IMMEDIATE SCIENCE REPORT
K047: Dating Relict Ice in the Dry Valleys
Antarctica New Zealand 2005/06
1 Scientific Programme
a. Context of research
The 8 Ma relict ground ice in Beacon Valley, Antarctica has been the topic of much debate since Sugden and others reported it in 1995 (Sugden et al. 1995). There is little debate about the age of the volcanic ash, which dates the ice, but the emplacement of this ash and origin of the ice continues to be a matter of contention. The occurrence of relict ice is not unique to Beacon Valley, with a range of occurrences now reported throughout the Dry Valleys (Dickinson et al. 2003a). Such ice is likely to be much older than even the oldest ice in the present ice sheet, making it important because of the paleoenvironmental and paleobiological record it may contain. The ice also represents a terrestrial analogue for ice that is thought to exist on Mars. Thus, the overall aim of this ongoing project is to understand all aspects of relict ice in the Dry Valleys and the information that it can provide. The specific aim of this proposal is to obtain observations and materials for establishing the setting of these ice bodies and dating the length of time they have been in their present situation. The latter can be achieved by a new method that is based on the undisturbed accumulation of 10Be in the rock debris overlying the ice.
In addition to Beacon Valley, relict ice has now been confirmed to exist in Pearse, Columnar, Kennar, and Victoria Valleys, and is thought to be widespread throughout the Dry Valleys (Fig. 1). Studies associated with this project suggest that relict ground ice in the Dry Valleys can originate from either stranded remnants of glaciers (Marchant et al. 2002; Sugden et al. 1995) or buried glacial lakes (Hall et al. 2002; Kelly et al. 2002). Ground ice that is not relict may also result from a variety of in situ processes (Dickinson et al. 2003a; Dickinson and Rosen 1999; Dickinson and Rosen 2003). Relict ground ice appears to have been stranded in valley bottoms and is found as a continuum between two end-members: 1) massive clear ice with bubbles and trace amounts of debris to 2) highly deformed, debris-rich ice. The massive ice may derive from lake ice or ice cored moraines of wet-based glaciers pre-dating the present valley floors or ice cored moraines from the margins of the more recent cold-based glaciers. Highly deformed debris-rich ice may result from accumulated strain of multiple advances and retreats of cold-based glaciers (Fitzsimons et al. 1999). Clues to these origins may be determined from the chemistry and stable isotopic ratios of the ice as well as gas analysis of its bubbles. Such studies will need to be complemented with descriptions and analyses of the surrounding glacial sediments.
The age of the relict ice is critical to its value as a record of past climate. The difficulties in dating it are best exemplified by the numerous and conflicting ages, which range from 0.5 to 8Ma, published for Beacon Valley ice (Schafer et al. 2000; Stone et al. 2002; Sugden et al. 1995; Tschudi 2000; Ng et al. 2005). We have collected samples of relict ice and its overlying sediment for use in a new and evolving dating technique that involves the use of atmospherically-derived 10Be. This technique has been used with limited success for over a decade in dating soils from temperate areas. Recently, it has been applied to Antarctic soils (Graham et al. 1995; Graham et al. 2002) and sediments page 2 (Dickinson et al. 2003b) where it has produced logical and reasonable dates. However, the method needs further development and testing against a surface of known age. For this we have collected samples of Hart Ash between the Meserve and Hart glaciers in the Wright Valley. This ash has a radiometric date of 3.9 Ma.
Our approach to dating the surface of the relict ice uses 10Be produced in the upper atmosphere, which in Antarctica, accumulates in the salt components of the soil surface through snowmelt and evaporation (see method section for more detail). Atmospherically-derived 10Be differs in concentration by 1-2 orders of magnitude from the 10Be produced in situ that is used for surface exposure dating. In soils and sediments from three other areas in Antarctica (Dickinson et al. 2003b; Graham et al. 1995; Graham et al. 2002), we have page 3 assumed a closed system of 10Be accumulation. We also assume the 9Be/10Be ratio is fixed at the surface, and we think it is locked into clays and salts. We found that the 10Be/9Be ratio of the fines decreased systematically with depth to yield a decay age for the soil and sediment. The decay with depth suggests that Be is somehow infiltrating into the ground, by a process we do not fully understand. Nevertheless, the decay ages that we have obtained are reasonable for the soils and sediment analysed. We believe that this method should be applicable to dating the soils and ice-cemented sediments that overlie relict ice in the Dry Valleys, and indeed other parts of the Transantarctic Mountains.
Lower Victoria Valley (14 – 21 Nov)
- Sample ice in modern glacial and lake environments at snout of Lower Victoria Glacier. Sample buried ice and ice cemented sediment down valley (stream) from Lower Victoria Glacier.
- Sample several soil profiles for atmospheric Be-10 on top of buried ice, down valley from Lower Vic Glacier.
- Sample inflationary sand soils on the interfluves of lateral melt water channels. These sands will be dated by OSL to get an accumulation rate and approximate age of interfluve surface.
- Collecting samples of granite plutons for Pb-Pb isotopic fingerprinting. This information will be used to identify sources of granitic clasts in glacial tills.
Wright Valley – Meserve Glacier (21 – 25 Nov)
- Sample several soil profiles, which are associated with the Hart Ash, for Atm Be-10. The Hart Ash has a K-Ar date of 3.9Ma and this will allow an independent test of the Be-10 method of dating.
- Observe Miocene-Pliocene sediments at Prospect Mesa to understand the context of the Hart Ash.
Beacon Valley (25 Nov – 3 Dec)
|1)||Sample several soil profiles for Atm Be-10 to understand relative rates of processes which occur in on top of the buried ice to.|
|2)||Collection and mapping of granite clasts in till deposits in and around Beacon Valley. These data will be used to fingerprint the granites to help understand their source in the tills.|
Kennar Valley (3 – 8 Dec)page 4
|1)||Collection of granite clasts from the Metschel Tillite. These samples will be ananlyed for Pb-Pb isotopic fingerprinting to understand their source and determine if they could contribute to tills in Beacon Valley.|
|2)||Reconnaissance of buried ice in the valley. If ice is present, then to understand its context with buried ice in Beacon Valley.|
Sampling sites were selected for the occurrence of massive relict ice. At each site, a 1.5 square metre pit was dug into the ice free soil or sediment above the relict ice. In some areas ice cemented sediment was above the relict ice. This was sampled by means of a small gasoline powered hammer drill with a diamond or carbide core bit. Once into the relatively sediment-free relict ice, a sipre auger with carbide cutters was used to core to a depth of about one metre.
Ian Graham and co-workers at GNS, Lower Hutt, will carry out the dating method using atmospheric 10Be. The procedure will be similar to that used in previous studies (Dickinson et al. 2003b; Graham et al. 1995; Graham et al. 2002). To streamline the method, we will only process the >62 micron fraction of sediment which we believe contains most of the Be.
Samples of granite used for fingerprinting will be cut (1-2 cm2 slabs) and rough polished. These will be placed in a laser ablate chamber attached to a multi-collector mass spectrometer. Lead isotopes 204,206 and 207 will be measured in the feldspars of each sample. Plots of 207Pb/204Pb vs 206Pb/204Pb will show areas of feldspar genesis which are unique to the magma bodies where granitic rocks crystallize. The Lead isotopic composition of feldspars are incorporated at the time of crystallization and form distinctive signatures which can be used for tracing the origin of the feldspar.
d. Results and discussions
Three members of the event spent 7 days in Lower Victoria Valley from 14 - 21 Nov and 4 days near the Meserve Glacier in the Wright Valley from 21 - 25 Nov. Ron Sletten joined the event in for 8 days in Beacon Valley (25 Nov – 3 Dec) and 5 days (3 - 8 Dec) in Kennar Valley. All totalled we collected 35 kg of surface sediments and about 40kg of granite. Preliminary mapping of granite clasts in Beacon Valley show they are concentrated in the northeastern part of the valley. There appears to be about 5 different types of granites which can be identified in hand sample. Further results will have to wait for laboratory analysis.
e. How this research fits in with future work being planned
Future research by this investigator will centre on the geochemistry and dating of relict ice and permafrosted sediments obtained from shallow cores. Based on the outcome of the proposed work, the intention for the 2007/08 season will be to core areas of relict ice. Experience has shown that two drilling areas per page 5 season are logistically and scientifically the most productive use of resources and time. However, a season between coring seasons for analysis of samples is necessary.
In two years, we hope to have funds available to drill Beacon Valley in a joint project (Chris McKay) with NASA. Beacon Valley contains an undertermined thickenss of debris-laden ice. The present shallow coring system provides the technical development and expertise that will be necessary to drill Beacon Valley, but the system will need to be scaled up in size. The McKay proposal calls for the development of a 'smart' drill head that is capable of obtaining aseptic samples and has sensors to determine the presence of organic material and conduct microbiological assays through non-destructive methods.
f. Contributions from visiting foreign scientists
This past season, is part of an on-going project that utilises shallow drilling technology in the Dry Valleys to study permafrost and relict ice. The project has numerous collaborations and linkages but one collaboration occurred for this season. Ron Sletten of the University of Washington provided expertise in the Beacon and kennar valleys and he will provide chemical and stable isotopic analyses of the relict ice samples.
A paper on landscape modification by meltwater from the Packard Glacier has been submitted to Boreas in Dec 2005. Results from OSL sampling of Victoria Valley sediments will be published as a paper in Holocene in May 2005. Results from the 10Be anaysis will first be published as an MSc thesis at Victoria University in 2006. Results from granite fingerprinting will be first published as an Hons Thesis at VUW. Copies of these will be sent to Antarctica NZ.
Further publications of the scientific results will be published in international peer-reviewed scientific journals. Copies of this work will also be sent, when available, to Antarctica NZ.
Thanks to the following:
Prof Peter Barrett, (Director, Antarctic Research Centre, VUW)
Dean Peterson, Paul Woodgate and Steve Brown (Antarctica NZ)
All of the Scott Base personnel (Nov-Dec 2005)
Websters Drilling, for equipment preparation and cargo handling
Funding and Support
Antarctica New Zealand; University Grants Committee, VUW; Foundation of Research and Technology, NZ