bluuebunny/crossref_metadata_2025 huggingface dataset:
Ice-shelf – ocean interactions at Fimbul Ice Shelf, Antarctica from oxygen isotope ratio measurements
Authors: Price M. R. , Heywood K. J. , Nicholls K. W.
Published: April 2010

Abstract. Melt water from the floating ice shelves at the margins of the southeastern Weddell Sea makes a significant contribution to the fresh water budget of the region. In February 2005 a multi-institution team conducted an oceanographic campaign at Fimbul Ice Shelf on the Greenwich Meridian as part of the Autosub Under Ice programme. This included a mission of the autonomous submarine Autosub 25 km into the cavity beneath Fimbul Ice Shelf, and a number of ship-based hydrographic sections on the continental shelf and adjacent to the ice shelf front. The measurements reveal two significant sources of glacial melt water at Fimbul Ice Shelf: the main cavity under the ice shelf and an ice tongue that protrudes from the main ice front and out over the continental slope into deep water. Glacial melt water is concentrated in a 200 m thick Ice Shelf Water (ISW) layer below the base of the ice shelf at 150–200 m, with a maximum glacial melt concentration of up to 1.16%. Some glacial melt is found throughout the water column, and much of this is from sources other than Fimbul Ice Shelf. However, at least 0.2% of the water in the ISW layer cannot be accounted for by other processes and must have been contributed by the ice shelf. Just downstream of Fimbul Ice Shelf we observe locally created ISW mixing out across the continental slope. The ISW formed here is much less dense than that formed in the southwest Weddell Sea, and will ultimately contribute a freshening (and reduction in δ18O) to the upper 100–150 m of the water column in the southeast Weddell Sea.
Ecological niche of three teuthophageous odontocetes in the northwestern Mediterranean Sea
Authors: Praca E. , Gannier A.
Published: April 2010

Abstract. In the northwestern Mediterranean Sea, sperm whales, pilot whales and Risso's dolphins prey on cephalopods exclusively or preferentially. In order to evaluate their competition, we modelled their habitat suitability with the Ecological Niche Factor Analysis (ENFA) and compared their ecological niche using a discriminant analysis. We used a long term (1995–2005) small boat data set, with visual and acoustic (sperm whale) detections. Risso's dolphin had the shallowest and the more spatially restricted principal habitat, mainly located on the upper part of the continental slope (640 m mean depth). With a wider principal habitat, at 1750 m depth in average, the sperm whale used a deeper part of the slope as well as close offshore waters. Finally, the pilot whale has the most oceanic habitat (2500 m mean depth) mainly located in the central Ligurian Sea and Provençal basin. Therefore, potential competition for food between these species may be reduced by the differentiation of their ecological niches.
Depth dependence of westward-propagating North Atlantic features diagnosed from altimetry and a numerical 1/6° model
Authors: Lecointre A. , Penduff T. , Cipollini P. , Tailleux R. , Barnier B.
Published: April 2010

Abstract. A 1/6° numerical simulation is used to investigate the vertical structure of westward propagation between 1993 and 2000 in the North Atlantic ocean. The realism of the simulated westward propagating signals, interpreted principally as the signature of first-mode baroclinic Rossby waves (RW), is first assessed by comparing the simulated amplitude and zonal phase speeds of Sea Level Anomalies (SLA) against TOPEX/Poseidon-ERS satellite altimeter data. Then, the (unobserved) subsurface signature of RW phase speeds is investigated from model outputs by means of the Radon Transform which was specifically adapted to focus on first-mode baroclinic RW. The analysis is performed on observed and simulated SLA and along 9 simulated isopycnal displacements spanning the 0–3250 m depth range. Simulated RW phase speeds agree well with their observed counterparts at the surface, although with a slight slow bias. Below the surface, the simulated phase speeds exhibit a systematic deceleration with increasing depth, by a factor that appears to vary geographically. Thus, while the reduction factor is about 15–18% on average at 3250 m over the region considered, it appears to be much weaker (about 5–8%) in the eddy-active Azores Current, where westward propagating structures might be more coherent in the vertical. These results suggest that the often-made normal-mode assumption of many WKB-based extended theories that the phase speed is independent of depth might need to be revisited. They also suggest that the vertical structure of westward propagating signals could significantly depend on their degree of nonlinearity, with the degree of vertical coherence possibly increasing with the degree of nonlinearity.
Influence of Rossby waves on primary production from a coupled physical-biogeochemical model in the North Atlantic Ocean
Authors: Charria G. , Dadou I. , Cipollini P. , Drévillon M. , Garçon V.
Published: April 2010

Abstract. How do Rossby waves influence primary production in the North Atlantic Ocean? Rossby waves have a clear signature on surface chlorophyll concentrations which can be explained by a combination of vertical and horizontal mechanisms (reviewed in Killworth et al., 2004). In this study, we aim to investigate the role of the different physical processes to explain the surface chlorophyll signatures and the consequences on primary production using a 3-D coupled physical/biogeochemical model for the year 1998. The analysis at 20 given latitudes, mainly located in the subtropical gyre, where Rossby waves are strongly correlated with a surface chlorophyll signature, shows that vertical and horizontal processes are involved in the surface chlorophyll anomalies. Furthermore, the ecosystem response is, as expected, stronger when vertical input of dissolved inorganic nitrogen is observed. The surface chlorophyll anomalies, induced by these physical mechanisms, have an impact on primary production. We then estimate that Rossby waves induce, locally in space and time, increases (generally associated with the wave crest) and decreases (generally associated with the wave trough) in primary production (~±20% of the estimated primary production). This symmetrical situation suggests a net weak effect of Rossby waves on primary production.
The structure of the Persian Gulf outflow subjected to density variations
Authors: Bidokhti A. A. , Ezam M.
Published: April 2010

Abstract. Oceanographic data and a dynamic model are used to consider the structure of Persian Gulf outflow. This outflow influences the physical properties of Oman seawater which appear in the CTD profiles of the Oman Sea. The observations show that thickness of the outflow, which is banked against the Oman coasts due to the earth rotation, is about 200 m with tongues extending east and north that may be due to the internal waves. A simple dynamical model of the outflow based on potential vorticity conservation is used to find the horizontal extension of the outflow from the coast. Typical mass transport estimate by the outflow is about 0.4 Sv, which is larger than those reported by others. This may be due to the fact the model is inviscid but the outflow is influenced by the bottom friction. Variability of the outflow structure may reflect the changing ecosystem of the Persian Gulf. Any change of the outflow source, the Persian Gulf Water (PGW), say salinity increase due to excessive evaporation (climate factor) or desalination (anthropogenic factors) of the PGW may change the outflow structure and the product waters in the Oman Sea. Hence, one can test different scenarios of changing the outflow source, the Persian Gulf Water (PGW), say by salinity increase due to excessive evaporation or desalination (ecosystem factors) of the PGW to estimate changes in the outflow structure and the product waters in the Oman Sea. The results of the model show that these can increase the outflow width and mass transport substantially.
A new parameterisation of salinity advection to prevent stratification from running away in a simple estuarine model
Authors: Blaise S. , Deleersnijder E.
Published: April 2010

Abstract. A new parameterisation of horizontal salinity advection for a one-dimensional water-column estuarine model, inspired by the first-order finite-difference upwind scheme, is presented. This parameterisation prevents stratification from growing indefinitely, a numerical artefact usually referred to as "runaway stratification". It is seen that, using this upwind-like parameterisation, the salinity must remain comprised between upper and lower bounds set a priori and that any initial over- or under-shooting is progressively eliminated. Simulations of idealised and realistic estuarine regimes indicate that the new parameterisation lead to results that are devoid of the runaway stratification artefact, as opposed to previously used models.
Sequential assimilation of multi-mission dynamical topography into a global finite-element ocean model
Authors: Skachko S. , Danilov S. , Janjić T. , Schröter J. , Sidorenko D.
Published: April 2010

Abstract. This study focuses on an accurate estimation of ocean circulation via assimilation of satellite measurements of ocean dynamical topography into the global finite-element ocean model (FEOM). The dynamical topography data are derived from a complex analysis of multi-mission altimetry data combined with a referenced earth geoid. The assimilation is split into two parts. First, the mean dynamic topography is adjusted. To this end an adiabatic pressure correction method is used which reduces model divergence from the real evolution. Second, a sequential assimilation technique is applied to improve the representation of thermodynamical processes by assimilating the time varying dynamic topography. A method is used according to which the temperature and salinity are updated following the vertical structure of the first baroclinic mode. It is shown that the method leads to a partially successful assimilation approach reducing the rms difference between the model and data from 16 cm to 2 cm. This improvement of the mean state is accompanied by significant improvement of temporal variability in our analysis. However, it remains suboptimal, showing a tendency in the forecast phase of returning toward a free run without data assimilation. Both the mean difference and standard deviation of the difference between the forecast and observation data are reduced as the result of assimilation.
Development of thermodynamic potentials for fluid water, ice and seawater: a new standard for oceanography
Authors: Feistel R. , Wright D. G. , Miyagawa K. , Hruby J. , Jackett D. R. , McDougall T. J. , Wagner W.
Published: April 2010

Abstract. A new seawater standard has been developed for oceanographic and engineering applications that consists of three independent thermodynamic potential functions, derived from extended distinct sets of very accurate experimental data. The results have been formulated as Releases of the International Association for the Properties of Water and Steam, IAPWS (1996, 2006, 2008) and are to be adopted internationally by other organizations in subsequent years. In order to successfully perform computations such as phase equilibria from combinations of these potential functions, mutual compatibility and consistency of these independent mathematical functions must be ensured. In this article, a brief review of their separate development and ranges of validity is given. We analyse background details on the conditions specified at their reference states, the triple point and the standard ocean state, to ensure the mutual consistency of the different formulations, and we consider the necessity and possibility of numerically evaluating metastable states of liquid water. Computed from this formulation in quadruple precision (128 bit floating point numbers), tables of numerical reference values are provided as anchor points for the consistent incorporation of additional potential functions in the future, and as unambiguous benchmarks to be used in the determination of numerical uncertainty estimates of double-precision implementations on different platforms that may be customized for special purposes.
Role of cabbeling in water densification in the Greenland Basin
Authors: Kasajima Y. , Johannessen T.
Published: April 2010

Abstract. The contribution of cabbeling mixing to water mass modification in the Greenland Sea was explored from hydrographic observation across the Greenland Basin in summer 2006. Neutral surface was chosen as a reference frame, and the strength of cabbeling mixing was determined by the dianeutral velocity magnitude. Water types in the area were classified into North Atlantic Water (NAW), modified North Atlantic Water (mNAW), water from Barents Sea near Bear Island (BIW), Arctic Intermediate Water (AIW) and Deep Water (DW), and significant cabbeling-induced velocity (>1 m/day) appeared at the interfaces of these water types below the seasonal pycnocline. The mixing between BIW and NAW in the eastern periphery was the most vigorous, where mixing-induced velocity reached 7.5 m/day which accompanied NAW production of 123 m3/day through transformation of BIW. Cabbeling in the Arctic Frontal Zone was found of two types; mixing within NAW in the upper layer and mixing within mNAW in the lower layer with a maximum velocity of 3 m/day. Source waters in the central Greenland Basin were AIW and mNAW and produced a vertical velocity of 4 m/day. In the western part of the Greenland Basin, the areas of active cabbeling were widely separated and each mixing point appeared rather weak, with a maximum velocity of 2.5 m/day. The average density gain in the eastern periphery was 0.003 kg/m3 while it was 0.001 kg/m3 in the other areas, though the impact of cabbeling on the bulk buoyancy change was highest in the western Greenland Sea. The frontal areas occupied approximately 50% of the whole analysis area and the total density gain due to cabbeling mixing in the Greenland Basin as a whole was estimated as 6.7×10−4 kg/m3.
Characterization of ASCAT measurements based on buoy and QuikSCAT wind vector observations
Authors: Bentamy A.
Published: April 2010

Abstract. The new scatterometer Advanced SCATterometer (ASCAT) onboard MetOp-A satellite provides surface wind speed and direction over global ocean with a spatial resolution of 25 km square over two swaths of 550 km widths. The accuracy of ASCAT wind retrievals is determined through various comparisons with moored buoys. The comparisons indicate that the remotely sensed wind speeds and directions agree well with buoy data. The root-mean-squared differences of the wind speed and direction are less than 1.72 m/s and 18°, respectively. At global scale, ASCAT winds are compared with surface winds derived from QuikSCAT scatterometer. The results confirm the buoy analyses, especially for wind speed ranging between 3 m/s and 20 m/s. For higher wind conditions, ASCAT is biased low. The ASCAT underestimation with respect to QuikSCAT winds is wind speed dependent. The comparisons based on the collocated scatterometer data collected after 17 October 2007 indicate that there are significant improvements compared to previous periods.
An ensemble study of extreme North Sea storm surges in a changing climate
Authors: Sterl A. , van den Brink H. , de Vries H. , Haarsma R. , van Meijgaard E.
Published: April 2010

Abstract. The height of storm surges is extremely important for a low-lying country like the Netherlands. By law, part of the coastal defence system has to withstand a water level that on average occurs only once every 10 000 years. The question then arises whether and how climate change affects the heights of extreme storm surges. Published research points to only small changes. However, due to the limited amount of data available results are usually limited to relatively frequent extremes like the annual 99%-ile. We here report on results from a 17-member ensemble of North Sea water levels spaning the period 1950–2100. It was created by forcing a surge model of the North Sea with meteorological output from a state-of-the-art global climate model which has been driven by greenhouse gas emissions following the SRES A1b scenario. The large ensemble size enables us to calculate 10 000 year return water levels with a low statistical uncertainty. We find no statistically significant change in the 10 000 year return values of surge heights along the Dutch during the 21st century. Also a higher sea level resulting from global warming does not impact the height of the storm surges. As a side effect of our simulations we also obtain results on the interplay between surge and tide.
Technical Note: Animal-borne CTD-Satellite Relay Data Loggers for real-time oceanographic data collection
Authors: Boehme L. , Lovell P. , Biuw M. , Roquet F. , Nicholson J. , Thorpe S. E. , Meredith M. P. , Fedak M.
Published: April 2010

Abstract. The increasing need for continuous monitoring of the world oceans has stimulated the development of a range of autonomous sampling platforms. One novel addition to these approaches is a small, relatively inexpensive data-relaying device that can be deployed on marine mammals to provide vertical oceanographic profiles throughout the upper 2000 m of the water column. When an animal dives, the CTD-Satellite Relay Data Logger (CTD-SRDL) records vertical profiles of temperature, conductivity and pressure. Data are compressed once the animal returns to the surface where it is located by, and relays data to, the Argos satellite system. The technical challenges met in the design of the CTD-SRDL are the maximising of energy efficiency by minimising size, whilst simultaneously maintaining the reliability of an instrument that cannot be recovered and is required to survive its lifetime attached to a marine mammal. The CTD-SRDLs record temperature and salinity with an accuracy of better than 0.005°C and 0.02 respectively. However, due to the limited availability of reference data for post-processing, data are often associated with slightly higher errors. The potential to collect large numbers of profiles cost-effectively makes data collection using CTD-SRDL technology particularly beneficial in regions where traditional oceanographic measurements are scarce. Depending on the CTD-SRDL configuration, it is possible to sample and transmit hydrographic profiles on a daily basis, providing valuable and often unique information for a real-time ocean observing system.
Controllability of mixing errors in a coupled physical biogeochemical model of the North Atlantic: a nonlinear study using anamorphosis
Authors: Béal D. , Brasseur P. , Brankart J.-M. , Ourmières Y. , Verron J.
Published: April 2010

Abstract. In biogeochemical models coupled to ocean circulation models, vertical mixing is an important physical process which governs the nutrient supply and the plankton residence in the euphotic layer. However, mixing is often poorly represented in numerical simulations because of approximate parameterizations of sub-grid scale turbulence, wind forcing errors and other mis-represented processes such as restratification by mesoscale eddies. Getting a sufficient knowledge of the nature and structure of these error sources is necessary to implement appropriate data assimilation methods and to evaluate their controllability by a given observation system. In this paper, Monte Carlo simulations are conducted to study mixing errors induced by approximate wind forcings in a three-dimensional coupled physical-biogeochemical model of the North Atlantic with a 1/4° horizontal resolution. An ensemble forecast involving 200 members is performed during the 1998 spring bloom, by prescribing realistic wind perturbations to generate mixing errors. It is shown that the biogeochemical response can be rather complex because of nonlinearities and threshold effects in the coupled model. In particular, the response of the surface phytoplankton depends on the region of interest and is particularly sensitive to the local stratification. We examine the robustness of the statistical relationships computed between the various physical and biogeochemical variables, and we show that significant information on the ecosystem can be obtained from observations of chlorophyll concentration or sea surface temperature. In order to improve the analysis step of sequential assimilation schemes, we propose to perform a simple nonlinear change of variables that operates separately on each state variable, by mapping their ensemble percentiles on the Gaussian percentiles. It is shown that this method is able to substantially reduce the estimation error with respect to the linear estimates computed by the Kalman filter.
Observations of turbulence beneath sea ice in southern McMurdo Sound, Antarctica
Authors: Stevens C. L. , Robinson N. J. , Williams M. J. M. , Haskell T. G.
Published: April 2010

Abstract. The first turbulence profiler observations beneath land fast sea ice which is directly adjacent to an Antarctic ice shelf are described. The stratification in the 325 m deep water column consisted of a layer of supercooled water in the upper 40 m lying above a quasi-linearly stratified water column with a sharp step in density at mid-depth. Turbulent energy dissipation rates were on average 3×10−8 m2 s−3 with peak bin-averaged values reaching 4×10−7 m2 s−3. The local dissipation rate per unit area was estimated to be 10 mWm−2 on average with a peak of 50 mWm−2. These values are consistent with a moderate baroclinic response to the tides. The small-scale turbulent energetics lie on the boundary between isotropy and buoyancy-affected. This will likely influence the formation and aggregation of frazil ice crystals within the supercooled layer. An estimate of the vertical diffusivity of mass Kρ yields a coefficient of around 10−3 m2 s−1. Combining this estimate of Kρ with available observations of average and maximum currents suggests the layer of supercooled water can persist for a distance of ~20 km from the front of the McMurdo Ice Shelf.
Variability of scaling time series in the sea ice drift dynamics in the Arctic Ocean
Authors: Chmel A. , Smirnov V. N. , Sheikin I. B.
Published: April 2010

Abstract. A motion of an individual ice field in the Arctic Ocean was monitored at the Russian research station North Pole 35 established on the ice pack in 2008. The ice field velocity (V) was found to be correlated with wind velocity (v) in main features, such as the positions of maxima and minima of V and v. However, the fine structure of the V-variation cannot be explained by the wind forcing only. There were periods of time when the field drift was highly affected by either the tidal activity or the interactions of ice sheets between each other. These data were put in comparison with the "waiting times" statistics that is with the distributions of lengths of time intervals between subsequent important local accelerations of the ice field. These distributions were measured in several time windows differing in the average wind velocity and/or the mechanical state of the ice pack. The distribution functions N(>τ) (N is the number of successive events of accelerations separated by the time interval that exceeds τ) constructed in different time windows demonstrated fractal or multifractal nature in the consolidated ice pack but were truly random when the ice field drifted in the highly fragmented sea ice. The latter result evidences the existence of a relationship between the long-range mechanical interactions in the pack and long-term memory (time scaling behavior) of the sea ice motion.
Comparative analysis of the multi-sensor global ocean colour data record
Authors: Djavidnia S. , Mélin F. , Hoepffner N.
Published: April 2010

Abstract. The extending record of ocean colour derived information, an important asset for the study of marine ecosystems and biogeochemistry, presently relies on individual satellite missions launched by several space agencies with differences in sensor design, calibration strategies and algorithms. In this study we present an extensive comparative analysis of standard products obtained from operational global ocean colour sensors (SeaWiFS, MERIS, MODIS-Aqua, MODIS-Terra), on both global and regional scales. The analysis is based on monthly mean chlorophyll-a (Chl-a) surface concentration between 2002 and 2009. Based on global statistics, the Chl-a records appear relatively consistent. The root mean square (RMS) difference Δ between (log-transformed) Chl-a from SeaWiFS and MODIS Aqua amounts to 0.137, with a bias of 0.074 (SeaWiFS Chl-a higher). The difference between these two products and MERIS Chl-a is approximately 0.15. Restricting the analysis to 2007 only, Δ between MODIS Aqua and Terra is 0.142. This global convergence is significantly modulated regionally. Statistics for biogeographic provinces representing a partition of the global ocean, show Δ values varying between 0.08 and 0.3. High latitude regions, as well as coastal and shelf provinces are generally the areas with the largest differences. Moreover, RMS differences and biases are modulated in time, with a coefficient of variation of Δ varying between 10% and 40%, with clear seasonal patterns in some provinces. The comparison of the province-averaged time series obtained from the various satellite products also shows a level of agreement that is geographically variable. Overall, the Chl-a SeaWiFS and MODIS Aqua series appear to have similar levels of variance and display high correlation coefficients, an agreement likely favoured by the common elements shared by the two missions. These results are degraded if the MERIS series is compared to either SeaWiFS or MODIS Aqua. An important outcome of the study is that the results of the inter-comparison analysis are variable with time and location, and therefore globally averaged statistics are not necessarily applicable on a seasonal or regional basis.
Subsurface primary production in the western subtropical North Pacific as evidence of large diapycnal diffusivity associated with the Subtropical Mode Water
Authors: Sukigara C. , Suga T. , Saino T. , Toyama K. , Yanagimoto D. , Hanawa K. , Shikama N.
Published: April 2010

Abstract. A profiling float equipped with a fluorometer, a dissolved oxygen sensor, and temperature and salinity sensors was deployed in the Subtropical Mode Water (STMW) formation region. It acquired quasi-Lagrangian, 5-day-interval time-series records from March to July 2006. The time-series distribution of chlorophyll a showed a sustained and sizable deep chlorophyll maximum at 50–80 m, just above the upper boundary of the STMW, throughout early summer (May–July). Vertically integrated chlorophyll values during this period consistently ranged from 15–30 mg m−2, indicating sustained primary production and a continuous supply of nutrients ranging from 10–30 mgN m−2 day−1. The time-series data showed no appreciable sporadic events of nutrient supply. Instead, our results support the recently measured large vertical diffusivity values (~5×10−4 m2 s
Variability of heat and salinity content in the North Atlantic in the last decade
Authors: Ivchenko V. O. , Wells N. C. , Aleynik D. L. , Shaw A. G. P.
Published: April 2010

Abstract. The analysis of the heat and salinity contents have been made for the Northern Atlantic for the decade between January 1999 and December 2008. This analysis is based on the Argo profiling data for the upper 2000 m. Basin-averaged values of anomaly of heat (AHC) and anomaly of salinity content (ASC) are robust and stable. The AHC and ASC demonstrate positive trends in the last decade in the upper 2000 m of the North Atlantic. The linear trend of AHC and ASC are (126.43±18.52)×1020 J, and (47.07±6.90)×1013 kg, respectively. Both trends are significant at 95% level of significance. The main contribution to the positive trend of AHC/ASC comes from the northern parts of the basin.
Upper Labrador Sea Water in the Irminger Sea during a weak convection period (2002–2006)
Authors: Louarn E. , Mercier H. , Morin P. , de Boisseson E. , Bacon S.
Published: April 2010

Abstract. Four cruises between 2002 and 2006 sampled physical and chemical tracers in the southern Irminger Sea during the period of weak convection in the North Atlantic Subpolar Gyre. The upper Labrador Sea Water (uLSW) shows complex and time variable patterns reflecting different formation sites: Irminger Sea, South Greenland and Labrador Sea.
Thermodynamic properties of sea air
Authors: Feistel R. , Kretzschmar H.-J. , Span R. , Hagen E. , Wright D. G. , Herrmann S.
Published: April 2010

Abstract. Very accurate thermodynamic potential functions are available for fluid water, ice, seawater and humid air covering wide ranges of temperature and pressure conditions. They permit the consistent computation of all equilibrium properties as, for example, required for coupled atmosphere–ocean models or the analysis of observational or experimental data. With the exception of humid air, these potential functions are already formulated as international standards released by the International Association for the Properties of Water and Steam (IAPWS), and have been adopted in 2009 for oceanography by IOC/UNESCO. In this paper, we derive a collection of formulas for important quantities expressed in terms of the thermodynamic potentials, valid for typical phase transitions and composite systems of humid air and water/ice/seawater. Particular attention is given to equilibria between seawater and humid air, referred to as ''sea air'' here. In a related initiative, these formulas will soon be implemented in a source-code library for easy practical use. The library is primarily aimed at oceanographic applications but will be relevant to air-sea interaction and meteorology as well. The formulas provided are valid for any consistent set of suitable thermodynamic potential functions. Here we adopt potential functions from previous publications in which they are constructed from theoretical laws and empirical data; they are briefly summarized in the appendix. The formulas make use of the full accuracy of these thermodynamic potentials, without additional approximations or empirical coefficients. They are expressed in the temperature scale ITS-90 and the 2008 Reference-Composition Salinity Scale.
First images and orientation of internal waves from a 3-D seismic oceanography data set
Authors: Blacic T. M. , Holbrook W. S.
Published: April 2010

Abstract. We present 3-D images of ocean finestructure from a unique industry-collected 3-D multichannel seismic dataset from the Gulf of Mexico that includes expendable bathythermograpgh casts for both swaths. 2-D processing reveals strong laterally continuous reflectors throughout the upper ~800 m as well as a few weaker but still distinct reflectors as deep as ~1100 m. Two bright reflections are traced across the 225-m-wide swath to produce reflector surface images that show the 3-D structure of internal waves. We show that the orientation of internal wave crests can be obtained by calculating the orientations of contours of reflector relief. Preliminary 3-D processing further illustrates the potential of 3-D seismic data in interpreting images of oceanic features such as internal wave strains. This work demonstrates the viability of imaging oceanic finestructure in 3-D and shows that, beyond simply providing a way to see what oceanic finestructure looks like, quantitative information such as the spatial orientation of features like internal waves and solitons can be obtained from 3-D seismic images. We expect complete, optimized 3-D processing to improve both the signal to noise ratio and spatial resolution of our images resulting in increased options for analysis and interpretation.
Modal composition of the central water in the North Atlantic subtropical gyre
Authors: Cianca A. , Santana R. , Marrero J. P. , Rueda M. J. , Llinás O.
Published: April 2010

Abstract. The modal composition of the Central Water in the North Atlantic subtropical gyre is not clearly defined, as there are some uncertainties related to mode identification, as well as modes which are not well documented. This study shows that eastern North Atlantic Central Water (eastern NACW) in the subtropical gyre is composed of three modes: The North Atlantic Subpolar Mode Water (NASPMW σt=27.1 to 27.3), the Madeira Mode Water (MMW σt=26.4 to 26.6), and the mode water with a σt near 27.0, which is currently not well documented. We confirmed this mode based on the similarities found between it and the mode waters already reported. The similarities were determined from comparative analyses of the temperature/salinity standard curves and the gradients of the potential density anomalies of two concurrent data sets from two subtropical time-series stations (Bermuda Atlantic Time-series Study, BATS, in the west, and European Station for Time-series in the Ocean Canary Islands, ESTOC, in the east). In order to establish the outcropping regions, the corresponding pycnostads were determined using another climatologic data set (World Ocean Database, WOD2005). In this case, the pycnostads were located based on the presence of standard deviation minima from the average density anomalies. Finally, we confirmed that the pycnostads corresponded to the temperature values related to the modes by overlaying the characteristic modal isotherm of each of the modes in the geographic distribution of the pycnostads. Sea surface temperature data (SST) from the Ocean Pathfinder Program (OPP) were used to estimate the isotherms. The results showed a clear correspondence between the modal isotherms and the pycnostads, for both the modes that have already been documented and the mode confirmed in this study.
Snapshot observation of physical structure and stratification in deep-water of the South Caspian Sea (western part)
Authors: Ghaffari P. , Lahijani H. A. , Azizpour J.
Published: April 2010

Abstract. In this article, we describe physical parameters structures and different water masses using CTD measurements in southwestern part of the Caspian Sea (CS) in adjacent to Anzali Port (AP). CTD profilings were conducted along a transect perpendicular to the coastline over 13 stations from the coast down to 720 m in winter 2008. According to the results the continental shelf waters are located in surface mixed layer. Surface mixed layer extends itself down to almost 100 m in outer areas of the continental shelf with a weak seasonal thermocline layer between 80 to 140 m. Freshwaters inflow of local rivers is clearly seen outside continental shelf at the surface layers. Investigating the dissolved oxygen reveals that winter convection is traceable down to 500 m in the lateral waters over the shelf break. Among the deeper stations that are located in continental rise and abyssal plain, 350 m seems to be threshold for penetration of seasonal changes; therefore deeper waters tend to be impermeable against seasonal variances. Despite to the small variations, stability is positive in most region of the study area and temperature plays an important role in static stability and in triggering the lateral mixing. In view of both temperature-salinity and temperature-oxygen distributions in the southwestern part of the CS, three different water masses are separable in cold phase. Snapshot observation of physical properties in the early winter 2008, to some extent revealed that a mixing was triggered at least in the lateral waters of the study area.
Mediterranean subsurface circulation estimated from Argo data in 2003–2009
Authors: Menna M. , Poulain P. M.
Published: April 2010

Abstract. Data from 38 Argo profiling floats are used to describe the subsurface Mediterranean currents for the period 2003–2009. These floats were programmed to execute 5-day cycles, to drift at a neutral parking depth of 350 m and measure temperature and salinity profiles from either 700 or 2000 m up to the surface. At the end of each cycle the floats remained at the sea surface for about 6 h, enough time to be localised and transmit the data to the Argos satellite system. The Argos positions were used to determine the float surface and subsurface displacements. At the surface, the float motion was approximated by a linear displacement and inertial motion. Subsurface velocities estimates were used to investigate the Mediterranean circulation at 350 m, to compute the pseudo-Eulerian statistics and to study the influence of bathymetry on the subsurface currents. Maximum speeds, as large as 33 cm/s, were found northeast of the Balearic Islands (Western basin) and in the Ierapetra eddy (Eastern basin). Typical speeds in the main along-slope currents (Liguro-Provençal-Catalan, Algerian and Libyo-Egyptian Currents) were ~20 cm/s. In the best sampled regions, the pseudo-Eulerian statistics show typical subsurface circulation pathways which can be related to the motion of Levantine Intermediate Water. In general our results agree with the qualitative subsurface circulation schemes proposed in the literature, except in the southern Ionian where we found westward-flowing subsurface currents. Fluctuating currents appeared to be usually larger than the mean flow. Subsurface currents were found to be essentially parallel to the isobaths over most of the areas characterized by strong bathymetry gradients, in particular, in the vicinity of the continental slopes.
Sediment 231Pa/230Th as a recorder of the rate of the Atlantic meridional overturning circulation: insights from a 2-D model
Authors: Luo Y. , Francois R. , Allen S. E.
Published: April 2010

Abstract. A two dimensional scavenging-circulation model is used to investigate the patterns of sediment 231Pa/230Th generated by the Atlantic Meridional Overturning Circulation (AMOC) and further advance the application of this proxy for ocean paleocirculation studies. The scavenging parameters and the geometry of the overturning circulation cell have been chosen so that the model generates meridional sections of dissolved 230Th and 231Pa consistent with published water column profiles and an additional 12 previously unpublished profiles measured in the North and Equatorial Atlantic. The processes that generate the meridional sections of dissolved and particulate 230Th, dissolved and particulate 231Pa, dissolved and particulate 231Pa/230Th, and sediment 231Pa/230Th are discussed in detail. The results indicate that the relationship between sediment 231Pa/230Th at any given site and the overturning circulation is very complex. They clearly show that constraining past changes in the strength and geometry of the AMOC requires an extensive data set and they suggest strategies to maximize information from a limited number of samples.
A model for predicting changes in the electrical conductivity, practical salinity, and absolute salinity of seawater due to variations in relative chemical composition
Authors: Pawlowicz R.
Published: April 2010

Abstract. Salinity determination in seawater has been carried out for almost 30 years using the 1978 Practical Salinity Standard. However, the numerical value of so-called practical salinity, computed from electrical conductivity, differs slightly from the true or absolute salinity, defined as the mass of dissolved solids per unit mass of seawater. The difference arises because more recent knowledge about the composition of seawater is not reflected in the definition of practical salinity, which was chosen to maintain historical continuity with previous measures, and because of spatial and temporal variations in the relative composition of seawater. Accounting for these variations in density calculations requires the calculation of a correction factor δSA, which is known to range from 0 to 0.03 g kg−1 in the world oceans. Here a mathematical model relating compositional perturbations to δSA is developed, by combining a chemical model for the composition of seawater with a mathematical model for predicting the conductivity of multi-component aqueous solutions. Model calculations generally agree with estimates of δSA based on fits to direct density measurements, and show that biogeochemical perturbations affect conductivity only weakly. However, small systematic differences between model and density-based estimates remain. These may arise for several reasons, including uncertainty about the biogeochemical processes involved in the increase in Total Alkalinity in the North Pacific, uncertainty in the carbon content of IAPSO standard seawater, and uncertainty about the haline contraction coefficient for the constituents involved in biogeochemical processes. This model may then be important in constraining these processes, as well as in future efforts to improve parameterizations for δSA.
Numerical simulations of spreading of the Persian Gulf outflow into the Oman Sea
Authors: Ezam M. , Bidokhti A. A. , Javid A. H.
Published: April 2010

Abstract. A three dimensional numerical model namely, (Princeton Ocean Model) and some observational data are used to study the Persian Gulf outflow structure and its spreading pathways during two different time of the year, mid-winter and early summer. A few available observations show that the Persian Gulf outflow source water exhibits seasonal variations in temperature and salinity. The numerical model is set up by CTD measurements at its western boundary and monthly surface wind speed on the model domain from ICAODS data. The results show that the outflow originates from two branches at different depths in the Persian Gulf. The permanent branch that may exist during the whole year in deeper parts at about 40 m and originates from inner parts of the Persian Gulf and the other one is a seasonal branch that starts to form the vicinity of southern coast during winter months (February). Near the Strait of Hormuz the two branches are jointed together and form the main outflow source. Our findings reveal that during the winter the outflow boundary current detaches from the coast just at the Ras Al Hamra Cape, however for the summer the outflow seems to follow the coast even after this Cape, and appears to separate from the coast at the Ras Al Hadd Cape. This behavior is explained as follow: more saline outflow during February causes higher density and so sinking to deeper zone during the winter. Thus, it moves to deeper parts at about 500 m in contrast with that of May which is at about 300 m. During February at Ras Al Hamra Cape the deeper and stronger outflow is more affected by the steep topography slope leading to vortex stretching mechanism which causes it to meander as an "S" shape, while during May, weaker and shallower outflow is less influenced by bottom topography and so it continues along the boundary.
On the multiple time scales of variability in the Northeast Pacific Ocean
Authors: Tokmakian R.
Published: April 2010

Abstract. The spatial and temporal sea surface height energy distribution of the Northeast Pacific Ocean is described and discussed. Using an altimetric data set covering 15 years (1993–2007), the energy within the 3–9 month band is primarily located within 10° of the coast. In the Gulf of Alaska, this energy signal is on the shelf, while further south, west of the California/Oregon coast, the significant energy in this band is west of the shelf break. In both cases, it is primarily forced by the local wind. Within the 2–3 year band, the signal reflects energy generated by local changes to the wind stress from large atmospheric shifts indicated by the Pacific North American Index and by advective or propagating processes related to El Niño-Southern Oscillation. Over the two 4–6 year periods within this data set, the change is primarily due to the large scale shift in atmospheric systems north of about 30° N which also affect changes in current strengths. Based on the distribution of the energy signal and its variability, a set of three winter-time indexes are suggested to characterize the distinct differences in the SSH anomalies in these areas.
Salinity-induced mixed and barrier layers in the southwestern tropical Atlantic Ocean off the northeast of Brazil
Authors: Araujo M. , Limongi C. , Servain J. , Silva M. , Lentini C. A. D.
Published: April 2010

Abstract. High resolution hydrographic observations of temperature and salinity were used to analyze the formation and distribution of isothermal (ZT), mixed (ZM) and barrier layers (BL) in a section of the southwestern Atlantic (0°30' N–14°00' S; 31°24'–41°48' W), adjacent to the northeastern Brazilian coast. Analyzed data consisted of 279 CTD casts acquired during two cruises under the Brazilian REVIZEE Program, one in late austral winter (August–October 1995) and another in austral summer (January–April 1997). Results indicated that the intrusion of subtropical Salinity Maximum Waters (SMW) brought by the South Equatorial Current (SEC) from the subtropical region into the western tropical Atlantic boundary is the major process contributing to the seasonal BL formation. During late austral winter, BL 5–90 m thickness (BLT) (median=15 m) was observed, but BLT>30 m was restricted to latitudes higher than 8° S as a result of a combination of deep isothermal layers (ZT≥90 m) and shallow mixed layers, where the latter was created by the intrusion of salty waters between 8–12.3° S. During austral summer, shallow isothermal and mixed layers prevailed and the BL formation was clearly driven by establishing a salt-induced pycnocline inside an isothermal layer. Observed BLT was less variable (5–70 m) and thicker (median=35 m). BLT≥30 m was observed not only in the southernmost part of the study area, as verified during late winter, but in the latitude range 2° S–14° S, where near surface salty waters were transported westward by the SEC flow.
Deep currents in the Gulf of Guinea: along slope propagation of intraseasonal waves
Authors: Guiavarc'h C. , Treguier A. M. , Vangriesheim A.
Published: April 2010

Abstract. In the Gulf of Guinea, intraseasonal variability is large at the equator and along the coast. Current data on the continental slope near 7.5° S show very energetic biweekly oscillations at 1300 m depth. A high resolution numerical model demonstrates that this deep variability is forced by equatorial winds, through the generation of equatorial Yanai waves that propagate eastward and at depth, and then poleward as coastal-trapped waves upon reaching the coast of Africa. Intraseasonal variability is intensified along the coast, especially in the 500–1500 m depth range, with the largest intensification in the 10–20 day period range. The structure of kinetic energy is well explained at first order by a linear model with six baroclinic modes. Along the equator, eastward intensification of energy and bottom intensification are in qualitative agreement with vertically propagating Yanai waves, although the signal is clearly influenced by the details of the bathymetry. Along the coast, vertical modes 3 to 5 are important close to the equator, and the signal is dominated by lower modes farther south. Additional current meter data on the continental slope near 3° N display an energy profile in the 10–20 day period band that is strikingly different from the one at 7.5° S, with surface intensification rather than bottom intensification and a secondary maximum near 800 m. The model reproduces these features and explains them: the surface intensification in the north is due to the regional wind forcing, and the north-south dissymetry of the deep signal is due to the presence of the zonal African coast near 5° N. A 4 years time series at 7.5° S displays intermittencies of the 10–20 day signal near the bottom. This intermittency is not correlated with fluctuations of the equatorial winds and does not seem to be a simple linear response to the wind forcing.