Biological Material in Ice Cores 
 
John C. Priscu 
Department of Land Resources and Environmental Sciences 
Montana State University 
Bozeman, Montana 59717 USA 
 
 
 Brent C. Christner 
Department of Land Resources and Environmental Sciences and Department of 
Earth Sciences 
Montana State University 
Bozeman, Montana 59717 USA 
 
 
Christine M. Foreman 
Department of Land Resources and Environmental Sciences and Center for Biofilm 
Engineering 
Montana State University 
Bozeman, Montana 59717 USA 
 
George Royston-Bishop 
Bristol Glaciology Center  
School of Geographical Sciences  
University of Bristol, BS8 1SS  
United Kingdom 
 
 
Keywords: Antarctica, bacteria, biogenic matter, evolution, Greenland, ice cores, 
icy biosphere, phylogeny, survival, viral particles 
Submitted to Encyclopedia of Quaternary Sciences 6 October 2005 
 2
Introduction 
 
Snow falling on polar and high altitude regions has formed ~1.6 x107 km2 of 
glacial ice that provides an invaluable archive of past conditions on Earth.  The expansive 
ice sheets of Greenland and Antarctica cover ~10% (>1.5 x 107 km2) of Earth’s terrestrial 
surface with ice and contain ~70% of the fresh water on the planet (Paterson 1994). 
Temperate glaciers cover more than 5 x 105 km2 and comprise ~3.5% of the glacial ice on 
our planet (Table 1). The present volume of the Earth’s glacier ice, if totally melted, rep-
resents about 80 m in potential sea-level rise with 91%, 8% and 1% represented by the 
East and West Antarctic Ice Sheets, the Greenland Ice Sheet, and mountain glaciers, 
respectively (Hambrey and Alean 2004).  
<Table 1 near here> 
Research on ice cores from polar and temperate glaciers has focused primarily on 
the reconstruction of the paleoclimate record to determine the mechanisms responsible 
for ice sheet mass balance, associated sea level change, and the processes leading to the 
transition between glacial and interglacial periods (e.g., Petit et al. 1999, Alley 2002). Ice 
cores collected from Greenland more than a decade ago provided important evidence 
showing persistent climate instability over the last glacial cycle. Data from the Antarctic 
Vostok ice core have shown that over the past 400,000 years, there was a clear 
correlation between temperature and greenhouse gases, implying that greenhouse gases 
contributed to the temperature observations during this period. A recent ice core collected 
as part of the European Project for Ice Coring in Antarctica (EPICA), which has 
produced a record spanning more than 900,000 years and covers more than eight glacial 
cycles (EPICA 2004), has extended this record. Information derived from the ice-core 
record allows predictions of future changes in climate and provides important data to 
anticipate how these changes will impact future societal issues on our planet.  
Atmospheric impurities deposited in glacial ice include aerosols emitted by the 
oceans and the continents, and anthropogenic activity. Figure 1 shows the process of 
glacial deposition together with the global distribution of glaciers on our planet. The cold, 
dry conditions typical of glacial periods reduced the hydrological cycle and precipitation 
rate. The reduced precipitation increased the residence time of aerosols and dust allowing 
 3
them to disperse to great distances. This paradigm is revealed in the dust record from the 
Vostok ice core, which shows that dust concentrations during glacial periods were ~50 
times greater than for interglacial periods (Petit et al. 1999; Figure 2). The isotopic (Sr 
and Nd) composition of dust in the Vostok core further shows that it originated in the 
Patagonian region of South America (Delmonte et al. 2004). Unfortunately, the biogenic 
nature of the aeolian dust particles in glacial ice has received relatively little attention 
despite its known role in microbial transport (Griffin et al. 2003). 
<Figure 1 & 2 near here> 
 The biological contents of ice cores were first investigated in the 1980’s by 
Abyzov (Abyzov 1993, Abyzov et al. 2001), who used microscopic observations and 
traditional cultivation methods to show that microorganisms were present in the Vostok 
ice core and were positively correlated with the concentration of dust particles. An 
example of dust and associated microbiota in the Sajama ice core (Bolivia) is shown in 
Figure 3. Abyzov’s results, although controversial, motivated other microbiologists to 
examine the biotic content of ice cores collected from many icy regions of our planet 
(e.g., Priscu et al. 1998, 1999, Karl et al. 1999, Christner et al. 2000, 2001, 2003; 
Castello et al. 2005). Anomalies in the concentration and isotope ratio in biogenic trace 
gases (e.g., CH4, N2O) trapped in temperate and polar glacial ice have led 
glaciogeochemists to suggest enzymatic alteration within the ice by in situ metabolism 
(Sowers 2001, Campen et al. 2003). These trace gas anomalies imply that 
microorganisms are actually metabolizing in solid ice following deposition. Collectively, 
these data infer that ice cores represent “ice museums” containing novel records of 
evolution and habitat variability on our planet. Clearly, biologists should be included in 
future ice coring efforts if we are to produce a comprehensive record of past conditions 
on Earth. We present an overview of recent investigations that focus on biogenic matter 
in ice cores collected from the polar ice sheets (Antarctica and Greenland) and from low 
latitude mountain glaciers. We conclude by discussing the metabolic and evolutionary 
potential of ice-bound microorganisms. 
<Figure 3 near here> 
 
 4
Biogenic matter in polar ice sheets and temperate mountain glaciers 
 The study of biogenic material in ice cores is in its infancy and, except for a few 
reports, was unheard of a decade ago. We now know that microorganisms and associated 
nonliving organic matter are present in virtually all ice samples examined for biological 
properties (Figure 4). The past decade has seen biological research in ice cores go from a 
novelty to a focused area of scientific research. 
<Figure 4 near here> 
    
The Vostok Ice Core  
 Vostok Station is centrally located on the East Antarctic Ice Sheet (78°27'51"S 
106°51'57"E; altitude 3448 masl) and sits over ~3743 m of ice. Nearly 20 years after 
Vostok Station was constructed for the purpose of paleoclimatic ice core research, 
airborne radio-echo surveys and satellite images revealed that a very large lake 
(Subglacial Lake Vostok) exists beneath the ice sheet (Kapitsa et al. 1996, Studinger et 
al. 2004) (Figure 5). A 3,623 m core (designated 5G) was recovered from the ice sheet by 
an international drilling team in 1998 before drilling was terminated ~120 m from the ice-
water interface to prevent contamination of the lake environment.  
<Figure 5 near here>  
 The upper 3310 m of the Vostok ice core has provided a detailed paleoclimate 
record spanning the past 420,000 years (Petit et al. 1999). However, the deepest portion 
of the ice core (3,539 to 3,623 m) has a chemistry, isotopic composition, and 
crystallography distinctly different from the overlying glacial ice (Jouzel et al. 1999, 
Figure 6). Geochemical and physical data from this deep ice indicate that it originated 
from the freezing (accretion) of subglacial lake water to the underside of the ice sheet. 
Microbiological studies of the Vostok glacial and accreted ice have indicated that low, 
but detectable, concentrations of prokaryotic cells (34 to 430 cells ml-1; Christner et al. 
unpublished) and DNA are present (Priscu et al. 1999, Christner et al. 2001, Bulat et al. 
2004), and a portion of the entrapped microbial assemblage is metabolically active when 
melted and exposed to nutrients (Karl et al. 1999, Christner et al. 2001).  Many of the 
bacterial cells are associated with non-living organic and inorganic particulate matter 
(Figure 7). Molecular identification of microbes within the accreted ice (by both culturing 
 5
and direct 16S rDNA amplification) show close agreement with present day surface 
microbiota that classify within the Proteobacteria (α, β, and γ), Low G + C Gram 
Positives, Actinobacteria, and the Cytophaga-Flavobacterium-Bacteroides line of descent 
(Priscu et al. 1999, Christner et al. 2001, Bulat et al. 2004). Recent data from the Vostok 
ice core, using electron backscatter scanning electron microscopy, have also shown that 
up to 40% of the particles in glacial ice from the Vostok core represents non-living 
biogenic matter; this value reaches 60% for accretion ice (Figure 8; Royston-Bishop, 
unpublished data). Dissolved organic carbon (DOC) in the Vostok core ranges from 4 
x10-7 M to 7x10-7 M in glacial ice and increases to almost 12x10-7 M in the underlying 
accretion ice. The dissolved and particulate organic fractions are positively correlated, 
inferring that these constituents co-varied in the atmosphere when deposited on the ice 
sheet or were produced within the glacial ice by complimentary in situ metabolic activity 
following deposition. The positive relationship between these fractions in accretion ice 
could result from complimentary in situ metabolism in either the ice itself or within Lake 
Vostok before the ice accreted to the bottom of the ice sheet.  
<Figure 6, 7, & 8 near here> 
There has been speculation that geothermal input into Lake Vostok may fuel 
chemolithoautotrophic microbial communities (Bulat et al. 2004). Importantly, it is still 
possible for a chemolithoautotrophic-based ecosystem to exist without invoking 
geothermal activity. A range of energy-rich reduced compounds (e.g., HS-, S0, and Fe2+) 
are supplied to the lake by the ice sheet itself, which alone can supply the energy and 
carbon required to support metabolic activity within the lake. Organisms trapped in the 
ice sheet can also provide the microbial seed to initiate the lake population (Priscu et al. 
1999, Karl et al. 1999). Although geothermal input is not required to support life within 
the lake, it can provide an additional energy source for microbial growth in the lake if 
present. While other views of life in Lake Vostok exist, they all imply that 
microorganisms are present in this subglacial environment, despite high pressure, 
constant cold, low nutrient input, and an absence of sunlight (e.g., Bulat et al. 2004, Petit 
et al. 2005, Priscu et al. 1999, Karl et al.. 1999). The exact nature of the biology in Lake 
Vostok awaits direct sampling of the lake water. 
 
 6
Ice Cores From Greenland  
Biological studies of glacial ice cores have focused primarily on Antarctic cores 
and non-polar, high elevation glaciers (Priscu and Christner 2004 and references within).  
However, new studies on ice cores drilled in Greenland (i.e., GISP2, Gow et al. 1997; 
NGRIP, Anderson et al. 2004) have yielded important data on the nature of biogenic 
matter within and below the Greenland Ice Sheet. Culturable bacteria were recovered 
from the “silty” ice in the basal portion of the GISP2 core, with reported total cell 
concentrations >107 cells ml-1 of melt water (Sheridan et al. 2003, Miteva et al. 2004).  
The bacteria entrapped in the deepest sediment-laden portion of the GISP2 core could 
have originated from both the overlying 120,000-year old glacial ice and the underlying 
glacial till. Phylogenetic analysis of 16S rRNA gene sequences in the silty ice revealed 
that 36% of the bacterial isolates obtained were related to genera previously documented 
in glacial and permanently cold environments (i.e., Methylobacterium, Rhodococcus, 
Mycobacterium, Sphingomonas, Arthrobacter, and Frigoribacterium; Miteva et al. 
2004), providing support for the notion that members of these genera are particularly 
adept at surviving freezing and persistence under cold and low or non-growth conditions. 
Refrozen, sediment-laden ice core samples from the subglacial environment in 
Greenland were recently obtained from the NorthGRIP borehole when pressurized, 
”pink”-colored basal water at the base of the ice sheet entered the lower 45 m of the 
borehole and froze (Anderson et al. 2004) (Figure 9).  Before this discovery, the 
existence of large amounts of water at the base of the Greenland ice sheet was not 
anticipated.  Although cell concentrations in this refrozen basal water were 10x greater 
than in the overlying glacial ice (basal ice=1.6 x 103 cells ml-1, glacial ice= 1.6 x 102 cells 
ml-1; Christner et al., unpublished), the basal material was extensively contaminated with 
the hydrocarbon fluid used for ice core drilling, making conclusions about the 
microbiology of the subglacial environment tentative. This subglacial debris contains 
minerals (e.g., sulfides and iron, which produced the pinkish color) and organic material 
from the bedrock, which could fuel microbially-mediated chemical weathering reactions 
(e.g., Tranter et al. 2002) and support a community isolated from direct input from the 
surface. The data collected so far show that Greenland, like Antarctica, contains 
microorganisms within glacial ice and in the liquid subsurface environment. 
 7
<Figure 9 near here> 
  
Temperate Mountain Glaciers 
Glacial ice cores from non-polar, low-latitude glaciers in the Andes, Himalayas, 
and New Zealand generally contain more recoverable bacteria (i.e., colony forming units) 
and a greater variety of species than those from polar ice cores (Christner et al. 2000, 
Christner et al. 2003, Xiang et al. 2005). This geographic difference is consistent with the 
closer proximity of mountain glaciers to locations with substantial vegetation and 
exposed soils, which serve as major sources of atmospheric particles.  Despite great 
differences in the environments contributing biological particles to polar and nonpolar 
glaciers, phylogenetic analysis reveals that many of the bacteria characterized from 
different geographical locations belong to the same genera and species (Priscu and 
Christner 2004). One striking result from biological studies of ice cores is that there is no 
consistent, monotonic decrease in the number of recoverable bacteria with increasing age 
of the ice core (Christner et al. 2000). Rather, the numbers of recoverable bacteria at 
different depths appear to be a reflection of the prevalent climate and individual events 
that occurred at the time of deposition.   
Cells revived from ice core samples have endured desiccation, high solar 
irradiation while at the surface, freezing, an extended period of frozen storage, and 
eventual thawing. Therefore, it is not surprising that a large number of the isolates 
recovered belong to bacterial groups that form spores (e.g., Bacillus and Actinomyces) or 
have thick cell walls and polysaccharide capsules. These structures would help overcome 
the stresses associated with water loss, namely increased intracellular solute 
concentrations, decreased cell size, a weakened cell membrane, and physical cell rupture 
caused by freezing and thawing. The high frequency of pigment production in recovered 
isolates from temperate ice cores (Christner et al. 2000) is consistent with the need to 
absorb harmful solar irradiation, which can cause lethal DNA damage.  Even though the 
surviving cells may have resistant structures and protective pigments, they must still 
incur some radiation and chemical damage during extended periods of inactivity. Long 
periods (30-180 days) of incubation were often necessary before visible colonies appear 
during culture efforts, yet the vast majority of the isolates could subsequently be 
 8
subcultured to the stationary phase in <1 week.  This observation indicates that time is 
required to repair accumulated cellular damage before growth and reproduction could 
begin.    
A significant number of glacial bacterial isolates are phylogenetically related to 
species recovered from Antarctic lake mats, sea ice, polar ice cores, and other 
predominantly cold environments (Priscu and Christner 2004). In terms of geographical 
differences between ice core sites, Bacillus and Paenibacillus relatives of strains 
prevalent in soils were most commonly isolated from nonpolar glacial ices, and species of 
Sphingomonas, Methylobacterium, Acinetobacter, and Arthrobacter were ubiquitous and 
recovered from both polar and nonpolar ice core locations. It is noteworthy that close 
relatives of the radiation-resistant type strains Methylobacterium radiotolerans and 
Acinetobacter radioresistens were also commonly isolated. The recovery of related 
microorganisms from many geographically diverse, but predominantly frozen 
environments, argues that these species probably have features that confer resistance to 
freezing and survival under frozen conditions. 
  
Methods For Measuring Biotic Matter In Ice Ccores 
Particles in ice cores are typically measured on discrete core segments (usually at 
a depth resolution of several meters) using instruments based on the Coulter principle 
(e.g., Delmonte et al. 2004).  These investigations focused on the size, concentration and 
source of the particles but failed to discriminate between biotic and abiotic forms, 
collectively referring to them as “dust”.  Most of the data on the abundance of 
microorganisms in ice cores are from light microscopy, epifluorescence microscopy and 
electron microscopy. Although these microscopic methods allow characterizing of the 
microorganisms both morphologically and physiologically, they are tedious and subject 
to large errors, particularly when cell density is low. Hence, microscopic analysis does 
not lend itself to high resolution, routine determinations of biogenic matter in ice cores.   
Borehole optical loggers have been used successfully to quantify the in situ 
abundance of dust in several systems and modifications are underway to incorporate filter 
fluorometers on the loggers to detect biota and biomolecules (Bay et al. 2005). Flow 
cytometers offer another promising method to detect and characterize biogenic matter 
 9
rapidly in ice cores retrieved from selected sites. Flow cytometers were developed for use 
in the medical field to rapidly enumerate, characterize and sort cells from blood and 
human tissues. More recently, they have been used to characterize viruses, bacteria and 
phytoplankton in natural marine environments (e.g., Minor and Nallathamby 2004). Flow 
cytometers examine particles in a focused stream of fluid directed individually in front of 
an optical beam. Morphologically characterization and enumeration of the particles 
(biotic and abiotic) can be made by their light scattering properties. The physiological 
properties of the microbial component of the “dust” can be determined by either 
autofluorescence or fluorescence induced by the addition of specific fluorescence probes 
(Bay et al. 2005). Autofluorescence or induced fluorescence allows microorganisms to be 
enumerated separately from abiotic particles, and can provide detailed physiological 
measurements such as DNA content, cell membrane integrity and metabolic potential.  
 Our laboratory has begun to use flow cytometry to characterize particulate matter in 
ice cores from Antarctic and Greenland.  Importantly, these ice cores all followed strict 
preparation and decontamination protocols outlined by Christner et al. (2005) before 
cytometric analyses to ensure samples were not contaminated. A Microcyte™ flow 
cytometer (www.biodetect.biz) was placed in a class 100 environmental chamber, and 
calibrated with fluorescent beads of known size and fluorescence quantum yield 
(Molecular Probes Inc.; www.probes.com). The fluorescent DNA probe Syto 60 
(Molecular Probes Inc) was added to melted ice cores and incubated in the dark for 5 
minutes before cytometric analysis. Forward light scatter was used to measure the size 
and abundance of the particles, while fluorescence counts discriminated the biotic from 
the abiotic particles in the samples.  Initial tests on Vostok glacial (1686 and 2334 m) and 
accretion ice (3612 m) showed that counts of total particles and DNA containing bacterial 
cell can be successfully determined (Figure 10).  Data obtained from these samples by 
flow cytometry were verified by epifluorescence microscopy of samples stained with the 
DNA probe SYBR Gold and by scanning electron microscopy (Christner et al. 2005). 
Two previous studies have also employed flow cytometers to enumerate microbes in 
glacial ice cores. Karl et al. (1999) used a flow cytometer to show that there were 500 to 
700 cells ml-1 in Vostok accretion ice from 3603 m, and Miteva et al. (2004) found 
concentrations of bacterial cells ranging from 6.1-9.1 x 107 cells ml-1 in ice cores taken 
 10
from the GISP2 (Greenland) “silty” ice (~10 m above bedrock). In both of these studies, 
as well as our own, small cells (~1 µm) dominated the populations found within ice 
cores. 
<Figure 10 near here>   
 
Metabolic and evolutionary potential of ice-bound microorganisms 
The question of whether or not the microorganisms in glacial ice are 
metabolically active has fundamental significance to both glacial microbiologists and 
geochemists. Microbiologists are most interested in the diversity, evolution, and survival 
mechanisms of microorganisms, whereas glacial geochemists are concerned that in situ 
microbial activity consumes or liberates trace gases, thereby effecting the absolute 
concentration and isotopic content of the gases under concern. If the gases within the ice 
core are significantly altered by biogenic activity, a reassessment of ice core paleo-gas 
records may be necessary (Campen et al. 2003, Sowers 2001).   
Priscu and Christner (2004) estimated that the polar ice sheets of Greenland and 
Antarctica contain a combined total of  9.6 x 1025 prokaryotic cells, which equates to 2.7 
x 10-3 petagrams (1Pg = 1015g) of organic carbon. This value represents a previously 
unrecognized carbon pool and approaches the bacterial carbon contained in all surface 
freshwaters on our planet (Whitman et al. 1998).  Paleoclimate studies have accurately 
dated layers within the ice caps of both Antarctica (Petit et al. 1999, EPICA 2004) and 
Greenland (Alley 2002), providing an important stratigraphic age record for these 
microbial ice repositories. This reservoir of ancient microorganisms, which can include 
fungi, bacteria, and viruses (Castello and Rogers 2005), provides an unexplored frontier 
for the study of microbial variability over at least eight glacial cycles (~1 million years). 
Data collected from selected habitats on our planet shows that microbial cells can be 
revived after extended entrapment in geological materials (Table 2). 
<Table 2 near here> 
A global assessment of prokaryotic diversity in glacial ice, based on 16S rRNA 
gene sequences, revealed that many of the isolates are related to psychrophilic and 
psychrotolerant species originated from sites ranging from aquatic and marine 
ecosystems to terrestrial soils, with little in common except that all are permanently cold 
 11
or frozen. The distribution of related species in geographically diverse glacial 
environments implies that members of these bacterial genera evolved under cold 
circumstances and likely possess similar strategies to survive freezing, and to metabolize 
at low temperatures. This paradigm supports the contention of others (e.g., Price 2000, 
Campen et al. 2003, Sowers 2001) that the organisms are actually metabolizing in “solid 
ice”, presumably within grain boundaries (Figure 11). If microorganisms are indeed 
metabolizing and growing within the ice itself, a completely new set of selection 
pressures must be considered. 
<Figure 11 near here> 
Rogers et al. (2004) postulated that selected pathogenic microbes survive and are 
recycled through ice in a process they call “genome recycling” (Figure 12). The premise 
of their contention is that organisms trapped in ice for hundreds of thousands to millions 
of years are eventually released when glaciers calve and the ice melts and mixes with the 
genomes of contemporary microbial populations. The mixing of ancient and modern 
genotypes may affect mutation rates, fitness, survival, pathogenecity and other 
characteristics through a change in allele proportions in the populations. Genome 
recycling is dependent on the revival and establishment of organisms once they emerge 
from the ice sheets and glaciers and transfer their genetic information to extant 
populations, which are then reincorporated into ice sheets and glaciers via aeolian 
processes. Rogers et al. (2004) estimate that 1017 to 1021 viable microorganisms are 
released annually from melting glacial ice.  
<Figure 12 near here> 
Castello et al. (2005) documented the recovery and identification of viable phage 
from the bacterium Bacillus subtilis, and also have amplifed genomic segments of tomato 
mosaic tobamovirus from ice cores assigned dates exceeding 100,000 years before 
present. Our laboratory has also observed free viral particles in both meteoric and 
accretion ice from the Vostok ice core (Figure 13), implying that viruses, like bacteria, 
are prevalent in glacial ice. These viral data, in concert with the concept of genome 
recycling proposed by Rogers et al. (2004), have led Smith et al. (2004) to postulate that 
glacial ice may provide a reservoir for pathogenic human viruses, particularly 
caliciviruses, influenza viruses, and enteroviruses. These viral groups occur in great 
 12
abundance, are readily transported in the atmosphere, and may participate in ongoing 
disease cycles once released from the ice. Smith et al. (2004) contend that icy reservoirs 
may explain cyclic calicivirus events and the decades-long disappearances and 
subsequent reappearances of influenza-A subtypes. Although further research on ice 
cores is required, these preliminary data infer that viral reservoirs provided by glacial ice 
should be considered in eradication efforts for pathogenic human viruses. 
<Figure 13 near here> 
 
Conclusions 
Glacial ice covers more than 15 x 106 km2 of our planet and has a role in driving 
all processes on Earth. Glacial ice also contains an important reservoir of information on 
past climatic events, extending back at least one million years. Paleoclimatologists have 
used this information to determine past climate changes and to predict what changes may 
occur in the future. Despite the wealth of information trapped in ice cores, little 
information exists on the microorganisms immured in the ice. Recent discoveries over the 
past decade have shown that glacial ice contains an important record of microorganisms 
on our planet that theoretically could be used to assess biogeochemical processes and 
habitat types that occurred during past glacial and interglacial periods. This record may 
also contain important information on microbial evolution and physiology, and provide 
new biomedical information on pathogens. It is important that biologists be included in 
future ice coring efforts if a comprehensive view of past conditions on Earth is to be 
obtained. Such information will benefit all sciences involved in deciphering the ice core 
record and will provide the necessary information in our search for life on other icy 
worlds.  
 
Acknowledgements 
 
We thank M. Tranter, B. Close, J. Mikucki, D. Mogk, E. Adams, and B. Arnold for ideas 
and assistance. Our efforts were supported by the following grants from the National 
Science Foundation to J.C.P (MCB 0237335, OPP 0096250, OPP 0085400, OPP 
0440943), C.M.F (OPP 0338342) and B.C.C. (RIB 0525567).  G.R.B. was supported by 
Natural Environment Research Council grants NER/A/S/2000/01144 and 
NER/B/S/2003/00762, NERC Studentship (NER/S/A/2002/10332). 
 13
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 17
 
 
Table 1. Aerial coverage by selected glaciated areas on Earth (data from the World 
Glacier Monitoring Service, 1989). 
 
Region  Surface Area (km 2) 
Percent of 
world total 
Polar  
     Antarctica  13,593,310 87.5 
     Greenland  1,726,400 10.88 
Polar total 15,319,710 96.58 
   
Temperate   
     Africa  10 <0.01 
     Asia and Eastern Europe  185,211 1.17 
     Australasia (i.e. New Zealand)  860 0.01 
     Europe (Western)  53,967 0.34 
     North America excluding Greenland  276,100 1.74 
     South America  25,908 0.16 
Temperate total 542,056 3.42 
   
World total  15,861,766  
 
 
 
 18
 
Table 2. Reports of viable microorganisms retrieved from icy habitats representing a 
range of temporal isolation. 
 
Investigators Location Age (years) 
Sheridan et al. (2003); 
Miteva et al. (2004) 
Glacial ice; GISP2, 
Greenland 120,000 
Abyzov (1993); Christner et 
al. (2005) 
Glacial ice: Vostok, 
Antarctica 420,000 
Christner et al. (2003) Glacial ice: Guliya, China 750,000 
Shi et al. (1997) Permafrost 3,000,000 
 
 19
List of Figures 
 
Figure 1. History of entrapped particles in glacial ice and the present-day distribution of 
glaciers.  (A) Schematic illustrating the range of source environments that contribute 
particles to the atmosphere.  (B) Advective currents, created by solar generated infared 
radiation, inject surface derived aerosols high in the atmosphere.  Such aerosols (red dots) 
may serve as primary ice nuclei in clouds, and are subsequently precipitated in snowfall 
or rain.  (C) In geographical locations where the annual temperature remains cold enough 
that snowfall accumulates annually, particles from the atmosphere are archived in a 
chronological sequence in firn and glacial ice.  (D) Global locations of present-day ice 
sheets and mountain glaciers (in blue).  Each glacial environment is unique, as the nearest 
ecosystems that would most likely contribute the majority of airborne biological particles 
are very different. Distribution data based in part on Satellite Image Atlas of Glaciers of 
the World (US Geological Survey, (2002) Satellite Image Atlas of Glaciers of the 
World). 
 
Figure 2. The climatic record over the last 420,000 years deduced from the first 3,310 m 
of the Vostok ice core (adapted from Petit et al, 1999). From top to bottom: Global ice 
volume (black; in relative units, redrawn from the data of Petit et al, 1999) as deduced 
from the marine sediment record. Temperature (orange; difference with the present 
surface temperature) deduced from the stable isotope composition of the ice. Records of 
CO2 (green; ppmv) are deduced from entrapped air bubbles. Profile of continental dust 
concentration (blue; ppm). 
 
Figure 3. Dust layer, core particles and associated microorganisms. (A) Cross sectional 
view of ice core recovered 112 m (deposited ~12000 years BP) below the surface from 
the Sajama ice cap, Bolivia. A large number of entrapped gas bubbles and macroscopic 
particles are visible. A prevalent dust layer is shown (pink arrows), characteristic of the 
increased concentrations of airborne particles associated with dry climatic conditions. (B)  
Low resolution scanning electron micrograph illustrating the range of biological and 
inorganic particles entrapped in this ice core sample. (C)  Pennate diatom that most likely 
originated from one of the many saline lakes and salt flats in the area. (D) Rod-shaped 
bacteria preserved within the ice. 
 
Figure 4. Scanning electron micrographs of particles from polar and non-polar regions on 
Earth. Images in the left panel of each set are low resolution micrographs (1000x) 
illustrating the elevated concentrations of particles from non-polar regions. The right 
panels show selected images of prokaryotic cells (Taylor Dome and Lake Vostok), an 
organic fiber (NGRIP), a diatom (Sajama) and a pollen grain (Guliya).  
 
Figure 5. Satellite image (A) of Antarctica showing the location of Lake Vostok (yellow 
box).  Digital mosaic compiled by the Canadian Space Agency (Alaska SAR Facility) 
using data from RADARSAT-1. (B) Image shows a perspective view of the ice surface 
above Lake Vostok compiled from ERS-1 radar altimeter data. Lake Vostok is the flat, 
featureless area formed where the glacial ice overrides the actual lake. Image courtesy of 
M. Studinger (Lamont Doherty Environmental Observatory, Columbia University, New 
 20
York) using RAMP elevation data provided by the National Snow and Ice Data Center 
(NSIDC). 
 
Figure 6. Shematic of the Vostok ice core showing the region of transition between 
glacial and accretion ice. The accretion ice is represented by dirty ice containing 
numerous sediment inclusions and clear ice, which was formed over the lake proper and 
is relatively free of sediment. The ice below 3,623 m has yet to be samples but it is 
thought to have formed over the lake proper like the clear ice above it. See Jouzel et al. 
(1999) for details of the transition zone.  
 
Figure 7. Scanning electron (A,B,C) and atomic force (D) microscope images of bacterial 
cells from Vostok accretion ice showing their close association with organic particles. 
The large particle in panel “A” was shown to be organic using backscattered electron 
imaging. The numbers on each panel refers to the depth from which the ice cores were 
collected. Samples for microscopy were prepared as outlined by Priscu et al. (1999).  
 
Figure 8. Scanning electron microscope images showing the relative amounts of 
particulate mineral and organic matter in a Vostok glacial ice core collected from 2,779 
m below the surface. Backscattered electron imaging was used to view the particles in 
panel B; only mineral particles are detectable using electron backscatter. Organic 
particles not detected by electron backscatter are denoted by the yellow outlines in panel 
A. The percentage of organic particles ice core below ~1,600 m, relative to the total 
particle count, is presented in panel C along with profiles of dissolved organic carbon 
(DOC). The positive relationship between particulate organic matter and DOC is shown 
in panel D. DOC and scanning electron microscope methodology are described in Priscu 
et al. (1999). 
 
Figure 9. Images of an ice core collected at a depth of ~3,310 m from the NGRIP 
(Greenland) drilling site (Anderson et al. 2004). The ice core contains both colored 
frozen basal water and glacial ice (A). Low resolution scanning electron micrographs of 
particles in glacial ice and adjacent frozen basal water are shown in (B) and (C), 
respectively. 
 
Figure 10. Preliminary flow cytometer data showing the relative abundance and size 
distribution of cellular and abiotic particles in Vostok glacial ice (A = 1,686 m; B = 2,334 
m) and accretion ice (C = 3,612 m). Cellular particles were characterized by their 
fluorescence induced with the DNA stain CYTO 60.  
 
Figure 11. Cross-polarized image (A) of a Vostok accretion ice core from 3,590 m below 
the surface showing the grain boundary between 2 crystals. Panel B shows a microscopic 
view of the same vein following treatment with an epoxy resin, which highlights the 
grain boundary. The grain boundaries in polycrystalline ice, particularly where they form 
triple junctions have been proposed as a site for life in solid ice (Price 2000). 
 
Figure 12. General scheme of genome recycling through glacial ice proposed by Rogers 
et al. (2004). Organisms immured in the ice for millennia are eventually released as the 
 21
glaciers calve or melt, releasing them to the environment where there genes can mix with 
contemporary gene pools. Organisms forming the new gene pools are eventually trapped 
as dust particles in the ice where they remain isolated until the next cycle begins. 
Courtesy of S. Rogers, Bowling Green State University. 
 
Figure 13.Viral particles observed in the Vostok ice core from selected depths in the 
glacial and accretion ice. All images were obtained by transmission electron microscopy. 
Courtesy of M. Young, Montana State University at Bozeman.