I'm pretty sure an iceberg is colder, as icecubes usually have the temperature of the freezer (~-2 to -3°C) and if an iceberg had that temperature in the ocean, which is of course warmer than 0°C, it'd either be melting very quickly or woulnt even have reached the size it has.
Most icebergs splittled from Arctica or Antarctica, eg are show fallen over centuries, pressed together to ice, and if the iceberg ice has been covered with tons of other ice over
centuries it'd surely be quite cold, in any case colder than -3°C
I'm just too smart for this world