IMMEDIATE SCIENCE REPORT
K049 NZ – ITASE: Holocene Climate Variability along the Victoria Land Coast
Antarctica New Zealand 2005/06
1 Scientific Programme
Seven key locations were identified for the NZ ITASE (International Transantarctic Scientific Expedition) programme. The analyses on the ice core from the first site, Victoria Lower Glacier in the McMurdo Dry Valleys, have been completed. During the 2003/04 field season we carried out a detailed reconnaissance of sites 2 and 3: Evans Piedmont Glacier (EPG) and Mt Erebus Saddle (MES) and determined the most suitable locations for the ice core recovery. During the 2004/05 field season we recovered to intermediate length ice cores (180m and 200m, respectively) from these locations and conduct further in-situ measurements, such as borehole temperature and light penetration characteristics, snow density and stratigraphy and its geographical variability. Furthermore, we installed a weather station and mass balance devices at EPG and cased the borehole at MES for future measurements. For the 2005/06 field season proposed to identify a drilling location and recover an intermediate length ice core from Whitehall Glacier in the vicinity of Cape Hallett. Due to logistical constraints of Antarctica New Zealand this was part of our programme was postponed and our field programme condensed accordingly. During the 2005/06 field season we re-visited VLG and EPG to conduct GPS measurements of the submerge velocity devices and to sample shallow snow pits. Furthermore, we retrieved the meteorological data and carried out maintenance work on the automatic weather station at EPG. Lastly we deployed 6m snow stakes at the high accumulation site at MES.
a. Context of the research
Unprecedented changes are occurring in the Earth's climate. The 1990's were the warmest decade in the last 2000 years and average global temperature is projected to rise between 1.4°C and 5.8°C by 2100 [IPCC 2001]. 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 and Jones 2003].
While meteorological records from instrumental and remote sensing data display the large intercontinental climate variability, they series are insufficient to infer trends or to understand the forcing, which renders prediction difficult [Jones et al. 1999; Mann and 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 ). 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 and 54 others 2005; Bertler et al. 2004a; Bertler et al. 2005a; Bertler et al. 2004b; 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.
Our 2005/60 field season comprises 4 objectives.
Automatic weather station maintenance and data retrieval
In 2004/05 we deployed an automatic weather station on Evans Piedmont Glacier. We anticipate to collect data from the site for at least two years. 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.
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 and 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, 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 and Whillans 2000; Hamilton et al. 1998] were deployed at Victoria Lower Glacier in 1999/2000 and two at Evans Piedmont Glacier in 2004/05.
High resolution snow pit sampling at Victoria Lower and Evans Piedmont Glacier
Intermediate length cores were recovered from Victoria Lower Glacier and Evans Piedmont Glacier in 2001/02 and 2004/05, respectively. High resolution samples from shallow snow pits are used to update the records and to investigate post-depositional changes in the snow signal, such as isotopic diffusion or nitrate loss. Furthermore, meteorological data recorded at Evans Piedmont Glacier and re-analysis data are used to calculate transfer functions and establish seasonality in the ice core record. In order to estimate the influence of small-scale local page 3 influences such as sastrugi features, we investigate spatial variability by studying physical properties of multiple snow pits at each location.
Snow Accumulation at Mt Erebus Saddle
We have recovered a 200m deep ice core from the slopes of Mt Erebus Saddle during the 2004/05 Antarctic field season. The site topography promotes strong winds leading to significant compaction of the surface snow (~0.45 gcm−3). Furthermore, average snow accumulation lies in the range of 72 – 150 cm yr−1 water equivalent. This is more than one order of magnitude higher than the regional average [Bertler et al. 2004a; Bertler et al. 2004b; Bromwich 1988; Bromwich et al. 1998] and provides ideal characteristics for a high resolution ice core gas record. To measure the accumulation rate at the drill site we deployed three snow stakes, which we hope will endure the high wind velocities and snow accumulation.
Automatic Weather Station at Evans Piedmont Glacier
An automatic weather station has been established near the 2004/2005 ice coring site that records several parameters to help characterise the meteorology and snow accumulation regime of the area (Fig.2).page 4
- Air Temperature at 2.5 height
- Snow accumulation, and air temperature at 1.5 m height
- Dew point temperature at 2.5 m height
- Solar radiation (incoming) at 2.5 m height
- Snow temperatures (thermistor resistance) from 0.135 to 2.085 m depth in at 13.5 cm intervals
To these were added as of 01 December 2005
- Barometric pressure
- Wind speed (ultrasonic)
- Wind direction (ultrasonic)
Submergence Velocity Measurements at Victoria Lower and Evans Piedmont Glacier
During the 1999/2000 season three submergence velocity devices [Hamilton and Whillans 2000] for mass balance measurements in the McMurdo Dry Valleys were installed (Fig.3). During the 2004/2005 season two submergence velocity devices have also been installed at EPG (Fig.3). 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.
Fig.3 a) Cartoon of the 'coffee can' submergence mass balance device. The device consists of a low-stretch, stainless steel wire attached to a metal anchor (initially a coffee can, hence the name) that is heated and placed into the drilling hole drilled in firn. The anchor is melted with the bottom of the ice and freezes in. The wire is stretched tight and guided by a stainless steel tube. The tube is held in place using plywood that was buried ~40cm into the snow to avoid melt around the darker wood surface. The top end of the wire has a loop and permanent marker, the tracking point (modified after Hamilton and Whillans 2000). b) picture of coffee can device deployed at Victoria Lower Glacier.
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. At Victoria Lower Glacier, the base station was deployed on a rocky platform at Staeffler Ridge <3km away from all mass page 5 balance sites. The proximity of the base station to the rover allowed the tracking points to be measured with a horizontal precision of <1mm and a vertical precision of <5mm. At Evans Piedmont Glacier base station data from the Cape Roberts permanent GPS/GLONASS and tide gauge observatory will be used. All GPS measurements are post-processed using precise orbits, which are published on-line at "http://igscb.jpl.nasa.gov/components/prods_cb.html". These data are corrected using GIPSY-OASIS II software and provide precise point positions by taking into account satellite orbit, Earth orientation, and clock solution from NASA Jet Propulsion Laboratory's independent analysis of globally distributed GPS receivers.
Fig. 4: a) submergence velocity device at VLG II (glacier tongue), b) temporary GPS base station at Staeffler Ridge, c) submergence velocity devices at EPG.
The rate of thickness change H, can then be calculated using [Hamilton et al. 1998]:
where: H= rate of thickness change (myr−1) bm= accumulation rate (Mgm−2yr−1) p= density at marker depth to account for densification processes (Mgm−3) z= vertical component of ice velocity (upward is positive, myr−1) α= surface slope (radians) u= horizontal velocity (myr−1 with azimuth)
High resolution snow pit sampling at VLG and EPG
At EPG and VLG I, 1m deep snow sequences were sampled with 1cm resolution for analysis on snow chemistry (Na, Ca, K, Mg, Cl, NO3, SO4, MS, Al, Fe, Si, Sr, Tr, Zn), isotopic composition page 6 (δ180 and δD), dust content and mineralogy. The snow sampling surface was cleaned with a pre-cleaned plastic spade, and subsequently with a sterile scalpel, at least 20cm horizontally into the snow to prevent sampling of contaminated snow. All tools, sampling equipment, and bottles were rinsed and soaked with ultra pure 18MΩ Millipore® water and dried in a class 100 clean room facility prior to fieldwork. A scalpel was used to collect 1cm thick samples. Sample were collected into sterile Nasco whirl-paks®. Tyvek® clean suits and dust free polyethylene gloves prevent sample contamination from personnel.
Snow Accumulation at Mt Erebus Saddle
To accommodate high accumulation rates of about 2m snow/year, 6m snow stakes that are anchored 2m into the ground were deployed. The three snow stakes, made of epoxy/carbon fibre, have been chosen for their flexibility to withstand high wind velocities in excess of 100knts.
d. Results and discussions
The weather station has only recorded data from 15th Nov 2004 to 1st Jun 2005, when it stopped due to storage limitations but remained operating throughout the winter. The storage limitations have been addressed for future measurements. The recorded data for solar irradiation, air temperature, snow temperature, dew point, and snow accumulation are shown in below (Fig.7).
The time scale is in decimal years; months are indicated on top.page 8
As shown in Fig.7 the decrease in solar irradiance from January to mid April is accompanied by cooling temperatures. Interestingly the temperature increases again from mid April until mid May before cooling once again. A higher frequency temperature variability is superimposed on this trend from mid February onwards with positive temperature deviations on a 4-6 day periodicity with an amplitude of up to 20K. The cause of these warm events could be katabatic outflow from the McKay Glacier portal. Due to the lack of barometric and wind data caused by hardware failure, we will use data from existing weather stations (e.g. Scott Base, Lake Vida, Terra Nova) and satellite imagery to investigate this pattern further. Temperatures in the snow pack measured concurrently at 16 depth horizons from 0.135m to 2.085m show the decreasing influence of air temperature variability with depth. While the temperature in the upper most horizon (starting at 13.5cm arriving in June at 43.5cm) ranges from −2°C to −30°C, at the deepest sensor (starting at 197.5cm arriving in June at 227.5cm) ranges from −17°C to −27°C. The snow temperatures have yet to be corrected for their change in depth, which increased by 30cm as shown in the snow accumulation graph below. The snow accumulation record shows that most of the precipitation occurred during three event of 5 to 15cm snow accumulation. The data show also that are no prolonged time periods of snow loss, except in the first 2-5 days after the snow precipitation event which is partly due to snow compaction. After this time period the snow surface remains stable. Overall, the data confirm EPG as an excellent ice core site. The snow pit data and submergence velocity measurements from EPG and VLG have yet to be processed.
e. Integration into future work
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 and 54 others 2005; Bertler et al. 2004a; Bertler et al. 2005a; Bertler et al. 2004b; Bertler et al. 2005b; Mayewski et al. 2005; Patterson et al. 2005] 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 and 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. It is those rapid climate change events that are of greatest concern to human civilisation in the near future. The NZ ITASE programme contains five objectives that are scientifically inter-linked to the following programmes.
The main objective of ITASE is to determine the spatial climate variability across Antarctica over the last 200 years, and where possible further back in time. The focus of the New Zealand ITASE group (this proposal) is to provide information from the climate sensitive, low altitude, coastal sites (Fig.8). This will capture the climate signature of the troposphere, which represents a regional account on the Ross Sea climate. Our preceding research showed that while the direct ENSO influence warms the eastern Ross Sea (oceanic forcing), the indirect ENSO influence dominated in the western Ross Sea, leading to the observed cooling in McMurdo Sound Region (atmospheric forcing) [Bertler et al. 2004a; Bertler et al. 2005b]. The comparison with data from other ITASE-nations will allow us to date relative phasing and signal migration velocities of these climate drivers across Antarctica.
Furthermore, the gas record will allow us to determine the role of CO2 and in rapid climate change events and the CO2 and methane source/sink fluxes of the Ross Sea. The isotopic fractionation of biogenic (terrestrial) material is –with the exception of C4 plants – enriched in the lighter 13C isotopes and carries therefore a different signature than ocean derived carbon, which shows no such enrichment [Indermühle et al. 1999; Sigman and Boyle 2000]. For this reason the change of isotopic ratio in CO2 and CH4 can be used to determine the change in sources of GHG concentration through time. This is particular important to determine the role of the oceans versus the atmosphere in rapid climate change [Broecker 2000; Broecker 2003; Ferretti et al. 2005; Schrag 2000; Stocker 1998; Stocker 2002; White 1993] and has the potential to detect influences of early human activities in the late Holocene [Ruddimann 2003].
In conjunction with the US-ITASE traverse of our collaboration partners altitude and continentality gradients across the Trans Antarctic Mountains (TAM) can be established. Temperature and humidity gradients across the TAM are amongst the most extreme on the continent and exceed the latitudinal gradients by more than one order of magnitude. The correlation between the US-ITASE polar plateau traverse (Fig.8) and our data will allow determining the climatic influence of the mountain range and also the position of the Antarctic Vortex, the geographical boundary of tropospheric and stratospheric influence.
2. Latitudinal Gradient Project Objective
Our project is expected to contribute an important data set to the Latitudinal Gradient Project, as it provides a history of temperature, humidity, sea ice cover, precipitation source, atmospheric circulation, and ocean productivity along the Victoria Coast for the last 1000 to 10,000 years depending on the site. This will help to determine whether the current ecological system found has evolved under prevailing climate, or how much time the ecological system had to adjust to potential climate change in the recent past. Furthermore, the timing and velocity of the Ross Ice Shelf retreat some 9 to 5ka years ago is still discussed controversially [Hall and Denton 2000; page 10 Steig et al. 1998; Steig et al. 2000]. Coastal ice core records are very sensitive to the change from an ice shelf environment to seasonally open water, which manifests itself in a shift in the chemical signature of snow and aerosol precipitation [Legrand and Mayewski 1997]. By dating the occurrence of the characteristic chemistry shift in the proposed ice cores locations (Fig.8), average retreat velocity can be calculated and its dependency on air temperature tested. This will also add to our knowledge on the current Ross Ice Shelf stability.
3. ANDRILL Objective
Proposed ice core locations no. 2 and 3 (Evans Piedmont and Mt. Erebus) are in the immediate vicinity of planned ANDRILL coring locations (Granite Harbour and Windless Bight). The ice core records will provide a high-resolution climate dataset, which serves as a reference for the younger part of marine record recovered through ANDRILL. This will provide the unique opportunity to compare contemporary on- and off-shore records.
4. Longer-Term Mass Balance Objective
During the 1999/2000 season mass balance measurement devices (submerge velocity method [Hamilton and Whillans 2000; Hamilton et al. 1998]) have been deployed at Victoria Lower Glacier and at Evans Piedmont Glacier during 2004/05. The measurements at Victoria Lower Glacier show that the glacier has a slightly negative mass balance, losing around 12cm thickness per year. A continuation of the measurements will allow monitoring changes in the ablation intensity of the McMurdo Sound Region.
5. The Antarctic – New Zealand Connection Objective
New Zealand's future economic and social development, environmental sustainability, and infrastructural planning relies critically upon the accurate assessment of the impact of "global warming" in our sector of the planet. A joint programme between IGNS, University of Maine, and Victoria University is investigating ice core records from New Zealand (Tasman Glacier and Mt. Ruapehu ice field). The comparison between our NZ and Antarctic ice core records will provide much needed data for the development of realistic regional climate models to predict NZ climate in the 21th Century [Mullan et al. 2001].
Publications since the 2004/05 Antarctic field season include: Bertler, N. A. N., Naish, T. R., Mayewski, P. A., and Barrett, P. J., 2006, Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica: Advances in Geosciences, 6 (83-86), SRef-ID:1680-7359/adgeo/2006-6-83. Bertler, N. A. N., and 54 others, 2005, Antarctic Snow Chemistry: Annals of Glaciology, 41 Bertler, N. A. N., Barrett, P. J., Mayewski, P. A., Fogt, R. L., Kreutz, K. J., and Shulmeister, J., 2005, Reply to comment by Doran et al. on "El Niño suppresses Antarctic warming": Geophysical Research Letters, 32 (L07707, doi:10.1029/2005GL022595). Bertler, N. A. N., Barrett, P. J., Mayewski, P. A., Sneed, S. B., Naish, T. R., and Morgenstern, U., 2005, Solar forcing recorded by aerosol concentrations in coastal Antarctic glacier ice, McMurdo Dry Valleys: Annals of Glaciology, 41. Mayewski, P. A., Frezzotti, M., Bertler, N. A. N., van Ommen, T., Hamilton, G. S., Jacka, T. H., Welch, B., and Frey, M., 2005, The International Trans-Antarctic Scientifc Expedition (ITASE) - An Overview: Annals of Glaciology. Patterson, N. G., Bertler, N. A. N., Naish, T. R., Morgenstern, U., and Rogers, K., 2005, ENSO variability in the deuterium excess record of a coastal Antarctic ice core from the McMurdo Dry Valleys, Victoria Land: Annals of Glaciology, 41. Bertler, N. A. N., Naish, T. R., Oerter, H., Kipfstuhl, S., Barrett, P. J., Mayewski, P. A., and Kreutz, K. J., in review, ENSO-driven temperature and snow accumulation variability in the McMurdo Dry Valleys, Antarctica: Antarctic Science. Witherow, R. A., Lyons, W. B., Welch, K. A., Bertler, N. A. N., Mayewski, P. A., Sneed, S. B., Nylen, T., Handley, M. J., and Fountain, A., in review, The aeolian flux of calcium, chloride and nitrate to the McMurdo Dry Valleys Landscape: Evidence from snow pit analysis: Antarctic Science.
We would like to thank Antarctica New Zealand staff based in Christchurch and Scott Base for their enthusiastic and innovative support with our project. We are indebt to Helicopter NZ staff, in particular Rob McPhearson. This project is funded by Victoria University of Wellington, Geological and Nuclear Sciences, FRST, and Marsden.
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