RESILIENT SHORES: After Sandy, climate scientists and architects explore how to co-exist with rising tides

Coastal Resilience
AFTER THE WIND, RAIN AND WAVES of Hurricane Sandy subsided, many of the modest homes in the Chelsea Heights section of Atlantic City, New Jersey, were filled to their windows with murky water. Residents returned to find roads inundated by the storm surge. Some maneuvered through the streets by boat.

This mode of transport could become more common in neighborhoods like Chelsea Heights as coastal planners rethink how to cope with the increasing risk of hurricane-induced flooding over the coming decades. Rather than seeking to defend buildings and infrastructure from storm surges, a team of architects and climate scientists is exploring a new vision, with an emphasis on living with rising waters. “Every house will be a waterfront house,” said Princeton Associate Professor of Architecture Paul Lewis. “We’re trying to find a way that canals can work their way through and connect each house, so that kayaks and other small boats are able to navigate through the water.”

The researchers aim for no less than a reinvention of flood hazard planning for the East Coast. A new approach, led by Princeton Professor of Architecture Guy Nordenson, rejects the strict dividing line between land and water that coastal planners historically have imposed, favoring the development of “amphibious suburbs” and landscapes that can tolerate periodic floods. These resilient designs can be readily modified as technologies, conditions and climate predictions change.

Discovery2014_CR_textbox1To plan for future flood risks, Princeton climate scientists are using mathematical models of hurricanes to predict storm surge levels over the next century, taking into account the effects of sea level rise at different locations. Four design teams — from Princeton, Harvard University, the City College of New York and the University of Pennsylvania — are using these projections to guide resilience plans for specific sites along the coast: Atlantic City; Narragansett Bay in Rhode Island; New York City’s Jamaica Bay; and Norfolk, Virginia. [See Planning for resilience up and down the coast.]

The designs will serve as a guide for the U.S. Army Corps of Engineers’ North Atlantic Coast Comprehensive Study, a plan to reduce the risk of flood damage to coastal communities, which is due to Congress in January 2015. “The Army Corps understands that they have to revisit what it means to make structures that are resilient,” said Enrique Ramirez, a postdoctoral research associate in architecture at Princeton and the project’s manager. He serves as a liaison between the design teams and Army Corps officials in regional districts.

The idea for the project grew out of Nordenson’s work on a pre-Sandy project to develop creative proposals for adaptation to rising sea levels in New York Harbor. The project culminated in a book, On the Water: Palisade Bay, and a 2010 exhibition, Rising Currents, at the New York City Museum of Modern Art. The proposals included repairing and lengthening existing piers, as well as planting wetlands and building up small islands inside the harbor. “It was forward thinking because we showed that there are benefits to building things in the water,” Nordenson said. Other Princeton contributors to On the Water were engineering professors James Smith and Ning Lin (then a graduate student) and climate scientist Michael Oppenheimer of the Woodrow Wilson School of Public and International Affairs.

Hurricane Sandy heightened the urgency of long-term coastal planning. While advising a New York State commission on future land use strategies, Nordenson began discussing a broader plan for the East Coast with Joseph Vietri of the U.S. Army Corps of Engineers and Nancy Kete of the Rockefeller Foundation. This discussion led to the Structures of Coastal Resilience project, which is funded by the Rockefeller Foundation and began in October 2013. The project is managed by Princeton’s Andlinger Center for Energy and the Environment and will extend resilient design concepts to other coastal regions, as well as integrate hurricane storm surge predictions with projections of local sea level rise.

One of the project’s goals is to encourage a reconsideration of the absolute flood zone boundaries on maps produced by the Federal Emergency Management Agency (FEMA), which determine building code requirements and insurance rates. Climate science shows that the geographical borders of flood risk should be based on the probabilities and outcomes of different storm events, not the placements of artificial levees that may be overtopped by high storm surges. Indeed, many of the homes and businesses ravaged by Hurricane Sandy were not located in flood hazard zones on FEMA’s maps. “Sandy really brought home the message that we have to do a lot better in the future,” said Oppenheimer, the Albert G. Milbank Professor of Geosciences and International Affairs. “Because while we sit here thinking about it, the risk is only increasing.”

Click to enlarge. The low-lying barrier island that is home to Atlantic City is particularly vulnerable to storm surges, especially in parts of the city, such as residential Chelsea Heights, that were built on wetlands. Researchers are exploring ways to make existing neighborhoods (Panel A) more resilient in the face of occasional storm surges. By raising houses, using roads as low levees and letting abandoned lots return to wetland conditions, these neighborhoods can become “amphibious suburbs” (Panel B). A similar approach can be applied to existing canal neighborhoods (Panel C), making them more resilient and tolerant of flooding (Panel D).

Click to enlarge. The low-lying barrier island that is home to Atlantic City is particularly vulnerable to storm surges, especially in parts of the city, such as residential Chelsea Heights, that were built on wetlands. Researchers are exploring ways to make existing neighborhoods (Panel A) more resilient in the face of occasional storm surges. By raising houses, using roads as low levees and letting abandoned lots return to wetland conditions, these neighborhoods can become “amphibious suburbs” (Panel B). A similar approach can be applied to existing canal neighborhoods (Panel C), making them more resilient and tolerant of flooding (Panel D).

Smarter building codes are also needed, according to Lin, an assistant professor of civil and environmental engineering, who heads the effort to predict storm surge levels. Current building code books primarily address earthquake risks. “A tiny few chapters are for wind, and very few pages are for flooding,” Lin said. Large-scale, long-term projects such as levees and seawalls have been the standard approach to coastal protection. But the Coastal Resilience team puts forth a different view, one of coping with occasional flooding rather than fighting it. “We will never be able to prevent such hazards. We can only be prepared to reduce their impact,” Lin said.

Resilient designs call for supporting, revitalizing and in some cases reengineering natural features such as wetlands and beach dunes. This so-called “soft infrastructure” can reduce the impact of waves, improve water quality and create new recreational spaces for coastal residents and visitors. Rather than the exclusive construction of barriers, the project’s plans include “layered systems of natural and engineered structures that will respond in different ways to different hazards,” Nordenson said. “It is a more nuanced and more resilient approach.”

Flexible design is also an important component of the project. Ideally, the sizes and arrangements of structures will be adaptable as predictive models improve. Scientists continue to debate how climate change will affect the strength and frequency of storms. “But we are trying to take what we know right now and do the best job we can in accounting for the uncertainties in what we know, and use that to explore how we should be thinking about adaptation,” said Smith, the William and Edna Macaleer Professor of Engineering and Applied Science and chair of the Department of Civil and Environmental Engineering at Princeton.

Meteorological measurements show that the extreme winds of a swirling hurricane transfer energy to the ocean surface. The winds and the storm’s low air pressure cause a dome of water to rise, generating a surge of high water when the storm makes landfall. “When you think of the storm, you think of the wind and the rain. That’s what seems scary,” said Talea Mayo, a postdoctoral research associate who is working with Lin to model storm surges. But the coastal storm surge was the main cause of deaths and property damages from Hurricane Sandy.

To predict future storm surges, Lin and Mayo are using thousands of synthetic hurricanes modeled by Kerry Emanuel, an atmospheric scientist at the Massachusetts Institute of Technology. “Anytime you’re studying hurricanes, especially so far north, your historical data are really limited because there just aren’t enough events,” Mayo said. “So instead of basing our risk analysis on historical data, we use synthetic data.”

Hurricane damage 1944

Storms have caused significant damage to Atlantic City’s iconic boardwalk throughout its existence. Shown here is South Inlet during the Great Atlantic Hurricane of 1944. Image from the archive of the Coastal and Hydraulics Laboratory, Engineer Research and Development Center, Vicksburg.

Emanuel’s team uses existing models of global climate circulation patterns to generate 3,000 synthetic, physically possible storms for nine different climate change scenarios at each of the four study sites — a total of more than 100,000 storms. These hurricanes exist only in computer code, but their wind speeds, air pressure levels and patterns of movement are based on physical laws and information from recorded storms. Mayo and Lin plug these parameters into algorithms that work like sophisticated versions of high school physics problems: solve the equations for conservation of mass and momentum to estimate maximum water levels at each site. Variations in tide levels, coastline shapes and seafloor topographies add additional layers of complexity.

To make reasonable projections of future flood hazards, the models must also account for sea level rise. According to geoscientist Chris Little, an associate research scholar working with Oppenheimer, storm surges are a short-term version of sea level rise. “They both contribute to coastal flooding,” Little said. “Climate change will be felt through the superposition of changes in long- and short-term variations in sea level.”

And when it comes to sea level rise, local projections are crucial for planning efforts. A constellation of factors influence regional differences in sea levels, including the vertical movement of the Earth’s surface, changes in ocean circulation and the melting of glacial ice. Little and Oppenheimer were among the authors of a study published in June 2014 in the journal Earth’s Future, which used model-based and historical tide gauge data for sites around the globe to project local sea levels over the next two centuries.

“We live in a hotspot, where the local sea level rise has been higher in the past than the global mean, and we expect it to continue to be higher in the future,” Oppenheimer said — as much as 40 percent higher than the worldwide average. One reason for this is that the land along the East Coast is slowly sinking (by a millimeter or two each year), a legacy of the ice sheet that covered much of North America until about 12,000 years ago. The ice sheet depressed Earth’s crust over present-day Canada, causing the liquid mantle beneath to bulge southward. Now that the glaciers have melted, the mantle is being gradually redistributed, flowing out from under the East Coast of the United States.

Sea levels respond slowly to changes in climate, including the current warming trend, caused in part by increased carbon dioxide levels from human activity. Because future carbon emissions depend on human decisions, predictions of sea level rise come with built-in uncertainty. This project attempts to meet this challenge head-on: “A major purpose of the project is to think about doing a more thorough job of assessing the uncertainty in these flood zones,” Little said. “I think it’s difficult but worthwhile.”

Resilient designs call for planning and reengineering natural features such as salt marshes, submerged aquatic vegetation and wetlands, as in this imagined coastline for Staten Island, south of Manhattan.

Resilient designs call for planning and reengineering natural features such as salt marshes, submerged aquatic vegetation and wetlands, as in this imagined coastline for Staten Island, south of Manhattan.

Because of this uncertainty, climate scientists deal in probabilities. The Princeton team has projected flood levels for storms with return periods of 100, 500 and 2,500 years. A return period of 100 years is akin to a “100-year flood” — this means that in any given year there is a 1 percent chance of that flood level occurring. These forecasted flood risks are key to making smart building and design decisions in the face of climate change. “Every decision-maker is going to look and decide what risk is tolerable for their region in the context of how much it would cost to defend against that risk,” Oppenheimer said.

The design teams are beginning to test their plans against the climate scientists’ predictions. Simulated local water levels will reveal which structures may be inundated by future storms and at what probabilities. These analyses may prompt the designers to adjust the heights of buildings, roads or beach dunes in their blueprints. And as the science improves, this process will repeat itself. “Over time, others can start to add things that we haven’t been able to include, like the relationship of the wind and the flood,” Nordenson said.

True resilience necessitates a change in outlook. In Atlantic City, the focus area for Lewis and the Princeton group, a narrow channel of water separates the Chelsea Heights neighborhood from the city’s famous boardwalk and high-rise casinos, where many residents work. “You have extensive areas of suburban neighborhoods that are built on wetlands,” said Lewis. “Two binary positions are retreat, where you return these to wetlands, and fortification, which is the seawall approach. And both of them are problematic.”

The team recognizes the social and economic importance of maintaining the neighborhood. But barricading it behind a seawall may be prohibitively expensive, not to mention unattractive. More important, metal or concrete seawalls can actually exacerbate flooding when areas behind them are inundated by heavy rain. Lewis and his team have a fundamentally different vision for places like Chelsea Heights: “We’re looking at developing an amphibious suburb,” he said. “We want water to come in. If there are berms [earthen seawalls] that are put in, they should be built with a series of valves.”

The plans for Chelsea Heights include raised homes and roads interspersed with canals and revitalized wetlands. Lewis hopes these ideas will be useful to policymakers and to the Army Corps of Engineers, which may apply the Princeton team’s concepts to Chelsea Heights and other similar communities along the New Jersey shore. By the end of this century, grassy suburban lawns may be transformed into salt marshes.

PLANNING FOR RESILIENCE UP AND DOWN THE COAST

Natural features play a pivotal role in the designs for two of the project’s other focal regions, New York’s Jamaica Bay and Rhode Island’s Narragansett Bay.

  • The plan for Jamaica Bay includes the use of local dredged materials to build up land for marsh terraces, which can serve to reduce wind fetch as well as improve water quality and encourage sediment deposition, according to Catherine Seavitt, an associate professor of landscape architecture at the City College of New York. In particular, her team hopes to expand the restoration of a native wetland grass, Spartina alterniflora, an effective attenuator of wind and waves that also provides valuable ecological habitat.
  • Michael Van Valkenburgh and Rosetta Elkin lead the Harvard design effort for Narragansett Bay. One of their plans involves relocating two critical reservoirs that supply drinking water to the city of Newport. The reservoirs are currently vulnerable to coastal flooding; the proposed project would use dredged material from the original reservoir to fill in and extend the existing maritime forest, now a rare ecosystem along the New England coast. The larger forest, designed by the team, would mitigate coastal erosion, attenuate wave action, and become a valuable recreational area for surrounding communities.
  • The project’s other site, the Norfolk, Virginia, area of Chesapeake Bay, calls for a more extensive reshuffling of settlement and infrastructure, according to Dilip da Cunha, an adjunct professor of landscape architecture at the University of Pennsylvania. Of the four sites, Norfolk is expected to see the most dramatic sea level rise, and is home to the world’s largest naval station and a vital commercial port. The UPenn team’s designs stem from the natural network of fractal-like interfaces where land and water meet. The plan seeks to bolster “fingers of higher ground” that will be more robust to gradual sea level rise as well as storm surges. “The higher grounds could be for housing, schools and other facilities, and the low grounds could accommodate various things, from marsh grasses to football fields,” da Cunha said. “Things that can take water in the case of a storm event, but will not endanger lives.”

-By Molly Sharlach

Secrets of the Southern Ocean

southernocean

Marine geochemistry specialist Robert Key doesn’t consider himself particularly prone to depression. Yet emails to his wife from a research vessel on the freezing waters of the Southern Ocean depicted an emotional slump amid harsh conditions and brutal working hours.

“It’s wet and windy and miserable, and if you’re down there in the winter, then it’s dark the whole time as well,” said Key, a research oceanographer in the Program in Atmospheric and Oceanic Sciences. “You’re away from contact with people. Essentially all you do is eat and work.”

Robert Key

Robert Key collects water samples during a research voyage aboard the NOAA vessel, the Ronald H. Brown. (Photo courtesy of Robert Key)

But Key and other Princeton researchers push through the challenging conditions because they want to learn more about the waters at the bottom of the globe, which have a significant impact on the Earth’s ecosystems and climate. By collecting and analyzing samples of seawater, and using the results to help construct computer models of the ocean and atmosphere, the scientists aim to understand the Southern Ocean’s major influence on the world’s carbon and nutrient cycles. In doing so, they hope to provide insight into what our planet will look like in an era of human-driven climate change.

Though it makes up less than a third of the world’s ocean coverage, the Southern Ocean surrounding Antarctica soaks up about half of the man-made carbon dioxide absorbed by the world’s oceans from the atmosphere each year. Its waters act as a giant pump, with currents that carry carbon dioxide down into the deep recesses of the ocean where the carbon can remain for roughly 1,000 years. In return, currents bring up frigid water from the deep, water that has never been exposed to today’s elevated levels of carbon dioxide and therefore is able to absorb more of the gas than today’s surface waters.

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This frigid water also absorbs heat: the Southern Ocean has helped prevent the planet from warming up as much as it might have by now from human activity, according to Jorge Sarmiento, the George J. Magee Professor of Geoscience and Geological Engineering. Because its waters are so cold, the Southern Ocean absorbs about 60 percent of the excess heat that moves annually from the atmosphere into the ocean.

Along with absorbing carbon dioxide and heat, the Southern Ocean regulates the movement of nutrients such as nitrogen and phosphorus. The ocean’s patterns of circulation transport nutrient-rich water from the deep ocean back to the surface, where currents carry the nutrients to the north. These nutrients provide three-quarters of the ocean’s biological productivity, spurring the production of plant matter called phytoplankton that serves as the basis of the aquatic food chain.

Slideshow of the summer voyage of the research vessel R/V S.A. Agulhas II:

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“It’s old, it’s cold and it’s rich,” said Sarmiento. These traits, he explained, enable the Southern Ocean to have the influence that it does over global climate and nutrient regulation — and challenges scientists to find out how this massive storage vessel for carbon, nutrients and heat might react to rising carbon emissions and climate change.

Southern Ocean diagramA key question is whether rising carbon emissions will boost or hamper the Southern Ocean’s ability to sponge up carbon dioxide. Changing wind and rainfall patterns due to a warming Earth could shift how much carbon and heat the Southern Ocean can store in either direction, according to Daniel Sigman, the Dusenbury Professor of Geological and Geophysical Sciences. If winds pick up, for example, then mixing between the Southern Ocean’s deep and shallow waters may pick up as well. If high-latitude rainfall increases, more freshwater on the polar ocean’s surface may mean a higher density difference between the surface and deep waters, leading to less mixing. Depending on the response of ocean biology to this range of possible changes in ocean circulation, the rate of carbon uptake may either rise or fall.

Scientists have built models to predict how the Southern Ocean’s carbon sink will behave over the next several decades. But these researchers lack sufficient observations of the Southern Ocean to adequately inform high-resolution models of the ocean’s circulation, to assess the predictive powers of their models, or even to understand which processes are the most important for the models to provide accurate simulations. Data for winter at the Southern Ocean is especially sparse. A major reason: the brutal working conditions in the winter.

“I thought I knew something about winds and bad waters and blizzards and storms,” said climate modeler Joellen Russell, who grew up in an Eskimo village 31 miles above the Arctic Circle. “I couldn’t get my head around it.” Russell, an associate professor at the University of Arizona who collaborates with Sarmiento, remembers being thrown across her cabin one night when a wave slammed against the side of the ship, and how buckets of water would crash onto the deck in such great volume that the water looked black. “You’re like, ‘I want to go home now,’” she said.

Slideshow of the winter voyage of the research vessel R/V S.A. Agulhas II:

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Field research in the Southern Ocean, which typically lasts between 30 to 70 days, holds scientists to a punishing schedule. They can work up to 18 hours a day, seven days a week. Russell described a typical night working in a chemistry lab during one of her research cruises: she slept on a bean bag on the lab’s floor, waking up every 15 minutes to a beeping noise reminding her to perform certain laboratory tasks. The workhorse nature of the job stems mainly from the high cost of being out on the water: tens of thousands of dollars per day. “Because it’s so expensive to get out there, you feel the pressure,” Russell said. “You want every last bit of data you can get.”

On board the ship

Researchers aboard the National Oceanic and Atmospheric Administration (NOAA)’s ship, the Ronald H. Brown, performed experiments in the ship’s laboratory to analyze water samples for nutrient levels, alkalinity and other factors during this research cruise in March and April 2010. Clockwise from front left are: Benjamin Botwe, assistant lecturer at the University of Ghana; Charles Fischer, oceanographer at NOAA Atlantic Oceanographic and Meteorological Laboratory; Calvin Mordy, associate at NOAA Pacific Marine Environmental Laboratory; Yui Takeshita, graduate student at Scripps Institution of Oceanography; and Laura Fantozzi, staff research associate at Scripps Institution of Oceanography. (Photo by Ivy Frenger)

Fortunately, researchers now can use robotic battery-powered floats that provide salinity and temperature measurements for up to five years. About 3,500 of these floats, called Argo floats, are making measurements around the world’s seas. Funding and management for the floats come from the contributions of 23 countries.

But there are measurements that Argo floats leave out, and Associate Professor of Geosciences Frederik Simons hopes to fill in some of the gaps with an instrument of his own. Simons has spent the past few years developing an autonomous buoy, in collaboration with University of Rhode Island professor Harold Vincent, that detects GPS position, time and ocean depth while measuring seismic waves generated by distant earthquakes that are converted to water pressure waves at the ocean floor. They call their instrument the Son-O-Mermaid.
Simons hopes the Son-O-Mermaid will overcome the paucity of oceanic data, particularly in the Southern Ocean. “We are making pictures of the interior of the Earth using waves recorded through the Earth,” said Simons. “When we do that, we can learn about mantle plumes, subduction zones, mid-ocean ridge earthquakes — basic questions that people wonder about.”

Though the Son-O-Mermaid, which can stay in the water in a range of ocean conditions, is set up for use in seismology, researchers could easily adapt it for their own use in physical, chemical or biological data collection, according to Simons.

A three-decade legacy

Much of the groundwork for today’s understanding of the Southern Ocean comes from earlier work by Sarmiento, whose interest in the Earth’s carbon cycle began around 1984. This was when he co-wrote — with J. Robert Toggweiler, an oceanographer at the National Oceanic and Atmospheric Administration’s Geophysical Fluid Dynamics Laboratory in Princeton — one of the first papers to point out that the Southern Ocean’s waters dictate the carbon dioxide content of the atmosphere. His paper was one of three to become so influential in the field as to be given a nickname: the “Harvardton Bears” papers, so named because their authors were affiliated with Princeton, Harvard or the University of Bern.

Jorge Sarmiento

Professor Jorge Sarmiento (Photo by Denise Applewhite)

This early work revealed that the Southern Ocean acts as a leak in the ocean’s biological pump. The Southern Ocean actually releases some carbon dioxide into the atmosphere because phytoplankton, which consume carbon dioxide as they grow, cannot keep up with the rapid supply of nutrients and carbon from the underlying deep ocean and leave much of it unused.

Sarmiento has continued to investigate the ocean’s role in global climate over the three decades since, with a particular focus on the Southern Ocean. In 1996, he constructed a model that predicted how future global warming would affect the ocean’s ability to absorb carbon dioxide: he suggested that warming would weaken the ocean’s circulation, which would in turn compromise the movement of carbon dioxide to deep waters. His further research proposed new ideas about why atmospheric carbon dioxide was lower during ice ages, and he identified pathways that nutrients follow as they migrate from the Southern Ocean to seas farther north.

“You just fall into something, a fascinating problem that you can’t let go of,” said Sarmiento. “Suddenly things come together and you get an answer, and it’s different from anything that anyone else has come up with.”

Sarmiento, who began his Princeton career as the University’s only biogeochemist, is now surrounded by several colleagues examining the oceans’ biogeochemical processes: Michael Bender, professor of geosciences; François Morel, the Albert G. Blanke Jr. Professor of Geosciences; Stephen Pacala, the Frederick D. Petrie Professor in Ecology and Evolutionary Biology; and Bess Ward, the William J. Sinclair Professor of Geosciences.

Sarmiento also has good company in researchers such as Sigman, who has made major contributions to scientists’ knowledge about the Southern Ocean. Sigman is trying to understand the role of the Southern Ocean in global climate by studying past climate changes and reconstructing the strength of the carbon dioxide leak back through Earth history.

In particular, Sigman is exploring the hypothesis that the Southern Ocean carbon dioxide leak was reduced during the ice ages.

Daniel Sigman

Professor Daniel Sigman (Photo by Denise Applewhite)

Sigman uses marine sediments to identify how iron — which is carried to the Southern Ocean in dust originating in Africa, Australia and South America — has affected phytoplankton growth in the Southern Ocean and contributed to the global climate cycles of the Earth’s last 1 million years.

An essential nutrient for phytoplankton, iron is relatively scarce in the Southern Ocean. The lack of iron prevents phytoplankton populations from growing to numbers large enough for them to fully consume the ocean’s nutrients, including carbon dioxide. This means that a lot of carbon dioxide can leak right back into the atmosphere.

This may not have always been the case, however. By studying marine sediments, Sigman and his colleagues found evidence that more dust deposits in the past may have enabled phytoplankton in the subAntarctic zone — the Southern Ocean region roughly 40 to 50 degrees above the South Pole — to consume more carbon dioxide, which may have helped hold down the global temperature. That lower temperature would have caused stronger ice ages starting 1 million years ago, the scientists wrote in a 2011 paper published in Nature. With more dust — and thus more iron — in the water, phytoplankton growth escalated and ensured that excess carbon in the water was consumed before it escaped into the atmosphere as carbon dioxide gas. This allowed heat-trapping carbon dioxide to stay in the ocean.

“Our hypothesis is that iron supply to the sub- Antarctic zone is one of the two key ingredients that lowers atmospheric carbon dioxide during ice ages,” Sigman said.

The other ingredient is changes in the mixing of water between the surface and the deep ocean. With colleagues from the Swiss Federal Institute of Technology in Zurich, Sigman found evidence that the subAntarctic zone changes were complemented by circulation changes in the Antarctic zone, the Southern Ocean region adjacent to the Antarctic continent and south of the subAntarctic zone. At the beginning of each ice age of the last million years, the Antarctic zone appeared to reduce its vertical mixing, which may have slowed the leakage of carbon dioxide to the atmosphere and trapped more of it in the ocean, providing the first cooling step of the impending ice age. The cooling, in turn, encouraged more dust to be deposited in the ocean, in part because continents became drier and dustier. And the phytoplankton fertilized by this dust may then have caused further carbon dioxide drawdown and global cooling.

These two factors — more dust-borne iron and more mixing of waters — could have allowed the Southern Ocean to absorb more carbon dioxide in the past. These findings may hint at how the Southern Ocean will change as the Earth warms in the next few years, Sigman said, with the possibility of more mixing and less iron input.

With the Southern Ocean playing a considerable role in what the climate might look like in years to come, scientists such as Sarmiento see it as their responsibility to uncover knowledge that will enable others to understand the systems at work. But though Sarmiento and Princeton’s other Southern Ocean specialists have made considerable strides in investigating the ocean’s place in the global climate, challenges remain — from increasing public awareness of the Southern Ocean’s critical importance to uncovering cost-effective, automated methods of obtaining more data from this poorly sampled region.

Key especially looks forward to the latter: he hopes that new technologies will afford him a break from the rigors of Southern Ocean fieldwork.

“It gets harder and harder to work a 72-hour week,” he said. “You get too old to go out to sea as much as I used to.”

-By Tara Thean