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How Corals Changed My Life

March 17, 2017

I’m a fifth year undergraduate at the Georgia Institute of Technology studying industrial and systems engineering, and I plan to attend graduate school this Fall–but not for anything related to industrial and systems engineering. I plan to pursue a PhD in geoscience, with a focus on paleoclimate. How did I end up here? What even is paleoclimate? I spent five years diligently studying stochastic systems, designing simulations, and developing optimization models. I even spent an entire year training to be an industrial engineer at a manufacturing plant. What made me decide to dedicate the next five years of my life to paleoclimate? Why does paleoclimate even matter? It all began when I was introduced to the endless wonders and wealth of information that corals can provide.

I started studying corals when I took a class by Dr. Kim Cobb, a professor in the school of Earth and Atmospheric Sciences at Georgia Tech. She was teaching a course on sustainability that I happened to be enrolled in to fulfill some breadth requirement for my degree. Although I enrolled in the course thinking it would be an easy-A class, I quickly became more and more enthralled by Dr. Cobb’s inspiring lectures on climate science, one of the most discussed topics concerning the sustainability of our beloved planet. Her passion for the subject was evident and it reminded me of how much I love and care for the Earth. It’s something that has always been a great interest of mine but has gotten lost in the midst of my time-consuming engineering studies. One day after class she announced that she was seeking an undergraduate research assistant for her climate lab. Having never been involved in research at an R1 research university (the highest research activity classification) and also wanting to experience ways to further pursue my long-lost passion for the Earth, I decided to join Dr. Cobb’s paleoclimate lab.

Paleoclimatology is the study of past climate. Why do we need to study past climate? If it is so important, how do we study past climate from times before we had thermometers? Instrumental climate data only extends to the mid 1800s (1), at best, and a century of climate data on a planet that has existed for over 4.5 billion years (2) is simply insufficient when trying to understand long term climate trends. This is particularly critical when trying to distinguish natural climate change from anthropogenic climate change. How do we know what the temperature was on Earth thousands or even millions of years ago? Luckily for us, the Earth is home to an archive of past environmental information. We can use geochemical proxies, which allow us to reconstruct past environmental conditions to understand atmospheric dynamics, oceanic circulation, hydrological properties, and so much more. The potential from these proxies is endless. These proxies, which are found in geological archives such as corals, tree rings, ice cores, and sediments, are covering the Earth. A wealth of knowledge is sitting at our fingertips, waiting to tell the stories of the conditions in which they have survived. My research in the Cobb lab involves geochemical proxies in corals, or more specifically, oxygen isotopes in the corals.

Because corals are so sensitive to changes in the condition of the waters they live in, their carbonate skeletons can be chemically analyzed along their growth axes to understand how the conditions of water have changed over time. These conditions include sea surface temperature (SST), salinity, and pH, which in turn tell us temperature in the area the corals are from, rainfall patterns, and intensity of ocean acidification (3). For instance, the coral oxygen isotopes are particularly sensitive to SST, with some influence from salinity. Thus, when we measure the coral oxygen isotopes of the coral from the surface all the way to the base of the coral, we can reconstruct the temperatures in which the coral grew. This is because warmer conditions cause coral oxygen isotope abundances to become depleted, whereas cooler conditions produce an enrichment of these isotopes in the coral skeleton. The reliability of this proxy has been vastly and rapidly improving through replication and, when available, comparison with instrumental SST records.

Dr. Cobb extracting a coral core from our research site at Kiritimati Island in the central Tropical Pacific
Dr. Cobb extracting a coral core from our research site at Kiritimati Island in the central Tropical Pacific

My undergraduate research project involves the paleoclimate reconstruction of corals in the central tropical Pacific during the massive El Niño event of 2015, which is the largest event on record as shown by some instrumental records. El Niño events are natural climate phenomena that occur every 2-7 years and bring climate extremes to various regions of the world, including heavy rainfall and severe droughts. For instance, if you are a resident of Georgia, you have noticed that this past winter has been unseasonably warm and dry. This is because we are currently experiencing a very strong La Niña event, which often brings climate extremes opposite those of an El Niño event (these strong La Niña events often occur for one or two years following a very strong El Niño event). In my research on this 2015 El Niño event, I have reconstructed SST by analyzing the coral oxygen isotopes in several cores from Kiritimati Island in the central tropical Pacific, in the heart of the El Niño region. I have several research goals in my project, but some of the major ones include: understanding the magnitude of the event by analyzing coral oxygen isotopes in an ensemble of corals from the central tropical Pacific, comparing that magnitude to instrumental records to understand how the signals differ, and comparing the magnitude to past coral oxygen isotopic records to understand the variability of El Niño events over time. Some findings suggest that these events are intensifying over time and becoming more variable, so this is an active area of research. Understanding these events in both the natural and anthropogenically-forced sense is critical when trying to understand human impact on the environment and trying to predict the occurrences of these events.

An algae-covered coral I’m studying. It died from the extreme ocean warming during the massive 2015 El Niño event
An algae-covered coral I’m studying. It died from the extreme ocean warming during the massive 2015 El Niño event

So how did these corals change my life? My research on corals has exposed me to a whole new world of science that I never knew I would be so passionate about. In about one year of undergraduate research I took on this independent project, learned how to use a mass spectrometer, did field work on Kiritimati Island, gave a talk at the world’s largest Earth Science conference in the world, and have been accepted to four graduate schools to pursue a PhD in paleoclimate. I also just found out today that I was awarded the National Science Foundation’s Graduate Research Fellowship, which provides me with funding to attend any graduate school for the next three years. If I hadn’t taken Dr. Cobb’s class and fallen in love with her coral climate science research, my life trajectory would be worlds different right now. I never imagined I would be in my fifth year of undergraduate studies and be so eager to spend another five years in school. However, I have been exposed to the world of geochemical proxies and I don’t ever want to leave. It took me two majors, one year of co-oping, one year of research, and five years of school to find my passion, but I wouldn’t change a thing about my undergraduate choices because they led me here. As for my next steps, my list of options for graduate research studies include water isotopes in ice cores, clumped isotopes in sediments, cosmogenic nuclides in subglacial bedrock, and maybe even more corals. I never thought this would be my life path but I’m excited to work on science no one has ever done before and answer questions about the universe that have never been answered. Speaking from experience, it doesn’t matter if you’re already going down one path in life. If you’re not sure if you’re making the right choices, try other things and see if you find something that would bring you more happiness.

Sources
Cobb, Kim. “Why Study Paleoclimate?”. http://shadow.eas.gatech.edu/~kcobb/
“How old is the Earth”. https://image.gsfc.nasa.gov/poetry/venus/q1152.html
“Picture Climate: How We Can Learn From Corals”. https://www.ncdc.noaa.gov/news/picture-climate-how-we-can-learn-corals

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Gemma OConnor
About Author

Gemma is a 5th year Industrial Engineering major at Georgia Tech. She is very passionate about climate science and conducts paleoclimate research that uses coral geochemistry to reconstruct temperature records in the central tropical Pacific.

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.