USING MANGROVE SUCCESSION TO MEASURE CHANGES IN THE RATE OF SEA LEVEL RISE ON SAN SALVADOR ISLAND, BAHAMAS: 1929-1994 AND 1994-2014

Mangroves are very sensitive to sea level change. In 1994 Paul Godfrey and his students used mangrove succession on San Salvador Island, and elevation data based on the 1927 datum, to calculate an approximate rate of sea level rise of 2 mm/yr for the period between 1927 and 1994. They were able to do this because the mangroves can be found growing around a series of saline, inland ponds in the northeast corner of the island. These ponds are fed by subsurface conduits that connect to the sea. Because they are protected from storm surges and wave action and because the tidal ranges are very small, they behave like "stilling wells." Hence the water elevation in the ponds at any given time is representative of average sea level. The mangroves establish their succession based on modern sea level, not the older datum. Thus Godfrey was able to establish a "mangrove-based" elevation for 1994 that could be compared with surveyed elevations based on bench marks that used the 1927 datum. According to a variety of studies, the rate of sea level rise increased around 1994. With this in mind, in 2014 we restablished five of Godfrey's transects and resurveyed them using his techniques. While our results were not as clear-cut as his, our data suggests that the rate of sea level rise has increased to approximately 3 mm/yr. This number is consistent with other studies using different proxies.