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I know it's been proven false in our world, but what is the most plausible mechanism by which an Open Polar Sea could form and persist? I don't mean all the ice melting, but an open sea as it was imagined, surrounded by ice, before people actually travelled there and found out it was wrong.

Clarification: I tried to make this clear, but I'm not looking for a 'global warming will melt it all' answer. The sea would still be surrounded by ice, as I said.

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It can be the volcanic activity, there can be a big underwater volcano, that boils and warms water and prevent it from turning into ice.

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    $\begingroup$ Possibly, but there would have to be a REALLY big heat source to clear something that can be called a 'sea'. $\endgroup$ – Adam Miller Dec 10 '14 at 0:25
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    $\begingroup$ I did find an article discussing the current impact of undersea volcanoes on the polar ice cap: dotearth.blogs.nytimes.com/2008/07/01/… In a word, there doesn't seem to be much at all. I'm now wondering about an upwelling of warmer deep-sea ocean water somehow. $\endgroup$ – Adam Miller Dec 10 '14 at 12:38
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    $\begingroup$ Yes, a "hot spot" like Hawaii. $\endgroup$ – JDługosz Dec 14 '15 at 23:57
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There has to be some sort of heat source for this to happen, and it can't be something temporary. Here are some ideas:

  • Volcanic Activity. Vodolaz095 beat me to posting this, but I was already working on it, so I can't claim priority but I can expand on it. For volcanic activity, you need a source. An underwater volcano is possible but a little unlikely - in its "volcano" form, that is. An enormous hydrothermal vent might be slightly more effective. You can clearly get to the necessary temperatures to melt ice - the hottest vents discovered on Earth are hotter than 400 degrees Celsius - but you need a way to get that hot water circulating around.

    You have to create ocean currents to get around this mess. You could, of course, use the temperature difference to have the water flow, but another way would be to take advantage of the Coriolis effect. The problem here is now that you aren't necessarily going to have the right kind of Coriolis effect at the poles, but perhaps you could figure something out. Maybe a huge amplification of a wobble of the planet's axis could solve this issue.

    Also, a small volcano isn't going to do any good. You need a string of them - like the mid-Atlantic ridge, except really active. Perhaps you could encircle the pole with a chain of large vents, thus providing a lot of heat.

  • Axis flip. Another idea (which won't work here, as per your comment) would be to have the planet's axis be flipped 90 degrees so that it points at the star. Mercury endures scorching temperatures because of its proximity to the Sun. Maybe move the planet back a bit further, so it's not too hot, and you'll have a pole that's too hot for ice, but just hot enough for liquid water.

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  • $\begingroup$ The axis flip wouldn't work. I'm trying for the classic vision of the open polar sea, where the earth is pretty much as-is, with only enough change to clear a 'sea' at the north pole. $\endgroup$ – Adam Miller Dec 10 '14 at 0:27
  • $\begingroup$ @AdamMiller - Okay, then the flip definitely wouldn't work. Go geothermal, instead. $\endgroup$ – HDE 226868 Dec 10 '14 at 0:29
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    $\begingroup$ Is a big enough vent (or field of vents) feasible? It would take a lot of energy to clear a significant amount of ice. Do we know of any hydrothermal vents currently extant under the polar ice cap, and if they have any effect on the surface temperature? $\endgroup$ – Adam Miller Dec 10 '14 at 0:32
  • $\begingroup$ @AdamMiller I don't know for sure, but they're almost always along plate boundaries. Make the area around the North Pole a continent, and you could have a string of huge vents. $\endgroup$ – HDE 226868 Dec 10 '14 at 0:35
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    $\begingroup$ @AdamMiller there are volcanos in Antartica. Mt. Erebus is active. $\endgroup$ – user487 Dec 10 '14 at 1:21
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It might be plausible. A very strong upwelling of deep water might be able to melt a significant area at the pole since the deep water is well above freezing. And a strong upwelling at the pole might not be impossible. If the polar ocean is large enough, the winds surrounding it will force the surface water to move away from the pole. The lost water must be replaced by deep water upwelling to the surface.

Now the bad news. It can't happen on Earth. The southern ocean is wide enough, has the winds, has the currents... But because there is a continent, the upwelling happens along its coasts, and just makes the southern oceans more fertile with the rich nutrients it brings to the surface. The northern currents are blocked by continents and in fact the Gulf stream feeds warm surface water to the polar ocean. Good for building harbours in Siberia, not so good for an open polar sea.

But at another planet where you can optimize the parameters for it? Why not? Ocean can transport lots of heat and with strong greenhouse effect the pole might not be all that cold during the summer. As others have noted, the Arctic ocean will be open in the future. A sea that is not quite open might have an open ocean at the middle due to strong upwelling.

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  • $\begingroup$ So what do you think could push the Gulf Stream up to the pole? Maybe if there were a higher ridge connecting the Svaldbards to Norway? $\endgroup$ – Adam Miller Dec 12 '14 at 1:55
  • $\begingroup$ @AdamMiller Did you comment the wrong answer? Only mention of Gulf Stream I make refers to the way it works right now. But I guess the shape of continents could push warm currents to the pole while leaving ice on the coasts surrounding it. $\endgroup$ – Ville Niemi Dec 12 '14 at 4:17
  • $\begingroup$ Yeah, that's what I was thinking. Ice tends to form more around coasts, so if the gulf stream parts that flow along Siberia were directed north, instead... $\endgroup$ – Adam Miller Dec 12 '14 at 19:08
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I'll start off by saying I'm not a physicist; that said what about the possibility of large natural deposits of highly radioactive elements either dissolved into the water or just jutting out of the sea floor?

Uranium and other long lived isotopes may provide a wide area heating mechanism to open up a polar sea. Its likely the surface wouldn't show readings of this radiation either (water absorbs a lot of radiation) and the sea would have some convection type currents. Radiation heats deep water which rises and replaces colder surface water, etc.

If the natural deposits don't work for whatever reason, perhaps the radioactive elements were deposited via planetary bombardment. Large radioactive asteroids bombarded the planet creating several "radio springs" that create liquid water pools in a polar region.

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    $\begingroup$ You may not be able to detect the radiation coming from the ocean bottom, but wouldn't you be able to detect the radon-222 bubbling up from the floor? If it were natural deposits the Rn-222 could presumably be trapped. Perhaps if asteroid deposits, they could be so old that have long since been sealed over. $\endgroup$ – Gary Walker Dec 14 '15 at 22:07
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Just how large of a sea are you considering? The larger the body of water, the more difficult this will be. How deep does the sea need to be? If the sea is relatively shallow, a hydrothermal field should be able to put out plenty of heat to keep the water above freezing. Shallower waters means less cold water circulating, so geothermal heating could be a significant factor.

Salinity can strongly influence the formation of ice as well, so this could be used.

Imagine a huge underwater caldera on the pole, much of which forms a large hydrothermal vent field (maybe a massive impact crater or perhaps a ring of underwater mountain ridges from plate tectonics depending on how big you want it). The vents produce lots of heat to keep the waters comparatively warm (can be well below the freezing point of fresh water but just above that of a dense brine), as well as release large amounts of salts from the crust to maintain very high salinity.

The ridge around the caldera comes up close to the surface, so there is little significant mixing of deep waters (so the water within the caldera remains a heavy brine with little overspill). The point at which waters freeze is just within the radius of the caldera - when seawater freezes, the salt is forced out of solution in a brine considerably denser than the surrounding water. If this dense brine falls on the inside of the ridge, it maintains and reinforces the salinity of the polar sea.

The combination of hydrothermal upwelling warming the waters (warm is a relative term) and being saturated with salt should prevent the water from freezing at the pole, yet be surrounded by ice just to the outside of the undersea ridges or caldera.

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The most reasonable way to get an open sea around the North Pole surrounded by colder areas is to have a warm current, like the Gulf Stream, be diverted into the Polar regions rather than be allowed to turn and head south again. Parts of the actual Gulf Stream reach as far North as the northern tip of Scandinavia and warm those waters. A larger and more directed stream might be tuned to deliver enough warm water to the Arctic Ocean to keep the ocean free of an ice cap.

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  • $\begingroup$ I think this is the best answer I've seen, though I'm still open to suggestions. $\endgroup$ – Adam Miller Dec 12 '14 at 1:51
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If you allow for alient teraformers from the distant past, then the how is just good engineering. That leaves the why. Why did the ancient teraformers leave open oceans at the top and bottom of their planet?

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    $\begingroup$ Magrathea - If you are invoking alien terraformers, at least give them credit by name. $\endgroup$ – Gary Walker Dec 14 '15 at 22:24
  • $\begingroup$ Known names are not a common attribute for either aliens, or other entities from the distant past. We may know that they were not part of our evolutionary tree, in which case we will call the "Aliens", or if we can't even tell that much, we might call them "Ancestors" or "The Ancients"; but real names surviving across the millenia... that is not very likely. $\endgroup$ – Henry Taylor Dec 15 '15 at 1:32
  • $\begingroup$ @Gary Walker, I totally missed your link to the Magrathea. Great Comment! $\endgroup$ – Henry Taylor Dec 16 '15 at 2:13
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When salt water freezes the water forms solid ice crystals that push the majority of the impurities out. If as the poles froze these impurities were concentrated into a polar sea, that sea could reach such high levels of solute concentrations that it would no longer freeze. Basically making a polar Dead Sea.

For this to happen the Polar Sea can't be connected to the rest of the world's oceans, so the bordering ice has to be deep enough, or the sea shallow enough, to prevent any exchange. Additionally, when the pole first began to freeze, it had to freeze from the border inward, so as to isolate the polar sea and concentrate all the salt in it. You could hypothesize that this was the result of currents or volcanic activity or anything else long ago. With this explanation your pole is still really cold, it just doesn't freeze because it is too salty.

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  • $\begingroup$ I like the idea, but the polar air is pretty dry. Wouldn't the "brine" dry out until it was covered over with salt, and then snow and ice? So you'd need a continued source of water, which would make getting the concentration needed difficult. $\endgroup$ – Ville Niemi Dec 11 '14 at 22:19
  • $\begingroup$ That is compelling. I think the surface gets too cold for salts to bring down the melting point, though. I do know that the Caspian Sea does freeze in the north, though it's relatively fresh there due to the incoming water from rivers. $\endgroup$ – Adam Miller Dec 12 '14 at 1:51

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