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That's an interesting map. Any idea why there are down and up arrows intermingled the way they are?

From my understanding the down arrows indicate the coast is expanding. The key at the bottom says the down arrows are negative sea level growth

I read that tide patterns are changing so locally measuring climate sea rise makes no sense yet, as tides superimpose ±8mm

So far you need the global integrate of all changes.

Likely changes to the coast itself. For example Louisiana and the gulf coast are going down faster, because of coastal erosion.

I would guess that the parts of Alaska that are seeing the sea level fall are due to the land rising from tectonic activity.

Things like changes in water temp and currents can also play a role.