Lower Manhattan is about twice the area that it used to be, because fill dirt was brought in. This increased the weight of the island. They also added several feet of concrete and a jungle of tall, heavy buildings. All of these things cause the land to sink – a lot. Three feet of concrete would make the land sink two feet.
Then, to add insult to injury they put the tide gauge on the fill dirt, which tends to compact on it’s own.
Lower Manhattan tide gauge.
After making the land sink, the final stage of the process is to blame the relative rise in sea level on CO2, even though it has been happening at a steady rate for more than 150 years.