Spatio-temporal Variability in Larval-Stage Feeding and Nutritional Sources as Factors Influencing Striped Bass (Morone saxatilis) Recruitment Success

Prey availability and feeding success affect survival of larval striped bass (Morone saxatilis) in Chesapeake Bay and contribute to the >30-fold interannual recruitment variability. Gut contents and stable isotope analyses (δ¹⁵N and δ¹³C) were conducted on striped bass larvae to evaluate sources of nutrition in 2007 and 2008, years of high and poor recruitment, respectively. Ichthyoplankton and zooplankton were surveyed in the upper Chesapeake Bay, in proximity to the estuarine turbidity maximum and associated salt front. Feeding incidence and numbers of prey per gut were similar in both years and varied in relation to the salt front. The primary prey in each year was the estuarine copepod Eurytemora affinis. Substantial consumption of the freshwater cladoceran Bosmina spp. also occurred, especially up-estuary of the salt front in 2007, demonstrating that secondary prey are important to larval diets in some years. Stable isotope analysis of yolk sac and feeding-stage larvae of striped bass revealed an ontogenetic shift from maternal stable isotope signatures to those indicative of prey source. Feeding-stage larvae from up-estuary locations had the most negative δ¹³C values, indicating a relatively high terrestrial carbon source in prey. Spatio-temporal variability in δ¹⁵N signatures of larvae followed similar trends of δ¹⁵N variability in zooplankton prey with the highest δ¹⁵N values up-estuary of the salt front and estuarine turbidity maximum. A stable isotope analysis on archived striped bass larvae collected in 1998 and 2003, years of moderate and high recruitment, respectively, expanded the documented range of isotope signatures but did not clearly distinguish effects of nutritional sources on recruitment.     

Comparison of intertidal habitat use and growth rates of two northern Puget Sound cohorts of 0+ age Dungeness crab,Cancer magister

Density, habitat use, and growth of intertidal 0+ age Dungeness crabs, Cancer magister, were examined at five northern Puget Sound (Washington, USA) sites between June 1984 and September 1987. Sampling was conducted biweekly during settlement, from June to September, and approximately monthly or bimonthly thereafter. Northern Puget Sound Dungeness crab populations appear to be largely supported by recruitment from inland parental stocks, but a smaller proportion of recruits originate from coastal or oceanic stocks, as evidenced by earlier settlement and larger size of the first instar. Settlement of Dungeness crabs in inland waters typically peaked in August, and interannual variation in year-class strength at settlement (measured as intertidal density) was low relative to that reported for coastal crab populations. Spatial and interannual differences in settlement densities were mediated by high postsettlement mortality, which varied inversely with habitat complexity. Seasonal densities were highest in mixed sand and gravel with an overstory of attached or drift macroalgae, intermediate in eelgrass (Zostera marina), and lowest on open sand. Postsettlement growth rates corresponded to seasonal water temperatures and were greatest for the coastal cohort that settled in May and June. This cohort was larger as first juvenile instars (7.2 mm carapace width, CW) and grew rapidly at summer temperatures in excess of 15°C to a size (>30 mm CW) that allowed emigration from intertidal to subtidal areas by September. The late summer cohort settled in August at 5.3 mm CW and soon after was subjected to decreasing autumn water temperatures. There crabs experienced little growth while over wintering in the intertidal, but growth rates increased in March, and the crabs emigrated in April and May, approximately 10 mo after settlement.     

Controls, variation, and a record of climate change in detailed stable isotope record in a single bryozoan skeleton

The long-lived (about 20 yr) bryozoan Adeonellopsis sp. from Doubtful Sound, New Zealand, precipitates aragonite in isotopic equilibrium with seawater, exerting no metabolic or kinetic effects. Oxygen isotope ratios (δ¹⁸O) in 61 subsamples (along three branches of a single unaltered colony) range from −0.09 to +0.68‰ PDB (mean = +0.36‰ PDB). Carbon isotope ratios (δ¹³C) range from +0.84 to +2.18‰ PDB (mean = +1.69‰ PDB). Typical of cool-water carbonates, δ¹⁸O-derived water temperatures range from 14.2 to 17.5 °C. Adeonellopsis has a minimum temperature growth threshold of 14 °C, recording only a partial record of environmental variation. By correlating seawater temperatures derived from δ¹⁸O with the Southern Oscillation Index, however, we were able to detect major events such as the 1983 El Niño. Interannual climatic variation can be recorded in skeletal carbonate isotopes. The range of within-colony isotopic variability found in this study (0.77‰ in δ¹⁸O and 1.34 in δ¹³C) means that among-colony variation must be treated cautiously. Temperate bryozoan isotopes have been tested in less than 2% of described extant species — this highly variable phylum is not yet fully understood.     

Plant growth and productivity along complex gradients in a Pacific northwest brackish intertidal marsh

Environmental characteristics were measured and recorded in the Skagit Marsh, a brackish intertidal marsh on Puget Sound, Washington. Four transects were placed perpendicular to a known gradient of increasing salinity which began with fresh water at the bank of one of the outlets of the Skagit River and reached a surface water salinity of 22‰ at a point alongshore 5 km north of the outlet. The environmental characteristics which were measured varied along gradients (soil texture, organic carbon in fines, soil column temperature, free soil water salinity) or had a patchy distribution (soil redox potential, soil macro-organic matter). Growth and production vary across the marsh. The maximum aboveground standing crop (1,742 g m^?2 dry weight) was measured at a site with 0–4‰ free soil water salinity, dominated by the sedgeCarex lyngbyei. In more saline areas (8–12‰), the bulrushScirpus americanus was dominant and standing crop values dropped to a third of the maximum. Species performance varied in a complex manner as did the environment.C. lyngbyei had diminished growth and decreased standing crop in areas where salinity was higher.S. americanus was equally productive in low elevation, high salinity sites and in high elevation, low salinity sites. An increase in shoot density for dominant species occurred in saline areas as individual shoot weights and leaf areas decreased. Because species responded differently, environmental variation was magnified in the population and community responses of the marsh vegetation.     

Small-scaled environmental changes: indications from stable isotopes of gastropods (Early Miocene, Korneuburg Basin, Austria)

The Korneuburg Basin, with mainly upper Lower Miocene (Karpatian) sediment filling, is divided by the Mollmannsdorf–Obergänserndorf Swell into two sub-basins characterised by different environmental settings. Paleoecological data indicate a marine northern part and a mainly estuarine southern part. Nevertheless, short-termed marine ingressions from the north allowed marine faunas (ostracods, molluscs, and echinoids) to temporarily settle the southern part of the basin. The carbon and oxygen isotopic composition of gastropod shells from these different environmental settings were investigated. Highest δ¹⁸O and δ¹³C values are found in Turritella shells from the northern part of the basin, and in Turritella shells from layers interpreted as a marine ingression in the south. Generally, components of the mudflat fauna (Tympanotonos cinctus, Granulolabium bicinctum, Terebralia bidendata, and Ocenebra crassilabiata) have slightly lower isotope values. Considerable freshwater influx in the southern part is documented by abundant freshwater genera such as Melanopsis, which show low carbon and oxygen isotope values. Data of identical taxa, especially Turritella and Granulolabium, reflect a trend from higher isotope values at the marine northern part to slightly lower values in the mainly estuarine southern part of the basin. Differences in δ¹⁸O between the marine and the estuarine assemblages are interpreted to be caused by changes in salinity and isotopic composition of ambient water rather than by temperature. Paleotemperature estimates derived from oxygen isotope data are in good agreement with existing paleoclimatic proxies for the Korneuburg Basin. Hence, an annual range of the sea-surface temperature from 13 to 26°C can be predicted within that protected basin.     

Human Influence at the Coast: Upland and Shoreline Stressors Affect Coastal Macrofauna and Are Mediated by Salinity

Observations and predictions regarding oceanic intrusions at the entrance to Puget Sound, WA (USA), are presented. Four years of seabed observations at Admiralty Inlet show episodic periods high salinity, coincident with landward residual currents near the seabed. The observed residual currents are consistent with an estuarine exchange flow during minimal tidal mixing, coincident with neap currents and maximum diurnal inequalities. These subtidal intrusions can carry dense water into Puget Sound and, thereby, renew the bottom water that is trapped landward of the sill. The oxygen concentration levels of these intrusions are often low, though not hypoxic, and may influence the oxygen levels in Puget Sound. The water mass properties of these intrusions are influenced strongly by regional dynamics, because the entrance to Puget Sound is connected to the open ocean via the Strait of Juan de Fuca. Coastal upwelling and discharge from the Fraser River discharge control the exchange flow in the Strait of Juan de Fuca and thus control the availability of dense water at the entrance to Puget Sound. The net effect of the tidal and regional dynamics is for intrusions with low oxygen levels to prevail in the late summer months. To predict intrusions in future years, an empirical method is developed and validated for daily application. The prediction method is based on publicly available operational data products and does not require in situ observations. In verification, 98% of intrusion events with dissolved oxygen less than 4.0 mg/L are successfully identified in a hindcast prediction for the 4-year observational record.     

Natural and Post-Urbanization Signatures of Hypoxia in Two Basins of Puget Sound: Historical Reconstruction of Redox Sensitive Metals and Organic Matter Inputs

Hypoxia has been observed in Hood Canal, Puget Sound, WA, USA since the 1970s. Four long sediment cores were collected in 2005 and age-dated to resolve natural and post-urbanization signatures of hypoxia and organic matter (OM) sources in two contrasting basins of Puget Sound: Main Basin and Hood Canal. Paleoecological indicators used for sediment reconstructions included pollen, stable carbon and nitrogen isotopes (??¹³C and ??¹⁵N), biomarkers of terrestrial OM (TOM), biogenic silica (BSi), and redox-sensitive metals (RSM). The sedimentary reconstructions illustrated a gradient in RSM enrichment factors as Hood Canal > Main Basin, southern > northern cores, and pre-1900s > 1900?C2005. The urbanization of Puget Sound watersheds during the 1900s was reflected as shifts in all the paleoecological signatures. Pollen distributions shifted from predominantly old growth conifer to successional alder, dominant OM signatures recorded a decrease in the proportion of marine OM (MOM) concomitant with an increase in the proportion of TOM, and the weight % of BSi decreased. However, these shifts were not coincidental with an overall increase in the enrichment of RSM or ??¹⁵N signatures indicative of cultural eutrophication. The increased percentage of TOM was independently verified by both the elemental ratios and lignin yields. In addition, isotopic signatures, BSi, and RSMs all suggest that OM shifts may be due to a reduction in primary productivity rather than an increase in OM regeneration in the water column or at the sediment/water interface. Therefore, the reconstructions suggested the Hood Canal has been under a more oxygenated ??stance?? during the twentieth century compared to prior periods. However, these 2005 cores and their resolutions do not encompass the period of high resolution water column measurements that showed short-lived hypoxia events and fish kills in Hood Canal during the early twenty-first century. The decoupling between the increased watershed-scale anthropogenic alterations recorded in the OM signatures and the relatively depleted RSM during the twentieth century suggests that physical processes, such as deep-water ventilation, may be responsible for the historical variation in oxygen levels. Specifically, climate oscillations may influence the ventilation and/or productivity of deep water in Puget Sound and particularly their least mixed regions.     

Isotopic variability in the aragonite shells of freshwater gastropods living in springs with nearly constant temperature and isotopic composition

We conducted a year-long, intensive monitoring program of live aquatic gastropods (Helisoma duryi, Melanoides tuberculata, Physa virgata, Pyrgulopsis sp., and Tyronia sp.) and their host springs in the Ash Meadows National Wildlife Refuge of southern Nevada. Our purpose was to constrain the degree of natural variation in the isotopic values of shell aragonite for gastropods living in near-constant conditions. Inter- and intraspecies variations, as well as within-shell variations, of δ¹⁸O and δ¹³C values for all taxa were larger than predicted based on variations in environmental conditions alone. This result suggests that different organisms growing in identical or nearly identical environmental conditions may not produce shells with equilibrium isotopic compositions and that these offsets from equilibrium may differ by small, but statistically significant amounts. For the gill-breathing, fully aquatic gastropods M. tuberculata, Pyrgulopsis sp., and Tyronia sp., the deviation of measured isotopic values compared to predicted values based on average environmental conditions were consistent with differences between taxa in the seasonal timing of shell growth. Measured values for the lung-breathing gastropods H. duryi and P. virgata were higher for δ¹⁸O and lower for δ¹³C than predicted at isotopic equilibrium, even when accounting for seasonality effects. We suggest that explaining the differences between the shell isotopic composition of lung- and gill-breathing snails requires a combination of both behavioral and physiologic factors. Our results illustrate the potential complexities of interpreting stable isotopic data from fossil gastropod shells even when environmental conditions are nearly constant, and place limitations on the paleoenvironmental deductions that can be made from the isotopic measurements on fossil gastropods.     

Integrating Multiple Natural Tags to Link Migration Patterns and Resource Partitioning Across a Subtropical Estuarine Gradient

Establishing links between migration patterns and trophic dynamics is paramount to ecological studies investigating the functional role habitats provide to resident and transient species. Natural tags in fishes, such as otolith chemistry and tissue stable isotopes, can help reconstruct previous environmental and dietary histories, although these approaches are rarely combined. A novel multiproxy natural tag approach was developed to estimate immigration patterns of juvenile Atlantic croaker Micropogonias undulatus, across contrasting salinity gradients in three subtropical estuaries of the western Gulf of Mexico. Juvenile young-of-year Atlantic croaker were collected along a latitudinal gradient that included positive, neutral, and negative estuaries, based on physicochemical (temperature, salinity, dissolved element) and isotopic (δ¹⁵N and δ¹³C) parameters. Otolith elemental chronologies of Sr/Ca and Ba/Ca were used to classify migratory types within each estuary, while tissue-specific isotope ratios revealed time since recent (liver~weeks) and longer term (muscle~months) diet shifts. Nitrogen isotopes in both liver and muscle tissues were highly correlated, suggesting tissue equilibrium and estuarine residence of at least 3 months, with geographic δ¹⁵N gradients reflecting the magnitude of anthropogenic nutrient enrichment within each estuary. Differences in isotopic equilibrium of muscle-liver δ¹³C values and variation in marginal edge otolith Sr/Ca and Ba/Ca suggested recent shifts in carbon source and habitat utilization, reflecting individualized movement across seascapes and connectivity of habitat mosaics. The multiproxy approach presented here identified diverse migration patterns and linked feeding and movement on regional (inter-estuary), local (intra-estuary), and individual scales to improve our understanding of habitat function across estuarine gradients.     

Salt-marsh tide pools as winter refuges for the mummichog,Fundulus heteroclitus,in New Jersey

Mummichog,Fundulus heteroclitus, were collected weekly from a southern New Jersey high-salinity salt marsh from October 1988 to June 1989 and from September 1989 to June 1990 to determine the overwintering habitat. Major habitat types sampled within the salt marsh were subtidal creek, intertidal creeks, and salt-marsh pools. Few individuals were collected in the intertidal creek or the subtidal creek from the end of October through the beginning of May for both years, when creek water temperatures were low. Both young-of-the-year and adults of both sexes were abundant in the salt-marsh pools (total lengths ranged from 29 mm to 125 mm) throughout the winter. In the spring, catch per unit effort (CPUE) within the tidal creek increased with increasing water temperature, while CPUE in marsh pools decreased with increases in estuarine water temperature. These collection patterns indicate that the majority ofF. heteroclitus may move from subtidal and intertidal creeks into salt-marsh pools in the late fall and leave in the spring. This seasonal movement could explain how fish survive winter environmental conditions because daily average water temperatures of salt-marsh pools were warmer than subtidal creek temperatures for much of the winter.     

Mg/Ca, Sr/Ca, and stable isotopes in modern and Holocene Protothaca staminea shells from a northern California coastal upwelling region

This study explores the potential of intertidal Protothaca staminea shells as high-resolution geochemical archives of environmental change in a coastal upwelling region. Mg/Ca and Sr/Ca ratios were analyzed by excimer laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) at sub-weekly temporal resolution in shells growing ∼1 mm per month. Growth patterns of a modern P. staminea shell from Humboldt Bay, California, collected in December 1999 made it possible to infer a lifespan from 1993 to 1998. Growth hiatuses in the shell may have excluded records of extreme events. Mg/Ca ratios appeared to be partly controlled by water temperature; the correlation coefficient between temperature and Mg/Ca was r = 0.71 in one of four growth increments. Significant year-to-year differences in the sensitivity of Mg/Ca to temperature in P. staminea could not be explained, however. Sr/Ca ratios appeared to be more closely related to shell growth rate. Oxygen isotopes, measured at 2-week temporal resolution in the same shell, did not show a clear relation to local temperature in summer, possibly because temperatures were higher and less variable at the King Salmon mudflat, where the shell was collected, than in the main channel of Humboldt Bay, where water properties were monitored. Negative shell δ¹³C values (<−0.5‰) marked spring and summer coastal upwelling events.The Mg contents of P. staminea midden shells dated to ∼3 ka and ∼9 ka were significantly lower than in the modern shell. This may have resulted from degradation of a Mg-rich shell organic matrix and precluded quantitative interpretation of the older high-resolution records. Elevated δ¹³C values in the ∼3 ka shell suggested that the individual grew in highly productive or stratified environment, such as a shallow coastal embayment or lagoon.     

Reconstructing Holocene palaeoclimate and palaeoceanography in Ìsafjarðardjúp,northwest Iceland,from two fjord records overprinted by relative sea‐level and local hydrographic changes

We reconstruct palaeoclimate and palaeoceanography of the Ísafjarðardjúp fjord system from two cores – one from the inner fjord and one near the fjord mouth – while separating the potential overprinting of relative sea‐level (RSL) and local fjord hydrographic changes on these records. The inner fjord core (B997‐339) reflects local fjord hydrography; the outer fjord core (MD99‐2266) reflects the regional oceanic signal. Glacial marine conditions ended at ca. 10 200 cal. a BP, indicated by both ice‐rafted debris records. The other proxy records show spatial and temporal variability within the fjord system. At the inner fjord site (B997‐339) foraminiferal assemblages and the δ¹⁸O record indicate lowered RSL between ca. 10 600 and 8900 cal. a BP and document the onset of fjord water overturning at ca. 8900 cal. a BP, which obscured the climate record. At the fjord mouth (MD99‐2266) mass accumulation rates suggest lowered RSL between ca. 10 200 and 5500 cal. a BP and local freshwater and/or reduced salinities of the Irminger Current water masses affected the δ¹⁸O signal between ca. 10 200 and 7900 cal. a BP. At MD99‐2266, foraminiferal fauna record the Holocene Thermal Maximum between ca. 8000 and 5700 cal. a BP and the onset of modern oceanic circulation at ca. 7000 cal. a BP. Copyright © 2010 John Wiley & Sons, Ltd.     

Contributions of coastal and watershed energy sources to secondary production in a Northeastern Pacific Estuary

We examined the relationship between variation in origin of organic matter and benthic secondary production in a shallow, macrotidal estuary on the United States Pacific Northwest coast, Willapa Bay, Washington. Spatial variation in energy sources and benthic productivity were investigated at both local (vertical height and cross-bank components) and regional (sites within the bay) scales. We determined the stable carbon isotope ratios of oysters (Crassostrea gigas) to evaluate marine versus terrestrial energy sources, compared growth rates of oysters, and made time series measurements of physical variablest at estuarine channel and intertidal stations. The stable carbon isotope ratios of oysters ranged from ?22‰ in inner portions of the estuary to ?18‰ near the mouth and oysters grown on the substrate surface were enriched in δ¹³C relative to those grown in the water column. These patterns are consistent with terrigenous inputs away from the estuary mouth and benthic microalgae in the diets of on-bottom oysters. The highest oyster growth was found at an inner estuary site where riverine inputs are relatively high and coincided, with high ammonium in the water column. However, for most sites in Willapa Bay, oyster growth actually declined away from the estuary mouth. Reducing the time available for feeding by transplanting oysters higher in the intertidal zone had significant negative effects on growth(e.g., a reduction of 27–35% over 0.5 m). Despite the fact that oysters grown on-bottom had access to different resources than those in the water column, their growth was slower at amy given tidal elevation, which may be due to on-bottom competition with other suspension feeders, boundary layer effects, or interference from turbidity. In a practical sense, oyster growers have been adjusting to allochthonous energetic support of food webs in Willapa Bay for more than a century, because they have traditionally moved oysters from southern parts of the bay where recruitment is relatively high to beds where market-size oysters can be grown closer to the mouth. This study provides mechanistic support for these practices and suggests that climatic events on a variety of temporal scales (Pacific Decadal Oscillation, upwelling events) could have economic consequences for aquaculture.     

Some observations on the life history of the amphipod crustacean,Hyale nilssoni (Rathke), in New Hampshire

Hyale nilssoni is an intertidal amphipod at open coastal and estuarine habitats in New Hampshire. Two juvenile recruitment peaks occurred during the year (spring and summerfall), with these peaks occurring earlier in the estuary. The spring peak coincided with increasing water temperature at both locations. Body sizes at the two habitats tended to be inversely related to water temperature resulting in a greater body size on the open coast. Energy demands on the animal associated with the fluctuating water temperatures and salinities likely attributed to the smaller body size of the animal in the estuarine population.     

The stable isotopic composition of coral skeletons: control by environmental variables

The reef corals Pocillopora damicornis and Montipora verrucosa were cultured under various controlled temperature and light conditions. The corals were analyzed for growth rate, tissue pigment content and skeletal ¹³C and ¹⁸O. Coral skeletal δ¹³C values varied with light dose and correlated with changes in zooxanthellar pigment. The δ¹³C values of skeletal aragonite seem to be modified by oxidation of photosynthetically produced organic matter.Functionally significant relationships between coral skeletal δ¹⁸O values and temperature have been determined. The temperature coefficients of the δ¹⁸O values [?4.4°C (%.)^?1] are similar to the first order coefficient in the equilibrium paleotemperature equation, but the δ¹⁸O values have taxonomically consistent offsets from equilibrium. The offsets may be attributed to the coral metabolism with slight but statistically significant differences between the two genera. Environmental and metabolic variables other than temperature have little or no effect on skeletal δ¹⁸O.     

Azaarenes in Puget sound sediments

The first quantitative measurements of azaarenes in marine sediments are reported for Puget Sound, in northwestern Washington State, U.S.A. Two- to four-ring azaarenes, in concentrations as low as 50 ppb (relative to organic carbon), are measured in ²¹⁰Pb dated sediments using glass capillary gas chromatography combined with nitrogen-selective detection.Azaarene distributions are geographically and temporally variable. Azaarene distributions in upper sediment layers suggest that total azaarene concentrations are related to proximity to urban areas, and may be anthropogenically derived. Subsurface maxima between 6 and 17 cm in several cores resemble similar maxima in PAH and organo-sulfur compounds. Trace quantities of azaarenes present in sediments, deposited prior to urbanization of the Puget Sound region, suggest low-level natural azaarene sources. One core containing particulate coal produced a concentrated and complex azaarene mixture, suggesting either introduction of mined coal or erosion of regional coal deposits. Analyses of possible azaarene sources indicate that although azaarene compositions vary between sources, coal azaarenes can be distinguished from petroleum azaarenes by their ratios of 2-ring to 3-ring azaarenes, and may identify predominant azaarene inputs in environmental samples. Gross differences in azaarene composition exist between European and American air particulates and sediments, suggesting differences in azaarene sources.     

Stable oxygen and carbon isotope profiles in an invasive bivalve (Corbicula fluminea) in North Carolina watersheds

The modern invasive bivalve Corbicula fluminea was collected in 2006 from three sites with different land uses located in a North Carolina River Basin. The primary objective was to describe the δ¹⁸O and δ¹³C profiles of C. fluminea shells under various land use conditions. An additional aim was to evaluate whether growth patterns of C. fluminea form seasonally. Annual shell growth patterns were measured from the umbo to the margin and co-varied with estimates of ambient water temperature, corresponding to seasonal variation. The C. fluminea growth patterns as translucent bands (slower growth) appeared to form during winter months and opaque bands (rapid growth) formed during summer. A mixed model analysis (ANOVA) showed a significant site level effect of δ¹⁸O and δ¹³C profiles examined among sites (F = 17.1; p = 0.003). A second model showed a borderline significant site effect among profiles with variability more pronounced at the urban site, Crabtree Creek (p = 0.085). Previous habitat assessment ratings and water chemistry measurements suggested that the urban site was more impacted by storm water runoff. Understanding δ¹⁸O and δ¹³C_SHELL profiles and shell growth patterns of the invasive bivalve (C. fluminea) may help establish a framework for using these animals as biomonitors to record water temperature and nutrient pollution.     

Sea-land oxygen isotopic relationships from planktonic foraminifera and speleothems in the Eastern Mediterranean region and their implication for paleorainfall during interglacial intervals

The oxygen and carbon stable isotope compositions of cave speleothems provide a powerful method for understanding continental climate change. Here, we examine the question of the regionality of this isotopic record and its linkage with the marine isotopic record in the Eastern Mediterranean (EM) region. The study presents a new, accurately dated 250-kyr δ¹⁸O and δ¹³C record determined from speleothems of the Peqiin Cave, Northern Israel. Its comparison with the continuous 185-kyr isotopic record of the Soreq Cave speleothems from Central Israel reveals striking similarities. Thus, a strong regional climatic signal, brought about by variations in temperature and rainfall amount, is reflected in both cave records. Low δ¹⁸O minima in the Peqiin profile for the last 250- to 185-kyr period (interglacial marine isotopic stage 7) match the timing of sapropels 9 to 7 and are indicative of high rainfall in the EM region at these times. The combined Soreq and Peqiin δ¹⁸O record for the last 250 kyr excellently matches the published Globigerinoides ruber (G. ruber) marine δ¹⁸O record for the EM Sea, with the isotopic compositional difference Δ_{G.ruber-speleothems} remaining relatively constant at −5.6 ± 0.7‰, thus establishing for the first time a robust, exploitable link between the land and the marine isotopic records. The correspondence of low δ¹⁸O speleothem values and high cave water stands with low G. ruber δ¹⁸O values during interglacial sapropel events indicates that these periods were characterized by enhanced rainfall in the EM land and sea regions. By use of sea surface temperatures derived from alkenone data as a proxy for land temperatures at the Soreq Cave, we calculate the paleorainfall δ¹⁸O values and its amounts. Maximum rainfall and lowest temperature conditions occurred at the beginning of the sapropel events and were followed by decrease in rainfall and increase in temperatures, leading to arid conditions. The record for the last 7000 yr shows a trend toward increasing aridity and agrees well with climatic and archeological data from North Africa and the Middle East.     

Stable isotope composition of subfossil Cerastoderma glaucum shells from the Szczecin Bay brackish deposits and its palaeogeographical implications (South Baltic Coast,Poland)

The environmental conditions of the Szczecin Bay, which existed prior to Szczecin Lagoon, have been reconstructed on the basis of the stable carbon and oxygen isotope (¹⁸O and ¹³C) analysis and radiocarbon dates obtained for subfossil shells of Cerastoderma (Cardium) glaucum. The shells in the collected core were well preserved in their life positions, representing a geochemical record of past temperature variation over the middle Holocene. Three major periods with different thermal conditions have been distinguished in the interval ~ 6000–4300 cal yr BP, when the important Littorina regional transgression took place. During the first period, 6000–5250 cal yr BP, water temperature decreased by 1.4°C, and then remained constant over the second period (5250–4750 cal yr BP). In contrast, during the third period (4750–4300 cal yr BP) both δ-values were highly variable and the mean summer temperature (March–November) increased by about 3.5°C. During first two periods, δ¹⁸O and δ¹³C were significantly correlated, indicating stability of the environmental conditions.     

Isotopic partitioning between scallop shell calcite and seawater: effect of shell growth rate

The relationship between molluscan shell growth rate and skeletal δ¹⁸O and δ¹³C was investigated in a detailed field study for the scallop, Pecten maximus. Seasonal variation in shell growth rate was found to be a governing factor influencing shell δ¹⁸O and δ¹³C. At low shell growth rates, shell δ¹⁸O were more positive (of the order +0.4‰) and δ¹³C more negative (up to −2‰) as compared with predicted values for precipitation of inorganic calcite in isotopic equilibrium with seawater. The deviations in δ¹⁸O were hypothesized as reflecting possible differences in solution carbonate chemistry at the site of mineralization in the extrapallial fluid as compared with that of the external seawater medium. The deviations in shell δ¹³C were consistent with incorporation of isotopically depleted respiratory ¹³C (i.e., a metabolic effect). A trend toward more depleted shell δ¹⁸O and δ¹³C values occurred at higher shell growth rates, with negative δ¹⁸O values as compared with predicted equilibrium at shell growth rates above 0.13 mm per day. These simultaneous negative deviations in skeletal δ¹⁸O and δ¹³C were interpreted as resulting from a kinetic effect. The implications for environmental reconstruction from molluscan isotopic records are discussed in light of a model of isotopic behavior based on the findings of the study.