Alice Staro

Salt marshes worldwide are threatened by sea‐level rise (SLR) and their survival is linked to the production of belowground biomass and mineral sediment deposition. While hurricanes can pose a significant threat to salt‐marsh stability, we show that a single, large magnitude storm can drive deposition surpassing long‐term annual accretion. However, the potential thickness of a single hurricane‐induced depositional layer remains poorly constrained. Here we assess storm sedimentation (geotechnical characteristics, layer thickness) along the border (∼10 off edge) of salt marshes behind four barrier‐island systems (Amelia Island, Sapelo Island, Hilton Head, Cape Romain). Analysis of short cores reveals the presence of Hurricane Irma‐related deposits in 32 of 37 sites (0.5–8.0 cm thick) composed of mud to muddy sand. Thickness of the event layer decreases from south (Amelia Island) to North (Cape Romain), corresponding to a decrease in wind velocity, wave energy, and storm surge due to increasing distance from the hurricane path. We found that marsh sites proximal to tidal inlets contained thicker sediment layers with coarser sand than sheltered sites. The heterogeneity in grain size indicates that localized hydrodynamics strongly influence variability in sediment reworking. Regression analyses showed a weak correlation of thickness with wave energy, sand–mud ratio, and storm inundation duration. However, we found a strong relationship ( R ² = 0.56) between storm layer thickness and vertical accretion rates at the same sites determined from 210Pb dating Hein et al. (2024), https://doi.org/10.1038/s43247‐024‐01219‐8 . This suggests that hurricanes are important contributors to marsh sedimentation, boosting accretion rates and enhancing their resilience to SLR.

Salt marshes worldwide are threatened by sea-level rise, and their survival is linked to production of belowground biomass and mineral sediment deposition. While hurricanes can pose a significant threat to salt-marsh stability, we show that a single, large magnitude storm can drive deposition surpassing those long-term annual accretion. However, the potential thickness of a single hurricane-induced depositional layer remains poorly constrained. Here we assess storm sedimentation (geotechnical characteristics, layer thickness) on salt marshes behind four barrier-island systems (Amelia Island, Sapelo Island, Hilton Head, Cape Romain). Analysis of short cores reveals presence of hurricane deposits in 32 of 37 sites, ranging in thickness from 0.5 to 8.0 cm and composed of mud to muddy sand. Thickness of the event layer decreases from south (Amelia Island) to North (Cape Romain), corresponding to a decrease in wind velocity, wave energy, and storm surge due to increasing distance from the hurricane path. We find that marsh sites proximal to tidal inlets contained thicker sediment layers containing coarser sand than sheltered sites. The heterogeneity in grain size indicates that localized hydrodynamics strongly influences variability in sediment reworking. Regression analyses showed weak correlation of thickness with wave energy, sand–mud ratio, and storm inundation duration. However, we found a strong relationship (R2= 0.64) between storm layer thickness and vertical accretion rates at the same sites determined from 210Pb dating. This suggests that hurricanes are important contributors to marsh sedimentation, boosting accretion rates and enhancing their resilience to sea-level rise.

Recent changes in US oceanographic assets are impacting scientists' ability to access seafloor and sub‐seafloor materials and thus constraining progress on science critical for societal needs. Here we identify national infrastructure needs to address critical science questions. This commentary reports on community‐driven discussions that took place during the 3‐day FUTURE of US Seafloor Sampling Capabilities 2024 Workshop , which used an “all‐hands‐on‐deck” approach to assess seafloor and sub‐seafloor sampling requirements of a broad range of scientific objectives, focusing on capabilities that could be supported through the US Academic Research Fleet (US‐ARF) now or in the near future. Cross‐cutting issues identified included weight and size limitations in the over‐boarding capabilities of the US‐ARF, a need to access material at depths greater than ∼20 m below the seafloor, sampling capabilities at the full range of ocean depths, technologies required for precise navigation‐guided sampling and drilling, resources to capitalize on the research potential of returned materials, and workforce development.

Coastal saltmarshes are an important and highly diverse ecosystem, shielding the mainland from erosion and flooding. Along the US East Coast these valuable wetlands are endangered due to climate change, sea-level rise, and reduced fluvial sediment fluxes. Although hurricanes are commonly an erosional agent, they may be responsible for delivering significant volumes of sediment to the marsh surface, which could aid resiliency by increasing vertical accretion. This study analyzes marsh sediment cores collected during December 2017 within the Georgia Bight, targeting deposits associated with Hurricane Irma, which caused significant wave energy and storm surge along the coast from Florida to South Carolina in September 2017.We have focused our initial research on samples from Sapelo Island (Georgia), where Hurricane Irma produced maximum wind velocities of 17.5 m/s and a 1.3 m storm surge, inundating the marsh for 14.8 hrs. We find that Irma-related layers are between 2 and 7 cm thick and well-oxidized. These deposits typically consist of laminated mud with low organic content (LOI: 10-25%) and low bulk density (0.3-0.8 g/cm3). On average, Irma event sediment thickness is 4 times the historical average annual accretion, which in Georgia salt marshes is 1.55 mm.A direct comparison of Irma-affiliated marsh accretion and historical rates is complicated due to differences in consolidation, rooting and vegetation, and the sedimentation history of the marsh. Nonetheless, the storm layer represents a significant addition of sediment to the marsh surface. Thus, future increases in event sedimentation, associated with increased frequency or severity of storms, could help compensate for sea-level rise and lessen the likelihood or extent of marsh loss due to submergence.

Magnetic anomalies over mid-ocean ridge flanks record the history of geomagnetic field reversals, and the width of magnetized crustal blocks can be combined with absolute dates to generate a Geomagnetic Polarity Time Scale (GPTS). We update here the current GPTS for the Late Cretaceous-Eocene (chrons C33-C13, ~84-33 Ma) by extending to several spreading centers the analysis that originally assumed smoothly varying spreading rates in the South Atlantic. We assembled magnetic anomaly tracks from the southern Pacific (23 ship tracks), the northern Pacific (35), the southern Atlantic (33), and the Indian Ocean (55). Tracks were projected onto plate tectonic flow line, and distances to magnetic polarity block boundaries were estimated by fitting measured magnetic anomalies with a Monte Carlo algorithm that iteratively changed block model distances and anomaly skewness angles. Distance data from each track were then assembled in summary sets of block model distances over 13 ridge flank regions. We obtained a final MQSD20 GPTS with another Monte Carlo algorithm that iteratively perturbs ages of polarity chron boundaries to minimize the variability of spreading rates over all ridge flanks and fit an up-to-date set of radioisotopic dates. The MQSD20 GPTS highlights a major plate motion change at ~47 Ma, when spreading rates decreased in the Indian Ocean as India collided with Eurasia while spreading rates increased in the South Atlantic and Northern Pacific and the Hawaii-Emperor seamount chain changed its orientation.