Tiny triangular, textured fossils of ancient pollen grains swim on a beautiful blue icy background on the cover of Nature’s December issue, released yesterday. Frozen in time, these fossilized pollen extracted from ocean sediments tell a story about how Antarctica’s largest ice sheet has changed throughout history.
Sophie Warny, Associate Professor in the LSU Department of Geology & Geophysics and Associate Professor and Curator of the Center for Excellence in Palynology (CENEX) in the LSU Museum of Natural Science, meticulously captured portraits of rare Antarctic pollen grains for a Nature research paper she co-authored. Sophie and collaborators at the University of Texas at Austin and the University of South Florida found that the East Antarctic Ice Sheet may not be as stable as it seems. This ice sheet has been very dynamic, with a long history of expanding and shrinking. The glaciers in this region may be particularly susceptible to climate change because they flow from the Aurora Basin, a region of East Antarctica that mostly lies below sea level.
This means that, today, the East Antarctic Ice Sheet may contribute substantially to global sea level rise as Earth’s climate warms.
But let’s get back to the role those tiny fossilized pollen grains played in helping researchers decipher the history of the East Antarctic Ice Sheet – and in earning this paper a spot on the illustrious cover of Nature magazine. Read on to learn about the story and science behind the Nature cover this month from LSU’s own ancient pollen expert Sophie Warny.
LSU College of Science: Congratulations on having your research featured on the cover of Nature Magazine this month! Can you give us some background on the cover and the science it represents?
Sophie Warny: The cover features microfossil pollen grains, which are one of the types of geological data our research team used to study the evolution of the East Antarctic Ice Sheet. Questions we are attempting to address are, has this ice sheet been stable over time, or does it have a history of expanding and retreating? And what factors drive sudden temperature shifts in Antarctica? Some of the most direct ways to answer these questions are for instance to use seismic evidences (what the lead author Sean Gulick did) and to quantify past environmental conditions both on land and in the ocean by studying the pollen, spores and dinoflagellate fossils contained in well-dated Antarctic sediments (my role). We can compare the types of microfossils we find to known drivers of temperature shifts such as atmospheric carbon dioxide concentration and oxygen isotope data.
The Center for Excellence in Palynology (CENEX) at LSU is one of the main centers in the United States that trains palynologists. Palynology is a branch of paleontology that focuses on microfossils that have organic walls and range in size from about 10 to 100 microns (the size of the width of human hair, or smaller). These microfossils, called “palynomorphs,” include pollen, spores and algae such as acritarchs or dinoflagellate cysts. These microscopic palynomorphs are extremely resistant and can be preserved throughout the geological record for millions of years. By extracting these microfossils from sediments and analyzing them, we can learn which species of plant and algae were present at a particular location over a wide range of geological time.
My portion of our study published in Nature this month was to evaluate what plants, if any, lived in the past at the location of the East Antarctic Ice Sheet, based on sediment recovered by the Antarctic expedition NBP14-02. We took core samples of mud below the seafloor on the East Antarctica Sabrina Coast and extracted and analyzed ancient pollen in the mud to determine the age of the samples. As an ice sheet advances, vegetation retreats and eventually disappears. The overall goal of the project, led by Sean Gulick at UT Austin and Amelia Shevenell at the University of South Florida, was to analyze the past evolution of the East Antarctic Ice Sheet. The palynological analysis my lab conducted was integrated into the objectives of my CAREER grant (U.S. National Science Foundation ANT-1048343), to decipher Antarctic climate variability during the Cenozoic era.
The microfossil samples recovered from expedition cores were simply amazing, and I was truly lucky to be given the chance to conduct analyses of these rare samples. Graduate student Catherine (Katy) Smith worked with me to evaluate the cores for this project as part of her Master’s thesis.
LSU College of Science: When did you learn you might be eligible for the cover art based on your Nature paper? What do you think made your piece especially attractive to the editors?
Sophie Warny: We were notified in the fall of 2017 that our paper was accepted. Once a paper is accepted in a journal, you have the option to submit a cover image. I discussed the possibility of submitting some pollen pictures with the lead authors, and they accepted. By then, I had to move quickly as the cover submission has to be done before the paper goes to press.
I immediately contacted Dr. Clayton Loehn at the Shared Instrumentation Facility at LSU and asked him if he could free up a day, even during the weekend or after hours, on the facility’s scanning electron microscope (SEM) for this submission. He did, and I prepared the sediment samples that I thought would have the best chance of a good microfossil recovery for imaging. I spent a day scanning the samples I had prepared in hopes of finding the perfectly positioned pollen grain from key plant species.
After taking a few good SEM shots, I cleaned the images in Adobe Photoshop. We submitted them shortly after that. I didn’t know if they would be selected, but it’s not every day that you have the chance to compete for a Nature cover, so I didn’t want to have any regrets of not submitting something! About a month later, we were notified that our submission was selected. Best Christmas present ever.
LSU College of Science: Can you tell us more about how the cover art was made? How do you get these close-up images of pollen? How much of this is science, how much is art?
Sophie Warny: The process to isolate these pollen grains from mud samples and take their pictures is quite long and difficult. First, you have to locate and retrieve sediments via seismic and other analyses. Getting the funding to go drill in Antarctica isn’t easy. The cores for this project were acquired by the two lead authors of our Nature paper. Then, the cores drilled in Antarctica have to be brought back to the Antarctic Research Facility in Tallahassee, Florida, which is currently the central point in the U.S. where Antarctic cores are stored.
Next, the cores have to be sampled. We collected about 20 grams of sediment from various levels in the cores. The next step is to extract the palynomorphs (like fossilized pollen) from the muddy sediment. For that, the samples have to be processed using chemical palynological techniques where the dried sediment is successively treated with hydrochloric acid and hydrofluoric acid to remove carbonates and silicates. After that step, we are left with a variety of organic components. To isolate the pollen and spores from this organic residue, we have to sieve the samples between a 10 and 250 µm fraction, and the remaining palynological fraction is mounted on microscope slides using glycerin jelly as a mounting medium.
Here at CENEX, we analyze these slides using an Olympus BX41 transmitted-light microscope with a 60x oil immersion objective to evaluate species abundance and diversity. With the knowledge of what species are present in which samples, we can then image particular pollen grains on an FEI Quanta 3D thermal field-emission sourced dual-beam scanning electron microscope (FIB-SEM) to get high-resolution images such as those seen on this month’s Nature cover!
LSU College of Science: Where did these pollen grains come from? What made you decide to image these pollen grains in such close-up detail?
Sophie Warny: The images on the Nature cover represent a group of rare Antarctic pollen grains. These particular specimens were extracted from sediments acquired in 2014 aboard the Research Vessel N.B. Palmer, from piston core JPC-55, off the Sabrina Coast of Antarctica. These specimens are part of a newly discovered palynoflora [the pollen and spores of a region or site, considered as a whole] that include the plant species Gambierina edwardsii and Phyllocladidites mawsonii, which were used to determine the age of sedimentary samples, as well as new species that we are currently in the process of describing and hope to submit for publication soon. The microscope slides are housed in the CENEX Pollen and Spore Collection at Louisiana State University (LSU) Museum of Natural Science.
I submitted nine images to Nature, and the Nature design group selected the six specimens that are on the cover. The use of various microscopes such as SEM is essential because pollen grains are tiny, measuring just a few microns across, so the only way to identify them is to go in close-up mode.
LSU College of Science: What do the different pollen shapes represent? How did you choose which shapes to include on the Nature cover?
Sophie Warny: Researchers at the Royal Botanic Gardens in Kew in the UK have estimated that there are about 391,000 species of vascular plants on Earth. This is just today. As geologists and paleontologists, we study what lived on our planet in the geological past. Many of the plants that existed in the Palaeozoic for instance, are now extinct. Because ancient sediments can contain pollen or spores from any of millions of different species, the job of a palynologist is extremely difficult and requires a very extensive specialized library. CENEX, thanks to partnerships with industry and various donations, has one of the largest palynological libraries in the world. The shape of a pollen grain or a spore is unique to a particular plant species, so the detailed study of the morphology of these specimens is key to taxonomic evaluation.
As far as choosing the shape, I really didn’t. These species are some of the most abundant present in Antarctic sediment sampled, so this was a natural selection process.
LSU College of Science: Why are the pollen grains on the cover different colors? Did you decide on the colors?
Sophie Warny: We were asked to provide a variety of colored images (the original images taken with the SEM are in grayscale), and the staff at Nature selected to include various colors. The colors do not have any scientific meaning.
LSU College of Science: What was it like working with the photo and graphics editors at Nature to create the cover? How did they tweak it? Did you learn anything useful in this process for future reference when submitting potential cover art?
Sophie Warny: That was actually super fast – it took them just a few hours to put the cover together from our images. I like that they choose an “icy” background to evoke the feeling that the sediments were recovered from Antarctica. The tough part was to agree on the few words that would be associated with the image on the cover. That took a lot of back and forth emails.
LSU College of Science: What are your top tips for other researchers interested in having their research graphics featured on the cover of Nature?
Sophie Warny: These covers take time, so you need to decide whether or not this is something that matters to you. I choose to dedicate a couple of days of my time playing with my raw SEM pictures, cropping them and coloring them. Not everyone enjoys spending time with Photoshop – it is probably the creative side in me that enjoys this. Also, you need to have the right item to illustrate. In our case, it was easy because pollen grains are just gorgeous, and some of these species are likely new to science, so they are very unique.
LSU College of Science: How is this cover art meaningful to you? Do you think it will have an impact for you personally or professionally? What kind of feedback have you gotten about the cover art so far?
Sophie Warny: My family and some of my colleagues have been very excited for me. The cover might not mean much for some scientific colleagues, but for me, having my SEM images on the cover of Nature is the best day of my career so far. It definitely made my day to receive the acceptance email.
I hope the cover will make our field of palynology better known. It is still used too rarely in the U.S. Very few universities teach our specialty, and many students graduate with an undergraduate degree in geology without knowing what palynology is or what microfossils are and what they can do. Yet, the field of palynology is extremely powerful and can provide a diversity of information for basic or applied research. For instance, our knowledge of plant evolution through time means that the pollen extracted from cuttings at exploration wells can be used to date oil-bearing sequences. Several of my former doctoral and master’s students are now leading biostratigraphers with major oil and gas companies.
In addition to dating, pollen and spores can be used to reconstruct past climates (as we did in this Nature paper) because the type and range of palynomorphs present in a sample may be unique to different locations, climates and environments. I hope that the cover will bring awareness to the fact that we know more and more about how our planet’s climate evolved and how it is going to respond to current climatic changes. We now know that the largest ice sheet in the world (the East Antarctic Ice Sheet), which if fully melted would contribute a total of over 50 meters of sea-level rise to the world oceans, is not as stable as we first thought.
Palynomorphs can also be used to predict future crop abundances, trace illegal imports of drugs or stolen goods, or to solve crime. I am very proud that my last doctoral student, Shannon Ferguson, is now a full-time forensic palynologist with the Department of Homeland Security.