Awesome Blue Holes
“It's like having this mini ocean…Its almost like being in a capsule in space and floating there. It's quite beautiful.”-Claire Paris-Limouzy, Ocean Scientist and Free Diver
Words by Pablo Schwarze | Drone footage by Abhi Chatterjee-Dutt
What are Blue Holes?
“Imagine walking into the ocean, just a few steps from the beach. As you swim a little further, the water beneath us suddenly plunges deep into a deep blue abyss, almost like we are floating in space.” Claire Beatrix Paris-Limouzy, an ocean scientist, describes the feeling of diving into a blue hole as “being suspended between two worlds—the light and the dark, the known and the unknown.”
We’ve probably learned that oceans cover 97% of the Earth's water and are home to amazing creatures like whales, dolphins, sharks, turtles, and colorful coral reefs. But have we ever heard of blue holes? These mysterious deep-blue, circular formations can be found near coastlines in places like Belize, the Bahamas, and Egypt. They are repositories of unique stories of our ice age (through their layers of sediments), fossils of extinct animals, archaeological artifacts, ancient caves, coral formations and a diversity of marine life – some explored and studied by scientists and divers, and others still to be explored, even perhaps to be discovered!
Blue holes are water filled vertical caverns or sinkholes in the ocean very similar to ones on land and are rich habitats of marine diversity. They are found in coastal regions where the bedrock is made of soluble material, such as limestone, marble, or gypsum. Blue holes typically contain tidally influenced water of fresh, marine, or mixed chemistry. They extend below sea level for most of their depth and may provide access to submerged cave passages.
A “mini ocean”, blue holes get their name due to their often circular deep blue water formation surrounded by the shallower light blue ring around them – this striking contrast can be seen through the lens of ocean photography as seen in this image of the Dean’s Blue Hole off the coast of the Bahamas. Blue holes’ unique formation close to the coastlines allow for shallow and deep diving explorations. Beyond the shallow ring they plunge into depths ranging from 300 feet to the deepest one, Taam Ja Blue Hole in Chetumal Bay in the Yucatan Peninsula which is 1380 feet! They reveal deep architectural crevices, caves, reef formation, sediment deposits and an alchemy of fresh and salt water that allow scientists to study complexities of our blue planet’s ecology.
Fun facts:
Fishermen and recreational divers were the first to discover blue holes!
The name "Great Blue Hole" was coined by British diver and author Ned Middleton
Famous ocean explorer Jacques Cousteau mapped the depths of the Great Blue Hole in 1971 using his submarine, the Nautilus.
How are Blue Holes Formed?
Blue Hole Formation
Blue holes formed during past ice ages when sea levels were 100-120 meters lower. Limestone and coral reefs exposed due to lower sea levels in ice ages eroded and collapsed into sinkholes. Later as ice age ended, water melted, sea levels rose, and the caverns got flooded with water creating blue holes. Three processes are key in the formation of blue holes – erosion, collapse, and flooding. These blue holes in the oceans have a unique geological and ecological footprint – preserving ancient evolutionary processes (ice age activities), and containing a mix of fresh, salt and mix water ecosystems.
Karst processes and Doline Formation
Exposed to rain and chemical weathering, these formations developed horizontal arms due to the corrosive reaction at the halocline between freshwater and saltwater. They form primarily through Karst processes involving the dissolution of limestone, gypsum, and marble, creating passages and cave systems. Blue holes can also be due to Doline formation. Dolines are depressions formed by the dissolution of surface rocks or collapse into underground voids leading to the formation of blue holes. Some blue holes, however, do not exhibit typical Karst features and may result from vertical reef development, bedrock dissolution, tidal forces, and sea level changes.
Shape and Sizes of Blue Holes
Blue holes can be in many shapes and sizes, but often are circular such as the Dean’s blue hole in the Bahamas. The circular shape is formed due to collapsed caverns, caused by rainwater erosion of exposed limestone which is porous and full of holes. The rain gradually washes away the irregular edges turning them into a circular shape. Irregular shaped blue holes are also found in the oceans, and the flooding with sea water that has calcium carbonate stops the erosion process and leaves it in its original irregular shape.
The Deep Blue Color
The name comes from the deep blue color which is caused by reflection and refraction of light in the deep corridors of its water, often surrounded by lighter turquoise of the shallow borders making a stunning ring around the hole.
Fun Fact:
Blue holes host diverse biological communities, including corals, sponges, mollusks, sea turtles, and various species of sharks
Culture and Myth
According to Caribbean folklore Lusca resides in the blue hole island of Andros, Bahamas. It is described as a giant octopus, a giant cuttlefish, or a half shark, half octopus. The Lusca is said to grow over 75 ft (23 m) long, but no cases have been proven of octopus species growing up to even half these lengths.
There is some fascination with such mythical creatures in popular culture. The reports of a Lusca monster attacking swimmers and divers were investigated by Jeremy Wade, the host of the television series River Monsters in the episode “Terror in Paradise” (season eight, episode four). After investigating reef sharks, tiger sharks, and the giant Pacific octopus, Wade settles on a large octopus being the most likely culprit for being the Lusca monster.
Lusca Fantastic Film Fest, named after this sea monster, is an annual event held in Puerto Rico. This festival showcases genres of films in the realm of fantasy, sci-fi, horror, dark humor, etc. The survival video game Stranded Deep features an enemy giant squid named Lusca the Great. The creature appears as the main antagonist of the 2010 film Sharktopus.
Fun Fact:
The Great Blue Hole in Belize is over 125 meters deep and is estimated to be around 150,000 years old!
What do Blue Holes tell us of Ocean life and our planet?
“People think about the ocean with some big organisms like marine mammals,… but the fish, they spawn and release in the ocean, millions of eggs, and those eggs hatch into baby fish, which are larval form. They look very different from the adult, because they adapt to the pelagic ocean, to the currents, and to survive in that very blue ocean environment. And this is what I study, I study what happened to these eggs…people used to think that they would only come back by chance, but by studying them, you can understand that these little creatures are very brave, they're like us, they have eyes, they can hear, they can smell, they can sense….And so my research has been focusing on trying to observe them, and because they're so small, you cannot, you know, what is easy to do, is big fish or marine mammals is to put a tag and follow them and see where they go, what they do. But they're so small, you cannot do that, you just maybe a few millimeters in size or less. So what I do is develop numerical models, where I simulate the ocean circulation and the behavior of these larvae in the ocean. It’s a bit like the science of Finding Nemo”
-Dr. Claire Beatrix Paris-Limouzy, Ocean Scientist and Free Diver
Biodiversity and Ecosystems
Through deep exploration of blue holes scientists document life around the rim of the hole and carbon, nutrients, and microscopic life throughout the hole and in its bottom sediments. A blue hole can be an oasis in an otherwise barren seafloor. Blue holes are diverse biological communities full of marine life, including corals, sponges, mollusks, sea turtles, sharks, and more.
Unique Sea Water Chemistry
The chemistry of seawater within blue holes is unique and exhibits interactions with groundwater and potentially aquifer layers. This connection provides crucial insights into carbon cycling between surface and groundwater. The varying water conditions, ranging from fresh to hyper saline, offer a valuable opportunity to study these interactions.
Preserving Historical Climate
Sediments that get deposited such as in the event of hurricanes can settle undisturbed for thousands of years. This allows scientists to gather vital knowledge of past hurricane activity and make predictions and simulate models about the future as well.
Windows Into Ancient Oceans
Blue holes also offer a glimpse into life in ancient, oxygen-deprived oceans, helping scientists understand what marine life was like millions of years ago. Exploration of blue holes, such as those led by Florida Atlantic University’s Harbor Branch Oceanographic Institute, reveals unique conditions like low oxygen, increased hydrogen sulfide, and heightened acidity—conditions that are becoming more common as the planet warms.
Insights Into Climate Change
Blue holes provide a natural laboratory to explore important questions relating to the planet’s warming and provide key insights into our future. Dr. Emily Hall lead scientist speaking to Newshound of the BBC, said this of their exploration of the Amberjack and Green Banana blue holes: "If you're swimming further away from the holes, it's pretty barren - there's not a whole lot out there on the bottom of the Gulf, but when you get closer you see soft corals and sea grasses, and then when you get to the hole it just explodes with life, it's really amazing.…What's going on out there, will they tell us anything about the future?
Natural Laboratories for Discovery
Are these holes unique or are they connected to each other genetically? Do fish that are around this hole leave there and go to another hole? Or are they nurseries for certain fish or other marine organisms?"
For scientists and explorers of blue holes – they truly are natural laboratories, nurseries and marine reserves that hold valuable knowledge of our past and perhaps clues to the future of the planet as well!
Blue Holes Free Diving Community – between science, spirituality, and human connection to our ocean planet
“I saw the advantage of being able to free dive because its stealth interaction with the animal when you are underwater with the wildlife. They're not afraid of you. …if you go, like a marine mammal like them, you have that advantage to be able to observe better, you know, in a free way, basically ... .I felt so connected with the ocean because as you go deeper, you find yourself. It's like, you disconnect it from the surface, from the noise, and you can learn who you are, basically .... Free diving is all about looking inside, so the first thing is to swim, to look inside, and then when you begin out…”
-Dr. Claire Beatrix Paris-Limouzy, Ocean Scientist and Free Diver
Claire Paris holds the United States national record as well as her first Pan American free diving record which she set in June 2022. For Claire Paris, free diving is more than a sport. It is a spiritual practice that allows her to be one with marine life and the ocean that sustains them.
Free diving is a form of diving, where you hold your breath and go underwater, resurfacing when you need oxygen. Free diving is done without any equipment such as oxygen tanks or scuba gear. It is an ancient practice dating back to the 5th century B.C. Greece. The modern sport of free diving began in the 19th century where the competition is to measure how deep one can dive holding one’s breath!
Some free divers, many of whom are the world’s record holders, and associated with blue holes are:
William Trubridge - Known for his record-breaking dives at Dean's Blue Hole in the Bahamas; Sara Campbell - A four-time world champion who has competed in the Blue Hole in Dahab, Egypt; Pim Vermeulen and Wendy Timmermans - Dutch national record holders who organize the Red Cup competition at the Blue Hole in Dahab, Egypt; Alexey Molchanov of Russia who holds several world records in different categories of free diving such as weights with bi-fins, and constant weights; Alessia Zecchini of Italy also holding a world record in free diving (constant weights; Kathryn Sedurska of Ukraine also a record holder in constant weight no fins; Nania Van Den Broek of the Netherlands holding a world record in variable weights free diving; and Peter Klovar of Croatia holding a record in free immersion diving! Herbert Nitsch of Austria is the current free diving world record champion, and "the deepest man on earth" having dived to a depth of 253.2 meters (831 feet) in the no limits category (no longer recognized for free diving records.)
Several free divers have contributed to scientific research in blue holes:
Jim Culter - A pioneer in the scientific exploration of blue holes in the Gulf of Mexico. He has worked with highly skilled volunteer technical divers to gather data on the unique biology, chemistry, and structure of these underwater features.
Dr. Emily Hall - Leading ongoing studies at Mote Marine Laboratory, she has conducted deep dives into sites like Amberjack Hole and Green Banana to explore their ecological and chemical properties.
These divers, along with their teams, have significantly advanced our understanding of blue holes by deploying specialized equipment and conducting in-depth studies of these unique underwater environments.
Click to read the full interview with Dr. Claire Paris-Limouzy.
More Fun Facts About Blue Holes
Blue holes are fascinating marine features with many intriguing aspects. Here are some more fun facts about them:
Biodiversity Hotspots: These underwater sinkholes are often oases of marine life, providing habitats for species that have adapted to their unique conditions. .
World Heritage Site: UNESCO declared the entire Belize Barrier Reef (including Great Blue Hole) a World Heritage Site.
IT TAKES LESS THAN 2 MINUTES
It’s like having this mini ocean…It’s almost like being in a capsule in space and floating there. It’s quite beautiful.
Looks very cool. Have been before