Coulman High Project
Extensive field surveys were conducted in Antarctica from November 2010 through January 2011 as part of the ANDRILL CHP (Fig.1). A significant amount of equipment, supplies and people safely traversed approximately 120 miles from McMurdo Station to establish a series of combined United States – New Zealand (US-NZ) field camps on the Ross Ice Shelf (RIS) at locations northeast of Ross Island. The ANDRILL hot water drill (HWD) system was used to melt 10 to 60 cm-diameter access holes through 250‐275 meters of ice shelf at each site to deploy a variety of sediment coring tools, cameras, oceanographic instruments, and a remotely operated vehicle (ROV) named SCINI (Submersible Capable of under-Ice Navigation and Imaging; Cazenave et al., 2011).
GPS stations were established at four sites to monitor lateral and vertical ice motions and a weather station was set up at Site M1 to monitor environmental conditions. The weather featured fairly consistent winds out of the south that calmed during the last half of December 2010 and the first half of January 2011. Low overcast or fog was often present in this time interval, which proved to be a hindrance to helicopter access.
Figure 1. This map shows the location of McMurdo Station on Ross Island, Antarctica, the traverse route to the ANDRILL CH survey area northeast of Ross Island, and the site locations described in the text (CH-1 and CH-2 (yellow circles) are the two proposed CHP drillsites; M1 and M2 (light blue circles) are the two oceanographic moorings; at Site 3 (blue circle), various oceanographic instruments and the SCINI ROV were repeatedly deployed over several days. GPS stations were deployed at each corner of the diamond marked by the four blue circles. Also shown are the locations of prior scientific drilling in Southern McMurdo Sound, including the ANDRILL drill sites (red circles) from the McMurdo Ice Shelf (MIS) and Southern McMurdo Sound (SMS) projects, and earlier Cape Roberts Project (CRP) and CIROS-1 drilling (green circles) conducted from sea ice platforms. Marine seismic survey lines were collected by the NBP-03-01 cruise on the Nathaniel B. Palmer over CH in 2003 (Decesari, 2006; Decesari, et al., 2007) following the calving of the C-19 iceberg in 2002; correlation paths to DSDP and CRP sites are indicated. (Inset) Ross Sea region, Antarctica.
Oceanographic moorings were deployed at two sites perpendicular to the ice edge for at least two full tidal cycles (M1 = 55 days; M2 = 52 days). The M1 mooring, ~6 km south of the ice shelf edge, was the primary responsibility of the NZ National Institute of Water & Atmospheric Research (NIWA) team, while the M2 mooring, ~17 km south of the ice shelf edge, was the primary responsibility of the team from Woods Hole Oceanographic Institution (WHOI). Each mooring was nominally comprised of a series of five temperature and conductivity loggers (Microcats) and five acoustic doppler current meters (Aquadops) that were spaced throughout the water column during deployment (Fig. 2). Data was recorded within each instrument and also transmitted to a surface inductive modem (SIM) buried in the snow at the ice shelf surface to ensure that data could be easily accessed in case the moorings were not recovered. The M2 mooring had an Iridium satellite communications (ISC) modem to transmit its data back to WHOI in near-real time during its deployment. The moorings were designed to measure tidal and ocean currents and water mass properties, to assess the environmental conditions in the sub-ice shelf ocean cavity, and to potentially serve as a prototype ice shelf installations to contribute to the Southern Ocean Observing System (SOOS; see Figure 31, Rintoul et al., 2012).
Figure 2. Schematic diagram (not to scale) of oceanographic moorings, M1 (NIWA) and M2 (WHOI), located 6 km and 17 km south of the ice front, respectively. These were deployed through the Ross Ice Shelf for two months during 2010-2011. Five pairs of instruments equipped with inductive modems were deployed at each site at depths distributed through the water column below the ice shelf (GW = grounding wire, SIM = surface inductive modem (yellow box buried in snow), ISC = iridium satellite communications (only M2); yellow ovals = Seabird microcat (MC) temperature/salinity loggers, red ovals = Nortek aquadop (AD) 6000 acoustic current meters).
Oceanographic data acquired from the moorings indicate diurnal current variability with maximum speed up to 25 m/s. Tidal harmonic analysis reveals that ~50% of the current velocity variability is caused by tides propagating around the ice shelf cavity (Arzeno et al., 2012a,b). The data from these moorings will also be used to address the role of advection and mixing of water masses across the shelf and under the ice shelf, especially when longer time series measurements are available. The NZ mooring (M1) was redeployed after its initial two-month deployment to provide long‐term observations under the RIS and this mooring still operating as of June 2012. The tidal current measurements and GPS data are being used to develop a tidal model for the drill site locations and model the behavior of the ANDRILL sea riser to determine the most robust drilling strategy for the ANDRILL CHP.
Operations in each of the primary hot water drill holes included multiple deployments of a video camera, gravity corer and a conductivity-temperature-depth (CTD) sensor. At Sie (see map above), multiple deployments of an upward-looking acoustic doppler current profiler (ACDP) and water samplers were made. These short-term deployments were meant to sample the water column and seafloor sediments, and observe the sea floor and the underside of the ice shelf. Video camera observations of the interior and basal surface of the RIS were integrated with conductivity‐temperature‐ depth (CTD) profiles through the ice shelf and into the water column at several sites to better understand salinity and temperature gradients within the ice shelf borehole.
The SCINI ROV was deployed multiple times down a ~30 cm-diameter hole at Site 3 and again near Site CH-1 (located ~10 and 6 km from the ice edge respectively) to explore the underside of the ice shelf while conducting operational testing. Three ROV engineers/pilots deployed the vehicle for twenty-nine hours spaced over fourteen dives with a maximum dive depth of ~300 mbMSL and a range of ~30 m around the ice hole. This was the first time to our knowledge that an ROV was deployed through an ice shelf in Antarctica and the results were phenomenal. SCINI cameras discovered and explored an unusual and possibly unique biological community dominated by anemones living inside burrows in the lower surface of the ice shelf and the ROV recovered many biological samples using an improvised suction sampler; these samples and extensive imagery, which is being further investigated, will provide preliminary information about the spatial distribution and nature of these organisms, as well as insights into the role of freezing and melting of ice, advection of water masses and nutrients, and other influences on their life cycle and ecology.
Finally, an over-ice wide-angle and hydrophone seismic experiment was conducted using an array of geophones buried in the snow and a seafloor hydrophone, and other geophysical data (gravity) were collected along the ice surface extension of marine seismic line NBP03-1A0 to improve interpretations of existing marine seismic reflection data and finalize proposed CHP drill site selections.
Arzeno, I.B., R. Beardsley, B. Owens, R. Limeburner, L. Padman, M. Williams, C. Stewart, C. Lee, M. Dinniman, and S. Springer, 2012a. Tides under the Ross Ice Shelf front: Contributions to mixing and melting. Ocean Sciences Meeting, February 20-24, 2012 (Salt Lake City, UT), TOS/AGU/ASLO Abstract Book, p. 17.
Arzeno, I.B., R. Beardsley, B. Owens, R. Limeburner, L. Padman, M. Williams, C. Stewart, and C. Lee, 2012b. Looking under the Ross Ice Shelf: Tidal and subtidal variability. Ocean Sciences Meeting, February 20-24, 2012 (Salt Lake City, UT), TOS/AGU/ASLO Abstract Book, p. 17.
Cazenave, F., R. Zook, D. Carroll, M. Flagg, and S. Kim, 2011. Development of the ROV SCINI and deployment in McMurdo Sound, Antarctica. The Journal of Ocean Technology, 6(3):39-58.
Rack, F., R. Levy, T. Falconer, R. Zook, P. Mahacek, D. Carroll, M. Williams, C. Stewart, R. Limeburner, and the ANDRILL Coulman High Project site survey team, 2011. Interdisciplinary outcomes of the ANDRILL Coulman High site surveys, 11th International Symposium on Antarctic Earth Sciences, Programme and Abstracts, July 10-15, 2011 (Edinburgh, Scotland, UK) p. 184.
Rintoul, S.R., M. Sparrow, M.P. Meredith, V. Wadley, K. Speer, E. Hoffman, C. Summerhayes, E. Urban, R. Bellerby, and 2012. The Southern Observing System: Initial Science and Implementation Strategy
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