Beneath the subtropical paradise, Bermuda hosts a vast network of caves which contains records of Earth’s climate history. Inside are mineral deposits called speleothems – including stalagmites on the cave floors more than six-foot tall. These grow slowly as water drips down from the cave ceiling, gaining a millimetre every few years.
The stalagmites record the chemical signals of the dripwater that formed them. Cold weather tends to be windier, for example, leading to more sea spray and more seawater in the dripwater. Analysing the chemistry of one of these stalagmites has thus enabled us to indirectly reconstruct past sea surface temperatures.
Our latest research, published in the journal Communications Earth & Environment, harnesses this information to show a long-term picture of Atlantic Ocean temperatures, with a datapoint every ten days back to the year 1449. This record shows the Gulf Stream moved northward 300 years ago – a sign that a major system of ocean currents called the Atlantic Meridional Overturning Circulation (Amoc) started weakening then.
