Developed by Stefan W. Vogel (NIU)

 

The GIPSIE is owned by NIU and will be deployed as a standard wire-line oceanographic profiling system. This instrument consists of an array of standard oceanographic instrumentation having sensors and samplers that include: CTD, Doppler current meter, transmissometer, laser particle-size analyzer, DO meter, automated 48-port water sampler, water column nutrient analyzer (Si, NO₃, PO₄, NH₄, CO₂, CH₄, chlorophyll), sediment porewater chemistry analyzer (T, pH, redox, O₂, H₂S, H₂, N₂O), and a down-looking color camera (see figure). Individual instruments are repacked and mounted in a profiling housing for deployment through narrow, 20 to 25cm diameter, ice boreholes. A borehole camera provides real-time video and a motorized porewater profiler extends the chemical measurements into the upper 50cm of subglacial sediment. The GIPSIE includes a real-time telemetry system, which allows focused investigations of specific targets as well as targeted sampling based on real-time information. The design is modular, allowing mission-specific configuration and the future addition of supplemental sensors. Each unit is also deployable individually as an autonomous instrumentation package for longer-term measurements, and as external instrument with the NIU Sub-Ice ROVer (SIR).

 

The GIPSIE serves two purposes:

(i)            to provide real-time in-situ measurements of critical physical and geochemical properties, which will guide

(ii)           the acquisition of water samples (multi-sampling capability).

 

GIPSIE data are intended for the following studies: (i) physical and geochemical properties of subglacial hydrology, (ii) water and nutrient fluxes across the ice sheet grounding zone, and (iii) sub-ice shelf circulation process. The real-time measurements visualize geochemical and physical properties in aqueous systems. Without such in-situ measurements water sampling is done blindly, based on assumptions, not data. In addition, temperature, pH, and gas pressure changes during sample recovery from a depth (~1000m in our case) initiate chemical processes. The results of these processes are later measured in the lab. In-situ measurements, together with on-site lab measurements of time critical parameters conducted directly after sample recovery, will provide information on the effect that the sample recovery process has on sample chemistry. This allows us to consider these effects in the interpretation of analytical data. The combination of in-situ with on-site measurements of time critical analytical work is especially important for pH and temperature dependent red-ox reactions, and pressure dependent outgassing of dissolved gases, as well as gas hydrate phase transition.

 

We anticipated deploying the GIPSIE or individual components at each RAGES drill site. Because of its modularity, the GIPSIE can be configured for mission-specific operations. By using fewer instruments, it can be configured so it is deployable into small subglacial cavities beneath ice, where the entire package would not fit. Opposite to conventional water samplers like bailers, the automated 48-port water sampler can sample water from a narrow gap at the ice-sediment interface and store the samples in sterilized and gas tight sampling bags. To prevent possible biological contamination, the instrumentation can be cleaned following environmental protection procedures like those used by Gaidos et al. (2004, 2008). The porewater profiler provides essential information on the red-ox state in subglacial and glacimarine sediment and the release of nutrients from sediment through microbes utilizing chemical energy of these processes.

 

The GIPSIE is an essential part of research intended to study: (i) the physical and geochemical properties of the subglacial hydrological system, (ii) associated fluxes of water and nutrients across the ice sheet grounding zone, (iii) sub-ice shelf circulation process and their role in the formation of Antarctic bottom water, and (iv) the dispersion of subglacially derived nutrients within the sub-ice shelf cavity, potentially contributing to the fertilization of the Antarctic ocean. A proper understanding of subglacial biogeochemistry allows the use of nutrients as natural biogeochemical tracers to quantify hydrological processes. It also enables improving interpretations of paleo-environmental and paleoclimatic conditions from the sedimentary record recovered from the base of the ice sheet by RAGES.

 

 

 

RAGES will employ a variety of oceanographic instruments that can be used in various combinations depending on the mission and objective of each deployment. The prime tool will be GIPSIE, Geochemical Instrumentation Package for Sub-Ice Exploration. Beyond GIPSIE we will have instrumentation to collect data from an oceanographic mooring at the borehole site while the SIR is operating over a larger area. The other forms of oceanographic instrumentation are long-term moorings that will be deployed during the last phase of operations when we are occupying a site. They will be left making their measurements for one year or more by relaying their data to surface recording units.

 

These instruments, owned by Northern Illinois University, are modular and components can be interchanged depending on borehole diameter and scientific data required. They can therefore take various forms, but are basically instrumented with CTD, DO meter, transmissometer, and Doppler current meter immediately below the ice

 

Various components of these instrument configurations include:

 

There are several optional configurations of this cluster. The basic configuration is:

Other options for mid-water nodes include:

Or:

 

Within these two configurations there are two unique components:

 

The ITP concept was developed at Woods Hole Oceanographic Institute (WHOI) for use in the arctic sea ice. RAGES version was constructed by McLane Research and is integrated with a Teledyne DVS current meter.

 

CT – conductivity and temperature

CTD – conductivity, temperature and depth

DVS - Doppler volume sampler current meter

 

A variety of sediment samplers are for recovering different types of sediment mainly based on their stiffness. Soft sediments are usually collected using short cores with wide barrels that do not disturb the sediment-water interface. Corers with deeper penetration usually encounter sediment with increasing stiffness and therefore need greater weight or other features, such as vibration or rotation to enable deeper penetration.

 

Simple gravity corers consist of a plastic liner inside a steel barrel with a weight on top that penetrates soft sediment by gravity. Water inside of the tube evacuates through a valve at the top. The wider the barrel the less disturbance and better penetration, in general. We plan to use a kasten-corer type that has a square barrel and are known to recover the sediment-water interface very well. Soft sediment can also be collected with the SIR.

 

This is a corer has a cutting shoe made of steel protecting the core liner inside a steel barrel. It is able to recover up to 3m of sediment depending on the stiffness and the number and size of clasts in the sediment.

A percussion sediment corer owned by NIU has been designed to permit recovery of up to 5m-long cores of stiff sediment. The tool will have some shared components and sensors GIPSIE. It is designed to fit through a 20cm (8in) borehole, and is a complementary technology to the SIR in that it can be used to collect larger samples from areas of particular interest as identified through SIR investigation.

 

This corer has an active hammer system driven by a water pump, which allows active penetration into stiffer sediment. Till deposited under the Antarctic Ice Sheet is notoriously difficult to penetrate due to is range of particle sizes (clay to boulder) and its high degree of consolidation from the overlying ice mass. The sediment corer has a double-wall barrel, which allows water from the top of the sediment corer to flow within the core barrel wall to the cutting shoe. This modification significantly reduces the amount of suction produced during recovery of the sediment corer without the need for an extra-heavy duty winch system to overcome the enormous suction during core recovery.

 

This is a significant technology development, intended to further Antarctic geoscience by significantly extending sedimentological sampling studies beyond the range currently accessible using piston coring and recovering sediment that rotary drilling cannot.

Borehole strings with inclinometers and thermistors are being constructed at UCSC. They will be frozen into the narrow 10cm boreholes across the grounding zone sites. Data are telemetered to the surface and will be used in combination with continuously recording GPS receivers (supplied by UNAVCO) to determine ice strain rates.

 

The combined approach of data from inclinometer/thermistor strings and GPS units constrains strain rates due to both horizontal and vertical pure shear and vertical simple shear as ice goes afloat. These measurements permit quantification of relevant terms in the 3D stress tensor by using measured strain rates and ice flow law with the ice viscosity parameter estimated from our vertical ice temperature determinations.

Strain measurements are at the core of the glaciological component of RAGES, and hence are important to obtain. The inclinometer/thermistor strings will be deployed at the end of operations at the RAGES field sites. The GPS units and the strings will be left out as long-term observatories for a year after deployment. The strings are disposable if environmentally agreeable; the GPS units will need collection.