For Jason’s 3rd dive on this cruise (and 673rd dive ever), we’ve moved on from the hot hydrothermal pits, ledges and chimneys near the summit of Loihi Seamount to its colder, lower-most flanks. Generally referred to as “FeMO Deep” (for its discovery during the first Fe-Oxidizing Microbial Observatory expedition in 2006), this site is 5+ kilometers below the surface and characterized by ultra-diffuse hydrothermal flow. In other words, it’s really far away and not very warm. Sort of like visiting another planet.
But ultra-diffuse though the hydrothermal flow may be, it’s still enough to support microbial life. And not just a little life, either. Among the pillow basalts strewn about this otherworldly deep-sea landscape are microbial mat communities that range from patches a few centimeters thick to extensive jelly-like blankets up to 2 meters thick (maybe even more) and thousands of square meters wide.
Why are these extraordinary mats here? Are their presence and extent controlled thermally, geochemically, and/or by biological adaptation? And how do these thick, iron- and manganese-rich mat environments get incorporated into the geologic record over long timescales? Could they be modern analogues for mineralogically similar geologic formations like jaspers and massive umber deposits? The samples we’re collecting at FeMO Deep will help us begin to address these questions.
In addition to syringe samples, we’ve been collecting scoops of mat and “slurp samples” (above), which are what they sound like: samples collected by slurping up large volumes of mat and water with a vacuum. Some slurp samples have been revealing color banding beneath the mat’s surface.
We’re collecting mat samples and electrochemical sensor data at both live mats and “moon mats”, or dead mats that are cold and cratered, like the surface of the moon. Why do some mats grow thick and wide, then die out? In this dynamic deep-sea environment, hydrothermal flow can be ephemeral, sometimes shutting off the energy supply in one place and turning it on in another.
All this fieldwork at FeMO Deep has kept us busy, but we still made time to look at some weird deep-sea creatures. Check out the bizarre purple tadpole-like fish spotted on the 8 pm–midnight watch—no one in the control van had ever seen one before.
–Cat Wolner, NSF
Photo credits: all photos from the Jason control van