Hercules Under the Sea
Findings Log: 5/13/11
Today we are descending with Little Hercules to a location on the eastern limb of the Galápagos Rift where a strong hydrothermal plume signal (4a west) was recently observed. Hopes are high, feelings were anxious. When exploring unknown areas of the deep-ocean, feelings of great anticipation change the way we think about deep-ocean geology and biology.
We are already discovering strong evidence for recent eruptions on the neighboring ridge segment: microbial blooms and the absence of any sessile animal colonization. We are visiting an area where we knew a vent field existed 6 years ago, that is now apparently no longer there. What will today bring?
Hercules Discovers Pillow Lava
At the bottom, we are exploring the landing site near 85° 54.648 W, 00° 46.104 N at a depth of 2560m before moving to the west. We have located what looks to be active fissures and grabens in the area. Upon reaching an active graben, Little Hercules moves through water laden with increasing particulates, and encounters pillow lavas that host increasing numbers of brachyuran crabs. It is clear that we are close to hydrothermal activity. Places of faulting are good candidates to find hydrothermal activity, as the breaks in the rocks provide the necessary permeability for hydrothermal vent formation and maintenance. We are coming upon the edge of an extensive field of empty clam shells, likely of the species Calyptogena magnifica. Patches of Riftia tubeworms, mostly small cm-long colonizing individuals, but a few large ones, with tube lengths reaching approximately 70 cm in length were observed living amid shimmering water rising from between pillow lavas and lobes. Grabens are an elongated block of the earth’s crust lying between two faults and displaced downward relative to the blocks on either side, as in a rift valley.
A Hidden Clam Forest
We begin surveying the vent field, exploring the areas of diffuse flow and then around the perimeter to get a sense of the dimensions of the entire field. A few live clams were observed in the active center of the field as well as in the margin (an abundance of shells were > 25 cm in length). In the active-flow areas, there was evidence of recent colonization by small (< 2cm long) tubeworms including Riftia, Oasisia, and potentially Tevnia, a species previously unknown from the Galapagos Rift, along with highly–abundant, yet small (< 3cm long) bathymodiolin mussels filling cracks and crevices in the lobate lavas.
The low-temperature hydrothermal vent field is named the “Tempus Fugit Vent Field”—loosely translated from Latin as “time waits for no one”
The Tempus Fugit Vent Field has been the focused location of varying periods of hydrothermal activity for at least the past 20 years, indicated by the presence of extensive beds of clam shells, broken and deteriorating, both along the margins of the field as well as in the central active venting area. Given the extent of living and dead clams around the periphery, this may be one of the largest vent fields found yet on the Galapagos Rift (spanning 130m by 40m).