RRS James Cook JC044
Cruise summary report
| Cruise Info. | |
| Ship name (ship code) | RRS James Cook (740H) |
| Cruise identifier | JC044 |
| Cruise period | 2010-03-25 — 2010-04-22 |
| Status | Completed |
| Port of departure | Port of Spain, Trinidad and Tobago |
| Port of return | Montego Bay, Jamaica |
| Purpose | Research |
| Objectives | JC044 is the first cruise in a two-cruise programme to locate hydrothermal vents on the Mid-Cayman Rise (MCR) and to investigate the nature of those vents. The programme is multi-disciplinary, bringing together biologists, chemists, geologists, geophysicists and physical oceanographers. The over arching goal of this first cruise was to locate sites of active hydrothermal venting and to investigate the chemistry of the venting plumes, the geological setting of the plumes and to understand the control that the local hydrography has on plume distribution.
We hypothesised that hydrothermal activity should be found on the MCR based on three lines of evidence: 1) there has been evidence for hydrothermal activity located on all of the worlds' spreading centres examine to date, including the ultra-slow spreading Gakkle Ridge in the Arctic (Edmonds et al, 2001), Knipovich Ridge in the Arctic (Connelly et al, 2007) and more recently on the South West Indian Ridge (German et al, 1999, Tao et al, 2007); 2) observations and modelling of heat flow within the crust of the Cayman Trough (Rosencrantz et al, 1998; ten Brink et al, 2002); 3) the resemblance of Mount Dent, a sea mount on the western side of the MCR to oceanic core complexes (OCC) on other slow spreading ridges (Smith et al, 2006). During OCC formation lower crustal and upper mantle rocks are extruded and exposed on the seafloor, high temperature venting has been found in association with these OCC's in other ocean areas (Beltenev et al, 2005) and the serpentinisation of exposed peridotites exposed may drive hydrothermal vent systems (Lowell and Rona, 2002) The Cayman Trough may have hydrothermal activity associated with the OCC Mt Dent, these areas have been suggested as host sites for hydrothermal systems similar to the Lost City site on the Atlantic Massif on the Mid-Atlantic Ridge. From data collected on the US cruise in October of 2009, two other possible sites of hydrothermal activity were located. One area in the north of the ridge showed a strong Light Scattering signal (LSS) with a high concentration of total iron and manganese and a high Eh signal, this is typical of a more basaltic hosted system such as that recently identified at in the Antarctic by, members of the present science team. In addition to this site there was a small amount of evidence for a site that was not only rich in particles but also had a marked methane anomaly, this resembles the type of chemical signal you find at mafic and ultramafic vent sites, such as the Rainbow hydrothermal vent field on the slow spreading MAR. The MCR may host deep-sea vent fauna with affinities to Mid-Atlantic vents as result of present-day hydrographic connections; alternatively it may host vent fauna with eastern Pacific affinities as a consequence of a deep-water connection prior to the closure of the Isthmus of Panama, or harbour unique fauna because of its isolation and depth. The MCR therefore presents a unique opportunity to determine the influences of hydrography, geological history, bathymetry and isolation on the global biogeography of chemosynthetic ecosystems, which is a key objective of the international Census of Marine Life ChEss (Chemosynthetic Ecosystems) programme. Investigating the deep-ocean biology of the MCR will therefore advance our understanding of patterns of biodiversity. We planned the work around a structured investigation of three main areas of suspected hydrothermal vent activity. The three areas were located on a research cruise with scientists from the United States who are associated with this present programme. The US cruise in October of 2009 involved both D. Connelly and C. Sands from this cruise. That cruise identified the three areas using a series of CTD casts with light scattering instrument and an Eh sensor to trace hydroth |
| Chief scientist | Douglas Connelly (National Oceanography Centre, Southampton) |
| Coordinating body | Natural Environment Research Council (NERC) |
| Cruise report |  (3.41 MB) |
| Ocean/sea areas | |
| General | Caribbean Sea |
| Specific | Cayman Trough |
| Track charts | (0.07 MB) |
| Measurements | |
| Physical oceanography | |
| CTD stations | Quantity: number of profiles = 71 Description: Vertical profiles of CTD operations, discrete samples. Analysed at NOC |
| Chemical oceanography | |
| Other dissolved gases | Quantity: number of profiles = 71 Description: Vertical profiles of CTD operations, discrete samples. Analysed at NOC |
| Phosphate | Quantity: number of profiles = 71 Description: Vertical profiles of CTD operations, discrete samples. Analysed at NOC |
| Total - P | Quantity: number of profiles = 71 Description: Vertical profiles of CTD operations, discrete samples. Analysed at NOC |
| Nitrate | Quantity: number of profiles = 71 Description: Vertical profiles of CTD operations, discrete samples. Analysed at NOC |
| Nitrite | Quantity: number of profiles = 71 Description: Vertical profiles of CTD operations, discrete samples. Analysed at NOC |
| Silicate | Quantity: number of profiles = 71 Description: Vertical profiles of CTD operations, discrete samples. Analysed at NOC |
| Alkalinity | Quantity: number of profiles = 71 Description: Vertical profiles of CTD operations, discrete samples. Analysed at NOC |
| Geology and geophysics | |
| Geophysical measurements made at depth | Quantity: track kilometres = 600 Description: TOBI Survey |
| Multi-beam echosounding | Quantity: survey square kilometres = 400 Description: Shipboard multibeam survey |
| Magnetic measurements | Quantity: track kilometres = 100 Description: Ship-towed magnetometer |
| Other geological/geophysical measurements | Quantity: track kilometres = 690 Description: Autosub surveys |
| Moorings, landers, buoys | |
| Physical oceanography | |
| CTD stations | 18° 21' 59" N 81° 39' 59" W — Series RCMs with C, T, D and oxygen sensor |
| Current meters | 18° 21' 59" N 81° 39' 59" W — Series RCMs with C, T, D and oxygen sensor |
| Chemical oceanography | |
| Oxygen | 18° 21' 59" N 81° 39' 59" W — Series RCMs with C, T, D and oxygen sensor |
