![\"An](\"https:\/\/ncseagrant.ncsu.edu\/coastwatch\/wp-content\/uploads\/sites\/13\/2021\/09\/Core-samples-1.png\")
Top: An illustration of salt marsh transgression and core sample placement. Courtesy of Antonio B. Rodriguez. Bottom: This core shows a sample of upland forest peat. Photo: Carson Miller.<\/figcaption><\/figure>\n\n\n\n
For our study, we wanted to know if major storms like hurricanes and nor\u2019easters contribute to salt marsh transgression. Storms are commonly associated with elevated water levels (albeit temporarily), and they deliver salt to upland soils. They also can cause inlets to form through barrier islands, thereby increasing the connection between ocean and estuary, resulting in higher tides over the marsh.<\/p>\n\n\n\n
We decided to look back in time to see how past storms have affected salt marsh movement along coastal North Carolina. As part of her master\u2019s thesis project at the University of North Carolina at Chapel Hill\u2019s Institute of Marine Sciences, graduate student Carson Miller measured rates of salt marsh transgression during a stormy period from about 1400 to 1675 C.E.<\/p>\n\n\n\n
During that 275-year stretch, the number of inlets through the Outer Banks was greater than it is today, stemming from an increase in nor\u2019easter activity and associated beach erosion, surge, and overwash, according to research published by colleagues at East Carolina University. Greater storminess during that time period wasn\u2019t restricted to North Carolina \u2014 it characterized the entire western North Atlantic.<\/p>\n\n\n\n
To reconstruct rates of salt marsh transgression, we collected sediment samples, called cores, from salt marshes that fringe bays near the Neuse River Estuary and Core Sound.<\/p>\n\n\n\n
We had positioned the cores in a line from the marsh\u2019s estuary edge to the upland forest boundary. Each core contained layers of salt marsh peat that had accumulated over time atop layers of upland forest peat. As a rule of thumb, the closer a core\u2019s location was to the forest, the less marsh peat there was in the sample, and the more recently the marsh had migrated to that area.<\/p>\n\n\n\n
In a given core sample, we identified the transition between upland forest peat and marsh peat by the absence of organisms found in brackish water typical of salt marsh habitat. The layer of marsh peat appearing at that transition represented when marsh grass first appeared in the upland area. To figure out that time period, we aged blades of grass stuck in the marsh peat using a tool called carbon-14 dating.<\/p>\n\n\n
![\"Carson](\"https:\/\/ncseagrant.ncsu.edu\/coastwatch\/wp-content\/uploads\/sites\/13\/2021\/09\/Core-sampling_Antonio-Rodriguez-scaled.jpg\")
Using the times that salt marsh first colonized upland areas and the distances between the cores, we could calculate rates of salt marsh transgression.<\/p>\n\n\n\n
We found that salt marshes at two different sites migrated 2 and 10 times faster, on average, during the 1400-1675 stormy period than the non-stormy period that followed. Sea level rise was less than 1 millimeter a year during both timespans.<\/p>\n\n\n\n
We also looked at transgression post-1865 \u2014 after the Industrial Revolution \u2014 when sea level rise had increased nearly three-fold, to 2.4 millimeters a year. Salt marsh transgression occurred on average 7 times faster than it did during the previous non-stormy period.<\/p>\n\n\n\n
The study highlights that, in addition to contributions from sea level rise, changes in storminess also modulate salt marsh transgression rates. This finding is important because both storminess and the rate of sea level rise are projected to increase in the future. As development along the landward edge of salt marsh continues, will the area of this essential habitat be maintained or lost?<\/p>\n\n\n\n
Antonio B. Rodriguez is a coastal geologist at the University of North Carolina at Chapel Hill\u2019s Institute of Marine Sciences, within the Department of Earth, Marine, and Environmental Sciences. Here, he describes research into how big storm events influence the rate of salt marsh migration into upland areas. The work was recently published in Quaternary Science Reviews. The first author is Carson Miller, who was a master\u2019s student in Rodriguez\u2019s lab at the time. Miller is now a doctoral candidate at the University of Texas at Austin where she\u2019s studying the geology of the Gulf of Mexico inner continental shelf. Grad student Molly Bost, a doctoral candidate at UNC studying oyster reefs, salt marshes, and tidal creeks, also contributed to the research. North Carolina Sea Grant provided research funding.<\/em><\/p>\n\n\n