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

IMMEDIATE SCIENCE REPORT K049 B: NZ-ITASE Climate Variability along the Victoria Land Coast – Trace element chemistry of Antarctic snow

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IMMEDIATE SCIENCE REPORT

K049 B: NZ-ITASE Climate Variability along the Victoria Land Coast – Trace element chemistry of Antarctic snow

Antarctica New Zealand 2007/08

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1 Scientific Programme

a. Context of research

To date, aerosol deposited trace element records have been poorly utilised in ice core research. They can however provide important tracers or proxies of atmospheric (e.g. regional circulation, moisture transport and precipitation) and oceanic (sea-ice extent and variability) processes. In conjunction with more traditional ice core analyses (isotopic and major ion variations), new knowledge of their past variability will allow an improved understanding of the Ross Sea climate system. This has the potential to provide information that can be related to the larger Antarctic atmospheric circulation systems; the El Nino Southern Oscillation (ENSO) 1, Southern Annular Mode (SAM) 2 and to a lesser degree the Antarctic Circumpolar Wave 1, whose relative importance remain controversial.

For this purpose, two coastal sampling sites have been chosen with variable climatic and sea ice cover influences. Whitehall Glacier, Northern Victoria Land coast was sampled in 2006/07 and provides an area of frequent and intense cyclonic activity due to its proximity to the Southern Ocean and Antarctic low pressure belt 1,3. This will be used in comparison of the predominantly katabatic controlled climate of Evans Piedmont Glacier that has been sampled in the most recent 2007/08 season 4.

This work contributes to the Antarctica NZ Scientific Strategy in the following sections:
  • 1C-1 What does the detailed (annual –decadal) regional climate record from ice-cores along Victoria Land Coast over the last 10,000 years tell us about patterns of climate behaviour in the region and linkages with the Southern Hemisphere climate patterns?5

    This project seeks to understand the relationship between atmospheric circulation and aerosol deposition in the recent instrumental record with the potential to extrapolate it back further into the ice core record.

  • 2C -1 – What drives natural seasonal and inter-annual variability in coastal ecosystems in the Ross Sea?5

    Southern Ocean Research and Antarctic Ecosystems Research all require a greater understanding of the climatic context conducted due to ecosystem dependency on climatic conditions.

b. Objectives

  1. Clean snow sampling at Evans Piedmont Glacier

    A primary objective of 2007/08 field season was to sample a high resolution snow record of the last decade, with emphasis on ultra-cleanliness, as concentration levels of trace elements in polar snow and ice are in the parts per trillion (ppt) to parts per quadrillion (ppq) range 6.

  2. Automatic Weather Station data retrieval, Evans Piedmont Glacier

    An automatic weather station (AWS) was installed by K049 in 2004/05 near the previous drill site and current sampling site. This data is important in establishing transfer functions between temporal variations in snow chemistry and meteorological parameters in order to quantitatively establish the use of trace elements as a climatic proxy.

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c. Methodology

Snow sampling

A 4m deep snow profile was sampled at 1cm resolution using ultra clean snow sampling methodology in order to maximise the array of potential measurable trace elements. These will include Al, As, Ba, Be, Cr, Co, Fe, Li, Mn, P, Rb, Sr, Ti, U, V, Zn. Isotopic (δ18O and δD) and major ion composition will also be measured.

Figure 1: Snow sampling using clean procedure

Figure 1: Snow sampling using clean procedure

All sampling vials, 60ml Nalgene HDPE (high density polythene), were pre-cleaned following the procedure of Osterberg et al6. Preparation includes soaking in 5% trace metal-grade HNO3 for 1 week, triple rinse in DI (deionised, 18 MΩ) water and again soaked in DI H2O. Sampling equipment was triple rinsed, soaked for 4 weeks and triple rinsed again in DI water.

The sampling surface was pre-cleaned using a clean metal spade and the removal of at least 20cm horizontally immediately prior to sampling with a ceramic (ZrO) knife. 1cm thick samples were cut horizontally across the snow into a HDPE tray and transferred into vials. Tyvek clean suits, facemasks and dust free polyethylene gloves were worn to prevent sample contamination from personnel.

Figure 2: AWS at Evans Piedmont Glacier

Figure 2: AWS at Evans Piedmont Glacier

Snow profiling

Density and temperature profiling was conducted at 5cm resolution once sampling was complete and the surface was freshly cut back. Cylinders of known volume were hammered into the fresh surface, filled, extracted and weighed to determine precise density measurements.

Physical description notes of crystal structure and the location of hoar horizons are used to provide a preliminary chronology. This was taken both during and after sampling, with the upper section constructed into a thin wall to determine these more clearly (Fig 3.) Stable isotope and chemical species characterised by seasonal changes (e.g. sea salt species Na, Sr) will be used to confirm this chronology.

Automatic weather station (AWS)

Wind speed and direction, air temperature, snow accumulation and temperature, barometric pressure, humidity, and solar radiation are recorded (Fig.2).

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d. Results and discussions

Snow profile

The presence of summer hoar horizons and changes in density suggests that the 4m pit represents 13 years of accumulation.

Figure 3: Snow profiling at Evans Piedmont Glacier; a) Density and observations used to locate hoar horizons (A), fresh un-compacted snow (D), normal density snow (B) and ice/ hard layers (C); b) Stratigraphy of upper 2m section of the pit.

Figure 3: Snow profiling at Evans Piedmont Glacier; a) Density and observations used to locate hoar horizons (A), fresh un-compacted snow (D), normal density snow (B) and ice/ hard layers (C); b) Stratigraphy of upper 2m section of the pit.

AWS

The weather station has recorded data from the 15th Nov 2004 through to collection on the 3/12/2007. A problem with storage limits prevented continual data throughout 2005, but this was addressed by K049 during 2005/06 season. The record from Nov 2004 to Dec 2007 for air temperature, snow depth (i.e. accumulation changes), solar radiation, pressure and snow temperature is shown below (Fig. 4).

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Figure 4: Meteorological data collected at Evans Piedmont Glacier.

Figure 4: Meteorological data collected at Evans Piedmont Glacier.

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e. How this research fits in with future work being planned;

This data will contribute to the NZ ITASE current research – Holocene Climate History from Coastal Ice - by providing new knowledge on the seasonal pattern of aerosol deposited trace elements in snow. The investigation will include determining the patterns of seasonal aerosol concentrations and their sources and sinks through correlation with both site specific meteorological data and regional re-analysis data. This will assist in the interpretation of deeper ice core trace element records and our understanding of the Ross Sea tropospheric circulation system in the past.

2 Acknowledgments

We would like to thank all who have been involved in this project - the very enthusiastic and helpful Antarctica New Zealand Staff at both Christchurch and Scott Base; New Zealand Post for their support of the Antarctica New Zealand Postgraduate Award; Helicopter NZ staff, in particular Rob McPhearson; and those who were unlucky enough to be in the field when pit digging was underway, Jody Burton and Billy Wallace. This would also not be possible without the colaboration of staff at the Climate Change Center, University of Maine and National Isotope Center, GNS, Wellington, in particular Valerie Claymore. This project is supported by Victoria University of Wellington, Geological and Nuclear Sciences, and FRST (VUWX0704 and C05X0202 grants).

References

1- Turner, J. Review - The El Nino-Southern Oscillation and Antarctica. International J. of Climatology 24, 1-31 (2004).

2- Thompson, D. W. J. & Solomon, S. Interpretation of recent Southern Hemisphere climate change. Science 296, 895-899 (2002).

3- Kwok, R. & Comiso, J. C. Southern Ocean climate and sea ice anomalies associated with the Southern Oscillation. J. of Climate 15, 487-501 (2002)

4- Bromwich, D. H., Carrasco, J., Liu, Z. & Tzeng, R.-Y. Hemispheric atmospheric variations and oceanographic impacts associated with katabatic surges across the Ross Ice Shelf, Antarctica. J of Geophys Research 98, 13,045-13,062 (1993)

5- Peterson D (ed). New Zealand Science in Antarctica and the Southern Ocean (2004-2009), 17pp, New Zealand Antarctica Programme, Christchurch (2004)

6- Osterberg, E., M. Handley, M., Sneed, S., Mayewski, P., Kreutz, K.,. Continuous ice core melter system with discrete sampling for major ion, trace element, and stable isotope analysis. Environmental Science Technology 40: 3355-3361. (2006)