A Snippet of Science at Cinder Cones Seep

Yesterday, we were excitingly able to put a new dive hole into Cinder Cones Seep. Cinder Cones is quite a special place, as it was the first site in Antarctica to show active methane seepage in 2011 and has been studied over the years since by the Cold Dark Benthos group. Given this, we have a number of observations and discoveries at this site that I would love to share with you, each more interesting than the last! In this post I will give you a few (non-exhaustive) examples of what has been found there over the years. This post will be largely microbial, but there is fascinating science being done up the entire food web.

One of the major questions at the site was whether anaerobic methanotrophs would show up at the site, as these microbes are largely responsible for filtering methane out of the seafloor across the rest of the globe. The initial response from 2012 to 2016 was indeed largely microbial, and the anaerobic methanotrophs we know to filter methane in other environments were observed.

Figure in Andrew's original Cinder Cones Paper titled: "Riddles in the cold: Antarctic endemism and microbial succession impact methane cycling in the Southern Ocean." In this paper he describes the microbial response to methane seepage at Cinder Cones and finds that anaerobic methanotrophs coupled to sulfate reducing bacteria are present. This process produces a lot of sulfide as a byproduct, leading to these white mats full of sulfide oxidizing bacteria on the seabed.

In 2022 and 2023, upon return to cinder cones the lab discovered that microbial mats were much sparser, replaced by an incredibly dense bed of anemones in their place. However, even though the microbial mats were absent, we continued to observe both methane seepage and methane use by the microbes in the seafloor.

Cinder cones a few days ago. The white dots on the seafloor are all anemones, blanketing the locations where the white microbial mats used to be!

Through experiments on the sediment, we found that the microbes responsible for filtering methane here likely shifted from those that couple with sulfate reducers to the archaeon Methanoperedens nitroreducens, and the bacterium Methylomirabilis oxyfera. One of the important parts of this finding is that the division time of these two microbes is much faster, and they can therefore respond to a new methane seep in a shorter time frame. This year we continue to explore these dynamics through observation, collection, and experimentation. I look forward to sharing more throughout the season and can be certain of one thing: things are never what you expect down here.