MarineE-Tech cruise to Tropic Seamount (11 November 2016)

We are now about two weeks into the RRS James Cook cruise, which departed from Santa Cruz, Tenerife, on 29 October 2016. The current cruise forms part of the MarineE-tech project (marine ferromanganese deposits — a major resource of e-tech elements).

ROV Autosub 6000 being launched

The project is funded by the NERC Security of Supply of Mineral Resources (SoS MinErals) research programme, which aims to understand 'e-tech' element cycling and concentration in natural systems, and to determine how to minimise the environmental impacts of extraction.

The e-tech elements are those mineral raw materials critical to environmental technologies and for which concerns about security of supply exist, such as:

  • cobalt
  • gallium
  • indium
  • selenium
  • tellurium
  • heavy rare earth elements

MarineE-tech aims to improve understanding of e-tech element concentration in sea-floor mineral deposits.

The project partners involved in this cruise are the BGS, the National Oceanography Centre (NOC), HR Wallingford and the University of São Paulo, who are running a parallel research programme on ferromanganese (Fe-Mn) deposits on the Rio Grande Rise, funded by the São Paulo State Research Foundation (FAPESP).

Study area

Fe-MN crusts

Some of the e-tech elements are highly concentrated in hydrogenous Fe-Mn crusts, which develop on oceanic submarine mountains, or seamounts.

The MarineE-tech study area is located in the north-east tropical Atlantic, about 650 km south of the Canary Islands (about two days' sailing on the RRS James Cook), and at the south-west end of the Canary Island Seamount Province. The islands, along with more than 100 seamounts that extend over a distance of some 1000 km, form one of the most significant volcanic provinces in the Atlantic Ocean.

Our research focuses on the Tropic Seamount, the southernmost in the archipelago (23.5° N, 20.4° W). Tropic Seamount has an area of about 770 km2, comparable to the island of Anglesey in North Wales. Previous, limited work has identified Fe-Mn crusts on this and a number of the other seamounts to the south of the Canary Islands.

Project aims

Fe-MN crusts

Fe-MN crusts being analysed

During the six-week cruise we plan to assess the distribution and thickness of the Fe-Mn deposits, through a combination of high-resolution sea-floor imaging and detailed sampling across the range of heterogeneous environments that exist on the seamount. The new samples will be used to characterise the gross geochemical composition of the crust, and the micro-scale mineralogical, textural, geochemical and isotopic composition of individual growth layers.

These data will be used to assess the significance of the temporal and spatial environmental factors, and the processes (including palaeo- and modern oceanographic conditions e.g. sea-bed morphology, sedimentation rates, upwelling rates and microbiology) that control the compositional, textural and thickness characteristics of sea-floor Fe-Mn deposits.

We will also be collecting data on the seamount ecosystem, and conducting plume generation and modelling experiments to investigate the potential environmental impacts from exploring for and extracting Fe-Mn deposits. We plan to acquire bulk samples of Fe-Mn crusts, which will be used to assess the potential for the recovery of e-tech elements from these resources using novel, low-energy and low-carbon extraction technologies such as bio-processing, ionic liquids and hollow-fibre membranes. This work is being led by the University of Bath.

Bathymetric surveying

New ship-board multibeam swath bathymetry

To date, we have been focusing on acquiring new bathymetry data across the seamount to inform subsequent mission planning. We are initially mapping the area using ship-board multibeam swath bathymetry (25 m resolution) and a geo-acoustic sub-bottom profiler. These data will be used to identify areas of rock outcrop (from acoustic backscatter), and sub-areas will be identified for detailed follow-up surveying using the NOC's Autosub 6000 autonomous underwater vehicle (AUV) and the remotely operated vehicle (ROV) Isis.

We have already conducted five AUV missions, principally to the test the Autosub 6000 for acquiring higher-resolution swath bathymetry (1 m resolution), sidescan sonar (5 cm resolution), sub-bottom profiles (10 cm resolution), colour still images and magnetic data. We have 24 hours of operation on the ship, divided between two science shifts (17 scientists in total), so we are almost continuously acquiring new data.

ROV and sea-floor lander operations

Manipulator arm of ROV Isis

Sea floor lander placed on the sea bed ready for monitoring and testing

The primary objective of the first ROV dive was to deploy a sea-floor lander platform on the summit of the seamount. This has been designed by HR Wallingford, with the objective of collecting time-series data on the hydrographic regime and sediment movement in the water column across the seamount. During the cruise we plan to generate sediment plumes on the sea floor by sucking up pelagic sediment with the ROV and blowing it into the water column. This will attempt to simulate potential disturbance associated with sea floor mining. The movement of the sediment plume will be monitored for several hours by a range of sensors on the lander and comparison made with results of previous modelling.

Additional hydrographic data will be obtained from three moorings that we have strategically positioned across the seamount. When we recover these at the end of the cruise they will have been deployed for at least 30 days, and provide a time series dataset on currents, temperature and conductivity (which can be corrected with temperature to give salinity) of the water column around the seamount.

Additional data on the water column are being collected by numerous CTD deployments (we have undertaken 16 to date), which measure conductivity, temperature and depth (pressure), and can collect water samples for subsequent analysis.

Why are we undertaking this research?

Cut sample of Fe-MN crust

The majority of Fe-Mn crusts samples collected from seamounts globally have been acquired by dredging. This indiscriminate technique provides little or no spatial control on the location or depth from which material is acquired. The high-resolution geochemical and isotopic research we are planning at BGS requires the acquisition of a new sample suite with good understanding of the spatial relationship between samples, in terms of their location on the seamount and water depths. In order to accomplish this, we plan to collect samples from specific locations using the manipulator arms on the ROV Isis and a new core drill attachment, which NOC have specifically built for this project. The second Isis mission tested the core drill and obtained a 20 cm rock sample.

We are also mapping the distribution of sediments, Fe-Mn crust, other rock types and sea floor fauna using the high resolution cameras on Isis during the ROV missions.

Contact

Please contact Paul Lusty for further information.