it depends on how much the oceans heat up. Most likely the answer will be a few tenths of a degree, and nothing to worry about.
One of the first victims of warming oceans is coral. The higher temps will bleach the coral having a major edffect on the food chain
Acidification is a problem.
In the past atmospheric CO2 levels have been regulated by cocolithophores which have the capability to trap vast quantities of CO2 in their tiny shells, chalk (the rock) is made of of billions of these creatures.
http://en.wikipedia.org/wiki/Coccolithop...
If we have acidic oceans this regulatory mechanism may not operate when it is needed next time around.
The main threat to marine life isn't ocean heating, so much as the changes in acidity.
Sessile organisms (such as corals) that require very specific conditions may be in trouble from heating, simply because they are less likely to find the conditions they need elsewhere if their current locations grow too warm. But most marine life forms can relatively easily move (either directly, or through their progeny) to a new location that is the correct temperature.
But acidity affects anything that makes a carbonate shell, and by extension anything that *eats* anything that makes a carbonate shell. Which includes certain species of algae.
Here are some links for more information:
http://en.wikipedia.org/wiki/Ocean_acidi...
http://www.pmel.noaa.gov/co2/story/Ocean...
http://oceanacidification.net/
http://www.nrdc.org/oceans/acidification...
http://ngm.nationalgeographic.com/2011/0...
The water temperature in the oceans varies enormously according to depth, temperature at the surface can be 30C while a hundred feet down can be 10C less, those marine creatures that can move, do just that move to the temps they like,
Our oceans will never become acid as they contain so much calcium which acts as a buffer. our rivers and lakes maybe at a danger of acidification, but not our seas.
If it heats up a little, practically nothing. If it heats up a lot, those species that were adapted to warmer water will move to previously colder water. There is very little evidence to suspect that it will heat up significantly enough to cause any problems IMO.
Blue whale
Dolhpin
Squid
And plakton
they will move north, no, south, no, east, no, west. yes they will move west
We have no global warming. Howevr in response to your question, the earth has been hotter and nothing has happened that can be directly attributed to GW, especially AGW.
I'd be more worried about acidity - this is changing the food chain
What sort of species would become extinct and why?
We will be eating boiled fish.
