The BIOS-operated marine atmospheric observatory, known as Tudor Hill, was rebuilt by volunteers last year after Hurricane Gonzalo's winds toppled it. Photo by Chris Burville.
Climbing 11 zig-zagging ladders to the top of the new aluminum tower at Tudor Hill Marine Atmospheric Observatory isn’t for the faint of heart. That gentle sea breeze seems more aggressive 75-feet (23 meters) off the ground, as it sweeps in from the sea and subtly sways the top platform’s array of samplers. Look down, and you can see that undersea cables still radiate out and disappear into the clear blue depths, remnants from when the site was a top-secret U.S. Navy listening station, and the Atlantic was rigged with hydrophones to detect Soviet subs on the frontline of the Cold War.
But really, it’s best not to look down. Instead, gaze out at the rain clouds churning along the horizon, and inhale to taste sea spray and dust carried on the wind. This air-sea interface is a frontline for scientists who study the tiny particles in the air capable of seeding clouds, depositing nutrients, or transporting contaminants. These aerosols, along with meteorological data and rainwater, have been collected at the Tudor Hill tower since 1988, producing a record of tremendous value to scientists. The site offers a way for researchers to sample the unique atmosphere over the middle of the ocean without spending days at sea or tens of thousands of dollars for time on a research vessel. And it is often a test bed for new techniques to study the interactions between atmosphere and ocean and how they shape our climate.
This year marks the beginning of a new chapter of research at Tudor Hill. Following Hurricane Gonzalo’s destruction of the original tower structure in October 2014, the scientific community and National Science Foundation rallied to restore the fallen Tudor Hill facility. After the site was cleared and renovated, volunteers helped to raise a new tower structure in December 2015. Four months later, BIOS scientist and principal investigator Andrew Peters had the tower’s sampling instruments up and running again, back on track gathering long-term measurements of ozone and greenhouse gases for NOAA, air column physics for NASA, and aerosol and precipitation samples for researchers around the world.
In celebration of the new and improved facility, eight researchers reflected on the history of atmospheric research in Bermuda to explain why the site is important to the scientific community. This oral history begins with recollections from Bob Duce, who established atmospheric studies in Bermuda early in his career at the University of Rhode Island and is now considered a pioneer of atmospheric chemistry.
Atmospheric Pollution Travels Beyond Borders
Bob Duce, Texas A&M University: In the early 1970s our research group decided Bermuda would be an excellent North Atlantic study location, because it was downwind of the major pollution sources in North America. On an island you can sample consistently for a long period of time and see trends over seasons and years, whereas on a ship you can go wherever you want, but you are limited to a few days of sampling. In addition, ships are notoriously dirty sampling platforms––it’s not easy to sample without contamination.
We first went to Bermuda in early summer of 1972, three of us and our wives, for about six weeks. We would leave the BIOS research station every day to go work on our first observation tower at High Point. This tower was identical in design to the later towers at Tudor Hill.
Tudor Hill tower in 1988. Photo by Bob Duce.
From this tower we measured considerable atmospheric particle pollution coming from North America. Many of these pollutants had never been measured in the middle of the Atlantic Ocean before, but we thought it was logical they would be there––we knew North American cities were polluting, and the wind was blowing over the ocean toward Bermuda.
Investigations into Acid Rain
Tom Church, University of Delaware: In January 1980 I met Tim Jickells on Bermuda. He reported, and I confirmed, low pH in Bermuda’s precipitation. I called Jim Galloway, who was in the Adirondacks shivering in a pay phone booth, to share this discovery.
Jim Galloway, University of Virginia: We really wanted to know—is there long-range transport of pollutants from North America in rainwater?
Bill Keene, University of Virginia: I started working in Bermuda in spring of 1980 with Jim Galloway. The goal was to understand the composition of precipitation in remote regions of the world, and the original surprise from this work was the fact that precipitation was so acidic on Bermuda. It wasn’t known at that time that our emissions causing acid rain had such a large footprint out over the ocean.
Tom Church: We launched WATOX (the Western Atlantic Ocean eXperiment) with continuous precipitation collection in Lewes, Delaware and in Bermuda. This expanded our monitoring network in the northeast US eastward over the ocean. With NOAA we also conducted intensive field campaigns from air and sea.
Jim Galloway: We had the U.S. Navy hurricane hunter planes, flew those all over the North Atlantic region taking samples.
Tom Church: When we went to sea, we were chasing specific storm events that can dump a ton of rain. You had to work fast to do some of the chemistry and process samples while they were fresh.
Bill Keene: The ship work, the aircraft work––those intensive campaigns are really enhanced because they are embedded in the long term, ground-based measurements from Tudor Hill.
Tom Church: Years later when I retired, I had a whole refrigerator with samples from the tower that I had to get rid of. It felt like throwing out fine wine.
Jim Galloway: We found that storms coming from the west (North America) had higher sulfate, higher nitrate, and lower pH than storms form the east. This was really the first time anyone had looked at the extent of long-range transfer of sulphate. It was a pretty heady time, and I have to say we had lots of fun together.
Bill Keene: Over time, the monitoring at Tudor Hill has shown a big reduction in the acidity of the precipitation.
Jim Galloway: Not only did the Clean Air Act decrease nitrate and sulfur concentrations in the United States, but it also decreased the transport to the ocean. With Tudor Hill data, we can see how a policy to protect human health and ecosystems within the U.S. also had great benefit outside the U.S.
It’s much easier doing interdisciplinary, collaborative work when you really like and trust the people you are working with. And when WATOX ended, we joined forces with Joe Prospero and others for AEROCE.
Aerosols and Precipitation across the Atlantic: The AEROCE Era, 1988-1998
Joe Prospero, University of Miami: Bob Duce and I had both taken an interest in atmospheric transport to the oceans, with me working in Barbados, and him first in Hawaii and then Bermuda. But I became more intimately involved with Bermuda in the mid-1980s when we started the Atmosphere-Ocean Chemistry Experiment (AEROCE) with the idea of sampling both aerosols and precipitation at stations across the Atlantic. By the late 1980s we had a station on Barbados, a station on a mountain ridge in Tenerife to focus on African dust, a station in Ireland near Galway, and a station on the south coast of Iceland to look at volcanic debris.
As part of that program, we set up the station at Tudor Hill in 1988, erecting the tower that was recently destroyed by Hurricane Gonzalo. We also had a smaller tower at St. David’s Head on the east coast of Bermuda. The atmospheric samplers on the towers were automatic, so they only sampled when the winds came from over the ocean. At St. David’s Head the sampler was activated when winds came from the East, and Tudor Hill would be off. Conversely when the winds arrived from the west, the Tudor Hill sampler would become active and St. David's Head would turn off. In this way, we built up a picture of the impact of winds arriving from all directions, and what they were carrying to Bermuda. It was one of the first experiments that attempted to look at the dynamic properties of the atmosphere from an ocean site.
Bob Duce: In AEROCE we examined a whole range of metals and elements, and lead from gasoline was a very important one. They all behaved very differently in terms of how they were attached to particles of different sizes, and how different wind regimes would introduce these particles to Bermuda.
Joe Prospero: Over time we built up a long data series where we could see changes on a day-to-day basis, but also seasonal changes related to specific events, like clean air from the North Atlantic subsiding from the stratosphere, polluted air from the U.S. and dust-laden air from Africa.
Of course one of our major interests was the impact of air transport from the U.S. We would see increases in aerosols that we related to human sources. For example, we could see cadmium and zinc related to emissions from oil refineries, automobiles, incinerators. We studied a large suite of elements that provided clues to the sources of these particles.
Bob Duce: When you have so many compounds and elements being measured, each becomes a tracer for a specific process, and together you can really see the whole picture. As I recall there were at least ten institutions involved in AEROCE, and this was one of the wonderful things: you can learn so much from what other people are learning, which in turn can help you figure out more about what you are working on and observing.
Joe Prospero: Within AEROCE, Bermuda played a big role because our measurements in the atmosphere could be related, in some cases, to what was being measured in various ocean processes in the Bermuda Atlantic Time-series Study. There have been a number of studies that used that data to examine the impact of dust and pollutants on primary productivity, which is relatively unique.
Bill Keene: Discovering the impact of Saharan dust in Bermuda was a big surprise at that time. We really hadn’t realized the dust stretched that far north.
Joe Prospero: Saharan dust carries iron, and marine biota have enzymes that require iron. On a global basis, there is now tremendous interest in the role of iron on primary productivity.
Bob Duce: Chemists and climate scientists didn’t recognize for a long time how important dust is to climate and ocean productivity.
Tom Church: From time to time, Bermuda will get several inches of rain in extreme events. It turns out when dust storms make their entry into the region, they may actually play a role in nucleating the precipitation. So for iron, one major rain event can end up introducing 50% of the iron that ocean region would ordinarily see in a whole year.
Joe Prospero: Dramatic changes over the time period we’ve observed show that dust emissions are very sensitive to climate variables, whether they are natural or anthropogenic. The big question is, to what degree is this variability due to natural or human forcing?
New Insights: Marine Nutrient Cycles
Pete Sedwick, Old Dominion University: After AEROCE ended, the use and maintenance of the tower dwindled. When I arrived at BIOS in 2001, the Tudor Hill site had fallen into serious disrepair. Part of the reason we were able to get funding to refurbish it is that there was a critical mass of people that saw the value of getting samples in the middle of the ocean, and were very supportive of it.
Tom Church: NSF’s marine chemistry division, and Don Rice in particular, played a heroic role making sure the tower had funds to continue unabated.
Pete Sedwick: One of the most interesting results from work we did at the tower and at sea was looking at the sources of iron getting into the ocean. Iron is an essential nutrient for plankton. While iron from Saharan dust is important, we found a lot of iron also came from pollution aerosols that reach Bermuda in the winter months, derived from the fuel combustion aerosols coming from North America. This iron was very water soluble, especially compared to the Saharan dust, which means it can be readily consumed by plankton.
To study elements present in seawater at very low concentrations, scientists must work in ultra-clean conditions to prevent sample contamination. Here, Pete Sedwick's team is working with BATS seawater samples in the clean chemistry lab van aboard RV Weatherbird II. From left to right are Pete Sedwick, Chris Marsay (then lead tower technician, now a postdoc at Skidaway Institute of Oceanography), and collaborators Simon Ussher (University of Plymouth) and Andrew Bowie (University of Tasmania), both of whom have conducted research related to aerosols collected at Tudor Hill. Photo courtesy of Pete Sedwick.
The Bermuda tower is particularly well positioned to see that contrast –– in the summer, winds from North Africa stretch across the Atlantic to Bermuda, and in the winter the cold fronts come in from North America.
Meredith Hastings, Brown University: We’ve been trying to figure out if the ocean is a passive receptor of nitrogen from the atmosphere, or if the ocean is participating in the atmospheric nitrogen cycle in some way. In terms of atmospheric chemistry, Bermuda is a great spot because you have such clear transport from the continents. When there are human influences on the chemistry, you should be able to see them.
If our Bermuda data are scalable, it suggests that the amount of nitrogen the ocean gets from human sources should be revised––from 80 percent, down to 30 percent. We’re really challenging our fundamental understanding of these processes.
Rebuilding the Tower
Andrew Peters: Unfortunately the Tudor Hill Marine Atmospheric Observatory was severely damaged by Hurricane Gonzalo.
Pete Sedwick: I remember going out after Hurricane Fabian (2003), which the tower survived, with a couple of chainsaws because there were so many downed trees on the road to the tower.
Andrew Peters: We fought our way through Gonzalo’s destruction with chainsaws, but when we made it to a point by the base and we couldn’t see the tower above the tree line, that’s when we knew it was bad.
Bill Keene: Several people offered help immediately, it just so happened we had a tower that had only been used intermittently since the 1990s. These towers last forever, they are incredibly robust things.
To their credit, NSF stepped in and provided the money. The Chemical Oceanography and Atmospheric Chemistry programs have continued to keep the site going as a resource for the community.
Andrew Peters: The hurricane damage allowed us to really look at the site and renovate completely, so it’s a blessing in disguise. We added a new habitation unit complete with kitchen and bunks. In the past, people have come out and undertaken what are called intensive sampling campaigns, so they’ll be out for 24, 48 hours at a time to take measurements every hour or few hours. But there hasn’t been a quiet place to rest. So this will be a really nice addition and increase the capability of the facility by enabling people to stay the night there if they want to, or at least giving them somewhere to have a cup of coffee.
Bill Keene: We replaced all the hardware on the tower, and bought a new top section. The foundation work has to be done at the site beforehand, but assembly goes quite quickly if it’s not windy. Six people can do it in a day.
Jim Galloway: Tudor Hill is a great sampling platform, and the fact that the site is associated with BIOS and the ship makes it even better. With Tudor Hill restored as a base for atmospheric research, and with the new glider program at BIOS, there will be great opportunities to ask questions about the exchange of nitrogen between the atmosphere and ocean.
Meredith Hastings: It just makes sense to support atmospheric research on a regular basis when you have this rich marine dataset to accompany it!
Bill Keene: For understanding climate, these long-term records provide the context for developing and training global models––everybody uses them.
In most of the global climate models we have now, marine aerosol production and processes are very poorly constrained, even though this is the biggest flux of particles to the atmosphere. To get climate right, you’ve got to get the particles in the atmosphere right. There are definitely still some big puzzles.
Andrew Peters: We are now back to full operations at Tudor Hill and the facility has recently been endorsed by the Surface Ocean-Lower Atmosphere Study (SOLAS), an international research initiative aiming to understand the key biogeochemical-physical interactions and feedbacks between the ocean and atmosphere. I’m really excited about this new lease on life for the Tudor Hill site and look forward to many more years of productive collaborative research in marine atmospheric sciences.
Robert Duce, University Distinguished Professor Emeritus, Departments of Oceanography and Atmospheric Sciences at Texas A&M University
Thomas Church is the E.I. du Pont Professor of Marine Studies, Emeritus at the University of Delaware, and BIOS Trustee
James N. Galloway, the Sidman P. Poole Professor of Environmental Sciences at the University of Virginia, and BIOS Trustee
William C. Keene, Research Professor of Environmental Sciences at the University of Virginia
Joseph M. Prospero, Professor Emeritus, Dept. Atmospheric Sciences & CIMAS, Rosenstiel School of Marine and Atmospheric Science at the University of Miami
Peter Sedwick, Professor of Ocean, Earth and Atmospheric Sciences at Old Dominion University
Meredith Hastings, Associate Professor of Environment and Society and Earth, Environmental and Planetary Sciences at Brown University
Andrew Peters, Associate Scientist at the Bermuda Institute of Ocean Sciences, and the Principle Investigator and Site Manager of the Tudor Hill Marine Atmospheric Observatory.