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Victoria University Antarctic Research Expedition Science and Logistics Reports 2007-08: VUWAE 52

IMMEDIATE SCIENCE REPORT K049A: NZ ITASE

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IMMEDIATE SCIENCE REPORT

K049A: NZ ITASE

Antarctica New Zealand 2007/08

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1 Scientific Programme

a. Context of your research

Unprecedented changes are occurring in the Earth's climate. 2005 and 1998 were the warmest two years in the instrumental global surface air temperature record since 1850. The global average surface temperature has increased, especially since about 1950 with 100-year trend (1906–2005) of 0.74°C ± 0.18°C (IPCC, 2007). Although the scientific evidence of global warming is now widely regarded as incontrovertible, predicting regional impacts is proving more problematic. Especially, conclusions of the Southern Hemisphere record are limited by the sparseness of available proxy data at present (Mann & Jones, 2003).

While meteorological records from instrumental and remote sensing data display the large intercontinental climate variability, the series are insufficient to infer trends or to understand the forcing, which renders prediction difficult (Jones et al., 1999; Mann & Jones, 2003). The long ice core records from the Antarctic interior and Greenland revolutionised our understanding of global climate and showed for the first time the occurrence of RCE (Rapid Climate Change Events) (for review e.g. Mayweski and White (2002)). To understand the drivers and consequences of climate change on timescales important to humans, a new focus of ice core work is now moving towards the acquisition of 'local' ice cores that overlap with and extend the instrumental records of the last 40 years back over the last several thousand years.

This has been a key motivation behind the US-led International Transantarctic Scientific Expedition (ITASE) of which New Zealand is a member. The NZ ITASE objective is to recover a series of ice cores from glaciers along a 14 degree latitudinal transect of the climatically sensitive Victoria Land coastline to establish the drivers and feedback mechanism of the Ross Sea climate variability (Bertler et al., 2004a; Bertler et al., 2004b; Bertler & 54 others, 2005; Bertler et al., 2005a; Bertler et al., 2005b; Patterson et al., 2005). Furthermore, the ice core records will provide a baseline for climate change in the region that will contribute to the NZ-led multinational Latitudinal Gradient Project as well as providing a reference record for the NZ-led ANDRILL objective to obtain a high-resolution sedimentary archive of Ross Ice Shelf stability.

b. Objectives

The 2008/08 field season comprised objectives at Skinner Saddle (SKS), Gawn Ice Piedmont (GIP). Evans Piedmont Glacier (EPG), and Victoria Lower Glacier (VLG).

Fig. 1: Overview map of the Ross Sea region showing the location of the satellite images A and C. A) Locations of sites in the McMurdo Sound region, C) Location of sites in the Byrd / Darwin Glaciers region. Satellite images are derived from MODIS

Fig. 1: Overview map of the Ross Sea region showing the location of the satellite images A and C. A) Locations of sites in the McMurdo Sound region, C) Location of sites in the Byrd / Darwin Glaciers region. Satellite images are derived from MODIS

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c. Objectives

Site survey at Skinner Saddle and Gawn Ice Piedmont

Ground penetrating radar (GPR) measurements provide an image of the internal layering of a glacier and the topography of the ice-rock interface beneath. We applied low and high frequency radar pulses (8 MHz, 35 MHz, 200MHz, and 500MHz) to map the bedrock interface and internal flow structures in the glacier. Those features are identified through reflectors that result from changes in physical and chemical properties, such as dust layers or aerosol and density variations and are thought to represent isochrones (Morse et al., 1998; Vaughan et al., 1999). The choice of antenna frequency involves a trade-off between penetration depth and mapping resolution. The control units were mounted on a Nansen Sledge, pulling transmitter and transceiver antennae. The sledge also carried high precision GPS antenna, which is tied to the temporary GPS base station deployed at the SKS and GIP camps.

Traverses totaling 150km at Skinner Saddle and 35km at Gawn Ice Piedmont have been surveyed with GPR. Excellent isochrone reflections are visible from both the bedrock/glacier interface and in the top part of the profile, which will also be used to investigate geographical and chronological accumulation changes. Further post-processing will enhance the reflectors and will correct for surface topography.

Fig. 2 A) ASTER satellite image of Skinner Saddle and vicinity. See Figure 1 for overview. Image from 31 October 2005. Yellow flag indicates location of camp, red flag indicates proposed drilling location. B) Digital elevation model. X/Y/Z grid in UTM 58 map units. Red lines indicate location of ground penetrating radar survey lines

Fig. 2 A) ASTER satellite image of Skinner Saddle and vicinity. See Figure 1 for overview. Image from 31 October 2005. Yellow flag indicates location of camp, red flag indicates proposed drilling location. B) Digital elevation model. X/Y/Z grid in UTM 58 map units. Red lines indicate location of ground penetrating radar survey lines

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Fig. 3 A) ASTER satellite image of Gawn Ice Piedmont and vicinity. See Figure 1 for overview. Image from 08 January 2004. Yellow flag indicates location of camp, red flag indicates proposed drilling location. B) Digital elevation model. X/Y/Z grid in UTM 58 map units. Red lines indicate location of ground penetrating radar survey lines

Fig. 3 A) ASTER satellite image of Gawn Ice Piedmont and vicinity. See Figure 1 for overview. Image from 08 January 2004. Yellow flag indicates location of camp, red flag indicates proposed drilling location. B) Digital elevation model. X/Y/Z grid in UTM 58 map units. Red lines indicate location of ground penetrating radar survey lines

Drilling of shallow firn cores at Skinner Saddle and Gawn Ice Piedmont

As part of the site reconnaissance we drilled a 17m and 13m deep firn core at SKS and GIP, respectively. The drilling system was kindly provided by the Alfred Wegener Institute. The initial data set from these cores allow us to calculate annual accumulation and establish transfer functions with meteorological data to establish the quality and sensitivity of the ice.

Fig. 4: Firn core drilling at GIP

Fig. 4: Firn core drilling at GIP

Automatic weather station set-up, maintenance, and data retrieval

In 2004/05 we deployed an automatic weather station on EPG. The data permit the calculation of transfer functions between ice core proxies and meteorological parameters, such as temperature, precipitation, meso-scale atmospheric circulation pattern, katabatic winds, and seasonality of snow accumulation. In addition a new snow accumulation sensor and high precision snow temperature probes allow us to monitor snow accumulation rates, the potential influence of snow loss through sublimation, wind erosion or melt, and the quality of preservation of the meteorological signal in the snow. Furthermore, the data allow us to estimate the uncertainty of re-analysis data (NCEP/NCAR and ERA-40 data) in the region. In addition we set-up a new automatic weather station at Skinner Saddle for the interpretation for our planned ice cores from Skinner Saddle and Gawn Ice Piedmont.

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Fig. 5: Automatic weather station at EPG (left image) and newly set-up weather station at SKS (right image)

Fig. 5: Automatic weather station at EPG (left image) and newly set-up weather station at SKS (right image)

Submergence Velocity Measurements at Victoria Lower and Evans Piedmont Glacier

The response time of a glacier to changes in accumulation or ablation is dependent on the size and thickness of the ice mass. In general, the response time of cold-based glaciers is positively correlated with the size of its ice mass, leading to long response times in Antarctica. For glaciers in the McMurdo Dry Valleys, with lengths on average of 5-10km and flow rates of 1 to 3 m/a, the response times are thought to range from 1,500a to 15,000a (Chinn, 1987; Chinn, 1998). Consequently, annual variations in surface elevation may only reflect changes in loss rates. As a result surface measurements of mass balance are difficult to interpret in terms of long-term mass balance (Hamilton & Whillans, 2000). This is especially the case in places like the McMurdo Dry Valleys where mass loss is thought to be predominately due to sublimation at ice cliffs and glacier surface caused by wind and solar radiation (Chinn, 1987; Chinn, 1998). For Victoria Lower Glacier (VLG), two mass balance measurements are available in the literature for 1983 and 1991 based on ice cliff characteristics and the motion of the glacier snout (Chinn, 1998). The measurements indicate that VLG was advancing 1.24m/a into Victoria Valley during this time period. However, the small number of observations (2) and the cliff's sensitivity to sublimation (contemporary surface ablation) result in a high uncertainty of longer term mass balance. To determine the longer-term mass balance of the glaciers, unaffected by annual surface variations, three 'coffee-can' or 'submergence velocity' devices (Hamilton et al., 1998; Hamilton & Whillans, 2000) were deployed at Victoria Lower Glacier in 1999/2000 and two at Evans Piedmont Glacier in 2004/05. These are annually re-measured to monitor mass balance changes.

Fig. 6: Submergence Velocity Measurements at VLG

Fig. 6: Submergence Velocity Measurements at VLG

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d. Methodology

Ground Penetrating Radar

For mapping glacier flow structures and the glacier-bedrock interface a 'GSSI SIR 3000 and GSSI SIR 10 A were used with a maximum time window of 8,000 and 10,000 ns, respectively. A 35MHz antennae-pair (Bistatic Radarteam SE-40), a 200MHz antennae-pair, and a single 500MHz antenna are pulled by a Nansen Sledge, which carries the control units. A Trimble 5700 differential, kinematic GPS, provides absolute positioning of the GPR data and allows survey of the glacier surface topography. GPR and GPS measurements are taken in kinematic mode.

Fig. 7: Photo showing Nansen sledge carrying GPR and crevasse rescue equipment

Fig. 7: Photo showing Nansen sledge carrying GPR and crevasse rescue equipment

Submergence Velocity Measurements at Victoria Lower and Evans Piedmont Glaciers

During the 1999/2000 season three submergence velocity devices (Hamilton & Whillans, 2000) for mass balance measurements in the McMurdo Dry Valleys were installed. During the 2004/2005 season two submergence velocity devices have also been installed at EPG. This method is used to determine mass balance by comparing vertical velocity of a marker in firn or ice with long-term, average snow accumulation rates. The movement of the marker is the result of three motions: firn compaction, gravitational glacial flow, and changes in mass balance. High precision GPS measurements are used to determine absolute position of the tracking point during subsequent years. Trimble 5700 base station and rover unit were used to measure the absolute position of the tracking point of the mass balance devices.

The rate of thickness change H, can then be calculated using (Hamilton et al., 1998): H=rate of thickness change (myr−1) bm=accumulation rate (Mgm−2yr−1) ρ=density at marker depth (Mgm−3) z=vertical component of ice velocity(myr−1) α=surface slope (radians) u=horizontal velocity (myr−1 with azimuth)

Fig. 8 Cartoon of the 'coffee can' submergence mass balance device (modified after Hamilton and Whillans 2000)and picture of coffee can device deployed at Victoria Lower Glacier.

Fig. 8 Cartoon of the 'coffee can' submergence mass balance device (modified after Hamilton and Whillans 2000)and picture of coffee can device deployed at Victoria Lower Glacier.

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Shallow Firn Core Analysis

The following parameters will be measured on the obtained firn cores and snow samples:
  • Oxygen and Hydrogen Isotope Ratio

    Oxygen isotope ratios are measured using a CO2 dual-inlet system coupled to a Micromass Isoprime mass spectrometer at GNS Science. The sample is measured in the presence of a standard CO2 gas. Sample duplicates and standard measurements showed a precision of ±0.08‰. Samples are analysed for stable hydrogen isotope radios δD via Cr reduction with a continuous Helium flow Eurovector elemental analyser coupled to a Micromass Isoprime mass spectrometer. Sample duplicates and standard measurements showed a precision of ±0.6‰.

  • Major Cations, Anions, and Methylsulfonate

    Major ion concentrations are measured for cations (Na, K, Mg, Ca, NH3) using a Dionex™ Ion Chromatograph with Dionex CS12 column and 20 mM methanesulfonic acid eluent. Anion concentrations (Cl, NO3, SO4) are measured with a Dionex AS11 column, 6.0 mM NaOH eluent. For both measurements a 0.25 mL sample loop is used. Methylsulfonate (MS) content is measured using a Dionex AS11 column with 0.1 mM NaOH eluent and a 1.60 mL sample loop

  • Trace Elements and Cations

    Samples are analysed for trace elements and cations (Al, Ca, Cu, Fe, K, Mg, Mn, Na, P, S, Si, Sr, and Zn) using a Perkin-Elmer Optima 3000 XL axial inductively coupled plasma optical emission spectroscopy with a CETAC ultrasonic nebuliser (ICP-OES-USN at UMaine) and a Finnigan Thermo inductively coupled plasma mass spectrometer (ICP-MS at VUW) for all other trace elements and selected isotopic ratios.

  • Dust concentration and mineralogy

    500cm3 volume of snow/ice is filtered through Whatman quantative 2.5μm ashless filter paper. The filter is burnt in a Vulcan A-550 furnace at 500°C for 24 hours. The residue is weight with a AG204 Mettler Toledo analytical balance, and reweighed after 24hours to check for moisture absorbance during cooling. Mineralogy is determined by mounting the dust samples in glycerol gelatine for examination under an optical particles found in the dust are analysed in a JEOL 733 Electron Microprobe at VUW.

e. Results and discussions

Ground Penetrating Radar (GPR)

Traverses totaling 150km at Skinner Saddle and 35km at Gawn Ice Piedmont have been surveyed with GPR. The measurements allowed us to identify an excellent drilling location at Skinner Saddle with smooth bedrock topography and a glacier thickness exceeding 600m at the proposed drilling location. Excellent isochrone reflections are visible throughout the profile to below 150m, which will also be used to investigate geographical and chronological accumulation changes. The region at Gawn Ice Piedmont is glaciologically more active (see Figure 9) and marginal weather conditions limited our ability to a more comprehensive survey, as achieved at Skinner Saddle. However, we identified a suitable drilling site with a undisturbed depth of at least 300m, which is deeper than the target depth of 200m for this site. Further post-processing will enhance the reflectors and will correct for surface topography.

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Fig. 9 Unprocessed ground penetrating radar profile from GIP showing proposed drill site in the centre of the image.

Fig. 9 Unprocessed ground penetrating radar profile from GIP showing proposed drill site in the centre of the image.

These images are used to create 3D model of bedrock topography (Fig.10) and/or individual isochrones to establish ice flow direction and shear stresses as well as geographical and temporal snow accumulation changes. This allows a comprehensive assessment of the suitability of the proposed drill site.

Fig. 10 Calculated bedrock topography at GIP showing proposed drill site in the centre of the image.

Fig. 10 Calculated bedrock topography at GIP showing proposed drill site in the centre of the image.

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Automatic Weather Station Data from Skinner Saddle and Evans Piedmont Glacier

The automatic weather station at SKS is operational since 01 Nov 2007. The recorded data for pressure, solar irradiation, air temperature, snow temperature, dew point, and snow accumulation for the time period of our deployment at SKS are shown in Fig.11.

Fig. 11: SKS automatic weather station data for 01 to 11 Nov 2007

Fig. 11: SKS automatic weather station data for 01 to 11 Nov 2007

Our weather station at EPG has been operational since October 2004. The current data set is shown in Fig. 12. The lack of data during winter 2005 is due to a technical failure.

Fig. 12: EPG automatic weather station data for Nov 2005 to Dec 2007

Fig. 12: EPG automatic weather station data for Nov 2005 to Dec 2007

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Physical snow properties at Victoria Lower Glacier

A shallow snow pit was investigated at VLG while we waited for our GPS mass balance measurements to be completed. The large seasonal temperature changes characteristic for this area produces some of the largest hoar (or cup) crystals on the planet.

Fig. 13: Cup crystals from Victoria Lower Glacier

Fig. 13: Cup crystals from Victoria Lower Glacier

f. How this research fits in with future work being planned

Our preceding research – Holocene Climate History from Coastal Ice – has identified the value of the specific characteristics of ice core records from coastal, low altitude sites (Bertler et al., 2004a; Bertler et al., 2004b; Bertler & 54 others, 2005; Bertler et al., 2005a; Bertler et al., 2005b; Mayewski et al., 2005; Patterson et al., 2005; Bertler et al., 2006a; Bertler et al., 2006b) and showed how tropical phenomena, such as ENSO have a significant influence on the Ross Sea Region. In contrast to Antarctica's interior, which is influenced by temperature inversion and climatic cooling of the stratosphere, the coastal sites are dominated by cyclonic activity, and hence by the climate of the lower troposphere (King & Turner, 1997). As a result, coastal sites are especially climate sensitive and show potential to archive local, rapid climate change events that are subdued or lost in the 'global' inland ice core records, such as Vostok. The reconnaissance work successfully identified two suitable drilling locations to provide such data.

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g. Contributions from visiting foreign scientists

We are grateful for the loan of the Alfred Wegener Institute (Germany) shallow firn drill. Futhermore, Prof. P. Kyle (USA) is providing 8 shallow firn cores from Mt Erebus, complementing our intermediate depth ice core from Mt Erebus Saddle. This will allow us to investigate in collaboration with Prof. P. Kyle volcanic history of Mt Erebus over the last hundred years or so.

2 Publications

AGSC Committee Members and others, (in review). "State of the Antarctic and Southern Ocean climate System (SASOCS)." Reviews of Geophysics.

Alloway, B. V., D. J. Lowe, et al. (2007). "Towards a climate event stratigraphy for New Zealand over the past 30,000 years." Journal of Quaternary Science 22(1): 9-35.

Bertler, N. A. N. and U. Morgenstern (in review). Climate Swings and Roundabouts - Cold Comfort. NZ Geoscience into the 21st Century. I. Graham and B. Hayward. Wellington

3 Acknowledgments

We would like to thank Antarctica New Zealand staff based in Christchurch and Scott Base for their dedicated and innovative support with our project, in particular E. Barnes, I. Miller, D. Peterson, Neil Gilbert, and P. Woodgate, and at Scott Base S.Trotter, K. Rigarlsford, J. Burton, D. Mahon, D. Miller, G. McElroy. We would like to thank ScanTec, especially Matt Watson for excellent ground penetrating radar surveys. We would like to thank Kenn Borek Twin Otter crews for their professional, practical, and friendly approach and attitude. We are indebt to Helicopter NZ staff, in particular Rob McPhearson, for his . We would like to thank the National Isotope Centre, GNS Science, Ms Valerie Claymore, the Geochemical Laboratory, Victoria University, Prof. Joel Baker, and the Climate Change Institute, University of Maine, Prof. Paul Mayewski for ice core analyses. We are indebt to the Alfred Wegener Institute for lending us the shallow firn drilling system. This project is funded by Victoria University of Wellington, GNS Science, and Foundation for Research, Science, and Technology (Grant No. VICX0704 and CO5X0202).

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