Definitions

Question 1

fast spreading

Answer 1

80-120 mm/yr. topographic high, very narrow rift zone (~50-100 m across), eruptions common, hydrothermal vents widely spaced, short-lived hydrothermal systems.

Question 2

intermediate spreading

Answer 2

50-80 mm/yr. topographic high, or axial valley, eruptions less frequent than fast-spreading, diking events without eruptions, may host high concentrations of vent fields.

Question 3

slow spreading

Answer 3

20-50 mm/yr. deep rift valleys, highly faulted, disrupted crust, mantle rocks exposed at the seafloor, 50,000 yrs between eruptions, long-lived hyrdothermal systems.

Question 4

magma chambers

Answer 4

provide heat that drives hydrothermal circulation. underly all of the 5 major vent fields on the Endeavour Segment.

Question 5

Intense seismic activity and faulting within the axial valley

Answer 5

believed to promote the long- lived hydrothermal fields and large sizes of the chimneys - One of the chimneys - Godzilla - reached 145 m tall in 1996.

Question 6

Seismic activity during opening of fractures

Answer 6

promotes hydrothermal flow and heat extraction from the crust = more intense hydrothermal activity and higher heat flux out of the system.

Question 7

From 1999-2007 seismic activity was high underneath the Endeavour Segment

Answer 7

Several seismic swarms are interpreted to reflect a ~ 6 year period of extension along the axis and diking events.

Question 8

dike injection

Answer 8

fundamental to formation of the oceanic crust. a) new, short-lived hydrothermal diffuse flow sites are formed in places where venting had not previously occurred; b) temperatures in pre-existing black smokers increase by 5-10 degrees or more; volatile concentrations increase rapidly in the black smoker fluids - particularly carbon dioxide and hydrogen; c) snow blowers form that may last from months to a year; d) vent animals rapidly colonize the new eruption sites (within 3 months or less). These environments change rapidly. The diking events are characterized by 1000’s of small earthquakes that occur as swarms over short-periods of times (days to a couple months). The earthquakes are small in magnitude (e.g.

Question 9

black smokers

Answer 9

some of the most extreme environments on earth. A microbe recovered from Endeavour held the highest temperature of life known for several years - 121°C. Microbes that include both Archaea and Bacteria are found within the walls.

Question 10

pacific vs Atlantic

Answer 10

Vent animal communities in the Pacific and Atlantic are different - for example, the Pacific vent sites are commonly dominated by tubeworms, while those in the Atlantic are commonly dominated by swarms of shrimp.

Question 11

The discovery of hydrothermal vents in 1977

Answer 11

was a major paradigm change because of the finding that hydrothermal vent animal communities were supported by chemosynthesis. In these environments, chemosynthetic microbes are the base of the food chain–they are the primary producers.

Question 12

Hydrothermal circulation in the oceanic crust is important because:

Answer 12

1) Significant cooling of the oceanic crust occurs during circulation of seawater and because of this significant heat is lost to the overlying ocean in the form of venting. 2) Profound changes in chemistry of both rocks and fluids occurs. 3) Venting forms important mineral deposits, which some countries are now mining for gold, mercury and copper. Smaller chimneys (less than 10m) indicate fast spreading and diking erupt ice events likely change the permeability of the crust by rearranging up flow channels. Common for eruptions to cover black smoker chimneys and sites of diffuse flow.

Question 13

profound changes occur in chemistry

Answer 13

1) all sulfate is lost due to precipitation of anhydrite (CaSO4), 2) all magnesium is lost - goes into alteration minerals (e.g. clay), 3) fluids become acidic, 4) fluids become enriched in magmatic gases, 5) rocks become depleted in metals - goes into fluids

Question 14

Gases such as carbon dioxide and hydrogen sulfide in the hydrothermal fluids

Answer 14

support novel microbial communities that thrive in the absence of oxygen. Unlike plants on the continents that utilize energy from the sun (photosynthesis), many microbes in the seafloor and vent environments utilize the gases - this process is called chemosynthesis and was a MAJOR, revolutionary discovery about vents. These single-celled organisms can also use various metals - arsenic, copper, cobalt, mercury, iron and even uranium.

Question 15

oceanic crust

Answer 15

largest fractured aquifer system on Earth. the entire volume of the ocean is circulated through the crust every 8-10 million years. A major discovery was that low temperature circulation of fluids away from spreading centers (i.e. on the ridge flanks and even farther away from the spreading centers) rivals that of all rivers to the oceans and is ~3 times greater than the sum of high temperature discharge at mid- ocean ridges.

Question 16

hydrothermal vents

Answer 16

entire volume of ocean circulates through the ocean crust every 8-10 mill yrs. earth’s geothermal output is ~44 TW with most heat loss occurring through the ocean basins. low temp. flow on ridge flanks rivals the discharge of all rivers to the ocean and is ~3 orders of magnitude greater than the sum of high-temp. discharge at mid ocean ridges

Question 17

megaplumes

Answer 17

may be common features of seafloor eruptions. One hypothesis is that they form during injection of 1200°C melt into water-saturated oceanic crust. This effectively vaporizes the crustal fluids, sending them into the overlying water column. The plumes rise >1000 m (>3000 feet) into the overlying ocean and are characterized by higher temperatures than background ocean waters, they have higher concentrations of methane, hydrogen, and helium. One of the most important discoveries is that these plumes entrain microbes that were once beneath the seafloor. Analyses of these organisms provides windows into the subsurface biosphere. Evidence that the organisms are from beneath the seafloor is that many require higher temperatures (>80-90°C), and they can not tolerate oxygen. Many also require carbon dioxide, a magmatic gas that is especially enriched in fluids during eruptions. This has lead to the hypothesis that the microbes undergo a bloom in the subsurface following a seafloor eruptions or diking event (and perhaps prior to an eruption).

Question 18

formation of megaplumes

Answer 18

never been directly witnessed. They can reach up 20-70 km in length and 20 km across. They may form during a single day.

Question 19

phase separation processes

Answer 19

which include both boiling and supercritical phase separation (condensation of brines) are important in both submarine hydrothermal vents and in magma chambers. Because seawater contains ~ 3.2 wt% NaCl (Sodium Chloride), it behaves very differently than pure water – hence both boiling and supercritical phase separation are common in submarine systems. At the critical point for seawater (298 bars = 2980 meters of water and at 405°C), the fluid properties are nonlinear - fluids become infinitely expandable/compressible.

Question 20

Many of the vent fluid compositions at Endeavour

Answer 20

reflect both boiling and phase separation at depth. For example, in 1999-2000 the highest temperature vents were boiling, resulting in near fresh water salinities. Other vents have fluid salinities twice that of seawater = condensation of brines at depth. These fluids are now venting out of the chimney orifices.

Question 21

boiling

Answer 21

In part governs composition of gases coming out of vents: boiling = higher gas concentrations, lower salinity of exiting fluids. Chlorinity influences metal complexing = boiling fluids increases metals in shallow systems.

Question 22

supercritical phase separation

Answer 22

Generates very high brine concentrations - occurs in both seawater-dominated systems and within magma chambers (@>700°C) up to 70 wt % NaCl.
Chlorinity influences metal complexing = magmatic fluids reach high concentrations of metals (chalcopyrite, pyrite). May influence microbial community composition in that halophiles (salt-loving organisms) have been found in high abundances in fluids at Endeavour- these organisms also tolerate very high metal concentrations.

Question 23

axial volacano

Answer 23

Axial is the largest and most magmatically active volcano off the WA-OR coast, having erupted in 1998 and 2011. It is on the Juan de Fuca Ridge (which spreads at ~ 6 cm per year- the rate that your finger nails grow) and hosts three hydrothermal fields. The basaltic melts have very high carbon dioxide concentrations. may erupt every 10-15 years.

Question 24

lost city

Answer 24

discovered in 2000. located far off axis (>20 km) of the Mid-Atlantic Ridge at a water depth of ~ 800 m. hosts 60 m tall carbonate chimneys that rest on mantle rocks. The site is located on the Atlantis Massif (mountain) that is formed by long-lived (> 1 million year) faulting that has stripped off volcanic and dike rocks, and most of the gabbros. Hence, the mountain is dominated by mantle rocks with few small gabbro bodies. As seawater migrates through the mantle rocks it undergoes serpentinization (alteration) reactions that produce fluids distinctly different than black smoker fluids.

Question 25

serpentinization

Answer 25

1) high pH (9-11) fluids that range in temperatures from ~40-90°C; very low metal concentrations; fluids are enriched in hydrogen, methane, and other low molecular weight hydrocarbons; carbon dioxide is absent! 2) The porous chimney walls host microbial communities that thrive off of methane and hydrogen. 3) Age dating indicates that Lost City has been active for at least 150,000 years, making this site the most long-lived hydrothermal field currently known in the worlds’ oceans.

Question 26

why the discovery of lost city changed how we view the role of black smokers in the origin of life

Answer 26

hosted on >1 mill yr old mantle rocks; 60m tall actively venting carbonate towers; venting

Question 27

black smoker chimneys

Answer 27

found on all spreading centers; fueled by cooling volcanoes; pressures 200-400 x atmospheric; boiling common; temps. reach >380C; fluids enriched in carbon dioxide, methane, hydrogen sulfide, metals, very acidic (pH 1-2); support dense and diverse biological communities; mixing of hydrothermal fluids and seawater causes metal-rich chimneys to form that reach 45 m in height; chimneys host diverse colonies of microbes that thrive on volcanic gases and metal-rich fluids; upper temp limit to life >122C.