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On a habitable world completely covered in water, with no land above sea-level, there would presumably be storms of biblical proportions. Suppose this world has oceans so deep that the deeper layers just have too much pressure for life of any kind to survive - from the planet's organisms' point of view, the sea would essentially be bottomless.

Without any seabed for shelter/anchorage, but also without any land to be beached on, would gigantic storms, waves etc. be seriously harmful to underwater creatures? When I say "seriously harmful", I mean so damaging as to make the very existence of complex sunlight-zone life on the world dubious.

Two points for further clarification:

  • The animals do not need to surface to breathe.
  • Yes, they could potentially take shelter in some kind of floating reef/microbial mat, but ignore that for the purposes of the question.
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    $\begingroup$ I don't see why the lack or continents alone would lead to much bigger storms. $\endgroup$ – Alexander Mar 18 at 18:18
  • $\begingroup$ Animals could evolve to make use of the storm, maybe. $\endgroup$ – Renan Mar 18 at 19:49
  • $\begingroup$ "No land above sea level" is not the same as "no seabed for shelter/anchorage". Is all of the seabed too deep on your world, or can you have underwater mountains, i.e. things that would be islands if the overall sea level were lower? $\endgroup$ – Monica Cellio Mar 19 at 3:30
  • $\begingroup$ @MonicaCellio Yes, take that all the seabed is too deep. $\endgroup$ – SealBoi Mar 19 at 7:53
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Photosynthesis can take place at depths of about 200m; so, as long as sustained storms do not significantly disturb life at those depths, then life would be fine.

To understand your risks, a wave only causes major disturbances down to about 1/2 the height of the wave, meaning you'd need storms to consistently produce 400m waves to kill off all life. However, in the open ocean (under Earth's gravity), wind can generally not produce a wave taller than 10m because as the wind whips it up bigger and bigger, the wave will begin to crest and gravity will force it to collapse in on itself. For this reason, waves bigger than 10m are almost always causes by seismic activity or from being pressed up on by a continental shelf. So, in your world, even if you had massive super storms constantly raging at the surface, just 5m down you'd have relatively calm water without any continental shelves to exasperate things giving you a 195m save zone for photosynthetic life.

So to answer your question, storms will not inhibit life.

That said, with no readily available access to ground minerals, your world may not be able to sustain life for completely different reasons. If your planet does not have underwater mountains that reach within 200m of sunlight or some other mechanism for uplifting significant mineral content into the upper layers of the ocean, it's unlikely for you to have the diversity of elements you would need for life.

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    $\begingroup$ Just as a minor note, satellite measurements have shown that transient rogue waves of 20 meters or more happen all the time. It's estimated that at any given moment there are at least ten 25-30 meter waves somewhere on Earth. $\endgroup$ – Keith Morrison Mar 19 at 1:05
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    $\begingroup$ Yes, the irony is that a near earth-sized deep ocean world covered in violent storms would actually have smaller max-sized waves than Earth because the conditions for waves to reach 25-30m would not really exist without shorelines. $\endgroup$ – Nosajimiki Mar 19 at 15:07
  • $\begingroup$ No, these rogue waves can happen in deep water as well. That's where most of them are. Just as some examples, the QE2 was hit by a 29 meter wave in the middle of the North Atlantic in 1995. MS Bremen and Caledonian Star were hit around the same time by 30 meters waves in the South Atlantic in 2001. The evidence indicates MV Derbyshire was sunk by rogue waves in deep water off Japan in 1980. $\endgroup$ – Keith Morrison Mar 19 at 15:31
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The climate of a planet is primarily driven by the energy imparted to it by its parent star and the difference in atmospheric circulation driven by the poles not rotating and the equator rotating at high speed. The most serious storms would probably occur on rapidly rotating planets with high solar input, but there is a limit to how high wind blown waves can get.

If there is no need to surface to breathe creatures on such a world would be able to avoid the effects of storms simply by diving down a few hundred metres and in most cases by diving just a few tens of metres.

It is hard to believe that wind-blown waves would be able to build to such intensity that this strategy would not work. Adding too much energy to the atmosphere would have the effect creating chaotic conditions in which it would be difficult for sufficiently large well-formed waves to exist as they would be hit by many other waves and variable wind conditions.

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No.

  • Earth has storms of biblical proportions that happen over its oceans. Perhaps a dolphin or whale is occasionally affected, but that's it. Those storms are a much greater danger to those of us dependent on its surface. Generally speaking, I doubt it matters how big a storm gets.

  • Your ocean bottom won't be smooth just because there's no surface land. You'll have ridges, sinkholes, canyons, areas of shallow water and areas of deep water. You'll have currents, waves, and tides (assuming a moon). You'll (presumably, it's your world) have coral reefs. If you draw a shape encompassing our own oceans starting at a depth of, say, 2 meters and encompassing everything deeper, you'd have your world in a nutshell. In other words, there will be plenty of places to hide if you can't get deep enough.

  • Your sea life will have evolved on that planet (I assume, you didn't say if they were transplanted or not). They will have adapted to whatever storms your world can throw at them just as all life on Earth has done. Can Mother Nature throw a curve ball that takes out a few creatures (like a wildfire on land)? Sure! But I don't think that's what you're asking about. I believe you're asking about within-the-statistical-norm storms — the kind life would have adapted to. (This is why I don't believe it matters how large your storms get.)

  • Earth has depths were no life can live, but it also has a very wide band of depth where life thrives, and at the bottom of that band are depths that wouldn't know a storm was raging no matter how biblical its proportions. Frankly, I'd doubt anything deeper than 100 meters would ever now a storm was in process.

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As for the storm's effect itself- no any storm wouldn't have that great an effect on the ocean life.

According to This Post on reddit any effects on the surface of the ocean reach about 1/2 that depth, with exceptions for phenomena caused by the ocean floor (e.g. a Tsunami).

That being said, if your ocean floor is over about 26,000 feet deep SOURCE, then life in general is going to have a hard time existing. That being said, they're still going to need something like geothermal vents or ocean fissure for it.

That's because of mineral loss over time, since any creature that dies would sink to the bottom of the ocean, and since nothing can get down that low to retrieve the mineral nutrients, slowly leeching it out of the ecosystem. (at the very least, nothing particularly mobile, I couldn't find max depth on micro-organisms or non-sunlight dependent plants).

So unless you've got something stirring up your ocean floor, two things will happen:

  1. The ocean will slowly become freshwater from all the minerals being effectively locked in the ocean floor.

  2. The ocean will slowly become devoid of life from the lack of minerals necessary for life (like potassium and iron).

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  • $\begingroup$ Could volcanic activity shake up the seabed enough to return minerals to the upper few kilometres? $\endgroup$ – SealBoi Mar 19 at 17:37
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    $\begingroup$ You could probably do some calculations using damped harmonic motion or max parabola heights. But if the matter gets enough vertical velocity to reach a given height with the damping effect from the water and negative acceleration due to gravity, you've got your answer. $\endgroup$ – David Mar 19 at 18:15

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