Applications of PB-210/RA-226 and PO-210/PB-210 disequilibria in the study of marine geochemical processes

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution November, 1975The distribution of Pb-210 and Po-210 in dissolved (0.4 micron) phases has been measured at ten stations in the tropical and eastern North Atlantic and at two stations in the Pacific. Both radionuclides occur principally in the dissolved phase. Unsupported Pb-210 activities, maintained by flux from the atmosphere, are present in the surface mixed layer and penetrate into the thermocline to depths of about 500 m. Dissolved Po-210 is ordinarily present in the mixed layer at less than equilibrium concentrations, suggesting rapid biological removal of this nuclide. Particulate matter is enriched in Po-210, with Po-210/Pb-210 activity ratios greater than 1.0, similar to those reported for phytoplankton. Box-model calculations yield a 2-y residence time for Pb-210 and a 0.6-y residence time for Po-210 in the mixed layer. These residence times are considerably longer than the time calculated for turnover of particles in the mixed layer (about 0.1 y). At depths of 100-300 m, Po-210 maxima occur and unsupported Po-210 is frequently present. Calculations indicate that at least 50% of the Po-210 removed from the mixed layer is recycled within the thermocline. Similar calculations for Pb-210 suggest much lower recycling efficiencies. Comparison of the Pb-210 distribution with the reported distribution of Ra-226 at nearby GEOSECS. stations has confirmed the widespread existence of a Pb-210/Ra-226 disequilibrium in the deep sea. Vertical profiles of particulate Pb-210 were used to test the hypothesis that Pb-210 is removed from deepwater by in situ scavenging. With the exception of one profile taken near the Mid-Atlantic Ridge, significant vertical gradients in particulate Pb-210 concentration were not observed, and it is necessary to invoke exceptionally high particle sinking velocities (>10 m/d) to account for the inferred Pb-210 flux. It is proposed that an additional sink for Pb-210 in the deep sea must be sought. Estimates of the dissolved Pb-210/Ra-226 activity ratio at depths greater than 1,000 m range from 0.2 to 0.8 and reveal a systematic increase, in both vertical and horizontal directions, with increasing distance from the sea floor. This observation implies rapid scavenging of Pb-210 at the sediment-water interface and is consistent with a horizontal eddy diffusivity of 3-6 x 107 cm2/s. The more reactive element Po, on the other hand, shows evidence of rapid in situ scavenging. In filtered sea water, Po-210 is deficient, on the average, by ca. 10% relative to Pb-210; a corresponding enrichment is found in the particulate phase. Total inventories of Pb-210 and Po-210 over the entire water column, however, show no significant departure from secular equilibrium, and reliable estimates of particle sinking rates cannot be made.Prepared under National Science Foundation Grant GA-41061 and U.S.A.E.C. Contract AT(11-1)

Density mapping with weak lensing and phase information

The available probes of the large scale structure in the Universe have distinct properties: galaxies are a high resolution but biased tracer of mass, while weak lensing avoids such biases but, due to low signal-to-noise ratio, has poor resolution. We investigate reconstructing the projected density field using the complementarity of weak lensing and galaxy positions. We propose a maximum-probability reconstruction of the 2D lensing convergence with a likelihood term for shear data and a prior on the Fourier phases constructed from the galaxy positions. By considering only the phases of the galaxy field, we evade the unknown value of the bias and allow it to be calibrated by lensing on a mode-by-mode basis. By applying this method to a realistic simulated galaxy shear catalogue, we find that a weak prior on phases provides a good quality reconstruction down to scales beyond l=1000, far into the noise domain of the lensing signal alone.Comment: 11 pages, 9 figures, published in MNRA

A modified wire clamp system for thirty-liter Niskin bottles

A modified clamping system for 30-liter Niskin bottles, consisting of a wire stop, a socket block, and a toggle clamp, has been designed and has been tested at sea. The modified system makes deployment and recovery of the Niskin bottles considerably easier than it is with the standard clamps .Funding was provided by the National Science Foundation under grant Number OCE 84-17910, and by the United States Department of Energy under contract Number DE-AC02-76EV03566

A large-volume, deep-sea submersible pumping system

Eight self-contained, in-situ pumps have been used effectively and routinely by our group for the past six years to collect both particulate and dissolved phases from large volumes of sea water. Multiple pumps are rapidly and easily deployed on the same wire, to any ocean depth, in almost any weather. Each is capable of drawing up to 200 liters per hour through four large Nuclepore™ filters, then through three cartridge filters. Pumping is controlled by a Sharp™ pocket computer suitably interfaced with the pump motor and flow meter. Endurance is about 15 hours. Total flow and flow rate are recorded, respectively, by a mechanical flow meter and the computer.Funding was provided by the National Science Foundation under Grant Number NSF OCE-8800620 and the Department of Energy under Grant DE-FG02-88ER60681

Models of the distribution of 210Pb in a section across the North Equatorial Atlantic Ocean

The deficiency of 210Pb relative to 226Ra in the world\u27s deep ocean is well documented, and the overall residence time of 210Pb bas been calculated to be about 15-100 years. It has been assumed, generally, that the removal mechanism is one of in situ adsorption on settling particles, but Bacon et al. (1976) suggested that a boundary scavenging process with diffusive and advective fluxes of 210Pb from the interior ocean may be a significant factor...

210Po and 210Pb distributions during a phytoplankton bloom in the North Atlantic: Implications for POC export

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Horowitz, E. J., Cochran, J. K., Bacon, M. P., & Hirschberg, D. J. 210Po and 210Pb distributions during a phytoplankton bloom in the North Atlantic: implications for POC export. Deep-Sea Research Part I: Oceanographic Research Papers, 164, (2020): 103339, doi:10.1016/j.dsr.2020.103339.During the North Atlantic Bloom Experiment (NABE) of the Joint Global Ocean Flux Study (JGOFS), water column sampling for particulate and dissolved 210Po and 210Pb was performed four times (26 April and 4, 20, 30 May 1989) during a month-long Lagrangian time-series occupation of the NABE site, as well as one-time samplings at stations during transit to and from the site. There are few prior studies documenting short-term changes in 210Po and 210Pb profiles over the course of a phytoplankton bloom, and we interpret the profiles in terms of the classical “steady-state” (SS) approach used in most studies, as well as by using a non-steady state approach suggested by the temporal evolution of the profiles. Changes in 210Po profiles during a bloom are expectable as this radionuclide is scavenged and exported. During NABE, 210Pb profiles also displayed non-steady state, with significant increases in upper water column inventory occurring midway through the experiment. Export of 210Po from the upper 150 m using the classic “steady-state” model shows increases from 0.5 ± 8.5 dpm m−2 d−1 to 68.2 ± 4.2 dpm m−2 d−1 over the ~one-month occupation. Application of a non-steady state model, including changes in both 210Pb and 210Po profiles, gives higher 210Po export fluxes. Detailed depth profiles of particulate organic carbon (>0.8 μm) and particulate 210Po (>0.4 μm) are available from the 20 and 30 May samplings and show maxima in POC/Po at ~37 m. Applying the POC/210Po ratios at 150 m to the “steady state” 210Po fluxes yields POC export from the upper 150 m of 8.2 ± 1.5 mmol C m− 2 d−1 on 20 May and 6.0 ± 1.6 mmol C m−2 d−1 on 30 May. The non-steady state model applied to the interval 20 to 30 May yields POC export of 24.3 mmol C m−2 d−1. The non-steady state (NSS) 210Po-derived POC fluxes are comparable to, but somewhat less than, those estimated previously from 234Th/238U disequilibrium for the same time interval (37.3 and 45.0 mmol m−2 d−1, depending on the POC/Th ratio used). In comparison, POC fluxes measured with a floating sediment trap deployed at 150 m from 20 to 30 May were 11.6 mmol m−2 d−1. These results suggest that non-steady state Po-derived POC fluxes during the NABE agree well with those derived from 234Th/238U disequilibrium and agree with sediment trap fluxes within a factor of ~2. However, unlike the 234Th-POC flux proxy, non-steady stage changes in profiles of 210Pb, the precursor of 210Po, must be considered.We are grateful to T. Hammar and A. Fleer (WHOI) for assistance at sea and in the laboratory. This work was supported originally by National Science Foundation (United States) grant OCE-8819544 to JKC and more recently by OCE-1736591. We thank Stephen Thurston (American Museum of Natural History) for graphics assistance Robert Aller, Steven Beaupre, and two anonymous reviewers for helpful comments

Error Avoiding Quantum Codes and Dynamical Stabilization of Grover's Algorithm

An error avoiding quantum code is presented which is capable of stabilizing Grover's quantum search algorithm against a particular class of coherent errors. This error avoiding code consists of states only which are factorizable in the computational basis. Furthermore, its redundancy is smaller than the one which is achievable with a general error correcting quantum code saturating the quantum Hamming bound. The fact that this code consists of factorizable states only may offer advantages for the implementation of quantum gates in the error free subspace

The Wide Field Spectrograph (WiFeS)

This paper describes the Wide Field Spectrograph (WiFeS) under construction at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) for the ANU 2.3m telescope at the Siding Spring Observatory. WiFeS is a powerful integral field, double-beam, concentric, image-slicing spectrograph designed to deliver excellent thoughput, wavelength stability, spectrophotometric performance and superb image quality along with wide spectral coverage throughout the 320-950 nm wavelength region. It provides a 25x38 arcsec. field with 0.5 arcsec. sampling along each of twenty five 38X1 arcsec slitlets. The output format is optimized to match the 4096x4096 pixel CCD detectors in each of two cameras individually optimized for the blue and the red ends of the spectrum, respectively. A process of "interleaved nod-and-shuffle" will be applied to permit quantum noise-limited sky subtraction. Using VPH gratings, spectral resolutions of 3000 and 7000 are provided. The full spectral range is covered in a single exposure at R=3000, and in two exposures in the R=7000 mode. The use of transmissive coated optics, VPH gratings and optimized mirror coatings ensures a throughput (including telescope atmosphere and detector) > 30% over a wide spectral range. The concentric image-slicer design ensures an excellent and uniform image quality across the full field. To maximize scientific return, the whole instrument is configured for remote observing, pipeline data reduction, and the accumulation of calibration image libraries.Comment: Accepted for publication in Astrophysics & Space Science, 16 pages, 14 figure

The thermodynamic balance of the Weddell Gyre

The thermodynamic balance of the Weddell Gyre is assessed from an inverse estimate of the circulation across the gyre's rim. The gyre experiences a weak net buoyancy gain that arises from a leading-order cancellation between two opposing contributions, linked to two cells of water mass transformation and diapycnal overturning. The lower cell involves a cooling-driven densification of 8.4 ± 2.0 Sv of Circumpolar Deep Water and Antarctic Bottom Water near the gyre's southern and western margins. The upper cell entails a freshening-driven conversion of 4.9 ± 2.0 Sv of Circumpolar Deep Water into lighter upper-ocean waters within the gyre interior. The distinct role of salinity between the two cells stems from opposing salinity changes induced by sea ice production, meteoric sources and admixture of fresh upper-ocean waters in the lower cell, which contrasts with coherent reductions in salinity associated with sea ice melting and meteoric sources in the upper cell

Finding Silver Linings in the Covid-19 Pandemic: A 2-Wave Study in the UK

The Covid-19 pandemic has resulted in widespread anxiety, fear and depression, yet focussing only on these negative issues may obscure the opportunity to promote positivity and resilience. Traumatic events can often result in positive life changes (adversarial growth) though there is little evidence in the context of pandemics, and no previous studies in Covid-19 with the general public. The present research investigated whether adversarial growth was perceived in Covid-19 and whether this could account for variance in wellbeing, over and above effects of personality traits. Participants recruited from the UK public ( N = 183) completed the Big Five Personality Inventory, the WHO-5 Wellbeing Scale and the Silver Lining Questionnaire (SLQ) measure of adversarial growth. Questionnaires were completed online, at two timepoints, nine months apart. At Time 1, wellbeing was negatively associated with trait Neuroticism and positively associated with Openness to experience. Both associations were positively mediated by SLQ score. At Time 2, SLQ score again mediated the effects of Openness on wellbeing, and also the influence of wellbeing at Time 1 on that at Time 2. Reported Silver Linings included strengthened personal relationships at Time 1, and improved ability to handle life events at Time 2. This suggests a shift from an appreciation of relationships to an awareness of personal development once life returned to some semblance of normality. Overall, results suggest that perceived adversarial growth supported wellbeing during the pandemic and highlight a focus for therapeutic intervention. </jats:p