bluuebunny/crossref_metadata_2025_split huggingface dataset:
Global teleconnections in the oceanic phosphorus cycle: Patterns, paths, and timescales
Authors: Holzer Mark , Primeau François W. 
Published: April 2013

AbstractNutrient transport and productivity teleconnections with the Southern Ocean are diagnosed in a data‐assimilated circulation model coupled to a jointly optimized simple phosphorus cycling model. The North Atlantic has the strongest extratropical teleconnections with the Southern Ocean: phosphate (PO4) last utilized in the Southern Ocean sustains 29 ± 6% of the subpolar and 14 ± 6% of the subtropical, new production in the North Atlantic. A PO4 path‐density diagnostic shows that these teleconnections are mediated by thermocline paths and reveals that most paths to anywhere north of 40°S lie in the deep Pacific. Forcing nearly complete Southern‐Ocean nutrient utilization increases the overall number of paths to anywhere north of 40°S, but reduces the number of paths from the Pacific to the North Atlantic by trapping nutrients in return paths to the Southern Ocean. At the same time, the mean export‐to‐uptake transit times to anywhere north of 40°S increase, while the mean transit times to the North Atlantic decrease. Correspondingly, the amount of North‐Atlantic production sustained by Southern‐Ocean export increases in spite of decreased total production in response to Southern‐Ocean nutrient trapping. The distributions of export‐to‐uptake, export‐to‐surface, and surface‐to‐surface transit times are computed and summarized in terms of their mean transit times and their mean interior residence times. The combined particle and advective–diffusive transport of nutrients is characterized by broad, skewed transit‐time distributions, which result in mean residence times much longer than the mean transit times, in turn much longer than the most probable transit times.
Small‐scale variability of the cross‐shelf flow over the outer shelf of the Ross Sea
Authors: Kohut Josh , Hunter Elias , Huber Bruce 
Published: April 2013

AbstractThe importance of cross‐shelf transport across the Ross Sea on local and remote processes has been well documented. In the Ross Sea, mid‐water intrusions of Circumpolar Deep Water (CDW) are modified by shelf water near the shelf break to form Modified Circumpolar Deep Water (MCDW). In 2010–2011, we deployed multi‐platform technologies focused on this MCDW intrusion in the vicinity of Mawson and Pennell Banks to better understand its role in ecosystem processes across the shelf. The high‐resolution time and space sampling provided by an underwater glider, a short‐term mooring, and a ship‐based survey highlight the scales over which these critical cross‐shelf transport processes occur. MCDW cores were observed as small‐scale well‐defined features over the western slopes of Pennell and Mawson Banks. The mean transport along Pennell Bank was estimated to be about 0.24 Sv but was highly variable in time (hours to days). The observations suggest that the core of MCDW is transported by a predominately barotropic flow that follows topography around the banks toward the south until the slope of the bank flattens and the warmer water moves up and over the bank. This pathway is shown to link the source MCDW with an area of high productivity over the shallows of Pennell Bank.
On the dynamics of the South China Sea deep circulation
Authors: Lan Jian , Zhang Ningning , Wang Yu 
Published: April 2013

AbstractIn the South China Sea (SCS), the deep water is confined to a bowel‐type trench, and the maximum depth is approximately 4700 m. The Luzon Strait is the only deep connection between the SCS and the Pacific Ocean, with the deepest sill at about 2400 m in the Bashi Channel. Using the Hybrid Coordinate Ocean Model, this study gives a good description of the SCS deep circulation. The most obvious features are basin‐scale cyclonic gyre and western intensification. The gyre is elliptical shaped, and its major axis is northeast‐southwest. A numerical experiment is designed to investigate what could be possibly responsible for the SCS deep circulation. The results reveal that the deepwater overflow through the Luzon Strait controls over the basin‐scale circulation structure in the deep SCS basin. The driving mechanism is elucidated based on the potential vorticity (PV) integral constraint, which means the PV inflow across the boundary is balanced by the net PV dissipation along the boundary.
A new observationally motivated Richardson number based mixing parametrization for oceanic mesoscale flow
Authors: Forryan Alexander , Martin Adrian P. , Srokosz Meric A. , Popova Ekaterina E. , Painter Stuart C. , Renner Angelika H. H. 
Published: April 2013

AbstractOcean models require subgrid‐scale parametrizations of vertical mixing expressed in terms of a quantity that is easily diagnosable from model output, such as the Richardson number. To date parametrizing mixing for low (<1) Richardson number flows, such as the Equatorial Undercurrent, has received the most attention. Here a new Richardson number parametrization is proposed that provides estimates of vertical turbulent diffusivity in the high Richardson number stratified shear flow that is associated with mesoscale ocean features such as eddies and fronts. This parametrization is based on direct observations of vertical turbulent diffusivity from three separate ocean regions in the North Atlantic and Southern Ocean and is found to be robust for values of the Richardson number greater than 1 at depths below the ocean surface boundary layer. The new parametrization gives substantially improved agreement with the observed mixing in the presence of mesoscale ocean features compared to existing Richardson number parametrizations.
Effects of transient bottom water currents and oxygen concentrations on benthic exchange rates as assessed by eddy correlation measurements
Authors: Holtappels Moritz , Glud Ronnie N. , Donis Daphne , Liu Bo , Hume Andrew , Wenzhöfer Frank , Kuypers Marcel M. M. 
Published: April 2013

AbstractEddy correlation (EC) measurements in the benthic boundary layer (BBL) allow estimating benthic O2 uptake from a point distant to the sediment surface. This noninvasive approach has clear advantages as it does not disturb natural hydrodynamic conditions, integrates the flux over a large foot‐print area and allows many repetitive flux measurements. A drawback is, however, that the measured flux in the bottom water is not necessarily equal to the flux across the sediment‐water interface. A fundamental assumption of the EC technique is that mean current velocities and mean O2 concentrations in the bottom water are in steady state, which is seldom the case in highly dynamic environments like coastal waters. Therefore, it is of great importance to estimate the error introduced by nonsteady state conditions. We investigated two cases of transient conditions. First, the case of transient O2 concentrations was examined using the theory of shear flow dispersion. A theoretical relationship between the change of O2 concentrations and the induced vertical O2 flux is introduced and applied to field measurements showing that changes of 5–10 μM O2 h−1 result in transient EC‐fluxes of 6–12 mmol O2 m−2 d−1, which is comparable to the O2 uptake of shelf sediments. Second, the case of transient velocities was examined with a 2D k‐ε turbulence model demonstrating that the vertical flux can be biased by 30–100% for several hours during changing current velocities from 2 to 10 cm s−1. Results are compared to field measurements and possible ways to analyze and correct EC‐flux estimates are discussed.
Gap‐leaping Kuroshio and blocking westward‐propagating Rossby wave and eddy in the Luzon Strait
Authors: Lu Jiuyou , Liu Qinyu 
Published: April 2013

AbstractBased on analysis of both observational data and data‐assimilation model product, it is shown that there exists a gap‐leaping path of the Kuroshio in the Luzon Strait. Numerical results of two sets of Hybrid Coordinate Ocean Model twin experiments indicate that bottom topography and islands in Luzon Strait exert control of Kuroshio's gap‐leaping behavior, especially existence of sharp northeast cape of Philippine Island is one of the most important factors for the gap‐leaping Kuroshio path in model simulation. Corresponding to the gap‐leaping Kuroshio, there is steep westward shoaling of thermocline in Luzon Strait. The enhanced upper‐layer stratification in South China Sea due to westward shoaling thermocline results in strong zonal potential vorticity (PV) gradient (one order higher than ß‐induced planetary PV gradient), and PV isolines are always parallel to the gap‐leaping path of the Kuroshio. This PV front acts as a dynamic barrier in the Luzon Strait, blocking the westward propagating Rossby waves and eddies from Pacific. This blocking effect is verified through sea‐surface height anomaly spectrum analysis, Radon Transform based Feature‐Tracking method, and eddy identification and tracking method. Numerical twin experiments demonstrate from another point of view that the gap‐leaping Kuroshio can efficiently block the westward propagating Rossby wave and eddy energy, while the fluctuating Kuroshio is less efficient for blocking.
Bathymetric effects on estuarine plume dynamics
Authors: Lee Jungwoo , Valle‐Levinson Arnoldo 
Published: April 2013

AbstractThe influence of bathymetry on an estuary plume at an estuary‐shelf transition is studied with a three‐dimensional ocean circulation model. To understand the response of the plume to bathymetry, several types of estuarine shapes and shelf geometries were adopted in this numerical study. The channel's shape and its width‐to‐depth aspect ratio affected the fate of the plume by determining flow characteristics inside the estuary. Moreover, the bathymetry of the shelf such as the shelf slope and the direction of a submarine channel defined the plume characteristics on the shelf. An estuarine channel with a triangular cross section generated relatively stronger exchange flows at midestuary than a rectangular cross section, which resulted in a larger surface plume over the shelf. The extension of the submarine channel onto the shelf favored increased plume water transport out to the shelf, a result of reduced frictional effects on the shelf. The orientation of the submarine channel changed the direction of the plume over the shelf, with no additional external forces. Two fronts developed at the edges of the submarine channel because of enhanced lateral shears in the flow. When the estuary was relatively wide compared to the internal Rossby radius (Kelvin number Ke ≥ 5), or when the relative strength of the freshwater discharge compared to the estuary width was weak (Rossby number Ro ≤ 0.05), the coastal plume did not expand up‐shelf. In fact, results indicated that freshwater up‐shelf transport in a coastal current, moving against Coriolis’ accelerations, was proportional to Ro.
Barotropic and baroclinic semidiurnal tidal currents in two contrasting coastal upwelling zones of Chile
Authors: Bravo L. , Ramos M. , Sobarzo M. , Pizarro O. , Valle‐Levinson A. 
Published: April 2013

ABSTRACTCurrent velocity observations from the continental shelves of Coquimbo (~30°S) and Concepcion (~36°30'S), central Chile, were analyzed to evaluate the role of water column stratification and shelf width on baroclinic semidiurnal tidal currents. Semidiurnal barotropic currents off both zones were typically < 5 cm/s, but depth‐dependent semidiurnal flows could exceed 10 cm s‐1 during stratified conditions. Both zones are recognized as pronounced upwelling centers, with maximum upwelling‐favorable winds in spring and summer, respectively. At the northern zone, stratification was mainly controlled by temperature differences between surface and bottom waters with maximum stratification during summer. The southern zone showed more stratification during winter because of freshwater input from local rivers. Consequently, greater variability in the baroclinic semidiurnal currents was observed during summer at the northern continental shelf and in winter at the south. In both regions, much of the semidiurnal variability was consistent with an internal wave's first baroclinic mode of wavelengths of ~10–13 km. Nevertheless, during the period of maximum energy fluxes off the north, the second baroclinic mode (wavelength ~7 km) was also important and matched periods of low upwelling index (relaxation of upwelling favorable winds). Typical energy fluxes during summer integrated in the water column, related to the semidiurnal internal tides were 0.12 W/m of the northern site and 0.1 W/m off the southern site. Possible sites of internal wave generation off the south were the Biobío submarine canyon and the slope/shelf break, while off the north, the generation site was the slope/shelf break.
Low‐frequency sea level variability in the southern Indian Ocean and its impacts on the oceanic meridional transports
Authors: Zhuang Wei , Feng Ming , Du Yan , Schiller Andreas , Wang Dongxiao 
Published: April 2013

AbstractSea levels in the southern Indian Ocean (SIO) display significant interannual to decadal variability. Off the northwest Australian coast, it has been demonstrated that sea level variability is mostly modulated by remote wind forcing from the tropical Pacific through equatorial and coastal waveguides. In this study, a linear reduced gravity model is used to investigate relative contributions of local wind forcing and remote forcing from the Pacific to the sea level variability of the SIO, with a focus on the western SIO. North of the South Equatorial Current bifurcation latitude (17ºS), model simulated sea levels are well correlated with altimeter observations at the dissipation timescale of about 3 years, suggesting that sea level variability on interannual‐to‐decadal timescales could well be explained by nondispersive baroclinic Rossby wave adjustment. The large sea level variability of the western SIO is primarily caused by westward‐propagating Rossby waves driven by wind stress curl in 70°E‐95°E, with a minor influence from the remote Pacific forcing. To the south, sea level variability at around 20ºS displays lower amplitude due to weaker wind variations at this latitude band, and the modeled sea level variability is weaker than observations. There is a close linkage between the cross‐basin sea level difference at 15ºS and the interior meridional ocean transport across this latitude on decadal timescales, as assessed with outputs from a data‐assimilation model. Thus, the meridional overturning cell of the SIO is influenced by both remote forcing from equatorial Pacific and local winds in the SIO.
Sensitivity and uncertainty analysis of model hypoxia estimates for the Texas‐Louisiana shelf
Authors: Mattern Jann Paul , Fennel, Katja , Dowd Michael 
Published: April 2013

AbstractNumerical ocean models are becoming increasingly important tools for marine research and for management of marine resources. It is therefore crucial that uncertainty in model predictions and model sensitivity to errors in the model inputs be quantified. We performed a combined sensitivity and uncertainty analysis for a realistic physical‐biological model of the Texas‐Louisiana shelf in the northern Gulf of Mexico. The model simulates the major physical and biological processes involved in the formation of the hypoxic zone that develops on the shelf every summer. With the help of a statistical emulator technique, we introduced uncertainty in selected model inputs and assessed the effects of these uncertainties on the predicted development and spatial distribution of bottom hypoxia. The uncertain inputs we examined belong to two categories: (i) biological inputs including river nutrient concentration, phytoplankton growth rate and initial and boundary conditions of biological variables, and (ii) physical inputs including freshwater river runoff, wind forcing, and mixing coefficients. We show that uncertainty in different inputs has distinct effects on model output which vary in magnitude, time, and space. Uncertainty in physical inputs was found to have a strong impact on estimates of hypoxia, e.g., hypoxic area estimates vary by more than 40%, due to a 20% variation in the freshwater river runoff.
Mesoscale eddies in the southern Gulf of California during summer: Characteristics and interaction with the wind stress
Authors: Lavín M. F. , Castro Rubén , Beier Emilio , Godínez Victor M. 
Published: April 2013

AbstractThe hydrodynamic characteristics of mesoscale eddies of the southern Gulf of California are described from observations made in August 2004. Vertical profiles to ~1000 m were made with a conductivity‐temperature‐depth (CTD) probe with dissolved oxygen and fluorescence sensors, and a lowered acoustic Doppler profiler. The four sampled eddies were aligned along the Gulf axis and had alternating sense of rotation. The Okubo‐Weiss parameter was used to calculate the eddy core radii, and it also revealed that the current field of almost all the sampled area was eddy dominated. The mean radii of the eddy cores varied between 32 and 36 km. Maximum surface velocities were 0.4–0.5 m/s. The anticyclonic eddies were 500–700 m deep, while the cyclones were 450–500 m deep. The depression of the isolines associated with the anticyclonic eddies was ~100 m at depths between 200 and 400 m; however, the thermocline/pycnocline, which spanned from ~20 to 75 m, was domed by ~10 m. The cyclonic eddies lifted the isolines by ~70 m at depths above 500 m, but the isolines were flat above ~60 m. This suggests that different dynamics operate in the layer above the strong and shallow pycnocline. In particular, the wind stress curl can affect circulation and pycnocline topography and, therefore, the patterns that appear in chlorophyll satellite images. In our case, the eddies were detectable in those images because of the chlorophyll‐enhanced streamers along their edges and, for anticyclones, probably because the chlorophyll maximum found at 40–50 m depth was domed following the pycnocline.
Estimation of phytoplankton size fractions based on spectral features of remote sensing ocean color data
Authors: Li Zuchuan , Li Lin , Song Kaishan , Cassar Nicolas 
Published: April 2013

AbstractThrough its influence on the structure of pelagic ecosystems, phytoplankton size distribution (pico‐, nano‐, and micro‐plankton) is believed to play a key role in “the biological pump.” In this paper, an algorithm is proposed to estimate phytoplankton size fractions (PSF) for micro‐, nano‐, and pico‐plankton (fm,fn, andfp, respectively) from the spectral features of remote‐sensing data. From remote‐sensing reflectance spectrum (Rrs(λ)), the algorithm constructs four types of spectral features: a normalizedRrs(λ), band ratios, continuum‐removed spectra, and spectral curvatures. Using support vector machine recursive feature elimination, the algorithm ranks the constructed spectral features andRrs(λ) according to their sensitivities to PSF which is then regressed against the sensitive spectral features through support vector regression. The algorithm is validated with (1) simulatedRrs(λ) and PSF, and (2)Rrs(λ) obtained by Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) and PSF determined from High‐Performance Liquid Chromatography (HPLC) pigments. The validation results show the overall effectiveness of the algorithm in estimating PSF, withR2of (1) 0.938 (fm) for the simulated SeaWiFS data set; and (2) 0.617 (fm), 0.475 (fn), and 0.587 (fp) for the SeaWiFS satellite data set. The validation results also indicate that continuum‐removed spectra and spectral curvatures are the dominant spectral features sensitive to PSF with their wavelengths mainly centered on the pigment‐absorption domain. Global spatial distributions offm,fn, andfpwere mapped with monthly SeaWiFS images. Overall, their biogeographical distributions are consistent with our current understanding that pico‐plankton account for a large proportion of total phytoplankton biomass in oligotrophic regions, nano‐plankton in transitional areas, and micro‐plankton in high‐productivity regions.
Formation of salinity maximum water and its contribution to the overturning circulation in the North Atlantic as revealed by a global general circulation model
Authors: Qu Tangdong , Gao Shan , Fukumori Ichiro 
Published: April 2013

AbstractThe formation of salinity maximum water in the North Atlantic is investigated using a simulated passive tracer and its adjoint. The results reveal that most salinity maximum water in the North Atlantic comes from the northwestern part of the subtropical gyre, and direct contribution from the evaporation‐precipitation maximum region via the surface Ekman current is minor. Water originating from the evaporation‐precipitation maximum region has to recirculate in the subtropical gyre before entering the sea surface salinity maximum region from the northwest. Once subducted, some portion (~10%) of the salinity maximum water enters the equatorial region in the shallow subtropical cell, but most (~70%) of it appears to turn northward to join the North Atlantic Deep Water. The latter pathway involves a three‐dimensional circulation. When the warm, fresh surface water flows northward along the western boundary, it turns eastward in the northern subtropical gyre. As a result of the large excess of evaporation over precipitation, this water gradually gains its salinity on the route, until it reaches the sea surface salinity maximum region in the central subtropical gyre. From there, the salinity maximum water is subducted and flows back to the western boundary in the depth range of the thermocline. With its high‐salinity nature, a major portion of this water penetrates into the subpolar region and directly contributes to the deep thermohaline circulation.
Seismic reflection imaging of shallow oceanographic structures
Authors: Piété Helen , Marié Louis , Marsset Bruno , Thomas Yannick , Gutscher Marc‐André 
Published: April 2013

AbstractMultichannel seismic (MCS) reflection profiling can provide high lateral resolution images of deep ocean thermohaline fine structure. However, the shallowest layers of the water column (z < 150 m) have remained unexplored by this technique until recently. In order to explore the feasibility of shallow seismic oceanography (SO), we reprocessed and analyzed four multichannel seismic reflection sections featuring reflectors at depths between 10 and 150 m. The influence of the acquisition parameters was quantified. Seismic data processing dedicated to SO was also investigated. Conventional seismic acquisition systems were found to be ill‐suited to the imaging of shallow oceanographic structures, because of a high antenna filter effect induced by large offsets and seismic trace lengths, and sources that typically cannot provide both a high level of emission and fine vertical resolution. We considered a test case, the imagery of the seasonal thermocline on the western Brittany continental shelf. New oceanographic data acquired in this area allowed simulation of the seismic acquisition. Sea trials of a specifically designed system were performed during the ASPEX survey, conducted in early summer 2012. The seismic device featured: (i) four seismic streamers, each consisting of six traces of 1.80 m; (ii) a 1000 J SIG sparker source, providing a 400 Hz signal with a level of emission of 205 dB re 1 μPa @ 1 m. This survey captured the 15 m thick, 30 m deep seasonal thermocline in unprecedented detail, showing images of vertical displacements most probably induced by internal waves.