Hurricanes can alter the rates and trajectories of biogeochemical cycling in coastal wetlands. Defoliation and vegetation death can lead to increased soil temperatures, and storm surge can variously cause erosion or deposition of sediment leading to changes in soil bulk density, nutrient composition, and redox characteristics. The objective of this study was to compare the biogeochemistry of pre-storm soils and a carbonate-rich sediment layer deposited by Hurricane Irma that made landfall in southwest Florida as a category 3 storm in September 2017. We predicted that indicators of biogeochemical activity (e.g., potential soil respiration rates, microbial biomass (MBC), and extracellular enzyme activities) would be lower in the storm sediment layer because of its lower organic matter content relative to pre-storm soils. There were few differences between the storm sediment and pre-storm soils at two of the sites closest to the Gulf of Mexico (GOM). This suggests that marine deposition regularly influences soil formation at these sites and is not something that occurs only during hurricanes. At a third site, 8 km from the GOM, the pre-storm soils had much greater concentrations of organic matter, total N, total P, MBC, and higher potential respiration rates than the storm layer. At this same site, CO2 fluxes from intact soil cores containing a layer of storm sediment were 30% lower than those without it. This suggests that sediment deposition from storm surge has the potential to preserve historically sequestered carbon in coastal soils through reduced respiratory losses.
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Hurricane Deposits on Carbonate Platforms: a case study of Hurricane Irma deposits on Little Ambergris Cay, Turks and Caicos Islands
The study of modern hurricane deposits is useful both in identifying ancient hurricane deposits in the rock record and predicting patterns of deposition and erosion produced by future storm events. Hurricane deposits on carbonate platforms have been studied less frequently than those along continental coasts. Here we present observations of the characteristics of deposition and scour caused by Hurricane Irma on Little Ambergris Cay, a small uninhabited island located near the southeastern edge of the Caicos platform in the Turks and Caicos Islands. Hurricane Irma passed directly over Little Ambergris Cay on September 7, 2017 as a Category 5 hurricane. We described and sampled multiple types of hurricane deposits and determined that the washover fans were the best sedimentological records for hurricane conditions, as they were subject to very little reworking over time. We compared different model predictions of storm tide and wave height with eyewitness reports and distributions of scour. Examining the washover fans allowed for the construction of a conceptual model for hurricane deposits formed in a high‐energy storm event on a carbonate platform. Characteristics of the washover fans were their small size, the lack of sedimentary structures, and very well‐sorted sediment. The size and distribution of carbonate boulders eroded and transported by the storm are consistent with depth‐averaged flow velocities in the range of 1.5‐5.3 m/s. The strength of the storm and the low‐lying topography, distinct features of a carbonate platform setting, contributed to high levels of sediment bypass and high flow velocities, resulting in small, unstructured deposits.
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- Award ID(s):
- 1831623
- NSF-PAR ID:
- 10171167
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Earth Surface
- ISSN:
- 2169-9003
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1029/2020JF005597
