INSPIRE
INternational South-East Pacific Investigation
into Reducing Environments
COMARGE Univ of California
•Where• •Why• •What• •Who• •How• •Back to ChEss Field Programmes•

Where would exploration take us?

We propose a novel, interdisciplinary investigation of interacting Earth-, Ocean- and Life-Science processes in the SE Pacific off Chile. The setting is close to the Chile Triple Junction where the south Chile Ridge is being subducted beneath the Andes at the Chile Trench.

The Chile Rise is one of the past geological pathways between the Pacific and Atlantic Oceans, because it was formerly connected to a complex mid-ocean ridge and subduction zone system, which connected across from the SEPR into the Atlantic between the tip of South America and the Antarctic Peninsula (Barker et al., 1991). For the last 10 Ma, however, the Chile Rise has been isolated from the Antarctic ridge system by subduction beneath South America. To date, the only hydrothermal information available on the Chile Rise is evidence of metalliferous input to the sediments in this region (Marienfeld and Marching, 1992).

The Peru-Chile margin and subduction zone contains unexplored hydrate deposits(Victor Gallardo, pers com) and seep sites venting methane-rich fluids. At shallower depths, between 200 m and 500 m below sea level, the Chile continental margin is intercepted by a well-developed oxygen minimum zone(OMZ). Where this OMZ impinges on the seafloor, dense mats of sulfur oxidizing bacteria (Thioploca) cover the sediments. Isotopic evidence and the occurrence of some symbiont-bearing species indicate that the nutrition of infaunal assemblages in this zone may rely on chemosynthesis (Levin, 2003). Many species of whales feed in the productive waters of the Peru-Chile margin (including minke, southern right, blue and humpback whales) and migrate through this area, moving between summer and winter feeding and breeding grounds. This suggests that whale carcasses have been falling to the sefloor regularly. Finally, the forests of southern Chile provide potential large amounts of sinking wood.
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Why the SE Pacific?

This area has been chosen because it contains a diversity of potential chemosynthetic sites (i.e. vents, seeps, whale falls, sunken wood and OMZ) in close geographic proximity. Investigation of comparable sites in this area will allow an improved understanding of the effects of local environmental factors vs dispersal potential across ocean basins in biogeography of deep-water chemosynthetic ecosystems (main goal of the ChEss project).

The site for our proposed study, the intersecting ridge and margin off Chile, is critical on several counts:

1- Unique natural laboratory: The Chile Triple Junction is one of only two modern sites on our planet where an active ridge crest is being swallowed by a subduction zone. This areas offers the opportunity to study the start (ridges) and end (subduction zones) points of plate tectonics in the same place.

2- Chemosynthetic ecosystems: The SE Pacific offers the unique opportunity to investigate a full spectrum of deep-sea chemosynthetic ecosystems in close proximity: hydrothermal vents, cold seeps, whale falls, wood falls, oxygen minimum zones (OMZs) and gas hydrates.

3- New life-forms: This is a unique unstidied region where we can expect to make big bio-discoveries.
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What are the scientific questions?

Geological hypotheses:

1- The Triple Junction would allow to assess what must be happening in the mantle near a subduction zone.
2- Triple junctions have been recurring around the edge of the Pacific for tens of millions of years. An actual example is southern California where a triple junction resulted in the development of the San Andreas Fault. Exploring the modern Chile Triple Junction may provide valuable insights elsewhere, with important implications in seismic risk evaluation of inhabited areas.
3- The Chile margin is promote to up to magnitude 9 earthquakes. A recent M9 earthquake in Chile (1960) accounts for more than 33% of ALL the seismic energy released by ALL earhquakes on Earth between 1920 and 1991. We plan to map the seafloor close to the epicentre, seek for the 15 m high fault-scarp that some studies predict was produced, and investigate potential for fluid flow linked to seismic activity.

Chemical hypotheses:

1- The complex plate tectonics of the SE Pacific is likely to dirve a wide range of fluid flow.
2- As well as typical black smokers, there is the potential for finding organic-rich fault-controlled vents. Such sites represent a possible mechanims for spontaneous abiotic organic synthesis, which are exciting potential processes linked to the origins of life.
3- Subduction zones are characterised by seepage of fluids rich in methane and sometimes more complex (and more valuable) hydrocarbons. Exploration of the Chile margin will determine the characteristics of fluid seepage in this area.
4- Present seismic data give evidence of abundant gas hydrates along the Chile margin. Gas hydrates are methane and water locked together in solid form. These systems are only stable under quite limited pressure-temperature conditions, and can be destabilised by release of pressure (e.g. through lowering of sea level linked to climate change) oruplift of the seabed (e.g. Andes"crumple zone"). Studying how hydrates become unstable and release their methane (potent greenhouse gas) may be of wide-ranging interst to any ocean margin where gas hydrates occur.
5- Gas hydrates are of increasing interest to the hydrocarbon industry as potential explotable resources.

Biological hypotheses: links to the ChEss - Census of Marine Life initiative

1- We expect the SE Pacific region, remote from all previous studied chemosynthetic ecosystems, to host new species as yet unknown to science, and may be even new assemblages that would fall into a new biogeographic province. 2- Phylogeographic studies on the species that compose the SE Pacific chemosynthetic communities will provide data to assess the mechanisms for gene flow to the area and connectivity with other ocean basins. Three main pathways are suggested: a) migration along the seafloor down the South American margin; b) larval dispersion in the circumpolar deepwater current, which flows NW-SE along the southern flank of the Chile Ridge before being deflected South then East throgh the Drake Passage into the South Atlantic; c) isolated evolution through in situ adaptation of local deep-sea fauna.
3- The close geographical proximity of different chemosynthetic sites (vents, seeps, OMZs, whale carcasses and wood falls) offer a unique opportunity to study the degree of species overlap between different ecosystems. This would provide essential data to assess phylogenetic and biogeographic questions related to the invasion and colonisation of chemosynthetic sites, both at ecological and evolutionary scales.
4- The physiological adaptations of chemosynthetic species to extreme environmental factors (i.e. high turbulence, high pressure, lack of light, high toxicity, high temperature at vents) offers potential findings of interest to biotechnological and pharmaceutical industries.
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First exploration of the Chile Triple Junction and Chile margin

Over 22 days in April 2010, an international team of scientists on board RV Melville conducted preliminary exploration for hydrothermal plume signals along the East Chile Rise where it intersects the continental margin at the Chile Triple Junction. T he AUV ABE, outfitted with cameras and chemical sensors, was used in combination with instrumentation to measure conductivity/temperature/depth (CTD), a video-guided sediment corer and a bottom trawl to locate and characterize heretofore unknown, and some barely known ecosystems. Evidence from in situ sensing and water-column chemistry indicate the presence of two sites of venting, one right at the triple junction and a second one 10 km north of the triple junction along axis. A hot sediment area and methane seeps were discovered within 30 km of each other.

Sampling has revealed the presence of chemosynthetic fauna, including Frenulate Siboglinids, juvenile Bivalves (unknown seep /vent affinities), unique Syllid polychaete, Xenophyophores, Ampharetids and Aplacophorans.

This cruise was supported by the University of California Ship Funds, the National Oceanic and Atmospheric Administration Office of Ocean Explorations and Research (NOAA-OER), the Census of Marine Life ChEss and COMARGE projects and the Total Foundation.

A project for further exploration, observation and sampling is being planned, including a new multidisciplinary cruise. A proposal is being developed between USA, German and Chilean colleagues to conduct further geological and AUV-based exploration in the INSPIRE region.

 

 
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