Instrumentation Package for Sub-Ice Exploration (IPSIE)
The IPSIEs are intended to help us study the physical and geochemical properties of the subglacial hydrological system and associated fluxes within that system.
Figure 1: Engineering schematic layout of the POP (Physical Oceanography Package) and the WIPSIE (Water chemistry Instrument Package for Sub-Ice Exploration) of the IPSIE sensors: 1- Contros nutrient stage (HydroC - CO2, CH4), 2- Envirotech nutrient stage (PO4, SiO4, NH4, NO3), 3- Envirotech water-bag sampler stage, 4- Bottom stage (down- and side-looking cameras with LED lights, Wetlab fluorometer and optical-backscatter (FLNTU), Contros electromagnetic current meter, Tritech altimeter), 5- WaDS pump stage, 6- lifting power and telemetry stage, 7- Physical properties stage (Seabird CTD and dissolve oxygen sensor, LISST Deep particle-size analyzer, Wetlab CStar transmissometer, Nortek Aquadopp Doppler current meter).
These units include a range of sensors that are designed for regular oceanographic and limnological uses. However, they have been redesigned from their common profiling deployment arrangement that is in a rosette, into a vertical array to fit down a 30cm-wide borehole in ice. To achieve this and ensure they are all sampling the same water, Tygon tubing connects them with an intake in the Bottom
These units include a range of sensors that are designed for regular oceanographic and limnological uses. However, they have been redesigned from their common profiling deployment arrangement that is in a rosette, into a vertical array to fit down a 30cm-wide borehole in ice. To achieve this and ensure they are all sampling the same water, Tygon tubing connects them with an intake in the Bottom Stage (Fig. 1) and a pump below the Power & Telemetry Stage to draw the water up through each stage.
The IPSIEs' design is modular, built in 'stages' each of which has instruments that can be connected together through the WaDS and electrical whips using flanges (Figs. 2 and 3) to bolt together their outer steel tube casings. This allows mission-specific configurations and the future addition of supplemental sensors. Each unit is also deployable individually as an autonomous instrumentation package for longer-term measurements. All the instruments are mounted in racks that then slide in the protective casings, which also have ports for those that need to be open to the water (e.g., Aquadopp) or those to which we need access.
We are planning to use two configurations of stages and instrumentation in Antarctica for WISSARD. One configuration is the Physical Oceanographic Package (POP) and the other is Water chemistry Instrument Package for Sub-Ice Exploration (WIPSIE) (Fig.4). All instruments within each configuration are listed in Figure 1 caption and are shown in additional figures set in their racks.
IPSIEs are deployed on a strengthened fiber-optic umbilical or "smart cable" and winch, the cable being directly terminated to the top Power & Telemetry Stage (Fig. 5). The other end of the fiber-optic cable is connected directly to the topside data system that, processes, plots, and archives all of the instrument data in real-time. Algorithms are built-in to the custom-designed data processing software to synchronize the data from each instrument in time and depth by using the known flow rate through the WaDS. These two stages are deployed each time with the IPSIE.
This telemetry system via the fiber-optic cable, allows focused investigations of specific targets as well as targeted sampling based on real-time information. The real-time measurements help us visualize and quantify physical and geochemical properties in aqueous systems. Without such in-situ measurements physical 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.
Figure 5: Motor and electronics stage with "telemetry brain" that is enlarged at the bottom left. The internal units of this stage are being slipped into the casing and it is then hoisted vertically to be connected to the WaDS stage with electronics and hydrolic hoses that are then primed before final set-up.
The other stage that is always attached in IPSIEs is the Bottom Stage (Fig. 6). That stage is important because it houses a Tritech altimeter to provide real-time distance above bottom. The Bottom Stage also contains side-looking and downward-looking cameras to help visually with any issues in the borehole and as we descend through the water column and stop just above the sediment floor. In addition, to these two critical components the other instruments in this stage are the Wetlab fluorometer and optical-backscatter (FLNTU) and Contros electromagnetic current meter that can determine velocity directly at the base of IPSIE.
The EnviroTech water bag sampler can collect sixsamples on one deployment (Fig. 7) and is astage in itself. It can be deployed with both the POP and WIPSIE configurations. Unlike conventional water samplers such as bailers, the automated water sampler can sample directly at the ice-sediment interface and store the samples in sterilized, gas tight bags.
The WISPIE configuration (Fig. 8) includes chemical instrumentation for measuring nutrients in the water column. It includes two stages: the Contros Nutrient Stage that has HydroC sensors for CO2 and CH4, and an EnviroTech Nutrient Stage with sensors for determining PO4, SiO4, NH4 and NO3. In-line filters at the limits of sand, silt and clay are mounted before water enters these nutrient sensors and can be used to quantify transmission (CStar) and backscatter sensors (FLNTU) and to verify particle size estimates of the LISST Deep (Fig. 10).
Figure 9. The POP Stage with a Seabird CTD and dissolved oxygen sensor, a Wetlabs CStar transmissometer, a Sequoia Scientific's LISST Deep particle-size analyzer and a Nortek Aquadopp Doppler current meter.