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Dorado Outcrop

A “fire hose” of cool hydrothermal (5-20°C) venting on a ridge flank

Discovery, sampling, and quantification of flows from cool yet massive ridge-flank hydrothermal springs on Dorado Outcrop, eastern Pacific Ocean

An expedition for investigating the Dorado Outctrop is scheduled for 6-27 November 2013 (cruise report now available) to explore for and sample from springs discharging cool (5 to 20°C) hydrothermal fluids on 23 million year old seafloor on the eastern flank of the East Pacific Rise. The Principal Investigators of this NSF-funded effort are Geoff Wheat (University of Alaska Fairbanks), Andrew Fisher (University of California Santa Cruz), and Samuel Hulme (Moss Landing Marine Laboratory). The expedition will include multi-beam mapping with a surface ship and the AUV Sentry, and seafloor exploration, sampling, and measurements using the ROV Jason.

Dorado Outcrop Site Maps. Top left: The Tico Flux area is located off the coast of Coast Rica on 18-24 Ma seafloor of the Cocos Plate, comprising lithosphere produced at the Cocos-Nazca Spreading Center and the East Pacific Rise. Top right: Multi-beam data overlain on gravitational bathymetry illustrate seafloor relief (modified from Hutnak et al., 2008). Dorado Outcrop and Tengosed Seamount are located within a 14,500 km2 area of cool seafloor, where the heat flux is generally 10-40% of lithospheric predictions. Bottom left: Fourteen gravity cores were taken on and near Dorado Outcrop providing a measure of the fluid composition in upper basaltic basement (from Wheat and Fisher 2008).

Regional data collected during two earlier surface ship programs, coupled with state-of-the-art surveying, measurement and sampling tools proposed herein, lend confidence that we will address the following three hypotheses. Dorado Outcrop:

  • produces 200-350 MW of lithospheric heat (equivalent to a black-smoker vent field) as a massive flow of cool hydrothermal fluid (≥ 103-104 L/s) having a temperature of 10-20°C;
  • discharges fluids that are chemically different from bottom seawater, resulting from seawater-basalt reactions within the crust and through diffusive exchange with sediment pore waters overlying basaltic crust as the basement (formation) fluid flows from recharge to discharge sites and sediment impact are greater than those from basalt even though fluids flow through the permeable basalt and not impermeable sediment; and
  • generates fluid, thermal, and chemical fluxes that have a regional influence and are globally representative of ridge flank hydrotherm systems (RFHS) in general, thus allowing an accurate assessment of geochemical budgets from RFHS. Given that the minimal salt content of rivers affects ocean chemical composition, chemical anomalies of similar magnitude in RFHS could also affect the composition of the oceans.

If proven correct, the proposed work will transform the now-common view of RFHS comprised of diffuse “seeps” of slowly moving fluids, rather than "fire hoses" of cool water that have a global impact. Given that this will be only the second natural hydrothermal effluent from a RFHS ever sampled from Earth, it is imperative that materials are sampled for microbiological characterization. Furthermore, this site has elements that are similar to and different from those at North Pond and on the eastern flank of the Juan de Fuca Ridge, making Dorado Outcrop an ideal location to further our understanding of microbiological processes and assess physico-chemical controls or triggers on microbial metabolic pathways. To advance such studies the Spring 2013 C-DEBI Call for Proposals highlights the desire for proposals to add-to the NSF proposed science.


-- UNOLS Expedition, December 7- December 23, 2013
AT26-09 Discovery, sampling, and quantification of flows from cool yet massive ridge flank hydrothermal springs on Dorado Outcrop, eastern Pacific Ocean
Chief scientist: C. Geoffrey Wheat
[Cruise Report]

UNOLS EXPEDITION, November - December 2014

Associated C-DEBI Funded Projects

> See the Dorado Outcrop NSF Proposal [PDF]
> Dorado Outcrop cruise prospectus [PDF]
> About our major programs
> Our expedition schedule


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