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Geosciences Column: Scientists pinpoint where seawater could be leaking into Antarctic ice shelves

Geosciences Column: Scientists pinpoint where seawater could be leaking into Antarctic ice shelves

Over the last few decades, Antarctic ice shelves have been disintegrating at a rapid rate, likely due to warming atmospheric and ocean temperatures, according to scientists. New research reveals that one type of threat to ice shelf stability might be more widespread that previously thought.

A study recently published in EGU’s open access journal The Cryosphere identified several regions in Antarctica were liquid seawater could be leaking into vulnerable layers of an ice shelf.

Scientists have known for some time now that seawater can seep into an ice shelf’s firn layer, the region of compacted snow that is on its way to becoming ice. This seawater infiltration presents an issue to the ice shelf’s stability, since as the seawater spreads throughout the firn layer, the water can create fractures and help expand crevasses already present in the frozen material. Past research has shown that the presence of liquid brine from seawater within an ice shelf is correlated to increased fracturing and calving.

While ice shelf collapse doesn’t directly contribute to sea level rise, since the ice is already floating, stable ice shelves often push back on land-based ice sheets and glaciers, slowing down ice flow into the ocean. Past research has suggested that once an ice shelf collapses, the rate of ice flow from unsupported glaciers can greatly accelerate.

To better understand Antarctic ice shelves’ risk of collapse, the researchers involved with this new study sought to identify where ice shelf firn layers are vulnerable to seawater infiltration. Using Antarctic geometry data, they mapped out the potential ‘brine zones’ within the continent’s ice shelves. These are regions of the ice shelf where the firn layer is both below the sea level and permeable enough to let seawater percolate through.

The results of their analysis revealed that almost all ice shelves in Antarctica have spots where seawater can potentially leak through their layers, with about 10-40 percent of the continent’s total ice shelf area possibly at risk of infiltration.

Map of potential brine zones areas around Antarctica. Map shows areas where permeable firn lies below sea level (the brine zone), with the threshold for firn permeability defined as 750 kg m−3 (red), 800 kg m−3 (yellow) and 830 kg m−3 (blue) calculated using Bedmap2 surface elevation. Bar charts show the mean percentage area of selected ice shelves covered by the brine zone. (Credit: S. Cook et al. 2018)

The researchers compared their estimated points to a map of previously confirmed brine zones, observed through ice cores or radar surveys. After reviewing these records, they identified only one record of brine presence that hadn’t been highlighted by their developed model.

The study found many areas in Antarctica where seawater infiltration could be possible, but has not been previously observed. The findings suggest that this firn layer vulnerability to seawater might be more widespread than previously believed.

The researchers suggest that the most likely new regions where brine from seawater may be present includes the Abbot Ice Shelf, Nickerson Ice Shelf, Sulzberger Ice Shelf, Rennick Ice Shelf, and slower-moving areas of Shackleton Ice Shelf. The regions all contain large swathes of permeable firn below sea level while also subject to relatively warm air temperatures and low flow speeds, the ideal conditions for maintaining liquid brine.

The study points out that there are still many uncertainties in this research, considering the unknowns still present in the data used for mapping and the factors that may influence seawater infiltration. For example, some areas that have large predicted brine zones have an unusually think layer of firn from heavy snowfall. This is the case for the Edward VIII Bay in eastern Antarctica. “Our results indicate the total ice shelf area where permeable firn lies below sea level, but this does not necessarily imply that the firn contains brine,” the authors of the study noted in their article.

Given their findings, the researchers involved recommend that this potentially widespread influence on ice shelves should be further examined and assessed by future studies.

By Olivia Trani, EGU Communications Officer

References

Cook, S., Galton-Fenzi, B. K., Ligtenberg, S. R. M. and Coleman, R.: Brief communication: widespread potential for seawater infiltration on Antarctic ice shelves, The Cryosphere, 12(12), 3853–3859, doi:10.5194/tc-12-3853-2018, 2018.

Hoegh-Guldberg, O., D. Jacob, M. Taylor, M. Bindi, S. Brown, I. Camilloni, A. Diedhiou, R. Djalante, K.L. Ebi, F. Engelbrecht, J.Guiot, Y. Hijioka, S. Mehrotra, A. Payne, S.I. Seneviratne, A. Thomas, R. Warren, and G. Zhou, 2018: Impacts of 1.5ºC Global Warming on Natural and Human Systems. In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C above pre-industrial levels and related global greenhouse gas emission pathways, in the context of strengthening the global response to the threat of climate change, sustainable development, and efforts to eradicate poverty [Masson-Delmotte, V., P. Zhai, H.-O. Pörtner, D. Roberts, J. Skea, P.R. Shukla, A. Pirani, W. Moufouma-Okia, C. Péan, R. Pidcock, S. Connors, J.B.R. Matthews, Y. Chen, X. Zhou, M.I.Gomis, E. Lonnoy, T.Maycock, M.Tignor, and T. Waterfield (eds.)]. In Press

Scambos, T. A.: Glacier acceleration and thinning after ice shelf collapse in the Larsen B embayment, Antarctica, Geophysical Research Letters, 31(18), doi:10.1029/2004gl020670, 2004.

Scambos, T., Fricker, H. A., Liu, C.-C., Bohlander, J., Fastook, J., Sargent, A., Massom, R. and Wu, A.-M.: Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups, Earth and Planetary Science Letters, 280(1–4), 51–60, doi:10.1016/j.epsl.2008.12.027, 2009.

State of the Cryosphere: Ice Shelves. National Snow & Ice Data Center

Geosciences Column: Using volcanoes to study carbon emissions’ long-term environmental effect

Geosciences Column: Using volcanoes to study carbon emissions’ long-term environmental effect

In a world where carbon dioxide levels are rapidly rising, how do you study the long-term effect of carbon emissions?

To answer this question, some scientists have turned to Mammoth Mountain, a volcano in California that’s been releasing carbon dioxide for years. Recently, a team of researchers found that this volcanic ecosystem could give clues to how plants respond to elevated levels of carbon dioxide over long periods of time. The scientists suggest that studying carbon-emitting volcanoes could give us a deeper understanding on how climate change will influence terrestrial ecosystems through the decades. The results of their study were published last month in EGU’s open access journal Biogeosciences.

Carbon emissions reached a record high in 2018, as fossil-fuel use contributed roughly 37.1 billion tonnes of carbon dioxide to the atmosphere. Emissions are expected to increase globally if left unabated, and ecologists have been trying to better understand how this trend will impact plant ecology. One popular technique, which involves exposing environments to increased levels of carbon dioxide, has been used since the 1990s to study climate change’s impact.

The method, also known as the Free-Air Carbon dioxide Enrichment (FACE) experiment, has offered valuable insight into this matter, but can only give a short-term perspective. As a result, it’s been more challenging for scientists to study the long-term impact that emissions have on plant communities and ecosystems, according to the new study.

FACE facilities, such as the Nevada Desert FACE Facility, creates 21st century atmospheric conditions in an otherwise natural environment. Credit: National Nuclear Security Administration / Nevada Site Office via Wikimedia Commons

Carbon-emitting volcanoes, on the other hand, are often well-studied systems and have been known to emit carbon dioxide for decades to even centuries. For example, experts have been collecting data on gas emissions from Mammoth Mountain, a lava dome complex in eastern California, for almost twenty years. The volcano releases carbon dioxide at high concentrations through faults and fissures on the mountainside, subsequently leaving its forest environment exposed to the emissions. In short, the volcanic ecosystem essentially acts like a natural FACE experiment site.

“This is where long-term localized emissions from volcanic [carbon dioxide] can play a game-changing role in how to assess the long-term [carbon dioxide] effect on ecosystems,” wrote the authors in their published study. Research with longer study periods would also allow scientists to assess climate change’s effect on long-term ecosystem dynamics, including plant acclimation and species dominance shifts.

Through this exploratory study, the researchers involved sought to better understand whether the long-term ecological response to carbon-emitting volcanoes is actually representative to the ecological impact of increased atmospheric carbon dioxide.

Remotely sensed imagery acquired over Mammoth Mountain, showing (a) maps of soil CO2 flux simulated based on accumulation chamber measurements, shown overlaid on aerial RGB image, (b) above-ground biomass (c) evapotranspiration, and (d) normalized difference vegetation index (NDVI). Credit: K. Cawse-Nicholson et al.

To do so, the scientists analysed characteristics of the forest ecosystem situated on the Mammoth Mountain volcano. With the help of airborne remote-sensing tools, the team measured several ecological variables, including the forest’s canopy greenness, height and nitrogen concentrations, evapotranspiration, and biomass. Additionally they examined the carbon dioxide fluxes within actively degassing areas on Mammoth Mountain.

They used all this data to model the structure, composition, and function of the volcano’s forest, as well as model how the ecosystem changes when exposed to increased carbon emissions. Their results revealed that the carbon dioxide fluxes from Mammoth Mountain’s soil were correlated to many of the ecological variables analysed. Additionally, the researchers discovered that parts of the observed environmental impact of the volcano’s emissions were consistent with outcomes from past FACE experiments.  

Given the results, the study suggests that these kind of volcanic systems could work as natural test environments for long-term climate research. “This methodology can be applied to any site that is exposed to elevated [carbon dioxide],” the researchers wrote. Given that some plant communities have been exposed to volcanic emissions for hundreds of years, this method could help paint a more comprehensive picture of our future environment as Earth’s climate changes.

By Olivia Trani, EGU Communications Officer

References

Cawse-Nicholson, K., Fisher, J. B., Famiglietti, C. A., Braverman, A., Schwandner, F. M., Lewicki, J. L., Townsend, P. A., Schimel, D. S., Pavlick, R., Bormann, K. J., Ferraz, A., Kang, E. L., Ma, P., Bogue, R. R., Youmans, T., and Pieri, D. C.: Ecosystem responses to elevated CO2 using airborne remote sensing at Mammoth Mountain, California, Biogeosciences, 15, 7403-7418, https://doi.org/10.5194/bg-15-7403-2018, 2018.

Geosciences Column: How climate change put a damper on the Maya civilisation

Geosciences Column: How climate change put a damper on the Maya civilisation

More than 4,000 years ago, when the Great Pyramid of Giza and Stonehenge were being built, the Maya civilisation emerged in Central America. The indigenous group prospered for thousands of years until its fall in the 13th century (potentially due to severe drought). However, thousands of years before this collapse, severely soggy conditions lasting for many centuries likely inhibited the civilisation’s development, according to a recent study published in EGU’s open access journal Climate of the Past.

During their most productive era, often referred to as the Classic period (300-800 CE), Maya communities had established a complex civilisation, with a network of highly populated cities, large-scale infrastructure, a thriving agricultural system and an advanced understanding in mathematics and astronomy. However, in their early days, dating back to at least 2600 BCE, the Maya people were largely mobile hunter-gatherers, hunting, fishing and foraging across the lowlands.

Around 1000 BCE, some Maya communities had started to transition away from their nomadic lifestyles, and instead were moving towards establishing more sedentary societies, building small villages and relying more heavily on cultivating crops for their sustenance. However, experts suggest that agricultural practices didn’t gain momentum until 400 BCE, raising the question as to why Maya development was delayed for so many centuries.

By analysing two new palaeo-precipitation records, Kees Nooren, lead author of the study and a researcher at Utrecht University in the Netherlands, and his colleagues were able to gain insight into the environmental conditions during this pivotal time, and the impact that climate change could have had on the Maya society.

To determine the regional climate conditions during this period of time, the authors examined a beach ridge plain in the Mexican state of Tabasco, off the Gulf of Mexico, which contains a long-term record of ridge elevation changes for much of the late Holocene. Since precipitation has a large influence on the elevation of this beach ridge, this record is a good indicator of how much rainfall and flooding may have occurred during Maya settlement.

A large part of the central Maya lowlands (outlined with a black dashed line) is drained by the Usumacinta (Us.) River (a). During the Pre-Classic period this river was the main supplier of sand contributing to the formation of the extensive beach ridge plain at the Gulf of Mexico coast (b). Periods of low rainfall result in low river discharges and are associated with relatively elevated beach ridges. Taken from Nooren, K et al., 2018

Additionally, the researchers also assessed core samples taken from Lake Tuspan, a shallow body of water in northern Guatemala that is situated within the Central Maya Lowlands. Because the lake receives its water almost exclusively from a small section of the region (770 square kilometres), its sediment layers provide a good record of rainfall on a very local scale.

The image on p. 74 of the Dresden Codex depicts a torrential downpour probably associated with a destructive flood (Thompson, 1972). Taken from Nooren, K et al., 2018

The research team’s analysis suggested that, starting around 1000-850 BCE, the region shifted from a relatively dry climate, to a wetter environment. Such conditions would have made a farming in this region more difficult and less appealing compared to foraging and hunting. The researchers suggest that this change in climate could be one of the reasons why Maya agricultural development was at a standstill for such a long time.

The researchers also propose that this long-term climate trend could have been brought on by a shift of the Intertropical Convergence Zone (ITCZ), a region near the equator where northeast and southeast winds intermingle and where most of the Earth’s rain makes landfall. The position of this zone can move naturally in response to Earth’s changes in insolation, and a northerly shift of the ITCZ could help account for some of the morphological changes the authors observed in the precipitation records.

After more than 450 years of excessive rainfall and large floods, the records then suggest that the region experienced drier conditions once again. By this time period, the Maya populations began to rapidly intensify their farming efforts and develop major cities, further suggesting that the wet conditions may have helped delay such efforts.

This is not the first time the Nooren and his colleagues have found evidence of major environmental influence on the Maya civilisation. For example, earlier research led by Nooren suggests that, in the 6th century, the El Chichón volcano in southern Mexico released massive amounts of sulfur into the stratosphere, triggering global climate change that likely contributed to a ‘dark age’ in Maya history for several decades. During this time, often referred to as the “Maya Hiatus,’ Maya societies experienced stagnation, increased warfare and political unrest. The research results were presented at the 2016 General Assembly and later published in Geology.

The results of these studies highlight how changes in our climate have greatly influenced communities and at times even shaped the course of societal history, both for better and for worse.

By Olivia Trani, EGU Communications Officer

References

Ebert, C. et al.: Regional response to drought during the formation and decline of Preclassic Maya societies. Quaternary Science Reviews 173:211-235, 2017

Nooren, K., Hoek, W. Z., Dermody, B. J., Galop, D., Metcalfe, S., Islebe, G., and Middelkoop, H.: Climate impact on the development of Pre-Classic Maya civilization. Clim. Past, 14, 1253-1273, 2018

Nooren, K.: Holocene evolution of the Tabasco delta – Mexico : impact of climate, volcanism and humans. Utrecht University Repository (Dissertation). 2017

Nooren, K. et al.: Explosive eruption of El Chichón volcano (Mexico) disrupted 6th century Maya civilization and contributed to global cooling, Geology, 45, 175-178, 2016

Press conference: Volcanoes, climate changes and droughts: civilisational resilience and collapse. European Geosciences Union General Assembly 2016

Caltech Climate Dynamics Group, Why does the ITCZ shift and how? 2016

Geosciences Column: The best spots to hunt for ancient ice cores

Geosciences Column: The best spots to hunt for ancient ice cores

Where in the world can you find some of Earth’s oldest ice? That is the question a team of French and US scientists aimed to answer. They recently identified spots in East Antarctica that likely have the right conditions to harbor ice that formed 1.5 million years ago. Scientists hope that obtaining and analysing an undisturbed sample of ice this old will give them clues about Earth’s ancient climate.

The team published their findings in The Cryosphere, an open access journal of the European Geosciences Union (EGU).

Why study ancient ice?

When snow falls and covers an ice sheet, it forms a fluffy airy layer of frozen mass. Over time, this snowy layer is compacted into solid ice under the weight of new snowfall, trapping pockets of air, like amber trapping prehistoric insects. For today’s scientists, these air bubbles, some sealed off thousands to millions of years ago, are snapshots of what the Earth’s atmosphere looked like at the time these pockets were locked in ice. Researchers can tap into these bubbles to understand how the proportion of greenhouse gases in our atmosphere have changed throughout time.

As of now, the oldest ice archive available to scientists only goes back 800,000 years, according to the authors of the study. While pretty ancient, this ice record missed out on some major climate events in Earth’s recent history. Scientists are particularly interested in studying the time between 1.2 million years ago and 900,000 years ago, a period scientifically referred to as the mid-Pleistocene transition.

In the last few million years leading up to this transition, the Earth’s climate would experience a period of variation, from cold glacial periods to warmer periods, every 40,000 years. However, after the mid-Pleistocene transition, Earth’s climate cycle lengthened in time, with each period of variation occurring every 100,000 years.  

Currently, there isn’t a scientific consensus on the origin of this transition or what factors were involved. By examining old ice samples and studying the composition of the atmospheric gases present throughout this transition, scientist hope to paint a clearer picture of this influential time. “Locating a future 1.5 [million-year]-old ice drill site was identified as one of the main goals of the ice-core community,” wrote the authors of the study.  

The quest for old ice

Finding ice older than 800,000 years is difficult since the Earth’s deepest, oldest ice are the most at risk of melting due to the planet’s internal heat. Places where an ice sheet’s layers are very thick have an even greater risk of melting.

Mesh, bedrock dataset (Fretwell et al., 2013; Young et al., 2017) and basal melt rate (Passalacqua et al., 2017) used for the simulation. Credit: O. Passalacqua et al. 2018.

“If the ice thickness is too high the old ice at the bottom is getting so warm by geothermal heating that it is melted away,” said Hubertus Fischer, a climate physics researcher from the University of Bern in Switzerland not involved in the study, in an earlier EGU press release.

Last summer, a team of researchers from Princeton University announced that they had unearthed an ice core that dates back 2.7 million years, but the sample’s layers of ice aren’t in chronological order, with ice less than 800,000 years old intermingling with the older frozen strata. Rather than presenting a seamless record of Earth’s climate history, the core can only offer ‘climate snapshots.’

Finding the best of the rest

The authors of the recent The Cryosphere study used a series of criteria to guide their search for sites that likely could produce ice cores that are both old and undisturbed. They established that potential sites should of course contain ice as old as 1.5 million years, but also have a high enough resolution for scientists to study frequent changes in Earth’s climate.

Additionally, the researchers established that sites should not be prone to folding or wrinkling, as these kinds of disturbances can interfere with the order of ice layers.

Lastly, they noted that the bedrock on which the ice sheet sits should be higher than any nearby subglacial lakes, since the lake water could increase the risk of ice melt.

Magenta boxes A, B and C correspond to areas that could be considered as our best oldest-ice targets. Colored points locate possible drill sites. Credit: O. Passalacqua et al. 2018.

 

Using these criteria, the researchers evaluated one region of East Antarctica, the Dome C summit, which scientists in the past have considered a good candidate site for finding old ice. They ran three-dimensional ice flow simulations to locate parts of the region that are the most likely to contain ancient ice, based on their established parameters.

By narrowing down the list of eligible sites, the researchers were able to pinpoint regions just a few square kilometres in size where intact 1.5 million-year-old ice are very likely to be found, according to their models. Their results revealed that some promising areas are situated a little less than 40 kilometres southwest of the Dome C summit.

The researchers hope their new findings will bring scientists one step closer towards finding Earth’s ancient ice.

By Olivia Trani, EGU Communications Officer