Mass Transport Estimates Research Articles

Experimental and simulation study of CO2 breakthrough curves in a fixed-bed adsorption process

This paper focuses on the laboratory experiments of low-temperature adsorption of CO2 at elevated pressure and on the validation of our mathematical model with the data obtained. The numerical approach uses fitting of adsorption isotherm parameters and sensitivity analysis of parameters influencing the breakthrough curve shape and onset time. We first evaluate the results of breakthrough experiments for zeolite 13X. Then, we use the results obtained to design a dynamic mathematical model to predict the breakthrough curve profile. Experimental results show that zeolite 13X possesses high adsorption capacities (over 10 % of its weight at adsorption temperatures of 293 K and below), as expected. The mathematical simulation was accurate at predicting the breakthrough onset time; however, this prediction accuracy declined with the outlet CO2 concentration exceeding 75 %, which is discussed. The sensitivity analysis indicated that the choice of different estimates of mass transport and bed porosity, as well as the choice of numerical scheme, can lead to a more accurate prediction, but the same set of parameters is not suitable for all process conditions.

Spatial distribution, vertical profiles and transport of legacy and emerging per- and polyfluoroalkyl substances in the Indian Ocean

The contamination status and transport of per- and polyfluoroalkyl substances (PFASs) in the seawater of the Indian Ocean (IO) and an adjacent subregion of the Northwest Pacific Ocean (NWPO) were investigated. Eight legacy PFASs were widely distributed in the surface seawater, and perfluoroheptanoic acid (PFHpA) and perfluorooctanoic acid (PFOA) were the two predominant PFASs. ΣPFAS concentration decreased in the following order: NWPO>Joining area of Asia and Indian-Pacific Oceans (JAIPO)>Northeast Indian Ocean>Southwest Indian Ocean. Hexafluoropropylene oxide-dimer acid, a replacement surfactant for PFOA was extensively detected in the IO (~34.8 pg/L) for the first time, showing an early sign of emerging PFAS spread in global open oceans. Eight depth profiles across the JAIPO (down to 5433 m depth) revealed a “surface-enrichment” and “depth-depletion” pattern for PFASs in the water column, and two noticeable fluctuations were mainly located at depths of 150–200 and 200–500 m. Physical processes, including eddy diffusion, and the origin and trajectory of water mass were crucial factors for structuring PFAS vertical profiles. Mass transport estimates revealed a remarkable PFOA contribution through the JAIPO to IO carried by the Indonesian Throughflow, and a nonnegligible PFHpA contribution from Antarctic Immediate Water to deep water of the JAIPO driven by thermohaline circulation.

The impact of error covariance matrix structure of GRACE’s gravity solution on the mass flux estimates of Greenland ice sheet

The error variance-covariance matrices of the monthly GRACE gravity field models are usually well-structured (e.g., order-leading) to contain the error information of the monthly gravity field models, and they are important information to further improve the accuracy of the estimated mass transportation by a post-processing scheme. Intensive studies have been performed to understand the impact of different approximations of the full error variance-covariance matrix on the mass estimates obtained with the conventional GRACE-post processing methods (e.g., the de-striping method). In this study, based on the variants of the mascon approach which treat monthly GRACE solutions as input, we consider four different structures to the error variance-covariance matrix, (i) full matrix, (ii) block diagonal matrix, (iii) diagonal matrix, and (iv) identity matrix, and examine their impact on the mass transport estimates in Greenland. Using both synthetic and real data, we analyze the results at four temporal scales: (i) the long-term decadal scale, (ii) the inter-annual scale, (iii) the seasonal scale, and (iv) the monthly scale. Based on the synthetic study, we find that for the recovery of the long-term trend, the application of the diagonal structure obtains the best estimates. This is caused by the amplification of the model error in the mascon approach when considering the full and block diagonal structures of error variance-covariance matrix, not due to any imperfection of them. Therefore, we emphasize that one should be aware of mascon model deficiency in the mascon approach. Furthermore, the best inter-annual, seasonal and monthly mass estimates are derived by considering the block diagonal and full structures. This is caused by the behavior of the bias and the unique parameterization error in the case of different structures. A similar finding is also presented in the real data case. Finally, our analysis denotes the necessity of releasing the block diagonal structure together with the official monthly gravity field model for the GRACE Follow-On mission, instead of releasing only the diagonal structure as done for the GRACE mission.

Transport of Legacy Perfluoroalkyl Substances and the Replacement Compound HFPO-DA through the Atlantic Gateway to the Arctic Ocean-Is the Arctic a Sink or a Source?

The spatial distribution of 29 per- and polyfluoroalkyl substances (PFASs) in seawater was investigated along a sampling transect from Europe to the Arctic and two transects within Fram Strait, located between Greenland and Svalbard, in the summer of 2018. Hexafluoropropylene oxide-dimer acid (HFPO-DA), a replacement compound for perfluorooctanoic acid (PFOA), was detected in Arctic seawater for the first time. This provides evidence for its long-range transport to remote areas. The total PFAS concentration was significantly enriched in the cold, low-salinity surface water exiting the Arctic compared to warmer, higher-salinity water from the North Atlantic entering the Arctic (260 ± 20 pg/L versus 190 ± 10 pg/L). The higher ratio of perfluoroheptanoic acid (PFHpA) to perfluorononanoic acid (PFNA) in outflowing water from the Arctic suggests a higher contribution of atmospheric sources compared to ocean circulation. An east-west cross section of the Fram Strait, which included seven depth profiles, revealed higher PFAS concentrations in the surface water layer than in intermediate waters and a negligible intrusion into deep waters (>1000 m). Mass transport estimates indicated a net inflow of PFASs with ≥8 perfluorinated carbons via the boundary currents and a net outflow of shorter-chain homologues. We hypothesize that this reflects higher contributions from atmospheric sources to the Arctic outflow and a higher retention of the long-chain compounds in melting snow and ice.

Meridional mass transport of bottom water in the South Atlantic

Estimates of the meridional mass transport of Antarctic Bottom Water, calculated using the coupled ocean- atmosphere model called “Earth System Model” in conjunction with the original data assimilation method are presented. We used the data of the latitudinal CTD sections of temperature and salinity of the WOCE international experiment in 1991-1995 for assimilation. Estimates of the current velocities of Antarctic Bottom Water with the assimilation of observational data are given. We used the author’s data assimilation method, which was previously referred as the generalized Kalman Filter (GKF) method. In the particular case it coincides with the classical Kalman method (EnKF). We also analyze the estimates of the mass transport by the standard dynamic scheme. It is shown that model calculations with data assimilation are qualitatively the same and are quantitatively close to the estimates of geostrophic flow transport based on the dynamic method.

Meridional Mass Transport of Bottom Water in the South Atlantic

Estimates of the meridional mass transport of Antarctic Bottom Water, calculated using the coupled ocean-atmosphere Earth System Model on the basis of the original data assimilation method are presented. For assimilation, we use data of the latitudinal CTD sections of temperature and salinity of the WOCE international experiment in 1991–1995. Estimates of the current velocities of Antarctic Bottom Water with the assimilation of observational data are given. We used the author’s data-assimilation method, which was previously referred to as the generalized Kalman Filter (GKF) method. In this particular case, it coincides with the classical Kalman method (EnKF). We also present the estimates of mass transport based on a standard geostrophic dynamic scheme. It is shown that model calculations with data assimilation are qualitatively the same and are quantitatively close to the estimates of the geostrophic flow transport based on the dynamic method.

Combination Analysis of Future Polar-Type Gravity Mission and GRACE Follow-On

Thanks to the unprecedented success of Gravity Recovery and Climate Experiment (GRACE), its successive mission GRACE Follow-On (GFO) has been in orbit since May 2018 to continue measuring the Earth’s mass transport. In order to possibly enhance GFO in terms of mass transport estimates, four orbit configurations of future polar-type gravity mission (FPG) (with the same payload accuracy and orbit parameters as GRACE, but differing in orbit inclination) are investigated by full-scale simulations in both standalone and jointly with GFO. The results demonstrate that the retrograde orbit modes used in FPG are generally superior to prograde in terms of gravity field estimation in the case of a joint GFO configuration. Considering the FPG’s independent capability, the orbit configurations with 89- and 91-degree inclinations (namely FPG-89 and FPG-91) are further analyzed by joint GFO monthly gravity field models over the period of one-year. Our analyses show that the FPG-91 basically outperforms the FPG-89 in mass change estimates, especially at the medium- and low-latitude regions. Compared to GFO & FPG-89, about 22% noise reduction over the ocean area and 17% over land areas are achieved by the GFO & FPG-91 combined model. Therefore, the FPG-91 is worthy to be recommended for the further orbit design of FPGs.

Current reversal and associated variability within the Corsica Channel: The 2004 case study

Flow reversals within the Corsica Channel, a strait East of Corsica, are investigated with a realistic, high-resolution (∼1.5km) numerical setup simulating the year 2004. The simulations compare well with available water mass transport estimates resulting in an annual mean of 0.49±0.49Sv. Similarly, the model agrees with hydrographic observations in the area, and current velocity measurements showing a flow in the Corsica Channel predominantly directed northward from the Tyrrhenian to the Ligurian Sea. On top of the well-documented Corsica Channel seasonal variability, a higher-frequency variability can be found throughout the year but more frequently during the summer season. This temporal variability, highest close to the western flank of the Channel, is of the order of a few days to a week and associated with reversals of the currents. We find that this variability is ascribed to periodic intrusions of the West Corsica Current on the Eastern side of the Island. Moreover, our findings suggest the importance, of a so-far neglected, across-channel variability of the meridional velocity throughout the entire 2004. This result potentially questions the single-mooring assumption that has always been at the center of the observational scheme. This assumption holds while looking at low-frequency/seasonal variability but fails when focusing on higher-frequency variability.

Seasonal crustal vertical deformation induced by environmental mass loading in mainland China derived from GPS, GRACE and surface loading models

Obvious seasonal crustal vertical deformation largely related to mass redistribution on the Earth’s surface can be captured by Gravity Recovery and Climate Experiment (GRACE), simulated by surface loading models (SLMs), and recorded by continuous Global Positioning System (GPS). Vertical deformation time series at 224 GPS stations with more than four-year continuous observations are compared with time series obtained by GRACE and SLMs with the aim of investigating the consistency of the seasonal crustal vertical deformation obtained by different techniques in mainland China. Results of these techniques show obvious seasonal vertical deformation with high consistency at almost all stations. The GPS-derived seasonal vertical deformation can be explained, to some content, by the environmental mass redistribution effect represented by GRACE and SLMs. Though the mean weighted root mean square reduction is 34% after removing the environmental mass loading from the monthly GPS height time series (up to 47% for the mean annual signals), systematic signals are still evident in the residual time series. The systematic residuals are probably attributed to GPS related errors, such as draconitic errors, while the leakage errors in the GRACE data processing and unmodeled components in land water storage should be considered in some regions. Additionally, the obvious seasonal residual perturbations in Southwest China may be related to the leakage errors in the GRACE data processing and large uncertainty in the land water storage in SLMs, indicating that GPS observations may provide more realistic mass transport estimates in Southwest China.

Comparison of different mass transport calculation methods for wind erosion quantification purposes

AbstractQuantitative estimation of the material transported by the wind under field conditions is essential for the study and control of wind erosion. A critical step of this calculation is the integration of the curve that relates the variation of the amount of the material carried by the wind with height. Several mathematical procedures have been proposed for this calculation, but results are scarce and controversial. One objective of this study was to assess the efficiency of three mathematical models (a rational, an exponential, and a simplified Gaussian function) for the calculation of the mass transport, as compared to the linear spline interpolation. Another objective of this study was to compare the mass transport calculated from field measurements obtained from a minimum of three discrete sampling heights with measurements of nine sampling heights. With this purpose, wind erosion was measured under low surface roughness conditions on an Entic Haplustoll during 25 events. The rational function was found to be mathematically limited for the estimation of wind eroded sediment mass flux. The simplified Gaussian model did not fit to the vertical mass flux profile data. Linear spline interpolation generally produced higher mass transport estimates than the exponential equation, and it proved to be a very flexible and robust method. Using different sampling arrangements and different mass flux models can produce differences of more than 45% in mass transport estimates, even under similar field conditions. Under the conditions of this study, at least three points between the soil surface and 1·5 m high, including one point as closest as possible to the surface, should be sampled in order to obtain accurate mass transport estimates. Additionally, the linear spline interpolation and the non‐linear regression using an exponential model, proved to be mathematically reliable methods for calculating the mass transport. Copyright © 2010 John Wiley & Sons, Ltd.

Evaluation of Different Methods to Assess Model Projections of the Future Evolution of the Atlantic Meridional Overturning Circulation

Abstract Climate models predict a gradual weakening of the North Atlantic meridional overturning circulation (MOC) during the twenty-first century due to increasing levels of greenhouse gas concentrations in the atmosphere. Using an ensemble of 16 different coupled climate models performed for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC), the evolution of the MOC during the twentieth and twenty-first centuries is analyzed by combining model simulations for the IPCC scenarios Twentieth-Century Climate in Coupled Models (20C3M) and Special Report on Emission Scenarios, A1B (SRESA1B). Earlier findings are confirmed that even for the same forcing scenario the model response is spread over a large range. However, no model predicts abrupt changes or a total collapse of the MOC. To reduce the uncertainty of the projections, different weighting procedures are applied to obtain “best estimates” of the future MOC evolution, considering the skill of each model to represent present day hydrographic fields of temperature, salinity, and pycnocline depth as well as observation-based mass transport estimates. Using different methods of weighting the various models together, all produce estimates that the MOC will weaken by 25%–30% from present day values by the year 2100; however, absolute values of the MOC and the degree of reduction differ among the weighting methods.

Ocean carbon cycling in the Indian Ocean: 2. Estimates of net community production

The spatiotemporal variability of ocean carbon cycling and air‐sea CO2 exchange in the Indian Ocean was examined using inorganic carbon data collected as part of the World Ocean Circulation Experiment (WOCE) cruises in 1995. Several carbon mass balance approaches were used to estimate rates of net community production (NCP) in the Indian Ocean. Carbon transports into and out of the Indian Ocean were derived using mass transport estimates of Robbins and Toole (1997) and Schmitz (1996), and transoceanic hydrographic and TCO2 sections at 32°S and across the Indonesian Throughflow. The derived NCP rates of 749 ± 227 to 1572 ± 180 Tg C yr−1 (0.75–1.57 Pg C yr−1) estimated by carbon mass balance were similar to new production rates (1100–1800 Tg C yr−1) determined for the Indian Ocean by a variety of other methods (Louanchi and Najjar, 2000; Gnanadesikan et al., 2002). Changes in carbon inventories of the surface layer were also used to evaluate the spatiotemporal patterns of NCP. Significant NCP occurred in all regions during the Northeast Monsoon and Spring Intermonsoon periods. During the Southwest Monsoon and Fall Intermonsoon periods, the trophic status appears to shift from net autotrophy to net heterotrophy, particularly in the Arabian Sea, Bay of Bengal, and 10°N to 10°S zones.

Responses in dissolved nutrients and epilithon abundance to spawning salmon in southeast Alaska streams

Spawning Pacific salmon (Oncorhynchus spp.) historically transported massive quantities of marine-derived nutrients (MDN) into nutrient-poor streams of the Pacific Northwest. In southeast Alaska, we measured the effects of MDN on streamwater chemistry and epilithon standing stock (1) through time during two consecutive years in one stream, Fish Creek; (2) over space in six salmon streams; and (3) in a controlled mesocosm experiment. In Fish Creek during strong salmon runs in 2000 and 2001, streamwater concentrations of ammonium (NH ) increased 101 4 fold and soluble reactive phosphorus (SRP) increased by 4- to 7-fold in the presence of salmon. NH and SRP also 1 4 increased with distance downstream in the salmon reach, likely related to a ‘carcass-loading’ effect. In contrast, nitrate (NO ) and dissolved organic carbon concentrations varied only with discharge. In 2000, epilithon chlorophyll 2 3 a increased by 20-fold during the salmon run, whereas no significant change was observed in 2001. Over space, the multistream survey revealed consistent increases in NH and SRP, but no pattern in epilithon response to the 1 4 salmon run. In the mesocosm experiment, NH , SRP, and epilithon standing stock all increased in the presence of 1 4 salmon carcasses in artificial streams. Overall, salmon clearly increased the concentrations of important dissolved nutrients in southeast Alaska streams. Responses in epilithon were more variable, however, suggesting that multiple environmental factors including light and disturbance likely regulate epilithon growth in salmon streams. Nutrient mass transport estimates revealed that a substantial amount of MDN (46%‐60% depending on element) is exported directly back to the estuarine environment, suggesting that salmon represent a key marine‐freshwater coupling in nutrient cycling.

A 1998–1992 comparison of inorganic carbon and its transport across 24.5°N in the Atlantic

Abstract In January and February 1998, when an unprecedented fourth repetition of the zonal hydrographic transect at 24.5°N in the Atlantic was undertaken, carbon measurements were obtained for the second time in less than a decade. The field of total carbon along this section is compared to that provided by 1992 cruise which followed a similar path (albeit in a different season). Consistent with the increase in atmospheric carbon levels, an increase in anthropogenic carbon concentrations of 8±3 μmol kg −1 was found in the surface layers. Using an inverse analysis to determine estimates of absolute velocity, the flux of inorganic carbon across 24.5° is estimated to be −0.74±0.91 and −1.31±0.99 PgC yr −1 southward in 1998 and 1992, respectively. Estimates of total inorganic carbon flux depend strongly upon the estimated mass transport, particularly of the Deep Western Boundary Current. The 1998 estimate reduces the large regional divergence in the meridional carbon transport suggested by previous studies and brings into question the idea that the tropical Atlantic constantly outgasses carbon, while the subpolar Atlantic sequesters it. Uncertainty in the carbon transports themselves, dominated by the uncertainty in the total mass transport estimates, are a hindrance to determining the “true” picture. The flux of anthropogenic carbon (C★ANTH) across the two transects is estimated as northward at 0.20±0.08 and 0.17±0.06 PgC yr −1 for the 1998 and 1992 sections, respectively. The net transport of C★ANTH across 24.5°N is strongly affected by the difference in concentrations between the northward flowing shallow Florida Current and the mass balancing, interior return flow. The net northward transport of C★ANTH is opposite the net flow of total carbon and suggests, as has been found by others, that the pre-industrial southward transport of carbon within the Atlantic was stronger than it is today. Combining these flux results with estimates of atmospheric and riverine inorganic carbon input, it is determined that today's oceanic carbon system differs from the pre-industrial system in that today there is an uptake of anthropogenic carbon to the south that is advected northward and stored within the North Atlantic basin.

Eolian transport, saline lake basins, and groundwater solutes

Eolian processes associated with saline lakes are shown to be important in determining solute concentration in groundwater in arid and semiarid areas. Steady state mass balance analyses of chloride in the groundwater at Double Lakes, a saline lake basin in the southern High Plains of Texas, United States, suggest that approximately 4.5 × 105 kg of chloride is removed from the relatively small (4.7 km2) basin floor each year by deflation. This mass enters the groundwater down the wind gradient from the lake, degrading the water quality. The estimates of mass transport were independently determined by evaluation of solutes in the unsaturated zone and by solute mass balance calculations of groundwater flux. Transport of salts from the lake was confirmed over a short term (2 years) by strategically placed dust collectors. Results consistent with those at Double Lake were obtained from dune surfaces collected upwind and downwind from a sabkha near the city of Abu Dhabi in the United Arab Emirates. The eolian transport process provides an explanation of the degraded groundwater quality associated with the 30–40 saline lake basins on the southern half of the southern High Plains of Texas and New Mexico and in many other arid and semiarid areas.

SELECTING A METHOD FOR ESTIMATING SUBSTANCE LOADINGS1

ABSTRACT: Four simple methods for estimating mass transport are evaluated in terms of the assumptions made about the properties of the data set being analyzed. The basic difference between the four methods considered are their assumptions regarding the manner in which concentration is distributed and the relationship between concentration and discharge. The most precise estimates of mass transport into and out of Schwatka Lake, Yukon Territory, were obtained from the model which assumes that concentration is log normally distributed and independent of discharge.

Near-surface flow of volcanic gases on Io

Significant near-surface flow of gas several hundred kilometers from Pele (Plume 1) on Io is indicated by a series of bright, elongate albedo markings. Particles produced at small, local vents are apparently carried as much as 70 km farther “downwind” from Pele. The gas densities and velocities necessary to suspend 0.1 to 10 μm particles at such a distance imply mass flow rates of 10 7 to 10 9 g/sec. Such flow rates are consistent with other estimates of mass transport by the plume. The large flow rates so far from the source allow an estimate of the rate of resurfacing of Io by lava flows and pyroclastics that is independent of estimates based on meteorite flux or on the amount of solids carried within the plumes themselves.

Water movements, sediment transport and deposition, Western Port, Victoria

Western Port is a tidal embayment, and the characteristics of oscillatory tidal currents, overall net and small-scale circulation patterns, and aspects of the mode, frequency and mass transport of sediment are presented. The results of the studies reported in this volume are both corroborative and complementary, and their integration has resulted in a much better understanding of the bay than could otherwise have been obtained. Consideration of dynamic process, sedimentation patterns and morphology has allowed the distinction of four “systems” within the bay: 1. (1) High-energy channel/bank system (Western Entrance to just beyond the Confluence Zone), characterised by strong tidal currents, varying degrees of surface wave activity, and a sandy substrate. Middle Bank represents the largest individual sand body in Western Port and is associated with intense sediment movement. Sand transported from Middle Bank through the Confluence Zone supplies and maintains the sandy deposits and beaches in the Lower North Arm and East Arm. Seismic evidence coupled with estimates of mass transport of sand suggest that during the Holocene, 10 3 to 10 4 g cm −1 yr −1 have been transported from Middle Bank to Cowes Bank in order to produce the extensive sedimentary complex in that region. 2. (2) Ebb/flood differentiated segments with contrasting intertidal sediments (lower North Arm, Corinella Segment), characterised by clearly differentiated flood- and ebb-dominant zones, sandy and muddy intertidal sediment deposition. 3. (3) Subtidal, partly enclosed mud-deposition basin (Rhyll Segment), characterised as a shallow, subtidal, depositional basin collecting fine sediments. A central clay-size zone is flanked by coarser sediments. Circulation is weak and sediment transport is minimal. 4. (4) Extensive intertidal flat systems with minor channels (Embayment Head), characterised by a web of minor channels, and luxuriant seagrass meadows except in the regions of the Bunyip and Lang Lang Rivers. Local flood- and ebb-dominant transport paths are defined by sandy deposits of reworked or autochthonous Pleistocene sands.