Marine macroinvertebrates are ideal sentinel organisms to monitor rapid environmental changes ass... more 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 Niño 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 carbonat...
ABSTRACT Despite the prevalence of Woodland-period middens on the Gulf of Mexico’s northern coast... more ABSTRACT Despite the prevalence of Woodland-period middens on the Gulf of Mexico’s northern coast, Woodland fisheries remain poorly known. Vertebrate and invertebrate assemblages from Plash Island (1BA134; cal AD 325–640) and Bayou St. John (1BA21; cal AD 650–1040) suggest this period was more than a prelude to Mississippian farming. Much of the coastal Woodland economy centered on reliable, productive estuarine resources, particularly molluscs and fishes that provided communities with multiple options in a resilient strategy employed for at least 700 years. A nuanced interpretation of coastal life as an array of flexible, managed responses to a dynamic estuarine environment is more plausible than a model that postulates seasonal abandonment of a productive coastal territory and valuable gear. We posit a more parsimonious interpretation: residents of Woodland fishing villages on the north-central Gulf coast skillfully and flexibly managed the opportunities and challenges of complex multi-season, year-round fisheries.
Archaeological evidence plays a key role in longitudinal studies of humans and climate. Climate p... more Archaeological evidence plays a key role in longitudinal studies of humans and climate. Climate proxy data from Peruvian archaeological sites provide a case study through insight into the history of the “flavors” or varieties of El Niño (EN) events after ∼11 ka: eastern Pacific EN, La Niña, coastal EN (COA), and central Pacific or Modoki EN (CP). Archaeological proxies are important to the coastal Peruvian case because more commonly used paleoclimate proxies are unavailable or equivocal. Previously, multiproxy evidence from the Peruvian coast and elsewhere suggested that EN frequency varied over the Holocene: 1) present in the Early Holocene; 2) absent or very low frequency during the Middle Holocene (∼9 to 6 ka); 3) low after ∼6 ka; and 4) rapidly increasing frequency after 3 ka. Despite skepticism about the reliability of archaeological proxies, nonarchaeological proxies seemed to confirm this archaeological EN reconstruction. Although there is consensus that EN frequency varied o...
Research at Crystal River and Roberts Island Shell Mound Complex, on the western coast of Florida... more Research at Crystal River and Roberts Island Shell Mound Complex, on the western coast of Florida, USA, offers a quantitative assessment of the temporality of shell deposit construction, Native subsistence practices, and mobility patterns through stable oxygen isotope data from eastern oyster (C. virginica). The δ18Owater values of oysters vary synchronously with salinity, assuming relatively constant δ18Owater/salinity gradients since the time of occupation, allowing for an examination of shifts in oyster habitat exploitation over time. Our previous (Thompson et al. 2015) study indicated that midden accumulation occurred throughout the year, while oysters from mound deposits were collected in colder months. New data indicate that in addition to differential season of collection, habitat exploitation also varied. During early occupation at the site, oysters were collected primarily from lower saline habitats, while in later phases oysters were obtained from higher salinity waters; we relate this to a lower sea level and concomitant settlement shift seaward. Additionally, oyster from later mound contexts was collected from higher saline habitats relative to those in midden contexts; Native people may have targeted specific bioherms at certain times for the year for feasting-related mound construction.
Oysters (Crassostrea virginica) were an important food resource for native peoples of the norther... more 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 (d 15 N) in bivalve shells have been used as modern proxies for estuarine N sources because they approximate d 15 N in suspended particulate matter. We tested the use of midden shell d 15 N 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 d 15 N, d 13 C, %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 d 15 N 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. d 15 N 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 À2 yr À1. 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 prehistoric N source to estuaries and are a potentially significant but previously uncharacterized estuarine N sink.
Marine macroinvertebrates are ideal sentinel organisms to monitor rapid environmental changes ass... more 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 Niño 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 carbonat...
ABSTRACT Despite the prevalence of Woodland-period middens on the Gulf of Mexico’s northern coast... more ABSTRACT Despite the prevalence of Woodland-period middens on the Gulf of Mexico’s northern coast, Woodland fisheries remain poorly known. Vertebrate and invertebrate assemblages from Plash Island (1BA134; cal AD 325–640) and Bayou St. John (1BA21; cal AD 650–1040) suggest this period was more than a prelude to Mississippian farming. Much of the coastal Woodland economy centered on reliable, productive estuarine resources, particularly molluscs and fishes that provided communities with multiple options in a resilient strategy employed for at least 700 years. A nuanced interpretation of coastal life as an array of flexible, managed responses to a dynamic estuarine environment is more plausible than a model that postulates seasonal abandonment of a productive coastal territory and valuable gear. We posit a more parsimonious interpretation: residents of Woodland fishing villages on the north-central Gulf coast skillfully and flexibly managed the opportunities and challenges of complex multi-season, year-round fisheries.
Archaeological evidence plays a key role in longitudinal studies of humans and climate. Climate p... more Archaeological evidence plays a key role in longitudinal studies of humans and climate. Climate proxy data from Peruvian archaeological sites provide a case study through insight into the history of the “flavors” or varieties of El Niño (EN) events after ∼11 ka: eastern Pacific EN, La Niña, coastal EN (COA), and central Pacific or Modoki EN (CP). Archaeological proxies are important to the coastal Peruvian case because more commonly used paleoclimate proxies are unavailable or equivocal. Previously, multiproxy evidence from the Peruvian coast and elsewhere suggested that EN frequency varied over the Holocene: 1) present in the Early Holocene; 2) absent or very low frequency during the Middle Holocene (∼9 to 6 ka); 3) low after ∼6 ka; and 4) rapidly increasing frequency after 3 ka. Despite skepticism about the reliability of archaeological proxies, nonarchaeological proxies seemed to confirm this archaeological EN reconstruction. Although there is consensus that EN frequency varied o...
Research at Crystal River and Roberts Island Shell Mound Complex, on the western coast of Florida... more Research at Crystal River and Roberts Island Shell Mound Complex, on the western coast of Florida, USA, offers a quantitative assessment of the temporality of shell deposit construction, Native subsistence practices, and mobility patterns through stable oxygen isotope data from eastern oyster (C. virginica). The δ18Owater values of oysters vary synchronously with salinity, assuming relatively constant δ18Owater/salinity gradients since the time of occupation, allowing for an examination of shifts in oyster habitat exploitation over time. Our previous (Thompson et al. 2015) study indicated that midden accumulation occurred throughout the year, while oysters from mound deposits were collected in colder months. New data indicate that in addition to differential season of collection, habitat exploitation also varied. During early occupation at the site, oysters were collected primarily from lower saline habitats, while in later phases oysters were obtained from higher salinity waters; we relate this to a lower sea level and concomitant settlement shift seaward. Additionally, oyster from later mound contexts was collected from higher saline habitats relative to those in midden contexts; Native people may have targeted specific bioherms at certain times for the year for feasting-related mound construction.
Oysters (Crassostrea virginica) were an important food resource for native peoples of the norther... more 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 (d 15 N) in bivalve shells have been used as modern proxies for estuarine N sources because they approximate d 15 N in suspended particulate matter. We tested the use of midden shell d 15 N 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 d 15 N, d 13 C, %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 d 15 N 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. d 15 N 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 À2 yr À1. 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 prehistoric N source to estuaries and are a potentially significant but previously uncharacterized estuarine N sink.
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