Dispersive behaviors of black drum and red drum: Is otolith Sr:Ca a reliable indicator of salinity history?

We tested the hypothesis that strontium:calcium (Sr:Ca) in otoliths are reflective of environmental salinity experienced by two estuarine fishes during early life. Laboratory and field experiments were performed to examine the effects of salinity and temperature on Sr:Ca in otoliths of black drum (Pogonias cromis) and red drum (Sciaenops ocellatus). Otolith Sr:Ca of juveniles reared at four salinities (5‰, 15‰, 25‰, 35‰) differed significantly forP. cromis while no salinity effect was observed forS. ocellatus. Otolith Sr:Ca of both species were not affected by temperature (23°C and 30°C), suggesting that partitioning of Sr in otoliths of these taxa is constant over the temperature range examined. A field verification trial was conducted forP. cromis and a positive relationship between otolith Sr:Ca and ambient salinity was observed, even though the percent variability explained was modest. A series of Sr:Ca point measurements were taken from the core to the edge of the otoliths of wildP. cromis andS. ocellatus, and otolith Sr:Ca chronologies of both species showed conspicuous declines during the first few months of life. While Sr:Ca chronologies of both species suggest that ingress is associated with a reduction in otolith Sr:Ca, inconsistencies in laboratory and field experiments intimate that Sr uptake in the otolith may be insensitive to salinity and regulated by other factors (aqueous chemistry, ontogenetic shifts in habitat, or physiology). Results from early life history transects of otolith Sr:Ca conform to expected patterns of estuarine ingress-egress during early life and indicate that the approach may be useful for detecting large-scale habitat transitions (marine to estuarine habitats).     

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.     

Facilitation of barium uptake into fish otoliths: Influence of strontium concentration and salinity

To reconstruct patterns of fish migration using otolith chemistry, it is essential to validate the relationship between elements in otoliths and the surrounding water, and in particular, how processes such as competition and facilitation among multiple elements influence otolith chemistry. Using a controlled laboratory experiment, juvenile black bream (Acanthopagrus butcheri) were reared in both brackish and seawater spiked with different concentrations of Sr and Ba. The addition of Sr to the solution facilitated the uptake of Ba into otoliths of fish reared in brackish water, but not in seawater. Conversely, Ba did not facilitate nor compete with the uptake of Sr in either brackish or seawater. In brackish water, Sr incorporation into otoliths may create crystal defects within the CaCO₃ matrix, enabling greater incorporation of Ba. Ba:Ca partition coefficients (D_Ba) for brackish and seawater were 0.058 and 0.136, respectively, whereas Sr:Ca partition coefficients (D_Sr) for brackish and seawater were 0.463 and 0.287, respectively. The influence of Sr on Ba incorporation in fish otoliths is important to consider when reconstructing migration histories of fish, especially in brackish water environments.     

Otolith Microchemistry Reveals Substantial Use of Freshwater by Southern Flounder in the Northern Gulf of Mexico

Southern flounder Paralichthys lethostigma is a recreationally and commercially important species along the western Atlantic and northern Gulf of Mexico coasts that can exhibit complex early-life habitat-use patterns. Herein, we used an otolith microchemical approach to test the conventional wisdom that juvenile southern flounder spend most of their early life in low-salinity areas of estuaries, focusing on the largely unstudied population in the Mobile-Tensaw Delta, AL. Analysis of strontium/calcium concentrations in otolith cores of age 0 juveniles demonstrated that 68% of these individuals hatched in high-salinity waters before moving into freshwater habitats, with the remaining individuals being spawned in or near freshwater habitat. Further, otolith edge Sr/Ca concentrations revealed that even juveniles used freshwater habitats, particularly during freshwater/oligohaline conditions in our study system. Otolith edge Sr/Ca ratios for fish collected during high-salinity periods differed significantly among collection regions, suggesting seasonal differences in patterns of habitat use between individuals collected upstream (i.e., freshwater habitats) vs. downstream (i.e., euryhaline habitats). These data support the hypothesis that early-life stages of a substantial portion of a coastal southern flounder population use freshwater habitat.     

Response to “Comment on ‘Otolith Microchemistry Reveals Substantial Use of Freshwater by Southern Flounder in the Northern Gulf of Mexico’” by Pedro Morais

Lowe et al. (Estuar Coast 34:630–639, 2011) used Sr/Ca in the otoliths of juvenile southern flounder (Paralichthys lethostigma) to demonstrate the importance of low-salinity habitats in the northern Gulf of Mexico during early life. While otolith cores indicated that most southern flounder originated in high-salinity environments (elevated Sr/Ca in otolith core) and moved into lower salinity habitats (decreased Sr/Ca outside of the otolith core), approximately one third of the sampled individuals had otolith core chemistry that indicated spawning or hatching in or near freshwater habitats (low Sr/Ca throughout the otolith). Morais (Estuar Coast 34:630–639, 2012) proposes a different interpretation: he suggests that the high Sr/Ca found in 68 % of juvenile otolith cores (and low Sr/Ca just outside of the core region) may be due to females hydrating their eggs in offshore (high-salinity) waters, with spawning, hatching, and egg/larval development all actually occurring in low-salinity environments (his “sea-run mother” hypothesis). While there is ample literature supporting the importance of maternal contributions to otolith microchemistry during vitellogenesis, it is our contention that such contributions ultimately depend on the ecology and reproductive physiology of each species. Further, a mass inshore migration of adult southern flounder during their spawning season is counter to the well-documented life history patterns for this species throughout its range. While we appreciate Morais' perspective, we continue to stand by the conclusion of our original paper.     

Inter-annual variability in isotope and elemental ratios recorded in otoliths of an anadromous fish

Isotope ratios and elemental concentrations in otoliths are often used as natural tags to reconstruct migratory movements and connectivity patterns in marine and anadromous fishes. Although differences in otolith geochemistry have been documented among geographically separated populations, inter-annual variation within locations is less frequently examined. We compared otolith isotope (δ¹⁸O and ⁸⁷Sr:⁸⁶Sr) and elemental ratios (Sr:Ca and Ba:Ca) from several annual cohorts of juvenile American shad (Alosa sapidissima) in three rivers. These four geochemical signatures distinguished among river-specific populations of this species at both large and small geographic scales, with δ¹⁸O and ⁸⁷Sr:⁸⁶Sr generating the majority of multivariate variation. We found significant variation among years for all variables in two to three rivers. However, the magnitude of variability differed among ratios, with δ¹⁸O ratios showing substantial inter-annual shifts while ⁸⁷Sr:⁸⁶Sr ratios were relatively stable across years. Sr:Ca and Ba:Ca ratios also varied among years. These results imply that investigators using environmentally labile signatures must quantify geochemical signatures for each cohort of interest in order to confidently identify origins of migrants.     

The impact of salinity on the Mg/Ca and Sr/Ca ratio in the benthic foraminifera Ammonia tepida: Results from culture experiments

Over the last decade, sea surface temperature (SST) reconstructed from the Mg/Ca ratio of foraminiferal calcite has increasingly been used, in combination with the δ¹⁸O signal measured on the same material, to calculate the δ¹⁸O_w, a proxy for sea surface salinity (SSS). A number of studies, however, have shown that the Mg/Ca ratio is also sensitive to other parameters, such as pH or , and salinity. To increase the reliability of foraminiferal Mg/Ca ratios as temperature proxies, these effects should be quantified in isolation. Individuals of the benthic foraminifera Ammonia tepida were cultured at three different salinities (20, 33 and 40 psu) and two temperatures (10-15 °C). The Mg/Ca and Sr/Ca ratios of newly formed calcite were analyzed by Laser Ablation ICP-MS and demonstrate that the Mg concentration in A. tepida is overall relatively low (mean value per experimental condition between 0.5 and 1.3 mmol/mol) when compared to other foraminiferal species, Sr being similar to other foraminiferal species. The Mg and Sr incorporation are both enhanced with increasing temperatures. However, the temperature dependency for Sr disappears when the distribution factor D_Sr is plotted as a function of calcite saturation state (Ω). This suggests that a kinetic process related to Ω is responsible for the observed dependency of Sr incorporation on sea water temperature. The inferred relative increase in D_Mg per unit salinity is 2.8% at 10 °C and 3.3% at 15 °C, for the salinity interval 20-40 psu. This implies that a salinity increase of 2 psu results in enhanced Mg incorporation equivalent to 1 °C temperature increase. The D_Sr increase per unit salinity is 0.8% at 10 °C and 1.3% at 15 °C, for the salinity interval 20-40 psu.     

A field experiment testing for correspondence between trace elements in otoliths and the environment and for evidence of adaptation to prior habitats

Site-specific variation in the trace element composition of fish otoliths can be used to identify fish to source, but the mechanisms controlling elemental composition are poorly understood. Environmental influences on the deposition of barium (Ba), copper (Cu), manganese (Mn), and strontium (Sr) in the otoliths of mudsuckers (Gillichthys mirabilis) were tested using a reciprocal field transplant experiment, in which fish from 3 estuaries were transplanted to each of the 3 estuaries. Fish originating from the 3 estuaries showed no differences in otolith chemistry that might reflect acclimation to past conditions in their home estuary or genetic differences among populations, which simplifies the interpretation of otolith chemistry. Cu and Mn concentrations in otoliths differed according to the site of transplant. Cu in otoliths showed the same pattern of difference among estuaries as did Cu in sediments, but there was no correspondence between Cu in otoliths and dissolved Cu. Ranked differences among estuaries in otolith Mn matched the ranking of estuary-specific differences in dissolved Mn, and there was no correspondence between the concentration of Mn in otoliths and sediments. Fish transplanted to different estuaries showed no differences in otolith concentrations of Ba or Sr, and the concentrations of Ba and Sr in the water column showed a similar lack of difference among estuaries. This study provides field evidence supporting the conclusion that the elemental composition of otoliths reflects environmental conditions to which fish have been recently exposed, but whether that correlation is with trace elements in the sediment or water column can vary.     

Comments on Lowe et al. “Otolith Microchemistry Reveals Substantial Use of Freshwater by Southern Flounder in the Northern Gulf of Mexico”

Lowe et al. (Estuaries and Coasts, 34:630–639, 2011) hypothesized that juvenile southern flounder Paralichthys lethostigma (Jordan and Gilbert 1884) would migrate from the Gulf of Mexico into the Mobile-Tensaw River Delta (AL, USA) and use low-salinity (oligohaline/freshwater) habitats during, at least, a portion of their first year of life. Thus, they analyzed the Sr/Ca ratio profiles along the sagittal otoliths of southern flounder collected in the Mobile-Tensaw River Delta and observed that one third of the flounders had low Sr/Ca levels in the otoliths’ core and throughout the otolith, suggesting that these fishes hatched in freshwater or low-salinity habitats where they spend the majority of their life. The other two thirds of southern flounder showed high levels of Sr/Ca ratio in the otoliths’ core following a marked decline of Sr/Ca ratio, which then maintained along the remainder of the otolith. This pattern was interpreted as larvae hatched in higher salinity waters before entering the Mobile-Tensaw River Delta; however, in this paper, I list several arguments to support an alternative interpretation for this pattern. I suggest that the high levels of Sr/Ca ratios in the otoliths’ core of southern flounder does not reflect the saline conditions where larvae hatched, instead it reflects the location where the female progenitor hydrated the eggs. Thus, adding my interpretation on the data of Lowe et al. (Estuaries and Coasts, 34:630–639, 2011), it seems that southern flounder might hatch in or near freshwater habitats and the migration of southern flounder into an estuarine ecosystem to spawn might exist.     

Phytoplankton Biomass and Composition in a River-Dominated Estuary During Two Summers of Contrasting River Discharge

Estuaries located in the northern Gulf of Mexico are expected to experience reduced river discharge due to increasing demand for freshwater and predicted periods of declining precipitation. Changes in freshwater and nutrient input might impact estuarine higher trophic level productivity through changes in phytoplankton quantity and quality. Phytoplankton biomass and composition were examined in Apalachicola Bay, Florida during two summers of contrasting river discharge. The <20 μm autotrophs were the main component (92?±?3 %; n?=?14) of phytoplankton biomass in lower (<25 psu) salinity waters. In these lower salinity waters containing higher dissolved inorganic nutrients, phycocyanin containing cyanobacteria made the greatest contribution to phytoplankton biomass (69?±?3 %; n?=?14) followed by <20 μm eukaryotes (19?±?1 %; n?=?14), and phycoerythrin containing cyanobacteria (4?±?1 %; n?=?14). In waters with salinity from 25 to 35 psu that were located within or in close proximity to the estuary, >20 μm diatoms were an increasingly (20 to 70 %) larger component of phytoplankton biomass. Lower summer river discharges that lead to an areal contraction of lower (5–25 psu) salinity waters composed of higher phytoplankton biomass dominated by small (<20 μm) autotrophs will lead to a concomitant areal expansion of higher (>25 psu) salinity waters composed of relatively lower phytoplankton biomass and a higher percent contribution by >20 μm diatoms. A reduction in summer river discharge that leads to such a change in quantity and quality of estuarine phytoplankton available will result in a reduction in estuarine zooplankton productivity and possibly the productivity of higher trophic levels.     

Fully Equipped to Succeed: Migratory Contingents Seen as an Intrinsic Potential for Striped Bass to Exploit a Heterogeneous Environment Early in Life

Migratory contingents, groups of individuals belonging to the same population that adopt different migratory patterns, have been identified in numerous Striped Bass (Morone saxatilis) populations along North American East Coast. We tested the hypothesis that migratory contingents may develop early in life to maximize the exploitation of the variety of habitats faced by a recently introduced fish population. Using the discriminatory power provided by otolith chemistry, we studied early-life history stages of Striped Bass in a recently reintroduced population in the St. Lawrence Estuary. Migratory patterns were inferred using multivariate analysis of four otolith trace elements (Sr, Ba, Mn, and Mg) on juveniles (0+ and 1+). Three migratory contingents were identified during early-life history stages: freshwater residents, oligohaline migrants, and mesohaline migrants. This study demonstrates the rapid establishment, in less than 10 years since initial stocking, of three migratory contingents initiated early in life among the St. Lawrence Striped Bass population. We postulate that diversification provided by the establishment of distinct migratory contingents among early-life history stages promotes the rapid colonization of new environments through the exploration and exploitation of an increased number of nursery habitats.     

柴达木察尔汗贝壳堤剖面Sr同位素及其环境意义

根据对柴达木盆地察尔汗古湖贝壳堤剖面酸不溶组分和酸溶组分的提取及其87Sr/86Sr的测定,结合沉积物中Rb/Sr的变化,指出Sr同位素组成特征可有效指示源区化学风化和沉积区古环境变化;依据酸溶组分中盐度指标Sr/Ca, Sr/Ba值与Sr同位素组成曲线的对比分析,揭示酸溶组分Sr同位素可以较好的指示水体形成时的盐度。通过分析贝壳堤剖面化学风化和部分盐度变化过程,探讨了研究区晚更新世39.6~ 17.1 ka BP(未经校正的AMS 14C测年结果,全文同)湖泊高湖面的演化历史。     

A Comparison of Otolith Geochemistry and Stable Isotope Markers to Track Fish Movement: Describing Estuarine Ingress by Larval and Post-larval Halibut

Estuarine recruitment of fishes is a potential bottleneck in the life cycle of many coastal species. We investigated patterns of size-at-ingress for larval and post-larval California halibut entering the Punta Banda Estuary (PBE), Mexico, using both otolith geochemistry and carbon stable isotope ratios (SIR). Juvenile halibut (n?=?126; 38–163 mm standard length [SL]) were collected from inside PBE and the adjacent exposed coast during the fall of 2003, and otoliths (geochemistry) and muscle tissues (SIR) were analyzed to reconstruct the environmental histories of individuals. Based on geochemical analyses, nearly all fish collected from PBE were characterized by a non-estuarine signature (e.g., low Mn and Ba) in the otolith growth bands deposited when fish were <30 mm SL. Although fish collected from the coast retained that signature throughout their lives, fish collected within PBE showed elevated concentrations of Mn and Ba in the otolith growth bands deposited once halibut were 30–70 mm SL, thereby recording ingress. Carbon SIR of juvenile halibut prey also differed between the estuary and coast. Muscle δ ¹³C values of halibut captured along the coast were consistent (ca.?15‰), while those captured in the estuary were variable and generally more enriched in ¹³C (?16‰ to ?11‰). Both natural tagging approaches agreed that most halibut (~75 %) enter PBE long after settlement (>?>?8–12 mm SL), although size-at-ingress estimates were significantly larger (mean difference = 27 mm; p?<?0.001) when derived via carbon SIR than with otolith geochemistry. Potential explanations for the differences in size-at-ingress estimates involve the magnitude of isotopic and trace element gradients at this ocean–estuary boundary, the temporal resolution of environmental tags stored within otoliths and soft tissues, and the size-at-capture or somatic growth rate of juvenile halibut. We conclude by discussing the relative merits of otolith geochemistry and SIR as natural tags, and by considering the implications of secondary dispersal into estuaries by post-larval fish.     

Trace-element variations in an annually layered stalagmite as recorders of climatic changes and anthropogenic pollution in Central China

We analyzed variations in the Sr/Ca, Ba/Ca, REE/Ca (REE: rare earth element), Zn/Ca, and Pb/Ca ratios preserved in an annually layered stalagmite, XL21, from central China. The stalagmite record spans the 95 year period AD 1914–2008. The Sr/Ca and Ba/Ca ratios have a significant positive correlation with the stalagmite's growth rate, suggesting that they were primarily controlled by growth-rate variations. Variations in REE/Ca ratios are consistent with local temperature changes, suggesting temperature influenced REE concentrations in the stalagmite over decadal to annual timescales. Higher temperature in this humid area can increase vegetation cover, microbial activity, and organic decomposition in the soil, resulting in enhanced pCO₂, organic matter concentration and reduced pH, and consequently increased REE mobilization from the overlying soil layer and host rock. Higher temperatures may also increase the natural Zn mobilization from the overlying soil mediated by organic matter and consequently may have led to increased Zn retention in XL21. An increasing trend is seen in the Pb/Ca ratios from XL21 since 1985, which is consistent with increased lead production in this area, and indicates an increase in mine-derived lead pollution in the local environment over the past 30 years.     

Important role of hornblende fractionation in generating the adakitic magmas in Tongling,Eastern China: evidence from amphibole megacryst and cumulate xenoliths and host gabbros

ABSTRACT

Tongling, in eastern China, is an area well-known for intra-plate adakites. Here, we present the mineral chemistry and zircon U–Pb ages for amphibole cumulate xenoliths, the mineral chemistry of amphibole megacrysts, and the whole–rock chemistry, zircon U–Pb age and Sr–Nd isotopic compositions of host gabbros from Tongling. Zircon U–Pb dating yields a crystallization age of 120.6 ± 1.2 Ma (MSWD = 4.2) for the host gabbros, which are characteristically depleted in high field strength elements (Nb, Ta, and Ti) and enriched in large ion lithophile elements (Ba and Sr), with εNd (t) of ?3.00 to ?4.52 and initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7068–0.7072, suggesting an enriched mantle source. Parental melts, as estimated from average amphibole megacryst and cumulate compositions, have Mg# values of 26–33, are enriched in Ba, Th, U, and Nd, and depleted in Nb, Ta, Zr, Hf, and Ti, similar to 136 Ma mafic magmas in Tongling. Zircon U–Pb dating yields a crystallization age of 135.4 ± 1.0 Ma (MSWD = 1.6) for the amphibole cumulates. It is concluded that the Tongling adakitic rocks were formed by polybaric crystallization involving early high-pressure intracrustal fractional crystallization of cumulates comprising hornblende and clinopyroxene, and late low-pressure fractional crystallization of hornblende and plagioclase phenocrysts. The flat subduction of Pacific plate and its subsequent foundering during the Cretaceous may have triggered the generation of extensive adakitic magmas and lithospheric thinning in the Lower Yangtze Region.     

A Possible Connectivity among Estuarine Tapertail Anchovy (<Emphasis Type="Italic">Coilia nasus</Emphasis>) Populations in the Yangtze River,Yellow Sea,and Poyang Lake

Estuarine tapertail anchovy (Coilia nasus) is a highly commercial and valuable anadromous fish species in China. Due to the complex anadromous life cycle, it remains difficult to assess the degree of connectivity among groups of C. nasus in the Yangtze River, its connecting lakes, and adjacent seas. In this study, laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) was used to analyze the element composition in the otolith nucleus region of C. nasus specimens from the Yangtze River Estuary, Poyang Lake, and Nantong coastal waters in the estuary adjacent to the Yellow Sea. The content ratios of seven elements (Na, Mn, Fe, Ni, Cu, Sr, and Ba) to Ca in the nucleus indicated a close relationship among C. nasus specimens collected from the Yangtze River Estuary (Spring group), Poyang Lake, and Yellow Sea, suggesting a possible connectivity mechanism for anchovies in the three water bodies. Poyang Lake, Yangtze River, and Yellow Sea seem to be the natal lake, migration pathway, and feeding ground, respectively.     

重庆羊子洞MIS5a/MIS4转换时期石笋微量元素记录及其气候意义

利用重庆丰都羊子洞石笋Y02 ICP-MS测年数据、微量元素数据和石笋氧同位素数据重建了三峡库区76~69 ka B.P.时段的古气候环境信息。将石笋Y02测试数据与太阳辐射曲线、格陵兰NGRIP冰芯和南海海表温度进行对比分析,结果显示石笋Mg/Ca主要响应降水变化,而Sr/Ca、Ba/Ca和U/Ca更多地响应地表土壤状况和当地大气粉尘活动,间接响应降水变化;石笋Y02 δ18O记录出现偏重的趋势比微量元素比值增大时间晚1 ka多,表明石笋微量元素比值可能还受到温度影响。     

Paleoenvironmental reconstruction of human activity in Central Arizona using shell chemistry of Hohokam canal ostracodes

The prehistoric Hohokam are the only known culture to develop large-scale irrigation systems before the arrival of Europeans to the United States. Hohokam social evolution was based, in part, on intensive agriculture. To date, most models of Hohokam irrigation agriculture (i.e., hydrologic and sedimentologic models) fail to address dynamics like flow regime, seasonality, canal use and abandonment (Henderson and Hackbarth, 1939). Biota recovered from Hohokam canals often include ostracodes, carbonate-secreting microcrustaceans that are sensitive to hydrochemical changes. ^m(Mg/Ca)_v and ^m(Sr/Ca)_v ratios in the ostracode Limnocythere staplini can be converted into approximate temperature and salinity values at the time of calcification. Ostracode shell chemistry is becoming a powerful tool for understanding the history of canal water chemistry, intensity of land use, and human impact on soil. This study uses multiple regression models to generate the first paleoenvironmental estimates of temperature and salinity from ostracode shell chemistry. Temperature estimates suggest that most canals were used between late winter (February–March) and the premonsoonal season (May–June). Salinity estimates apparently vary over time. Both paleoenvironmental estimates are in good agreement with history records for the Phoenix area. © 1997 John Wiley & Sons, Inc.     

广东三水盆地古近系心组生油层的元素地球化学特征

沉积物的元素地球化学特征是对沉积盆地水体环境以及古气候条件变化的响应。本文根据元素（Al、Fe、Mg、Ca、K、Na、P、V、Ni、Co、Cr、Cu、Zn、Sr、Ba、Cd、Li、Mn、Pb、Ti）的含量及其比值（Al/Ti、Fe/Mn、Sr/Ba、Mg/Ca、Sr/Ca、Na/Ca、V/Cr、Ni/Co、Ni/V）的变化，对三水盆地古近系心组红岗段生油层的沉积条件进行了系统分析。心组红岗段下部（亚段A）表现为较稳定的地球化学特征。各元素丰度及其比值指示这一时期陆源输入持续较高、且物源组成变化不大。由于海水入侵的影响，湖盆水体盐度相对较高，底部水体以弱氧化条件为主，O₂-H₂S界面位于水/沉积物界面附近。红岗段中上部（亚段B、C）的元素地球化学特征变化较为频繁且幅度很大，反映古气候和湖盆沉积条件的迅速变迁。在潮湿气候条件下，沉积物的地球化学特征表现为以Al、Ti为代表的外源元素含量及其比值较高，而Mg、Ca等盆内化学沉积元素含量较低。古氧气指标指示底部水体为还原环境，有利于有机质保存。因而，相应于较高的有机碳含量。在间歇性干旱时期，陆源输入减少，外源元素含量及其比值显著降低。随着蒸发作用的加强，水体盐度加大，内源元素丰度以及Mg/Ca、Sr/Ba、Sr/Ca和Na/Ca比值大幅度上升。底部水体为氧化环境，O₂-H₂S界面多位于水/沉积物界面或沉积物中。上述两种气候条件在红岗段中上部沉积时期交替出现。红岗段沉积后期由于淡水的长期输入，湖水出现逐渐淡化趋势。     

Annual trace element cycles in calcite–aragonite speleothems: evidence of drought in the western Mediterranean 1200–1100 yr BP

Each of two calcitic stalagmites from Grotte de Clamouse, Herault, southern France, displays a discrete aragonite layer dated at around 1100 yr BP. The layer of fanning aragonite ray crystals is immediately preceded by calcite with Mg and Sr compositions that are uniquely high for the past 3 kyr. Trace element compositions close to the boundary between original aragonite and calcite are consistent with quasi‐equilibrium partitioning of trace elements between the phases. Study of modern dripwaters demonstrates that pronounced covariation of Mg/Ca and Sr/Ca ratios in dripwater occurs owing to large amounts of calcite precipitation upflow of the drips that fed the stalagmites. Trace element to Ca ratios are enhanced during seasonally dry periods. Ion microprobe data demonstrate a pronounced covariation of trace elements, including Mg and Sr in calcite, and Sr, U and Ba in aragonite. The mean peak spacing is close to the long‐term mean of annual growth rates determined by differences in U‐series ages and so the trace element peaks are interpreted as annual. The trace element chemistry of the stalagmites on annual to inter‐annual scales thus directly reflects the amounts of prior calcite precipitation, interpreted as an index of aridity. The longer‐term context is a multi‐decadal period of aridity (1200–1100 yr BP) possibly correlated with an analogous episode in Central America. The arid period culminated in the nucleation of aragonite, but within a decade was followed by a return to precursor conditions. Copyright © 2005 John Wiley & Sons, Ltd.