Sub-annual Resolution Research Articles

Analysis of geological Sr isotope markers in fish otoliths with subannual resolution using laser ablation-multicollector-ICP-mass spectrometry

In this pilot study, laser ablation-multicol- lector-inductively coupled plasma-mass spectrome- try (LA-MC-ICP-MS) and Sr isotope geochemistry were applied to fish life-history studies through the micro-analysis of Sr abundance and 87 Sr/ 86 Sr in the otoliths of an anadromous fish. With a laser sampling area of 70-lm diameter, LA-MC-ICP-MS of a deep-sea coral gave precision values for 87 Sr/ 86 Sr determina- tion of approximately 0.04% relative standard devia- tion with an accuracy to <1r of seawater. Analyses of different sides of the same otolith and different oto- liths from the same fish gave reproducible results overall, which suggested that at the Sr concentrations found in the freshwater portions of the otoliths (ca. 500 lg/g) LA-MC-ICP-MS can be reliably employed. Subtle isotopic differences occurred between a pair of otoliths from one fish, which may be due either to sampling resolution limitations imposed by the size of the laser spot, or to asymmetrical otolith growth which incorporated environmental Sr in one otolith but not the other at certain times. New information about fish provenance which could not be gained from Sr concentration data alone included insights into the movements of individuals between isotopically contrasting freshwater environments. LA-MC-ICP- MS of calcified tissues, in combination with Sr sotope geochemistry, has the potential to retrieve new data about fish life-history movements which complement the information from other techniques.

Annual to sub-annual resolution of multiple trace-element trends in speleothems

This study aims to establish evidence for the widespread existence of preserved high-resolution trace element variations in speleothems that may have climatic significance. Ion microprobe analysis of speleothems reveals that annual to sub-annual variations in element chemistry exist at five, shallow western European cave sites (Crag Cave, County Kerry and Ballynamintra, County Waterford, Ireland; Uamh an Tartair, Sutherland, Scotland; Grotte Pere-Noël, Belgium; Grotta di Ernesto, NE Italy) with widely varying climatic, geomorphic and geological settings. The variations are not restricted to species (Mg, Sr and Ba) known to substitute directly for Ca in the calcite lattice, but include H, F, Na and P. Phosphorus (as phosphate) displays the greatest variability and may have the most significance as a proxy for the seasonal temperature cycle because of its role as a nutrient element. The technique allows estimation of growth rate of speleothems at any interval of interest, which is one of several possible uses in palaeoclimatology.

Trace element variation in speleothem aragonite: potential for palaeoenvironmental reconstruction

Trace element variation in annually laminated stalagmites has the potential to record long-term, high-resolution palaeoclimatic data provided both (1) the relationship between trace element content in the carbonate and the climate, and (2) the mechanism of stalagmite growth, are understood. Here we report a secondary ion mass spectrometry (SIMS) study of an aragonitic speleothem (T7) from Cold Air Cave, Southern Africa, which achieves small (μm) spatial resolution and ppm precision. T7 has a series of fine visible laminae believed to be annual to subannual. This article establishes (1) the usefulness of SIMS in analyzing speleothem aragonite at the spatial resolution and precision relevant to climatic studies, (2) the distribution of trace elements in aragonite on micron scales and their relationship to models for speleothem growth and (3) the potential of aragonite speleothems to encode climatic data at subannual resolution. Complex reproducible oscillations in Sr/Ca and Ba/Ca are observed parallel to the growth direction of the speleothem. However, in addition to this variability, we observe trace element oscillations perpendicular to the growth direction and infer that aragonite crystallites in the speleothem are laterally, as well as vertically zoned. Stepscans parallel to the growth direction demonstrate complex zoning patterns from which simple climatic data are difficult to extract due to small-scale lateral heterogeneity in the aragonite. However, time-series analysis of the whole data set reveals regular cycles in Sr/Ca and Ba/Ca at a scale that matches the magnitude of the visible laminae. On this basis, it appears that within the complex geochemical variability, there resides a regular environmental control, possibly variation in water throughput, hence rainfall.

Diatomaceous sediments from the Miocene Monterey Formation, California; a lamina-scale investigation of biological, ecological, and sedimentary processes

Finely laminated diatomaceous sediments from the Miocene Monterey Formation, Lompoc, Santa Barbara County, California, record the mutualistic coupling of life processes and environmental evolution at subannual and subseasonal resolution. In this study we present a new classification of lamina and couplet styles based on couplet bimodality, lamina thickness, compositional domination, lamina spacing, and cyclicity. We also describe five distinct lamina types with emphasis on paleoenvironmental settings, paleoecological associations, and biologically mediated sedimentary/taphonomic processes. Detrital laminae, consisting of silt, clay, and robust diatoms, were deposited from continental runoff during rainy seasons. Thin biosiliceous laminae consist of either moderately preserved high-diversity diatom assemblages, or well-preserved monogeneric phytoplankton assemblages. Most thick, continuous diatomaceous laminae are composed of well-preserved monogeneric and monospecific diatom assemblages that likely experienced biologically induced aggregation and rapid sedimentation without grazing. Thick, discontinuous diatomaceous laminae consist of either Thalassiothrix longissima mats or Chaetoceros setae. Mat laminae reflect stratified water conditions and high biomass conditions developed via vertically migrating diatom mats. Setae laminae are problematic to interpret. Macerated biosilica laminae, consisting of closely packed and highly fragmented biosilica from a variety of taxa, reflect intense zooplankton maceration and dissolution of diverse phytoplankton assemblages. Our results illustrate how different lamina types and associations can be used to proxy specific ecological and oceanographic conditions. This study provides a foundation for developing a high-resolution time series of paleoenvironmental variability recorded by biological event strata in hemipelagic sediments.

Temperature history and accumulation timing for the snowpack at GISP2, central Greenland

AbstractPrevious research has documented a close association between high-resolution snow-pit profiles of hydrogen and oxygen stable-isotope ratios and multi-year Special Sensor Microwave/lmager (SSM/I) 37 GHz brightness temperature data in central Greenland. Comparison of the SSM/I data to profiles obtained during the 1989-91 field seasons indicated thatδD andδ18O data from the near-surface snow at the Greenland summit are a reliable, high-resolution temperature proxy. To test this new technique further, additional stable-isotope data were obtained from a 2 m snow pit constructed during late-June 1995 near the GISP2 site.This new profile, supported by pit stratigraphy and chemistry data, confirms the utility of comparing stable-isotope records with SSM/I brightness temperatures. The sub-annual variation of theδDrecord at the GISP2 site was determined using 15 match points, from approximately December 1991 through June 1995 and was guided in part by time-constrained hoar layers. The close association of these temperature proxies supports the assertion that snow accumulation occurs frequently through the year and that the isotope record initially contains temperature information from many times of the year. This is also independently confirmed by analysis of H2O2data. The slope of the multi-yearTvsδcorrelation was evaluated along with the sub-annual variation in the amount, rate and timing of accumulation. These new results are consistent with those from the previous study and they also demonstrate that the snow in this area initially contains temperature and chemical records with sub-annual resolution. This encourages confident interpretation of the paleoclimatic signal variations in the GISP2 and GRIP deep cores.

Temperature history and accumulation timing for the snowpack at GISP2, central Greenland

AbstractPrevious research has documented a close association between high-resolution snow-pit profiles of hydrogen and oxygen stable-isotope ratios and multi-year Special Sensor Microwave/lmager (SSM/I) 37 GHz brightness temperature data in central Greenland. Comparison of the SSM/I data to profiles obtained during the 1989-91 field seasons indicated that δD and δ18O data from the near-surface snow at the Greenland summit are a reliable, high-resolution temperature proxy. To test this new technique further, additional stable-isotope data were obtained from a 2 m snow pit constructed during late-June 1995 near the GISP2 site.This new profile, supported by pit stratigraphy and chemistry data, confirms the utility of comparing stable-isotope records with SSM/I brightness temperatures. The sub-annual variation of the δD record at the GISP2 site was determined using 15 match points, from approximately December 1991 through June 1995 and was guided in part by time-constrained hoar layers. The close association of these temperature proxies supports the assertion that snow accumulation occurs frequently through the year and that the isotope record initially contains temperature information from many times of the year. This is also independently confirmed by analysis of H2O2 data. The slope of the multi-year T vs δ correlation was evaluated along with the sub-annual variation in the amount, rate and timing of accumulation. These new results are consistent with those from the previous study and they also demonstrate that the snow in this area initially contains temperature and chemical records with sub-annual resolution. This encourages confident interpretation of the paleoclimatic signal variations in the GISP2 and GRIP deep cores.

Tracing short cycles in long records: the study of inter-annual to inter-centennial climate change from long sediment records, examples from the Santa Barbara Basin

We present a review of digital imaging techniques to obtain highest resolution colour/greyvalue time-series from geological material. From suitable sediments these methods can yield time-series with subannual resolution. They can be utilized for the detection of high-frequency (&lt; 300 years) climate change over long periods of time. Automated laminae counting produces a high-precision stratigraphy and data on the laminae thickness. The application of the methods to drill cores from the Santa Barbara Basin demonstrates the power of the techniques in detecting rapid climate change. El Niño/Southern Oscillation cycles as well as solar and lunar cycles could be detected from both, the greyvalue and the laminae thickness time-series. Evolutionary power spectra, calculated from the colour/greyvalue time-series, reveal dramatic variations in the power and frequency of rapid climate oscillations during the Holocene.

Fluctuations in the Earth's rotation since 1830 from high-resolution astronomical data

SUMMARY Fluctuations in the Earth's rotation since 1830, as evidenced by changes in the length of the day, are derived from astronomical data having subannual resolution. Before 1955.5, timings of linar occultations are used; after 1955.5, the data are taken from the time series TAI-UT1. Although the data in the earliest period, 1830–90, display decade fluctuations in the length of the day, they are not accurate enough to reveal interannual variations. In this regard, also, the results from 1890–1925 are somewhat dubious. The quality of the data after 1925, though, is such that the temporal behaviour of the interannual fluctuations in the length of the day can be traced with confidence. We present plots of the interannual fluctuations in the period 1890–1987 and the longer-term decade fluctuations in the period 1830–1983. The interannual fluctuations in the length of the day since 1925 are compared with an index of the El Nino/Southern Oscillation (ENSO) phenomenon in the ocean-atmosphere system and are subjected to spectral analysis. The results support the conclusions reached by other authors that these fluctuations are linked to circulation changes in the atmosphere associated with ENSO, and in part to the quasi-biennial oscillation in the equatorial stratosphere's zonal winds. A spectral analysis of our 62 yr series of length of day values since 1925 reveals two significant peaks in the interannual range 2–4 yr. One is roughly biennial and the other is about twice this period, broadly supporting results obtained previously from shorter records. Our analysis of high-resolution data, therefore, contributes to ongoing efforts to establish a close relationship between the length of the day and aspects of the global climate system in the period before modern data became available in 1955.5.

Highest telescope

Determination of carbon isotope (δ13C) values of tree-ring tissue is a well-established method to reconstruct past climate variability at annual resolution, but such records are limited in tropical latitudes due to the lack of well-defined annual growth bands. Recent work has demonstrated the potential for high-resolution, intra-ring δ13C records to help define ring boundaries in tropical environments and provide additional climate information at sub-annual resolution. Here we present a high-resolution, intra-ring carbon isotope (δ13C) record of the Hawaiian endemic species Sophora chrysophylla (also known as “māmane”) in order to assess the ability to extract seasonal climate information from these drought tolerant trees. Tree cores were sampled from high-elevation māmane trees growing on the west side of Mauna Kea, Big Island. Across our entire dataset (1986–2008), we identified a notable decreasing linear trend in the δ13C record of 0.061‰/year that can be attributed to changes in the δ13C value of atmospheric CO2 and pCO2 concentration associated with fossil fuel burning. Correcting for these affects yields a nearly flat δ13C record with a slope of − 0.0075‰/year, suggesting no long-term trends in climate across the study period. We observe a quasi-periodic change in the δ13C values [Δ(δ13C)] measured within each ring that averages 1.09 ± 0.50‰ (± 1σ, n = 23) in amplitude. These variations are interpreted as the intra-annual isotopic signal in tree photosynthesis. The δ13C variability correlates with the visible ring structure of the sample, suggesting the presence of annual growth rings at this tropical high elevation site.We applied these data to a model that relates the Δ(δ13C) value to seasonal changes in precipitation in order to reconstruct annual changes in total summer (May through October) and winter (November through April) precipitation at the site. Across the 23-year record (1986–2008; n = 579 δ13C measurements), reconstructed values for the ratio of summer to winter precipitation, total summer precipitation, and total winter precipitation correlate well with rainfall data collected from a nearby weather station (r = 0.65, 0.36, and 0.70, respectively). These results support application of this model to reconstruct inter-annual changes in seasonal precipitation from long-term tree-ring chronologies. They also demonstrate the potential of using māmane δ13C for future long-term climate reconstructions.

Semiconduction and cation valencies in manganese ferrites : F.K. Lotgering (Philips Research Laboratories, N.V. Philips' Gloeilampenfabrieken, Eindhoven, The Netherlands)

Stalagmites are important palaeo-climatic archives since their chemical and isotopic signatures have the potential to record high-resolution changes in temperature and precipitation over thousands of years. We present three U/Th-dated records of stalagmites (MA1–MA3) in the superhumid southern Andes, Chile (53°S). They grew simultaneously during the last five thousand years (ka BP) in a cave that developed in schist and granodiorite. Major and trace elements as well as the C and O isotope compositions of the stalagmites were analysed at high spatial and temporal resolution as proxies for palaeo-temperature and palaeo-precipitation. Calibrations are based on data from five years of monitoring the climate and hydrology inside and outside the cave and on data from 100 years of regional weather station records.Water-insoluble elements such as Y and HREE in the stalagmites indicate the amount of incorporated siliciclastic detritus. Monitoring shows that the quantity of detritus is controlled by the drip water rate once a threshold level has been exceeded. In general, drip rate variations of the stalagmites depend on the amount of rainfall. However, different drip-water pathways above each drip location gave rise to individual drip rate levels. Only one of the three stalagmites (MA1) had sufficiently high drip rates to record detrital proxies over its complete length. Carbonate-compatible element contents (e.g. U, Sr, Mg), which were measured up to sub-annual resolution, document changes in meteoric precipitation and related drip-water dilution. In addition, these soluble elements are controlled by leaching during weathering of the host rock and soils depending on the pH of acidic pore waters in the peaty soils of the cave’s catchment area. In general, higher rainfall resulted in a lower concentration of these elements and vice versa. The Mg/Ca record of stalagmite MA1 was calibrated against meteoric precipitation records for the last 100 years from two regional weather stations. Carbonate-compatible soluble elements show similar patterns in the three stalagmites with generally high values when drip rates and detrital tracers were low and vice versa. δ13C and δ18O values are highly correlated in each stalagmite suggesting a predominantly drip rate dependent kinetic control by evaporation and/or outgassing. Only C and O isotopes from stalagmite MA1 that received the highest drip rates show a good correlation between detrital proxy elements and carbonate-compatible elements. A temperature-related change in rainwater isotope values modified the MA1 record during the Little Ice Age (∼0.7–0.1 ka BP) that was ∼1.5 °C colder than today. The isotopic composition of the stalagmites MA2 and MA3 that formed at lower drip rates shows a poor correlation with stalagmite MA1 and all other chemical proxies of MA1. ‘Hendy tests’ indicate that the degassing-controlled isotope fractionation of MA2 and MA3 had already started at the cave roof, especially when drip rates were low. Changing pathways and residence times of the seepage water caused a non-climatically controlled isotope fractionation, which may be generally important in ventilated caves during phases of low drip rates. Our proxies indicate that the Neoglacial cold phases from ∼3.5 to 2.5 and from ∼0.7 to 0.1 ka BP were characterised by 30% lower precipitation compared with the Medieval Warm Period from 1.2 to 0.8 ka BP, which was extremely humid in this region.