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Kirstin Fawcett/MEDILL

Northwestern University student researcher Kayleen McMonigall carries a homemade contraption fashioned out of PVC piping and synthetic fiber mesh. McMonigall designed the screen with geologist Patricia Beddows, assistant chair of Northwestern University's Department of Earth and Planetary Sciences. The two planned to float their hand-fashioned tool in the cave's water, where it could potentially isolate a growing calcite raft. 

 


NU researcher explores caves, sinkholes and urban threats in the Yucatan

by Kirstin Fawcett
Aug 07, 2013


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Kirstin Fawcett/MEDILL

Pet Cemetery, a large cave in Quintana Roo, Mexico, is a striking example of a cenote, or underground sinkhole. It boasts ancient stalactites, vegetation, and prehistoric mammal bones submerged in its waters. 

Yucatan3

Courtesy of Kirstin Fawcett/MEDILL

Northwestern University Medill graduate Kirstin Fawcett (MSJ '13) joined NU geologist Trish Beddows and her field research team as an embedded science reporter in the Yucatan Peninsula.

I’ve gone scuba diving under golden mangrove roots, watched dozens of baby loggerhead turtles squiggle out of a sand nest and into the ocean, and snorkeled in an underground cave with fantastic stalactite formations and prehistoric mammal bones nestled in its bottom depths.

I’ve learned approximately two words of Spanish per day and acquired approximately 2 million mosquito bites per night as part of my time learning the science behind rapid changes – large-scale urbanization and development, reef deterioration, and pollution threats to the aquifer – that are hitting the Caribbean coast of the Yucatan Peninsula.

It was the close of my first week as an embedded science reporter on a Medill journalism fellowship from Northwestern University.

In mid-June, I flew to Mexico to shadow Patricia Beddows, a well-known Northwestern geologist with a focus on caves and karst, a geology with soluble bedrock (such as limestone) where caves form. When karst extends to the surface, sinkholes may be a prominent feature of the landscape.

Trish is involved with countless research projects delving into the Yucatan’s landscape. Just a sampling of them involves reconstructing past sea levels in the Yucatan by studying calcite raft formation; exploring virgin cave passages; and learning how and why Mexico’s underground aquifer system is threatened by inadequate, and often inappropriate, wastewater and sewage management and handling of solid municipal waste.

Sadly, Trish telephoned me the night before I flew out to the Yucatan. She had a family emergency, and she had to return to Ottawa, her home city. I asked if I should reschedule my trip, but Trish told me to come anyway. One of her PhD students, Emiliano Monroy-Rios, was staying behind in Akumal to work with Kayleen McMonigal, a 20-year-old undergraduate biology student. The students and Trish had brainstormed an experiment in which they hoped to grow calcite rafts in an undisturbed cave, and Emiliano and Kayleen planned to proceed with the experiment in Trish’s absence. So the following morning I packed my carabineers and cargo pants (good for caving, according to Trish!) and flew out to Cancun.

I should probably explain what a calcite raft is before I continue. The Yucatan Peninsula is geologically interesting because it is flat and low-lying, with limestone bedrock. The limestone is peppered with caves and sinkholes called cenotes. One of the Yucatan’s most intriguing features is this intricate karst topography that includes miles of underground rivers. Cave divers and explorers have attempted to chart various routes, but they’ve only mapped a small fraction of the sprawling system that lies beneath the ground.

The shallow caves are filled with fresh water from past rainfall. Calcite rafts float on the stagnant water, and at first glance resemble flat, lacy snowflakes. Due to the dissolving limestone, the water contains significant concentrations of calcium and carbonate ions. The off-gasing of carbon dioxide causes the calcite ions to form calcite rafts, which float because of surface tension. These rafts are delicate and sink at the slightest disturbance, forming a sediment layer at the bottom of the cave.

Calcite rafts are known to form and accumulate in a great number of locations, but nobody’s actually observed a calcite raft’s formation in nature. Trish hoped to use a time-lapse camera and detailed observations to record their life cycle, and utilize her findings to reconstruct how these rafts sink, deposit sediment, and form sea levels.

On my first full day in the Yucatan, Emiliano and Kayleen headed off to a hardware store in Tulum for materials to build two contraptions out of screening and PVC pipe. To give you some idea of what they look, the two devices were essentially window screens with PVC piping serving as frames. They drilled holes in one of the contraptions’ PVC frames and left the other intact. The goals were to find a relatively untouched cave on a piece of private property, gain access and place the contraptions into the water. The hole-less contraption would float, and the other would sink. These contraptions would allow Kayleen and Emiliano to isolate a potential floating calcite raft in the screening and allow it to grow there. They would catch any sinking calcite rafts with the sunken screen. Together, this would give them an idea of how much calcite raft sediment formed on the cave’s bottom in a measurable amount of time and let them know the speed at which calcite rates formed on the surface.

It’s been a week, but Kayleen hasn’t seen any results. Emiliano had to fly to Mexico City on personal business. We think that an influx of fresh rainwater – it’s the beginning of Mexico’s rainy season, and we’ve witnessed the occasional downpour – has interfered with the calcite rafts’ formations. Ideal conditions for calcite raft formation include still water, possibly little rainfall, and a cave undisturbed by visitors.

The Yucatan tends to get blown off as a party-hearty beach destination. However, I think it’s fascinating that Mexico has tens of thousands of fresh water sinkholes across the landscape – all perfect for swimming, exploring, diving, and studying at one’s own pace. Some of the largest, such as Xel-Ha, have been turned into amusement parks with zip lines, snorkel tours, and colored lights. Others are advertised by the side of the road and marketed as low-key pit stops where one can buy a soda at a small adjacent market and enjoy a refreshing dip. Still, the majority are undiscovered or located on private property. New ones are found all the time. And the only contact many tourists have with the sinkholes -- called cenotes - are through chartered day trips or a guidebook that mentions them in a passing reference.

Cenotes served as the Maya’s only source of fresh water. In turn, they used them to perform rituals to the Gods. The Maya viewed them as a source of life and as an entrance to the underworld. They are literally the veins of the earth, and their existence is threatened by unregulated waste and water pollution caused by overdevelopment and tourism. This poses a threat to the entire karst landscape.

I get access to a new and undiscovered cenote. My new friend Jacobo’s cousin has one on his property, and he’s agreed to let me in. I’m very excited to see one up close. I feel like an explorer – it’s a different world underneath the soil. So far, I’ve visited five cenotes.

I’ve also been working on a little side project – Mexican cooking! My new friend Jacobo, who runs a quiet cenote park called El-Toh, taught Kayleen and me how to make tortillas espanola, rice, guacamole, and frijoles from scratch. I’ve learned a lot about Mexican food from Jacobo. He’s full of interesting anecdotes concerning home-caught and cooked delicacies including snake, rabbit, and iguana.

The cost of living is minimal here and I’m gaining such wonderful access to little-explored areas of the jungle. Trish has access to fantastic sources, scuba diving, and Maya culture. And now that she’s arrived, I have my own personal walking guidebook to educate me further about the Yucatan. This almost makes up for the mosquito bites. Almost!
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This story was made possible in part by a grant from Carnegie Corporation of New York. The statements made and views expressed are solely the responsibility of the author.