Ordovician paleontology in Australia and its global significance

Ordovician strata in the Cliefden Caves area, New South Wales: a case study in the preservation of a globally significant paleontological site

By I. G. Percival, B. D. Webby, and H. D. T. Burkitt

Summarized by Joseph Stump. Joseph Stump is an undergraduate geology major at the University of South Florida. After graduating high school in Sebring, Florida in 2004, Joseph was unsure about which career he wanted to pursue, making college difficult without an end goal to strive towards. In 2006 he enlisted in the United States Army as an airborne Satellite Communications Operator and Maintainer. Staff Sergeant Stump received an honorable discharge from the Army in 2016 and has been using the Post 9/11 GI Bill to earn his degree since then. Thus far, he has completed an Associates in Arts in Engineering from Hillsborough Community College and is currently in his final year of obtaining his B.S. in Geology, with a minor in Geographical Information System Technology. Joseph is set to graduate in Summer 2020. Upon graduation, he would like to pursue a career studying/monitoring/managing Florida’s water resources and coastal habitats.

Methods: The article utilized data gathered from at least 60 published scientific papers and nearly 300 species of fossils (including calcisponge stromatoporoids, sponges, corals, trilobites, nautiloids, conodonts, brachiopods, radiolarians, and cyanobacteria (‘algae’)) within the Cliefden Caves area of New South Wales, Australia, with several of these being endemic (localized) to this area, to support its significance for preservation of global significance. The main threat to this area, and the need for the preservation, is the proposed construction of a dam, which would result in the flooding and destruction of valuable scientific lands and the fossils within it. 

Results: The fossils contained within the rocks of this area include the world’s oldest known brachiopod shell beds. Brachiopod shells are excellent zone fossils, meaning they can help reconstruct the environment by the shape of their shells. Brachiopods are generally zoned by sediment grain size relationships of their shell shapes; meaning, certain species of brachiopods seem to correlate with different sizes of grains (i.e., different environments). Also present are the earliest indisputable rugose corals found anywhere on Earth, an extinct type of coral. If the proposed dam construction is approved in this area, one of the most diverse deep-water sponge faunas ever recorded is in jeopardy of being destroyed and lost from the fossil record forever. The authors of this article all agree that, despite the significant research already done on the area by scientists, there is more to be discovered in the area that holds truths to the history of life on Earth.

A Belubula shell bed from Cliefden Caves; this specific type only occurs in this locality, so far as scientists know. These brachiopods are preserved mostly articulated (both shells together) and in situ (in place where they originally lived on the sediment). Scale bar is a Australian 50 cent coin (32mm diameter)

Why is this study important? This area is important to study due to its ability to better understand the Earth’s geologic and paleontological history. During the Ordovician, the oldest complete vertebrate fossils can be found, and this is where plant life began to migrate onto land, with animals soon to follow. It is also important to understand the climate of Earth during this time frame, as it exploded with diversity (i.e., the Ordovician Radiation), but it ended with what some consider the second largest extinction in Earth’s biological record. Some argue that this extinction was not ecologically major; however, the best way to understand these events and uncover the facts is to study the geologic and paleontological evidence left behind (where available). The issue with studying the geology/paleontology of the Ordovician is the lack of availability of fossil evidence relative to other periods. The end of the Ordovician is marked by glaciation. When a glaciation occurs, oceanic water regresses (moves away from land) and when the glaciers melt, the ocean transgresses (moves towards land). The problem is that these dynamic ocean conditions causes major erosion of any sediments/fossils deposited and often deletes them from the geologic record as an unconformity (“missing time” in a sample of sediments). The flooding that will result from constructing a dam in the region will have the same history erasing effects on the paleo environment as the ancient sea-level changes.

The Big Picture: Human population growth requires a higher demand on water and electricity; however, the current plans of placing a dam in the Cliefden Caves area of New South Wales will have significant negative impacts on the availability of current geologic and paleontological important rocks. A universal fact of life is that if history is not learned from, it is doomed to be repeated. Current global conditions are trending towards a climate that is uninhabitable by the human species. The significance of understanding these events is that measures could possibly be put into effect to mitigate or prevent global cataclysm of anthropogenic causation. Although geological and paleontological research does not often go synonymous with saving lives, the discoveries from their research can potentially impact the longevity of our species and others’.

Citation: Percival, I.G., Webby, B.D., and Burkitt, H. D. T. “Ordovician strata in the Cliefden Caves area, New South Wales: a case study in the preservation of a globally significant paleontological site.” Australian Journal of Earth Sciences, 2019. https://doi.org/10.1080/08120099.2019.1574271

 

Will NASA’s Dragonfly Mission Encounter Dust Devils on Titan?

Dust Devils on Titan

Brian Jackson, Ralph D. Lorenz, Jason W. Barnes, and Michelle Szurgot

Summarized by Lisette Melendez

What data were used? In 2019, NASA announced a brand-new mission: Dragonfly. The objective? To visit Titan, the largest moon of Saturn and the only place in our universe (besides Earth) where distinct evidence of surface liquid has been discovered. Titan’s environment is very similar to that of very early Earth, with a nitrogen-rich atmosphere and volcanic activity. By studying Titan’s chemistry, scientists can discover more about the origin of life itself. It’s a very exciting mission, but it’s important for scientists to prepare for all the different obstacles the rotorcraft will encounter on Titan’s surface, including hazardous weather phenomena like dust devils.

An illustration of NASA’s Dragonfly rotorcraft-lander approaching the dunes on Saturn’s exotic moon: Titan. Credits: NASA/JHU-APL

We’ve learned more about weather patterns on Titan through NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017. This study focuses on how dust storms are identified on other celestial bodies and what implications they hold for the Dragonfly mission. Cassini identified three regional dust storms within the equator near the “Shangri-La” dune fields that were chosen as Dragonfly’s landing spot. The study of these dust storms in Titan’s unique environment (with clouds and rain of methane!) can help us learn more about how they operate and life dust in the first place. This study also draws from observations by the Huygens probe for information on Titan’s temperatures and atmosphere.

Methods: In order to determine the weather conditions necessary for a dust storm on Titan, scientists need data on various atmospheric circumstances, such as temperature, elevation, and pressure. By analyzing the images and observations collected by Cassini and Huygens and combining these findings with data collected by observing dust devils here on Earth, scientists were able to model the surface conditions that were suitable for dust devil formation as well as the size of these storms. The study focused on dust devils on the equator because that’s where we have the most data available about Titan’s weather conditions.

An illustration of the Cassini-Huygens space-research mission, which was a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ISA) to study Saturn and its many moons. Credit: NASA/JPL

Results: Many of the atmosphere conditions identified on Titan are favorable for the formation of dust devils. On Earth, dust devils are generally hindered by the presence of liquid because the increased particle cohesion (i.e., how sticky the particles are to one another) prevents wind from being able to lift the dust particles. Observations show that the equator of Titan is very arid and dry, with methane downpours only occurring in areas once every 10 Earth years. By looking at surface humidity levels measured by Huygens, it shows that the surface is too dry for even cloud formation. The abundance of dunes and dust storms provides further evidence that Titan has the ideal environment for dust devils.

An image of a dust devil in Kansas. Credit: The Thunderbolts Project

However, there are some surface conditions on Titan that may reduce the occurrence of dust devils, including the possibility of insufficient wind speeds. Additional work is required to model typical speeds on Titan’s surface.

Why is this study important? This study is important because it helps predict the occurrence of dust devils on Titan when Dragonfly is scheduled to arrive in 2034. This study outlines what remains unknown about the formation of dust devils and how Dragonfly presents the opportunity to study wind-related phenomena in a novel environment.

The big picture: After analyzing the environment on the surface of Titan based on the data currently available, it is concluded that the dust devils will most likely not pose a threat to the Dragonfly rovercraft (since they are too slow in the given conditions). Nevertheless, the mission can provide crucial insight to the creation of dust devils and how frequently they occur on other celestial bodies. Dragonfly provides us the opportunity to learn so much more about extraterrestrial worlds, and we’re all very excited for its departure!

Citation: Jackson, B., Lorenz, R. D., Barnes, J.W., & Szurgot, M. (2020). Dust devils on Titan. Journal of Geophysical Research: Planets, 125, e2019JE006238. https://doi.org/10.1029/2019JE006238

Climate Change and Encephalitis

The potential impact of climate change on the transmission risk of tick-borne encephalitis in Hungary

Kyeongah Nah, Ákos Bede-Fazekas, Attila János Trájer, and Jianhong Wu

Summarized by Kailey McCain

What data were used? The data collected for this study includes the monthly average temperature values in Hungary from the years 1961-1990. Specifically, for the past climate data,researchers used the CarpatClim-Hu database. For future climate predictions, the researchers used two distinct climate models: ALADIN-Climate 4.5 and RegCM 3.1. Additionally, previously established models for Tick-borne Encephalitis virus (i.e., a human viral infectious disease) transmission was used. Models help us hypothesize how different scenarios will look, by allowing us to input a lot of different types of data to understand large future patterns, like the one in this article! 

Methodology: By using the previous climate data for the years 1961-1990, the researchers established a predictive warming model for the years 2021-2050 and 2071-2100 in Hungary. This data was then compared to the tick-borne encephalitis virus (TBEV) transmission model to establish correlations between the data sets. This model broke down the transmission into various factors: reproduction numbers, duration of infestation, and density. The dynamics of transmission can be visualized in figure 1.

Figure 1: This figure shows an extensive diagram of how an infected tick spreads the disease to humans, livestock, and other animals. The inner circle represents the stages from larva, to nymph, to mature tick; then it branches to external transmission.

Results: The predictive climate model showed a steady increase in temperature for the age ranges 2021-2050 and 2071-2100, and the TBEV model resulted in an increase in tick population and transmission. These increases can be positively correlated (linked) to warming climate because previous data shows that a higher temperature speeds up the rate of sexual maturity in ticks; meaning, this allows the tick to reproduce at an increased rate. Moreover, research has shown that a warming climate leads to the elongation of tick questing season; which increases the chance for transmission. When a tick is questing (shown in figure 2), it is strategically placed on vegetation in order to grab a hold of by passers. 

Figure 2: This image represents a questing tick sitting on the edge of a lead with their legs spread out, and ready for attachment.

Why is this study important? This study is important because it shows the dynamic effects climate change has on global health. It also conveys an important message that the prevention of climate change is not only a biological and geological problem, but a public health problem, too. This means that solutions for reducing the impacts of climate change have to be creative and have to be from a lot of different types of researchers! 

The big picture: This study helps us understand the ways in which infectious diseases, (e.g., Tick-Borne Encephalitis Virus) are affected by climate change. As well as giving a glimpse into the future of what disease transmission will look like if prevention protocols are not put in place.

Citation: Kyeongah Nah, Ákos Bede-Fazekas, Attila János Trájer, & Jianhong Wu. (2020). The potential impact of climate change on the transmission risk of tick-borne encephalitis in Hungary. BMC Infectious Diseases, 20(1), 1–10. https://doi.org/10.1186/s12879-019-4734-4

The projected timing of abrupt ecological disruption from climate change

The projected timing of abrupt ecological disruption from climate change

Christopher H. Trisos, Cory Merow & Alex L. Pigot

Summarized by Shaina Sadai

What data were used? The data used is a combination of climate model output and ecological data for 30,652 marine and terrestrial species. For each species they determine the climate conditions and spatial extents that a species is known to have existed in throughout history. The climate model output that was used were temperature and precipitation data from 22 different models and 3 emissions scenarios (RCP2.6, 4.5, 8.5).

Methods: The authors created species assemblages contained in 100km^2 grid cells. Using these they generated ‘horizon profiles’ which give the percentage species within each assemblage that would experience climate conditions exceeding those of their historic limits at a given time. They cross referenced when each species would be living for more than 5 years straight in an area where the temperature exceeded the maximum temperature they have been known to exist at through their history in order to quantify when a species crossed their ecological limit. By repeating this method across the planet they were able to construct horizon profiles at many locations, including sensitive ecosystems such as the Amazon Basin and Gobi Desert.

Results: One of the most striking results is how abrupt impacts to biodiversity could be. The profiles show that an average of over 70% of species in a given assemblage were exposed to conditions exceeding their limits within a single decade, regardless of climate model of emissions scenario. This was in part due to the species within a region evolving for similar temperature ranges. The abruptness of when ecological limits were breached was even higher for marine ecosystems than terrestrial ones. Tropical species are particularly vulnerable to having a higher percentage of species exposed to dangerous temperatures by the end of the century because they already exist in places where they are close to their temperature limits. Polar species were also highly vulnerable due to the rapid rate of changes occurring in these regions.

Under higher emissions scenarios (RCP8.5) temperature thresholds are exceeded sooner with some occurring even before 2030. The most vulnerable regions were the Amazon, Indian subcontinent, and Indo-Pacific regions where by 2100 over 90% of species in any assemblage were exposed to temperatures over their limits. In contrast the low emissions scenario (RCP2.6) delays the point at which vulnerable species are at risk by 60 years. If warming by the end of the century is kept below 2C only 2% of species assemblages will be exposed to abrupt exposure events.

Why is this study important? This study was able to use a combination of data on species’ ecological limits and climate model data to give a robust picture of when and where species assemblages may cross safe limits. It shows the potential for abrupt loss, particularly of biodiverse ecosystems, and can help inform policy efforts and future research needed to assess risk.  If emissions are decreased and the rate of temperature increase is slower it gives species more time to adapt.

The big picture: We must prepare for significant impacts to ecosystems and biodiversity under a changing climate, and take steps to prevent serious ecological harm. Yet again we see that early mitigation is crucial to mitigate harm.

Citation:
Trisos, C.H., Merow, C. & Pigot, A.L. The projected timing of abrupt ecological disruption from climate change. Nature 580, 496–501 (2020). https://doi.org/10.1038/s41586-020-2189-9

How Eurypterids of the Finger Lakes, New York Lived and Died

Paleoecology and Taphonomy of Some Eurypterid-bearing Horizons in the Finger Lakes Region of New York State

Stephen M. Mayer

This news article was summarized by Alexander Favaro. Alexander Favaro is a first-generation student attending the University of South Florida, pursuing a B.S. in Geology. He hopes to follow his passion of being a paleobiologist. His interests have been broadly focused on paleoecology and understanding evolutionary trends. 

What data were used? The study used well-preserved fossils from the upper Silurian Fiddlers Green Formation in New York, the Lower Devonian Olney Member in Finger Lakes New York, Split Rock Quarry near Syracuse New York, and the Samuel J. Ciurca Eurypterid Collection at Yale Peabody Museum of Natural History. These data were used to make interpretations of eurypterid lifestyles and processes of fossilization. 

Methods: Sedimentological variables and the body and trace fossils found within a rock unit were used to interpret the depositional environment (what type of environment the rocks were formed in) of a formation. Field collection was done at the Phelps Member and Cayuga Junction (which are located in the Fiddlers Green Formation), as well as Split Rock Quarry in Syracuse, New York. The Yale Peabody Museum of Natural History was used to supplement eurypterid data through their collection. The position in which each eurypterid was found, as well as their size, was used to describe their age, ecology, and how they likely died.

Figure 1. Eurypterus remipes, which shows the U-shaped body posture. The metasoma (last 7-12 segments of the eurypterid) and telson (spine like protrusion at the end of the abdomen on the right of this image) were twisted 1260 in relation to the prosoma (head section) and mesosoma (first 1-6 segments of the eurypterid). This specimen was found in the Phelps Member, New York.

Results: Many eurypterid exuviae (shed exoskeleton) were found, while eurypterid bodies were less abundant. The most common eurypterid fossils found in Phelps were Eurypterus remipes. Cayuga Junction also possessed Eurypterus remipes but were far less common. At Split Rock Quarry, Erieopterus microphthalmus were found in localized calcareous (chalky limestone) bands. 

 The study found that between 61 carapaces, the average size of eurypterids in the Phelps Member fell between 15-25mm. The variations in size indicated that immature species and adults were living amongst each other. 

Since eurypterids were chelicerate arthropods (like arachnids, sea spiders, and horseshoe crabs), scientists have suggested that eurypterids would undergo a group spawning and then molt (shed their exoskeleton) together (similarly to a horseshoe crab). This would explain the high number of shed exuviae and variable size ranges found in the formations.

Fossil evidence indicated that eurypterid corpses were highly affected by currents, which would cause a variety of contortions in a carcass. The observed eurypterid corpse conditions were categorized as: a non-contorted corpse, an angular contortion up to 900, a U-shaped flexure of the body and tail (as seen in Figure 1), and a contortion where the body and tail flipped above or below the head (though this was rare). Aside from flexure of the body, some contortions were caused by sediment that anchored a section of the eurypterid while the un-covered portions moved freely due to current movement. Eurypterus remipes and Erieopterus microphthalmus both displayed similar contortions and so they were able to determine that the contortion patterns weren’t exclusive to one genus of eurypterid. 

Why is this study important? The study gave insight into the life and death of a once thriving taxon that has close relatives still alive today in the form of arachnids, sea spiders, and horseshoe crabs. Fossil evidence at Phelps suggested that eurypterids may have mass-molted, similarly to horseshoe crabs. The paleoecological evidence found gave a key insight into a behavior which has also been observed in modern, related organisms.

The big picture: The analysis performed on both trace fossils and carcasses gave both paleoecological and taphonomic (how an organism is fossilized after death) insight. Combined, taphonomy and paleoecology provides a more refined idea of how ancient organisms lived, died, and how their bodies would have been fossilized. 

Citation: Mayer, S. M. Paleoecology and Taphonomy of Some Eurypterid-Bearing Horizons in the Finger Lakes Region of New York State.

How Climate Change in Serbia is Impacting the Rate of Cancer and Infectious Diseases

Assessment of climate change impact on the malaria vector Anopheles hyrcanus, West Nile disease, and incidence of melanoma in the Vojvodina Province (Serbia) using data from a regional climate model 

By: Dragutin T. Mihailović, Dusan Petrić, Tamas Petrović, Ivana Hrnjaković- Cvjetković, Vladimir Djurdjevic, Emilija Nikolić-Đoric, Ilija Arsenić, Mina PetrićID, Gordan Mimić, Aleksandra Ignjatović-Cupina 

Summarized by: Kailey McCain

What data were used? Researchers assessed climate change and UV radiation (UVR) and compared it to data collected over ten years from mosquito field collections at over 166 sites across Serbia. Additionally, public health records for the circulation of vector-borne disease (I.e., illnesses spread by mosquitoes and ticks), specifically the West Nile Virus, and the incidence of melanoma (i.e., a serious form of skin cancer) were collected and compared.

Methods: The climate change and UVR doses were collected by using EBU-POM model (a type of regional climate model) for the time periods: 1961-2000 and 2001-2030. As for the collection of the mosquito data, two different dry-ice baited traps (dry-ice is a solid form of carbon dioxide, which is a natural attractive substance for mosquitos) were used. The various sites were chosen by entomologists (i.e., scientists who study insects) to obtain a diverse data set. The mosquitoes collected were then anesthetised, separated by location, species, sex, and then tested for a specific RNA (I.e., a single stranded molecule) strand that would indicate the mosquito was carrying the West Nile Virus.

Furthermore, the researchers measured the rate of melanoma incidences in Serbia by using two different indicators: new number of cases versus time and number of new cases versus population size. The defined time period for data collection was 10 years (1995-2004). With this data, the researchers compared the rate of incidence to the climate data previously collected.

Fig 1: This diagram shows the linear trend in annual temperature fluctuations throughout Serbia from the time period 1990-2030; as well as depicts the mosquito prevalence found at the various collection sites.

Results: From the data collected via the regional climate model, a linear upwards trend in temperature in Serbia was recorded. The prevalence of mosquitoes was also found to increase linearly throughout the time period. The culmination of these results can be seen in figure 1.

As for the melanoma data, the researchers found a linear increase in UVR doses for the time period. This data was found to be correlated to an increase in melanoma incidences throughout Serbia and this data can be visualized in figure 2.

Why is this study important? Disease prevalence and distribution have always been difficult to predict due to the varying ecological factors that play important roles. Research like this is especially important because it allows scientists to simulate future spreads of vector-borne diseases within European countries. This can eventually lead to the development of public health surveillance technology and overall prevention.

Fig 2: Diagram (a) depicts the increased temperature rates throughout Serbia, and diagram (b) depicts the UV radiation doses on the various provinces throughout Serbia. Diagram (c) shows the linear relationship of UV doses versus the time period 1990-2030. The data shows a clear increase in “hot days” (HD) and “warm days” (WD) through time. Diagram (d) shows a linear relationship between UVR dose versus melanoma incidence rate from 1995-2004.

The big picture: This study aimed to correlate changes in temperature and UV radiation to the spread of diseases and cancer. With vector-borne diseases being the most sensitive to ecological conditions, researchers chose the West Nile Virus to act as a proxy to all mosquito transmitted diseases. As expected, the data supports the claim that increased temperatures trigger an enhanced risk for not only infectious diseases, but certain cancers as well.

Citation: Mihailović, D. T., Petrić, D., Petrović, T., Hrnjaković-Cvjetković, I., Djurdjevic, V., Nikolić-Đorić, E., Arsenić, I., Petrić, M., Mimić, G., & Ignjatović-Ćupina, A. (2020). Assessment of climate change impact on the malaria vector Anopheles hyrcanus, West Nile disease, and incidence of melanoma in the Vojvodina Province (Serbia) using data from a regional climate model. PLoS ONE, 15(1), 1–17. https://doi.org/10.1371/journal.pone.0227679

How coastal wetlands can help reduce property damage from storm surge and sea level rise

Valuing natural habitats for enhancing coastal resilience: Wetlands reduce property damage from storm surge and sea level rise

by: Ali Mohammad Rezaie, Jarrod Loerzel, Celso M. Ferreira

Summarized by: Mckenna Dyjak

What data were used?: This study used coastal storm surge modeling and an economic analysis to estimate the monetary value of wetland ecosystem services (positive benefits of natural communities to people). One of the ecosystem services provided by wetlands is that  they are great at controlling flooding; their flood protection value was estimated using the protected coastal wetlands and marshes near the Jacques Cousteau National Estuarine Research Reserve (JCNERR) in New Jersey. 

Methods: Storm surge flooding was determined for historical storms (e.g., Hurricane Sandy in 2012) and future storms that account for habitat migration and sea level rise. Each storm had modelled flooding scenarios for both the presence and absence of the coastal wetland/marsh. The model also incorporated ways to account for monetary value of physical damage by using property values.

Results:  This study found that coastal wetlands and marshes can reduce flood depth/damage by 14% which can save up to $13.1 to $32.1 million in property damage costs. The results suggest that one square kilometer (~0.4 square miles) of natural coastal wetland habitats have a flood protection value of $7,000 to $138,000 under future conditions (Figure 1).

Figure 1. This graph shows the estimated monetary value of coastal marshes flood protection in different storm scenarios per square kilometer. A “25 year Storm” or “50 year Storm” is a storm event that occurs once on average in the time span given.

Why is this study important?: Natural coastal wetlands and marshes contribute many vital ecosystem services such as providing habitats for wildlife, helping protect against coastal erosion, and purifying water. Assigning a monetary value to these natural habitats for their flood protection can highlight another aspect of their importance and urge people to protect these important coastal communities. The results from this study can allow the public and private sectors to develop and practice sustainable methods to preserve the ecosystems.

The bigger picture: Storm events, such as hurricanes, are predicted to become more frequent and more severe due to climate change. As the oceans continue to warm (an estimated increase of 1-4 degrees Celsius in mean global temperatures by 2100) hurricanes are predicted to intensify in wind speed and precipitation. Storm surge is known to be the most dangerous aspect of hurricanes and causes deadly flooding. As sea levels rise and ocean water expands due to warming, storm surges will become more severe during major storm events. This study has shown that coastal wetlands and marshes are considered our “first line of defense” in these circumstances. We must take care of and protect our natural habitats because they provide us with many services that we are unaware and likely unappreciative of.

Citation: Rezaie AM, Loerzel J, Ferreira CM (2020) Valuing natural habitats for enhancing coastal resilience: Wetlands reduce property damage from storm surge and sea level rise. 

How fossil collection methods can affect paleoecological datasets

The influence of collection method on paleoecological datasets: In-place versus surface-collected fossil samples in the Pennsylvanian Finis Shale, Texas, USA

Frank L. Forcino, Emily S. Stafford

Summarized by Mckenna Dyjak

What data were used?: Two different fossil collecting methods were compared using the Pennsylvanian marine invertebrate assemblages of the Finis Shale in Texas. In-place bulk-sediment methods and surface sampling methods were used to see how these different methods could influence taxonomic (groups of animals) samples. 

Methods: The bulk-sediment sampling method involves removing a mass of sediment and later washing and sieving the material to retrieve the fossil samples; surface sampling is a simpler method in which the top layer of sediment is removed and the exposed fossils are collected by hand. The samples were collected in the Finis Shale in Texas at stratigraphically equivalent (layers of rock deposited at the same time) locations to ensure continuity in the two methods. The bulk-sediment and surface pick-up samples were analyzed for differences in composition and abundance of fossil species (i.e., paleocommunities) using PERMANOVA (a type of analysis used to test if samples differ significantly from each other).

Results: The study found that the bulk-collected samples differed from the surface-collected samples. The relative abundance of the major taxonomic groups (brachiopods and mollusks), composition, and distribution varied considerably in both collecting methods. For example, there was a higher relative abundance of brachiopods in the bulk-collected samples and a higher relative abundance of gastropods in the surface-collected samples.

Figure 1. Comparison of relative abundance of fossil groups between in-place and surface samples. Note the different abundances from each of the collection methods.
(SpE = Spillway East outcrop, SpW = Spillway West outcrop, CW = Causeway Road outcrop)

Why is this study important?: Bulk-sediment sampling and surface sampling methods produce significantly different results, which would end up affecting the overall interpretation of the history of the site. The surface-collected fossils may be influenced by stratigraphic mixing (mixing of materials from different rock layers), collector bias (which can influence a fossil’s potential to be found and collected; for example, larger fossils are more likely to be collected), and destruction of fossils due to weathering. Bulk-sediment sampling will likely have a more accurate representation of the ancient community, because the fossils likely experienced the least amount of alteration during the process of the organism becoming a fossil (also known as taphonomy).

The bigger picture: The amount of things that have to go right in order for an organism to become a fossil is a lengthy list (read more about the fossilization process here). There are many biases that can contribute to the incompleteness of the fossil record such as environments that favor preservation (e.g., low oxygen), as well as poor preservation value of soft tissues, like skin. Scientists must do what they can in order to collect accurate data of the fossil record since there are already so many natural biases. Knowing which fossil collecting methods produce the most accurate results is important when advocating for the paleocommunity.

Citation: Forcino FL, Stafford ES (2020) The influence of collection method on paleoecological datasets: In-place versus surface-collected fossil samples in the Pennsylvanian Finis Shale, Texas, USA. PLoS ONE 15(2): e0228944. https://doi.org/10.1371/journal.pone.0228944

Organic carbon stored in Florida lakes

Organic carbon sequestration in sediments of subtropical Florida lakes

Matthew N. Waters, William F. Kenney, Mark Brenner, Benjamin C. Webster

Summarized by Mckenna Dyjak

What data were used? A broad range of Florida lakes were chosen based on size, nutrient concentrations (nitrogen and phosphorus), trophic state (amount of biologic activity that takes place), and location. The lakes were surveyed using soft sediment samples to identify the best drilling sites for sediment cores. After drilling, the cores were dated and the organic carbon (OC) content and burial rates were calculated. Organic carbon can be stored in sediments and buried, which temporarily removes it from the atmosphere.

Methods: The sediment cores were taken using a piston corer commonly used to retrieve soft sediments. Each core was dated using ²¹⁰Pb which is a common radioactive isotope found in lake environments and can be used to date sediments up to 100 years. Radioactive isotopes can be used to date rocks and sediments based on their natural decay rate (half-life). The organic carbon content of the cores was measured using a Carlo-Erba NA-1500 Elemental Analyzer which is an instrument that can determine the total carbon present in a sediment sample. To calculate the organic carbon deposition rates, the accumulation of sediment rates were multiplied by the proportion of OC found in the sediment. A recent increase of eutrophication (high amount of nutrients present in lakes) needed to be taken into account when calculating the OC deposition rate, so the sediments were divided into pre-1950 and post-1950 deposits to depict the change in industrial activity and agriculture. 

Results: The OC burial rate was highest in the shallower lakes and decreased as the depths increased (can be seen in Figure 1). This is different from the rates for temperate (mild temperatures) bodies of water, where OC burial rates decreased as the lakes got bigger. They found a 51% increase in OC burial rates in the post-1950 deposits which corresponds to the increase in eutrophication in the lakes.

Figure 1. Graph showing the correlation between depth and organic carbon (OC) burial rate. The OC burial rate increases as the depth decreases in meters.

Why is this study important? Cultural eutrophication is caused by an increase of nutrients in waterways such as phosphorus and nitrogen (commonly found in lawn fertilizers) which cause harmful algal blooms; these algal blooms remove oxygen from the water and can mess up the entire ecosystem. The lack of oxygen and harmful algal blooms can lead to habitat loss and loss of biodiversity. This study highlights the effects and severity of cultural eutrophication in Florida’s subtropical lakes.

The bigger picture: Managing carbon and removing it from the atmosphere (i.e., carbon sequestration) is an important aspect of climate mitigation. The carbon can be removed from the atmosphere and stored in places known as carbon sinks (natural environments that can absorb carbon dioxide from the atmosphere). This study shows that subtropical Florida lakes are effective carbon sinks for organic carbon that deserve to be protected from nutrient runoff that causes eutrophication.

Citation: Walters, M. N., Kenney, W. F., Brenner, M., and Webster, B. C. (2019). Organic carbon sequestration in sediments of subtropical Florida lakes. PLoS OnE 14(12), e0226273. doi: 10.1371/journal.pone.0226273

The Clues Ancient Glaciers Leave Behind on Mars

Transient post-glacial processes on Mars: Geomorphologic evidence for a paraglacial period

by: Erica R. Jawin, James W. Head, David R. Marchant 

Summarized by: Lisette Melendez

Figure 1: A map of the crater in the midlatitudes on Mars, showing the geologic features that were created due to deglaciation, like gullies and spatulate depressions. These same features can be found in post-glacial environments on Earth!

What data were used? Mars, just like Earth, goes through a cycle of glaciation and deglaciation. The rise and fall of glaciers on Mars is influenced primarily by the planet’s obliquity, or the tilt of its axis. During times of higher obliquity, the planet’s tilt is greater, hence its poles are exposed to more sunlight and the glaciers leave the poles and travel towards the middle of the planet. As the cycle continues and the tilt is lower, the glaciers leave the midlatitudes and migrate towards the poles once again. The period of time where environments are adjusting to deglaciation is known as a paraglacial period, and it comes with a group of identifying features that are well studied here on Earth. This study applies what we’ve learned about the kinds of geologic features that are left behind by glaciers on Earth to the environment on Mars. The area that is left behind by a glacier is known as a glacial deposit. By analyzing images of craters on Mars taken by cameras aboard the Mars Reconnaissance Orbiter, scientists are able to find evidence of paraglacial periods and how long they last on Mars.

Figure 2: A photo of two retreating glaciers in the Antarctic Valley that are leaving behind ridges that are comparable to the ones found on the Martian surface.

Methods:  After choosing a crater in the midlatitudes of Mars, the scientists began breaking down the features found in the images of the crater and mapping out the terrain, as shown in Figure 1. Glaciers leave behind special signatures in the rocks on Earth (e.g., here are some Time Scavengers posts about glacial geology on Earth: glaciers in Connecticut River Valley and glaciers in the Bay of Fundy), and the objective was to identify these same features on Mars. In order to further understand the processes that were occurring in the crater on Mars, analyses of places with the same climate and geologic features on Earth were used! The climate on Mars is arid and freezing, similar to the McMurdo Dry Valleys in Antarctica.

Figure 3: A diagram that shows the process of forming gullies and debris fans (piles of sediment), which can be seen in real-life in the next figure.

Results: Several geologic features that, when found together, are indicative of glaciers migrating away were found in this crater on Mars. Some of these features include ridges becoming increasingly deformed as one looks further downslope, as shown in Figure 2, where the ridges of the glacial deposits in Antarctica are more deformed at the bottom of the picture. Spoon-like holes, called spatulate depressions, were also found on both the Antarctic glacial deposits and the Martian crater, formed by ice weathering away. As glaciers retreat, they often leave behind steep slopes in their wake. These slopes are unstable, and over time, sediment flows downward and builds up on the sides to stabilize the slope, as shown in Figure 3. Gullies, which are a geologic feature formed by the path that the sediment took to travel downward, and the resulting triangular piles of sediment can be found both in the crater on Mars and on Earth, shown side by side in Figure 4.

Why is this study important? This study is important because it increases our understanding of the time frames of climate cycles on Mars, and also highlights the similarities and differences between Mars and Earth. On Earth, paraglacial periods are relatively short, and the features left behind are likely to be eroded away by rainfall, rivers, and vegetation. These features are better preserved on Mars, an extremely cold and dry planet that doesn’t have the same erosive forces.

Figure 4: An example of gullies and debris fans on Mars (left) and on Earth (right).

The big picture:  Understanding the formation of geologic features on Earth is essential to uncovering the geologic history of the rest of our planets. This study showed that several features that form after a glacier migrates away can be found both on Earth and on Mars. The key difference is the time frame: on Earth, the paraglacial period is relatively rapid, while on Mars, it takes place on the scale of millions of years. 

Citation:mJawin, E. R., Head, J. W. & Marchant, D. R. Transient post-glacial processes on Mars: Geomorphologic evidence for a paraglacial period. Icarus 309, 187–206 (2018).