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The Gamburtsev Subglacial Mountains (GSM) in central East Antarctica are completely buried beneath the East Antarctic Ice Sheet. The GSM are known to be underlain by anomalously thick crust (~50–60 km) and ~200 km thick Precambrian lithosphere, but their crustal-scale geology remains less well- studied. Little is known about the 3D heterogeneity in crustal architecture beneath the GSM, and how this may relate to larger-scale tectonic processes responsible for Gondwana amalgamation.Here, we use airborne gravity and aeromagnetic anomalies to explore the crustal architecture of the GSM in unprecedented detail. The gravity and magnetic images show three distinct geophysical domains, and a dense lower crustal root is modelled beneath the northern and central domains. We propose that the root may reflect magmatic underplating, associated with Pan-African age back-arc basin formation and inversion, followed by the collision of Australo-Antarctica and Indo-Antarctica. The high frequency linear magnetic patterns parallel to the Gamburtsev Suture zone, suggest that the upper crustal architecture is dominated by thrust and strike-slip faults, formed within a large-scale transpressional fault system.We calculated a 2D gravity and magnetic model along a passive seismic profile to investigate the crustal architecture of the GSM, with the aid of depth to magnetic source estimates. By combining the crustal model with geological constraints, we propose a new evolutionary model suggesting that the crust of the northern and central GSM domains formed part of a cryptic accretionary orogen, of proposed Pan-African (~650-550 Ma?) age. The inferred accretionary stage was followed by continental collision (~540-520 Ma?) along the Gamburtsev suture, which is linked here to Gondwana amalgamation.

A series of sub-parallel linear glacial scours are identified on the crest of the Baoshi Seamount in the Northwind Abyssal Plain by compiling new multibeam data acquired during the 9th Chinese Arctic Research Expedition (CHINARE-Arc9) in 2018 and previously published data. The new data reveal scours that developed at water depths of 850–1 030 m with an orientation of about 75°/255°. The maximum water depth occurs in the southernmost scour and is deeper than that from previous investigations, which showed a maximum scouring depth of about 900 m on the seamount. The topographic and geomorphological characteristics suggest that these scours resulted from erosion by the ice shelf extending from the Chukchi margin and/or Laurentide Ice Sheet that grounded on the crest of the seamount and moved in a NE-SW direction. Other possibilities of their genesis include armadas of large icebergs/multi-keel icebergs calved from the Chukchi Shelf or the Laurentide Ice Sheet. The new data provide new constraints for assessing the extent and volume of the ice sheet in the Chukchi area during glacial maxima.

With the launch of altimetry satellites with different observation frequencies and different survey missions, it is necessary to integrate multi-satellites altimeter data to establish a new global marine gravity anomaly model. Based on Ka-band sea surface heights (SSHs) from SARAL/AltiKA and Ku-band SSHs from other satellites (including HY-2A) in geodetic missions and exact repeat missions, the global marine gravity anomaly model of SDUST2021GRA on a 1′ × 1′ grid is derived. Gridded deflections of vertical (DOV) are determined from along-track geoid gradients by the least squares collocation method, in which the noise variances of along-track geoid gradients are obtained by the iteration method for Ka-band geodetic mission and by the SSH crossover discrepancies for other altimetry missions. SDUST2021GRA is recovered from the gridded DOVs by the inverse Vening Meinesz formula, and analyzed by comparing with the recognized marine gravity anomaly models of DTU17 and SIO V30.1. Finally, the accuracy of SDUST2021GRA, DTU17, and SIO V30.1 is assessed by preprocessed shipborne gravity anomalies. In conclusion, the differences between SDUST2021GRA and recognized models are small, indicating the reliability of SDUST2021GRA. The differences are mainly concentrated between −5 and 5 mGal, which accounts for more than 95 % of the total number. Assessed by shipborne gravity, the accuracy of SDUST2021GRA is 2.37 mGal globally, which is higher than that of DTU17 (2.74 mGal) and SIO V30.1 (2.69 mGal). The precision advantage of SDUST2021GRA is mainly concentrated in offshore areas. HY-2A-measured altimeter data have an important role on gravity anomaly recovery in areas with complex coastlines and many islands. SDUST2021GRA is concluded to reach an international advanced level for the altimeter-derived marine gravity model, especially in the offshore area. The SDUST2021GRA model data are freely available at https://doi.org/10.5281/zenodo.6668159 (Zhu et al., 2022).

This article focuses on the determination and the validation of a new global mean sea surface (MSS) model which is named as SDUST2020 (Shandong University of Science and Technology 2020) with a grid of 1′×1′. This new model is established with 19-year moving average method and merges multi-satellite altimetry data over 27-year (from January 1993 to December 2019). The data of HY-2A, Jason-3 and Sentinel-3A are first ingested in the SDUST2020 MSS, but not in any other global MSS model, such as CLS15 and DTU18 MSS models. Validations, including the comparison with CLS15 and DTU18 MSS models, the comparison with GPS-leveled tide gauges and the comparison with altimeter data, are performed to estimate the quality of the SDUST2020 MSS model, and all the results show that the SDUST2020 MSS model is accurate and reliable. The SDUST2020 MSS dataset are freely available at the site (data DOI: https://doi.org/10.5281/zenodo.6555990, Yuan et al., 2022).

Marine gravimeter has been proved to be the primary technique to efficiently obtain middle-to-short wavelength signals of the earth’s gravity field in geodesy, geodynamics and marine sciences research. In recent years, some prototypes of inertial platform and strapdown marine gravimeters have been developed, where the inertial platform gravimeter systems include CHZ-II and ZL11, and strapdown gravimeter systems include SAG-2M and SGA-WZ. In order to validate the performance of these marine gravimeter prototypes, a synchronous test with the widely used gravimeters GT-2M and LCR arranged on the same vessel was carried out in the north of South China Sea. All the data are processed according to the survey standard flow, and the performance is estimated by analyzing the errors of the repeat lines and the crossover points under the same environment. The compared results show that all the six gravimeters can meet the precision requirement of marine gravity survey. Meanwhile, the precision results of the improved gravimeters can get close to the precision of gravimeter GT-2M, higher than the precision gravimeter LCR.

In this study, intermediate frequency induction heat treatment (IFIHT) is applied to cold-rolled ribbed steel rebar with low-cost Q235 as raw material, and a combination of excellent ductility and high strength has been achieved, which surmounts the bottleneck of cold-rolled rebar. To reveal the mechanisms behind the excellent mechanical properties, multi-scale characterizations are carried out to study the microstructure and the micro-strain. The results suggest that IFIHT after cold deformation not only facilitates partial recrystallization and dislocation annihilation, but also restricts grain coarsening. High proportion of high angle grain boundaries improve the dislocation accumulation ability, the defect-free recrystallized grains and the sub-grains with a high degree of dislocation annihilation facilitate dislocations slipping, therefore good ductility is achieved. In addition, the high angle grain boundaries formed through recrystallization and dislocations left after partial recrystallization ensures high strength. The enhancement of dislocation storage capacity of grains leads to the improvement of work hardening ability, which reflects in the form of high uniform elongation in the stress-strain curves.

Ground-based GNSS (Global Navigation Satellite System) reference stations lack the capacity to provide data for ocean regions with sufficient spatial-temporal resolution, limiting the detailed study of the equatorial ionization anomaly (EIA). Thus, this study collected kinematic multi-GNSS data on the ionospheric Total Electron Content (TEC) during two research cruises across the equator in the Western Pacific Ocean in 2014 (31 October–8 November) and 2015 (29 March–6 April). The purpose of the study was to use sufficient spatial–temporal resolution data to conduct a detailed analysis of the diurnal variation of the equatorial ionization anomaly in different seasons. The two-year data collected were used to draw the following conclusions. During the test in 2014, the EIA phenomenon in the Northern and Southern Hemispheres was relatively obvious. The maximum values occurred at local time (LT) 15:00 (~136TECu) and LT22:00 (~107TECu) in the Northern Hemisphere and at LT14:00 (100TECu) and LT22:00 (80TECu) in the Southern Hemisphere. During the test in 2015, the EIA in the Southern Hemisphere reached its maximum level at LT14:00 (~115TECu) and LT20:00 (~85TECu). However, the EIA phenomenon in the Northern Hemisphere was weakened, and a maximum value occurred only at LT 15:00 (~85TECu). The intensity contrast was reversed. The EIA phenomenon manifests a strong hemisphere asymmetry in this region.

SUMMARY HY-2A is China's first satellite altimeter mission, launched in Aug. 2011. Its geodetic mission (GM) started from 2016 March 30 till present, collecting sea surface heights for about five 168-d cycles. To test how the HY-2A altimeter performs in marine gravity derivation, we use the least-squares collocation method to determine marine gravity anomalies on 1′ × 1′ grids around the South China Sea (covering 0°–30°N, 105°E–125°E) from the HY-2A/GM-measured geoid gradients. We assess the qualities of the HY-2A/GM-derived gravity over different depths and areas using the bias and tilt-adjusted ship-borne gravity anomalies from the U.S. National Centers for Environmental Information (NCEI) and the Second Institute of Oceanography, Ministry of Natural Resources (MNR) of P. R. China. The RMS difference between the HY-2A/GM-derived and the NCEI ship-borne gravity is 5.91 mGal, and is 5.33 mGal when replacing the HY-2A value from the Scripps Institution of Oceanography (SIO) V23.1 value. The RMS difference between the HY-2A/GM-derived and the MNR ship-borne gravity is 2.90 mGal, and is 2.76 mGal when replacing the HY-2A value from the SIO V23.1 value. The RMS difference between the HY-2A and SIO V23.1 value is 3.57 mGal in open sea areas at least 20 km far away from the coast. In general, the difference between the HY-2A/GM-derived gravity and ship-borne gravity decreases with decreasing gravity field roughness and increasing depth. HY-2A results in the lowest gravity accuracy in areas with islands or reefs. Our assessment result suggests that HY-2A can compete with other Ku-band altimeter missions in marine gravity derivation.

The South China Sea (SCS) is situated at the junction of Eurasian, Indo-Australian, and Philippine sea plates. Its stress state provides significant information about the regional tectonic structure associated with interaction among the three plates. The stress field of the SCS is composed of horizontal and vertical stress fields. We calculate the vertically averaged deviatoric stress field using horizontal gradients of gravitational potential energy obtained by high-resolution sea-surface height data (SSH) from satellite Haiyang-2A. The vertical tectonic stress field is computed based on the Bouguer gravity anomaly derived from SSH and topographic data.The vertically averaged deviatoric stress field is consistent with the GPS velocity field, the focal mechanism, and the mantle flow stress field of the South China Sea. Moreover, it also indicates the Red River-Ailaoshan Fault zone on the west of the SCS and the Manila subduction on the east. The vertical tectonic stress field removing the influence of sediment indicates upward stress of the lithosphere in the SCS ocean basin. The stress field model therefore provides a powerful tool for understanding regional tectonic activities around the SCS.

Shipborne gravity can be used to refine altimeter-derived gravity whose accuracy is low in shallow waters and areas with complex submarine topography. As altimeter-derived gravity only within a small radius around the shipborne data can be corrected by traditional methods, a new method based on multi-layer perceptron (MLP) neural network is proposed to refine the altimeter-derived gravity. Input variables of MLP include the positional information at observation points and geophysical information (from our own South China Sea gravity anomaly model (SCSGA) V1.0 and bathymetry model ETOPO1) at grid points around observation points. Output variables of MLP are the refined residual gravity anomalies at observation points. Training shipborne data are classified into four cases to train four MLP models, which are used to predict the refined gravity anomaly model SCSGA V1.1. Then all of the training shipborne data are used for training an MLP model to predict the refined gravity anomaly model SCSGA V1.2. Assessed by testing shipborne data, the accuracy of SCSGA V1.2 is 0.14 mGal higher than that of SCSGA V1.0, and similar to that of SCSGA V1.1. Compared with the original gravity anomaly model (SCSGA V1.0), the accuracy of the refined gravity anomaly model (SCSGA V1.2) by MLP is improved by 4.4% in areas where the training data are concentrated, and also improved by 2.2% in other areas. Therefore, the method of MLP can be used to refine the altimeter-derived gravity model by shipborne gravity, overcoming the problem of limited correction radius for traditional methods.

Deriving marine gravity is one of the important applications of satellite altimetry in earth science. The quality of marine gravity derived from each altimeter data always is limited by the range measurement on the certain ground track spacing. We assess the performance of Jason-2/geodetic-mission (GM) altimeter in deriving marine gravity by the improved range from waveform retracking. The singular value decomposition was applied to denoise waveforms, and the waveform derivative retracking was employed to improve the sea surface heights (SSHs). Finally, Jason-2/GM-derived gravity anomalies on 1′ × 1′ grids were determined by the least-squares collocation method based on the resample 5 Hz SSHs around the South China Sea (SCS). Assessed by ship-borne data from different institutions, the accuracy of Jason-2/GM-derived gravity is consistent with that of the V27.1 and DTU13 models. Moreover, with the application of waveform derivative retracking, the accuracy of gravity anomalies has improved from 6.6 mGal before retracking to 5.5 mGal after retracking over the open ocean, and from 8.9 to 7.4 mGal over the coastal area. It is better than the results obtained by traditional retracking methods, including off-center of gravity (OCOG), 5-β, threshold, Ice-1, and maximum likelihood estimator-4 (MLE4). Furthermore, evaluated by V27.1 and DTU13, the result shows root mean square (RMS) difference of 2.0 mGal and 3.0 mGal, respectively. Therefore, the waveform derivative retracking is an effective method for altimeter data, and the accuracy of derived gravity is an improvement by retracked SSHs.

High-precision and high-resolution gravity fields can be derived from multi-source satellite altimeter data. A gravity anomaly model around the South China Sea (SCSGA) V1.0 on a 1′ × 1′ grid is established from sea surface heights (SSHs) of several geodetic missions (GMs) and exact repeat missions. Gridded deflections of the vertical are first calculated from SSHs by the least squares collocation (LSC) method and then used to derive gravity anomalies by the inverse Vening Meinesz formula. In gravity derivation processing, we establish an approximate relationship among the precision of altimetric gravity, precision of geoid gradients, and density of geoid gradients (the average number of geoid gradients per 1′ × 1′ region). The weights of geoid gradients from the Ka-band altimeter for the LSC are innovatively determined by an iterative method. Finally, SCSGA V1.0 is assessed by ship-borne gravity anomalies and marine gravity models. The performance of GMs in gravity derivation is evaluated. In general, the altimetric gravity precision in regions with many islands and reefs increases more obviously than those in other regions when the geoid gradient density increases. The standard deviation of SCSGA V1.0 is 2.78 mGal, which is slightly better than those of four recognized global marine gravity models around the SCS. CryoSat-2 is the most important dataset for SCSGA V1.0. Ka-band SARAL/AltiKa plays a major role in gravity derivation, and the contribution of Haiyang-2A is greater than those of other Ku-band satellites, except CryoSat-2. SCSGA V1.0 is concluded to reach an international advanced level for marine gravity from altimeter data around the SCS.

The Pliocene saw multiple advances and retreats of the ice-sheet margin in East Antarctica. Amery Ice Shelf (AIS) is the largest ice shelf in East Antarctica and also the largest single ice stream draining from the Antarctic Plateau. It buttresses the Lambert Glacier drainage system, and accounts for 14% of the outflow from the East Antarctic Ice Sheet (EAIS). However, evidence for the state of the EAIS during the Pliocene is sparse and difficult to interpret unequivocally. Marine geological-geophysical data collected from the continental shelf in Prydz Bay, Antarctica, including seismic-reflection data, bathymetry, core records from ODP drilling and gravity coring sites, reveal a complex paleo-subglacial drainage system linked to an offshore depositional regime dominated on a trough mouth fan (TMF). Detailed seismic stratigraphic and facies analysis reveals the glacial evolution of Prydz Bay shelf and its TMF, including several glacial expansions across the shelf indicated by erosional surfaces and stratal bodies with chaotic acoustic character. The geometry of seismic sequences suggests that the glaciers and their associated TMF developed after a major episode of shelf and slope erosion during the Pliocene-Pleistocene. The shelf in Prydz Bay is dominated by a wide, south-north trending glacially-eroded trough (the Prydz Channel: -500~-1000 m depth) and shallower banks (-500~0 m depth). Well preserved grounding zone wedges areevidenced by prograding foreset deposits. Evidence for erosion of the wedges and/or lineations that extend across their upper surfaces indifferent water depths ranging from 200 m to 800 m imply their formation during multiple glacial stages or cycles. Stacked erosional surfaces reveal major cross-shelf glacial expansions and the development of deep channel systems (up to -500 m depth) associated with extensive subglacial meltwater in Prydz Bay. These glacial related features provide good constraints for reconstructing the stability of the Pliocene EAIS.

The North Palawan Canyon is a large, previously undescribed submarine canyon that incises the continental shelf and slope of the southern South China Sea. Using multibeam bathymetric data and two-d...

The equivalent magnetization (EM) and mantle Bouguer anomaly (MBA) were calculated along the ultraslow-spreading Mohns Ridge axis in the Norwegian-Greenland Sea. The magnetic anomaly and the associated EM were compared with the bathymetry, MBA, seismically determined crustal structure and geochemical data at both the inter-segment scale (>60 km) and the intra-segment scale (20–60 km). At the inter-segment scale, the magnetic highs at the segment centers are independent of the MBA. Of the 13 segments, 9 with magnetic anomalies >700 nT coincide with axial volcanic ridges identified from multibeam bathymetry maps, which suggests that the magnetic highs at the segment centers may be more associated with the extrusive lavas rather than the amount of magma supply. With few exceptions, the magnetic anomaly lows associated with MBA highs at the segment ends increase from south to north. This trend might be explained by thickened extrusive basalts and/or more serpentinized peridotites at the segment ends in the north. At the intra-segment scale, the most prominent features are the decreases in the magnetic anomalies and associated EMs from the segment centers to the ends. The intra-segment magnetic anomalies have positive and negative correlations with the bathymetry and MBA, respectively. The magnetic signal modeled by the seismically determined layer 2A with an assumed constant magnetization is remarkably consistent with the observed magnetic anomaly, which strongly suggests that the thickness of the extrusive basalts dominates the magnetic structure in each segment along the Mohns Ridge. In general, the thickness of the extrusive basalts dominates the magnetic structure along the Mohns Ridge, whereas the contributions from serpentinized peridotites may be significant at the segment ends and may produce long-wavelength magnetic variations. The magnetic data can be used as an indicator of the thickness of the extrusive basalts within segments along the ultraslow-spreading Mohns Ridge.

The global ionospheric model based on the reference stations of the Global Navigation Satellite System (GNSS) of the International GNSS Services is presently the most commonly used products of the global ionosphere. It is very important to comprehensively analyze and evaluate the accuracy and reliability of the model for the reasonable use of this kind of ionospheric product. In terms of receiver station deployment, this work is different from the traditional performance evaluation of the global ionosphere model based on observation data of ground-based static reference stations. The preliminary evaluation and analysis of the the global ionospheric model was conducted with the dynamic observation data across different latitudes over the southern oceans. The validation results showed that the accuracy of the global ionospheric model over the southern oceans is about 5 TECu, which deviates from the measured ionospheric TEC by about −0.6 TECu.

International audience

Repeat multibeam bathymetric surveys conducted in 2004, 2005 and 2018 show that seven slope-confined canyons on the continental slope of the Pearl River Mouth Basin, South China Sea, were dominated by large volume, widespread erosion. Erosion volumes were up to 3.4 times greater than deposition volumes. Erosion-dominated areas of the canyons are up to 2.3 times greater than areas dominated by deposition. Average rates of erosion (ranging from 0.7 to 0.8 m/yr) were greater than average rates of deposition (ranging from 0.5 to 0.8 m/yr). In plan view, the erosion-dominated zones exhibit two characteristic shapes: (1) linear, found mainly in upper canyon reaches, distributed predominantly along canyon axes and at the base of eastern canyon walls, and; (2) blocky, found mainly in lower canyon reaches, widely distributed along the steep canyon walls and on lower-canyon interfluves. The deposition-dominated zones are scattered along canyon floors and walls. Seismic reflection data show lateral shifts of canyon fill deposits through time, indicative of longer-term eastward canyon migration. The linear erosion-dominated zones may be attributed to erosive turbidity currents triggered by energetic internal solitary waves shoaling on the shelf. The eastward canyon shifts were likely induced by rapid near-bed eastward currents generated mainly by westward propagating powerful internal solitary waves of depression. The widespread erosion in the deeper canyon areas and interfluves is likely a consequence of slope instabilities associated with the presence of gas hydrates. This study indicates that active sedimentary processes can occur in slope-confined canyons even during sea level highstands. Local, site-specific oceanographic and geological features (e.g., internal solitary waves, gas hydrates) can significantly increase sedimentary activity in and around submarine canyons.

New analysis of the geophysical data of the ultraslow-spreading Mohns Ridge and its off-axis structure reveals a distinctive asymmetric structure. We calculate residual bathymetry (RB) and residual mantle Bouguer gravity anomaly (RMBA) and decompose the anomalies into symmetric and asymmetric components between the ridge conjugates. The western flank of the Mohns Ridge at crustal age of ~50–15 Ma is characterized by a broad zone of elevated RB and more negative RMBA, which we term the Vesteris Plateau (VP). The VP anomaly has a surface area of ~1.12 × 105 km2 and an excess crust volume of ~2.33 × 105 km3, making it a significant anomaly comparable to other anomalies such as the Bermuda Rise. Extending north of the Kolbeinsey Ridge for more than 500 km, the VP lies above an anomalous upper mantle region of low shear-wave seismic velocity, indicating that the VP might represent the northernmost reach of the Iceland-Jan Mayen mantle anomaly. In addition, the western ridge flank of the Mohns Ridge at crustal age of 6–0 Ma is associated with higher RB and more positive RMBA relative to the eastern conjugate, indicating tectonic uplift and associated exposure of lower crust and upper mantle near the ridge axis.

Overflows through oceanic gateways govern the exchange of water masses in the world's ocean basins. These exchanges also involve energy, salinity, nutrients, and carbon. As such, the physical features that control overflows can exert a strong influence on regional and global climate. Here, we present the first description of sedimentary processes generated by the overflow of Pacific Deep Water (OPDW). This mass flows southward at approximately 2000–3450 m water depth within the Luzon Trough (gateway) from the Pacific Ocean into the South China Sea. OPDW can be divided into: a) a lower, denser layer (including an associated weak counter-current), which has generated a large contourite depositional system (CDS-1) that includes large erosional (channel and moat), depositional (mounded and plastered drift), and mixed (terrace) contourite features along the trough bottom and walls, and b) an upper mixing layer, which has not generated any significant depositional or erosional contourite features. Where OPDW does not reach the seafloor, it is underlain by bottom water that circulates more sluggishly but has generated a second contourite depositional system (CDS-2) made of a large sheet-like drift. The OPDW flow has generally enhanced since the middle to late Miocene, except in the shallower northernmost corridor. In the deeper main trough, reductions in width and depth of the gateway by Taiwan orogenic events have likely accelerated the overflow. The latest significant enhancening may promote widespread development of contourite depositional systems along the South China Sea's lower continental slope and adjacent deeper areas. This work highlights the importance of gateway-confined overflows in controlling the morphology and sedimentary evolution of adjacent deep marine sedimentary systems. A clear understanding of overflow processes and their products is essential for decoding tectonic control in oceanographic or paleoceanographic processes.

In this paper, we consider a stochastic nonautonomous rabies epidemic model. By using Khasminskii’s theory of periodic solutions and constructing a suitable stochastic Lyapunov function, we show that the stochastic nonautonomous epidemic model admits at least one nontrivial positive T -periodic solution under certain condition.

The strapdown gravimetry system uses the combination of an Inertial Measuring Unit (IMU) and a Global Navigation Satellite System (GNSS) to measure the Earth&rsquo, s gravity field. Due to limited accuracies of IMU and GNSS, early strapdown gravimetry systems were more often used in airborne surveys, but less used in marine surveys. We developed a strapdown inertial navigation system (SINS), the Sea-Air Gravimeter-2Marine (SAG-2M), using novel IMU components, whose accuracy was further improved with the application of Precise Point Positioning (PPP) and enhanced algorithm, making it possible to be used in marine gravity survey. The testing results of the SAG-2M were compared to those of the Lacoste and Romberg S-129 gravimeter on the same ship in the South China Sea basin. The cruise lasted for 50 days, during which 134 effective gravity profiles were measured, resulting in 174 crossover points. The results showed that, for the SAG-2M, the root mean square (RMS) crossover points were 1.35 mGal before difference adjustment and 0.69 mGal after difference adjustment, for the S-129 gravimeter, they were 5.62 mGal and 0.95 mGal, correspondingly. In calm sea conditions, the results of the two systems were relatively consistent at all wavelengths. However, in rough sea conditions, since the SAG-2M was not affected by the cross-coupling effect, its data demonstrated less high-frequency jump. A physical platform adopted in SAG-2M can further make the transition data effective when the ship is turning around. Therefore, SAG-2M was able to improve the proportion of valid data and the efficiency of data post-processing for measurements taken during the cruise. The testing results indicate that in terms of accuracy and efficiency in the marine gravity survey, SAG-2M is better than S-129. In addition, as the miniaturization and precision of inertial components are developing continuously, SAG-2M also shows great potential in miniaturization.

The measurement of atmospheric water vapor (WV) content and variability is important for meteorological and climatological research. A technique for the remote sensing of atmospheric WV content using ground-based Global Positioning System (GPS) has become available, which can routinely achieve accuracies for integrated WV content of 1–2 kg/m2. Some experimental work has shown that the accuracy of WV measurements from a moving platform is comparable to that of (static) land-based receivers. Extending this technique into the marine environment on a moving platform would be greatly beneficial for many aspects of meteorological research, such as the calibration of satellite data, investigation of the air-sea interface, as well as forecasting and climatological studies. In this study, kinematic precise point positioning has been developed to investigate WV in the Arctic Ocean (80°–87°N) and annual variations are obtained for 2008 and 2012 that are identical to those related to the enhanced greenhouse effect.

Spreading rate is a primary factor of mantle melting and tectonic behavior of the global mid-ocean ridges. The spreading rate of the Gakkel ridge decreases gradually from west to east. However, the Gakkel ridge can be divided into four thick-and-thin zones with varying crustal thicknesses along ridge axis. This phenomenon indicates that mantle melting of the Gakkel ridge is not a simple function of spreading rate. Mantle temperature, water content, mantle composition, and other factors are important in crustal accretion processes. Based on gravity-derived crustal thickness and wet melting model, we estimate that the mantle potential temperatures of the four zones are 1 270, 1 220, 1 280, and 1 280°C (assuming that mantle water content equals to global average value), with corresponding mantle water contents of 210, 0, 340, and 280 mg/kg (assuming that mantle potential temperature is 1 260°C), respectivly. The western thinned crust zone is best modeled with low mantle temperature, whereas the other zones are mainly controlled by the enhanced conduction caused by the slower spreading rate. Along the Gakkel ridge, the crustal thickness is consistent with rock samples types. Predominated serpentinized peridotite and basalt are found in the area with crustal thickness 〈1.5 km and 〉2.5 km, respectively. The rock samples are including from basalt to peridotite in the area with crustal thickness between 1.5 and 2.5 km. Based on this consistency, the traditional magmatic accretion zone accounted for only 44% and amagmatic accretion accounted for 29% of the Gakkel ridge. The amagmatic accretion is a significant characteristic of the ultra-slow spreading ridge.

Luo, X.; Gao, J.; Jin, X.; Li, J., and Chu, F., 2015. A primary research on marine magnetic disturbance correction method using uncombined precise point positioning. Marine magnetic survey is an important mean of geophysical exploration. The magnetic disturbance magnitude, the start and end time, and perfecting magnetic disturbance model are important for magnetic survey. In this paper, on the basis of that dual-frequency GNSS is able to get the ionospheric total electron content, reflect the nature of the magnetic disturbance characteristics, etc. the study of magnetic disturbance correction in marine magnetism measurements using dual-frequency GNSS is carried out. Through quality controlled by the dual-frequency GNSS phase observations, ionospheric total electron content solved by static and dynamic at slant direction. Comparing the solving with geomagnetic observatories and marine magnetic measurements, the solution showed that there is relatively strong correlation between ionospheric total e...

Luo, X.; Gao, J.; Jin, X.; Li, J., and Chu, F., 2015. The latest application to determine tide height in a large-scale sea using shipborne GPS based on precise point positioning and EGM2008. GPS data dedicated to tidal level are usually processed using differential techniques. Unfortunately, the precision of resulting kinematic positions is baseline-length dependent. So, high precision tidal level measurements using differential GPS techniques are limited to coasts, lakes, and rivers. Recent improvements in GPS satellite products (orbits, clocks, and phase biases) make Precise Point Positioning (PPP) technique reach cm-level in three dimensions. At same time, EGM2008 determine the sea level also reached centimeter level. So Precise Point Positioning technique with EGM2008 opens up tidal level measurements without Tidal Gauges. This paper recalls the concept of PPP technique and discusses the precision of GPS shipborne positioning. Tidal data of large-scale sea are calculated from PPP and EGM2008....