Composition of the early Oligocene ocean from coral stable isotope and elemental chemistry

A sectioned and polished specimen of the coral Archohelia vicksburgensis from the early Oligocene Byram Formation (～30 Ma) near Vicksburg, Mississippi, reveals 12 prominent annual growth bands. Stable oxygen isotopic compositions of 77 growth‐band‐parallel microsamples of original aragonite exhibit well‐constrained fluctuations that range between ?2.0 and ?4.8. Variation in δ¹⁸O of coral carbonate reflects seasonal variation in temperature ranging from 12 to 24 °C about a mean of 18 °C. These values are consistent with those derived from a bivalve and a fish otolith from the same unit, each using independently derived palaeotemperature equations. Mg/Ca and Sr/Ca ratios were determined for 40 additional samples spanning five of the 12 annual bands. Palaeotemperatures calculated using elemental‐ratio thermometers calibrated on modern corals are consistently lower; mean temperature from Mg/Ca ratios are 12.5 ± 1 °C while those from Sr/Ca are 5.8 ± 2.2 °C. Assuming that δ¹⁸O‐derived temperatures are correct, relationships between temperature and elemental ratio for corals growing in today's ocean can be used to estimate Oligocene palaeoseawater Mg/Ca and Sr/Ca ratios. Calculations indicate that early Oligocene seawater Mg/Ca was ～81% (4.2 mol mol^?1) and Sr/Ca ～109% (9.9 mmol mol^?1) of modern values. Oligocene seawater with this degree of Mg depletion and Sr enrichment is in good agreement with that expected during the Palaeogene transition from ‘calcite’ to ‘aragonite’ seas. Lower Oligocene Mg/Ca probably reflects a decrease toward the present day in sea‐floor hydrothermal activity and concomitant decrease in scavenging of magnesium from seawater. Elevated Sr/Ca ratio may record lesser amounts of Oligocene aragonite precipitation and a correspondingly lower flux of strontium into the sedimentary carbonate reservoir than today.     

Foraminiferal distribution on the continental margin off Nova Scotia

Q-mode factor analysis of total foraminiferal abundance data (living plus dead) from 250 grab samples taken from the continental margin off Nova Scotia allows the determination of eight factor assemblages. On the northeastern shelf, an exclusively agglutinated assemblage dominated byAdercotryma glomerata occupies both banks and basins. Central shelf basins contain a predominantly calcareous assemblage dominated byGlobobulimina auriculata andNonionellina labradorica. Transitional between these two factor assemblages is an agglutinated assemblage dominated bySaccammina atlantica. Consistently present along the shelf edge is aTrifarina angulosa assemblage. In northeastern bays and a few samples near Sable Island, an agglutinatedEggerella advena assemblage is found. A relict and transport affected assemblage dominated byElphidium excavatum occurs in the southwestern approaches to Emerald Basin. Sandy/gravelly areas of the inner shelf and outer bank regions are characterized by aCibicides lobatulus assemblage.The statistical relationships of these defined assemblages to various aspects of the marine environment (depth, temperature, salinity, percent gravel, sand and mud) were investigated through multiple regression techniques. Results indicate that the present foraminiferal distribution patterns off Nova Scotia are influenced by the prevailing watermass characters and substrate. TheAdercotryma glomerata assemblage is influenced by the presence of cold, (0–4°C) low salinity waters (32–33‰) of arctic, Labrador Current origin. The central basin assemblage (G. auriculata) is related to warmer (8–12°C) more saline waters (35‰) of slope origin. The transition between these two bottom waters is marked by the opportunisticSaccammina atlantica assemblage. Preferred substrate character possibly determines the occurrence of theCibicides lobatulus, Islandiella islandica andEggerella advena assemblages.Trifarina angulosa shows a significant relationship to salinity and depth.Although the surficial sediments on the Nova Scotian Shelf are largely the product of reworking of glacial deposits during late glacial and early Holocene times, all but theE. excavatum factor assemblage appear to be in equilibrium with the modern oceanographic regime.     

Evaporation effects as reflected in freshwaters and ostracod calcite from modern environments in Central and Northeast Yakutia (East Siberia,Russia)

Taxonomical and geochemical investigations on freshwater ostracods from 15 waters in Central and Northeast (NE) Yakutia have been undertaken in order to estimate their potential usefulness in palaeoenvironmental reconstructions based on regional fossil records. Higher variability in environmental factors such as pH, electrical conductivity, and ionic content was observed in thermokarst-affected lakes in Central Yakutia than in NE Yakutia lakes. Species diversity of freshwater ostracods reached up to eight taxa per lake, mostly dominated by Candona weltneri Hartwig 1899, in Central Yakutia, whereas in NE Yakutian waters the diversity was lower and Candona muelleri jakutica Pietrzeniuk 1977 or Fabaeformiscandona inaequivalvis (Sars 1898) had highest frequencies. Coupled analyses of stable isotopes (δ¹⁸O, δ¹³C) and element ratios (Sr/Ca, Mg/Ca) were performed on both host waters and ostracod calcite, aiming to estimate the modern relationships. Correlations between host waters and ostracod calcite of single species were found for δ¹⁸O, δ¹³C and Sr/Ca and Mg/Ca ratios. The relationships between δ¹⁸O, Mg/Ca and Sr/Ca ratios and electrical conductivity (salinity) as an expression of solute concentrations in the waters mainly controlled by evaporation are more complicated but evident, and may be useful in future interpretation of geochemical data from fossil Siberian ostracods. Handling editor: K. Martens     

The distribution of living benthic foraminifera on the continental slope and rise off southwest Norway

Surface sediment samples taken by ? corer from 45 stations on the Norwegian continental margin and in the Norway Basin have been investigated for their benthic foraminiferal content. Unlike previous studies, the living benthic foraminiferal fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Factor analysis of both the living and dead faunal data reveals six living species assemblages and five corresponding dead assemblages. The additional living assemblage is characterized by the arenaceous speciesCribrostomoides subglobosum that dominates between 1400 and 2000 m water depth, but is rare in the dead faunal data.Trifarina angulosa and, to a lesser extent,Cibicides lobatulus characterize the shallowest foraminiferal assemblage from 200 to 600 m water depth, where it is associated with strong bottom currents and warm, saline Atlantic water of the North Atlantic Drift. On the slope between 600 and 1200 m water depth, theMelonis zaandami Species Assemblage dominates, particularly in areas characterized today by rapid sedimentation of terrigeneous material. Between 1000 and 1400 m depth, where the slope is covered by fine grained, organic-rich, terrigeneous mud, the living foraminiferal assemblage is characterized byCassidulina teretis andPullenia bulloides. Below 1400 m, three foraminiferal assemblages are found:C. subglobosum is found from 1400 to 2000 m,Cibicidoides wuellerstorfi andEpistominella exigua predominantly live from 2000 to 3000 m water depth, and below 3000 m,Oridorsalis umbonatus andTriloculina frigida dominate the fauna.All of theElphidium excavatum tests found in this study and theCassidulina reniforme tests found above 500 m water depth were found to be reworked.Analysis of the sediment grain-size distribution and the organic carbon content in surface samples from the deepest stations suggest that the abundance ofC. wuellerstorfi andE. exigua is positively correlated to relatively coarse (caused by planktic foraminifera) and organic-rich sediments, whereas high frequencies ofO. umbonatus andT. frigida coincide with low organic carbon content. We suggest thatC. wuellerstorfi is adapted to deep-sea environments with relatively high food supply, tolerating relatively low interstitial water oxygen content, whereasO. umbonatus may tolerate lower food supply prefering well-oxygenated interstitial waters.     

Examining water temperature proxies in<Emphasis Type="Italic"> Porites</Emphasis> corals from the Great Barrier Reef: a cross-shelf comparison

Cores from colonies of the coral species Porites sp. were collected from inshore, mid-shelf, and outer reef localities (central Great Barrier Reef) to test the robustness of the major elemental sea surface temperature (SST) proxies (B/Ca, Mg/Ca, Sr/Ca, U/Ca) to the influence of inshore processes. Time series analyses of Sr/Ca, U/Ca, B/Ca, and Mg/Ca are compared to sea surface temperature (SST) in order to provide calibrations for these elements. This study shows that there are significant variations between the corals with respect to some of the proxies. In some cases, variations of ~6 °C are observed for a single U/Ca value. This magnitude of variation is also seen in the Mg/Ca proxy and, to a smaller extent, in the B/Ca–SST relationship. In two of the corals, both Mg/Ca and U/Ca do not follow a seasonal signal. The Mg/Ca and U/Ca ratios for two inshore corals are significantly different than the offshore corals (lower and higher, respectively). The other two proxies (B/Ca and Sr/Ca) do not display any inshore vs. offshore variations except for one inshore site that did not have a clear seasonal signal for either of these proxies. The Sr/Ca–SST relationship is the most robust, with a temperature variation of ~2 °C for a single Sr/Ca value, which is within error for this technique.     

Spatial and temporal variations in otolith chemistry and relationships with water chemistry: a useful tool to distinguish Atlantic salmon Salmo salar parr from different natal streams

Otolith elemental (Sr:Ca, Ba:Ca, Mn:Ca, Mg:Ca and Rb:Ca) and isotopic (⁸⁷Sr:⁸⁶Sr) profiles from several annual cohorts of juvenile Atlantic salmon Salmo salar were related to the physico‐chemical characteristics (chemical signatures, flow rate, temperature and conductivity) of their natal rivers over an annual hydrological cycle. Only Sr:Ca, Ba:Ca and ⁸⁷Sr:⁸⁶Sr in otoliths were determined by their respective ratios in the ambient water. Sr:Ca ratios in stream waters fluctuated strongly on a seasonal basis, but these fluctuations, mainly driven by water flow regimes, were not recorded in the otoliths. Otolith Sr:Ca ratios remained constant during freshwater residency at a given site and were exclusively related to water Sr:Ca ratios during low flow periods. While interannual differences in otolith elemental composition among rivers were observed, this variability was minor compared to geographic variability and did not limit classification of juveniles to their natal stream. Success in discriminating fish from different sites was greatest using Sr isotopes as it remained relatively constant across years at a given location.     

Benthic foraminiferal turnover across the Cretaceous/Paleogene boundary at Agost (southeastern Spain): paleoenvironmental inferences

We studied Upper Cretaceous and Lower Paleogene benthic foraminifera from the Agost section (southeastern Spain) to infer paleobathymetrical changes and paleoenvironmental turnover across the Cretaceous/Paleogene (K/P) transition. Benthic foraminifera indicate uppermost bathyal depths at Agost during the Abathomphalus mayaroensis Biochron (from about 400 kyr before the K/P boundary) through the early Plummerita hantkeninoides Biochron (about 120–150 kyr before that boundary). The depth increased to middle bathyal for the remainder of the Cretaceous, and remained so for the Danian part of the studied section (Parasubbotina pseudobulloides Biochron, at least 200 kyr after the K/P boundary). There were no perceivable bathymetrical changes at the K/P boundary, where 5% of the species became extinct, and the species composition of the benthic foraminiferal fauna changed considerably. Below the boundary, infaunal morphogroups constitute up to 65–73% of the faunas. Directly above the boundary, in the black clays of the lower Guembelitria cretacea Biozone, benthic foraminifera are rare. Several opportunistic taxa (e.g. the agglutinant Haplophragmoides sp.) have short peaks in relative abundance, possibly reflecting low-oxygen conditions as well as environmental instability, with benthos receiving food from short-lived, local blooms of primary producers. Above the clays through the end of the studied interval, epifaunal morphogroups dominate (up to 70% of the assemblages) or there is an even mixture or epifaunal and infaunal morphogroups. Infaunal groups do not recover to pre-extinction relative abundances, indicating that the food supply to the benthos did not recover fully over the studied interval (about 200 kyr after the K/P boundary). The benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact, which severely destabilized primary producers and the oceanic food web that was dependent upon them.     

Hydrochemistry from Sr and Mg contents of ostracodes in Pleistocene lacustrine deposits,Baza Basin (SE Spain)

A reconstruction of the early Pleistocene paleohydrochemistry based on the Mg, Sr and Ca content of the Cyprideis valves is presented for shallow lacustrine sequences of the Baza basin. A large number of environmental changes in this marginal area has been recorded by the recurrent alternation of two fossil assemblages which differ in their salinity requirements. Measurements of the Sr/Ca and Mg/Ca ratios of individual calcite shells of Cyprideis show that the water in the higher saline stages (with thalassic organisms indicating marine-like conditions) was of non-marine origin. The Sr/Ca values of Cyprideis valves from sands deposited during a saline water phase show lower values than those from an overlying carbonate sequence which was formed under lower salinity conditions. These unexpected values are assumed to be the result of major changes in the chemical composition of the water in shallow, littoral ponded areas of a hydrologically complex lake. In the sequences that originated in these areas, Sr/Ca values may be used only as salinity indicators within each portion of the sequence formed in a single, continuous evolution. In more open areas, the wide fluctuations of Sr/Ca and Mg/Ca recorded in ostracodes from individual layers of rippled ostracode-shell sands probably reflect the mixing of valves from changing short-term environmental conditions.     

Magnesium and strontium in non-marine ostracod shells as indicators of palaeosalinity and palaeotemperature

Measurements of the Ca, Sr, and Mg contents of individual calcitic shells of non-marine ostracods and their host waters, both in lakes and controlled aquaria, permit the calculation of the distribution coefficients of Sr/Ca and Mg/Ca partitioning in ostracod shells. We report new K_D[Sr] for seven genera of non-marine ostracods and K_D[Mg] for Cyprideis at 25°C.Strontium partitioning is virtually temperature-independent, and is related to the Sr/Ca of the host water, and in Ca²⁺-saturated waters, to the salinity of the water. Magnesium partitioning is dependent on both temperature and Mg/Ca of the host water.For simple closed-basin lakes (crater lakes are ideal), the Sr content of ostracods is a sensitive indicator of salinity and thus evaporation/precipitation changes, which in turn, indicate variations in continental climate. A 10000-year continuous palaeosalinity record established by Sr and Mg contents of fossil ostracods for Lake Keilambete, southeastern Australia, is in close agreement with an independent palaeosalinity estimate based on sediment textures.We suggest rules that allow Sr and Mg analyses of suites of individual fossil ostracod shells from lacustrine sediments to be interpreted in terms of palaeosalinity and palaeotemperature variations.     

Benthic foraminiferal paleoenvironmental reconstruction from the Upper Coniacian-Lower Campanian succession in north-western Tunisia

Quantitative analysis of benthic foraminifera is used to characterize the paleoenvironments of the Upper Coniacian-Lower Campanian succession in the Jbil section of north-western Tunisia. Foraminiferal parameters and benthic foraminiferal assemblages show that the studied section includes four distinct paleoenvironmental phases. From oldest to youngest, these are as follows: (1) an interval with a Praebulimina reussi assemblage with infaunal ratios as high as 96.1%. High abundances of P. reussi, reflecting an increase in organic matter flux to the seafloor (meso-to eutrophic) under oxygenated bottom-water conditions. (2) An interval characterized by a Gavelinella costulata assemblage with mixed infaunal/epifaunal foraminifera with higher Fisher's alpha values (ranging from 4 to 15.2), reflecting mesotrophic conditions in an outer shelf environment. (3) An interval with a Gaudryina laevigata assemblage indicative of a middle to outer shelf environment; there is a considerable increase in infaunal agglutinated foraminifera, as well as a relatively abundant and moderately diversified oxic/suboxic foraminifera. (4) The final interval occurs in the lower Campanian (the Globotruncana ventricosa Zone) and includes a Bolivinoides decoratus assemblage reflecting an outer shelf to upper bathyal environment. It contains a higher planktonic percentage and biodiversity with a slight increase in dysoxic species; the mixed infaunal/epifaunal content (57.6 to 73.3%) reflects mesotrophic conditions. Four well-recognized major sea-level falls are matched by the dual signatures of eustatic sea-level changes. These are coincident with the results of this study, which represent the first documentation of these events in Tunisian faunal and paleoenvironmental changes, at the following boundaries: Coniacian/Santonian, intra-Santonian, Santonian/Campanian, and intra-early Campanian.     

Relationship of surface sediments and benthic foraminiferal distribution patterns in the Norwegian Channel (northern North Sea)

Our study of the distribution of benthic foraminifers in surface sediment samples from the Norwegian Channel has shown that eight species and five different assemblages are important. The assemblages are dominated byUvigerina peregrina, Bolivina skagerrakensis, Cassidulina laevigata, Elphidium excavatum andBulimina marginata, respectively.Hyalinea balthica, Melonis barleeanum andTrifarina angulosa are also abundant. The first four assemblages and their dominant species can be related to certain water masses with known characteristics. Two species are related to certain types of substrate;M. barleeanum seems to prefer a fine-grained substrate, whileT. angulosa occurs most abundantly where the content of silt and clay is low.B. skagerrakensis andH. balthica occur most abundantly in sediments with a high content of organic carbon, whileT. angulosa shows inverse correlation to the organic carbon content.     

Carbon and oxygen isotope geochemistry of live (stained) benthic foraminifera from the Aleutian Margin and the Southern Australian Margin

Comparisons of ambient bottom-water geochemistry and stable isotopic values of the tests of living (stained) calcareous benthic foraminifera from the North Pacific (on the Aleutian Margin, water depth 1988 m) and Murray Canyons group in the Southern Indian Ocean (Australian Margin, water depths 2476 m and 1634 m) provide modern environmental analogs to calibrate paleoenvironmental assessments. Consistent with the hypothesis that microhabitat preferences influence foraminiferal isotopic values, benthic foraminifera from both margins were depleted in ¹³C with respect to bottom-water dissolved inorganic carbon (DIC). The carbon isotope values of deep infaunal foraminifera (Chilostomella oolina, Globobulimina pacifica) showed greater differences from estimates of those of DIC than shallow benthic foraminifera (Bulimina mexicana, Bolivinita quadrilatera, Pullenia bulloides). This study provides new isotopic and ecological information for B. quadrilatera. The mean Δδ¹³C value, defined as foraminiferal δ¹³C values minus estimated ambient δ¹³C values from the Aleutian Margin, is 0.97‰ higher for G. pacifica than the mean from the Murray Canyon. This difference may result either from genetic or biological differences between the populations or from differences in environmental isotopic influences (such as pore water differences) that were not accounted for in the equilibrium calculations. These analyses provide calibration information for the evaluation of bottom water conditions and circulation patterns of ancient oceans based on fossil foraminiferal geochemistry.     

Effect of salinity and seawater calcite saturation state on Mg and Sr incorporation in cultured planktonic foraminifera

Trace elements incorporated in planktonic foraminiferal test carbonate are commonly used as paleoproxies. For instance, Mg/Ca ratios are frequently used for reconstructing sea surface temperature and, together with the foraminiferal stable oxygen isotope ratios, are also used as paleosalinity proxy. Foraminiferal Sr/Ca ratios constitute another example of the application of trace elements in paleostudies since they may reflect the Sr/Ca values of seawater. However, over the past few decades it has been proven that the incorporation of trace elements in foraminiferal calcite is controlled by more than one environmental parameter. To quantify the effect of salinity on Mg and Sr incorporation planktonic foraminifera Globigerinoides sacculifer (sensu stricto) were grown in the laboratory under different environmental conditions. Laboratory experiments allowed us to separate a direct salinity effect from a possible independent impact through differences in the calcite saturation state of the seawater (Ω). Although the temperature effect is more important than the salinity effect, a change of 4 salinity units is equivalent to a 1 °C bias on Mg/Ca-based temperatures. This effect of salinity on Mg incorporation is minor. However, when using Mg/Ca-based temperatures in combination with foraminiferal δ¹⁸O to calculate salinity, it cannot be neglected. The present study shows salinity as the overriding control on Mg incorporation within the range of Ω studied (Ω between 5.25 and 6.50; [CO₃²⁻] between 218 and 270 μmol/kg) at a constant temperature of 26 °C. In contrast, Ω appears to be the main control on foraminiferal Sr incorporation (0.10 mmol/mol per 100 µmol/kg rise in [CO₃²⁻]), whereas salinity has a non significant influence on Sr/Ca.     

Epibiont foraminifera of Sertella frigida (Waters) (Bryozoa, Cheilostomata) from Terranova Bay, Ross Sea, Antarctica

Several arenaceous and calcareous foraminifera epibionts of Sertella frigida (Waters) (Bryozoa, Cheilostomata), collected in Terranova Bay during the 1989–90 Italian Antarctic expedition, were studied. Arenaceous species, such as Psammosphaera fusca Schulze f. adhearescens Rhumbler, Haplophragmoides canariensis d'Orbigny, Portatrochammina antarctica (Parr), and Trochammina arctica Hedley, Hurdle and Burdett, are a conspicuous component of the epifaunal community. The calcareous foraminifers encrusting S. frigida are mostly represented by Cibicides refulgens Montfort and Rosalina globularis d'Orbigny. Foraminifera were found only in the basal part of the bryozoan colonies. The presence of many juveniles provided evidence that foraminifers were reproducing at the time of sampling. Psammosphaera fusca f. adhaerescens was found exclusively inside the zooids of S. frigida. The large number of individuals associated with the bryozoan suggest that P. fusca f. adhaerescens finds optimum conditions (shelter, food, and grains for shell building) for growth inside the zooids of S. frigida. The other species occurred most commonly adhered to the trabeculae or to the zooid orifices of S. frigida. An elevated position offers a better chance to catch food particles from the overlying water column. Foraminifers could benefit also from bryozoan feeding currents. The availability of resuspended organic material could provide a more consistent source of food in a highly seasonal oligotrophic environment. Received: 8 February 1995/Accepted: 30 June 1996     

Asteriscus v. lapillus: comparing the chemistry of two otolith types and their ability to delineate riverine populations of common carp Cyprinus carpio

The chemical composition of common carp Cyprinus carpio asteriscus (vaterite) and lapillus (aragonite) otoliths from the same individual and reflecting the same growth period was measured to (1) determine whether there are differences in the uptake of trace metals (Mg:Ca, Mn:Ca, Sr:Ca and Ba:Ca ) and Sr isotope ratios (⁸⁷Sr:⁸⁶Sr) in co‐precipitating lapilli and asterisci and (2) compare the ability of multi‐element and isotopic signatures from lapilli, asterisci and both otolith types combined to discriminate C. carpio populations over a large spatial scale within a river basin. Depth profile analyses at the otolith edge using laser‐ablation inductively coupled plasma mass spectrometry showed that asterisci were enriched in Mg and Mn and depleted in Sr and Ba relative to lapilli, whilst ⁸⁷Sr:⁸⁶Sr values were nearly identical in both otolith types. Significant spatial differences among capture locations were found when all trace element and Sr isotope ratio data were aggregated into a multi‐element and isotopic signature, regardless of which otolith type was used or if they were used in combination. Discriminatory power was enhanced, however, when data for both otolith types were combined, suggesting that analysis of multiple otolith types may be useful for studies attempting to delineate C. carpio populations at finer spatial or temporal scales.     

Particle size selection in individuals from epifaunal versus infaunal populations of the nereidid polychaete Neanthes succinea(Polychaeta: Nereididae)

Neanthes succinea (Frey & Leuckart, 1847) is a common nereidid polychaete of both epifaunal and infaunal estuarine habitats. The gut contents of individuals collected from two epifaunal and two infaunal habitats are compared. Our a priori expectation was that individuals from epifaunal habitats would be classified as macrophagous with guts indicating carnivory and/or macroalgal herbivory, while individuals from infaunal habitats would be classified as microphagous with guts indicating deposit feeding. At all four locations gut contents indicated deposit feeding with little indication of macrophagous feeding. Average particle sizes for mineral grains did not differ between the four collection sites. For the two infaunal locations mean size of the mineral grains in gut contents was significantly smaller than ambient sediments. In addition to mineral grains, guts contained diatoms, dinoflagellates, macrophytic detritus, protozoan tests, and a variety of metazoans. Our study demonstrates that caution is necessary when inferring feeding type from morphology and that population and habitat specific differences in diet can occur within the same species.     

Minor- and trace-element intra-shell variations in Santonian inoceramids (Basque-Cantabrian Basin,northern Spain): diagenetic and primary causes

Santonian deep- and platform-marine facies inoceramids from the Basque-Cantabrian Basin show clear saw-toothed intra-shell variations with respect to Mg/Ca, Sr/Ca, Na/Ca, Ba/Ca, Fe/Ca and Mn/Ca ratios. Under cathodoluminescence, the most luminescent zones in all the inoceramids present lower Mg/Ca and Sr/Ca (up to 48% and 35% lower values, respectively) and higher Fe/Ca and Mn/Ca ratios (up to 362% and 819% higher values, respectively), which is indicative of diagenetic modification. In contrast, the least luminescent zones show higher Mg/Ca and Sr/Ca ratios and lower Fe/Ca and Mn/Ca. These findings, along with the presence of frequent, well-correlated Mg/Ca, Sr/Ca and Na/Ca ratios, inversely related to Fe/Ca and Mn/Ca, in the weakest luminescent zones suggest major retention of the primary intra-shell variations in these zones. Moreover, Ba/Ca profiles, not connected with the general cathodoluminescence behaviour of the shells, also point towards partial retention of the primary patterns. The saw-toothed intra-shell variations are thought to be caused by the distinct geochemical signals acquired originally by the inoceramid alternating clear and dark growth lines. The deposition of the growth lines and thus the saw-toothed intra-shell variations may be mainly related to periodically changing palaeoenvironmental conditions, such as seawater temperature variations and phytodetritus rainfall. This interpretation is supported by the appearance of highly similar chemical saw-toothed variations in the extant shallow-marine Atrina rigida shell.     

Chemical and isotopic composition of karstic lakes in Jamaica,West Indies

Lakes in the limestone region of Jamaica exhibit a range of chemical characteristics that reflect varying inputs from precipitation, surface runoff and groundwater, together with the subsequent evolution of the water within the limnic environment. Detailed spatial and temporal sampling was conducted on one lake, Wallywash Great Pond. Chemical data, together with D/H, ¹⁸O/¹⁶O, ¹³C/¹²C and ⁸⁷Sr/⁸⁶Sr ratios confirm that the karstic spring waters entering the lake evolve chemically through degassing, mixing with rainfall and runoff, biogenic decalcification (resulting mainly from bicarbonate assimilation by the high biomass of submerged macrophytes), and evaporation. Modern carbonate sedimentation in Wallywash Great Pond is largely of high-Mg calcite. This is consistent with Mg/Ca molar ratios >2 within much of the lake. However, aragonite forms on the adaxial leaf surfaces of Potamogeton spp. This may be explained either as a result of locally elevated Mg concentrations or a high degree of supersaturation favouring very rapid carbonate precipitation. Two small lakes to the north of Wallywash Great Pond show minor influence of the Na-Cl dominated coastal aquifer, suggesting that coastal lakes are sensitive to variations in the boundary between fresh and brackish groundwater caused by changes in climate or sea level. Their ¹³C/¹²C ratios are strongly influenced by biogenic CO₂ derived from plant respiration or decay.     

Test of soil extractants for their suitability in predicting Ca/Sr ratios in leaves and stems of sugar maple seedlings

Differential uptake and translocation of Ca and Sr in organisms have been reported, calling into question the use of Sr to track Ca cycling in the environment. We investigated the relationship between Ca/Sr ratios in soil extracts of various strengths (H₂O, NH₄Cl, and NH₄EDTA) and seedlings of sugar maple (Acer saccharum Marsh.) grown from natural regeneration on 37 sites. Our objectives were to determine if Ca/Sr ratios in soil extracts are correlated with those in sugar maple tissues, and what soil extractant best duplicate plant tissue Ca/Sr ratios. Leaves had higher Ca/Sr ratios than stems and the extractants did not produce equal Ca/Sr ratios: H₂O had the lowest Ca/Sr, and NH₄EDTA the highest. The relationships between soil extract Ca/Sr ratios and leaf and stem Ca/Sr ratios were significant and linear, but the slopes differed among extractants. The lowest slope (0.45) was observed for the water extract/leaves and the highest (2.15) for the NH₄EDTA extract/stem with discrimination factors ranging from 0.22 with NH₄EDTA to 1.59 for water. Leaf extracts were more strongly correlated with soil Ca/Sr than stem extracts (R ² of 0.57–0.7 vs. R ² of 0.45–0.6, respectively). These findings support the use of Ca/Sr ratios in plants to track their source of soil Ca, but they highlight the need to calibrate the relationships for the plant tissue and soil extractant used.