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Somes J
2011-Dec-26, 04:40 AM
I'm thinking of portraying a world in my hard SF setting that is a wet Earthlike superterrestrial with a deep global ocean, very little land (say < 1% of the surface is land) and a hothouse climate - comparable to Cretaceous or PETM Earth, with tropical/subtropical temperatures extending well into the mid-lattitudes and even the poles being warm (5-20 C). Some things I'm wondering about such a world:

1) How powerful/nasty would ocean storms, especially cyclones, get on this world? Between the hot climate and lack of land it sounds like the perfect recipe to get some really evil storms, so much so that I'm wondering whether it would be habitable to a preindustrial agricultural human culture (which is supposed to have existed on the planet in the past). From pg. 27 of Life in the hothouse: how a living planet survives climate change (http://books.google.com/books?id=1fYO6l8x8ScC&printsec=frontcover#v=onepage&q&f=false) by Melanie Lenart:


Like washboard bumps on a dirt road, the bumps in hammocky tempestites tend to be evenly spaced. The "wavelength" - that is, the distance between the bumps - reflects the severity of the storm... Basically, bigger waves yield bigger wavelengths. ... The tempestites laid down during the mid-Cretaceous contained wavelengths 20 feet apart, triple the distance of those formed by even the most severe modern storms. I'm wondering if this would be a good indicator of how strong storms would be on this world, or would the lack of continents to obstruct cyclone paths make for even more powerful storms than this?

2) In a situation like this, is it likely that you'd get semi-permanent cyclones, something like Jupiter's Great Red Spot?

Thanks.

Ara Pacis
2011-Dec-26, 06:45 AM
What is the composition of the atmopshere, axial inclination, orbital elements, etc, that create differentiated airmasses? You need more than heat and water, you need know the various lapse rates (http://en.wikipedia.org/wiki/Lapse_rate#Significance_in_meteorology) (vertical) as well.

Somes J
2011-Dec-26, 07:36 AM
What is the composition of the atmopshere More-or-less Earthlike, a lot more carbon dioxide (thousands of ppm), maybe a bit less oxygen, maybe somewhat more nitrogen (say 1.5 bars overall atmospheric pressure).


axial inclination I'm thinking either somewhat less than Earth (say 10 degrees) or essentially 0 degrees with a seasonless climate. I haven't decided.


orbital elements Roughly Earth-equivalent insolation orbit of Gliese 75 (http://www.solstation.com/stars/hr511.htm) (maybe a bit farther out, compensated for by higher atmospheric CO2), so IIRC we're probably looking at a year of between 7-8 months.

JCoyote
2011-Dec-26, 10:16 AM
Did the "humans" evolve there or were they transplanted there? On a planet with 1% landmass, I would be surprised if any species evolved that wasn't amphibious. It doesn't feel like enough space to support the competitive development of mega-fauna on land. Now a humanoid amphibious species? The planet having massive storms would also be a push against non-amphibious land dwellers. While a species might seek out land to escape predation as they sleep or whatnot, if the storms were too nasty at the moment they take the risk of staying in the ocean til it passes.

If some powerful group transplanted humans to that environment, it would not be surprising to see the humans adapted to amphibious lifestyle. Setting up some functional gills might not be too hard for a group advanced enough to perform interstellar species transplantation. Given the environment, local technological infrastructure would be difficult to create or maintain. So even if they were explicitly part of an interstellar civilization, they could end up hitting the stone age in only a few generations if they were cut off.

eburacum45
2011-Dec-26, 06:06 PM
There is a very interesting discussion about weather on a planet with no continents here
http://www.bautforum.com/showthread.php/83001-Some-Earth-Without-Land-Masses-Questions.?

Basically, one might expect a central belt of doldrums associated with the intertropical convergence zone, a mid-latitude band of westerlies and circulation in between. Hurricanes could form and keep blowing, unless they run into cooler regions. but the planet might look quite regular, even banded.

A diagram of idealised circulation can be found here.
http://www.aircraftpilots.com/tutorials/meteorology/section4.html

Ara Pacis
2011-Dec-26, 06:28 PM
So, it's like Earth except for the ways it's not like Earth. That leaves a lot of room for interpretation. If the planet is larger than Earth, the density of the atmosphere may be thicker and less solar energy may make it to the surface, assuming that there isn't a permanent veil of clouds. Without any land and and with a low or non-existent tilt, you probably won't have much in the way of differential heating to drive wind and you won't have mountains to create dry air.

Romanus
2011-Dec-26, 06:53 PM
Storms tend to be self-limiting on Earth; even in the western Pacific--the most favorable region for their formation on the planet--they don't form continuously. Almost all tropical cyclones have a poleward component that eventually takes them out of their favored development regions. Tropical cyclones are also ultimately limited by their reliance on a surface energy source (warm water), while storms such as those in the atmospheres of Jupiter and Saturn are probably driven more by a combination of internal heat and latitudinal wind shear (e.g., the GRS is being "rolled" between two opposing jet streams), and are unaffected by "surface" conditions.

Somes J
2011-Dec-26, 10:49 PM
One possibility I was thinking of for dealing with possible super-hurricane problems would be to make the planet cooler, so there would be a large cool zone around the poles where big storms would tend to dissipate. One issue with that though is I still like the idea of a hothouse world, simply because I like the aesthetic of having no solid surface at all except for the islands, and the only hothouse climates I've been able to find information on in Earth's past tended to be quite warm at the poles. Hence why I'm potentially leaning toward a seasonless climate - I would think that should encourage large climate differences with lattitude because there'd be no moderating summer or winter swings (if a place is cool it's cool all year, if warm then warm all year), and the poles could be cool enough that on Earth there would be a seasonal ice cap, but here there isn't because they have a perpetual mid-spring/fall equivalent climate. Would that kind of set-up be plausible?


Did the "humans" evolve there or were they transplanted there? On a planet with 1% landmass, I would be surprised if any species evolved that wasn't amphibious. It doesn't feel like enough space to support the competitive development of mega-fauna on land. The humans originally arrived there via spacecraft. This is also a universe where most suitable planets in the Earth-equivalent insolation zone were subject to terraforming by a long-gone alien race in the deep past (say ~100 myr ago), so there would be introduced terrestrial fauna and flora if not indigenous ones. I suspect you'd have flightless birds (or equivalent) being the dominant modern terrestrial fauna over much of what land there is, as long-distance fliers would be some of the best equipped to colonize widely scattered new land masses emerging from the ocean.


If some powerful group transplanted humans to that environment, it would not be surprising to see the humans adapted to amphibious lifestyle. Setting up some functional gills might not be too hard for a group advanced enough to perform interstellar species transplantation. I don't think I really want to go in that direction. One thing I did think of was you might see a lot of castle-like structures and seaside communities perched on coastal hills. On seeing them we'd probably think of defense against invaders and pirates, but they're actually largely fortresses against hurricanes (thick windowless walls and heavy doors to protect against flying debris, on high ground to keep above storm surge and floods, high watchtowers where people keep on eye on the horizon for large, dark cloud banks, with bells to warn everybody around that they'd better find shelter). You might get a lot of pretty extensive seawalls too.


and you won't have mountains to create dry air. There would be some mountains - what land there is would be the planet's highest mountainous regions, so I imagine they would tend to be fairly rugged. I doubt they'd generally be all that high above sea level though, simply because much of their height above the "continental" platforms would be below sea level.

Trakar
2011-Dec-27, 01:29 AM
I'm thinking of portraying a world in my hard SF setting that is a wet Earthlike superterrestrial with a deep global ocean, very little land (say < 1% of the surface is land) and a hothouse climate - comparable to Cretaceous or PETM Earth, with tropical/subtropical temperatures extending well into the mid-lattitudes and even the poles being warm (5-20 C). Some things I'm wondering about such a world:

1) How powerful/nasty would ocean storms, especially cyclones, get on this world? Between the hot climate and lack of land it sounds like the perfect recipe to get some really evil storms, so much so that I'm wondering whether it would be habitable to a preindustrial agricultural human culture (which is supposed to have existed on the planet in the past). From pg. 27 of Life in the hothouse: how a living planet survives climate change (http://books.google.com/books?id=1fYO6l8x8ScC&printsec=frontcover#v=onepage&q&f=false) by Melanie Lenart:

I'm wondering if this would be a good indicator of how strong storms would be on this world, or would the lack of continents to obstruct cyclone paths make for even more powerful storms than this?

2) In a situation like this, is it likely that you'd get semi-permanent cyclones, something like Jupiter's Great Red Spot?

Thanks.

Dr. Ray Pierrehumbert
http://geosci.uchicago.edu/~rtp1/

I highly recommend his planetary climate book (http://geosci.uchicago.edu/~rtp1/PrinciplesPlanetaryClimate/index.html)and can say that he has been known to directly engage public questions that tickle his intrigue!

aside from this, I'll give a look through my paper database and see what seems relevent, but offhand, if the planetary climate is stable, I'm not sure that there would be huge storms as such are a means of distributing and equalizing temp differences. with a smooth surface, no mountain ranges to deflect air flow, you may end up with more of a permanently overcast sauna environment than colliding air masses with large temperature differentials (think about how we used to imagine Venus in the '40s and early '50s). You could give it a more elliptical orbit and a high axial tilt which might exaggerate the seasons and give something more like what you seem to be looking for.

Ara Pacis
2011-Dec-27, 03:17 AM
There would be some mountains - what land there is would be the planet's highest mountainous regions, so I imagine they would tend to be fairly rugged. I doubt they'd generally be all that high above sea level though, simply because much of their height above the "continental" platforms would be below sea level.Well that might create a micro-climate for that 1% of land, but it wouldn't affect the vast majority of the planet, but that's kinda how it works here now since land is less than 30%.

What's more important is how deep is the hydrosphere and how does the bathymetry affect oceanic currents. Even if the "land" doesn't break the surface, it can affect the flow of water. If you were to have a ring of seamounts very close to the surface at high latitudes, it might keep the cool water separate, which might drive atmospheric interactions. Also, large areas of shallow seas might heat up more and drive climate and weather. And shallow seas allow for more animals to live and die and decay or be buried in sediment and affect the carbon cycle. If your planet is too dull and boring geographically, then you won't have enough capacity for delta in the system to drive violent weather since everything may tend to even out through less violent means. Recall that even hurricanes often start as waves coming off the African desert.

Somes J
2011-Dec-27, 03:59 AM
What's more important is how deep is the hydrosphere and how does the bathymetry affect oceanic currents. The oceans are generally pretty deep - I would guess average 2-4 km over the continental platforms and 5-7 km over the ocean basins, maybe divide those figures by 1.4X to account for the higher gravity, which I would think would both compress the oceans and depress the topography. I would guess shallow seas would be pretty limited in extent, much like land.

I'm not sure what deeply submerged continental platforms would look like, I'm guessing with less erosion underwater and little sediment accumulation (so little land for sediment to wash from) they'd probably be pretty rugged.

It's a bigger and younger planet than Earth, so I think geologic activity should be pretty high - I'd see lots of midocean ridges and a highly broken/scattered continental crust due to highly active plate tectonics. The ocean floor would probably be a pretty complex and rugged terrain overall, I think, but most of that would be very deep underwater.

Ara Pacis
2011-Dec-27, 07:11 AM
The oceans are generally pretty deep - I would guess average 2-4 km over the continental platforms and 5-7 km over the ocean basins, maybe divide those figures by 1.4X to account for the higher gravity, which I would think would both compress the oceans and depress the topography. I would guess shallow seas would be pretty limited in extent, much like land.It's your planet, but some of the characteristics you want may be contradictory. BTW, water, being a liquid, is incompressible.


I'm not sure what deeply submerged continental platforms would look like, I'm guessing with less erosion underwater and little sediment accumulation (so little land for sediment to wash from) they'd probably be pretty rugged.There will be erosion if there are currents, if there is life, if there are tides, if there is geologic action, if there is chemistry. If the water is stagnant and anoxic, maybe not so much.


It's a bigger and younger planet than Earth, so I think geologic activity should be pretty high - I'd see lots of midocean ridges and a highly broken/scattered continental crust due to highly active plate tectonics. The ocean floor would probably be a pretty complex and rugged terrain overall, I think, but most of that would be very deep underwater.When you say bigger, do you mean diameter or mass?

Trakar
2011-Dec-27, 09:39 AM
It's your planet, but some of the characteristics you want may be contradictory. BTW, water, being a liquid, is incompressible.


At STP this is a good general rule of thumb, but the lower levels of an ocean world aren't likely to reflect STP.

At the bottom of the Mariana Trench the pressure is the equivilant of 1,087 Atmospheres and water volume is compressed about 0.002%(this doesn't include temp changes which would further diminish the volume a bit).

Increase the volume of our oceans with another 4 kilometers of water over a larger planet and bump our gravity up a few tenths and I'm sure we'd get an even more noticeable difference. Not sure that it'd be quite enough to form any of the more exotic ices but it would be much denser than any water we are more typically familiar with.

{neither liquids or solids, are truely incompressible, just much more incompressible than gases. In some modern weapon pits we are compressing metal under the pressure equivilances of 100 million (or more in some advanced designs) atmospheres, resulting in increased densities 2+ times its normal state}

chornedsnorkack
2011-Dec-27, 07:14 PM
What is the distribution of that 1 % land?

1 % land on exactly Earth sized planet is 5,1 million square km. The continent of Australia is 7,7 million square km.

Yes, you are going to have a lot of specialized terrestrial fauna. Look at Hawaii - just 16 600 square km, yet diverse specialized terrestrial fauna of honeycreepers et cetera.

Look at Indian Ocean. 75 million square km of water.

Less than 1 % of land away from shores of Indonesia etc.. Of which 590 000 square km is Madagascar. The rest includes high islands of Comoros, Mascarenes, Seychelles, Kerguelen, a few smaller like Amsterdam, Christmas, Edward, and low islands like Aldabra, Amirantes, Chagos and Maldives - about 10 000 square km of high islands and I guess under 1000 square km low islands.

Quite some megafauna. Aepyornis, giant lemurs and dwarf hippopotami of Madagascar. Dodos and solitaires of Mascarenes are not "mega" for man, but they are mega for pigeons. Giant turtles of Aldabra and other Seychelles.

Similar picture for Pacific. Drawing a border offshore so as to leave Japan, Philippines and New Guinea to the continents, less than 0,3 % of land, most of which is New Zealand. The rest are high islands like Tonga, Rarotonga, Tahiti, Pitcairn, Easter Island, Galapagos, Hawaii, Carolines and Marianas, and low islands like Tuamotu, Tuvalu and Marshalls. As for megafauna, Galapagos has turtles; Hawaii and New Caledonia certainly had sizable flightless birds.

Falling back to stone age? Polynesians certainly did: they came from Indonesia where they knew metals and pottery, but forgot both.

Mind you, you can assume quite technically advanced society if you want. Japan minus Hokkaido is under 300 000 square km - only slightly bigger than New Zealand. You could have advanced society like the 17th...19th century closed Japan, and your 5 million square km combined allows for even bigger archipelagoes. Japanese did manage to smelt iron and copper.

Geologically, do you expect any low islands/coral atolls?

Regarding atmospheric composition: lower oxygen concentration is liable to affect burning of fire. And that would affect preindustrial (and industrial) humans.

Ara Pacis
2011-Dec-27, 08:15 PM
Right, Trakar, but do you think the ocean water would be compressed to 71% of its STP volume on earth? Do you think that would depress the topography of the seafloor?

Somes J
2011-Dec-27, 09:27 PM
It's your planet, but some of the characteristics you want may be contradictory. Which ones?


BTW, water, being a liquid, is incompressible. Thanks, I did not know that. Though for my purposes I don't think it would make much difference. The significant point was, with higher gravity, I would think the mountains and plateaus would probably be lower, and the ocean correspondingly wouldn't need to be as deep to drown the continents so completely. So the continental platforms might be under 1.5-3 km of water average, with this being the equivalent of a sea level 2-4 km higher than ours for Earth's topography.


When you say bigger, do you mean diameter or mass? Both. ~2.4X Earth's mass and ~1.4X its diameter.


Not sure that it'd be quite enough to form any of the more exotic ices but it would be much denser than any water we are more typically familiar with. I haven't really investigated this, but in Stephen Baxter's Ark (http://en.wikipedia.org/wiki/Ark_(Baxter_novel)) there was mention of the formation of exotic ices at the bottom of a very deep global ocean as a potential issue at one point, and it was brought up that this wouldn't happen at the bottom of a ~15 km ocean. I figured from that it probably wouldn't be an issue for the mostly much shallower oceans on my planet.


What is the distribution of that 1 % land? I'm thinking mostly quite small islands (e.g. like Hawaii), with the odd Philippines/Japan/NZ-sized landmass. Maybe an Indonesia-sized archipelago or two.


Geologically, do you expect any low islands/coral atolls? There should be a coral-equivalent, and with the warm climate I think you'd probably quite a lot of reefs, where a suitable platform existed.

chornedsnorkack
2011-Dec-27, 10:48 PM
Water, like all substances, is compressible. See the phase diagrams at
http://www.lsbu.ac.uk/water/phase.html
At 100 MPa, equivalent to about 10 km in 1 g, water is about 5 % denser.

Note that high pressure ices will form only at pressures well over 600 MPa.

Trakar
2011-Dec-28, 02:58 AM
Right, Trakar, but do you think the ocean water would be compressed to 71% of its STP volume on earth?

I think I said what I meant, as to how much the water was compressed, 71% would surprise me, but until we have enough specifics to run some actual calculations, it would be hard to say with any surety. Where are you deriving this figure of 71% from?


Do you think that would depress the topography of the seafloor?

Ice sheets and caps depress the topology of continental crust, why wouldn't the mass of 5-7000meters of water on planet with higher gravity depress the topology of seafloor?

Trakar
2011-Dec-28, 03:11 AM
... There should be a coral-equivalent, and with the warm climate I think you'd probably quite a lot of reefs, where a suitable platform existed.

most reefs are shallow water affairs (plants need light - and coral is an animal but most types exist in an interdependent partnership with specific types of algae. The algae need the light, if the water is too deep the algae can't get enough light and they die, when they die, the coral polyps' waste products build up in it's little self-secreted limestone shell and it becomes anoxic and the polyp dies.

Ara Pacis
2011-Dec-28, 06:48 AM
I think I said what I meant, as to how much the water was compressed, 71% would surprise me, but until we have enough specifics to run some actual calculations, it would be hard to say with any surety. Where are you deriving this figure of 71% from?I'm not sure, the OP tossed out dividing the crust and hydrosphere by 1.4 to account for higher gravity. At least, that's what it sounded like he was saying here in post #11

The oceans are generally pretty deep - I would guess average 2-4 km over the continental platforms and 5-7 km over the ocean basins, maybe divide those figures by 1.4X to account for the higher gravity, which I would think would both compress the oceans and depress the topography. I would guess shallow seas would be pretty limited in extent, much like land.I worked out his numbers and I come up with a surface gravitational acceleration of 12.0246 m/s2 or about 23% higher gravity than Earth (with a 12.5% lower density, 4.823g/cm2), in case that helps you sort it out.


Ice sheets and caps depress the topology of continental crust, why wouldn't the mass of 5-7000meters of water on planet with higher gravity depress the topology of seafloor?Because ice sheets, except for an extreme snowball climate, don't cover the entire planet, only a certain area. In that area, the mantle flows out from under the crust to balance out the loading in a process called isostasy. Water doesn't pile up at altitude like snow on ice sheets with high elevations, but seeks it's own level, generally at lower altitude. The weight of water in a basin can cause isostatic adjustment to deform and elevate the topography along its periphery to shallower depths or to elevations above the surface. However, if the entire planet is mostly underwater with a relatively even depth, there's not much in the way of static mass disparities above the crust to drive major isostatic deformations. Moreover, if the crustal rock is denser than the ocean water, then the rock that is elevated above the seafloor (seamounts, islands) would be a heavier mass upon the mantle than an adjoining area of seafloor at the same level that only has a water column above it.

But anyways, I don't think that's what the OP was talking about, he was talking about the topology having less relief/elevation due to gravity and/or water pressure (but not due to erosion, which he doesn't think is possible at depth). Perhaps he's referring to the angle of repose, or maybe straight up gravitational distortion of rock. I would ask how much smaller do you think sandstone or shale might be at such depths and pressures and accelerations, but those are sedimentary rocks, which can't exist without erosion.

Somes J
2011-Dec-28, 07:19 AM
The whole compressibility/incompressibility of water tangent is really probably going to be pretty irrelevant for my purposes. I doubt the exact pressure at the bottom of the ocean or mass of the oceans is going to be important to anything I write. I was just trying to estimate how deep the ocean would be on average, and for that only the response of large rock masses (mountains etc.) to higher gravity is really relevant, as that would influence the topographic variation, and hence difference in height between the high mountain peaks/highlands that poke above sea level and the submerged continental platforms.

chornedsnorkack
2011-Dec-28, 08:28 AM
The density of water does affect the relief of seafloor. The effect of water compression, however, is minor.
It is easier to hold up a mountain, density say 2,5, in water, density 1,0, than in air, density 0,0. But the difference between 1,0 and 1,1 is small.

Ara Pacis
2011-Dec-28, 10:07 AM
Which ones?

Well, they are your parameters to choose. A larger world with more gravity probably means a thicker and denser atmosphere. Add more CO2 to the dense mix and it may be toxic to humans, even at a few thousand ppmv (http://en.wikipedia.org/wiki/Hypercapnia#During_diving). Maybe they can physically adjust, maybe they'll need scuba gear to go outside. With a denser atmosphere the surface winds may blow more slowly, although they'll have more force. The ocean might be acidic.

Your planet's design seems to be mostly homogeneous, which is probably okay if you don't want giant storms. The hothouse concept for earth will vary from your planet due to it's differences and can't be directly extrapolated. You need to work out the actual chemical and physical cycles involved. With no major topography altering atmospheric and hydrospheric currents, I suspect you'd get a banded pattern. Depending on the density and other variables, even with a banded pattern you may not get a steep thermal gradient poleward as the thermal capacity of a thick atmosphere and thick hydrosphere might still develop an equilibrium at a high thermal level. In other words, I doubt there would be an ice cap (floating or grounded), as the development of an icecap would probably cause instabilities in the banded flows due to chemistry, temperature and density.

This doesn't mean that large tropical cyclones couldn't form, but that will depend on lapse rates and other meteorological parameters which remain to be determined. It's not heat alone, but how that heat is allowed to do work through phase-change dynamics that may or may not be permitted or favorable in your planet's atmosphere due to its different physical and chemical makeup. Not to mention that a relatively stable system on your homogenized world might reach equilibrium with a persistent cloud layer that prevents ocean surface heating to drive evaporation and convection anyways, similar to Venus. On Earth, cyclones tend to be initiated by disturbances, often caused by continental land effect (which you don't have), and they are often nurtured by favorable cyclic thermal oscillations in the basins, which can't exist on your world due to the lack of constraining structures. Thinking about Venus, I wonder if the cloud base would be much higher than what we see on Earth, which might mean that even if storms were possible in that atmosphere, they might rage well above the heads of the surface dwellers who might not feel the effects as strongly at the bottom of the denser and more stable lower atmosphere.

Also, life might not be likely due to the planet's design. With minimal shallow water, the entire planet's surface is essentially a pelagic zone. Any life will have to be free floating and it won't be as productive as shallow seas tend to be where light can reach the bottom. without continental erosion, there might not be a lot of nutrients flowing into the sea either. It might be plausible for deep water gyres to bring stuff up from the bottom, but it's not clear if the homogeneous-turned-banded system would have enough momentum to lift anything from that deep fast enough. That's assuming that life could survive in what is likely an acidic ocean with no or little erosion to bind carbon from the atmosphere, although life might adapt or evolve to survive or even thrive. However, without plant-like life capable of producing oxygen for the atmosphere, the cycle of that very reactive and life-essential chemical might not leave enough to support human life.

These are just thoughts, more questions than answers, to point you towards the solutions you seek.

Ara Pacis
2011-Dec-28, 10:14 AM
The whole compressibility/incompressibility of water tangent is really probably going to be pretty irrelevant for my purposes. I doubt the exact pressure at the bottom of the ocean or mass of the oceans is going to be important to anything I write. I was just trying to estimate how deep the ocean would be on average, and for that only the response of large rock masses (mountains etc.) to higher gravity is really relevant, as that would influence the topographic variation, and hence difference in height between the high mountain peaks/highlands that poke above sea level and the submerged continental platforms.Ah, but the topography, even underwater, affects currents and thermal transport and can have a major effect on climate and weather.

chornedsnorkack
2011-Dec-28, 10:19 AM
Ah, but the topography, even underwater, affects currents and thermal transport and can have a major effect on climate and weather.

Outside the polar areas (where ocean overturns to the bottom) the ocean would stratify, so the surface currents would only affect the top few hundreds of metres and thus be unaffected by even substantial topography beneath a couple of km. The currents of Atlanitc, Indian and Pacific oceans ignore the central ridges.

Trakar
2011-Dec-29, 03:46 AM
I'm not sure, the OP tossed out dividing the crust and hydrosphere by 1.4 to account for higher gravity. At least, that's what it sounded like he was saying here in post #11
I worked out his numbers and I come up with a surface gravitational acceleration of 12.0246 m/s2 or about 23% higher gravity than Earth (with a 12.5% lower density, 4.823g/cm2), in case that helps you sort it out.

Ah, I see. That does make sense. I had rather blown off his "1.4" as it sounded very off-the-cuff and not well considered. I'll have to run through the numbers a bit more carefully as I got different numbers in my mental run through, but yes, plausibly no where near 71% of the volume.

Just for fun

Mass
2.4 times ME = (~5.97 10^27g)(2.4) = 1.43x10^28 grams

Diameter
1.4 times ME = 12,756km x 1.4 = 17,858 km

Radius
17,858/2 = 8,929 km

convert to cm
(8.9 x 10^3)(1 x 10^5) = 8.9 x 10^8 cm

Volume
4/3 (Pi)(8.9 x 10^8)^3 = 2.95 x 10^27 cc

Density
Mass/volume = (1.43^28)/(2.95^27) = 4.85g/cc (close enough for baut board - differences probably due to rounding choices)

If we assumed same density as Earth it'd give us a total mass of
5.97 x 2.95^27 = 1.77x10^28g or very close to 3x the Earth's mass

In the first case we get a surface acceleration due to gravity of about 12.1m/s^2 or about 1.24 Earth g

In the second case, we get 13.72m/s^2 and about 1.4g

I don't believe either case would significantly alter what we've each already acknowledged and more or less agreed upon.



Because ice sheets, except for an extreme snowball climate, don't cover the entire planet, only a certain area. In that area, the mantle flows out from under the crust to balance out the loading in a process called isostasy. Water doesn't pile up at altitude like snow on ice sheets with high elevations, but seeks it's own level, generally at lower altitude. The weight of water in a basin can cause isostatic adjustment to deform and elevate the topography along its periphery to shallower depths or to elevations above the surface. However, if the entire planet is mostly underwater with a relatively even depth, there's not much in the way of static mass disparities above the crust to drive major isostatic deformations. Moreover, if the crustal rock is denser than the ocean water, then the rock that is elevated above the seafloor (seamounts, islands) would be a heavier mass upon the mantle than an adjoining area of seafloor at the same level that only has a water column above it.

Of course, this is reasonable. I wasn't looking or talking about comparative deformations between crust that is topped by more crust as compared to crust that is topped by water, rather crust that is topped by water versus crust that is topped by atmosphere. IOW, if you removed all the water, you would get some crustal rebound, just as, if you suddenly added several kilometers to the Earth's sea level you should expect some deformation of some underlying topologies. Regardless, I was assuming minor differences, that may or may not have more of an influence on plate tectonic issues, not any great crushing of subsea surface features, which as you say, seem to be more in line with the OP's implications.



But anyways, I don't think that's what the OP was talking about, he was talking about the topology having less relief/elevation due to gravity and/or water pressure (but not due to erosion, which he doesn't think is possible at depth). Perhaps he's referring to the angle of repose, or maybe straight up gravitational distortion of rock. I would ask how much smaller do you think sandstone or shale might be at such depths and pressures and accelerations, but those are sedimentary rocks, which can't exist without erosion.

So long as there are currents that interact with the seafloor, there should be some level of erosion.

eburacum45
2011-Dec-29, 04:31 PM
If we assumed same density as Earth it'd give us a total mass of 5.97 x 2.95^27 = 1.77x10^28g or very close to 3x the Earth's mass.
A planet with 3 x Earth's mass but the same composition would be significantly denser than our planet. Both the rocky mantle and the metallic core would be compressed by the extra mass and gravity. I (very) roughly estimate the radius of such a planet to be about 8750 km, with a density of about 6.4 g/cm3.

Ara Pacis
2011-Dec-29, 10:39 PM
Outside the polar areas (where ocean overturns to the bottom) the ocean would stratify, so the surface currents would only affect the top few hundreds of metres and thus be unaffected by even substantial topography beneath a couple of km. The currents of Atlanitc, Indian and Pacific oceans ignore the central ridges....on Earth, which still has a remnant cryosphere.

This is why I asked about topography since significant topography that rises to elevations very near to the surface (within that hundreds of meters) might have an effect. I also recall reading about smaller scale oceanic vortices (than the large ocean-spanning gyres) that can mix up the water column.

Anyways, you're assuming there would be overturn at the arctic due to density differences, but it's not yet been shown that this proposed planet would have such steep temperature gradients or density differences. Without continents to erode and with a high ocean volume to seafloor ratio, there might not be enough dissolved ions to create a fluid comparable to terran seawater to generate a thermohaline setup.

On Earth, continental land-masses affect the fluid dynamics of oceans, but on a planet without landmasses of such scales, would the fluid instead rotate in bands as is shown in rotating water tank experiments of gas giants?

Ara Pacis
2011-Dec-29, 11:24 PM
Ah, I see. That does make sense. I had rather blown off his "1.4" as it sounded very off-the-cuff and not well considered. I'll have to run through the numbers a bit more carefully as I got different numbers in my mental run through, but yes, plausibly no where near 71% of the volume.

I don't believe either case would significantly alter what we've each already acknowledged and more or less agreed upon.FYI, I used the mean radius of Earth instead of the equatorial radius. I used some online calculators instead of working it out myself, so that may account for some differences (volume for me was ~2.97 x 10^27 cc).


Of course, this is reasonable. I wasn't looking or talking about comparative deformations between crust that is topped by more crust as compared to crust that is topped by water, rather crust that is topped by water versus crust that is topped by atmosphere. IOW, if you removed all the water, you would get some crustal rebound, just as, if you suddenly added several kilometers to the Earth's sea level you should expect some deformation of some underlying topologies. Regardless, I was assuming minor differences, that may or may not have more of an influence on plate tectonic issues, not any great crushing of subsea surface features, which as you say, seem to be more in line with the OP's implications.I think we agree here. What do you think of the additional water on this planet and water's lubricating effect on crustal boundaries? With less dry land, more faults are lubricated, and the water is also under higher pressure. I wonder if we'd see faster tectonic movement.


So long as there are currents that interact with the seafloor, there should be some level of erosion.That's the thing, I'm not sure there would be currents, at least not like on Earth. And if the seafloor is mostly flat as the OP suggests, there's less surface area for erosion. Moreover, there would be less vorticity in any currents that do exist which could cause erosion and little topographical relief for landslide effects. Even on Earth the rate of sediment deposition in the middle of the oceans is abysmal (pun intended). It's not that I disagree with the OP on erosion necessarily, but he says rugged and then he says flat, so it's unclear.

Trakar
2011-Dec-30, 02:34 AM
...I think we agree here. What do you think of the additional water on this planet and water's lubricating effect on crustal boundaries? With less dry land, more faults are lubricated, and the water is also under higher pressure. I wonder if we'd see faster tectonic movement...

A distinct possibility, its hard to say for sure without a lot more details than we have to work with, but to be fair, creating worlds is hard work!
:)



That's the thing, I'm not sure there would be currents, at least not like on Earth. And if the seafloor is mostly flat as the OP suggests, there's less surface area for erosion. Moreover, there would be less vorticity in any currents that do exist which could cause erosion and little topographical relief for landslide effects. Even on Earth the rate of sediment deposition in the middle of the oceans is abysmal (pun intended). It's not that I disagree with the OP on erosion necessarily, but he says rugged and then he says flat, so it's unclear.

That's part of what we're doing here, trying to help him understand what contradictions and issues we notice that his concepts seem to embody and what needs to be done to work with, or around, those issues. Whether or not it helps,...only Somes can say!

chornedsnorkack
2011-Dec-30, 08:59 AM
...on Earth, which still has a remnant cryosphere.

Which does not reach Mediterranean, nor Red Sea.


Anyways, you're assuming there would be overturn at the arctic due to density differences, but it's not yet been shown that this proposed planet would have such steep temperature gradients or density differences.
You do not need steep temperature gradients. Remember that the thermal expansion of water increases rapidly on warming (indeed, it is zero at +4 for fresh water). +20 degree water would still be significantly denser than water at +25 or +30, and sink to the bottom - as it does in Red Sea. So if your poles are at +10 or +20, they still have enough contrast with tropics.



Without continents to erode and with a high ocean volume to seafloor ratio, there might not be enough dissolved ions to create a fluid comparable to terran seawater to generate a thermohaline setup.
Without continental basins to create rock salt deposits, the salt stockpile of the planet may stay in the ocean and make it saltier than on Earth.

Of course the ocean might be more brackish (consider the range in nitrogen stockpiles). But even if it were completely fresh (unlikely, there would be some salt and nowhere to flush it to), the density would simply depend on temperature alone. So the densest water would be at poles, unless they cool below +4.


On Earth, continental land-masses affect the fluid dynamics of oceans, but on a planet without landmasses of such scales, would the fluid instead rotate in bands as is shown in rotating water tank experiments of gas giants?

Probably. It would be not just southern Westerly current that circles the planet unobstructed, but all other bands as well.

Ara Pacis
2011-Dec-30, 11:10 PM
Which does not reach Mediterranean, nor Red Sea.Right, but a strong component of those currents is driven by evaporation of a mostly enclosed basin, which is unlikely to exist on a wide scale on his planet as described.


You do not need steep temperature gradients. Remember that the thermal expansion of water increases rapidly on warming (indeed, it is zero at +4 for fresh water). +20 degree water would still be significantly denser than water at +25 or +30, and sink to the bottom - as it does in Red Sea. So if your poles are at +10 or +20, they still have enough contrast with tropics.I'll take your word for it, since I'm not familiar with water thermal densities. But with the possible banding, will global homogenizing mixing still be prevented?

Moreover, will thermal transport via a thicker and denser atmosphere keep the surface homogeneously warm around the planet? The higher CO2 and the larger depth of that atmosphere will increase the greenhouse effect compared to Earth. With warmer temperatures and more water with no drying mechanism, we might expect to see a lot of humidity and that might increase cloudiness, which could also act as a thermal blanket. The question is how will the cloudiness be cyclical, like daily sun and nightly condensation into clouds/fog, and will it absorb or deflect more solar energy on net to create regional differences?


Without continental basins to create rock salt deposits, the salt stockpile of the planet may stay in the ocean and make it saltier than on Earth.

Of course the ocean might be more brackish (consider the range in nitrogen stockpiles). But even if it were completely fresh (unlikely, there would be some salt and nowhere to flush it to), the density would simply depend on temperature alone. So the densest water would be at poles, unless they cool below +4.But where will the salt come from in the first place?


Probably. It would be not just southern Westerly current that circles the planet unobstructed, but all other bands as well.I wonder how much vorticity and mixing we'd get at the band margins.

Somes J
2012-Jan-02, 09:37 PM
It's not that I disagree with the OP on erosion necessarily, but he says rugged and then he says flat, so it's unclear. I never intended to suggest the ocean floor would be flat, I'm not sure where you got that from.

I would guess that the deeper parts of the ocean (what is the oceanic crust on Earth) would probably look fairly similar to Earth's deep ocean floors, though with more tectonic activity (and hence more midocean ridges, trenches, and other such landforms) and less sediment accumulation. The submerged "continents" I'm less sure of, a mostly submerged continental platform is a landform you don't really see on Earth, but I would guess with less erosion underwater and little sediment accumulation they'd likely be pretty rugged.

Trakar
2012-Jan-02, 09:45 PM
I never intended to suggest the ocean floor would be flat, I'm not sure where you got that from.

I would guess that the deeper parts of the ocean (what is the oceanic crust on Earth) would probably look fairly similar to Earth's deep ocean floors, though with more tectonic activity (and hence more midocean ridges, trenches, and other such landforms) and less sediment accumulation. The submerged "continents" I'm less sure of, a mostly submerged continental platform is a landform you don't really see on Earth, but I would guess with less erosion underwater and little sediment accumulation they'd likely be pretty rugged.

Roughly equivilant to coastal shelfs

chornedsnorkack
2012-Jan-03, 02:35 PM
Compare Zealandia. Or Kerguelen Plateau.

Ara Pacis
2012-Jan-04, 09:48 PM
I never intended to suggest the ocean floor would be flat, I'm not sure where you got that from.Extrapolating from where you said that the landforms would be compressed in posts #11 and #16. I think I see what you're getting at now, but I don't see how you get the gravity compression. With only 23% more gravity, why and by how much do you think the topology would be compressed.


I would guess that the deeper parts of the ocean (what is the oceanic crust on Earth) would probably look fairly similar to Earth's deep ocean floors, though with more tectonic activity (and hence more midocean ridges, trenches, and other such landforms) and less sediment accumulation. The submerged "continents" I'm less sure of, a mostly submerged continental platform is a landform you don't really see on Earth, but I would guess with less erosion underwater and little sediment accumulation they'd likely be pretty rugged.The reason I've been asking about bathymetry is to see if it affects thermal circulations that affect global climate. Someone else referred to surface currents (top few hundred meters, Gulf stream is surface to 800-1200m deep), but some suggest that it's the deep, dense and cold water movement that draws on the light, warm surface waters (North Atlantic Deep Water is down to 4km deep). So, substantial near surface continental cratons might affect heat transport and affect the climate of your world, affecting the possibility of storms.

BTW, there are lots of submerged continental areas on Earth, many of which were dry land during the ice ages. Sundaland, Doggerland, Beringia, The Bahamas, Large areas of the continental shelf around Florida and the Gulf of Mexico coast as well as the east coast of the US and elsewhere. If you have a near surface continental area close to a pole, you might see a lack of mixing start to cause sea ice, which if it gets deep enough might ground on the subsurface rock, grow taller and start supporting shelves and start affecting planetary albedo and lower sea levels elsewhere, as well as influencing global atmospheric currents.

chornedsnorkack
2012-Jan-05, 03:59 PM
If you have a near surface continental area close to a pole, you might see a lack of mixing start to cause sea ice, which if it gets deep enough might ground on the subsurface rock, grow taller and start supporting shelves

Shelves are by definition not grounded. Compare Berkner "Island".

But note that the open ocean ice cover of both Antarctic and Arctic is no thicker than a few m. The shelf glaciers mainly originate from grounded glaciers.

What would Antarctic look like if there were no continent-sized grounded ice sheet, only a few islands? Would the seas in between be open water, sea ice or ice shelves?

Trakar
2012-Jan-05, 05:12 PM
Shelves are by definition not grounded. Compare Berkner "Island".

But note that the open ocean ice cover of both Antarctic and Arctic is no thicker than a few m. The shelf glaciers mainly originate from grounded glaciers.

What would Antarctic look like if there were no continent-sized grounded ice sheet, only a few islands? Would the seas in between be open water, sea ice or ice shelves?

You do realize that there is an entire, above sea level continent under the antarctic ice cap,...don't you?
5th largest on the planet, much larger than all of Europe.

chornedsnorkack
2012-Jan-05, 06:04 PM
You do realize that there is an entire, above sea level continent under the antarctic ice cap,...don't you?
5th largest on the planet, much larger than all of Europe.

There are large areas of ice grounded below sea level. The area of bedrock above sea level may be smaller than in Europe.

The area where ice is grounded over or under sea level combined is certainly somewhat bigger than whole Europe.

Ara Pacis
2012-Jan-05, 06:27 PM
Shelves are by definition not grounded. Compare Berkner "Island".Yeah, that would be why I made the distinction.


What would Antarctic look like if there were no continent-sized grounded ice sheet, only a few islands? Would the seas in between be open water, sea ice or ice shelves?That depends on how long you wait for isostatic rebound to have an effect.

Trakar
2012-Jan-05, 07:55 PM
There are large areas of ice grounded below sea level. The area of bedrock above sea level may be smaller than in Europe.

The area where ice is grounded over or under sea level combined is certainly somewhat bigger than whole Europe.

I was only speaking of the underlying continent but I must have fat-fingered my calculator because taking the following numbers (from encyclopedia (http://books.google.com/books?id=6uFd1mICC98C&pg=PA13&lpg=PA13&dq=underlying+continent+of+antarctica&source=bl&ots=oY6Kmc_vPx&sig=JRvvbj8824t3-W6H6bMqmnIJd-E&hl=en&sa=X&ei=Dv0FT5nuFoqniALd0IWCDA&ved=0CC8Q6AEwAQ#v=onepage&q=underlying%20continent%20of%20antarctica&f=false)- pg 13) for Antarctica which measures out at around 4.84 million square miles, if we include all the ice shelves that expands to 5.46 million square miles and compares to Europe at 2.84 million square miles, I get figures of 1.7X larger than Europe without ice, and 1.9X larger than Europe with Ice. If I am looking at improper numbers here please direct me to a better more accurate source of information.

significantly larger than Austrailia at 3.0 million sq. miles

nearly 3/4 the size of S. America

larger than the contiguous continental US (lower 48) at 3.1 Million square miles

A big chunk of real estate.

Trakar
2012-Jan-05, 08:21 PM
Yeah, that would be why I made the distinction.

That depends on how long you wait for isostatic rebound to have an effect.

According to the same above source, Antarctica is depressed 3-400 meters by all the ice, so if it all rose equally by that amount (unlikely) both of the large islands would be reunited with the mainland, of course, with all the ice gone, we'd have quite a rise in sea level as well, so we'd have to look a specific geographies of those straits to see how things shake out.

neilzero
2013-Jun-07, 05:00 PM
Water has a maximum density at 4 degrees c = 39 degrees f, so the deep basins will have lots of water at 4 degrees c. The less deep water will be warmer Summer and Fall, and colder, Winter and Spring.
At high pressure methane and water form a solid compound that decomposes at lower pressure. Neil