Bomb-produced radiocarbon validation of growth-increment crossdating allows marine paleoclimate reconstruction

The bivalve Pacific geoduck (Panopea generosa) has been used in the eastern North Pacific Ocean to create proxies for environmental factors such as temperature and oceanographic conditions. This type of research depends upon accurate age determination of Pacific geoducks, which historically was based on shell growth-increment counts. A recent study comparing age estimates generated by the dendrochronology (tree-ring science) procedure of crossdating to those estimated from growth-increment counts found a significant difference between the methods for geoduck older than 30 years. Compared to the traditional age determination method of counting growth increments, the crossdating method estimates a greater longevity in this species, with some individuals living in excess of 150 years. In the present study, the accuracy of each method was independently assessed using bomb-produced radiocarbon (C-14) techniques. Specimens whose birth years were estimated to be within the era of the bomb-produced marine C-14 increase and where the differences between ages estimated by the two methods were greatest were selected for C-14 analysis. The difference between age estimates from traditional growth-increment counts and those from crossdating was evaluated using their respective C-14 chronologies in comparisons to a reference chronology as a standard. The comparisons relied on Bayesian nonlinear models using Markov Chain Monte Carlo simulation. This method of analysis showed that with a 50% probability geoducks were aged correctly when using the crossdating method, compared to the growth increment counts which had a 50% probability of underestimating the age by 4 years. Therefore, the crossdated age estimates were found to be more accurate than increment counts. Furthermore, these results provide new confidence in using Pacific geoduck biochronologies for paleoclimate and paleoenvironmental reconstruction. Published by Elsevier B.V.Keywords: Age determination, Pacific geoduck, Bomb-produced radiocarbon, Bayesian models, Shell growth-increment counts, Crossdating, Panopea generos

Bayesian hierarchical modeling of Pacific geoduck growth increment data and climate indices

Growth increment widths from hard structures of marine and freshwater fish and bivalve species are increasingly used to model growth and elucidate relationships with environmental variability. Fully characterizing the intrinsic age-related growth variation among individuals within and between populations, while estimating the extrinsic environmental effects simultaneously, can be challenging. Using the long-lived bivalve Pacific geoduck (Panopea generosa), we develop an integrated approach to analyze the relationship between growth increment data and climate indices using Bayesian hierarchical methods. Fitting models to growth increment data from multiple individuals over two sites, we examined different covariance structures related to random individual effects, long- and short-term environmental effects and unexplained errors. The best fitting hierarchical model accounted for a site-specific mean growth response, individual growth variability through random parameter effects, and site-specific error variances. Extrinsic environmental effects on growth were also significant and included a random year effect and the Pacific Decadal Oscillation (PDO) as a predictor of mean growth across both individuals and sites. Once intrinsic age-related growth was accounted for. PDO accounted for 18% to total variability in growth increment data: geoduck shell size was predicted to increase as a function of larger PDO anomalies. However, the greatest variability in growth increment data was explained by random year effects (similar to 60-70%), and while largely unexplained, sea surface temperature (SST) is a likely determinant on geoduck growth rates showing a positive growth-SST response. Published by Elsevier B.V

A transformative approach to ageing fish otoliths using Fourier transform-near infrared spectroscopy (NIRS): a case study of eastern Bering Sea walleye pollock (Gadus chalcogrammus)

We investigated the use of Fourier transform-near infrared spectroscopy (FT-NIRS), which is a method of measuring light absorbance signatures, to derive ages from eastern Bering Sea walleye pollock (Gadus chalcogrammus) otoliths. This approach is based on a predictive model between near infrared spectra in the otolith and fish age, which is calibrated and validated. The advantage of FT-NIRS over traditional methods is the speed and repeatability with which age estimates are generated. The application of FT-NIRS to walleye Pollock otoliths yielded r2 values between 0.91 and 0.95 for the calibration models, and good validation performance (between 0.82 and 0.93). This approach can be expected to predict fish age within Âą 1.0 year of age 67% of the time. When comparing approaches, the FT-NIRS had as good or slightly better precision (75% agreement) than the traditional ageing (66% agreement), and showed little or no bias at age before 12 years of age. Once the predictive FT-NIR model is calibrated and validated, age-estimates using FT-NIRS can be done at 10 times the rate compared to traditional methods.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Mechanical and optical manipulation of porphyrin rings at the submicrometre scale

Scanning probe microscopes (SPMs) and especially the atomic force microscope (AFM) can be used as tools for modifying surface structures on the submicrometre and even nanometre scale. For this purpose an advanced interface has been developed to facilitate these manipulations and greatly increase the number of possible applications. In this paper this interface (the nanoManipulator, developed at the University of North Carolina at Chapel Hill) is implemented on a combined AFM-confocal microscope. This setup allows AFM imaging, manipulations and fluorescence imaging of the same area on the sample. The new setup is tested on ringlike structures of a porphyrin derivative (BP6). A small amount of the fluorescent material could be displaced with the AFM tip. A special tool (sweep mode) allowed a modification of around 130 nm, which was afterwards detectable with the confocal microscope. The resolution attainable in these kind of experiments could go down below 100 nm and is primarily determined by the tip and sample geometry. Comparable with this experiment is the application of a near-field scanning optical microscope (NSOM) to make photochemical modifications. Using the excitation power coming from the NSOM probe the fluorescence can be quenched by bleaching a selected area instead of displacing the material. Application on the BP6 rings led to a modification of 280 nm wide. AFM can perform modifications on a smaller scale but is less selective than NSOM. Optical investigation of the changes after AFM manipulation can give more elaborate information on the modifications. This will extend the possible applications of the techniques and may ultimately go down to the single-molecule level