The Baltic Sea has had a dramatic geologic past, complete with advancing and retreating glaciers and shifting inputs of fresh and salt water. All of these changes are recorded in the layers of sediments that collect at the seafloor—layers that were buried along with the microbes colonizing them. Scientists have long debated whether these organisms beneath the Baltic Sea, as well as other bodies of water, are thriving and dividing or just barely surviving.

new paper in Environmental Microbiology Reports suggests that deep microbes are doing just fine. Deep Life Community members Laura Zinke, Jan Amend (both at University of Southern California, USA), Jordan Bird, Karen Lloyd (both at University of Tennessee, USA), Bo Barker Jørgensen (Aarhus University, Denmark), and Brandi Kiel Reese (Texas A&M University, USA), along with Ian Marshall (Aarhus University, Denmark) and Megan Mullis (Texas A&M University, USA), analyzed Baltic Sea sediments to see what kinds of microbial activities occur at depths down to 42 meters below the seafloor. The researchers found that resident microbes are surprisingly active in this high-carbon, low-energy environment.