P1 – The deep ocean hosts astonishing life forms that thrive in some of the harshest conditions on Earth – the deep seafloor. At 1500 m depth (4920 ft) beneath the ocean surface a 0.5 m diameter “Dumbo” octopus traverses a lobate lava flow on Axial Seamount, Juan de Fuca Ridge.
P2 – Frozen lava columns mark the drain out and subsequent cataclysmic collapse of lava lake ceilings formed during ponding of 1200 °C (2192 °F) melt at the MOR. At a mile or more beneath the ocean surface, the near freezing sea water rapidly quenches the molten lava, forming glass-covered ﬂows that reﬂect the dynamic nature of submarine eruptions.
P7 – The discovery of high-temperature hot springs systems in 1979 was made at MOR spreading center, the East Pacific Rise at 21° N. These high-temperature vents issues jets of metal-rich superheated fluids from the seafloor and are one of the most profound scientific discoveries ever made. Within these extreme environments, characterized by darkness and hundreds of atmospheres of pressure, life was found to not only survive, but flourish. The lush and vibrant communities of tubeworms, sprouting bright red plumes, in areas typically devoid of much color was a startling discovery. Equally surprising was the presence of microorganisms thriving, in the absence of sunlight, by metabolizing volcanic gases at temperatures in excess of 90 °C (194 °F). With the advent of genomic sequencing, we are now gaining insight into the vast diversity of microbes that live on and within the seafloor.
P8 – One of the most spectacular events in crustal formation is the release of billions of microbes from the seafloor during and following seafloor volcanic eruptions. The microbes form whitish sulfide-rich particles that are ejected in dense, billowing streams from the seafloor – called snowblowers, such as the one imaged here following the 2011 eruption on Axial Seamount.
1.1 - The deep-diving submersible Alvin preparing to dive to the axis of the Juan de Fuca Ridge. Alvin carries one pilot and two observers and has made more than 4600 dives to the seafloor since it was built in the 1960s. Alvin currently descends to a maximum depth of 4500 m; however, its titanium personnel sphere was replaced in 2013 with one that is certified to dive in 6500 m. The support ship for Alvin is the research vessel (R/V) Atlantis, operated by the Woods Hole Oceanographic Institution.
1.17 – Maurice “Doc” Ewing (top, left) and Allyn Vine (top, right) on the R/V Atlantis holding one of the first deep-sea cameras in the late 1950s. David Owen deploying a deep-sea camera from R/V Vema in the late 1950s (bottom).
1.25 – The newest deep-diving human-occupied submersible – Alvin, of WHOI – was placed into service and certified in early 2014. It is currently certified to -400 m, but will eventually be able to dive to 6500 m with two observers and one pilot, as it has done throughout its operational career.
1.30 – The AUV ABE (Autonomous Benthis Explorer) developed and operated by WHOI (left) being launched in 2001. The WHOI AUV Sentry (right) has a dive capability of 6 km and includes multibeam, sidescan, and CHIPR sub-bottom sonar, and a variety of water properties sensors, as well as a digital still camera and strobes that enable it to take continuous photographic images of the seafloor. Sentry has now replaced ABE as the AUV system in the National Deep Submergence Facility at WHOI.
1.35 – REMUS (Remote Environmental Monitoring UnitS) are a class of torpedo-shaped AUV’s (left) operated by the Ocean Systems Laboratory (OSL) at WHOI that provide autonomous survey capability over a depth range from 100t o 6000 m. The vehicles have been used for measurement of coastal water properties and currents, high-resolution sidescan and multibeam mapping, and for military applications associated with mine clearing operations in coastal waters. A REMUS 6000 A UV being recovered (right). The OSL Group, operation three REMUS 6000 vehicles simultaneously during several cruises, was responsible for the search and discovery of the black box of Air France Flight 447 (Fig. 1.36) which crashed into themed-Atlantic near 2° N and 32° W in June 2009, on the east flank of the Mid-Atlantic Ridge in water depths of approximately 4 km.
1.41 – Ocean-bottom seismometers (OBSs) on the back deck of the R/V Wecoma of Oregon State University (top) in preparation for deployment for the CASCADIA experiment, an onshore and offshore seismic experiment designed to study large magnitude (>9) megathrust earthquakes along the Washington and Oregon coast (http://cascadia.uoregon.edu/CIET/). An OBS being deployed from R/V Oceanus (bottom left) and the electronics of an OBS housed in a glass pressure sphere (bottom right).
1.48 – Illustration showing the ROV Jason2 and a deep-sea light system used for illuminating the seafloor for high-definition video imaging during a University of Washington experiment on Juan de Fuca Ridge in 2005, in preparation for the installation of NEPTUNE.
1.49 – Illustration depicting the main components of a telepresence system – the ROV at the seafloor making observations (lower left and center), and the fiber-optic cable transmitting data and imagery from the ROV up the cable to the support ship and the scientists onboard (upper right). Via the Internet, these data and imagery are now streamed live to shore-based laboratories, educators and to the general public, who experience real-time interactions with scientists and engineers while getting information from the ROV as it explores the ocean depths (right).
1.50 – A high-definition still camera (foreground) deployed in front of “Mushroom Vent” on Axial Seamount on the Juan de Fuca Ridge as part of the Ocean Observing Initiative experiment, and a 3D thermistor array (blue rods in background) positioned over a diffuse flow vent. The orange coil of cable is the power and data “extension” cord, a fiber-optic cable that transmits the imagery and thermistor data from the instruments back to shore-based laboratories for analysis. Field of view – 6 m.
2.14 – A step-like pattern of increasing compressional wave velocity with depth is typical of the layered structure of the oceanic crust (left). Contacts between layers and the internal structure of layers are best modeled as velocity gradients corresponding to gradational compositional changes (White et al, 1992). Laboratory measurements of compressional wave velocities of oceanic and ophiolite rocks link the internal structure of ophiolite complexes to the velocity structure of oceanic crust (right).
2.15 – The first samples obtained from the seafloor were recovered by dredging – dragging a strong, steel mesh bag across steep, rugged areas of the seafloor. The dredge is connected to the ship by -1-2 cm thick steel wire rope able to withstand 10-25 tons of tension. Dredging continues to be an important means of collecting large volumes of oceanic rocks and for reconnaissance petrological and geochemical studies of the crust.
2.18 – Investigations of the axial regions of active spreading centers (left) and major escarpment “tectonic windows” (right) provide different but complementary perspectives on the oceanic crust and seafloor spreading processes. Numbered black lines showing locations of near-bottom studies – both submersible dives and camera tows. White stars show locations of ODP/IODP drill holes.
2.22 – Drilling into exposures of plutonic rocks on the seafloor has recovered extensive cores of deep crustal gabbroic rocks with diverse textures and mineralogies (left) and serpentinized upper mantle peridotites (right). ODP Leg 154, Holes 924 and 920. Cores are about 5 cm wide.
2.26 – Summary of the layered structure seen in many ophiolite complexes correlated with the oceanic crust and upper mantle. The recurring sequence of rock units in ophiolite complexes inspired the views adopted by the 1972 Geological Society of America Penrose Conference (Table 2.2)
3.2 – The global MOR system is a continuous network of volcanic and tectonic features marking divergent lithosphere plate boundaries. This global perspective highlights the MOR (relatively shallow, light-green area on the seafloor) as it encircles the globe. Differences in morphology of these different parts of the MOR reflect the very different structural, petrological, and morphological characteristics as a function of spreading rate and magma budget. The East Pacific Rise (left globe) is a fast- to superfast-spreading ridge, while the Mid-Atlantic Ridge (middle) is a slow-spreading ridge. MORs in the floor of the Indian Ocean (right) include the Southeast Indian Ridge and Central Indian Ridge spreading at intermediate rates, and the ultraslow-spreading Southwest Indian Ridge.
3.7 – The morphology of spreading centers and adjacent abyssal hills varies dramatically with spreading rate. These images are all at the same scale and have the same color-coded depth scale (lower right). Smooth axial highs with small axial summit depressions occur at high spreading rates, such as the East Pacific Rise. Both axial highs and rift valleys occur at ridges with intermediate rates, such as the Juan de Fuca Ridge. The slow-spreading MAR has a broad rift valley and rugged terrain including dome-like oceanic core complexes. Ultraslow-spreading ridges, such as the Southwest Indian Ridge, have segmented rift valleys and complex, rugged terrain with abyssal hills that are much more irregular and varied than the others shown here.
3.14 – Shaded relief image of the Cleft Segment of the Juan de Fuca Ridge, one of the most intensively studied intermediate-rate ridges, looking from the south (- 44°33’ N) to the north (- 45°05’ N). The elevated summit area (gray to pink) is cut by a distinct -2 km wide rift valley, bounded by fault scarps, which bisects the linear ridges to either side. Young lavas occur in the axial valley (neovolcanic zone) but also occur as isolated flows on the flanks of the bounding crestal ridges. Note the AST or “cleft” is apparent as a thin linear fissure that bisects the axis in the middle of the axial valley. Light gray color is depth range from 2100 to 2200 l’ dark green > 2600 m (modified from Stakes et al, 2006).
3.32 – Tectonic windows into intermediate- to fast – spreading crust of the Pacific provide extensive exposures of upper crustal rock units. Exposures of pillow lavas, sheeted dike complexes, faulted lavas and dikes, and gabbroic rocks occur in a regular layered sequence as found in many ophiolite complexes. Field of view -2 m, except for the gabbroic rock (lower right), which is about 20 cm long.
3.41 – Locations of tectonic windows (escarpments) and deep crustal drill holes in slow- and ultraslow- spreading crust (above): ATM, Atlantis Massif; GOR, Gorringe Bank (Gettysburg and Ormond Seamounts); KTR, King’s Trough; MARK, MAR at Kane Transform; MCSC, Mid-Cayman Spreading Center; OFZ, Oceanographer Transform Fault; SMARK, Southern MARK Area; TAG, TransAtlantic Geotraverse Area; VTF, VemaTransform Fault. Note that the Atlantis II Transform is on the Southwest Indian Ridge. Columnar sections (below) summarizing geology in tectonic windows and deep crustal drill holes in ultraslow- to slow-spreading crust reveal complex geological structures. Only at the Vema Transform does there appear to be a “normal” crustal structure with the rock units anticipated from ophiolites. Other areas show lava lying directly over variably deformed and metamorphosed gabbroic and serpentinized ultramafic rocks. (Data from OTTER, 1984; Karson, 1998; Blackman et al, 2002; Godard et al, 2003; Dick et al, 2008.)
3.44 – Schematic diagram of a fast-spreading ridge and crustal accretion processes creating a uniform crustal structure from a continuous axial magma chamber.
3.45 – Schematic diagram of a slow-spreading ridge and crustal accretion processes creating heterogeneous and discontinuous crustal structure.
4.1 – This 1 m tall “chimlet” at the top of the black smoker chimney called Sully is at a depth of 2200 m on the Juan de Fuca Ridge. It billows 360 °C, metal-rich fluids and is built on a -5 m tall mound of sulfide debris. It hosts a vibrant colony of tubeworms with bright red plumes.
4.2 – Sully, in 2006, hosted multiple black smoker orifices and extinct oxidized sulfide debris. Areas of robust, low- to moderate-temperature diffuse flow support “fat” healthy tubeworms (Ridgeia piscesae) reaching – 0.75 m in length.
4.29 – A community of tubeworms (rifita rachyptila), brachyuran crabs, and vent fish (Thermarces Cerberus) thrive in nutrient-rich, warm fluids issuing from Tubeworm Pillar on the EPR at 9° N. Crabs are ~5 cm across. In 2004, these animals perished at this site due to a rapid cessation of venting, and the 11 m tall sulfide pillar was subsequently destroyed during eruptive events in 2005-2006.
4.30 – The TAG Hydrothermal Field supports dense aggregations of shrimp (Rimicaris exoculata). These animals are of interest because, even though they have no eyestalks, they have a dorsal organ hosting a visual pigment that absorbs maximally near 500 nm. High-temperature chimneys emit light in the non-visible spectrum, supporting the idea that shrimp detect dim light with their non-image-forming “eyes.”
4.31 – Global distribution of distinct biogeographic regions currently recognized for MOR hydrothermal vent fauna [including some non-ridge sites; after Rogers et al. (2012)]. The regional suites of species characteristics of hydrothermal vents can be considerably different in various parts of the world ocean as a consequence of the evolutionary history of the different ocean basins. Vicariant events and physical oceanographic process, species-specific variation in the life histories of individual species, rates of seafloor spreading, and the frequency and spacing of active venting along the MOR system may impact faunal distribution.
4.68 – The actively venting Nature Tower, on the east side of Lost City, rises 30 m above the surrounding seafloor. Significant limestone talus at the base₄ of the structure attests to the collapse of spires and rebuilding as part of the evolution of these complex chimneys. The ROV Hercules and support vehicle Argus are embedded in the photo for scale.
4.83 – The outsides of the active chimneys at Lost City are covered in dense strands of filamentous bacteria that thrive in the mix zones of high-pH, CH₄- and H₂-rich hydrothermal fluids and seawater. The carbonate interstices shrouded by these filamentous microbes serve as microhabitats for numerous species of small gastropods, polychaetes, and amphipods.
4.85 – Geryonid crabs are common features among the ledges and outcrops in the periphery of the main field. Males of this genus will hold the female underneath for long periods of time (e.g., weeks) prior to mating.
4.117 – This black smoker edifice called Bastille, in the Main Endeavour Field, rises m