Regional shifts in paleohurricane activity over the last 1500 years derived from blue hole sediments offshore of Middle Caicos Island

Highlights

• A transect of sediment cores from a Middle Caicos blue hole records hurricanes passing to the south of the island.

• Compiled Bahama Archipelago blue hole records show multi-decadal periods of elevated storm strikes over the past 1500 years.

• Paleohurricane compilations support evidence for a basin-wide storm increase during the early Medieval Climate Anomaly.

• Century-scale periods with more storms in the Bahama Archipelago and New England coincide with less storms on the Gulf Coast.

Abstract

Coastal communities are vulnerable to sea-level rise and hurricane-induced flooding. Our ability to assess flooding risk at coastal locations is restricted by the short observational record and limited knowledge on storm surge generation during hurricanes of different strength, size and orientation. Here, we present a transect of sediment cores collected from a blue hole near Middle Caicos in the Turks & Caicos Islands. Storm deposits found across cores in the transect record the passage of hurricanes passing to the south of Middle Caicos over the past 1500 years including Hurricane Irma in 2017. The record indicates historically unprecedented multi-decadal periods of elevated storm strikes on the island. We add this new reconstruction to a compilation of near-annually resolved paleohurricane records of the past millennium in The Bahamas. This compilation indicates increased storm activity in The Bahamas from 650 to 800 CE, 930 to 1040 CE, and 1400 to 1800 CE. Taken together with compilations of published paleohurricane records from New England and the Gulf Coast of Florida, we observe periods of elevated hurricane activity in all three spatially disparate regions over the past millennium and periods when New England and the Bahama Archipelago are active while the Gulf Coast of Florida is not. We argue that both regional-scale changes in vertical wind shear patterns and shifting storm tracks may explain the discrepancies we observe between different regions of the North Atlantic. This research informs how hurricane frequency has changed over the past 1500 years specifically in the Turks & Caicos Islands and regionally along the Bahama Archipelago.

Introduction

Each year, tropical cyclones (TCs) form in the tropical North Atlantic Ocean moving through the Caribbean Sea, Gulf of Mexico, and/or along the U.S. eastern seaboard. As these storms approach land, they induce strong winds, storm surge and heavy rain which cause massive economic and human losses in coastal communities (Dinan et al., 2016). These losses are expected to increase in the next century with projected increases in TC intensity, rising sea levels and growing coastal populations (Knutson et al., 2020). Providing coastal communities with longer term information and context on the scale and probability of TC events is important for local planning as well as the sustainable economic development of these areas.

Unfortunately, there is still significant uncertainty on how North Atlantic TC properties (e.g., frequency, intensity, speed, tracks) will change both on a basin-scale and a regional-scale. The current set of TC observations suffers from data quality issues (Landsea et al., 2004, 2010, 2010; Vecchi and Knutson, 2008, 2011, 2011; Villarini et al., 2011; Landsea and Franklin, 2013) and only extends back over the past 169 years (1851–2020 CE). This short observational record does not allow for elucidating hurricane-climate interactions on long timescales or during climatic regimes that differ from the modern.

TC properties are related to large-scale ambient environmental conditions in the Atlantic. In particular, sea surface temperatures (SSTs) and vertical wind shear (VWS) strongly influence hurricane potential intensity (Emanuel 1987, 1988) and genesis (Camargo et al., 2007; Emanuel, 1989), respectively. Warmer SSTs provide energy to TCs in the form of moist enthalpy and TCs only develop over ocean water with surface temperature exceeding 26°C (Emanuel, 2003; Gray, 1998). Lower vertical wind shear, defined as the difference between horizontal winds in the upper (200 hPa) and lower (850 hPa) troposphere, favors hurricane convective organization and intensification (Merrill, 1987; Rios-Berrios and Torn, 2017).

There are a variety of different regional and remote climate oscillations and external forcing factors that influence changes in atmospheric steering currents, SST, and VWS patterns in the Atlantic. These include the North Atlantic Oscillation (Elsner and Kocher, 2000; Kossin et al., 2010), Atlantic Multidecadal Variability (Goldenberg et al., 2001; Clement et al., 2015; Ting et al., 2019), El Niño Southern Oscillation (ENSO) (Gray, 1984; Goldenberg and Shapiro, 1996; Chu, 2004), and volcanic eruptions (Evan, 2012; Korty et al., 2012; Pausata and Camargo, 2019), among others. Many of these mechanisms have multivariate, multi-scalar, and non-linear responses and occur on different timescales. This makes it very difficult to fully characterize the response of TC activity to these phenomena, especially over the short observational record.

There is a growing number of paleohurricane reconstructions from geologic archives that extend observations of landfalling hurricanes back thousands of years along the North American coastline (e.g., Boldt et al., 2010; Lane et al., 2011; Mallinson et al., 2011; Donnelly et al., 2015; van Hengstum et al., 2016; Bregy et al., 2018). Recent studies have obtained Common Era paleohurricane records from sediment cores in blue holes scattered across the hurricane-prone tropics (e.g., Denommee et al., 2014; van Hengstum et al., 2014; Wallace et al., 2019; Bramante et al., 2020; Schmitt et al., 2020; Winkler et al., 2020). Blue holes serve as giant traps for sediment from surrounding reefs and lagoons suspended and transported during storm events (Shinn et al., 1996).

Recent reconstructions of hurricane activity over the past millennium from blue holes in The Bahamas include Wallace et al., 2019, 2021 and Winkler et al. (2020). Each of these reconstructions capture modern coarse-grained deposits that date to known historical hurricanes (≥Category 2 on the Saffir Simpson Scale) passing proximal to each site, which when synthesized support century-scale changes in hurricane activity over the past millennium (Wallace et al., 2021). Each island experienced extended periods of substantially elevated storm strikes interspersed with periods of relatively few TC landfalls. These reconstructions taken together allow us to better understand how hurricane activity in The Bahamas has changed over the past 1000 to 1500 years. With less than 169 years of observational data of hurricane strikes in this region (Knapp et al., 2010), these paleo-records provide one of the few means to constrain how Bahamian hurricane activity changes on long timescales (multi-decadal to centennial scale).

Constraining how these documented long-term changes in hurricane activity relate to climate is more difficult. Each single paleohurricane reconstruction only captures changes in storm activity at or near its location, which may or may not be indicative of broader variance in hurricane climate throughout the Western North Atlantic. A recent proxy-model comparison study (Wallace et al., 2020) using the South Andros paleo record (Wallace et al., 2019) and synthetic TCs generated using a statistical deterministic hurricane model (Emanuel et al., 2006, Emanuel et al., 2008) shows that the centennial-scale shifts in hurricane frequency captured in individual records from The Bahamas can be created by random variability (i.e., local weather patterns-steering winds, moist convection) not climate. To confidently identify hurricane risk for the entire Bahama Archipelago, one must compile records from across that area to better sample a representative population of storm passage. Working towards the goal of generating a large regional database of high-resolution hurricane reconstructions spanning the last millennium from the North Atlantic, here we update the paleohurricane compilations of Wallace et al. (2021) with a new high-resolution record from Middle Caicos Island.