Adrift along the Sundarbans mangroves, east India

Mid March 2021, I set out with 2 other wildlife enthusiasts to explore the Sundarbans delta in east India. The 3-hour journey from Kolkata city, on a busy road fringed by industrial towns tapered off at Gadkhali port – civilization’s last ‘land’ frontier before the largest  continuous mangrove stretch in the world. We arrived after dusk, boarded our boat (with a crew of 2 naturalists, 3 boatmen, and a chef!), and were adrift upon dark waterways guided by twinkling village lights. In our haste, we thought little of just how ‘remote’ this wilderness was. 

The next morning, we woke up to a different world – sheer, open stretches of water that melted away into the morning haze. Nothing quite prepares you for the Sundarbans, one imagines river deltas as narrow channels of water interrupted by little islands, yet that morning, with no other islands visible on the horizon, it seemed more like a sea than a river. For the next three days, we’d be exploring the Sundarbans – among the most difficult terrains for civilization and wildlife watching, from dawn to dusk. 

A stand of 'sundari' trees (Heritiera fomes) with a distinct line of discolouration marking the high tide line.
A stand of ‘sundari’ trees (Heritiera fomes) with a distinct line of discolouration marking the high tide line.
Photo credits: Devayani Khare

Formed as several rivers, including the Hooghly, Ganges, Brahmaputra, Meghna, and other channels with different local names, combine and flow towards the sea. The Sundarbans named for the ‘sundari’ trees (Heritiera fomes) + ‘ban’ the local word for forests, covers roughly 10,000 sq. km (3900 sq. miles), partly in India and partly in Bangladesh. Of the delta’s 104 islands that fall within India’s territory, just a handful of islands are inhabited, while the rest form the buffer and core zones of the Sundarbans National Park. With its incredible, fragile biodiversity, the Sundarbans was also declared a UNESCO World Heritage Site in 1987.

As idyllic as remote islands seem, the Sundarbans has always been a dangerous landscape, and not just on account of the tigers. Rapid coastline erosion, riverbanks and islands shape-shift due to the accumulation or removal of sediment or silt, and extreme events like cyclones are commonly experienced in the Bay of Bengal [1] – the sea that the delta opens out into. Cyclones like Amphan (May 2020), Fani and Bulbul (both 2019) were among the 13 supercyclones this area has witnessed in the past two decades [2]. Research across the world has shown that dense mangrove vegetation reduces the wave height and wave energy during storms[4], and can thereby dampen the effect of extreme events like storms and cyclones.  Yet, deforestation has thinned out the ‘protective shield’ of mangrove, and the ‘sundari’ trees which the forests were named after have been declared endangered by the IUCN. 

There is less than a century’s worth of geoscience research available for the region, and it indicates that the delta is in constant flux: sediment building and eroding away at its banks. This makes embankments and other coastal engineering solutions unviable, and farming is a poor prospect[3]. Rising sea-levels caused by climate change may further fragment the habitat and cause greater salinity in the water, both of which will adversely affect the fauna and flora. The short data record makes it difficult to understand long-term cycles for better mitigation in the near future.

A partly leucistic i.e lacking skin pigment, saltwater crocodile (Crocodylus porosus) basking along the banks - crocodiles and tigers account for most of the human-wildlife conflicts in the Sundarbans.
A partly leucistic i.e lacking skin pigment, saltwater crocodile (Crocodylus porosus) basking along the banks – crocodiles and tigers account for most of the human-wildlife conflicts in the Sundarbans.
Photo credits: Devayani Khare

For locals, livelihood options are limited: near-subsistence farming or fishing (saltwater fish, shellfish, and crabs), boat-operated trade with the mainland, timber-felling (most of it illegal), honey, fruit, resin and medicinal plant extraction governed by the forest authorities and forest range services with a high risk of man-wildlife conflicts. Fly ash trade with Bangladesh flourishes, but as Kolkata is the major hub of operations with the Sundarbans merely a thoroughfare, there are few local job opportunities. However, in recent years, tourism within the delta has emerged as an economic champion: encouraging private investment in infrastructure, accelerating development with over 30 hotels and resorts ranging from economic to luxury, and the promise of further expansion.

Yet tourism development is a two-edged sword: in India, it has often been blind to the carrying capacity, local needs, and risks of a destination. The recent, mid-March 2021 election drive saw promises being made by the central government – Rs 2 lakh crore/trillion (that’s over 13 billion USD!) investment to develop the Sundarbans into the most advanced region in the West Bengal state. Even if this is empty political rhetoric, development of the Sundarban delta is an imminent threat – as not all of it will consider the ecological role of mangroves, the complexities of sediment transfer, the storm-dampening effects nor the local socio-economic and political context.

A crested serpent eagle (Spilornis cheela) is one among many raptors that haunt the mangrove stretches in search of snakes and lizards.
Photo credits: Devayani Khare

Over the three days, we cruised along the Sundarbans. Wildlife sightings were few, and far between – yet offered rare glimpses into the resilience of creatures in this adverse, brackish landscape. Ever so often, we encountered holidaymakers and casual tourists: there were more of them than the wildlife enthusiasts, reflecting what tourism development would mean for the Sundarbans. I believe everyone should have access to a destination, however sensitisation, awareness, and education is a crucial part of tourism, especially in landscapes as fragile as deltas. In this context, geoscience can lay the foundations to ensure biodiversity, people, livelihoods, and infrastructure are resilient to environmental change and natural hazards, and how tourism can be beneficial in the long-term.

Cited Literature:

[1] Dasgupta, Susmita, David Wheeler, Md. Istiak Sobhan, Sunando Bandyopadhyay, Ainun Nishat, and Tapas Paul. 2020. Coping with Climate Change in the Sundarbans: Lessons from Multidisciplinary Studies. International Development in Focus. Washington, DC: World Bank. doi:10.1596/978-1-4648-1587-4. License: Creative Commons Attribution CC BY 3.0 IGO

[2] Cracks in the shield: How the Sundarbans is dying and making Bengal prone to cyclones, News Laundry, Dec 2020

[3] Sunando Bandyopadhyay, Dipanwita Mukherjee, Sima Bag, Dilip Kumar Pal, Rabindra Kumar Das, and Kalyan Rudra. 2004. 20th Century Evolution of banks and islands of the Hugli estuary, West Bengal, India: evidences from maps, images and GPS survey. Geomorphology and Environment.
[4] McIvor, A.L., Spencer, T., Möller, I. and Spalding. M. (2012) Storm surge reduction by mangroves. Natural Coastal Protection Series: Report 2. Cambridge Coastal Research Unit Working Paper 41. Published by The Nature Conservancy and Wetlands International. 35 pages. ISSN 2050-7941. URL: http://www.naturalcoastalprotection.org/documents/storm-surge-reduction-by-mangroves


Adrift along the Sundarbans mangroves, east India by Devayani Khare is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

What Lies Beneath: Tracing Magma Interactions Within Earth’s Crust

Featured Image: Yosemite National Park, California, USA by Thomas H. from Pixabay 

Paper: Feldspar recycling across magma mush bodies during the voluminous Half Dome and Cathedral Peak stages of the Tuolumne intrusive complex, Yosemite National Park, California, USA

Authors: Louis F. Oppenheim, Valbone Memeti, Calvin G. Barnes, Melissa Chambers, Joachim Krause, and Rosario Esposito

Earth’s landscapes provide evidence of the geological processes which have shaped it over the past 4 billion years.  The Earth’s crust, our planet’s outermost layer, preserves an extensive record of these processes. Within the crust igneous rocks which were once molten at depth and fed active volcanic eruptions, preserve evidence of the inner workings of volcanoes. These inner workings or “magmatic plumbing systems” are the focus of recent work by Oppenheim et al. (2021). In this work, Oppenheim and co-authors studied the crystal record of fossilized plumbing systems in order to provide new insights into the storage conditions and transport mechanisms of magma within Earths’ crust.

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Do Hurricanes Choke on Dust?

Satellite image showing plume of dust drifting from north Africa

Paper – Influence of Saharan Dust on the Large‐Scale Meteorological Environment for Development of Tropical Cyclone Over North Atlantic Ocean Basin
Authors – Yue Sun and Chuanfeng Zhao

Several times a year, strong gusts blow dust from the Sahara Desert westwards over the Atlantic Ocean. When the plume reaches the Caribbean, many residents experience respiratory irritation and allergic reactions to the dust. On particularly bad days, those with sensitivities to or certain pre-existing conditions are urged to stay indoors. The haze reduces visibility and casts a dull filter over the landscape.

There are several effects of Saharan dust on the climate and environment, but a more immediate product of the plumes is their effect on hurricane activity. Many researchers have investigated whether tropical cyclones are suppressed by the dust, but the large-scale link between dust storms and individual elements of hurricane formation has been difficult to demonstrate. Now, a 2020 paper by researchers at the Beijing Normal University in China has explored the influence of Saharan dust on the main factors of hurricane formation. They considered how observations of weather variables like humidity levels, changes in wind speed and direction and ocean temperatures were affected by dust plumes from June to September of 2000 to 2018. The study area included most of West Africa, the Atlantic Ocean, the Caribbean and the Gulf of Mexico (0°W to 80°W and 0°N to 40°N). 

June 24 2020 Saharan Dust plume was captured by the VIIRS data from NASA/NOAA’s Suomi NPP satellite. The bright streaks are sunlight reflecting off the ocean. Credits: NASA/NOAA, Colin Seftor.

The researchers used observations of dust quantities at different levels of the atmosphere and statistical analysis to review the link between dust levels, each weather variable, and the development of tropical systems. They found that, though the air is warmer at the layer where the dust travels, the sea surface temperatures are much lower during and after dust events. Humidity also decreases at lower levels of the atmosphere (but increases at mid-levels) due to the effects of the dust. On the continent, dust also raises surface temperatures. The difference between the warmer land and cooler seas increases wind shear, which in turn suppresses storm systems.

Researchers concluded that there is a statistically significant link between Saharan dust and the meteorological factors that result in hurricanes. Tropical cyclones are less likely when dust is active in the Atlantic since they thrive in high humidity and warmth, both of which are stifled by large dust plumes. 

The authors’ work fits with previous simulations that modeled potential interactions of the dust layer with tropical cyclones, as well as documented trends in hurricane timing and dust activity. While the authors did not explore other factors, additional research could show the effects of ocean currents and other meteorological variables on these findings, adding valuable information to our understanding of why hurricanes form. One such research direction might explore the major influence of El Niño and La Niña years on storm formation. The authors did not discuss the effect of dust on storms that have already formed, but in 2001, National Oceanic and Atmospheric Administration satellites observed the Saharan dust preventing Erin, the 6th tropical depression of the season, from strengthening4. Once free of the dust, Erin became the first hurricane of that year.

In addition to helping keep hurricanes away, Saharan dust plumes are also important for their role in ecosystems on land and in the ocean. As the plume drifts, dust settles into the ocean, adding millions of tonnes of nutrients to the marine environment. This supports the growth of tiny plant-like organisms called phytoplankton that absorb carbon dioxide from the air and water and produce oxygen. Phytoplankton are crucial to marine ecosystems and lock away carbon from the atmosphere when they die and settle to the ocean floor. The nutrients in the dust also encourage the growth of plants on land. This is great for the forests in the Caribbean and parts of South America in the path of the dust.

Despite the sinus issues and darkened skies, the dust has several long- and short-term benefits. So, the next time the forecast shows plumes of dust moving across the Atlantic, remember that it’s not all bad news. 

Do Hurricanes Choke on Dust? by Davitia James is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Taking the measure of the measurer

Featured image: A USGS “Did you feel it?” map for a M6.5 earthquake that occurred in the Monte Cristo Range in Nevada on May 15th, 2020 (public domain)

Paper: Which earthquake accounts matter?
Authors: Susan E. Hough and Stacey S. Martin

Seismologists who study earthquakes spend much of their time looking at wiggly lines that represent recordings of ground motion from seismometers, but in places where those data aren’t available, we often turn to what we call “macroseismic” data: eyewitness accounts from people who felt the shaking. But when we ask people on the ground, “Did you feel it?,” who is answering?

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Plants may help solve the climate crisis, but is there enough water for everyone?

Featured image: Sugarcane plantation to produce ethanol in Brazil by José Reynaldo da Fonseca on Wikipedia under CC BY 2.5.

Paper: Stenzel, F., Greve, P., Lucht, W. et al. Irrigation of biomass plantations may globally increase water stress more than climate change. Nat Commun 12, 1512 (2021). https://doi.org/10.1038/s41467-021-21640-3

In order to mitigate the effects of the climate crisis, we must stay under a 1.5℃ average global temperature increase from pre-industrial levels. To help reach this goal, there is growing interest in “negative emission technologies”, which are methods of removing greenhouse gases, like carbon dioxide, from the atmosphere. These carbon capture technologies have been around since the 1970s, but the best carbon capture technology might be as simple as plants.  Fabian Stenzel and his team explain that cultivating fast-growing plant species, processing them into biomass, and capturing any emitted carbon dioxide therein, would actually result in negative emissions. Specifically, creating biomass through this method can capture upwards of 2 gigatons of carbon per year by 2050 (that’s close to the mass of 12 million blue whales). Burning this would also unlock an incredibly energy dense source of power. While burning the biomass would inevitably release carbon dioxide into the atmosphere, the process of growing it would drastically offset this by removing a much larger amount. However, one crucial question needs to be answered: will we have enough water to pull it off?

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You are what you eat…and also where you fish

Article: Why productive lakes are larger mercury sedimentary sinks than oligotrophic brown water lakes

Authors: Martin Schütze, Philipp Gatz, Benjamin‐Silas Gilfedder, Harald Biester

Advisories and outreach campaigns have worked for years to help us understand how the fish we eat impacts the amount of hazardous mercury we consume. Mercury is present in the environment naturally in several forms, but consumption advisories warn against methyl-mercury. This substance not only moves throughout the aquatic ecosystem, but bio-accumulates, or increases in concentration, as it moves higher in the food chain.  But the size of the fish is not the only influence on its mercury levels – it may also matter where it lives. 

Most mercury in lakes is initially deposited from the atmosphere. These levels vary regionally, influenced by things like weather patterns and local industry. Mercury is also deposited on land, though, and it can eventually leach and erode from soils, moving through surface and groundwater into local lakes. Researchers have known for some time that the vegetation and soil types in the watershed can influence mercury influx to lakes; for example, coniferous trees generally take up more mercury from the atmosphere than deciduous trees, making the forest litter and, eventually, the organic rich layers of forest soils more concentrated in mercury in coniferous forests. 

A recent German study compared mercury levels in two sets of lakes, looking at everything from surrounding vegetation and topography to local weather patterns, and found that previously observed findings held up; mercury levels were higher in leaf litter and organic soils than other surrounding sediments, and higher in areas with more coniferous vegetation. However, when the authors undertook mathematical modelling to balance the input of mercury from atmospheric deposition and local erosion to the outflow, the numbers didn’t add up the same way in all the lakes.

The difference, they documented, was in the productivity of the lakes. Algae scavenge mercury from the water column and, when they die and sink, take the mercury along. This leads to mercury deposition in the lake sediments. By comparing measurements of mercury in the water column, in accumulated sediments on the lake floors, and in sediment ‘traps’ that collect sediment as it is falling through the water column, the researchers showed that large algal blooms significantly increase the transport of mercury from the water column into lake sediments. In a set of forested, alpine lakes that were low in nutrients and had few algal blooms, the monitoring data showed that most of the mercury inputs were eventually lost to a combination of river outflow, re-emission to the atmosphere, and sediment burial. In lakes with higher nutrient loads and more common algal blooms, a similar input of mercury was translated into a much higher flux to the lake sediments, which they traced to the concentration of mercury in the algal organic matter.

The high rate of mercury delivery to lake sediments, especially in very productive lakes, may be bad news for fishing. The high rate of organic matter input to the sediment also leads to a low-oxygen environment which can spur the bacterially-mediated chemical process that turns mercury into the methyl-mercury form. When it is released and recycled from the sediments, it works its way up the food chain. Lakes in many parts of the world are seeing increased algal growth from warmer temperatures and higher nutrient input, and the resultant highly-visible algal blooms may have a significant impact on the invisible movement of hazardous mercury to consumers at the top.


You are what you eat…and also where you fish by Avery Shinneman is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

How does climate change impact extreme cold outbreaks in the United States?

Featured image from CJ on Pixabay

Article: Quantifying Human-Induced Dynamic and Thermodynamic Contributions to Severe Cold Outbreaks Like November 2019 in the Eastern United States
Authors: C. Zhou, A. Dai, J. Wang, and D. Chen

Questions about extreme cold outbreaks have been featured in the U.S. news recently, as a majority of the country experienced record-breaking cold temperatures during the week of February 8, 2021. Was this extreme cold related to climate change? Will we see more of these events in the future? As Texans faced extensive blackouts due to issues with electricity generation and transmission because of the cold, meteorologists and news reporters tried to answer these questions as best they could. But what does the latest climate science say about the link, if any, between extreme cold outbreaks and climate change?

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Prehistoric Microbial Meals Found in the Australian Outback

Featured Image: Rock fracture from the Dresser Formation, Australia. Fluid inclusions are trapped in the white stripes. Image courtesy Ser Amantio di Nicolao, used with permission.

Paper: Ingredients for microbial life preserved in 3.5 billion-year-old fluid inclusions

Authors: Helge Mißbach, Jan-Peter Duda, Alfons M. van den Kerkhof, Volker Lüders, Andreas Pack, Joachim Reitner, Volker Thiel

Just a few weeks ago NASA made a historic landing of the Perseverance rover on Mars.  This rover symbolizes our human drive for exploration and the need to find the origins of life to answer the big question—are we alone in the universe?  In addition to extraterrestrial investigation and research, we can address this fundamental question here on our own planet by digging into extreme environments that are analogs for ancient Earth or other planets.  These unusual environments, such as hydrothermal vents in our deepest oceans, boiling hot springs in Yellowstone, and prehistoric lakes in South America, can give us glimpses of ancient information and clues about to the ingredients of life.  By discovering our own origins of life, we can begin to understand how it may evolve on other planets.

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Hunting for Antibiotics in Caves

Featured Image courtesy Doronenko and Wikimedia Commons

Paper: High-Throughput Sequencing Analysis of the Actinobacterial Spatial Diversity in Moonmilk Deposits.

Authors: Marta Maciejewska , Magdalena Całusińska, Luc Cornet, Delphine Adam, Igor S. Pessi, Sandrine Malchair, Philippe Delfosse, Denis Baurain, Hazel A. Barton, Monique Carnol and Sébastien Rigali

Do you ever think about the microbes around you when you go caving? Me neither, but a team of scientists from Belgium did. 

Actinobacteria are found in many places around the world, including volcanic terrains and ice caves. They are of particular importance to cave ecosystems and structure since the formation of speleothems (cave formations) like moon milk is thought to be aided by Actinobacteria. These microbes are known for their ability to produce filaments and aid calcium carbonate deposition and precipitation, which could be important for the mineral deposition that forms speleothems. 

Moonmilk deposits from Bergmilchkammer cave (1862/20), courtesy Doronenko and Wikimedia Commons

Despite the importance of microbes in caves, our understanding of microbial communities and spatial distribution within a cave is still fairly limited, i.e. we still don’t know which microbes dominate cave formations and where they live. An international team of scientists set out to answer these questions using three speleothems in the Grotte des Collemboles (English: Springtails’ Cave) in Belgium. Using sterile scalpels, the team scraped soft moonmilk deposits from the walls of the cave into tubes to understand whether different speleothems in the same cave have different bacterial communities.

Using high-throughput DNA sequencing, they found that all the moonmilk deposits had over 700 species in common but distinct communities of bacteria. At least 10% of the species on a particular speleothem were unique to it, and they identified over 4,000 species in total. Actinobacteria was the second-most abundant group (after Proteobacteria) across deposits and many Actinobacterial groups like Nocardia, Pseudonocardia and Streptomyces were found at every speleothem.

Within Actinobacteria, the genus Streptomyces showed the highest diversity (19 species) across all sites even though they only comprised 3% of the actinobacterial community. Interestingly, the team could only grow 5 of these Streptomyces in the lab, which reinforces the significant obstacles to culturing microorganisms still faced by microbiologists.

Streptomyces coelicolor colonies, courtesy Norwich Research Park Image Library

Streptomyces are already a prodigious source of antibiotics and other biologically important compounds, but could these speleothem communities be a source of novel antibiotic compounds? The answer might be worth exploring, given the diversity of Streptomyces found in just this one cave but also the emerging roles of other Actinobacteria in antibiotic production.

The difficulty of growing in situ the bacteria we find in cave formations might complicate our ability to study the compounds they produce, but such adventures could still offer fascinating insights into the microbial inhabitants of caves and how they help bind mineral formations together. The next time you go caving, hopefully you’ll think about the Actinobacteria that surround you!

Creative Commons License

Hunting for Antibiotics in Caves by Janani Hariharan is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.

Tiny Crystals, Big Story: Time capsules from the Early Mars

Featured Image: Zircon grain under the Scanning Electron Microscope (SEM). Image used with permission from Wikipedia (Emmanuel Roquette).

Article: The internal structure and geodynamics of Mars inferred from a 4.2-Gyr zircon record.

Authors: Maria M. Costa, Ninna K. Jensen, Laura C. Bouvier, James N. Connelly, Takashi Mikouchi, Matthew S. A. Horstwood, Jussi-Petteri Suuronen, Frédéric Moynier, Zhengbin Deng, Arnaud Agranier, Laure A. J. Martin, Tim E. Johnson, Alexander A. Nemchin, and Martin Bizzarro

While sitting in Geology 101 studying the geological time scale, most of us have gone through this experience where we imagined ourselves going back in time; visualizing mammoths passing by, dinosaurs hunting and fighting. But all these pictures start to become hazy and unclear when we reach close to 4 billion years. It is the time for which we have no rock records, and this is where zircons or what I would like to call “tiny survivors” comes in.

Continue reading “Tiny Crystals, Big Story: Time capsules from the Early Mars”