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
When we bring up a sediment core, the coarse sand layers are often evident to the naked eye. But closer examination can tell us much more about these hurricanes of the past.
I use X-rays to measure changes in the density of sediment, X-ray fluorescence to examine elemental changes that can reveal if sediment came from land or sea, and sediment textural analysis that examines the grain size.
To figure out the age of each layer, we typically use radiocarbon dating. By measuring the amount of carbon-14, a radioactive isotope, in shells or other organic material found at various points in the core, I can create a statistical model that predicts the age of sediments throughout the core.
So far, my colleagues and I have published five paleohurricane records with nearly annual detail from blue holes on islands across the Bahamas.
Each record shows periods of significant increase in storm frequency lasting decades and sometimes centuries.
The records vary, showing that a single location might not reflect broader regional trends.
For example, Thatchpoint Blue Hole on Great Abaco Island in the northern Bahamas includes evidence of at least 13 hurricanes per century that were Category 2 or above between the years 1500 and 1670. That significantly exceeds the rate of nine per century documented since 1850. During the same period, 1500 to 1670, blue holes at Andros Island, just 186 miles (300 kilometers) south of Abaco, documented the lowest levels of local hurricane activity observed in this region during the past 1,500 years.
Together, however, these records offer a glimpse of broad regional patterns. They’re also giving us new insight into the ways ocean and atmospheric changes can influence hurricane frequency.
While rising sea surface temperatures provide more energy that can fuel more powerful and destructive hurricanes, their frequency – how often they form – isn’t necessarily affected in the same way. Some studies have predicted the total number of hurricanes will actually decrease in the future.
The compiled Bahamian records document substantially higher hurricane frequency in the northern Caribbean during the Little Ice Age, around 1300 to 1850, than in the past 100 years.