The Sinking Lands

Land motion drives varying rates of sea level along the US East Coast

From Science Magazine

Along the US East Coast, the Earth’s continued response to the end of the last ice age explains variances in relative sea level rates
Chestnut Hill, Mass. (12/20/2018) – Along the East Coast of the United States, relative sea level change does not happen uniformly between Maine and Florida.

Data have shown that sea level rise in the Mid-Atlantic region surpassed changes in relative sea level along the coastlines of the South Atlantic and the Gulf of Maine. A team of researchers took a look back at historical data through new analytical methods to pinpoint the reason behind the different rates of sea level change.

Assessing data from a range of sources and previous studies, the team concluded that the movement of the earth – referred to as vertical land motion – is the dominant force behind variations in rates of sea level rise up and down the East Coast, the team reports today in the journal Nature.

Across the past century, records indicated that sea level rise has varied – from approximately 1.5 feet along the shores of the Chesapeake Bay in Virginia and the beaches near Cape Hatteras, North Carolina, to approximately one foot near New York City and Miami. Along the coast of Maine, sea level rose only about a half a foot.

The team found that vertical land motion is the primary factor influencing the spatial variability in relative sea level rates, explaining 75 percent of the observed variation along the East Coast, according to the report, titled “Origin of spatial variation in the US East Coast sea-level trends during 1900-2017.” More than two-thirds – or 69 percent – of the observed vertical land motion is due to ongoing effects from the last ice age.

“This ice age effect is the largest in Maryland, Virginia, and North Carolina,” said Boston College Assistant Professor of Earth and Environmental Studies Carling C. Hay, a co-author of the report with colleagues from Woods Hole Oceanographic Institution, Harvard University, Tufts University, and Atmospheric and Environmental Research, Inc.

“The remaining sea level trends that cannot be explained by vertical land motion also exhibit significant structure, with rates of sea level rise increasing from northern Maine to southern Florida,” Hay said. “This spatial structure is consistent with patterns associated with the combined effects of ice melt, groundwater pumping, and dam building over the last century.”

I first learned about isostasy, the rebound of the land previously under glaciers, and the settling of land further south back in my freshman oceanography 100 class, let's see; that must have been 1970, which means it was well known previously. I guess it's nice that they managed to narrow down where its effects are the most important, but this shouldn't come as any great surprise.

I'm going to break out the graph again.:

Oh look, 3.15 mm per year here in Maryland, with no sign of acceleration since 1900. And here in Maryland where the land is sinking the fastest due to the effects of the last glaciation (not to mention water withdrawal)! Now, the global sea level rise rate commonly cited is about 3.3 mm per year. Something does not compute. At least in part, this is due to the fact that the global sea level rise is being measured by satellite, and it's known to have calibration problems. They also add a fudge to account for what they claim is on ongoing increase in the volume of the ocean basin.