However, in recent decades the sea has dominated the once vibrant coastal margin, thrusting further inland as sea levels rise. Over the past century, sea levels along New Jersey have risen 0.45 meters, more than double the global average of 0.18 meters. By 2100, the sea could rise by more than a meter.
This dramatic sea level rise has proven disastrous for the mosaic of marshes along the New Jersey shoreline, many of which have already succumbed to the sea. However, the extent of the loss of these wetlands is difficult to apprehend because environmental monitoring is only a few decades old.
Without an idea of the natural conditions of a wetland, ecological restoration is daunting. Having this information is crucial, says Enache. “Without [it], you are in the dark. Luckily, some of this missing data is saved in the academy’s diatom cache.
Like most coastal margins, New Jersey is familiar with sea level rise. During the Pleistocene, when New Jersey was covered in ice and home to behemoths, sea ice sucked up reserves of seawater. There are around 18,000 years ago, sea levels fell more than 130 meters below their current level, extending the New Jersey shoreline 110 kilometers further out into the Atlantic Ocean.
The end of the last ice age triggered a steady rise in sea level. The retreat of the ice caps caused parts of New Jersey to sink. According to Jennifer Walker, a sea level researcher at Rutgers University, this subsidence, combined with melting glaciers, has proven to be a powerful mix of rapid sea level rise.
In a published study Last year, Walker looked to the past to put New Jersey’s current sea level rise into context. “If we can understand how temperatures, atmosphere and sea level changes are all interconnected in the past, that’s what we can use to project changes into the future.”
To assess sea level fluctuations over the past 2,000 years, his team examined the shells of single-celled protists called foraminifera that are finely calibrated for specific environmental conditions. This makes it a valuable indicator for piecing together changes in sea level. New Jersey is experiencing the fastest sea level rise in 2,000 years.
The NJDEP hoped that diatoms could serve as a similar tool for understanding how coastal marshes have responded to rising seas. Like foraminifera, each species of diatom is extremely sensitive to environmental conditions. For example, species like the rolling pin microcephalic nitschia thrive in nitrogen-rich environments, making their shells a common sign of nutrient pollution. Other species, like Diploneis smithii, whose segmented shell resembles a slender trilobite, prefer saline waters. Their existence inland is a good indication of past sea level intrusion and helps researchers infer which marshes have been prone to flooding in the past.
To identify where these microscopic indicators once existed, NJDEP deployed a team of researchers to several marshes along the coastline, ranging from heavily polluted wetlands in the north to near-pristine tidal marshes in the south. At each site, they dug into marsh mud, sampling up to 2 meters deep in some places. Enache compares this method to cutting a stack of pancakes – as you cut deeper, you’re essentially stepping back in time, from the steaming pancake right next to the griddle to the soggy pancake lying at the bottom of the stack. Digging deeper, researchers went back decades. In total, they took nine cores from five wetlands.