30 Breakthroughs: Earth & Ecosystem Processes

November 10, 2021

Susan Lozier

Overturning Assumptions

For years, many scientists assumed that waters in the Labrador Sea off Canada were the primary drivers of Atlantic meridional overturning circulation (MOC), a deep-sea process in which warm, salty waters from the tropics mix with colder, fresher water and sink into the depths, carrying vast amounts of climate-warming anthropogenic carbon with them.

A landmark study in 2019 by former Nicholas School faculty member Susan Lozier sank that theory. Based on empirical data from a 21-month study of the North Atlantic basin, Lozier’s paper showed that waters in the eastern section of the basin, between Scotland and Greenland, were the MOC’s main drivers.

The paper also showed the rate of overturning taking place in those waters may be starting to change. “We found overturning variability in the eastern section of the North Atlantic was seven times greater than in the Labrador Sea over the study period,” says Lozier, a physical oceanographer who is now dean of the College of Sciences at Georgia Tech.

It’s too soon to know if this means the MOC is weakening, but informed by Lozier’s findings, scientists are now better positioned to predict future changes and project what their impacts could be.

Wildfires’ Unexpected Impacts on Oceans

Over the years, research by Nicolas Cassar has yielded some eye-opening findings about carbon cycling and the oceanic food web.

But a study he published earlier this year may have triggered the biggest “aha" moment yet.

Cassar’s research showed that emissions from wildfires that ravaged Australia in 2019 and 2020 triggered widespread algal blooms in the Southern Ocean, thousands of miles downwind to the east.

Tiny aerosol particles of iron in the windborne smoke and ash fertilized the water as they fell into it, providing nutrients to fuel carbon dioxide-absorbing blooms at a scale unprecedented in the region. The study—which is the first to conclusively link a large-scale response in marine life to fertilization by iron aerosols from a wildfire—raises intriguing new questions about the role wildfires may play in spurring the growth of microscopic marine algae known as phytoplankton, which absorb large quantities of climate-warming carbon dioxide from Earth’s atmosphere through photosynthesis and convert it into organic matter, forming the foundation of the ocean’s food web.

The algal blooms triggered by the Australian wildfires were so intense and extensive that the subsequent increase in photosynthesis may have temporarily offset a substantial fraction of the fires’ CO² emissions, Cassar says. But it’s still unclear how much of the carbon absorbed by that event, or by algal blooms triggered by other wildfires, remains safely stored away in the ocean and how much is released back into the atmosphere. Determining that, Cassar says, is the next big challenge.

Technology is the New Geology

Earth has entered a new era, the Anthropocene, or Age of Humans, and one of its defining characteristics, says Peter Haff, professor emeritus of earth science, is that technology is now shaping our environment in ways that geological forces such as wind, water, fire or ice shaped past ages.

Haff’s influential scholarship on the matter, summarized in papers published in 2013 and 2014, has been a powerful force for advancing the scientific validity of the Anthropocene, building consensus on when it began, and conceptualizing the far-reaching impacts technology will have in this new age.

Humans have invented technologies that can now think and communicate with each other and react in real time to the world around them, Haff argues, and wireless connectivity has allowed these technologies to form new types of hybrid ecosystems that turn our farms, factories, homes and cities into a semi-autonomous network of responsive environments. This network, which he calls the technosphere, has its own definable behaviors and internal dynamics, which humans currently drive but don’t really control.

The lines between biology, geology and technology are blurring, he says, and although it’s a world of humans’ own making, we’re no longer flying solo at its helm.

Why Coastlines Change

By applying the lessons of chaos and complexity research to shorelines, a 2001 study by Brad Murray revealed how simple interactions between sand and incoming waves can cause a shoreline to change in surprising ways.

Using computer simulation powered by an advanced mathematical model, Murray and his team showed that when waves approach the shore at angles greater than 45 degrees, they cause “bumps” in the shoreline, areas of erosion or beach buildup that, though isolated at first, can grow and interact with each other. Over time, the model showed, this can lead to the development of large capes and broad bays, or the building up of one stretch of shoreline at the expense of another located tens of kilometers away.

Those findings—now so widely accepted they seem like simple truths—laid the foundation for a new theoretical framework for understanding large-scale coastal change. Follow-up studies, many led or co-led by Murray, professor of geomorphology and coastal processes, have shed light on how coastlines change in response to a changing climate, underscoring the need for a new approach to coastal management planning.