Hydrothermal vents from the Azores

Transcription

1 Hydrothermal vents from the Azores Ana Colaço Center of IMAR from University of Azores Departement of Oceanography and Fisheries 1

2 Hydrothermal vents are zones of fluid expulsion from the sea floor, normally associated with sea floor spreading or tectonic plate subduction. Minerals contained within the expelled fluids are utilised as an energy source for vent bacteria. These specialised microbes form the basis of a unique class of ecosystem operating independently from the photosynthetically driven system that dominates the rest of the biosphere. Humphris and McCollum, Oceanus, 41 (2), 1998 Water infiltrates through fissures in tectonic active areas Mostly spreading centres (ridges) Water heats up and picks up minerals from the rocks Returns to surface as hot (up to 400 C) mineral laden (mostly sulphidic) fluid Black Smokers (hotter) Translucid smokers (cooler C) Minerals precipitate either immediately or travel some distance and form metalliferous deposits 2

3 Missão SEHAMA, 2002 FCT IFREMER ATOS Missão SEHAMA, 2002 FCT IFREMER ATOS IFREMER ATOS Missão SEHAMA, 2002 FCT IFREMER ATOS Missão SEHAMA, 2002 FCT Missão SEHAMA, 2002 FCT 3

4 Deep-sea ecosystem km² 200 m 3800 m Darkness / cold (t < 4 C) species Biomass < 1 g/m² 4

5 Hydrothermal chemistry Chemical reactions: Sulphates reduced to sulphides Nitrates reduced to ammonia The bicarbonate converted in CO 2 Mg is removed Reduced forms of Fe, Ni, Cu, Zn are produced 5

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7 National Geographic Symbiotrophic species 7

8 Azores Triple Junction 32 sp. Rainbow 2300 m IFREMER 183km 70 sp. IFREMER Lucky Strike 1700 m 89km 37 sp. IFREMER Menez Gwen 840 m 8

9 When compared with seawaetr fluids are very rich in metals Missão SEHAMA, 2002 FCT Missão SEHAMA, 2002 FCT Menez Gwen 840m Lucky Strike 1700 Rainbow 2300 Seawater ph H 2 S (mm) ~0 CO 2 (mm) <16 - CH 4 (mm) ~0 Cl (mm) Fe (µm) < Cu (µm) <2 < Zn (µm) <2 < Missão SEHAMA, 2002 FCT Douville, Charlou et al. (2002), Charlou, Donval et al. (2000), Charlou, Donval et al. (2002) 9

10 Tarasov et al, Chemical Geology 10

11 Canet and Prol-Ledesma Geological Society of America Special Paper

12 SSHV are found in various tectonic settings, mostly in relation to plate margins. Thus, they are located along island arcs and in shallow segments of mid ocean ridges under the influence of hot spots Shallow water hydrothermal vents typically release free gas and hot water, thus creating extreme local conditions. These systems are strongly variable in space and time, and are often ephemeral (i.e. display a short duration ranging from months to decades) ImagDop 12

13 Fluids within a shallow water submarine hydrothermal system may be derived from any one or a combination of the following sources: meteoric water, seawater, magmatic water ImagDop 13

14 ImagDop/NIO Shallow, Deep vent differences A striking feature of SSHV is the presence of exsolved gas, producing a conspicuous bubbling Lower temperatures than those discharged d by black smokers; nevertheless, they can transport dissolved metals in amounts enough high to produce deposits of oxides, sulfides, and precious SSVH can show intermediate geochemical and mineralogical characteristics between deep sea vents and sublacustrine hot springs Biotic communities inhabiting SSHV clearly differ from those of deepsea vents by the presence ofdiatoms, bacterial and algal mats, and phytoplankton. Deep sea vents host a vast diversity of highly specialized and symbiotrophic species, and their communities show a more complex structure, with vertical and lateral zoning and a greater biomass Formation of large sulfide rich structures, such as mounds and chimneys, is a distinguishing feature of deep sea vents. 14

15 Tarasov et al, Chemical Geology 15

16 Shallow submarine hydrothermal sites occur along the flanks of volcanic islands and the tops of seamounts. Research on these systems is important because: They are considered modern analogs for epithermal metal deposits, They may have significant impact on the chemistry and ecology of the surrounding environment, Knowledge gained from these systems can help to understand the elements cycling and sediment alterations, which in turn may be applied to deep water systems and the genesis of ore deposits. ImagDop/NIO 16

17 Canet and Prol-Ledesma Geological Society of America Special Paper 422 Shallow-water hydrothermal system of Palaeochori Bay, Milos Island, Greece. Visual impression of the site, gas bubbles indicate active venting, brown and white surfaces correspond to different geochemical precipitates (courtesy of Roy Price) 17

18 Canet and Prol-Ledesma Geological Society of America Special Paper

19 Shallow water hydrothermal vents in the Azores ImagDop 19

20 (solid, spreading ridges; dashed, transform faults; dotted, uncertain boundary). Red dots are teleseisms (courtesy of National Geophysical Data Center) and triangles are active and dormant volcanoes. Vogt & Young,

21 Vogt & Young, 2004 ImagDop 21

22 ImagDop 22

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24 250 ImagDop 200 ImagDop 150 White Zone Yellow zone T(ºC) S (µm) ph H2(µM)/100 CH4(µM) Cu(µM) Pb(nM) Ba(µM) Fe(µM)/100 Mn(µM) M) Co(µM) Cd(µM) ImagDop ImagDop 24

25 Plumas de bolhas a 200 metros nos flancos do Banco D. João de Castro 25

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27 Vent scenario 27

28 ImagDop 28

29 ImagDop ImagDop ImagDop ImagDop 29

30 What we want to do: Multibeam mapping Video transects with the ROV SP Video transects with divers with scooters Photographs on a 2 3 meters circle Choose sites to sample 30

31 Planning M T W Th F Talks Divers??? END ROV and Multibeam Multibeam ROV and Divers?? The video and photographs will be used to Georeferenced photo mosaicking ROV and divers one hour before the High and Low tide 31

32 Sampling for characterization: 2.0m 1.0m 0.5m 0m Gases Fluids Sediments Microbes Algae Animals 32