Archaeological Shell Middens Research Articles

The effects of Mid-Holocene foragers on the European oyster in Denmark

Oysters (Ostreidae) play a pivotal role in the health and productivity of marine ecosystems. Their unique ability to filter water, provide habitat, and contribute to nutrient cycling has remained underused in many parts of Europe following the destruction of vast oyster beds in the 19th and 20th centuries. The burgeoning field of oyster restoration for aquaculture has recognized the potential of these bivalves in promoting ecosystem resilience and enhancing biodiversity. Restoring oysters to previous levels requires the establishment of ecological baselines that ideally take into account the long-term changes of animal behavior as well as the surrounding environment prior to significant human intervention, an extremely challenging task. Archaeological shell middens are invaluable baseline archives and provide exclusive insights into past ecosystems. Here, we use demographic information from over 2,000 analyzed European oyster (Ostrea edulis) shells dating from ~5,660 to 2,600 cal BCE (calibrated years BCE), the largest archaeological growth rate dataset of mollusks yet. Through the analysis of size as well as ontogenetic age, we decouple anthropogenic from environmental impacts throughout Denmark. Our data show definitive influence of oyster size-age structure through human harvesting during the Mid-Holocene, with older oysters in the Mesolithic (mean: 4.9 y) than the Neolithic (mean: 3.7 y), irrespective of changes in growth rate. Furthermore, we present the metrics for long-term sustainable harvesting of oysters across environmental and socioeconomic transitions, providing demographic targets for current oyster restoration projects and valuable context in mitigating the impact of modern climatic change.

Shell Midden Archaeology: Current Trends and Future Directions

Since the 19th century, the study of shell middens has played an important role in archaeological research. Shell midden and broader coastal archaeology have transformed our understanding of human relationships with aquatic habitats, demonstrating the importance of marine environments to human evolution and ecology, the colonization of islands and establishment of maritime trade networks, changing social and political dynamics, and a variety of other issues. During the past two decades, shell midden research has greatly increased, marking an exciting time for new discoveries and heightened collaboration with Indigenous communities. Several key research trends in shell midden archaeology during the past 10–15 years include research on site distribution and temporality, underwater archaeology, historical ecology, terraforming, landscape legacies, and community collaboration. These research trends demonstrate the ways in which shell midden archaeologists are shaping our understanding of the human past and environmental change around the world.

A Holocene Seabird Extinction in Maine: The Great Auk

Seabirds are the most threatened of any living group of birds, continuing a larger pattern of elevated Holocene bird extinctions on islands and coastlines. The Great Auk (Charadriiformes: Pinguinus impennis) was found on both coasts of the Atlantic during the Holocene until its last sighting on Iceland in 1844. Far more is known about the population structure and genetic diversity of NE Atlantic populations, and the latest surviving populations were documented from the British Isles in 1834. While sightings from Canada suggest Great Auks disappeared by 1800, no systematic evaluation of extinction timing has been conducted for this coast. Determining extinction timing of the Great Auk in Maine allows a comparison to be made to populations in other areas of the Atlantic Ocean, and raises the question: was the Maine population’s fate different due to regional, cultural, or other factors? There is a single eye-witness record in the late 17th century at “Black Point”, now Scarborough, Maine. To address this gap, we compiled a radiocarbon dataset on associated material from Maine archaeological shell middens. These 91 dates from 13 sites situate the Great Auk in Maine from about 180 to 4,555 years before present. The majority of these dates are from charcoal samples, but also include shells, ceramics, and bone, and cultural contexts span the Middle and Late Ceramic Periods. To account for differences in stratigraphic control and sampling material, we assigned quality scores, and used these scores to run a sensitivity analysis in extinction timing with the GRIWM model. Disentangling the spatiotemporal dynamics of the Great Auk extinction in Maine is useful in determining how to conserve current species in decline and modern insular seabirds in Maine, such as the puffin. Future study will include new radiocarbon dating of bones as well as isotopic and morphometric analysis to unfold more chapters of the Maine Great Auk’s narrative.

Climate change, migrations, and the peopling of sine-Saloum mangroves (Senegal) in the past 6000 years

We present a reconstruction of human demography and shell fishing activity in the Sine-Saloum mangrove Delta (Senegal) in the past 6000 years using the summed probability density (SPD) of radiocarbon dates in archaeological shell middens. We explore how this local history relates to the climatic and political history of West Africa. We find that traces of human presence were scarce from 6000 to 2000 yr BP, partly because the geomorphology of the estuary was less favorable to human settlements at that time. A specialized shell fishing population migrated massively to the Sine-Saloum around 2000 yr BP, at the end of the aridification trend that followed the African humid period. This population, likely coming from the northern coast in search of land and resources, fleeing from aridity and the subsequent warfare, found refuge in the coastal mangroves and reached a maximum activity at about 1700 yr BP. This period corresponds to the beginning of trans-Saharan trade, and to a political complexification that would give rise to the Ghana empire. The incoming migration may have occurred in two waves as suggested by two peaks in the SPD curve at 200–400 CE and 600–800 CE and by cultural differences within the Delta. Most sites in the Sine-Saloum islands were abandoned in the early 15th century, before the arrival of Europeans, possibly because intensive shell fishing was not sustainable anymore, or because of the regional political destabilization associated to the fall of the Ghana empire and the beginning of the Mali empire. Shortly after, in agreement with oral traditions, a new population lead by the Manding Guelwars, moved to the Sine Saloum after a military defeat and founded the modern towns. They had a reduced shellfishing activity compared to previous inhabitants, possibly because activities were more oriented to the new trade with Europeans or to a prosperous agriculture in more humid climatic conditions that prevailed from 1500 to 1800 CE.

Compilation of a database of Holocene nearshore marine mollusk shell geochemistry from the California Current System

Abstract. The shells of marine invertebrates can serve as high-resolution records of oceanographic and atmospheric change through time. In particular, oxygen and carbon isotope analyses of nearshore marine calcifiers that grow by accretion over their lifespans provide seasonal records of environmental and oceanographic conditions. Archaeological shell middens generated by Indigenous communities along the northwest coast of North America contain shells harvested over multiple seasons for millennia. These shell middens, as well as analyses of archival and modern shells, have the potential to provide multi-site, seasonal archives of nearshore conditions throughout the Holocene. A significant volume of oxygen and carbon isotope data from archaeological shells exist, yet they are separately published in archaeological, geochemical, and paleoceanographic journals and have not been comprehensively analyzed to examine oceanographic change over time. Here, we compiled a database of previously published oxygen and carbon isotope data from archaeological, archival, and modern marine mollusks from the California Current System (North American coast of the northeast Pacific, 32 to 55∘ N). This database includes oxygen and carbon isotope data from 598 modern, archaeological, and sub-fossil shells from 8880 years before present (BP) to the present, from which there are 4917 total δ13C and 7366 total δ18O measurements. Shell dating and sampling strategies vary among studies (1–345 samples per shell, mean 44.7 samples per shell) and vary significantly by journal discipline. Data are from various bivalves and gastropod species, with Mytilus spp. being the most commonly analyzed taxon. This novel database can be used to investigate changes in nearshore sea surface conditions including warm–cool oscillations, heat waves, and upwelling intensity, and it provides nearshore calcium carbonate δ13C and δ18O values that can be compared to the vast collections of offshore foraminiferal calcium carbonate δ13C and δ18O data from marine sediment cores. By utilizing previously published geochemical data from midden and museum shells rather than sampling new specimens, future scientific research can reduce or omit the alteration or destruction of culturally valued specimens and sites. The dataset is publicly available through PANGAEA at https://doi.org/10.1594/PANGAEA.941373 (Palmer et al., 2021).

Examining the potential of Pacific abalone as a novel high-resolution archive of upwelling in the California Current

Upwelling is a dynamic oceanographic process that brings cold, nutrient-rich waters to the surface. These nutrients encourage primary productivity, forming the foundation of coastal food webs and the fisheries depending on them. Understanding past variability in the occurrence of upwelling and primary productivity may offer insight into how upwelling dynamics and ecosystem productivity could vary in the future. Numerous proxies from sediment cores inform most upwelling reconstructions; however, their temporal resolution is typically decadal at best. However, questions regarding ecosystem responses to changes in physical processes require data with seasonal to sub-seasonal resolution because such data provide additional insight into seasonal extremes (e.g., surface temperature, precipitation, etc.). The calcium carbonate skeletons of mollusks provide invaluable data from stable oxygen (δ18O) and carbon (δ13C) isotopes that generate high-resolution reconstructions of environmental variables. Recent studies of stable nitrogen (δ15N) isotopes in mollusk shell organic materials demonstrate the potential to produce high-resolution reconstructions of nutrient cycling. Collectively, these measurements may provide insight into upwelling conditions over the life of the organism. This study presents preliminary data exploring the potential of analyzing a suite of stable nitrogen, oxygen and carbon isotope data from analysis of Pacific abalone shells (Haliotis cracherodii). We present sub-seasonal δ15N time series data that, together with δ18O and δ13C, reflect seasonal variability closely linked to upwelling. δ15N values range from 8.3‰ to 11.0‰ and align closely with δ18O values, which range from −0.5‰ to 1.1‰. Implications of this research are twofold: 1) Isotopic analyses from abalone shells may provide detailed knowledge on primary productivity during upwelling as well as limited productivity when upwelling is greatly reduced and 2) archaeological shell middens in the Channel Islands contain an abundance of both abalone dating back to the early Holocene, presenting the opportunity to reconstruct upwelling conditions throughout the Holocene.

Characterising Inter-Individual Growth Variability of Patella vulgata Shell Through Calcein Marking Experiments: Consequences for Palaeo-Environmental Studies

ABSTRACT Sclerochronological data from archaeological shell middens provides crucial information about past environments and subsistence practices of coastal human populations. These studies rely on a strong knowledge of species-specific growth patterns, as it is the main driver of the quantity and quality of information recorded in biogenic carbonates. The limpet Patella vulgata is highly represented in eastern Atlantic shell middens. In this study, the micro-increment formation of its shell was investigated through in situ marking experiments, using calcein fluorochrome (150 mg.L−1) coupled with cohort study and local SST recording. Calcein-stained growth structures confirmed the efficacy of the fluorochrome, and our results shows a disturbed tidal increment formation, with on average more than one increment per day, but less than one increment per tide. Growth is not mainly influenced by environmental factors, but could be forced by competition among limpets and endogenous factor (age and sex), resulting in a highly heterogenous population in terms of growth rates. Growth interruption could not be detected solely by micro-increment observation, causing a major issue for cross-calibration with recorded temperatures, sclerochronological estimation of growth and isotopic profiles. For palaeo-environmental application, we recommend to consider that there is no general population pattern, even at a micro-habitat scale.

Using sea urchin remains to infer the health of kelp forest ecosystems in the past: Identification, quantification, and allometric reconstructions of harvested sea urchin (Strongylocentrotus spp.) on California’s Channel Islands

Sea urchins, one of the few echinoids harvested for human consumption, are found in archaeological sites from coastal settings around the world spanning at least the past ∼15,000 years. Sea urchin tests and spines are commonly found in archaeological shell middens on California’s Channel Islands, sometimes forming dense “urchin lenses.” Though ubiquitous, the fragile nature of their test (outer shell) results in a high degree of fragmentation, complicating identification and quantification in archaeological assemblages. I discuss issues regarding archaeological sea urchin remains off the coast of western North America and present a method for estimating the sizes of harvested purple (Strongylocentrotus purpuratus) and red (Mesocentrotus franciscanus) sea urchins through allometry, allowing archaeologists to configure size/age estimates for harvested populations in the past. These methods are applied to two archaeological assemblages from San Nicolas and San Miguel islands, revealing evidence of a potential urchin proliferation event in the California Bight during the late Middle Holocene, and relative consistency in the primary types and sizes of harvested specimens through time. As a keystone species dominating ecological interactions in kelp forest ecosystems, sea urchin remains can provide deep historical perspective on the relative state of intertidal ecosystems.

Kinetics and fractionation of carbon and oxygen isotopes during the solid-phase transformation of biogenic aragonite to calcite: The effect of organic matter

The phase transformation of biogenic shells from aragonite to calcite can modify the primary carbon and oxygen isotopic values (δ13C and δ18O), and thus affect their significance as paleoenvironmental proxies. While the biasing of δ13C and δ18O by dissolution and reprecipitation phase transformation (DR) has been extensively studied, thermal solid-phase transformation (SPT) in archaeological shell middens is rarely considered. In this study, the effects of intra-crystalline organic matter on the kinetics and carbon and oxygen isotopic fractionation during thermal SPT are evaluated by comparing two sets of experiments on powdered aragonite snail shells heated in air and pure nitrogen atmospheres. The results show that during heating temperature below 400 °C, the intra-crystalline organic matter could inhibit the phase transformation due to the shielding effect of organic matter, while during heating temperature above 400 °C, the decomposition of the intra-crystalline organic matter increases the kinetic rate of the phase transformation. The activation energy for the phase transformation was determined to be +150.5 kJ·mol−1, lower than that of +247 kJ·mol−1 obtained for abiogenic polycrystalline aragonite and close to that of +158 to +163 kJ·mol−1 for abiogenic single crystal aragonite. This is attributed to the larger lattice parameter c in biogenic aragonite and the increasing porosity of calcium carbonate with the decomposition of organic matter. In a nitrogen atmosphere, the deviation of δ13C and δ18O between the heated sample (the mixture of aragonite and calcite) and the original shell aragonite (Δ13CM-A and Δ18OM-A) is negligible during heating temperature below 400 °C; however, Δ13CM-A (from −0.43‰ to 0.00‰) and Δ18OM-A (from −1.54‰ to −0.02‰) are significant during heating temperature above 400 °C. The temperature-dependence of Δ13CM-A in biogenic carbonates is much more significant than that in abiogenic carbonates, which clearly reflects the occurrence of isotopic exchange between the intra-crystalline organic matter and the carbonates. In air, the heating-induced calcium carbonate is depleted in δ13C by up to −0.48‰ and in δ18O by up to −3.46‰, compared with the original samples, which is mainly caused by isotopic exchange with the external carbon dioxide in air and the intra-crystalline organic matter, with the latter being the dominant source. Our results demonstrate that the decomposition of the intra-crystalline organic matter increases the kinetic rate and induces carbon and oxygen isotope fractionation during SPT from aragonite to calcite. This study provides direct evidence for evaluating the preservation of carbon and oxygen isotopes of biogenic calcium carbonate shells which have undergone the SPT process in archaeological shell middens.

Scale of time-averaging in archaeological shell middens from the Canary Islands

Scale of time-averaging in archaeological shell middens from the Canary Islands

Scale of time-averaging in archaeological shell middens from the Canary Islands

Characterizing the degree of disturbance in archaeological deposits is critically important for archaeologists assessing foraging strategies, environmental conditions, or behavior patterns of ancient human groups. Qualitative techniques (e.g. micromorphology analysis) have previously been applied to assess the degree of disturbance (age-mixing) in archaeological sites; however, quantitative dating of material in the sites provides a more robust assessment of potential age-mixing. Unfortunately, because of budget constraints, archaeologists are frequently forced to rely on few quantitative age dates for an assemblage, thus obfuscating the signal of age-mixing of the deposit. The development of an affordable and rapid carbonate-target accelerator mass spectrometry (AMS) radiocarbon (14C) dating method provides a cost-effective way to retrieve more quantitative dates from carbonate material in archaeological assemblages to assess the degree of age-mixing in the deposit. This study tests this new technique and dates numerous harvested marine limpet shells from archaeological sites in the Canary Islands to determine whether there is multidecadal to multicentennial age-mixing. A total of 58 shells retrieved from six sites and three islands yielded uncalibrated radiocarbon ages ranging from 2265 ± 40 to 765 ± 35 BP, coinciding with the time of prehistoric human occupation in these islands. While most shells from the same stratum showed statistically equivalent ages, in some cases we detected age ranges that exceeded the imprecisions from analytical errors. This investigation is one of the first to quantitatively illustrate that shells retrieved from depth intervals without evident stratigraphic disturbance do not always contain contemporaneous remains and, therefore, dating each specimen is valuable for developing further paleoclimatic and paleoanthropological inferences. This study presents the first report of carbonate-target 14C ages from archaeological shell middens, and suggests that this novel radiocarbon methodology can be applied to these sites, thus allowing the generation of a more comprehensive chronology.

Sustainable harvesting of Conomurex luhuanus and Rochia nilotica by Indigenous Australians on the Great Barrier Reef over the past 2000 years

Offshore island colonisation and use around the northern Australian coastline in the mid-to-late Holocene is associated with expanding Aboriginal and Torres Strait Islander populations and intensifying land-use activities. However, few explicit tests of the long-term effects of shellfish forager decision-making and associated impacts on intertidal ecosystems in these newly colonised island environments have been undertaken. We report morphometric analyses on two key reef flat Great Barrier Reef shellfish species, strawberry conch Conomurex luhuanus (n = 360) and top shell Rochia nilotica (n = 45), from two late Holocene archaeological shell midden assemblages on Lizard Island, northeast Queensland. Human foraging pressure was assessed through reconstructions of population age structure across time, highlighting the importance of determining size-at-age habitat preferences and species behaviour patterns when assessing long-term anthropogenic impacts on shellfish populations. Results show no evidence for resource depression across the late Holocene which is broadly in keeping with previous findings at other locales on the Great Barrier Reef, but contrary to expectations of resource intensification models. We conclude that the rich and abundant resources of reef flat environments were resilient to relatively low intensity and likely episodic Indigenous foraging. This sustainability contrasts with the scale and impacts of intensive industrialised harvesting in the historic period.

Estudio experimental de alteración térmica sobre exoesqueletos de moluscos marinos (nacella magellanica) y sus implicancias para la interpretación de conjuntos arqueomalacológicos de concheros en patagonia argentina

The results of the experimental program on current calcareous exoskeletons of Nacella magellanica (Patellidae, Gasteropoda) are presented. This species of mollusc is one of the main that composes the archaeological shell middens in continental Patagonia argentine. We sought to obtain evidence of diagnostic features and modifications generated on the exoskeletons as a consequence of the thermal exposure process. Different samples were submitted to controlled burning under laboratory conditions in a muffle with digital thermocouple to obtain greater control over temperatures (from 0°C to 700°C). Structural, chromatic and textural analysis of samples exposed to heat were carried out. A first approach to the application of the indicators obtained in the experimental program for the analysis and interpretation of arqueomalacologicas assemblages recovered in systematic excavations in shell middens on the northern coast of Santa Cruz, Patagonia Argentina, was performed. This information was complemented with anthracological studies of carbons recovered in the same sites. The analysis of the experimental results and archaeomalacological remains allowed us to estimate that archaeological shells would have been subjected to temperatures of between 300°C and 400°C. Finally, the importance of the experimental approach is highlighted to understand characteristics of materials that make up the archaeological sites.

Integrating zooarchaeology in the conservation of coastal-marine ecosystems in Brazil

Sambaquis are archaeological shell mounds and middens formed by pre-Columbian populations inhabiting the Atlantic Forest coast of Brazil between the Middle and Late Holocene. Beyond their recognized cultural values, sambaquis are valuable biological archives for tracking changes in past biodiversity and informing modern conservation studies and management. In this contribution we reviewed the published record of faunal remains from archaeological sites located in Babitonga Bay, in the state of Santa Catarina, southern Brazil. Through a literature review covering 110 sites, we assembled a comprehensive survey of terrestrial and marine taxa exploited by human groups in this area between ca. 5500 and 370 years ago. A total of 244 species were recorded, of which 14 are currently endangered and 12 are no longer present in Babitonga Bay. This zooarchaeological synthesis provides snapshots of past biodiversity, adding a novel contribution to current debates around the conservation biology of one of the world's most threatened tropical biomes.

Modern drought conditions in western Sahel unprecedented in the past 1600 years

As climate model uncertainties remain very large for future rainfall in the Sahel, a multi-centennial perspective is required to assess the situation of current Sahel climate in the context of global warming. We present here the first record of hydroclimatic variability over the past 1600 years in Senegal, obtained from stable oxygen isotope analyses (δ18O) in archaeological shell middens from the Saloum Delta. During the preindustrial period, the region was relatively humid, with maximum humidity reached during the period from AD 1500 to AD 1800, referred to as the Little Ice Age. A significant negative link is observed at the centennial scale between global temperature and humidity in the Sahel that is at odds with the expected effects of latitudinal shifts of the intertropical convergence zone during the last millennium. In the context of the past 1600 years, the Western Sahel appears to be experiencing today unprecedented drought conditions. The rapid aridification that started ca. AD 1800 and the recent emergence of Sahel drought from the natural variability point to an anthropogenic forcing of Sahel drying trend. This new long-term perspective suggests that the recovery of Sahel rainfall in the last decade may only result from short-term internal variability, and supports climate models that predict an increase of Sahel drought under future greenhouse climate.

Mollusk carbonate thermal behaviour and its implications in understanding prehistoric fire events in shell middens

Archaeological shell middens are particularly important for reconstructing prehistoric human subsistence strategies. However, very little is known about shellfish processing, especially when related to the use of fire for dietary and disposal purposes. To shed light on prehistoric food processing techniques, an experimental study was undertaken on modern gastropod shells (Phorcus lineatus). The shells were exposed to high temperatures (200–700 °C) to investigate subsequent mineralogy and macro- and microstructural changes. Afterwards, the three-pronged approach was applied to archaeological shells from Haua Fteah cave, Libya (Phorcus turbinatus) and from shell midden sites in the United Arab Emirates (Anadara uropigimelana and Terebralia palustris) to determine exposure temperatures. Results indicated that shells from the Haua Fteah were exposed to high temperatures (600–700 °C) during the Mesolithic period (ca. 12.7–9 ka), whereas specimens from the Neolithic period (ca. 8.5–5.4 ka) were mainly exposed to lower temperatures (300–500 °C). The thermally-induced changes in A. uropigimelana and T. palustris shells from the South East Arabian archaeological sites were similar to those seen in Phorcus spp. suggesting a broad applicability of the experimental results at an interspecific level. Although heat significantly altered the appearance and mineralogy of the shells, 14CAMS ages obtained on burnt shells fit within the expected age ranges for their associated archaeological contexts, indicating that robust radiocarbon ages may still be obtained from burnt shells. Our study indicates that the combination of microstructural and mineralogical observations can provide important information to infer shellfish processing strategies in prehistoric cultures and their change through time.

δ18O of Fissurella maxima as a proxy for reconstructing Early Holocene sea surface temperatures in the coastal Atacama desert (25°S)

Fissurella maxima is a keyhole limpet that is abundant and well preserved in archaeological shell midden sites along the coast of Chile, making it an appropriate species to use for reconstructions of past sea surface temperature (SST). In the present study we evaluate the potential of F. maxima shells as a proxy of SST by analysing δ18O of modern shells collected alive from the Atacama desert (area of Taltal, 25°S) and archaeological shells from two Early Holocene rockshelter sites: 224A and Paposo Norte 9. Reconstructed SST from modern F. maxima shells were related to SST obtained from in situ thermometers, supporting the use of this mollusc species as a paleotemperature archive. Mean SST reconstructed from Early Holocene archaeological shells (14.13 °C) was 2.86 °C cooler than mean temperature recorded in modern shells (16.99 °C). Mean SST reconstructed from modern shells was ~1.04 °C warmer than the mean temperature of in situ thermometers (15.95°C). Hence the paleo–SST data from archaeological sites 224A and Paposo Norte 9 enrich the Early Holocene nearshore paleoceanographic scenario of the Pacific coast of South America, with mean SST cooler than present-day SST. Our results validate the use of F. maxima shells as a SST proxy and contribute to a better understanding of the latitudinal distribution of the coastal upwelling regime during the Early Holocene, temporal changes in the structure of the Humboldt Current along the Holocene, and its influence on human adaptation through the prehistory of South America.

Marine Reservoir Effect Values from Shell-Middens of San Matías Gulf, Northern Patagonia (Argentina): A 5000-yr Record

ABSTRACTTen marine reservoir effect (R) values were obtained from archaeological shell-middens along the San Matías Gulf, North Patagonian Atlantic coast, Argentina. They were determined by accelerator mass spectrometry (AMS) measurements on marine shell (Mytilidae) and charcoal samples (burned, short-lived plants) derived from a common stratigraphic unit. The R values fluctuate between 205±48 and 358±56 14C yr BP from ca. 5300 to ca. 700 14C yr BP with no obvious temporal trend. Calculated ΔR values fluctuate between +30±66 and –162±48 yr during the same time span. Local factors such as restricted connection with the open sea or presence of aged carbonates do not appear to have had an influence on this effect along the gulf coastline. The mean R value obtained (266 ± 51 yr) constitutes a useful value for correcting ages in shells from abundant archaeological deposits recorded in the area since Middle Holocene times.

Loco or no Loco? Holocene Climatic Fluctuations, Human Demography, and Community Based Management of Coastal Resources in Northern Chile

The abundance of the southern Pacific mollusk loco (Concholepas concholepas), among other conspicuous marine supplies, are often cited as critical resources behind the long-term cultural and demographic fluctuations of prehistoric hunter-gatherers at the coastal Atacama Desert. These societies inhabited one of the world’s most productive marine environments flanked by one the world’s driest deserts. Both of these environments have witnessed significant ecological variation since people first colonized them at the end of the Pleistocene (c. 13,000 cal yr BP). Here, we examine the relationship between the relative abundance of shellfish (a staple resource) along a 9,500-year sequence of archaeological shell midden accumulations at Caleta (a small inlet or cove) Vitor, with past demographic trends (established via summed probability distributions of radiocarbon ages) and technological innovations together with paleoceanographic data on past primary productivity. We find that shellfish extraction varied considerably from one cultural period to the next in terms of the number of species and their abundance, with diversity increasing during periods of regionally decreased productivity. Such shifts in consumption patterns are considered community based management decisions, and for the most part they were synchronous with large and unusual regional demographic fluctuations experienced by prehistoric coastal societies in northern Chile. When taken together with their technological innovations, our data illustrates how these human groups tailored their socio-cultural patterns to what were often abrupt and prolonged environmental changes throughout the Holocene.

Prehistoric cooking versus accurate palaeotemperature records in shell\xa0midden constituents

The reconstruction of pre-depositional cooking treatments used by prehistoric coastal populations for processing aquatic faunal resources is often difficult in archaeological shell midden assemblages. Besides limiting our knowledge of various social, cultural, economic and technological aspects of shell midden formation, unknown pre-depositional cooking techniques can also introduce large errors in palaeoclimate reconstructions as they can considerably alter the geochemical proxy signatures in calcareous skeletal structures such as bivalve shells or fish otoliths. Based on experimental and archaeological data, we show that carbonate clumped-isotope thermometry can be used to detect and reconstruct prehistoric processing methods in skeletal aragonite from archaeological shell midden assemblages. Given the temperature-dependent re-equilibration of clumped isotopes in aragonitic carbonates, this allows specific processing, cooking or trash dispersal strategies such as boiling, roasting, or burning to be differentiated. Besides permitting the detailed reconstruction of cultural or technological aspects of shell midden formation, this also allows erroneous palaeoclimate reconstructions to be avoided as all aragonitic shells subjected to pre-historic cooking methods show a clear alteration of their initial oxygen isotopic composition.