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Imaggeo on Mondays: A prehistoric forest

Imaggeo on Mondays: A prehistoric forest

This stunning vista encompasses the south-western wilderness of Tasmania as seen from the Tahune air walk 60 m above the Huon river valley. In front lies the beginning of a huge UNESCO World Heritage Site, covering almost a fourth of the area of Tasmania. The site mostly consists of a pristine, temperate rainforest of Gondwanan origin that is home to the tallest flowering trees in the world; Eucalyptus spp. reach up to 100 m height in this region.

“I have never tasted the sense of a more remote place than this one. Give me more,” says Vytas Huth, who captured this stunning shot.

Gondwana was a supercontinent, consisting of present day Africa, South America, India, Madagascar, Australia and New Zealand. It formed when the even larger supercontinent of Pangaea broke up 250 million years ago.

Slowly, Gondwana started to break apart too. India tore away first, followed by Africa and then New Zealand. By the end of the Cretaceous, 65 million years ago, only South America, Australia and Antarctica remained joined.  It took a further 20 million years before Australia and Antarctica separated.

By the time Australia started being pulled northwards, the first glaciers were forming on Antarctica, as it began freezing over. Atop the old rocks which made up its bulk, animals and plants of ancient origin, travel northwards with the Land Down Under.

Because India and Africa broke away from the supercontinent so early on, few hallmarks of ancient Gondwana wildlife are left in their present biodiversity. In contrast, Australia and Tasmania remained connected to Antarctica and South America much longer and there are clear similarities in species across these continents.

“Fossil evidence suggests that temperate rainforest once extended across Australia, Antarctica, South America and New Zealand around 45 million years ago. Such fossils and the surviving species in Tasmania provide evidence of the ancient link to Gondwana”, reports the Tasmania Parks & Wildlife Service.

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

August GeoRoundUp: the best of the Earth sciences from around the web

August GeoRoundUp: the best of the Earth sciences from around the web

Drawing inspiration from popular stories on our social media channels, as well as unique and quirky research news, this monthly column aims to bring you the best of the Earth and planetary sciences from around the web.

Major Stories

On August 25th Hurricane Harvey made landfall along the southern coast of the U.S.A, bringing record breaking rainfall, widespread flooding and a natural disaster on a scale not seen in the country for a long time. In fact, it’s the first time since 2005 a major hurricane has threatened mainland U.S.A. – a record long period.

But Harvey’s story began long before it brought destruction to Texas and Louisiana.

On August 17th,the National Space Agency (NASA) satellite’s first spotted a tropical depression forming off the coast of the Lesser Antilles. From there the storm moved into the eastern Caribbean and was upgraded to Tropical Storm Harvey where it already started dropping very heavy rainfall. By August 21st, it had fragmented into disorganised thunderstorms and was spotted near Honduras, where heavy local rainfall and gusty winds were predicted.

Over the next few days the remnants of the storm travelled westwards towards Nicaragua, Honduras, Belize and the Yucatan Peninsula. Forecasters predicted that, owing to warm waters of the Gulf of Mexico and favorable vertical wind shear, there was a high chance the system could reform once it moved into the Bay of Campeche (in the southern area of the Gulf of Mexico) on August 23rd. By August 24th data acquired with NASA satellites showed Harvey had began to intensify and reorganise. Heavy rainfall was found in the system.

Harvey continued to strengthen as it traveled across the Gulf of Mexico and weather warnings were issued for the central coast of Texas. Citizens were told to expect life-threatening storm surges and freshwater flooding. On August 25th, Harvey was upgraded to a devastating Category 4 hurricane, when sustained wind speeds topped 215 kph.

Since making landfall on Friday and stalling over Texas (Louisiana is also affected) – despite being downgraded to a tropical storm as it weakened – it has broken records of it’s own. “No hurricane, typhoon, or tropical storm, in all of recorded history, has dropped as much water on a single major city as Hurricane Harvey is in the process of doing right now in Houston (Texas)”, reports Forbes. In fact, the National Weather Service had to update the colour charts on their graphics in order to effectively map it. This visualisation maps Harvey’s destructive path through Texas.

A snaptshot from the tweet by the official Twitter account for NOAA’s National Weather Service.

So far the death toll is reported to be between 15 to 23 people, with the Houston Police Chief saying 30,000 people are expected to need temporary shelter and 2,000 people in the city had to be rescued by emergency services (figures correct at time of writing).

Many factors contributed toward making Hurricane Harvey so destructive. “The steering currents that would normally lift it out of that region aren’t there,” J. Marshall Shepherd, director of the atmospheric sciences program at the University of Georgia, told the New York Times. The storm surge has blocked much of the drainage which would take rainfall away from inland areas. And while it isn’t possible to say climate change caused the hurricane, “it has contributed to making it worse”, says Michael E Mann. The director of the Earth System Science Center at Pennsylvania State University argues that rising sea levels and ocean water temperatures in the region (brought about by climate change) contributed to greater rainfall and flooding.

A man carries his cattle on his shoulder as he moves to safer ground at Topa village in Saptari. Credit: The Guardian.

While all eyes are on Houston, India, Bangladesh and Nepal are also suffering the consequences of devastating flooding brought about a strong monsoon. The United Nations estimates that 41 million people are affected by the disaster across the three countires. Over 1200 people are reported dead. Authorities are stuggling with the scale of the humanitarian crisis: “Their most urgent concern is to accessing safe water and sanitation facilities,” the UN Office for the Coordination of Humanitarian Affairs (OCHA) said earlier this week, citing national authorities. And its not only people at risk. Indian authorities reported large swathes of a famous wildlife reserve park have been destroyed. In Mumbai, the downpour caused a building to collapse killing 12 people and up to 25 more are feared trapped.Photo galleries give a sense of the scale of the disaster.

Districts affected by flooding. Credit: Guardian graphic | Source: ReliefWeb. Data as of 29 August 2017

What you might have missed

In fact, it’s highly unlikely you missed the coverage of this month’s total solar eclipse over much of Northern America. But on account of it being the second biggest story this month, we felt it couldn’t be left out of the round-up. We particularly like this photo gallery which boasts some spectacular images of the astronomical event.

This composite image, made from seven frames, shows the International Space Station, with a crew of six onboard, as it transits the Sun at roughly five miles per second during a partial solar eclipse, Monday, Aug. 21, 2017 near Banner, Wyoming. Credit: (NASA/Joel Kowsky)

Since the end of July, wildfires have been raging in southwest Greenland. While small scale fires are not unheard of on the island otherwise known for its thick ice cap and deep fjords, the fires this month are estimated to extend over 1,200 hectares. What started the fires remains unknown, as do the fuel sources and the long-term impacts of the burn.

The U.S.A’s National Oceanic and Atmospheric Administration highlighted that the fires are a source of sooty “black carbon”. As the ash falls on the pristine white ice sheet, it turns the surface black, which can make it melt faster. Greenland police recently reported that unexpected rain haf all but extinguished the massive fires; though the situation continues to be monitored, as smouldering patches run the risk of reigniting the flames.

 

 

 

Links we liked

The EGU story

Do you enjoy the EGU’s annual General Assembly but wish you could play a more active role in shaping the scientific programme? Now is your chance! Help shape the scientific programme of EGU 2018.

From today, until 8 Sep 2017, you can suggest:

  • Sessions (with conveners and description), or;
  • Modifications to the existing skeleton programme sessions
  • NEW! Suggestions for Short courses (SC) will also take place during this period
  • From now until 18 January 2018, propose Townhall and splinter meetings

And don’t forget! To stay abreast of all the EGU’s events and activities, from highlighting papers published in our open access journals to providing news relating to EGU’s scientific divisions and meetings, including the General Assembly, subscribe to receive our monthly newsletter.

 

Imaggeo on Mondays: Low tide at Alexandra Fjord

Imaggeo on Mondays: Low tide at Alexandra Fjord

Today’s post takes us to the far northern reaches of our planet, to a desert like nothing you’ve seen before.

This picture is a view to the north across Alexandra Fjord, on the east coast of Ellesmere Island, in the Canadian High Arctic, with Sphynx island in the middle of the fjord. The south shore of Alexandra Fjord includes a polar oasis, an area of tundra vegetation and relatively mild climatic conditions normally found hundreds of kilometres further south. The oasis is surrounded by glaciers and icefields to the south, and polar desert on mountains to the east and west. Polar deserts can also be seen on the far shore in this picture; another scientist working in this area once described to me the ease of “doing geology” from the air due to the lack of plant or developed soil cover on much of the landscape.

The tundra ecosystems of the valley produce and consume greenhouse gases carbon dioxide, methane, and nitrous oxide because of the actions of soil dwelling microorganisms. The surrounding deserts appear nearly lifeless, with only scattered plants sheltered from the harsh winds on barren, rocky ground. Nonetheless, on a per-area basis these deserts contribute nearly as much to greenhouse gas processes as the oasis ecosystems, particularly nitrous oxide.

The surface of Alexandra Fjord freezes completely each winter, to a depth sufficient to support the weight of small aircraft. Researchers visiting this area in April and May land and take off from the ice, but we arrived in late June and used the raised beach cresh that sits some 100 metres inland as our runway. As the 24-hour daylight of summer warms the land and the sea, the ice breaks up and is flushed out towards the Davis Straight to the east. Small pieces of pack ice and small icebergs frequently ground on the shore of the fjord at each low tide, creating a stark and beautiful landscape of ice, land, and water that is best viewed at a distance due to the tendency of polar bears to wander along the shoreline in search of seals and other food.

By Martin Brummell, University of Waterloo, Ontario, Canada

Imaggeo is the EGU’s online open access geosciences image repository. All geoscientists (and others) can submit their photographs and videos to this repository and, since it is open access, these images can be used for free by scientists for their presentations or publications, by educators and the general public, and some images can even be used freely for commercial purposes. Photographers also retain full rights of use, as Imaggeo images are licensed and distributed by the EGU under a Creative Commons licence. Submit your photos at http://imaggeo.egu.eu/upload/.

 

GeoSciences Column: When could humans last walk, on land, between Asia & America?

GeoSciences Column: When could humans last walk, on land, between Asia & America?

Though now submerged under 53 m of ocean waters, there once was a land bridge which connected North America with Asia, allowing the passage of species, including early humans, between the two continents. A new study, published in the EGU’s open access journal Climate of the Past, explores when the land bridge was last inundated, cutting off the link between the two landmasses.

The Bering Strait, a narrow passage of water, connects the Arctic Ocean with the Pacific Ocean. Located slightly south of the Arctic Circle, the shallow, navigable, 85 km wide waterway is all that separates the U.S.A and Russia. There is strong evidence to suggest that, not so long ago, it was possible to walk between the two*.

The Paleolithic people of the Americas. Evidence suggests big-animal hunters crossed the Bering Strait from Eurasia into North America over a land and ice bridge (Beringia). Image: The American Indian by Clark Wissler (1917). Distributed via Wikipedia.

In fact, though the subject of a heated, ongoing debate, this route is thought to be one of the ones taken by some of the very first human colonisers of the Americas, some 16, 500 years ago.

Finding out exactly when the Bering Strait last flooded is important, not only because it ends the last period when animals and humans could cross between North America and northeast Asia, but because an open strait affects the two oceans it connects. It plays a role in how waters move around in the Arctic Ocean, as well as how masses of water with different properties (oxygen and/or salt concentrations and temperatures, for example) arrange themselves. The implications are significant: currently, the heat transported to Arctic waters (from the Pacific) via the Bering Strait determines the extend of Arctic sea ice.

As a result, a closed strait has global climatic implications, which adds to the importance of knowing when the strait last flooded.

The new study uses geophysical data which allowed the team of authors to create a 3D image of the Herald Canyon (within the Bering Strait). They combined this map with data acquired from cylindrical sections of sediment drilled from the ocean floor to build a picture of how the environments in the region of the Bering Strait changed towards the end of the last glaciation (at the start of a time known as the Holocene, approximately 11,700 years ago, when the last ‘ice age’ ended).

At depths between 412 and 400 cm in the cores, the sediment experiences changes in physical and chemical properties which, the researchers argue, represent the time when Pacific water began to enter the Arctic Ocean via the Bearing strait. Radiocarbon dating puts the age of this transition at approximately 11, 000 years ago.

Above this transition in the core, the scientist identified high concentrations of biogenic silica (which comes from the skeletons of marine creatures such as diatoms – a type of algae – and sponges); a characteristic signature of Pacific waters. Elevated concentrations of a carbon isotope called delta carbon thirteen (δ 13Corg), are further evidence that marine waters were present at that time, as they indicate larger contributions from phytoplankton.

The sediments below the transition consist of sandy clayey silts, which the team interpret as deposited near to the shore with the input of terrestrial materials. Above the transition, the sediments become olive-grey in colour and are exclusively made up of silt. Combined with the evidence from the chemical data, the team argue, these sediments were deposited in an exclusively marine environment, likely influenced by Pacific waters.

Combining geophysical data with information gathered from sediment cores allowed the researchers to establish when the Bering Strait closed. This image is a 3-D view of the bathymetry of Herald Canyon and the chirp sonar profiles acquired along crossing transects. Locations of the coring sites are shown by black bars. Figure taken from M. Jakobsson et al. 2017.

The timing of the sudden flooding of the Bering Strait and the submergence of the land bridge which connected North America with northeast Asia, coincides with a period of time characterised by Meltwater pulse 1B, when sea levels were rising rapidly as a result of meltwater input to the oceans from the collapse of continental ice sheets at the end of the last glaciation.

The reestablishment of the Pacific-Arctic water connection, say the researchers, would have had a big impact on the circulation of water in the Arctic Ocean, sea ice, ecology and potentially the Earth’s climate during the early Holocene. Know that we are more certain about when the Bering Strait reflooded, scientist can work towards quantifying these impacts in more detail.

By Laura Roberts Artal, EGU Communications Officer

 

*Authors’s note: In fact, during the winter months, when sea ice covers the strait, it is still possible to cross from Russia to the U.S.A (and vice versa) on foot. Eight people have accomplished the feat throughout the 20th Century. Links to some recent attempts can be found at the end of this post.

References and resources:

Jakobsson, M., Pearce, C., Cronin, T. M., Backman, J., Anderson, L. G., Barrientos, N., Björk, G., Coxall, H., de Boer, A., Mayer, L. A., Mörth, C.-M., Nilsson, J., Rattray, J. E., Stranne, C., Semiletov, I., and O’Regan, M.: Post-glacial flooding of the Bering Land Bridge dated to 11 cal ka BP based on new geophysical and sediment records, Clim. Past, 13, 991-1005, https://doi.org/10.5194/cp-13-991-2017, 2017.

Barton, C. M., Clark, G. A., Yesner, D. R., and Pearson, G. A.: The Settlement of the American Continents: A Multidisciplinay Approach to Human Biogeography, The University of Arizona Press, Tuscon, 2004.

Goebel, T., Waters, M. R., and Rourke, D. H.: The Late Pleistocene Dispersal of Modern Humans in the Americas, Science, 319,1497–1502, https://doi.org/10.1126/science.1153569, 2008

Epic explorer crossed frozen sea (BBC): http://news.bbc.co.uk/2/hi/uk_news/england/humber/4872348.stm

Korean team crossed Bering Strait (The Korean Herald): http://www.koreaherald.com/view.php?ud=20120301000341

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