Introduction

With the rapid development of analytical methodology and drilling techniques, it is important to procure ultra clean ice cores for trace studies (metals, ions, biological parameters etc.). Up to now most laboratories working on trace metals have adopted methods for de-contaminating their ice cores. Though effective and widely accepted, these procedures use large volumes of core, and are very time consuming. Quite often a single core can only be used for trace metal analysis, leaving nothing for other types of samples. Moreover, it is difficult to control and remove penetrating contamination when handling the firn sections of an ice core. One of our goals was to significantly reduce contamination during the drilling, handling and shipping processes.

This poster introduces a new CS (Clean Simon) drill, which is designed to provide ice cores free of metals contamination. The drill is light, sturdy and easy to operate. The field test of this drill in April 2000 on Devon Ice Cap, Nanuvut, Canada, is briefly explained here.

Camp site arrangement

The field camp was arranged to keep the drilling site away from daily camp activities. The drilling site was selected on the far North side of the camping area. The camp consisted of one parcoll, three pyramid tents, one long house storage, one fuel cache, an aircraft loading area and an outhouse to the South.

The drilling site consisted of two parts; a drilling shelter (two long-house tents combined) and a generator tent (a Polar Haven). The Polar Haven was situated on the West Side of the East-facing drilling shelter to minimize generator contamination. Winds blew primarily from North to South during the drilling. There was a minimum of activity on the North side apart from the drilling itself, with occasional aircraft flying upwind of the drill site.

Clean drill: Titanium Drill

The clean drill sonde is similar to the (earlier) steel version (refer to photo 2). It is modified from the SIMON drill (Terrain Science Division, Geological Survey Canada) with titanium replacing steel barrels, and providing more clearance inside to receive plastic liner inserts. Major modifications focused on the drill head, drill bits, chips guide, inner/outer barrels and core insert mechanism.

Modifications were carried out by Icefield Instruments Inc. (Whitehorse, Yukon, Canada). Because the drilled core is slipped directly into a plastic insert, the core is taken out of the inner barrel from the front end instead of the tail end (as in 'regular' tipping tower drills). Thus the drill head is not fastened on the barrel with screws, but threads onto the inner barrel as shown in photos 3, 4 and 5.

The CS drill can provide 8.5 cm diameter cores to a depth of about 400 meters. Operation is possible with a two-person crew, though a crew of three is recommended. There is no significant difference from regular drill operation, although use of the inserts and the need for ultra-cleanliness adds about 50% more time to the surface part of the drilling cycle.

Sample handling and precautions

The Devon 2000 field trip started in early April on Devon Ice Cap, Nanavut, Canada. Due to time limitations no special effort was made to clean the new drill before it was shipped up North. As a pre-cleaning method in the field, a short core of about 13 meters was drilled before the clean core drilling process began. We assumed the drill would be significantly cleaned since the TiN coating on the drill head and nylon chips guide in the barrel, showed signs of polishing by the 13-m drilling operation. Due to the harsh environment (temperatures ranged from -25 to -30 degrees C) at the drilling site and our insufficient preparation, some of the cleaning procedures and precautions could not be put into practice. At the start of the drilling (up to Core #15, 14.50 meters from surface), personnel who handled the core insert assembly and recovery, wore regular cold gear and polyethylene gloves. Extra-large clean-room type jackets (Tyvek) were prepared, but proved too small to cover a parka. Therefore, core sections drilled at this stage may have some dust contamination from ordinary winter clothing. A modified jacket (Tyvek coat) was used after core #15. Though still not ideal for this clean core drilling operation, it should have minimised dust from clothing to some degree.

It is preferred to have the drilling staff wear clean jackets during the drilling operation (mandatory for the core handler).

Ice core Insert pre-treatment and pre-cleaning

Ice core containers, which were inserted into the drill's inner barrel to protect the core from contamination, were purchased commercially. The inserts were made of high-density polyethylene, while the cover end caps were made of low-density polyethylene.

To ease the ice core entry, one end of the insert had to be slightly enlarged. For operational convenience, both ends were slightly enlarged using an aluminum mandrel (titanium mandrels can, and should be used in the future), taking about four minutes for each insert.

Aluminum detritus from the mandrel was found on some of the inserts after enlargement. Also, water for cooling down the inserts was from the laboratory tap. To eliminate any contamination of aluminum and water, the inserts were cleaned with a 25% HNO3 acid solution. The acid used was trace metal (TM) grade. Each cleaning took about 15-20 minutes, and was followed by DDW (double distilled water) rinse. This cleaning procedure has not yet been checked for efficiency, though the aluminum contamination should be substantially reduced.

Since we intended to obtain clean ice cores, clean inserts are a prerequisite. Further treatment of the inserts was carried out in MRD's (Mineral Resources Division, GSC) class-100 clean room by submerging the tubes in 0.5% TM grade HNO3 for at least 24 hours.

Ice core handling

During the drilling, the core handler used plastic gloves at all times, making no direct contact with the ice cores which stayed snugly inside their inserts. Once retrieved from the titanium barrel, both ends of the ice core tube were immediately covered with pre-cleaned polyethylene covers. Then the insert was sealed in the same polyethylene lay-flat material that covered the empty insert (airtight).

The sealed cores were then carefully packed in Styrofoam core boxes protected by shock absorbing bubble-wrap. This process helps protect the cores from fracture during handling and shipping. Less sublimation in storage can be expected because the cores are relatively tightly packed in the inserts, minimizing air circulation. The quality of cores collected with this clean drill can be kept at a high level for a long period of time.

Sample analysis is under way. For more information please contact Dr. David Fisher.

To get up close and personal with an ice core drill, go to CS drill photo details.

This poster assembled and written by James Zheng, edited for the web by Roy M. Koerner and John Sekerka.