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Lithospheric weakening mechanisms in non-volcanic segments of active continental rifts remain poorly understood, raising important questions about the geodynamic processes that drive magma-poor rifting. Here, we investigate the crustal and uppermost mantle structure beneath the non-volcanic Albertine-Rhino Graben (ARG) and the adjoining volcanic Edward-George Rift (EGR), East Africa. The ARG exhibits anomalous focusing of intra-rift faulting typically associated with magma-rich, early-stage rifts. Through field observations of rift structures, combined with 3D inversions and 2D forward modeling of gravity data, we investigate the potential controls on intra-rift tectonic strain in a setting with little to no magmatism. Field ground-truthing in the southern ARG reveals prominent rift-axial basement-rooted faulting that post-dates the establishment of border faults. Gravity inversion results show low-density anomalies extending from the surface to about 50 km depth beneath both the EGR and southern ARG, with the strongest anomalies under the ARG at around 15 km. 2D gravity modeling suggests that the lower crust and uppermost mantle are both thinned and less dense beneath these rift segments. In the EGR, crustal thinning and low-density anomalies align with low P-wave velocity zones, suggesting the presence of melt. Given the similar degree of crustal thinning and de-densification in the southern ARG, we infer that trapped lower-crustal melts may also exist beneath the rift, potentially contributing to the early focusing of intra-rift strain. We propose that in non-volcanic rifts, deep, unexposed (‘blind’) melts may play a key role in mechanical weakening of the lithosphere, enabling continued tectonic extension even in the absence of significant surface volcanism. 

Abstract Dissolved inorganic carbon (DIC) and its stable carbon isotope (δ¹³C‐DIC) are valuable parameters for studying the aquatic carbon cycle and quantifying ocean anthropogenic carbon accumulation rates. However, the potential of this coupled pair is underexploited as only 15% or less of cruise samples have been analyzed forδ¹³C‐DIC because the traditional isotope analysis is labor‐intensive and restricted to onshore laboratories. Here, we improved the analytical precision and reported the protocol of an automated, efficient, and high‐precision method for ship‐based DIC andδ¹³C‐DIC analysis based on cavity ring‐down spectroscopy (CRDS). We also introduced a set of stable in‐house standards to ensure accurate and consistent DIC andδ¹³C‐DIC measurements, especially on prolonged cruises. With this method, we analyzed over 1600 discrete seawater samples over a 40‐d cruise along the North American eastern ocean margin in summer 2022, representing the first effort to collect a large dataset ofδ¹³C‐DIC onboard of any oceanographic expedition. We evaluated the method's uncertainty, which was 1.2 μmol kg⁻¹for the DIC concentration and 0.03‰ for theδ¹³C‐DIC value (1σ). An interlaboratory comparison of onboard DIC concentration analysis revealed an average offset of 2.0 ± 3.8 μmol kg⁻¹between CRDS and the coulometry‐based results. The cross‐validation ofδ¹³C‐DIC in the deep‐ocean data exhibited a mean difference of only −0.03‰ ± 0.07‰, emphasizing the consistency with historical data. Potential applications in aquatic biogeochemistry are discussed. 

This is the TDEFNODE block inversion software used in the study "Constraining the Kinematics of the Victoria Microplate and the Northern Western Branch of the East African Rift System; The software is installed and run on a Linux terminal. All the files needed to run TDEFNODE for this study, along with their outputs, are included in TDEFNODE_block_inversion_modeling_NWB_Kwagalakwe_2025_v2.tar.gz, which is a revised version of TDEFNODE_block_inversion_modeling_NWB_Kwagalakwe_2025.tar.gz (Version v1). 

Tide and salinity data collected at minute intervals over multiple semidiurnal tides were used to investigate the source of water (e.g., seawater, river, groundwater and rain) and their relative timing in mixing at the mouth of a river, a tidal creek at mid-estuary and a tidal creek at the shoreline at the head of a tropical mangrove estuary. Our objectives were to document the temporal changes in tide induced water level changes and salinity at each location and to use the relationship between salinity and water level to elucidate the sources of water and the timing of different sources of water in the hydrologic mixing processes. The data trends in tide vs. salinity (T-S) plots for the river mouth revealed mixing with seawater during rising tides and freshwater diluted seawater (brackish) drainage from the mangrove forest during ebb tides. In the mangrove creek at mid-estuary, the data trends in the T-S plots for rising tides initially showed constant salinity, followed by sharp rises in salinity to peak tide caused by seawater intrusion. The salinity decreased precipitously at the start of tidal ebbing due to influx of freshwater (rain) diluted brackish water from the mangrove forest. The data trends in the T-S plots for the tidal creek at the shoreline located at the estuary head showed constant salinity which decreased only near peak rising tide because of river dilution. During tidal ebbing, the salinity further decreased from groundwater influx before increasing to background salinity, which stayed constant to low tide. Establishing T-S patterns for multiple locations in mangrove estuaries over sub-tidal to tidal scales define the expected salinity variations in seawater-freshwater mixing which can be used to (1) establish baseline hydrologic and salinity (hydrochemical) conditions for temporal and spatial assessments and (2) serve to guide short to long-term sampling regimes for scientific studies and estuarine ecosystem management. 

Rapid urbanization and insufficient waste management are threatening the environmentally and culturally vital Wouri Estuary. Solutions are needed to save these and other mangroves around the world.