Low-frequency interaction between horizontal and overturning gyres in the ocean

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L18614, doi:10.1029/2008GL035206.Low-frequency variability of the horizontal circulation in an idealized, eddy-permitting, numerical model drives the dominant mode of low-frequency variability in the meridional overturning circulation. This coupling takes place through the influence of lateral advection in the cyclonic high-latitude boundary current on the mixed layer depth along the boundary. The mean and low-frequency variability of the meridional overturning circulation are well predicted by a diagnostic estimate that assumes the downwelling is controlled by the thermal wind shear within the mixed layer along the boundary, which is in turn determined by a simple balance between lateral advection and surface cooling. The more general result is the demonstration that the mean and low frequency variability of the meridional overturning streamfunction are controlled by the baroclinic pressure gradient within the mixed layer along the boundary, which may be influenced by numerous factors such as low-frequency variability in lateral advection, wind stress, surface buoyancy fluxes, or ice melt and freshwater runoff.This work was supported by NSF grants OCE-0423975 and OCE-0726339

The Coherent Structures of Shallowwater Turbulence: Deformationradius Effects, Cyclone/Anticyclone Asymmetry and Gravitywave Generation

Over a large range of Rossby and Froude numbers, we investigate the dynamics of initially balanced decaying turbulence in a shallow rotating fluid layer. As in the case of incompressible two‐dimensional decaying turbulence, coherent vortex structures spontaneously emerge from the initially random flow. However, owing to the presence of a free surface, a wealth of new phenomena appear in the shallow‐water system. The upscale energy cascade, common to strongly rotating flows, is arrested by the presence of a finite Rossby deformation radius. Moreover, in contrast to near‐geostrophic dynamics, a strong asymmetry is observed to develop as the Froude number is increased, leading to a clear dominance of anticyclonic vortices over cyclonic ones, even though no β effect is present in the system. Finally, we observe gravity waves to be generated around the vortex structures, and, in the strongest cases, they appear in the form of shocks. We briefly discuss the relevance of this study to the vortices observed in Jupiter’s atmosphere

Inter-annual and inter-seasonal variability of the Orkney wave power resource

The waters surrounding the Orkney archipelago in the north of Scotland are one of the key regions in the world suitable for exploitation of both wave and tidal energy resources. Accordingly, Orkney waters are currently host to 1.08 GW of UK Crown Estate leased wave and tidal energy projects, with a further 0.5 GW leased in the southern part of the adjacent Pentland Firth. Although several wave resource models exist of the region, most of these models are commercial, and hence the results not publicly available, or have insufficient spatial/temporal resolution to accurately quantify the wave power resource of the region. In particular, no study has satisfactorily resolved the inter-annual and inter-seasonal variability of the wave resource around Orkney. Here, the SWAN wave model was run at high resolution on a high performance computing system, quantifying the Orkney wave power resource over a ten year period (2003–2012), a decade which witnessed considerable inter-annual variability in the wave climate. The results of the validated wave model demonstrate that there is considerable variability of the wave resource surrounding Orkney, with an extended winter (December–January–February–March, DJFM) mean wave power ranging from 10 to 25 kW/m over the decade of our study. Further, the results demonstrate that there is considerably less uncertainty (30%) in the high energy region to the west of Orkney during winter months, in contrast to much greater uncertainty (60%) in the lower energy region to the east of Orkney. The DJFM wave resource to the west of Orkney correlated well with the DJFM North Atlantic Oscillation (NAO). Although a longer simulated time period would be required to fully resolve inter-decadal variability, these preliminary results demonstrate that due to considerable inter-annual variability in the NAO, it is important to carefully consider the time period used to quantify the wave power resource of Orkney, or regions with similar exposure to the North Atlantic. Finally, our study reveals that there is significantly less variability in the practical wave power resource, since much of the variability in the theoretical resource is contained within relatively few extreme events, when a wave device enters survival mode

Physical controls on the macrofaunal benthic biomass in Barrow Canyon, Chukchi Sea

Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(5), (2021): e2020JC017091, https://doi.org/10.1029/2020JC017091.A region of exceptionally high macrofaunal benthic biomass exists in Barrow Canyon, implying a carbon export process that is locally concentrated. Here we offer an explanation for this benthic “hotspot” using shipboard data together with a set of dynamical equations. Repeat occupations of the Distributed Biological Observatory transect in Barrow Canyon reveal that when the northward flow is strong and the density front in the canyon is sharp, plumes of fluorescence and oxygen extend from the pycnocline to the seafloor in the vicinity of the hotspot. By solving the quasi-geostrophic omega equation with an analytical flow field fashioned after the observations, we diagnose the vertical velocity in the canyon. This reveals that, as the along stream flow converges into the canyon, it drives a secondary circulation cell with strong downwelling on the cyclonic side of the northward flow. The downwelling quickly advects material from the pycnocline to the seafloor in a vertical plume analogous to those seen in the observations. The plume occurs only when the phytoplankton reside in the pycnocline, since the near-surface vertical velocity is weak, also consistent with the observations. Using a wind-based proxy to represent the strength of the northward flow and hence the pumping, in conjunction with a satellite-derived phytoplankton source function, we construct a time series of carbon supply to the bottom of Barrow Canyon.This work was funded by National Science Foundation grants PLR-1504333 and OPP-1733564 (Robert S. Pickart, Frank Bahr), OPP-1822334 (Michael A. Spall), PLR-1304563 (Kevin R. Arrigo), OPP-1204082 and OPP-1702456 (Jacqueline M. Grebmeier); National Oceanic and Atmospheric Administration grants NA14OAR4320158 and NA19OAR4320074 (Robert S. Pickart, Peigen Lin, Leah T. McRaven), CINAR-22309.02 (Jacqueline M. Grebmeier)

Optimal treatment allocations in space and time for on-line control of an emerging infectious disease

A key component in controlling the spread of an epidemic is deciding where, whenand to whom to apply an intervention.We develop a framework for using data to informthese decisionsin realtime.We formalize a treatment allocation strategy as a sequence of functions, oneper treatment period, that map up-to-date information on the spread of an infectious diseaseto a subset of locations where treatment should be allocated. An optimal allocation strategyoptimizes some cumulative outcome, e.g. the number of uninfected locations, the geographicfootprint of the disease or the cost of the epidemic. Estimation of an optimal allocation strategyfor an emerging infectious disease is challenging because spatial proximity induces interferencebetween locations, the number of possible allocations is exponential in the number oflocations, and because disease dynamics and intervention effectiveness are unknown at outbreak.We derive a Bayesian on-line estimator of the optimal allocation strategy that combinessimulation–optimization with Thompson sampling.The estimator proposed performs favourablyin simulation experiments. This work is motivated by and illustrated using data on the spread ofwhite nose syndrome, which is a highly fatal infectious disease devastating bat populations inNorth America

Manganese tricarbonyl complexes with asymmetric 2 2‑iminopyridine ligands: toward decoupling steric and electronic 3 factors in electrocatalytic CO2 reduction

Manganese tricarbonyl bromide complexes incorporating IP (2-(phenylimino)pyridine) derivatives, [MnBr(CO)3(IP)], are demonstrated as a new group of catalysts for CO2 reduction, which represent the first example of utilization of (phenylimino)pyridine ligands on manganese centers for this purpose. The key feature is the asymmetric structure of the redox-noninnocent ligand that permits independent tuning of its steric and electronic properties. The α-diimine ligands and five new Mn(I) compounds have been synthesized, isolated in high yields, and fully characterized, including X-ray crystallography. Their electrochemical and electrocatalytic behavior was investigated using cyclic voltammetry and UV−vis−IR spectroelectrochemistry within an OTTLE cell. Mechanistic investigations under an inert atmosphere have revealed differences in the nature of the reduction products as a function of steric bulk of the ligand. The direct ECE (electrochemical−chemical−electrochemical) formation of a five-coordinate anion [Mn(CO)3(IP)]−, a product of two-electron reduction of the parent complex, is observed in the case of the bulky DIPIMP (2-[((2,6-diisopropylphenyl)imino)methyl]pyridine), TBIMP (2-[((2-tert-butylphenyl)imino)methyl]-pyridine), and TBIEP (2-[((2-tert-butylphenyl)imino)ethyl]pyridine) derivatives. This process is replaced for the least sterically demanding IP ligand in [MnBr(CO)3(IMP)] (2-[(phenylimino)methyl]pyridine) by the stepwise formation of such a monoanion via an ECEC(E) mechanism involving also the intermediate Mn−Mn dimer [Mn(CO)3(IMP)]2. The complex [MnBr(CO)3(IPIMP)] (2-[((2-diisopropylphenyl)imino)methyl]pyridine), which carries a moderately electron donating, moderately bulky IP ligand, shows an intermediate behavior where both the five-coordinate anion and its dimeric precursor are jointly detected on the time scale of the spectroelectrochemical experiments. Under an atmosphere of CO2 the studied complexes, except for the DIPIMP derivative, rapidly coordinate CO2, forming stable bicarbonate intermediates, with no dimer being observed. Such behavior indicates that the CO2 binding is outcompeting another pathway: viz., the dimerization reaction between the five-coordinate anion and the neutral parent complex. The bicarbonate intermediate species undergo reduction at more negative potentials (ca. −2.2 V vs Fc/Fc+ ), recovering [Mn(CO)3(IP)]− and triggering the catalytic production of CO

The North Icelandic Jet and its relationship to the North Icelandic Irminger Current

Author Posting. © The Authors, 2017. This article is posted here by permission of Sears Foundation for Marine Research for personal use, not for redistribution. The definitive version was published in Journal of Marine Research 75 (2017): 605-639, doi:10.1357/002224017822109505.Shipboard hydrographic and velocity sections are used to quantify aspects of the North Icelandic Jet (NIJ), which transports dense overflow water to Denmark Strait, and the North Icelandic Irminger Current (NIIC), which imports Atlantic water to the Iceland Sea. The mean transports of the two currents are comparable, in line with previous notions that there is a local overturning cell in the Iceland Sea that transforms the Atlantic water to dense overflow water. As the NIJ and NIIC flow along the north side of Iceland, they appear to share a common front when the bottom topography steers them close together, but even when they are separate there is a poleward flow inshore of the NIJ. The interannual variability in salinity of the inflowing NIIC is in phase with that of the outflowing NIJ. It is suggested, however, that the NIIC signal does not dictate that of the NIJ. Instead, the combination of liquid and solid freshwater flux from the east Greenland boundary can account for the observed net freshening of the NIIC to the NIJ for the densest half of the overturning circulation in the northwest Iceland Sea. This implies that the remaining overturning must occur in a different geographic area, consistent with earlier model results. The year-to-year variability in salinity of the NIJ can be explained by applying annual anomalies of evaporation minus precipitation over the Iceland Sea to a one-dimensional mixing model. These anomalies vary in phase with the wind stress curl over the North Atlantic subpolar gyre, which previous studies have shown drives the interannual variation in salinity of the inflowing NIIC.Funding for the project was provided by the National Science Foundation under grants OCE-1558742 (RSP, MAS, DJT, CN), OCE-1433170 (MAS), and OCE-0959381 (DM); the Norwegian Research Council under grant agreement no. 231647 (KV); the Bergen Research Foundation (KV); the European Union Seventh Framework Programme (FP7 2007-2013) under grant agreement 308299 (NACLIM project, KV, HV, and SJ); and the Natural Sciences and Engineering Research Council of Canada (GWKM)

A Hybrid Global Minimization Scheme for Accurate Source Localization in Sensor Networks

We consider the localization problem of multiple wideband sources in a multi-path environment by coherently taking into account the attenuation characteristics and the time delays in the reception of the signal. Our proposed method leaves the space for unavailability of an accurate signal attenuation model in the environment by considering the model as an unknown function with reasonable prior assumptions about its functional space. Such approach is capable of enhancing the localization performance compared to only utilizing the signal attenuation information or the time delays. In this paper, the localization problem is modeled as a cost function in terms of the source locations, attenuation model parameters and the multi-path parameters. To globally perform the minimization, we propose a hybrid algorithm combining the differential evolution algorithm with the Levenberg-Marquardt algorithm. Besides the proposed combination of optimization schemes, supporting the technical details such as closed forms of cost function sensitivity matrices are provided. Finally, the validity of the proposed method is examined in several localization scenarios, taking into account the noise in the environment, the multi-path phenomenon and considering the sensors not being synchronized

Excess deaths from COVID-19 and other causes by region, neighbourhood deprivation level and place of death during the first 30 weeks of the pandemic in England and Wales: A retrospective registry study

Background: Excess deaths during the COVID-19 pandemic compared with those expected from historical trends have been unequally distributed, both geographically and socioeconomically. Not all excess deaths have been directly related to COVID-19 infection. We investigated geographical and socioeconomic patterns in excess deaths for major groups of underlying causes during the pandemic. Methods: Weekly mortality data from 27/12/2014 to 2/10/2020 for England and Wales were obtained from the Office of National Statistics. Negative binomial regressions were used to model death counts based on pre-pandemic trends for deaths caused directly by COVID-19 (and other respiratory causes) and those caused indirectly by it (cardiovascular disease or diabetes, cancers, and all other indirect causes) over the first 30 weeks of the pandemic (7/3/2020–2/10/2020). Findings: There were 62,321 (95% CI: 58,849 to 65,793) excess deaths in England and Wales in the first 30 weeks of the pandemic. Of these, 46,221 (95% CI: 45,439 to 47,003) were attributable to respiratory causes, including COVID-19, and 16,100 (95% CI: 13,410 to 18,790) to other causes. Rates of all-cause excess mortality ranged from 78 per 100,000 in the South West of England and in Wales to 130 per 100,000 in the West Midlands; and from 93 per 100,000 in the most affluent fifth of areas to 124 per 100,000 in the most deprived. The most deprived areas had the highest rates of death attributable to COVID-19 and other indirect deaths, but there was no socioeconomic gradient for excess deaths from cardiovascular disease/diabetes and cancer. Interpretation: During the first 30 weeks of the COVID-19 pandemic there was significant geographic and socioeconomic variation in excess deaths for respiratory causes, but not for cardiovascular disease, diabetes and cancer. Pandemic recovery plans, including vaccination programmes, should take account of individual characteristics including health, socioeconomic status and place of residence. Funding: None

Eddies in the Canada Basin, Arctic Ocean, observed from ice-tethered profilers

Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 133–145, doi:10.1175/2007JPO3782.1.Five ice-tethered profilers (ITPs), deployed between 2004 and 2006, have provided detailed potential temperature θ and salinity S profiles from 21 anticyclonic eddy encounters in the central Canada Basin of the Arctic Ocean. The 12–35-m-thick eddies have center depths between 42 and 69 m in the Arctic halocline, and are shallower and less dense than the majority of eddies observed previously in the central Canada Basin. They are characterized by anomalously cold θ and low stratification, and have horizontal scales on the order of, or less than, the Rossby radius of deformation (about 10 km). Maximum azimuthal speeds estimated from dynamic heights (assuming cyclogeostrophic balance) are between 9 and 26 cm s−1, an order of magnitude larger than typical ambient flow speeds in the central basin. Eddy θ–S and potential vorticity properties, as well as horizontal and vertical scales, are consistent with their formation by instability of a surface front at about 80°N that appears in historical CTD and expendable CTD (XCTD) measurements. This would suggest eddy lifetimes longer than 6 months. While the baroclinic instability of boundary currents cannot be ruled out as a generation mechanism, it is less likely since deeper eddies that would originate from the deeper-reaching boundary flows are not observed in the survey region.The engineering design work for the ITP was initiated by the Cecil H. and Ida M. Green Technology Innovation Program (an internal program at the Woods Hole Oceanographic Institution). Prototype development and construction were funded jointly by the U.S. National Science Foundation (NSF) Oceanographic Technology and Interdisciplinary Coordination Program and Office of Polar Programs (OPP) under Award OCE-0324233. Continued support has been provided by the OPP Arctic Sciences Section under Award ARC-0519899 and internal WHOI funding