GeoLog

Ice Age

Imaggeo on Mondays: The Gower Peninsula, a coast marked by time

Imaggeo on Mondays: The Gower Peninsula, a coast marked by time

The Gower Peninsula in South Wales, United Kingdom, is a spectacular site to view a sunset. However, to geologists, the shore is also a prime spot to find artifacts from Earth’s ancient and recent past.

“The limestone coastline is dotted with caves that are rich in Quaternary flora and fauna,” said Mike Smith a visiting researcher at Plymouth University (UK) and photographer of this featured image. “Including the famous Red Lady of Paviland, the oldest known ceremonial burial in Western Europe, at 30,000 years before present.”

The peninsula is also known for its “dramatic and visible evidence of climate change over a range of temporal scales,” according to Smith.

A solifluction terrace on the Rhossili Bay in the Gower Peninsula.
Credit: Stephen Codrington. Planet Geography 3rd Edition, 2005 (distributed via Wikimedia Commons).

For example, at the peak of Earth’s most recent glacial period, when the northern ice sheets had made their greatest advances southward, the Gower Peninsula was one of the southern most regions overcome by ice.

Though the last glacial period ended more than 11,00 years ago, you can find evidence of this tundra environment today, if you know what to look for.

For instance, much of the Peninsula’s coastlines are lined by small steeply sloping ridges, separating the coast’s green hillslopes from its sandy beaches. These structures are often referred to as solifluction terraces, and are formed when frozen ground thaws, causing soil, rock and other debris to move downslope.

Additionally, the Gower Peninsula is also host to remnants of our very recent history.

Pictured above are the remains of the shipwrecked Helvetica, a cargo vessel from the late 19th century that had been transporting 500 tons of timber before meeting its untimely end on the banks of Worm’s Head, a small rocky island just a few kilometres long, visible from the peninsula’s shores.

On 1 November, 1887, strong gales just off the coast had taken a hold of the ship, leaving it unable to dock at Swansea Harbour. Instead, the forceful winds blew the vessel into the sandbank of Helwick Sands and then dragged the ship to its final resting place, the shores of Worm’s Head. Helvetica’s captain and crew were forced to abandon ship, and after its cargo was relocated and salvageable parts stripped away, the ship settled deep into the sand.

“The Helvetica is now permanently buried in the beach on a coastline that is bordered by extensive sand dune systems,” remarks Smith.  With each year since, the Atlantic has reclaimed more of the ship, and now just the bare bones of the wreckage remain.

References

Helvetica (Explore Gower)

Hall, Adrian. Cairngorm Landscapes [Edinburgh, Scotland], Solifluction, 2002

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

GeoTalk: Talking about ‘ocean burps’ with James Rae

GeoTalk: Talking about ‘ocean burps’ with James Rae

Trying to understand the reasons behind the global warming of our climate is a never ending quest for scientists across the geosciences. Scientists often rely on deciphering past change to help us understand, and perhaps predict, what might happen in the future. Many will be familiar with the common saying ‘the past is the key to the future’. This is exactly what James Rae, a research fellow at the Earth & Environmental Sciences Department at the Universty of St. Andrews and this year’s recipient of the Biogeosciences Division Outstanding Young Scientists Award, has been focusing his efforts on. James’ research interest lies in understanding past climate change and he was recognised by the Biogeosciences Division after the publication of his research into ocean ‘burps’ – he and his colleagues found that changes in ocean circulation in the North Pacific caused a massive ‘burp’ of CO2 to be released from the deep ocean into the atmosphere, helping to warm the planet sufficiently to trigger the end of the ice age.

Before we get stuck into the details of your work, could you introduce yourself and tell us a little more about yourself and your career?

My name’s James Rae and I’m a geoscientist at the University of St Andrews. I actually grew up just down the road – in Edinburgh – but only just moved back to Scotland last year, after studies in Oxford, Bristol, and California. The locals tell me that the transition from LA to St Andrews shouldn’t be too tough – apparently St Andrews is “one of the sunniest places in the whole of Scotland”!

I got into geosciences through a love of the outdoors and outdoor sports – mountain biking, surfing, snowboarding, climbing – and though most of my work is now in a super clean lab, I still try to get out in the Scottish Highlands whenever possible.

My career to date has focussed on using geochemistry to reconstruct past environmental change. This means I make measurements of the chemistry of things like shells, fossils, rocks, and ice, which often reflect aspects of the environment they formed in. So by making a series of these measurements on fossil shells back through time we can see how the environment changed in the past. My specialty is using boron in tiny fossil shells, called foraminifera, to reconstruct past CO2 change.

So, ocean ‘burps’? During EGU 2015, you received the Biogeosciences Division Outstanding Young Scientists Award for your study of this unusual phenomenon. Can you tell us more about those?

One of the most interesting things about the ice ages of the last few million years is that they seem to be punctuated with really dramatic rapid climate change. The most recent examples of this are at the end of the last ice age – between about 20 and 10 thousand years ago – where we see intervals of rapid CO2 rise recorded in ice cores. The only place where you can quickly get enough carbon to drive these CO2 changes is the deep ocean. During ice ages we think CO2 gets hidden away beneath the waves, at water depths of 2000 – 5000m, and because the Pacific is so big it’s likely that a lot of this CO2 is stored down there. Other scientists had suggested that this CO2 remerged at the end of the last ice age in the ocean round Antarctica. However my research shows that it could also “burp” out in the North Pacific.

Schematic of how James use boron isotope measurements in foraminifera to reconstruct pH and CO2. Credit: James Rae

Schematic of how James use boron isotope measurements in foraminifera to reconstruct pH and CO2. Credit: James Rae

And how exactly did the release of CO2 in these ‘burps’ affect the climate of the ice age?

Our Pacific “burp” happens right at the beginning of the end of the last ice age – it coincides with the first CO2 rise that heralds the start of the deglaciation. It’s possible that the warming associated with the CO2 “burp” helped push the earth out of it’s ice age, though we need to do more work to test this. But even aside from the CO2, the change in circulation that drove this event had a big influence on local climate. Although most of the Northern Hemisphere is really cold at this time the North Pacific is actually quite warm, which I think is a result of this unusual circulation state.

So, the Northern Hemisphere was very cold at this time; can you describe a little more what the Earth might have looked at during this time and how the local climate of the North Pacific might have been different?

At the end of the last ice age massive ice sheets still covered much of North America and Northern Europe. Over St Andrews the ice was around a kilometre thick. Then, at the beginning of the last deglaciation, in an interval called Heinrich Stadial 1, the ice sheets round the North Atlantic start collapsing. This flooded the North Atlantic Ocean with fresh water and reduced the Atlantic overturning circulation that currently provides heat to this region. As a result much of the Northern Hemisphere got colder. However the climate in the North Pacific does something very different. Likely in response to the big cooling in the North Atlantic, there was a large change in the position of major rain belts, like the Westerly storm track and East Asian Monsoon, and we think this acted to make the North Pacific more salty. This led to a more vigorous overturning circulation in the Pacific, a regional warming, and a burp of CO2 release from the deep sea.

What is the next step, if you like, in order to better understand ocean ‘burps’?

At the moment our key evidence for the North Pacific burp comes from a single sediment core. To test the idea we really need to make more measurements from other cores in this region. Our main evidence for ocean CO2 change also currently comes from records from the deep ocean. One of my PhD students is currently making new records to test how much CO2 made it up from the deep to the surface ocean, and from there to the atmosphere. Finally, with collaborators in Switzerland and the US we’re also testing the physical driving mechanisms of this circulation change using state of the art climate models.

(L) An ocean cruise on which the sediment cores used in the study are collected. (R) Benthic foraminifera - James uses these to make measurements of the chemistry of these to reconstruct past climate change. Credit: James Rae

(L) An ocean cruise on which the sediment cores used in the study are collected. (R) Benthic foraminifera – James uses these to make measurements of the chemistry of these to reconstruct past climate change. Credit: James Rae

You’ve enjoyed success as a researcher, not least your 2015 EGU Award. As an early career researcher, do you have any words of advice for masters and PhD students who are hoping to pursue a career as a scientist in the Earth sciences?

Do what you really enjoy. This feeds in to everything else you do; it means you’ll work hard and carefully in lab, find the reading interesting, and be able to present your work effectively to your colleagues. We do science because we love it, so it’s really important to find topics within your field that you love working on. I think it’s also helpful to find skills to be a specialist in and be known for, but then to try to apply these broadly to big picture questions in geosciences.

Imaggeo on Mondays: Drumlins Clew Bay

Imaggeo on Mondays: Drumlins Clew Bay

During ice ages landscapes are sculpted by the power of advancing glaciers. From rock scratches, to changing mountains and the formation of corries, cirques and aretes, through to the formation of valleys and fjords, the effects of past glaciations are evident across the northern hemisphere landscape.

Perhaps not so familiar, drumlin fields are also vestiges of the erosive power of ancient ice sheets. Glacial deposits tend to be angular and poorly sorted, meaning they come in lots of different sizes and shapes. The extreme of this are glacial erratics. Drumlins are are elongated hills made up of glacial deposits and they represent bedforms produced below rapidly moving ice. Our Imaggeo on Monday’s image this week is of Clew Bay in western Ireland and shows the streamlining of drumlins into an extensive drumlin field of glacial sediment. The drumlins here formed during the rapid thinning of the fast moving central parts of the western sector of the British-Irish Ice Sheet, in a process known as deglacial downdraw – probably between 18,000 and 16,000 years ago. The ice was streaming through bays in western Ireland both during and at the end of the Last Glacial Maximum (also known as LGM). This was the time in which the ice sheets covered most of northern America, Europe and Asia. In Clew Bay the ice was a minimum of 800m thick and flowing out into a series of tidewater glaciers situated along the length of Ireland’s western shelf.

By Prof. Peter Coxon, Head of Geography, School of Natural Sciences, Trinity College Dublin & Laura Roberts

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