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S h e l fSite F 2014

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Site E 2014Figure 5. Nov 2014 images from below the MIS. Panel A is site F, panels B and D are site E. Panel C depicts benthic communities observed at E. Supercooling was present at all sites in 2014 (Fig. 2 orange profiles, T<T

f) and the ice

morphology is rough with platelet ice.

A B

C D

Figure 4. Below the MIS in Nov 2015 at SIMPLE Site. Supercooling was present (Fig. 2 blue profiles, T<T

f),

panel A is a closeup of accreting ice below the shelf, B is the ARTEMIS HUD, and C shows rough morphology with platelet ice crystals below adjacent sea ice.

A B

C

#3609

ASTEP NNX14AC01GPI Britney Schmidt

J. D. Lawrence1, B. E. Schmidt1, L. Winslow2, P. Doran3, J. J. Buffo1, S. Kim4, C. C. Walker1, M. Skidmore5, K. M. Soderlund6, D. D. Blankenship6, N. Bramall7, A. Johnson8, F. Rack9, E. Clark10, P. Kimball10, W. C. Stone10, SIMPLE Field Teams*

McMurdo Ice Shelf as an ocean world analog: supercooled water and ice mass balance

Acknowledgments Inga Smith, Monica Nelson (University of Otago, NZ), Craig Stevens, Natalie Robinson (National Institute of Water and Atmospheric Research, NZ). The authors thank Chad Naughton, Stephen Zellerhoff, and the entire McMurdo Station staff for the success of the SIMPLE project. Background from the Polar Geospatial Center.

1Georgia Institute of Technology (jlawrence@gatech.edu), 2Rensselaer Polytechnic Institute, 3Louisiana State University, 4San José State University, 5Montana State University, 6University of Texas Institute for Geophysics, 7Leiden Measurement Technology, 8University of Illinois at Chicago, 9University of Nebraska-Lincoln, 10Stone Aerospace, 11Moss Landing Marine Labs

*Additional SIMPLE Field Team Members2015 (left): C. Flesher10, J. Harman10, K. Huffstutler10, J. Lawrence3, D. Mattson, J. Moor10, B. Pease10, K. Richmond10, M. Scully10, V. Siegel10

2012 & 2014: L. Barker11, J. Burnett9, J. Greenbaum6, M. Hynes11, M. Meister1, M. West1, A. Spears1, D. Young6, B. Zook9. Contributors: B. Hogan, L. Linzey

Figure 3. Adapted from the 2017 Europa Lander SDT Report, this schematic diagrams some of the ice-ocean and intra-ice processes hypothesized to be occuring on Europa. With temperatures and pressures similar to Earth (low gravity compensated by thick ice), the ice pump may operate to entrain materials which can then be transported through the shell via diapirs [2].

Background

The regions below Antarctica’s ice shelves are among Earth’s largest remaining unexplored environments, and are important analogs for the physical processes occuring on other ocean worlds such as Europa or Enceladus. On Earth, these processes control sub-shelf ice flux through supercooling (the ice pump, Fig. 1) [1], provide habitable niches at the ice-ocean interface, and entrain and transport organics through the ice [2].

NASA’s Astrobiology Science & Technology for Exploring Planets program funded the Sub-ice Investigation of Marine and PLanetary-analog Ecosystems project to explore beneath the McMurdo (MIS) and Ross (RIS) Ice Shelves with submersible vehicles (ROV/AUVs). Here, we characterize the relationship between ice and ocean with salinity, temperature, and depth (CTD) data (Fig. 2) compared to imagery from beneath the MIS (Figs. 4, 5, 6).

Methods

ROV/AUVs Deployed• SCINI (SJS), 2012• Icefin (Georgia Tech, Fig. 7), 2014• ARTEMIS (Stone Aerospace), 2015 • RBR Concerto CTD (independent sensor, hand-deployed)

Data Collected• 35 conductivity, temperature, and depth (CTD) profiles• Sub-shelf and sea ice imagery • Up to the full water column, ~500 m below the MIS

Data Processing• Via Gibb Sea Water Python module (gsw 3.0.3) according to the TEOS-10 standards [3]• Calculated (SA, [g kg-1]), conservative temperature (Θ, [°C]), surface and in situ freezing points (T

f)

Note: SA differs from practical salinity [psu], and is reported utilizing v3.0 of the McDougall et al., (2012) database

Takeaways Supercooling & the Ice Pump • Varies spatially (Fig. 2) and temporally in Antarctica • If no supercooling was present, ice was ablated (Fig. 4)• If supercooling was present, so was accreting ice (Fig. 5, 6)

Astrobiology ImplicationsEuropa and Enceladus likely have a similar ice pump mechanisms, influencing: • Ocean-surface material cycling • Ice shell thicknesses • Basal interface habitability and organics entrainment • Ocean circulation

AUV/ROV exploration of Earth’s cryosphere advances: • Ability to model ice processes on other ocean worlds • Autonomous robotics for in situ planetary exploration • Terrestrial climate change & sea level rise models

Science Module• Sonar, pH, ORP, C/FDOM• Camera, laser scale

[1] Lewis and Perkin, JGR (1985) [2] Report of the Europa Lander Science Definition Team (2017)[3] IOC et al. IOC Manuals and Guides No. 56, UNESCO (2010)

A B

C D

Figure 6. A-D: Imagery from SCINI looking upward at the MIS from 23 Dec 2012 at the SCINI site. No supercooling was detected here (Fig. 2 green profile, T>T

f) and the ice is smooth and ablated.

Figure 1. The ‘Ice Pump’, or how basal melting and freezing redistributes ice via supercooling. High Salinity Shelf Water (HSSW) forms in a polynya from the brine rejected by sea ice formation (1) and sinks, flowing into the shelf cavity (2). At depth, the freezing point (T

f)

is lower and the ‘warm’ HSSW causes melting. Fresher, buoyant Ice Shelf Water (ISW) forms as a result, fixed at the deep Tf (3). As ISW

rises and pressure falls, Tf increases and so the ISW becomes supercooled. As a result, frazil ice forms at the basal interface or in the

water column and accretes into marine ice (4). Camp icons indicate prior investigations below the Ross Ice Shelf.

marine ice accretion

meteoric ice melt

polynya sea ice

High Salinity Shelf Water (HSSW)

Ice Shelf Water (ISW)

Continental Shelf

brine rejection

1000 mT

F = -2.7°C

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F = -2.3 °C

0 mT

F = -1.9 °C

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WISSARD 2015

RISP 1977

SIMPLE2012, 2014, 2017

frazil

500 km 0 km

1500 mT

F = -3.1°C

RossIce Shelf

*

*penguin not to scale

1

2

3

4

Images courtesy Matt Meister (GT)

Future From 2017 to 2019, we will deploy the ROV/AUV Icefin (Georgia Tech, below), beneath the MIS and RIS as part of the next field campaign, RISE UP (NASA NNX16AL07G).

Figure 2. Temp vs. salnity of water columns corrresponding to 2012, 2014, and 2015 images. Black line is the freezing temp (T

f)- note

where water is colder than Tf (ISW) accreting ice

is observed (Figs. 6, 7). If the water is warmer than T

f (HSSW), the ice appears smooth (Fig. 5)

Tf line

HSSW

ISW

Figure 6

Figure 4Figure 5

Forward Module• Sonar, CTD, DO• Camera, laser

Figure 7.