Thursday, 12 October 2017

The zeal in Zealandia: revealing a lost continent

From an outsider's standpoint, geology appears to be a highly conservative science. As I have mentioned on numerous occasions, it seems astonishing that it took over four decades for Alfred Wegener's continental drift hypothesis to be formalised - via the paradigm-shifting discovery of sea floor spreading - into the theory of plate tectonics. I suppose that like evolution by natural selection, the mechanism, once stated, seems blindingly obvious in hindsight.

Regardless, the geological establishment appears to have been stubbornly opposed to the ideas of an outsider (Wegener was a meteorologist) who was unable to provide proof of an exact mechanism. This was despite the fact that the primary alternative, hypothetical submerged (but extremely convenient) land bridges, appear even more far-fetched.

Over the past few decades geophysical data has been accumulating that should generate rewrites of texts from the most basic level upwards. Namely, that the islands making up New Zealand are merely the tip of the iceberg, accounting for just six per cent of a mostly submerged 'lost' continent. Once part of the Southern Hemisphere's Gondwana, in 1995 the newly discovered continent was given the name Zealandia. Approximately five million square kilometres in size, it broke away from the Australasian region of Gondwana around 70-80 million years ago.

After a decade or two of fairly lacklustre reporting, 2017 seems to be the year in which Zealandia is taking-off in the public domain. First, the Geological Society of America published a paper in February. stating that Zealandia should be officially declared as a continent. Then in July the drill ship Joides Resolution began the two month long Expedition 371, a research trip under the International Ocean Discovery Programme (IODP). Scientists from twelve countries undertook deep sea drilling, gaining data on plate tectonics, palaeontology and climate history as well as research directly relevant to understanding the geology of the newest continent.

It is surprising then to learn that geologists first mooted the idea as early as the 1960s but that apart from some marine core samples collected in 1971, no-one undertook the necessary ocean-based research until very recently. Earth resources satellites have helped somewhat, but nothing could replace the evidence that emerged with deep drilling of the seabed. Therefore I wonder what has sparked the sudden interest in an idea that has been around for so long?

One possibility is the large amount of data that the international geological community required to prove the theory beyond doubt, coupled with the fact that this sort of research has little in the way of an obvious immediate practical benefit. It is extremely expensive to undertake deep sea drilling and few vessels are equipped for the purpose. Joides Resolution itself will be forty years old next year, having undergone several years' of refit to keep it going. Those areas of sea bed with potential oil or gas deposits may gain high-fidelity surveying, but compared to fossil fuels, fossil biota and sea bed strata research are very much at the whim of international project funding. In the case of the IODP, governments are cutting budgets on what are deemed non-essential projects, so it remains to be seen whether the intended follow-up trips will occur.

It would be disappointing if there was no further research as despite the acceptance of Zealandia, there is still a great deal of disagreement about what is known as the Oligocene Drowning. I first came across the notion of an eighth continent in the excellent 2007 book In Search of Ancient New Zealand, written by geologist / palaeontologist Hamish Campbell and natural history writer Gerard Hutching. The reason that over ninety per cent of Zealandia is underwater is due to the lack of thickness of its continental land mass - only 20-30km - making it far less buoyant than other continents.

But has this submerged percentage varied during the past eighty million years? There are some very divided opinions about this, with palaeontologists, geneticists and other disciplines taking sides with different camps of geologists. These can be roughly summarised as Moa's Ark versus the Oligocene Drowning, or to be more precise, what percentage, if any, of New Zealand's unique plants and animals are locally-derived Gondwanan survivors and how many have arrived by sea or air within the past twenty or so million years?

The arguments are many and varied, with each side claiming that the other has misinterpreted limited or inaccurate data. If Zealandia has at any time been entirely submerged, then presumably next to none of the current fauna and flora can have remained in situ since the continent broke away from Gondwana. The evidence for and against includes geology, macro- and micro-fossils, and genetic comparisons, but nothing as yet provides enough certainty for a water-tight case in either direction. In Search of Ancient New Zealand examines evidence that all Zealandia was under water around twenty-three million years ago, during the event known as the Oligocene Drowning. However, Hamish Campbell's subsequent 2014 book (co-written with Nick Mortimer) Zealandia: Our continent revealed discusses the finding of land-eroded sediments during this epoch, implying not all the continent was submerged.

It's easy to see why experts might be reticent to alter their initial stance, since in addition to the conservative nature of geology there are other non-science factors such as patriotism at stake. New Zealand's unusual biota is a key element of its national identity, so for New Zealand scientists it's pretty much a case of damage it at your own peril! In 2003 I visited the predator-free Karori Wildlife Reserve in Wellington. Six years later it was rebranded as Zealandia, deliberately referencing the eighth continent and with more than a hint of support for Moa's Ark, i.e. an unbroken chain of home-grown oddities such as the reptile tuatara and insect weta. With the nation's reliance on tourism and the use of the '100% Pure New Zealand' slogan, a lot rests on the idea of unique and long-isolated wildlife. If the flightless kakapo parrot for example turns out not to be very Kiwi after all, then who knows how the country's reputation might suffer.

What isn't well known, even within New Zealand, is that some of the best known animals and plants are very recent arrivals. In addition to the numerous species deliberately or accidentally introduced by settlers in the past two hundred years, birds such as the silvereye / waxeye (Zosterops lateralis) and Welcome swallow (Hirundo neoxena) are self-introduced, as is the monarch butterfly.

The volcanic island of Rangitoto in Auckland's Hauraki Gulf is only about six centuries old and yet - without any human intervention - has gained the largest pohutukawa forest in the world, presumably all thanks to seeds spread on the wind and by birds. Therefore it cannot be confirmed with any certainty just how long the ancestors of the current flora and fauna have survived in the locality. A number of New Zealand scientists are probably worried that some of the nation's best-loved species may have arrived relatively recently from across the Tasman; a fossil discovered in 2013 suggests that the flightless kiwi is a fairly close cousin of the Australian emu and so is descended from a bird that flew to New Zealand before settling into an ecological niche that didn't require flight.

Other paleontological evidence supports the Moa's Ark hypothesis: since 2001 work on a lake bed at St Bathans, Central Otago has produced a wide range of 16 million year-old fossils, including three bones from a mouse-sized land mammal. The diversity of the assemblage indicates that unless there was some uniquely rapid colonisation and subsequent speciation, there must have been above-water regions throughout the Oligocene. In addition, whereas the pro-underwater faction have concentrated on vertebrates, research into smaller critters such as giant land snails (which are unable to survive in salt water conditions) supports the opposite proposition.

So all in all, there is as yet no definitive proof one way or the other. What's interesting about this particular set of hypotheses is the way in which an array of disciplines are coming together to provide a more accurate picture of New Zealand's past. By working together, they also seem to be reducing the inertia that has led geology to overlook new ideas for far too long; Zealandia, your time has come!

Wednesday, 27 September 2017

Cow farts and climate fiddling: has agriculture prevented a new glaciation?

Call me an old grouch, but I have to say that one of my bugbears is the use of the term 'ice age' when what is usually meant is a glacial period. We currently live in an interglacial (i.e. warmer) era, the last glaciation having ended about 11,700 years ago. These periods are part of the Quaternary glaciation that has existed for almost 2.6 million years and deserving of the name 'Ice Age', with alternating but irregular cycles of warm and cold. There, that wasn't too difficult now, was it?

What is rather more interesting is that certain geology textbooks published from the 1940s to 1970s hypothesised that the Earth is overdue for the next glaciation. Since the evidence suggests the last glacial era ended in a matter of decades, the proposed future growth of the ice sheets could be equally rapid. Subsequent research has shown this notion to be flawed, with reliance on extremely limited data leading to over-confident conclusions. In fact, current estimates put interglacial periods as lasting anywhere from ten thousand to fifty thousand years, so even without human intervention in global climate, there would presumably be little to panic about just yet.

Over the past three decades or so this cooling hypothesis has given way to the opposing notion of a rapid increase in global temperatures. You only have to read such recent news items as the breakaway of a six thousand square kilometre piece of the Antarctic ice shelf to realise something is going on, regardless of whether you believe it is manmade, natural or a combination of both. But there is a minority of scientists who claim there is evidence for global warming - and an associated postponement of the next glaciation - having begun thousands of years prior to the Industrial Revolution. This then generates two key questions:

  1. Has there been a genuine steady increase in global temperature or is the data flawed?
  2. Assuming the increase to be accurate, is it due to natural changes (e.g. orbital variations or fluctuations in solar output) or is it anthropogenic, that is caused by human activity?

As anyone with even a vague interest in or knowledge of climate understands, the study of temperature variation over long timescales is fraught with issues, with computer modelling often seen as the only way to fill in the gaps. Therefore, like weather forecasting, it is far from being an exact science (insert as many smileys here as deemed appropriate). Although there are climate-recording techniques involving dendrochronology (tree rings) and coral growth that cover the past few thousand years, and ice cores that go back hundreds of thousands, there are still gaps and assumptions that mean the reconstructions involve variable margins of error. One cross-discipline assumption is that species found in the fossil record thrived in environments - and crucially at temperatures - similar to their descendants today. All in all this indicates that none of the numerous charts and diagrams displaying global temperatures over the past twelve thousand years are completely accurate, being more along the lines of a reconstruction via extrapolation.

Having looked at some of these charts I have to say that to my untrained eye there is extremely limited correlation for the majority of the post-glacial epoch. There have been several short-term fluctuations in both directions in the past two thousand years alone, from the so-called Mediaeval Warm Period to the Little Ice Age of the Thirteenth to Nineteenth centuries. One issue of great importance is just how wide a region did these two anomalous periods cover outside of Europe and western Asia? Assuming however that the gradual warming hypothesis is correct, what are the pertinent details?

Developed in the 1920s, the Milankovitch cycles provide a reasonable fit for the evidence of regular, long-term variations in the global climate. The theory states that changes in the Earth's orbit and axial tilt are the primary causes of these variations, although the timelines do not provide indisputable correlation. This margin of error has helped to lead other researchers towards an anthropogenic cause for a gradual increase in planet-wide warming since the last glaciation.

The first I heard of this was via Professor Iain Stewart's 2010 BBC series How Earth Made Us, in which he summarised the ideas of American palaeoclimatologist Professor William Ruddiman, author of Plows, Plagues and Petroleum: How Humans Took Control of Climate. Although many authors, Jared Diamond amongst them, have noted the effects of regional climate on local agriculture and indeed the society engaged in farming, Professor Ruddiman is a key exponent of the reverse: that pre-industrial global warming has resulted from human activities. Specifically, he argues that the development of agriculture has led to increases in atmospheric methane and carbon dioxide, creating an artificial greenhouse effect long before burning fossil fuels became ubiquitous. It is this form of climate change that has been cited as postponing the next glaciation, assuming that the current interglacial is at the shorter end of such timescales. Ruddiman's research defines two major causes for an increase in these greenhouse gases:

  1. Increased carbon dioxide emissions from burning vegetation, especially trees, as a form of land clearance, i.e. slash and burn agriculture.
  2. Increased methane from certain crops, especially rice, and from ruminant species, mostly cattle and sheep/goat.

There are of course issues surrounding many of the details, even down to accurately pinpointing the start dates of human agriculture around the world. The earliest evidence of farming in the Near East is usually dated to a few millennia after the end of the last glaciation, with animal husbandry preceding the cultivation of crops. One key issue concerns the lack of sophistication in estimating the area of cultivated land and ruminant population size until comparatively recent times, especially outside of Western Europe. Therefore generally unsatisfactory data concerning global climate is accompanied by even less knowledge concerning the scale of agriculture across the planet for most of its existence.

The archaeological evidence in New Zealand proves without a doubt that the ancestors of today's Maori, who probably first settled the islands in the Thirteenth Century, undertook enormous land clearance schemes. Therefore even cultures remote from the primary agricultural civilisations have used similar techniques on a wide scale. The magnitude of these works challenges the assumption that until chemical fertilisers and pesticides were developed in the Twentieth Century, the area of land required per person had altered little since the first farmers. In a 2013 report Professor Ruddiman claims that the level of agriculture practiced by New Zealand Maori is just one example of wider-scale agricultural land use in pre-industrial societies.

As for the role played by domesticated livestock, Ruddiman goes on to argue that ice core data shows an anomalous increase in atmospheric methane from circa 3000BCE onwards. He hypothesises that a rising human population led to a corresponding increase in the scale of agriculture, with rice paddies and ruminants the prime suspects. As mentioned above, the number of animals and size of cultivated areas remain largely conjectural for much of the period in question.  Estimates suggest that contemporary livestock are responsible for 37% of anthropogenic methane and 9% of anthropogenic carbon dioxide whilst cultivated rice may be generating up to 20% of anthropogenic methane. Extrapolating back in time allows the hypothesis to gain credence, despite lack of access to exact data.

In addition, researchers both in support and opposition to pre-industrial anthropogenic global warming admit that the complexity of feedback loops, particularly with respect to the role of temperature variation in the oceans, further complicates matters. Indeed, such intricacy, including the potential latency between cause and effect, means that proponents of Professor Ruddiman's ideas could be using selective data for support whilst suppressing its antithesis. Needless to say, cherry-picking results is hardly model science.

There are certainly some intriguing aspects to this idea of pre-industrial anthropogenic climate change, but personally I think the jury is still out (as I believe it is for the majority of professionals in this area).  There just isn't the level of data to guarantee its validity and what data is available doesn't provide enough correlation to rule out other causes. I still think such research is useful, since it could well prove essential in the fight to mitigate industrial-era global warming. The more we know about longer term variations in climate change, the better the chance we have of understanding the causes - and potentially the solutions - to our current predicament. And who knows, the research might even persuade a few of the naysayers to move in the right direction. That can't be bad!