Holocene foraminiferal assemblages from Firth of Tay, Antarctic Peninsula: Paleoclimate implications

By: Wojciech Majewski & John B. Anderson

Summarized by: Baron Hoffmeister

What data were used?: This study analyzed 166 sediment samples taken from sediment cores in the Antarctic Peninsula. 

Methods: This study used a quantitative analysis of foraminifera assemblages found in sediment cores to determine past environmental factors relating to climate change.  

Results: This study found that different foraminifera and their physical attributes correlate with several different environmental conditions during the Holocene epoch, the geologic time unit that spans from nearly 11,000 years ago to present time ( figure 1). A time span between 9400 years and 7750 years before present time was correlated with having coarse (large) sediment and coarse foraminifera. This indicates a high influence from warming sea currents that melted glaciers and deposited coarse sediments. This was a period of glacial retreat and warming temperatures. From 7750 to 6000 years before the present, the elevated appearance of foraminifera species M. arenacea represents open water and conditions in which glaciers were spread out from each other. The foraminifera species M. arenacea is also known for its tolerance to cold corrosive bottom waters and high salinity fluctuations. The assemblage dominated by M. arenacea indicates that the bottom waters at this time dissolved other species of foraminifera, and M. arenacea was the dominant foraminifera species at this time. Foraminifera tests, (i.e., their shells) are made of calcium carbonate, and it dissolves in acidic conditions. Around 3500 years before the present time, it was found that due to an increase in abundance of foraminifera species P. bartrami–P. antarctica is when the cooling trend of the mid-Holocene occurred. There weren’t any corresponding foraminifera assemblages found that correlate with warming over the last century. 

Why is this study important?: The results of this study allow us to better understand how foraminifera can relate to changing environmental conditions. This study provides a more cohesive understanding of climate change and how glacier and ocean currents around the south pole respond to changes in climate. The data used in this study can be used in future studies regarding foraminifera assemblages and their implication on climate change. 

The big picture: Foraminifera are some of the most abundant shelled organisms in marine environments and can be used to reconstruct past climatic conditions. The importance of understanding how these organisms correlate to climate change can help link current-day climate trends to prehistoric climate events. This can be used to make predictions on how climate change is occurring currently, and what the effects of it might be worldwide. 

Citation: Majewski, W., & Anderson, J. B. (2009). Holocene foraminiferal assemblages from Firth of Tay, Antarctic Peninsula: Paleoclimate implications. Marine Micropaleontology, 73(3-4), 135-147. doi:10.1016/j.marmicro.2009.08.003

Limnological Investigation of Antarctic Lakes and their Paleoclimate Implications

By: Pawan Govil

Summarized by: Baron Hoffmeister 

What data were used?: A 78 cm sediment core from a freshwater lake in Larsemann Hills, East Antarctica was used to interpret historic climate patterns from the late Quaternary period. 

Methods: The sediment core was analyzed using grain size distribution, as well as biological productivity indicators such as organic carbon and biogenic silica. Biogenic silica makes up diatom cell walls and is commonly called opal. This study used radiocarbon dating to measure total organic carbon present, and the biogenic silica was also evaluated using a wet alkaline extraction. A wet alkaline extraction is a method that isolates plasmid DNA or RNA from bacteria. This was used to determine the biogeochemical attributes of this lake.

Results: Using radiocarbon dating, this study found that this core is from the Holocene Epoch, a time that began around 11,700 years ago. This core was dated to be 8,300 years old. Most of the material in the core was sand, and clay and silt were rarer (sand, clay, and silt are defined by grain size in geology- sand is the coarsest grain size in this example; figure 1)The silica content within this was very low, indicating a very low abundance of silicate microfossils. The total carbon was low or negligible in the lower part of the core, likely due to the high sedimentation rates of sand during this time. The area of the core that had the most organic carbon was the top of the core that contained the small amounts of clay and silt. This study showed that this was due to a build of algae. The particles of clay and silt prevented oxygen from  decomposing the organic matter. This indicates that during this time, approximately 4,000 years ago, there were low sedimentation rates and low oxygen levels in this lake. This algal mat at the top of the core indicates warming temperatures during this time, and that the lake had little interference with glacial ice. The fine grained sediments were deposited due to ice meltwater (as water slows down, fine grained sediments drop out of water suspension) and can be seen in the upper core. The lower portion of the core contains high sand content, which implies glacial river input (i.e.,fluvioglacial) before 6,000 ago. The overall paleoproductivity implications of the core are as follows.  From 8,300 ago to around 6,000 years ago there was a period of warming. Around 4,000 ago, the warm temperatures allowed the lake to be free of ice and exposed to sunlight, and therefore this was the highest level of productivity and can be reflected in the upper core’s higher total carbon content. 

Why is this study important?: Antarctica and its surrounding oceans influence climate across the entire planet. Antarctica holds around 90% of the world’s ice and about 70% of the world’s freshwater trapped in ice. The ability to be able to interpret past climate conditions that influenced climate patterns in Antarctica can allow scientists to better predict current day climatic changes in Antarctica and its effects globally.  More information about Antarctica and its ice sheets can be found here. 

The big picture: Today, the ice sheets are melting at a rate that has never been seen before. The effects of this could be catastrophic to life on Earth. Studies like these can allow scientists to better understand current-day climate patterns that could potentially help reduce the impact of widespread climate change. 

Citation: Govil, P. (2019). Limnological Investigation of Antarctic Lakes and their Paleoclimatic Implications. Ministry of Earth Sciences, (24), 289-303. Retrieved May 24, 2020.

A new large Late Cretaceous lamniform shark from North America, with comments on the taxonomy, paleoecology, and evolution of the genus Cretodus

by: Kenshu Shimada, Micheal J. Everhart

Summarized by: Baron Hoffmeister

What data were used? : This study examined a partial skeleton of the Late Cretaceous shark, Cretodus, collected from the Blue Hill Shale in north-central Kansas, U.S.A. It had unique teeth not present in any other species of Cretodus. 

Methods: This study used a taxonomic analysis of the fossilized remains found and compared them to other members of the Cretodus genus. 

Results: The study found that the species of the fossilized partial shark skeleton found does not share enough similar features with any of the other four known species within the genus Cretodus. Therefore it has been listed as a new species, C. houghtonorum. Researchers found that it had a unique tooth size and pattern that didn’t match any previously discovered species (figure 1). Its calcified cartilage scales along with the inference that this shark had a large girth due to its bone structure that was preserved, indicated that this organism was likely a sluggish shark that lived in a nearshore environment. This study examined growth bands in its vertebral column and found that this shark had a lifespan of around 51 years. 

Why is this study important? Aside from discovering a new species, this study recognizes the fact that the evolutionary relationships of several shark families is still relatively unknown. However, this new finding provides data linking it with other members at the genus level. Without understanding these relationships, it’s difficult to understand the distribution of these organisms, how they changed over time, and why they went extinct. 

The big picture: Overall, this study is useful in determining possible links between extant and extinct shark species. This study provides data that can rework our understanding of evolutionary traits between extinct and modern-day sharks as well. The skeletal and dental data found in this study can be useful for other studies incorporating evolutionary trends, prehistoric ecology, and the taxonomic differences within the genus Cretodus.

Citation:  Shimada, K., & Everhart, M. J. (2019). A new large Late Cretaceous lamniform shark from North America, with comments on the taxonomy, paleoecology, and evolution of the genus Cretodus. Journal of Vertebrate Paleontology, 39(4). doi: 10.1080/02724634.2019.1673399

Climate-mediated changes in predator-prey interactions in the fossil record: a case study using shell-drilling gastropods from the Pleistocene Japan Sea

Tomoki Chiba and Shinichi Sato

Summarized by Baron Hoffmeister

What data were used? This study used a predator-prey analysis of drill holes found on fossil bivalve (clam) shells produced by gastropods (snails) found in the Oga Peninsula off the coast of Japan.

Methods: This study used computer analysis on fossil assemblages of bivalves to determine the location of predatory drill holes and the species of bivalves which indicated whether they are warm water dominant or cold water dominant species. The location of the drill holes on the bivalve shells was also analyzed to determine different predatory gastropods (Figure 1).

Results: This study showed that drilling predation was influenced by the change of sea surface temperatures and sea level due to glacial-interglacial climate cycles. A glacial period occurs due to cool temperatures and glacial advancement, and an interglacial period occurs when glaciers retreat and sea level rises due to warming temperatures. As warm water currents decrease, so does the presence of warm-water predator gastropods. This causes them to shift their range, therefore changing rates of predator and prey interactions. In this study, predation slowed as seawater temperatures decreased and in turn found that this moderated the predation pressure between the gastropods and bivalve prey. This study also found that predator and prey interactions in a shallow-marine ecosystem are likely to weaken with cooling temperatures and strengthen with warming temperatures.

Why is this study important? This study indicates that predator-prey relationships can be used to help interpret changing climates and the implications it has on ecosystems. This study also notes that ocean climate variability has large implications of range shifts which can be used to interpret how organisms respond to changing climate conditions.

The big picture: The information found in this study can be used to help interpret current-day climate change and its influence on predator-prey relationships in relation to the biogeographical distribution of species due to ocean temperatures. This is useful for identifying ecosystems globally.

Citation:

Chiba, T., and Sato, S. I.. (2016). Climate-mediated changes in predator-prey interactions in the fossil record: a case study using shell-drilling gastropods from the Pleistocene Japan Sea. Paleobiology 42(2), 257–268. doi: 10.1017/pab.2015.38

Little Ice Age climatic erraticism as an analogue for future enhanced hydroclimatic variability across the American Southwest

by: Julie Loisel, Glen M. MacDonald, Marcus J. Thomson

Summarized by: Baron Hoffmeister

What data were used? This study used climate data from climate proxy databases and dendrochronology  along with computer software for modeling climate patterns  

Methods: This study used climate proxy data in conjunction with computer modeling and simulation software to determine hydroclimatic variability (i.e. the change in water conditions) in the North American Southwest.

Results: This study found that in the North American southwest is prone to variable climate conditions such as drought, as well as rapid snowmelt and severe rainstorms that can lead to flooding. Hydroclimatic variability in the southwest has not remained constant over the past one thousand years. In fact, there was high climate variability in the North American southwest during the Medieval Climate Anomaly (MCA; i.e. a period of warm climate that lasted from 950 c. to 1250) and the Little Ice Age (i.e. a period of cooling right after the MCA lasting until about 1850). Results show that the Little Ice Age had a higher amount of variability than the Medieval Climate Anomaly (see Figure 1). This was confirmed using climate data from tree ring growth analysis (i.e. the space between rings indicates the amount of growth) obtained by the North American Drought Atlas, a network of climate data points covering North America (figure 2), as well as climate proxy data from the El Junco diatom index from the Galapagos Islands. A diatom is a single-celled alga with cell walls made of silica. The oxygen used to make the silica is preserved in their shells and can be helpful climate proxy data.

This study also compared climate proxy records from fossil-coral oxygen isotopic records from Palmyra island in the tropical Pacific that recorded El Niño Southern oscillation patterns. El Niño Southern Oscillation is a weather pattern that has irregular periods of variation in wind and sea surface temperatures over the tropical eastern Pacific. Records of these weather patterns can be found in assemblages of certain coral fossils which serve as indicators for sea surface temperatures from the past. These were all analyzed and compared with the El Junco diatom index, and tree ring growth data using computer software. The researchers found a correlation between the El Niño Southern Oscillatory system and drought amplitude in the North American southwest increasing hydroclimatic variability. Also, with recent weather patterns, the computer simulations suggest that a ‘warm Little Ice Age’ scenario with high hydroclimatic variability accompanied by periods of warm and dry conditions is likely to occur sometime during the 21st century. 

Why is this study important? This study shows how past climate change can help us understand how climate can change in the future and what the effects of that might be. In the North American southwest, hydroclimatic variability can lead to floods and drought impairing proper land management. Without experiments like this, climate change and its global effects cannot be understood. The results produced from this study can be used as a model for developing other climate reconstruction models.  

The big picture: This study explores the potential for climate variability modeling using historical climatic data as a reliable indicator for future climate predictions. It is important to be able to understand these historical climate events and weather patterns along with their effects on environments. Successfully being able to do this can lead to well-rounded land and water resource management in the face of climate change. 

Citation: Loisel, J., Macdonald, G. M., & Thomson, M. J. (2017). Little Ice Age climatic erraticism as an analogue for future enhanced hydroclimatic variability across the American Southwest. Plos One, 12(10). doi: 10.1371/journal.pone.0186282

A new model of Holocene reef initiation and growth in response to sea-level rise on the Southern Great Barrier Reef

by: Sanborn et al. 

Summarized by: Baron Hoffmeister

What data were used?: This study analyzed sediment cores taken from the One Tree Reef of the Southern Great Barrier Reef in Queensland, Australia. Data was collected from the layers and sediment grains found within core samples taken from 12 different locations on the reef.

Methods: This study used biogenetic facies interpretation (i.e. physical, chemical, and biological aspects found within sediment and rock formations) from core samples to reconstruct reef growth and sea-level conditions.

Results: This study concluded that reef growth after a significant sea-level rise in the Pleistocene occurred in three stages. The first stage occurred over eight thousand years ago and was a rapid and shallow coral growth in presumably clear water. The average growth was around 6mm per year. The second stage of reef growth was between seven to eight thousand years ago, and this occurred with either turbid (i.e. cloudy water) or deeper water (i.e. over 5 meters in depth) conditions. The average growth was around 3mm per year. The third stage of growth was composed of shallow branching coral assemblages averaging 5mm of growth per year. This was referred to as a “catch up” in the reef growth sequence and continued until the reef reached the top of the sea level. It is hypothesized that more sediment-tolerant corals continued to slowly build up across the reef during this time. These are the types of corals that are now dominant on the Great Barrier Reef. This study also successfully identified six coral assemblages, and three algae assemblages correlating with specific paleoenvironments, creating a new model (see figure 1) for interpretation of samples containing similar assemblages for future studies. Using geochronology (i.e. dating rock formations) a lag of 700-1000 years of reef growth was confirmed in this experiment. There was a significant gap of growth on the wind-sheltered portion of the reef, which is the opposite of what was hypothesized previously (that corals would grow faster in wind-sheltered areas). Figure 1 shows a new model for reef growth response from the results found in this study.

Why is this study important?  This study is important for determining how corals and other reef-building organisms respond to environmental change and stress like sea-level change. Understanding past environmental conditions are crucial for understanding how current environmental conditions can affect reef growth today.

The big picture: This study not only provides new and important data of reef growth response to historical climatic changes but can also be used to predict present-day reef response to sea-level change. As sea level continues to occur, a more comprehensive understanding of the way coral and reef-building organisms respond to environmental changes could lead to preserving the reefs as the ocean conditions change. The new model this study found can provide important data for how reefs grow, and provide important paleoenvironmental interpretation data.  

Citation: Sanborn, Kelsey L., Jody M. Webster, Gregory E. Webb, Juan Carlos Braga, Marc Humblet, Luke Nothdurft, Madhavi A. Patterson et al. “A new model of Holocene reef initiation and growth in response to sea-level rise on the Southern Great Barrier Reef.” Sedimentary Geology 397 (2020): 105556. https://doi.org/10.1016/j.sedgeo.2019.105556

North Pacific climate recorded in growth rings of geoduck clams: A new tool for paleoenvironmental reconstruction

Robert C. Francis, Nathan J. Mantua, Edward L. Miles, David L. Peterson

Summarized by Baron Hoffmeister

What data were used? Growth chronology (i.e growth patterns that accumulate over years in the shell of the organism, similar to tree rings) of geoduck clams (see figure 1) collected in Washington, USA were used to reconstruct sea-surface temperatures (SST) in the Strait of Juan de Fuca.  

Methods: This study used growth ring data in geoduck clams to determine how sea surface temperatures affected the shell growth (something called “accretion”) within these organisms over their life span. 

Results: Geoduck clams are a part of the class Bivalvia (i.e., a marine or freshwater mollusk that has its soft body compressed by a shell; this includes other organisms like snails and squids). These organisms produce their own shells, and the shells continue to grow as these organisms age (unlike organisms like mammals, who stop growing at a certain age). The shell accretion of these organisms can be observed under a microscope from samples of the shells. These are called growth lines and the spacing in between lines indicates how much new shell material the organism produced during a certain period of time (see figure 2). The growth lines of the geoduck clams found within Strait of Juan de Fuca correlated strongly with sea-surface temperatures. Researchers found that when the water was warmer, more growth was observed. This is common for a number of marine bivalves, and these proxy methods help construct a better understanding of sea surface temperatures from the past. 

 

Why is this study important? This study helps reconstruct environmental conditions and researchers can use this data in conjunction with other climate proxies to better understand how current climate patterns and ocean temperatures can affect marine ecosystems in the North Pacific basin.

The big picture: This study is important, not only for creating a more cohesive climate proxy database, but also indicating that shell accretion in specific marine organisms can provide important climatic data. Bivalves have a large geographic range and the data collected from these organisms through shell accretion studies can allow us to have a better understanding of historic climate conditions worldwide. 

Citation:

Francis, R. C., Mantua, N. J., Miles, E. L., & Peterson, D. L. (2004). North Pacific climate recorded in growth rings of geoduck clams: A new tool for paleoenvironmental reconstruction. Geophysical Research Letters, 31(6).