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.