Captain’s Log – Entry #6: Underwater Caves and Alcoves

By Nathalie Cabrol

I have been watching them from the south shore for long enough and other activities have prevented me from exploring them earlier but today is the day. The west shore of Laguna Negra is characterized by a very large basalt exposure where underwater caves and alcoves are abundant. I am pretty sure those are being used as shelters by life, and possibly hold more biodiversity than we have observed so far. We leave early with Chris. The lake is a mirror, which makes the trip in Margaritaville (one of our boats) easy. While we head for our destination, Liam, Sandy, and Cristian pay a last visit to PLL on the northwest shore. Sandy did not have the chance yet to get on the lake and Cristian needs to learn how to maintain PLL while we will be away.

Ducks are flying away as we approach. The air is crisp but not cold. Every detail of the landscape is sharp. It does not take too long to reach our destination. Chris turns left into a hidden alcove and I discover a series of caves, not high enough to stand but close. We land at the largest one. From the report of the first exploration of Laguna Negra in March 1873 that the managers of Aguas Andinas gave me on December 16 when we met, I know that this cave is officially known as the Cave of the Amazons. The book is illustrated with amazing reproductions of photo plates 140 years old. If one is not paying attention too much, it could appear that time has stood still since then. Yet, the Echaurren glacier was lower than today. It is still very humbling to see that these shores were explored that long ago. The exploration party stayed for a week and came with horses and mules. That we shared…

Their camp was maybe 100 m to the west of ours. When I get back home and have time, I will put side by side their illustrations and ours: Two groups separated by almost one-and-half centuries but bound by the same interest, that of understanding what would be the future of their water resources. However, they came and left with a more optimistic vision than the one we have today. They returned to Santiago with the news of large reservoirs, and plans to build a dam that would supply water to the capital city, the dam of El Yeso, which is now standing less than two kilometers from where we are on the other side of the hill.

I start preparing my diving gear. I only have equipment for free diving so there will be no underwater cave exploration but rather a reconnaissance of where they are, and what type of organisms live there. Some of the caves are only partially submerged and have air pockets that will allow me to venture a bit farther.

It does not take me long to be ready. I had donned my suit before we left. I am wearing the dual GoPro camera system that allows 3D rendition of films. Hopefully, this time it will work without a glitch. The water is so transparent. As we were approaching, the bathymetric system was reading near 50 m depth and we still could see the huge granite blocks at the bottom. The cliffs are falling straight down into the water. There too, no real transition between the shore and the lake bottom. Just a small shelf and then… down. I still find a few blocks that allow me to enter the water without a problem, but more importantly, will give me a solid footing to get out.

Here we go. The GoPro is on. Laguna Negra has this uncanny ability to envelop you as soon as you get in. It is a deep blue blanket that surrounds you immediately. Over the past few dives, I have learned not to be spooked by it anymore. In fact, I am sort of expecting it now and it finally feels comfortable. Looking around me, I am surrounded by giant blocks, and yes, a flotilla of small trout. They look at me with curiosity but no fear.

I start with a quick reconnaissance of the near shore morphology. Macrophytes are still present in abundance but other types of algae are there too that I do not recognize. Those actually almost look like stalactites. They are hanging downward in the water and can grow several meters long. Looking closer at the macrophytes, I see something I did not see on those of the southern shore. They are encased by a whitish, translucent, almost gooey material, which I mistake for a moment for fish eggs. At closer look, it seems to be some sort of envelope that contains millions of air bubbles. I have seen the same process taking place in the High Andes at Laguna Blanca. Those algae produce billions of oxygen bubbles every day. This is how our planet’s atmosphere changed drastically a few billion years ago, although this theory has started to be challenged.

If this is really the scenario that played out, that was one of the first real ecological disasters, killing most life that could not adapt to a O2 atmosphere. I often wonder if this is why we are taking such poor care of our environment. After all, if we are the result of an ecological disaster, maybe, very deep inside, it is rooted in us that messing with the environment is a good thing…Going beyond cynicism, watching these algae doing what their ancestors have done for billions of years gives a direct connection to our evolution, to where we are coming from, and it is also a warning. We live in a natural system of many components. Destabilizing one or more leads to feedback mechanisms and loops we have poor or no control over and very little ability to correct.

I move on. I pass by many similar alcoves and then, I am surrounded by a sea of red, literally. The time to adjust my vision, I recognize these tiny (0.5-1 mm) organisms, their long antennae floating in the water. They are old friends of mine from many prior lakes in the High Andes. Their morphology is easily recognizable. Millions of copepods are surrounding me in a very large swarm. I slowly move my hand to see them swim around and away. That was unexpected. A week ago, Ruben was mentioning that he was surprised by their low number in the south shore. Well, I guess they are here. Also, if I am not mistaken, the water seems slightly warmer. With all this fractured basalt, the springs, and an active volcano (Tupungato) not too far away, I would not be surprised if a number of springs that enter Laguna Negra were actually hydrothermal. In fact, coming by boat, we could see patches of grass stained yellow, as if burned by acidic waters. The other possibility is that I am getting really used to this cold water…

The copepods are red, very red. That surprises me a little. The water is highly transparent, that’s a fact. However, they have so much water column to work with and we are not that high in elevation, so although I have not checked the UV here, I would expect it to be substantially lower than at Licancabur, which is located about 3300 m higher. I might be wrong and these are still tiny organisms needing protection against an abundance of UV. Besides, they are apparently very close to the surface too and we are about one hour away from solar noon. Maybe they share the same behavior as those of Licancabur and Laguna Blanca (5,914 m and 4,340 m elevation, respectively). We saw them swimming at solar noon at the surface while the UV index was scarily between 24 and 29. Maybe they do not care about the short UVB that is irradiating them. Who knows. The biologists will have to help us unravel that part of the story. The experience gained with the High Lakes Project in the past nine years will be very helpful here.

I leave the copepods to go back south. I have to be careful not to venture too much farther away from where the boat landed. The water is cold and I do not want to be caught starting to get chills in an area where there is no place to get on shore. I pass by the main cave where Chris is sitting, patiently waiting for me, and keeping one eye on me and one on possible rock glaciers on the other shore. I sign that everything is fine. The area allows me to get into a partially submerged cave. I have room to breath. I sneak up on a very large fish who is obviously sleeping. It does not move. I am standing right on top of it, maybe a meter or so above, no more. This time the camera is rolling and I am making sure to capture its image. It completely ignores me until I start moving on. At this time, it realizes that it is not the largest fish in that lake and darts away from me. In the time I will spend near and in those alcoves, I will see a total of 3 large fishes (30-50 cm long). The others are medium to small-size trouts.

As I proceed with my reconnaissance, I noticed that the walls of the cliff that plunges into the deep of the lake are also covered in algae, very low profile and light ones. They, too, are producing oxygen. I play for a moment with the bubbles and move on again. This underwater landscape is amazing: bright algae lit-up by the sun are dancing in the current with, in the background, the dark blue of the depth, which, where I am reaches over 100 m. I will have to come back with a rebreather next year. For today, it is a shallow depth investigation, 5 m deep maximum.

I pass through the macrophytes and then venture farther away from the shore. Bubbles are coming straight up in a column in front of me. I look below and see no fish or algae. Maybe there is a spring. Strangely, the bubbles stop. Weird. Time to go back. I spot my landing made of a few blocks conveniently arranged in a staircase-like fashion. There is so much work to be done here next year, so much sampling to do. We will have to go through these alcoves and small caves one by one. And they are only the beginning. There are many more of those not only on the other side of the northwest branch of Laguna Negra, but on the northeast branch as well. We will need more diving flexibility.

I do not know what the biodiversity of Laguna Negra is. It is hard for me to assess. This is not my area of expertise. I have learned to be cautious in the High Andes where certainly life is abundant in the altitude lakes but cladograms show it is not so diverse. Is it the case here too? We will see in the future. What I do notice from this reconnaissance is that life occupies every possible niche we have explored so far. It will be interesting to compare what biodiversity characterizes Laguna Negra, already in stage 2 of deglaciation, with Station Lake in the Echaurren valley, which is still in stage 1.

As I resurface, I can see Mariner 1 (the Zodiac) about 1 km away next to PLL, near the opposite shore. About 50 meters from it, and close to Victoria’s Cascade, a tiny orange dot shows the emplacement of the buoy that holds its twin sonde located where the waters from Station Lake cascade down into those of Laguna Negra. I smile because this summarizes in many ways what has been accomplished in these 17 days: PLL is now sending back data to the US. With its twin sonde, they are like a time machine recording the changes that occur when glaciers disappear, a space-for-time substitution experiment of sorts. It is up to us to understand what they mean. I am sure Ruben will like it. That could make a very informative comparison with his own study in the Alps.

Time to come back to camp. Margaritaville does very well, helped by almost no wind. The camera was still recording as I was coming out of the water. This time, unless something went terribly wrong, I am pretty sure we have 45 minutes of underwater documentation. Jeff (Moersch), who loaned me the camera for this dive and the previous, will process the movie. The 3D should definitely, and most literally, add a dimension to it. Hopefully, it should help the biologists for the planning of next year field campaign, and that is also something I really like about our investigation so far. Our bathymetric mapping (plus the scientific rationale provided by the rest of the team) has helped the engineers decide on where to moor PLL. This underwater documentation will help future planning for bio-sampling. This team is working as one, the data from one group helping the others farther their research; brought together, they give a unique view of the richness and evolution of the Laguna Negra system. After our “mule days” of the beginning, I cannot help but think we came together very strongly and made this first field campaign a success. For now, I let Chris take us back “home,” toward the white domes on the south shore I can see straight ahead. My only ambition at the moment: a large bowl of David’s warm soup. I might get used to it but the waters of Laguna Negra are still cold…

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