Why are there circles of melted snow on this icy pond?

Gas bubbles from rotting vegetation are the likely cause in this instance. See this article for an explanation:

Looks like the same thing, good explanation.

There are species of seals who actively keep holes open in the ice to use as breathing holes, allowing them to hunt fish even in frozen-over bodies of water.

They're all ocean-dwelling species in the arctic or antarctic oceans, so this isn't the answer to your specific question, but I just think they're neat.

Before reading the "so this isn't the answer to your specific question, but I just think they're neat." My mind went:
A seal? At this time of year? At this time of day? In this part of the country? Localized entirely within their pond?
- Yes!

fish farts

- Some of these fish are not looking very healthy
I'll get back to you with some readings
I snorted my coffee, thanks.
- Huh... Like off a key or in a line or something? Also... Why?

I'm not a hydrologist, but I suspect it's due to areas of upwelling warmer water. Alternatively, the ice could have formed, but these spots are where the surface was too unstable to permit that (wind?)

Yep, this is it. The ice is thinner in those areas, allowing more heat from the water to reach the surface
That, or some very adventurous ice fishermen were out already. people who ice fish are a strange lot. In the nearest hole, you can see in the center where it was drilled down. They could be trying a new pond looking for where the fish are laying.
(I wouldn't trust the ice this early in the year with my worst enemy- mostly because they could probably break out on the way back up. shhhh)

Ice doesn't form with even thickness naturally, when it warms back up outside, the thinner parts melt faster, and it kind of snowballs due to currents created and stuff like that. So even if the thin areas didn't start out that much thinner, they end up melting way faster anyway.

GOT DAMN LOCH NESS MONSTA I TOLD YOU I AIN'T GOT NO TREE FIDDY

My best hyptothesis is that in the center of each of those disks a hole may have been or still is through which pond water is wicking upwards and melting the snow in a circular fashion before freezing and coming to a halt. Hence the almost perfect circular shape and the weird lighter color in the center ... notice the crack in the center of the disk in the foreground?

Aliums 👽

Onions?
- Onion-based aliens.
  ...........they have layers.

Might be eddy currents.

Good guess. Also rocks closer to the surface can transfer heat to the surrounding water.

Fish ghosts.

Throws dart...

.

Geothermal vents, or radioactive rocks.

The one time when "swamp gas" is the answer, and you miss it. For shame...

Where the fish peed.

My hypothesis:

So, basic principles out of the way first, dark absorbs more sun, white reflects it. As the snow melts and reveals the darker colored water beneath, this will begin a runaway feedback loop that will slowly melt more and more ice. Assuming it's not too cold out, anyway.

Since this is actually a runaway feedback loop that is going to eventually melt the whole surface of this body of water, we just need to get it started, and everywhere it starts, it'll spread from. All we need, is something that darkens the surface of the snow.

In the case of that center circle, it's hard to make out, but I think I see a stick jutting out in the exact center. A brown stick, no less.

Having been around melting ice a lot I think this is closer to the right answer. Also decomposing things give off heat. Any vegetation that is decomposing will accelerate ice melting.

That's where decomposing bodies in barrels are releasing gas bubbles as the corpse decomposes. Both because the bubbles are warmer from decomposition and because they disturb the surface of the water, ice formation is disrupted in "warmer below freezing" temperatures.

Source: I'm just winging it bro.

most likely due to varying depth. More shallow will stay warmer I believe because the earth holds temperature longer.

Source: I have a ground source heat pump, which is equivalent to saying I stayed at a holiday inn last night. But it might still be true.

HOTEL, MOTEL
- You can bring your girlfriends, and meet me at the hotel room.
Shallow water freezes first. Ice acts as an insulator so deep water will get cold but not freeze.
This is likely caused by vegetation at the bottom rotting and the gas rising up till it collects in on area, making the ice thinner and thus higher.
- Not following why shallow water freezes first.

Hot fish.

-Rod Stewart and Tina Turner intensify-
- Cod Stewart and Tuna Turner

Some stormwater management ponds have aeration systems.

Swirls in the water?

Bird? Snowball? Looks more "soggy" than melted, necessarily.

It is a neat effect. Have you tried making your own melt circle?

Thought the same, maybe there were ducks hanging out earlier on.
- Duck butts look warm, that's probably it.
So, when people go ice fishing, they use an ice auger to drill through the ice. think of it as a 6" (or so) drill bit. for a variety of reasons, when you break through, water usually gets pulled up onto the surface (it's common to pump the hand crank augers up and down, or with powered augers, well, usually you don't stop as you break through.)
if you look at the bit front and center, you can see cracks and the hole in the center of the wetspot