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.
2. Proposed Programme
Due to re-organisation of PICO (Polar Ice Coring Office, now Ice Core Drilling Service), the original plan of this season 'Holocene Glacial Ice - a Continuous Paleothermometer' has been altered, with the deep drilling (~240m) at Victoria Lower Glacier (VLG) postponed until season 2001/2002. Instead we introduce some of the modules planned for our third field season; 'Ancient Ice Deposits -Windows into the Past'. The remaining project outline has been followed as proposed.
Hence the main emphasis of this year's fieldwork was to conclude the preparation for drilling and interpreting a 10,000 year climate record and to page 3 investigate the western snout of VLG for the possibility of providing a Pleistocene climate record.
- to map bedrock topography and internal glacial structures of VLG
- to sample four snow pits on VLG, Baldwin and Wilson Piedmont Glacier
- to recover shallow ice and firn cores from VLG and Wilson Piedmont Glacier
- to measure the current glacial mass balance of VLG
- to record the weather observations from VLG, Baldwin, and Wilson Piedmont Glacier and to compare them with climate records from Marble Point, Lake Vanda and Lake Vida
- to measure current dust flux
- to quantify radiant heat flux in the snow pack and albedo values
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.page 4
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.
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.
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).page 5
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.
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.page 6
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.
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.
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.
Ground Penetrating Radar (GPR) Measurements
A GPR system was hired from Auckland University and GroundSearch Ltd. We employed three different antennae (35, 200 and 400 MHz). The 35 MHz antenna pair was used in differential mode, so absolute depths of the glacier could be calculated. The system was deployed on a Nansen sledge towed and secured by two skidoos, allowing a vast area of the glacier to be investigated.
Differential Global Positioning System (GPS) Measurements
The GPS system Trimble 4000 SSE performed well, with the base station installed on the southern glacier margin. The GPS system was used for our GPR and mass balance measurements.
Snow Profiling and Sampling
Four snow profiles (5, 1, 4 and 3m) were described and sampled. After a detailed description of the physical features, the pits were sampled in 1cm resolution for isotopic ratios and major ion content. In order to avoid contamination of the chemistry samples, clean suits and high density polyethylene gloves were used. All sampling tools have been regularly cleaned with methanol. Dust and beta activity samples were taken with 5cm spacing. While the dust could be filtered in the field, the radioactivity samples had to be transported back to NZ. Density and temperature values were measured on site.
Ice Core Drilling
For the ice core drilling the PICO (Polar Ice Coring Office) hand auger with power head was used. The system was received in poor condition, and drilling hard ice was not possible. However Scott Base supplied numerous spare parts, wherefore the drilling performance was improved and firn cores were recovered.
Borehole Temperature Measurement
Coupled conductivity wire were used to read the temperature profile. The meter displayed a high sensitivity to the ambient air temperature and had to be kept above 0°C.page 8
A climate station was installed at Victoria Lower Glacier for eight weeks. The record included air temperature, relative humidity, wind speed and direction, air pressure, and snow pack temperature.
Current Dust and Diatom Flux
In order to measure current dust and diatom flux on Victoria Lower Glacier two traps were deployed in the proximity of the VLG camp (VIC 1). The containers in the traps were collected and replaced every three days.
Current Ablations Measurements
15 Ablation stakes were placed at VLG in the vicinity of the climate station. The relative change of snow depth was measured weekly or after individual snowfall events.
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.
- 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