We're decoding ancient hurricanes' traces on the sea floor – and evidence from millennia of Atlantic storms is not good news for the coast
Published in Science & Technology News
Others, including from Atlantic Canada, North Carolina, northwestern Florida, Mississippi and Puerto Rico, are lower-resolution, meaning it is nearly impossible to discern individual hurricane layers deposited within decades of one another. But they can be highly informative for determining the timing of the most intense hurricanes, which can have significant impacts on coastal ecosystems.
It’s the records from the Bahamas, however, with nearly annual resolution, that are crucial for seeing the long-term picture for the Atlantic Basin.
The Bahamas are exceptionally vulnerable to the impacts of major hurricanes because of their geographic location.
In the North Atlantic, 85% of all major hurricanes form in what is known as the Main Development Region, off western Africa. Looking just at observed hurricane tracks from the past 170 years, my analysis shows that about 86% of major hurricanes that affect the Bahamas also form in that region, suggesting the frequency variability in the Bahamas may be representative of the basin.
A substantial percentage of North Atlantic storms also pass over or near these islands, so these records appear to reflect changes in overall North Atlantic hurricane frequency through time.
By coupling coastal sediment records from the Bahamas with records from sites farther north, we can explore how changes in ocean surface temperatures, ocean currents, global-scale wind patterns and atmospheric pressure gradients affect regional hurricane frequency.
As sea surface temperatures rise, warmer water provides more energy that can fuel more powerful and destructive hurricanes. However, the frequency of hurricanes – how often they form – isn’t necessarily affected in the same way.
Some of the best locations for studying past hurricane activity are large, near-shore sinkholes known as blue holes.
Blue holes get their name from their deep blue color. They formed when carbonate rock dissolved to form underwater caves. Eventually, the ceilings collapsed, leaving behind sinkholes. The Bahamas has thousands of blue holes, some as wide as a third of a mile and as deep as a 60-story building.
They tend to have deep vertical walls that can trap sediments – including sand transported by strong hurricanes. Fortuitously, deep blue holes often have little oxygen at the bottom, which slows decay, helping to preserve organic matter in the sediment through time.