Stable isotope geochemistry of massive ice

The monograph summarises stable-isotope research on massive ice in the Russian and North American Arctic, and includes the latest understanding of massive-ice formation. A new classification of massive-ice complexes is proposed, encompassing the range and variability of massive ice. It distinguishes two new categories of massive-ice complexes: homogeneous massive-ice complexes have a similar structure, properties and genesis throughout, whereas heterogeneous massive-ice complexes vary spatially (in their structure and properties) and genetically within a locality and consist of two or more homogeneous massive-ice bodies. Analysis of pollen and spores in massive ice from Subarctic regions and from ice and snow cover of Arctic ice caps assists with interpretation of the origin of massive ice. Radiocarbon ages of massive ice and host sediments are considered together with isotope values of heavy oxygen and deuterium from massive ice plotted at a uniform scale in order to assist interpretation and correlation of the ice. The monograph is intended for both undergraduates and graduate students, and will assist researchers in geocryology, glaciology, geomorphology, Quate rnary geology and palaeoclimatology in understanding of the origin and palaeoenvironmental significance of massive ice.


INTRODUCTION
The research on massive ice began for one of the authors in July 1977 during the boating expedition of the Geological Faculty of Moscow State University in the Yuribey River valley (68°26´N, 72°08´E) on central Yamal Peninsula, west Siberia.Here, the senior author encountered a complex exposure of massive-ice bodies that probably represent an assemblage of buried river ice and injection (intrusive) ice.This exposure has contributed significantly to the development of a new massive-ice classification by Y.K. Vasil' chuk, the basic principles of which are set out in Fig. 1.A new classification of massive ice, as well as most of the currently available data on the stable isotope geochemistry of massive iсe are summarized in the two-volume monograph Yu.K.Vasilchuk [2012,2014], a critical analysis which is mainly devoted to this paper.

STUDY AREA
The paper is based primarily on the senior author's experience, involvement and field studies over more than 35 years (from 1977 to 2014) in numerous expeditions concerning massive ice in Russian permafrost.It also summarizes the experience of many international researchers, and describes exposures with large bodies of massive ice in west and east Siberia, Chukotka, Alaska and Yukon, the Tuktoyaktuk Coastlands, the Canadian Arctic Archipelago and Russian Arctic islands, China and the Antarctic.

MASSIVE-ICE CLASSIFICATION
Yu. Vasil'chuk [2012] presents a new classification of massive-ice bodies and includes two new categories: homogeneous and heterogeneous (Fig. 1).Homogeneous massive-ice bodies have a similar genesis, composition and properties in all parts of a massive-ice complex, whereas heterogeneous massive-ice bodies have a variable genesis, composition and properties across a massiveice complex, and consist of two or more homogeneous ice bodies.The distinction between homogeneous and heterogeneous massive-ice bodies elucidates the wider complex structure of massive-ice bodies and encourages the search for different mechanisms of ice formation.

Homogeneous massive-ice complexes
Homogeneous massive-ice complexes are usually no more than a few meters high, m 20-30 m wide and occur as single layers of ice or, less commonly, as multiple layers of the same genesis.Typical examples of segregated (or infiltrated and segregated) ice were studied by Y.K. Vasilchuk [1992] in the first terrace of the Gyda River estuary (70°53′N, 78°30´E).Four similar lens-shaped bodies of massive ice (up to 0.3-0.4m thick and 6-8 m wide) were composed of clear ice and, as a rule, associated with peat.The structure of the ice bodies and their bedding parallel to the sedimentary stratification suggest that they formed synchronously with the accumulation and freezing of the ground mass, consistent with the occurrence of a 4.5 m high syngenetic ice wedge in the sedimentary sequence.The ice is interpreted as infiltrated or segregated in origin.The wide range of δ 18 O values (-33.8 to -16.2O) in these ice bodies indicates closedsystem freezing with a small inflow of water from outside the system.Such a wide range of the heavy oxygen values indicates significant cryogenic fractionation during freezing of waters whose initial average composition was close to -20O.This could occur only under conditions of closed-system freezing, when isotopically heavier ice was the first to form (δ 18   those at present.In view of the radiocarbon age of the ground mass (more than 15 14 C ages from 10,260 to 15,890 BP obtained on allochthonous peat), the accumulation of the ground mass and the formation of massive ice and the syngenetic ice wedge occurred no earlier than 14,000-11,000 years ago [Y.K. Vasilchuk, 1992].

Heterogeneous massive-ice complexes
Heterogeneous massive-ice complexes comprise two or more ice layers (tiers) of different genesis.The layers may be in contact or adjacent to each other, influencing the shape of the ice complex and the conditions of its occurrence.Examples include massive ice of the Yuribey River valley (Fig. 2a), massive ice in the Erkutayaha River valley [Y.K. Vasil'chuk et al., 2012] in the south of Yamal Peninsula (Fig. 2b, 3), and in many places in the Bovanenkovo gas condensate field [Y.K. Vasil'chuk et al., 2009Vasil'chuk et al., , 2014;;Kritsuk, 2012].
The second division of the classification distinguishes between autochthonous (i.e., intrasedimental in terms of Mackay and Dallimore [1992]) and allochthonous (i.e.buried) ice (see Fig. 1).Heterogeneous massive-ice complexes can include a combination of autochthonous and allochthonous deposits.The third division classifies the massive ice according to its specific genetic process (e.g., injection,

MODERN AND HOLOCENE ANALOGUES OF PLEISTOCENE MASSIVE ICE, AND THE MAIN HYPOTHESES OF MASSIVE-ICE FORMATION
Vasil'chuk [2012] discusses modern and Holocene analogues of Pleistocene massive ice, beginning with massive ice in marine sediments.One of the most convincing analogues of Pleistocene massive ice is Holocene massive segregated ice 8-9 m thick on the Fosheim Peninsula, Ellesmere Island, in the Canadian Arctic (79°59´N, 85°56´W; Pollard and Bell, 1998].The δ 18 O values of the ice range between -28.9 and -34.8O for reticulate ice, -33.1 and -36.8O for massive ice, and -36.1O for an ice vein in adjacent Tertiary sandstone.The massive ice is interpreted as intrasedimental ice because: a) it is conformably overlain by marine sediments and contains internal structures parallel the upper ice contact; the ice lacks evidence for primary thaw or erosional contacts, which would indicate buried ice; and b) sediment within inclusions in the massive ice is similar to the overlying marine sediments, indicating that the overlying sediment was deposited before the ice formed.Radiocarbon ages of shells from raised marine deposits in the Slidre River valley suggest that the Holocene marine limit was likely established by 10.6 ka BP, with sea level remaining high (within 10 m of marine limit) until 8.7 ka BP or later.The massive-ice deposits formed time transgressively as permafrost aggraded into marine sediments during the Holocene [Pollard and Bell, 1998].Ice segregation occurred as permafrost aggraded downward through a fine-grained layer of silt that overlay saturated sands with an ample water source.The injection of water under high pressure into the overlying frozen bedrock at Eureka Sound formed intrusive massive ice [Robinson and Pollard, 1998].As a result, a heterogeneous massive-ice complex (according to Y.K. Vasil'chuk's classification) developed.
Massive-ice bodies are extraordinarily widespread in Holocene sediments of the first lagoon-marine terrace and the modern lagoon-marine floodplain of the Ob Bay, at the mouth of the Sabettayaha River, in west Siberia (71°15´N, 72°06´E).More than 1000 boreholes through Holocene marine lagoon and floodplain deposits have been analyzed  syngenetically during freezing of watersaturated soils under intensive cryogenic fractionation in the late Holocene.Thick massive-ice bodies also occur in saline sediments, for example a 14 m thick massive ice layer in beach sediments near the mouth of the Khatanga River [Ponomarev, 1960], fresh (salinity is 620 mg/l) massive ice at a depth of 19-29 m beneath the sea bottom [Melnikov and Spesivtsev, 2000], and a 1.5 m thick layer of salty ice at the depth about 10 m in sediments beneath the shallow waters of the Mechigmen Gulf (Chukotka).Y.K.
Vasil'chuk proposed the original mechanism of the formation of icy bodies in saline lake (meromictic lakes) sediments.
Other possible modern and Holocene analogues of Pleistocene massive ice are freshwater ice deposits in shallow, saline (up to 103 g/1) lakes at 4117-4730 m above sea level (asl) in Bolivia.The ice deposits (consisting of several ice lenses, each up to 1 m thick) are up to several hundred meters wide and elevated up to 7 m above the lake or playa surface.They are located near the lake or salar (salt-crust desert) margins; some are completely surrounded by water, others by playa deposits or salt crusts [Hurlbert and Chang, 1984].The δ 18 O values for the ice lenses (-10.6 to -11.5O) are much lower than those of lakewater (+ 13.5O) but similar to those of precipitation (δ 18 O value in fresh snow -13.2O).
Ice in the cores of modern pingos provides another analogue of Pleistocene massive-ice deposits.Holmsen [1914] proposed the infiltrated and segregated hypothesis of massive-ice genesis.He hypothesized that the formation of thick (up to 15 m) massive ground-ice deposits is linked to the infiltration of surface water through seasonally thawed ground and the freezing of this water on the top [see also Zhestkova and Shur, 1978].Vtyurin [1975] favoured ice segregation, with the most favorable conditions for the formation of massive segregated ice being near the contact between clayey sediments and water-bearing coarse-grained sediments.Gasanov [1969] hypothesized that the main factor of ice formation is water intrusion, and distinguished different types of intrusive ice: seasonal intrusive ice, multi-seasonal intrusive ice (short-term permafrost), intrusive ice, repeated intrusive ice and hydrolaccoliths.Mackay [1971Mackay [ , 1973] ] proposed that the mechanism of water injection and segregation in closed-system conditions that is widely applied to explain pingo growth can also apply to the mechanism of massive-ice formation.

COMPARISON OF POLLEN SPECTRA OF MASSIVE ICE AND GLACIERS FOR CRYOGENIC INDICATION
Palynological analysis of deposit-forming ground ice has identified several distinctive characteristics of the pollen spectra.First, pollen and spores are present in almost all types of deposit-forming ground ice, at concentrations from 50 to 1500 units per 1 kg ice or 1 litre of ice meltwater.Second, pollen spectra with characteristics similar to those of subfossil tundra, including the predominance of dwarf birch and ericaceous pollen and green moss spores, occur in most massive-ice deposits.Isotope data summarized from Chukotka include homogeneous autochthonous massive ice at the Koolen' Lake, near the town of Anadyr' and at Onemen Bay [Vasil'chuk, 1992], Tanyurer River valley [Kotov, 1998], and heterogeneous allochthonous and autochthonous massive ice in the Amguema River valley [Korolyov, 1993].
Finally, heterogeneous allochthonous and autochthonous massive-ice bodies are found on Novaya Siberia Island (75°05´N, 148°27´E).Ivanova [2012] showed that δ 18 О values of massive ice there vary from -8.9 to -29O, and δD values vary from -66.8 to -228.4O.The δ 18 O and δD values in the upper and lower horizons of massive ice are very different.These data can be interpreted to indicate an injected origin for the lower horizon of massive ice, and a segregation origin for the upper horizon [Ivanova, 2012].Massive ice within but close to the glacial limit of the Laurentide Ice Sheet, on Herschel Island (69°N, 139°W), in the southern Beaufort Sea, is highly depleted in heavy isotopes (mean δ 18 O value: -33O; δD: -258O; [Fritz et al., 2011[Fritz et al., , 2012]]).These authors noted that such stable isotope signatures indicate a full-glacial water source for the massive ice on Herschel Island.However, an origin as glacially deformed segregated or segregated-intrusive ice cannot be excluded.Pollard [1990] concluded that segregated ice is the most common massive-ice type in this area and in places constitutes up to 70 % of the upper 10-15 m of permafrost.Y.K. Vasil' chuk suggested that the origin of massive ice on Herschel Island varies, and the ice includes both heterogeneous and homogeneous types.

DATING OF MASSIVE ICE OF RUSSIA AND NORTH AMERICA, AND CORRELATION OF STABLE ISOTOPE CURVES
Radiocarbon dating of organic material in the sediments that surround massive ice in Russia and Canada, and direct accelerator mass spectrometry (AMS) radiocarbon dating of organic microinclusions and trapped gases within massive ice in Canada are analyzed by Vasil' chuk [2014].The radiocarbon ages suggest that most of the massive ice accumulated between the Holocene and 20-40 ka BP (Fig. 4).
Comparison of isotopic plots of massive ice in Russia and Canada (Fig. 5-7) shows that they have more similarities than differences in the regional isotopic record of ice formation.An initial isotopic signature indicates the nature of the water and the conditions of ice formation.Ice segregation in a closed system leads to a contrasting distribution of δ 18 O and δD values, both vertically and laterally (Fig. 5).The shape of isotopic plots of massive ice relates to the type of ice formation.Homogeneous, undifferentiated isotope plots with a narrow range of isotopic changes (δ 18 O range < 4O, ΔδD range < < 32O) characterize massive ice formed in an open system, with freezing of inflowing water under homogeneous conditions.By contrast, isotope plots with a wide range of isotopic changes (Δδ 18 O range > 8O, ΔδD range > 64O) characterize massive ice formed in a closed system, where there is no inflowing water.Closed-system freezing is typical of segregation ice formation, or rarely for the final phase of injection ice formation when there is no inflow of water (Fig. 6 and 7).Vasil'chuk, 1992], e -Tanyurer River valley [Kotov, 1998], f -Peninsula Point (4.5 km southwest of Tuktoyaktuk) [Kato et al., 1988], g -Peninsula Point [Moorman et al., 1998]; h -Herschel Island [Moorman et al., 1996].a -Cape Shpindler on Yugorski Peninsula: 1-5 -different parts of exposure [Ingólfsson and Lokrantz, 2003]; b -Yuribey, Gydan Peninsula [Kritsuk, 2010]; c -i -different parts of the Ledyanaya Gora (or Ice Mountain) exposure, on the right bank of the Yenisey River near the Arctic Circle [Vaikmäe and Karpov, 1986; Vaikmäe and Y.K. Vasil'chuk, 1991]; j -Onemen Bay, Chukotka [Kotov, 2001].a -Involuted Hill site, to the northeast of Tuktoyaktuk [Mackay, 1983]; b -Peninsula Point (4.5 km southwest of Tuktoyaktuk) [Fujino et al., 1988]; c -Peninsula Point [Moorman et al., 1998]; d -7 km to the east of Ya Ya Lake, on southern Richard Island [Dallimore and Wolfe, 1988]; e -Lousy Point, near Ya Ya Lake, on southern Richard Island [Dallimore and Wolfe, 1988], f -g Willow River region, Aklavik Plateau, Richardson Mountains: f -profile of site WR-00-5, g -profile of site WR-00-3 [Lacelle et al., 2004]; h -5 km southwest of Tuktoyaktuk [Kato and Fujino, 1981]; i -southern Eskimo Lakes region, Tuktoyaktuk Coastlands [French and Harry, 1990], j -Crumbling Point, Summer Island, Tuktoyaktuk Coastlands [Murton et al., 2005].

CONCLUSIONS
The study considers practically all the selected ages and mechanisms of massiveice formation.The senior author proposed the original mechanism of the formation of massive ice in saline lake sediments.New mechanisms will undoubtedly be proposed in the future.
A new genetic classification of massive-ice deposits introduces two new categories at its highest level: homogeneous and heterogeneous massive-ice deposits.
Assemblages of different massive-ice types are common in permafrost exposures in the Yamal Peninsula of west Siberia and the Tuktoyaktuk Coastlands and Yukon of northwest Canada.
Plotting of isotopic data from massive ice on graphs with a single vertical and horizontal size facilitates objective assessment of the isotopic characteristics of massive ice.
O values of about -16 and -18O), while the δ 18 O values of the remaining water were about -22O.The partial freezing of the water led to the formation of ice with δ 18 O values of about -20O, while the rest of the water had δ 18 O values of about -24 to -25O.Repeated freezing of this water provided extremely low δ 18 O values (about -34O) in the last portions of the water to freeze.The low average δ 18 O values in this massive ice (about -20O) indicate that the ice formed under conditions more severe than

Fig. 6 .
Fig. 6.The comparison of oxygen isotope plots of massive ice from Russian permafrost, formed under open-and closed-system freezing.

Fig. 7 .
Fig. 7.The comparison of oxygen isotope plots of massive ice of Canadian permafrost, formed under open-and closed-system freezing: In conclusion, the massive ice at Ledyanaya Gora can be regarded as heterogeneous autochthonous massive ice.
Ingólfsson and Lokrantz [2003]s frequently contain redeposited pre-Quaternary palynomorphs of Cenozoic, Mesozoic and Palaeozoic age.Fourth, pollen of о 44´E).For the massive-ice body at Cape Shpindler in the Yugorski Peninsula (69°43´N; 62°48´E),Ingólfsson and Lokrantz [2003]concluded that it is buried glacier ice and suggested that it is older than 190-200 kyr, whereasLeibmanet al. [2003], horizontally layered ice.The range of δ 18 О (~4O) and δD (~ 20O) values indicates comparatively small fluctuations of the isotopic composition for ice with different characteristics: pure white ice has δ 18 О values from -19.6 to -20.5O, and δD varies from 18 O = -20.7 O).This similarity, coupled with a significant change from a salinity of 10-80 mg/l in the upper part of the massive ice to one of 200-340 mg/l in the middle and lower parts of it, according Y.K. Vasil'chuk, indicates an intrasedimental origin.