Environmental changes in the aftermath of Neoproterozoic glaciations: a biogeochemical study of sediments from SW-Gondwana

Abstract The late Neoproterozoic or Ediacaran period, (635 to -543 Ma) is a primordial time in the Earth history corresponding to the beginning of animal life and the most extreme ice ages on Earth. In this dissertation, palaeoenvironmental conditions were reconstructed for Ediacaran, post-Gaskiers shelf deposits in SW- Gondwana and their changes were evaluated according to the diversity of organisms. The present study addresses the question of interactions between biodiversity and environmental change by using the elemental and isotopic geochemistry of sedimentary rocks and associated organic matter, as well as the distribution of hydrocarbon biomarkers. The studied sedimentary sequences are from a large basin extended from the Paraguay belt to the Rio de la Plata craton, including the Corumbâ Group in SW-Brazil (Paraguay belt), the Arroyo del Soldado Group in Uruguay and the Sierras Bayas Group in Argentina (both in the Rio de la Plata craton). Several geochemical signatures of the sediments from Corumbâ and Sierras Bayas groups provides evidence for an euxinic setting in the Ediacaran Ocean: 1) The occurrence of syngenetic pyrite in the Corumbâ Group together with hydrocarbon biomarkers of an anoxic microbial consortium including traces of gammacerane, a distribution of hopanes with maxima at C29 as well as a low pristane/phytane (Pr/Ph) ratio; 2) the occurrence of 34S enrichments within sulfides of the Sierras Bayas Group exceeding the sulfur isotopic composition of coeval carbonate-associated sulfate. In the Arroyo del Soldado Group, an event of reducing conditions was revealed by higher concentrations of redox-sensitive trace elements and negative 513Ccar shifts in all sections. This event is extended to the whole unit in the deepest section and is restricted to tempestites in the two other shallow sections. The persistent negative. ôl3Ccar values recorded at the basinal setting implies strong isotopic gradient between shallow and deep water environments and therefore, a locus of deposition below the redox chemocline. In all studied sections, the excursions, the strong enrichment of authigenic trace-elements, the occurrence of longer chain «-alkanes, gammacerane and low Pr/Ph and Ph/>;-C]a ratios, combined with the previous sedimentological and paleontological observations indicate that the chemistry of the ocean was strongly controlled by the oxygen availability; waters being moderately oxic at the surface and anoxic at depth for much of the Neoproterozoic. This water column stratification was favourable to the storage of large amounts of nutrients in the deep ocean. During upwelling periods, the export of these nutrient-rich waters may have triggered an important bioproductivity in surface waters. Drops in Al3Cc,,.](Cr and positive ôl3Ccllr excursions highlight the increase in primary productivity. Preservation of organic carbon was ensured by reducing conditions at the bottom. The Al3ccar.kcr excursions could also reflect changes in the composition of the primary biomass. New geochemical evidence from SW-Gondwana sections supports a stratified Ediacaran ocean, outside restricted or hypersaline environments, in the aftermath of glaciations. The association of ocean stratification and the appearance of metazoans support the model that the evolution of eukaryotic life was related to the increase of oxygen levels in surface environments due to an efficient recycling of nutrients in the anoxic deep ocean. Résumé Le Néoprotérozoïque terminal, ou Édiacarien (635 à -543 Ma), est un période de première importance dans l'histoire de la Terre, car elle correspond a l'apparition des métazoaires pendant un intervalle de glaciations extrêmes. Le présent mémoire se propose de reconstituer les conditions paléoenvironnementales des dépôts de plateforme mis en place durant l'Édiacarien, au sud-ouest du Gondwana. Les interactions entre changements environnementaux et biodiversité sont évaluées en s'appuyant d'une part sur la composition élémentaire et isotopique des roches sédimentaires et de leur matière organique, et d'autre part sur la distribution moléculaire de biomarqueurs hydrocarbonés. Les séquences sédimentaires étudiées proviennent d'un grand bassin qui s'étend de la chaîne du Paraguay jusqu'au craton du Rio de la Plata. La séquence du Groupe Corumbâ au Sud Ouest du Brésil se situe dans la chaîne du Paraguay, tandis que le Groupe Arroyo del Soldado en Uruguay et le Groupe Sierras Bayas en Argentine sont situés sur le craton du Rio de la Plata. L'étude géochimique des sédiments des groupes Corumbâ et Sierras Bayas révèle de façon claire des conditions euxiniques dans l'océan édiacarien. On trouve ainsi, dans le Groupe Corumbâ, les biomarqueurs d'un cortège microbien anoxique et sulfurique comprenant des bactéries sulfato-réductrices, et dans les sulfures du Groupe Sierras Bayas, des enrichissements en Î4S excédant les rapports isotopiques du soufre dans le sulfate cogénétique associé aux carbonates. Dans la séquence de l'Arroyo del Soldado, un événement réducteur est mis en évidence par des teneurs plus élevées en éléments traces sensibles aux conditions redox et par des excursions négatives du 613Ccardans toutes les coupes. Cet événement affecte la totalité de la section la plus profonde et n'apparaît que dans les tempestites dans les sections les moins profondes. La persistance de valeurs négatives du ô13Ccarau large implique un gradient isotopique prononcé entre les environnements superficiels et profonds, et donc, ta présence d'une chémocline redox. Les excursions du. ôBCcar, l'enrichissement authigène en éléments traces, la présence de gammacérane et de rt-alcanes à longue chaîne, ainsi que de faibles rapports Pr/Ph et Ph/«-Cl8, viennent s'ajouter aux observations préliminaires sur la sédimentologie et la paléontologie pour indiquer que la chimie de l'océan était fortement contrôlée par la disponibilité d'oxygène, les eaux étant modérément oxiques à la surface et anoxiques en profondeur pendant la plus grande partie du Néoprotérozoïque. La stratification de la colonne d'eau était favorable au stockage de grandes quantités de nutriments dans l'océan profond. Dans les zones d'upwelling, la migration d'eaux profondes riches en nutriment vers la surface a pu provoquer une bioproductivité prononcée dans les eaux de surface. La conservation du carbone organique était assurée par les conditions anoxiques prévalant au fond. Les excursions du A13Ccar.kt.r pourraient aussi refléter des changements dans la biomasse primaire. Le présent travail apporte donc de nouvelles preuves qu'un océan stratifié s'est maintenu à la suite des glaciations néoprotérozoïques dans le Sud Ouest du Gondwana. L'association d'un océan stratifié et de l'apparition de la vie animale est en accord avec le modèle stipulant que l'évolution de la vie est associée à une meilleure oxygénation des environnements de surface. Résumé pour le grand public La période Ediacarienne (635 à -543 Ma) à la fin du Précambrien est l'une de plus énigmatiques dans l'histoire de la Terre, car elle est caractérisée par la diversification de la vie multicellulaire (eucaryote) pendant un intervalle de glaciations extrêmes. Dans ce travail de thèse, nous cherchons à déceler l'existence éventuelle d'un lien entre ces changements environnementaux et l'évolution de la vie eucaryote à travers une étude biogéochimique. La biogéochimie est l'étude des activités biologiques dans la géosphère, telles que celles intervenant dans les cycles des éléments chimiques (y compris les isotopes stables) et celles de production de composés carbonés caractérisant certains groups d'organismes ou taxons. La recherche des signatures paléoenvironnementales dans les roches précambriennes a été fortement facilitée par l'utilisation des biomarqueurs ou fossiles moléculaires. Ces composés, provenant des lipides biologiques (molécules avec des fonctions spécifiques dans les organismes), peuvent être reliés à des taxons spécifiques ou à des voies métaboliques. La transformation d'un biolipide en fossile moléculaire intervient lorsque des restes organiques déposés dans un substrat subissent un enfouissement et une augmentation de la pression (diagenèse). Ce processus mène à la formation de kérogène, un grand agrégat chimique de matière organique insoluble dans des solvants organiques, et de bitume ou fraction soluble (extractible) de la matière organique. L'analyse intégrée du kérogène et du bitume fournit des indications précieuses pour les reconstitutions paléoenvironnementales. Des conditions paléoenvironnementales ont ainsi été déterminées pour une plateforme marine Ediacarienne située dans la partie sud-américaine du bloc occidental du paléocontinent Gondwana. Les séquences sédimentaires étudiées appartiennent au même bassin qui s'étend de la ceinture du Paraguay (Groupe Corumbâ, Brésil) au craton du Rio de la Plata (Groupes Arroyo del Soldado, Uruguay et Sierras Bayas, Argentina). Nous nous sommes intéressés aux isotopes stables de carbonates et de la matière organique associée (kérogène et bitume), aux éléments majeurs et traces, ainsi qu'aux biomarqueurs caractérisant ces roches. Les résultats de cette dissertation suggèrent qu'au cours de l'Édiacarien, suite aux glaciations néoprotérozoïques dans le bloc occidental du Gondwana, l'océan était stratifié en zones spécifiques d'eaux riches en sulfures et dépourvues d'oxygène (euxiniques). L'association d'un océan stratifié et de l'apparition de la vie animale est en accord avec le modèle stipulant que l'évolution de la vie est associée à une meilleure oxygénation des environnements de surface. Les excursions isotopiques (tendance à des valeurs positives ou négatives) en constante fluctuation pour le carbone et très positives pour le soufre des sulfures, l'enrichissement en éléments trace et la présence de certains composés (e.g. gammacerane; Pr/Ph et Ph/«-Ci8 en basse proportion) conjugués aux observations sédimentologiques et paléontologiques des différents profils étudiés indiquent que la chimie de l'océan était fortement contrôlée par la disponibilité d'oxygène, avec des eaux modérément oxygénées en surface et euxiniques en profondeur pour la plupart du Néoprotérozoïque.

A comparison of alpha and gamma spectrometry for environmental natural radioactivity surveys.

An alpha-spectrometry, using automated borate fusion and sequential extraction and exchange chromatography, was used to determine the uranium and thorium based on environmental radioactivity of 20 soil samples. The same set of the samples was analysed using gamma-spectrometry with an HPGe detector. The two data sets were checked for coherence using Z-score and chi2 statistical tests. We show that gamma-spectrometry is a valid alternative to time-consuming alpha-spectrometry for the determination of natural uranium and thorium activity in soil (activity range: 12.5-58.2 Bq/kg). The measured activities were compared with the theoretical activities to ensure secular equilibrium in the 238U and 232Th series. For 226Ra, a special study was made on deconvolution of the 186 keV multiplet with the Levenberg-Marquardt algorithm. Finally, the combined use of Z-score and chi2-tests was found to be a powerful tool for comparing the results obtained with two different methods.

Biogeochemical processes controlling oxygen and carbon isotopes of diatom silica in Late Glacial to Holocene lacustrine rhythmites

Biogeochemical cycles and sedimentary records in lakes are related to climate controls on hydrology and catchment processes. Changes in the isotopic imposition of the diatom frustules (δ 18 O diatom and δ 13 C diatom ) in lacustrine sediments can be used to reconstruct palaeoclimatic and palaeoenvironmental changes. The Lago Chungará (Andean Altiplano, 18°15 ′ S, 69°10 ′ W, 4520 masl) diatomaceous laminated sediments are made up of white and green multiannual rhythmites. White laminae were formed during short-term diatom super-blooms, and are composed almost exclusively of large-sized Cyclostephanos andinus.These diatoms bloom during mixing events when recycled nutrients from the bottom waters are brought to the surface and/or when nutrients are introduced from the catchment during periods of strong runoff. Conversely, the green laminae are thought to have been deposited over several years and are composed of a mixture of diatoms (mainly smaller valves of C. andinus and Discostella stelligera ) and organic matter. These green laminae reflect the lake's hydrological recovery from a status favouring the diatom super-blooms (white laminae) towards baseline conditions. δ 18 O diatom and δ 13 C diatom from 11,990 to 11,530 cal years BP allow us to reconstruct shifts in the precipitation/evaporation ratio and changes in the lake water dissolved carbon concentration, respectively. δ 18 O diatom values indicate that white laminae formation occurred mainly during low lake level stages, whereas green laminae formation generally occurred during high lake level stages. The isotope and chronostratigraphical data together suggest that white laminae deposition is caused by extraordinary environmental events. El Niño-Southern Oscillation and changes in solar activity are the most likely climate forcing mechanisms that could trigger such events, favouring hydrological changes at interannual-to-decadal scale. This study demonstrates the potential for laminated lake sediments to document extreme pluriannual events.

Environmental determinants of foraging strategies in Cory"s shearwaters Calonectris diomedea

Despite the advent of devices to track seabird movements, the extent to which productive areas and oceanic winds influence foraging strategies is still not fully understood. We investigated the main environmental determinants of foraging strategies in Cory"s shearwaters Calonectris diomedea by combining satellite-tracking information from 14 birds breeding on the Canary Islands with concurrent data on chlorophyll a (chl a) concentrations and oceanic winds. Additionally, we took blood samples at the end of each foraging trip and analysed carbon (C) and nitrogen (N) stable isotopes to examine the use of trophic resources. All birds showed commuting trips, concentrating foraging activity exclusively on the African continental shelf. Foraging locations showed a strong association with chl a concentrations, suggesting birds select foraging areas according to prey availability. In contrast with other breeding colonies where Cory"s shearwaters use a dual-foraging method, birds showed a unimodal strategy and did not show differences in C and N isotope signatures in plasma, confirming that close proximity to highly productive areas strongly influences foraging strategies. In addition, birds tracked during 2 consecutive trips foraged in the same area, suggesting that high resource availability promotes fidelity to feeding grounds also at coarse scales. Persistent northeast trade winds blew during the study period, and commuting trips followed a consistent clockwise movement with a southwest heading while the birds foraged along the continental shelf, suggesting that birds used tail winds to reduce their flying costs. Our results corroborate that oceanographic conditions in the vicinity of the breeding colony have a strong effect on foraging strategies of pelagic seabirds.

Conservative nutrient use by big-leaf mahogany (Swietenia macrophylla king) planted under contrasting environmental conditions

We analyzed the nutritional composition and isotope ratios (C and N) of big-leaf mahogany (Swietenia macrophylla King) leaves in plantations established on contrasting soils and climates in Central America (State of Quintana Roo, Yucatán, México) and South America (State of Pará, Brazil). The objective was to determine the adaptability of this species to large differences in nutrient availability and rainfall regimes. Nutrient concentrations of leaves and soils were determined spectrophotometrically, and isotope ratios were measured using mass spectrometric techniques.In Pará soils were sandier, and acidic, receiving above 2000 mm of rain, whereas in Quintana Roo soils were predominantly clayey, with neutral to alkaline pH due to the underlying calcareous substrate, with about 1300 mm of rain. Leaf area/weight ratio was similar for both sites, but leaves from Quintana Roo were significantly smaller. Average N and K concentrations of adult leaves were similar, whereas Ca concentration was only slightly lower in Pará in spite of large differences in Ca availability. Leaves from this site had slightly higher P and lower Al concentrations. Differences in water use efficiency as measured by the natural abundance of 13C were negligible, the main effect of lower rainfall in Quintana Roo seemed to be a reduction in leaf area. The N isotope signature (δ15N) was more positive in Pará than in Quintana Roo, suggesting higher denitrification rates in the former. Results reveal a calciotrophic behavior and a remarkable capacity of mahogany to compensate for large differences in soil texture and nutrient availability.

“Pussy cat, pussy cat where have you been..?” Evaluating the use of stable isotopes, radiogenic isotopes and trace elements for investigating the ecology of Panthera leo

1. Understanding the behaviour and ecology of large carnivores is becoming increasingly important as the list of endangered species grows, with felids such as Panthera leo in some locations heading dangerously close to extinction in the wild. In order to have more reliable and effective tools to understand animal behaviour, movement and diet, we need to develop novel, integrated approaches and effective techniques to capture a detailed profile of animal foraging and movement patterns. 2. Ecological studies have shown considerable interest in using stable isotope methods, both to investigate the nature of animal feeding habits, and to map their geographical location. However, recent work has suggested that stable isotope analyses of felid fur and bone is very complex and does not correlate directly with the isotopic composition of precipitation (and hence geographical location). 3. We present new data that suggest these previous findings may be atypical, and demonstrate that isotope analyses of Felidae are suitable for both evaluating dietary inputs and establishing geo-location as they have strong environmental referents to both food and water. These data provide new evidence of an important methodology that can be applied to the family Felidae for future research in ecology, conservation, wildlife forensics and archaeological science.

Radon in groundwaters from Guarany aquifer, South America: environmental and exploration implications

Groundwater and sandstone samples were analyzed for radon in Guarany aquifer, Parana sedimentary basin, South America. The dissolved radon ranged between 3 and 3303 pCi/l, being lognormally distributed, with a modal value of 1315 pCi/l, and a median value of 330 pCi/l. Rn-222 leakage experiments for sandstones yielded a theoretical value of 1390 pCi/l for Rn-222 in water, showing that theoretical modeling can reliably be used to interpret laboratory and field data. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

Weathering rates at Alto Sorocaba basin, Brazil, using U-isotopes and major cations

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The U-isotopes modeling in aquifers from Pocos de Caldas plateau, Brazil

U-modeled groundwater residence times were estimated by changes in U-234/U-238 activity ratio (AR) and U content of groundwaters from Pocos de Caldas city situated at the Pocos de Caldas alkaline massif, Brazil. The estimated ages are more realistic than others generated by the use of hydraulic conductivity data and available information about the weathering rate of rocks in the plateau. The U-234/U-238 AR and reciprocal of the dissolved U-content data also defined a ternary plot that allowed the calculation of the relative volume of three source waters for the mixed water. Such U-isotopes modeling for mixing calculations indicated that the dominant phase (68%) in the mixture is thermal.

A method for evaluating Ra-228 in environmental matrices and its use at Pocos de Caldas plateau, Brazil

This work describes a methodology developed for performing the extraction, detection and quantification of Ra-228 in waters, suspended solids and sediments. The technique proved to be useful for analyzing samples from the hydrological environment of Morro do Ferro, Pocos de Caldas plateau, Brazil. The 228Ra activity in underground waters of 5 boreholes drilled in the area varied from 0.02 up to 14.5 Bq/l, whereas for the surficial waters the variation was from 0.04 to 0.51 Bq/l; for the suspended solids, the values ranged from 1.5 up to 419 Bq/g, whereas it was possible to find a value of 2.04 Bq/g for the sediments. These results show the applicability of the method for characterizing different matrices of environmental interest. (C) 2002 Elsevier B.V. Ltd. All rights reserved.

A comparative study of aquifer systems occurring at the Paraná sedimentary basin, Brazil: U-isotopes contribution

The radioactivity due to 238U and 234U in three aquifer systems occurring within the Paraná sedimentary basin, South America, has been investigated. Uranium is much less dissolved from fractured igneous rocks than from the porous sedimentary rocks as indicated by the U-mobility coefficients between 7. 6 × 10-6 and 1. 2 × 10-3 g cm-3. These values are also compatible with the U preference ratios relative to Na, K, Ca, Mg and SiO2, which showed that U is never preferentially mobilized in the liquid phase during the flow occurring in cracks, fissures, fractures and faults of the igneous basaltic rocks. Experimental dissolution of diabase grains on a time-scale laboratory has demonstrated that the U dissolution appeared to be a two-stage process characterized by linear and second-order kinetics. The U dissolution rate was 8 × 10-16 mol m-2 s-1 that is within the range of 4 × 10-16-3 × 10-14 mol m-2 s-1 estimated for other rock types. The 234U/238U activity ratio of dissolved U in solutions was higher than unity, a typical result expected during the water-rock interactions when preferential 234U-leach from the rock surfaces takes place. Some U-isotopes data allowed estimating 320 ka for the groundwater residence time in a sector of a transect in São Paulo State. A modeling has been also realized considering all U-isotopes data obtained in Bauru (35 samples), Serra Geral (16 samples) and Guarani (29 samples) aquifers. The results indicated that the Bauru aquifer waters may result from the admixture of waters from Guarani (1. 5 %) and Serra Geral (98. 5 %) aquifers. © 2012 Springer-Verlag.

Hydrochemical and stable isotopes (H, O, S) signatures in deep groundwaters of Parana basin, Brazil

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Exploring physical processes related to past climate proxies: lake sediments and stable water isotopes

Proxy data are essential for the investigation of climate variability on time scales larger than the historical meteorological observation period. The potential value of a proxy depends on our ability to understand and quantify the physical processes that relate the corresponding climate parameter and the signal in the proxy archive. These processes can be explored under present-day conditions. In this thesis, both statistical and physical models are applied for their analysis, focusing on two specific types of proxies, lake sediment data and stable water isotopes.rnIn the first part of this work, the basis is established for statistically calibrating new proxies from lake sediments in western Germany. A comprehensive meteorological and hydrological data set is compiled and statistically analyzed. In this way, meteorological times series are identified that can be applied for the calibration of various climate proxies. A particular focus is laid on the investigation of extreme weather events, which have rarely been the objective of paleoclimate reconstructions so far. Subsequently, a concrete example of a proxy calibration is presented. Maxima in the quartz grain concentration from a lake sediment core are compared to recent windstorms. The latter are identified from the meteorological data with the help of a newly developed windstorm index, combining local measurements and reanalysis data. The statistical significance of the correlation between extreme windstorms and signals in the sediment is verified with the help of a Monte Carlo method. This correlation is fundamental for employing lake sediment data as a new proxy to reconstruct windstorm records of the geological past.rnThe second part of this thesis deals with the analysis and simulation of stable water isotopes in atmospheric vapor on daily time scales. In this way, a better understanding of the physical processes determining these isotope ratios can be obtained, which is an important prerequisite for the interpretation of isotope data from ice cores and the reconstruction of past temperature. In particular, the focus here is on the deuterium excess and its relation to the environmental conditions during evaporation of water from the ocean. As a basis for the diagnostic analysis and for evaluating the simulations, isotope measurements from Rehovot (Israel) are used, provided by the Weizmann Institute of Science. First, a Lagrangian moisture source diagnostic is employed in order to establish quantitative linkages between the measurements and the evaporation conditions of the vapor (and thus to calibrate the isotope signal). A strong negative correlation between relative humidity in the source regions and measured deuterium excess is found. On the contrary, sea surface temperature in the evaporation regions does not correlate well with deuterium excess. Although requiring confirmation by isotope data from different regions and longer time scales, this weak correlation might be of major importance for the reconstruction of moisture source temperatures from ice core data. Second, the Lagrangian source diagnostic is combined with a Craig-Gordon fractionation parameterization for the identified evaporation events in order to simulate the isotope ratios at Rehovot. In this way, the Craig-Gordon model can be directly evaluated with atmospheric isotope data, and better constraints for uncertain model parameters can be obtained. A comparison of the simulated deuterium excess with the measurements reveals that a much better agreement can be achieved using a wind speed independent formulation of the non-equilibrium fractionation factor instead of the classical parameterization introduced by Merlivat and Jouzel, which is widely applied in isotope GCMs. Finally, the first steps of the implementation of water isotope physics in the limited-area COSMO model are described, and an approach is outlined that allows to compare simulated isotope ratios to measurements in an event-based manner by using a water tagging technique. The good agreement between model results from several case studies and measurements at Rehovot demonstrates the applicability of the approach. Because the model can be run with high, potentially cloud-resolving spatial resolution, and because it contains sophisticated parameterizations of many atmospheric processes, a complete implementation of isotope physics will allow detailed, process-oriented studies of the complex variability of stable isotopes in atmospheric waters in future research.rn

High-resolution reconstruction of Holocene climate variability and environmental changes in the North Pacific using bivalve shells

Bivalve mollusk shells are useful tools for multi-species and multi-proxy paleoenvironmental reconstructions with a high temporal and spatial resolution. Past environmental conditions can be reconstructed from shell growth and stable oxygen and carbon isotope ratios, which present an archive for temperature, freshwater fluxes and primary productivity. The purpose of this thesis is the reconstruction of Holocene climate and environmental variations in the North Pacific with a high spatial and temporal resolution using marine bivalve shells. This thesis focuses on several different Holocene time periods and multiple regions in the North Pacific, including: Japan, Alaska (AK), British Columbia (BC) and Washington State, which are affected by the monsoon, Pacific Decadal Oscillation (PDO) and El Niño/Southern Oscillation (ENSO). Such high-resolution proxy data from the marine realm of mid- and high-latitudes are still rare. Therefore, this study contributes to the optimization and verification of climate models. However, before using bivalves for environmental reconstructions and seasonality studies, life history traits must be well studied to temporally align and interpret the geochemical record. These calibration studies are essential to ascertain the usefulness of selected bivalve species as paleoclimate proxy archives. This work focuses on two bivalve species, the short-lived Saxidomus gigantea and the long-lived Panopea abrupta. Sclerochronology and oxygen isotope ratios of different shell layers of P. abrupta were studied in order to test the reliability of this species as a climate archive. The annual increments are clearly discernable in umbonal shell portions and the increments widths should be measured in these shell portions. A reliable reconstruction of paleotemperatures may only be achieved by exclusively sampling the outer shell layer of multiple contemporaneous specimens. Life history traits (e.g., timing of growth line formation, duration of the growing season and growth rates) and stable isotope ratios of recent S. gigantea from AK and BC were analyzed in detail. Furthermore, a growth-temperature model based on S. gigantea shells from Alaska was established, which provides a better understanding of the hydrological changes related to the Alaska Coastal Current (ACC). This approach allows the independent measurement of water temperature and salinity from variations in the width of lunar daily growth increments of S. gigantea. Temperature explains 70% of the variability in shell growth. The model was calibrated and tested with modern shells and then applied to archaeological specimens. The time period between 988 and 1447 cal yrs BP was characterized by colder (~1-2°C) and much drier (2-5 PSU) summers, and a likely much slower flowing ACC than at present. In contrast, the summers during the time interval of 599-1014 cal yrs BP were colder (up to 3°C) and fresher (1-2 PSU) than today. The Aleutian Low may have been stronger and the ACC was probably flowing faster during this time.