microbialite

Coming back from a great flight in the subs, I am even more excited about the lake! What an amazing place!

I had a great flight – the goal was to fly a contour at 15m depth on the east side of the South Basin (north section). That was just fascinating! A specific objective was to identify rock slides, to enable the afternoon flight to document and sample some of these rock slides. Why? Well, one of our hypotheses is that microbialites need rocks to start their growth. The sediment around is so soft, that it seems hard for any large structure to just grow in it. Using video to image these rock slides, we find that at significant depth we just see the rocks. As we get shallower first there is a thin cover of microbialites on the rocks, and then with increasingly shallower depth the microbialites get bigger and bigger! At this point there is no sign of the rock that’s likely underneath. So does this prove that microbialites always need a rock? Well not really! Just nearby there were landslides with no microbialites on them. Why is that? It’s the same type of rock, likely the same lake chemistry, and likely the same biology. But there is such a difference! Then later in the dive I also found areas with scattered microbialites, which certainly didn’t look like they depended on rocks for their growth. Examples of these relationships are seen throughout the lake, but it is this field season that we are meticulously documenting them. And while we are certainly showing some relationships are true, what we see raises even more questions!

Another big question we are asking is if the microbialites are currently growing. On this dive it was sad for me to see that there was a lot of trash on the lake bottom. But this trash is also like a natural experiment to look at microbialite growth. In this case, we can look at whether there is anything growing on the trash, or also on trees that have fallen into the lake. In the case of trash, we know it got there less than ~100 years ago, and a lot of the trash in this area was covered with about 0.5 cm (1/5 inch) of microbialite growth! So we now know that the microbialites are currently growing, at least in that part of the lake. So then we ask why is there such a difference in sizes for different parts of the lake? Just a few hundred meters south of my dive, Mike Gernhardt was exploring unusually large structures: 2 meters tall, by 3 meters wide (6 ft tall, by 10 ft wide). Where I was flying, most of the structures were small: maximum height of 20 cm (8 inches). So why is there such a difference? Is microbialite growth constant, or does their growth effectively turn on and off? Do the microbialites grow faster in one area than another because of slight water chemistry differences? Or something else? We haven’t seen any of these chemistry differences yet, but it could be something we haven’t measured … yet.

We started out 5 years ago with so many questions. Now we have more and more questions, but it is also nice to see that some answers are coming in as well. As we analyze the wealth of data we are collecting with the DeepWorker submarines, we are sure to answer more and more of these intriguing questions.

-Mars