Just a little info to add to the knowlege base here on MFK:
I have a globe in front of me. The Amazon Basin is contained between the equator and ten degrees South. San Diego is at about 32 degrees N. and L.A. is at about 34 degrees N.
The North and South part have no bearing except that the seasons are reversed. The lattitude dictates the annual average temperature. I really don't see a problem with an outdoor pond in So. Cal. as long as the temp is kept warm enough during the winter (if you want to call it that). A small pond can have large temp fluctuations especially if it has a large surface to depth ratio. Think of cooling at the surface vs. thermal mass. Drag yourself out of bed around six in the morning and take the temp of the pond. Then take it again late in the afternoon. Compare the temp difference. If it is a wide difference, I would wait for the Spring to put him in. If the pond is large enough for constant temps and the lowest temp is within a safe range for your arow than I would feel confident about adding him. He will enjoy the extra cruising room.
Btw, the Amazon, since it is at the equator, has very constant temperatures from winter to summer due to the location on the earth. The seasons are created by the wabble of the earth and the angle of the suns rays. At the equator, the angle of the suns rays are nearly identical from summer to winter. The farther away you get from the equator, the larger the difference of that angle between the seasons. For instance, use a flashlight to simulate the suns rays...shining the light straight down keeps all the light rays condensed into a tight spot. By angling the light to one side, the rays are spread out to a larger area. There are fewer rays to keep the larger area warm. Now at the equator, the land is mostly perpendicular to the sun as in the first example. It is this way during the summer and winter. At higher lattitudes, during the winter there is more drastic spreading of the light rays due to the curvature of the earth. This is what compounds our problems with keeping outdoor ponds.