Early-Middle Holocene Cultural and Climate Shifts in NW Africa

Home , African humid period, Helix melanostoma

Early-Middle Holocene Cultural and Climate Shifts in NW Africa:

Paleoenvironmental Reconstruction Using Stable Isotopes of Land Snail

Shells.

A thesis submitted to the Graduate School

of the University of Cincinnati in partial

fulfillment of the requirements for the degree of

Master of Science

Department of Geology

McMicken College of Arts and Sciences

By:

Abigail Padgett

B.S. University of Mississippi, 2016

Advisory Committee:

Yurena Yanes, Ph.D – Committee Chair

Andrew Czaja, Ph.D

Aaron Diefendorf, Ph.D

Abstract

The long–term response of humans to climate/environmental changes can be assessed by studying climate proxy records extracted from well–described, dated, and preserved archaeological sequences. Two Holocene Capsian sites from NE Algeria, document a marked change in subsistence strategies near 8,200 cal yrs BP. To examine the potential relationship between cultural shifts and environmental change, analyses were conducted using the stable oxygen (δ18O) and carbon (δ13C) isotopic composition of archaeological shells of the terrestrial gastropod Helix melanostoma from the early to mid–Holocene (10,500 to 6,500 cal yrs BP). This study provides intra–shell and whole shell isotopic profiles to infer seasonal, as well as average local environmental conditions in NE Algeria. The δ18O and δ13C results illustrate that conditions were notably wetter between ~10,000–8,500 cal yrs BP, coinciding with the African Humid

Period (AHP), whereas the environment turned significantly drier at ~8,160-7,300 cal yrs BP, immediately after the 8,200 cal yrs BP climate event. These results suggest that noticeable humidity fluctuations occurred during the Early Holocene in NE Algeria and could have impacted the economy and strategies of prehistoric human groups in the area.

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Acknowledgements

This research would not have been possible without the guidance and support from the following people:

First, I would like to sincerely thank the Department of Geology at the University of Cincinnati and it’s faculty members for giving me the opportunity to study what I love, travel, and meet many great people. I am truly honored to have been apart of such a wonderful community.

Biggest thanks to my advisor and role model, Dr. Yurena Yanes. I am so appreciative for Dr. Yanes’ patience, honesty, advice, and financial support over the past two years. Her dedication has pushed me to become a better scientist and overall person. I have truly grown as an individual under her guidance and I am lucky to have her as an advisor and friend.

Much appreciation extends out to my committee members, Dr. Andy Czaja and Dr. Aaron Diefendorf, and my collaborator, Dr. David Lubell, for all the contributions feedback, edits, and questions that encouraged me to think critically. I would also like to acknowledge the Society for Sedimentary Geology for providing funding to this project. This work was also possible with the help from the University of Illinois Natural History Survey for providing access to some of the sample material used for this research.

Lab members Wesley Parker, Evan New, Nora Soto, and Richard Stephenson made my time in the Yanes Lab a tremendous and supportive experience. I am grateful to have found lifetime friends in each of them. I also express much recognition to Anastasia Fries, Sonia Sanchez, Julianne Fernandez, Tim Paton, Shannon Neale, Zoey Dodson, Jenelle Wallace, and the rest of my fellow graduate students for your kindness, friendship, and willingness to give advice, and discuss research.

Finally, I would like to thank my parents, grandparents, and other family members for all your continuous support and love throughout this endeavor. A special thanks to my sister Rachel for our almost daily chats that always made me laugh, even on the worst days. I would like to dedicate this thesis to my father, Joey Padgett and grandmother Barbara Guin– thank you for believing in me and supporting my decision to go into the field of geoscience. I truly could not have made it this far without you all.

Table of Contents

Abstract……………………………………………………………………………….…… ii

Acknowledgements…………………………………………………………………….…. iv

List of Figures………………………………………………………………………….…. vii

List of Tables……………………………………………………………………………....viii

1. Introduction………………………………………………………………………………1

2. Background……………………………………………………………………………… 3

2.1 Capsian Culture…………………………………………………………………. 3

2.2 Present Day Climate & Climate Mechanisms in NE Algeria……………………4

2.3 Holocene Climate History in NW Africa……………………………………….. 7

2.4 Current Vegetation in NE Algeria………………………………………………. 8

3. Methods………………………………………………………………………………….. 9

3.1 Archaeological Context of Kef Zoura D………………………………………... 9

3.2 Archaeological Context of Aïn Misteheyia……………………………………. 10

3.3 Ecology of Helix melanostoma………………………………………………… 11

3.4 Environmental controls on land snail shell δ18O………………………………. 12

3.5 Environmental controls on land snail shell δ13C………………………………. 14

3.6 Sample Selection………………………………………………………………. 16

3.7 Radiocarbon Dating of Shells…………………………………………………. 16

3.8 Stable Isotope Analysis…………………………………………………………17

4. Results………………………………………………………………………………….. 20

4.1 AMS Radiocarbon Dates…………………………………………………….... 20

4.2 Oxygen stable isotope composition of modern shells……………………….. 21

4.2.1 Intra-shell data……………………………………………………..... 21

4.2.2 Whole shell data…………………………………………………….. 22

4.3 Oxygen stable isotope composition of archaeological shells…………………..22

4.3.1 Intra–shell data……………………………………………………… 22

4.3.2 Whole shell data…………………………………………………….. 23

4.4 Carbon stable isotope composition of modern shells………………………..... 24

4.4.1 Intra–shell data……………………………………………………… 24

4.4.2 Whole shell data……………………………………………………. 24

4.5 Carbon stable isotope composition of archaeological shells…………………. 24

4.5.1 Intra–shell data……………………………………………………... 24

4.5.2 Whole shell data……………………………………………………. 25

5. Discussion……………………………………………………………………………... 26

5.1 Environmental significance of δ18O in modern shells……………………….. 26

5.2 Paleoclimatic inferences from δ18O in archaeological shells………………... 28

5.3 Environmental significance of δ13C in modern shells……………………….. 31

5.4 Paleoclimatic inferences from δ13C in archaeological shells………………... 32

5.5 Climate mechanisms explaining observed patterns…………………………..34

5.6 Has Holocene climate change triggered cultural shifts in NE Algeria? ……..35

6. Conclusion…………………………………………………………………………….36

Figures………………………………………………………………………………….. 38

Tables…………………………………………………………………………………… 47

References…………………………………………………………………….………… 52

List of Figures

Figure 1: Geographical setting of the Maghreb region in NW Africa. ………………… 38

Figure 2: Geographical location of the studied archeological sites in northeast Algeria.

Figure courtesy of David Lubell, University of Waterloo. Modified from the original

in Lubell et al. (1976). …………………………………………………………………… 39

Figure 3: Present-day climate data for the study area in NE Algeria.

From Bowen, (2017); Bowen et al., (2005); www.noaa.gov; and www.IAEA.org. ………40

Figure 4: Box plots of intra-shell Helix melanostoma δ18O and δ13C divided by their respective age. …………………………………………………………………………… 41

Figure 5: Intra-shell δ18O values in Helix melanostoma shells throughout snail lifespan. ………………………………………………………………………………42

Figure 6: Box plots of Helix melanostoma average δ18O and δ13C according to their respective age. ……………………………………………………………………………. 43

Figure 7: Intra-shell δ13C of Helix melanostoma shells throughout snail lifespan. …….. 44

Figure 8: Comparison of δ18O and δ13C of Helix melanostoma from NE Algeria (this study)

and Libya from Prendergast et al., (2016). ……………………………………………….. 45

Figure 9: Relationship between intra–shell and whole shell Helix melanostoma δ18O and

the documented change is subsistence strategies within the Capsian archaeological records

in NE Algeria. ………………………………………………………………………………46

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List of Tables

Table 1: Modern monthly climate data in NE Algeria for the recording period between 1998 and 2006. From Bowen, (2017); Bowen et al., (2005); www.noaa.gov; www.iaea.org……………………………………………………………………………… 47

Table 2: AMS 14C dates of archeological Helix melanostoma shells from Capsian archaeological sites, NE Algeria. ………………………………………………….……… 48

Table 3: Intra-shell oxygen stable isotopes of modern and archaeological Helix melanostoma shells from Capsian archaeological sites, NE Algeria. …………………….. 49

Table 4: Intra-shell carbon stable isotopes of modern and archaeological Helix melanostoma shells from Capsian archaeological sites, NE Algeria. …………………….. 50

Table 5: Whole-shell oxygen and carbon stable isotopes of modern and archaeological… 51

Helix melanostoma shells from NE Algeria.

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1. Introduction

Climate is a major contributing factor to human civilization and livelihood. The relationship between climate and humans affects migration and settlement patterns, dietary resource availability, enhances certain cultural practices, and motivates the development of technology (Buckland et al., 1996; deMenocal, 2001; Mayewski et al., 2004). Climatic extremes can lead to environmental thresholds that result in alterations in human subsistence strategies, human migration to more climatically preferred locales, or societal collapse all together (Cullen et al., 2000; deMenocal, 2001; Luzzadder-Beach et al., 2012). One major scientific challenge of the 21st century is to determine how civilization will respond to the rapidly changing global climate. Understanding the rate and consequences of climate change on human populations is therefore critical for better predicting the consequences of future climate change and enhancing the sustainability of modern societies (deMenocal, 2001). The study of long-term effects of abrupt climate change upon ancient human cultures has been investigated using archeological and continental and marine climate records throughout the world (Buckland et al., 1996; Cullen et al., 2000; deMenocal, 2001; Haug et al., 2003). However, continental climate proxies from the

African Maghreb (countries of Morocco, Mauritania, Algeria Tunisia, and Libya) have been less explored in comparison with other areas (Figure 1). This is largely due to geo-political issues over the past century, but also because of the rarity of prehistoric archeological sites that could be definitively identified as having been occupied coincident with periods of abrupt climatic change.

Joint preservation of environmental and cultural information is ideal for directly examining how long–term environmental changes may have impacted human groups (Lubell, 2016).

Archaeological records provide the ability to investigate the relationship between climate and humans due to the combined preservation of cultural transitions as well as paleoenvironmental proxies within the archive. Extensive archaeological investigations from several excavation sites in NW Africa have suggested a major change in economic and subsistence strategies within the

Capsian occupation (Jackes and Lubell, 2008; Lubell, 2001, 2016).

Land snails are frequently abundant and well preserved in Holocene archaeological sites around the Mediterranean, and especially in NW Africa (Aouadi et al., 2014; Hutterer et al.,

2011; Lubell 2004; Lubell et al., 1976; Prendergast et al., 2015; Taylor et al., 2011). The Cheria–

Télidjène Basin in NE Algeria hosts two well–described archaeological sites that contain a large amount of well–preserved land snail shells, making these sites ideal for investigation. Snail shells preserve important environmental information about the time in which they live within the chemistry of their shell growth increments (Andrus, 2011; Balakrishnan and Yapp, 2004; Carter,

1990; Goodfriend, 1992; Yapp, 1979). Specifically, stable isotopes in land snail carbonate shells have been increasingly used as Holocene paleoenvironmental proxies over the last few decades

(Colonese et al., 2013; Ghosh et al., 2017; Prendergast et al., 2016; Rangarajan et al., 2013;

Yanes et al., 2013, 2011). Stable isotope ratios of oxygen (18O/16O) and carbon (13C/12C) in land snail shells can provide valuable information about the water and vegetation taken up by the snail during its lifetime. Although snail records may be discontinuous, the shell can provide very high–resolution snapshots when measured along growth direction. The oxygen (δ18O) and carbon

(δ13C) isotope composition of the shells are representative of the local natural environmental conditions in which the snails lived because, the shells are precipitated in equilibrium with surrounding environmental conditions (Grossman and Ku, 1986). This study provides two approaches to infer different aspects of climate: (1) whole–shell isotopic data to assess average

(dominant) climate conditions throughout the Early-Middle Holocene in Algeria, and (2) intra– shell isotopic profiles along ontogeny to assess high–resolution (seasonal) snapshots.

The research herein examines the Capsian archaeological record at two sites in the Cheria–

Télidjène Basin in NE Algeria (Fig. 2): (1) to determine if there were significant local climate changes during the early to mid–Holocene using stable oxygen and carbon isotope compositions of land snails, and (2) to assess if there is a correlation between local abrupt climate shifts and subsistence strategy changes within the Capsian culture in NE Algeria during the early–mid-

Holocene. Based on what is known about Holocene climate change in North Africa, this research test the hypothesis that NE Algeria was wetter during the Early Holocene (i.e., onset of the

African Humid Period (Adkins et al., 2006; deMenocal et al., 2000a) but notably drier following the 8,200 cal BP cold event, which likely promoted changes in the subsistence patterns of the

Capsian people. The results from snails are compared to other paleoclimate records from North

Africa and discussed in the context of regional climate mechanisms.

2. Background

2.1 Capsian Culture

Capsian hunter-gatherer groups occupied the Maghreb region of NE Algeria, Tunisia and

NW Libya from approximately 11,000 to 6,000 cal BP (Aouadi et al., 2014; Kherbouche et al.,

2016; Lubell, 2001; Prendergast et al., 2016). Similar but not identical archaeological remains, not called Capsian, occur in western Algeria and eastern Morocco. Capsian settlements are typically found inland from the coast, most commonly on high interior plateau. The majority of

Capsian settlements occur as open-air mounds near springs or passes, but occasionally occur in

caves and rock shelters along limestone escarpments and contain no structures other than hearths and burial cairns (Lubell, 2001). It is not certain whether Capsian population occupied settlements perennial or seasonally because there are many proposed hypotheses for and against year-round occupation (Lubell et al., 1976,1982, 1984; Rahmani, 2004). Capsian archaeological sites are high in artifact density, consisting of lithic and bone tools, some small carvings and shell beads (both marine and ostrich), fire-cracked rocks, human burials, vertebrate bones, and large amounts of land snail shells of varying species (Lubell, 2001, 2016,; Rahmani, 2004).

Capsian groups were among the last foragers in North Africa (Rahmani, 2004). Archeological evidence suggests a pure hunting-gathering-foraging subsistence strategy with no evidence of domestication of plants and animals (Jackes and Lubell, 2008; Lubell et al., 1976; Rahmani,

2004). Vertebrates both large and small were the primary dietary source of protein. In addition, land snails are incredibly frequent within Capsian deposits, and are considered an important component of Capsian diet, although not the dominant source (Lubell, 2001). The archaeological record of some Capsian sites exhibit abrupt change in subsistence strategies reflected in a marked change around 8,000 cal yrs BP in faunal remains, stone tool technology and typology, and land snail species. This change marks the transition from Typical Capsian to Upper Capsian occupation, the two phases within the Capsian sequence in NW Africa (Lubell, 2016).

2.2 Present day climate and climate mechanisms in NE Algeria

The current climate in NE Algeria is a Mediterranean–type climate, characterized by hot, arid summers and mild, wet winters (Table 1, Fig. 3). Average monthly temperature and precipitation values for the 1998–2006 recording period were obtained from the NOAA climate database (www.noaa.gov). Temperature, precipitation, and relative humidity (RH) values were

measured at WMO station 60419 in Constantine, Algeria that is approximately 30 km north of the study site. The precipitation δ18O values for the study site were obtained from the Online

Isotopes in Precipitation Calculator (OIPC) (Bowen, 2017; Bowen et al., 2005). The OIPC δ18O data calculate precipitation oxygen isotope values using data acquired from the Global Network of Isotopes in Precipitation (GNIP) with model criterion including latitude, altitude, vapor transport pathways, and Rayleigh distillation (Bowen and Revenaugh, 2003; Bowen and

Wilkinson, 2002). Moreover, precipitation δ18O values directly measured in monthly basis from

1998 through 2006 from the Algiers water station were obtained from the Global Network of

Isotopes in Precipitation (GNIP) database (IAEA/WMO, 2015). Algiers is located on the

Mediterranean coast, approximately 400 km NW of the study location.

The region today is semi–arid, with the total annual precipitation (averaged over nine years; 1998–2006) about 524 mm. Precipitation is heaviest in December–May (351 mm) and lightest between June and August (32 mm) (Fig. 3A). Mean yearly air temperature is 16°C, ranging from 26°C in July to 6°C in January (Fig. 3B). Relative humidity (RH) in NE Algeria inversely correlates to temperature, and has a mean annual value of 65%. RH ranges from approximately 42% in July to 76% in January and December (Fig. 3C). The mean annual OIPC

18 δ O value is –2.9‰, and ranges from –6.6‰ in January to +0.7‰ in August (Fig. 3D). Mean annual measured precipitation δ18O for Algiers is –2.5‰, and ranges from –5.5‰ in November to 0‰ in July and August (Fig. 3D).

There are several climate mechanisms that control the weather and climate of modern NW

Africa. The entire Mediterranean region is considered a transitional zone, where both inter- tropical convergence zone (ITCZ) and mid–latitude Westerlies systems affect variations in climate, therefore yielding multiple rainwater sources that vary throughout the year. The majority

of rainfall occurs in winter (November to March), and is brought to North Africa from the

Westerlies, when cool dry North Atlantic air masses interact with the warm humid

Mediterranean air (Kostopoulou and Jones, 2007; Rohli and Vega, 2008). Storm intensity of the

Westerlies depends, partially, upon the North Atlantic Oscillation index (NAO). High NAO index moves storms further north during summer months and low NAO index in winter months brings increased rainfall and storms (Kostopoulou and Jones, 2007). During the summer months, the Azores High moves northward, creating high-pressure systems in the Mediterranean causing a dry and relatively stable climate, with minimal rainfall (Gat and Carmi, 1970). Three primary source trajectories for Mediterranean precipitation have been defined, each with their own distinct isotopic character. Precipitation primarily falls during cooler months from October to

March (Gat and Carmi, 1970; Rindsberger et al., 1983). The air mass responsible for ~60% of precipitation in northern Africa is derived from the north Atlantic, moving southeast from NW

Europe. This trajectory brings cool, continental air that mixes with warm Mediterranean air, causing intense rainfall periods and is characterized by lower precipitation δ18O values (< –6‰, approximately). The second trajectory brings cool air from the west across the Mediterranean and the coast of the African continent, causing a long but less intense interaction resulting in lower amounts of precipitation that is enriched in 18O (> –3%, approximately). The third trajectory travels from the west across the northern perimeter of the African continent, the precipitation is characterized by few, short but intense rainfall events and is typically the most depleted in 18O (< –7‰, approximately) (Gat and Carmi, 1970; Rindsberger et al., 1983).

2.3 Holocene Climate History in NW Africa

The Holocene paleoclimate of NW Africa has been reconstructed by a number of proxies, including offshore sediment cores, phytoliths, paleo–lake levels, and tufas (Adkins et al., 2006; deMenocal et al., 2000a; Shipp et al., 2013). These published studies indicate that at the beginning of the Holocene (11,700 cal BP), climate conditions in NW Africa were humid.

Monsoonal rainfall was heaviest from approximately 10,000 to 5,000 cal BP, causing higher relative humidity levels in northern Africa compared to today (Kutzbach, 1981). This humid period continued throughout the early Holocene, reaching a maximum around 9,500 cal BP

(Adkins et al., 2006). This period of moist conditions during the early Holocene is referred to as the African Humid Period (AHP), and has been explained by an increase in precipitation as a result of a northward shift of the inter–tropical convergence zone (ITCZ) (deMenocal, 2001;

Lézine, 2017). This humid period was interrupted by an abrupt cooling event around 8,200 cal

(Adkins et al., 2006; Alley and Ágústsdóttir, 2005; Shipp et al., 2013). Paleoclimate studies in

Algeria using phytolith proxies suggests a dry environment with little rainfall around 7,800 cal

BP (Shipp et al., 2013). Multiple paleoclimate studies in NW Africa lead to the general conclusion that a short cool arid period occurs following 8,200 cal BP, the longevity and exact onset of the period in NW Africa is debated and varies regionally but seems to end no later than

7,500 cal BP (Adkins et al., 2006; Alley and Ágústsdóttir, 2005; deMenocal, 2001; Giraudi et al.,

2013). This event is referred to as the 8,200 cal BP event, a short–lived global cold anomaly affecting predominantly the Northern hemisphere, with the greatest effects in the north Atlantic

(Alley and Ágústsdóttir, 2005; Matero et al., 2017). The event is widely accepted to have been initiated by the drainage of proglacial Lake Agassiz and Lake Ojibway into the north Atlantic

(Kendall et al., 2008). The pronounced cooling event is associated with a slowdown of the North

Atlantic Deep Water thermohaline cycle (NADW) and southward shift of the ITCZ (Kim et al.,

2007). Sea-surface temperature (SST) reconstructions using alkenone paleothermometry suggest that the influx of cold fresh-water propagated to the North Atlantic subtropics via the Canary

Current resulting in a long-term cooling of the eastern North Atlantic and western Mediterranean region (Kim et al., 2007). Climate conditions of North Africa became more humid following the

8,200 cal BP event, but not as humid as the conditions prior to the 8,200 cal BP event, and more humid than the present (deMenocal et al., 2000a; Lubell, 2001).

2.4 Current vegetation in NE Algeria

The vegetation in Northern Algeria is characterized predominantly by steppic vegetation, which includes alpha grass (Stipa tenacissma) and low-lying bushes (Artemisia herba alba and

A. campestris). Some pines (Pinus halepensis), oak (Quercus ilex) and juniper (Juniperus phoenicia) stand on what remains of heavily eroded slopes (Lubell et al., 1976). The perennial needle grasses as well as all trees and bushes in the region follow a C3 (Calvin-Benson) photosynthetic pathway and are a typical feature of steppic vegetation in the study region

(Cerling and Quade, 1993; Lattanzi, 2010; Prendergast et al., 2016). In the study region, native

C3 plants overwhelmingly dominate the landscape, while plants that follow C4 (Hatch-Slack) and

Crassulacean Acid Metabolism (CAM) carbon fixation pathways are rare. C3 plants are favored by cooler and wetter climates, with warm and arid summers.

Over the past 2,000 years, the study region has been heavily cultivated, resulting in significant erosion rates (Lubell et al., 1976; Morales et al., 2013). The region today is primarily farmed for C3 cereal and vegetable crops grown in irrigated fields as well as apricot and olive tree arboriculture (Boudjelal et al., 2013; Lubell et al., 1976). Although the humidity in northern

Africa fluctuated throughout the Holocene, C3 vegetation has been the dominant vegetation type for the past ~11,000 years with negligible presence of native or cultivated C4 and CAM plants

(Morales et al., 2013; Prendergast et al., 2017, 2016).

3. Methods

3.1 Archaeological context of Kef Zoura D

Kef Zoura D (KZD) is a Capsian rock shelter site in the southern part of the Télidjène

Basin, Algeria (Fig. 2) that has been excellently preserved most likely due to the morphology of the shelter (Lubell, 2016). The shelter is located about 1,000 m above sea level, and is over 30 m long and 6 m wide (Lubell, 2016, 2001). Capsian occupation at KZD occurred from ~10,400 to

6,500 cal BP based on 21 radiocarbon dates of charcoal, mammal bones, and land snail shells.

Land snail shells are abundant in the deposits and were used as one of the main tools for interpreting the KZD stratigraphy and determining the division between the two types of Capsian occupation observed (Lubell, 2016). During excavation, the stratigraphic layers were divided into 5 units, I–III representing “Upper Capsian” occupation and IV–V representing “Typical

Capsian” occupation. Units were identified in part based on land snail genera, because dominant genera changed through time (Jackes and Lubell, 2008). The top three units are classified as

Upper Capsian, and contain specimens that have been dated from ~8,200 to ~6,600 cal BP based on 14 radiocarbon dates from charcoal and one radiocarbon date from a snail shell. The bottom two units are considered Typical Capsian, and were dated between ~9,200 and 10,400 cal BP based on six radiocarbon dates, three using charcoal, two using mammal bone, and one using a land snail shell. The older units have a high frequency of the land snail species Helix

melanostoma, large vertebrate bones, and larger tools. The upper levels contain smaller mammal bones and tools, and exhibit a high concentration of H. melanostoma shells (Jackes and Lubell,

2008).

3.2 Archaeological context of Aïn Misteheyia

Aïn Misteheyia is an open-air Capsian archaeological site located at about 1,100 m above sea level in the NW section of the Télidjène Basin, Algeria. The site is relatively small compared to other Capsian sites, with a diameter of 40 m and a maximum depth of 1.5m. Based on 14 radiocarbon dates from snail shells (12) and human collagen (2) and five Optically-Stimulated

Luminescence (OSL) dates of fired clay (1) and quartz grains (4) within the site stratigraphy, the site records a Capsian history of about 3,000 years, between ~10,100 to 7,400 cal BP (Lubell,

2001; Lubell et al., 2009). Like many other Capsian sites in Northern Africa, land snail shells dominate the archaeological record at Aïn Misteheyia. Sites such as this are referred to as escargotières, a term coined by the French archaeologists who first excavated the region (Jackes and Lubell, 2008; Lubell, 2016). The stratigraphy is sometimes difficult to follow due to deflation and compaction, but two main levels have been recognized, Upper Capsian and Typical

Capsian. Evidence of the two levels is not well defined and therefore cannot be confirmed at this site, but is hypothesized based on comparison with the evidence at site Kef Zoura D.

Typical Capsian dates vary in age from approximately 10,600 to 8,500 cal BP, based on radiocarbon dates of charcoal and land snail shells (Lubell, 2016). These layers are rich in ancient land snail shells, with Helix melanostoma being the most abundant species throughout the record. Apart from shells, bones of predominantly larger mammals and large stone tools such as flakes and blades made of local flint are also well preserved in the stratigraphy of the site. The

Upper Capsian dates range from approximately 8,500 to at least 6,800 cal BP, based on radiocarbon dating of land snail shells (Lubell, 2016). The layers within the Upper Capsian mainly consist of numerous land snail shells, dominated by the species Helicella sitifensis, bones of smaller mammals, and smaller stone tools (Jackes and Lubell, 2008).

3.3 Ecology of Helix melanostoma

The pulmonate terrestrial gastropod, Helix melanostoma, is one of the most abundant species found in archaeological and geological deposits around the Mediterranean (D. L. Lubell,

2004), and is one of the more common land snails found in North Africa and the eastern

Mediterranean (Lubell, 2001). Helix melanostoma can have a lifespan of several years, lives in shaded humid bush-land areas and seems to prefer soils rich in calcium carbonate (Hill et al.,

2017; Lubell et al., 1976; Prendergast et al., 2016). Species of the genus Helix live on average 1–

3 years, but have been known to live for up to 4–5 years. Adult Helix melanostoma are >10 mm in size. Observations at Aïn Misteheyia and in Libya suggest Helix melanostoma undergoes periods of dormancy, typically referred to as aestivation during the driest days of the summer months and hibernation during the coldest days of the winter months, and are expected to be most active during the fall and spring months. During these periods of inactivity, snails bury themselves under damp soils and develop a thick epiphragm, i.e., mucus covering and sealing the aperture, in order to retain moisture and protect the snail from predation (Hill et al., 2017; Lubell et al., 1976; Yanes et al., 2013). In Algeria, the epiphragm of Helix melanostoma is much thicker during the winter months as opposed to summer, which suggests shorter periods of aestivation in the summer and longer periods of hibernation in the winter (Lubell et al., 1976). Therefore, only

the active period of the snail lifespan will be recorded within the aragonitic shell because snails grow during periods of activity (Goodfriend, 1992).

Very little information is available regarding the ecology and geographical distribution of

Helix melanostoma in northern Africa. Some field observations of the species have been made during various studies at Capsian archaeological sites across north Africa (Barker et al., 2010;

Hill et al., 2017; Lubell et al., 1976; Prendergast et al., 2015). Adult Helix melanostoma collected from Capsian sites range approximately in size from 32 to 16 mm, and is the largest land snail species found among Capsian archaeological sites (Lubell et al., 1976; Prendergast et al., 2015;

Shipp et al., 2013). Helix melanostoma can be classified as juvenile when shells preserve the shell aperture intact and shell basal diameter is smaller (Hill, 2015; Prendergast et al., 2015).

Snail growth rates are largely unknown for most species, including those of Helix melanostoma. Other most commonly studied species like Cornu aspersum, formally known as

Helix aspersa (“the common garden snail”) are known to reach maturity in the wild during the second year, so snails reach sexual maturity and a shell diameter >25 mm in the second year, likely growing ~1 mm of shell per month in the first two years of the snail lifespan. Factors affecting growth rates include abiotic (temperature, humidity) and biotic (food availability, crowding) factors (Cowie and Cain, 1983).

3.4 Environmental controls on land snail shell δ18O

The shell δ18O primarily reflects the environmental water taken up by the snail

(Goodfriend, 1992). Thus, snail shell δ18O has been primarily used to reconstruct precipitation

δ18O, which, in turn, is related to climate (Dansgaard, 1964). Land snails are good proxies for assessing changes in environmental waters due to high water turnover and low metabolic rates

(Goodfriend et al., 1989). Land snail shells are precipitated from bicarbonate in the snail body fluid derived from atmospheric water vapor and liquid water imbibed by the snail, thus providing a record of environmental water fluxes via the δ18O value of the carbonate shell (Goodfriend,

1992; Goodfriend et al., 1989; McConnaughey and Gillikin, 2008; Prendergast et al., 2015;

Balakrishnan and Yapp, 2004). In more arid climates, the correlation between snail shell δ18O and precipitation δ18O may be complicated because atmospheric water vapor is affected by evaporation and other moisture sources such as nearby water bodies (Goodfriend et al., 1989;

Prendergast et al., 2015). The amount of rainfall can potentially influence shell δ18O values in tropical regions. Increased rainfall results in lower precipitation δ18O values, and decreased rainfall and more evaporation will result in higher precipitation δ18O (Dansgaard, 1964).

The shell carbonate δ18O does not necessarily reflect the mean annual precipitation δ18O because it has been observed that Helix melanostoma can be dormant during the coldest and hottest days of the winter and summer seasons (Goodfriend, 1992). Prendergast et al. (2015) conducted a modern calibration study using Helix melanostoma from Libya and concluded that whole-shell δ18O values were strongly correlated with local precipitation δ18O and rainfall amount. In fact, up to 90% of the oxygen isotopic variability of snail shells could be explained by variations in rainfall amount. Based on this published research, it is assumed that the shell

δ18O of Helix melanostoma from Algeria primarily responds to local variations in precipitation

δ18O and precipitation amount, with higher shell δ18O values reflecting lower precipitation (drier conditions) whereas lower δ18O values depict higher rainfall (wetter conditions).

3.5 Environmental controls on land snail shell δ13C

The photosynthetic pathway that plants follow is the largest influencer of carbon isotope fractionation, apart from enzyme Rubisco–which converts atmospheric CO2 to sugars

(Diefendorf and Freimuth, 2017). Terrestrial plants follow three different metabolic pathways

(C3, C4, and CAM). Each metabolic pathway fractionates atmospheric CO2 differently, resulting in plant tissues with different δ13C values (Farquhar et al., 1989; Prendergast et al., 2017). Many

13 temperate plants are C3 plants and have a global δ C range between –33‰ to –23‰, with a global average of -27‰ to -26‰ (Sharp, 2007). C3 plants are highly water–efficient, are more successful in warm and drier regions with pronounced summer rainfalls, and have the largest net fractionation (Diefendorf and Freimuth, 2017; Sharp, 2007). C4 photosynthesis has the smallest net fractionation and is overall less efficient than C3 photosynthesis because photorespiration, the process of O2 intake and CO2 generation, is reduced in C4 plants (Farquhar et al., 1989; Seibt et

13 al., 2008; Sharp, 2007). C4 plants have a global δ C range between –16‰ to –9‰, with an average of -13‰, to -12‰ (Sharp, 2007). Plants with the CAM photosynthetic pathway have intermediate fractionation, and can exhibit values similar to both C3 and C4 as well as values in between. CAM plants are most abundant in tropical and subtropical regions, but can extend to higher latitudes (Sharp, 2007).

Carbonate in terrestrial snail shells is formed from the bicarbonate within snail body fluids.

13 The δ C of land snail shells are primarily influenced by metabolic CO2 (diet) (Stott et al., 2002), and in some cases, ingested carbonates (such as limestone) (e.g., Balakrishnan and Yapp, 2004;

Yanes et al., 2008; Hill et al., 2017). Accordingly, δ13C values of land snail shell carbonate primarily inform about the δ13C values of consumed and assimilated vegetation. Ingestion of carbonates can affect shell δ13C values, resulting in slightly higher shell δ13C than if snails

consumed only plant matter (Yanes et al., 2008). The influence of ingested carbonates on shell

13 δ C values varies with species and localities (Goodfriend and Ellis, 2002). The land snail Helix aspersa has been known to exhibit no influence of carbonate intake on the δ13C values in their

13 shells (Stott, 2002). Stott, (2002) observed that there is a greater offset between shell δ C values

13 13 13 and snail diet δ C values of C3 plants (Δ C = 13.8 ± 0.5‰) versus C4 plants (Δ C = 4.9 ±

0.9‰). Therefore, land snails consuming a predominantly C3 plant diet will have shells with

13 significantly more negative δ C values than those consuming C4 plants. A mixed C3/C4 diet will yield intermediate shell δ13C values (Balakrishnan et al., 2005).

A modern calibration study of Helix melanostoma from Libya suggest that whole-shell

13 13 δ C values primarily records the vegetation δ C, with negligible effects from atmospheric CO2 and limestone ingestion (Prendergast et al., 2017). Based on this published research from Libya, it is assumed in the present study that the shell δ13C of Helix melanostoma from Algeria primarily reflects the average δ13C values of surrounding vegetation.

13 The correlation between plant and snail shell δ C values has implications for palaeoenvironmental reconstruction as the type of vegetation present is related to environmental elements such as rainfall amount (Prendergast et al., 2017). The effects of aridity may also be seen within C3-dominated plant communities such as the Télidjène Basin region, as water stress leads to more positive δ13C in plants, which, in turn, would result in higher snail shell δ13C

13 values. Thus, in NE Algeria, a C3-dominated region, higher shell δ C values should depict higher plant δ13C, reflecting somewhat drier conditions (more water stress), whereas lower shell

δ13C are indicative of lower plant δ13C values (reduced water stress) during wetter scenarios

(Prendergast et al., 2017).

3.6 Sample selection

Land snail shells used in this study were obtained from collections of both Dr. David

Lubell at the University of Waterloo and The University of Illinois Champagne-Urbana Natural

History Survey (UINHS). The samples collected by Dr. Lubell were recovered during excavation of Aïn Misteheyia and Kef Zoura D in the 1970s whereas the UINHS samples were collected by

Alonzo Pond and his students in 1930 and subsequently analyzed by F.C. Baker (1938) (Baker,

1938). Well-preserved, whole specimens of Helix melanostoma were selected because of their edible size and abundance within the stratigraphy at both Aïn Misteheyia and Kef Zoura D sites.

Moreover, other paleoclimate studies using land snails from Libya in Northern Africa have also employed this species and demonstrated their validity as credible paleoclimate archives

(Prendergast et al., 2015, 2016, 2017).

3.7 Radiocarbon Dating of Shells

Five Helix melanostoma shells, three from Aïn Misteheyia and two from Kef Zoura D were selected for AMS 14C dating. The last growth episode (shell lip) of samples were dated at the W.M. Keck Carbon Cycle AMS Laboratory at the University of California, Irvine. Due to the potential ingestion of limestone throughout the snail’s lifespan, the shell lip was selected to minimize the error associated to dead carbon assimilation (Goodfriend, 1999). Shell samples were cleaned with deionized water to remove detrital contaminants and then leached in dilute

HCL to remove secondary carbonate. To produce CO2, the shells underwent an acid hydrolysis procedure, with 85% phosphoric acid in disposable septum-sealed reactors. CO2 was reduced to graphite with hydrogen and an iron powder catalyst at 560 °C. In this process Mg(ClO4)2 is used to remove water. Samples processed in this laboratory using this method have exhibited 0.3 %

precision and 55,000 yr backgrounds (https://www.ess.uci.edu/group/ams/facility/ams).

Resultant radiocarbon dates (in 14C years) were then corrected for age offset proposed in (Hill et al., 2017). Dietary carbon is composed of carbon derived from living tissue, and “old” carbon derived from dead tissue or local carbonate rocks. Therefore, the age acquired from AMS radiocarbon dating will be slightly older that the true age of the shell. The age offset and uncertainty in 14C years was calculated using the following equations from (Hill et al., 2017):

!" ! !!!!"" (1) �ℎ�� = −8033 ∗ ln ( !" ) ! !!"#

14 14 14 Where Shell reservoir offset = 476 ± 48 C years; F Cshell = C measurement of the shell; and

14 14 14 F Catm = atmospheric C. The number -8033 is derived from the Libby half-life of C (T1/2 =

5,568 yr).

!" !" (2) Uncertainty or sigma = 8033 * ( ! ! !!!"" !"#$% )! + ( ! ! !"# !"#$! )! !!"! !!!"" !"#$%&"' !!"! !"# !"#$%&"'

Corrected radiocarbon dates were then calibrated using the INTCAL calibration curve 7.1

(http://calib.org/calib/calib.html) (Stuiver and Reimer, 1993). Calibrated radiocarbon ages were reported using the 2-sigma (2σ) age range to ensure a 95.4% probability that the real age falls within the range of the radiocarbon ages.

3.8 Stable Isotope Analysis

A total of thirty-nine Helix melanostoma shells were selected for oxygen and carbon isotopic analysis. Each shell was selected based on preservation quality, site provenance, and predicted age. Laboratory analyses for both intra-shell and whole shell samples were conducted

at the Stable Isotope Laboratory of the Department of Earth and Environmental Sciences at the

University of Kentucky (two samples) and the University of New Mexico Center for Stable

Isotopes (thirty–seven samples). At the University of Kentucky, the sample carbonate was placed in a vial that was subsequently flushed with helium and then converted to carbon dioxide (CO2)

o by adding 0.1mL of 100% phosphoric acid (H3PO4) at 25 C. The CO2 was then analyzed for

δ18O and δ13C at a constant 25oC for a 24 hour period using a Gasbench II™ peripheral device attached to a Finnigan Delta V isotope ratio mass spectrometer (IRMS). Results were normalized to the Vienna Pee Dee Belemnite (V-PDB) scale using internal working standards, which were referenced against the international standards NBS19. Analytical uncertainty was

±0.1‰ for both carbon and oxygen isotopes based on the repeated measurements of in-house and international (NBS19) standards throughout each run sequence.

Thirty-seven samples were measured at the Center for Stable Isotopes, University of New

Mexico via standard protocol addressed by (Spötl and Vennemann, 2003). The samples were loaded in 12 mL borosilicate exetainer™ vials. Vials were subsequently flushed with helium and the samples were reacted for a 12 hour period with H3PO4 at 50°C. The evolved CO2 was measured by a continuous flow Isotope Ratio Mass Spectrometry using a Gasbench device coupled to a Thermo Fisher Scientific Delta V Plus Isotope Ratio Mass Spectrometer. The results are reported using the delta notation, versus V-PDB. Reproducibility was better than ±0.1‰ for both δ18O and δ13C based on repeats of a laboratory standard (Carrara Marble). The laboratory standards were calibrated versus NBS19, for which the δ18O is -2.2‰ and δ13C is 1.95‰.

Mean isotopic data for all samples are reported in delta (δ) notation in relation to the international standard Pee Dee Belemnite (PDB): where

18 13 δ O or δ C = [(Rsample/Rstandard) –1]*1000 (‰)

and R is the 18O/16O or 13C/12C ratio, respectively.

The carbon stable isotope analyses of all modern shells were corrected for the Suess Effect by adding +1.6‰ (Köhler, 2016) to measured shell δ13C values. The archaeological samples date to pre-industrial times (~11,300–7,000 cal BP), and therefore were not corrected.

For isotopic analyses, two different sampling approaches were followed:

(1) Intra-shell time-series. The shells for intra–shell sampling were obtained from the

Lubell collection due to the established modern and archaeological context of the shells. Seven

Helix melanostoma shells, one modern and six archaeological, were selected for intra-shell micromilling along ontogeny. This approach was used to evaluate potential variations in the magnitude of seasonality (variation in precipitation δ18O and vegetation δ13C) at different time- intervals recorded in each analyzed shell. A Dremel® 4000 drill was used to sample approximately every 1mm beginning with the last growth episode along the shell growth axis, ending at the protoconch (or apex) which represents the earliest shell growth episode. Shell powder was collected on weighing paper and then transferred to 0.5 ml polypropylene micro– centrifuge tubes. A total of 277 samples were analyzed, with each shell yielding an average of 40 samples per shell.

(2) Whole shell samples. Thirty–two entire Helix melanostoma shells, eight modern and twenty–four archaeological, were selected for whole shell isotopic analyses. The eight modern samples can be divided into two groups: three shells that were collected by David Lubell in

1973, and five samples collected by Alonzo Pond and his students in 1930. All archaeological samples were obtained from the Lubell collection with well-understood archaeological context.

This second approach was used to assess potential variations in the average (dominant) environmental conditions throughout the Early-Middle Holocene. This approach and species were also used in other nearby study in Libya, northern Africa (Prendergast et al., 2016) and therefore, regional comparisons between records are suitable. Shells were individually finely crushed manually using an agate mortar and pestle. Shell powder was collected on weighing paper and then transferred to 0.5 ml polypropylene micro-centrifuge tubes.

4. Results

4.1 AMS radiocarbon dates

A total of five AMS radiocarbon dates were acquired from the shell lip of five selected individuals (Table 2). The shell lip represents the last shell growth episode and is assumed to incorporate less dead carbon due to smaller intake in the late stages of shell ontogeny

(Goodfriend, 1999). However, new research by Hill et al., (2017) showed that Helix melanostoma from North Africa is, on average, 476±48 years older than true age, even at the shell lip region. Thus, the reported ages are corrected for “old carbon anomaly” and calibrated to calendar years (see also Methods section above).

The calibrated AMS 14C results indicate that the dated shells range in age from 10,100 to

6,550 cal BP (rounded to the nearest 50th) (Table 2). These ages coincide with the published chronology of other dated samples using charcoal, shells and bones retrieved from the studied

sites (Jackes and Lubell, 2008; Lubell, 2016; Lubell et al., 2009). The oldest dated shell was collected from Aïn Misteheyia K9 at the 140–145 cm level and yielded a median probability calibrated age of 10,100 cal BP (9,900–10,100 cal BP). The two shells collected at Kef Zoura D yielded a median probability calibrated ages of 9,050 cal BP (2σ range= 8,800–8,850 cal BP) and

8,000 cal BP (2σ range= 7,900–8,000 cal BP). The oldest Kef Zoura D shell was collected from excavation unit T20–5 at the 80–90 cm level. The younger Kef Zoura D shell was collected from excavation unit F20B at the 82–104 cm level. A fourth shell, collected at Aïn Misteheyia K10/Ib within the 30–35 cm level, yielded a median probability calibrated age of 7,650 cal BP (2σ range= 7,550–7,750 cal BP). The youngest dated shell was collected at Aïn Misteheyia K10/Ib within the 30–35 cm level and yielded a median probability calibrated age of 6,700 cal BP (2σ range= 6,550–6,800 cal BP).

4.2 Oxygen isotope composition of modern shells

4.2.1 Intra-shell data

The δ18O values obtained from the modern Helix melanostoma shell (Amm80H5) ranged from –3.0‰ to +3.5‰ (n=55), with a mean value of –0.5‰±1.4 (Table 3; Fig. 4A; Fig. 5G).

Thus, the analyzed modern shell showed significantly different δ18O values across ontogeny. The

18 mean δ O of the precipitation in NE Algeria is –2.9‰ and ranged from –6.6‰ to +0.7‰ (Fig.

3D). The range of precipitation δ18O (up to ~7‰) is similar to that observed in the shell

Amm80H5 (6.5‰). Average shell Amm80H5 δ18O was ~2‰ higher than the precipitation δ18O

(Table 3; Fig. 5G).

4.2.2 Whole shell data

The δ18O values of eight entire Helix melanostoma shells from Algeria ranged from –

3.3‰ to –0.1‰, with a mean value of –1.8‰±1.1 (Table 5; Fig. 6A). Modern samples were collected on two different dates, three shells in 1973 and five shells in the 1930s. Shells collected during 1973 (n=3) ranged in δ18O from –1.3‰ to –0.1‰, with a mean value of –0.7‰±0.6.

Shells collected during 1930s (n=5) ranged in δ18O from –3.3‰ to –1.7‰, with a mean value of

–2.5‰±0.7. Thus, shells collected during 1973 shells were about 2‰ more positive than shells retrieved during 1930s.

4.3 Oxygen stable isotope composition of archeological shells

4.3.1 Intra-shell data

Six archaeological H. melanostoma specimens measured along shell growth direction ranged in δ18O from –7.0‰ to +3.5‰ (Table 3; Figure 5A–F). A 6,550–6,800 cal BP shell, collected at Aïn Misteheyia K10/Ib within the 30–35 cm level, has a mean δ18O value of –1.8 ±

0.9‰, varying between –4.6‰ and –0.9‰ (n=39) (Fig. 5F). The 7,550–7,750 cal BP shell, collected at Aïn Misteheyia K10/Ib within the 30–35 cm level, has a mean δ18O value of +1.4‰, ranging from +0.7‰ to +1.8‰ (n=30) (Fig. 5E). The 7,900–8,000 cal BP shell, collected from

Kef Zoura D excavation unit F20B at the 82–104 cm level, has a mean δ18O value of –1.5±0.4‰, varying between –2.6‰ and –1.1‰ (n=23) (Fig. 5D). The 8,800–8,850 cal BP shell, collected from Kef Zoura D excavation unit T20–5 at the 80–90 cm level has a mean δ18O value of –

3.0±2.0‰, ranging from –7.0‰ to –0.5‰(n=42) (Fig. 5C). The 9,900–10,100 cal BP, collected at Aïn Misteheyia K9 within the 140–145 cm level, shell has a mean δ18O value of –1.2±0.3‰,

varying between –3.6‰ and +0.6‰(n=54) (Fig. 5B). The 9,800–10,100 cal BP shell, collected at Aïn Misteheyia K9 within the 140–145 cm level, has a mean δ18O value of –2.3±1.5‰, varying from –4.8‰ to +0.4‰ (n=34) (Fig. 5A).

In summary, shells dated in age between 10,100 and 8,850 cal BP on average showed significantly low δ18O values compared to shells that date between ~8,000–7,550 cal BP, and a large degree of seasonality (between 4 and 6‰). Shells dated within ~1,000 years following the

8,200 cal BP event, i.e., shells with an age of ~8,000–7,550 cal BP, displayed the highest δ18O values (up to ~1‰ higher than modern shells) (Fig. 5D–E), and minimal degree of seasonality

(Table 3). The intrashell δ18O values along ontogeny showed quasi-sinusoidal cycles for most of the shells (Fig. 5). However, the shells dated at 8,000–7,550 cal BP displayed nearly constant

δ18O values along ontogeny (Fig. 5D–E).

4.3.2 Whole shell data

The δ18O values of entire archaeological Helix melanostoma shells (n=24) from the

Télidjène Basin, Algeria ranged from –3.2‰ to –0.9‰, with a mean value of -2.6‰±0.7 (Table

18 5; Fig. 6A). The oldest shells δ O (10,400–9,900 cal BP), collected from Aïn Misteheyia M10 excavation level 135–140 cm and Aïn Misteheyia K9 level 140–145 cm, ranged from –3.2‰ to –

1.6‰ (n=8), with a mean value of –2.4‰±0.6. The 8,850–8,600 cal BP shells, collected from

Kef Zoura D excavation unit T20–5 within the 80–90 cm level, ranged in δ18O from –3.2‰ to –

1.1‰ (n=8), with the same mean value of –2.4‰±0.7. In contrast, the 7,750–6,550 cal BP shells, collected at Aïn Misteheyia K10/Ib within the 30–35 cm level, were significantly higher in δ18O, ranging from –2.2‰ to –0.9‰ (n=8), with a mean value of –1.7‰±0.4 (Table 5). These whole– shell δ18O results are in agreement with the intrashell δ18O values described above.

4.4 Carbon stable isotope values of modern shells

4.4.1 Intra-shell data

The Suess effect–corrected δ13C values obtained from the modern H. melanostoma shell

Amm80H5 ranged from –10.0‰ to –8.2‰ (n=55), with a total range of 1.8‰ (Table 4, Fig. 4B) and showed a mean δ13C value of –8.8‰ ±0.4 (Fig. 7G).

4.4.2 Whole shell data

The Suess-effect corrected δ13C values of eight entire modern Helix melanostoma shells from Algeria ranged from –10.1‰ to –8.2‰, with a mean value of –9.3‰±0.7 (Table 5; Fig.

6B). Shells collected during 1973 ranged in δ13C values from –10.8‰ to –9.3‰, with a mean value of –9.8‰±0.4. Shells collected during 1930 ranged in δ13C from –9.4‰ to –8.2‰, with a mean value of –9.1‰±0.6. Thus, modern shells from both collecting years showed comparable

13 13 δ C in the shell, with mean δ C values of shells from 1930 being ~0.7‰ higher than shells from

1973.

4.5 Carbon stable isotope composition of archeological shells

4.5.1 Intra-shell data

The δ13C values for six archaeological Helix melanostoma specimens ranged from –

12.0‰ to –8.2‰ (Table 4; Fig. 7A–F). The 6,550–6,800 cal BP shell, collected at Aïn

Misteheyia K10/Ib within the 30–35 cm level, has a mean δ13C value of –9.3 ± 0.3‰, ranged

from –9.8‰ to –8.7‰ (n=39) (Fig. 7F). The 7,550–7,750 cal BP shell, collected at Aïn

Misteheyia K10/Ib within the 30–35 cm level, has a mean δ13C value of –9.4 ± 0.5‰, varying between –10.3‰ and –8.5‰ (n=30) (Fig. 7E). The 7,900–8,000 cal BP shell, collected from Kef

Zoura D excavation unit F20B at the 82–104 cm level, has the lowest δ13C value, with a mean of

–11.3 ± 0.4‰, ranging from –12.0‰ to –10.6‰ (n=23) (Fig. 7D). The 8,800–8,850 cal BP shell, collected from Kef Zoura D excavation unit T20–5 at the 80–90 cm level has a mean δ13C value of –9.7 ±0.8‰, ranged from –11.3‰ to –8.6‰ (n=42) (Fig. 7C). The 9,900–10,100 cal BP shell, collected at Aïn Misteheyia K9 within the 140–145 cm level, has a mean δ13C value of –9.6 ±

0.3‰, varied between –10.3‰ and –8.9‰(n=54) (Fig. 7B). Finally, the 9,800–10,100 cal BP shell, collected at Aïn Misteheyia K9 within the 140–145 cm level, has a mean δ13C value of –

9.5 ±0.5‰, ranging from –10.4‰ to –8.7‰ (n=34) (Fig. 7A).

In summary, modern shells showed the highest δ13C values (Avg. δ13C= –8.8‰), even after

Suess Effect correction, whereas archeological shells were slightly lower in δ13C (Avg. δ13C= –

9.8‰) values, particularly the 7,900–8,000 cal BP shell, which exhibited the lowest δ13C values

(Avg. δ13C= –11.3‰) throughout the record (Fig. 4B; Fig. 7D).

Intrashell δ13C values do not exhibit consistent seasonal cycles as observed in the δ18O profiles of many shells (Fig. 5). Interestingly, the earliest (ontogenetically older) parts of the shells always recorded higher δ13C values than the average value for that shell (Fig. 7).

4.5.2 Whole shell data

The δ13C values of entire archaeological Helix melanostoma shells (n=24) from the

Télidjène Basin, Algeria ranged from –10.3‰ to –8.8‰, with a mean value of –9.4‰±0.4

(Table 5; Fig. 6B). 10,400–9,900 cal BP shells, collected from Aïn Misteheyia M10 excavation

level 135–140 cm and Aïn Misteheyia K9 level 140–145 cm, showed δ13C values ranging from –

10.1‰ to –9.2‰ (n=8), with a mean value of –9.6‰±0.3. 8,600–8,850 cal BP shells, collected from Kef Zoura D excavation unit T20–5 within the 80–90 cm level, ranged from –10.3‰ to –

8.8‰ (n=8), with a mean value of –9.4‰±0.5. Finally, the 6,550–7,750 cal BP shells, collected from Aïn Misteheyia K10/Ib excavation level 30–35 cm, ranged from –9.5‰ to –9.0‰ (n=8), with a mean value of –9.3‰±0.2. Although the mean shell δ13C value of each analyzed time interval is similar, the range of δ13C values seems variable between shells (Table 5).

5. Discussion

5.1 Environmental significance of δ18O in modern shells

In land snails, ingested liquid water (i.e., precipitation) is considered the primary control on snail body water δ18O and shell δ18O because shell carbonate is precipitated from the animal's extrapalial fluid (Prendergast and Stevens, 2014). A field study from Libya showed that precipitation δ18O was the primary control on the body water δ18O values of Helix melanostoma

(Prendergast et al., 2015). Considering that Helix melanostoma from Algeria probably exhibits similar ecology, physiology and behavior compared with individuals from Libya, it can be

18 assumed that precipitation is also the primary control on shell δ O values in Algeria. Several other studies that have measured other species of modern snails from different regions found similar correlations between rain and shell δ18O (e.g., Lécolle, 1985; Yanes et al., 2009;

Zanchetta et al., 2005). The measured shell δ18O values, however, is typically several permil more positive than expected if in equilibrium with rainfall (Lécolle, 1985), and this has been

explained by water loss through evaporative processes experienced by the snail during its lifetime (Balakrishnan and Yapp, 2004).

The δ18O values of Helix melanostoma modern shells from this study are 1.1‰ higher than measured local rainwaters, on average. The group of eight-measured modern whole–shells show the largest range in δ18O values, between –3.3‰ and –0.1‰ (Fig. 6A). This large range in shell

δ18O values suggests climate variability associated to different source water trajectories influencing North Africa. The 1930 shells are ~2‰ more negative in δ18O than shells retrieved in

1973. This drastic difference between groups of shells can be explained by different climate regimes at those two decades. For example, a drought period began around 1965 in the western

Sahel region (Nicholson et al., 1998; Zeng, 2003). It is possible that this drought event eventually affected regions to the north, including Algeria around 1973, resulting in shells growing during drier conditions and therefore, with higher shell δ18O values. Alternatively, this isotopic difference between individuals of the same species, size and region, but collected at different times (1973 versus 1930) could be explained as variations in active and dormant periods of snails. However, the large isotopic difference between shells from both periods seems too large to be explained by variations in active period alone.

Modern Algerian Helix melanostoma shells exhibit more negative δ18O values (~1‰, on average) compared to analyzed Libyan Helix melanostoma δ18O values by Prendergast et al.

(2015). This can be explained by different δ18O values of the modern precipitation in both regions. Based on the Online Isotope Precipitation Calculator (OIPC) mean monthly estimates, the modern precipitation δ18O value in Algeria during the snail active period is about –4.0‰

(SMOW), assuming minimal shell growth during the summer season. Using the same OIPC estimates for Libya and assuming minimal snail growth in the summer season as well, modern

precipitation δ18O values in Shahat, Libya are –3.4‰, on average. This near 1‰ offset in rainwater δ18O values agrees with the observed ~1‰ offset in land snail shell δ18O from Algeria and Libya (Fig. 8A). These coherent relationships further reinforce that Algerian Helix melanostoma shells primarily reflect precipitation δ18O values in the shell and are useful for paleoenvironmental studies.

18 The intra–shell samples represent the fluctuations in shell δ O values throughout the snail’s lifespan. The modern Helix melanostoma measured via intra–shell method was also collected in 1973 and showed an average δ18O value of –0.1‰ (Fig. 4; Fig. 5A). The relatively high intra–shell δ18O values obtained here are coherent with whole shell δ18O values of 1973 specimens (Fig. 6A). The analyzed shell shows two to three marked seasonal cycles along ontogeny, suggesting that, if indeed these cycles represent near yearly growth episodes, then,

Helix melanostoma should have had a lifespan of around 2–3 years, which is consistent with lifespan estimates from the ecological literature. Therefore, it is assumed that the observed intra– shell δ18O value cycles likely mimicked, at least partially, the seasonal variation of local rain

δ18O.

5.2 Paleoclimatic inferences from archeological shell δ18O values

The isotopic composition of snail shells retrieved from archaeological records provide invaluable local climatic and environmental context during ancient human occupation. Thus, archeological shells can be used to test how climate change may correlate with shifts in human subsistence and behavior in the past.

Whole shell δ18O values at three major time-intervals over the course of the early to middle Holocene suggest significant variations in precipitation δ18O in Algeria as recorded in the

18 shells. Thus, during the earliest Holocene (10,400–9,900 cal BP) shell δ O values were significantly negative (–3.2‰ to –1.6‰). Similarly, around the early Holocene (8,850–8,600 cal

BP), shell δ18O values remained low (–3.2‰ to –1.1‰). These results suggest that between

10,400 and 8,600 cal BP, NE Algeria was significantly wetter, with lower precipitation δ18O values recorded in snail shells than at present. These results are consistent with the previously described “African Humid Period” of the early Holocene studied throughout different regions of

NW Africa, a time of increased monsoon activity in North Africa from 11,000 to 6,000 cal BP

(Adkins et al., 2006; deMenocal et al., 2000a).

Interestingly, whole shells from after the 8,200 cal BP event (dated between 7,750–6,550 cal BP) exhibited significantly higher δ18O values (–2.2‰ to –0.9‰) (see Table 5, Fig. 6A)

These higher shell δ18O values suggest significantly drier conditions (i.e., higher precipitation

δ18O values and lower rainfall totals) than during the two preceding wetter time–intervals.

Accordingly, archeological Helix melanostoma shells from NE Algeria support the hypothesis that the 8,200 cal BP event was the beginning of a pronounced arid episode in the North African region that seems to have lasted several centuries.

The intra-shell δ18O values of analyzed H. melanostoma specimens showed comparable patterns to the whole-shell oxygen isotope results discussed above. Shells dated between 10,100–

8,800 cal BP have, on average, lower intra-shell δ18O values likely in response to increased precipitation during the Early Holocene (Fig. 4A; Fig. 5A–C). In contrast, shells dating after

8,000 cal BP showed intra-shell δ18O values that were significantly higher, in agreement with whole-shell δ18O results described above. The 7,550–7,750 cal BP shell retrieved from Aïn

Misteheyia is drastically enriched in 18O in comparison to any other analyzed shells (Fig. 5E).

This supports a climate scenario of drier atmospheric conditions (lower precipitation amount) in

NE Algeria after 8,200–8,000 cal BP (Rognon, 1987; Shipp et al., 2013). This interpretation from archeological snail shells is consistent with the well–documented 8,200 cal BP cold event in the Northern Hemisphere (Alley and Ágústsdóttir, 2005; Thomas et al., 2007) and other studies in the region that have documented noticeable aridity during and immediately after the

8,200 cal BP event (Shipp et al., 2013).

Whole shell oxygen isotope analyses of archeological Helix melanostoma from Libya measured by Prendergast et al. (2016) showed comparable trends to individuals from NE

Algeria, supporting the interpretation that comparable climate shifts occurred during the early

Holocene in the broader geographical context of North Africa (Prendergast et al., 2016). Thus, archeological land snail records from both Libya and Algeria support the presence of a marked arid event at between 8,000 and 7,300 years ago. As observed for modern shells, whole-shell

δ18O data of archeological shells from Libya reported by Prendergast et al. (2016) consistently exhibited ~1‰ more positive δ18O values than Algerian intra-shell and whole-shell δ18O values of archaeological specimens (Fig. 8A). The observed patterns suggest that throughout the early- middle Holocene, precipitation δ18O values during snail active period in Algeria has remained, on average, 1‰ higher than in Libya.

Intra–shell δ18O values can be indicative of seasonal changes in rainfall within the snail active period. Two samples that date closely after the 8,200 cal BP cold event (Fig 5D–E) have little to negligible fluctuation in intra–shell δ18O values. The apparent lack of seasonality observed in these two specimens could be explained by a change in snail active periods in response to increased aridity and perhaps, decreased temperature. Thus, Helix melanostoma may have been unable to adapt to an abruptly changing environment quick enough, resulting in shorter lifespans. Alternatively, the degree of seasonality in the precipitation δ18O following the

8,200 cal BP event may have been significantly reduced at that time. These two hypotheses, however, remain to be tested in the future with additional samples.

5.3 Environmental significance of δ13C in modern shells

Diet is the primary factor driving δ13C values in terrestrial snail shells (Balakrishnan and

Yapp, 2004), and therefore field studies have observed correlations between the δ13C of the snail shell and the local vegetation (Yanes et al., 2013; Prendergast et al., 2017). According to laboratory experiments using Helix aspersa (currently known as Cornu aspersum), snail shell carbonate is approximately 13‰ higher in δ13C than their dietary intake (Metref et al., 2003;

Stott, 2002). The measured modern individuals from Algeria showed a rather narrow range (from

13 –10.1‰ to –8.2‰) in shell δ C, confirming that Helix melanostoma have followed a pure C3 plant diet only, (with predicted plant δ13C values < –23‰; see section 3.5). These results are consistent with the current dominance of C3 vegetation in Algeria and are comparable to results reported by Prendergast et al. (2017). Modern Helix melanostoma from Libya also followed a pure C3 plant diet without noticeable influence of other carbon sources (Prendergast et al., 2017).

Accordingly, variations in shell δ13C values of archeological shells from northern Africa should likely reflect variations in the water use efficiency of C3 plants ingested by the snails

(Prendergast et al., 2017). In contrast to δ18O values, whole shells collected in 1973 showed similar δ13C values to whole shells retrieved in 1930 (Fig. 6B). This suggests that potential drought fluctuations affecting northern Africa in the 1900’s have impacted snails (and the

18 13 precipitation δ O values) more significantly than C3 plants (and the plant δ C values).

Intra-shell δ13C values can be used to evaluate seasonal variations in a snail’s diet, and therefore, seasonal variations in vegetation δ13C (Yanes et al., 2014). The modern shell collected

in 1973 that was analyzed along ontogeny did not show distinctive seasonal cycles in δ13C values

(Fig. 7G) suggesting that the snail diet remained comparable along the snail’s lifespan. The intra–shell δ13C values are consistent with whole shell δ13C values described above.

5.4 Paleovegetation inferences from archeological shell δ13C

Carbon isotope ratios in land snail shells can be used as a proxy for paleodistribution patterns of vegetation as well as identifying water stress in environments dominated by C3 type vegetation (Prendergast et al., 2016). The dominance of C3 vegetation in the Télidjène Basin region is indicative of temperate climate conditions. Even though there is a significant fractionation between snail diet and shell, shell δ13C values often correlate with δ13C values of local vegetation (Balakrishnan and Yapp, 2004). Ingestion of plants with low δ13C values will be seen as low δ13C values within the carbonate shell, and high δ13C plant values will result in higher δ13C values in the snail shell (Stott, 2002).

Whole-shell δ13C of archaeological samples ranged from –10.2‰ to –8.7‰ suggesting that land snail diet has consisted of predominantly C3 plant intake throughout the Holocene without

13 any convincing incorporation of C4 plants. Thus, snail shell δ C supports the hypothesis that NE

Algeria has been dominated by C3 type vegetation throughout the early–middle Holocene. Shipp et al. (2013) concludes that C3 plants were dominant at Ain Misteheyia during the early–mid

Holocene based on phytolith evidence. Variations in whole shell δ13C may be explained by fluctuations in water stress experienced by plants ingested by the snails. Similar findings have been documented in land snails from Libya and indicate a dominance of C3 vegetation during the early–middle Holocene in North Africa (Fig. 8B) (Prendergast et al., 2016, 2017). However, in contrast to whole-shell δ18O values, whole-shell δ13C results do not show statistically significant

variations throughout the Holocene. This suggests that shell δ18O values are more sensitive to moisture shifts than shell δ13C.

Intra-shell δ13C values can be used to evaluate seasonal vegetation variations in diet

(Baldini et al., 2007; Yanes et al., 2014, 2012). Interestingly, the six archaeological samples that were analyzed for δ13C along ontogeny did not show clear seasonal cycles as documented in most shell δ18O profiles. This suggests that the snail’s vegetation intake remained comparable year round. Measured shells showed more negative δ13C values during early ontogenic (juvenile) stages than towards the last growth episodes (Fig 7A–F). Higher δ13C values in the juvenile stages of shell growth could be explained by a higher intake of limestone to promote shell growth (Goodfriend, 1999; Yanes et al., 2012). Therefore, snail’s vegetation intake may have been similar throughout its lifespan.

The 7,900–8,000 cal BP shell displays the lowest mean δ13C value, approximately ~2‰ more negative compared to the other five Holocene samples analyzed (Fig. 7D). All samples except the 7,900–8,000 cal BP shell displayed relatively consistent mean δ13C values near –

9.5‰. This implies that snail diet and/or environmental conditions affecting vegetation were changing around 8,000 cal BP. The lower shell δ13C values around 8,000 cal BP could suggest

18 that the C3 plants are reflecting a different isotopic signature. In contrast to intra-shell δ O patterns, intra-shell δ13C values do not show a significant increase with respect to other shells, suggesting that an aridity event was not as preserved in the consumed vegetation by the snails. If this interpretation is correct, then land snails appear to be more sensitive to fluctuations in

13 humidity and may be a more sensitive moisture proxy than shell δ C values in C3 dominated regions.

5.5 Climate Mechanisms explaining the observed patterns

Archeological whole shell and intra–shell δ18O values of Helix melanostoma have shown that precipitation δ18O fluctuated during the early-middle Holocene in NE Algeria. Snails suggest that conditions were humid during the early Holocene (between ~10,400 and 8,600 cal BP) but were interrupted by a noticeable dry event between at least 8,000–7,550 cal BP. These paleo– precipitation estimates from snails are in agreement with other studies in North Africa (Adkins et al., 2006; Prendergast et al., 2016) and can be explained by fluctuations in climate mechanisms operating during the Holocene. It has been suggested that the rapid influx of cold water into the

North Atlantic during the 8,200 cal BP event caused a southward shift in the inter–tropical convergence zone (ITCZ), which resulted in drier (and most likely cooler) conditions in Africa

(Wang et al., 2001). Studies have suggested that the 8,200 cal BP event was likely longer-lived in Africa than the duration documented in the Greenland ice cores. Thus, numerous studies suggest that conditions became more arid between ~8,200–7,000 cal BP in northern Africa

(Alley and Ágústsdóttir, 2005; DeMenocal et al., 2000b; Lamb and Kaars, 1995; Prendergast et al., 2016). Several other studies have shown that cooling temperatures in the North Atlantic caused droughts in the Asian and African monsoonal regions (Alley and Ágústsdóttir, 2005;

Wang et al., 2001).

The African Monsoon system has been considered to be the dominant precipitation source in North Africa (Adkins et al., 2006). West African Monsoon today responds to variations in the

ITCZ. Thus, a south migration of the ITCZ results in a dry episode in NW Africa whereas a north migration of the ITCZ results in increased rainfall. It is possible that around the 8,200 cal

BP event, a southward shift of the ITCZ resulted in reduced West African Monsoon season and

ultimately, caused a marked drought event that has been clearly recorded in Helix melanostoma shells.

5.6 Has Holocene local climate change triggered cultural shifts in NE Algeria?

Recent zooarchaeological studies have observed changes in subsistence strategies of

Capsian populations in North Africa during the Holocene (Aouadi et al., 2014; Jackes and Lubell

2008; Lubell, 2004, 2016;). The results presented here support the hypothesis that climate change may have impacted the Capsian subsistence regime in NE Algeria. It is agreed that there was a change between Typical and Upper Capsian in lithic tools, species of animals that were exploited, and change in dominant snail species represented, all around 8,000–7,550 cal BP

(Lubell, 2016; D. Lubell, 2004). AMS 14C dates of land snail shells collected from archaeological layers coinciding with the Capsian subsistence change yield 2–σ age ranges

(8,000–7,900 and 7,750–7,550) that coincide with times following the recognized 8,200 cal BP cold event in northern Africa. Stable oxygen isotope analysis of shells within the layers exhibiting abrupt cultural changes exhibited the highest values indicative of drier conditions

(Fig. 9). The results of this study have important implications for the prehistoric archaeology of

NW Africa. The changing environment, inferred from land snail shells, likely impacted water availability and thus the abundance of both plant and animal species in the region. The archaeological record of both Aïn Misteheyia and Kef Zoura D imply that Capsian groups adapted to their changing environment by altering their subsistence practices. Although other factors not contemplated here may have played a role in the cultural shift of Capsian groups in

NE Algeria following the 8,200 cal BP event, local snail records suggest that multi-century to millennial climate change should have at least partially impacted human groups in the region.

6. Conclusions

Whole-shell δ18O values of archeological Helix melanostoma snails retrieved from two archeological records in NE Algeria illustrate that conditions were significantly wetter during the early Holocene (between ~10,400 and 8,600 cal BP) but shifted to drier conditions between

8,000–7,550 cal BP. These inferred early Holocene wetter and drier scenarios from snail shells coincide with the African Humid Period and the 8,200 cal BP cold event, respectively. Intra– shell δ18O values along ontogeny showed significantly reduced seasonality following the 8,200 cal BP event, suggesting that snails either experienced shorter growing periods or that seasonality in precipitation was less marked than during wetter conditions. The results from NE

Algeria are consistent with archeological Helix melanostoma δ18O records from Libya and suggest that the sharp drought event following 8,200 cal BP was noticeable throughout northern

Africa and is clearly reflected in land snail shells. This dry episode likely affected Capsian groups living in the region and may have in part driven subsistence modifications following

8,200 cal BP. Whole-shell and intra–shell δ13C values of archeological shells support the view that C3 plants were dominant throughout the early Holocene, and that the potential effects of

18 water stress in consumed C3 plants were less noticeable than in snail shell δ O. These results provide evidence for rapid climate change that coincides with documented cultural and subsistence change within the Capsian culture. This documented cultural change is likely due to forced adaptations in response to the changing environment (i.e., increasing aridity), and thus gives insights into the resiliency of the Capsian peoples. Although the 8,200 cal BP event is known as a cold event in much of the Northern Hemisphere, it was here documented as an arid episode in NE Algeria. Understanding past cultural responses to rapid climate changes may help assessing affects modern climate change in regions across the globe. Global climate phenomena

can have different regional impacts; therefore it is important to understand how global climate events are felt on a regional and even local scale.

Figures

Figure 1: Geographical setting of the Maghreb region in NW Africa. Countries of the Maghreb include (east to west) Mauritania, Morocco, Algeria, Tunisia, and Libya.

Figure 2: Geographical location of the studied archeological sites in northeast Algeria. Figure courtesy of David Lubell, University of Waterloo. Modified from the original in Lubell et al. (1976).

30# 100#

A B' 90# Total#Average## 25# 80# PrecipitaJon:#524#mm##

70# 20# 60#

15# 50#

40# 10# 30# Precipitation (mm) Precipitation Temperature (°C) Temperature 20# 5# 10#

0# 0#

80# 2# C' D OIPC# 75# 1# ISOSCAPE# GNIP#

70# ' 0# 65# ?1# 60# ?2# 55# ?3# 50# ?4# 45# δ18O'(‰,'V:SMOW) Rela%ve'Humidity'(%)' 40# ?5# 35# ?6# 30# ?7# Jan# Feb# Mar# Apr# May#June# July# Aug# Sept# Oct# Nov# Dec# Jan# Feb# Mar# Apr# May#June# July# Aug# Sept# Oct# Nov# Dec#

Figure 3: Present-day climate data for study area in NE Algeria. A: Average monthly precipitation (mm) for 1998–2006 obtained from NOAA climate database (www.noaa.gov) B: Average monthly temperature ( °C) for 1998-2006 obtained from NOAA climate database (www.noaa.gov). C: Average monthly relative humidity taken from NOAA (www.noaa.gov). D: Average δ18O of the precipitation for study site (Grey) obtained from the Online Isotopes in Precipitation Calculator (OIPC)(www.waterisotopes.org) and Average δ18O of the precipitation at the Algiers, Algeria water station from 1998-2006 (Red) obtained from the Global Network of Isotopes in Precipitation database GNIP (IAEA.org).

n=30

n=54 n=34

n=39 n=42 n=23 ‰(PDB) O 18

δ n=55

- Shell Shell

9,900– 9,800– 8,800– 7,900– 7,550– 6,550– Modern, 10,100 10,100 8,850 8,000 7,750 6,800 1973 B 2-σ Age (cal BP) n=55 n=30 n=42 n=54 n=39 n=34

C‰(PDB) n=23 13 δ Shell Shell

9,900– 9,900– 8,850– 7,900– 7,550– 6,550– Modern, 10,100 10,100 8,800 8,000 7,750 6,800 1973 2-σ Age (cal BP)

Figure 4: Box plots of intra-shell Helix melanostoma δ18O (A) and δ13C (B) divided by their respective age. Each box plot depicts multiple samples from an individual shell. n = number of samples analyzed per shell.

4 4 4 A BB C C 2 9,900–10,100 cal BP 2 9,800–10,100 cal BP 2 8,800–8,850 cal BP

(PDB) 0 0

‰ -2 -2 -2 O

18 -4 -4 -4 δ

-6 -6 -6

-8 -8

Shell Shell -8 1 5 9 13 17 21 25 29 33 37 41 45 49 53 1 5 9 13 17 21 25 29 33 1 5 9 13 17 21 25 29 33 37 41 4 4 4 F D 7,900–8,000 cal BP E 7,550–7,750 cal BP F 6,550–6,800 cal BP 2 2 2

(PDB) 0 0 0

‰ -2 -2 -2 O

18 -4 -4 -4 δ -6 -6 -6

-8 -8 -8 Shell Shell

1 3 5 7 9 11 13 15 17 19 21 23 1 5 9 13 17 21 25 29 1 5 9 13 17 21 25 29 33 37

4 Distance from the lip (mm) Distance from the lip (mm) G 2 Modern, 1973 (PDB)

‰ -2 O

18 -4 δ

-6

Shell Shell -8

1 5 9 13 17 21 25 29 33 37 41 45 49 53 Distance from the lip (mm)

Figure 5: Intra-shell δ18O values in Helix melanostoma shells throughout snail lifespan. Dashed line represents the average δ18O value within a shell. Intrashell δ18O values along shell growth direction are presented separately for a snail shell dated at 9,900–10,100 cal BP (A); 9,800–10,100 cal BP (B); 8,800–8,850 cal BP (C); 7,900–8,000 cal BP (D); 7,550– 7,750 cal BP (E); 6,550–6,800 cal BP (F); and modern, 1973 (G). Sample provenance information listed in Table 3.

n=8 n=8

n=8 n=5 n=3 ‰(PDB) O 8 1 δ Shell Shell

9,900– 8,600– 6,550– Modern, Modern, 10,400 8,850 7,750 1930 1973

2-σ Age (cal BP)

B n=5

n=8

n=8 n=8 n=3 C‰(PDB) 13 δ Shell Shell

9,900– 8,600– 6,550– Modern, Modern, 10,400 8,850 7,750 1930 1973

2-σ Age (cal BP)

Figure 6: Box plots of Helix melanostoma average δ18O (A) and δ13C (B) according to their respective age. Each box plot depicts whole-shells that vary in age within their respective age range. n = number of individual shells analyzed per unit (see table 5).

!6$ !6$ !6$ A B C C' !7$ 9,900–10,100'cal'BP'!! !7$ 9,800–10,100'cal'BP! !7$ 8,800–8,850 cal BP !8$ !8$ !8$

!9$ !9$ !9$ C‰(PDB)

13 !10$ !10$ !10$ δ !11$ !11$ !11$

!12$ !12$ !12$

Shell Shell !13$ !13$ !13$ 1$ 5$ 9$ 13$ 17$ 21$ 25$ 29$ 33$ 37$ 41$ 45$ 49$ 53$ 1$ 5$ 9$ 13$ 17$ 21$ 25$ 29$ 33$ 1$ 5$ 9$ 13$ 17$ 21$ 25$ 29$ 33$ 37$ 41$

!6$ !6$ !6$ D F' !7$ 7,900–8,000'cal'BP! !7$ E' 7,550–7,750'cal'BP' !7$ 6,550–6,800'cal'BP' !8$ !8$ !8$

!9$ !9$ !9$ C‰(PDB)

13 !10$ !10$ !10$ δ !11$ !11$ !11$

!12$ !12$ !12$ Shell Shell

!13$ !13$ !13$ 1$ 5$ 9$ 13$ 17$ 21$ 25$ 29$ 33$ 37$ 1$ 5$ 9$ 13$ 17$ 21$ 25$ 29$

1$ 5$ 9$ 13$ 17$ 21$ !6$ Distance from shell lip Distance from shell lip !7$ G' Modern,'1973'! (mm) (mm) !8$

!9$ C‰(PDB)

13 !10$ δ !11$

!12$

Shell Shell !13$ 1$ 5$ 9$ 13$ 17$ 21$ 25$ 29$ 33$ 37$ 41$ 45$ 49$ 53$

Distance from shell lip (mm)

Figure 7: Intra-shell δ13C values in Helix melanostoma shells throughout snail lifespan. Dashed line represents the average δ13C value within a shell. Intrashell δ13C values along shell growth axis are presented separately for a snail dated at 9,900–10,100 cal BP (A); 9,800–10,100 cal BP (B); 8,800–8,850 cal BP (C); 7,900–8,000 cal BP (D); 7,550–7,750 cal BP (E); 6,550–6,800 cal BP (F); and modern, 1973 (G). Sample provenance information listed in Table 4.

A 3

-1 ‰(PDB)

O -2 8 1

δ -3

-4 Shell Shell

-5

-6 11 10 9 8 7 6 5 4 3 2 1 0 -1

-5 B -6

-7

-8

‰(PDB) -9 C 3 1

δ -10

-11 Shell Shell

-12

-13 11 10 9 8 7 6 5 4 3 2 1 0 -1 Age (Ka BP)

Figure 8: Comparison of δ18O (A) and δ13C (B) of Helix melanostoma from NE Algeria (this study; red quadrat symbols) and Libya (from Prendergast et al., 2016; blue quadrat symbols). Average shell δ18O and δ13C values from the intrashell analyses in the present work are also shown in the plot for comparison (red diamond symbols). Shaded region represents the timing of the 8,200 cal BP event in North Africa.

A B Typical Capsian Upper Capsian Typical Capsian Upper Capsian

‰(PDB) ‰(PDB) O O 8 8 1 1 δ δ Shell Shell Shell

9,950– 8,600– 6,550– 9,900– 9,800– 9,530- 7,900– 7,550– 6,550– 10,400 8,850 7,750 10,100 10,100 9,560 8,000 7,750 6,800

Age (cal BP) Age (cal BP)

Figure 9: Relationship between whole shell (A) and intra-shell (B) Helix melanostoma δ18O and the documented change in subsistence strategies within the Capsian archaeological records in NE Algeria. Shaded region represents the onset of the 8,200 cal BP event and approximate longevity of an aridity event in North Africa.

Tables

Table 1: Modern monthly climate data in NE Algeria for the recording period between 1998 and 2006.

Month Precipitation Temperature Relative Estimated Measured a b 18 18 (mm) (°C) Humidity δ O (‰, δ O (‰, c d e (%) V-SMOW) V-SMOW)

January 78.6 6.0 76 -6.6 -4.8 February 42.4 6.8 73 -5.8 -4.6 March 33.8 10.6 72 -5.2 -3.1 April 50.0 13.2 70 -3.4 -2.5 May 53.5 17.3 65 -1.1 -0.8 June 15.1 23.4 54 0.7 0.9 July 6.0 26.0 42 0.3 0.0 August 11.8 25.9 48 0.7 0.0 September 41.4 21.2 60 -1.2 -3.0 October 30.2 17.7 68 -2.2 -2.1 November 67.6 11.0 75 -4.2 -5.5 December 94.0 7.3 76 -6.2 -4.8 Average 43.7 15.6 65 -2.9 -2.5

a: Average monthly precipitation (mm) for 1998–2006 obtained from NOAA climate database (www.noaa.gov) b: Average monthly temperature ( °C) for 1998-2006 obtained from NOAA climate database (www.noaa.gov) c: Average monthly relative humidity (%) acquired from the NOAA (www.noaa.gov). d: Average δ18O of the precipitation obtained from the Online Isotopes in Precipitation Calculator (OIPC) (Bowen, (2017); Bowen et al., (2005); www.waterisotopes.org) e: Average δ18O of the precipitation from Algiers, Algeria water station data from GNIP (www.IAEA.org)

Table 2: AMS 14C dates for Helix melanostoma shells from Capsian archaeological sites, NE Algeria.

Sample ID Site Provenance 14C age ± Corrected ± 2-σ Age Median Lab (BP)a 14C age (Cal BP)c Probability Code (BP)b AMK9140 _ Aïn K9 140– 9,900- UCI- 145H1 Misteheyia 145 cm 9,445 20 8,969 52 10,100 10,100 176116

APUC- Kef Zoura T20–5 80- 8,800- UCI- KZD3 D 90 cm 8,595 25 8,119 54 8,850 9,050 194114

APUC- Kef Zoura F20B: 82– 7,900- UCI- KZD2E D 104 cm 7,650 30 7,174 54 8,000 8,000 194117

APUC- Aïn K10/1b 30– 7,500- UCI- AM1B Misteheyia 35 cm 7,270 25 6,794 54 7,750 7,650 194116

APUC- Aïn K10/1b 30– 6,550- UCI- AM1A Misteheyia 35 cm 6,365 25 5,889 57 6,800 6,700 194115

a: 14C ages from the shell lip. b: 14C ages corrected for old carbon by subtracting 476±48 (Hill et al., 2017). c: 2-σ Age (Cal BP) rounded to nearest 50. Calibrations were done using IntCal13 and CALIB 7.10 (Stuiver and Reimer, 1993).

Table 3: Intra-shell oxygen stable isotopes of modern and archaeological Helix melanostoma shells from Capsian archaeological sites, NE Algeria.

Sample ID Collection Provenance Age # of Average STD Min Max Range Location (cal BP) Samples δ18O‰ (PDB)

Amm80H5 Télidjène N/A Modern, 55 -0.5 1.4 -3.0 3.5 6.5 Basin, 1973 Algeria APUC- Aïn K10/1b 6,550- 39 -1.8 0.9 -4.6 -0.3 4.3 AM1A Misteheyia 30–35 cm 6,800 APUC- Aïn K10/1b 7,550- 30 1.4 0.2 0.7 1.8 1.1 AM1B Misteheyia 30–35 cm 7,750 APUC- Kef Zoura F20B: 82– 7,900- 23 -1.5 0.4 -2.6 -1.1 1.5 KZD2E D 104 cm 8,000 APUC- Kef Zoura T20–5 80- 8,800- 42 -3.0 2.0 -7.0 -0.5 6.5 KZD3 D 90 cm 8,850 AMK9140_ Aïn K9 140– 9,900- 54 -1.2 1.0 -3.6 0.6 4.2 145H1 Misteheyia 145 cm 10,100 APUC- Aïn K9 140– 9,800– 34 -2.3 1.5 -4.8 -0.4 4.4 AM2B Misteheyia 145 cm 10,100

Table 4: Intra-shell carbon stable isotopes of modern and archaeological Helix melanostoma shells from Capsian archaeological sites, NE Algeria.

Sample ID Collection Provenance Age # of Average STD Min Max Range Location (cal BP) Samples δ13C‰ (PDB) Amm80H5 Télidjène N/A Modern 55 -8.8 0.4 -10.0 -8.2 1.8 Basin, Algeria 1973 APUC- Aïn Misteheyia K10/1b 30– 6,550- 39 -9.3 0.3 -8.7 -9.8 1.1 AM1A 35 cm 6,800 APUC- Aïn Misteheyia K10/1b 30– 7,550- 30 -9.4 0.5 -10.3 -8.5 1.8 AM1B 35 cm 7,750 APUC- Kef Zoura D F20B: 82– 7,900- 23 -11.3 0.4 -12.0 - 1.4 KZD2E 104 cm 8,000 10.6 APUC- Kef Zoura D T20–5 80- 8,800- 42 -9.7 0.8 -11.3 -8.6 2.7 KZD3 90 cm 8,850 AMK9140 Aïn Misteheyia K9 140– 9,900- 54 -9.6 0.3 -10.3 -8.9 1.4 _-145H1 145 cm 10,100 APUC- Aïn Misteheyia K9 140– 9,800– 34 -9.5 0.5 -10.4 -8.7 1.7 AM2B 145 cm 10,100

Table 5: Whole shell oxygen and carbon stable isotopes of modern and archaeological Helix melanostoma shells from NE Algeria.

Sample ID Collection Provenance Age (cal BP) δ 18O‰(PDB) δ13C‰(PDB) Location Télidjène Basin N/A Modern, 1973 -1.3 -7.7 APUC-MOD1 Algeria Télidjène Basin N/A Modern, 1973 -0.1 -8.5 APUC-MOD4 Algeria Télidjène Basin N/A Modern, 1973 -0.8 -8.3 APUC-MOD5 Algeria APUC-MOD6 Algeria N/A Modern, 1930 -1.7 -6.6 APUC-MOD7 Algeria N/A Modern, 1930 -3.3 -8.3 APUC-MOD8 Algeria N/A Modern, 1930 -2.7 -7.8 APUC-MOD9 Algeria N/A Modern, 1930 -1.9 -7.1 APUC-MOD10 Algeria N/A Modern, 1930 -2.8 -7.6 APUC-AMK10-3 Aïn Misteheyia K10/1b 30–35 cm 6,550–7,750 -2.2 -7.9 APUC-AMK10-1 Aïn Misteheyia K10/1b 30–35 cm 6,550–7,750 -2.2 -7.7 APUC-AMK10-8 Aïn Misteheyia K10/1b 30–35 cm 6,550–7,750 -1.7 -7.4 APUC-AMK10-2 Aïn Misteheyia K10/1b 30–35 cm 6,550–7,750 -1.7 -7.6 APUC-AMK10-5 Aïn Misteheyia K10/1b 30–35 cm 6,550–7,750 -1.7 -7.7 APUC-AMK10-6 Aïn Misteheyia K10/1b 30–35 cm 6,550–7,750 -1.7 -7.7 APUC-AMK10-7 Aïn Misteheyia K10/1b 30–35 cm 6,550–7,750 -1.3 -7.6 APUC-AMK10-2 Aïn Misteheyia K10/1b 30–35 cm 6,550–7,750 -0.9 -7.8 APUC-KZD-3 Kef Zoura D T20–5 80–90 cm 8,600-8,850 -1.1 -8.7 APUC-KZD-2 Kef Zoura D T20–5 80–90 cm 8,600-8,850 -2.1 -7.1 APUC-KZD-6 Kef Zoura D T20–5 80–90 cm 8,600-8,850 -2.1 -7.9 APUC-KZD-4 Kef Zoura D T20–5 80–90 cm 8,600-8,850 -2.7 -7.4 APUC-KZD-8 Kef Zoura D T20–5 80–90 cm 8,600-8,850 -2.2 -8.2 APUC-KZD-7 Kef Zoura D T20–5 80–90 cm 8,600-8,850 -2.4 -7.6 APUC-KZD-5 Kef Zoura D T20–5 80–90 cm 8,600-8,850 -3.2 -7.2 APUC-KZD-1 Kef Zoura D T20–5 80–90 cm 8,600-8,850 -3.2 -8.0 APUC-AMK9-1 Aïn Misteheyia K9 140–145 cm 9,900-10,300 -3.1 -8.2 APUC-AMM10-2 Aïn Misteheyia M10 135–140 cm 9,950–10,400 -3.2 -8.1 APUC-AMM10-3 Aïn Misteheyia M10 135–140 cm 9,950–10,400 -2.8 -7.6 APUC-AMM10-4 Aïn Misteheyia M10 135–140 cm 9,950–10,400 -3.0 -7.8 APUC-AMM10-5 Aïn Misteheyia M10 135–140 cm 9,950–10,400 -1.6 -8.5 APUC-AMM10-7 Aïn Misteheyia M10 135–140 cm 9,950–10,400 -1.8 -8.4 APUC-AMM10-1 Aïn Misteheyia M10 135–140 cm 9,950–10,400 -2.1 -8.0 APUC-AMM10-6 Aïn Misteheyia M10 135–140 cm 9,950–10,400 -1.8 -7.6

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