Sunday morning dawns on the Alvin hangar, but where are the divers? Starting at 5 am, the Alvin crew springs into action and prepares the sampling basket, and also this dive’s pilot, Jefferson Grau, is ready, but who are the science observers? Traditionally, their identity is a closely guarded secret until the last moment…
At last, at dawns early light, the science observers step forward: Andreas Teske together with first-time diver Brett Baker! He is certainly one of the most calm and composed dive novices ever, and looks forward to this experience with an open mind, come what may. After all, newbie divers can always write a trip advisor review.
The first task of the day is to obtain as many sediment cores as possible from this yellow mat, called Aceto Balsamico since it is very rich in acetate; it also has very high loads of ammonia, some methane, a lot of sulfide, diverse low-molecular weight fermentation products, and who knows what else besides. Its moderate temperates, only 20 to 25C warm at 45 cm depth, means it is microbially inhabited and active.
From time to time, small fish swim across it and presumably leave tracks in the yellow/lime green cover; on close inspection the yellow material turns out to be fluffy and filamentous. A new type of sulfur-oxidizing bacteria perhaps?
A few meters ahead, we meet an old friend, Marker 14. Back in 2009, the Marker 14 site contained the most heavily instrumented and exhaustively sampled mat; much of what we know today about Guaymas Basin microbial mat structure and function we owe to this very cooperative sampling location. It will be featured again prominantly in Brett’s upcoming genome paper, as some of our best data are from site. However, in Guaymas Basin you do not encouter the same hydrothermal mat twice; the landscape is constantly changing. Against this background of constant change, the persistence of the Aceto Balsamico mat site is a small miracle.
After a big coring session [36 cores] we leave for Rebecca’s Roost, the largest hydrothermal edifice in this part of Guaymas Basin, a massive hydrothermal tower 20 meters tall. Sulfidic, warm vent fluids seep through the base of this huge formation and create a hydrothermal garden of Riftia tubeworms and Beggiatoa mats.
At the top of Rebecca’s Roost, ca. 20 meters above the seafloor, hydrothermal mineral formations grow sideways into the cold ocean water, as vent water escapes laterally and its minerals precipitate to form pagoda roofs. The central channel ends in an elaborate small chimney that is venting hot water; this structure is so delicate that touching it with the robot arm would probably crumble it to pieces. The rooftop landscape of Rebeccas’s Roost brings serious competition for anything created by Antoni Gaudi in Barcelona; Mother Nature has the best artworks to her credit.
The robot arm of Alvin is breaking some chunks of rock from this active mineral formation, a flange that protrudes sideways below the top chimney. The white and yellow color indicates the presence of sulfide, and growth of Beggiatoa mats; some Riftia have settled here as well. Small chunks of rock fall down and tumble to the seafloor far below; it feels as if Alvin hovers in the canopy of an enormous hydrothermal tree and collects samples from its branches.
At last, our time is up and we have to return to the surface. Will this particular Alvin science observer write a good tripadvisor review?