Doing archaeology on dry land is one thing, but digging underwater is quite another. Sara Rich tells us how to excavate a site that now lies on the bottom of the sea floor.
Imagine you’ve just discovered the remains of an 8,000 year-old village. Now imagine that village now lies at the bottom of an underwater cliff, on the edge of a shipping lane, where the tides are strong and the water is so murky that it’s practically dark, along with the possibility of the occasional passing shark…
Those are the exact conditions we’ll be facing when we dive down to the bottom of the sea next week to rescue what remains of Bouldnor Cliff, just off the coast of the Isle of Wight.
This incredible site was first discovered by a lobster, and has since produced rare evidence of life during the Mesolithic, including a boat abandoned mid-construction, wheat imported from the Middle East and general family life.
If you’ll be following our updates on Facebook, then here are some of the things you can expect to see us dealing with that your usual land-based archaeologists never do…
1. Contend with underwater wildlife
Terrestrial archaeologists may complain about rampaging sheep, or cattle that occasionally break loose from neighbouring fields, but underwater archaeologists may have to deal with anything from jellyfish to sharks. In fact, clever octopi are frequently found to helpfully ‘assist’ by gathering pottery sherds and bits of wood or flint into piles for us. I’ve even known one who gathered up things like ceramic handles, metal concretions, and ballast stones, and shoved them all into the amphora we were preparing to lift, just to make sure we didn’t forget them on the seabed… you can imagine the confusion this caused on the surface!
Even more gregarious than the octopi are the dolphins. They can be so talkative that their chatter obscures underwater communications between divers and the support team on the surface. Sea turtles and sharks are also curious animals that have been known to circle or nudge us to find out what we’re doing down there and how they can volunteer…
2. Check the waves, not just the weather
For directors of terrestrial digs, checking the weather in the days leading up to the excavation is obviously important; heavy rain can put a damper on operations by flooding the trenches and making the work generally a bit wet and miserable.
But underwater, our trenches are always flooded.
Nevertheless, we still have to check the weather. While we can still work in rain, underwater digs might be called off by the threat of lightning, or by winds resulting in high waves and an unstable support vessel, which can make getting in and out of the water very, very dangerous.
3. Consult the moon (yes, really!)
Fieldwork on land is often planned for summer to minimize the risk of inclement weather. Underwater, especially in areas of strong tidal currents such as the south coast of England, it’s the tide times that are even more relevant than the season, temperature, or wind chill.
Because the tides are a result of the earth’s relationship with the moon, the best times to dive are shortly after the new moon, and the further away the moon is from earth during its orbit, the greater window of productivity we have. Diving on monthly neap tides means being able to stay down for a longer period of slack, before the ebb or flood comes in and threatens to whisk divers and artefacts alike out to sea.
4. Pack your underwater trowel
Only joking. We use much of the same equipment to dig, including trowels, shovels, levels, compass, camera, string, tape measures, site plans, tracing paper, pencils, record sheets, log books, artefact bags and boxes, first aid kits… But for the underwater archaeologists, the list goes on. We need tanks, inflatable jackets and buoyancy control devices, underwater knives, drysuits, undersuits, fins, mask, first stage, regulators, inflator hoses, emergency oxygen, dive computer, chronograph, harness, weight belt, flashlights, spare batteries, camera strobes, coms, depth gauge, tool bag, surface marker buoy… and back-ups of all these.
5. Make sure you’ve got something to hold on to
Sometimes the tides and currents can be so strong that we have to be ready for them by placing temporary frames into the seafloor for us to grab onto for leverage or if things get hairy. If a terrestrial archaeologist suddenly found themselves digging in a hurricane, you’d definitely want something to hang on to! But these frames can also serve other purposes, like providing a locational frame of reference in low visibility, or for use with a grid for mapping the site’s features.
6. Be ready for even the simplest tasks to be 10x more difficult
Assuming you’ve remembered all the kit you need before jumping in, even the simplest tasks on land are exponentially more difficult underwater. Opening a ziplock bag in the dark with 3mm neoprene gloves can be a lesson in patience; positioning oneself to face into the tide so that the bag stays open while placing the artefact inside, then zipping it back shut while finning at full speed to keep from being swept off the site … well, these are the challenges that make the temporary structures needed when doing underwater fieldwork, as much internal as external fortifications.
7. Dig with your back to the current
The thing we most often get asked about is how we actually dig. It’s actually pretty much the same, except that once you’ve disturbed the ground, the fine sediment becomes suspended in midstream. In areas with little to no current, underwater archaeologists use airlifts and dredges to ‘hoover’ the sediment and redeposit it elsewhere; but in a strong tidal current, airlifts are not logistically possible. So we use the same logic as field archaeologists who dig with their backs to the wind – in our case, the currents also wash all that muck away! Simple, unless there’s someone else working downstream!
8. Get to grips with some special underwater digging techniques
Working underwater is always a race against time. How long you spend digging is limited by your air supply, the depth (and thus the increased amount of nitrogen absorbed into the bloodstream over time), and the tidal window. And because of these limitations and the uniqueness of every site, innovative modifications of the typical archaeological fare are called for in order to maximize efficiency at the bottom. At Bouldnor Cliff, purpose-made aluminum boxes were designed to cut through the sediment and bring the earth back up to surface, where it could be excavated in a more controlled manner. Photogrammetry targets and scales have to be weighted so they don’t floast away, ropes and lines minimized to avoid entanglement, and labels fastened with copper nails that resist corrosion. There is a lot to consider at all times, but experience, resourcefulness, and creative problem solving are what help keep us underwater archaeologists productive and safe.
DigVentures crowdfunds archaeological projects that everyone can be part of, in the UK and overseas. With help from people all over the world, we investigate the past and publish our discoveries online for free. Become a DigVentures Subscriber and be part of great archaeology - all year round!