Currents on a planet with equatorial ocean

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Buran
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Currents on a planet with equatorial ocean

Post by Buran »

I've made a planet with an ocean that wraps around the equator, and I'm not sure what the consequences for this are.

Here's the map:
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I have very little knowledge on how ocean currents work, so I don't know how they would behave in this situation. Any advice?

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Re: Currents on a planet with equatorial ocean

Post by gufferdk »

There are 3 things that drive ocean currents: differences in water temperature, differences in salinity and differences in air pressure.
I the last is probably the easiest to begin with but the other two creates interesting effects as well such as The Denmark Strait Cataract where warm water from the gulf stream hits Greenland and increases in desity due to being a) cooled; b) freezing increasing the salinity of the reamaining water. This water descends and new warm water flows in. This and similar systems near antarctica powers the thermohaline circulation, a system of warm surface currents and cold deep-sea currents. This might actually be able to diminish the effects of a global warming because incresing temperature would disable the pumps through less cooling and a thick blocking layer of fresh or brackish water at the surface due to melting of ice, which would severely weaken The Gulf Stream and The North Atlantic Drift, which would severely cool the northeastern Atlantic, which would lead to more sea ice, leading to more reflection of sunlight meaning less energy absorbed by the Earth weakening the effect of climate change. This is not something to rely on to counter climate change as it may or may not happen and would make much of Northern and Western Europe significantly less inhabitable.

Enough rambling, onto the main point about how to ocean currents. What I find easiest is to consider winds first and then other stuff later if necessary. All the directions assumes a counter-clockwise spinning planet when observed from the north pole downwards. If this is not the case, reverse all directions. I am also going to ignore monsoons. That shouldn't matter much in your case though.
1. The Equatorial currents: Somewhere between 15 degrees north/south and the equtor there will usually be two reasonable strong currents going westwards.This may change a bit depending on the layout of continents.
2. The Equatorial counter-current: In places where the equtorial currents are both present they often move so much water that inbetween them an east-going counter-current forms. This can also be quite strong.
In your case I think this is mostly the case in the big south-eastern ocean, whereas along the continents you will probably mostly see the north equatorial current.

3. The West Wind Drift: Around 45 degrees latitude eastwards currents form. These are also strong but can be spread out more all the way up or down to the 60ths.
In your case this causes currents in the northern central ocean, the northwester ocean the southeastern ocean and probably also to the south of the southern continents.

4. The East Wind Drift: Closer to the poles than 60 degress, centered on 70 or 75 you get wastwards currents. These are weak and may be blocked by ice. They don't happen much on Earth.
In your case I would say that they probably happen in the N. Cen. and NW and assuming that the pack-ice on the south pole is either a max or an average and not a min they definitely happen there.

5. Connecting the dots: Water doesn't appear magically out of nowhere so all loops should be closed with currents going up and down coasts. When water hits a coast it is likely to both go northwards and southwards if it can do so.
In your case i would say that this is mostly straight forward though I am not sure how strong or weak the currents in the straits between the southern continents and in the northeast you will probably see a more spread-out group of small currents (depending on how shallow the light blue water is) rather than one big one.

6. Temperatures: The relative temperature of water has a huge effect on the climate. Currents that are moving towards the poles generally are warmer than the surroundings and currents that are going towards the equator are colder than the sorroundings. Currents moving in parallel to the parallels gradually gain the temperature of the surroundings given enough time.

I sadly don't know enough about this topic to help you with figuring out a thermohaline circulation and similar interesting things but i hope this was helpful.

Edit: formatting and spelling (there are probably still spelling mistakes though)
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Re: Currents on a planet with equatorial ocean

Post by Soap »

A minor addition: not ALL currents are closed loops, as far as i know. e.g. the Gulf Stream in northern Europe doesnt loop back around to the southwest. Instead, once in a while a current just slips underwater and then flows very slowly along the depths of the ocean.

My own planet also has a wide-open equator, and I've just simply assumed a single unbroken equatorial current along the lines of what Earth has around Antarctica. If I happen to be wrong, I'll change it, but it wont affect my stories because, since there's no land there, there's no significant animal life and certainly no humans that would be affected by the change.
Sunàqʷa the Sea Lamprey says:
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Re: Currents on a planet with equatorial ocean

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Soap wrote:A minor addition: not ALL currents are closed loops, as far as i know. e.g. the Gulf Stream in northern Europe doesnt loop back around to the southwest. Instead, once in a while a current just slips underwater and then flows very slowly along the depths of the ocean.
You are right that most of the water from the gulf stream hits the pack ice or Greenland and the just sinks down into the deep cold currents of the thermohaline circulation but some of it travels down the east greenland current up the west greenland current and then the labrador current down to the north atlantic drift again, closing the loop: https://upload.wikimedia.org/wikipedia/ ... ss%293.png
My own planet also has a wide-open equator, and I've just simply assumed a single unbroken equatorial current along the lines of what Earth has around Antarctica. If I happen to be wrong, I'll change it, but it wont affect my stories because, since there's no land there, there's no significant animal life and certainly no humans that would be affected by the change.
Unless some weird shit is happening in that ocean I can see no reason for you not getting a pacific-style situation with two relatively wide westwards equatorial currents and a narrower counter-current in the middle, more or less coinciding with the ITCZ (and the associated doldrums) potentially being a major annoyance for anyone trying to sail across the equator out on the open sea.
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Re: Currents on a planet with equatorial ocean

Post by Buran »

gufferdk wrote:I sadly don't know enough about this topic to help you with figuring out a thermohaline circulation and similar interesting things but i hope this was helpful.
It was, thanks! I made this rough sketch of the currents based on your advice:
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Red is hot, purple is cold. Does it look alright to you?

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Re: Currents on a planet with equatorial ocean

Post by gufferdk »

Seems mostly reasonable though there are a few things:
  • Your west wind drifts are too far north and south. Assuming that the map is equirectangular they are hanging out near 70 degrees rather than their home in the forties and fifties. Unlike on earth you have plenty of space for some east wind drift to happen around 70 (cases marked with orange in image).
  • There are a few irregularities in the equatorial currents (marked with yellow) the leftmost is probably ok but on the right one i wouldn't expect the south equatorial current to be so far north, especially considering that continents like to drag the ITCZ towards themselves.
  • The currents marked with pink in the northern island sea are weird. Dependig on how deep some of the straits are the ones in the top right may be fine, especially the smaller arrow but the larger ones seem weird. Unless there is a big difference in sea depth between right part and the left part the arrow in the top right will probably be more spread out but if there is a big step it is very much justfied.
  • I am not sure about the currents in the southern straits (marked with (dashed) brown)). The windsin the are will probably be dominated by a large oceanic high pressure center (brown with white spots) and a number of smaller local ones forming over the seas around the 30th parallel. This coupled with the powers from the equtorial current and the wast wind drift means that the currents are likely to be unpredictable and you will probably see a bunch of small local gyres that may be seasonally disturbed, most significantly i would expect a gyre to form in the 3rd strait counting from the left.
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Re: Currents on a planet with equatorial ocean

Post by Buran »

Sorry to necro, but I wanted a second opinion (once again) before proceeding. How's this? (Black is warm relative to the surroundings, white is cool).
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