower than 7, so this is at best a straw man. The IPCC project a reduction by 0.3 - 0.4 units by 2100 (e.g. AR4 WG1 report) (current pH is about 8.14). The pH does not need to fall as far as 7 for there to be substantial impacts (see the three sources given for details).
I suspect this is just silly pedantry on the grounds that a pH greater than 7 is alkaline, so it is inaccurate to say that it isn't ocean acidification but ocean dealkalinisation. However this is bogus as pH is getting more acidic and less alkaline as the pH drops, so it is perfectly correct to say that the oceans are becoming more acidic, even if the pH remains higher than 8. It is a bit like defining "hot" as meaning above 0C and "cold" as below 0C and then complaining when someone describes a change from 2C to 1C as "becoming colder" and insisting on it being described as "becoming less warm".
The glossary of the IPCC A4 report defines ocean acidification as "A decrease in the pH of seawater due to the uptake of anthropogenic carbon dioxide", so they make it very clear that they mean only a decrease in pH. Scientific terminology varies from field to field, if you want to understand the science, you do need to understand the terminology used in that field and not to try to impose your own definitions on what they have said.
Having now seen the video, my suspicion was entirely correct. The OED defines "acidification" as "The action or process of making something (more) acidic; conversion into an acid; addition of acid. Cf. acidify v.". The inclusion of "(more)" means that the scientists use of the term is completely in accordance with normal English usage. Senator Ericksen at about 1:03:15 makes a comment that suggests that he understands that "less alkaline" and "more acidic" means essentially the same thing.
BTW, a pH of 8.2 is not "strongly alkaline" as Easterbrook states, that is just hyperbole. If seawater is "strongly alkaline", one wonders how he would describe drain cleaner! ;o)
Having looked at the video again, excluding the pedantry issue, Easterbrook only makes one scientific argument, which happens to be incorrect (which makes it rather ironic he described it as Chemistry 101 ;o). He states "The effect of global warming is to make the oceans more alkaline, not more acidic, because warming drives CO2 out of the oceans". Now it is true that the solubility of CO2 in water decreases with increasing temperature, but that is only part of Henry's law the other part is that the solubility depends on the difference in partial pressure in the atmosphere and the concentration in the water (the constant of proportionality depends on temperature). So increasing temperatures will have the effect of reducing solubility, but the increasing partial pressure of CO2 will have the opposite effect, tending to increase solubility. Which effect is strongest? Well the fact that the oceans are acidifying (rather than becoming more alkaline as Easterbrook predicts) and that atmospheric CO2 levels are rising at only about half the rate of anthropogenic emissions is very strong evidence that the oceans are taking up large amounts of CO2. It is the interplay of these two factors that to a large extent explains why CO2 levels have been so stable for the last million years, the pre-industrial equilibrium is the point where these two influences balance.
There is a good series of articles on Ocean Acidification at SkepticalScience.com, written by Doug Mackie that sets out the basics in some detail.