Sulphur clouds, Haloclines & Cenotes

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February 14th 2012
Published: March 4th 2012
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This blog is about all of our dives whilst in Mexico, some of the best dives we have ever done.

Let me start with some definitions.

A sulphur cloud- A layer of Hydrogen Sulphide, which is formed by the bacterial decomposition of organic material that has fallen into the cenote.

A Halocline- The point at which fresh water and sea water meet creating a layer of water that shimmers.

A Cenote- A sinkhole resulting from the collapse of limestone bedrock.

It had been a while since our last dive (nearly two years to be precise) so before jumping in at the deep end and starting with a dive in a cenote we decided to brush up on our dive skills with an ocean dive. The house reef had very little in terms of fish, we saw one baby turtle and one lion fish, which I am told should be killed if they are seen in the gulf of Mexico as they are not native to these waters. The reef itself looked completely damaged, it was bleached white and had clearly been damaged by humans too. I’m glad we did this dive though as Nikki and I both needed the refresher.

Now on to the interesting stuff.

Our first cenote dive was grand cenote. The name is actually quite deceiving as this is not the biggest cenote by a long stretch. I find it quite cool that to get to the dive site, when diving cenotes, you load up a van and drive in to the jungle. We suited up and walked down in to the cenote, it is a big round circle in the ground with crystal clear fresh water in. Underneath the ground we were walking on there are an unlimited number of caves connecting the cenotes, as we were going through our dive briefing two guys next to us were having their cave diving briefing.

Nikki and I are not cave dive trained so could not do any cave dives but when diving cenotes you dive in caverns, which by definition is the same as a cave dive with one exception, you can always see light coming in from somewhere, in a cave you are in total darkness.

Diving cenotes are like diving in under water cathedrals. I can understand how some people may not like diving in them as at times there are some very tight gaps to get through and a nervous diver could panic. I LOVED diving the cenotes.

The deepest we reached whilst diving Grand cenote was only about 10 metres & most of the cenote dives on the Riviera Maya are around the same depth.

Our next two dives were on the same day as each other and these dives were two of my favourite dives ever.

First was Angelita, another cenote but this one did not have any caverns or caves, it was just a drop straight down and at the deepest we reached 44 metres. There are no fish and there is practically no plant life at all. So why was it so good you ask?

Well to start there is a 15 foot jump to get into the water which is pretty cool for any dive. At around 15 metres you begin to see a tree emerging, at that depth it is pretty dark so it sort of feels like you are in a forest at night. Then at the bottom of the tree you begin to see a mist, it looks like a very dense fog. Then you realise it can’t be fog it’s a dive & it looks too light in colour to be sand. This was the start of a sulphur cloud.

Nikki had a bit of trouble equalising at the start of this dive and as we reached the sulphur cloud I began to have trouble equalising. The pain was excruciating. I swam back up to ease the pain and try to equalise as I did Nikki and our instructor began to disappear into the mist of the sulphur cloud. Noooooo I couldn’t believe it I was almost in the sulphur cloud when the pain started, I blew as hard as I could to equalise and the suddenly, like the sound of a dive tank being switched on, I felt a release in my ear.

I began to follow Nikki and our instructor into the cloud and as I did I got pain again but this time in my other ear. I decided not to leave the sulphur cloud and instead blew as hard as I could. This was a huge mistake. As I blew to try to equalise I must have scrunched up my face and as I did I let a lot of water in to my mask, which I subsequently inhaled. As I was in a sulphur cloud guess what the water smelt like? That’s right, rotten eggs. I began to choke so much I was almost sick. Still in pain and now coughing and gagging I cleared my mask and was now completely submerged in the sulphur cloud, I could not see a thing. I managed to catch a glimpse of two torch lights and knew it was Nikki and out instructor.

After eventually sorting my ears out I was now free to enjoy the rest of the dive. I tried to switch my camera on and it wouldn’t come on. I couldn’t see the camera properly to see if it had flooded but assumed that was what had happened. I then found Nikki and our instructor at the bottom of the cenote underneath the cloud. We only spent a few minutes here before swimming back up, I didn’t realise it at the time but the sulphur cloud started at 18 metres and finished at about 40 metres. I continued to try to switch my camera on whilst in the sulphur cloud and all of a sudden it started to work again near the top of the cloud but it didn’t switch on straight away, for some reason it turned in to a clock first until I pressed some buttons and was able to take pictures.

I don’t know what exactly happened to my camera, if there was some sort of interference from the sulphur cloud or if me inhaling some of the sulphur was making me hallucinate but when I finished the dive my camera was fine. On the way up I looked at my gauge, I’d tried to look at it whilst in the sulphur cloud but it was way too misty to see, at 23 metres I looked and I only had 30 bar of air left. I showed our instructor and as we made our way up to 5 metres for our 3 minute decompression stop I saw the instructor unwind his second stage regulator, I assumed it was for me as my air was so low but then I saw him pass it to Nikki. Luckily I managed to finish the dive with 10 bar left but Nikki had actually ran out of air! Both scary and exciting all at the same time.

The next dive was Calavera, also known as the temple of doom or skull cave. Another big jump to get in to this cenote and the water was much colder here. I had a 3mm full body wetsuit and was shivering, Nikki had a 3mm full body wetsuit AND a 3mm short wetsuit over the top of that and she was still cold. As I mentioned before we are not cave dive trained but this dive has lots of little caves, our dive instructor said they were caverns but we were nowhere near any light and quite far into the cave. When you dive cenotes you are constantly going up and down and in this particular cenote there was a halocline, you jump in to fresh water and at around 10 metres the water meets salt water.

It’s pretty surreal to see a shimmering layer in the water and what I found even more surreal was how much it affected my buoyancy. As I began my descent into the halocline I could feel the temperature difference in the salt water, I tried to descend in to it further but bounced up as my BCD had too much air in it. It’s a crazy feeling bouncing off of water and the opposite happened on the way up, as I went in to the freezing cold fresh water I began to swim up into it but as soon as I stop kicking my fins I sank like a rock on to the halocline.

When you are actually in the halocline it is how I imagine a dive would be if you had no mask on, everything is just a blurred haze. Obviously being crazy about pictures I tried to take a picture of the halocline. Guess what? It came out blurry lol. Inside the cenote the formations are amazing and the reason this dive is called the skull cave is because a lot of the formations look like skulls (couldn’t see it myself).

Our last dive was the largest cavern system in the Riviera Maya, Dos Ojos. There are actually two dives you can do at Dos Ojos but we only actually did one, the Bat Cave. In terms of distance it is the shorter of the two dives but there are a lot more formations to see here. I would describe it as an underwater cathedral.

I, like most divers, love diving with big fish, however even if you go to a known cleaning station or feeding spot you are never guaranteed to see them. I love diving wrecks even more as no matter what time of the year you go to the dive the wreck is always going to be there plus there can be some pretty cool history about why the wreck is there. I now love cavern diving and intend to do my cave diving course at some point. With the right skills, confidence and camera you could spend hours diving the same caves taking pictures of the different formations.

Roll on the next dive trip.

Additional photos below
Photos: 29, Displayed: 28


Streak of lightStreak of light
Streak of light

This is what happens when you shine your torch in to a sulphur cloud.

5th March 2012

Love the pics!
As you know, did the same last summer...and I can confirm, this is something! You've got great pictures!
5th March 2012

I remember reading your blog and looking forward to the dives, I didn't even realise you could dive cenotes in Mexico until your blog!
5th March 2012

An engrossing read
A really atmospheric story and photographs that captivated me for the whole blog. What camera do you use underwater?
5th March 2012

Thanks Shane, I use a Canon ixus 90. I'd love to get underwater housing for my SLR but I'm too worried it will flood and leave me cameraless for the rest of my trip.
5th March 2012

Thanks and agree re the flooding issue! A good SLR housing costs more than an underwater compact camera, so I can also see the financial sense in not purchasing the housing. Seeing the mood you conveyed in these photos has convinced me of the need to purchase a small underwater camera for my snorkelling.

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