There is no practical significance for the United States to link gold. Specifically, it depends on the contract with the largest trading volume and positions, because futures contracts generally expire in 1 year, and the linkage is for the sake of price continuity and has no substantive significance.

It is normal for the US dollar and London gold to move in exactly the same direction, because all speculation is gold. There are arbitrage opportunities when there are spreads, so the trend is generally the same.

American gold is a real gold futures.

London gold trading is spot trading, not futures in a strict sense (full of market makers and black market trading)