Steric Components Research Articles

Spectral analysis of sea level during the altimetry era, and evidence for GIA and glacial melting fingerprints

We study the spatial patterns of the mass and steric components of sea-level change during the “altimetry era” (1992–today), and we characterize them at different scales by the orthonormal functions method. The spectrum of the altimetry-derived rate of sea-level rise is red and decays with increasing wavenumber nearly following a power law with exponent ≈2. By analyzing the degree correlation and the admittance function, we find that the altimetric rate of sea-level change is coherent with the total steric field in the whole range of wavelengths considered (down to ≈1000km), but particularly for wavelengths exceeding ≈2000km. Thermosteric and halosteric components are moderately anti-correlated within the range of wavelengths 1000–4000km. Their power spectrum varies significantly with the wavelength and, for ≈2000km, it is equally partitioned between the two components. The power of regional sea-level variations driven by Glacial Isostatic Adjustment and the melting of continental ice sheets is small compared to that held by the steric component, which explains most of the regional variability shown by the altimetry record. This causes the elusiveness of the “static” sea-level fingerprints, which at present are hidden in the pattern of the residual sea-level (i.e., the altimetry-derived sea-level minus the steric component). However, we find that at harmonic degree 2, mainly associated with rotational variations, the power of glacial melting is significant and it will progressively increase during next century in response to global warming. We also estimate that at the end of the Mid-Holocene the strength of the glacial isostatic readjustment fingerprints was ≈10 times larger than today, well above the long-wavelength component of residual sea-level.

Sea level budget in the Bay of Bengal (2002–2014) from GRACE and altimetry

AbstractSea level rise is perceived as a major threat to the densely populated coast of the Bay of Bengal. Addressing future rise requires understanding the present‐day sea level budget. Using a novel method and data from the Gravity Recovery and Climate Experiment (GRACE) satellite, we partition altimetric sea level rise (6.1 mm/a over 2002–2014) into mass and steric components. We find that current mass trends in the Bay of Bengal are slightly above global mean, while steric trends appear much larger: 2.2–3.1 mm/a if we disregard a residual required to close the budget, and 4.3–4.6 mm/a if, as an upper bound, we attribute this residual entirely to steric expansion. Our method differs from published approaches in that it explains altimetry and GRACE data in a least squares inversion, while mass anomalies are parameterized through gravitationally self‐consistent fingerprints, and steric expansion through EOFs. We validate our estimates by comparing to Argo and modeling for the Indian Ocean, and by comparing total water storage change (TWSC) for the Ganges and Brahmaputra basins to the conventional GRACE approach. We find good agreement for TWSC, and reasonable agreement for steric heights, depending on the ocean region and Argo product. We ascribe differences to weaknesses of the Argo data, but we also find the inversion to be to some extent sensitive with respect to the EOFs. Finally, combining our estimates with CMIP5‐simulations, we estimate that Bay of Bengal absolute sea level may rise for additional 37 cm under the RCP4.5 scenario and 40 cm under RCP8.5 until 2050, with respect to 2005.

Revisiting the contemporary sea-level budget on global and regional scales

Dividing the sea-level budget into contributions from ice sheets and glaciers, the water cycle, steric expansion, and crustal movement is challenging, especially on regional scales. Here, Gravity Recovery And Climate Experiment (GRACE) gravity observations and sea-level anomalies from altimetry are used in a joint inversion, ensuring a consistent decomposition of the global and regional sea-level rise budget. Over the years 2002-2014, we find a global mean steric trend of 1.38 ± 0.16 mm/y, compared with a total trend of 2.74 ± 0.58 mm/y. This is significantly larger than steric trends derived from in situ temperature/salinity profiles and models which range from 0.66 ± 0.2 to 0.94 ± 0.1 mm/y. Mass contributions from ice sheets and glaciers (1.37 ± 0.09 mm/y, accelerating with 0.03 ± 0.02 mm/y(2)) are offset by a negative hydrological component (-0.29 ± 0.26 mm/y). The combined mass rate (1.08 ± 0.3 mm/y) is smaller than previous GRACE estimates (up to 2 mm/y), but it is consistent with the sum of individual contributions (ice sheets, glaciers, and hydrology) found in literature. The altimetric sea-level budget is closed by coestimating a remaining component of 0.22 ± 0.26 mm/y. Well above average sea-level rise is found regionally near the Philippines (14.7 ± 4.39 mm/y) and Indonesia (8.3 ± 4.7 mm/y) which is dominated by steric components (11.2 ± 3.58 mm/y and 6.4 ± 3.18 mm/y, respectively). In contrast, in the central and Eastern part of the Pacific, negative steric trends (down to -2.8 ± 1.53 mm/y) are detected. Significant regional components are found, up to 5.3 ± 2.6 mm/y in the northwest Atlantic, which are likely due to ocean bottom pressure variations.

Competition Between π-π and C-H/π Interactions: A Comparison of the Structural and Electronic Properties of Alkoxy-Substituted 1,8-Bis((propyloxyphenyl)ethynyl)naphthalenes.

The structural and electronic consequences of π-π and C-H/π interactions in two alkoxy-substituted 1,8-bis- ((propyloxyphenyl)ethynyl)naphthalenes are explored by using X-ray crystallography and electronic structure computations. The crystal structure of analogue 4, bearing an alkoxy side chain in the 4-position of each of the phenyl rings, adopts a π-stacked geometry, whereas analogue 8, bearing alkoxy groups at both the 2- and the 5-positions of each ring, has a geometry in which the rings are splayed away from a π-stacked arrangement. Symmetry-adapted perturbation theory analysis was performed on the two analogues to evaluate the interactions between the phenylethynyl arms in each molecule in terms of electrostatic, steric, polarization, and London dispersion components. The computations support the expectation that the π-stacked geometry of the alkoxyphenyl units in 4 is simply a consequence of maximizing π-π interactions. However, the splayed geometry of 8 results from a more subtle competition between different noncovalent interactions: this geometry provides a favorable anti-alignment of C-O bond dipoles, and two C-H/π interactions in which hydrogen atoms of the alkyl side chains interact favorably with the π electrons of the other phenyl ring. These favorable interactions overcome competing π-π interactions to give rise to a geometry in which the phenylethynyl substituents are in an offset, unstacked arrangement.

Global sea level variations from altimetry, GRACE and Argo data over 2005–2014

Total sea level variations (SLVs) are caused by two major components: steric variations due to thermal expansion of seawater, and mass-induced variations due to mass exchange between ocean and land. In this study, the global SLV and its steric and mass components were estimated by satellite altimetry, Argo float data and the Gravity Recovery and Climate Experiment (GRACE) data over 2005–2014. Space gravimetry observations from GRACE suggested that two-thirds of the global mean sea level rise rate observed by altimetry (i.e., 3.1 ± 0.3 mm/a from 2005 to 2014) could be explained by an increase in ocean mass. Furthermore, the global mean sea level was observed to drop significantly during the 2010/2011 La Niña event, which may be attributed to the decline of ocean mass and steric SLV. Since early 2011, the global mean sea level began to rise rapidly, which was attributed to an increase in ocean mass. The findings in this study suggested that the global mean sea-level budget was closed from 2005 to 2014 based on altimetry, GRACE, and Argo data.

Proximity effect: insight into the fundamental forces governing chemical reactivity of aromatic systems.

The analysis of different layers of proximity effect in ortho-substituted aromatic compounds, using a DFT-level study, is reported. Polar and steric components of the proximity effect have been partitioned by applying multivariate regression analysis to an unusual six-electron heteroelectrocyclic reaction of the ortho-substituted nitrosostyrenes. The two pathways, 1,5- and 1,6-cyclizations, emanating from these substrates result into zwitterionic five-membered and neutral six-membered rings, respectively. The substituents at position 1, which are adjacent to the polar nitroso group, influenced the barrier primarily through electronic effect. Furthermore, a mechanistic shift from the 1,5 to 1,6 pathway, for certain substrates, is explained by the electronic repulsion. In contrast to position 1, the substituents on position 4 stereoelectronically interacted with a bulkier alkene moiety. Furthermore, unlike position 1, the position-4-substituted substrates are predicted to give only 1,5 products. A comparison of the two ortho positions with position 2, which is meta to the nitroso and para to the alkene, revealed an intriguing relationship between various electronic factors.

Spatial trend patterns in the Pacific Ocean sea level during the altimetry era: the contribution of thermocline depth change and internal climate variability

This study investigates the spatial trend patterns and variability of observed sea level and upper ocean thermal structure in the Pacific Ocean during the altimetry era (1993–2012), and the role of thermocline depth changes. The observed sea level trend pattern in this region results from the superposition of two main signals: (1) a strong broad-scale V-shaped positive trend anomaly extending to mid-latitudes in the central Pacific and (2) another very strong positive trend anomaly located in the western tropical Pacific within about 120° E–160° E and 20° S–20° N latitude. In this study, we focus on the tropical Pacific (20° N–20° S) where the strongest trends in sea level are observed. By making use of in situ observational data, we study the impact of thermocline depth changes on steric sea level between the surface and 700 m and its relation with the altimetry-based observed sea level changes. This is done by calculating the time-varying thermocline depth (using the 20 °C isotherm depth as a proxy) and estimating the sea level trend patterns of the thermocline-attributed individual steric components. We show that it is essentially the vertical movement of the thermocline that governs most of the observed sea level changes and trends in the tropical Pacific. Furthermore, we also show that in the equatorial band, the changes in the upper ocean thermal structure are in direct response to the zonal wind stress. Away from the equatorial band (say, within 5°–15° latitude), the changes in the upper ocean thermal structure are consistent with the wind stress-generated Rossby waves. We also estimate the contribution of the Interdecadal Pacific Oscillation (IPO) on the vertical thermal structure of the tropical Pacific Ocean. Removing the IPO contribution to the upper layer steric sea level provides a non-negligible residual pattern, suggesting that IPO-related internal ocean variability alone cannot account for the observed trend patterns in the Pacific sea level. It is likely that the residual signal may also reflect non-linear interactions between different natural modes like El Nino Southern Oscillation (ENSO), IPO, etc.

Sea-level rise in the Mediterranean Sea by 2050: Roles of terrestrial ice melt, steric effects and glacial isostatic adjustment

To assess the regional pattern of future low-frequency sea-level variations in the Mediterranean Sea, we combine the terrestrial ice melt, the glacio-isostatic and the steric sea-level components. The first is obtained from global scenarios for the future mass balance of the Greenland and Antarctica ice sheets, glaciers and ice caps. The second is based on modeling, using different assumptions about the Earth's rheology and the chronology of deglaciation since the Last Glacial Maximum. The third is obtained from published simulations based on regional atmosphere–ocean coupled models. From a minimum and a maximum scenario by 2040–2050, we find that the total, basin averaged sea-level rise will be 9.8 and 25.6cm. The terrestrial ice melt component will exceed the steric contribution, which however will show the strongest regional imprint. Glacial isostatic adjustment will have comparatively minor effects. According to our estimates, at the Mediterranean Sea tide gauges, the rate of sea-level change will increase, by 2050, by a factor of ~1–6 relative to the observed long-term rates.

Effect of La Niña on The Global Mean Sea Level And North Pacifc Ocean Mass Over 2005-2011

Abstract Interannual fluctuations of the global mean sea level are highly correlated with El Niño-Southern Oscillation (ENSO) events, with positive/negative anomalies during El Niño/La Niña. In a previous study we showed that during the 1997 - 1998 El Niño, a positive anomaly observed in the global mean sea level was mostly caused by an increase of the ocean mass component rather than by steric (thermal) effects. This result was related to an increase of precipitation over the tropical ocean and a deficit in land water storage. In the present study, we investigate the effect of the recent 2008 and 2011 La Niña events on the satellite altimetry-based global mean sea level. We find that the large global mean sea level drop associated with the 2011 La Niña results from the combined decrease of the steric and ocean mass components, with a slightly dominant contribution from the latter. We show that the ocean mass contribution to the global mean sea level drop is spatially confined over the north eastern tropical Pacific (just as was found previously for the 1997 - 1998 El Niño, but with opposite sign). Corresponding ocean mass spatial pattern is closely correlated to observed sea level and steric spatial patterns over the duration of the La Niña event. This is also observed for previous El Niño and La Niña events. Such a drop in ocean mass during ENSO in the eastern part of the tropical Pacific has not been reported before. It is possibly related to a temporary decrease in the net precipitation over the north eastern Pacific (opposite situation was found during the 1997 - 1998 El Niño).

Deinking flexographic-printed papers: Destabilization of flexographic ink dispersions with copper compounds

Flexographic printing inks form electrosterically stabilized colloidal dispersions in water that display extreme stability at the alkaline pH values of most wastepaper deinking systems. A significant amount of U.S. newspapers are now printed using water-based flexographic inks, and the residual inks from these sources are problematic to remove in deinking plants. A successful flocculant for flexographic ink particles used in deinking plant filtrate streams requires that both the electrostatic and steric components of colloidal stabilization be eliminated simultaneously. The present study shows the advantageous characteristics of cupric chloride in achieving rapid flocculation of flexographic inks. Flocculation experiments were performed with a model ink as well as a mixture of offset and flexographic inks from recycled newspapers. The critical coagulation concentration of cupric chloride has been compared to other chloride, nitrate, and copper salts. Copper(II) chloride has been found to be significantly more effective than other such salts in achieving destabilization and aggregation of flexographic ink particles. A possible flocculation mechanism of flexographic ink particles by cupric chloride is presented.

The genesis of sea level variability in the Barents Sea

The regional variability of sea level is an integral indicator of changing oceanographic conditions due to different processes of oceanic, atmospheric, and terrestrial origin. The present study explores the nature of sea level variability in the Barents Sea—a marginal shelf sea of the Arctic Ocean. A characteristic feature that distinguishes this sea from other Arctic shelf seas is that it is largely ice free throughout the year. This allows continuous monitoring of sea level by space-borne altimeters. In this work we combine satellite altimetry, ocean gravity measurements by GRACE satellites, available hydrography data, and a high-resolution ocean data synthesis product to estimate the steric and mass-related components of sea level in the Barents Sea. We present one of the first observational evidence of the local importance of the mass-related sea level changes. The observed 1–3 month phase lag between the annual cycles of sea level in the Barents Sea and in the Nordic seas (Norwegian, Iceland, Greenland seas) is explained by the annual mass-related changes. The analysis of the barotropic vorticity budget shows that the mass-related sea level variability in the central part of the Barents Sea is determined by the combined effect of wind stress, flow over the varying bottom topography, and dissipation, while the impact of vorticity fluxes is negligible. Overall, the steric sea level has smaller amplitudes and mainly varies on the seasonal time scale. The thermosteric sea level is the main contributor to the steric sea level along the pathways of the Atlantic inflow into the Barents Sea. The relative contribution of the halosteric sea level is dominant in the southeastern, eastern, and northern parts of the Barents Sea, modulated by the seasonal sea ice formation/melt as well as by continental runoff. The variability of the thermosteric sea level in the Barents Sea is mostly driven by variations in the net surface heat flux, whereas the contribution of heat advection becomes as important as the ocean-atmosphere heat exchange at interannual time scales.

Reliability of the steric and mass components of Mediterranean sea level as estimated from hydrographic gridded products

The steric component of Mediterranean sea level as obtained from different hydrographic gridded products is compared for the last decades. The widely used MEDATLAS2, ENACT/ENSEMBLES, ISHIIV6.7, and ISHIIV6.12 databases show large discrepancies, mainly derived from the halosteric component. The validation of the mass component against gravimetry data suggests that ENACT is slightly more accurate than the other data sets. Concerning long‐term trends, the thermosteric component computed down to the bottom for the period 1960–2000 ranges from −0.06 ± 0.12 to 0.09 ± 0.16 mm/yr. Halosteric trends are negative for all products, but the magnitude and spatial patterns provided by the four products are statistically inconsistent among them. This prevents giving consistent figures for the overall steric term and mass term. Conversely, the trend of the freshwater content of the Mediterranean basin can be estimated more accurately, ranging from 1.0 to 1.3 mm/yr for the period 1960–2000.

On the interpretation of the steric and mass components of sea level variability: The case of the Mediterranean basin

A common practice in sea level research is to analyze separately the variability of the steric and mass components of sea level. However, there are conceptual and practical issues that have sometimes been misinterpreted, leading to erroneous and contradictory conclusions on regional sea level variability. The crucial point to be noted is that the steric component does not account for volume changes but does for volume changes per mass unit (i.e., density changes). This indicates that the steric component only represents actual volume changes when the mass of the considered water body remains constant. This is for instance the case of thermal expansions/contractions due to surface heat fluxes. Conversely, salinity changes are often linked to net mass changes and therefore not only affect the steric component but also imply a change in the mass component that must be considered when quantifying the overall sea level budget. In this paper, we clarify the interpretation of the steric and mass components by identifying the main physical processes contributing to each of them, with particular emphasis on the role of salinity. The case of the Mediterranean Sea is examined as a paradigmatic example of a semienclosed basin where sea level components must be carefully interpreted. Because of the significant salinity changes shown by most projections of the Mediterranean climate, a misinterpretation of the steric and mass components can lead to underestimations of ~40 cm in the sea level of the Mediterranean Sea projected for the end of the 21st century.

Structural requirements of organophosphorus insecticides (OPI) to inhibit chicken yolk sac membrane kynurenine formamidase related to OPI teratogenesis

This paper provides new information related to the mechanism of OPI (organophosphorus insecticides) teratogenesis. The COMFA (comparative molecular field analysis) and COMSIA (comparative molecular similarity indices analysis) suggest that the electrostatic and steric fields are the best predictors of OPI structural requirements to inhibit in ovo chicken embryo yolk sac membrane kynurenine formamidase, the proposed target for OPI teratogens. The dominant electrostatic interactions are localized at nitrogen-1, nitrogen-3, nitrogen of 2-amino substituent of the pyrimidinyl of pyrimidinyl phosphorothioates, and the oxygen of crotonamide carbonyl in crotonamide phosphates. Bulkiness of the substituents at carbon-2 and carbon-6 of the pyrimidinyls and/or N-substituents and carbon-3 substituents of crotonamides are the steric structural components that contribute to superiority of those OPI as in ovo inhibitors of kynurenine formamidase.

Coastal sea level changes in Europe from GPS, tide gauge, satellite altimetry and GRACE, 1993–2011

Sea level changes are threatening the human living environments, particularly along the European Coasts with highly dense population. In this paper, coastal sea level changes in western and southern Europe are investigated for the period 1993–2011 using Global Positioning System (GPS), Tide Gauge (TG), Satellite Altimetry (SA), Gravity Recovery and Climate Experiment (GRACE) and geophysical models. The mean secular trend is 2.26±0.52mm/y from satellite altimetry, 2.43±0.61mm/y from TG+GPS and 1.99±0.67mm/y from GRACE mass plus steric components, which have a remarkably good agreement. For the seasonal variations, annual amplitudes of satellite altimetry and TG+GPS results are almost similar, while GRACE Mass+Steric results are a little smaller. The annual phases agree remarkably well for three independent techniques. The annual cycle is mainly driven by the steric contributions, while the annual phases of non-steric (mass component) sea level changes are almost a half year later than the steric sea level changes.

Tide gauge‐based sea level variations since 1950 along the Norwegian and Russian coasts of the Arctic Ocean: Contribution of the steric and mass components

We investigate sea level change and variability in some areas of the Arctic region over the 1950–2009 period. Analysis of 62 long tide gauge records available during the studied period along the Norwegian and Russian coastlines shows that coastal mean sea level (corrected for Glacial Isostatic Adjustment and inverted barometer effects) in these two areas was almost stable until about 1980 but since then displayed a clear increasing trend. Until the mid‐1990s, the mean coastal sea level closely follows the fluctuations of the Arctic Oscillation (AO) index, but after the mid‐to‐late 1990s the co‐fluctuation with the AO disappears. Since 1995, the coastal mean sea level (average of the Norwegian and Russian tide gauge data) presents an increasing trend of ∼4 mm/yr. Using in situ ocean temperature and salinity data down to 700 m from three different databases, we estimated the thermosteric, halosteric and steric (sum of thermosteric and halosteric) sea level since 1970 in the North Atlantic and Nordic Seas region (incomplete data coverage prevented us from analyzing steric data along the Russian coast). We note a strong anti‐correlation between the thermosteric and halosteric components both in terms of spatial trends and regionally averaged time series. The latter show a strong change as of ∼1995 that indicates simultaneous increase in temperature and salinity, a result confirmed by the Empirical Orthogonal Function decomposition over the studied region. Regionally distributed steric data are compared to altimetry‐based sea level over 1993–2009. Spatial trend patterns of observed (altimetry‐based) sea level over 1993–2009 are largely explained by steric patterns, but residual spatial trends suggest that other factors contribute, in particular regional ocean mass changes. Focusing again on Norwegian tide gauges, we then compare observed coastal mean sea level with the steric sea level and the ocean mass component estimated with GRACE space gravimetry data and conclude that the mass component has been increasing since 2003, possibly because of the recent acceleration in land ice melt.

3,3′-Substituted BINAP derivatives containing C-bound substituents: applications in asymmetric hydrogenation reactions

The synthesis and resolution of the first 3,3′-disubstituted BINAP ligands containing C-bonded substituents are described. An ortho-metallation/electrophile capture sequence was used to obtain the key trisubstituted naphthalene intermediate available and this intermediate was successfully converted into the desired ligands. Minor changes in the steric and stereoelectronic components of the 3,3′-substituents on the enantioselectivity and product enantiosense were also assessed in the context of the Rh-catalyzed asymmetric hydrogenation of enamides. A comparison of the absolute stereochemistry of the products derived from 3,3′-disubstituted BINAPs containing C-bonded substituents with their O-bound counterparts indicated that the product enantiosense could be dictated by increased steric bulk due to the 3 and 3′-substituents.

On the interpretation of the steric and mass components of sea level variability. The case of the Mediterranean basin.

On the interpretation of the steric and mass components of sea level variability. The case of the Mediterranean basin.

Thin wetting film from aqueous solution of polyoxyalkylated DETA (Diethylenetriamine) polymeric surfactant

Thin wetting films from aqueous solutions of the polymeric surfactant polyoxyalkylated diethylenetriamine (DETA), have been studied on hydrophilic SiO 2-glass surface. The wetting (receding) contact angles θ r of the solution on the glass surface have been measured, using the sessile drop method. Also the contact angle θ aq of a drop of doubly distilled water on the same glass surface pre-treated with DETA polymeric surfactant solution has been measured. The receding contact angles θ r versus polymeric surfactant concentration C s curves showed a maximum at θ r ≈ 22° in the concentration range of 10 −6–2 × 10 −5 mol dm −3 DETA. The equilibrium thickness h of wetting films from DETA aqueous solution on hydrophilic SiO 2-glass surface, pre-treated with surfactant solution, has been measured using the micro-interferometric method at various concentrations, C s. At very low C s (between 10 −11 and 10 −8 mol dm −3) the h-values are almost constant, then they increase with increasing C s reaching a maximum at 1.5 × 10 −6 mol dm −3, after which they decrease with further increase in C s. Both θ r and h exhibit largest values in the concentration range between 2 × 10 −6 and 2 × 10 −5 mol dm −3 DETA. The analysis of the results obtained shows that the stability of the wetting films from aqueous solutions of DETA is determined by the electrostatic, steric, and hydrophobic components of disjoining pressure, respectively by the adsorption and orientation of the polymeric DETA molecules on the SiO 2-glass surface.

Synergistic application of target structure-based alignment and 3D-QSAR study of protein tyrosine phosphatase 1B (PTP1B) inhibitors

Protein tyrosine phosphatase 1B (PTP1B) has been demonstrated to play a key role in the negative signaling pathway of insulin. Potent and orally active PTP1B inhibitors are considered to be promising pharmacological agents for the treatment of type 2 diabetes and resistance to weight gain. CoMFA studies were performed on a set of PTP1B inhibitors, which are known to bind simultaneously to the active site as well as a sub-binding site. An alignment, based on eight different crystal structure complexes of PTP1B was carried out to study the synergistic application of the alignment on CoMFA. The CoMFA model with statistical parameters \( r_{\text{cv}}^{ 2} = 0. 50 6,\;r_{\text{ncv}}^{ 2} = 0. 9 8 5 \), standard error of estimate 0.12, and F = 244.4 was found to be significant. The steric and electrostatic components presumably play an important role to achieve activity and selectivity in this series of molecules.