THE EFFECTS OF CLIMATE CHANGE ON THE GEOMORPHOLOGY OF THREE GEORGIA BARRIER ISLANDS FROM 1988–2021: SAPELO, BLACKBEARD, AND CABRETTA

The Georgia coast has 16 barrier islands which are key geologic features that protect the mainland from storms. As storm surge, storm intensity, and sea level rise increase, these barrier islands are at an increased risk of geomorphological change. Another compounding factor is the global mean sea level rise, achieving ~ 10.2 cm in the last 33 yrs. In the past 30–50 yrs, storm frequency, intensity, and duration have increased along with increased storm surge. Storm surge is an agent of geomorphologic change on barrier island systems, but the effects on the islands due to climate change are poorly understood. Here, we examine three of Georgia’s barrier islands, Sapelo, Cabretta, and Blackbeard Island, to document geomorphic change in this closely associated island triad.

Google Earth Pro images from 1988 to 2021 were used to measure linear change of key features: Erosion and deposition of the northern parts of Sapelo and Blackbeard islands, spit deposition in southern Sapelo and Blackbeard Islands, and loss of the northern marsh system for Cabretta Island. Results indicate that north Blackbeard Island is growing at a current rate of 3.9 m yr^-1, while the northern part of the Sapelo-Cabretta system is shrinking by 23.6 m yr^-1. These rates have increased since 1988. Northern Blackbeard is growing faster each year compared to northern Sapelo, which is shrinking each year. Sapelo and Blackbeard Island spits have grown in 33 yrs totaling 163.9 m and 608.3 m, respectively. However, Blackbeard’s spit growth is much more rapid than Sapelo’s, increasing by 17.8 m yr^-1 compared to Sapelo's spit growth at 2.5 m yr^-1. Lastly, the marsh ecosystem on northern Cabretta has dramatically changed from 1988 to 2021, with 93% (250,000 m²) of the marsh lost. This loss skyrocketed starting in 2005 corresponding to increased storms and geomorphic changes among the barrier island triad. Today Cabretta’s northern marsh ecosystem is represented only by a slice of high marsh; in a few more years, this marsh may cease to exist. It was important to study these three barrier islands as a system, what we call the barrier island triad. In the future, if storm and sea level rates continue, Blackbeard Island may be the only survivor of this triad.