Category Archives: SciComm

A Murex tattoo

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The Saturday Evening Post, March 4, 1944, featured on its cover the iconic Norman Rockwell portrait of The Tattoo Artist. The artist (a friend of Rockwell’s), his backside bulging towards the viewer, has crossed out the names of former loves and is in the process of immortalizing ‘Betty’ on the arm of a grateful sailor. The fickleness of love permanently inked on its next port of call.  A simple picture at first glance, but imbued with all kinds of hidden meaning: personal goals or conquests, the lighter side of global conflict, the personal choices one makes in life and their consequences (intended or otherwise), and the role of so many different tattoo motifs as symbols, metaphors, or memories.

Tattoos have been around for thousands of years, but their introduction to western societies is relatively recent.  Sailors, returning to Britain from Cook’s 18th century voyages to Polynesia, displayed adornments on various bits of their anatomy to a shocked audience.  Motifs such as anchors and doves signified high seas adventures. You could measure the metal of a traveler by their inked motifs. Fast forward 250 years, and you’re more likely to discover a liking for large trucks or serpentine entwinement, a favourite cat, or perhaps the cast of Star Trek that might indicate the traveler ventured no further than their living room.

I chose an iconic New Zealand seashell, a snail, for the most mundane reason; I have stood on several specimens, embedding them in my foot. They remind me of my time on deserted beaches skirting Great Exhibition Bay, along New Zealand’s northernmost coast.

Poirieria zelandica belongs to the family of marine snails (gastropods) known as the Muricidae, commonly referred to as Murex. There are more than 1600 identified species seas-wide. They constitute some of the most ornate, spiniest shells known, including the fabulous Venus Comb Shell (Murex pecten).

Murex grow their spines for protection (including protection against marauding feet), and for support in soft sands and muds.  They tend to live between 20-200m water depth.  Most dine on clams or other snails (particularly those that don’t have spines). Like many marine snails, they have a built-in, tongue-like drill or rasp, called a radula, that they use to bore into hard clam shells.  Some species also secrete an acid into the boring, to help dissolve the hard, calcium carbonate shell of its prey. The Murex will then suck out the juicy, clam-chowdery bits.

The New Zealand species of Poirieria can be found from one end of the country to the other, but more commonly occurs along our northern, subtropical to temperate coasts. It is not as spiny as the tropical Venus Comb shell, but it is quite robust. Empty shells, as I have discovered from time to time, lie on the beach with their longest spines upwards.

I am happy with the inked product; I made the right choice. There will be no need for crossing out or strike through. There will be no need for a replacement, no spurning of my regard for it being part of my life. All I require now is a suitable compliment, for the other arm.

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Nitrate in excess; a burgeoning, global contamination problem

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A “Nitrate timebomb”.  Last week’s media metaphor (Nov 10, 2017), was no doubt intended to create visions of dire deeds. After all, it seems that explosions are not in short supply these days. The actual story though is more droll, based as it is on the slow leakage of excess chemicals called nitrates, into the global environment. No fireworks; only leakage. The headline in several media outlets, only lasted a day or two, barely scratching our collective consciousness. Perhaps the problem is too big, or too remote – a candidate for the too-hard-basket. As Mark Twain might have said, “I guess so, I dunno”.

Nitrogen itself is not a concern; every breath we take contains 80% N2. It’s what we do with nitrogen that is causing problems, particularly in natural systems like soils, surface waters, groundwater aquifers, and ultimately, the oceans. The scientific paper that caused these brief media conniptions was published this month in Nature Communications (it is Open Access).

In natural earth systems, nitrogen and its chemically reactive derivatives such as ammonia (NH3), nitrates (NO3), and nitrites (NO2), participate in a grand cycle that, next to carbon, is absolutely critical to our well-being; nitrogen is involved in many biochemical reactions (for example all amino acids and proteins). The so-called nitrate timebomb exists because we have messed with this cycle.  The cartoon below shows some of the loops, twists and turns that compounds of nitrogen make as they journey through various earth systems.

There are complex feedback processes among natural systems, like soils, vegetation, animals, water and so on, that account annually for the addition of about 210 million tonnes of reactive nitrogen. Most of this nitrogen is consumed naturally so that a reasonable balance is maintained. But our own activities, particularly combustion (industry, engines, and forests), sewage, fertilizer production, and agriculture, have almost doubled the amount of available reactive nitrogen added annually. Most of this additional nitrogen upsets the natural balance.

Plants do not get their nitrogen nutrition directly from air; instead they rely on nitrogen being transformed chemically to compounds that are soluble in water, some as ammonia, but predominantly as nitrates. The important drivers of nitrogen fixing are soil and plant-root microbiota, principally bacteria and fungi. Lightning also produces small amounts of reactive nitrogen. In natural systems, most soil fixing of nitrate keeps pace with plant uptake; there is little or no excess nitrate. Agriculture has taken advantage of vegetations’ predilection for nitrogen, by producing ever-increasing volumes of fertilizer.  In most cases, the nitrogen is present as nitrate; it is a form immediately available for plants to use (as long as there is also water available). The application of fertilizers has been a major boon to global food production; fertilizer production has increased globally by a factor of 10 since 1950.

But increased food production has come at a price: huge tracts of the world’s soils have been seriously degraded, and and excess nitrate is adversely affecting other parts of the ecosystem. Too often, fertilizer is applied in quantities that ensures nitrate-nitrogen is available in-excess of a plant’s needs.  However, the excess nitrate doesn’t just disappear – in fact it is stored in soils and subsoil materials (for months, years, decades), and eventually it is transported by gradual seepage into shallow groundwater aquifers and surface waterways (streams, lakes).  Globally, nitrates are the most common groundwater contaminant.

Levels of nitrate contamination in soils and water are determined by several factors, including:

  • Proximity to nitrate sources,
  • The initial nitrate (fertilizer, sewage) input),
  • The permeability of the soil and subsoil (i.e. the ease with which it will move through soil pores),
  • Precipitation rates – high rainfall will tend to dilute excess nitrate,
  • Irrigation will exacerbate nitrate leaching from surface applications to groundwater,
  • The depth to the local watertable, and the rate at which groundwater flows through an aquifer before being intercepted by wells or freshwater-marine water bodies.

The World Health Organisation recommends no more than 10 milligrams per liter (10 mg/L) nitrate-nitrogen in drinking water, a value adopted by many countries. Shallow aquifer systems (less than 30-40m deep) tend to be most susceptible to nitrate (and other) contamination, particularly if agricultural practices occur in the same watershed (the USGS has released contaminant probability maps).  Although there are significant regional differences, most aquifers in this category, on a global scale, have between 1-10 mg/L nitrates, and many exceed this value, some by 1 and 2 orders of magnitude. This includes aquifers in the USA and Europe, China, and India (there are many other examples).

Nitrate contamination in shallow aquifers will eventually find its way to surface water bodies such as rivers, lakes, and nearshore marine environments.  Nitrate leaching (commonly in parallel with phosphates) is strongly implicated in promoting algal blooms in surface water, blooms that in many cases are toxic to marine and freshwater life, and people. Algal blooms also reduce the amount of dissolved oxygen in water, and in extreme circumstances can render water bodies biologically ‘dead’.  The coastal province of Shandong, China, for example, is notorious for producing massive blooms of green marine algae, that most analysts consider result from agricultural and sewage effluent.

Not all phytoplankton blooms in oceans and lakes are caused by anthropogenic nitrates (and phosphates), but it seems that an increasing number of them are.

Nitrate in groundwater systems has been known for decades. However, it has taken longer for us (collectively) to realize that huge volumes of nitrate are being stored in subsoils between the surface and the watertable; the estimate quoted in the recent Nature Communications paper, indicates between 600 million and 1800 million tonnes of peak nitrate storage between 1900 and 2000.  The concern is that this nitrate lies in-waiting.  The rate of nitrate movement through subsoil materials is highly variable, but generally very slow – commonly on the order of decades.  This means that, even if we were to immediately cut further increases in anthropogenic nitrate, many subsoil and aquifer systems would take decades to flush the offending contaminants. And therein lies the other conundrum – nitrates will continue to be flushed into our waterways for the foreseeable future.

The nitrate problem is gaining recognition.  Its solution requires a rethink of established agricultural and waste disposal practices, of entrenched corporate attitudes that more (fertilizer) is always better, and the political will to work through the multitude of issues.

The problem is huge, but we need to make certain it is not put in the ‘too-hard basket’.

 

 

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Subcutaneous oceans on distant moons; Enceladus and Europa

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Our blue Earth, rising above the lunar horizon, is an abiding image of our watery state that must evoke an emotional response in any sensible person. Cloud-swirled, Van Gogh-like. Such a blue – there’s nothing like it, at least in our own solar system.  A visitor to Mars three billion years ago might have also seen a red planet daubed blue, but all those expanses of water have since vanished, replaced by seas of sand.

Earth’s oceans are unique in our corner of the universe. Except for a thin carapace of ice at the poles, they are in a liquid state, and are in direct contact with the atmosphere to the extent that feed-back processes control weather patterns and climates.  Sufficient gravitational pull plus the damping effect of our atmosphere, prevents H2O from being stripped from our planet by solar radiation (again, unlike Mars). Our oceans exist because of this finely tuned balancing act.

The discovery in 2005 of liquid water on other planetary bodies in the Solar System, was a momentous event. Spacecraft Cassini provided the data during its flyby of Enceladus, a diminutive moon of Saturn (radius is only 252km). Cassini discovered water vapour in geysers, or plumes jetting from Enceladus’ surface.  In 2013, Hubble added to the excitement when it imaged what many astronomers interpreted as a vapour plume erupting from Europa, one of Jupiter’s icy moons.

Hubble’s analysis indicated both hydrogen and oxygen in the vapour, most likely as water. Logic, and our knowledge of physical processes dictate that the water vapour in both cases is likely derived from liquid water.  But unlike Earth’s ruffled oceans, the water on Enceladus and Europa lies beneath icy crusts; the oceans on these moons are subcutaneous.

Discovery of the plumes confirmed previous (scientific) suspicions that Enceladus possessed a liquid ocean.  Two additional lines of evidence include:

  • Its orbit around Saturn is perturbed by a wobble that can only be explained by a liquid interior, and
  • A density of 1.61 grams per cubic centimeter (g/cc) is significantly greater than the average density of the gas giant Saturn (about 0.69 g/cc); for comparison, water has a density of 1 g/cc, and Earth averages 5.51 g/cc.  Enceladus’ density is reasonably explained by a global model that pictures a rocky core, a liquid interior, and an icy crust.

Enceladus is one of the brightest objects in the Solar System, its smooth surface reflecting almost 100% of sunlight; the corresponding surface temperature is a cool -201oC.  There are craters in various states of preservation, but large tracts have no craters at all, suggesting that the icy surface has been renewed from time to time. Large fractures, particularly in the south pole region have been nicknamed ‘tiger stripes’; these fissures are the locus of vapour jets and sprays.  Material from the jets is incorporated into Saturn’s E-ring (Enceladus orbits Saturn within the E-ring).

Following the discovery, Cassini was reprogrammed to do several flybys, including five trips through the plumes.  On-board analysis (using a mass spectrometer) shows the vapour consists mostly of water, with minor carbon dioxide. Trace compounds that have also caused some excitement include ammonia (NH3), Hydrogen (H2) and several organic molecules including benzene species (6 carbon atoms joined in a hexagon).

Ice particles in the plume also contain sodium – it appears the subcutaneous ocean is salty. Nano-scale particles of silica (a few billionths of a metre) have also been discovered which helps to confirm the rock core, but also suggests that temperatures deep in the ocean could be as high as 90oC. Temperatures this high would promote chemical reactions between the ocean water and the rocky core.

The data, exciting as it is, presents something of a conundrum; significant heat is required to maintain a liquid ocean (i.e. to prevent it from freezing solid), particularly if toasty warm hydrothermal activity is also present.  Current thinking invokes tidal friction as a source of heat. Enceladus’ orbit is slightly elliptical, such that the moon develops a slight bulge when it is closest to Saturn (it is pulled out of shape), but returns to an almost spherical form when farthest away.  The process is analogous to our own moon’s gravitational effect that produces ocean tides. Recent modelling suggests that most of this heat is generated in the core and transferred to the liquid ocean.

 

Not to be outdone, Jupiter’s moon Europa (image at top of page), a bit smaller than our own lunar orb, has an icy surface riven by fractures and ice rafts, but very few craters, all indicating a tectonically active, geologically young crust. In fact, some regions appear quite broken and jumbled, and are referred to as chaos regions that may have formed by collapse of the crust.  Ice rafts here bear an uncanny resemblance to rafted Arctic ice.

Like Enceladus, Europa too may have a subcutaneous liquid ocean.  The primary evidence in this case is derived from measurements of Jupiter’s magnetic field (by spacecraft Galileo). The magnetic field generated by Jupiter is disturbed by Europa, in a way that is best explained by the moon containing a deep, salty, liquid ocean.  The latest Hubble images of erupting plumes are helping to consolidate this hypothesis.  Like Enceladus, it is probably heat, generated by tidal friction, that prevents the liquid mass from freezing.

Imaging of Europa’s surface by Galileo during one of its close encounters (about 22,000 km), shows an array of broken and fractured segments of ice; in the close-up image, fracture widths range from about a kilometre or less, to more than 50km. The detail illustrates a remarkable degree of ice fracturing and annealing over many generations.  Red hues are thought to be mineral deposits which, if confirmed, would provide further evidence of a rocky core, and chemical interactions between the core and liquid ocean.

I never tire of seeing the new imagery and data that the various space probes and telescopes produce. Every week seems to herald some new discovery.  Cassini, of course, has done its bit for science. Next in line is Europa. Europa Clipper, a tall-ship name given to a new-generation space probe, has become a NASA priority, planned for the 2020s. Clipper may also act as a pathfinder for a future robotic lander mission.  In both missions, the possibility that Europa’s ocean might harbour life forms is never far from scientists’ planning (and perhaps dreaming). The onboard instruments will certainly be tasked with this in mind.

Meanwhile, there are years of Cassini and Galileo data still to be analysed. The science never stops.

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Lahars; train-wreck geology

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Christmas morning in New Zealand is synonymous with mid-summer barbecues at the beach, deservedly lazy times, perhaps a bit of over-indulgence. That morning, in 1953, Kiwis were expecting to awaken to news of the Royal tour; the newly crowned Queen was doing the rounds of towns and countryside, perfecting that royal wave to flag-waving folk lining the streets. Instead, they awoke to the news of a train disaster near Mt. Ruapehu, one of three active volcanoes in central North Island; a railway bridge on Whangaehu River, near Tangiwai, had been washed out on Christmas Eve.  Train carriages were strewn along the river banks, 151 people were killed.  The culprit was a geological phenomenon known as a lahar.

The slopes of most volcanoes are strewn with an assortment of volcanic debris (volcanic ash, chunks of lava flow, lava bombs, fragments from hot ash clouds).  If there is a sudden addition of water to this mix of loose rock, then, under the constant influence of gravity, the entire conglomeration will begin to move.  Volcano slopes tend to be steep, and the watery mixture quickly gains speed and momentum, guided by gullies and existing river channels. These highly mobile mud-rock-water slurries commonly attain speeds of 50km/hour, but have been clocked at more than 140km/hour. They are lahars, a kind of debris flow that contains mostly volcanic fragments and is initiated on the slopes of volcanoes. Their mobility and speed make them highly destructive.

Lahars can develop at any stage of a volcano’s life; during eruptions when hot materials melt snow and ice, and long after eruptions during major precipitation events. They can also arise from the breaching of crater lakes, and it is this mechanism that was responsible for the Tangiwai disaster in 1953.

Historically, Crater Lake has been a pretty constant feature of Ruapehu. The lake levels and temperatures fluctuate with the mood of the volcano, and it is monitored closely for its more temperamental activity (Ruapehu and its surrounds are one of the most popular skiing and hiking areas in New Zealand). Late in 2006, the lake level rose significantly, and scientific monitoring equipment was put in place in anticipation of a break-out. Ruapehu duly complied on March 18, 2007; the lake dam (consisting of volcanic ash and rubble) was breached. The sudden rush of water mixed with the abundant supply of rocky debris in the headwaters of Whangaehu River, producing a lahar that careened headlong down the valley. A GNS Science video of the event, featuring volcanologist Brad Scott, shows some of the classic features of lahars, including:

  • Lahars can develop very quickly,
  • Lahars are a bit like wet concrete, although sloppier,
  • They are highly mobile, are capable of moving at high speeds, and frequently carry large boulders and trees,
  • They eroded river channels through which they tend to be focused, incorporating more debris and water into the flow, such that the lahar can grow in size as it moves downslope.
  • Lahars can travel 10s of kilometres from their source.

Some older video sequences shot in Japan, although a bit fuzzy, demonstrate the incredible destructive power of lahars. In the first clip, a lahar generated on the slopes of Mt Unzen grows rapidly, spilling over the river banks.  At about 8 seconds into the clip, there is a large surge in flow; surges like this are common in lahars (and other debris flows). Houses, vehicles and bridges are obliterated in seconds in flows of this size.

Some of the largest debris flows known are lahars. During the 1985 eruption of the Colombian volcano Nevado del Ruiz, hot pyroclastic flows melted summit ice and snow, providing enough water to generate several lahars; these flows traveled upwards of 100 km, killing 23,000 people. En route, they grew in volume to about four times their original size, by incorporating water and sediment from the river valleys.

By an unfortunate coincidence, the 1991 eruption of Pinatubo (Philippines) occurred while a typhoon was passing overhead. Torrential rain, mixing with the new influx of ash and debris, generated a lahar that killed 1500.

Lahars pose risks in regions of both active and dormant volcanoes, and hence are commonly the subject of geological mapping, modelling, and experimentation. One such experimental site is a USGS facility in Oregon, that uses an artificial flume (channel) to examine and measure the attributes of debris flows.  Data from experiments and geological studies like these are used to evaluate the efficacy of lahar early warning systems.

As a geologist, I have come across several examples of ancient lahars; they are fascinating deposits in their own right. We can identify common physical attributes, even in rocks many millions of years old (such as the size range of volcanic fragments in an almost chaotic mix – everything from boulders to mud-sized particles).  We also have a good theoretical understanding of the kind of power and mechanics required to move large boulders in flows like these, for example the effects of buoyancy and turbulence. But theories designed to explain ancient events, do not convey a sense of the immediate destructive power, the mayhem and terror that lahars can foist on a landscape. The rock record may contain a few fossilized, broken and shattered tree trunks, but no trains or houses.  It is, unfortunately, the observations, images, and historical notes of more recent lahar events that teaches us these brutal lessons.

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Overture to a cave; the spectacle of jointing in ancient basalt lava flows

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Saturday August 8, 1829, Felix Mendelssohn and his traveling companion Karl Klingemann, took a boat trip to Fingal’s Cave, the entrance to a world beneath Staffa, an inconspicuous dot on the edge of the Atlantic. Staffa is part of the Hebrides Archipelago, west Scotland. Celtic legend called it Uahm Binn, ‘The Cave of Melody’, that in story was part of a bridge extending to the iconic Giant’s Causeway in County Antrim (Northern Ireland).  The Celtic name is apt; Atlantic swells echoing countless songs.  Klingemann later wrote “Fingal’s Cave…its many pillars making it look like the inside of an immense organ, black and resounding, and absolutely without purpose, and quite alone, the wide grey sea within and without.”. Continue reading

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Dirt; Soil degradation is a global problem we inflict on ourselves

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The media loves hyperbole. In some ways they remind me of ‘The end is nigh’ cartoon guy. This week (Oct 16, 2017) it’s ‘Ecological Armageddon’, a kind of end-of-the-world announcement that is founded on what looks like a drastic reduction in the insect biomass in parts of Germany; 75% of insects have disappeared since 1989. I don’t mean to trivialise these alarming reports, because if it turns out to be a phenomenon of more global extent (the collapse of bee colonies does not augur well), then the ramifications for activities like food production could be dire. The report’s authors note that the cause of this reduction is not yet understood, a sensible comment based on the limited scope of their study (the paper is Open Access). But their caution has not stifled speculation and hyperbole.

The demise of insects segues into the topic of this blog; the alarming rate at which soils, globally, are being degraded. There is a symbiotic relationship between soils and insects, linked primarily to the vital role both play in vegetation productivity. Continue reading

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Near Earth Objects; the database designed to save humanity

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The media love natural disasters, even those that don’t exist. Last week (early October, 2017), dramatic footage of a (simulated) super-volcano eruption beneath Auckland city was aired by several international media outlets, with headlines announcing the city’s calamitous destruction. But there is no super-volcano beneath Auckland. The excitement was short-lived.  While Auckland smouldered (as if that wasn’t enough), it was announced that New Zealand’s North Island could experience a subduction zone earthquake that, in its aftermath, would leave 1000s dead. An interesting backdrop to New Zealand’s recent election. Having scared the local population to death, our purveyors of science moved on to the next concern; other “what ifs…”.

Asteroid impacts are no longer de rigueur; perhaps it’s the turn of super-volcanoes’, or because NASA and the European Space Agency (ESA) have stated, with some confidence, that no large impacts are expected within the next 100 years. And whereas the media may find this Continue reading

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