"What these fossil reefs show is that the last time Earth warmed like it is today, sea level did not rise steadily," said Rice marine geologist André Droxler, a study co-author. "Instead, sea level rose quite fast, paused, and then shot up again in another burst and so on."
André Droxler (seated) and Pankaj Khanna aboard the Schmidt Ocean Institute's research vessel Falkor in 2012. Mark Schrope / Schmidt Ocean Institute
"This has profound implications for the future study of sea-level rise," he said.
Because scientists did not previously have specific evidence of punctuated decade-scale sea-level rise, they had little choice but to present the risks of sea-level rise in a linear, per-year format, Droxler said. For example, the International Panel on Climate Change, the authoritative scientific source about the impacts of human-induced climate change, "had to simply take the projected rise for a century, divide by 100 and say, 'We expect sea level to rise this much per year,'" he said.
"Our results offer evidence that sea level may not rise in an orderly, linear fashion," said Rice coastal geologist and study co-author Jeff Nittrouer.
Given that more than half a billion people live within a few meters of modern sea level, he said punctuated sea-level rise poses a particular risk to those communities that are not prepared for future inundation.
"We have observed sea level rise steadily in contemporary time," Nittrouer said. "However, our findings show that sea-level rise could be considerably faster than anything yet observed, and because of this situation, coastal communities need to be prepared for potential inundation."
The study's evidence came from a 2012 cruise by the Schmidt Ocean Institute's research vessel Falkor. During the cruise, Droxler, study lead author and Rice graduate student Pankaj Khanna and Harte Research Institute colleagues John Tunnell Jr. and Thomas Shirley used the Falkor's multibeam echo sounder to map 10 fossil reef sites offshore Texas. The echo sounder is a state-of-the-art sonar that produces high-resolution 3-D images of the seafloor.
The Schmidt Ocean Institute's research vessel Falkor mapped 10 fossil reef sites offshore Texas with the latest generation of multibeam echo sounder, a state-of-the-art sonar that produces high-resolution 3-D images of the seafloor. Schmidt Ocean Institute
The fossil reefs lie 30-50 miles offshore Corpus Christi beneath about 195 feet of water. Sunlight does not reach them at that depth, but because corals live in symbiosis with algae, they need sunlight to live and only grow at or very near sea level. Based on previous studies of the Texas coastline during the last ice age as well as the dates of fossils samples collected from the reefs in previous expeditions, the Rice team surmised that the reefs began forming about 19,000 years ago when melting ice caps and glaciers were causing sea level to rise across the globe.
"The coral reefs' evolution and demise have been preserved," Khanna said. "Their history is written in their morphology—the shapes and forms in which they grew. And the high-resolution 3-D imaging system on the R/V Falkor allowed us to observe those forms in extraordinary detail for the first time."
A high-resolution 3-D map of Southern Bank off the South Texas coast clearly reveals terraces, which are a characteristic coral reef response to rising sea level. P. Khanna / Rice University
All the sites in the study had reefs with terraces. Khanna said the stair-like terraces are typical of coral reef structures and are signatures of rising seas. For example, as a reef is growing at the ocean's surface, it can build up only so fast. If sea level rises too fast, it will drown the reef in place, but if the rate is slightly slower, the reef can adopt a strategy called backstepping. When a reef backsteps, the ocean-facing side of the reef breaks up incoming waves just enough to allow the reef to build up a vertical step.
A 3-D representation of Dream Bank, a long-dead reef offshore South Texas. The vertical scale of the image has been increased to clearly illustrate the terrace structures that form due to rising sea levels via a process known as backstepping.P. Khanna / Rice University
"In our case, each of these steps reveals how the reef adapted to a sudden, punctuated burst of sea-level rise," Khanna said. "The terraces behind each step are the parts of the reef that grew and filled in during the pauses between bursts."
Some sites had as many as six terraces. The researchers said it's important to note that even though the sites in the study are as much as 75 miles apart, the depth of the terraces lined up at each site. Droxler and Nittrouer credited the find to Khanna's determination. Analysis of the data from the mapping mission took more than a year, and the time needed to respond to questions that arose during the publication's peer-review process was even longer.
"That's the way science works," Droxler said. "This is the first evidence ever offered for sea-level rise on a time scale ranging from decades to one century, and our colleagues expected ironclad evidence to back that claim."
Nittrouer said the scenario of punctuated sea-level rise is one that many scientists had previously suspected.
"Scientists have talked about the possibility that continental ice could recede rapidly," he said. "The idea is that sudden changes could arise when threshold conditions are met—for example, a tipping point arises whereby a large amount of ice is released suddenly into global oceans. When melted, this adds water volume and raises global sea level."
Khanna said it's likely that additional fossil evidence of punctuated sea-level rise will be found in the rock record at sites around the globe.
"Based on what we've found, it is possible that sea-level rise over decadal time scales will be a key storyline in future climate predictions," he said.
The research was supported by Rice University, the Harte Research Institute at Texas A&M University-Corpus Christi and the Schmidt Ocean Institute.
Eye-Catching Designs Made from Recycled Plastic Bottles
waterlust.com / @abamabam
The company sells a range of eco-friendly items like leggings, rash guards, and board shorts that are made using recycled post-consumer plastic bottles. There are currently 16 causes represented by distinct marine-life patterns, from whale shark research and invasive lionfish removal to sockeye salmon monitoring and abalone restoration.
One such organization is Get Inspired, a nonprofit that specializes in ocean restoration and environmental education. Get Inspired founder, marine biologist Nancy Caruso, says supporting on-the-ground efforts is one thing that sets Waterlust apart, like their apparel line that supports Get Inspired abalone restoration programs.
"All of us [conservation partners] are doing something," Caruso said. "We're not putting up exhibits and talking about it — although that is important — we're in the field."
Waterlust not only helps its conservation partners financially so they can continue their important work. It also helps them get the word out about what they're doing, whether that's through social media spotlights, photo and video projects, or the informative note card that comes with each piece of apparel.
"They're doing their part for sure, pushing the information out across all of their channels, and I think that's what makes them so interesting," Caruso said.
And then there are the clothes, which speak for themselves.
Advocate Apparel to Start Conversations About Conservation
waterlust.com / @oceanraysphotography
Waterlust's concept of "advocate apparel" encourages people to see getting dressed every day as an opportunity to not only express their individuality and style, but also to advance the conversation around marine science. By infusing science into clothing, people can visually represent species and ecosystems in need of advocacy — something that, more often than not, leads to a teaching moment.
"When people wear Waterlust gear, it's just a matter of time before somebody asks them about the bright, funky designs," said Waterlust's CEO, Patrick Rynne. "That moment is incredibly special, because it creates an intimate opportunity for the wearer to share what they've learned with another."
The idea for the company came to Rynne when he was a Ph.D. student in marine science.
"I was surrounded by incredible people that were discovering fascinating things but noticed that often their work wasn't reaching the general public in creative and engaging ways," he said. "That seemed like a missed opportunity with big implications."
Waterlust initially focused on conventional media, like film and photography, to promote ocean science, but the team quickly realized engagement on social media didn't translate to action or even knowledge sharing offscreen.
Rynne also saw the "in one ear, out the other" issue in the classroom — if students didn't repeatedly engage with the topics they learned, they'd quickly forget them.
"We decided that if we truly wanted to achieve our goal of bringing science into people's lives and have it stick, it would need to be through a process that is frequently repeated, fun, and functional," Rynne said. "That's when we thought about clothing."
Support Marine Research and Sustainability in Style
To date, Waterlust has sold tens of thousands of pieces of apparel in over 100 countries, and the interactions its products have sparked have had clear implications for furthering science communication.
For Caruso alone, it's led to opportunities to share her abalone restoration methods with communities far and wide.
"It moves my small little world of what I'm doing here in Orange County, California, across the entire globe," she said. "That's one of the beautiful things about our partnership."
Check out all of the different eco-conscious apparel options available from Waterlust to help promote ocean conservation.
Melissa Smith is an avid writer, scuba diver, backpacker, and all-around outdoor enthusiast. She graduated from the University of Florida with degrees in journalism and sustainable studies. Before joining EcoWatch, Melissa worked as the managing editor of Scuba Diving magazine and the communications manager of The Ocean Agency, a non-profit that's featured in the Emmy award-winning documentary Chasing Coral.