Floodwaters in the town of Bushmans River, South Africa, following unusually heavy rain associated with the Benguela Niño
Shutterstock/David Steele
Scientists from Syracuse University, George Mason University and the University of Connecticut are using hydrogen isotopes locked up in 'fossilised' plant material embedded in ocean floor sediments to analyse the changes in weather patterns in Southern Africa, in order to try to predict the effects of current changes.
The 'fossils' are in the form of stable flakes of the waxy substance that coats plant leaves. These get washed into the ocean when they flake off the leaves and eventually sink to the ocean floor where they become embedded in the layers of silt in chronological order. The team measured the ratio of the two stable isotopes of hydrogen (1H and 2H or deuterium) in of thin sections core samples of the ocean floor deposits. This ratio is directly related to the rainfall on the adjacent land.
This is only possible because childish creationist claims that the Universe is only 8-10,000 years old are not only quantitatively wrong, but wrong by many orders of magnitude, and quite laughably so to anyone who has even the slightest understanding of the subject.
How are hydrogen isotopes locked up in plant matter in ocean floor sediment used to measure rainfall in geological history? Studying the hydrogen isotopes (particularly deuterium, or heavy hydrogen) in plant matter found in ocean floor sediment can provide valuable insights into past rainfall patterns in geological history. This is done through a process known as stable isotope analysis. Here's how it works:The study is explained in a Syracuse University news release:The key principle here is that the isotopic composition of rainfall is linked to the climate conditions at the time of precipitation. More negative δD values (indicating higher deuterium content) in plant material suggest periods of drier conditions, whereas less negative δD values indicate wetter conditions. This information can help reconstruct the history of precipitation in a given region over geological timescales. This method is often used in paleoclimatology to understand past climate variability and can provide valuable data for studying long-term climate trends and variations. It's particularly useful when other climate proxies like ice cores, tree rings, or sediment records are not available or not as reliable for the specific region and time period of interest.
- Isotopic Fractionation: When water evaporates from the Earth's surface, it tends to preferentially evaporate the lighter isotope of hydrogen, 1H (protium), over the heavier isotope, deuterium (2H). This process is known as isotopic fractionation.
- Rainfall and Plant Uptake: When rain falls, it contains a mixture of hydrogen isotopes, but the rainwater is enriched in 1H due to the fractionation process. Plants take up the water from the environment, and the ratio of 1H to deuterium in plant matter reflects the isotopic composition of the precipitation it received.
- Sediment Deposition: Over time, plant matter can become buried in ocean floor sediments, preserving the isotopic signature of the past rainfall.
- Analysis: Scientists can drill sediment cores from the ocean floor and extract the plant material. By analyzing the hydrogen isotopic composition of this plant material, they can determine the historical isotopic composition of the rainfall. This, in turn, provides information about past climate conditions.
How is the isotopic ratio affected by the amount of rainfall?
The isotopic ratio of hydrogen in precipitation, specifically the ratio of deuterium (2H) to protium (1H), is affected by the amount of rainfall in a given region. This is because the process of isotopic fractionation, which occurs during the formation and movement of clouds and precipitation, is influenced by the amount of moisture in the atmosphere. Here's how it works:In summary, the amount of rainfall affects the isotopic ratio of hydrogen in precipitation in the following ways:
- Isotopic Fractionation with Precipitation: As moisture in the atmosphere condenses to form clouds and subsequently falls as precipitation, the fractionation process leads to the enrichment of lighter isotopes, such as 1H (protium), in the water molecules that make up the raindrops. This means that the heavier isotope, deuterium (2H), is left behind to a greater extent in the remaining atmospheric moisture.
- Effect of Rainfall Amount: The amount of rainfall can influence the extent of this isotopic fractionation. In regions with heavy and prolonged rainfall, the fractionation process can lead to a greater depletion of deuterium in the remaining atmospheric moisture. In contrast, in regions with less rainfall, the fractionation process may not be as pronounced, resulting in a less negative δD value, which represents the isotopic ratio of hydrogen.
Therefore, when scientists analyze the isotopic composition of rainfall, they can use the δD value as a proxy for the amount and intensity of rainfall in a particular region or during a specific time period in geological history. This information can be valuable for understanding past climate conditions, especially in regions where historical rainfall data may be scarce or unreliable.
- Heavier rainfall can result in more significant isotopic fractionation, leading to more depleted δD values (more negative values) in the resulting precipitation.
- Lighter or less intense rainfall may lead to a smaller degree of isotopic fractionation and, as a result, less depleted δD values.
In a study published in Geophysical Research Letters, researchers used chemicals from preserved plant matter to pinpoint the processes responsible for changes in past rainfall and drought in southwestern Africa, with implications for the future.The teams open access paper in Geophysical Research Letters is interesting in having Key Points and a Plain Language Summary:
In September 2023, extreme rains struck South Africa’s Western Cape province, flooding villages and leaving a trail of destruction. The catastrophic devastation is just one recent example in a string of extreme weather events that are growing more common around the world. Fueled by rising sea surface temperatures from global warming, torrential storms are increasing both in frequency and magnitude. Concurrently, global warming is also producing the opposite effect in other instances, as a mega-drought recently threatened the water supply of Cape Town in southwestern Africa to the point where residents were at risk of running out of water. This one-two punch of weather extremes are devastating habitats, ecosystems and human infrastructure.
With global warming apparently here to stay, a team of paleoclimatologists from Syracuse University, George Mason University and the University of Connecticut are studying an ancient source to determine future rainfall and drought patterns: fossilized plants that lived on Earth millions of years ago.
In a study led by Claire Rubbelke, a Ph.D. candidate in Earth and Environmental Sciences in Syracuse University’s College of Arts and Sciences (A&S), and Tripti Bhattacharya, Thonis Family Professor of Earth and Environmental Sciences in A&S, researchers zeroed in on the Pliocene epoch (~3 million years ago) – a time when conditions were very similar to today. Despite warmer temperatures, many parts of the world, including southwestern Africa, experienced dramatic increases in rainfall over land, likely caused by warmer than normal sea surface temperatures. This mimics a modern event called a Benguela Niño, where researchers believe shifting winds cause warm waters to move southward along the coast of Africa causing enhanced rainfall over typically arid regions.
The team’s work was inspired by collaborator and study co-author Natalie Burls, associate professor in the Department of Atmospheric, Oceanic and Earth Sciences at George Mason University. Burls, an oceanographer and climate scientist from South Africa who received a Ph.D. at the University of Cape Town, has long been intrigued by the way geological evidence from past warm climates in Earth’s history can help researchers make sense of future rainfall and drought conditions.In the present day, the intensity and location of extreme precipitation from Benguela Niño events appear to be influenced by both Atlantic and Indian Ocean sea surface temperatures. During the Pliocene, it appears that these Benguela Niño-like conditions may have been a permanent feature.
Claire B. Rubbelke, first author
Department of Earth and Environmental Sciences
Syracuse University, Syracuse, NY, USA.
To study the impact of global warming on precipitation from millions of years in the past, the team analyzed ‘molecular fossils’ in the form of ancient leaf waxes.This study, which explored how past warm climates can inform us on what to expect in the future as our planet warms, brings to the fore the important role of ocean warming patterns. It’s important to understand how these patterns determine the response of the hydrological cycle over southwest Africa to global warming.
Associate Professor Natalie J. Burls, co-author.
Atmospheric, Oceanic, and Earth Sciences
George Mason University, Fairfax, VA, USA.
Plants use hydrogen from rainwater to produce the waxy outer coating on their leaves, which survives in ocean sediment for millions of years. The leaf wax functions as a time capsule preserved in ocean sediment.These are compounds produced by leaves to protect themselves from drying out. They get shed from leaf surfaces and find their way to ocean sediments, where we can extract them and study their chemical composition.
Professor Tripti Bhattacharya, co-author
Department of Earth and Environmental Sciences
Syracuse University, Syracuse, NY, USA.
After transporting the millions-year-old sediment from Africa to their lab in Syracuse, Rubbelke and Bhattacharya used heat and pressure to extract lipids (e.g. fat molecules), and then used a variety of solvents to isolate the exact class of molecules that they were looking to measure. From those molecules, they determined the number of different types of hydrogen present.
Researchers dilute sediment cores with a variety of solvents. The samples are forced through a column of silica gel, which traps the unwanted chemicals and leaves the alkanes they want to measure. The dark line at the bottom of the liquid in the middle three columns is where some extra chemicals are getting stuck, while other chemicals can traverse through the gel to drip into vials at the bottom.
By comparing their data to climate models, they verify how well those models capture past climate change, which can in turn improve the accuracy of those models to predict future rainfall. As Bhattacharya notes, this is critical because climate models often disagree on whether certain regions will get wetter or drier in response to global warming.When we measure the amount of heavy and light isotopes of hydrogen in the waxes, it reveals different physical processes like increased rainfall, or how far the water vapor travels. We can therefore identify changes in these processes by looking at long-term changes of hydrogen.
Claire B. Rubbelke
The study’s third author, Ran Feng, assistant professor of Earth sciences at the University of Connecticut, helped analyze the comparison data and specifically examined the proposed mechanism that explains the Pliocene wet conditions in southwest Africa. She says many features of ongoing climate change are reincarnations of the past warm climates.We are using real world data from the ancient geologic past to improve our ability to model rainfall changes as the planet warms.
Professor Tripti Bhattacharya
Rubbelke, whose interest in paleoclimate research started in high school while studying ice cores and oxygen isotopes, says that the work she is doing alongside Bhattacharya at Syracuse is particularly fulfilling because they are contributing valuable data to an area where there is currently a knowledge gap.In our case, we have shown that sea surface temperature pattern surrounding South Africa is key to explaining the past hydroclimate conditions of this region. Looking into the future, how this sea surface temperature pattern may evolve has profound implications to the environmental changes in South Africa.
Assistant Professor Ran Feng, co-author
Department of Earth Sciences
University of Connecticut, Storrs, CT, USA.
This research is really cool because not a lot of paleoclimate records from the Southern Hemisphere exist, compared to the Northern Hemisphere at least. I feel like I’m really contributing to an international research effort to rectify that.
Claire B. Rubbelke.A key aspect of helping vulnerable communities involves improving our ability to predict hydroclimate extremes. Our study directly speaks to this need, as we show that sea surface temperature patterns strongly influence climate models’ ability to predict changes in rainfall in southwestern Africa.
Professor Tripti BhattacharyaAs to whether the future will be wetter or drier in southwestern Africa, the team’s results suggests that both are possible, depending on where extreme sea surface temperatures are occurring.
While not much can be done to reverse global warming, short of cutting the use of fossil fuels completely, the researchers say this study illuminates the need for vulnerable communities to have the tools and resources to adapt to these seemingly more frequent extreme weather events.
AbstractThe embarrassing thing for creationists in this work is that if the sediment on the ocean floor were just a few thousand years old, there would be long sections where the ratio of hydrogen isotopes was constant, yet, as can be seen in the illustration above, it varies considerably between very short sections of the core sample, showing the record of millions, not thousands of years. Since these measurements do not depend on radioactive decay rates (both hydrogen and deuterium are stable isotopes) but on evaporation rates, which in turn is related to atomic weight, creationists can't claim that radioactive decay rates have changed over time.
Future projections of southwestern African hydroclimate are highly uncertain. However, insights from past warm climates, like the Pliocene, can reveal mechanisms of future change and help benchmark models. Using leaf wax hydrogen isotopes to reconstruct precipitation (δDp) from Namibia over the past 5 million years, we find a long-term depletion trend (−50‰). Empirical mode decomposition indicates this trend is linked to sea surface temperatures (SSTs) within the Benguela Upwelling System, but modulated by Indian Ocean SSTs on shorter timescales. The influence of SSTs on reconstructed regional hydroclimate is similar to that observed during modern Benguela Niño events, which bring extreme flooding to the region. Isotope-enabled simulations and PlioMIP2 results suggest that capturing a Benguela Niño-like state is key to accurately simulating Pliocene, and future, regional hydroclimate. This has implications for future regional climate, since an increased frequency of Benguela Niños poses risk to the ecosystems and industries in the region.
Key Points
- Plio-Pleistocene changes in the hydrogen stable isotopic signature of leaf waxes from Southern Africa are linked to Benguela temperatures
- Higher frequency shifts in the record are likely driven by Indian Ocean temperatures via a mechanism observed in the modern
- Isotope-enabled simulations suggest that capturing this mechanism may be key to accurately simulating past and future regional hydroclimate
Plain Language Summary
Rainfall in southwestern Africa will likely be impacted by human-caused climate change, but climate models disagree on whether the region will get wetter or drier as the planet warms. Previous studies, which used plant pollen preserved in ocean sediment, tell us that southwestern Africa was wetter during the Pliocene, a warm period approximately 5.3 to 2.5 million-years-ago, and got drier over time as Earth cooled. This drying is thought to be caused by a concurrent decrease in temperatures within the eastern South Atlantic Ocean. In this study we measure hydrogen isotopes in ancient plant matter and use statistical tools which indicate that rainfall patterns in southwestern Africa are also impacted by changes in Indian Ocean temperatures. This combined Atlantic and Indian Ocean influence is similar to events that we observe in modern times where areas of arid southwestern Africa get short bouts of very strong rainfall when the coastal waters warm. The area that gets strong rainfall depends on where the warm water occurs along the western coast and whether there's also warmer- or colder-than-normal water in the Indian Ocean. If the Pliocene ocean temperature patterns resembled these events, we may need to do further studies to determine whether they will become more common in the future.
(a) Modern climatology of the South Africa from reanalysis data. Markers show the location of ODP and IODP drill sites in the Benguela Upwelling System and Agulhas Current (gray squares) and coretop samples (white diamond). Black outlines Kunene in the north and Cuvelai in the south drainage basins. (b) The δDp record from ODP 1081 (green, this study) and CIRCE coretop 211 (tan, this study), (c) sum of the first two IMFs, (d)sum of the third and fourth intrinsic mode function (IMF), and (e) fifth IMF. (f) TEX86 derived sea surface temperature (SST) record for IODP U1478 (Taylor et al., 2021), (g) alkenone derived SST for ODP 1087 (Petrick et al., 2015), and (h) alkenone derived SST for ODP 1081 (Rosell-Melé et al., 2014). The gray bar highlights the mid-Piacenzian warm period. (i) Running correlation between IMF3 + 4 and the U1478 SST (orange line) as well as 1087 SST (gray line), overlain with IMF3 + 4 timeseries. (j) Running correlation between IMF5 and the 1081 SST (teal), overlain with IMF5 timeseries. The dashed line marks 0 correlation, and the dotted lines mark ±95% significance bounds for correlation coefficient (note that positive is down on y axis).Rubbelke, C. B., Bhattacharya, T., Feng, R., Burls, N. J., Knapp, S., & McClymont, E. L. (2023).
Plio-Pleistocene Southwest African Hydroclimate modulated by Benguela and Indian Ocean temperatures.
Geophysical Research Letters, 50, e2023GL103003. https://doi.org/10.1029/2023GL103003
Copyright: © 2023 The authors.
Published by John Wiley & Sons, Inc. Open access.
Reprinted under a Creative Commons Attribution-NonCommercial 4.0 International license (CC BY-NC 4.0 DEED)
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