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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

Enmeshed in the gears of publishing – lessons from working as a young editor

Enmeshed in the gears of publishing – lessons from working as a young editor

Editors of scientific journals play an important role in the process research publication. They act as the midpoint between authors and reviewers, and set the direction of a given journal. However, for an early career scientist like me (I only defended my PhD in early December 2016) the intricacies of editorial work remained somewhat mysterious. Many academic journals tend to appoint established, more senior scientists to these roles, and while most scientists interact with editors regularly their role is not commonly taught to more junior researchers. I was fortunate to get the chance to work, short term, as an associate editor at Nature Geoscience in the first 4 months of this year (2017). During that time, I learned a number of lessons about scientific publishing that I felt could be valuable to the community at large.

What does an editor actually do?

The role of the editor is often hidden to readers; in both paywalled and open-access journals the notes and thoughts editors make on submitted manuscripts are generally kept private. One of the first things to appreciate is that editors judge whether a manuscript meets a set of editorial thresholds that would make it appropriate for the journal in question, rather than whether the study is correctly designed or the results are robust. I’d argue most editors are looking for a balance of an advance beyond existing literature and the level of interest a manuscript offers for their audience.

At each step of the publication process, from initial submission, through judging referee comments, to making a final decision, the editor is making a judgement whether the manuscript still meets those editorial thresholds.

The vast majority of the papers I got the chance to read were pretty fascinating, but since the journal I was working for is targeted at the whole Earth science community some of these were a bit too esoteric, and as such didn’t fit the thresholds we set to appeal to the journal audience.

I actually found judging papers on the basis of editorial thresholds refreshing – in our capacity as peer reviewers, most scientists are naturally sceptical of methodology and conclusions in other studies, but as an editor in most cases I was able to take the authors conclusions at face-value, and leave the critical assessment to referees.

That’s where the important difference lies; even though editors are generally scientists by training, since they are naturally not experts in every field that they receive papers from, it’s paramount to find reviewers who have the appropriate expertise and to ask them the right set of questions. In journals with academic editors, the editors may have more leeway to make critical comments, but impartiality is key.

Much of this may be already clear to many readers, but perhaps less so to more junior scientists. Many of the editorial decisions are somewhat subjective, like gauging the level of interest to a journal audience.

In the context of open access research journals, I think it’s worth asking whether the editorial decisions should also be made openly readable by authors and referees – this might aid potential authors in deciding how to pitch their articles to a given journal. This feeds into my next point – what are journals looking for?

By which metrics do journals judge studies?
The second big thing I picked up is that the amount of work does not always equate to a paper being appropriate for a given journal. Invariably, authors have clearly worked hard, and it’s often really tricky to explain to authors that their study is not a good fit for the journal you’re working for.

Speaking somewhat cynically, journals run for profit are interested in articles that can sell more copies or subscriptions. Since the audiences are primarily scientists, “scientific significance” will be a dominant consideration, but Nature and subsidiary journals also directly compare the mainstream media coverage of some of their articles with that of Science – that competition is important to their business.

Many other authors have discussed the relative merits of “prestige” journals (including Nobel prize winners – https://www.theguardian.com/science/2013/dec/09/nobel-winner-boycott-science-journals), and all I’ll add here is what strikes me most is that ‘number of grad student hours worked’ is often not related to those articles that would be of a broader interest to the more mainstream media. The majority of articles don’t attract media attention of course, but I’d also argue that “scientific significance” is not strongly linked to the amount of time that goes into each study.

In the long run, high quality science tends to ensure a strong readership of any journal, but in my experience as an editor the quality of science in submitted manuscripts tends to be universally strong – the scientific method is followed, conclusions are robust, but in some cases they’re just pitched at the wrong audience. I’d argue this is why some studies have found in meta-analysis that in the majority of cases, articles that are initially rejected are later accepted in journals of similar ‘prestige’ (Weller et al. 2001, Moore et al. 2017).

As such, it’s imperative that authors tailor their manuscripts to the appropriate audience. Editors from every journal are picking from the same pool of peer reviewers, and so the quality of reviews should also be consistent, which ultimately determines the robustness of a study; so to meet editorial thresholds, prospective authors should think about who is reading the journal.
It’s certainly a fine line to walk – studies that are confirmatory of prior work tend to attract fewer readers, and as such editors may be less inclined to take an interest, but these are nonetheless important for the scientific canon.

In my short time as an editor I certainly didn’t see a way around these problems, but it was eye-opening to see the gears of the publication system – the machine from within, as it were.

Who gets to review?
One of the most time-consuming jobs of an editor is finding referees for manuscripts. It generally takes as long, if not far longer, than reading the manuscript in detail!

The ideal set of referees should first have the required set of expertise to properly assess the paper in question, and then beyond that be representative of the field at large. Moreover, they need to have no conflict of interest with the authors of the paper. There are an awful lot of scientists working in the world at the moment, but in some sub-fields it can be pretty hard to find individuals who fit all these categories.

For example, some studies in smaller research fields with a large number of senior co-authors often unintentionally rule out vast swathes of their colleagues as referees, simply because they have collaborated extensively.

Ironically, working with everyone in your field leaves no-one left to review your work! I have no doubt that the vast majority of scientists would be able to referee a colleagues work impartially, but striving for truly impartial review should be an aim of an editor.

As mentioned above, finding referees who represent the field is also important. More senior scientists have a greater range of experience, but tend to have less time available to review, while junior researchers can often provide more in-depth reviews of specific aspects. Referees from a range of geographic locations help provide diversity of opinion, as well as a fair balance in terms of gender.

It was certainly informative to compare the diversity of authors with the diversity of the referees they recommended, who in general tend to be more male dominated and more US-centric than the authors themselves.

A positive way of looking at this might be that this represents a diversifying Earth science community; recommended referees tend to be more established scientists, so greater author diversity might represent a changing demographic. On the other hand, it’s certainly worth bearing in mind that since reviewing is increasingly becoming a metric by which scientists themselves are judged, recommending referees who are more diverse is a way of encouraging a more varied and open community.

What’s the job like?
Editorial work is definitely rewarding – I certainly felt part of the scientific process, and providing a service to authors and the readership community is the main remit of the job.

I got to read a lot of interesting science from a range of different places, and worked with some highly motivated people. It’s a steep learning curve, and tends to be consistently busy; papers are always coming in, so there’s always a need to keep working.

Perhaps I’m biased, but I’d also suggest that scientists could work as editors at almost any stage in their careers, and it offers a neat place between the world of academia and science communication, which I found fascinating.

By Robert Emberson, freelance science writer

References

Moore, S., Neylon, C., Eve, M. P., O’Donnell, D. P., and Pattinson, D. 2017. “Excellence R Us”: university research and the fetishisation of excellence. Palgrave Communications, 3, 16105

Weller A.C. 2001 Editorial Peer Review: Its Strengths and Weaknesses. Information Today: Medford NJ

GeoSciences Column: Can seismic signals help understand landslides and rockfalls?

GeoSciences Column: Can seismic signals help understand landslides and rockfalls?

From the top of a small gully in the French Alps, a 472 kg block is launched into the chasm. Every detail of it’s trajectory down the slope is scrutinised by two cameras and a network of seismometers. They zealously record every bounce, scrape and tumble – precious data in the quest to better understand landslides.

What makes landslides tick?

In 2016, fatalities caused by landslides tipped 2,250 people. The United States Geological Survey (USGS) estimates that between 25 and 50 people are killed, annually, by landslides in the United States alone. Quantifying the economic losses caused by landslides is no easy task, but the costs are known to be of economic significance.

It is paramount that the mechanisms which govern landslides are better understood in hopes that the knowledge will lead to improved risk management in the future.

But landslides and rockfalls are rarely observed in real-time. Deciphering an event, when all you have left behind is a pile of debris, is no easy task. The next best thing (if not better than!) to witnessing a landslide (from a safe distance) is having a permanent record of its movement as it travels down a slope.

Although traditionally used to study earthquakes, seismometers have now become so sophisticated they are able to detect the slightest ground movements; whether they come from deep within the bowels of the planet or are triggered by events at the surface. For some year’s now they have been an invaluable tool in detecting mass movements (an all-encompassing term for the movement of bed rock, rock debris, soil, or mud down a slope) across the globe.

More recently, processing recorded seismic signals triggered by large catastrophic events has not only allowed to identify when and where they occurred, but also their force, how quickly they travel, gain speed and their direction of movement.

This approach gives only a limited amount of data for scientists to work with. After all, large, catastrophic, mass movements represent only a fraction of the landslide and rockfall events that occur worldwide. To gain a fuller understanding of landslide processes, information about the smaller events is needed too.

So, what if scientists could use a seismic signal which is generated by all mass movements, independent of their size?

The high-frequency seismic signal

A high-frequency seismic signal is generated as the individual particles, which combined make up a landslide or rockfall, bounce and tumble against the underlying layer of rock. Would it be possible to, retrospectively, find out information about the size and speed at which individual particles traveled from this seismic signal alone?

This very question is what took a team of scientists up into the valleys of the French Alps.

At a place where erosion carves gullies into lime-rich muds, the researchers set-up two video cameras and network of seismometers. They then launched a total of 28 blocks, of weights ranging from 76 to 472 kg, down a 200 m long gully and used the data acquired to reconstruct the precise trajectory of each block.

The impacts of each block on the underlying geology, as seen on camera, were plotted on a 3D representation of the terrain’s surface. From the time of impact, block flight time and trajectory, the team were able to find out the velocity at which the blocks travelled and the energy they carried.

View from (a) the first and (b) the second video cameras deployed at the bottom of the slope. The ground control points are indicated by blue points. (c) Trajectory reconstruction for block 4 on the DEM, built from lidar acquisition, superimposed on an orthophoto
of the Rioux-Bourdoux slopes. Each point indicates the position of an impact and the colour gradient represents the chronology of these impacts (blue for the first impact and red for the last one). K2 is a three-component short-period seismometer and K1, K3 and K3 are vertical-only seismometers. CMG1 is a broad-band seismometer. From Hibert, C. et al., 2017. (Click to enlarge)

As each block impacted the ground, it generated a high-frequency seismic signal, which was recorded by the seismometers. The signals were processed to see if information about the (now known) properties of the blocks could be recovered.

Following a detailed analysis, the team of scientists, who recently published their results in the EGU’s open access journal Earth Surface Dynamics, found a correlation between the amplitude (the height of the wave from it’s resting position), as well as the energy of the seismic signals and the mass and velocities of the blocks before impact. This suggests that indeed, these high-frequency seismic signal can be used to find out details about rockfall and landslide dynamics.

But much work is left to be done.

There is no doubt that the type of substrate on which the particles/blocks bounce upon play a large part in governing the dynamics of mass movements. In the case of the French Alps experiment, the underlying geology of lime-rich muds was very soft and absorbed some of the energy of the impacts. Other experiments (which didn’t use single blocks), performed in hard volcanic and metamorphic rocks, found energy absorption was lessened. To really get to the bottom of how much of a role the substrate plays, single-block, controlled release experiments, like the one described in the paper, should be performed on a variety of rock types.

At the same time, while this experiment certainly highlights a link between seismic signals and individual blocks, rockfalls and landslides are made up of hundreds of thousands of particles, all of which interact with one another as they cascade down a slope. How do these complex interactions influence the seismic signals?

By Laura Roberts Artal, EGU Communications Officer

References and resources:

Hibert, C., Malet, J.-P., Bourrier, F., Provost, F., Berger, F., Bornemann, P., Tardif, P., and Mermin, E.: Single-block rockfall dynamics inferred from seismic signal analysis, Earth Surf. Dynam., 5, 283-292, doi:10.5194/esurf-5-283-2017, 2017.

USGS FAQs: How many deaths result from landslides each year?

The human cost of landslides in 2016 by David Petley, published, 30 January 2017 in The Landslide Blog, AGU Blogosphere.

[Paywalled] Klose M., Highland L., Damm B., Terhorst B.: Industrialized Countries: Challenges, Concepts, and Case Study. In: Sassa K., Canuti P., Yin Y. (eds) Landslide Science for a Safer Geoenvironment. Springer, Cham, (2014)

 

The publication issue: the opinions of EGU early career scientists!

The publication issue: the opinions of EGU early career scientists!

The EGU’s General Assemblies have a long tradition of Great Debates – sessions of Union-wide interest which aim to discuss some of the greatest challenges faced by our discipline. Past topics have included exploitation of mineral resources at the sea bed, water security given an ever growing population and climate geoengineering, to name but a few.  This year’s meeting saw the first Great Debate aimed, specifically, at an Early Career Scientist (ECS) audience which boasted an innovative format too: Should early career scientists be judged by their publication record? A set of group debates. Today’s post, written by Mathew Stiller-Reeve, a convener of the session, summarises some of the main outcomes of the discussion.

We, early career scientists, are told that we need to become expert writers, presenters, and teachers if we are going to make it in the world of research. Many of us agree such transferrable skills are extremely important. But if we invest time in developing these skills, it sometimes feels like time wasted. All said and done, we only seem to be judged on our publication record and our h-index. How many papers have we published in high impact journals, and how often have they been cited?

Early career scientists seem very clued up on transferrable skills. They want to invest in these skills. Therefore, we wanted to hear from them about whether ‘early career scientists [should] be judged mainly on their publication record?’ And so we put this question to them (and others) at a Great Debate at the EGU’s 2017 General Assembly. We also wanted to test out a new format where the audience had the opportunity to voice their opinions about important issues concerning modern academia. The publication issue affects us all, so we should have a say.

With only 8 people at each table and over 40 minutes to debate, everyone had an opportunity to speak their mind and contribute to developing solutions. The room was buzzing with over 100 early career and more established scientists discussing, agreeing, disagreeing, and finding compromises.

In the end, each table was tasked to debate and boil their thoughts down to one or two policy-type statements. These statements will be presented to the EGU Council to inform them of where EGU early career scientists stand on this matter.

So without further ado, here are the conclusions of the tables:

– We need more criteria. Quality is most important, measured by prizes, PhD results and the incorporation of the community via new media.

-More activities need to be taken into account in a measurable way, but according to scaled categories #notjustanumber.

-The current system is cheap, easy and fast. A person should be judged on the broader contributions to society, to their colleagues, to their disciplines. We should move beyond metrics.

-Because scientists are more than a list of publications, assess them individually. Talk to them and read their output, including publications, blogs and chapter/book contributions.

-We should not be judged on publication record alone. We need a multi-variant set of criteria for assessment for judgment of impact beyond just academic publications.

-One suggestion is a weighted metric depending on the position you’re applying for which considers other factors such as teaching, outreach, conference participation etc.

-No, the h-index should not be the sole number, even though it is not a totally useless number.

-Quality should be judged on more than quantity and the large number of authors on publications devaluates the contributions of early career scientists.

-Publications are the accepted way of communication in science, but there is not any one number describing the quality of the early career scientist, whom in our humble opinion should not only be judged on the quantity of papers but also on their quality as a part of a complete set of research skills, including other contributions such as project development.

-We acknowledge the publication record as a reliable metric, but we suggest an additional step for assessing applications, based on video or audio presentations to emphasize your other outstanding qualities.

-We doubt that we are mainly judged on our publication record and we think that publications should be part of what we are judged on.

-When hiring, follow the example of the Medical Department at Utrecht University: only ask for the 3 papers, teaching or outreach experiences you think are important for the position you are applying for: we are more than numbers.

Should they be adopted? Do you agree? How can we adopt them?

The message in many of the statements from the Early Career Scientists at the European Geosciences Union is quite clear: We are more than numbers! Several suggestions arose from the debate: new metrics, video presentations, and even new application processes. Now the statements from the debate are recorded. This will hopefully inspire us (and others) to find better solutions. At the very least, the discussion has begun. Solutions are impossible if we don’t talk!

By Mathew Stiller-Reeve, co-founder of ClimateSnack and researcher at Bjerknes Centre for Climate Research, Norway

Editor’s note: This is a guest blog post that expresses the opinion of its author and those who participated at the Great Debate during the General Assembly, whose views may differ from those of the European Geosciences Union. We hope the post can serve to generate discussion and a civilised debate amongst our readers.

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