Through The Sandglass

"Extinguished by strangers with sand."

Seventy years ago, on the 7th of September, 1940, the London Blitz began – it would continue for eight months. Looking at map of the more than 800 recorded events of that first day and night, I find that an incendiary bomb landed in the street outside what is, today, my apartment, ironically in front of the fire station that was, for a long time, the headquarters of the London Fire Brigade. It’s that fire station building, and the associated pub, that are the only survivors from that time. The Guardian newspaper has a comprehensive online article and associated set of resources on the events of that first day, and it was there that the following quotation caught my eye:

The fire brigade was nearly overwhelmed. At the start of the war, London had just 120 red fire engines and 2,000 motorised pumps. That night's records repeatedly say "Extinguished by handpump" or "Extinguished by strangers with sand."

Sunday sand: up close and personal

 

I’ve written before about the extraordinary life and accomplishments of Ralph Bagnold, “The man who figured out how deserts work.” Back in 2007, I was lucky enough to go on one of my “trips of a lifetime” and follow, as closely as possible given the minefields, in his footsteps and tyre tracks in the Western Desert of Egypt (and bits of Sudan and Libya). Bagnold followed scientific method carefully and scrupulously, building equations from first principles to describe the movement of sand, then constructing experimental tests of those equations in a wind tunnel, modifying and reworking the theory, until it was ready to be further tested in the field. In 1938, he established himself at a base camp at the foot of the cliffs of the towering plateau of the Gilf Kebir in Egypt’s southwest corner and waited for a sandstorm. While he waited, he tested his instrumentation:

 

After several events of sand being dramatically on the move, he had results that, although like all field measurements, imperfect, nevertheless supported and augmented his mathematical and laboratory results: the science of sand transport was set on the foundations that continue to support it today. In 2007, we visited the dune under which  Bagnold had camped 69 years before.

 

The remains of the structures that Bagnold and his companions had built for the camp were still there, but very much the worse for wear. Benzene cans with the Shell logo were still lying around – the desert is kind to such artifacts. 

 

The image at the head of this post shows sand from Bagnold’s dune at various magnifications – typical desert quartz grains, painted with a translucent veneer of iron, many of them rounded by abrasion in the wind but many of them also chipped and angular as a result of those impacts. Look closely at any individual grain, and we see the texture of its surface, a microscopic topography, the physiognomy of the grain. The closer we look, the more complex does that topography become, and there’s a whole sub-discipline of geology that devotes itself to reading the geological runes of grain surface textures, reconstructing the stories that those miniature landscapes have to tell.

A while ago, I was approached by Aspex, a company in Pittsburgh that specialises in bench-top scanning electron microscopes, yet another example of sophisticated technology becoming ever-smaller – see the details here. As part of their marketing campaign, Aspex were offering free electron microscope scans of anything, so, of course, I sent them a few sand grains, including samples from Bagnold’s dune. So, continuing our increasingly detailed scrutiny of individual sand grains, here are some examples:

 

The scales are in microns (also known more officially as micrometers or micrometres), one of which is a millionth of a meter. The sand grain is around half a millimetre across; a couple of typical bacteria would cover the area of the highest magnification image. Altogether, from the photograph of the sand at the left of the image at the head of the post, to this, the highest magnification from the scanning electron microscope, our scrutiny has taken us through, roughly, a multiple of ten thousand times.

Up close and personal, worlds within worlds: William Blake would have been astonished by the scanning electron microscope. I’ll end with other, more accessible views, this time using transmitted light, the illumination behind the grains revealing different aspects of their character….

 

[My thanks to Jeffrey Tabaka at Aspex for arranging to provide the scanning electron microscope images and to Stephen Bagnold for the photograph of his father at work]

Mesmerising Mars

 

Following up on bits and pieces of news, I periodically find myself on one of the Mars imagery sites, lost in wonder; it’s a time-consuming process. So, I thought, why not, again, lure readers of this blog to accompany me on these extraordinary journeys? Scientific Frontline, a site that I just discovered, compiles a wide variety of images into all kinds of galleries, not just of things extraterrestrial. It’s from there that the stunning image above comes, originally, of course, from NASA/JPL/University of Arizona and the Mars Reconnaissance Orbiter. The description is as follows:

Dunes within a crater on Mars are visible in this HiRISE image. This crater is located in the southern hemisphere where it was winter at the time this image was taken.
This observation documents new seasonal processes occurring on dunes at this latitude, as well as other interesting phenomena. The bright tones are interpreted as carbon dioxide or water frost. This is generally concentrated on the east-facing slopes of the dunes, which are in shadow and therefore cooler. Some dark spots on the dunes may be areas that have defrosted more than surrounding terrain.
Landslides and dark-toned streaks are seen on many of the west-facing dune slopes. The general dune morphology indicates formation by westerly winds. However, zooming in on the image shows smaller scale ripples that appear to have been formed by winds blowing from the south and north.
[Written by: Nathan Bridges & Kelly Kolb]

And, speaking of winter dunes, direct from the high resolution imaging site at the University of Arizona:

 

Mars has a vast sea of sand dunes in the high latitude region encircling its North polar cap, known as the North polar erg. These dunes are made up of basalt and gypsum sand grains. In some regions of the North polar erg where the sand supply is limited they take on an elongated crescent shape. The icy ground that the dunes are on top of has irregular polygonal patterns. In other areas with an abundant supply of sand the dunes are continuous (see also PSP_007494_2580).
The entire North polar erg is covered in the winter with a seasonal polar cap composed of carbon dioxide (dry ice). In the spring time this seasonal polar cap evaporates.
[Written by: Candy Hansen]

And then, off we go into the stunning landscapes of the planet (it’s clearly not geomorphology, but does anyone know the correct term?)

 

This observation shows a portion of the central sedimentary deposits in Pasteur Crater.
The deposits in this image now being eroded into knobs and ridges. The erosion is probably dominated by wind, as most of the ridges are parallel. This is common in wind-eroded features, with the ridges generally aligned with the prevailing wind.
At high resolution, layering is revealed in many of the knobs and outcrops. The horizontal layers indicate that the material was deposited uniformly over a broad area. Possible origins include volcanic airfall or lacustrine (lake) deposits. After deposition, the rock in this area has been fractured and faulted, forming a diverse array of cracks.
The mottled appearance of much of the image is caused by dark, featureless patches which may be wind-blown dust. These have interacted with lighter-toned ridges and ripples which are probably also formed by aeolian (wind) processes. In places, the dark patches partially cover the ripples, indicating that they have moved more recently, but they must be thin because the ripples frequently stand above surrounding dark material.
The ripples exhibit multiple interacting orientations in some places, producing networks of small ridges which reflect movement in winds from several directions.
[Written by: Colin Dundas]

We should not forget the European Space Agency project – the Mars Express high resolution stereo-photography and mineral mapping mission (whose lander, the Beagle 2, so ignominiously plummeted to the surface of Mars in 2003). The imaging orbiter was originally expected to have a relatively short life, but its operations have been extended several times and are continuing; its recent image of Orcus Patera, a mysteriously elongated crater, has been in the news last week ("scientists are baffled..."). I particularly like the image below (I have inserted a perspective detail) from early on in the mission: a dune field in the crater Argyre Planitia. I assume that the dark colour results from basaltic sands being constantly reworked by the winds as opposed to being covered in dust, but why is the dune field so compact and isolated? A reflection of the complex wind circulation patterns? Note that 3D images are available from the website.

 

These images, taken by the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express spacecraft, show a Martian crater with a dune field on its floor.
The images were taken during orbit 427 in May 2004, and show the crater with a dune field located in the north-western part of the Argyre Planitia crater basin.

The images are centred at Mars longitude 303° East and latitude 43° South. The image resolution is approximately 16.2 metres per pixel.  The crater is about 45 kilometres wide and 2 kilometres deep. In the north-eastern part of this crater, the complex dune field is 7 kilometres wide by 12 kilometres long. In arid zones on Earth, these features are called ‘barchanes’, [sic: they mean, of course, “barchans”] which are dunes having an asymmetrical profile, with a gentle slope on the wind-facing side and a steep slope on the lee-side. The dune field shown here suggests an easterly wind direction with its steeper western part. The composition of the dune material is not certain, but the dark sands could be of basaltic origin.

Enough, I must stop – good luck!

 

 

Sunday sand: the treasures of Bretignolles

 

Bretignolles-sur-Mer is but one of the many seaside resorts along the Atlantic Coast of France, but for those interested in unusual sands, it’s a special destination: this is one of my favourites and a classic amongst arenophiles. As you walk on to theshore, you can’t help but notice the strange purple-red-rust-black sand piled up at the top of the beach, against the concrete wall. In fact, you can see this band of colour on Google Earth.

 

Look more closely, and you’ll see how this sand contrasts with the more typically coloured grains of the rest of the beach, and how the two conspire to create natural designs sculpted by waves and the receding tide.

  

Pick up a handful of this sand and you’ll be surprised – it’s distinctly heavier than you would expect, and there’s a reason for this. It’s a placer deposit, a concentration of heavier minerals winnowed by storms and dumped at the top of the beach. I’ve written about placers before, particularly in the context of the California Gold Rush; natural processes of granular segregation by waves, tides, and rivers, take heavier mineral grains originally dispersed through the sand and concentrate them – placer deposits are commercially significant around the world for a wide variety of industrial minerals and precious stones, not just gold.

This concentration is clear in the image at the head of this post – whereas the normal beach sand at Bretignolles is dominated, as is so often the case, by clear quartz grains, there are few of these to be seen in the placer sand. Instead, we see a dazzling variety of red, orange, pink, and black grains. So what are these minerals?

Any beach sand represents a recipe of local ingredients: sand formed from the weathering and erosion of rocks exposed along the coast, mixed with the generally even greater volumes of material sampled from the geology of the interior by rivers, flushed down to the coast and then relentlessly distributed by waves and currents along the shore. Bretignolles, although culturally lying in the Department of the Vendée, samples its sand grains from the southernmost outcrops of Brittany. And Brittany has a long and torrid geological story to tell. Without worrying about the details, a glance at the geological map of this part of France reveals the complexity of this recipe:

 

It’s a tangled fabric of colours, each one a different rock type, apparently stirred together and then shot through with faults on all scales. This is the Armorican Massif, named after the old area of Gaul, its geological – and cultural and linguistic - history linked to parts of Cornwall. The tangled fabric is testament to not just one drama of colliding tectonic plates and mountain-building, but two: first, the Cadomian Orogeny (mountain-building event) around 600 million years ago, then the Hercynian or Variscan orogeny. This series of chaotic and complex tectonic events lasted more than 100 million years, creating the Ouachitas and the Appalachians together with much of old Europe, and ended up welding the supercontinent of Pangaea together 280 million years ago.

What we see today in the geology of Brittany are the roots of these old mountain belts – the younger and shallower rocks have been stripped off to reveal the foundations forged in the extreme pressures and temperatures deep in the crust. And it’s these baked and tortured, metamorphic, rocks that the sands of Bretignolles come from.

The red and pinkish colours are grains of garnet, a mineral name that covers a wide variety of compositions – all silicate minerals, but with varying proportions of calcium, magnesium, aluminium, iron, and chromium; those proportions determine the colour. The black grains are iron oxides of various types, among them magnetite (hence much of the heaviness of the sand).

 

There are also grains in this sand that I really can’t identify – metamorphic rocks contain exotic and diverse ingredients. But the “treasure” can be seen in the centre of the image above: bright, sparking blue, sapphire. This is the aluminium oxide mineral, corundum, which also comes in a range of colours, and thus some of these varieties are gemstones: if it’s red, it’s a ruby, blue is a  sapphire.

Of course these sapphire grains (e.g., below, close-up and personal) are not things you would put in a ring that would be appreciated as a gift, but I hope you would agree that they are treasures – and beautiful examples of the stories that sand can tell.  

 

[I was directed to Bretignolles by Carla, a Dutch sand collector to whom I am grateful for this and many things.]

Oil-eating bacteria: a new member of the family brings good news

 

I find fascinating, and many readers also seem to, the role of oil-eating bacteria in the Gulf of Mexico disaster. Fascinating for any number of reasons: not only is the role of such microbes in the normal ecosystem remarkable, but their appetite for hydrocarbons contributes significantly to the removal of spilt oil on the surface and at depth – and equally remarkable is, in reality, how little we know about them. I first described alcanivorax borkumensis back at the beginning of June, with follow-ups a couple of weeks later and then in July. Now, in the interests of updating this ever-evolving theme – and finding the science in the “debate” about what has happened to the oil – here’s some extremely interesting news. Workers at the Lawrence Berkeley National Laboratory have just described their discovery “that microbial activity, spearheaded by a new and unclassified species, degrades oil much faster than anticipated.” The italics are mine.

Here's the Berkeley Lab press release – a noteworthy and, to me at least, astonishing detail is the device used: “Sample analysis was boosted by the use of the latest edition of the award-winning Berkeley Lab PhyloChip – a unique credit card-sized DNA-based microarray that can be used to quickly, accurately and comprehensively detect the presence of up to 50,000 different species of bacteria and archaea in a single sample from any environmental source, without the need of culturing.”

Study shows deepwater oil plume in Gulf degraded by microbes

Aug 24 2010

In the aftermath of the explosion of BP’s Deepwater Horizon drilling rig in the Gulf of Mexico, a dispersed oil plume  was formed at a depth between 3,600 and 4,000 feet and extending some 10 miles out from the wellhead. An intensive study by scientists with the Lawrence Berkeley National Laboratory (Berkeley Lab) found that microbial activity, spearheaded by a new and unclassified species, degrades oil much faster than anticipated. This degradation appears to take place without a significant level of oxygen depletion.

“Our findings show that the influx of oil profoundly altered the microbial community by significantly stimulating deep-sea psychrophilic (cold temperature) gamma-proteobacteria that are closely related to known petroleum-degrading microbes,” says Terry Hazen, a microbial ecologist with Berkeley Lab’s Earth Sciences Division and principal investigator with the Energy Biosciences Institute, who led this study. “This enrichment of psychrophilic petroleum degraders with their rapid oil biodegradation rates appears to be one of the major mechanisms behind the rapid decline of the deepwater dispersed oil plume that has been observed.”

The uncontrolled oil blowout in the Gulf of Mexico from BP’s deepwater well was the deepest and one of the largest oil leaks in history. The extreme depths in the water column and the magnitude of this event posed a great many questions. In addition, to prevent large amounts of the highly flammable Gulf light crude from reaching the surface, BP deployed an unprecedented quantity of the commercial oil dispersant COREXIT 9500 at the wellhead, creating a plume of micron-sized petroleum particles. Although the environmental effects of COREXIT have been studied in surface water applications for more than a decade, its potential impact and effectiveness in the deep waters of the Gulf marine ecosystem were unknown.

Analysis by Hazen and his colleagues of microbial genes in the dispersed oil plume revealed a variety of hydrocarbon-degraders, some of which were strongly correlated with the concentration changes of various oil contaminants. Analysis of changes in the oil composition as the plume extended from the wellhead pointed to faster than expected biodegradation rates with the half-life of alkanes ranging from 1.2 to 6.1 days.

“Our findings, which provide the first data ever on microbial activity from a deepwater dispersed oil plume, suggest that a great potential for intrinsic bioremediation of oil plumes exists in the deep-sea,” Hazen says. “These findings also show that psychrophilic oil-degrading microbial populations and their associated microbial communities play a significant role in controlling the ultimate fates and consequences of deep-sea oil plumes in the Gulf of Mexico.”

Hazen and his colleagues began their study on May 25, 2010. At that time, the deep reaches of the Gulf of Mexico were a relatively unexplored microbial habitat, where temperatures hover around 5 degrees Celsius, the pressure is enormous, and there is normally little carbon present.

“We deployed on two ships to determine the physical, chemical and microbiological properties of the deepwater oil plume,” Hazen says. “The oil escaping from the damaged wellhead represented an enormous carbon input to the water column ecosystem and while we suspected that hydrocarbon components in the oil could potentially serve as a carbon substrate for deep-sea microbes, scientific data was needed for informed decisions.”

Hazen, who has studied numerous oil-spill sites in the past, is the leader of the Ecology Department and Center for Environmental Biotechnology at Berkeley Lab’s Earth Sciences Division.  He conducted this research under an existing grant he holds with the Energy Biosciences Institute (EBI) to study microbial enhanced hydrocarbon recovery. EBI is a partnership led by the University of California (UC) Berkeley and including Berkeley Lab and the University of Illinois that is funded by a $500 million, 10-year grant from BP.

Results in the Science paper are based on the analysis of more than 200 samples collected from 17 deepwater sites between May 25 and June 2, 2010. Sample analysis was boosted by the use of the latest edition of the award-winning Berkeley Lab PhyloChip – a unique credit card-sized DNA-based microarray that can be used to quickly, accurately and comprehensively detect the presence of up to 50,000 different species of bacteria and archaea in a single sample from any environmental source, without the need of culturing. Use of the Phylochip enabled Hazen and his colleagues to determine that the dominant microbe in the oil plume is a new species, closely related to members of Oceanospirillales family, particularly Oleispirea antarctica and Oceaniserpentilla haliotis.

Hazen and his colleagues attribute the faster than expected rates of oil biodegradation at the 5 degrees Celsius temperature in part to the nature of Gulf light crude, which contains a large volatile component that is more biodegradable. The use of the COREXIT dispersant may have also accelerated biodegradation because of the small size of the oil particles and the low overall concentrations of oil in the plume. In addition, frequent episodic oil leaks from natural seeps in the Gulf seabed may have led to adaptations over long periods of time by the deep-sea microbial community that speed up hydrocarbon degradation rates.

One of the concerns raised about microbial degradation of the oil in a deepwater plume is that the microbes would also be consuming large portions of oxygen in the plume, creating so-called “dead-zones” in the water column where life cannot be sustained. In their study, the Berkeley Lab researchers found that oxygen saturation outside the plume was 67-percent while within the plume it was 59-percent.

“The low concentrations of iron in seawater may have prevented oxygen concentrations dropping more precipitously from biodegradation demand on the petroleum, since many hydrocarbon-degrading enzymes have iron as a component,” Hazen says. “There’s not enough iron to form more of these enzymes, which would degrade the carbon faster but also consume more oxygen.”

 

[Image at the head of this post from the press release and the Terry Hazen group. The results of this research were reported in the journal Science (August 26, 2010 on-line) in a paper titled “Deep-sea oil plume enriches indigenous oil-degrading bacteria.” Co-authoring the paper with Hazen were Eric Dubinsky, Todd DeSantis, Gary Andersen, Yvette  Piceno, Navjeet Singh, Janet Jansson, Alexander Probst, Sharon Borglin, Julian Fortney, William Stringfellow, Markus Bill, Mark Conrad, Lauren Tom, Krystle Chavarria, Thana Alusi, Regina Lamendella, Dominique Joyner, Chelsea Spier, Jacob Baelum, Manfred Auer, Marcin Zemla, Romy Chakraborty, Eric Sonnenthal, Patrik D’haeseleer, Hoi-Ying  Holman, Shariff Osman, Zhenmei Lu, Joy Van Nostrand, Ye Deng, Jizhong Zhou and Olivia Mason.]