Monthly Archives: September 2017

A greener earth; Earth’s vegetation is responding to increasing atmospheric CO2

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Photosynthesis, a process that had its beginnings about 2.5 billion years ago, has an awesome responsibility; it keeps us breathing. It is a metabolic process in plants that uses the energy from sunlight to drive chemical reactions; reactions that produce amino acids, proteins, sugars and other compounds that create the architecture of plants.  The process takes atmospheric CO2, converts the carbon plus other nutrients to organic compounds, then expels the left-over oxygen. Plants help regulate the composition of the atmosphere – they are our other set of lungs.

It has been shown experimentally that photosynthesis increases in many kinds of plants (some more than others), as the supply of atmospheric CO2 also increases. On a global scale, this is referred to as greening of the earth, where both regional studies, and more recently satellite data show an overall increase in plant growth, and an increase in growing seasons. In Europe and North America, the seasonal leaf-out (or bud-break) for the period 1950 to the 1990s was 2-4 weeks earlier than pre-1950.

Plant growth responds to several environmental factors, such as temperature, soil health, and the availability of water and nutrients. Modelling of plant response to these various controls suggests that globally about 70% of the increased growth (greening) is due to increases in CO2 fertilization. The remaining 30% reflect changes in nitrogen uptake, regional temperature and precipitation, and land-use.

These observations and models are important because they help to define how critical parts of the carbon cycle might respond to increasing CO2 and to changes in climate.  Increased growth means that carbon sequestration in plants, and eventually in soils, is also increasing. A 2015 study has shown that there is significantly greater CO2 uptake in the tropics compared with higher latitudes, although the authors comment that continued deforestation, plus potential changes in climate conditions, might offset this process.

Quantifying the multitude of positive and negative feedback processes in the carbon cycle is a recognized challenge in climate science. Increased uptake of CO2 by plants is a negative feedback that helps reduce the excess gas in the atmosphere.  However, there are important caveats and limitations to this process; some of these are listed below.

  • Plants, in adapting to increased CO2, may reach a point where there is no additional growth. Increased CO2 concentrations result in the closure of leaf stomata. Stomata are the microscopic vents in leaves that allow CO2 to enter, and water to leave (evapotranspiration) the leaf structure. Closure of stomata is used by plants to regulate water loss, but closure will also restrict the amount of absorbed CO2.
  • Nitrogen is a critical plant nutrient. It has been experimentally determined that increased CO2 can lead to a decreased uptake of nitrogen; this negative response persists even when plant growth is enhanced by CO2. The long-term effects of lower N are not well understood. Nitrogen is a key ingredient of plant proteins, so does a potential reduction in its uptake mean lower protein levels in food crops?
  • Other nutrients, such as phosphorous and potassium, are critical for plant growth. Leaf growth cannot continue unabated without sympathetic development of roots, for which both potassium and phosphorous are necessary ingredients. Increased leaf greening may be limited by the availability of these other nutrients.
  • How do soil microorganisms respond to increasing CO2? Microorganisms are responsible for mediating the delivery of most nutrients to plants, but they are highly susceptible to soil erosion, deforestation, and changes in soil chemistry such as pH.

The response by vegetation to increasing atmospheric CO2 is an important feedback in the carbon cycle. The earth is greening, but it is also clear that the current vegetation cover is not capable of sequestering all produced CO2, because atmospheric levels of the gas continue to rise.  Deforestation in tropical regions is certainly not helping in this regard. The importance of understanding such changes cannot be understated; plants, both macroscopic and microscopic, are a critical part of the food chain. Plants can adapt to environmental changes, but that capability is highly variable among the different kinds of vegetation. Plant adaptability also has its limits.

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Hold a ‘0’ to the light and look through it – there is nothing, and everything

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Several years ago I read Jerry P. King’s The Art of Mathematics (1992). Chapter 3 deals with Numbers, and in it is a statement that has bothered me ever since “Although they are the most fundamental of mathematical objects, the natural numbers are not found in nature.” There are real numbers, but none exist in the natural universe. We may count two people, write the number on a piece of paper, or solve an equation that gives the answer as two, but the number ‘two’ does not exist – we cannot pick it up or put it under a microscope. I have kept an eye out for ‘one’, but even this basic singularity is elusive. Numbers, it seems, are an abstraction.

So where does this leave ‘zero’? Zero means nothing, zilch, emptiness; so is it even a natural number – is it an integer? Several commentators of mathematics and science have suggested that the invention of ‘zero’ was as important as that of the wheel. Our system of numbering depends on it. One becomes 100 by adding a couple of zeros. It is essential to calculus and algebra, and for solving equations. Without zero, there would be no binary code, and no computers (at least as we know them).

In our numbering system, zero is a place holder; it occupies the place where no integer occurs. So in the number 1001, the zeros indicates that there are no 10s or 100s integers; without the 0s we would have the number 11. Our place value system is constructed around a base of 10, usually referred to as base 10. This means that every time we add an integer to a number, the place value column increases by a factor of 10; 1 becomes 10, becomes 100, becomes 1001, and so on. The place value numbering system was probably invented by the Babylonians about 2000 BC. Their numbering system also used a base 60, that was inherited from the Sumerians between 2000 and 3000 BC. However, they had no zero, or any kind of symbol that might represent zero, until later when they introduced spaces between digits to indicate ‘nothing’. In other words, it wasn’t a number.

Zero, as a number, was probably invented in India in the first few centuries AD. Until recently, the oldest known formulation was recorded on a tablet that describes a 9th Century Hindu temple, in the old fortified city of Gwalior. The zeros here are dots, but this notation shows that the base 10 place-value numbering system was probably commonplace by 876 AD.

The dot notation is also found on an ancient birch-bark manuscript – the Bakhshali manuscript, discovered in 1881 (in what is now Pakistan), of which 70 fragments remain. The manuscript is held at the Bodleian Library, Oxford University. There has been significant debate about its age, but what is now generally conceded is that it is a copy of a much older manuscript. Until recently, it was considered to be 8th century, with some scholars placing it as early as 3rd or 4th century. It is a mathematical tome of remarkable sophistication, that contains examples of linear and quadratic equations, formulae for square roots and other functions, and arithmetic and geometric progressions, all of which use zero (dots) as a place holder. Carbon dating of the bark (reported September 14, 2017) now shows that the manuscript is indeed 3rd or 4th century, with the oldest pages between 224-383 AD.

The first definition of zero as an actual number was made in 628 AD by Hindu astronomer and mathematician Brahmagupta.  The work, known as Brahma-sphuta-siddhanta, outlines how zero is derived by subtracting a number from itself. This was a seminal work, not only in astronomy, but in mathematics; its translation into Arabic about 771 AD, was probably an important contribution to the Arabic invention of algebra.

Zero, in the form of a dot, had evolved as place-holder and as an actual number in India by the 7th Century. By some circuitous route, Persian translations of Sanskrit manuscripts provided a basis for Arab developments in mathematics. The first record of zero being represented as an enclosed symbol, a circle (or oval, with nothing inside it) in 976 AD, was in the writings of one Muḥammad ibn Mūsā al-Khwārizmī, a Persian mathematician; it was given the name Sifr (Arabic for ‘empty’).  Not long after, Arabic numerals, that now included ‘0’, reached Europe. Leonardo of Pisa, otherwise known as Fibonacci, was instrumental in advertising the utility of the numeral system in his 1202 composition Liber Abaci (Book of Calculation) – almost 600 years after Brahmagupt’s opus.

According to the Merriam-Webster Dictionary, the word ‘zero’ was first used in English in 1598, but I have yet to find the context for this. The etymology of ‘zero’ mimics the history of its formulation, beginning with the Arabic sifr, that on arriving in Europe, perhaps through Italy (zero) and France (zéro), finally entered the English language as zero.

Hold a ‘0’ to the light, and look through it – there is nothing, and everything. Look through the zero to new worlds, new views of the universe. The history of zero has done just that, from tentative, humble beginnings it now helps us create so many possibilities.  I wrote this piece 2 days after Cassini’s final descent into Saturn’s atmosphere. I wonder if such flights would have been possible if not for the genius of zero?

Check out this YouTube video about the Bakhshali manuscript (Bodleian Library)

Here’s a couple of books on the topic:

The Nothing that is: A natural history of zero, Robert Kaplan, Oxford University Press, 2000

Zero: The biography of a dangerous idea. Charles Seif. Penguin, 2000

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Springs and seeps

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It rains quite a bit on Mamaku Plateau, the tableland underlain by volcanic debris that was violently deposited 240,000 years ago; an eruption that also gave rise to the Lake Rotorua caldera (central North Island, New Zealand). Some of that rain seeps into the myriad fractures, nooks and crannies, and heads west as groundwater. Fifty to 100 years later, that same water emerges, chilled (a cool 11oC), at Blue Springs (about 40km west of Rotorua). Spring water here flows at 42 cubic metres per minute (9,240 gallons per minute), enough to maintain a decent-sized stream (Waihou Stream).

Fresh water springs have been sources of life, driven conflicts, and kindled the imagination for thousands of years. Greek muses frolicked in the Pierian Spring (somewhere in Macedonia); its waters a fount of knowledge. After spending a lifetime underground in,

         A secret system of caves and conduits; hear the springs

         That spurt out everywhere with a chuckle… (W.H. Auden, In Praise of Limestone, 1948). Gleeful emergence.

Springs may be cold or hot (thermal); they sometimes have dissolved minerals that are deposited near or at the surface where the spring exits.  Dissolved silica or calcium carbonate (tufa) are common in thermal springs. Thermal springs are also fed by groundwater but are heated by deep external sources, like magma chambers. Buoyancy and convection (hot water rises, cold water sinks), play an important role in driving the hot fluids to the surface.

Some springs, like the Devil’s Postpile National Monument in California, have naturally dissolved carbon dioxide, providing a kind of backyard sodastream. Buoyancy forces are also important for driving oil and gas to the surface (hydrocarbons seeps). In this case, the hydrocarbons are derived from oil or gas prone rocks at depth.

Fresh water springs commonly emerge where the watertable intersects the ground surface (water from an unconfined aquifer).  In some regions, particularly those in limestone country, springs discharge from aquifers at depth (confined aquifers) that have elevated pressure, where the water flows through conduits in rock (such as faults and fractures); this is also referred to as artesian flow. Sinkholes are an extreme expression of this kind of groundwater seepage.

The different kinds of fresh water spring all have one thing in common – the direction of flow is dictated by a decrease in pressure (from high to low pressure), or in more technical terms, from high to low hydraulic head.

Gravity is the dominant driving force for groundwater flow in most groundwater systems, including spring flow. The easiest way to grasp this is to look at surface topography; groundwater at high elevations has greater hydraulic potential, or gravitational energy, than that at lower elevations. Thus, if an upland watertable intersects the surface at a lower elevation, for example along a valley, then springs will develop at or below that point of contact – this is illustrated in the block diagram.

In layered rock, groundwater can seep through a permeable aquifer until it reaches an impermeable barrier, such as a mudstone or shale. If the contact between the two layers is exposed, the groundwater can emerge as contact springs. In the example shown here from Grand Canyon, Arizona, springs emerge at the contact between an impermeable limestone below, and the permeable limestone above through which the groundwater has percolated.

Conduits for groundwater flow and spring discharge are provided by fault planes that, in some circumstances, may tap into several aquifers. In the diagram below, groundwater flow in the sand aquifer is diverted by a fault plane. If there is sufficient hydraulic head in the aquifer (think of this as the potential energy available from the force of gravity), the groundwater will emerge where the fault plane intersects the surface.

Fractures and joints are common in hard rock.  Most igneous and metamorphic rocks typically have little or no permeability, except where they have been fractured by tectonic forces, or jointed during cooling (typical of lava flows).  Groundwater can flow through these crevices and emerge as springs. Seepage is common on exposed rock faces; freezing during the winter can produce some spectacular ice shows.

Perhaps one of the more extreme expressions of groundwater seepage and spring discharge occurs in regions underlain by limestone and salt (or salt domes). Both rock types tend to dissolve with groundwater seepage, enlarging fractures, and creating underground caverns and waterways (in limestones, stalactites and stalagmites are part of this process).  As caverns become larger, the roof rock becomes unstable and collapses; the surface manifestation of this is a sinkhole. Florida is a region particularly prone to sinkhole formation, and it is not uncommon for entire houses to be swallowed by the collapsing surface. Sinkholes commonly fill with water, derived from the aquifer below. And while local governments and individuals may find such geological structures a nuisance, it seems that local alligator populations are thrilled with the opportunity for a new beach or swimming hole.

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In praise of field work

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The class field trip is underway.  Teacher hands out the rap-around, virtual imaging glasses, and you are transported to a green horizon. In the background, there is an annoying kind of buzz, as teacher relates the topic of enquiry, asks questions, provides comments. Fellow students may even be projected into your virtual reality, their essence reduced to pixels. There’s a resounding crash – one student, suffering from vertigo, has fallen off their chair. Another has just thrown up from motion sickness.  All in a day’s field study. Off come the glasses. The green horizon vanishes. All except one of your classmates are still in their chairs, surrounded by the same four classroom walls. What was learned?

Real field schools and class trips, i.e. those outside the classroom, are the bane of educational institution administrators; even teachers find them disruptive. There are health, safety, and liability considerations, budget restrictions and teaching loads, and perhaps worst of all, field trips wreak havoc with those finely tuned curriculum timetables. Field trips are an administrative pain in the neck. And yet they are utterly indispensable to science and the humanities, whether applied to learners or hardened practitioners.

The ‘field’ can be almost anywhere. Geologists traipse the countryside in search of ancient worlds; they could just as easily explore from a drilling rig or the International Space Station. Soil biologists dig dirt. Botanists crawl through the undergrowth. Can you imagine learning chemistry and never experiencing a laboratory, or geophysics and never having the chance to trudge along a gravity transect? Field work is a grand learning experiment that brings together observation and data collection, creative thinking and language, conjecture and hypothesis. In the field, all our senses are assaulted; they engage our brain in three-dimensional visualization. The sights, smells, sounds and feel of the earth, allow us to extend our understanding beyond the immediately visible. Enjoying the vista from a ridge top, while catching one’s breath, contributes to the learning process. My own geological excursions to Ellesmere Island (Canadian Arctic) and Hudson Bay, Hutton’s Unconformity on Arran (Scotland), Atacama volcanoes, or New Zealand wilderness, provided hard data and a myriad tangible and intangible images, the kind of learning that no other experience could provide. In the field, our learning becomes both sensual and cerebral; we can visualize in our mind’s eye the things we cannot sense directly, beneath, within, and beyond the earth. And once we have this learned skill, we can project our understanding to worlds past and future; dimension number four. In the field, we can begin to get a feel for deep time.

Field work provides critical learning in the real world, learning that is conscious and retrievable, and learning that is not always explicable, even subliminal. Technology does not replace this kind of learning, but it can enhance it. We can go into the field with as little as a pencil and notebook. Or we can take with us, instruments that provide measures of earth properties, or real-time satellite imagery. Exploring the deep oceans and our solar system require special equipment. The Mars rovers are a projection of our own field activities (albeit quite expensive) – they observe, take samples, analyse, and transmit data.

Whether our feet are firmly planted on terra firma or leaving footprints on the Moon, our senses, intellect, and language provide us with learning pathways that are necessary to understand the complexity of the universe. Bowing to administrative objections deprives all students of the ultimate learning experience. Field excursions, the kind that go beyond the classroom or office, are utterly indispensable.

 

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