A novel chemical fossil of palaeo sea ice: IP25

Abstract 

A novel chemical fossil of palaeo sea ice: IP 25 

Simon T. Belt a, *, Guillaume Massé a , Steven J. Rowland a , Michel Poulin b , 

Christine Michel c , Bernard LeBlanc c 

a Petroleum and Environmental Geochemistry Group, School of Environmental Sciences, University of Plymouth, Drake Circus, 

Plymouth, Devon PL4 8AA, UK 

b Research Division, Canadian Museum of Nature, P.O. Box 36, Ottawa, Ont., Canada K1P 6P4 

c Freshwater Institute, Fisheries and Oceans Canada, 501 University Crescent, Winnipeg, Man., Canada R3T 2N6 

Received 12 July 2006; received in revised form 20 September 2006; accepted 26 September 2006 

A unique and novel organic compound has been detected in sea ice samples from three locations in the Canadian Arctic, 

thousands of kilometers apart. It is likely that this biomarker is produced by diatoms living in the sea ice and we provide 

evidence which suggests that the compound, a C25 monounsaturated hydrocarbon (IP25), may be a specific, sensitive and 

stable proxy for sea ice in sediments over at least the Holocene. Since it has not been reported before, we confirmed its 

identity by synthesis and used the synthesized compound as a reference for quantifying IP 25 in a range of sediments from 

an East-West transect in the Canadian Arctic. The recent sediments are either seasonally covered with ice or have permanent 

ice cover. Older sediments containing IP25 have been dated using radiocarbon methods to at least 9000 yr. If the concept 

proves generally applicable, monitoring IP25 in further sediment cores along with other accepted proxies, should allow 

movements in the position of the ice edge throughout the Holocene (at least) to be better determined, which is essential for 

accurate calibration of climate prediction models. A similar approach for Antarctic samples of ice and sediments would 

also seem worthwhile. 

Ó 2006 Elsevier Ltd. All rights reserved. 

1. Introduction 

1.1. Polar sea ice and climate change 

Organic Geochemistry 38 (2007) 16–27 

Polar sea ice plays a fundamental role in determining 

the rate of global climate change by influencing 

the exchange of heat and moisture between 

polar oceans and the atmosphere, since it reflects 

* 

Corresponding author. Tel.: +44 1752 233042; fax: +44 1752 

232406. 

E-mail address: sbelt@plymouth.ac.uk (S.T. Belt). 

0146-6380/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. 

doi:10.1016/j.orggeochem.2006.09.013 

Organic 

Geochemistry 

www.elsevier.com/locate/orggeochem 

much of the incoming solar radiation (the albedo 

effect; Thomas and Dieckmann, 2003). In addition, 

it contributes to circulation models of numerous 

oceanic processes (e.g. thermohaline circulation), 

many of which have further positive feedback mechanisms 

in relation to sea ice extent (Thomas and 

Dieckmann, 2003). Consequently, the retreat of 

sea ice from the Arctic regions during the last 30 

years has been receiving considerable attention 

(Johannessen et al., 1995, 1999; De la Mare, 1997; 

Vinnikov et al., 1999; Francis et al., 2005; Stroeve 

et al., 2005; Divine and Dick, 2006) It is therefore

essential to improve our knowledge of historical sea 

ice fluctuations and the associated variations in climate 

in order to better refine and calibrate models 

of future climate change. In recent times (the last 

30 years), satellite imaging methods have enabled 

sea ice coverage determination to become both rigorous 

and routine (Johannessen et al., 1995, 1999; 

Vinnikov et al., 1999; Francis et al., 2005; Stroeve 

et al., 2005), while historical sealing and whaling 

records provide some information for the last 300 

years (De la Mare, 1997; Divine and Dick, 2006). 

However, there is a paucity of meaningful records 

of sea ice over longer timescales, principally since 

the melt process leaves behind a relatively poor geological 

record. Of the proxy measures that exist for 

the determination of palaeo sea ice cover, one 

method relies on the preservation in sediments of 

fossil siliceous frustules (or skeleta) of diatomaceous 

sea ice algae (Thomas and Dieckmann, 2003; Gersonde 

and Zielinski, 2000). These microalgae can 

be distinguished from open water diatoms or flora 

found in multi-year ice. The sea ice diatoms inhabit 

the underside of first year ice at the interface with 

nutrient-rich seawater, where light penetration 

through the ice is adequate and where microscopic 

capillaries and brine pockets provide a unique ecological 

niche (Thomas and Dieckmann, 2003). 

When the ice melts, or the microalgae die or are 

grazed by zooplankton, the silica and organic compounds 

of which these microalgae (diatoms) are 

comprised, settle through the water column before 

reaching the sediment. However, poor preservation 

of the thin siliceous frustules of diatoms sometimes 

makes it difficult to carry out unambiguous identification, 

and the majority of organic compounds 

found in sea ice diatoms are not preserved well 

and suffer biodegradation in the water column or 

sediment. Of those which do survive, most are 

non-specific for sea ice diatoms, rendering them 

unsuitable as specific sea ice proxies. 

In order to be useful as an indicator of the presence 

of former sea ice, a chemical biomarker must 

originate within the sea ice and be absent from open 

waters (i.e. be specific), be sufficiently resistant to 

degradation in the water column and to other diagenetic 

changes in the sediment (i.e. be stable) and be 

produced in sufficient quantity for straightforward 

detection, both amongst the numerous other compounds 

in sediments and with meaningful geological 

resolution (i.e. be sensitive). The ketones measured 

in the well known U k0 

37 alkenone index, which has 

provided a useful and widely used chemical proxy 

S.T. Belt et al. / Organic Geochemistry 38 (2007) 16–27 17 

for the determination of mean summer or spring 

sea surface temperatures of open waters (e.g. Brassell 

et al., 1986), have many of these attributes. 

1.2. Diatom specific isoprenoids as a new chemical 

proxy 

C25 and C30 highly branched isoprenoid (HBI) 

alkenes, known as haslenes and rhizenes, respectively, 

are biosynthesised by a limited number of 

diatom genera; notably some Haslea spp., Rhizosolenia 

spp., Pleurosigma spp. and some Navicula 

spp. (Volkman et al., 1994; Massé et al., 2004; Sinninghe 

Damsté et al., 2004). In Haslea ostrearia 

(Gaillon) Simonsen, the extent of unsaturation in 

the haslenes co-varies with culture temperature. 

Thus, tetra- and tri-unsaturated haslenes are produced 

as the major isomers at 25 °C and 15 °C 

respectively, while at 5 °C, diunsaturated haslenes 

(hasladienes) are biosynthesized as the major isomers 

(Rowland et al., 2001). Haslea spp. have been 

identified as minor members of both Arctic (Poulin, 

1990; Booth and Horner, 1998; Riedel et al., 2003) 

and Antarctic (Pakhomov et al., 2001) sea ice diatom 

populations and hasladienes have been found 

in mixed diatom populations obtained from Antarctic 

sea ice (Nichols et al., 1988; Johns et al., 1999). 

We hypothesised that a similar dependence of 

unsaturation on temperature might lead to the production 

of monounsaturated haslenes in sea ice populations 

of Haslea spp., and that, on the melting or 

grazing of the ice, such compounds might be better 

preserved in sediments than the more unsaturated 

HBIs, including trienes and tetraenes. Previously, 

synthesized haslane (Robson and Rowland, 1986) 

and mono-unsaturated haslenes have been shown 

to be relatively resistant to biodegradation compared 

to unbranched alkanes and alkenes (Robson 

and Rowland, 1988) and, even hasladienes undergo 

little diagenetic reaction compared with the more 

unsaturated HBIs (Belt et al., 2000b), suggesting 

that the monoenes would be even more stable. As 

such, HBI monoenes should have the potential to 

serve as proxy measures of contemporary and historical 

sea ice when detected in polar ice and sediments 

respectively. Although we were aware of a 

limited number of reports of haslene monoenes of 

unknown biological origin in sediments from temperate 

and sub-tropical environments (Dunlop and 

Jefferies, 1985; Xu et al., 2006), the specificity of 

the biosynthetic process in the genus Haslea Simonsen 

(Massé et al., 2004), encouraged us to postulate

18 S.T. Belt et al. / Organic Geochemistry 38 (2007) 16–27 

that monoenes in sea ice and/or polar sediments 

might be structurally specific and different from 

those found in non-polar regions. In order to test 

this hypothesis, we examined the hydrocarbon content 

of sea ice obtained from three distinct regions 

of the Canadian Arctic, together with recent and 

ancient (Holocene) sediments collected from across 

the Canadian sub- and High Arctic regions, including 

those seasonally covered with ice. We also examined 

the hydrocarbon extracts from assemblages of 

open water phytoplankton in order to determine 

whether the chemicals present in sea ice were sea 

ice restricted or not. 

2. Experimental 

2.1. Sea ice and sediment sampling 

Sea ice sampling (Fig. 1) was performed in 

McDougall Sound (May 2003; Site 1), Franklin 

Bay (May 2004; Site 2) and Button Bay (April 

2005; Site 3). Ice samples were collected using a 

MARK II ice corer at a site where snow cover 

was at a minimum. For diatom analysis, the bottom 

sections (5 cm) of three cores were combined in a 

dark isothermal container. In the laboratory, these 

sections were allowed to melt at room temperature 

(15 °C) and two sub-samples (25 ml) were preserved 

with 1% formaldehyde (1 ml) prior to analysis. For 

each sampling site, a further three ice cores were collected 

and kept frozen for hydrocarbon analysis. 

Sediment material was obtained in three stages. 

First, surface and down-core material (seven locations, 

NOW-1 – NOW-5, WEI-1,2; Fig. 1, Table 

1) was obtained from the Geological Survey of Canada 

(Atlantic Division, Bedford Institute of Oceanography). 

Second, surface sediment samples were 

collected from Button Bay (April 2005; ARC-8; 

Fig. 1, Table 2) using an Ekman grab sampler. 

Third, combinations of surface sediment (box 

core; 50 cm · 50 cm · 80 cm), trigger weight cores 

(99.2 mm internal diameter) and piston cores 

(99.2 mm internal diameter) were obtained from 

seven locations (ARC-1 to ARC-7; Fig. 1, Table 

2) during the CCGS Amundsen Leg 1 ArcticNet 

cruise (August/September 2005). Sub-samples of 

surface and core material ( 20 °C) and the remaining 

core material (< 4 °C) were stored in the dark 

prior to analysis. 

2.2. Diatom analysis 

Diatom material from sea ice was prepared 

according to Hendey (1974). Cleaned diatom frus- 

Fig. 1. Map of sampling locations for sea ice and sediment samples. , Sea ice; , NOW sediments; , WEI sediments; , ARC sediments. 

Individual numbering corresponds to specific locations cited in the text.

Table 1 

Summary of Arctic sediments corresponding to North Water (NOW) and Ellesmere Island (WEI) regions of the Canadian High Arctic 

Sample Cruise 

number 

Table 2 

Summary of Arctic sediments obtained during the ArcticNet 2005 cruise and from Churchill, Hudson Bay (NB IP 25 concentrations for 

ARC-5 have not been determined) 

Sediment ArcticNet stations Water 

depth (m) 

tules were examined with light microscopy and, to 

achieve unambiguous identification of some of the 

species, some preparations were examined using 

scanning electron microscopy (Jeol 6400F). 

2.3. Lipid analysis 

Hole Water 

depth (m) 

NOW-1 84015 71 538 Annual/ 

seasonal 

NOW-2 84015 61 578 Annual/ 


NOW-3 84015 67 677 Annual/ 


NOW-4 91039 8twc 663 Annual/ 


NOW-5 91039 26d 450 Annual/ 


Sea ice sections (200–300 ml) were freeze-dried 

and an internal standard was added to permit quantification 

using GC–MS (7-hexylnonadecane, 

1.5 lg sample 1 ). The freeze-dried samples were 

extracted using a mixture of CH2Cl2/CH3OH (50/ 

50; 5 ml) to yield a total organic extract (TOE). 

The TOE was saponified with 2 ml 5% KOH in 

CH3OH/water (80/20) at 80 °C for 30 min to hydrolyse 

triglyceride esters of fatty acids. The nonsaponifiable 

lipids (NSLs) were re-extracted into 

hexane (3 · 1 ml) and dried over anhydrous 

Na2SO4. Following derivatisation (100 ll BSTFA- 

TMCS (99/1), 30 min at 70 °C), these NSLs were 

analysed using GC–MS and purified using a two 

stage chromatography procedure if necessary 

(Section 2.4). 

Ice cover Date of 

collection 

Ice cover Date of 

collection 

Latitude (N) Longitude 

(W) 

23-09-1984 75°23.58 0 79°21.30 0 0.53 

22-09-1984 76°12.90 0 83°03.18 0 0.56 

22-09-1984 76°01.38 0 82°35.70 0 0.33 

27-08-1991 77°15.96 0 74°19.92 0 0.29 

06-09-1991 75°29.52 0 78°10.98 0 0.16 

WEI-1 85200 38 134 Permanent 07-08-1985 81°01.80 0 96°38.28 0 n.d. 

WEI-2 85200 50 115 Permanent 10-08-1985 81°02.58 0 96°28.38 0 n.d. 

n.d., not detected. 


Latitude 

(N) 

Longitude 

(W) 

ARC-1 2 – North Water 703 Annual/seasonal 20-08-2005 77°49.75 0 74°39.97 0 0.31 

ARC-2 3 – Lancaster Sound 811 Annual/seasonal 23-08-2005 74°02.95 0 79°54.41 0 0.33 

ARC-3 4 – Barrow Strait 347 Annual/seasonal 24-08-2005 74°16.05 0 91°06.38 0 1.52 

ARC-4 6 – Victoria Strait 61 Annual/seasonal 27-08-2005 69°09.94 0 100°41.72 0 0.37 

ARC-5 7 – Dease Strait 112 Annual/seasonal 30-08-2005 68°59.45 0 106°34.27 0 – 

ARC-6 11 – Franklin Bay 253 Annual/seasonal 10-09-2005 70°19.49 0 126°23.50 0 0.14 

ARC-7 12 – Amundsen Gulf 219 Annual/seasonal 13-09-2005 69°54.81 0 122°57.96 0 0.16 

ARC-8 Button Bay, Churchill 15 Annual/seasonal 03-05-2005 58°50.00 0 94°20.00 0 0.15 

Individual compounds were identified on the 

basis of comparison between their GC retention 

indices and mass spectra with those of authentic 

standards. A similar procedure was used for sediment 

samples except that the internal standard 

(1.5 lg) was added to the wet sediment material 

(5 g) immediately before extraction. 

2.4. Purification of individual compounds 

IP 25 (lg/g 

w.w.) 

IP25 

(lg/g w.w.) 

Hydrocarbons were separated from phytol, sterols 

and other compounds in the NSLs using open 

column chromatography (50:1 SiO2:NSLs (w/w)). 

The hydrocarbons were eluted with hexane (5 column 

volumes) while the more polar compounds were 

obtained as a single fraction using CH 2Cl 2 (2 column 

volumes) followed by (CH 3) 2CO (2 column volumes). 

In some cases, individual lipids from the 

hydrocarbon fraction were then separated with silver 

ion chromatography (5:95 AgNO3:SiO2). Saturated 

hydrocarbons were eluted with hexane (5 column 

volumes), monoene 1 was obtained using CH2Cl2


(2 column volumes) and the more unsaturated 

alkenes were eluted using a mixture of CH2Cl2/ 

(CH3)2CO (60/40, 2 column volumes). Structures of 

the C25 HBI alkenes discussed are shown in Fig. 2. 

2.5. Lipid analysis 

1 2 

Fig. 2. Chemical structures of IP 25 (1), C 25 HBI monoene (2) and 

C25 HBI diene (3). The double bond in IP25 is located at C23–24. 

A Hewlett-Packard 5890 Series II gas chromatograph 

(GC), fitted with a 30 m fused silica HP-1 column 

(0.25 mm i.d., 0.25 lm film) and coupled to a 

HO 

HO 

Br 

Br 

Br 

Br 

3 

(iv) 

5970 Series mass selective detector (MSD) was used 

to perform gas chromatography–mass spectrometry 

(GC–MS) analysis. The GC oven temperature was 

programmed from 40 to 300 °C at5°C min 1 and 

held at the final temperature for 10 min. Operating 

conditions for the mass spectrometer were 280 °C 

for the ion source temperature and 70 eV for the 

ionisation energy. Spectra (m/z 40–550) were collected 

using Hewlett-Packard MS-Chemstation 

software. 

2.6. Synthesis of C25 HBI monoenes 1 and 2 

2.6.1. Monoene 1 

Synthesis of 1 was performed via a 5 step procedure 

as shown in Fig. 3. To diene 3 (5 mg, 

14.4 lmol) in CH2Cl2 (1 ml) was added m-chloroperoxybenzoic 

acid (MCPBA) (6.25 mg, 14.4 lmol) 

dissolved in CH2Cl2 (1 ml) and the resulting solution 

was heated at 50 °C for 4 h. Following solvent 

evaporation (N 2), the reaction mixture was redissolved 

in hexane and subjected to column chromatography, 

whereby unreacted 3 and epoxide 4 

(3 mg) were obtained by elution with hexane and 

(i) 

3 4 

6 

7 

(iii) 

(v) 

Fig. 3. Synthetic scheme for the preparation of the C 25 monoene (IP 25) found in Arctic sea ice and sediments: (i) MCPBA, CH 2Cl 2,4h, 

50 °C; (ii) TBABr3, CH2Cl2, 0.5 h, 25 °C; (iii) HClO4, THF/H2O, 1 h, 25 °C; (iv) PtO2/H2, CH3CO2H, 5 h, 25 °C; (v) Zn, t-BME, 

CH3CO2H, 12 h, 25 °C. 

(ii) 

Br 

Br 

O 

O 

5 

1

CH2Cl2, respectively. Epoxide 4 (3 mg, 8.2 lmol) in 

CH2Cl2 (1 ml) was added to 2 equiv. of tetra-n-butylammonium 

tribromide in CH2Cl2 (1 ml) and the 

resulting solution left at room temperature (1 h). 

After solvent evaporation (N 2), the reaction mixture 

was redissolved in hexane and subjected to column 

chromatography, whereby the dibromo-epoxide 5 

(4.1 mg) was obtained by elution with hexane. Following 

reaction of dibromo-epoxide 5 (4.1 mg, 

7.8 lmol; H2O/THF (3 ml, 40/60)) with HClO4 

(75 ll; 3 h), the reaction was quenched with saturated 

NaHCO3 (3 ml) and the products re-extracted 

into hexane (2 · 3 ml). Solvent removal yielded the 

dibromo-diol 6 (3.5 mg). H 2 was bubbled through 

a solution of 6 (3.5 mg, 6.4 lmol) in CH 3CO 2H 

(1 ml) in the presence of PtO2 Æ 2H2O (0.05 g). After 

5 h, the sample was filtered through a glass Pasteur 

pipette containing anhydrous sodium Na2SO4. Following 

solvent evaporation (N2), the reaction mixture 

was redissolved in hexane and subjected to 

column chromatography, whereby dibromide 7 

(1.9 mg) and unreacted 6 were obtained by elution 

with hexane and CH 2Cl 2, respectively. Dibromide 

7 (1.9 mg, 3.7 lmol) was dissolved in a mixture of 

tert-butyl methyl ether (2 ml) and CH3CO2H 

(1 ml); 20 mg of zinc dust was added and the mixture 

was stirred at room temperature (12 h). After 

filtering (Na2SO4) and removal of the solvent (N2), 

the reaction mixture was redissolved in H 2O (2 ml) 

and the products reextracted into hexane 

(2 · 3 ml). Removal of the hexane yielded 1.1 mg 

of 1. 


2.6.2. Monoene 2 

H2 was bubbled through a solution of diene 3 

obtained previously by extraction from H. ostrearia 

(5 mg, 14.4 lmol) in hexane (5 ml) in the presence of 

PtO2 Æ 2H2O (0.1 g). Aliquots were removed at regular 

intervals (each 30 s) to monitor the hydrogenation 

progress with GC–MS. Following 

hydrogenation, samples were filtered through a glass 

Pasteur pipette containing anhydrous Na2SO4 and 

the solvent was removed under N2 prior to analysis. 

Monoene 2 was separated from 3 and its saturated 

analogue using silver ion chromatography as 

described above to yield 0.7 mg (2 lmol) of pure 2. 

2.6.3. NMR characterisation of C 25 monoene 1 

1 H and 13 C NMR spectroscopy were used to 

characterise the C25 monoene 1. Spectra were 

obtained using a Jeol EX 270 spectrometer operating 

at 270 and 68 MHz for 1 H and 13 C respectively, 

and processed using DELTA software. Spectra were 

recorded in CDCl 3 and chemical shifts were referenced 

relative to residual proton signals or to the 

central line of 13 C multiplets of the solvent ( 1 H: 

7.24 ppm, 13 C: 77.0 ppm). Selected NMR data: 1 H 

(d/ppm): 5.69 (m, 1H, –CH@CH2), 4.92 (m, 2H, – 

CH@CH2); 13 C(d/ppm): 145.1 (CH@CH2), 114.3 

(CH@CH2). 

2.7. Dating of core material 

Determination of the age of the longest core 

obtained from the ArcticNet cruise was achieved 

Table 3 

Summary of phytoplankton samples collected across the Canadian High Arctic during the ArcticNet cruise in 2005 

Sample ARCTICNET station Date of collection Water depth (m) Latitude Longitude 

PHK-1 Pond Inlet 14-08-2005 751 72.47 0 039 00 78.07 0 505 00 

PHK-2 BA01 – North Water 16-08-2005 676 76.17 0 924 00 71.24 0 525 00 




PHK-6 3 – Lancaster Sound 22-08-2005 817 74.02 0 895 00 79.55 0 684 00 

PHK-7 4 – Barrow Strait 24-08-2005 332 74.15 0 519 00 91.11 0 273 00 

PHK-8 6 – Victoria Strait 27-08-2005 65 69.10 0 092 00 100.42 0 145 00 

PHK-9 7 – Dease Strait 30-08-2005 120 69.00 0 054 00 106.35 0 009 00 

PHK-10 204 02-09-2005 65 71.08 0 473 00 128.11 0 283 00 

PHK-11 CA-05-05 03-09-2005 211 71.16 0 727 00 127.28 0 988 00 

PHK-12 10 – Beaufort Sea 05-09-2005 220 71.33 0 500 00 140.04 0 200 00 

PHK-13 CA-04-05 06-09-2005 335 71.05 0 027 00 133.34 0 289 00 

PHK-14 CA-08-05 09-09-2005 414 71.00 0 000 00 125.55 0 000 00 

PHK-15 11a – Franklin Bay 11-09-2005 263 70.20 0 264 00 126.22 0 106 00 

PHK-16 11b – Franklin Bay 11-09-2005 256 70.20 0 310 00 126.21 0 675 00 

PHK-17 CA-18-04 12-09-2005 609 70.39 0 174 00 122.59 0 450 00 

PHK-18 12 – Amundsen Gulf 13-09-2005 219 69.54 0 813 00 122.57 0 957 00


using radiocarbon ( 14 C) dating of foraminifera 

shells [Neogloboquadrina pachyderma (s)] isolated 

from the base of the core obtained from Lancaster 

Sound (641 cm). A sub-sample of the sediment 

(50 g) was air-dried, sieved (63 lm) and the foraminifera 

isolated by hand under a microscope. 

Approximately 200 specimens were analysed using 

accelerator mass spectrometry (Beta Analytic Inc., 

USA). 

2.8. Phytoplankton collection 

Surface and near surface (1–50 m water depth) 

samples of phytoplankton were obtained via horizontal 

and vertical trawling (75 lm) of late summer 

ice-free waters across the entire East-West transect 

of the Canadian High Arctic during the ArcticNet 

cruise (August/September 2005, Table 3). Aliquots 

of the phytoplankton concentrates were preserved 

(Lugol) prior to diatom analysis. The remaining 

concentrates were extracted and analysed as per 

other lipid analyses described previously. 

3. Results and discussion 

3.1. Analysis of Arctic sea ice and phytoplankton 

assemblages 

As part of an initial study, sea ice samples from 

three well-separated regions of the Canadian suband 

High Arctic (McDougall Sound, Franklin Bay 

and Button Bay; Fig. 1) were obtained. In all three 

cases, analysis with light and electron microscopy 

revealed the presence of characteristic Arctic sea 

ice diatoms, including members of the common genera 

Nitzschia Hassall, Fragilariopsis Hustedt, 

Entomoneis Ehrenberg, Navicula Bory and Pseudogomphonema 

Medlin (Thomas and Dieckmann, 

2003; Poulin, 1990). Significantly, and as expected 

from previous reports (Poulin, 1990; Booth and 

Horner, 1998; Riedel et al., 2003), low abundances 

(1–3%) of a number of Haslea spp. were present in 

each case. Thus, Haslea crucigeroides (Hustedt) 

Simonsen, Haslea vitrea (Cleve) Simonsen and 

Haslea kjellmanii (Cleve) Simonsen were readily 

detected. 

Examination of the hydrocarbon fractions from 

the extracted sea ice samples from each of the three 

Arctic locations (Fig. 1) using GC–MS revealed the 

occurrence of C25 HBI dienes and trienes, one of the 

former having also been identified in Antarctic sea 

ice diatoms and sediments (Nichols et al., 1988; 

Johns et al., 1999) but not, to date, in sea ice. In 

addition, a more abundant haslene isomer was identified, 

which had one degree of unsaturation (Figs. 4 

and 5). In order to confirm that it was a monounsaturated 

haslene (rather than a related monocyclic 

compound; Belt et al., 2001), the isomer was hydrogenated 

to the parent haslane (Robson and Rowland, 

1986). Comparison of the retention index 

and mass spectrum of this monoene with those 

reported previously for HBI monoenes (Dunlop 

and Jefferies, 1985; Xu et al., 2006) demonstrated 

clearly that the sea ice derived compound was structurally 

different from any of the other HBI monoenes 

identified previously in sediments (e.g. 2, 

Fig. 2). Given the structural relationships of the 

20 30 40 50 

15 

a 

b 

c 

n-C21:6 

24.5 29.5 34.5 

* 

Time 

* + ( Δ6,17) 

C25:2 

( Δ5,6) 

C25:2 

( Δ5,6) 

C25:3 

n-C21:6 

* + ( Δ6,17) 

C25:2 ( Δ7,20) 

C25:3 

( Δ6,17) 

C25:3 

* 

Fig. 4. Partial total ion current chromatograms of hydrocarbon 

fractions from extracted Arctic sea ice: (a) McDougall Sound 

(Site 1); (b) Franklin Bay (Site 2); (c) Button Bay (Site 3). The 

peak labelled * is due to the C25 HBI monoene, IP25. Filled circles 

denote n-alkanes, C20–C23.

co-occurring HBI dienes and trienes, along with the 

structures of previously reported HBI monoenes, 

the most likely isomeric form of the new compound 

appeared to be 1, with a double bond at C23-24 

(Fig. 2). Confirmation of this assignment was 

achieved by independent synthesis of 1 and 2 from 

the previously characterised diene 3. With the structure 

of synthetic 1 firmly established using NMR 

spectroscopy, gas chromatographic and mass spectral 

analysis showed it to be the same isomer as that 

found in the Arctic sea ice samples (Fig. 5). 

In contrast to these observations of microflora 

and hydrocarbons found in Arctic sea ice, both 

Haslea spp. and the new monoene were absent or, 

at least, were below our limits of detection, from 

samples of open water phytoplankton obtained 

from eighteen sampling locations across the entire 

East-West transect of the Canadian High Arctic 

(Table 3). As such, the novel C25 HBI monoene 

appears to be specific to Arctic sea ice. Given the 

ubiquity of haslene production by members of the 

genus Haslea, we suggest that species such as H. 

vitrea and H. crucigeroides, present in all the sea 

ice samples we examined, are the probable sources 

of this novel biomarker. Confirmation of this 

hypothesis will require culturing of individual species 

under sea ice conditions. However, regardless 

of the exact species of diatom which is/are the 

source(s) of the alkene, we propose the term IP25 


140 

196 

210 224 

50 100 150 200 

m/z 

250 300 350 

Fig. 5. Mass spectrum of IP25 corresponding to the D23, 24 HBI monoene found in the hydrocarbon fractions of Arctic sea ice and 

sediment extracts. RIHP 1 = 2090; RIZB–WAX = 2056. 

266 

280 

350 

as a suitable reference term for this compound, since 

it corresponds to an Ice Proxy with a 25 carbon 

atom skeleton. 

3.2. C25 HBIs in Arctic sediments 

We have also carried out core top and partial 

down-core analyses of hydrocarbon fractions from 

sediment extracts obtained from a total of fifteen 

locations across the Canadian Arctic (Fig. 1). Initially, 

we analysed sediments from locations 

between Greenland and Ellesmere Island in the 

northwest region of Baffin Bay (Table 1). This area, 

known as the North Water Polynya (NOW), is one 

of the most productive areas of the Arctic, with an 

annual phytoplankton production of up to 

250 g C m 2 (Klein et al., 2002). When the hydrocarbon 

fractions from the NOW surface sediments 

(NOW-1 to NOW-5) were examined using GC– 

MS, the same HBI isomers found in sea ice were 

present, with IP25 occurring as the most abundant 

isomer in all cases (Fig. 6). Further, in two out of 

the five sediments from this region (NOW-1, 

NOW-2), IP25 was present as the most abundant 

compound in the hydrocarbon fraction. In contrast, 

haslenes were absent from surface sediments from 

West Ellesmere Island (WEI-1, WEI-2). Thick, 

multi-year ice occurs to the West of Ellesmere 

Island and so little biological activity occurs in this


a 

b 

c 

d 

e 

Fig. 6. Partial total ion current chromatograms of hydrocarbon 

extracts from Arctic sediments: (a) ARC-1; (b) ARC-3; (c) ARC- 

4; (d) ARC-7; (e) WEI-1. The peaks labelled * and are due to 

IP25 and the internal standard respectively. Filled circles denote 

n-alkanes, C 20–C 24. Note, the absence of IP 25 in (e). 

region and the presence of the sea ice derived chemical 

would not be expected. 

In measurements designed to investigate the 

wider occurrence of the haslenes in Arctic sediments, 

we obtained a series of seven sediment cores 

corresponding to an East-West transect of the 

Canadian High Arctic, together with some surface 

sediment material from Churchill, South-West Hudson 

Bay (ARC-1–ARC-8; Fig. 1, Table 2). Consistent 

with the findings from the NOW sediments, 

haslenes were present in all core top material, with 

IP 25 occurring as the most abundant isomer in all 

cases (Fig. 6). For Barrow Strait (ARC-3), Victoria 

Strait (ARC-4) and Dease Strait (ARC-5), we also 

carried out partial down-core analysis and found 

IP25 at 1 m intervals in each of the three cores. 

For the longest core (ARC-3), accelerator mass 

spectrometric ( 14 C) dating of planktonic foraminifera 

[Neogloboquadrina pachyderma (s)] isolated from 

the core bottom (641 cm) yielded a date of 

9150 ± 200 yr BP. 

4. Discussion 

Reconstruction of the palaeo-glacial ocean surface 

is clearly a crucial and challenging task which 

has occupied scientists for at least 30 years (Hays 

et al., 1976; Kucera et al., 2005). To date, the most 

reliable reconstructions of sea ice boundaries have 

relied on counting at least 300 diatom valves or 

radiolarian skeletons in each sediment sub-sample 

using high quality photomicroscopes and skilled, 

specialist operators (e.g. Gersonde et al., 2005). 

The species distributions and abundance data, corrected 

for the dominance of some species, are compared 

with modern analogues where possible and 

treated by a variety of statistical methods and equations 

(Gersonde et al., 2005). Even so, in some environments, 

dissolution of the siliceous diatom 

frustules prevents identification or diatom counting. 

Thus, for instance, major uncertainties still exist 

concerning the reconstruction of summer sea ice 

extent in the Antarctic. The presence or absence of 

calcareous microfossils such as planktonic foraminifera 

has also been used as a proxy for previous 

sea ice cover (e.g. Rahman and de Vernal, 1994), 

though abundances and species diversity are often 

very low, with only Neogloboquadrina pachyderma 

being present at higher latitude. Dissolution of aragonite/carbonate 

microfossils is a further limitation 

with this method. Finally, the occurrence of dinoflagellate 

cysts has been used as a proxy measure of 

Arctic sea ice (De Vernal et al., 2000; Mudie et al., 

2001), partly due to their stability under a wide 

range of environmental conditions. However, further 

work is needed to understand the controls governing 

cyst formation and, rather like other proxy

measures, the strict association of cysts with sea ice 

is implied rather than known. Indeed, few current 

proxy methods are direct indicators of sea ice, but 

rather indicate the presence or absence of permanent 

ice or of ice free waters. Clearly, complementary 

sea ice proxies are desirable. 

Our studies have shown that the C 25 haslene, 

IP25, is present in Arctic sea ice from at least three 

diverse locations, yet absent from the phytoplankton. 

Previous studies of HBI-producing diatoms 

(e.g. Haslea spp.) suggest that haslenes are probably 

produced in the chloroplasts of the algae (Massé 

et al., 2004), but the roles of the compounds are 

unknown. Nevertheless, whilst the specific source(s) 

of IP 25 have not been firmly identified and, indeed, 

such species may not necessarily be particularly 

abundant, it is known that Haslea spp. produce very 

high concentrations of lipids, including haslenes. As 

such, haslenes may be readily detected and measured 

in sea ice and sediments even if the source 

organisms are relatively low in abundance. In addition, 

the unique isomeric form of IP 25, which 

enables it to be distinguished from other sedimentary 

HBI monoenes detected in temperate and tropical 

environments, ensures that its detection can be 

strongly associated with a sea ice origin. In our 

experience, IP25 can be detected from < 1 g of sediment, 

which should permit a detailed and high resolution 

sediment core analysis to be carried out, 

possibly with sub-decadal resolution. 

Having confirmed the occurrence of IP 25 in Arctic 

sea ice and sediments, it will be important to 

establish how its concentration in sediments can 

be used to obtain a quantitative assessment of previous 

ice cover. To date, the specificity of the biomarker 

to sea ice (cf. open waters) means that its 

detection in sediments can be used as a presence/ 

absence indicator of previous sea ice cover, as evidenced 

by its occurrence in core top sediments from 

regions of known recent sea ice cover (Tables 1 and 

2) and its absence from regions of permanent ice 

cover (WEI sediments, Table 1) or ice free conditions 

(Rowland and Robson, 1990; Belt et al., 

2000a). A more quantitative measure of sea ice 

cover may only be achievable through use with 

other proxies and/or an improved understanding 

of fluxes from the sea ice to sediments and subsequent 

sedimentary processes. This, in part, depends 

on the ecology of the source organism(s) of IP25. 

Currently, little is known about the strict ecological 

cycle of the so-called ice-restricted diatoms, in particular, 

the fate of such species under ice-free condi- 


tions and the subsequent seeding of sea ice during 

winter/spring. If such species (perhaps confusingly 

referred to as benthic species since they are normally 

found to be present at the sea ice surface rather than 

in the benthos), seed the ice from the benthos of 

shallow waters of coastal regions then, potentially, 

biomarkers such as IP 25 may be present in sediments 

as a result of direct deposition in addition to transfer 

from the sea ice. However, this cannot be the 

case for most of the sediments studied here since 

IP25 has been readily detected in core top sediments 

collected from regions with water depths considerably 

greater than the photic zone. In addition, the 

ubiquity and uniformity of diatom populations 

across the Arctic is not consistent with a model of 

re-suspension of diatoms from coastal sediments. 

Alternatively, the seeding of sea ice by diatoms 

may occur more directly from species, residual in 

the water column, that originate from the melt process 

during the summer, but survive sediment deposition 

or grazing. Although both Haslea spp. and 

IP 25 were not found in our numerous open water 

samples, this may be attributable to procedural 

detection limits rather than strict absence. Diatom 

populations of so-called ice restricted species have 

been detected in Arctic open waters (Riedel et al., 

2003; Von Quillfeldt, 2000) although, even when 

detected, their concentrations are typically at least 

three orders of magnitude lower than for the corresponding 

sea ice, and the values are (not surprisingly) 

at a maximum during the most rapid melt 

periods (e.g. July). It is also noteworthy that concentrations 

of diatoms in laboratory cultures are 

amplified typically by six or seven orders of magnitude 

during the exponential growing phase (Wraige 

et al., 1997, 1999). Thus, seeding of sea ice from 

ultra-low concentrations of diatoms in the plankton 

remains a reasonable alternative to re-suspension 

from the benthos. In either case, our studies indicate 

that IP25 is highly specific to sea ice even if its 

sources, in the strictest sense, may not be. 

In terms of sedimentary processes, it will be 

important to evaluate the diagenetic properties of 

IP25 in order that more detailed down-core concentrations 

can be interpreted more quantitatively for 

determination of previous sea ice cover. This will 

require laboratory simulations of diagenesis of 

IP25 and/or selection of appropriate reference biomarkers 

with similar degradation properties. Similarly, 

since sediments are susceptible to advection 

and re-working, it will be necessary to establish 

the extent of these processes in order that spatial


and temporal sea ice reconstruction can be 

achieved. Feasibly, this could be performed by the 

parallel dating of IP25 ( 14 C) and planktonic foraminifera 

where both are sufficiently abundant. To conclude, 

our next step will be to quantify IP 25 in 

sediments in order to make comparisons with satellite 

and historical records and with other palaeo sea 

ice proxy measurements for the global Holocene 

(Bond and Lotti, 1995; Andrews et al., 1999; De 

Vernal and Hillaire-Marcel, 2000; Gersonde and 

Zielinski, 2000; Levac et al., 2001). 

5. Conclusions 

In summary, the newly characterised HBI monoene 

represents a potentially specific, stable and sensitive 

proxy measure of Arctic sea ice and its 

presence in Arctic sediment cores may well prove 

to be a reliable indicator of the presence of the palaeo-ice 

edge and of sea ice duration. Such data will 

be invaluable in the reconstruction of the former 

extent of the Arctic polar ice cap, a necessary prerequisite 

for the accurate calibration of global climate 

models. Application of the same principles to 

reconstruction of Antarctic sea ice edge would seem 

an obvious further application since a related compound 

has been reported to occur in sediments and 

mixed sea ice diatoms, but not, as yet, in individual 

species of sea ice diatoms. 

Acknowledgements 

This work was supported by the (UK) Natural 

Environment Research Council (NE/D000068/1), 

the Seale-Hayne Educational Trust, Fisheries and 

Oceans Canada (Strategic Science Fund to C. Michel), 

the Canadian Museum of Nature Research 

Fund, and the Natural Sciences and Engineering Research 

Council of Canada Network Grant (Canadian 

Arctic Shelf Exchange Study). The authors 

are members of ArcticNet Networks of Centres of 

Excellence Canada funded by the Natural Sciences 

and Engineering Research Council, the Canadian 

Institutes of Health Research, the Social Sciences 

and Humanities Research Council, and Industry 

Canada. Logistical support was provided by the Polar 

Continental Shelf Project (Natural Resources 

Canada), the Churchill Northern Research Centre, 

and the Centre for Earth Observation Science 

(CEOS, University of Manitoba). We thank the officers 

and crew of the CCGS Amundsen for invaluable 

support, A. Rochon (ISMER-UQAR) and co-work- 

ers, together with C. Smart and G. Price (University 

of Plymouth) for help in obtaining and processing 

sediment cores and M. Rózańska for help in collecting 

ice samples. NOW and WEI sediment material 

was provided by the Bedford Institute of Oceanography, 

Dartmouth, Nova Scotia, Canada. We thank 

an anonymous reviewer for helpful comments 

regarding the importance of considering sedimentary 

processes for future interpretations of IP25 data. 

Associate Editor—S. Schouten 

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A novel chemical fossil of palaeo sea ice: IP25

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