When a tanker hauling almost 54 million liters (14.2 million gallons) of fuel ran aground on a shoal near Nunivak Island, Alaska, in June, it may have been relying on outdated maps to chart its course.
According to the U.S. National Oceanic and Atmospheric Administration (NOAA), 1.5 percent of U.S. Arctic waters have been surveyed with modern survey methods. Many of the charts, including those covering the waters off western Alaska and the Aleutian Islands, contain information that dates back to before World War II. Other regions remain entirely unsurveyed.
Loss of sea ice is contributing to increased commercial activity in the region, putting pressure on NOAA to update its nautical charts with ocean depths and identify dangers to navigation.
Arctic Deeply speaks with NOAA’s Captain Rick Brennan, who has commanded survey vessels through Alaskan waters, about the challenges of charting Arctic waters in a changing environment.
Arctic Deeply: We often hear that only a small percentage of the Arctic has been mapped to modern standards. What does that mean?
Rick Brennan: Some of the charts go back to Captain Cook’s days or when the Russians still owned Alaska. In the Alaska region as a whole (not just the Arctic area), we have depth values on the charts, but much of that data goes back to when they were using a lead line, which is exactly what it sounds like – a big hunk of lead that was tied to the end of a rope and lowered to the seafloor. Imagine a human swinging that around – you’re not getting a lot of measurements on the seafloor.
After the Titanic had its accident, we started using sonar technology. If we pointed sound at the seafloor we could get a measurement there. But much like the lead line, that only provided depths directly below the ship and only where it went. A ship could pass on one side or another of a wreck and you wouldn’t know it was there.
Now, fast-forward to the 1980s. We’re using different sonar technologies, called side-scan sonar, that allow us to see not just below the ship, but on either side of the ship. That provided us with a picture of the seafloor, but no depths. And then we started using multibeam sonar technology, which provides information on a swath of the seafloor that may be up to seven times the depth there. When PCs and computers started to make their entry and you didn’t need a huge mainframe to make those computations, all that started to move onto ships and improve our mapping capability.
When we speak of modern techniques, we’re talking about multibeam surveys. It means we have fully insonified the seafloor and have depths across a swath, so that we know everything that was down there at the time of the survey.
Arctic Deeply: Are Arctic marine areas less mapped than other regions in the U.S.?
Brennan: It is much further behind for a number of reasons. The traffic is not quite as dense as you would see in the lower 48 [states]. In the historic past there was a lot more ice cover then there is now, so the ability to survey was much more restricted then than it is now.
The other thing is that in the Bering Sea and the Chukchi Sea, those areas are relatively shallow. The ability to cover that, as you remember the swath width is relative to the depth, so the narrower the swath is the more times you have to go back and forth to fully insonify the seafloor. Think about having to mow your lawn with a lawnmower that is only 30cm [12in] wide, versus one that is 90cm [36in] wide. It will take a lot more passes.
Arctic Deeply: What areas are being surveyed now?
Brennan: We have tried to focus it in areas where there is a real economic need for the local community and where there is ship traffic: the Red Dog Mine and Kotzebue, Port Clarence. We also have some surveys around Port Hope and St. Lawrence Island. We have been pushing up the Aleutian Chain. Once you get north of Unimak Pass, the level of effort it takes to get a ship or contractor up there, goes up significantly.
Arctic Deeply: What’s the driver behind updating the maps?
Brennan: Certainly in the last 5–10 years, the focus on the Arctic has become greater. To be fair, we had already been surveying in Alaska – the NOAA ship Rainier has been surveying in Alaska its entire 48-year life. The NOAA ship Fairweather has done the same thing, with a 10–15 year break. We’ve had quite a bit of resources focused explicitly on Alaska and more generally on the Arctic, to make sure that that area of growing traffic has up-to-date data.
Arctic Deeply: Are there big differences between the existing information and what actually exists, or is the seafloor constantly changing?
Brennan: It’s a difficult question, because it is such a huge area. There are areas where it is incredibly boring. There are others where we find amazing things. Near Chirikof Island there are slip faults in the Earth, where the whole ground has shifted, and we see that in the data, too. We also see drowned riverbeds, from periods when the sea level was significantly lower than it is today, and drowned volcanoes on the seafloor.
The seafloor is constantly changing. Most people get this impression that once you’ve surveyed, you’re done. No, no, no. When you mow your lawn in June, are you finished? No, you have to mow it again next week.
We can see that change from one day to the next, particularly where you have high currents and sediment, which can create sand waves on the seafloor. In deep water, where there are strong currents, these sand waves will typically be 3–10m [9–30ft] tall and they move. They march around the seafloor, back and forth like a spider web in the wind. Where you have those, [the] shallowest point on the sand wave one day, it could be 10–30m [30–90ft] somewhere else the next day.
Arctic Deeply: Does climate change and the increase in spring river runoff make the seafloor less predictable?
Brennan: Yes, absolutely. Take the Yukon River, for example. In the spring it looks like a chocolate milkshake. The glacial till that gets into the river is so fine, it’s ground stone, and it settles. We have to provide new charts to the entrance of the Yukon River every year.
Tug and barge traffic goes up the Yukon to supply these remote settlements with fuel and food and other supplies. When they come back in the spring to bring the goods in, the river will have changed completely from the last time they were up there. It takes more time, because they are literally bumping along the riverbed to find the safe water. They have to back off and navigate around the sediments.
Arctic Deeply: How is technology improving mapping in the North?
Brennan: We are looking to use satellites to help guide us, to let us know where the seafloor is changing the most and where we should apply our efforts. The LiDAR [laser] technology mounted to planes now allows them to go into much shallower waters and closer to shorelines, and produce data that is almost as good as our sonars on ships. That is very exciting because it allows us to map all the nearshore areas regularly and routinely. We hope that we can do that every five years, something my predecessors couldn’t have dreamed of. We’re also using a lot of autonomous surface vehicles.
But we have issues with our fleet. I’m not a young man any more and neither are our ships. The fleet is aging and we need to replace those to continue the work that we do.
I think the work that we do is significantly important to to the way of life of those living in the Arctic – and for their survival. We take it very seriously.
This story has been updated to reflect the progress NOAA has made in surveying U.S. Arctic waters.