Environmental context

While annual temperatures within this period would have fluctuated, towards its end there was a major climatic reversal centered on 8200 BP (Alley et al. 1997; Alley and ágústdóttir 2005). This had widespread, hemispheric impacts, felt intensely at the latitude of Argyll (Seppa et al. 2007) and involved a temperature depression in parts of the North Atlantic of up to 4°C. North-west Europe was markedly more arid. This 8.2 ka event is attributed to the abrupt collapse of the North American or Laurentide ice sheet, which through its effect on North Atlantic Ocean circulation, probably shutting down the gulf stream, altered global atmospheric circulation. Stager and Mayewski (1997) and Debret et al. (2009) suggested that the present atmospheric circulation system only emerged with the collapse of this huge ice sheet.

Throughout this period sea level continued to rise, as described above and perhaps accelerated by the 8200 BP event. But sea level change was not the only alteration to the Early Holocene coastline of significance to early prehistoric communities. The availability of resources and the pattern of settlement would have also been influenced by the erosion and deposition of sediment, changes in sea temperature and salinity, the extent of storminess and of tidal extremes. While we can be confident such changes would have occurred, direct evidence is regrettably sparse.

Bond et al. (1997) has identified the transport from the Arctic Ocean of “armadas” of icebergs as far south as the Irish west coast periodically in the Holocene at c. 11,150, 10,250, 9350, 8200, 5900, 4200 BP and c. 1350 BP. Thornalley, Elderfield and McCave (2009) analysed fluctuating surface and deep-water temperature and salinity south of Iceland. Changes in either will have affected the abundance and locations of spawning and feeding grounds for fish populations. They recognise falling salinity from the start of the Holocene to c. 8000 BP: the 8200 BP event freshened by 0.4psu the North Atlantic. Seawater was well mixed and fresh after this event for c. 1000 cal years until c. 7000 BP. Salinity then increased to its present day values at c. 5000 BP.

Sediment-stratigraphic and biological RSL indicators tend to describe mean sea levels, not tidal or wave extremes. Jardine (1987) mapped a series of storm-beach gravel ridges on Oronsay, thought to be of mid-Holocene age, one at least perhaps 10m above contemporary mean sea level. Smith et al. (2007) surveyed storm beach ridges probably dating to the mid-Holocene on the west and east coasts of Bute, which reached up to 3m higher than contemporary mean sea level, even though such early Holocene storm beaches had been deposited from a significantly lower sea level. The systematic mapping and dating of further storm beaches would provide data, though biased to Devensian Lateglacial and post-6000 BP events, to infer past periods of increased storminess, the degree of exposure of particular parts of the coast and the modelling of wave extremes that may have been critical to travel by sea.

Other than the on-going changes in sea level, tidal range, salinity and storminess, the major on-going environment change throughout this period was that of vegetation. This influenced the availability and type of animal resources for hunting, of plant foods, raw materials, and of materials used for medicines. Vegetation cover also influenced visibility across and the ease of movement through the landscape. Moreover, human impacts on the landscape are likely to be most evident on vegetation cover and potentially detectable via the palynological record, while microscopic charcoal within sediment cores might provide evidence for human activity in the absence of archaeological sites. Fortunately, in contrast to other aspects of environmental change we have considered, the evidence for vegetation change within Argyll is relatively abundant.

Palynological records have been derived from numerous sediment cores distributed throughout Argyll, probably the densest array in Scotland (Figure 25). Those by Durno with Mercer on Jura and are of historical interest only (Edwards 2000) but many analyses are cutting-edge. Most of these are uniformly of high quality with regard to pollen taxonomy and temporal resolution, though in many there was no recording of microscopic charcoal. Most are ‘sensitive’ sites, describing plant communities and their changes at spatial scales small enough to identify and be supportive of archaeological evidence for similarly small-scale human activities. For those pollen sites lacking 14C-derived chronologies their attribution to the Mesolithic is based on the rise of Alnus (alder) pollen after c. 7000 cal BP and the absence of a mid-Holocene Ulmus (elm) decline, known from elsewhere in southern Britain. In general, birch and hazel trees were the predominant trees within the early Holocene woodland. These were subsequently out-competed by the broad-leaf taxa such as oak and elm after c. 9000 BP; one must note, however, considerable degrees of local variability reflecting variations in topography, aspect, exposure, soils and so forth.

Some of the sediment cores located on Figure 25 were taken to understand the dynamics of de-glaciation of ice sheets and valley glaciers of GS-1 (the Younger Dryas or Loch Lomond Stadial). Those along Loch Awe at Ford, Inverliever and Barachander (Tipping 1987, 1988, 1989a) and in Cowal at Na Lona Min (Tipping 1986) do not extend to sediments younger than c. 11,000 BP. However, those on Rannoch Moor at Clashgour, Corrour, Kingshouse and Rannoch Station (Walker and Lowe 1977, 1979, 1981, 1985, 1987), on Loch Linnhe at Lairigmor (Walker and Lowe 1981) and on Mull at Coire Clachach, Fhuaran, Gribun and Torness (Lowe and Walker 1986) also describe plant communities for the bulk of the Mesolithic period. None of these sites have records of microscopic charcoal.

A cluster of pollen sites on Islay were analysed to understand Mesolithic vegetation history and human disturbance to plant communities including Coulerach (Bunting et al. 2000), Bealach Froige, Cultoon, Gruinart, Loch Gorm and Sorn Valley (Edwards 2000) and Loch a’Bhogaidh (Edwards and Berridge 1994; Edwards and Mithen 1995). Analyses at Loch Cholla, Colonsay were intended to understand the Oronsay shell middens excavated by Mellars (Andrews et al. 1987). On Coll, the site of Loch an-t Sagairt remains to be fully published (Wicks and Mithen 2013). Edwards, Langdon and Sugden (2007) tried to disentangle anthropogenic from climatic effects on the vegetation at Loch an’t Suidhe on Mull around c. 8200 BP. The site of Rhoin Farm, west of Campbeltown, was analysed by Edwards and Mackintosh (1988; Edwards 1990) to explore pre-elm decline agricultural activity.

The difficulties of defining an unambiguous hunter-gatherer signal in pollen records are many, not least because new data on the intensity of abrupt climate change introduce mechanisms by which vegetation can be naturally disturbed. Tipping (1996) argued, for instance, that relative drought increased the likelihood of wildfires in northern Scotland, although this has been contested by Bishop et al. (2015). Random events such as lightning-strike fires and tree-felling in storms (eg Tipping (2008) at Clashgour on Rannoch Moor) are feasible sources of woodland change. Edwards et al. (2007) elegantly evaluated human-climate agencies at Loch an’t Suidhe on Mull across the major early Holocene abrupt climate change event at c. 8200 cal BP. Losses of deciduous woodland around 8300 BP are accompanied by increases in microscopic charcoal, which were argued to have been anthropogenic in origin because climatic deterioration was recorded from chironomid analyses after, not during woodland loss. Errors in 14C dating may explain why the climatic deterioration appears not to be that at c. 8200 cal BP (though see Edwards et al. 2007 for other interpretations) but do not detract from their more general conclusions.

On Islay, Mesolithic anthropogenic activity has been suggested from closely-spaced pollen analyses seeming to describe short-lived vegetation disturbance, accompanied by burning (Edwards 2000). Events are diachronous across the island, which Edwards (2000) uses to dismiss climatic causation. Disturbance was particularly widespread in the 8th millennium BP. The astonishing find of burnt hazel nuts – the product of perhaps some 15000 trees – at Staosnaig on Colonsay (Mithen et al. 2001) excited much interest, with the suggestion that the pollen record should be able to detect this event (Edwards 2000), although Andrews et al. (1987a) had not reported Mesolithic-age anthropogenic impacts on Colonsay. Andrews (in McCullagh 1989) also identified possible anthropogenic woodland disturbance on Islay, around the Sorn Valley, around 7900 BP. In the Oban area significant woodland loss, associated with burning, is also recorded for short time intervals throughout the Mesolithic.

Lowe and Walker (1986; Walker and Lowe 1977, 1979, 1981, 1985, 1987) were unable to detect Mesolithic period anthropogenic signals in any of their fourteen sites they examined in Argyll. This may in part be because microscopic charcoal had not been recorded, or because the time interval between pollen samples was too coarse, but this is an intriguing if negative result. Trees may have also been at a low density which impedes detecting an anthropogenic impact: on Colonsay, for instance, Andrews et al. (1987a) reported that tree pollen rarely exceeds 20% total pollen and spores concluding that the landscape must have been quite open, maintained by a high degree of exposure to winds. Walker and Lowe (1985) also infer a high degree of exposure to wind from the low representation of trees at sites on Mull, and around Iona Loch the dominant vegetation in the Mesolithic is a grass-heath with few trees (Scaife and Dimbleby 1990). It is difficult to see in these open settings why people would have needed to disturb woodland: models for anthropogenic interference derived from the closed deciduous woodlands of eastern England (Simmons 1996) need not have applied to the Scottish west coast. Other landscapes appear more wooded, but nevertheless the precise ‘ecology’ of these disturbances in western Scotland, and if purposeful what they achieved, needs to be explored much more fully. This is now a pressing need because if anthropogenic signals in Mesolithic-age pollen records along the Scottish west coast can be demonstrated, the technique is one of the few that could test Wicks and Mithen’s (2014) suggestion of population collapse in and after the 8200 BP abrupt climate change.