[jauntywundrkind]

The thermohalice cycle is a prime exchanger of water. Hot gulf stream water goes north, cools, and sinks, displacing existing cold water there & oxygenating lower levels of ocean.

We risk losing this major ocean oxygenator. I haven't heard any good theories for what happens instead, if theres still some kind of gulf stream but it mainly hugs the coast. There's been incredible warming of the Gulf of Maine in the past couple decades, for example, and that seems nowhere near deep enough to have this kind of thermohalice exchange.