Amazonian rainforest tree mortality driven by climate and functional traits
Izabela Aleixo, Darren Norris, Lia Hemeric, Antenor Barbosa, Eduardo Prata, Flávia Costa, & Lourens Poorter
The Problem: Climate scientists are constantly learning and sharing new details about climate change and its possible effects in the future. However, many of the impacts of climate change have already surfaced and revealed the fragility of our ecosystems. Recently, scientists have observed increasing tree mortality in tropical forests, which are some of the most biodiverse and ecologically important places in the world. Could tree mortality be another consequence of climate change–one that’s happening right now? This study by Aleixo and others (2019) explores this possible connection between modern climate change and downfall of tropical forests.
What data were used? This study uses monthly climate and tree mortality records along with about 50 years of observational data in the Amazon rainforest. Climate data include precipitation, temperature, and humidity. Tree mortality data is categorized by specific traits such as wood density (soft or hard), successional position (when a species colonizes a new area), and leaf phenology (deciduous or evergreen).
Methods: Aleixo and others (2019) tracked global climate and tree mortality in an area of the Amazon rainforest monthly for one year. They looked for increased tree mortality that aligned with variations in the climate data. They also examined tree mortality of different species traits during significant climate events in the past 50 years. These events include climate anomalies like El Niño or La Niña (click here to learn more about these).
Results: This study found that Amazon tree mortality is driven by climate, but the relationship is complex. For example, droughts can lead to immediate or slow tree death, depending on the mechanisms at play. Additionally, if a tree has harder wood, it is less likely to die during a drought. Aleixo and others (2019) also found that weather events like low rainfall or high temperatures can either immediately enhance tree mortality or cause increased mortality up to two years later. Similar outcomes are associated with years where El Niño or La Niña are particularly extreme. Various species traits may protect trees from dying under certain weather or climate events, but no single Amazon species is completely safe from the effects of climate change.
Why is this study important? As our climate continues to change and weather events become more extreme, the future of our forests remains uncertain. Even the most biodiverse and ecologically robust regions in the world are susceptible to the effects of climate change. This study provides a modern framework for us to understand those effects. From this, scientists can refine dynamic global vegetation models that predict how forests will respond to climate variability in the future.
Citation: Aleixo, I., D. Norris, L. Hemerik, A. Barbosa, E. Prata, F. Costa, and L. Poorter (2019), Amazonian rainforest tree mortality driven by climate and functional traits, Nature Climate Change, 9(5), 384-388, doi:10.1038/s41558-019-0458-0.
A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error Jesús A. Ballesteros and Prashant P. Sharma Summarized by Maggie Limbeck
What data were used? Data were collected from whole genome sequence projects and RNA sequence libraries for all 53 organisms included in this study. Because there are four living species of horseshoe crabs and many living representatives of arachnids (spiders, scorpions, ticks) genetic data was able to be used as opposed to morphologic (shape and form) data. Organisms from Pancrustacea (crabs, lobsters, etc.) and Myriapoda (centipedes and millipedes) were used as outgroup organisms, organisms that are included in the analysis because they are part of the larger group that all of these animals fit into (Arthropoda) but have been determined to not be closely related to the organisms that they cared about in this study.
Methods: Several different methods were used in this study to estimate the evolutionary relationships between horseshoe crabs and arachnids. By using multiple different phylogenetic methods (different calculations and models to estimate relationships between organisms) these researchers had several different results to compare and determine what relationships always showed up in the analyses. In addition to all of these different methods that were used, two different scenarios were tested in each method. The researchers wanted to be able to run their data and see what results they got, but also test the existing hypothesis that horseshoe crabs are sister taxa to land-based arachnids.
Results: The vast majority of the phylogenetic trees that were produced in these different analyses showed that horseshoe crabs are “nested” or included in the group Arachnida and are sister taxa to Ricinulei (hooded tick spiders). The only analyses that returned results different from this, were those that were forced to keep horseshoe crabs as sister taxa to the land-based arachnids, but those trees had very low statistical support of being accurate.
Why is this study important? This study is particularly cool because it highlights interesting problems associated with using genetic data versus morphologic data and problems with understanding evolution in groups that diversified quickly. Chelicerates (the group of Arthropods that have pincers like spiders, scorpions, horseshoe crabs) diversified quickly, live in both aquatic and terrestrial settings, and have many features like venom, that all appeared in a short time frame geologically. By gaining a better understanding of the relationships between the members of Chelicerata and Arachnida researchers can start to look at the rates at which these features developed and the timing of becoming a largely land-based group. This is also an important study because it has demonstrated that relationships we thought were true for horseshoe crabs and arachnids for a long time may not actually be the case.
The big picture: The research done in this study really highlights the major differences in relationships that can be demonstrated depending on whether you are using morphological data or genetic data. This study found that by using genetic data for 53 different, but related organisms, that horseshoe crabs belong within the group Arachnida rather than a sister taxa to the group. It’s also really cool that this study was able to demonstrate evolutionary relationships that are contrary to what have long been believed to be true.
Jesús A Ballesteros, Prashant P Sharma; A Critical Appraisal of the Placement of Xiphosura (Chelicerata) with Account of Known Sources of Phylogenetic Error, Systematic Biology, syz011, https://doi.org/10.1093/sysbio/syz011
Morphospace expansion paces taxonomic diversification after end Cretaceous mass extinction
Christopher M. Lowery and Andrew J. Fraass
Summarized by Adriane Lam
The Problem: There is no doubt that species today are going extinct due to human activities, such as habitat loss, climate change, and the introduction of invasive species that take over areas. For example, the Florida Panther used to range throughout the southeastern U.S., but due to humans expanding into their habitat, they now only occupy a mere 5% of their former range. Polar bears are also facing loss of their habitat due to melting ice and snow caused by human-induced warming. But if humans were to disappear tomorrow, how long would it take for Earth’s flora and fauna to bounce back to the number of species before humans were here? This is a hard question to answer, but to begin to quantify this, paleontologists can use the fossil record.
In this study, the scientists looked at the time before, during, and after the end-Cretaceous mass extinction event that took place ~66 million years ago. This was one of the largest mass extinction events in Earth’s history, where about 75% of all species on Earth went extinct, including the non-avian dinosaurs. It is also an important mass extinction event to study because the event that wiped out all those species was very rapid. During other mass extinction events in Earth’s history, the extinction events themselves took on the order of millions to hundreds of thousands of years (read more about extinctions here).
The rate at which humans are altering the Earth today is unprecedented to any climate change event in the geologic past (see our ‘CO2: Past, Present, & Future’ page for more details). Thus, scientists need to compare the rate at which we are losing species today under a very fast climate change scenario to another event that was also very fast. Therefore, studying the end-Cretaceous mass extinction is particularly valuable: it was a very quick event and one that is most comparable to the rate at which we are losing species today.
Data Used: In this study, the scientists used the fossil record of planktic foraminifera to see how long it took for life to recovered after a mass extinction event, the end-Cretaceous mass extinction. Planktic foraminifera are single-celled protists (not animals) that live in open-marine environments. They have occupied our oceans for the past ~165 million years. These protists produce a calcium carbonate (same material seashells are made of) shell, or “test,” that grows to be about the size of a grain of sand. When the foraminifera die, its shell sinks to the seafloor. Over millions of years, these shells are preserved at the bottom of the ocean. Making the fossil record of planktic foraminifera an archive of extinction and evolution events for the past 165 million years of Earth’s history! The scientists who conducted this study used this amazing fossil archive to see how long it took these marine protists to return to pre-extinction levels after the end-Cretaceous mass extinction.
Methods: As part of his master’s project, Andy Fraass compiled a database of first and last occurrences of planktic foraminifera species. First and last occurrence datums are often used in paleontology to examine how long in geologic time a species existed. The authors used these data to examine when planktic foraminifera species evolved and went extinct (Figure 1).
This dataset collected, but left unpublished until this paper, also included measurements of the species’ tests, such as the number of chambers in the shell, how quickly the chambers expanded from the earliest chamber to the last, etc. From these measurements, the authors calculated test complexity. This is a metric that shows how ‘complex’ planktic foraminifera shells became through time. For example, a species with a simple shell might have simple chambers arranged in a spiral pattern. A more complex species might have a more extreme test (Figure 2). The test complexity of each species was then given a score, with 1 being the simplest, and 4 being the most complex or extreme.
In foraminifera, the shape of the test can be assumed to have some sort of relationship to the organism’s life strategy, or its niche, basically. A species’ niche is where and how it can live and interact with the environment. For example, humans occupy a broad range of niches: our technology allows us to live in very hot to very cold climates. On the other hand, polar bears have a very narrow niche. These animals only live in the tundra biome in the Northern Hemisphere on the ice and hunt seals. A specific foraminifera might only live at a particular depth in the ocean, or in water that’s above or below a certain temperature, or in regions with a certain abundance of food, etc. These niches are the scaffolding on which species diversity is built.
During a mass extinction event niche spaces are often completely disrupted or destroyed along with the species that occupy them. Thus, paleontologists have hypothesized that after an extinction event, the number of species cannot simply bounce back to what it was before, but the number and size of niche spaces has to be rebuilt first. This may cause the observed delay in the recovery of species after mass extinction events. This paper provided the first test of that hypothesis with real data.
Because the shape and characteristics of a planktic foraminifera’s shell is related to its niche, the authors used average test complexity of all the foraminifera that were alive at different points in time to reconstruct how many niches were occupied by forams before and after the end-Cretaceous mass extinction. Higher average complexity suggests a wider variety of niches were occupied, while lower complexity suggests that fewer niches existed.
Results: The authors found that there was a huge drop in the number of species after the end-Cretaceous mass extinction (Figure 1), which was not a surprise and something we have know about for a while. But the other finding was that along with a huge drop in the number of species was also a huge drop in the test complexity (Figure 3). It took about 5 million years for test complexity to reach the levels it was at before the mass extinction event. That’s a really long time!
Another interesting find is that test complexity increased before species diversified. That is, new niches were created faster than new species to fill them after the mass extinction event. This study shows that before a lot of new species can evolve, there need to be a few species that evolve and open new niche spaces first.
Why is this study important? Today, humans are having a huge effect on the ability of species to survive on our planet. Through destruction of species’ habitats and niche space, we are pushing more and more species to the brink of extinction. Importantly, there are also thousands of species that have already gone extinct from human activities (such as the Tasmanian Tiger, Passenger Pigeon, Sea Mink, Caribbean Monk Seal, Quagga, Elephant Bird, Haast’s Eagle, and many more). If we keep causing animals to go extinct, we may see a loss of biodiversity that rivals those of mass extinctions that have taken place in the geologic past. But until now, we didn’t really know how long it took for new niche spaces to be filled and how that would affect how fast new species can fill those niche spaces.
This study gives us a clue: it may take as long as 5 million years after a mass extinction event for new niche spaces to be created. It then takes additional five million years for diversity, or the number of species, to rebound to pre-extinction levels. The bottom line is that it takes 10 million years for the biosphere to recover from a mass extinction event. This means that even though humans have been on Earth for a very short period of time (geologically speaking), we will have a huge impact on the flora and fauna, even if we were to disappear tomorrow.
Citation: Lowery, C. M., and Fraass, A. J., 2019. Morphospace expansion paces taxonomic diversification after end Cretaceous mass extinction. Nature Ecology & Evolution https://doi.org/10.1038/s41559-019-0835-0
A seismically induced onshore surge deposit at the KPg boundary, North Dakota
Robert A. DePalma, Jan Smit, David A. Burnham, Klaudia Kuiper, Phillip L. Manning, Anton Oleinik, Peter Larson, Florentin J. Maurrasse, Johan Vellekoop, Mark A. Richards, Loren Gurche, and Walter Alvarez
Summarized by Jen Bauer, Maggie Limbeck, and Adriane Lam, who also comment on the controversy below
What data were used?
Data used in this study were identified from a new site, which the authors call Tanis (named after the ancient Egyptian city in the Nile River Delta), in the layers of rocks called the Hell Creek Formation. This formation is famous amongst paleontologists because it contains lots of dinosaur fossils from the late Cretaceous (about 66 million years ago). In this study, scientists found a new layer of fossils within the Hell Creek Formation that is unlike anything paleontologists have seen before. Those who found the site examined the rock’s features and fossils, which includes densely packed fish fossils and ejecta from the Chicxulub meteoric impact. The Chicxulub impact is what caused the dinosaurs to go extinct, and finding a layer of rock that was deposited minutes to hours after the impactor struck Earth is a very rare and exciting find.
This study included a variety of approaches. The rock features (called sedimentology) and fossil features of the Tanis area and event deposit are described to determine what caused this deposit in the first place. The authors also identified other pieces of evidence to aid in better understanding the situation at hand. Ejecta deposits were described as well, in comparison to ejecta deposits that are found closer to the impact site in the Yucatan Peninsula, Mexico.
Much of the sedimentology can be related to other aspects of the Hell Creek Formation in southwestern North Dakota that is an ancient river deposit that has some marine influence. In the Cretaceous period, central North America’s topography was very low which allowed for a seaway to form. This was called the Western Interior Seaway, and was home to a diverse number of animals such as plesiosaurs, mososaurs, large sharks, and ammonites. Several rivers likely drained into the Western Interior Seaway, much like the Mississippi River drains into the Gulf of Mexico today.
From studying the characteristics of the rocks within the Tanis site, the authors of the study concluded that this site was part of one of the rivers that drained into the Western Interior Seaway long ago. When the impactor struck Earth in the Yucatan Peninsula, it send huge waves (tsunamis) into the Western Interior Seaway and into the rivers that drained into the seaway. These huge waves pushed fish, ammonites, and other creatures into the seaway and into the rivers. The Tanis site is one such place where these animals that were pushed into the rivers were deposited and preserved. But not only were marine animals preserved at the site, but also land plants, such as tree limbs and flowers.
The fossils found in the Tanis deposits are all oriented in the same direction, indicating that they have been aligned by flowing water. The abundance and remarkable preservation of these fossil fishes and tree limbs suggest a very rapid burial event (the best preserved fossils are often the ones that experience very quick burial after death). The orientation of the fossils at the site along with the mix of marine and terrestrial life further supports that these fossils were deposited from very large waves from the asteroid impact disturbed this region.
Within the Tanis deposit there are also ejecta spherules, microkrystites, shocked minerals, and unaltered impact-melt glass. These are features that are commonly associated with the Chicxulub Impactor. When the impactor struck Earth, it was so hot it melted the underlying rock, sending tiny bits of molten rock into the atmosphere. These bits of molten rock quickly cooled and eventually fell back down to Earth, where today they are found all over the world. Today, these ejecta spherules and impact melt-glass all mark the huge end-Cretaceous mass extinction event that occurred 66 million years ago.
Why is this study important?
The Cretaceous-Paleogene (K/Pg) extinction event is one of the ‘Big Five’ mass extinction events (click here to read more about extinction). Like many extinction events, it is often difficult to determine the specific causes of mass destruction. However, the K/Pg extinction event is unique because scientists have many lines of evidence that a huge impactor struck Earth, sending clouds of ash and gas into Earth’s atmosphere. The new Tanis site that the authors uncovered preserves a snapshot into this catastrophic event.
This finding is very important because scientists know better understand what happened directly after the impactor hit Earth. In addition, several new species of fish have been discovered at the Tanis site, which will be important for additional studies about fish evolution through time.
DePalma, R.A., Smit, J., Burnham, D.A., Kuiper, K., Manning, P.L., Oleinik, A., Larson, P., Maurrasse, F.J., Vellekoop, J., Richards, M.A., Gurche, L., and Alvarez, W. 2019. A seismically induced onshore surge deposit at the KPg boundary, North Dakota. Proceedings of the National Academy of Sciences (PNAS), doi: 10.1073/pnas.1817407116
What’s all the commotion about?
It’s not every day that paleontologists make the national news, but this paper and the article written about it in the New Yorker (click here) caused a lot of commotion within the paleontological world. This is a great and potentially groundbreaking find, however, what caused the commotion was the sensationalist attitude of the New Yorker piece that left a lot of paleontologists uncomfortable. So what’s the big deal here? We break down a few (not all) of the issues with this article:
1. Breaking of Embargo
Although the published study is very exciting and will add greatly to our knowledge about the end-Cretaceous mass extinction event, the media hype around the study was handled very poorly for several reasons. All published studies go through peer review. This is when a paper is sent out to multiple other scientists who read the article and make sure that it is scientifically sound and is a good piece of science based upon other good science. During this waiting period while the paper is going through peer review or being finalized with publishers, the authors should avoid talking with popular media or publicizing their paper. When publishing in academia there is a period of time (embargo) where access to the findings of a paper is not allowed to the public. This is for a variety of reasons, having to do with copyright transfer, finances to support the journal or publisher, and more.
The New Yorker press article was released almost an entire week before being available for the community to examine. This means that the embargo was violated.
The reason embargos exist is to give journalists and the researchers they talk to some time to look at fresh findings and determine what the story is, whether it’s worth telling, and if there’s anything suspicious about what’s presented. – Riley Black (Slate article)
2. Paleontologists as Rough-and-Tough Dudes (and Unusual Folks)
The New Yorker article was also controversial because it framed paleontologists as belonging to a narrow demographic (read: white men who love the outdoors). Not all of us in paleontology are men, not all of us are white, and not all of us came into geology loving the outdoors (see the great diversity of folks working in paleontology on our ‘Meet the Scientist’ blog). Paleontologists have had to work very hard to break through the stereotypical conception of what we do and who we are, and this article did not help to address the great diversity of scientists working in the field of paleontology.
In addition, the New Yorker article only quoted and interviewed other male scientists, many of whom have been working in the field for decades. The article left out the voices of women and early-career researchers who have made valuable contributions to the field of paleontology. For more on this, read the Slate article by science writer, Riley Black “It’s Time for the Heroic Male Paleontologist Trope to Go Extinct”.
This article also reinforces the “lone-wolf” stereotype of geologists and paleontologists-a man going out west, few to no other people around, and spending his days looking for paleontological treasure. This image is perpetuated through the article because the author chose to continually highlight the privacy and secrecy asked by the De Palma. While this is certainly an attitude held by some paleontologists, the reality is that the majority of us work in teams. Time Scavengers is run by a large team of people and so is our research! Like working in any field, we all have our strengths and better science happens when we invite people to work with us who have different strengths and can help us.
Lastly, the article frames paleontologists in a not-so-flattering light. In one paragraph, the article states “…I thought that he was likely exaggerating, or that he might even be crazy. (Paleontology has more than its share of unusual people).” Firstly, what does unusual even mean? The STEM (Science, Technology, Engineering, Maths) fields are full of intelligent, diverse, and colorful folks from all walks of life. To imply that any one branch of science has ‘its share of unusual people’ is unfair and regressive.
3. Dinosaurs as the Star of the Show
Paleontology is not just diverse in terms of the people who work in the field, but also in terms of the different types of life that we work with. For example, our Time Scavengers team, we have folks who work with fossil plankton and echinoderms. In fact, most paleontologists work with invertebrates- animals that do not have backbones, or any bones at all. Some of the most foundational findings in paleontology are based on the fossil record of invertebrates and early vertebrates. Regardless, most of the public’s fascination lies with dinosaurs (we understand, they were gigantic, ferocious, and unlike anything that’s alive today).
However, this fascination with dinosaurs can lead to over exaggeration of studies and sensationalizing, which is exactly what happened with this article. The published study of the Tanis site only mentions one dinosaur bone out of all the fossils found. The real story here is about the wonderful assortment of fish, tree, and flower fossils, some of which are completely new to paleontologists.
Dr. Steve Bursatte, Paleontologist at University of Edinburgh commented on both the New Yorker article and the PNAS article on his Twitter account, click here to read more. He comments on the broken embargo and how the New Yorker article sensationalized the ‘dinosaur’ side of the story.
4. Proper Handling of Museum-Quality Specimens
The article that was published in the New Yorker raised a lot of concerns within the paleontology community regarding the handling and storage of the fossils that were found at the Tanis site. It is clear from the article that DePalma had a bad experience early on with fossils that he had loaned a museum not being returned to him, however, by maintaining control over the management of his specimens, it undermines those people working in museums who have degrees and years of experience handling fossil and other specimen collections. Anyone who has borrowed specimens from a museum knows the immense amount of paperwork that goes in on all ends to make sure the specimens leave a well documented trail.
Jess Miller-Camp, Paleontology Collections Manager and Digitization Project Coordinator at Indiana University commented on the New Yorker article and addressed her concerns as a museum professional, click here to read her Twitter thread. She comments on the process of loaning specimens to and from museums and proper ettiqute. Read her thread to learn more about this and why museums should be asked to comment.
In 1997, a T. rex nicknamed Sue was sold at a Sotheby’s auction, to the Field Museum of Natural History, in Chicago, for more than $8.3 million.
This quote is misleading. No museum would have adequate funds to secure Sue. The California State University system, Walt Disney Parks and Resorts, McDonald’s, Ronald McDonald House Charities, and other individual donors aided in purchasing Sue for the Field Museum. The Field Museum rallied resources to ensure this valuable specimen remained in a public institution.
In addition to proper storage and archiving of fossils, one of the key tenets of any kind of scientific research is reproducibility– how well can other scientists replicate the results that you got. In paleontology, being able to look at the exact same fossils that another scientists looked at is a key part to reproducibility, as well as allowing the science of paleontology to advance. Whenever a paleontologist finds something they think is “new” to science, or is a really important find (special preservation, currently undocumented here, etc.) if you want to publish a paper on that fossil, the fossil needs to be placed in a public institution like a museum or a similarly accredited fossil repository. This way, future scientists are able to track down that fossil you published on and continue working on understanding it, or using it in other studies. Keeping fossils that are published on in museums is also critical because it ensures that that fossil has a safe place to be stored after being worked on and is less likely to be lost in an office or lab space!
5. Respecting the Land and Indigenous People
In the field of paleontology, people, who are more often than not white, venture into another country or a part of the ‘wilderness’ to find fossils and sites that are completely new and never-before-discovered or seen. These lands that contain fossils were owned by indigenous people long before Europeans arrived in North America, and were likely known about centuries before. Often, when sensational popular science paleontology articles are published, the authors leave out the voices of indigenous people and respect for their land. In the New Yorker article, there was no mention of the indigenous people that lived in the Dakotas, or how their ancestors perceived the dinosaur and fish fossils in the area. To frame amazing paleontological finds as being in desolate wastelands is harmful and erases the narratives of people who have lived in these lands for centuries.
For a more thorough discussion on this topic, click here to read the Twitter thread by Dr. Katherine Crocker.
Click here to read a article written by Dr. Roy Plotnick in Medium that also summarizes the issues and causes of commotion surrounding this astounding find.
Global environmental consequences of twenty-first-century ice-sheet melt
Nicholas R. Golledge, Elizabeth D. Keller, Natalya Gomez, Kaitlin A. Naughten, Jorge Bernales, Luke D. Trusel, and Tamsin L. Edwards Summarized by Megan Thompson-Munson
The problem: Global policymakers rely heavily on scientific studies to inform their decisions about climate-related policies. However, many climate change scenarios outlined in these studies’ models fail to address the ice-ocean-atmosphere feedbacks that may be triggered by ice sheet melting.
What data were used? To incorporate ice-ocean-atmosphere feedbacks in their estimation of climate consequences, the authors use climate models and data from 23 empirical studies. These data include measurements of the changes in total ice mass, surface mass balance, ice shelf melt, and iceberg calving of the Antarctic and Greenland ice sheets.
Total ice mass is simply the volume of ice that makes up the ice sheet. Measuring the change in mass over time tells us whether the ice sheet is shrinking or growing, and at what rate that mass is changing. Spoiler alert: the ice sheets are most definitely shrinking.
A component of the changes to total ice mass is surface mass balance. This concept describes the balance between net accumulation and net ablation occurring on the surface of the ice sheet. The key process in accumulation is snowfall, while ablation is the process of melting. Thus, we can determine surface mass balance by subtracting the amount of melting from the amount of snowfall.
Two other components of determining changes to total ice mass are ice shelf melt and iceberg calving (Figure 1). Ice shelves are areas of the ice sheet that extend off the continent and over ocean water. When they melt, they directly feed the ocean with freshwater that had previously been trapped in frozen form. Similarly, the process of icebergs calving (i.e. when ice chunks separate from a marine-terminating glacier) removes mass from the ice sheet and adds it to the ocean.
Methods: The authors input a series of different climate scenarios into a model that predicts the effects of climate warming and ice sheet melting on ice-ocean-atmosphere feedback loops (Figure 2). Their model varies the monthly and yearly climate conditions over a period from 1860 to 2100 to assess the effects of thinning ice sheets. Starting the model in the past means that they can compare the predictions of the model with actual data from the 23 supplementary studies that collectively span 1900 to 2017.
Results: The model scenarios paired with empirical climate studies come to three main conclusions concerning the future thinning of ice sheets. First, as the Greenland Ice Sheet loses mass, the increasing amount of fresh meltwater will slow circulation of the Atlantic Ocean. The Atlantic meridional overturning ocean circulation (AMOC) is driven by temperature and salt gradients. Thus, a large contribution of cold freshwater would alter the speed of AMOC. Second, as Antarctica continues to deliver meltwater to the ocean, warm water will be trapped below the ocean surface. This creates a positive feedback loop in which Antarctic ice loss will increase from meltwater input to the ocean. Finally, the model predicts that any future ice sheet melt with elevate global temperature variability and contribute an additional 25 centimeters (10 inches) to sea level by the year 2100.
Why is this study important? Our climate is warming, the ice sheets are melting, and the consequences of those changes are substantial. We study past climates to better understand our modern and future climates, and we heavily rely on model predictions to look toward the future. This paper address a key component missing from many climate models (the ice-ocean-atmosphere feedbacks that may result from future ice sheet melting) and shows that some models have underestimated the severity of ice sheet melting consequences. Model predictions are critical tools in global policymaking, so ensuring that those models are comprehensive is essential. Moreover, this paper calls for continued observations of the effects of climate change on ice sheets, oceans, and the atmosphere. Further incorporation of data into models will only help improve their predictions of a future climate that demands new environmental policies.
Citation: Golledge, N.R., Keller, E.D., Gomez, N., Naughten, K.A., Bernales, J., Trusel, L.D., and Edwards, T.L., 2019, Global environmental consequences of twenty-first-century ice-sheet melt: Nature, p. 65-72, https://doi.org/10.1038/s41586-019-0889-9.
Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene
Richard Levy, David Harwood, Fabio Florindo, Francesca Sangiorgi, Robert Tripati, Hilmar von Eynatten, Edward Gasson, Gerhard Kuhn, Aradhna Tripati, Robert DeConto, Christopher Fielding, Brad Field, Nicholas Golledge, Robert McKay, Timothy Naish, Matthew Olney, David Pollard, Stefan Schouten, Franco Talarico, Sophie Warny, Veronica Willmott, Gary Acton, Kurt Panter, Timothy Paulsen, Marco Taviani, and SMS Science Team
The Problem: The early to mid-Miocene (23 to 14 million years ago) is an interval of geologic time where atmospheric carbon dioxide (CO2) concentrations (about 280 to 500 parts per million) were similar to those that are projected for the coming decades under human-induced climate change. Thus, this interval of time is interesting for geologists because we can use the geologic record from this time to interpret how our oceans, atmosphere, and ice sheets ‘behave’ under warming scenarios. Understanding the extent to which the Earth will warm, weather patterns will change, and sea levels will rise in the coming decades can help scientists, the public, and policy makers prepare for our future. Related to sea level rises is understanding how much continental ice sheets, such as those on Greenland and Antarctica, will melt.
In this study, geologists use several methods to determine how sensitive Antarctic ice sheets are to increases in atmospheric CO2 concentrations 23 to 14 million years ago. The results from this study are useful in that we can determine how much Antarctic ice may melt in the coming decades, which would add to sea level rise.
Methods: To interpret how sensitive Antarctic ice is to atmospheric warming (or increased average global warming), the scientists use sediments obtained in a drilled core from the coastal margin of Antarctica (an ideal location to study the melting and growth of ice sheets). The core was drilled in 2006 and 2007 as part of the ANDRILL (ANtarctic DRILLing Project) scientific drilling project from the McMurdo sector of Antarctica. The core is approximately 1,138 meters long, and contain sediments that are dated at over 20 million years old!
This study is very unique and fun because the scientists use several proxies (or naturally-occurring records) to interpret what the margin of Antarctica looked like through time. The presence and abundance (or numbers) of plankton (such as foraminifera) and pollen grains indicate when the margin of Antarctica was warmer, and ice sheets had melted back. For example, when the ice around Antarctica melted back, this allowed more room and soil for plants to grow. The lithology, or general characteristics of the sediments and rocks collected in the ANDRILL core, was also used as a clue to the changing environment of Antarctica through the study interval. Just knowing the different sediment types through time is a very powerful proxy itself!
Results: Using all the different methods and proxies, the geologists were able to interpret how Antarctic ice sheets melted and re-grew through the Miocene interval. They determined that several times from 23 to 14 million years ago, ice grew and retreated inland. They found that Antarctic ice becomes very sensitive to small changes in the amount of carbon dioxide in the atmosphere.
To best illustrate their findings, the authors of this study created four ‘environmental motifs’. These are images of what the scientists think the Antarctic margin looked like through time. Note that there are only four motifs; these just capture the major environments that the scientists inferred from their data. There were likely other ‘in-between’ environments. But notice how dynamic the ice sheet around the Antarctic margin were: the ice melted and then re-grew quite a bit in response to warming and cooling events through the Miocene!
Why is this study important? This study highlights and solidifies the hypothesis that Antarctic ice sheets were very sensitive to changes in atmospheric carbon dioxide concentrations during the Miocene. The findings of the study also indicate that Antarctic ice will behave similarly under increased warming predicted for Earth’s future. Melting ice will have a huge impact on sea level, which will make living on coastal lands hard or impossible due to flooding.
Citation: Levy, R. H., Harwood, D., Florindo, F., Sangiorgio, F., Tripati, R., von Eynatten, H., Gasson, E., Kuhn, G., Tripati, A., DeConto, R., Fielding, C., Field, B., Golledge, N., McKay, R.,, Naish, T., Olney, M., Pollard, D., Schouten, S., Talarico, F., Warny, S., Willmott, V., Acton, G., Panter, K., Paulsen, T., Taviani, M., and the SMS Science Team, 2016. Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene. PNAS 113(13), 3453-3458. doi: 10.1073/pnas.1516030113.
A re-interpretation of the ambulacral system of Eumorphocystis (Blastozoa, Echinodermata) and its bearing on the evolution of early crinoids
by: Sarah L. Sheffield and Colin D. Sumrall Summarized by Sarah Sheffield
What data were used? New echinoderm fossils found in Oklahoma, USA, along with other fossil species of echinoderms. The new fossils had unusual features preserved.
Methods: This study used an evolutionary (phylogenetic) analysis of a range of echinoderm species, to determine evolutionary relationships of large groups of echinoderms.
Results:Eumorphocystis is a fossil echinoderm (the group that contains sea stars) that belongs to the Blastozoa group within Echinodermata. However, it has unusual features that make it unlike any other known blastozoan: it has arms that extend off of the body, which is something we see in another group of echinoderms, called crinoids. Further, these arms have a very similar type of arrangement to the crinoids: the arms have three distinct pieces to them (see figure). Researchers placed data concerning the features of these arms, and the rest of the fossils’ features, into computer programs and determined likely evolutionary relationships from the data. The results indicate that Eumorphocystis is closely related to crinoids and could indicate that crinoids share common ancestry with blastozoans.
Why is this study important? This study indicates that our understanding of the big relationships within Echinodermata need to be revised. Without an accurate understanding of these evolutionary relationships, we can’t begin to understand how these organisms actually changed through time-what patterns they showed moving across the world, how these organisms responded to climate change through time, or even why these organisms eventually went extinct.
The big picture: This study shows that crinoids could actually belong within Blastozoa, which could change a lot of what we currently understand about the echinoderm tree of life. Overall, this study could help us understand how different body plan evolved in Echinodermata and how these large groups within Echinodermata are actually related to one another. Data from this study can be used in the future to start to understand evolutionary trends in echinoderms.
Citation: Sheffield, S.L., Sumrall, C.D., 2018, A re-interpretation of the ambulacral system of Eumorphocystis (Blastozoa, Echinodermata) and its bearing on the evolution of early crinoids: Palaeontology, p. 1-11. https://doi.org/10.1111/pala.12396
To read more about Diploporitans please click here to read a recent post by Sarah on Palaeontology[online].
Minimal East Antarctic Ice Sheet retreat onto land during the past eight million years
Jeremy D. Shakun, Lee B. Corbett, Paul R. Bierman, Kristen Underwood, Donna M. Rizzo, Susan R. Zimmerman, Mark W. Caffee, Tim Naish, Nicholas R. Golledge, & Carling C. Hay
The problem: There has been debate among scientists if the East Antarctic Ice Sheet melted substantially during the Pliocene (~5.3-2.6 million years ago) and Miocene (23-5.3 million years ago) when the amount of carbon dioxide in the atmosphere was higher (and thus the global average temperatures were much warmer). Some scientists think that as the Earth was warmer during this time, the ice melted back substantially, thus exposing some land surface on East Antarctica. Other scientists think this is not possible based on other lines of evidence. This study set out to investigate whether or not the ice sheet melted back and exposed land by measuring the amount of cosmogenic nuclides, Beryllium 10 and Aluminum 26 (written as 10Be and 26Al). Both 10Be and 26Al occur in rocks that have been exposed to the sun (to read more about cosmogenic nuclides, click here).
Methods: First, the researchers of the study needed to obtain rocks and sediment that was underneath East Antarctica. Lucky for them, there was already drilled cores from this area! In 2006-2007, a team of scientists went to Antarctica for the purpose of recovering sediment cores from beneath the East Antarctic Ice Sheet. The team ended up with two cores that were more than 1,200 meters (0.75 miles) in length. The project was called ANDRILL, and you can read more about it here. The cores are stored in a special facility, and any scientist that wants material (rocks and sediment) from the cores can request it.
Once the scientists in this study had the sediment and rocks, they cleaned the rocks of the very fine sediment until they had a good amount of rocks, which were mostly quartz. They then used a certain method to extract and measure the amounts of 10Be and 26Al in the rocks. The idea is that with long-term exposure to sunlight, the rocks would contain high amounts of 10Be and 26Al. This would indicate that at the time the rocks were deposited millions of years ago, the ice on East Antarctica would have to be melted away, and the land surface exposed.
Results: The scientists found little, if any, of 10Be and 26Al in their samples. This indicates that the rocks were not exposed to sunlight, and thus the glacier that covers East Antarctica did not melt back and expose the land surface millions of years ago.
Why is this study important? This study used a novel approach and really cool method to investigate a problem that scientists didn’t agree upon. It also indicates, to some degree, how much the glacier on East Antarctica melted during interglacial (warm periods within an ice age) times over the last millions of years.
Citation: Shakun, J. D., Corbett, L. B., Bierman, P. R., Underwood, K., Rizzo, D. M., Zimmerman, S. R., Caffee, M. W., Naish, T., Golledge, N. R., Hay, C. C. 2018. Minimal East Antarctic Ice Sheet retreat onto land during the past eight million years. Nature. doi:10.1038/s41586-018-0155-6
Unique pelvic fin in a tetrapod-like fossil fish, and the evolution of limb patterning
Jonathan E. Jeffery, Glenn W. Storrs, Timothy Holland, Clifford J. Tabin, and Per E. Ahlberg Summarized by Jen Bauer
What data were used? The data were primarily gained from a single fossil specimen (with both pelvic fins) from the Museum of Comparative Zoology (MCZ) at Harvard University. But several have been described and are stored at the MCZ.
Methods: First the specimen had to be carefully prepared as the bones are still embedded in matrix. Any broken pieces of the fossil were glued back together. The fossils were imaged using a micro computed tomography (CT) scanner, which takes many fine images through the specimen using X-rays. The images can then be compiled and reconstructed in more complex 3D rendering programs. In this study, the authors used Avizo. The fossil specimens (real and digital) were examined thoroughly. These authors used the data collected from their thorough examinations and used it to explore developmental and evolutionary questions.
Results: The new data shows the general tetrapod pattern of a humerus (arm bone that connects to your shoulder) connecting with the forearm bones. In a phylogenetic, or evolutionary, context this provides additional information in the transition from fin limbs to tetrapod (animals with four legs) limbs we can easily recognize today – these are represented in the diagrams above the tree. The developmental comparisons of modern skeletons and allows the researchers to compare modern animal growth to these extinct forms. It is still unclear how the three bones came from the one (refer to the tree figure). The researchers ruled out a known protein can cause duplications of bones because each of these three bones is distinct, rather than having two of the same bone repeated.
Why is this study important? The three forearm bones in these pelvic limbs was an unexpected result from this study. It is quite different, even from the upper limbs in the same specimen and starkly different from other early finned fish. This study provides new evidence on the transition from fin to true limb. This specimen suggests that the fore-fins suggests that the mechanism of transition from fin to limb happens first in the fore-fins and later in the hind-fins.
The big picture: The fish to tetrapod transition has been well studied and is very important to understanding the evolution of most of terrestrial life. It is really difficult to find these specimens because they only preserve in very specific environments. This specimen is particularly important because it provides some new information that could help scientists reinterpret previously confusing results when the fore-fin/limb looks quite different from the hind-fin/limb in these more transitional forms.
Citation: Jeffery, J.E., Storrs, G.W., Holland, T., Tabin, C.J., and Ahlberg, P.E. 2018. Unique pelvic fin in a tetrapod-like fossil fish, and the evolution of limb patterning. PNAS, doi: 10.1073/pnas.1810845115
Climate change and coffee: assessing vulnerability by modeling future climate suitability in the Caribbean island of Puerto Rico
Stephen J. Fain, Maya Quiñones, Nora L. Álvarez-Berríos, Isabel K. Parés-Ramos, William A. Gould
What data were used?
This study investigated the effects of climate change on coffee production in Puerto Rico. Although coffee is grown in several countries around the world, by 1899 the country was the sixth largest producer of coffee, with over 40% of its cultivated area dedicated to coffee production. Coffee was grown in great numbers into the 1990’s, when harvests were more than 12 million kilograms per year. Coffee plants are mostly grown in mountainous regions on land that is owned by independent farmers. Two species of coffee, Coffea arabica and Coffea canephora, are plants that are shade-loving and thrive within a narrow range of climatic conditions. In other words, the plants cannot tolerate huge changes in temperature, moisture, and precipitation. Increased temperature has caused the plants to decrease quality, have stunted growth, and exhibit growth abnormalities. With reduced crops and quality, Puerto Rican farmers will have reduced yields, reduced income, and thus will not be able to hold as many employees to care for the plants and pick the coffee beans.
The authors of this study wanted to investigate how these two species of coffee plants will fair under climate change scenarios projected for the future. The scientists first gathered data about what temperature, moisture content, and precipitation amounts were favorable for the coffee plants. Then, the authors used a climate model with three different emissions scenarios (amount of CO2 that is projected to be released into the atmosphere in the future): A2 Scenario, which is the highest emissions scenario; A1B Scenario, which is the mid to low emissions model; and the B1 Scenario, which is the lowest CO2 emissions scenario. They modeled how climatic variables (such as temperature and precipitation) will change over time under these three emissions scenarios for five time periods: 1960-1990; 2011-2040; 2041-2070; and 2071-2099.
The authors came up with an index to for each time period to assess how well coffee will fare under climate change. The index ranged from 0 to 5, with 0 being unfavorable conditions, and 5 indicating favorable coffee growth conditions.
The model for 1991-2010 was used as a baseline for which to compare the other four models to. In this model, the amount of land that is most suitable for coffee growth (suitability index of 5) is confined to the mountainous regions of Puerto Rico.
Other models for future years under the high, mid-low, and low CO2 emissions scenarios all indicate that as climate change induces increased warming over Puerto Rico, less and less land will be suitable for coffee growth.
Under the high emissions scenario (A2), the top ten coffee-producing areas in Puerto Rico are expected to lose 47% of their high-quality coffee producing range by 2040! Under the low emissions scenario (B1), this loss is reduced to 21% by 2040. After the year 2040 in both scenarios, the amount of land that will be lost for coffee production greatly increases. Under the low emissions scenario (B1), the island’s top ten producing municipalities may face a 60% decline in prime coffee-growing habitat. Under the high-emissions scenario, this number increases to 84%.
In the A2 (high emissions) scenario, the island only retains 289 km2 of highly suitable growth space (index of 5 in figures) from 2041-2070, which declines to only 24 km2 by 2071-2099! For comparison, under the low emissions (B1) scenario, Puerto Rico retains 680 km2 of highly sustainable coffee growth space by 2041, which is reduced to an area of 329 km2 by 2071-2099.
Why is this study important?
As less land is available to grow high-quality coffee, the island of Puerto Rico will lose money from reduced exports. In effect, the people of the island who rely on the coffee industry will suffer financially, as the growth of the plants provides thousands of residents with income and financial stability. This study highlights just one way in which climate change will negatively affect a country’s economy and people.
The big picture
Climate change will lead to increased warming in tropical and sub-tropical areas, such as Puerto Rico. With increased warming comes a change in climate and weather regimes, most of which will have a negative impact on the region and the people who live there.
Fain, S. J., Quiñones, M., Álvarez-Berríos, N. L., Parés-Ramos, I. K., and Gould, W. A., 2018. Climate change and coffee: Assessing vulnerability by modeling future climate suitability in the Caribbean island of Puerto Rico. Climatic Change 146, 175-186.