Findings Log: 7/24/11
We are diving at ~800m. The ROV Little Herc is moving upslope and exploring the rim of the feature, which probably used to be an island shore a long time ago, before resuming movement towards the summit. Upslope, there is an increase in abundance (number of species per unit area) of organisms, and there is a general trend of high abundance of corals, but with low diversity–that is, we are encountering lots of the same species. There is a clear difference in the types of species colonizing the summit margin, compared to lower depths, which are separated by a flat area. The summit margin can be characterized by a high abundance of white brachiopods (these shelled organisms look superficially like clams, but are actually not at all related) and pink brittle stars. The rocks are a puzzling red color, which prompts several hypotheses about their origin. One hypothesis from shore-side scientists is that the rocks are actually fossil shallow-water corals that were formed during a period at which the seamount was above or near the sea surface.
Findings Log: 7/17/11
The area we are looking at over the past few days is a small site along the globe-encircling chain of volcanoes called the Mid-Ocean Ridge. We know there are frequent eruptions along the Mid-Ocean Ridge but we can only put a time and date on the few that we’ve serendipitously come across or monitored with fixed hydrophones (underwater microphones) in a few small areas. Sometimes we see indication of seafloor spreading events (or their immediate aftermath) by detecting the warm and turbid plumes rising up into the water column. This is what attracted us to the sites we are now exploring on the seafloor. This “seam” is where new ocean crust is “born” as molten rock intrudes in long thin dikes, spreading apart the ocean crust and often erupting onto the seafloor. The birth is accompanied by venting of nutrient rich fluids that feed a rapid growth of microbial communities followed by colonization of higher level chemosynthetic organisms such as the giant tubeworms and clams found on the Galapagos Ridge.
Findings Log: 6/30/11
During our third ROV dive on the Galápagos Rift, while searching for active hydrothermal vents, we are experiencing a strong signal in Seirios’ sonar. Immediately, we are approaching the object in near darkness, the form of a towering hydrothermal sulfide spire appeared, then another, and then another, all lining up west-to-east within the graben (an oblong geologic depression) that we are following. However, rather than billowing jets of superheated black fluid and adornment with lush vent animals, these giants are dormant with only rocky remnants of past black smoker chimneys and scars in the rock where colonies of tubeworms once lived. It is like discovering a once bustling city in the jungle, like Machu Picchu in Peru, that was now ghostly dormant. It must have been a very impressive and vibrant sight at the peak of its activity.
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).