Even at similar latitudes they appear to be quite different from one another.

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    $\begingroup$ Which country are you asking about? This is an international site. $\endgroup$
    – Fred
    Jul 5 '15 at 7:41
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    $\begingroup$ That statement is true in most continents! That is the awesome part about it. Just look at the Namibia, Perú, California, west Africa upwellings! $\endgroup$
    – arkaia
    Jul 5 '15 at 18:58
  • $\begingroup$ Australia has to be different! The Leeuwin current is a warm ocean current which flows southwards near the western coast of Australia [en.wikipedia.org/wiki/Leeuwin_Current] $\endgroup$
    – Fred
    Jul 6 '15 at 3:37
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    $\begingroup$ @Fred That's true! The Leeuwin current actually shields Australia from the West Australia current...which flows equatorward and would otherwise bring cold water northward. I don't know much about the Leeuwin current, but I'd guess that it's trapped to the continental shelf, fed by the Indonesian Throughflow water that doesn't connect to the equatorial Indian Ocean currents. Shelves are important, and I clearly don't know enough about them >.> $\endgroup$ Jul 6 '15 at 15:16
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    $\begingroup$ The ocean at Newfoundland (Canada east coast) freezes in winter, but the ocean at British Columbia certainly doesn't. So it's not universally true; in Canada it isn't. $\endgroup$
    – gerrit
    Jul 8 '15 at 13:48

This is a good overview of ocean surface currents, which includes a schematic like this one:

Surface currents

In the mid-latitudes, you get gyre circulations that move poleward along the eastern coasts of continents (the western edges of the ocean), bringing warm water. The water off the east coasts of these places is thus warmer than you would expect for that latitude. The return flow on the eastern edges of ocean basins (west coast of continents) brings cold water from poleward of that latitude.

There are a few things to note about this circulation, though, since that analysis applies to the mid-latitudes only. There are opposite gyres closer to the poles that make the east coasts much colder than expected. (Compare the Alaska current to the Labrador, which is off the east coast of Canada.) The circulation near the equator is a lot more complex and interesting, especially where it meets up with other gyres.

There are some strange and fascinating reasons why the circulation is the way it is, but that answer is the result of an entire oceanography course...

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    $\begingroup$ I'm going to throw this out there. That looks a lot like the Coriolis effect, (cept for at the poles and the Equatorial Counters), upload.wikimedia.org/wikipedia/commons/6/69/… You probobly knew that. :-) $\endgroup$
    – userLTK
    Jul 7 '15 at 9:18
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    $\begingroup$ @userLTK It's related to that! Sverdrup balance says that the torque that winds exert on a column of water -- which would normally change its angular momentum -- is balanced by the water moving poleward or equatorward to adjust the Coriolis component of its angular momentum. Thus total angular momentum is roughly conserved, until the flow meets a western boundary current and friction takes over. $\endgroup$ Jul 7 '15 at 13:06
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    $\begingroup$ @JarethHolt You should also consider coastal upwelling that is related to Ekman transport and which brings deeper (and therefore) colder water to the surface. The Humboldt current at the Peruan coats is one good example. Deep and cold water is also nutrient-rich which turns this regions into flourishing marine environments. $\endgroup$
    – makra
    Jul 20 '15 at 9:35

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