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The Chukchi Sea shelf (CSS) is a highly productive region in the Arctic Ocean and it is highly efficient for absorbing atmospheric carbon dioxide and exporting and retaining carbon in the deep sea. However, with global warming, the carbon retention time in CSS may decrease, leading to less efficient carbon export. Here, we investigate the seasonal variability of carbonate chemistry in CSS using three sets of late‐ vs. early‐summer reoccupations of the same transect. Our findings demonstrate substantially increased and rapid degradation of biologically produced organic matter and therefore acidification over time in the southern CSS due to earlier sea‐ice retreat, resulting in significantly shorter carbon retention time. In sharp contrast, no increased degradation has been observed in the northern CSS where photosynthesis has just commenced. In the future, climate change would further diminish the carbon export capacity and exacerbate seasonal acidification not only within CSS but also across other polar coastal oceans. [ABSTRACT FROM AUTHOR]

In recent years, noticeable subsidence depressions have occurred along the coastal zone of the Yellow River Delta. In some coastal areas, the average annual subsidence varies from tens of millimeters to hundreds of millimeters. Although some studies have discovered a significant land subsidence funnel in the coastal zone of the Yellow River Delta, it has rarely been reported in recent years. Using Sentinel-1A/1B images from the last five years and permanent scatterers interferometric synthetic aperture radar technology, we found a typical subsidence bowl in the northeastern part of the delta, with a cumulative settlement of nearly 1 m over five years. In addition, we used the approach of soil mechanics to simulate the settlement of confined brine layers with different thicknesses under drainage conditions. We found that the 15 m thick confined aquifer can produce 1 m of settlement for every 15% decrease in water content. The simulation results explain the large settlement of the brine industrial area. This study can provide guidance for brine mining in the future. If we continue to overexploit underground brine, there will be more severe land subsidence in the delta in the future. [ABSTRACT FROM AUTHOR]

The satellite observations unveiled that the July sea ice extent of the Arctic shrank to the lowest value, since 1979, in 2020 with a major ice retreat in the Eurasian shelf seas including Kara, Laptev, and East Siberian seas. Based on the ERA-5 reanalysis products, we explored the impacts of warm and moist air-mass transport on this extreme event. The results revealed that anomalously high energy and moisture converged into these regions in the spring months (April to June) of 2020, leading to a burst of high moisture content and warming within the atmospheric column. The convergence is accompanied by local enhanced downward longwave surface radiation and turbulent fluxes, which is favorable for initiating an early melt onset in the region with severe ice loss. Once the melt begins, solar radiation plays a decisive role in leading to further sea ice depletion due to ice–albedo positive feedback. The typical trajectories of the synoptic cyclones that occurred on the Eurasian side in spring 2020 agree well with the path of atmospheric flow. Assessments suggest that variations in characteristics of the spring cyclones are conducive to the severe melt of sea ice. We argue that large-scale atmospheric circulation and synoptic cyclones acted in concert to trigger the exceptional poleward transport of total energy and moisture from April to June to cause this record minimum of sea ice extent in the following July. [ABSTRACT FROM AUTHOR]

Recently, many of the world's major river deltas have been sinking, making them increasingly vulnerable to floods and storm surges, salinization and permanent inundation. For the Yellow River delta, annual subsidence rates of several to dozens of centimeters have been reported in the past few years. The extraction of a considerable amount of groundwater due to continuous pumping is suggested as the main driver of the groundwater depression cone. Despite its scale and severity, methods to quantify subsidence are scarce. We introduce a soil mechanics approach to quantify subsidence due to the compaction of soft soil. The largest reduction in soft soil thickness, which is more than 2.6 m, occurred in the salt field area to the north of the Yellow River. Furthermore, by estimating the primary consolidation of soft soil, the subsidence caused by groundwater exploitation is quantified. In the coastal area of the delta, due to excessive exploitation of shallow underground brine resources, the maximum accumulated subsidence is as high as 2 m. Since the natural consolidation of these deltaic sediments has ended, if the current groundwater exploitation intensity is maintained, major subsidence disasters, such as subsidence depressions and ground fissures, will occur. [ABSTRACT FROM AUTHOR]