Mesolithic geoarchaeological investigations in the Outer Thames Estuary

October 2019

esse Archaeology Portway House Old Sarum Park Salisbury SP EB

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wessexarchaeology Mesolithic geoarchaeological investigations in the Outer Thames Estuary by Alex Brown and John Russell with contributions by Catherine Barnett, Nigel Cameron, Rob Scaife, Chris J. Stevens and Sarah F. Wyles and illustrations by Kitty Foster

Introduction This paper presents the results of geoarchaeological analysis of semi-terrestrial organic deposits recovered in three cores from the Outer Thames Estuary (Fig. 1). The cores are located up to 12 km off the current Kent coast, within an area that at the height of the last ice age formed part of a vast habitable plain connecting Britain with the rest of the European continent. Over the last 13,000 years this landscape (including the North Sea and English Channel) has been gradually lost to sea-level rise as the climate warmed and the ice-sheets retreated, with particularly rapid sea-level rise ~60m occurring during the early Holocene (11,500–7000 cal. BP). Marine geophysical surveying around the British Isles has transformed our understanding of these former palaeolandscapes, providing an increasingly detailed picture of the submerged palaeogeography of areas including the southern North Sea and English Channel (Gaffney et al. 2007; Bickett 2011; Dix and Sturt 2011; Tappin et al. 2011). Geophysical data, together with extensive borehole surveys, have been critical in identifying key locations for the recovery of deposits with geoarchaeological potential, and that may have formed a focus for past human activity. Much of this work has been in response to commercial aggregate dredging, fishing, oil and gas exploration, and more recently offshore windfarm developments (Bicket and Tizzard 2015). Despite the increased volume of research within offshore areas, there remains a scarcity of well- dated palaeoenvironmental studies investigating landscape and environmental change. Regional and national maritime-focused research agendas have stressed the need for improved temporal and spatial resolution of archaeological and palaeoenvironmental data from offshore areas (Bicket 2011; Ransley et al. 2013; Flemming et al. 2014), both crucial in ground truthing established palaeogeographic reconstructions. The three palaeoenvironmental sequences presented here (VC606, VC608 and VC7) are important therefore in contributing to our understanding of the palaeogeographic development of the English Channel and wider southern North Sea basin. They derive from two distinct areas (Fig. 1), the first (VC606 and 608) located off the north coast of Kent within the export cable route of the London Array offshore windfarm, and the second area (VC7) 12.km off the north-east coast of Kent within the route of the Nemo Link UK-Belgium Electrical Interconnector. Both projects required programmes of mitigation to minimise the impact of development on the seabed and the archaeological, geological and palaeoenvironmental resource (Wessex Archaeology 2005; 2016; Dong Energy 2013; Nemo Link 2013). Within both areas marine geophysical surveys have

1 identified former channels (termed palaeochannels) that would have formed part of the wider palaeodrainage of the River Thames-Medway. Initially freshwater, these rivers and channels would have becoming increasingly tidal as sea-levels rose and the coastline retreated inland, before eventually being infilled, submerged and sealed by modern seabed sediment. These relict former channels (termed palaeochannels) often contain organic sediment in the form of peat deposits, reflecting the development of a series of rich wetland ecosystems that would have presented attractive opportunities to human exploitation and settlement. The studies presented here provide an important opportunity to investigate patterns of physical and environmental change in the Outer Thames Estuary during the early Holocene. Occurring in the context of rapidly rising sea-levels, they provide the opportunity to consider how the changing physical environment impacted on past human communities during the Mesolithic period.

The Outer Thames Estuary: archaeological and palaeoenvironmental background Archaeological Background The Mesolithic covers a period of almost 6000 years between the end of the Devensian Ice Age c. 9700 cal. BC, and the first appearance of crop and animal domestication c. 4000 cal. BC. Research into the Mesolithic has for a long time lagged behind that of later prehistoric periods, despite covering roughly half the current post-glacial period. Our understanding of the Mesolithic has for a long time been dominated by the exceptional early Mesolithic site at Star Carr (Clark 1954; Mellars and Dark 1998; Conneller 2016; Milner et al. 2018a;b). However, more recently there has been an increasing focus on the evidence from coastal and intertidal settings where oxygen free conditions result in the preservation of a range of organic remains and artefacts (Bell 2007; Waddington and Pedersen 2007). Moreover, there has been a renewed interest in the archaeology of the North Sea basin, stimulated by Bryony Coles seminal article on Doggerland (Coles 1998), and supported by an increasing number of developer- funded investigations within the maritime zone, including the southern North Sea (Gaffney et al. 2007; Fitch 2011), English Channel (Dix and Sturt 2011) and Solent (Momber et al. 2012). The Mesolithic archaeology of the Outer Thames Estuary is represented by a small number of finds dredged up from offshore locations off the north Kent coast. These finds include tranchet axes recovered in the proximity of core VC608, off-shore from Reculver and 1.5km north-east of Herne Bay Pier (Wessex Archaeology 2015). Recovery of Mesolithic finds from offshore contexts is inevitably biased in favour of large easily identifiable artefacts such as tranchet axes. Smaller artefacts, including microliths and associated debitage, are very unlikely to be recovered as chance finds. The offshore archaeological record for the Mesolithic is therefore highly fragmentary in nature and difficult to interpret and compare with known Mesolithic sites in Kent. Although a large number of Mesolithic sites and finds have been identified across south-eastern England (see Pope et al. 2019), fewer sites are known from Kent and the Mesolithic settlement of the county remains poorly understood. At a country level there is an apparent lower concentration of sites

2 on the chalk Downs of eastern compared to western Kent (Parfitt and Halliwell 2014). Most Mesolithic finds from northern Kent have been recovered from riverine locations or near the current coastal margins, again often chance finds (e.g. Bishop and Bagwell 2005), with a recent review of prehistoric settlement on the North Kent coast suggesting sparse settlement during the Mesolithic (Allen 2009). However, the scarcity of sites may in large part reflect issues of site visibility, with many sites likely sealed beneath deep colluvial and alluvial sequences (Pope et al. 2019), or difficult to positively identify where sites and scatters lack diagnostic Mesolithic material. However, two significant new sites have recently been studied at Shorne Wood Country Park and Ranscombe (c. 4km south-east of Gravesend), both including large collections of struck flint (3000 and 5000 respectively), including microliths, axes and adzes (Mayfield 2012). A smaller assemblage of diagnostically Mesolithic struck flint was recovered from a series of features at Tongs Meadow, Harrietsham (4km east of Maidstone), although it is possible the features are natural, e.g. tree-throw holes (Riccoboni and Swift 2011). Mesolithic flints have also been recovered from a peat-filled lake at Darenth (Philp 1984) and from a palaeochannel at Cheesemans Green, Ashford (Wessex Archaeology 2011). More widely across Kent important Mesolithic sites include a habitation site at Addington (approximately 5 km south of Gravesend) that comprised an undated pollen study (Dimbleby 1963), and a site at Finglesham (3 km north-west of Deal) close to the east Kent coast. The latter site included a preponderance of axes and adzes but no microliths, suggesting activity at the Finglesham site may have included the felling and working of timber (Parfitt and Halliwell 2014). The tool component of Mesolithic assemblages provides a guide to site function; a broader range of tool types could suggest a larger range of activities, perhaps associated with lengthier occupation, whilst a more restricted tool assemblage may be related to specific activity sites occupied for shorter durations (e.g. Shott 1986). The mode of settlement and range of activities at a site may also have changed during the life-history of a site, although this is difficult to discern in unstratified lithic assemblages lacking spatial and chronological resolution. Moreover, the chance and biased nature of finds from offshore locations makes it extremely difficult to understand the type of sites and range of activities represented in the former coastal lowlands, and importantly, their relationship to sites identified on the adjacent dry ground in Kent. For example, do offshore sites represent an extension of settlement patterns identified for Kent, perhaps involving seasonal movement between lowland-upland and coastal-inland areas? Or do chance finds from offshore locations reflect groups predominantly focused on lowland landscapes and perhaps involving only episodic visits to inland/upland locales?

Palaeoenvironmental background Palaeoenvironmental analyses play an important role in Mesolithic studies, helping to understand the environmental context of human activity in relation to patterns of climate and environmental change during the early Holocene. The environmental history of the English Channel is inexorably linked to sea-level rise, that increased from 60 m to 7 m below present sea level over the course of the Mesolithic

3 period (Cameron et al. 1992). Large parts of the Outer Thames Estuary were probably inundated by c. 6000 cal. BC, fringed by a range of low-lying wetland landscapes including mudflats, saltmarsh, tall herb swamps and carr woodland. Although sea-level rise resulted in the progressive inundation and loss of large areas of formerly habitable coastal plain, it would have been an important factor in the continual development of resource-rich wetland environments attractive to both humans and animals. Some of these wetlands are preserved as discrete peat deposits, recovered in cores and with significant potential for palaeoenvironmental reconstructions. There is a significant amount of palaeoenvironmental data from within the Thames Estuary, although this is largely focused within the Inner Thames Estuary. Here the late Mesolithic is well- represented in numerous sediment profiles (Sidell et al. 2000; Wilkinson et al. 2000; Branch et al. 2012; Batchelor et al. 2014; Green et al. 2014). By comparison, there is little palaeoenvironmental data of Mesolithic date from Kent and Essex apart from an isolated pollen study from the Isle of Grain, dating to 9030–8720 cal. BP (7080–6770 cal. BC) and Queenborough, Isle of Sheppey, dating to 5750–5370 cal. BC (Russell et al. 2011). The three sequences presented here are therefore of added significance in view of the paucity of palaeoenvironmental data from the Outer Thames Estuary.

Sites Nemo Link Borehole VC7 is located 12 km east of Ramsgate along the route of the Nemo Link UK-Belgium Electrical Interconnector. VC7 lies on the margins of a palaeochannel feature (palaeochannel 7500) identified from the geophysical data, orientated north-west to south-east and approximately 250 m wide, and can be traced for approximately 500 m. The underlying geology comprises Upper Cretaceous Chalk weathered into a chalk putty, probably during the last glacial period (Marine Isotope Stage 2 MIS2). Overlying the weathered bedrock are Holocene deposits of peat and alluvium preserved within what is thought to have been a relatively minor tributary of the Thames palaeodrainage. These channel systems are thought to be long-lived, potentially pre-dating the Anglian glaciation, undergoing repeated cut and fill events over successive Quaternary transgressive-regressive cycles (Dix and Sturt 2011).

London Array Boreholes VC606 and VC608 are located 10 and 6 km respectively off the north coast of Kent, taken as part of geotechnical survey work for the export cable route of the London Array offshore windfarm. The underlying geology in the area is predominantly London Clay, overlain by Pleistocene and Holocene deposits mapped by the British Geological Survey (BGS) (Larminie 1989; 1990) predominantly from seismic surveys. Pleistocene sediments were identified during borehole surveying within the windfarm area where they are thought to correspond with the Thames-Medway Pleistocene fluvial terrace complex postulated by Bridgland (Wessex Archaeology 2008; 2009; Bridgland 2002).

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Holocene deposits were identified across the windfarm and cable route in the form of sands, gravels, silts, clays and peats.

Methods The analyses described below form part of an integrated multiproxy approach to investigating boreholes VC606, VC608 and VC7. Together these techniques provide a comprehensive means of understanding the depositional and environmental context of the sediments, helping to reconstructing changes in the past physical and vegetation environments within which human communities were likely to active. Pollen analysis is the principal palaeoenvironmental technique used in environmental archaeology to reconstruct past vegetation change, providing an important environmental context for past human activity. Pollen is best preserved in waterlogged organic sediment such as peat and organic- rich alluvium where the pollen is most likely to derive from flowering plants growing in the surrounding landscape. The source area of pollen is likely to include both plants growing locally and from within a few kilometres surrounding the site, with a component of the pollen derived from larger distances included in the background pollen rain. Although there is no archaeology from the sites, evidence for human activity may be present in the pollen evidence in the form of episodes of impact/manipulation of the surrounding vegetation, for example, as phases of woodland clearance or burning of the vegetation. Plant macrofossils (e.g. seeds and wood) were also analysed from several samples, reflecting those plants derived from the immediate environment, providing important data on the local vegetation for comparison with the pollen data. The pollen and plant macrofossil data are complemented by analysis of diatoms (unicellular algae), ostracods (bivalve crustacea) and foraminifera (marine protozoa). These microfaunal remains occur in a wide range of marine and semi-terrestrial environments and provide important comparative indicators on past coastal change, complemented by analysis of molluscan remains. Analysis can help to distinguish evidence for sea-level and coastal change not immediately apparent in the pollen record, including shifts between freshwater and marine environments or the influence of meltwater pulses or storm/tidal events on semi-terrestrial environments.

Pollen Thirty-four samples of 1.5 ml volume were prepared from boreholes VC606, VC608 and VC7 using standard pollen extraction methods (Moore et al. 1991). Pollen was identified and counted using an Olympus BH2 biological microscope with Leitz optics. A minimum of 500 pollen grains of dry land species was counted for each level where preservation allowed, and between 600í800 grains where preservation was better. Fern spores and miscellaneous taxa (largely pre-Quaternary palynomorphs and Pediastrum) were also identified and counted and calculated as a percentage of total dry land pollen (tdlp) plus the sum of the respective category. Taxonomy in general follows Moore and Webb (1978) modified according to Bennett et al. (1994) for pollen types. The pollen diagram was produced using

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Tilia version 1.7.16 (Grimm 2011), with pollen zones based on observed changes in the palynological assemblages.

Diatoms Twelve samples were prepared for diatom analysis from boreholes VC606 and VC608. Diatom preparation, counting and analysis followed standard techniques (Battarbee et al. 2001). Diatom flora and taxonomic publications were consulted to assist with identification, including Hendey (1964), Werff and Huls (1957í74), Hartley et al. (1996), Krammer and Lange-Bertalot (1986í1991) and Witkowski et al. (2000). Diatom species salinity preferences are discussed using the classification data in Denys (1992), Vos and de Wolf (1993) and the halobian groups of Hustdedt (1953; 1957).

Ostracod and foraminifera Forty samples were analysed from boreholes VC606, VC608 and VC7 for ostracod and foraminifera. Samples 25 ml were disaggregated in a weak solution of Hydrogen Peroxide and water and washed through a 63 μm sieve, with the remaining sediment dried and processed through a nest of sieves (150 μm, 250 μm and 500 μm). Microfossils were extracted under transmitted light using a Vikers binocular microscope at x10í60 magnification. Where possible a minimum of 100 specimens per samples were picked out. Identification and environmental interpretation of ostracods follows Athersuch et al. (1989) and Meisch (2000) and Murray for foraminifera (Murray 1979; 1991; 2006).

Plant macrofossils Samples were wet-sieved through a stack of sieves of 4 mm, 2 mm, 1 mm, 500 μm and 250 μm mesh sizes and visually inspected under a x10í40 magnification stereo-binocular microscope. Identifications followed the nomenclature of Stace (1997). Charcoal was prepared according to Leney and Casteel (1975). Fragments were fractured with a razor blade to expose transverse (T), radial longitudinal (RL) and tangential longitudinal (TL) sections. Charcoal was identified using a Kyowa ME-LUX2 bi-focual epi-illuminated microscope at x50, x100 and x400 magnification.

Molluscs Seven samples were processed through a nest of sieves of 1 mm, 500 μm, 250 μm, 125 μm and 63 μm. Apical and diagnostic shell fragments were extracted from the fractions >250 μm. The shells were identified and quantified using a Lecia MS5 light microscope at up to x40 magnification. Nomenclature followed Anderson (2000), with habitat preference following Kerney (1999) and Barrett and Yonge (1958).

Radiocarbon dating

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Six radiocarbon dates were obtained from SUERC (Scottish Universities Environmental Research Centre), two each from boreholes VC606, VC608 and VC7. The two dates on marine shells were calibrated against the Marine13 radiocarbon curve (Reimer et al. 2013) with the four dates on terrestrial material calibrated against the Intcal13 radiocarbon curve. The radiocarbon dates (Table 1) were calibrated using OxCal 4.1 (Bronk Ramsey 2009) and using a delta-R value of zero and rounded outward to 10 years (Mook 1986, 799).

Results Radiocarbon dating The six radiocarbon dates provide an indication of the range in date and accumulation rate of organic deposits and relationship to sea-level rise (considered below), with each of the organic deposits recorded between 34.38 and 7.28 mbOD (Table 1). Two radiocarbon dates from borehole VC7 on a waterlogged stem and Phragmites australis (common reed) produced early Mesolithic dates of 8915±30 BP (GU-íFDO%& DQG 8855±35 BP (GU-íFDO%&  7DEOH %RWKGDWHVDUHRIDEURDGO\VLPLODUDJHEXW FRLQFLGHRQDSODWHDXLQWKHFDOLEUDWLRQFXUYHDWíFDOBC, which limits any greater precision. Only the stems of Phragmites were dated lying horizontally within the sediment and therefore likely to represent contemporary shoots growing at or near the time of sediment deposition. Roots of Phragmites were expressly avoided as the root system can penetrate up to four metres down the profile. The dates from the Phragmites stems are therefore considered reliable. From borehole VC606 two samples on marine shell and charred stem/seeds produced late Mesolithic dates of 7680±35 BP (GU- í FDO %&  DQG “ %3 *8-52623, íFDO%& UHVSHFWLYHO\ 7DEOH 7KHGDWHVVXJJHVWWKHPRIVHGLPHQWDFFXPXODWHG relatively rapidly over a period of between 330–670 years. Two further samples were dated from borehole VC608, on marine shell and charred stems, producing late Mesolithic dates of 6925±35 BP (GU-íFDO%& DQG“%3 *8-íFDO%& UHVSHFWLYHO\ 7DEOH 1). The dates, similar to borehole VC606, suggest rapid sediment accumulation, with 0.84 m accumulating over a period between 190 and 500 years.

Table 1. AMS radiocarbon dates, boreholes VC606, VC608 and VC7. Depths = metres below Ordnance Datum (mbOD), *VPDB (Vienna Pee Dee Belemnite), wl = waterlogged. Laboratory No Material dated Depth Age BP į13 C (‰) Age range Age range cal. (mbOD) or relative to cal. BC BP VPDB* Borehole VC608 GU-52622 Marine shell 7.28 6906±27 *0.2 5540í5390 7490í7340 Peringia ulva

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GU-26377 Waterlogged woody 8.12 6925±35 -24.9 5890í5730 7840í7680 stems Borehole VC606 GU-52623 Marine shell 12.82 7532±26 *-2.4 6130í5970 8080í7920 Littorina GU-26378 Charred stems, 15.08 7680±35 -26.2 6600í6460 8550í8410 Atriplex/wl seed of Suaeda maritima Borehole VC7 GU-36005 Phragmites australis 34.13 8855±35 -25.0 8210í7840 10160í9770 stem GU-36006 Waterlogged stem 34.38 8915±30 -28.7 8240í7960 10190í9910

Borehole VC7 The sediments in borehole VC7 comprise chalk overlain by channel edge alluvium and peat infilling palaeochannel 7500, in turn sealed by recent seabed sediments. Four pollen zones were identified in borehole VC7 (Fig. 2, VC7-1 to VC7-4). Within zone CV7- 1 (34.65 to 34.54 mbOD) Pinus was the dominant tree with some Corylus avellana type and some occasional herbs (Poaceae and Cyperaceae) and fern spores. Pinus remains dominant in zone VC7-2 (34.5 to 34.27 mbOD), but with increasing values of Corylus avellana type and Ulmus and Quercus also recorded. Ulmus, Quercus and Corylus avellana type become the dominant trees in zone VC7-3 (34.27 to 34.20 mbOD), with lesser quantities of Pinus and some Salix. Pinus, Ulmus, Quercus and Corylus avellana type are the dominant trees in zone VC7-4 (34.20 to 34.0 mbOD). Ostracods and foraminifera were largely absent below 34.25 mbOD, with only occasional freshwater ostracods (Limnocythere sp.) recorded. At 34.18 and 34.13 mbOD non-marine freshwater ostracods were recovered, including Candona neglecta, Notodromas monacha and Metacypris cordata. (Table 2). From 34.08 to 31.58 mbOD a diverse assemblage of estuarine and shallow marine ostracod and foraminifera were present; the ostracods were dominated by Cyprideis torosa, with abundant foraminifera including Ammonia and Elphidium.

Table 2. Abundance of ostracod and foraminifera, borehole VC7 (No ostracod or foraminifera were recorded from samples at 34.48, 34.38, 34.28 and 34.18 mbOD); o = present, x = 2í9 specimens, xx = 9í50 specimens, xxx = > 50 specimens Depth (mbOD) 34.63 34.18 34.13 34.08 34.03 33.98 33.93 33.88 33.83 33 31.58 Ostracod Aurila convexa ------x - - Candona sp. - - - - - o - - - - - Candona neglecta - x ------

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Depth (mbOD) 34.63 34.18 34.13 34.08 34.03 33.98 33.93 33.88 33.83 33 31.58 Candoniids - - x ------Cyprideis torosa smooth - - - xx x x - xx x xx xx Elofsonella sp. - - - x xx ------Elofsonia sp. ------x - - - Eucythere sp. ------x - - - Hemicythere villosa ------x - Heterocythereis ------x albomaculata Heterocythereis sp. ------o Ostracods Hirschmannia viridis - - - - - x - - - - - Leptocythere spp. - - - x - x - - - - o Leptocythere pellucida - - - x x - - x xx x - Limnocythere sp. o ------Loxoconcha elliptica - - - o - - - - - x - Loxoconcha rhomboidea - - - x x - - o - o x Loxoconcha sp. - - - - - x - - - - - Metacypris cordata - xx x ------Notodromas monacha - - x ------Palmoconcha sp. ------x - Paracytherois flexuosa - - - - o ------Propontocypris sp. ------o - o o Semicytherura sp. - - - - - x - - - x - Xesteloberis - - - o ------Foraminifera Ammonia spp. - - - - - x - - - xx xx Ammonia batavus - - - xx x xx - xx x xx xx Ammonia beccarii - - - xx - xx - xx x xx xx Astergerinata mamilla - - - - - x - - x - - Buliminella ------o x elegantissima Elphidium sp. - - - x - xx - - x x xx Elphidium crispum - - - - - x - xx x - - Elphidium cuvillieri ------o - - - - Elphidium gerthi ------x - Elphidium macellum - - - - - x - - - x x Fursenkoiina fusiformis ------Gavelinopsis praegeri ------x - - Haynesina germanica - - - x x xx xx x xx xx Jadammina macrescens - - - x x xx xx x xx xx Lagena semistriata ------x - Lagena spp. ------o Miliolids - - - - xx xx - xx - xx xxx

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Depth (mbOD) 34.63 34.18 34.13 34.08 34.03 33.98 33.93 33.88 33.83 33 31.58 Massilina secans - - - - o - - xx - - - Miliolinella subrotunda - - - - - x - - - x xx Quinqueloculina ------o x x dimidiata Quinqueloculina ------o xx x seminulum Quinqueloculina sp. - - - - - x - - - x xx Rosalina sp. - - - x - - - - - o Rotaliid ------x xx xx

Eight samples were analysed for molluscan remains (Table 3). The basal three samples contain an almost equal number of land snails (Carychium minimum, Succinea/Oxyloma asp. And Vertigo Substriata) and freshwater aquatic species (Bithynia sp., Valvata cristata, Galba truncatula and Anisus leucostoma). The sample from 34.33 to 34.28 mbOD includes a small predominantly freshwater assemblage, with high quantities of aquatic molluscs, including Bithynia tentaculata and Valvata cristata recorded from 34.23 to 34.18 and 34.18 to 34.13 mbOD. Large quantities of marine and brackish water molluscs were recorded from 34.03 mbOD, dominated by shells of Peringia ulva.

Table 3. Results of molluscan analysis, borehole VC7 (MNI = minimum number of individuals) 34.53í 34.48í 34.38í 34.28í 34.18í 34.13í 33.98í 33.83í Depth (mbOD) 34.58 34.53 34.43 34.33 34.23 34.18 34.03 33.88 Volume (ml) 175 175 125 175 150 120 175 250 Land snails (MNI) Carychium cf. minimum - 1 1 - - - - - Carychium tridentatum 3 1 ------Succinea/Oxyloma spp. 2 5 ------Cochlicopa spp. 1 1 ------Vertigo cf. substriata - 1 ------Vertigo spp. 1 ------Vallonia costata - 1 ------Vallonia spp. - - - - 1 - - - Dercoceras/Limax 2 2 1 - - - - - Trochulus hispidus 1 1 ------Cepaea/Arianta sp. - 1 - - 1 - - - Aquatic Snails (MNI) Valvata cristata 4 7 - 1 47 77 - - Bithynia tentaculata - - - - 1 6 - - Bithynia spp. 2 2 - - 6 35 - - Bithynia opercula 9 9 2 - 15 160 - - Galba truncatula 1 - 3 - 3 1 - - Lymnaea palustris - - - - - 1 - -

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34.53í 34.48í 34.38í 34.28í 34.18í 34.13í 33.98í 33.83í Depth (mbOD) 34.58 34.53 34.43 34.33 34.23 34.18 34.03 33.88 Volume (ml) 175 175 125 175 150 120 175 250 Radix balthica - - - - - 2 - - Lymnaea/Galba/Radix spp. - 2 - - 2 - - - Planorbis planorbis 1 - - - 2 4 - - Planorbis carinatus - - - - - 2 - - Anisus leucostoma 1 - - - 1 9 - - Bathyomphalus contortus (Linnaeus) - - - - 1 3 - - Gyraulus crista - 1 - - 1 3 - - Hippeutis complanatus - 1 - - - 4 - - Planorbids 1 - - - 2 - - - Acroloxus lacustris - - - - - 2 - - Pisidium spp. - 1 1 - - - - - Peringia ulvae ------25 55 Ecrobia ventrosa ------2 7 Peringia/Ecrobia sp. - 1 - 1 - - 180 271 Chlamys cf. varia ------3 Chlamys sp. ------1 Cerastoderma edule ------1 4 Cerastoderma/Cardium sp. ------4 11 Tellina cf. crassa ------2 Tellina/Scrobicularia type ------2 13 Mytilus edulis ------1 4 Anomia ephippium ------1 1 Gibbula sp. ------5 2 Littorina cf. saxtilis ------3 3 Littorina cf. littoralis ------1 - Rissoidae ------18 30 Veneracea ------9 8 Ocenebra erinacea ------1 - Total (MNI) 20 29 6 2 68 149 253 415 Total (MNI) Land snails 10 14 2 0 2 0 0 0 Total (MNI) Aquatic snails 10 15 4 2 66 149 253 415

Borehole VC606 Borehole VC606 comprises a sequence of organic estuarine alluvium (peaty clay) overlain by silty clay estuarine alluvium and recent seabed sediments. Two distinct pollen zones were identified in borehole VC606 (VC606-1 and VC606-2, Fig. 3). Zone VC606-1 (15.24 to 15.02 mbOD) was characterised by high levels of herb pollen dominated by Chenopodiaceae (goosefoots), Poaceae (grasses) and Potamogeton (pondweed). Tree and shrub pollen were present in large quantities, including Pinus (pine) with Quercus (oak), Corylus avellana type (hazel) and Ulmus (elm), with smaller quantities of Betula

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(birch), Tilia (lime) and Alnus (alder). Zone VC606-2 (15.02 to 12.58 mbOD) was characterised by substantially fewer herbs, with Chenopodiaceae almost absent in the upper levels, and large quantities of tree and shrub pollen including Corylus avellana type, Quercus and Ulmus dominant. Fen/marsh taxa (Cyperaceae – sedges; Typha latifolia – bulrush; Typha angustifolia – lesser bulrush) and fern spores were relatively few through this zone. Diatoms were only present in the top four samples from 15.08 to 12.58 mbOD (Fig. 4). Freshwater diatoms dominated at 15.02 mbOD, particularly aerophilous taxa including Hantzschia amphioxys, Pinnularia borealis and Nitzschia terrestris. At -14.98 mOD freshwater taxa decline to 20%, with brackish and marine diatoms increasing to 40%, comprised mainly of benthic taxa such as Diploneis didyma, Nitzschia navicularis, Nitzschia punctata and Scoliopleura tumida. The upper two samples are dominated by a mixture of brackish and marine diatoms, with an increasing proportion of marine species towards the top of the sequence, dominated by the marine planktonic diatoms Paralia sulcata and Cymatosira belgica. The marine and brackish non-planktonic diatom Cocconeis scutellum was common in both samples, along with brackish benthic diatoms such as Diploneis didyma and Nitzschia punctata; and the planktonic, estuarine diatom Cyclotella striata. Ostracod and foraminifera were variably preserved through borehole VC606 (Table 4). Ostracod are not present below 14.62 mbOD. However, within the peat at 15.08 to 15.06 mbOD a monospecific assemblage of the agglutinating salt marsh foraminifera Trochammina inflate was recorded. Saltmarsh and brackish water foraminifera dominate the assemblages from 14.98 and 14.62 mbOD, including Ammonia beccarii, Elphidium williamsoni, Jadammina macrescens and Haynesina germanica. Ostracods are present at 14.62 mbOD where they are dominated by estuarine and brackish species, including Loxoconcha elliptica and Cyprideis torosa. Outer estuarine and marine tolerant ostracods also occur, with Loxoconcha rhomboidea becoming dominant at 14.26 mbOD. Ostracods are notably sparse between 13.90 and 12.82 mbOD. From 14.26 mbOD abundant rotaliid forms dominated by Ammonia beccarii were recorded, which is known to prefer near marine salinities, and is recorded in increasing numbers up the profile. An increasing number of outer estuarine and shallow marine foraminifera are recorded at 12.82 and 12.58 mbOD. The single molluscan samples from 12.82 mbOD predominantly contained the brackish-saline tolerant Peringia ulvae along with a small number of other coastal, brackish and estuarine molluscs (Table 5).

Table 4. Abundance of ostracod and foraminifera, borehole VC606; o = present, x = 1í9 specimens, xx = 9í50 specimens, xxx = > 50 specimens, xxxx = > 100 specimens. No microfauna were recorded from samples at 15.2 and 15.28 mbOD.

Depth (mbOD) 12.58 12.82 13.06 13.58 13.9 14.26 14.62 14.98 15.06 15.08 Ostracods Cyprideis torosa smooth ------x - - -

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Leptocythere lacertosa x ------Leptocythere spp. - - - - - x x - - - Loxoconcha elliptica - - - - - xxx xxx - - - Loxoconcha elliptica x ------Loxoconcha rhomboidea xx - - - - xx x - - - Propontocypris spp. x - - - - x x - - - Semicytherura sella - - - o - - x - - - Foraminifera Ammonia batavus x x xxxx xx xx x - - - - Ammonia beccarii xxxx xxxx xxxx xxxx xxxx xxxx xxxx xx - - Buliminella elegantissima - o ------Elphidium crispum x ------Elphidium cuvilleri x ------Elphidium williamsoni - xxx - xx x x xx x - - Elphidiumsp. xx ------Haynesina germanica xx - x xx x x xx - - - Jadammina macrescens - xx - - x x xx xxxx - - Lagena semistriata - x ------Lagena sp. - o ------Quinqueloculina bicornis - o ------Trochammina inflata ------x xx

Table 5. Results of molluscan analysis boreholes VC606 and VC608 (both samples 20 cm3 volume) Core VC606 VC608 Depth (mbOD) 12.82 7.28 Peringia ulvae 65 33 Ecrobia ventrosa 7 2 Peringia/Ecrobia sp. 17 21 Tellina cf. crassa 3 - Tellina sp. 1 - Littorina littorea 3 - Littorina saxatilis 1 - Cerastoderma edule 4 -

Cerastoderma/Cardium sp. 3 - Mytilus edulis + - Total 104 56

Borehole VC608 Borehole VC608 comprises a gleyed soil horizon overlain by a sequence of peat, organic estuarine alluvium (peaty clay) and silty clay alluvium in turn sealed by seabed sediments. Two distinct pollen zones were identified in borehole VC608 (VC608-1 and VC608-2, Fig. 5). Zone VC608-1 (8.24 to 8.13 mbOD) is dominated by trees and shrubs, including large quantities of Pinus along with Quercus,

13

Ulmus, Corylus avellana type and Tilia. Small quantities of herbs include Poaceae, Chenopodiaceae, Asteraceae (daisies) and Cyperaceae. Fern spores were dominated by Dryopteris (ferns) and Polypodium (polypodies). Zone VC608-2 (8.13 to 6.98 mbOD) is characterised by a sharp reduction in Pinus and fern spores. There are greater values of Quercus, Ulmus and Corylus avellana-type. In addition to small numbers of Tilia, Fraxinus (ash) and Alnus, a single grain of Abies (fir) was also noted. Herbs are an important component including Chenopodiaceae, Poaceae and Asteraceae. Halophytic communities were represented by grains of Plumbaginaceae (leadworts), Plantago maritima (sea plantain), Spergularia type (sea spurreys) and Aster type. Substantial quantities of Potamogeton type (pondweed) at the base of the zone are thought to refer to Triglochin maritima (sea arrow grass) rather than pondweed. Diatoms were present in all six samples, comprising only a small component throughout of freshwater and slightly brackish water tolerant taxa (Fig. 6). Brackish diatoms are dominant at the base of borehole VC608 with a maximum of 66% at 8.02 mbOD; the most common taxa are benthic species including Caloneis westii, Diploneis didyma, Nitzschia navicularis, Nitzschia granulata and Nitzschia punctata. From the base of the sequence up to 7.46 mbOD, the percentage of marine diatoms increase to a maximum of 67%, particularly the coastal planktonic species Paralia sulcate, whilst brackish benthic diatoms decrease. Benthic diatoms recover to 46% at 7.28 mbOD, along with a high proportion of benthic and brackish shallow-water taxa. Ostracods were present in the uppermost four samples with foraminifera present in eight of the samples (Table 6). At 8.12 mbOD foraminifera are dominated by the agglutinating saltmarsh taxon Trochammina inflate, with a few specimens recorded at 8.10 mbOD, and Ammonia at -7.65 mOD. From 7.28 to 6.76 mbOD the samples were dominated by saltmarsh and brackish estuary species, dominated by a high abundance of Elphidium and including Ammonia becarrii, Elphidium williamsoni, Haynesina germanica and Jadammina Macrescens. Some marine elements were noted, including Miliolids, Lagena semistriata and the ecophenotypical variant Ammonia batavus, a species commonly found at the mouths of estuaries. Ostracods from 7.26 to 6.98 mbOD are characterised by a mixture of estuarine (including Cyprideis torosa, Elofsonia baltica, Leptocythere castanea, Leptocythere lacertosa and Loxoconcha elliptica) and outer estuarine/marine ostracods (including Loxoconcha rhomoidea Leptocythere psammophila and Hemicythere villosa). The largest ostracod fauna was recovered from 7.13 mbOD, including the estuarine taxon Cyprideis torosa. The single molluscan sample from 7.28 mbOD (Table 5) produced a significant number of Peringia ulvae shells and a few shells of Ecrobia ventrose, the latter known to favour low to moderate saline waters in quiet estuaries, ditches in coastal marshes and lagoons behind shingle bars.

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Table 6. Abundance of ostracod and foraminifera, borehole VC608; o = present, x = 1í9 specimens, xx = 9í50 specimens, xxx = > 50 specimens, xxxx = >100 specimens. No microfauna were recorded from 7.85 and 8.02 mbOD Depth (mbOD) 6.76 6.98 7.13 7.28 7.46 7.65 8.1 8.12 Ostracods Aurila convexa xx - x - - - - - Cyprideis torosa smooth x - xxx x - - - - Elofsonia baltica - x ------Eucythere spp. - xx ------Hemicythere villosa - - - x - - - - Leptocythere ?macallana - x ------Leptocythere castanea - - x - - - - - Leptocythere lacertosa - x xx - - - - - Leptocythere pellucida xx ------Leptocythere psammophila - - xx - - - - - Leptocythere spp. - x x - - - - - Loxoconcha elliptica x - x - - - - - Loxoconcha elliptica - xx x - - - - - Loxoconcha rhomboidea x x x x - - - - Palmoconcha guttata - x ------Paradoxostoma sp. - - x - - - - - Pontocythere x - x - - - - - Propontocypris spp. x xx ------Propontocypris trigonella - - x - - - - - Foraminifera Ammonia batavus xx x x - - - - - Ammonia beccarii. xx xxxx xxx x - x - - Elphidium crispum - - o - o - - - Elphidium cuvilleri - x ------Elphidium williamsoni xxx xxx xxx xxx - - - - Elphidiumsp. - x x x - - - - Haynesina germanica xx xx xx x - - - - Jadammina macrescens xx xx xx x - - - - Lagena semistriata xx x x - - - - - Massilina secans - x x - - - - - Miliolinella subrotundata xx x ------Trochammina inflata ------x xxxx

Discussion The three palaeoenvironmental studies presented here are amongst the first such studies within the offshore zone of the Outer Thames Estuary. Together the data have enhanced our understanding of the development of this palaeolandscape during the early Holocene, occurring in the context of rapidly rising post-glacial sea-levels.

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Early Holocene vegetation environments The earliest sequence is borehole VC7 from palaeochannel 7500, with the peat dated to 8240í7840 cal. BC. Here the pollen shows a clear sequence of woodland development with pine dominating before around 8000 cal. BC, with hazel becoming more important thereafter. These two taxa form the classic boreal woodland, but with oak and elm beginning to appear from c. 8000 cal. BC onwards. Hazel would have formed part of both the understorey of the dry ground woodland, growing along the woodland edge, and at the local-scale as a component of damp carr-type woodland along with willow. The carr woodland also comprised a ground flora of ferns and patches of sedge fen and reedswamp. The ostracod and molluscan data demonstrate that this was a freshwater-dominated environment, but with an increasing marine component recorded from 34.03 mbOD. Boreholes VC606 (6600í5970 cal. BC) and VC608 (5890í5390 cal. BC) are significantly later in date to borehole VC7, dating to the later rather than early Mesolithic. The base of the two pollen sequences show a boreal woodland flora of pine and hazel, similar to borehole VC7, but very quickly giving way to a woodland dominated by oak, elm and hazel. The peaty clay at the base of borehole VC606 includes pollen of halophytic species indicative of saltmarsh environments in the vicinity, followed by a transition to tidal flats, corroborated by the microfaunal and molluscan data. Borehole VC608 exhibits a very similar sequence, with semi-terrestrial peat sealed by estuarine alluvium comprising pollen, microfauna and molluscs characteristic of the development of high salt marsh and tidal mudflats. Contemporary pollen records are rare within the Outer Thames Estuary apart from isolated sequences from the Isle of Grain and Isle of Sheppey (Russell et al. 2011). The sequence from the Isle of Grain is dated to 7080í6770 cal. BC and is dominated by oak-elm-hazel woodland but with indications locally of areas of tall-herb fen within an increasingly tidal environment. To the east at Queenborough, on the Isle of Sheppey, a peat dated to between 5750í5370 cal. BC likewise contained oak-elm-hazel woodland with local near-shore halophytic habitats and with microfaunal evidence suggesting deposition in a lagoon setting (Russell et al. 2011). The majority of palaeoenvironmental reconstructions are located within the Inner Thames Estuary where peats are widely recorded, primarily covering the Late Mesolithic to Bronze Age (Sidell et al. 2000; Wilkinson et al. 2000; Branch et al. 2012, Green et al. 2014) but with rare deposits of Late Glacial date (Morley 2010). In places throughout the Inner Thames Estuary, sequences of alluvium and peat in-filled the remnants of the late Pleistocene cold-climate braided river system. Some of these channels were only reactivated and in-filled later in the Holocene as groundwater levels rose, forming a dynamic landscape of low-lying wetlands. Later peats sealed the underlying late Pleistocene/early Holocene topography, forming a broad floodplain dominated by alder-willow carr woodland, with the dry ground during the late Mesolithic including a woodland cover dominated by lime, oak and elm (Green et al. 2014).

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Sea-level rise The radiocarbon dates from boreholes VC7. VC606 and VC608 have been plotted against the relative sea-level curve (Fig. 7), of Shennan and Horton (2002) and Siddall et al. (2003). The organic deposits have probably suffered from a degree of post-depositional auto-compaction which is likely to have reduced the altitudinal height of the upper surface of the peats. However, the base of the peats all lie on bedrock and are thus relatively good sea-level index points (SLIPs). Basal radiocarbon dates were recorded at depths of 34.38mbOD (VC7), 15.08 mbOD (VC606) and 8.12 mbOD (VC608). The foraminifera recorded from these levels in boreholes VC606 and VC608 are characteristic of high saltmarsh around the Mean High Water Spring Tide Level (MHWST) and below the Highest Astronomical Tide (HAT) (Horton and Edwards 2006). At Herne Bay, MHWST is recorded at 2.48 metres above Ordnance Datum (maOD) (Admiralty Chart 1607). Assuming a similar tidal range during the Mesolithic period, added to the depths of the radiocarbon dates, the results are comparable to existing sea-level curves (Shennan and Horton 2002; Siddall et al. 2003). Together with the SLIP from borehole VC7, they provide some indications of mean sea-level during the Mesolithic period, rising rapidly from 34 mbOD (c. 8200 cal. BC) to 8 mbOD (5800 cal. BC), equating to approximately 26 m over roughly two and half thousand years and a significant loss over time of former coastal lowlands. The dates on organic alluvium from VC606 and VC608 along the London Array offshore cable route equate with approximately 6.9 m of sea-level rise over a 700 to 1100-year period (between 6600–6460 and 5890–5730 cal BC) and a coastal setback during this period in places of perhaps as much as 5 km or more (Fig. 8). Offshore peat deposits were also recorded at Cockleshell Hard on the eastern tip of the Isle of Grain (Jelgersma 1979). Recent work here in advance of the BritNed High Voltage interconnector recorded a submerged forest at around 28.5 mbOD dating to 9030í8720 cal. BP (7080í6770 cal. BC) (Russell et al. 2011). The rates of sea-level rise apparent from these locations are comparable to those noted by other sea-level studies (Devoy 1979; Jelgersma 1979; Long 1992; 1995; Hijma and Cohen 2010; Bradley et al. 2011; Shennan et al. 2006). The rapid rise in post-glacial sea-levels, occurring under the influence of deglaciation and crustal rebound, is further modulated by two major Holocene geological ‘events’ – the 8.2 ka and Storegga events. The 8.2 ka event is a period of abrupt climate cooling generally considered to have been caused by the collapse of the North American Laurentide Ice Sheet and the drainage of two massive proglacial lakes (Lake Agassiz and Lake Ojibway). The draining of these proglacial lakes will have released a significant volume of cold freshwater into the North Atlantic over a short period of time, leading to a weakening of the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is the system of ocean currents that carry warm water and heat from the tropics into the North Atlantic, that when weakened resulted in a cooling of temperatures within the North Hemisphere (Matero et al. 2017) – in addition to rising water levels as a result of the meltwater pulse. The 8.2 ka event was first recognised in the Greenland GISP2 ice core where analysis suggested a decline in temperatures in Greenland of up

17 to 3.3±1.1°C, occurring in less than 20 years and lasting for approximately 150 years before temperatures returned to prior levels (Kobashi et al. 2007). Comparable palaeoclimate data for cooling been produced on cave stalagmites from Spain, China, Brazil and Madagascar (Cheng et al. 2009; Domínguez-Villar 2009) that attest to the wide geographic impact of 8.2 ka event. Recent climate modelling has suggested however that the lake outbursts were insufficient alone to account for the climate cooling and that the 8.2 ka event was instead caused by a centennial meltwater pulse resulting from the collapse of the Hudson Bay ice saddle (Matero et al. 2017). The impact of the 8.2 ka event on vegetation appears complex and varied and it is difficult to detect a consistent regional response (see Seddon et al. 2015). There is some evidence for spatial variation in response between high and lower latitudes with a more limited impact on vegetation seen in higher altitude sites in northern compared to southern latitudes (Seppä et al. 2007). Declines in hazel in Irish sequences have been ascribed to the 8.2 ka event (Holmes et al. 2016), with vegetation responses and a strong increase in continentality identified in the southern Carpathian Mountains of Romania (Pál et al. 2014) and declining arboreal pollen frequencies further afield in south Korea (Park et al. 2018). Within coastal environments a significant meltwater pulse resulted in a large jump in sea-levels of up to 2.11±0.89m (Hijma and Cohen 2010; Kendall et al. 2008; Törnqvist and Hijma 2012). This is preceded by additional jumps in sea-level from c. 8.5 ka, dated from basal peats in the Rhine-Meuse delta to between 8544í8375 cal. BP (Hijma and Cohen 2010). Irrespective of the precise cause, the resulting meltwater pulse is likely to have resulted in a period of accelerated inundation of coastal lowlands, that along with temperature fluctuations, may have had effect (direct and/or indirect) on contemporary Mesolithic communities. The Storegga underwater landslide occurred at approximately 8200 year ago at around the same time as the 8.2 ka event, though the two are not necessarily directly linked. The Storegga landslide triggering a giant tsunami, with traces apparent in deposits along the coasts of Norway and Scotland and is argued to have resulted in the final inundation of the North Sea basin (Weninger et al. 2008). The shift from peaty clay to estuarine alluvium in borehole VC606 is dated to shortly after 8550í8410 cal. BP (6660í6460 cal. BP). The similarity to dates from the Rhine-Meuse delta (Hijma and Cohen 2010), strongly suggests a link between a meltwater pulse and accelerated inundation in VC606. However, although Storegga tsunami deposits have been identified along the coast of the Shetland Islands and Scotland (Bondevik et al. 2005; Smith et al. 2004), there is no convincing evidence that the tsunami had a direct effect within either the southern North Sea basin or English Channel (Gearey et al. 2017; Brown et al. 2018).

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Landscape change and human occupation Although most offshore artefacts are chance finds, including a Mesolithic tranchet axe in proximity to borehole VC608, they nonetheless demonstrate that this was an actively inhabited landscape rather than simply a land-bridge between continental Europe and Britain. However, as highlighted earlier, the nature of offshore archaeological discoveries makes them difficult to interpret and compare with Mesolithic sites from North Kent. Artefacts dredged up from the seabed simply represent those items large enough to be easily identified. Many smaller artefacts such as microliths and associated debitage are highly unlikely to be recognised, so it remains almost impossible to determine whether known artefacts represent isolated finds or originally formed components of larger assemblages and sites. This in turn makes it difficult to interpret the range of likely activities or forms of occupation occurring in the current offshore zone, and equally challenging to compare this evidence with the range of activities and sites represented on the associated dry ground. Moreover, patterns of Mesolithic settlement are likely to have been complex and diverse, with different settlement modes operating within a region at any given time, and capable of adapting to changing environmental conditions. In situations of topographical variation, such as the Thames Estuary region, a degree of variability in settlement patterns should be expected. For example, settlement may have involved movement between wetland and dry ground, upland and lowland, as well as movement along the river Thames and its tributaries. Lithic assemblages may reflect settlement modes over timescales from long-term occupation through to short-term specialist activity sites, involving repeated to single visits. Site occupation may have operated on a seasonal basis, although seasonal bimodal models (upland summer and lowland winter activity) (e.g. Clark 1972) are increasingly seen as simplistic in view of the complex evidence for multiple seasonal occupation of Mesolithic sites such as Star Carr in the Vale of Pickering (Milner et al. 2018a; b) and Goldcliff in the Severn Estuary (Bell 2007). Understanding the intricacies of occupation at sites such as Starr Carr and Goldcliff has only been possible through careful analysis of palaeoenvironmental data preserved in waterlogged anoxic (oxygen-free) sediments. Most Mesolithic sites in Kent are surface lithic scatters and lack comparable scientific datasets. Consequently, any interpretation of site function based solely on lithics is likely to belie the true range of activities and modes of settlement occurring on a site, a situation compounded in offshore areas by the limited number and chance nature of discoveries. The high biodiversity of lowland, coastal and riverine landscapes in the Thames Estuary is likely to have been attractive to hunter-gatherer communities throughout the year, with activities likely including fowling, fishing, hunting and gathering. At the same time these landscapes would have been vulnerable to progressively rising post-glacial sea-levels, creating a highly dynamic and changeable landscape. However, despite the sizeable literature on the Mesolithic occupation of coastal landscapes within and surrounding the North Sea basin (Waddington and Pedersen 2007; Coles 1998; Reid 1913; Fleming 2004) there has been little discussion of the ways in which humans may have responded to the dramatic changes in the physical landscape brought about by sea-level rise (see Leary 2009; 2011).

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Was the impact of sea-level rise perceptible to communities over the course of an individual lifespan? Protracted, gradual sea-level rise during the early Holocene, in the region of 12í13 mm/year between c. 9700í5000 cal. BC (Smith et al. 2011), may have been an accepted aspect of life that communities were adapted to deal with, providing equal opportunity as well as hindrance to exploitation. The age and depth of semi-terrestrial deposits from boreholes VC7, VC606 and VC608, now located between 6 to 12 km offshore, gives some indication of the land area inundated within the Outer Thames Estuary between c. 8200 and 5400 cal. BC. The topography along the export cable route of the London Array windfarm extending onshore is illustrated schematically (Fig. 8) and provides some indication of the template on which Mesolithic human activity would have occurred. The land available for occupation will have progressively shrunk with rising sea-levels, although the impact will have varied locally dependent on topography. Low-lying areas of more shallow relief along the encroaching coasts and incipient outer estuary of the Thames will have been more vulnerable to drastic inundation and landscape change compared to areas with steeper gradient or more pronounced relief. Much of the landscape illustrated in Figure 8 will have been available for exploitation by early Mesolithic hunter-gatherer communities, but even by c. 8000 cal. BC, with sea-levels around 35mbOD, the coastline would already have been making serious inroads into the former terrestrial lowlands. Two thousand years later, sea-levels were as much as 26m higher and in places the position of the coastline may have shifted by as much as 30km. Late Mesolithic communities will therefore have been occupying a landscape significantly reduced in area relative to their early Mesolithic forebears. The coastline along the North Kent coast is likely to have been highly indented, with numerous inlets along a low-lying coastal plain, in places dropping off sharply in elevation, perhaps including isolated islands cut off by rising sea-levels (Figs 1 and 8). The result would have been a highly dynamic environmental setting including a range of habitats (e.g. reedswamp, fen and saltmarsh) attractive to hunter-gatherers. The perception of and/or response of hunter-gatherers to landscape changes is difficult to gauge. Settlement and subsistence patterns are likely to have been influenced to a lesser or greater degree by a range of interlinked factors including the biotic productivity of the landscape and sudden or drastic climate events. These factors may have had an influence on population densities and levels of mobility. Mesolithic finds do become more frequent in Kent after c. 6000 BC, perhaps reflecting either a real increase in population and/or a response to the loss of coastal lowland habitats. Leary considered a range of resilience strategies that communities may have used to deal with change, including flexible mobility, diversification of food supply, intensification of resource use, resource sharing and an increase in social interaction, experimentation and innovation (Leary 2011). These issues are problematic to answer in offshore locations because of the chance and often unstratified nature of archaeological finds and current scarcity of related palaeoenvironmental data. Although locating archaeological sites remains highly challenging, it remains important to consider landscape and environmental change from a social perspective. Not all the impacts of sea-level

20 rise were necessarily negative and the ability of hunter-gatherer communities to adapt to changing environmental circumstances requires more even consideration alongside the palaeoenvironmental data.

Conclusion The three palaeoenvironmental sequences presented provide important new data on the changing environment and physical landscape of the outer Thames Estuary during the early Holocene. Together they contribute towards a greater understanding of the major changes that occurred in the wider North Sea basin and English Channel region in the context of rapidly rising post-glacial sea-levels. During the roughly 2500-year period between c. 8250–5400 cal. BC sea-levels rose approximately 26 m at a rate of 12í13 mm/year, inundating large areas of coastal-fringing landscape. The impact of sea-level rise would have been most apparent in areas of low relief particularly around river and estuary mouths. As old land was lost new wetland habitats developed along the continually resetting coastline, including resource-rich saltmarshes and reed swamps attractive to both humans and animals. The dry ground was dominated by a dense cover of woodland, by pine-hazel woodland before 8000 cal. BC, but after this by the increasing prevalence of oak, elm and lime, representing the typical climax woodland that dominated the mid-Holocene. The adaptability of human communities to rising sea-levels and loss/creation of key habitats has been considered at a theoretical level but is hampered by a lack of stratified archaeological remains from current marine environments. However, Mesolithic hunter- gatherer societies are likely to have been highly attuned to their landscapes and able to adapt to changing circumstances brought on by sea-level rise. This raises important issues of the adaptability and resilience of current urban and sedentary societies to current rates of global rising sea-levels (3 mm/year) much less than those experienced during the early Holocene, but that are likely to have far greater societal impact.

Acknowledgements Thanks are due to Bronagh Bryne (London Array Ltd.) and Rachel McCall (TÜV SÜD PMSS) on behalf of National Grid Nemo Link Ltd for their assistance during the project. Claire Griffiths and Rhianna Roberts (MarineSpace) are thanked for assistance with the project. We are grateful to Jane Corcoran (Historic England Science Advisor South East) and Stuart Churchley (Historic England’s Marine Planning Unit) for providing useful comments on a draft of this report. The project was managed by John Russell and Philippa Bradley; the latter edited this report.

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Notes on the Contributors: Alex Brown, BA, MSc, PhD: is Principal Geoarchaeologist at Wessex Archaeology with experience in palynology, environmental archaeology, geomorphology and sedimentology within a diverse range of wetland contexts. His principal research interests are in the environmental archaeology of wetlands, and in particular, the environmental impact of conquest and colonisation during the medieval and post- medieval periods. He has worked extensively across Europe and is currently contributing to projects in the Baltic, southern France, Spain, Venice and Mauritius. John Russell, B.A., MSc, formerly of Wessex Archaeology: has over 25 years’ experience in commercial archaeology directing work on a variety of terrestrial and intertidal archaeological excavations. He has significant experience working on coastal and marine sites and is a specialist in the analysis of foraminifera and ostracods. He has also worked on sites in Orkney, Libya, Bermuda and New York. He recently left Wessex Archaeology to take up a consultancy post in London working on the Thames Tideway Scheme. Catherine Barnett, BSc, MSc, PhD, formerly of Wessex Archaeology: has a background in Quaternary sedimentology and palaeoecology and is a specialist in wood and charcoal analysis. Her work centres on the application of scientific techniques to answer archaeological questions. She was responsible for the palaeoenvironmental and scientific elements of the Silchester Insula IX and II post-excavation analysis and publications and manages the Calleva Iron Age Environs project (University of Reading). She is currently Principal Archaeologist at Stantec UK. Nigel Cameron is an honorary senior research fellow in the environmental change research centre with the Department of Geology at University College London. He is a recognised specialist in the analysis of diatoms with a focus on tracking environmental change. He and has worked extensively across Europe and beyond, including Tasmania. Rob Scaife, PhD: is a visiting professor of Environmental Archaeology and a Reader in Palaeoecology at the University of Southampton. He is a palynologist and archaeobotanist with experience in diatoms, phytoliths and charred plant remains. Most of his work is archaeologically related within southern England and specially London, but he has also worked on vegetation history in Italy, Barbados, the Falkland Islands and more recently Turkey, Chile and Peru. Chris Stevens, BSc, PhD, formerly of Wessex Archaeology: is an archaeobotanist with extensive experience in commercial archaeology, with a background in waterlogged, charred plants and marine shells. He has worked extensively across the UK in addition to sites in Italy and Egypt. He is also a recognised expert in radiocarbon dating. Sarah Wyles, BA, formerly of Wessex Archaeology: is an experienced archaeobotanist working for Cotswold Archaeology, with wide-ranging experience of all site-types across all major chronological periods. Her experience extends to the management and assessment of archaeobotanical samples, and she specialises in the analysis of molluscs from marine, terrestrial, freshwater and brackish environments.

29

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