Stable Isotope Results Research Articles

Differing modes of animal exploitation in North-Pontic Eneolithic and Bronze Age Societies

ABSTRACTThis paper presents new results of an interdisciplinary investigation of the diet and subsistence strategies of populations living in the North-Pontic region during the Eneolithic and the Early Bronze Age (ca. 3800 BC to the 2500 BC). New organic residue analyses of >200 sherds from five Eneolithic sites and two Early Bronze Age settlements are presented. The molecular and stable isotope results are discussed in relation to zooarchaeological evidence. Overall, the findings suggest that each community relied on either a hunting- or a husbandry-based subsistence strategy dependent upon the ecosystem in which they settled; horses and wild animals dominated subsistence in the forest-steppe communities in contrast to ruminant husbandry in the steppe.

Authigenic 10Be/9Be ratio signature of the Matuyama–Brunhes boundary in the Montalbano Jonico marine succession

Geomagnetic dipole moment (GDM) lows associated with polarity reversals or geomagnetic excursions induce significant modulation of the cosmogenic nuclide Beryllium-10 (10Be) production. Hence, the reconstruction of atmospheric 10Be production rates from natural archives such as marine sedimentary sequences or ice cores constitutes a complementary approach, independent from paleomagnetic measurements, to decipher past GDM fluctuations. This is particularly important in the Montalbano Jonico succession (South Italy) since it is candidate to host the Global Stratotype Section and Point of the Middle Pleistocene Stage but where the magnetostratigraphic positioning of the Matuyama–Brunhes boundary (MBB) has not been available up to now. This study presents (1) original authigenic 10Be cosmogenic nuclide and 9Be stable isotope results, and (2) new high-resolution benthic oxygen isotope record covering termination IX and Marine Isotope Stage (MIS) 19. A robust chronological framework is established on the basis of (i) our oxygen isotope stratigraphy, using the strong analogies between MIS 1 and MIS 19c in terms of orbital forcing and CO2 level, and (ii) one precise 40Ar/39Ar date obtained in the tephra layer V4. The authigenic 10Be/9Be ratio record marks the atmospheric 10Be overproduction linked to the dipole low accompanying the MBB transition, with a characteristic twofold increase of the 10Be production at the end of MIS 19c and early MIS 19b. This signature is similar to those described in both marine and ice core records. The detailed chronostratigraphy constrained by a radiometrically-dated tephra layer (773.9±1.3 ka) within the MBB interval, makes it possible to discuss the structure and to assess the timing of the 10Be-production changes, and thus the MBB geomagnetic variations, with an unprecedented accuracy for a marine archive (sedimentation rates ∼80 cm/ka). These new cosmogenic nuclide production signatures provide the only missing constraint required for retaining the Montalbano Jonico succession as a global-scale correlation reference section for the Early–Middle Pleistocene boundary.

Macroinvertebrate community structure and feeding interactions along a pollution gradient in Gilgel Gibe watershed, Ethiopia: Implications for biomonitoring

Feeding interactions among functional feeding groups (FFGs) of macroinvertebrates are robust indicators of aquatic ecosystem interactions. They provide information regarding organic matter processing, habitat condition and trophic dynamics. In tropical rivers with pronounced wet and dry seasons, macroinvertebrate based ecological monitoring tools are explicitly focused on metrics and indices, while ignoring interactions of FFGs. Therefore, the objective of this study was to investigate the functional feeding type metrics, diversity indices and feeding interactions among FFGs of macroinvertebrates along the water pollution gradient in Gilgel Gibe watershed, Ethiopia. Water quality parameters and macroinvertebrate community attributes were assessed for samples collected from upstream sites (15 sites), urban-impacted stretches (12 sites) and wetland-affected river zones (7 sites) of the watershed during the rainy (July) and dry (February) seasons. To understand the effect of pollution on the feeding interactions, stable carbon and nitrogen isotopes were analyzed. Macroinvertebrate-based diversity indices and functional feeding type metric showed deterioration of ecological integrity at the urban-impacted sites and substantial recovery in the wetland-affected downstream sites. Omnivorous feeding behavior of macroinvertebrates was noted for the upstream sites, whereas clear trophic guilds of FFGs were suggested for the wetland-affected river zones by the stable isotope results. The results of pollution gradient analysis and feeding interactions among FFGs revealed that the urban-impacted sites showed weaker interactions when compared to upstream and wetland influenced sites. This affirms the potential importance of feeding interactions among FFGs of macroinvertebrates in water quality monitoring.

Resilience and local dietary adaptation in rural Poland, 1000–1400 CE

In Europe during the medieval period, new constraints were introduced to the balance of people’s food production, distribution and consumption. As a proxy indicator of diet, stable isotope ratios from osseous remains offer a window into past human lifeways and the adoption of new dietary regimes. We report stable carbon and nitrogen isotope results of a large diachronic study of skeletons from Poland’s Pomeranian region in the Vistula River valley, using concepts of resilience, agency, and transition in bioarchaeological research frameworks to explain pace of diet change and intra-population variations in diet. Two skeletal samples are from 10 to 13th century Kałdus, an economic center of the early Piast dynasty, and two are from 12 to 14th century Gruczno, a neighboring agricultural village. Humans exhibit a mean δ15N value of 9.8±0.9‰, a mean δ13Ccoll value of −19.4±0.9‰, and a mean δ13Cap value of −12.74±1.30‰. Despite similar time periods and shared geographic region, Kałdus and Gruczno differ markedly in terms of fish and millet consumption. Diet does not change according to expectations based on the Christianization, urbanization, and marketization of Poland at this time. Rather than broad national trends affecting what people ate, more significant influences on diet appear to have been local sociodemographic conditions, to which people adjusted in ways that enabled them to retain fundamental aspects of their daily lives spanning the medieval period.

Regional trends in evaporation loss and water yield based on stable isotope mass balance of lakes: The Ontario Precambrian Shield surveys

Stable isotopes of water, oxygen-18 and deuterium, were measured in water samples collected from a network of 300 lakes sampled in six ∼100km2 blocks (centred at 49.72°N, 91.46°W; 48.49°N, 91.58°W; 50.25°N, 86.62°W; 49.78°N, 83.98°W; 48.24°N, 85.49°W; 47.73, 84.52°W) within Precambrian shield drainages in the vicinity of Lake Superior, northern Ontario, Canada. Additional sampling was also conducted within the Turkey Lakes watershed (47.03°N, 84.38°W), a research basin situated in the Algoma region located 50km north of Sault Saint Marie, Ontario. The studies were undertaken to gain a better understanding of hydrology and geochemistry of watersheds in the region in order to better predict acid sensitivity of lakes. The main objective of this paper is to describe the hydrologic variations observed based on stable isotope results. Evaporative isotopic enrichment of lake water was found to be systematic across the region, and its deviation from the isotopic composition of precipitation was used to estimate the evaporation/inflow to the lakes as well as runoff (or water yield) based on a simple isotope mass balance model. The analysis illustrates significant variability in the water yield to lakes and reveals a pattern of positively skewed distributions in all six widely spaced blocks, suggesting that a high proportion of lakes have relatively limited runoff whereas relatively few have greater runoff. Such basic information on the drainage structure of an area can be valuable for site-specific hydrologic assessments but also has significant implications for critical loads assessment, as low runoff systems tend to be less buffered and therefore are more sensitive to acidification. Importantly, the Turkey Lakes sampling program also suggests that isotope-based water yield is comparable in magnitude to hydrometric gauging estimates, and also establishes that uncertainty related to stratification can be as high as ±20% or more for individual lakes, although it likely has only a minor influence on regional survey results. While further analysis in gauged lake watersheds would be beneficial to constraining the accuracy of the method or calibrating it for operational use, it is nevertheless a powerful tool in its present form for lake-to-lake and regional runoff inter-comparisons.

Radioisotopic age, formation, and preservation of Late Pleistocene human footprints at Engare Sero, Tanzania

We report on the radioisotopic age, formation, and preservation of a late Pleistocene human footprint site in northern Tanzania on the southern shore of Lake Natron near the village of Engare Sero. Over 400 human footprints, as well as tracks of zebra and bovid, are preserved in a series of volcaniclastic deposits. Based on field mapping along with geochemical and grain-size analyses, we propose that these deposits originated as proximal volcanic material from the nearby active volcano, Oldoinyo L'engai, and were then fluvially transported to the footprint site. Stable isotope results (δ18O and δ13C) suggest that the footprints were originally emplaced on a mudflat saturated by a freshwater spring and were later inundated by the rising alkaline waters of Lake Natron. We employed the 40Ar/39Ar and 14C dating methods to investigate the age of the site and determined that the footprint level is older than 5760±30yrs. BP and younger than 19.1±3.1ka. These radioisotopic ages are supported by stratigraphic correlations with previously documented debris avalanche deposits and the stable isotope signatures associated with the most recent highstand of Lake Natron, further constraining the age to latest Pleistocene. Since modern humans (Homo sapiens) were present in Africa ca. 200ka, Engare Sero represents the most abundant and best-preserved footprint site of anatomically modern Homo sapiens currently known in Africa. Fossil footprints are a snapshot in time, recording behavior at a specific moment in history; but the actual duration of time captured by the snapshot is often not well defined. Through analog experiments, we constrain the depositional window in which the prints were made, buried, and ultimately preserved to within a few hours to days or months.

Child Health in Five Early Medieval Irish Sites: A Multidisciplinary Approach

AbstractWith the aim to reconstruct child health in five early medieval (5th–12th c. CE) Irish sites, an osteoarchaeological study of three biological stress indicators – cribra orbitalia, linear enamel hypoplasia (LEH) and periostitis – has been conducted on 229 skeletons. In addition, Irish early medieval written sources testifying on child health during this period were consulted. These data were furthermore combined with the results of stable isotope analyses (nitrogen and carbon) conducted on subadult bone specimens. Cribra orbitalia was found in 27.5% of the studied individuals (48.6% of subadults were affected), with only two cases active at the time of death. The prevalence of LEH per individual is 63.5% (78.9% in subadults and 59.7% in adults). The age ranges of LEH formation vary between 1.9 and 4.8 years for the maxillary teeth and between 1.8 and 6.2 years for the mandibular teeth. Periosteal inflammations were recorded in over one third of the studied subadults (36.2%) with six cases active at the time of death. The stable isotope results suggest a diet based on terrestrial food sources, with little or no marine input. The presented data strongly suggest that most of the individuals were exposed to a high level of physiological stress during their childhood, and as such does not support the so called ‘osteological paradox’ hypothesis. The observed disturbances were probably caused by a synergistic effect of various biological and socio‐cultural factors. Although the historical records indicate certain differences in diet and lifestyle between social classes and the sexes, this study showed that the children of all ages had poor health in all social classes across a wide geographical location for the full time period of the early medieval. Copyright © 2016 John Wiley & Sons, Ltd.

Chemical and isotopic characteristics of groundwater-dominated Radovna River (NW Slovenia)

In order to investigate stream water, spring waters and water from a borehole facies, weathering processes, residence times and average recharge altitudes in the Radovna River valley were analysed for their concentrations of dissolved Ca2+, Mg2+, K+, Na+, HCO3 −, Cl−, NO3 −, SO4 2− and for the isotope compositions of hydrogen, oxygen and dissolved inorganic carbon (DIC). All water samples show a Ca2+–HCO3 − water facies with low contents of K+, Na+, Cl−, NO3 − and SO4 2−. Water–rock interaction and carbonate weathering are the significant contributors to water geochemistry. Analysis of the water chemistry indicates that waters drain a monolithological terrain and non-anthropogenically influenced watershed. The δ 2H and δ 18O values are seasonally dependent on the snowmelt, precipitation and evaporation. The average recharge altitudes for all sampling locations are between 1120 and 2130 m. The average residence time for the stream water is 2.4 years and for karst springs 1.2 years. The δ 13CDIC values in all samples are influenced by dissolution of carbonates, degradation of organic matter and by equilibrium with atmospheric CO2. All geochemical and isotope analyses show changes in stream water in the downstream direction and are highly dependent on the inflow of karstic spring. Based on hydrogeological mapping, geochemical and stable isotope results, a conceptual hydrogeological model of the Radovna system, in which karstic and alluvial aquifers are in contact, was determined.

Abiotically-formed, primary dolomite in the mid-Eocene lacustrine succession at Gebel El-Goza El-Hamra, NE Egypt: An approach to the role of smectitic clays

This study discusses the role of smectitic clays in the formation of an abiotic (physio-chemical) primary dolomite within an evaporative alkaline-saline marginal lake system, in the absence of carbonate precursor and microbes. The present work has been achieved in terms of textural, mineralogical, and geochemical characteristics of dolostones in the Mid-Eocene (Bartonian) lacustrine succession cropping out at Gebel El-Goza El-Hamra (Shabrawet area, NE Egypt). This lacustrine succession is 15–16m thick, and made up of alternating horizontal beds of dolostone, marlstone and mudrock that show some pedogenic and subaerial exposure features. The dolostones are composed mainly of dolomite (60–90%), smectite (20–30%) and quartz grains (5–10%). The dolomite comprises fine-crystalline rhombs to micro-spherical crystals with no obvious relics of microbial activity and/or carbonate precursor. It is, ordered, nearly stoichiometric (with 46–50% mole of MgCO3) and has δ18O and δ13C values ranging from +0.44 to +2.96 VPDB ‰, and 0.93 to −8.95 VPDB ‰, respectively. The smectite occurs as thin mats that are commonly intergrown and associated with dolomite. Mineralogical, textural and stable isotopic results of the dolomite indicated that the dolomite was formed as an abiotic primary precipitate in alkaline saline lacustrine systems. In this respect, the gel-like highly viscous smectitic medium plus progressive CO2 degassing, elevated evaporation, low sedimentation rate, low sulphates level and alkaline soil solution lowered the kinetic barriers of dolomite precipitation from solution and promoted the incorporation of Mg2+ in the structure of dolomite. Consequently, the presence of smectitic clays in evaporative saline lakes is significant for dolomite formation because they can generate a gel-like highly viscous medium and provide Mg2+ that can facilitate the physcio-chemical precipitation of primary dolomite from solution at ambient temperatures. However, more work is needed to better characterize the role of clays during dolomite formation in alkaline lacustrine environments at ambient temperatures.

Stable oxygen isotope evidence for mobility in medieval and post-medieval Trondheim, Norway

Immigration and mobility in the medieval and post-medieval periods in Norway have, up until now, mainly been discussed on the basis of historical sources. This paper presents the results of stable oxygen isotope (δ18O) analyses of the 1st and 3rd molars from 95 individuals from medieval and post-medieval Trondheim, as well as new information about the δ18O composition in the precipitation and drinking water in Trondheim. Through these analyses, the authors have attempted to shed light on the age of migrating individuals and directions of migration, to investigate temporal changes with regard to migration, and to make suggestions regarding the proportion of immigrants to locals in the population.The results show that the majority of the immigrants came from areas to the north or east of Trondheim, and some travelled at least 800–1000km to come to Trondheim. It has also been shown that a large proportion of the medieval individuals moved during childhood. Both with regard to child mobility and migration in general, the evidence suggests that the migratory activity decreased from the medieval to the post-medieval period.

A palaeodietary investigation of a multi-period churchyard in Stavanger, Norway, using stable isotope analysis (C, N, H, S) on bone collagen

Stable isotopes (C, N, H and S) chemically record information in bone about numerous aspects of past human lives, such as diet, residence and migration. Although widely applied, few stable isotope studies have been carried out for palaeodietary research using Norwegian material, and none from the southwest coast. The first animal and human stable isotope values from the Norwegian Stavanger region are presented in this study, revealing changes in dietary habits through a period of cultural, religious and economic changes in Norway, from the 9th century AD to the post-reformation period (17th century/early 18th century AD). 14C-datings of some skeletons that gave ages between AD 800–1150 (calibrated, 2 sigma) raise questions about their origin and the expansion of Christianity. The stable isotope results indicate a high protein diet with a substantial amount of marine input. Across the centuries, changing dietary patterns emerge that are probably related to changes in Christian rituals and people's lifestyle. The intensification of fishing activities that characterises medieval Europe is also visible in the isotopic record of Stavanger. The multi-proxy approach in this study proved useful as the addition of hydrogen stable isotopic data allows for improved interpretation of the palaeodiet, whereas sulphur stable isotope data needs further exploration in order to indicate possible migration.

Stable isotope on the evaluation of water quality in the presence of WWTPs in rivers.

We investigated the distribution of nitrogen compounds in Han River as well as two tributaries of Tancheon and Jungrangcheon. Particularly, we observed the significant releases of NH4 (+)-N from effluent of wastewater treatment plants (WWTPs) in two tributaries that has resulted in the increases of ammonium nitrogen (NH4 (+)-N) in Han River as well as in Tancheon and Jungrangcheon. Due to the increases of NH4 (+)-N in two tributaries, the larger distribution of δ(15)N-NH4 (+) was observed than those of δ(15)N-NO3 (-) in downstream. We calculated the contribution rate of ammonium nitrogen and nitrate nitrogen from effluent to downstream according to the results of stable isotope. The contribution rates of δ(15)N-NH4 (+) from effluent to downstream were significant that ranged between 53 and 100% in Tancheon and between 27 and 100% in Jungrangcheon. While the contribution of δ(15)N-NO3 (-) was not significant in Tancheon, it was occasionally observed in Jungrangcheon. These results demonstrated that WWTPs are the major sources of NH4 (+)-N in two tributaries, which caused the distinguishable stable isotope of δ(15)N-NH4 (+). Therefore, the stable isotope of δ(15)N-NH4 (+) could be a useful parameter or tracer for the evaluation of NH4-N released from WWTPs in rivers.

Isotopic perspectives (δ(13) C, δ(15) N, δ(34) S) of diet, social complexity, and animal husbandry during the proto-shang period (ca. 2000-1600 BC) of China.

To examine dietary patterns and animal husbandry practices and assess the links between human diet and sex, age, burial direction/position, and social status (as inferred by type of grave goods) during the transformative Proto-Shang (ca. 2000-1600 BC) period of China. Stable isotope ratios of carbon (δ(13) C), nitrogen (δ(15) N), and sulfur (δ(34) S) were analyzed from human (n = 83) and animal (n = 36) bone collagen at the site of Nancheng in Hebei Province, China. The Proto-Shang population consumed a predominately C4 diet (δ(13) C = -6.8 ± 0.4‰; δ(15) N = 9.4 ± 0.6‰), but a single individual (M70) had a mixed C3 /C4 diet (δ(13) C = -14.9‰; δ(15) N = 10.1‰). The δ(34) S measurement of M70 (8.8‰) is similar to the local animals (8.2 ± 2.6‰) and the other members of the population (7.0 ± 0.8‰) suggesting this individual may not have been a migrant even though the burial direction (north-south) and position (flexed) was different than the majority of the graves in the cemetery. From comparison with the faunal bone collagen stable isotope results, the Nancheng population ate millets with varying levels of animal protein consumption focused primarily on pigs and possibly cattle and dogs, but sheep/goats, and deer were not eaten in significant amounts. Analysis of the isotopic results in relation to other contemporary sites such as Liuzhuang and Xinzhai show strikingly similar patterns, suggesting that the sheep/goats were likely raised mainly for their secondary products (e.g., wool). No link between diet and sex was found at the population level, but when the data were sorted by age and sex, the older males (>40 years old) were found to have significantly lower δ(13) C values (-6.6 ± 0.3‰; n = 18) compared to the younger males (<40 years old) (-7.3 ± 0.5‰; n = 8). Further, no significant correlations between diet and burial direction/position or social status (based on the type of grave goods) were found at Nancheng, possibly indicating that the dietary social stratification of the later Shang and Zhou Dynasties had yet to be established in Chinese society at this time. Am J Phys Anthropol 160:433-445, 2016.. © 2016 Wiley Periodicals, Inc.

Reconciling oxygen isotope sclerochronology with interpretations of millennia of seasonal shellfish collection on the Pacific Northwest Coast

The results of high-resolution stable oxygen isotope (δ18O) sclerochronology of 139 butter clam (Saxidomus gigantea) shells from nine archaeological shell midden sites on the central coast of British Columbia, Canada demonstrate clear patterns of multi-season harvest at most sites and specific seasonal harvest at particular site locations. Although the results are based on small numbers of shells relative to an unknown number of seasonal clam harvesting events over the centuries or millennia of site occupation, they can be interpreted with confidence based on regional inter-site consistency, fit with a broader range of ancillary archaeological evidence, and the relative stability of seasonal patterns through iterative increases in sample size. On the basis of these results we outline a pragmatic approach to the selection of shells for seasonality analysis and for the interpretation of seasonal harvest patterns. This approach depends neither on the indeterminate reliability of probabilistic sampling of midden deposits and constituents or the prohibitively costly and still potentially unreliable use of large shell samples drawn from deposits distributed across sites.

Hydrogeochemical and isotope geochemical study of northwestern Algerian thermal waters

Northwestern Algeria is characterized by a large number of thermal waters and volcanic eruptions and belongs to the Alpine-Magrebide belt. The geothermal reservoirs that feed these reservoirs are mainly hosted by a fractured Jurassic limestone and dolomite sequence. Seven samples were collected from thermal springs of near-neutral pH (6.2 to 7.56) with discharge temperatures between 42.9 and 66.1 °C. Hydrogeochemical analyses of the thermal waters reveal four types (Na+-Ca2+-Cl−, Na+-Ca2+-Cl−-HCO3 −, Na+-Ca2+-Cl−-SO4 2−, and Na+-HCO3 −-Cl−) and show high total dissolved solids up to 4002 mg/L. Stable isotopic results (δ18 O and δ D) indicate that the thermal waters are of meteoric origin deeply infiltrated and heated by advective heat anomalies and raised up to the surface through deep-seated faults acting as hydrothermal conduits. The estimated reservoir temperatures using silica geothermometers and fluid-mineral equilibria overlap between 66 and 125 °C, while Na/K and K/Mg geothermometers give much higher and lower results, respectively, and are mainly influenced by mixing with cooler Mg groundwaters as indicated by the Na-K-Mg plot in the immature water field and in silica and chloride mixing models. Thermal waters deeply circulated and heated at a depth of 2 km were supplied by the higher geothermal gradients, which can reach 42.8 °C km−1 due to the complex geological setting.

Role of alternating redox conditions in the formation of organic-rich interval in the Middle Devonian Marcellus Shale, Appalachian Basin, USA

Geochemical, isotopic and petrographic analyses were performed on a 30-m core of the Marcellus Shale obtained from Greene County, Pennsylvania, to understand the dominant controls on organic matter deposition in the black shale study units. Our study suggests that the regeneration of nutrients, such as nitrogen (N) and phosphorous (P), may have played a key role in the formation of organic carbon (OC)-rich intervals in the Marcellus Shale. The decomposition of organic matter is likely to have released N and P into the water column, and the episodic upward mixing of these nutrient-enriched waters enhanced primary production. The ratios of Corg/Nbulk and Corg/Ptot are significantly higher in the OC-rich zone of the core (i.e., defined as TOC>4% and located between 2393 and 2406.5m depth). The high Corg/Ptot and Corg/Nbulk ratios of the preserved organic matter may reflect the release of N and P by microbial processes, indicating the recycling of nutrients during deposition of the OC-rich interval. In addition, our data show a positive relationships between the Corg/Ptot and Corg/Nbulk ratios and the organic carbon content, which indicate that the recycled nutrients may have promoted primary productivity, resulting in higher OC accumulation in some intervals. The geochemical and stable isotopic results also suggest that the alternating redox conditions in the water mass were favorable for nutrient regeneration. Highly variable trace metal concentrations (e.g., U, Mo, and V) in the OC-rich zone and a wide range of δ15N and δ34Spyr values towards the top of the OC-rich zone suggest fluctuations between anoxic and suboxic water conditions. Finally, sedimentary features and agglutinated benthic foraminifera in the OC-rich zone support the existence of short-term fluctuations between suboxic and anoxic conditions near the sediment–water interface. Multiple lines of evidence suggest that nutrient regeneration due to alternating redox conditions may have played an important role in the formation of OC-rich intervals in the Marcellus Shale.

Stable Isotopic Detection of Manual Intervention Among the Faunal Assemblage from a Majiayao Site in NW China

AbstractFaunal remains from Shannashuzha in Minxian County, Gansu Province, China were isotopically analyzed to understand animal husbandry, and thus human subsistence strategy, during the Majiayao culture (5200–4800 cal yr BP) period. Stable carbon isotopic results reveal that only two pig samples clearly show a C4-dominated diet with a mean δ13C value of –8.5‰, which possibly indicated controlled feeding practices by human beings. No other significant manual intervention can be observed among the remaining samples, suggesting that both wild and domesticated meat sources were used at Shannashuzha. Statistically, Bos are indistinguishable from Cervidae based solely on isotopic results, suggesting that Bos may have remained in wild form during the Majiayao culture period. The presence of hare/rabbit, bamboo rat, and badger reflects the diversified food exploitation behavior.

Feeding habits of the short-finned squidIllex coindetiiin the western Mediterranean Sea using combined stomach content and isotopic analysis

The ommastrephid squid,Illex coindetii, is one of the most abundant cephalopods in the Mediterranean Sea and an important predator in the ecosystem. In the present study, we examined the diet habits ofI. coindetiiin the north-western Mediterranean Sea by combining two complementary approaches: stomach content and stable isotopic analyses. Specifically, we examined whether the diet differed between sizes and seasons. Stomach content results indicated that the diet ofI. coindetiiwas composed of 35 prey items including four major groups; namely the crustaceansPasiphaea sivado, Amphipods, squid of the Order Teuthida, and pelagic and mesopelagic fish. Differences were found among different ontogenetic sizes: juvenile individuals fed mainly on crustaceans (%IRI = 77.59), whereas adult individuals fed on a wider range of prey items, including the shrimpP. sivado(%IRI = 33.21), the amphipodAnchylomera blossevillei(%IRI = 0.91), the decapodPlesionikasp. (%IRI = 0.19), the carangidTrachurus trachurus(%IRI = 0.34) and some Myctophids species (%IRI = 0.21). Differences were also found between seasons in the year. In winter, crustaceans were the main prey items, whereas in summer the diversity of prey was higher, including fish, crustaceans and molluscs. Similar to the stomach contents, stable isotopic results indicated differences among sizes. δ15N values were higher in adult squids than in juveniles because they fed on prey at higher trophic levels. In conclusion, this study indicates that feeding habits ofI. coindetiivary seasonally and ontogenetically. These feeding variations may be associated with trophic competence scenarios based on size, and also with the availability and abundance of prey throughout the year.

Diet analysis of Alaska Arctic snow crabs (Chionoecetes opilio) using stomach contents and δ13C and δ15N stable isotopes

We used stomach content and stable δ13C and δ15N isotope analyses to investigate male and female snow crab diets over a range of body sizes (30–130mm carapace width) in five regions of the Pacific Arctic (southern and northern Chukchi Sea, western, central, and Canadian Beaufort Sea). Snow crab stomach contents from the southern Chukchi Sea were also compared to available prey biomass and abundance. Snow crabs consumed four main prey taxa: polychaetes, decapod crustaceans (crabs, amphipods), echinoderms (mainly ophiuroids), and mollusks (bivalves, gastropods). Both approaches revealed regional differences. Crab diets in the two Chukchi regions were similar to those in the western Beaufort (highest bivalve, amphipod, and crustacean consumption). The Canadian Beaufort region was most unique in prey composition and in stable isotope values. We also observed a trend of decreasing carbon stable isotopes in crabs from the Chukchi to those in the Canadian Beaufort, likely reflecting the increasing use of terrestrial carbon sources towards the eastern regions of the Beaufort Sea from Mackenzie River influx. Cannibalism on snow crabs was higher in the Chukchi regions relative to the Beaufort regions. We suggest that cannibalism may have an impact on recruitment in the Chukchi Sea via reduction of cohort strength after settlement to the benthos, as known from the Canadian Atlantic. Prey composition varied with crab size only in some size classes in the southern Chukchi and central Beaufort, while stable isotope results showed no size-dependent differences. Slightly although significantly higher mean carbon isotope values for males in the southern Chukchi may not be reflective of a gender-specific pattern but rather be driven by low sample size. Finally, the lack of prey selection relative to availability in crabs in the southern Chukchi suggests that crabs consume individual prey taxa in relative proportions to prey field abundances. The present study is the first to provide a baseline of the omnivorous role of snow crabs across the entire Pacific Arctic, as well as evidence for cannibalism in the Chukchi Sea. In light of climate change predictions for the Alaska Arctic, and the potential for future fisheries harvest of snow crabs in this region, continued monitoring of snow crabs, including population and trophic dynamics, is increasingly important to assess snow crab impacts on benthic communities and vice versa.

Paleoenvironmental changes in northern Mongolia during the last deglaciation revealed by trace element records in ostracods from Lake Hovsgol

Ostracods possess bivalve carapaces composed of low-Mg calcite, which can be preserved in a variety of sedimentary environments. They are a useful paleoenvironmental indicator, in particular for non-marine environments. Although previous studies of Lake Baikal and Lake Hovsgol have provided some evidence of large-scale paleoenvironmental changes in central Asia during the late Pleistocene, trace element records in ostracods from these two lakes, which may reveal the detailed limnological processes, have not yet been reported. In this study, we analyzed stable isotopes and trace elements in ostracods in three gravity core sediments recovered from Lake Hovsgol, northern Mongolia, to reconstruct the long-term limnological histories of the lake. Radiocarbon dating results indicated that ostracod-bearing core sediments were deposited from ∼14.5 to 21.5 ka, which corresponds to the early stage of the last deglaciation, including the Last Glacial Maximum (LGM). The Mg/Ca and Sr/Ca ratios from two species of ostracods, C. lacustris and L. inopinata, ranged from 4 to 25 and 3–5 mmol/mol, respectively, with distinct and consistent decreasing trends. The changes in the Mg/Ca and Sr/Ca ratios indicate that the salinity of the lake water decreased substantially at the initial transition from the last glacial to the current interglacial period, which was mainly due to the ice melting and introducing fresh water into the lake. Changes in the Fe/Ca and U/Ca ratios were interpreted as water circulation changes in the bottom of the lake. After the LGM, the Fe/Ca and U/Ca ratios gradually increased, indicating that inflowing cold water induced stronger water circulation and subsequently a higher dissolved oxygen content in the bottom water of the lake. The Mn/Ca ratio had the opposite trend to the U/Ca and Fe/Ca ratios, which suggests that it was affected by the weathering intensity in the area around Lake Hovsgol. The stable isotopic results for C. lacustris support our paleoenvironmental interpretations in the region on the basis of trace elements. As a result, ostracod geochemical records from Lake Hovsgol, northern Mongolia, provide new insights into paleoenvironmental changes in central Asia during the onset of the last deglaciation.