The ocean as source or sink of reactive trace-gases

Summary After a brief review on recent experimental work on the uptake resp release of SO₂ and NH₃ by the ocean, new results on the distribution of these reactive trace-gases in the marine atmosphere are presented. In the case of SO₂ there is no doubt that the ocean acts as a sink. In the case of NH₃ new observations and calculations show that under certain conditions the ocean may be a NH₃ source.     

Development of guidelines for ammonia in estuarine and marine water systems

The water quality guideline trigger value for ammonia in estuarine and marine waters has been revised with the addition of 38 new results to the data set of 21 used in earlier guideline derivations. Using species sensitivity distributions, a new trigger value of 460 μg total NH₃-N/L was derived for slightly to moderately disturbed systems (95% protection concentration, PC95), with a value of 160 μg total NH₃-N/L applying to waters of high conservation value (PC99). For sediment pore waters, a guideline trigger value of 3.9 mg total NH₃-N/L, derived from the 80th percentile of background data from Sydney Harbour, is recommended. This value is likely to be exceeded in degraded sediments subject to dredging; however, ocean disposal of such sediments results in rapid decreases in porewater ammonia and a guideline trigger value for dissolved ammonia during disposal of dredged sediments of 1550 μg total NH₃-N/L is proposed.     

Seasonal study of uptake and regeneration of nitrogen on the Scotian Shelf

Nitrate and ammonium uptake and regeneration rates were measured in the euphotic zone of the Scotian Shelf during three cruises (spring, summer and late winter). Nitrate, as a portion of the total nitrogen assimilated (NO₃⁻ uptake/total (NO₃⁻ + NH₄⁻) uptake), decreased with increasing ambient NH₄⁺ concentration and depth. Values integrated through the euphotic zone averaged 30% in the summer, and 27% in the spring, indicating that a large portion of phytoplankton growth was supported by ‘regenerated’ production (NH₄⁺) during those periods. In winter, growth was supported primarily by ‘new’ production since NO₃⁻ uptake represented 67% of the total nitrogen uptake during that period. In all seasons the phytoplankton showed a consistent preference for NH₄⁺ utilization relative to NO₃, despite the abundance of NO₃ at times. In 21 of 23 measurements, NH₄⁺ remineralization exceeded uptake, suggesting that phytoplankton nitrogen requirements were met or exceeded by in situ NH₄⁺ regeneration. Remineralization rates covaried with both productivity (¹⁴C) and NH₄⁺ uptake rates within the euphotic zone. These relationships were most apparent during the summer when nitrogen and carbon fluxes and algal biomass (Chl a) were greatest. The experimental approach used in this study demonstrates a seasonal pattern of NH₄⁺ and NO₃⁻ utilization previously unreported for Scotian Shelf waters.     

不同水生植物对富营养化水体无机氮吸收动力学特征

采用浓度梯度法,研究了鸢尾(Iris louisiana)、狐尾藻(Myriophyllum verticillatum)、茭白(Zizania latifolia)和水芹(Oenanthe clecumbens)对硝态氮(NO₃^--N)和铵态氮(NH₄⁺-N)吸收动力学特征.结果表明:4种水生植物对水体NO₃^--N和NH₄⁺-N吸收可用Michaelis-Menten酶动力学方程描述,随溶液NO₃^--N和NH₄⁺-N浓度增加,植物吸收NO₃^--N和NH₄⁺-N速率增加,当溶液NO₃^--N和NH₄⁺-N浓度接近于2.0 mmol/L时,吸收速率增加趋缓;4种水生植物对NO₃^--N和NH₄⁺-N的V_max值大小为水芹 >茭白 >鸢尾 >狐尾藻,对NO₃^--N的K_m值大小为水芹 >鸢尾=茭白=狐尾藻,对NH₄⁺-N的K_m值大小为水芹 >狐尾藻 >茭白=鸢尾.根据吸收动力学参数(V_max,K_m)判断水芹适宜于净化NO₃^--N和NH₄⁺-N浓度较高的水体,茭白、鸢尾和狐尾藻适合净化NO₃^--N和NH₄⁺-N浓度较低水体;4种水生植物对NO₃^--N、NH₄⁺-N表现出不同的吸收偏好性,鸢尾吸收NO₃^--N的潜力大于吸收NH₄⁺-N的,但对NH₄⁺-N的亲和力大于NO₃^--N,表明能在NO₃^--N浓度较高环境中优先吸收NH₄⁺-N.狐尾藻和水芹对NO₃^--N和NH₄⁺-N能均衡吸收.茭白对NH₄⁺-N具有较高的吸收潜力与亲和力.     

Impact of overlying water velocity on ammonium uptake by benthic biofilms

The effect of the overlying water velocity on ammonium (NH₄⁺) uptake by benthic biofilms was studied in a recirculating laboratory flume (260 cm long, 29 cm wide), packed with 5 cm of silica sand arranged into bedforms. NH₄⁺ uptake was determined as the reduction in NH₄⁺ concentration in the water at average overlying water velocities of 0.8, 2, 4 and 8 cm s^?1. NH₄⁺ uptake was relatively constant under laminar flow conditions but increased when the flow regime became turbulent (>4 cm s^?1). This pattern was observed for two biofilms differing in their total biomass and in the abundance of the ammonia‐oxidizing bacteria, thus indicating that NH₄⁺ uptake was strongly controlled by mass‐transfer processes. The near stoichiometric relationship between the rates of NH₄⁺ uptake and nitrate (NO₃^?) accumulation suggests that aerobic nitrification was the main route for NH₄⁺ uptake. Microelectrode measurements showed a sharp decline of oxygen concentrations and pH values within the biofilms, thus supporting strong nitrification activity within the surficial section of the benthic biofilms. The results of this study highlight the key role of hydrodynamic conditions in regulating NH₄⁺ uptake in the transition from laminar to turbulent flow conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Suspended solids induce increasing microbial ammonium recycling along the river-estuary continuum of the Yangtze River

Many large rivers worldwide are enriched with high levels of suspended solids (SS), which are known to be hotspots of many nitrogen (N) transformation processes (e.g., denitrification, nitrification). However, the influence of SS on microbial ammonium (NH₄⁺) recycling remains unclear. Water column NH₄⁺ regeneration rates (REGs) and potential uptake rates (U_pots) as well as community biological NH₄⁺ demand (CBAD) was measured in the river-estuary continuum of the third longest river in the world—Yangtze River, which has dramatic SS gradients. We found that REGs, U_pots, and CBAD all increased downriver, with higher REGs, U_pots, and CBAD in the estuary than in the river sections. The regeneration and uptake of NH₄⁺ were nearly balanced in the river sections, while the positive CBAD in the estuary indicated obvious NH₄⁺ demand of microbes. Concentrations of SS, which also control the content of chemical oxygen demand and particulate N, were the main factor influencing NH₄⁺ recycling rates and CBAD. SS-induced regenerated NH₄⁺ in the river-estuary continuum of Yangtze River was estimated to be 11.02 × 10⁸ kg N yr⁻¹ and accounted for about 14% of total N inputs, suggesting that regenerated NH₄⁺ is an important N source for microbes and may influence nutrient dynamics in lower coasts. To our knowledge, this is the first study to report NH₄⁺ recycling in Yangtze River with an emphasis on its influencing factors and contribution to N budgets.     

Changes in the patterns of inorganic nitrogen and TN/TP ratio and the associated mechanism of biological regulation in the shallow lakes of the middle and lower reaches of the Yangtze River

The changes of NH₃-N, NO₃-N, NO₂-N and TN/TP were studied during growth and non-growth season in 33 subtropical shallow lakes in the middle and lower reaches of the Yangtze River. There were significant positive correlations among all nutrient concentrations, and the correlations were better in growth season than in non-growth season. When TP>0.1 mgL^?1, NH₃-N increased sharply in non-growth season with increasing TP, and NO₃-N increased in growth season but decreased in non-growth season with TP. These might be attributed to lower dissolved oxygen and low temperature in non-growth season of the hypereutrophic lakes, since nitrification is more sensitive to dissolved oxygen and temperature than antinitrification. When 0.1 mgL^?1>TP>0.035 mgL^?1, TN and all kinds of inorganic nitrogen were lower in growth season than in non-growth season, and phytoplankton might be the vital regulating factor. When TP<0.035 mgL^?1, inorganic nitrogen concentrations were relatively low and NH₃-N, NO₂-N had significant correlations with phytoplankton, indicating that NH₃-N and NO₂-N might be limiting factors to phytoplankton. In addition, TN/TP went down with decline in TP concentration, and TN and inorganic nitrogen concentrations were obviously lower in growth season than in non-growth season, suggesting that decreasing nitrogen (especially NH₃-N and NO₃-N) was an important reason for the decreasing TN/TP in growth season. The ranges of TN/TP were closely related to trophic level in both growth and non-growth seasons, and it is apparent that in the eutrophic and hypertrophic state the TN/TP ratio was obviously lower in growth season than in non-growth season. The changes of the TN/TP ratio were closely correlated with trophic levels, and both declines of TN in the water column and TP release from the sediment were important factors for the decline of the TN/TP ratio in growth season.     

Regional deep sounding at high latitudes of the Northern Hemisphere

Methods were developed for carrying out spherical harmonical analysis of disturbed diurnal variations over a limited territory at high latitudes of the Northern Hemisphere. The ratios ?_n^{|staggered||m} of the external and internal parts of the magnetic potential were evaluated for spherical harmonics 4 ? n ? 12. Different from generally accepted ?_n^{|staggered||m} values for S_q variations (2 ÷ 3), they proved to be considerably higher and attained 10 for n ? 8. This result testifies to a small contribution of induced fields into disturbed diurnal variations observed at high latitudes.A deep sounding was carried out from spherical analysis data. It is shown that the mean distribution of the electrical conductivity at high latitudes σ(r) is the same as the global mean distribution for the whole Earth and that, consequently, it may serve as a reference for local soundings.     

Re-assessing the nitrogen signal in continental margin sediments: New insights from the high northern latitudes

Organic and inorganic nitrogen and their isotopic signatures were studied in continental margin sediments off Spitsbergen. We present evidence that land-derived inorganic nitrogen strongly dilutes the particulate organic signal in coastal and fjord settings and accounts for up to 70% of the total nitrogen content. Spatial heterogeneity in inorganic nitrogen along the coast is less likely to be influenced by clay mineral assemblages or various substrates than by the supply of terrestrial organic matter (TOM) within eroded soil material into selected fjords and onto the shelf. The δ¹⁵N signal of the inorganic nitrogen (δ¹⁵N_inorg) in sediments off Spitsbergen seems to be appropriate to trace TOM supply from various climate- and ecosystem zones and elucidates the dominant transport media of terrigenous sediments to the marine realm. Moreover, we postulate that with the study of sedimentary δ¹⁵N_inorg in the Atlantic–Arctic gateway, climatically induced changes in catchment's vegetations in high northern latitudes may be reconstructed. The δ¹⁵N_org signal is primarily controlled by the availability of nitrate in the dominating ocean current systems and the corresponding degree of utilization of the nitrate pool in the euphotic zone. Not only does this new approach allow for a detailed view into the nitrogen cycle for settings with purely primary-produced organic matter supply, it also provides new insights into both the deposition of marine and terrestrial nitrogen and its ecosystem response to (paleo-) climate changes.     

Nd and Sr isotopic variations of Early Paleozoic oceans

We report¹⁴³Nd/¹⁴⁴Nd and⁸⁷Sr/⁸⁶Sr isotopic data for Lower Paleozoic phosphatic brachiopod and conodont fossils. The data appear to represent the isotopic values of Early Paleozoic seawaters. We show that different paleoceanic water masses can be distinguished on the basis of their ε_Nd signatures. Two sides of what is classically considered one circulating Iapetus Ocean have different ε_Nd signatures from at least the Middle Cambrian until the Late Middle Ordovician. We infer two ocean basins between North America and Baltica separated by an island and/or shoal circulation barrier. Thus, it appears necessary to redefine the area of the Iapetus Ocean. The ε_Nd signature of the redefined smaller Iapetus Ocean ranges from −5 to −9 and the ε_Nd signature of the larger, coeval Panthalassa Ocean, including part of what was formerly called the Iapetus Ocean, ranges from −10 to −20. The first time that the ε_Nd values are identical in these two water masses is coincident with the onset of the Taconic Orogeny of North America. The paleogeographic geometry we infer from this work is consistent with paleogeographic reconstructions having the Baltica continent at very high latitudes in the Early/Middle Ordovician. The ε_Nd and faunal distribution support temperature-controlled conodont faunal provinciality. A rough mean age for exposed continental crust in the Early Paleozoic can be obtained from the average ε_Nd value of Early Paleozoic Oceans. The data suggest that the mean age of the crust as a function of time has remained essentially constant or even decreased during the past 500 Ma, and suggest substantial additions of new crust to the continents through the Phanerozoic.     

Ammonium Ion, Humic Materials, and Trihalomethane Potential in Northeastern Kansas Ground Waters

Glacial buried-valley aquifers serve as primary sources of potable ground water in northeastern Kansas. A long known problem, however, is that a large percentage of well waters in this region exceed the U.S. Environmental Protection Agency (EPA) limits for nitrate (NO⁻₃). A detailed study of the hydrogeology and water quality of the buried valleys has confirmed the nitrate problem and led to a recognition that some well waters with low ( 5 mg/l) NO⁻₃ concentrations have anomalous ( 0.5 mg/l) ammonium ion (NH⁺₄) levels, with an NH⁺₄ range from <0.1 to 4.8 mg/l. The extractable NH⁺₄ concentrations in related glacial sediments range up to approximately 75 mg/kg, and the amounts generally increase from an average of 2 mg/kg in the topsoil downward to bedrock. Migration of brines from subjacent Permian or Pennsylvanian bedrock into the unconsolidated sediments locally may cause desorption of NH⁺₄ and an increase in its levels in the associated ground waters. Numerous test holes drilled in the study area showed a black scum on the fluid and cuttings, which may be from buried humic materials. Recently measured total organic carbon (TOC) contents of the ground waters confirm a significant level in some areas, with a range from 0.1 to 2.4 mg/l as C. Chlorination of water with dissolved organics may lead to production of halogenated compounds. Two public-water-supply well waters contained total trihalomethane (TTHM) levels close to the maximum contaminant level (MCL) of 100 /μg/l in chlorinated samples quenched after one week. The presence of NH⁺₄ inhibits the formation of THMs, but it also can give rise to odor and taste problems in the finished water. The inhibition of THM formation by NH⁺₄ is achieved by reactions which compete with the organics for combination with chlorine. These reactions make maintaining appropriate chlorine residuals difficult and also may lead to production of undesirable side products. Present efforts to evaluate the regional water-quality problems are focused in Nemaha County, Kansas.     

Änderungen der chemischen Eigenschaften des Klärschlammes bei der Methanfermentation

Zusammenfassung Im Verlauf der anaeroben Fermentation des Kl?rschlammes kommt es zu ?nderungen der chemischen Eigenschaften. Die organischen Stoffe werden in wasserl?sliche Verbindungen mit niedrigerem Molekülgewicht, diese dann weiter in Mineralkomponenten CH₄, CO₂, NH₃ und H₂S zersetzt. In der vorliegenden Arbeit sind diese ?nderungen quantitativ ausgewertet, und die Kinetik ihres Verlaufes wurde verfolgt. Die erzielten Ergebnisse sind in Tabellen und Abbildungen zusammengefasst.

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Summary The anaerobic methane fermentation of sewage sludge caused changes of its chemical properties. Organic matter is decomposed into water soluble compounds of minor molecular weight, and subjected to further decomposition into mineral components CH₄, CO₂, NH₃ and H₂S. This paper deals with these changes in a quantitative evaluation, the kinetics of their course being followed as well. The attained results are summarized into tables and graphs.

     

Examining the fate of WWTP effluent nitrogen using δ 15N–NH4 +, δ 15N–NO 3 − and δ 15N of submersed macrophytes

The use of submersed macrophyte tissue δ ¹⁵N to quantify the level of WWTP effluent use in a highly urbanized and agricultural river was evaluated using several methods. Macrophytes, NH₄ ⁺ and NO₃ ^? were collected by canoe along two 10 km reaches of river, upstream and downstream of two major municipal WWTPs over 3 years. NH₄ ⁺ decreased in concentration while δ ¹⁵N–NH₄ ⁺ increased as a function of distance downstream of both WWTPs, changing in one survey from 13 to 31 ‰ over 1 km. This increase is attributed to the combined effects of volatilization, nitrification and uptake. While NO ₃ ^? concentrations increased downstream of the WWTP over one of the survey reaches, δ ¹⁵N–NO ₃ ^? showed no prominent trend with distance at either. Macrophyte tissue δ ¹⁵N increased with distance downstream of both WWTPs, with a slope not significantly different from that of δ ¹⁵N–NH₄ ⁺ suggesting that macrophytes incorporate effluent NH₄ ⁺ as their main N source in those areas. However, mixing models suggest that towards the end of the reach, where source separation is distinct, macrophytes may utilize background NO ₃ ^? . Our study indicates the difficulty of deriving precise estimates of effluent use by macrophytes in a system where the δ ¹⁵N of the effluent changes rapidly. It also illustrates the utility of macrophytes in describing those changes where the effluent is too attenuated to allow for direct isotopic analysis.     

太湖霍甫水丝蚓(Limnodrilus hoffmeisteri) NH4+-N和PO43--P的潜在释放量

为了研究太湖底栖动物优势种类——霍甫水丝蚓(Limnodrilus hoffmeisteri)对于湖泊富营养化的影响,以温度和密度为模拟控制条件,对太湖霍甫水丝蚓进行营养盐释放的室内控制实验,研究温度和密度的变化对霍甫水丝蚓NH_4~+-N和PO_4~(3-)-P释放率的影响,根据霍甫水丝蚓铵态氮(NH_4~+-N)和磷酸盐(PO_4~(3-)-P)释放率与温度的关系方程,结合太湖霍甫水丝蚓2007-2010年的生物量估算其对太湖水体氮磷的潜在贡献.结果表明,随温度升高太湖霍甫水丝蚓NH_4~+-N和PO_4~(3-)-P的释放率均呈现逐渐升高的趋势,而密度变化对霍甫水丝蚓NH_4~+-N和PO_4~(3-)-P释放率的影响均不显著,太湖霍甫水丝蚓NH_4~+-N和PO_4~(3-)-P年平均释放量分别为1925.5和210.0 t,分别可达到全太湖沉积物-水界面NH_4~+-N和PO_4~(3-)-P的年净通量的19.3%和23.3%,表明霍甫水丝蚓的营养盐释放对于湖泊生物地化循环和湖泊富营养化具有显著的影响.     

The distribution of bomb-produced tritium and radiocarbon at GEOSECS station 347 in the eastern North Pacific

Following Roether et al. [1] an upwelling model has been tested to explain the distribution of bomb-produced tritium at the GEOSECS I test station off Baja, California. We have extended their treatment to include the time histories for tritium and for bomb radiocarbon now available for this station. If the CO₂ gas exchange rate at this station is similar to the ocean average value of 20 moles/m² yr, then the upwelling rate must be quite small (<3 m/yr). However, a satisfactory match to the time histories of¹⁴C and of³H is achieved only if an upwelling rate of 40 m/yr is used. In this case, however, a CO₂ exchange rate of 70 moles/m² yr would be required to match the observed surface water¹⁴C/C ratios and a tritium input 4 times the expected value would be needed. The inconsistency in the bomb¹⁴C time history obtained using the accepted CO₂ exchange rate is likely the result of horizontal effects which void the validity of one dimensional modeling in this region of the ocean.     

太湖西北湖区浮游植物和无机、有机氮的时空分布特征

以太湖重度蓝藻水华发生的西北湖区为研究对象,从河口至湖心区设置5个采样点,于2012年10月至2013年10月逐月采集表层水体样品,测定了水温、溶解氧和浮游细菌丰度,并分析了浮游植物群落结构的组成、溶解性无机氮(DIN)和有机氮(DON)浓度以及氮磷比.研究结果表明,太湖西北湖区浮游植物主要由蓝藻、硅藻、绿藻和隐藻组成.可能由于风、浪等混合作用使太湖西北湖区不同采样点之间蓝藻细胞密度没有显著差异.蓝藻生物量在浮游植物中所占比例最高为34%±15%,春季部分点位隐藻生物量高于50%,表明隐藻与蓝藻的相互竞争趋势显著.CCA排序图结果表明,DIN、DON浓度以及总氮∶总磷比(TN∶TP比)是影响西北湖区浮游植物优势属分布的重要环境因子.5个采样点铵态氮(NH_4~+-N)与DIN浓度具有显著差异,与DON浓度没有显著差异.夏季蓝藻水华暴发期间,可能由于蓝藻的吸收利用引起NH_4~+-N和硝态氮(NO_3~--N)浓度迅速降低.此外,由于NH_4~+-N浓度还可能受到沉积物NH_4~+-N释放的影响,因此,蓝藻细胞密度与NO_3~--N的相关系数和显著水平均高于NH_4~+-N.夏季TN∶TP比和DIN∶TP比降至最低,表明该湖区浮游植物,尤其是蓝藻的生长可能受到氮限制.蓝藻细胞密度与DON浓度呈显著负相关,表明在氮限制条件下,DON可能是蓝藻氮素利用的重要补充.     

Untersuchung der CO2-Konzentration im Tropopausenniveau

Zusammenfassung Zwischen 50° bis 85°N Breite wurde die atmosphärische CO₂-Konzentration während mehrerer Messflüge registriert. Diese war oberhalb der Tropopause bis zu 7 ppm (im Mittel etwa 2 ppm) niedriger als in der oberen Troposphäre. Im Jahresmittel entspricht diese CO₂-Konzentrationsdifferenz einem Fluss von etwa 10^–2 g CO₂/cm² Jahr aus der nördlichen Troposphäre in die Stratosphäre. Die Bedeutung dieser CO₂-Konzentrationsunterschiede für den atmosphärischen CO₂-Haushalt sowie für die Strahlungsbilanz im Tropopausenniveau kann erst nach Vorlage weiterer, über das ganze Jahr verteilter Messdaten erfolgen.

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Summary CO₂-concentration was measured during several flights in northern latitudes (50°–85°). Above Tropopause CO₂-concentration was up to 7 ppm (as a mean some 2 ppm) smaller than in upper troposphere. As a mean this difference in CO₂-concentration cm² year conforms to a CO₂-flux of some 10^–2 g CO₂/cm² year from northern troposphere into stratosphere. The importance of these CO₂-differences for atmospheric CO₂-system and for radiation balance in tropopause-height may be considered as soon as more CO₂-concentration data for the whole year are available.

     

城市污染河道沉积物可提取态氮的提取方式比较

以城市污染河道——南京仙林大学城九乡河表层沉积物为研究对象,探讨沉积物常用提取剂(1 mol/L KCl、2 mol/L KCl、4 mol/L KCl和0.01 mol/L CaCl2)在不同液土比(5∶1、10∶1、50∶1和100∶1)条件下,对城市污染河道沉积物可提取态氮(NH4+-N、NO3--N)测定的影响.结果表明:KCl的提取效果要优于CaCl2,二者NH4+-N提取量分别为312.17～479.23、177.52～339.31 mg/kg,NO3--N提取量分别为4.49～21.56、4.25～8.53 mg/kg;可提取态氮提取量随液土比增高而增大,其中1 mol/L KCl组,液土比100∶1时NH4+-N和NO3--N提取量分别比液土比5∶1时增加41.97%和187.08%;NH4+-N提取量随提取剂浓度增高而增大,NO3--N随提取剂浓度增高而降低;采用1 mol/L KCl提取剂、液土比100∶1的组合联合提取城市污染河道沉积物中的NH4+-N、NO3--N,提取效果较好.     

High resolution Thex stratigraphy of sediments from high-latitude areas (Norwegian Sea, Fram Strait)

We present data on the average sedimentation rates (ranging from 1.6 cm/kyr to 3 cm/kyr) for the last 300.000 years based on δ¹⁸O analyses of foraminifera in a core from the Norwegian Sea and ²³⁰Th_ex measurements in cores from the Norwegian Sea and the Fram Strait (Arctic Ocean). Furthermore, we relate ²³⁰Th_ex variations downcore to the various oxygen isotope stages. This correlation is tentatively interpreted as being a result of the paleoceanographic and paleoclimatic control of bioproductivity. It is shown that based on the average sedimentation rates and characteristic ²³⁰Th_ex variations carbonate-poor sediment cores from northern latitudes can be correlated.     

Variability of the Gravity-to-Height Ratio Due to Surface Loads

We study the ratio between the gravity variation and vertical displacement on the surface of a self-gravitating earth model when a surface load is applied. We adopt a theoretical and numerical point of view, excluding any observations. First, we investigate the spectral behavior of the ratio of the harmonic components of the gravity variation and vertical displacement. Then, we model the gravity-to-height ratio for different surface loads (continental hydrology, atmospheric pressure, ocean tides) using outputs of global numerical models in order to relate the predicted spatial values to theoretical mean values deduced from the spectral domain. For locations inside loaded areas, the ratio is highly variable because of the Newtonian attraction of the local masses and depends on the size of the load. For the hydrological loading (soil moisture and snow), the mean ratio over the continents is  ?0.87 μGal mm^?1, but increases with decreasing size of the river basins. For the atmospheric loading, assuming an inverted-barometer response of the ocean, the ratio is positive, with larger values for high latitudes (0.49 μGal mm^?1)—particularly on the coasts—than for lower latitudes (0.30 μGal mm^?1). The ratio, however, is much less variable outside the loaded areas: in desert areas such as the Sahara and Arabia, its mean value is  ?0.28 μGal mm^?1. For the ocean tidal loading, we find a mean ratio of  ?0.26 μGal mm^?1 over the continents for the diurnal tidal waves. Both results are close to the theoretical mean value of  ?0.26 μGal mm^?1 combining elastic and remote attraction contributions.