Seawater Density Research Articles

Thermal radiation energy due to SWCNTs on MHD nanofluid flow in the presence of seawater/water: Lie group transformation

Abstract An investigation of the boundary layer nanofluids flow over a porous wedge in the presence of uniform transverse magnetic field and thermal radiation energy has been analyzed. Water and seawater based nanofluid containing copper, aluminum oxide and Single Walled Carbon nanotubes (SWCNTs) is taken into consideration. The governing equations in terms of ODEs are solved using fourth–fifth order Runge–Kutta–Fehlberg method with shooting technique. Approximate solution of temperature, velocity, the rate of heat transfer and the shear stress at the wedge are illustrated graphically for several values of the pertinent parameters. Thermal conductivity enhancements of water and seawater in the presence of single-walled carbon nanotubes (SWCNTs) are presented. The thermal boundary layer of SWCNTs–water is compared to SWCNTs–seawater on absorbing the incident thermal energy radiation and transmitting it to the nanofluid by convection. Momentum and thermal boundary layer thickness for SWCNTs–seawater is stronger than SWCNTs–water with increase of the radiation parameter because of low thermal conductivity of seawater. The rate of heat transfer of Cu–seawater is significantly stronger than all the other mixtures in the flow regime because of the combined effects of density of copper and seawater.

Influence of the Leeuwin Current on the epipelagic euphausiid assemblages of the south-east Indian Ocean

The Leeuwin Current is an anomalous eastern boundary current which transports warm, low salinity water poleward off Western Australia. This study investigated epipelagic euphausiids in the Leeuwin Current system from 22°S to 34°S focusing on the latitudinal gradient in species richness and whether variability in euphausiid assemblages was associated with an increase in seawater density across latitude. Twenty-eight species of euphausiids (including five new records) were identified from the study area. Species richness remained relatively constant across latitude as the distribution of seven tropical species, including the dominant Pseudeuphausia latifrons, extended south of 30°S. Euphausiid assemblages from the northern shelf stations were distinct from the oceanic, shelf break and southern shelf assemblages which, though clustering together, showed evidence of latitudinal shifts and day/night influence, particularly at oceanic stations. Distance-based linear models confirmed that, of the environmental variables examined, mean seawater density was the only significant explanatory variable accounting for 32, 27 and 71% of the variation for shelf, shelf break and night oceanic assemblages, respectively. This study provides the first account of the diversity, distribution and abundance of euphausiids along the entire western seaboard of Australia and enhances understanding of the influence of the Leeuwin Current on holoplanktonic biota.

Carbonate mounds in the Santaren Channel, Bahamas: A current-dominated periplatform depositional regime

New hydroacoustic data, high resolution multichannel seismic reflection data, CTD casts and sampling document the dominance of bottom currents and the occurrence of carbonate mounds in the Santaren Channel off Great Bahama Bank and Cay Sal Bank. Based on these data sets, three types of carbonate mounds have been identified in water depths between 285 and 685m. Their distribution is strongly related to the present current regime. Bank-driven sediments are caught up by the currents and redeposited mainly in the channel center, resulting in the accumulation of giant confined drifts flanked by moats. The moats at the banks toe-of-slope are formed by a southward and northward flowing water mass, respectively, mainly Antarctic Intermediate Water and Subtropical Underwater. The observed carbonate mounds are concentrated in these moats. Mound type 1 has an elongated shape parallel to the prevailing bottom current direction, a gently inclined flank facing the water flow and a steep flank in its current shadow. Its upstream flank is covered by a thin sediment wedge whereas the lee side is marked by a parabolic scour. Type 1 occurs at both bank margins but mainly off Great Bahama Bank, consisting of cold-water coral rubble floating in a sediment matrix and is, thus, interpreted as cold-water coral mound. By contrast, type 2 mounds are restricted to the Cay Sal margin and have a predominately conical outline. Bottom samples including living sessile crinoids show that its surface must be lithified and colonized by macroepibenthos, except corals. The mounds are situated in pockmark-like depressions that are underlain by fluid escape structures like pipes and chimneys. These fluid pathways are generated by a network of fractures. Mound type 2 is probably formed by abiotic carbonate precipitation; however, a chemoherm nature cannot be ruled out. Mound type 3 has a conical to polygonal shape and occurs off Cay Sal Bank and Great Bahama Bank. It is surrounded by a scour which is elongated in downcurrent and crescent in upcurrent direction. A sediment bulge formed at its front. This type is consistent with blocks and boulders colonized by macroepibenthos and related to gravity-controlled mass movements at the steep bank slopes.Principally, two habitats can be distinguished: the Great Bahama Bank periplatform deep-water province dominated by mound type 1 and the Cay Sal Bank slope to basin province occupied by mound type 2 that is associated with pockmark-like structures. Mound type 3 occurs in both habitats. Physical water mass properties for the existence of cold-water corals are limited to a depth range of ca. 430 to 685m, with seawater densities (σ-θ) of 26.93 to 27.29kg/m and temperatures below 13°C. Their dominance off Great Bahama Bank might be addressed to a more effective food supply induced by local downwelling.

Paleoseawater density reconstruction and its implication for cold‐water coral carbonate mounds in the northeast Atlantic through time

AbstractCarbonate buildups and mounds are impressive biogenic structures throughout Earth history. In the recent NE Atlantic, cold‐water coral (CWC) reefs form giant carbonate mounds of up to 300 m of elevation. The expansion of these coral carbonate mounds is paced by climatic changes during the past 2.7 Myr. Environmental control on their development is directly linked to controls on its main constructors, the reef‐building CWCs. Seawater density has been identified as one of the main controlling parameter of CWC growth in the NE Atlantic. One possibility is the formation of a pycnocline above the carbonate mounds, which is increasing the hydrodynamic regime, supporting elevated food supply, and possibly facilitating the distribution of coral larvae. The potential to reconstruct past seawater densities from stable oxygen isotopes of benthic foraminifera has been further developed: a regional equation gives reliable results for three different settings,peak interglacials(e.g., Holocene),peak glacials(e.g., Last Glacial Maximum), andintermediatesetting (between the two extremes). Seawater densities are reconstructed for two different NE Atlantic CWC carbonate mounds in the Porcupine Seabight indicating that the development of carbonate mounds is predominantly found at a seawater density range between 27.3 and 27.7 kg m−3(σΘnotation). Comparable to recent conditions, we interpret the reconstructed density range as a pycnocline serving as boundary layer, on which currents develop, carrying nutrition and possibly coral larvae. The close correlation of CWC reef growth with reconstructed seawater densities through the Pleistocene highlights the importance of pycnoclines and intermediate water mass dynamics.

Sea surface density gradients in the Nordic Seas during the Holocene as revealed by paired microfossil and isotope proxies

AbstractWe attempt to assess the Holocene surface‐subsurface seawater density gradient on millennial time scale based on the reconstruction of potential density (σθ) by combining data from dinoflagellate cyst assemblages and planktic foraminiferal (Neogloboquadrina pachyderma (s)) stable oxygen isotopes (δ18Oc). Following several calibration exercises, the likeliness of favorable seasonal preconditioning to open ocean convection is evaluated. The reconstructed σθ values reveal unfavorable conditions for vertical convection in the western Nordic Seas prior to ~7–6.5 ka B.P., with a westward increase and persistence of surface water buoyancy. Active overturning became more likely after 6.5 ka B.P. as suggested by a reduced and recurrently inverted vertical σθ gradient, while intermittent eastward spreading of lower density surface waters continued to modulate the area of potential overturning. Despite some reservation regarding the accuracy of the σθ values reconstructed, the documentation of relative changes of σθ gradients through time and space is suggested as a helpful tool for the appraisal of past overturning likeliness.

A method to measure the density of seawater accurately to the level of 10−6

A substitution method to measure seawater density relative to pure water density using vibrating tube densimeters was realized and validated. Standard uncertainties of 1 g m−3 at atmospheric pressure, 10 g m−3 up to 10 MPa, and 20 g m−3 to 65 MPa in the temperature range of 5 °C to 35 °C and for salt contents up to 35 g kg−1 were achieved. The realization was validated by comparison measurements with a hydrostatic weighing apparatus for atmospheric pressure. For high pressures, literature values of seawater compressibility were compared with substitution measurements of the realized apparatus.

Effect of Sulfuric Acid Concentration on Electrochemical Characteristics of Nano Porous Structure Formed by Anodizing Process.

Aluminum alloy is a very strong reactivity material, but it has excellent corrosion resistance due to protective oxide film created in air. However, it is not practical because the film thickness is uneven and varies depending on the generation condition. Therefore, aluminum anodizing was performed to form film with commercially applicable hardness, corrosion resistance, and wear resistance. This offers such advantages as commercial applicability to large areas and low prices. In this study, the electrochemical characteristics with concentration of sulfuric acid electrolyte were compared with the two-step anodizing method which is widely used. A surface observation revealed regular structures and pores with the size of several tens of nm, and the anodized film presented excellent corrosion resistance with considerably low corrosion current density in sea water.

Inversion of Seawater Physical Properties Based on Allied Elastic Impedance

Inversion of seawater physical parameters (temperature, salinity and density) from seismic data is an important part of Seismic Oceanography, which was raised recent years to study physical oceanography. However present methods have problems that inversion accuracy is not high or inverted parameters are incomprehensive. To overcome these problems, this paper derives Allied Elastic Impedance (AEI), from which we can extract acoustic velocity and density of seawater directly. Furthermore this paper proposes a method to fit temperature and salinity with acoustic velocity and density respectively, breaking through the limitation that temperature and salinity can only be extracted from acoustic velocity. After applying it to model and real data, we find that this method not only solves the problem that ocean density is hard to extract, but also increases accuracy of other parameters, with the temperature and salinity resolution of 0.06°C and 0.02 psu respectively. All results show that AEI is promising in inversion of seawater physical parameters.

海水密度人工跃变技术实验研究

密度跃层是大洋海水的一种重要水文现象，它对船舶尤其是水下航行器影响巨大，如能设法将其用于对抗敌水下航行器无疑具有独特的价值，为此本文提出了一种海水密度的人工跃变技术。其核心思想是，利用专用的材料和设备，通过特定的机理在设定海域生成大量均匀分布的气泡，以形成足够规模的海水密度人工跃变区域。本文为了验证该海水密度人工跃变技术的可行性而设计了验证性实验，实验结果表明了该技术深入研究的价值和在未来装备发展中的显著优势。 The pycnocline is an important hydrologic phenomenon of seawater, having great impact for un-derwater vehicle, which would undoubtedly have distinctive value if it can be used to against op-posed underwater vehicle. So, this paper presents a manually jumped technique of seawater density. The core idea is that a large number of bubbles which is formatted by special mechanism in the scheduled sea waters are diffused by using special-purpose materials and equipments to form enough scale manually jumped area of seawater density. The paper designs the verification experiment in order to verify the technique, and the result shows the value of further study and the advantage in the future equipment development.

대한해협에서의 수온 및 염도변화를 고려한 선박의 저항성능 예측을 위한 기초 연구

Recently, shipping operators have been making efforts to reduce the fuel cost in various ways, such as trim optimization and bulb re-design. Furthermore, IMO restricts the hydro-dioxide emissions to the environment based on the EEDI (Energy Efficiency Design Index), EEOI (Energy Efficiency Operational Indicator), and SEEMP (Ship Energy Efficiency Management Plan). In particular, ship speed is one of the most important factors for calculating the EEDI, which is based on methods suggested by ITTC (International Towing Tank Conference) or ISO (International Standardization Organization). Many shipbuilding companies in Korea have carried out speed trials around the Korea Straits. However, the conditions for these speed trials have not been exactly the same as those for model tests. Therefore, a ship’s speed is corrected by measured environmental data such as the seawater temperature, density, wind, waves, swell, drift, and rudder angle to match the conditions of the model tests. In this study, fundamental research was performed to evaluate the ship resistance performance due to changes in the water temperature and salinity, comparing the ISO method and numerical simulation. A numerical simulation of a KCS (KRISO Container ship) with a free-surface was performed using the commercial software Star-CCM+ under three conditions that were assumed based on the water temperature and salinity data in the Korea Straits. In the simulation results, the resistance increased under low water temperature & high salinity conditions, and it decreased under high water temperature & low salinity conditions. In addition, the ISO method showed the same result as the simulation.

A sum greater than its parts: merging multi‐predator tracking studies to increase ecological understanding

Understanding how animals find prey in heterogeneous environments is a central goal of ecology. Placing this process in an environmental context requires a lot of information regarding the characteristics of both the habitat selected by the animal and its surroundings. In high‐latitude marine systems, information about subsurface habitats of marine predators is often very limited. Animal‐borne oceanographic instruments have added a new modality to improve our understanding of marine predators and their habitats. While these instruments do not collect environmental information beyond that experienced by the animals carrying them, our study makes use of an oceanographic dataset collected by southern elephant seals (Mirounga leonina; N = 15), to provide environmental context for two sympatrically foraging penguin species in the waters close to the subantarctic island of Bouvetøya. The seals collected 154 CTD profiles during the study period, averaging 4.9 (±3.67) profiles per day, documenting the stratification of the upper water layer in terms of both seawater density and temperature. Using these data, we quantitatively describe the relationship between the diving behavior of the penguins (N = 3,745 dives) and the hydrographic properties of the three‐dimensional area in which they were foraging. Both penguin species appeared to favor water characterized by a shallow mixed layer. The chinstrap penguins (Pygoscelis antarctica) dove within a shallow, unstable body of water close to the colony, whereas macaroni penguins (Eudyptes chrysolophus) exploited the bottom of the surface mixed layer further offshore. The hydrographic properties preferred by the penguins match closely those that describe the highest densities of their preferred prey, krill (Euphausia superba), identified during a temporally and spatially concurrent study. We demonstrate how merging multiple telemetric data streams from animals can shed new light on aspects of foraging behavior beyond simply relating movements to two‐dimensional, remotely sensed measurements of the environment.

First Aid Oxygen Treatment for Decompression Illness in the Goat After Simulated Submarine Escape.

Personnel responding to a distressed submarine incident require information on likely casualty levels and the severity and progression of decompression illness (DCI). Recompression may not be immediately available. First aid oxygen (FAo₂) can be administered; however, there is no direct evidence of its efficacy in this scenario. Trials were conducted between 2004 and 2006. Goats exposed to raised pressure for 24 h ('saturation') were either returned directly to atmospheric pressure (Phase A, N = 40) or exposed to simulated submarine escape at a depth of 656 ft (200 m; assumed seawater density = 1019.72 kg · m(-3); Phase B, N = 39). The pressure during saturation was selected to provoke 50% DCI. Cases of DCI were randomly assigned to receive FAo₂or air. DCI cases were: limb pain in 39 subjects, neurological in 6, respiratory in 4, and pulmonary barotrauma in 1 subject. In Phase A, 5/12 subjects in the FAo₂group and 0/11 in the air control group achieved permanent resolution of DCI. In Phase B, 6/8 subjects in the FAo₂group and 5/8 in the air control group achieved permanent resolution. In both Phases, levels of venous gas bubbles reduced sooner with FAo₂. Of three cases of neurological DCI receiving FAo₂, two showed permanent resolution. In total, four cases of respiratory DCI occurred; none of these resolved, with three being treated with FAo₂and one in the air control. Oxygen can be an effective first aid measure for DCI following submarine escape. However, it should not be used as a replacement for recompression therapy.

Internal wave parameters retrieval from space-borne SAR image

Based on oceanic internal wave SAR imaging mechanism and the microwave scattering imaging model for oceanic surface features, we developed a new method to extract internal wave parameters from SAR imagery. Firstly, the initial wind fields are derived from NCEP reanalysis data, the sea water density and oceanic internal wave pycnocline depth are estimated from the Levites data, the surface currents induced by the internal wave are calculated according to the KDV equation. The NRCS profile is then simulated by solving the action balance equation and using the sea surface radar backscatter model. Both the winds and internal wave pycnocline depth are adjusted by using the dichotomy method step by step to make the simulated data approach the SAR image. Then, the wind speed, pycnocline depth, the phase speed, the group velocity and the amplitude of internal wave can be retrieved from SAR imagery when a best fit between simulated signals and the SAR image appears. The method is tested on one scene SAR image near Dongsha Island, in the South China Sea, results show that the simulated oceanic internal wave NRCS profile is in good agreement with that on the SAR image with the correlation coefficient as high as 90%, and the amplitude of oceanic internal wave retrieved from the SAR imagery is comparable with the SODA data. Besides, the phase speeds retrieved from other 16 scene SAR images in the South China Sea are in good agreement with the empirical formula which describes the relations between internal wave phase speed and water depths, both the root mean square and relative error are less than 0.11 m∙s–1 and 7%, respectively, indicating that SAR images are useful for internal wave parameters retrieval and the method developed in this paper is convergent and applicable.

In situ observations of a doliolid bloom in a warm water filament using a video plankton recorder: Bloom development, fate, and effect on biogeochemical cycles and planktonic food webs

AbstractWe investigated distribution patterns of a doliolid (Dolioletta gegenbauri) bloom in relation to the physical environment using a video plankton recorder in the Oyashio–Kuroshio mixed water region. Using 12 km transects, doliolid blooms were encountered at a horizontal scale of about 2–3 km, which corresponds to submesoscale physical events. Doliolids were also consistently encountered in the subsurface layer above the pycnocline in warmer (> 14ºC) and higher‐salinity (> 34) water masses, and seawater density was the most critical factor affecting distribution depth. Compared to previous studies, the density and biomass of the blooms observed in this study (77 mgC m−3and 4600 inds m−3) were highest in the open ocean. Bloom formation consisted of two phases; first, the seeding population of a nurse stage increased rapidly to 2000 inds m−3by asexual reproduction, followed by asexual production of phorozooids. Estimated population clearance rates revealed that these dense patches could potentially sweep the surrounding water within 2–3 d. The incidence of exhausted and shrunken zooids was significantly correlated with patch density, suggesting that mortality was due to overgrazing. Shrunken doliolids appeared to sink below the pycnocline, corresponding to 8–17% of the particulate organic carbon flux at 150 m. Hydromedusae, pelagic polycheates, and sapphirinid copepods preyed on the doliolids. These results indicate that doliolids, which were seeded by populations originating from the Kuroshio, formed dense blooms in response to submesoscale physical events and would alter the sinking particle properties (i.e., biological pump) and the epipelagic food web structure through their grazing and mortality.

A marine sink for chlorine in natural organic matter

Chloride is abundant in oceans, but is relatively unreactive. Spectroscopic imaging reveals the presence of a chloride sink in organochlorine compounds that can be produced abiotically or by phytoplankton. Chloride—the most abundant ion in sea water1—affects ocean salinity, and thereby seawater density and ocean circulation. Its lack of reactivity gives it an extremely long residence time2. Other halogens are known to be incorporated into marine organic matter3,4,5. However, evidence of similar transformations of seawater chloride is lacking, aside from emissions of volatile organochlorine by marine algae6,7,8. Here we report high organochlorine concentrations from 180 to 700 mg kg−1 in natural particulate organic matter that settled into sediment traps at depths between 800 and 3,200 m in the Arabian Sea, taken between 1994 and 1995. X-ray spectromicroscopic imaging of chlorine bonding reveals that this organochlorine exists primarily in concentrated aliphatic forms consistent with lipid chlorination, along with a more diffuse aromatic fraction. High aliphatic organochlorine in particulate material from cultured phytoplankton suggests that primary production is a source of chlorinated organic matter. We also found that particulate algal detritus can act as an organic substrate for abiotic reactions involving Fe2+, H2O2 or light that incorporate chlorine into organic matter at levels up to several grams per kilogram. We conclude that transformations of marine chloride to non-volatile organochlorine through biological and abiotic pathways represent an oceanic sink for this relatively unreactive element.

Morphology Alters Fluid Transport and the Ability of Organisms to Mix Oceanic Waters.

Mixing in the ocean is opposed by the stratification of fluid, such that density of seawater increases with greater depth. The mechanisms by which mixing occurs have been attributed largely to physical processes that include atmospheric forcing, tides, and internal waves. Biogenic mixing, another potential source of mixing in the ocean, may generate significant transport of fluid during diel vertical migrations of organisms. Biogenic mixing is not limited to the near-surface or to regions of rough bottom topography, as are other physical mixing processes, and may contribute significantly to the energy budget of mixing in mid-ocean. "Fluid drift", a mechanism first described by Charles Galton Darwin, has been identified as a mechanism that allows for long-distance, vertical transport of fluid by the smallest of swimming organisms. However, little is known about how fluid drift varies with morphology and behavior of swimming organisms. We conducted numerical simulations of theoretical and experimentally measured flows of swimming medusae (Phyllorhiza sp.), and compared the volume of the drift induced by these flows. Our numerical simulations of fluid drift showed that morphology coupled with swimming behavior alters the transport of fluid both spatially and temporally. Given empirical velocity field data, the methods presented here allow us to systematically compare fluid transport across taxa, and enable us to deduce the potential of swimming organisms to influence fluid transport.

Accurate polynomial expressions for the density and specific volume of seawater using the TEOS-10 standard

A new set of approximations to the standard TEOS-10 equation of state are presented. These follow a polynomial form, making it computationally efficient for use in numerical ocean models. Two versions are provided, the first being a fit of density for Boussinesq ocean models, and the second fitting specific volume which is more suitable for compressible models. Both versions are given as the sum of a vertical reference profile (6th-order polynomial) and an anomaly (52-term polynomial, cubic in pressure), with relative errors of ∼0.1% on the thermal expansion coefficients. A 75-term polynomial expression is also presented for computing specific volume, with a better accuracy than the existing TEOS-10 48-term rational approximation, especially regarding the sound speed, and it is suggested that this expression represents a valuable approximation of the TEOS-10 equation of state for hydrographic data analysis. In the last section, practical aspects about the implementation of TEOS-10 in ocean models are discussed.

The Eugen Seibold coral mounds offshore western Morocco: oceanographic and bathymetric boundary conditions of a newly discovered cold-water coral province

This study reports a new cold-water coral (CWC) province covering ~410 km2 off western Morocco (ca. 31°N) ~40 nautical miles north of the Agadir Canyon system between 678 and 863 m water depth, here named the Eugen Seibold coral mounds. Individual mounds are up to 12 m high with slope angles varying between 3° and 12°. Hydroacoustic data revealed mound axes lengths of 80 to 240 m. Slope angle, mound height, and density of mounds decrease with increasing water depth. The deepest mounds are composed of dead and fragmented Lophelia pertusa branches. Living CWCs, mainly L. pertusa, were sampled with box cores between 678 and 719 m water depth. Conductivity-temperature-depth (CTD) measurements revealed living CWC colonies to occur within the deeper part of the North Atlantic Central Water (NACW; conservative temperature Θ of 9.78–9.94 °C, absolute salinity SA of ca. 35.632 g/kg, and seawater density σΘ of 27.31–27.33 kg/m3). Comparable CWC reefs off Mauritania (17°N–18°N) and on the Renard Ridge (35°N) in the Gulf of Cadiz, the latter consisting only of a dead CWC fabric, are also located in the deeper layer of the NACW slightly above the Mediterranean Outflow Water. The new CWC province, with its thin cover of living corals and much larger accumulations of dead thickets and fragmented coral rubble, was successfully discovered by CTD reconnaissance applying seawater density as a potential indicator of CWC occurrences, followed by hydroacoustic mapping. U-Th isotope systematics for macroscopically altered buried Lophelia material (25 cm sediment depth) yielded absolute ages dating back to the late Holocene at least.

3D MODELS COMPARISON OF COMPLEX SHELL IN UNDERWATER AND DRY ENVIRONMENTS

Abstract. In marine biology the shape, morphology, texture and dimensions of the shells and organisms like sponges and gorgonians are very important parameters. For example, a particular type of gorgonian grows every year only few millimeters; this estimation was conducted without any measurement instrument but it has been provided after successive observational studies, because this organism is very fragile: the contact could compromise its structure and outliving. Non-contact measurement system has to be used to preserve such organisms: the photogrammetry is a method capable to assure high accuracy without contact. Nevertheless, the achievement of a 3D photogrammetric model of complex object (as gorgonians or particular shells) is a challenge in normal environments, either with metric camera or with consumer camera. Indeed, the successful of automatic target-less image orientation and the image matching algorithms is strictly correlated to the object texture properties and of camera calibration quality as well. In the underwater scenario, the environment conditions strongly influence the results quality; in particular, water’s turbidity, the presence of suspension, flare and other optical aberrations decrease the image quality reducing the accuracy and increasing the noise on the 3D model. Furthermore, seawater density variability influences its refraction index and consequently the interior orientation camera parameters. For this reason, the camera calibration has to be performed in the same survey conditions. In this paper, a comparison between the 3D models of a Charonia Tritonis shell are carried out through surveys conducted both in dry and underwater environments.

Steric sea level variability (1993–2010) in an ensemble of ocean reanalyses and objective analyses

Quantifying the effect of the seawater density changes on sea level variability is of crucial importance for climate change studies, as the sea level cumulative rise can be regarded as both an important climate change indicator and a possible danger for human activities in coastal areas. In this work, as part of the Ocean Reanalysis Intercomparison Project, the global and regional steric sea level changes are estimated and compared from an ensemble of 16 ocean reanalyses and 4 objective analyses. These estimates are initially compared with a satellite-derived (altimetry minus gravimetry) dataset for a short period (2003–2010). The ensemble mean exhibits a significant high correlation at both global and regional scale, and the ensemble of ocean reanalyses outperforms that of objective analyses, in particular in the Southern Ocean. The reanalysis ensemble mean thus represents a valuable tool for further analyses, although large uncertainties remain for the inter-annual trends. Within the extended intercomparison period that spans the altimetry era (1993–2010), we find that the ensemble of reanalyses and objective analyses are in good agreement, and both detect a trend of the global steric sea level of 1.0 and 1.1 ± 0.05 mm/year, respectively. However, the spread among the products of the halosteric component trend exceeds the mean trend itself, questioning the reliability of its estimate. This is related to the scarcity of salinity observations before the Argo era. Furthermore, the impact of deep ocean layers is non-negligible on the steric sea level variability (22 and 12 % for the layers below 700 and 1500 m of depth, respectively), although the small deep ocean trends are not significant with respect to the products spread.