M. Bayani Cardenas’s research while affiliated with University of Texas at Austin and other places

Submarine groundwater discharge (SGD) is a nutrient source to coastal waters. However, most SGD estimates are restricted to a local scale and hardly distinguish contributions from fresh (FSGD) and recirculated (RSGD) SGD. Here, we compiled data on radium/radon of groundwater (n ~ 2000) and seawater (n ~ 10,000) samples along ~18,000 km of China’s coastal seas to resolve large scale FSGD and RSGD and their associated nutrient loads. Nearshore-scale FSGD ( ~ 3.56 × 10⁸ m³ d⁻¹) was only 2% of the total SGD but comparable to RSGD in terms of nutrient loads. Despite large uncertainties quantified via Monte Carlo simulations, SGD was a dominant contributor to China’s coastal nutrient budgets, with dissolved inorganic nitrogen, phosphorus and silicate fluxes of ~395, 2.9, and 581 Gmol a⁻¹, respectively. Total SGD accounted for 19–54% of nutrient inputs, exceeding inputs from atmospheric deposition and rivers. Overall, SGD helps sustaining primary production along one of the most human-impacted marginal seas on Earth.

The editorial team of AGU Advances is grateful for the excellent contributions of our peer reviewers. We rely on their expertise to ensure that the manuscripts submitted to the journal undergo a rigorous, fair, and timely review. Remarkably, during 2024, the journal benefitted from the dedication from 273 reviewers, contributing a total of 338 reviews. These reviewers represented 24 countries. These reviewers provided insights of tremendous and generous value, and they assisted our authors in strengthening the rigor, quality, and presentation of their scholarship. Peer reviewing provides a natural way to engage in continuous learning and professional development. The majority of our reviewers are geoscientists, although we also have interdisciplinary contributions as the scope of Advances covers the extended domain of geosciences, intersecting with economics, communication and computational science, and the social sciences at large. Authors benefit greatly from reviewers' comments and suggestions: already more than 10 years ago, a study reported that most authors (90%) believe that peer review improved the last paper they published (Mulligan et al., 2013, https://doi.org/10.1002/asi.22798). Although the research and publishing arena is rapidly changing, peer review is considered the optimal standard for evaluating and selecting quality scientific manuscripts for publication, and therefore is highly deserving of our appreciation. We thank all of our peer reviewers for their selfless service and dedication to the scientific community. Your continuing support to the authors and editorial team of AGU Advances is deeply appreciated.

Rationale Suites of trace elements are routinely used in speleothems as proxies to understand periods of past climate change. Laser ablation techniques are regularly implemented to acquire high resolution (50‐μm) trace element concentrations in carbonate archives for paleoclimatology. There exists limited research investigating Laser Ablation‐Inductively Coupled Plasma‐Mass Spectrometry (LA‐ICP‐MS) protocols using speleothem samples. This study investigates the difference between using matrix (carbonate) and nonmatrix (silicate) matched reference materials and the utility of 1‐point versus multiple point calibration curves. Methods Following an extensive review of published literature on speleothem LA‐ICP‐MS analyses, we conducted two laser ablation experimental runs 8 months apart on a 2.7‐cm section of a natural speleothem using matrix and nonmatrix matched reference materials. We used a 193‐nm wavelength Analyte G2 laser attached to a X‐Series‐2 ICP‐MS, a silicate reference material, and three carbonate reference materials. Next, we calculated concentrations using a 1‐point calibration curve, a 2‐point calibration curve, and a 3‐point calibration curve. Results The analysis of matrix and nonmatrix matched reference materials demonstrates that the trends of trace elements/Ca are minimally impacted by the matrix material of the standard. We also show that 2‐ and 3‐point calibration curves bracket the range of sample concentrations compared to a 1‐point (silicate) calibration curve. The calculated cave‐air temperatures using Mg/Ca concentrations fall within error of each other regardless of the calibration curve approach applied. Conclusions Our experiments provide a proof of concept on the conventional setup of standards during LA‐ICP‐MS speleothem analysis. We suggest the use of at minimum a 2‐point (silicate plus carbonate or carbonates) calibration curve that crucially bracket the range of sample concentrations rather than relying on a 1‐point silicate standard that does not bracket the sample concentration. Finally, our results have implications for both speleothem studies that use LA‐ICP‐MS analytical techniques and additional carbonate archives.

Coastal ecosystems play a major role in marine carbon budgets, but substantial uncertainties remain in the sources and fluxes of coastal carbon dioxide (CO 2 ). Here, we assess when, where, and how submarine groundwater discharge (SGD) releases CO 2 to shallow coastal ecosystems. Time-series observations of dissolved CO 2 and radon ( ²²² Rn, a natural groundwater tracer) across 40 coastal systems from 14 countries revealed large SGD-derived CO 2 fluxes. The mean groundwater partial pressure of CO 2 was 35 times higher than surface seawater. The mean SGD-derived CO 2 flux was 148 ± 226 millimoles per square meter per day (mmol m ⁻² day ⁻¹ ), resulting in a mean water-air CO 2 flux of 80 ± 133 mmol m ⁻² day ⁻¹ . Tidal rather than diel cycles drove CO 2 enrichment in most ecosystems. Tidally driven SGD was the primary CO 2 source in mangroves, salt marshes, tidal flats, estuaries, and canals. Overall, we expand current knowledge of marine carbon cycles by demonstrating SGD as an important source of CO 2 that requires inclusion in coastal carbon budgets.

The hydrology of thawing permafrost affects the fate of the vast amount of permafrost carbon due to its controls on waterlogging, redox status, and transport. However, regional mapping of soil water storage in the soil layer that experiences the annual freeze-thaw cycle above permafrost, known as the active layer, remains a formidable challenge over remote arctic regions. This study shows that Interferometric Synthetic Aperture Radar (InSAR) observations can be used to estimate the amount of soil water originating from the active layer seasonal thaw. Our ALOS InSAR results, validated by in situ observations, show that the thickness of the soil water that experiences the annual freeze-thaw cycle ranges from 0 to 75 cm in a 60-by-100-km area near the Toolik Field Station on the North Slope of Alaska. Notably, the spatial distribution of the soil water correlates with surface topography and land vegetation cover types. We found that pixel-mismatching of the topographic map and radar images is the primary error source in the Toolik ALOS InSAR data. The amount of pixel misregistration, the local slope, and the InSAR perpendicular baseline influence the observed errors in InSAR Line-Of-Sight (LOS) distance measurements non-linearly. For most of the study area with a percent slope of less than 5%, the LOS error from pixel misregistration is less than 1 cm, translating to less than 14 cm of error in the soil water estimates.

Fresh submarine groundwater discharge (FSGD) can deliver significant fluxes of water and solutes from land to sea. In the Arctic, which accounts for ∼34% of coastlines globally, direct observations and knowledge of FSGD are scarce. Through integration of observations and process‐based models, we found that regardless of ice‐bonded permafrost depth at the shore, summer SGD flow dynamics along portions of the Beaufort Sea coast of Alaska are similar to those in lower latitudes. Calculated summer FSGD fluxes in the Arctic are generally higher relative to low latitudes. The FSGD organic carbon and nitrogen fluxes are likely larger than summer riverine input. The FSGD also has very high CO2 making it a potentially significant source of inorganic carbon. Thus, the biogeochemistry of Arctic coastal waters is potentially influenced by groundwater inputs during summer. These water and solute fluxes will likely increase as coastal permafrost across the Arctic thaws.

Plain Language Summary Submarine groundwater discharge (SGD) is the flow of groundwater from land to sea. SGD in volcanic areas can have high temperatures, high concentrations of heavy metals, high CO2, and can be acidic, all of which impact sensitive coastal ecosystems. Quantifying volcanic SGD is important yet challenging because the flow can be diffuse and broadly distributed. At a volcanic area in the Philippines, the unique combination of satellite and drone‐based thermal infrared remote sensing, ground‐based fiber‐optic distributed temperature sensing, and in situ thermal profiling in coastal sediment identified the multi‐scale nature of SGD and quantified flow rates. We identified SGD across ∼30 km of coastline. The different approaches revealed numerous SGD signals from the intertidal zone (the region between high and low tide) to about a hundred meters offshore. At some locations, active seepage areas reached temperatures up to 80°C, and we calculated groundwater flow rates to be as high as 150 cm/day. SGD is therefore locally prominent and regionally important across the study area.