Rapid inundation of southern Florida coastline despite low relative sea-level rise rates during the late-Holocene

Abstract

Sediment cores from Florida Bay, Everglades National Park were examined to determine ecosystem response to relative sea-level rise (RSLR) over the Holocene. High-resolution multiproxy analysis from four sites show freshwater wetlands transitioned to mangrove environments 4–3.6 ka, followed by estuarine environments 3.4–2.8 ka, during a period of enhanced climate variability. We calculate a RSLR rate of 0.67 ± 0.1 mm yr −1 between ~4.2–2.8 ka, 4–6 times lower than current rates. Despite low RSLR rates, the rapid mangrove to estuarine transgression was facilitated by a period of prolonged droughts and frequent storms. These findings suggest that with higher and accelerating RSLR today, enhanced climate variability could further hasten the loss of mangrove-lined coastlines, compounded by the reductions in natural flow to the coast caused by water management. Climate variability is nonlinear, and when superimposed on increases in RSLR, can complicate estimated trajectories of coastal inundation for resource management and urban planning.

Impacts of Hurricane Irma on Florida Bay Islands, Everglades National Park, USA

“…To improve our understanding of how physical processes have controlled distribution of coastal vegetation (primarily mangroves) and how these processes interact to shape the coastal environment of south Florida, we conducted fieldwork and collected sediment cores from four islands in Florida Bay in 2014 ( Fig. 1; Jones et al 2019).…”

“…Detailed studies of the impacts of hurricanes on the islands in Florida Bay have not been conducted since the 1960s when Hurricanes Donna (1960) and Betsy (1965) passed over the bay. Hurricane Irma provided an opportunity for us to directly observe and document the effects of a major storm event on the four islands in Florida Bay that we previously visited and cored in 2014 (Jones et al 2019) and to utilize methods and equipment not available in the 1960s. The primary goal of this study is to compare the constructive (primarily deposition) and destructive (primarily erosion and loss of vegetation) aspects of the storm to provide context for interpreting long-term impacts of storms on the south Florida coastline and island resiliency.…”

“…Specifically, our objectives in this study are to (1) determine if Irma caused a net gain or loss of landmass and/or elevation to the islands; (2) examine the sedimentary, biochemical, and/or geochemical signatures of the storm; and (3) observe changes to the mangroves and other vegetation. By identifying distinctive storm signatures that might be preserved in the sediment record, we hope to improve our ability in future studies to interpret the sediment core record of storm history from these islands and to use these tools to test the hypothesis proposed in Jones et al (2019). Understanding long-term (decadal to centennial) patterns of storm frequency and impacts on the islands and coast of south Florida will provide insights to future coastal ecosystem responses under predicted storm, climate, and sea-level rise scenarios.…”

“…The area was a dense mangrove forest prior to the Labor Day storm based on historical accounts, but each subsequent storm has contributed cumulative impacts, setting back mangrove recovery from prior storms, leading to the conversion of this site to extensive mudflats (Wanless et al 1994;Smith et al 2009). Coupled with elevated rates of sea-level rise, repeated storm overstepping could facilitate rapid shoreline transgression, as is believed to have occurred in south Florida in the late Holocene (Jones et al 2019).…”

“…Both destructive and constructive effects of hurricanes have been described (Cahoon 2006;Twilley 2007;Smith et al 2009;Whelan et al 2009;Castaeda-Moya et al 2010;Breithaupt et al this volume), and recognition of the net long-term (decadal to centennial-scale) impacts of these storms is imperative for future planning in the coastal region (Greening et al 2006). Jones et al (2019) have suggested that climate variability played a significant role in rapid (< 200 years) transgression of the south Florida coastline between 3400 and 2800 years before present, during a time of relatively low rates of sea-level rise. Their findings highlight the importance of understanding whether the net effect of storms on the coast is constructive or destructive as resource…”