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WP7 Mission-specific subseafloor sampling
WP leader: Catherine Mével, IPG Paris, France
The deep-sea environment is influenced by a number of processes that are occurring beneath the seafloor, and the need for mission-specific sampling tools is equally diverse and highly multidisciplinary. Deep-sea ecosystems are sustained by fluid venting that supply nutrients (methane, sulphur, metals) at plate margins (e.g. mid-ocean ridges, subduction zones, and transform margins). Fluid flow is guided by faulting patterns and is, therefore, influenced by tectonic activity. Several subseafloor processes generate hazardous events such as earthquakes, tsunamis, volcanic eruptions and flank collapses, sediment mass wasting and submarine landslides (see WP4 above). Gas hydrate, i.e. natural gas embedded in “ice crystals”, is trapped in sediments under specific pressure and temperature conditions; changes in environmental conditions may result in a sudden discharge of huge volumes of methane gas that may trigger submarine slides, and influence the climate (e.g. WP5 above). Moreover, the material deposited on the seafloor represents a record of environmental changes over time. In particular, the sediments are invaluable archives of climate change, essential to predict the future. The subseafloor formations also host a completely unexpected and little explored deep biosphere. The subseafloor environment can only to some degree be studied by remote methods. Drilling has the major advantage of providing samples and boreholes that can be re-entered, in which downhole measurements of in situ properties and installations of instruments for long-term observation can be made. Access to subseafloor samples of drill cores, as well as logging data and long-term monitoring in boreholes, allows key questions to be addressed, and therefore is absolutely essential to understand deep sea subseafloor processes and how they affect ecosystems nowadays.
Subseafloor sampling can been achieved using different types of tools. Ocean drilling to large depths requires the operation of sophisticated and expensive drill ships. Therefore, their operation is best achieved through international collaboration in large scientific programmes. The current programme, IODP (www.iodp.org) has a total funding of $1.5 billion for its 10-year science plan and is thus the largest international geoscientific research program ever. The initial science plan of IODP has identified three major thrusts of research: (1) the deep biosphere and the subseafloor ocean; (2) environmental change, processes and effects; and (3) solid earth cycles and geodynamics (see IODP Initial Science Plan). The program is led by the United States and Japan and has been adopted by 20 nations. Sixteen European countries and Canada has formed the European consortium ECORD, which is a contributing member of IODP. European scientists can submit proposals for future IODP expeditions as well as engineering development, apply to participate on upcoming IODP expeditions, apply to use data from IODP expeditions, and participate in scientific panels within the IODP science advisory structure.
IODP offers access to three drilling platforms: a riserless vessel, the JOIDES Resolution, operated by the USA, a riser vessel, the Chikyu, operated by Japan, and Mission Specific Platforms (MSP), leased on a case by case basis to operate in areas not accessible by the two other drillships (i.e. shallow waters and ice-covered areas). The two drillships are equipped with state of the art laboratories where the cores are described and measurements are performed shortly after retrieved on deck. In addition, they are equipped with measurement-while-drilling and logging-while drilling systems, as well as traditional logging tools and instruments for long term monitoring such as CORKs and borehole observatories. The equipment of the MSPs varies from case to case with the scientific demand. MSPs are operated by ECORD. The concept of MSPs was successfully tested during IODP Expedition 302 when the first climate records under the Arctic Ocean were collected by the joint efforts of two icebreakers that broke up the moving ice of the Arctic Ocean and a drill ship (see also WP2, and ESO documentation).
Ocean drilling to shallow depths can be implemented using less expensive drill equipment. Piston coring is a fairly simple technique that has been used in particular by the IMAGES program to obtain long cores of deep-sea sediments. The Calypso corer, operated from the RV Marion Dufresne, was the unique tool so far that allowed to recover up to 60 m of somewhat disturbed sediment. New corers have been recently developed and their performances need to be assessed. Seafloor drill rigs operable from a standard vessel have been developed by BGS [RockDrill] and MARUM at the University Bremen [MeBo]). These portable drilling systems are landed on the seafloor and operated remotely from a ship, which means that a dedicated drilling vessel is not required. It allows the retrieving of cores to a maximum depth of ~50m in both soft sediments and hard (i.e. crustal) rock. Another successful application of the mission-specific drilling concept was the EC-funded PROMESS project, which drilled several sites in the Mediterranean using a leased ship. Finally, it is important to liaise with the Aurora Borealis project, which is listed on the ESFRI list. This vessel is designed to drill the seafloor beneath the ice pack. If funded, this vessel will be a powerful tool to drill in the Arctic and the Antarctic. Through INSU/CNRS, ECORD is a member of the EC-funded ERICON-AB project to support the preparatory phase of the development.
There are two key aspects to be recognised in subseafloor sampling and drilling: a) to understand the subbottom processes and how they affect the surface (fluid flow, nutrient supply, etc.), and b) to collect subbottom samples as a window into the past in order to learn about ancient ecosystems and paleo-environmental conditions that may have caused extinction of species, global warming, etc. The latter is of particular interest, because the role of viruses or other destructive compounds is poorly constrained. For instance, the Mediterranean Sea is one of the few places on Earth where anoxic deposits rich in former life and organic matter occur (so-called sapropels). Sampling them under anoxic conditions for DNA study and cultivation would represent a big step and outstanding future challenge, and stands in a line with earlier successful conventional coring (ODP Leg 160). Other examples include recent BGS rock drill sampling at hydrothermal vent sites in the Tyrrhenian Sea (cruise RV Meteor M73/2), where solid sulphide ores were recovered in very shallow water depth. Vent-specific macrofauna as well as microfaunal assemblages were recovered in addition to sulphide crusts in an active subduction setting. Similar shallow drilling takes currently place to assess the potential impact on shallow water ecosystems in the North Sea in offshore wind farm areas, and it seems vital that similar, mission-specific drilling is used to carry out similar work along the deeper slopes and deep sea to ensure the sustainable use of those areas along the European ocean margins.
In addition to direct sampling, the seafloor can be probed by additional instruments to collect physical parameters critical for subseafloor and seafloor ecosystems. Although those may be gathered by transducers attached to the sampling/drilling device, or into an instrument that logs the borehole while or after drilling, such in situ technology is regarded in more detail in WP8 (see below).
The current drilling-, sampling-, logging- and observation technology must be developed to improve the quality of samples and borehole measurements. This will ultimately lead to the sustainable use of the deep-sea and subseafloor, and a closer link to industry equally interested in understanding the subbottom of the continental margins (hydrocarbons, offshore construction, CO2 sequestration, to name just a few). Sediment disturbance during piston coring, sediment-, fluid- and gas hydrate sampling under in situ conditions, uncontaminated deep biosphere sampling, development of sensors for measuring key parameters in boreholes at high pressures and temperatures, are examples of emerging issues in the field of submarine drilling that need to be address. Given this background, WP7 aims at ensuring that the most appropriate technology is available for subseafloor sampling to address the key scientific questions, and eventually lead to challenging drilling projects. Moreover, how to organise the access to these subseafloor-sampling tools for the future European science community will be a fundamental goal of the WP.
The major aim of WP7 is to ensure that the technology required to provide subseafloor samples is accessible to the science community. This can be achieved by bringing together experts in the various techniques utilised for subseafloor sampling, interested scientists and engineers. Advice from the Engineering Development Panel (EDP) and the Scientific Technology Panel (STP) of IODP, as well as from the International Continental Drilling program (ICDP) will be particularly important. It is also essential that this group works in consultation with the other WPs,. A liaison mechanism between WPs 1-8 will be established by participation in the first and second stage workshops of WPs 1-6 (see Gannt diagram below), and is already in place for WP8. Particularly important issues identified by the science community, such as core disturbance, contamination, preservations of in situ conditions, will be addressed. The objective is the development of strategies and recommendations to the various national and European programmes/funding bodies for a facilitated access to subseafloor samples, in situ measurements and instrumentation. The maintained access to ocean drilling will be particularly critical. WP7 and WP8 will intensely interact to ensure the maximum efficiency in use of equipment and infrastructures on a broader scale. This will provide a link between processes related to geology and biology in the subseafloor to its effects at ecosystems on the seafloor and the overlying water column.
List of WP7 participants (Level 3)