137 research outputs found
Alternative data reduction for precise and accurate isotope ratio determination via LA-MC-ICP-MS
An alternative approach for the evaluation of isotope ratio data using LA-MC-ICP-MS will be presented. In contrast to previously applied methods it is based on the simultaneous
responses of all analyte isotopes of interest and the relevant interferences without performing a conventional background correction.
Significant improvements in precision and accuracy can
be achieved when applying this new method and will be
discussed based on the results of two first methodical
applications: a) radiogenic and stable Sr isotopes in carbonates b) stable chlorine isotopes of pyrohydrolytic extracts.
In carbonates an external reproducibility of the 87Sr/86Sr
ratios of about 19 ppm (RSD) was achieved, an improvement
of about a factor of 5. For recent and sub-recent marine
carbonates a mean radiogenic strontium isotope ratio 87Sr/86Sr of 0.709170 ± 0.000007 (2SE) was determined, which agrees well with the value of 0.7091741 ± 0.0000024 (2SE) reported for modern sea water [1].
Stable chlorine isotope ratios were determined ablating
pyrohydrolytic extracts with a reproducibility of about 0.05‰ (RSD). For basaltic reference material JB1a and JB2 chlorine isotope ratios were determined relative to SMOC (standard mean ocean chlorinity) δ37ClJB-1a = (-0.99 ± 0.06) ‰ and δ37ClJB-2 = (-0.60 ± 0.03) ‰ (2SE), respectively, in accordance with published data [2].
The described strategies for data reduction are considered
to be generally applicable for all isotope ratio measurements using LA-MC-ICP-MS.
[1] McArthur, Rio, Massari, Castradori, Bailey, Thirlwall &
Houghton (2006) Palaeogeo. Palaeoclim. Palaeoeco. 242,
126, doi: 10.1016/j.palaeo.2006.06.004 [2] Fietzke,. Frische, Hansteen & Eisenhauer (2008) J. Anal. At. Spectrom. 2008, doi:10.1039/B718597A
Coralline alga reveals first marine record of subarctic North Pacific climate change
While recent changes in subarctic North Pacific climate had dramatic effects on ecosystems and fishery yields, past climate dynamics and teleconnection patterns are poorly understood due to the absence of century-long high-resolution marine records. We present the first 117-year long annually resolved marine climate history from the western Bering Sea/Aleutian Island region using information contained in the calcitic skeleton of the long-lived crustose coralline red alga Clathromorphum nereostratum, a previously unused climate archive. The skeletal δ18O-time series indicates significant warming and/or freshening of surface waters after the middle of the 20th century. Furthermore, the time series is spatiotemporally correlated with Pacific Decadal Oscillation (PDO) and tropical El Niño-Southern Oscillation (ENSO) indices. Even though the western Bering Sea/Aleutian Island region is believed to be outside the area of significant marine response to ENSO, we propose that an ENSO signal is transmitted via the Alaskan Stream from the Eastern North Pacific, a region of known ENSO teleconnections
Using B isotopes and B/Ca in corals from low saturation springs to constrain calcification mechanisms
Ocean acidification is expected to negatively impact calcifying organisms, yet we lack understanding of their acclimation potential in the natural environment. Here we measured geochemical proxies (δ11B and B/Ca) in Porites astreoides corals that have been growing for their entire life under low aragonite saturation (Ωsw: 0.77–1.85). This allowed us to assess the ability of these corals to manipulate the chemical conditions at the site of calcification (Ωcf), and hence their potential to acclimate to changing Ωsw. We show that lifelong exposure to low Ωsw did not enable the corals to acclimate and reach similar Ωcf as corals grown under ambient conditions. The lower Ωcf at the site of calcification can explain a large proportion of the decreasing P. astreoides calcification rates at low Ωsw. The naturally elevated seawater dissolved inorganic carbon concentration at this study site shed light on how different carbonate chemistry parameters affect calcification conditions in corals
Ca, Mo and U isotopes suggest Neoproterozoic-like ocean conditions during the Late Permian Mass Extinction
Automatic Generation of Invariants for Circular Derivations in {SUP(LA)} 1
The hierarchic combination of linear arithmetic and firstorder logic with free function symbols, FOL(LA), results in a strictly more expressive logic than its two parts. The SUP(LA) calculus can be turned into a decision procedure for interesting fragments of FOL(LA). For example, reachability problems for timed automata can be decided by SUP(LA) using an appropriate translation into FOL(LA). In this paper, we extend the SUP(LA) calculus with an additional inference rule, automatically generating inductive invariants from partial SUP(LA) derivations. The rule enables decidability of more expressive fragments, including reachability for timed automata with unbounded integer variables. We have implemented the rule in the SPASS(LA) theorem prover with promising results, showing that it can considerably speed up proof search and enable termination of saturation for practically relevant problems
A Reduction from Unbounded Linear Mixed Arithmetic Problems into Bounded Problems
We present a combination of the Mixed-Echelon-Hermite transformation and the
Double-Bounded Reduction for systems of linear mixed arithmetic that preserve
satisfiability and can be computed in polynomial time. Together, the two
transformations turn any system of linear mixed constraints into a bounded
system, i.e., a system for which termination can be achieved easily. Existing
approaches for linear mixed arithmetic, e.g., branch-and-bound and cuts from
proofs, only explore a finite search space after application of our two
transformations. Instead of generating a priori bounds for the variables, e.g.,
as suggested by Papadimitriou, unbounded variables are eliminated through the
two transformations. The transformations orient themselves on the structure of
an input system instead of computing a priori (over-)approximations out of the
available constants. Experiments provide further evidence to the efficiency of
the transformations in practice. We also present a polynomial method for
converting certificates of (un)satisfiability from the transformed to the
original system
Cold-water corals in the Bay of Biscay - occurrences and distribution in space and time (TransBiscay) - Cruise No. M84/5, May 31 - June 21, 2011, Vigo (Spain) - Brest (France)
The scientific objectives of METEOR cruise M84/5 focused on the measurement
and analysis of the environmental controls of modern and fossil cold-water coral growth
along a transect in the Bay of Biscay. In four working areas we successfully deployed lander
systems and CTD/Ro’s to document the physical and hydrochemical characteristics of bottom
water masses and the water column in general. These are used to shed light on potential
linkages to modern cold-water coral growth and distribution. These investigations were
flanked by plankton tows in surface waters. The base for all investigations was a thorough
hydroacoustic survey to characterize potential cold-water coral bearing areas with living
colonies. Based on these maps we deployed all video-guided gear such as the OFOS-video
sled, the TV grab, and the lander systems. Benthic assemblages and sedimentary structures
have been documented and sampled with the OFOS and a box corer. Simultaneously, genetic
samples of the living coral material were taken for additional studies. Furthermore, we have
taken gravity cores to investigate the paleoceanographic conditions as well as the timing of
cold-water coral colonization in the Bay of Biscay. Along with the coring efforts, a detailed
sampling and study of porewater properties was performed. An additional aim of this cruise
was to investigate the influence of boundary exchange processes on the Neodymium isotopy
in bottom waters along the pathway of the Mediterranean Outflow water (MOW) by taking
multiple samples with the CTD/Ro.
The new data and samples of this METEOR cruise will provide the framework to
investigate the timing of cold-water coral colonization in the Bay of Biscay, as well as its
interplay with the ambient hydrography and geochemistry. This successful cruise has
provided the basis to investigate the scientific aims of this expedition in great detail
North Pacific twentieth century decadal-scale variability is unique for the past 342 years
Reconstructed sea surface temperatures (SSTs) derived from Mg/Ca measurements in nine encrusting coralline algal skeletons from the Aleutian archipelago in the northernmost Pacific Ocean reveal an overall increase in SST from 1665 to 2007. In the Aleutian SST reconstruction, decadal-scale variability is a transient feature present during the 1700s and early 1800s and then fully emerging post-1950. SSTs vary coherently with available instrument records of cyclone variance and vacillate in and out of coherence with multicentennial Pacific Northwest drought reconstructions as a response to SST-driven alterations of storm tracks reaching North America. These results indicate that an influence of decadal-scale variability on the North Pacific storm tracks only became apparent during the midtwentieth century. Furthermore, what has been assumed as natural variability in the North Pacific, based on twentieth century instrumental data, is not consistent with the long-term natural variability evident in reconstructed SSTs predating the anthropogenic influence
- …