We're decoding ancient hurricanes' traces on the sea floor – and evidence from millennia of Atlantic storms is not good news for the coast
Buyerself.com, is a shopping platform where buyers can purchase products and services at their desired prices. It also serves as a tool for sellers to find real buyers by publishing purchase orders in their local areas or countries. With Buyerself.com, users can easily find buyers in their proximity and in their country, and can easily create purchase orders. Buyerself.com and our apps are available for download on iOS and Android devices, and can be signed up with a single email. Sign up now and start shopping for your desired products and services at your target prices, or find real buyers for your products with Buyerself.com. Sign up now and start selling
The Buyerself mobile application offers great advantages to its first users. Download and enjoy the benefits.
Deep "blue holes" like this one off Belize can gather evidence of hurricanes. The TerraMar Project, CC BY
If you look back at the history of Atlantic hurricanes since the late 1700s, it seems like hurricane frequency is increasing.
The year 2020 had the most tropical cyclones in the Atlantic at 31, and 2021 had the third highest after 2005. The past decade has seen five of the six most destructive Atlantic hurricanes in modern history.
Then comes a year like 2022, with no major hurricane landfalls until Fiona and Ian struck at the end of September. The Atlantic hurricane season, ending November 30, had a total of eight hurricanes and 14 named storms. It is worth remembering that small sample sizes can be misleading when assessing trends in hurricane behavior. Hurricane behavior is subject to so many natural variations from year to year and even decade to decade that we have to look much further back in time to see the true trends.
Luckily, hurricanes leave telltale evidence going back thousands of years.
Two thousand years of this evidence suggests that the Atlantic has experienced even more turbulent periods in the past than in recent years. These are not good news. It tells coastal oceanographers like me that we may be vastly underestimating the threat hurricanes pose to the Caribbean and US coasts in the future.
The natural record left by hurricanes
As a hurricane approaches land, its winds whip up powerful waves and currents that can sweep coarse sand and gravel into swamps and deep coastal ponds, sinkholes, and lagoons.
Under normal conditions, fine sand and organic matter such as leaves and seeds fall into these areas and settle to the bottom. When coarse sand and gravel are flushed in, a clear layer remains.
Imagine cutting through a layered cake - you can see each layer of frosting. Scientists can observe the same effect by plunging a long tube into the bottom of these coastal swamps and ponds and pulling up several meters of sediment in what is called a sediment core. By examining the layers of sediment, we can see when coarse sand appeared, suggesting extreme coastal flooding from a hurricane.
Using these sediment cores, we have been able to document evidence of Atlantic hurricane activity for thousands of years.
The red dots indicate large sand deposits dating back approximately 1,060 years. The yellow dots are estimated dates from radiocarbon dating of small bivalves. Tyler Winkler
We now have dozens of chronologies of hurricane activity in various locations -- including New England, the Florida Gulf Coast, the Florida Keys, and Belize -- that reveal patterns of hurricane frequency on a decade-to-century scale.
Others, including Atlantic Canada, North Carolina, Northwest Florida, Mississippi and Puerto Rico, have lower resolution, meaning it's almost impossible to spot individual hurricane layers that have been deposited over decades. However, they can be very informative in determining the timing of the strongest hurricanes that can have significant impacts on coastal ecosystems.
However, it is the near-annual resolution records from the Bahamas that are critical to seeing the long-term picture of the Atlantic Basin.
Why the Bahamas are so important
The Bahamas is exceptionally vulnerable to the effects of severe hurricanes due to its geographic location.
In the North Atlantic, 85% of all major hurricanes occur in the so-called main development region off West Africa. Looking only at observed hurricane tracks over the past 170 years, my analysis shows that about 86% of the major hurricanes that affect the Bahamas also form in this region, suggesting that frequency variability in the Bahamas is representative of the basin could be.
Atlantic hurricane tracks from 1851 to 2012. Nilfanion/Wikimedia
A significant percentage of North Atlantic storms also pass over or near these islands, so these records appear to reflect changes in North Atlantic hurricane frequency over time.
By coupling coastal sediment records from the Bahamas with records from locations further north, we can study how changes in sea surface temperatures, ocean currents, global wind patterns, and atmospheric pressure gradients affect regional hurricane frequency.
As sea surface temperatures rise, warmer water provides more energy that can fuel more powerful and destructive hurricanes. However, the frequency of hurricanes — how often they form — isn't necessarily affected in the same way.
Hurricane Dorian swept across the Bahamas in 2019 as a powerful Category 5 storm. Laura Dauphin/NASA Earth Observatory
The mysteries hidden in blue holes
Some of the best places to study past hurricane activity are in large, offshore sinkholes known as blue holes.
Blue holes get their name from their deep blue color. They were formed when carbonate rocks dissolved and underwater caves formed. Eventually the ceilings collapsed, leaving sinkholes. There are thousands of blue holes in the Bahamas, some as wide as a third of a mile and as deep as a 60-story building.
They tend to have deep vertical walls that can trap sediment — including sand carried by powerful hurricanes. Fortunately, deep blue holes at the bottom are often low in oxygen, which slows decay and helps preserve organic material in the sediment over time.
Hines Blue Hole in the Bahamas is about 100 meters deep. Seismic logging shows approximately 200 feet (more than 60 meters) of accumulated sediment. Pete van Hengstum; Tyler Winkler
Breaking up a sediment core
When we lift a sediment core, the coarse layers of sand are often visible to the naked eye. But a closer look can tell us a lot more about these hurricanes of the past.
I use X-rays to measure changes in the density of sediments, X-ray fluorescence to study elemental changes that can reveal whether sediments are terrestrial or marine, and sediment structure analyzes to study grain size.
To determine the age of each layer, we typically use radiocarbon dating. By measuring the amount of carbon-14, a radioactive isotope, in shells or other organic material found at different locations in the core, I can create a statistical model that predicts the age of sediments throughout the core.
So far, my colleagues and I have released five paleohurricane records with near-yearly detail from island blue holes in the Bahamas.
Each record shows periods of significant increase in storm frequency lasting decades and sometimes centuries.
The red dots show the locations of high-resolution paleohurricane records. Map shows frequency of Category 2 or greater hurricanes from 1850 to 2019. Tyler Winkler
Records vary and show that a single site may not reflect broader regional trends.
For example, Thatchpoint Blue Hole on Great Abaco Island in the northern Bahamas contains evidence of at least 13 Category 2 or higher hurricanes per century between the years 1500 and 1670. This greatly exceeds the rate of nine per century documented since 1850 during the same period, 1500 to 1670, blue holes on the island of Andros, just 300 kilometers south of Abaco, documented the lowest levels of local hurricane activity recorded in that region in the past 1,500 years.
Patterns of recognition in the Atlantic basin
Together, however, these records offer insight into broad regional patterns. They also give us new insights into how ocean and atmospheric changes can affect hurricane frequency.
While rising sea surface temperatures provide more energy that can fuel stronger and more destructive hurricanes, their frequency -- how often they form -- isn't necessarily affected in the same way. Some studies predict that the total number of hurricanes will actually decrease in the future.
Comparing paleohurricane records from multiple locations reveals periods of higher frequency. Periods highlighted include the Little Ice Age, a period of cooler conditions in the North Atlantic from 1300 to 1850, and the Medieval Warm Period from 900 to 1250. Tyler Winkler
The compiled records of the Bahamas document a much higher frequency of hurricanes in the northern Caribbean during the Little Ice Age between 1300 and 1850 than in the past 100 years.
This was a time when North Atlantic surface temperatures were generally cooler than they are today. But it also coincided with an intensified West African monsoon. The monsoon may have produced more thunderstorms off the west coast of Africa, which act as low-pressure seeds for hurricanes.
Steering winds and vertical wind shear are also likely to affect a region's hurricane frequency over time. The Little Ice Age active interval observed in most Bahamian records coincides with increased hurricane attacks along the US East Coast from 1500 to 1670, but at the same time it was a calmer period in the Gulf of Mexico, central Bahamas and the United States southern caribbean.
Records from places further north tell us more about the climate. That's because changes in sea temperature and climate conditions are likely to be much more important in controlling regional impacts in areas like the northeastern US and Atlantic Canada, where cooler climate conditions are often unfavorable to storms.
A warning for the islands
I'm currently developing coastal storm records in places like Newfoundland and Mexico. With these records, we can better anticipate the impact of future climate change on storm activity and coastal flooding.
Meanwhile, in the Bahamas, rising sea levels are putting the islands at increasing risk, with even weaker hurricanes able to cause damaging flooding. Given the expected intensity of storms, any increase in storm frequency could be devastating.
This article is a re-publication of The Conversation, an independent non-profit news site dedicated to sharing ideas from academic experts. It was written by: Tyler Winkler, Woods Hole Oceanographic Institution. The Conversation has a variety of fascinating free newsletters.
Some coastal areas are more vulnerable to devastating hurricanes -- a weather forecaster explains why
Hurricane Ian ends 2 weeks of extreme storms around the world: Here's what we know about how climate change drives tropical cyclones
Tyler Winkler does not work for, advise, own any interest in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations other than her academic appointment.
Kentucky mom says Bryan Kohberger is her 'divine masculine' and claims she sent him letters and dolled up pics
Prince George, Princess Charlotte, and Prince Louis Are Banned from Doing This at Home
Instagram Model Goes Viral After Revealing Her 38J Breast Implant Popped
Sounds Like Netflix Made A Big Whoops When It Posted Its New Account Sharing Rule Changes This Week, Fans Are Not Pleased
MGH co-workers of Duxbury mom charged in deaths of her kids share words of support as GoFundMe grows
Brandon Aiyuk reveals NSFW reaction to Brock Purdy becoming starter