All the tropics folks have a habit of going on and on about species diversity, but it turns out the poles aren't as desolate as many expected. The Census of Marine Life has just released a report documenting about 7,500 species in the Antarctic and 5,500 in the Arctic including several hundred critters possibly new to science.
Stories circulating the media call the tally 'astonishing', but I'm honestly not surprised given how little we know about these regions. The most interesting revelation... Despite the 8,000 miles between them, at least 235 species live in both polar seas. Pretty cool, huh? So how do you think they ended up a world apart?
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Interesting mystery. Life always prevails and survives in spite of the wrath of the elements. It has done so countless times during the desolate draconian epochs of our planet's history. Scarcely surprising, although always a source of wonder. Dienococcus radiodurans, anyone?
A few items that come to mind. The Arctic Tern, which migrates seasonally between the Arctic and Antarctic. A few whales may be capable of swimming the distance, and surviving in the various water temperatures. There are long, wide currents of Antarctic bottom water in every ocean. Near the surface, there is the Humboldt current which brings extremely cold Antarctic water all the way from the Antarctic to the equator - thus resulting in penguins in the Galapagos. Finally, just 15,000 years ago, the climate was about 10C cooler globally, in a major glaciation. This made the distance between the Arctic and Antarctic environments much smaller. While in most glaciations NH ice sheets did not advance much further south than the US Canada border, there were a few in which NH ice sheets advanced as far south as Kansas. For something like 70-90% of the last 2.5 million years, the climate was experiencing a major glaciation.
Lots of fascinating directions to look in for the answer to how so many species came to live in both polar seas.
Thermohaline circulation/ the ocean conveyer belt transports water all around the world, and it reaches both poles. Larvae could be transported by this... though it seems unlikely because the currents are slow and go through tropical regions. An interesting question indeed.