Victoria University Antarctic Research Expedition Science and Logistics Reports 2000-01: VUWAE 45

Holocene Climate History from Coastal Ice - K047B

IMMEDIATE SCIENTIFIC REPORT

K 047 B Holocene Climate History from Coastal Ice

Antarctica New Zealand 2000/01

Holocene Climate History from Coastal Ice - K047B

1. Popular Summery of Scientific Work Achieved

The dynamic climate system of Victoria Valley is created by the interacting influences of the Dry Valleys, the East Antarctic Ice Sheet and the Ross Sea. The sensitive balance and strong contrasts in this system means even subtle shifts in the regional annual temperature, sea ice extent, snow cover etc. significantly alter the local weather pattern. As such, a climate record of the Victoria Valley provides an ideal opportunity to study rapid, high frequency climatic variations.

During season 1999/2000 several shallow (30m) firn cores have been recovered from Victoria Lower and Baldwin Glacier. Their chemical and isotopic signals display the dynamics of the Victoria Valley, confirming the value of a long paleoclimate record from Victoria Lower Glacier (VLG). A 240m core from VLG is expected to provide a continuous data set of 10,000 years climate history, and will be recovered during the 2001/2002 season.

To fully explore the paleoclimatic significance of the ice cores, the Lower Victoria glacial system and the local climatic pattern have to be understood. For this bedrock topography and interior structures of VLG have been mapped, snow pits at VLG, Baldwin Glacier and Wilson Piedmont Glacier investigated and sampled, and current mass balance measured. A weather station, dust traps and ablation stakes haven been installed at VLG for the duration of eight weeks (Map 1).

In order to extend our record beyond 10,000 years, ice at the western snout of VLG (VIC2), has been investigated and sampled to determine its likely Pleistocene age.

3. Scientific Endeavours and Achievements

The second field season of our project: Holocene Climate History from Coastal Ice has been interesting and successful. Four main sites have been visited: Victoria Lower Glacier (VIC 1 and 2), Baldwin Glacier and Wilson Piedmont Glacier.

Victoria Lower Glacier S77°19.810′, E162°31.991′

In order to map bedrock topography and internal structures of Victoria Lower Glacier, we used ground penetrating radar, employing different antennae frequencies (35, 200, and 400MHz) for different resolution and penetration depths. The radar profiles are accurately located using differential, kinematic GPS, with a base station device deployed on the southern margin of the glacier. The radar profile displays a glacier depth of 240m at the proposed deep drilling site (VIC1), with a maximum depth of 350m further to the north and confirms the suitability of VIC1 for a long-term paleoclimate record. The internal structures indicate the possibility of an inverse flow to the west of the Wilson Piedmont Glacier during the last 18,000 years.

Fig. 1: Ground penetrating radar Measurement

Fig. 1: Ground penetrating radar Measurement

Eight shallow firn and ice cores have been recovered from VLG. The sites are aligned along two transects perpendicular to each other. One from west to east along the glacier axis (glacier snout towards the future deep drilling site, located on the glacier dome) and one south to north, across the glacier with the deep drilling site in the middle (Map 1). The west-east sequence cuts across the assumed Pleistocene ice towards the active, Holocene part of Victoria Lower Glacier. Although no extended ice core could be recovered from the western snout, enough material was recovered to extract methane from the enclosed air bubbles to determine, whether this part of the glacier is in fact of Pleistocene age. The sequence of cores will allow us to test the results of the GPR and to quantify the variability of the climate record on the glacier.

Two snow profiles (5m and 1m depth at VIC1 and VIC2) have been investigated and sampled in 1cm resolution for major ion content, isotope ratios, and in 5cm resolution for dust flux and beta radioactivity. The samples were stored below 2m depth in a cave within the pit to secure temperatures below −17C. Temperature, crystal geometry, and density of the snow profile have been measured on site.

Fig.2: Snow profile sampling

Fig.2: Snow profile sampling

Mass balance measurements, deployed during season 1999/2000 season, have been continued using high precision, differential, static GPS. The device has been left at the site (VIC 1) for future measurements and a new system has been installed at VIC2 (Map 1). The setup allows to quantify total accumulation or ablation of the glacier.

Fig.3: Mass balance device

Fig.3: Mass balance device

A climate station, measuring temperature, wind speed and direction, relative humidity, solar radiation and snow pack temperature had been installed for the duration of eight weeks in the proximity of Victoria Lower Glacier Camp (VIC1).

The correlation of our observations with meteorological records from Marble Point, Lake Vida and Lake Vanda will determine the differences between local weather pattern. This will help us to establish transfer functions between the 40 year Marble Point record and our ice core parameter.

Fig.4: Climate Station at VIC 1

Fig.4: Climate Station at VIC 1

Furthermore temporary ablation stakes for mass balance measurements and dust/diatom traps have been employed for the same length of time. The ablation stakes were used to quantify weekly changes in snow cover due to precipitation and ablation. Dust mineralogy, grain size and relative quantity will be correlated with the VLG weather record to determine source areas and associated wind characteristics. Diatom analysis serves as a reference record for species found in the snow and ice samples.

Baldwin Glacier S77°19.836′, E162°32.019′

Baldwin Glacier serves as a reference record for our Victoria Lower Glacier analyses. The differences in the data set will allow to separate the regional input from the local one. A 4m snow profile has been sampled in 1cm resolution for major ion content, isotope ratios, and in 5cm resolution for dust flux and beta radioactivity. Temperature, crystal geometry, and density have been measured on site. Due to unusually high snowfall during November 2000 we were able to take contemporary snow samples during different synoptic weather conditions. Dust samples have been collected from the rocky outcrops around the glacier to allow the source area of the dust in the ice cores to be determined and distinguished from the Victoria Lower Glacier Source.

To study post-depositional processes within the snow pack, a radiation and snow temperature flux device have been installed for the time of our staying on Baldwin Glacier. The radiation device measures incoming and outgoing levels, so a radiation balance can be calculated. The temperature flux device measures the temperature at different heights in the snow pack, allowing the warming or cooling gradient within the pack to be calculated and modelled.

Hourly weather observations on site will be correlated with the measurements from the climate station on Victoria Lower Glacier to construct typical weather patterns of the region.

The glacier topography has been surveyed in the vicinity of our study site using differential, static GPS to correct for the slope angle.

Wilson Piedmont Glacier S77°16.000′, E163°15.000′

The site at the Wilson Piedmont Glacier allows investigation of succeeding precipitation composition from the sea to the Dry Valleys, and serves therefore as a reference for our Victoria Lower Glacier record. The correlation between the data sets enables us to distinguish between marine and terrestrial major ion species and their varying influence through seasons and time. A 3m snow profile has been sampled in 1cm resolution for major ion content, isotope ratios, and in 5cm resolution for dust flux and beta radioactivity analyses. Temperature, crystal geometry, and density have been measured on site.

A shallow (23m) firn core has been recovered from the Wilson Piedmont Glacier. The correlation of this transect of cores from the coast to the Dry Valleys enables a model of input source and timing to be established.

Fig.5: Drilling of firn cores at Wilson Piedmont Glacier

Fig.5: Drilling of firn cores at Wilson Piedmont Glacier

Borehole temperature indicates an average annual temperature of −21.6C, with the winter wave located between 3 and 8m depth. The glacier topography has been surveyed in the vicinity of our study site using differential, static GSP.

Six hourly weather observations on site will be correlated with the measurements from the climate station on Victoria Lower Glacier and assist in tracing typical weather paths.

Crary Laboratory

Ice cores were to be split and logged in a working freezer at the Crary laboratory, McMurdo Station, over a two week period. An ice core light table helped to record crystal structures, melt and dust layers and to identify areas of material loss. However the fresh water ice core band saw had been used by other research groups to cut sea ice cores and fish, which prohibited the use of the saw for our samples. For this reason we were unable to split the cores, and they were subsequently all sent to the United States for processing.

Methodology

4. Publications

The results will be published in peer reviewed papers in co-authorship with Peter Barrett, Paul Mayewski, Matt Watson, James Shulmeister, Warren Dickinson, Alex Pyne, Todd Saywers, Karl Kreutz, and Tony Gow.

5. Acknowledgements

Many people were involved in the successful completing of this field season. Of particular note are:
  • Peter Barrett, Warren Dickinson, Alex Pyne and Jamie Shulmeister for useful discussion on scientific goals and field techniques
  • Scott Base Staff, especially Peter Cleary for field assistance, logistical and mechanical support,
  • Paul Mayewski, Gordon Hamilton, for providing the laboratory facilities in the United States
  • Tim Haskell, for providing freezer facilities in New Zealand
  • PICO, especially Dave Giles, for technical advice on the drilling gear
  • Crary Laboratory, especially Robbie Score, Berg Field Center, US Science Cargo and NSF, especially Julie Palais, for logistical and mechanical support at McMurdo Station