Developer blog for the Holocene section, which aims to explore likely changes in the local sound environment since the end of the last glacial period 12,000 years ago.

DEVELOPER BLOG | GRAPHICS

25 JANUARY 2013

Late Pleistocene British mammals

The Late Glacial British mammal fauna had familiar and now-extinct species before the onset of the Younger Dryas cold period.

IN 1871, COLONEL Richard Irving Dodge of the United States Army encountered a seemingly limitless herd of bison along the Arkansas River. After riding through it for a day or so he estimated the herd to be around 25 miles wide and 50 miles long. He later recalled that the herd’s density was some 15 to 20 animals per acre, making a total herd size of 12–16 million [1].

Plate from Richard Irving Dodge’s The Hunting Grounds of the Great West; A Description of the Plains, Game, and Indians of the Great North American Desert, 1877.


Members of the genus Homo have form for wiping out large, charismatic animal species. Giant tortoises were the first to go in Africa due to predation by early Homo habilis populations nearly 2.5 million years. The same fate was inflicted on the giant tortoises of India and Indonesia after Homo erectus migrated there from Africa.

The bison herds which Colonel Dodge encountered were all but exterminated in the US during later years. In Europe a few hundred bison remain, lurking in the Białowieża Forest straddling the border between Poland and Belarus. Wild horses feature prominently in late Paleolithic European cave paintings but today only around 250 of their nearest living relatives Equus ferus przewalskii survive on the Mongolian steppes.

During earlier interglacial periods tens of thousands years ago, Britain was inhabited by cave bears, hippos, giant beavers and three different species of rhinoceros [2]. Today, we have 31 native terrestrial mammal species, compared to 52 in France and 47 in Germany. Ireland has just 20 species. This east-to-west species gradient is due, in part, to some species not making it to Britain and Ireland from their continental refuges before the land bridges disappeared. Despite the example of the giant tortoises of Africa and India, not all loss of biodiversity is necessarily due to hunting overkill.

Derek Yalden’s magisterial The History of British Mammals [3] gives a comprehensive account of the mammal fauna existing in Britain during the dog-days of the last glacial period, a time of slightly warmer conditions called the Windermere Interstadial. This in turn would be ended abruptly by the Younger Dryas reglaciation beginning 12,800 years ago and ending, along with the Pleistocene epoch, 11,700 years ago. Yalden argues at some length that the disappearance of many mammal species during those times was due to climatic and environmental change, rather than hunting.

The array of mammals in Britain during the Windermere Interstadial was like a cross between those now found in Poland and southern Sweden, with the addition of some now-extinct species. Woolly Mammoths lingered on in Britain until perhaps 15,000 years ago. Remains found in the sticky grey clay of a kettle-hole in Shropshire included those of an adult and three juveniles, preserved where they’d been trapped and died.

The Irish Elk Megaloceros giganteus left remains dating to around 14,500 years ago in Kent’s Cavern in Devon. Males stood nearly 7 feet or 2.1 metres tall at the shoulders and had antlers spreading to a width of 12 feet or 3.7 metres. Assuming that bigger might mean louder, these beasts would have made impressive roars during the rutting season.

An Irish Elk watches his domain in a painting by Charles R. Knight from 1906.


Other Windermere Interstadial British mammals are familiar from modern-day European and Scandinavian mammal fauna. They included Brown Bears, Red Deer, Wolves, Red and Arctic foxes, Elk, Mountain Hares, Beavers and Lynx. An example of the Saiga Antelope Saiga tartarica unearthed in Twickenham probably dates to before the end of the Last Glacial Maximum some 18,000 years ago, but remains dating to around 14,000 years ago have been found in the Mendip area of Somerset.

Britain during the Interstadial was dominated by open birch woodland, similar to the environment favoured by animals such as Elk in Scandinavia today. Willows were also present, along with various shrubs, crowberry, and juniper. This would have been a productive environment capable of supporting large numbers of animals, with longer growing seasons than its modern-day equivalents at more northerly latitudes.

The abrupt onset of the Younger Dryas reglaciation killed off the birch woodland and so the tundra environment of the Last Glacial Maximum returned. Sites in south-east England show traces of wedge-shaped formations in the ground made by cycles of freezing and thawing. There was a crash in the diversity of the British mammal fauna, with only Wild Horses and Reindeer representing the hoofed species. Cold-adapted small mammals benefited, including Steppe Pikas, whose high-pitched alarm calls would have been heard in southern England. There were also Arctic Lemmings and Ground Squirrels, both of which would have been preyed upon by a slightly larger form of the Polecat Mustela putorius, remains of which were found in the Ightham Fissures in Kent.

A Wild Horse in a 17,000-year-old painting at Lascaux in France. Wild Horses were the second most important prey animal after reindeer for Late Paleolithic hunters in Britain [5].


The last of the Irish Elk in Britain date to the early part of the Younger Dryas just over 12,500 years ago. The human occupation of Britain seems to have ceased altogether during the reglaciation, with people retreating to refuges in southern Europe, so the hunting overkill explanation is unlikely to explain much. Instead, the growing season contracted by around 30 days a year during the Younger Dryas and computer modelling suggests that the reduced food supply would have had a fatal impact on the fertility rates of a large ungulate species like the Irish Elk [4].

The cold period ended as quickly as it had started, and the Holocene epoch began with average July temperatures rising from around 7C to 17C over fifty years or less. The small mammals of the tundra fauna were quickly replaced by the more familiar temperate fauna. Some the larger mammals survived for a few centuries, judging from remains of Wild Horses found in Kent and of Reindeer in Yorkshire, but they too gave way to Aurochs, Red Deer and others. The Pleistocene epoch had come to an end, and with it the presence of animals which now seem almost mythical.

REFERENCES

1. Shaw, J.H., 1995. How many bison originally populated Western rangelands? Rangelands, 17(5), 148–150.

2. Currant, A., 1989. The Quaternary origins of the modern British mammal fauna. Biological Journal of the Linnean Society, 38, 23–30.

3. Yalden, D., 2003. The History of British Mammals.

4. Worman, C.O, Driscoll, T., 2008. Getting to the hart of the matter: did antlers truly cause the extinction of the Irish elk? Oikos, 117, 1397–1405

5. Campbell, J.B., 1977. The Upper Paleolithic of Britain.

2 JANUARY 2013

Reconstructing the Holocene climate

Climate research is resolving the prehistoric Holocene trends of rainfall and temperature to millennia and individual centuries.

WITHOUT THE PRESENCE of human beings, the sound environment of the Thames floodplain and its modest, surrounding hills would have changed slowly and with little drama throughout the Holocene epoch.

In this alternative timeline, birch and pine trees begin to colonise the steppe-tundra after the cold period of the Younger Dryas ends 11,500 years ago. Britain is still a peninsula of Europe, and the Thames only a tributary of a greater European river system feeding into the Rhine. Vast herds of bison and wild horses thunder across the grasslands, free to roam the Eurasian steppe.

As the climate warms, sea levels begin to rise. Around 8,000 years ago the Norwegian coastal shelf collapses and a tsunami rolls across the marshlands and low-lying plains of what’s now the North Sea, and Britain becomes an island.

The pine forests give way to mixed broadleaf trees. The Thames turns into a tidal river, with mudflats in its lower reaches luring flocks of wading birds during winter. The estuary inundates and retreats from a plain of peat bogs, which in turn are colonised in places by yew trees, making an environment with no exact parallel in the present. Beneath the dense yew canopy all is strangely quiet.

Britain’s terrestrial animals and non-migrating birds are now marooned. In time, the throttling of gene flow between them and their European cousins will cause them to become separate species, and the calls of some begin to sound different. Or else sea levels fall once again and glaciers return to scour the land like a palimpsest before a new cycle of warmth and colonisation. All this passes unremarked.

The cumulative effects of human activity which make Stratford or Richmond sound the way they do depend on the climate having been fairly stable for the past few thousand years. The ultimate causes of this likely lie with changes in the Earth’s orbit and its angle of rotation. Around 11,000 years ago, the amount of sunlight falling on what would eventually become a London rooftop or stretch of pavement was around 9% higher in summer and 14% lower in winter than today.

There’s no simple correspondence between orbital changes and surface temperatures [1], but the general trend during the early Holocene epoch was for winter and summer temperatures to diverge less, with much of the gap’s closing due to the winter months growing warmer [2].

The most widely publicised climate graphs tend to show global or hemispheric temperature trends. Fortunately, there’s been a great deal of lesser-known research focusing on the British and European climates of the past. One particularly accessible book is Hubert Lamb’s Climate, History and the Modern World. Although published in 1982 it can still be read profitably today.

Lamb was the climatologist responsible for founding the Climatic Research Unit at the University of East Anglia and recent weather station data released by them can give some clues as to whether there might be current European and Fennoscandian analogues for earlier British conditions. In Climate, History and the Modern World, Lamb presented estimates of Central England summer and winter temperatures derived from fossil pollen remains:

Central England temperatures derived from pollen remains


The smooth curves depicted by Lamb result from them being drawn along data points between 500 and 1,000 years apart. Short-lived perturbations to the climate may not show up. For comparison, an annual mean temperature reconstruction from later work has been shown also [1], based on the analysis of beetle remains. It suggests that the depths of the Younger Dryas reglaciation, some 12,000 years ago, were rather colder than Lamb’s estimates.

Another accessible climate history book, published in 2003, is Philip Eden’s Weather and climate in history. Some of the dating seems as if calendar years and radiocarbon years are being conflated, but nonetheless Eden provides a very useful summary of the Holocene climate. He also provides temperature estimates for southern England.

According to Eden, the middle of the Younger Dryas saw January temperatures of between -16 and -20°C and Julys of 8 to 12°C. They then climbed rapidly, in a period of perhaps little more than 50 years, to Januarys of 0 to 4°C and Julys of 14 to 18°C. The warming trend slowed but didn’t reach a peak in central and northern Europe until between 6,000 and 3,500 years ago, a period termed the Climatic Optimum. Winters were between 2 and 2.5°C warmer, and summers 1.5 to 2°C warmer.

The tree-line in the Scottish highlands was as much as 180 metres above its present level of 600 metres. Around 4,000 years ago on Dartmoor, Bronze Age farmers were able to cultivate their crops around 150–200 metres higher than would be possible now. Eden states that it was generally drier and less stormy during the Climatic Optimum. The semi-permanent area of high pressure which today loiters over the Azores then often extended across western Europe and Britain. In winter, the Atlantic storm track went much further north too. Mean annual rainfall was initially around 15–20% lower, although this began to increase later on during the Optimum.

Conditions began to deteriorate around 3,500 years ago with the climate becoming wetter and average temperatures falling by around 1.5°C. Bronze Age settlements on high ground were abandoned. Eden thinks it likely that gales become more common as the Atlantic storm track shifted south towards its present-day position.

By 300 BC, well into the Iron Age, the stormy weather was its worst, with rainfall some 40–50% higher than today. The Somerset Levels became marshland and it seems reasonable to guess that the environment of the Thames floodplain was affected in the same way. The inhabitants of the time responded by building wooden causeways through the marshes and by using roads on high ground. Eden states that summer temperatures were ‘at least as low’ as they were during the Little Ice Age of 16–17th centuries, when the Thames in London coould freeze to a depth of nearly a foot.

Conditions began to improve slightly after 250 BC, growing warmer and producing a period of relatively stable climate lasting until 400 AD. Sea levels rose by between one and two metres, inundating the Fens and Norfolk Broads. Eventually written records begin to tell the story of Britain’s climate, with some accounts of the earliest times being entertainingly dubious. Dr Thomas Short’s A General Chronological History of the Air, Weather, Seasons, Meteors, etc., published in 1749, tells us that in AD 4 there was a ‘rain of blood’ in London lasting five hours, heavy casualties from a Thames flood in AD 7 or 9, and that Westminster was destroyed by a hurricane in AD 18 – all some years before the arrival of literate chroniclers during the Roman conquest of AD 43.

Access to greater computer power and the development of new sources of data for past rainfall and temperature mean that researchers can now speculate about the prehistoric Holocene climate to a resolution of individual centuries. Methods include gathering information from river deposits [3], including those from several sites near the Thames, and integrating wide arrays of different proxy-climate records such as mineral deposits in caves, insect remains, and levels of preserved oxygen isotopes [4].

REFERENCES

1. Briffa, K.R. and Atkinson, T.C., 1997. Reconstructing Late-Glacial and Holocene Climates. Climates of the British Isles: Past, Present and Future, 84–111.

2. Davis, B.A.S., Brewer, S., Stevenson, A.C. and Guiot, J., 2003. The temperature of Europe during the Holocene reconstructed from pollen data. Quaternary Science Reviews, 22, 1701–1716.

3. Macklin, M.G. and Lewin, J., 2003. River sediments, great floods and centennial-scale Holocene climate change. Journal of Quaternary Science, 18, 101–105.

4. Charman, D.J., 2010. Centennial climate variability in the British Isles during the mid-late Holocene. Quaternary Science Reviews, 29, 1539-1554.

11 NOVEMBER 2012

First steps towards a timeline

A simple-but-useful timeline can be made by displaying climate data with stratigraphic and archaeological periods.

THE HOLOCENE SOUND project aims to describe likely changes in the local auditory environment across time and space. In practical terms, this means being able to say something informative about how Piccadilly might have sounded two hundred years ago, or Bermondsey 7,000 years ago.

More is known about local conditions the nearer we get to the present day, so the resolution with which we can pinpoint the where and when of sound will also increase. But this doesn’t mean that nothing useful can be inferred about eras before recorded history. Both maps and timelines can be informed by data from climate studies, archaeology, pollen remains, variations in soil type, changes in sea level and much else.

Below is a diagram representing a first step towards a timeline.

Greenland ice-core data with British stratigraphic and archaeological timelines


The graph line shows temperature proxy data taken from Greenland ice-cores. The ratio of two oxygen isotopes, O-18 and O-16, which are present in the cores allows past temperatures to be determined, and they give us some idea about conditions in the Northern Hemipshere as a whole. (For a recent critique, see the paper by Liu et al., 2012.)

The big climate events of the past 20,000 extend from the Last Glacial Maximum, when a single British-Irish ice sheet extended to the Welsh borders, curving northwards across the Pennines before descending again to where the Wash is today.

After this comes an oscillation between warm and cold conditions known in the British context as the Windermere interstadial. Then there is the rapid onset, perhaps noticeable during a single human lifetime, of a severe cold period known as the Younger Dryas, during which glaciers reappeared in the Scottish Highlands.

The Holocene epoch begins as temperatures climb again. Since then they’ve been comparatively stable, allowing civilisation to develop. The blue bar includes the five Holocene stratigraphic periods of the Blytt-Sernander climate classification system. During the Pre-Boreal period, the vast steppe-tundra of Eurasia began to be colonised by pioneering tree species such as mountain birch. In the Boreal period, the climate was initially colder and drier than today with pine forests dominating.

Rainfall and temperatures, especially at higher latitudes, rose during the Atlantic phase. It was warmer than today and this period falls within another climate episode termed the Holocene Climate Optimum. The Sub-Boreal was cooler and drier than the Atlantic period, and this in turn was succeeded by the Sub-Atlantic, which extends from around 2,600 years ago to the present.

Just as many categories we use to carve up the natural world look fuzzier the more closely they’re inspected, so the start and end dates of these climate periods are partly the result of convention. This is also true for many of the archaeological periods shown in the purple bar. The change from the hunter-gathering lifestyle of the Mesolithic to the crops and livestock of the Neolithic was gradual.

The later ages of Bronze and Iron came about faster and introduced metallic sounds to the world. Roman settlement began at AD 43, and industrialisation started with the first factories around the middle of the 18th century.

At least some of this is familiar to many people, and so the simple timeline serves as a useful foundation for what follows.

28 OCTOBER 2012

The lie of the land

A contour map of the London area shows the extent of the Thames floodplain and the action of water on the surrounding landscape.

THE THAMES COILS across an alluvial bed of sand, gravel and clay, which in turn is nested inside a bow-shaped syncline of chalk. The North Downs mark the upthrust of one side of the syncline.

The contour map below was drawn over a few weeks and in it those and other features are very obvious. The wide tonal range makes the London area look more dramatic than it is, but it’s intriguing how clearly the Thames floodplain can be seen.

The Lea Valley is also visible, and the delicate tracery of our smaller rivers and streams seems like a landscape of canyons. But the highest areas are little more than nubs and bumps on the ground. Westerham Heights in the borough of Bromley peaks at 245 metres, and most other notable London hills such as Muswell Hill and Shooter’s Hill are even less Olympian at 105 and 132 metres respectively. But that’s ideal for urban growth.

Contour height map of London


The contour map allows a three-dimensional relief map to rendered by the scenery generator program Vue D’Esprit. Below the Thames floodplain and surrounding hills are viewed from the east. The Lea Valley is visible to the right and the high ground of Shooter’s Hill and Lesnes Abbey Woods is to the left.

Relief map rendered from the east


The same model viewed from the west. The hills of Richmond Park and Wimbledon Common can be made out on the right. In both renderings the lighting angle has been set just above the horizon to accentuate the terrain.

Relief map rendered from the west


The model will serve as the basis for more detailed and realistic landscapes, to be populated with the right kinds of trees and other vegetation for different points in the past. Once you know what was growing somewhere, you also have an idea of what animals were living there, and what sounds might have been heard.

28 OCTOBER 2012

Welcome to the Holocene

The start of a new site section exploring changes to the sounds of what’s now the Greater London area over the last 12,000 years.

THE HOLOCENE IS the geological epoch which began around 12,000 years ago with the passing of the last glacial period. Our present warm window of opportunity is what’s termed an interglacial. It’s part of the last of eight glacial cycles making up the 2.6 million year-long Quaternary period.

Throughout the Holocene, humans have been busy transforming the planet in ways they were unable to do before. In the previous epoch, the Pleistocene, there were no crops, no domesticated animals other than dogs, no writing or metallurgy, no villages or cities. The people of the late Pleistocene were similar to us in many ways but not quite the same, and there were far fewer of them.

This new part of the London Sound Survey sets out to make a well-informed account of the changing soundscape of the Greater London area for the entire Holocene period. Large tasks become possible once they’re decomposed into smaller tasks. The developer blog will help do that by building and displaying the palettes of images, references and sounds which will eventually be brought together in a new interface.

The simple guiding question will be: What did it sound like then? All tangents will eventually loop back to it, whether they’re explorations of the changes in language, climate, land use, society or technology. Some of the ground has already been prepared in modest ways with the historical references and radio actuality sections.

The oldest surviving recordings of a public event in London are the Crystal Palace cylinders of 1888. Written descriptions extend back another nine centuries. The very earliest accounts, such as those of King Athelstan’s coronation at Kingston-upon-Thames in 924 and the Danes’ destruction of London Bridge in 1014, were written by people far removed from the events they described.

Fairly reliable accounts of London sounds begin with Samuel Pepys’s diaries around 350 years ago. Inferences must be drawn for the remaining 97% of the Holocene, but there has never been a better time than now for gathering the information needed. More and more academic journals are available as electronic editions, researchers can be reached by email, and datasets of all kinds are becoming publicly accessible.

Those of us brought up in London, and who have stuffed some decades under our expanding belts, will already know from memory how the city’s sounds have changed. We have heard a fragment of the long shift from times where kinship and, later, class were the primary social facts, towards the present age of the individual. It is as individuals that we now choose much of what we hear.