pinecone/core-2020-05-10-deduplication huggingface dataset:
Acoustic scattering from a suspension of flocculated sediments

A series of controlled laboratory experiments have been conducted to investigate the backscatter of high frequency sound (3-5 MHz) from suspensions of fine sediment in its unflocculated (primary) state and at various levels of flocculation. The size and fall-velocity distribution of the flocs was determined using an optical system and a settling tube, thus allowing floc density to be determined. The measurements have conclusively demonstrated that the acoustic properties of the flocculated particles are not solely controlled by the primary particles; some aspect of the floc structure is influencing the scattering characteristics. The overall trend is for the form function (Ks) to increase as the degree of flocculation increase. This trend was also observed in the total scattering cross section (inline image) but this result is dependent on the assumption that viscous absorption for flocculated particles is negligible. The measured scattering properties are compared to the predicted values from two theoretical models, the elastic (ES) and fluid sphere (FS) models. While the results show that, in their current form, neither model is capable of adequately representing the scattering characteristics of a suspension of flocculated particles, the two models did provide upper (ES) and lower (FS) bounds to the measurements. In terms of the operational use of acoustics to measure the concentration of flocculated sediments, empirical relationships could be fitted to the observations but, until a better theoretical understanding of how sound interacts with flocculated particles is achieved, the fitting of such empirical relations may be somewhat premature
Reduction of Near-Inertial energy through the dependence of wind stress on the Ocean-Surface velocity

A realistic primitive-equation model of the Southern Ocean at eddying spatial resolution is used to examine the effect of ocean-surface-velocity dependence of the wind stress on the strength of near-inertial oscillations. Accounting for the ocean-surface-velocity dependence of the wind stress leads to a large reduction of wind-induced near-inertial energy of approximately 40 percent and of wind power input into the near-inertial frequency band of approximately 20 percent. A large part of this reduction can be explained by the leading-order modification to the wind stress if the ocean-surface velocity is included. The strength of the reduction is shown to be modulated by the inverse of the ocean-surface-mixed-layer depth. We conclude that the effect of surface-velocity dependence of the wind stress should be taken into account when estimating the wind-power input into the near-inertial frequency band and when estimating near-inertial energy levels in the ocean due to wind forcing
Estimation of relative phycoerythrin concentrations from hyperspectral underwater radiance measurements - a statistical approach.

Phycobiliproteins are a family of water-soluble pigment proteins that play an important role as accessory or antenna pigments and absorb in the green part of the light spectrum poorly used by chlorophyll a. The phycoerythrins (PEs) are one of four types of phycobiliproteins that are generally distinguished based on their absorption properties. As PEs are water soluble, they are generally not captured with conventional pigment analysis. Here we present a statistical model based on in situ measurements of three transatlantic cruises which allows us to derive relative PE concentration from standardized hyperspectral underwater radiance measurements (Lu). The model relies on Empirical Orthogonal Function (EOF) analysis of Lu spectra and, subsequently, a Generalized Linear Model with measured PE concentrations as the response variable and EOF loadings as predictor variables. The method is used to predict relative PE concentrations throughout the water column and to calculate integrated PE estimates based on those profiles
Lateral diffusivity from tracer release experiments in the tropical North Atlantic thermocline

Lateral diffusivity is computed from a tracer release experiment in the northeastern tropical Atlantic thermocline. The uncertainties of the estimates are inferred from a synthetic particle release using a high-resolution ocean circulation model. The main method employed to compute zonal and meridional components of lateral diffusivity is the growth of the second moment of a cloud of tracer. The application of an areal comparison method for estimating tracer-based diffusivity in the field experiments is also discussed. The best estimate of meridional eddy diffusivity in the Guinea Upwelling region at about 300 m depth is estimated to be inline image m2 s−1. The zonal component of lateral diffusivity is estimated to be inline image m2 s−1, while areal comparison method yields areal equivalent zonal diffusivity component of inline image m2 s−1. In comparison to Ky, Kx is about twice larger, resulting from the tracer patch stretching by zonal jets. Employed conceptual jet model indicates that zonal jet velocities of about inline image m s−1 are required to explain the enhancement of the zonal eddy diffusivity component. Finally, different sampling strategies are tested on synthetic tracer release experiments. They indicate that the best sampling strategy is a sparse regular sampling grid covering most of the tracer patch
Oceanographic observations at the shelf break of the Amundsen Sea, Antarctica

The glaciers draining into the Amundsen Sea Embayment are rapidly losing mass, making a significant contribution to current sea level rise. Studies of Pine Island Glacier (PIG) in this region indicate that the mass loss is associated with rapid melting of its floating ice shelf driven by warm Circumpolar Deep Water (CDW) that is able to penetrate all the way to its grounding line, and that recent intensification of the mass loss is associated with higher melt rates and stronger subice-shelf circulation. CDW is sourced from within the Antarctic Circumpolar Current (ACC) situated well north of the glacial ice fronts. To be able to access the Amundsen Sea glaciers, CDW must first cross the continental shelf break where the deep ocean meets the shallower waters of the continental shelf. Here, we present data that shows how CDW moves along the continental slope and across the shelf break into the Amundsen Sea. On-shelf flow of CDW is enhanced where a subsea trough bisects the shelf edge. A previously unreported undercurrent is observed flowing eastward along the shelf edge and when this current encounters the trough mouth it circulates southward into the trough and toward the glaciers. Upwelling associated with this trough circulation appears to allow Lower CDW onto the shelf that would otherwise be blocked by the topography. These observations concur with the results of a theoretical modeling study of circulation in a similar topographic setting and also with the results of a regional ocean/ice modeling study of the Amundsen Sea specifically
Sea level rise and tidal power plants in the Gulf of Maine

The response of the Bay of Fundy and Gulf of Maine to large-scale tidal power plants and future sea-level rise is investigated using an established numerical tidal model. Free stream tidal turbines were simulated within the Bay of Fundy by implementing an additional bed friction term, Kt. The present-day maximum tidal power output was determined to be 7.1 GW, and required Ktâ��=â��0.03. Extraction at this level would lead to large changes in the tidal amplitudes across the Gulf of Maine. With future SLR implemented, the energy available for extraction increases with 0.5â��1 GW per m SLR. SLR simulations without tidal power extraction revealed that the response of the semidiurnal tides to SLR is highly dependent on how changes in sea level are implemented in the model. When extensive flood defenses are assumed at the present-day coast line, the response to SLR is far larger than when land is allowed to (permanently) flood. For example, within the Bay of Fundy itself, the M2 amplitude increases with nearly 0.12 m per m SLR without flooding, but it changes with only 0.03 m per m SLR with flooding. We suggest that this is due to the flooding of land cells changing the resonant properties of the basin
The impact of rapid coastline changes and sea level rise on the tides in the Bohai Sea, China

[1] The tidal regime in the Bohai Sea, China, is investigated using observations and an established numerical tidal model. The area has recently experienced rapid coastline changes due to natural developments of the Yellow River delta and large-scale anthropogenic land reclamation. These morphological changes are not reflected in most global bathymetric databases and are thus rarely incorporated into investigations of the Bohai Sea. It is shown that there have indeed been significant changes in the tidal regime in the Bohai Sea over the last 35 years, with M2 amplitudes changing up to 20 cm in some parts. The model captures some of these changes when the appropriate bathymetries are used. Furthermore, the simulations show that the tides in the Bohai Sea have become more sensitive to future sea level rise and the way in which it is implemented in the model (i.e., whether or not flood defenses are included). These sensitivity changes are due to the recent coastal developments
Superelevation and overspill control secondary flow dynamics in submarine channels

In subaerial and submarine meander bends, fluid flow travels downstream in a helical spiral, the structure of which is determined by centrifugal, hydrostatic, baroclinic, and Coriolis forces that together balance frictional stresses generated by the flow. The sense of rotation of this helical flow, and in particular, whether the near bed flow is directed toward the inner bank, e.g., “river-normal,” or outer bank, e.g., “river-reversed,” is crucial to the morphodynamic evolution of the channel. However, in recent years, there has been a debate over the river-normal or river-reversed nature of submarine flows. Herein, we develop a novel three-dimensional closure of secondary flow dynamics, incorporating downstream convective material transport, to cast new light on this debate. Specifically, we show that the presence of net radial material transport, arising from flow superelevation and overspill, exerts a key control on the near bed orientation of secondary flow in submarine meanders. Our analysis implies that river-reversed flows are likely to be much more prevalent throughout submarine-canyon fan systems than prior studies have indicated
Getz Ice Shelf melting response to changes in ocean forcing

The large and complex Getz Ice Shelf extends along nearly half of the West Antarctic coastline in the Amundsen Sea, and is exposed to a more variable ocean environment than most other Pacific sector ice shelves. Ocean temperature, salinity and dissolved oxygen profiles acquired near its sub-ice cavity openings are used here to estimate seawater transports and meltwater fractions. More complete coverage during 2000 and 2007 brackets most of the variability observed from 1994 to 2011, and yearlong records near one ice front support the use of summer profiles to determine annual basal melt rates. We find area average rates of 1.1 and 4.1 m/yr, higher in 2007 when a larger volume of warmer deep water occupied the adjacent continental shelf, and the ocean circulation was stronger. Results are consistent with changes in thermocline depths relative to ice shelf draft and mass transports onto the adjacent continental shelf. We also calculate steady state and actual melting of 2.5 and 4.6 m/yr in 2007-2008 from satellite measurements of ice flux, modeled accumulation, and thinning from 2003-2008. This implies a positive mass balance in 2000, but negative in 2007, when the Getz was producing more meltwater than any of the larger, slower-melting or smaller, faster-melting ice shelves
Generation of baroclinic tides over an isolated underwater bank

The interaction of stratified tidal flow with an isolated bank (Jones Bank in the Celtic Sea) was investigated numerically and using observational data collected during the 25th research cruise of the R/V James Cook in July 2008. Two scenarios of observed wave generation, one with pure tidal forcing and another with an extra background current, were reproduced numerically and compared against the observational data. It was found that the tidal currents alone produced subcritical conditions for the first-mode internal wave generation and supercritical flow for the second-mode waves. Under these conditions, the first-mode waves with amplitudes up to 10 m freely radiated from the bank, gradually transforming into attenuating dissipative baroclinic bores. Due to supercritical conditions, the second-mode waves were arrested at the lee side of the bank for 3 h where they grew in amplitude (up to 35 m) and after their release propagated as a series of second-mode internal solitary waves. The additional background current that was measured near the bank in the middle of June 2008 radically changed the conditions of wave generation. A strong southeastern current arrested the first-mode perturbations at the NE flank of the bank for 2 h, where they grew in amplitude to almost 40 m and disintegrated into packets of first-mode internal solitary waves after their release. For the second-mode perturbations, the flow was substantially supercritical for more than one fourth of a tidal period so that these waves were just washed away from the generation site without any visible amplification. © 2013. American Geophysical Union. All Rights Reserved
Near-coastal circulation in the Northern Humboldt Current System from shipboard ADCP data

International audienceThe near-coastal circulation of the Northern Humboldt Current System is described analyzing ∼8700 velocity profiles acquired by a shipboard acoustic Doppler current profiler (SADCP) during 21 surveys realized between 2008 and 2012 along the Peruvian coast. This data set permits observation of (i) part of the Peru Coastal Current and the Peru Oceanic Current that flow equatorward in near-surface layers close to the coast and farther than ∼150 km from the coast, respectively; (ii) the Peru-Chile Undercurrent (PCUC) flowing poleward in subsurface layers along the outer continental shelf and inner slope; (iii) the near-surfacing Equatorial Undercurrent renamed as Ecuador-Peru Coastal Current that feeds the PCUC; and (iv) a deep equatorward current, referred to as the Chile-Peru Deep Coastal Current, flowing below the PCUC. A focus in the PCUC core layer shows that this current exhibits typical velocities of 5-10 cm s<sup>−1</sup>. The PCUC deepens with an increasing thickness poleward, consistent with the alongshore conservation of potential vorticity. The PCUC mass transport increases from ∼1.8 Sv at 5°S to a maximum value of ∼5.2 Sv at 15°S, partly explained by the Sverdrup balance. The PCUC experiences relatively weak seasonal variability and the confluence of eddy-like structures and coastal currents strongly complicates the circulation. The PCUC intensity is also affected by the southward propagation of coastally trapped waves, as revealed by a strong PCUC intensification in March 2010 coincident with the passage of a downwelling coastal wave associated with a weak El Niño event
Moored surface buoy observations of the diurnal warm layer

An extensive data set is used to examine the dynamics of diurnal warming in the upper ocean. The data set comprises more than 4700 days of measurements at five sites in the tropics and subtropics, obtained from surface moorings equipped to make comprehensive meteorological, incoming solar and infrared radiation, and high-resolution subsurface temperature (and, in some cases, velocity) measurements. The observations, which include surface warmings of up to 3.4°C, are compared with a selection of existing models of the diurnal warm layer (DWL). A simple one-layer physical model is shown to give a reasonable estimate of both the magnitude of diurnal surface warming (model-observation correlation 0.88) and the structure and temporal evolution of the DWL. Novel observations of velocity shear obtained during 346 days at one site, incorporating high-resolution (1 m) upper ocean (5–15 m) acoustic Doppler current profile measurements, are also shown to be in reasonable agreement with estimates from the physical model (daily maximum shear model-observation correlation 0.77). Physics-based improvements to the one-layer model (incorporation of rotation and freshwater terms) are discussed, though they do not provide significant improvements against the observations reported here. The simplicity and limitations of the physical model are used to discuss DWL dynamics. The physical model is shown to give better model performance under the range of forcing conditions experienced across the five sites than the more empirical models
Unusual subpolar North Atlantic phytoplankton bloom in 2010: Volcanic fertilisation or North Atlantic Oscillation?

In summer and autumn 2010, a highly anomalous phytoplankton bloom, with chlorophyll concentration more than double that of previous years, was observed in the Irminger Basin, southwest of Iceland. Two unusual events occurred during 2010 which had the potential to promote the unusual bloom. First, in spring 2010, the Eyjafjallajökull volcano in Iceland erupted, depositing large quantities of tephra into the subpolar North Atlantic. Second, during the winter of 2009/2010 the North Atlantic Oscillation (NAO) became extremely negative, developing into the second strongest negative NAO on record. Hydrographic conditions were highly anomalous in the region, with an influx of freshwater spreading through the basin, and unusual nutrient and mixed layer depth conditions. Here we use a combination of satellite, modeled and in situ data to investigate whether the input of iron from the volcanic eruption or change in hydrographic conditions due to the extreme negative NAO were responsible for the anomalous phytoplankton bloom. We conclude that changes in physical forcing driven by the NAO, and not the volcanic eruption, stimulated the unusual bloom
Tide-surge adjoint modeling: A new technique to understand forecast uncertainty

For a simple dynamical system, such as a pendulum, it is easy to deduce where and when applied forcing might produce a particular response. However, for a complex nonlinear dynamical system such as the ocean or atmosphere, this is not as obvious. Knowing when or where the system is most sensitive, to observational uncertainty or otherwise, is key to understanding the physical processes, improving and providing reliable forecasts. We describe the application of adjoint modeling to determine the sensitivity of sea level at a UK coastal location, Sheerness, to perturbations in wind stress preceding an extreme North Sea storm surge event on 9 November 2007. Sea level at Sheerness is one of the most important factors used to decide whether to close the Thames Flood Barrier, which protects London. Adjoint modeling has been used by meteorologists since the 1990s, but is a relatively new technique for ocean modeling. It may be used to determine system sensitivity beyond the scope of ensemble modeling and in a computationally efficient way. Using estimates of wind stress error from Met Office forecasts, we find that for this event total sea level at Sheerness is most sensitive in the 3 h preceding the time of its unperturbed maximum level and over a radius of approximately 300 km. We also find that the pattern of sensitivity follows a simple sequence when considered in the reverse-time direction
Sea level changes at Tenerife Island (NE Tropical Atlantic) since 1927

Hourly sea level observations measured by five tide gauges at Santa Cruz harbor (Tenerife Island), in the Northeastern Tropical Atlantic, have been merged to build a consistent and almost continuous sea level record starting in 1927. Datum continuity was ensured using high precision leveling information. The time series underwent a detailed quality control in order to remove outliers, time drifts, and datum shifts. The resulting sea level record was then used to describe the low frequency (interannual to decadal) sea level variability at Tenerife. It was found that at interannual and longer time scales, the observed sea level changes are primarily driven by steric sea level variations. Such steric changes are originated by coastal trapped waves induced by longshore winds along the continental coast and propagate poleward. Observed sea level rise at Tenerife was 2.09 ± 0.04 mm/yr since 1927. According to the hydrographic observations in the area, only half of this trend was attributed to steric sea level changes for the top 500 m, at least since 1950
Seasonal circulation over the Catalan inner-shelf (northwest Mediterranean Sea)

This study characterizes the seasonal cycle of the Catalan inner-shelf circulation using observations and complementary numerical results. The relation between seasonal circulation and forcing mechanisms is explored through the depth-averaged momentum balance, for the period between May 2010 and April 2011, when velocity observations were partially available. The monthly-mean along-shelf flow is mainly controlled by the along-shelf pressure gradient and by surface and bottom stresses. During summer, fall, and winter, the along-shelf momentum balance is dominated by the barotropic pressure gradient and local winds. During spring, both wind stress and pressure gradient act in the same direction and are compensated by bottom stress. In the cross-shelf direction the dominant forces are in geostrophic balance, consistent with dynamic altimetry data. Key Points A hydrodynamic model is implemented for the first time in Catalan inner-shelf. Frictional and pressure gradient are revealed as the main forcing mechanisms A clear seasonal pattern is found in the current velocity.Peer ReviewedPostprint (published version
Evaluating the balance between vertical diffusive nitrate supply and nitrogen fixation with reference to nitrate uptake in the eastern subtropical North Atlantic Ocean

The balance between N2 fixation and diffusive NO3− supply is a key determinant for assessing the importance of both processes for new production in subtropical waters. Here we report observations of integrated N2 fixation rates from the eastern subtropical North Atlantic Ocean with coincident estimates of diffusive NO3− supply. We find the average rate of N2 fixation is equivalent to 62% of the diffusive NO3− supply, though N2 fixation could exceed the diffusive flux at individual stations. Turbulent diffusivity measurements across the nitracline indicate a mean diffusivity of 0.077 cm2 s−1. If approximations for methodological underestimates in the dominant N2 fixation technique are considered, the magnitude of N2 fixation is shown to represent 100% of the NO3− flux on average, and can be almost threefold higher at individual stations. As the study site is characterized by low rates of N2 fixation compared to other sectors of the North Atlantic this confirms N2 fixation as a major source term across the subtropical North Atlantic. The seasonal context of our observations suggests environmental factors underlie the in situ variability in observed N2 fixation rates, and may well explain lower previous assessments of the importance of N2 fixation relative to diffusive NO3− supply in this region. The diffusive NO3− supply provides <20% of measurable NO3− uptake with the remainder supplied via other mechanisms, most notably nitrification. The mean integrated rate of N2 fixation equates to just 8% of the NO3− consumed on a daily basis by the phytoplankton community