It also seems to me that if oceans are increasing their CO2 content in the ocean water, then oceans are getting colder, and if the oceans are getting warm then they would release a large amount of CO2.

Now, there are ways that ocean can absorb additional CO2- through life process which have made all the limestone deposits in the world [one reason why people looking for past life on Mars were eager to find any sign if limestone on Mars- it would prove past life on Mars].
But temperature differences in the Ocean without considering this life process will absorb and release CO2 depending on temperature of ocean.
Now, the "last best hope" of the people who believe in GW being significantly affected by human activity, is basically that because they don't proof of atmospheric rise in global temperature they are claiming that the rise of temperature is being held in the ocean [it's hiding:]. But if this were true than the ocean would release CO2.

Now, people are vaguely serious know that CO2 increase in the atmosphere is related to rising global temperature. The historical record typically shows the rising CO2 levels FOLLOW as a "apparently" as a RESULT of global warming.

The Little Ice Age is something that most scientists accept. It's a measure of how wacky one is a global warming nut the degree in which the Little Ice Age is rejected or downplayed as having much affect.

Since the end of the Little Ice Age most scientists seem to accept the conclusion that Global temperatures have risen by about 1 F or maybe as much as 1 C. And we talking about global air temperature. If we want to include Ocean temperature, we really need to distingtish between ocean surface temperature and the vast majority of the rest of the ocean. Most of the ocean is ink blackness with only the various animals lighting this world.
The oceans dominate this world- we are a water planet. The oceans hold more life than is on the land. The ocean recieve more energy from the Sun than the land, and therefore because the process of water evaporating from ocean (taking energy out of the ocean) and water falling as rain (releasing some of this energy) and even without raining distributing the ocean heat, the ocean dominates climate on land and entire global climate.
We know very little about the oceans, some say we know more about the Moon than we know about the oceans, somewhere around 90% of ocean is in constant darkness. The general topographical region of the ocean is mapped, fairly recent we discovered the black smokers and the eco system it support, there are other eco system we are finding out about, but all of this is *probably* just small fraction of what will be discovered. The ocean of course is a 3rd dimensional environment, with just it's surface area being 70% of total Earth surface surface area, but it's the miles of depth which adds to it's immense nature and truely makes it undiscovered terrority which has dwarfed human efforts in exploration.
The average temperature of the ocean is simply unknown- which of course, makes it a perfect place to hide "the global warmth" for the "fake but accurate crowd". A small literally immeasurable increase in ocean average temperature would equal enormous energy. To measure an increase one would need very accurate measure and then a some amount time in order to evalute whether it warming or cooling- we don't have the first part of this and certainly not the latter part of it.
I think it fairly safe to say that earth's oceans have never frozen solid, though in very early geological life of Earth they may have periods when all oceans have boiled, having the entire ocean as water vapor is a bit hard to imagine, but when consider the scale of Earth in comparison to the ocean, the oceans shrink to insignificant "wetness" of the planet, combined with energy of say 100 mile in diameter rock hitting and the enormous amount of energy involved, well, the oceans are a mere leaf in the wind. All humans of course would killed merely from the increase in atmospheric pressure, nevermind the general heat, earthquakes, atmospheric shockwaves, the pulse of superheated air, and heat flash of infrared and other radiations- surviving it would require a technology capable having a "submarine" that is capable of traveling through volcanic lava- way out of our league. Hmm, actually some kind super specialize airplane- nuclear powered, built stronger than tank, etc, could be possible. Though going into space would be much easier and safer.
Anywho, where was I? Right, Earth's ocean probably never froze and of course in recent times [last 100,000 years] not even vaguely possible or impossible, if you like. During ice ages the ocean would still be the engine that warms the planet- the land would reflect even a higher percentage of the sun's energy and ocean would continue absorbing energy as they do currently. It seems quite possible due a number of factors that pacific islands could be on average be warmer than today. Anyway it doesn't seem like ocean temperature would be much different- with 100 meters of ocean in the form pure water ice, that will have slight effect upon the ocean salinity, thereby require warmer ocean surface temperature to evaporate water. The lower sea level create the land bridge between America and Asia and of course stop cold arctic waters from flowing through there.
Even if global warming is mostly due to varing amount of solar energy and surface ocean temperature were as much 1 degree cooler due to this, the entire ocean would not be cooler by 1 degree- rather some fraction of it. It seems that only by increasing the "production" of arctic cold water is going to a way of significantly decreasing ocean temperature.