Qian Yuan | Search USGS

USGS2025

Marine-sourced sediment supply supports salt marsh resilience to sea level rise in the Northeastern US

Salt marshes rely on sediment to maintain elevation and resist sea level rise (SLR). While riverine sediment is well studied, marine-sourced sediment remains understudied, particularly in regions with limited river input. We examined the influence of marine-sourced sediment on salt marsh stability across 103 sites in the Northeastern US, using a new satellite-derived suspended sediment concentration (SSC) product. Marsh vulnerability was assessed using the Unvegetated-to-Vegetated Ratio (UVVR) and relative marsh elevation (Z*). We identified two thresholds: SSC >20 mg/L and RSLR <5.2 mm/year. Marshes meeting either threshold tended to remain intact, while those with both low SSC and high RSLR were more vulnerable to degradation. A north–south gradient was observed, with most unstable marshes in the southern region, where SSC declined by 0.9% per decade on average, compared to 0.072% in the north. These findings highlight the need to include coastal sediment dynamics in restoration and adaptation planning.

Northeastern United States↗

USGS2023

Moon-forming impactor as a source of Earth’s basal mantle anomalies

Seismic images of Earth’s interior have revealed two continent-sized anomalies with low seismic velocities, known as the large low-velocity provinces (LLVPs), in the lowermost mantle . The LLVPs are often interpreted as intrinsically dense heterogeneities that are compositionally distinct from the surrounding mantle . Here we show that LLVPs may represent buried relics of Theia mantle material (TMM) that was preserved in proto-Earth’s mantle after the Moon-forming giant impact . Our canonical giant-impact simulations show that a fraction of Theia’s mantle could have been delivered to proto-Earth’s solid lower mantle. We find that TMM is intrinsically 2.0–3.5% denser than proto-Earth’s mantle based on models of Theia’s mantle and the observed higher FeO content of the Moon. Our mantle convection models show that dense TMM blobs with a size of tens of kilometres after the impact can later sink and accumulate into LLVP-like thermochemical piles atop Earth’s core and survive to the present day. The LLVPs may, thus, be a natural consequence of the Moon-forming giant impact. Because giant impacts are common at the end stages of planet accretion, similar mantle heterogeneities caused by impacts may also exist in the interiors of other planetary bodies.

Nature↗