Ross Ice Shelf Cavity Ocean Data

Date 2017-12-01
Temporal extent 2017-12-03 -2018-02-27
Author(s) Stevens CraigORCID1, Brewer Mike1, Grant Brett1
Affiliation(s) 1 : NIWA, New Zealand
DOI 10.17882/74128
Publisher SEANOE
Keyword(s) ice shelf cavity, Ross Ice Shelf, ocean mooring, hydrography, CTD profile, current meter, microstructure profile
Abstract

Here we provide data from the Ross Ice Shelf ocean cavity.  Location  -  The HWD2 Camp was established in October of 2017 at 80o 39.497’S, 174o 27.678’E where the ice is moving seaward at around ~600 m a-1 and is sourced from the Transantarctic Mountains.  Profiling Instruments -  Profiling was primarily conducted with an RBR Concerto CTD (conductivity-temperature depth) profiling instrument, and this was cross-calibrated against irregular profiles with an RBR Duet (pressure and temperature only), a SBE37 MicroCat CTD as well as moored SBE37 MicroCat CTDs.  The RBR unit is small and has suitable sensor capability (temperature and conductivity accuracies of ±0.002°C and ±0.003 mS cm-1).  Its conductivity cell design is not prone to fouling by ice crystals, making it ideal for work in the sometimes crystal-laden borehole conditions.   We were inconsistent in how we mounted the CTD on its protective frame and this appeared to make small difference in the conductivity signal (resulting in an ~0.03 psu variation).  This was post-corrected based on the essentially invariant mooring data from the lower water column as well as SBE37 cross-calibration profile data. Because of the potential for sediment contamination of the sensors, the profiles were mostly conservative in their proximity to the sea floor. On several occasions, profiles were conducted all the way to the sea floor. The temperature and salinity are presented in EOS-80 in order to compare with available data.  Eighty three profiles are provided here (ctd_HWD2_*.dat). In addition, limited microstructure profiling was conducted to provide insight into some of the mixing details.

The profiles were conducted by lowering the instrument to the ice base then commencing a sequence of three up-down “yo-yos” before returning to the surface and downloading. A data segment is included here (VMP_HWD2.dat). There were some challenges registering the vertical coordinate for the profiles.  The melting of the borehole generates a trapped pool of relatively fresh water.  The interface between this and the ocean should be near the base of the hole or a little higher – with seawater intrusion.  However, there were some instances where the interface was at a higher pressure (i.e. apparently in the open water column). The best explanation for this is that the water in the borehole is not at static equilibrium for some period after initial melting. We use 34.3 psu as a cut-off, in addition to a pressure criterion to identify the top of the useful oceanic profile.  It is also not inconceivable that water was being ejected from the hole, but it is unlikely that this would have impacted in the consistent observed pattern.  Instrumented Mooring - The mooring instruments at HWD2-A comprised 5 Nortek Aquadopp single point current meters in titanium housings reporting to the surface (30-minute interval, Table SI-Three) via an inductive modem to a Sound-9 data logger and Iridium transmitter. The current meter measurements were corrected to account for the 138o magnetic declination offset (i.e. the south magnetic pole is to the north-west of the field site).  Five files are provided here (HWD2_Init_rcm*.dat4).  Details in: Stevens C, Hulbe C, Brewer M, Stewart C, Robinson N, Ohneiser C and Jendersie J, 2020. Ocean mixing and heat transport processes observed under the Ross Ice Shelf controls its basal melting, accepted PNAS, May 2020.

Licence CC-BY
Acknowledgments This research was facilitated by the New Zealand Antarctic Research Institute (NZARI) funded Aotearoa New Zealand Ross Ice Shelf Programme and the Victoria University of Wellington Hot Water Drilling initiative. We thank the Victoria University of Wellington Hot Water Drilling Team led by Alex Pyne and Darcy Mendeno. Jeff Dunne, Lana Hastie and Kurt Roberts made it possible to work at camp. Dan Lowry, Gavin Dunbar and Gary Wilson provided field assistance and invaluable discussions. Brett Grant, Pete de Joux and Nick Eaton developed and mobilised the instrumentation. Logistics support and flights were provided by Antarctica New Zealand and Kenn Borek Air. Additional support was provided by NIWA Strategic Science Investment Funding, the Deep South National Science Challenge and the Antarctic Science Platform. Further details in: Stevens C, Hulbe C, Brewer M, Stewart C, Robinson N, Ohneiser C and Jendersie J, 2020. Ocean mixing and heat transport processes observed under the Ross Ice Shelf controls its basal melting, accepted PNAS, May 2020.
Sensor metadata

CTD profiles.

Eighty three profiles are provided here (ctd_HWD2_*.dat) using RBR Concerto CTD (conductivity temperature depth).

Example Header:

ctd_HWD2_2.dat
SN=60418 RBR Concerto
Experiment: HWD2 Nov/Dec 2017
80o 39.497’S, 174o 27.678’E
Ross Ice Shelf Antarctica
collected by NZ NIWA
Craig Stevens & Mike Brewer
salinity post-corrected -0.0800000 using moored sensors
day of year UTC       343.27563
1:  Prs   pressure dbar
2:  Tpot  potential temperature degC
3:  Sal   salinity practical units psu

====================================================================

Instrumented Mooring

Five files are provided here (HWD2_Init_rcm*.dat4). The mooring instruments at HWD2-A comprised 5 Nortek Aquadopp single point current meters in titanium housings reporting to the surface (30-minute interval, Table SI-Three) via an inductive modem to a Sound-9 data logger and Iridium transmitter. The current meter measurements were corrected to account for the 138o magnetic declination offset (i.e. the south magnetic pole is to the north-west of the field site). 

Example header:

HWD2_Init_rcm2.dat4
Nortek Aquadopp 6000m  SN
Experiment: HWD2 Nov/Dec 2017
80o 39.497’S, 174o 27.678’E
Ross Ice Shelf Antarctica
collected by NZ NIWA
Craig Stevens & Mike Brewer
Initial rcm data
nominal pressure*      360 dbar
*some pressure issues
written using hwd2_mooring_write.pro 18may2020
1:  year
2:  month
3:  day
4:  hour
5:  minute
6:  pressure dbar
7:  temperature degC
8:  speed m/s
9:  dir    deg TN
Year Mo Da Hr Mi    Prs         Temp        Speed      dirn

====================================================================

A single microstructure profile segment is included (VMP_HWD2.dat).

VMP_HWD2.dat
SN=215 Rockland VMP250-IR
Experiment: HWD2 Nov/Dec 2017
80o 39.497’S, 174o 27.678’E
Ross Ice Shelf Antarctica
collected by NZ NIWA
Craig Stevens & Mike Brewer
microstructure profile segment
original file: VMP_H003.p
13Dec2017 0445 UTC
written using VMP_HWD_plot_v2 18may2020
1:  Prs   pressure dbar
2:  Tpot  potential temperature degC
3:  Sal   salinity practical units psu
4:  Tgrad temperature gradient degC/m
       Prs            Tpot             Sal              Tgrad

======================================================================

Details in: Stevens C, Hulbe C, Brewer M, Stewart C, Robinson N, Ohneiser C and Jendersie J, 2020. Ocean mixing and heat transport processes observed under the Ross Ice Shelf controls its basal melting, accepted PNAS, May 2020.

Data
File Size Format Processing Access
Ross Ice Shelf Ocean Cavity data 9 MB ASC Processed data Open access
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How to cite 

Stevens Craig, Brewer Mike, Grant Brett (2017). Ross Ice Shelf Cavity Ocean Data. SEANOE. https://doi.org/10.17882/74128


In addition to properly cite this dataset, it would be appreciated that the following work(s) be cited too, when using this dataset in a publication :


Stevens Craig, Hulbe Christina, Brewer Mike, Stewart Craig, Robinson Natalie, Ohneiser Christian, Jendersie Stefan (2020). Ocean mixing and heat transport processes observed under the Ross Ice Shelf control its basal melting. Proceedings of the National Academy of Sciences, 117(29), 16799-16804. https://doi.org/10.1073/pnas.1910760117