National Geological and Geophysical Data Preservation Program

Physical Sample Preservation and Curation

Improved storage of physical samples

Improved storage of physical samples

Sample Storage

Different types of samples require different storage environments, and methods of pre-storage preparation and curation. As a general rule, all samples are subject to having their fundamental scientific and commercial values increased as knowledge and information about them increase. Materials are subject to lessening of value through physical degradation and loss of information and documentation. 

Environmental control

The primary concern for any archival repository, including geological repositories, is the preservation of integrity for their holdings. Similar to analog records, physical sample archives require environmental controls that exclude the ambient environment, and maintain optimal conditions to preserve the longevity of their holdings. Issues such as projected use of the samples, access frequency, and nature of research can dictate the requirements needed to appropriately store these collections.

Ice, Marine and Well Water Samples and Cores

Ice cores at the National Science Foundation Ice Core Facility (NSF-ICF) are stored in facilities that maintain temperatures far below freezing (archival temperature is maintained at -35º C) with little fluctuation to avoid melting and loss of potential chemical and paleoatmospheric information. The cold laboratory at the NSF-ICF facility includes a Class 100 clean room and maintains a temperature of -22º C. Marine and lacustrine soft sediment cores have refrigerated or freezing storage requirements, as fluctuations in air temperature and humidity can degrade the viability of the samples for geochemical and geophysical properties research, as well as promote organic growth. Preserved water well cores require storage in sealed, air-evacuated tubes containing native groundwater with chemically-enhanced reducing conditions, or are dessicated under reducing conditions.

Rock Cores and Samples

Rock cores with little to no moisture content must be protected from natural hazards (i.e., extreme weather). The assurance of reasonably protected indoor storage is widely recognized as crucial for any sample archive. Large rock core collections are stored in low-humidity, climate-controlled warehouses at the USGS Denver Core Research Center (CRC) and the Bureau of Economic Geology (BEG) repository in Houston. Due to lacking facilities and resources, other rock core collections are stored in non-controlled shipping containers; while this is not ideal, the materials are not directly exposed to weather, which preserves their integrity for research.

Unique and Hazardous Samples

Samples that require special and unique methods of preservation are abundant. Radioactive samples require isolation, which may include systematically controlled ventilation. Samples of gas hydrate require extreme cold (stored in liquid nitrogen dewars) to preserve their integrity, or must be kept under high pressure in Parr vessels.

Sample preparation

Samples collected in the field used for analysis in the laboratory need to be prepared for the various studies. Preparation of samples prior to incorporation into storage collections varies by sample type, and the nature of study for which they are collected.

Preparing the Sample for Addition to the Collections

Drill core cuttings, typically kept in 50 gram aliquots, are either washed or unwashed, depending on whether drilling mud may be safely removed from the rock type (clay cuttings are generally not washed). Washed and unwashed splits of cuttings may both be retained for archiving. Water well cores may require the environmental control treatment (evacuation, reducing treatment, sealed tubes). Ice cores require atmospheric isolation in vapor barrier sleeves inside reduced circulation reflective capped cardboard tubes, beginning at time of removal from core barrel after drilling. For drilled continental rock samples, as well as hand samples and marine rock dredges, needs for physical care may be less stringent, but accessible storage, tracking, and organizational care remain important. At the Kentucky Geological Survey core library, new cores are immediately identified and depth intervals, sequence numbers of boxes, total span depth, and condition of core are recorded. Cores may be retrieved from the field, or delivered to the facility by donors. Containers (boxes) are repaired or replaced as needed, wood crates may be replaced with cardboard. “Call numbers” are assigned, labels printed, and box numbers (separate from other sample identification numbers) assigned, all before cores are placed on pallets and racked.

Photographic Documentation

Photography is increasingly a standard preparation procedure for newly collected samples. Soft sediment marine and lacustrine cores are imaged for viewing in high definition and large format, as a primary mode of visual stratigraphy presented over the Web, and through data visualization systems such as Corewall. Ice cores are digitally photographed at high pixel density, and the images are made available on the Web to supplant the need for viewing in low-temperature environments. At the USGS CRC, photographs of core samples have long been an initial step in sample preparation. Plane-polarized light photographs of sample thin sections are generated, linked to other sample information and data, and made available on the Web. Availability of photographs on the Web efficiently provides information to researchers, often allowing identification of samples of interest and potentially precluding the need to travel to the sample repository.

Relocating collections 

Various repositories express differing degrees of caution toward the hazards of moving collections of physical samples. At the Kentucky Geological Survey sample repository, all boxes of samples (including paper records) are assigned sequential numbers, independent of other sample classification codes, for the purpose of re-ordering after moves, and three separate moves of location have been conducted without serious incidents. Metal storage containers have been used to temporary store sample pallets while more appropriate storage facilities are sought. Storage containers may be an adequate short-term storage solution depending on sample types, ambient temperature, and humidity.

Accessing collections

Sample repositories are obliged to establish policies that balance the security and preservation of collections with the needs of the research community requiring access to thre resources. These policies highlight issues such as making samples available for destructive analysis, guidance and regulations regarding access to samples for in-lab sample inspection, and lending of samples for non-destructive outside use.

NSF-Ice Core Facility Freezer

National Science Foundation - Ice Core Facility managed by the USGS, located in Denver, Colorado.

NSF-ICF sample acquisition and storage cost is resource-intensive, due to remote sampling location(s) (primarily, Antarctica) and vigilant maintenance of the 20,000 square foot freezer storage facility. The National Science Foundation has established guidelines for sample access and use. Sample access and assistance in subsample preparation are granted by a sample allocation committee, a subset of the governing board, on the basis of scientific merit of research proposal, availability and value of ice core segments being requested, and credibility and continuity of funding for the research investigator submitting the proposal. 

At many repositories, policies and regulations for acquisition of samples from collections and facilities for in-lab sampling and preparation are prominently and clearly posted on websites or in publications. Return of unused portions of samples and estimated publication schedules of analytical and interpretive results are typical repository requirements. The Florida Geological Survey maintains standard research proposal forms on its website, summarizing policy requirements and expectations, which include an assessment of available resources related to the requested samples (e.g., previous analytical results, thin sections) prior to being granted sample approval. And, “value added” products (e.g., thin sections, smear slides) made from the repository samples by the requestors be given to the repository at the completion of the research project.

Large warehouse with rows and rows of cores stacked to the ceiling

U.S. Geological Survey Core Research Center at the Denver Federal Center. 

The USGS CRC in Denver has a policy of enhancing the visibility of core characteristics by longitudinally cutting core into half-rounds, thereby saving a large fraction of required storage space by halving the diameter of the archived samples, which are stored in boxes on warehouse shelving. The mating half-rounds of the cores are subsequently made available for redistribution for research. Clients place orders for boxes of core half-rounds to be examined in examination rooms provided in CRC facilities, after CRC employees “pick” the orders from the coded shelved array of boxes, by means of high-lift warehouse vehicles. The CRC, like many other repositories, has specific and typically well-publicized requirements for sampling and analyses.

Some repositories have long standing policies for periodic or scheduled provision of certain types of samples to specific museums with which they have intragovernmental or other formal relationships, as a part of educational outreach programs. Some agreements include specimen loans, or outright sample transfer (e.g., the Florida Geological Survey provides samples to the State Museum of Natural History). 

Repositories face varying external threats to their collections. At the Kenyan National Anthropological Collections, extensive structural and procedural security precautions have been taken to prevent unauthorized entry and destruction of the collection, reportedly by anti-evolution extremists. The Danish national ice core lab has actively decided to limit public disclosure of the exact physical location of the storage collection, purportedly due to similar concerns. Some repository professionals advocate the concept of omitting from publically-accessible records (sample coding) information relating to the specific collection location of samples of sensitive economic or paleontological interest.

Physical aspects of storage

Repositories are typically under substantial logistical and financial restriction, and therefore, construction of physical storage facilities are widely constrained. Shelving, environmental controls (temperature and humidity), boxing for core, and types of containers for non core samples vary widely. The discrepancy between high costs of sample acquisition and relatively low costs of sample storage typically lead repositories to retain holdings in non-ideal conditions; stored in obsolete wooden core boxes, reclaimed glass containers, non-environmentally controlled buildings, and ocean shipping containers that are difficult to access. For many repositories, better storage environments (climate control, space-efficient shelving, uniformity of containers) are a long term goal while concentrating on efforts to retain and increase valuable holdings. Websites and other published documents for many repositories provide candid descriptions of their facilities and physical methods of sample storage.