Assessing the Recalibration Interval for Nearshore Sediment Assemblages after Hurricane Irma: implications for Developing Long-term Records of Overwash Deposits

Author

Stephen MitchellFollow

Date of Award

Fall 2020

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Ocean Science and Engineering

Committee Chair

Dr. Davin Wallace

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Dr. Jessica Pilarczyk

Committee Member 3

Dr. Jeremy Deans

Committee Member 3 School

Biological, Environmental, and Earth Sciences

Abstract

Surface distributions are commonly collected to assist with overwash interpretation; however, many of these are first established immediately after a major overwash event as part of a post-event field survey. This study documents the impacts of Hurricane Irma, a Category 5 storm, on nearshore sediments off the coast of Anegada (British Virgin Islands) using distributions of Homotrema rubra, an encrusting foraminifer with a defined provenance in coral reef ecosystems. Over four sampling intervals spanning 2 years, from six months pre-Hurricane Irma to 18 months post-Hurricane Irma, surface sediment was collected from three shore-perpendicular transects on both the northern and southern shores of Anegada. Partitioning Around Medoids cluster analysis using the Homotrema data revealed that Hurricane Irma introduced an influx of well-preserved fragments into the reef flat (10% increase along the Windlass Bight transect and 13 % increase along the Soldier Point transect, the two northern transects) and homogenized the sediments, limiting the foraminifer’s utility as a known sediment transport indicator. The homogenization of sediments along the two northern transects (i.e., reef proximal) persisted for 7-18 months, at which point Homotrema distributions returned to near pre-Hurricane Irma conditions. However, the southern transect (i.e., absence of reef), where Homotrema concentrations are significantly less, failed to recalibrate within the time period assessed by this study. Post-event recalibration intervals will vary based on site and event, however, our results suggest that a waiting period of at least 18 months is recommended before collecting surface sediment samples from nearshore environments offshore Anegada.

Copyright

Stephen P. Mitchell, 2020

Recommended Citation

Mitchell, Stephen, "Assessing the Recalibration Interval for Nearshore Sediment Assemblages after Hurricane Irma: implications for Developing Long-term Records of Overwash Deposits" (2020). Master's Theses. 777.
https://aquila.usm.edu/masters_theses/777