Clams and climate in the Kodiak Archipelago, Alaska: insights from oxygen isotope sclerochronological analysis of S. gigantea from middle to late holocene archaeological deposits

The paleoenvironmental record reflects fluctuating marine conditions throughout the Gulf of Alaska during the Late Holocene. The effects of changes in regional climate patterns, as well as human responses to such change, however, can exhibit great variability locally. In the Kodiak Archipelago in the Gulf of Alaska, changing environmental conditions, population growth, technological transitions, and contact with other communities likely promoted the transition from needs based maritime hunter-gatherers to surplus based, semi-permanent villages. The precise role of climate in this transition is understudied. Few paleoclimate reconstructions are available for the Kodiak Archipelago and while climate reconstructions for the Gulf of Alaska are not uncommon, regional climate reconstructions are often insufficient for archaeological research. Many climate reconstructions lack sub-annual resolution and cannot produce a detailed understanding of seasonal behaviors in human populations. Sclerochronological and sclerochemical analysis of shellfish remains from archaeological sites in the archipelago may provide additional paleoenvironmental information. The length of shellfish growing season has been found to decrease with increasing latitude and decreasing temperature. Measuring and comparing the length of seasonal shell growth in select species of bivalves may complement stable oxygen isotope analysis, together providing a more precise paleoclimate reconstruction. This research utilizes the growth of Saxidomus gigantea, abundant both on modern and ancient coastlines to provide information about the length of its growing seasons. Archaeological samples were obtained from four sites from the Kodiak Archipelago, Alaska to determine if changes in seasonality, as measured by the number of circalunidian growth increments in one year, is detectable through time. Three samples from the Rice Ridge site (KOD-363), five samples from the Uyak site (KOD-145) represent sequences from Kachemak period, two samples from the Settlement Point site (AFG-105), and two samples from the New Karluk site (KAR-001) were analyzed.Accepted manuscrip

Centuries of Marine Radiocarbon Reservoir Age Variation Within Archaeological Mesodesma donacium Shells From Southern Peru

Mollusk shells provide brief (\u3c5 yr per shell) records of past marine conditions, including marine radiocarbon reservoir age (R) and upwelling. We report 21 14C ages and R calculations on small (~2 mg) samples from 2 Mesodesma donacium (surf clam) shells. These shells were excavated from a semi-subterranean house floor stratum 14C dated to 7625 ± 35 BP at site QJ-280, Quebrada Jaguay, southern Peru. The ranges in marine 14C ages (and thus R) from the 2 shells are 530 and 170 14C yr; R from individual aragonite samples spans 130 ± 60 to 730 ± 170 14C yr. This intrashell 14C variability suggests that 14C dating of small (time-slice much less than 1 yr) marine samples from a variable-R (i.e. variable-upwelling) environment may introduce centuries of chronometric uncertainty

El Nin˜o Impact on Mollusk Biomineralization: Implications for Trace Element Proxy Reconstructions and the Paleo-Archeological Record

Marine macroinvertebrates are ideal sentinel organisms to monitor rapid environmental changes associated with climatic phenomena. These organisms build up protective exoskeletons incrementally by biologically-controlled mineralization, which is deeply rooted in long-term evolutionary processes. Recent studies relating potential rapid environmental fluctuations to climate change, such as ocean acidification, suggest modifications on carbonate biominerals of marine invertebrates. However, the influence of known, and recurrent, climatic events on these biological processes during active mineralization is still insufficiently understood. Analysis of Peruvian cockles from the 1982–83 large magnitude El Nin˜o event shows significant alterations of the chemico-structure of carbonate biominerals. Here, we show that bivalves modify the main biomineralization mechanism during the event to continue shell secretion. As a result, magnesium content increases to stabilize amorphous calcium carbonate (ACC), inducing a rise in Mg/Ca unrelated to the associated increase in sea-surface temperature. Analysis of variations in Sr/Ca also suggests that this proxy should not be used in these bivalves to detect the temperature anomaly, while Ba/Ca peaks are recorded in shells in response to an increase in productivity, or dissolved barium in seawater, after the event. Presented data contribute to a better understanding of the effects of abrupt climate change on shell biomineralization, while also offering an alternative view of bivalve elemental proxy reconstructions.Furthermore, biomineralization changes in mollusk shells can be used as a novel potential proxy to provide a more nuanced historical record of El Nin˜o and similar rapid environmental change events

A Multi-Proxy Assessment of the Impact of Environmental Instability on Late Holocene (4500-3800 BP) Native American Villages of the Georgia Coast

Circular shell rings along the South Atlantic Coast of North America are the remnants of some of the earliest villages that emerged during the Late Archaic (5000-3000 BP). Many of these villages, however, were abandoned during the Terminal Late Archaic (ca 3800-3000 BP). We combine Bayesian chronological modeling with mollusk shell geochemistry and oyster paleobiology to understand the nature and timing of environmental change associated with the emergence and abandonment of circular shell ring villages on Sapelo Island, Georgia. Our Bayesian models indicate that Native Americans occupied the three Sapelo shell rings at varying times with some generational overlap. By the end of the complex\u27s occupation, only Ring III was occupied before abandonment ca. 3845 BP. Ring III also consists of statistically smaller oysters harvested from less saline estuaries compared to earlier occupations. Integrating shell biochemical and paleobiological data with recent tree ring analyses shows a clear pattern of environmental fluctuations throughout the period in which the rings were occupied. We argue that as the environment became unstable around 4300 BP, aggregation at villages provided a way to effectively manage fisheries that are highly sensitive to environmental change. However, with the eventual collapse of oyster fisheries and subsequent rebound in environmental conditions ca. post-3800 BP, people dispersed from shell rings, and shifted to non-marine subsistence economies and other types of settlements. This study provides the most comprehensive evidence for correlations between large-scale environmental change and societal transformations on the Georgia coast during the Late Archaic period

Fundamental questions and applications of sclerochronology: Community-defined research priorities.

Horizon scanning is an increasingly common strategy to identify key research needs and frame future agendas in science. Here, we present the results of the first such exercise for the field of sclerochronology, thereby providing an overview of persistent and emergent research questions that should be addressed by future studies. Through online correspondence following the 5th International Sclerochronology Conference in 2019, participants submitted and rated questions that addressed either knowledge gaps or promising applications of sclerochronology. An initial list of 130 questions was compiled based on contributions of conference attendees and reviewed by expert panels formed during the conference. Herein, we present and discuss the 50 questions rated to be of the highest priority, determined through an online survey distributed to sclerochronology community members post the conference. The final list (1) includes important questions related to mechanisms of biological control over biomineralization, (2) highlights state of the art applications of sclerochronological methods and data for solving long-standing questions in other fields such as climate science and ecology, and (3) emphasizesthe need for common standards for data management and analysis. Although research priorities are continually reassessed, our list provides a roadmap that can be used to motivate research efforts and advance sclerochronology towardnew, and more powerful, applications.N/

Fundamental questions and applications of sclerochronology: Community-defined research priorities

Horizon scanning is an increasingly common strategy to identify key research needs and frame future agendas in science. Here, we present the results of the first such exercise for the field of sclerochronology, thereby providing an overview of persistent and emergent research questions that should be addressed by future studies. Through online correspondence following the 5th International Sclerochronology Conference in 2019, participants submitted and rated questions that addressed either knowledge gaps or promising applications of sclerochronology. An initial list of 130 questions was compiled based on contributions of conference attendees and reviewed by expert panels formed during the conference. Herein, we present and discuss the 50 questions rated to be of the highest priority, determined through an online survey distributed to sclerochronology community members post the conference. The final list: (1) includes important questions related to mechanisms of biological control over biomineralization; (2) highlights state of the art applications of sclerochronological methods and data for solving long-standing questions in other fields such as climate science and ecology: and (3) emphasizes the need for common standards for data management and analysis. Although research priorities are continually reassessed, our list provides a roadmap that can be used to motivate research efforts and advance sclerochronology toward new, and more powerful, applications

Mineralogy and seasonal growth of South Pacific mussel valves

Choromytilus chorus and Aulacomya ater are among the most common mussel species in the South Pacific. However, little sclerochronological analysis has been conducted on them, even though they are found in both archaeological sites and sub-fossil deposits and could potentially be useful paleoclimate proxies. One valve from each species was analyzed via x-ray diffraction (XRD) and Raman spectroscopy to determine the shell's mineralogy. C. chorus is mostly calcite with aragonite in some zones, while A. ater is mostly aragonite with less calcite. There are abrupt and continuous boundaries between the two calcite layers and across the aragonite-calcite interface of C. chorus. All of the boundaries in C. chorus can be seen in cross section under reflected or transmitted light along the longest growth axis. The boundaries between mineralogical and structural variations in A. ater are not as visually distinct, and thus may render the species problematic for oxygen isotope analysis. Comparison of C. chorus oxygen isotope profiles to regional temperature records and local water δ18O suggest the sampled shells' lifespan was between one and two years of age. Analyses of the oxygen isotope profiles indicate nearly continuous shell growth throughout the first year of life, with a marked decrease or periods of cessation in shell growth in the second year in the larger specimens analyzed. This growth pattern may make the valves useful as proxies for at least one year of paleoclimatic/paleoenvironmental data. Three out of the four specimens of C. chorus analyzed for oxygen isotopes display a prominent growth break on the outer surface of their valves and each appear roughly contemporaneous. Oxygen isotope analysis indicates that the prominent growth breaks in each of the three valves were formed just before the peak SST of January of 2006 occurred. Qualitative seasonal variations are recorded in the δ18O profiles of the four shells, and median annual δ18O values are in general agreement between individuals. However, the full range of the winter to summer seasonal shift in SST was not recorded by all C. chorus valves. Therefore, caution should be exercised when utilizing C. chorus valves to interpret changes in seasonality. (Published By University of Alabama Libraries

Sclerochronological Basis for Growth Band Counting: A Reliable Technique for Life-span Determination of \u3cem\u3eCrassostrea virginica\u3c/em\u3e from the Mid-Atlantic United States

Widely used sclerochronological methods for biologically aging fossilized oysters, such as δ18O and Mg/Ca analyses, are costly, time-consuming, and not always practical for population-level analyses. A method that relies on visible morphological features, such as growth bands, to determine the lifespan of Crassostrea virginica would provide a cost-efficient and reliable alternative. Previous studies have assessed whether counting growth bands can be used to biologically age C. virginica from the southeastern U.S. but have produced conflicting results. For this study, we conducted subseasonal sclerochronological analyses on Pleistocene C. virginica from the mid-Atlantic U.S. to determine whether growth band counting could be used to reliably measure oyster lifespan. A highly significant correlation exists between δ18O peaks and major (annual) grey growth bands in these oysters. Major grey and white growth bands differ significantly with respect to δ18O values. These data suggest that, for C. virginica from the Pleistocene of the mid-Atlantic U.S., major grey growth bands are accreted during the colder months of the year and can be used as annual markers to biologically age specimens. The results presented here differ from previous studies that reported no link between growth bands and δ18O values, possibly because the latter focused on lower latitude regions with different seasonal temperature regimes and sampled only the early stages of growth, which contain morphological features that could be confused with major growth bands. While growth band counting of oysters shows promise as a method for biologically aging oysters that experience high seasonal temperature variability, future studies are needed to assess its applicability over a broader geographic range

From Middens to Modern Estuaries, Oyster Shells Sequester Source-Specific Nitrogen

Oysters (Crassostrea virginica) were an important food resource for native peoples of the northern Gulf of Mexico, who deposited waste shells in middens. Nitrogen (N) stable isotopes (δ15N) in bivalve shells have been used as modern proxies for estuarine N sources because they approximate δ15N in suspended particulate matter. We tested the use of midden shell δ15N as a proxy for ancient estuarine N sources. We hypothesized that isotopic signatures in ancient shells from coastal Mississippi would differ from modern shells due to increased anthropogenic N sources, such as wastewater, through time. We decalcified shells using an acidification technique previously developed for modern bivalves, but modified to determine δ15N, δ13C, %N, and % organic C of these low-N, high-C specimens. The modified method resulted in the greatest percentage of usable data from midden shells. Our results showed that oyster shell δ15N did not significantly differ between ancient (500–2100 years old) and modern oysters from the same locations where the sites had undergone relatively little land-use change. δ15N values in modern shells, however, were positively correlated with water column nitrate concentrations associated with urbanization. When N content and total shell mass were combined, we estimated that middens sequestered 410–39,000 kg of relic N, buried at a rate of up to 5 kg N m−2 yr−1. This study provides a relatively simple technique to assess baseline conditions in ecosystems over long time scales by demonstrating that midden shells can be an indicator of pre-historic N source to estuariesand are a potentially significant but previously uncharacterized estuarine N sink