Pollen traces shipwrecks' roots
Plants give boats a biological birth certificate.
How do you work out where an ancient ship was originally built? Try looking at the pollen caught in the joints of the wreck, suggests a French ecologist.
Serge Muller, of the University of Montpellier II in France, says the range of pollen found on a shipwreck gives a snapshot of the plant species local to the boat's birthplace. The sticky resin used to seal a boat's hull can catch and trap pollen, giving the boat a biological 'birth certificate'.
"I see tremendous potential for this method," says Robert Hohlfelder, an archaeologist at the University of Colorado, Boulder. "We're always searching for new ways to investigate shipwrecks. At the moment it's almost impossible to do."
Muller has used the method to trace the origins of a shipwreck off the south coast of France. The Baie-de-l'Amitié, a 2,000-year-old wreck that now lies near the port of Cap d'Agde, was constructed east of Italy, he concludes1.
If that is true, it might force historians to revise some of their ideas about ancient transport. Archaeologists had thought that small boats such as the Baie-de-l'Amitié were only used to carry freight over small distances, says Muller. But his analysis indicates that it travelled clear across the Mediterranean.
Hohlfelder says he wouldn't be surprised if the ships had travelled the distance to carry grapes or wine between ports. "Before the wine industry developed in France, a lot of wine was imported from Italy," he says.
Pollen is a good detective's tool, says pollen expert Madeline Harley of the Royal Botanic Gardens in Kew, UK. The grains can be preserved for millions of years, and have highly characteristic features. "It's like a thumbprint for a species," she says.
Archaeologists can gain some clues to a ship's background by dating its timber. But it is hard to extract clues about the location of the shipyard from these beams, as the wood was often imported from distant sources.
Local pollen, however, would become incorporated into the ship as it is being built, says Muller. The Baie-de-l'Amitié contains both wood and pollen from Platanus, a tree that is restricted to the eastern Mediterranean. The presence of pollen from weeds - such as Haplophyllum, most species of which are found east of Italy - also supports Muller's theory of the boat's origins.
Hohlfelder hopes to use Muller's method to pinpoint where the Persians constructed the fleet with which they invaded Greece in the fifth century BC. More than 1,000 of these ships are thought to lie 100 metres beneath the Aegean Sea. "But we just don't know where the shipyards were," Hohlfelder says.
- Muller, S. D. Palynological study of antique shipwrecks from the western Mediterranean Sea, France. Journal of Archaeological Science, 31, 343 - 349, doi:10.1016/j.jas.2003.09.005 (2004).