You are currently viewing a new version of our website. To view the old version click .
MDPIMDPI
Search all articles
Water
Download PDF
  • Article
  • Open Access

26 January 2023

Wetlands in the Pleistocene Steppe-Tundra Landscapes of Beringia, Their Insects, and the Role of Aeolian Sedimentation

Laboratory of Arthropods, Borissiak Paleontological Institute, RAS, Profsoyuznaya 123, Moscow 117868, Russia
Water2023, 15(3), 494;https://doi.org/10.3390/w15030494
This article belongs to the Section Water and Climate Change
Version Notes
Order Reprints
Review Reports

Abstract

Analysis of the database of Beringian subfossil insect assemblages showed a relatively low role of aquatic, riparian, and wetland species of insects with hard exoskeleton in the Pleistocene communities and an increase in their proportions and taxonomic diversity in the Holocene. Aquatic insects were represented in all types of geological deposits and in some paleosols, but their proportions varied in different depositional environments. Poor representation of aquatic insects and a lack of freshwater invertebrates in the Late Pleistocene ice-rich deposits of Beringia called Siberian Yedoma or Yukon Muck attest to the predominantly aeolian origin of this phenomenon.

1. Introduction

Aquatic insects played an immense role in continental ecosystems of the past. Most of the recorded fossil insects come from sediments of water origin [1]. Aquatic insects dominate many fossil assemblages; in some facies, they are extremely abundant and widespread. Among insects, only aquatic species are suitable for stratigraphic purposes: for example, the mayfly Ephemeropsis trisetalis (Eichwald, 1864) and the beetle larvae Coptoclava longipoda (Ping, 1928) are used for the stratigraphic correlation of the Early Cretaceous of Transbaikalia, Mongolia and North-Eastern China [1].
Quaternary insects that are relatively young and not fully fossilized could be found in various depositional environments from alluvial and lacustrine to loesses and paleosols. The proportion of aquatic species in Quaternary insect assemblages varies widely, from high to low to the complete absence. Almost all Quaternary insects are modern species [2]; they are not used in the traditional chrono-stratigraphy, which is based on evolutionary changes, but can contribute to the climate-based stratigraphic correlation. Aquatic insects provide important information on climate-related large-scale range shifts, local extinctions, and expansions [3]. For example, the fossil Helophorus orientalis Motschulsky, 1860 was found in the Pleistocene of Europe, far from its modern range that includes North America and Asia.
A unique example of a low evolutionary rate is the aquatic beetle Helophorus sibiricus Motschulsky, 1860. The well-preserved fossil from the Early Miocene of Siberia is morphologically identical to the modern H. sibiricus [4]; this is the oldest recorded evidence of a “living fossil” among hydrophiloid beetles and probably the only one properly documented case among all beetles.
Beetles can help in solving some specific geological tasks. The presence of aquatic insects in presumably windborne loess-like deposits, the low proportions of forest insects in “forest beds” and many other interesting discrepancies affect our assumptions about the depositional environments. That is of special importance for the long and emotional discussion of the origin of the ice-rich silty sediment called “Yedoma” (Figure 1a,b) in North-Eastern Siberia [5] and the Yukon Muck in North America.
Figure 1. Sections where insects come from: (a) Kurungnakh Island in the Lena Delta, Pleistocene peat, (b) Bykovsky Peninsula (Yakutia), ice-rich section Mamontovy Khayata, (c) Undulung River (northern Yakutia), Holocene peat, (d) Kyzyl-Syr at the Viluy River, Yakutia, peat layer in the sand, (e) Bolshoy Laykhovsky Island, section Zimovie—lake sediment with ice wedge cast.
This paper is focused on aquatic, riparian, and wetland insects with a solid chitin exoskeleton from the spacious ice-free land of Beringia (Figure 2). This land is stretched across the north-western part of North America and in the north-eastern part of Asia, including the Bering Strait (the Bering Land Bridge of the Pleistocene).
Figure 2. Map of Beringian regions East Beringia: AC—Alaska, Central and East; BB—Bluefish River Basin and Porcupine River; ER—Eagle River, KG Klondike Gold Field, NS—North Slope of Alaska, OC—Old Crow River. West Beringia: CY Central Yakutia, KL—Kolyma Lowland, LS—Laptev Sea coast and Lena Delta, MR—Magadan Region, SC—South Chukotka, WC—West Chukotka, YL—Yana-Indigirka Lowland. Localities mentioned in the text: (1) Kurungnakh Island Lena Delta, CY 72°21′ N 126°30′ E; (2) Samoylov Island, Lena Delta, LS 72°22′ N 126°28′ E; (3) Mamontovy Khayata, Bykovsky Peninsula, LS, 71°47′ N 129°26′ E; (4) Zimovie, Bol. Lyakhovsky Island, LS, 73°20′ N, 141°21′ E; (5) Ulakhan-Sullar, Aducha River, CY, 67°41′ N, 135°44′ E; (6) Undulung River, CY 65°54′ N 126°02′ E; (7) Kyzyl-Syr, Vilyuy River, CY, 63°58′ N 123°24′ E; (8) Kharyyalakh middle Lena River, CY, 63°10′ N 129°44′ E; (9) Peschanaya Gora, middle Lena River, CY, 62°88′ N 129°81′ E; (10) Ust-Buotama, middle Lena River, CY, 61°14′ N 128°37′ E; (11) Keremesit River, YL, 70°32′ N 149°41′ E; (12) Khomus-Yuryakh River, KL, 69°59′ N, 153°35′ E; (13) Alazea River, KL, 69°20′ N, 155°00′ E; (14) Main River, SC, 64°35′ N 171°06′ E; (15) Titaluk River, NS, 69°43′ N 155°15′ W; (16) Ikpikpuk River, NS, 69°35′ N 154°55′ W; (17) Old Crow 67°53′ N 139°46′ W; (18) Porcupine River, BB, 67°29′ N 139°56′ W; (19) Hollis Mine, KG, 63°54′ N 139°26′ W; (20) Lucky Lady, KG, 63°41′ N 139°02′ W; (21) Quartz Creek, KG, 63°49′ N 139°2′ W.
We aimed to describe subfossil insect assemblages specifically for various depositional environments in the region and further apply the association between deposition types and the insect assemblages to answer the question of the origins of the specific Late Pleistocene ice-rich sediments, Yedoma.

2. Materials and Methods

According to the classical taphonomy [6,7], almost all body fossils are preserved in aquatic depositional environments. This assumption is valid for true fossils [1] but relatively young late Neogene–Quaternary subfossil insects potentially can be found in deposits of various origins, including loesses and paleosols.
Insect remains of the Late Neogene and Quaternary are represented by the chitin devoid of soft tissues. The fossilization process of Beringian insects is not complete yet, because of the comparatively short period of time since their burial and due to the excellent preservation properties of the permafrost. These insect assemblages can be termed as taphocoenosis, an assemblage of dead organisms buried in the sediment without mineralization and other taphonomic changes.
In the Late Neogene and Quaternary deposits, we can find separated fragments of beetles, ants, true bugs (Hemiptera), and other hard chitin insects. In many cases the number of preserved fragments differs from their number in living insects: for example, we have recorded one head, two pronotums, ten left elytra and 20 right elytra in a single sample. This means that insect bodies were disassembled prior to the burial, and the fragments were transported and sorted by their size, shape, etc., during redeposition. However, in some cases, the number of fragments may coincide with that in the living organisms, and therefore, the Fragment Correlation (FC) can be of use as an indicator of the transportation mode and sedimentation type.
The degree of preservation is another variable. Permafrost provides excellent preservation of organic remains, but some of them may be broken and worn. Such damage may point to the long-distance transport of macrofossils prior to their redeposition. For instance, round stains and holes on chitin fragments are indicative of the long exposure of the fragments at the day surface prior to their burial (S. Kiselev, pers. comm.). Therefore, the reconstruction of depositional environments can be carried out by combining information on proportions of various ecological groups, number of fragments preserved, and even wear marks on insect macrofossils.

2.1. Lacustrine Deposits

Lakes were widespread in Beringia through the entire Quaternary period, including the recent time (Figure 3a).
Figure 3. Lacustrine deposit. Sedimentation with local water invertebrates: (a) middle size tundra lakes, Old Crow Flat; (b) Ulakhan-Sullar deposit with shells.
Thermokarst lakes typically formed during interglacial intervals [8,9]. The thermokarst lakes start growing on ice-rich sediments as a result of climate warming. They accumulate organic matter from the eroding ground around the lake and from the thawing deposit beneath the lake. The thickness of the resulting lake deposits may reach several meters. Thawed ice wedges form small local depressions, ice wedge casts (Figure 1e) that can accumulate sediments of seasonal/temporary ponds or lacustrine sediments.
During cold climatic phases, some lakes were permanently covered by ice. These lakes are expected to be lifeless, with deposits lacking any organic inclusions. Subfossil insects and freshwater invertebrates are excellent indicators that allow one to identify such lakes. The absence of insect remains indicates that the lakes were lifeless indeed, but we know examples of some seemingly empty inorganic sediments that contained plenty of small chitin fragments. It means that water in the lake was open at least during the short summertime.
In cold climates, short-lived lakes often form in interdunal depressions. In a geological section, such sediment looks like a thin dark-colored layer bedded between sand deposits (Figure 1d). Wind may also create shallow depressions in the steppe that are filled by water during the spring season or even longer (Figure 4a). The cold climate may prevent complete desiccation of such a water body, but its volume would undergo dramatic seasonal changes. As we will see later, similar steppe lakes or “sloughs“ played an important role in the ecosystems of Beringia.
Figure 4. Sources of insects in Yedoma deposit: (a) lake in steppe meadow near Yakutsk, (b) silt with tiny grass roots, Bykovsky Peninsula, (c) sandy silt with grass roots, Main River, Chukotka.
Lacustrine deposits are characterized by a high proportion of water insects, and the presence of shells of freshwater Gastropoda and Bivalvia (Figure 3b), statoblasts of freshwater Bryozoa (Phylactolaemata), Daphnia winter eggs (ephippia), Ostracod shells, flatworm eggs, and some other invertebrates. Sediments of the central/inner part of big lakes rarely contain the remains of wingless terrestrial beetles, and found fragments are strongly damaged [10]. Good burial conditions for any terrestrial insects exist in coastal parts of lakes, in the zone of plant debris accumulation (Figure 5a). Buried insect assemblages from lake shore sediments include the entire range of terrestrial and water-related taxa. The FC of water beetles and bugs is usually normal (close to 1) here, while the FC of terrestrial beetles is anomalous.
Figure 5. Grass and wood detritus: (a) plant detritus at the lake shore, Lesser Slave Lake, Canada, (b) modern alluvium with plant detritus at the Lena River, (c) section Kyzyl-Syr at the Viluy River, Yakutia with plant detritus layer at the base, (d) plant detritus in the section Old Crow River, CRH 44.

2.2. Alluvium

Fluvial deposits, such as riverbeds, old channels, and floodplains, are common in Beringia (Figure 6). With a few exceptions, insects are rarely found in the modern riverbed alluvium (alluvial deposits with crossbedding), but in the Pleistocene situation was different. There are several sites (Figure 6c) where cross-bedded sandy-gravelly alluvial deposits yielded plenty of plant debris and insect fragments. Surprisingly, the richest beetle assemblages in Beringia (Titaluk and Ikpikpuk Rivers of the North Slope of Alaska, and Keremesit, Khomus-Yuryakh and Adycha Rivers from Yakutia) were collected from this type of alluvium [8,11]. While on average, a standard 40 to 50 L sample contains 100 to 200 insect fragments, the number of fragments in the above-mentioned Beringian alluvium varied from 600 fragments per ten L sample to 8000 fragments per standard sample, with the set of species typical for the region [8].
Figure 6. River valleys and alluvial deposit: (a) Adycha, Yakutia in September 2019; riverbed is partly exposed, (b) Titaluk, North Slope of Alaska, in May 2003; water level is high, floodplain is partly flooded, (c) Pleistocene alluvial deposit at the Titaluk River with plant debris and numerous insects, (d,e) young floodplain deposit at the Lena River.
Modern floodplain deposits commonly include layers or lenses of plant debris (Figure 5b). Similar layers were common in the Pleistocene; they yield a highly variable number of insect fragments upon wet sieving (Figure 5c,d) [10]. Probably, plant debris and dead insects were brought to the riverbed during the low water season by the river current and wind, and this material was trapped in zigzag structures at the edges of sand beaches, in their contact zone with flowing water (Figure 6a). Insect remains have been distinctly sorted there, with the hard and round heads and pronotums accumulated within gravel lenses, and flat light elytra concentrated in sand deposits and layers of plant debris. FC of all insects was anomalous. The proportion of water insects was relatively low. Ecological affiliation of insects from the assemblage is mixed without the strong dominance of either group.
Holocene floodplain deposits are often sampled in the river terraces (Figure 6d,e). Insect assemblages from the Holocene floodplain deposits are not necessarily numerous, but usually taxonomically diverse. FC may be either normal or anomalous. The proportion of water insects is often low, but riparian species are well represented. Preservation varies from poor to good.

2.3. Peatland Deposits

Peat seems to be an excellent repository of subfossil insects. However, our experience shows that this assumption is not always true. For example, a sample from the promisingly looking Holocene peat layer (Figure 1c) contained no insects. Sphagnum peat is usually insect-free; the best yield is expected from the peat of mixed origin (mosses, grasses, and leaves) and the peat that contains mineral inclusions. Bog tussocks are often exposed in Beringian sections (Figure 7), and insects can be found under the tussocks and between them. If the peat contains insects, the FC here is usually normal, preservation is good, and water and wetland taxa are well presented [12,13,14]. Sometimes organic-rich paleosols are described as “peat beds” in the field. In this case, we notice a lack of wetland taxa among plants and insects [8].
Figure 7. Boggy sediment: (a) moss and tussocks sedges in tundra, Dempster Hwy, Yukon, (b) peat tussocks, top of Mamontovy Khayata section, Bykovsky Peninsula, northern Yakutia.

2.4. Wetland Deposits

Distinctive “grassy” deltaic deposits were observed in the delta of the Lena River (Figure 8). The deposits consist of tall stems of wetland grassy species interspersed with a very small proportion of sand. Sampling such sediment is hard work, with the result not worth the effort. Insect remains are rare in the “grassy deposits” and include mainly aquatic species, such as caddisflies [15].
Figure 8. Grass-rich sedimentation: (a) grassy edge of a water body in the tundra near Anadyr, Chukotka. (b) Grassy deposits in the Holocene section on the Samoylov Island, Lena Delta.

2.5. Subaerial Deposits

Classic taphonomy suggests that subaerial surfaces are generally unstable in time, with a low probability of fossilization and of long-term preservation of insect remains [1]. Fossil insects are either absent or extremely rare in Pre-Quaternary aeolian deposits and paleosols, and even in the Quaternary subaerial deposits, insect remains are preserved selectively. Mid-latitudes loesses and paleosols in dry sites rarely contain any insect remains, but paleosols and archeological sites in wet settings can be rich in insects. Northern localities provide a better preservation of organic inclusions due to permafrost. In Beringia, paleosols (Figure 8) are the best source of subfossil insects [16,17]. Impressive assemblages were collected from paleosols buried under volcanic tephra [18,19,20]. Insects from buried paleosols are well preserved, FC is normal, species of true aquatic invertebrates are absent, but some water beetles that can migrate to the soil for wintering are found.
We have observed accumulation of insect remains in a modern sand dune (Figure 9d) at the Lena River [21]. A layer of plant detritus buried under the dune sand yielded insect fragments that were exhumed by wind from the soil buried nearby. Such paleosol-aeolian transfer and redeposition was probably common in the wind-prone Pleistocene landscapes of Beringia.
Figure 9. Subaerial deposit: (a) modern soil, Central Yakutia, (b) late Pleistocene paleosol, Kharyyalakh, Central Yakutia, (c) aeolian deposit with a layer of plant debris and insect fragments, (d) recent aeolian deposit with plant debris and insects, Ust-Buotama dune, Central Yakutia.

3. Results

The method of paleoenvironmental reconstruction that involves macroremains of insects is based on the analysis of shares of certain ecological groups [22,23,24]. Water-related insects belong to two groups: aq (aquatic) and ri (riparian and wetland). The aquatic group (Table 1) includes beetles of the following families: Gyrinidae, Haliplidae, Dytiscidae, Hydraenidae, Dryopidae, some Hydrophilidae, and a few Curculionidae; water bugs Veliidae and Corixidae (Figure 10); larvae of Ephemeroptera, Odonata, and Trichoptera (Figure 11). Aquatic beetles and bugs can migrate from water to terrain and occur in nearby soil, but their larvae reside in water permanently. So, the finds of these strictly aquatic insects are indicative of the aquatic environment, while other insects can be found outside of water bodies. For the purposes of this study, we did not include in the analysis small aquatic Diptera.
Table 1. List of aquatic beetles from Quaternary deposit of Beringia.
Figure 10. Remains of aquatic insects who can migrate from the water: (a)—Gyrinus sp. (b)—Gyrinus natator, (c)—Gyrinus opacus, (d)—Colymbetes sp., (e)—Colymbetes dolabratus, (f)—Hygrotus sp., (g)—Agabus arcticus, (h)—A. moestus, (i)—A. serricornis, (j)—A. affinis, (k)—Ilybius sp., (l)—Hydroporus fuscipennis, (m)—Oreodytes dauricus, (n)—Haliplius immaculatus, (o)—Helophorus splendidus, (p)—H. tuberculatus, (q)—Hydrobius fuscipes, (r)—Cymbiodyta marginella, (s)—Enochrus ochropterus, (t)—Coelostoma orbiculare, (u)—Hydrochara caraboides, (v)—Ochthebius cribricollis, (w)—Limnebius sp., (x)—Bagous limosus, (y)—Eubrychius velutus, (z)—Sigara fallenoidea. (a,i,k,s,w,y,z)—Kharyyalakh, Holocene; (b,r)—Kyzyl-Syr, late Pleistocene (MIS3) peat; (c,j,l,m,u)—Peschanaya Gora: (c,j,m,t)—late Pleistocene (MIS2), (l,u)—Holocene; (d,l,z);—Ulakhan-Sullar, middle Pleistocene; (e,h,q)—Old Crow: (e,q)—middle Pleistocene, (h)—late Pleistocene; (f)—Undulung River, Holocene; (g)—Porcupine River, late Pleistocene (MIS5); (n)—Alazea River, Holocene; (o,x)—Kyzyl-Syr, late Pleistocene; (p,v)—Quartz Creek: (p)—Holocene, 26—late Pleistocene (MIS3).
Figure 11. Remains of true aquatic insects: (a)—Odonata larvae wing pad., (b–d)—plant-silt cases of Trichoptera, Brachycentridae: (b)—Brachycentrus subnubilus, (c)—Micrasema sp., (d)—Micrasema gelidum, (e) sand case of Apataniidae, (f) sand case of Molanna sp., (g,h)—Limnephilus spp.: (g) plant case, (h) sand case, (i) shell case, (j) case from shells, seeds and a beetle elytron; (a,b,h)—Kharyyalakh, Holocene, (c) Old Crow, late Pleistocene (MIS5), (d,e,f) Ulakhan-Sullar, middle Pleistocene, (g) Kyzyl-Syr, late Pleistocene (MIS3) peat, (i,j) Peschanay Gora, late Pleistocene (MIS2).
The group “ri” (Table 2) includes beetles of families Carabidae, Hydrophilidae, Staphylinidae, Scarabaeidae, Scirtidae, Heteroceridae, Elateridae, Coccinellidae, Chrysomelidae, Curculionidae, and bugs Saldidae. These insects live on wet ground, in plant litter near water bodies (Figure 12), or on riparian and wetland vegetation (Figure 13). Many riparian species can migrate to dry soils for wintering. In the cold climate, some riparian species occasionally visit dry and sunny spots to get some heat necessary for their development. Anyway, the find of “ri” group suggests that a water body existed not far from the place of burial of the insect remains.
Table 2. List of riparian and wetland insects from Quaternary deposit of Beringia.
Figure 12. Remains of insects from riparian vegetation: (a)—Cyphon variabilis; (b)—Donacia sp.; (c)—Donacia crassipes; (d)—D. splendens; (e)—D. semicuprea; (f)—Plateumaris sericea; (g)—Grypus equiseti; (h)—Notaris aethiops; (i)—N. bimaculatus, (j)—Limnobaris dolorosa; (a,b,f,j) Peschanaya Gora, Holocene, (b) Ulakhan-Sullar, late Pleistocene; (d) Kyzyl-Syr, late Pleistocene (MIS3) peat; (g)—Ust-Buotama, Holocene, (h,i(a)) Lucky Lady: (h) Holocene, (i(a)) late Pleistocene (MIS 5); (i(b)) Ulakhan-Sullar, middle Pleistocene.
Figure 13. Remains of insects from plant litter, muddy and sandy water edges: (a)—Elaphrus lapponicus, (b)—E. parviceps, (c)—E. angusticollis, (d)—E. clairvillei, (e)—Nebria frigida, (f)—N. rufescens, (g)—Bembidion mutatum, (h)—B. arcticum, (i)—B. umiatense, (j)—B. lapponicum, (k)—Dyschiriodes melancholicus, (l)—Dyschirius polius, (m)—Agonum sexpunctatum, (n)—A. cupreum, (o)—A. consimile, (p)—Georyssus crenulatus, (q)—Cercyon borealis, (r)—Aegalia kamtschatica, (s)—Heterocerus fenestratus, (t)—Negastrius restrictulus, (u)—Hypnoidus bicolor, (v)—Bledius viriosus, (w)—Stenus fuscipes, (x)—S. aureoles, (y)—S. palustris, (z)—Stenus sp., (AA)—Salda littoralis, (BB)—Saldula fucicola, (CC)—Teloleuca pellucens, (DD)—Chiloxanthus stellatus. ((a),BB) Ulakhan-Sullar: (a(a)) middle Pleistocene, (BB) late Pleistocene; (b,d,h,l) Lucky Lady, (g) Hollis Mine, (e,l,n,o,t,u,v) Quartz Creek: (a(b),b,d,e,n,o,u,v)—Holocene, (g): middle Pleistocene, (c,h,i,l,u)—late Pleistocene), (f,CC) Ust-Buotama, (j,k,p,r,t(a),w,DD)—Kharyyalakh, Holocene, (m)—Kyzyl-Syr, late Pleistocene (MIS3) peat, (q) Undulung River, late Pleistocene, (x,y,z)—Batagay, late Pleistocene, (AA) Kyzyl-Syr, late Pleistocene.
The Beringia database (the Siberian part by [25]; the North American part prepared for publication by Kuzmina) was used to estimate the proportions between subfossil insects belonging to different ecological groups. The list of all Beringian subfossil insects includes 107,537 individuals from 1202 samples in 100 sites (Table 3).
Table 3. Occurrence of water indicators and their percentage of assemblages in different stratigraphic units.
The list of aquatic species includes 4489 specimens from 610 samples in 70 sites. The number of individuals of aquatic insects comprises only 4% of all specimens, but the group is recorded in 51% of samples and in 70% of localities.
The list of riparian species includes 5083 individuals from 656 samples in 74 sites. The proportion of the “ri” group is slightly larger than the “aq” group. The number of specimens of riparian insects comprises 5% of the total; the group is recorded in 55% of samples and in 74% of localities. We can see that both aquatic and riparian insects are less common than could be expected according to the classic taphonomic assumptions. The role of aquatic and riparian species in the subfossil assemblages is low, and many samples do not have any near-water taxa at all.
Distribution of water-related groups by geological epochs is shown in Table 3. The proportion of the “aq” group slightly increased in the Late Neogene, was low during the Pleistocene, except the warm MIS 5 interval, and then significantly increased in the Holocene. Similarly, the proportion of the “ri” group increased in the late Neogene, decreased in the Early Pleistocene, and was low in the Middle Pleistocene; it increased during the warm interval MIS 5, remaining low in the cold stages of the Late Pleistocene, and increased in the Holocene.
The clearest reaction of entomofauna on the climatic changes is reflected in the difference between the MIS5 and MIS4-2 intervals of the Late Pleistocene. Insect assemblages from cold intervals obviously yielded less water-related taxa. It must be noted that warm climatic phases of the Early-Middle Pleistocene are poorly sampled; most of the studied assemblages belong to cold phases.
Proportions of aquatic and riparian species in assemblages from different depositional environments are presented in the Table 4. Types of deposits were determined based on their diagnostic geological features.
Table 4. Occurrence of water indicators and their percentage of assemblages in different sedimentation types.
The lowermost share of aquatic species is observed in assemblages from paleosols. Aquatic insects are usually absent in paleosol samples, but there are some exceptions. The sample OC-45 from the Old Crow site in Yukon (Table 4) is significantly different from the other three samples, while this layer was described in the field as a paleosol. In the sample, the remains of gilled aquatic taxa and caddisfly larvae were found. While the aquatic species could potentially migrate to the paleosol from the nearby water body, the presence of caddisfly larvae suggests that this paleosol was covered by water and mixed with floodplain deposits. In other samples from paleosols, riparian insects were absent or present in low numbers, except the above-described assemblage OC-45.
Peat deposits yielded a higher-than-average share of aquatic and riparian insects with a high taxonomic diversity. The proportion of aquatic species in the peat depends on the presence of open water within the peatland.

4. Discussion

The existence of the steppe-tundra or the mammoth steppe biomes in the Pleistocene was postulated based on the studies of mammal [26,27], insect [8,9,22,28], and plant [29] remains. The steppe-tundra is an extinct non-analogue landscape that served as the favorable habitat for mammals typical of tundra (e.g., caribou) and steppe (saiga, horse, bison). In the entomofauna of this period, we can notice a combination of the tundra ground beetle Pterostichus brevicornis (Kirby, 1837) and the steppe weevil Stephanocleonus eruditus Faust 1890.
A treeless aridic landscape of the north keeps water better than the southern grasslands. There are two main factors of water accumulation: the long winters that prevent full evaporation of shallow lakes and the permafrost. Ground ice (Figure 1a–c) acts as a diligent host, incorporating most of the water, excluding the water from the atmospheric cycle, and releasing the water when the ground becomes eroded due to extra heat or mechanical damage. Numerous frost cracks turn into seasonal ponds in the spring.
The steppe-tundra vegetation existed in Beringia at least since the Early Pleistocene [27]. The tundra biome was established even earlier; it is rooted in the Late Neogene boreal forest community [30]. Many species of tundra insects probably originated from the open boggy areas inside the boreal forest. Being adapted to the treeless wetlands, they could occupy wet depressions in the Pleistocene steppe-tundra as well as in the modern wet tundra.
Hydrophilic and xerophilic parts of the steppe-tundra insect community coexisted in the same climate but the temperature range of their microhabitats could be significantly different. The Mutual Climatic Range (MCR) method allows one to calculate average temperatures of January and July in the past using the modern distribution of beetle species. Application of the MCR for steppe-tundra assemblages from the lower Kolyma River showed that temperature ranges of steppe and tundra species either overlapped slightly or did not overlap at all [31]. This means that the heat balance of wet and dry sites was very different.
The proportion of thermophilus steppe species decreased during the warm intervals [8], including the Last Interglaciation (MIS5). During MIS5, some hydrophilic species became good temperature indicators. The ground beetle Dyschirius laevifasciatus Horn 1878, which currently inhabits riparian sites not much north of the Central-Western Alberta, has been found in MIS5 deposits at the Porcupine River in the northern Yukon [32]. This find validates the hypothesis that the climate of MIS5 was warmer than modern.
The relatively low proportion of the water and riparian insects in the Pleistocene subfossil assemblages could have two explanations: (1) The role of the wetland environment in the steppe-tundra was indeed low. (2) The insects were accumulated mostly in aeolian sediments and paleosols.
The origins of the Yedoma, the ice-rich silty deposit with huge ice wedges, dated by the Late Pleistocene, were long discussed by permafrost experts and paleontologists. The Yedoma (Figure 1a–c and Figure 4b,c) are widespread in both parts of Beringia. Its frozen silt contains well-preserved remains of plants and animals, including insects. Numerous insect samples come from Yedoma because of its richness; we can take a sample anywhere within the Yedoma and expect a good result. The hypotheses of the Yedoma origin are alluvial (floodplain), deltaic, proluviual, nival, aeolian, and polygenetic [33]. Despite the type of accumulation, silt particles initially result from the cryogenic weathering.
For the Eastern Beringian analogue of the Yedoma, the “Yukon muck”, the aeolian origin is widely accepted by the Western scientific community [34]. Russian scientists mostly admit the polygenetic origin of the Yedoma with the significant role of floodplain sediments in its formation [35], but recently, the Aeolian theory gained popularity there as well. One of the features of the Yedoma is the presence of tiny rootlets of grasses (Figure 4b,c). S. Gubin [36] described the layers with rootlets as “cryopedoliths”—poorly developed cryogenic soils that were affected by the repeated influx of silt on the surface.
The aeolian dust can be deposited on all surfaces, including grassy vegetation of the steppe patches and surfaces of local water bodies. Even considering that some aquatic species can migrate from water to the soil, by finding such species, we certainly know that the water existed somewhere nearby. The waterborne origin of a sediment can be validated if we find remains of freshwater crustaceans. Ostracods is a proper group for such verification; they are common in the Yedoma, well preserved, and their small size allows for detailed sampling. Comparing the insect record (after [13]) and the ostracod record (after [37]) from the Yedoma of the reference section Mamontovy Khayata (Bykovsky Peninsula at Laptev Sea coast), we can determine what layers are of a water origin.
The 40-m-high sea bluff (Figure 14) consists of frozen silt with lenses of plant detritus and gigantic ice wedges. The accumulation started more than 46 thousand years ago; the silt unit formed during the Middle Weichselian (MW) and the Late Weichselian (LW) intervals of the Late Pleistocene. The Early Holocene peat layer is situated on the top of the section, it thicknesses varies from one to three meters.
Figure 14. Distribution of aquatic and riparian insects in the section Mamontovy Khayata, Bykovsky Peninsula, Northern-East Siberia [13] compared with the ostracod record [37].
Ostracod bulk samples were taken throughout the section except some inaccessible loci. To obtain insect assemblages, large sediment samples (40–50 L) were wet sieved during three field seasons. The record is considerably detailed except the lower part, where too little sediment was exposed and hence, available for processing.
In the lower part of the section (MW1), we can see a prominent peak of the ostracod concentration and a higher-than-average proportion of aquatic insects there (Figure 14). In the upper part of the section (MW2), the ostracods almost completely disappeared while the proportion of aquatic insects slightly decreased. Ostracods appeared again in LW1, but their proportion is significantly lower than in MW1. Aquatic insects are generally sparse there. At the next stage, LW2, ostracods are absent, and the proportion of aquatic insects is low.
An unusual picture was observed in the early Holocene peat above the Yedoma (Figure 14). Aquatic insects dominated the assemblage, contributing over 50%, but only solitary ostracods were recorded. The sample was collected from the lower contact of the peat unit with the Holocene lacustrine sediment and, probably, the ostracod finds came from the buried moss, while the majority of the insect assemblage originated from both the lacustrine and peat deposits.
Even more interesting concordance and discrepancy is observed in the Yedoma part of the section. The high concentration of ostracod in MW1 points to predominantly aquatic sedimentation. In MW1, we observe a clear discrepancy—the aquatic insects peak while the ostracods are absent. Later in LW1, the curves of both groups are correlated and indicate mixed deposition. Both curves closely repeat each other in the LW2 part. According to the complete insect record [13] the terminal stage of the late Pleistocene was arid and relatively warm. It appears that the sedimentation during that stage was predominantly aeolian.
The Yedoma of the section Mamontovy Khayata does not have clear indicators of lacustrine deposition; it consists mostly of monotonous silt, sometimes with layers of allochthonous peat of various thickness that may rarely include moss. However, aquatic insects and ostracods are recorded at most sampling depths in the section. Probably, predominantly aeolian silt deposition on terrestrial surface (day surface) alternated here with the silt deposition in short-lived shallow lakes.

5. Conclusions

Generally, aquatic riparian and wetland taxa play a secondary role in the Pleistocene insect assemblages of the Beringia. Poor presentation of these groups could be explained by the limited extent of wetlands in the cryo-arid climate and by the specifics of the regional sedimentation. Occurrence of hydrophilic and xerophilic groups of insects and the proportions of each group in subfossil assemblages was closely associated with the depositional environments. Aeolian deposits and paleosols preserved a small number of aquatic insects that have hard chitin. The beetles could die far away from their burial place, with their empty exoskeleton transported later by wind or water streams to local depressions in the terrain and lake shores. Lack of dense riparian vegetation eased transportation of the insect remains from the terrain to the water. As a result, a significant part of remains of terrestrial insects ended up in alluvial and lacustrine sites.
Mixed insect assemblages could form in loess-like deposits if the dust fell into shallow short-lived lakes. Paleosols may preserve dead beetles and bugs that migrated from nearby water to the soil for wintering.
Our co-analysis of different sedimentation types and proportions of ecological groups of insects in each depositional environment attested to the predominantly aeolian origin of the specific, ice-rich Late Pleistocene deposit called Yedoma.
Proportions of hydrophilic species increased during warm climatic stages. This could be a taphonomic phenomenon associated with the distribution of shrubs and trees, as an expansion of riparian vegetation during the warm stages would prevent free transportation of terrestrial insects from the terrain to water. Climates of the warm stages were less windy; the vegetated ground produced less dust. Hence, during the wet and warm stages, the local entomofauna was reflected in subfossil assemblages more adequately than during cold phases.
The Holocene warming initiated permafrost thawing and formation of numerous thermocarst lakes. The role of wetlands dramatically increased in the Early Holocene and that is clearly reflected in subfossil insect assemblages.

Funding

The study was supported by Russian Foundation for Basic Research (RFBR) grant Number 20-04-00165.

Institutional Review Board Statement

Not applicable.

Data Availability Statement

All material examined in this study are openly available at the facilities listed above.

Acknowledgments

The author thanks Elena Ponomarenko who carefully read and proofed the manuscript.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Zherikhin, V.V. Pattern of insect burial and conservation. In History of Insects; Rasnitsyn, A.P., Quicke, D.L.J., Eds.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 2002; pp. 17–64. ISBN 978-0-306-47577-1. [Google Scholar]
  2. Coope, G.R. Constancy of insect species versus inconstancy of Quaternary environments. In Diversity of Insect Faunas; Mound, L.A., Waloff, N., Eds.; Blackwell Science: Oxford, UK, 1978; pp. 176–187. [Google Scholar]
  3. Abellán, P.; Benetti, C.J.; Angus, R.B.; Ribera, I. A review of Quaternary range shifts in European aquatic Coleoptera. Global Ecol. Biogeogr. 2011, 20, 87–100. [Google Scholar] [CrossRef]
  4. Fikáček, M.; Prokin, A.; Angus, R.B. A long-living species of the hydrophiloid beetles: Helophorus sibiricus from the early Miocene deposits of Kartashevo (Siberia, Russia). ZooKeys 2011, 130, 239–254. [Google Scholar] [CrossRef]
  5. Shur, Y.; Fortier, D.; Jorgenson, M.T.; Kanevskiy, M.; Schirrmeister, L.; Strauss, J.; Vasiliev, A.; Ward Jones, M. Yedoma Permafrost Genesis: Over 150 Years of Mystery and Controversy. Front. Earth Sci. 2022, 9, 757891. [Google Scholar] [CrossRef]
  6. Efremov, I.A. Taphonomy: A new branch of paleontology. Pan-Am. Geol. 1940, 74, 81–93. [Google Scholar]
  7. Martin, R.E. Taphonomy. A Process Approach; Cambridge Paleobiology Series; Cambridge University Press: Cambridge, UK, 1999; Volume 4. [Google Scholar]
  8. Kuzmina, S.A. Quaternary Insects and Environment of the Northeastern Asia. Ltd., Pleiades Publishing, Ltd. Paleontol. J. Suppl. 2015, 49, 1–189. [Google Scholar] [CrossRef]
  9. Kiselev, S.V.; Nazarov, V.I. Late Cenozoic Insects of Northern Eurasia. Pleiades Publishing, Ltd. Paleontol. J. Suppl. 2009, 43, 1–128. [Google Scholar] [CrossRef]
  10. Kuzmina, S.; Froese, D.G.; Jensen, B.J.L.; Hall, E.; Zazula, G.D. Middle Pleistocene (MIS 7) to Holocene fossil insect assemblages from the Old Crow basin, northern Yukon, Canada. Quatern. Intern. 2014, 341, 216–242. [Google Scholar] [CrossRef]
  11. Kuzmina, S.A.; Elias, S.A.; Kotov, A.A. Late Quaternary insects and freshwater invertebrates of the Alaskan North Slope and paleoenvironmental reconstructions in Arctic Alaska. Invert. Zool. 2019, 16, 89–125. [Google Scholar] [CrossRef]
  12. Andreev, A.A.; Grosse, G.; Schirrmeister, L.; Kuznetsova, T.V.; Kuzmina, S.A.; Bobrov, A.A.; Tarasov, P.E.; Novenko, E.Y.; Meyer, H.; Derevyagin, A.Y.; et al. Weichselian and Holocene palaeoenvironmental history of the Bol’shoy Lyakhovsky Island, New Siberian Archipelago, Arctic Siberia. Boreas 2009, 38, 72–110. [Google Scholar] [CrossRef]
  13. Sher, A.V.; Kuzmina, S.A.; Kuznetsova, T.V.; Sulerzhitsky, L.D. New insights into the Weichselian environment and climate of the Eastern-Siberian Artic, derived from fossil insects, plants, and mammals. Quatern. Sci. Rev. 2005, 24, 533–569. [Google Scholar] [CrossRef]
  14. Wetterich, S.; Kuzmina, S.; Andreev, A.A.; Kienast, F.; Meyer, H.; Schirrmeister, L.; Kuznetsova, T.; Sierralta, M. Palaeoenvironmental dynamics inferred from late Quaternary permafrost deposits on Kurungnakh Island, Lena Delta, Northeast Siberia, Russia. Quatern. Sci. Rev. 2008, 27, 1523–1540. [Google Scholar] [CrossRef]
  15. Kuzmina, S.A.; Wetterich, S.; Meyer, H. Paleoecological and sedimentological studies f Permafrost deposits in the Central Lena Delta (Kurungnakh and Samoylov Islands). Russian German Cooperation SYSTEM LAPTEV SEA The expedition 2002. Rep. Polar Res. 2003, 466, 71–81. [Google Scholar]
  16. Wooller, M.J.; Zazula, G.D.; Blinnikov, M.; Gaglioti, B.V.; Bigelow, N.H.; Sanborn, P.; Kuzmina, S.; La Farge, C. The detailed paleoecology of a mid-Wisconsinan interstadial (ca. 32 000 14C yr BP) vegetation surface from interior Alaska. Journ. Quatern. Sci. 2011, 26, 746–756. [Google Scholar] [CrossRef]
  17. Zanina, O.G.; Gubin, S.V.; Kuzmina, S.A.; Maximovich, S.V.; Lopatina, D.A. Late-Pleistocene (MIS 3-2) palaeoenvironments as recorded by sediments, palaeosols, and ground-squirrel nests at Duvanny Yar, Kolyma lowland, northeast Siberia. Quatern. Sci. Rev. 2011, 30, 2107–2123. [Google Scholar] [CrossRef]
  18. Kuzmina, S.; Elias, S.; Matheus, P.; Storer, J.E.; Sher, A. Paleoenvironmental reconstruction of the Last Glacial Maximum, inferred from insect fossils from a buried soil at Tempest Lake, Seward Peninsula, Alaska. Palaeogeogr. Palaeoclim. Palaeoecol. 2008, 267, 245–255. [Google Scholar] [CrossRef]
  19. Reyes, A.V.; Jensen, B.J.L.; Zazula, G.D.; Ager, T.A.; Kuzmina, S.; La Farge, C.; Froese, D.G. A Late–Middle Pleistocene (Marine Isotope Stage 6) vegetated surface buried by Old Crow tephra at the Palisades, interior Alaska. Quatern. Sci. Rev. 2010, 29, 801–811. [Google Scholar] [CrossRef]
  20. Zazula, G.D.; Froese, D.G.; Elias, S.; Kuzmina, S.; Farge, C.L.; Reyes, A.V.; Sanborn, P.T.; Schweger, C.E.; Scott Smith, C.A.; Mathewes, R.W. Vegetation buried under Dawson tephra (25,300 14C years BP) and locally diverse late Pleistocene paleoenvironments of Goldbottom Creek, Yukon, Canada. Palaeogeogr. Palaeoclim. Palaeoecol. 2006, 242, 253–286. [Google Scholar] [CrossRef]
  21. Kuzmina, S.A.; Basilyan, A.E. First finds of the fossil insects in the Quaternary aeolian deposit of the Central Yakutia and their role in the environmental reconstructions. Routes of evolutionary geography. Issue 2. In Proceedings of the 2nd Scientific Conference in Memory of Prof. A.A. Velichko, Moscow, Russia, 22–25 November 2021; pp. 170–173. (In Russian). [Google Scholar]
  22. Kiselev, S.V. Late Cenozoic Coleoptera of North-East Siberia; Nauka: Moscow, Russia, 1981. (In Russian) [Google Scholar]
  23. Sher, A.V.; Kuzmina, S. Beetle records/Late Pleistocene of Northern Asia. In Encyclopedia of Quaternary Science; Elias, S., Ed.; Elsevier: Amsterdam, The Netherlands, 2007; Volume 1, pp. 246–267. [Google Scholar]
  24. Kuzmina, S.A. Macroentomology Analysis: Methods, Opportunities, and Examples of Reconstructions of Paleoclimatic and Paleoenvironmental Conditions in the Quaternary of the Northeastern Siberia. Contemporary Probl. Ecol. 2017, 10, 336–349, Pleiades Publishing, Ltd., 2017. Original Russian Text S.A. Kuzmina, 2017, published in Sibirskii Ekologicheskii Zhurnal, 2017, 4, 381–398. [Google Scholar] [CrossRef]
  25. Kuzmina, S. New approach to the Quaternary studies: QINSIB–The database of Siberian fossil insects. Quatern. Intern. 2014, 341, 283–293. [Google Scholar] [CrossRef]
  26. Guthrie, R.D. Origin and causes of the mammoth steppe: A story of cloud cover, woolly mammal tooth pits, buckles, and inside-out Beringia. Quat. Sci. Rev. 2001, 20, 549–574. [Google Scholar] [CrossRef]
  27. Sher, A.V. Pleistocene mammals and stratigraphy of the far northeast USSR and North America. Internal. Geol. Rev. 1974, 16, 1–284. [Google Scholar]
  28. Matthews, J.V., Jr.; Telka, A. Insect Fossils from the Yukon. In Insects of the Yukon; Danks, H.V., Downes, J.A., Eds.; Biological Survey of Canada (Terrestrial Arthropods): Ottawa, Canada, 1997; pp. 911–962. [Google Scholar]
  29. Zazula, G.D.; Froese, D.G.; Schweger, C.E.; Mathewes, C.E.; Beaudoin, A.B.; Telka, A.M.; Harington, C.R.; Westgate, J.A. Ice age steppe vegetation in east Beringia. Nature 2003, 423, 603. [Google Scholar] [CrossRef]
  30. Matthews, J.V., Jr. Tertiary and Quaternary environments: Historical background for an analysis of the Canadian insect fauna.Canada and its insect fauna. Mem. Ent. Soc. Can. 1979, 108, 31–86. [Google Scholar] [CrossRef]
  31. Alfimov, A.V.; Berman, D.I.; Sher, A.V. Tundra-steppe insect assemblages and reconstruction of Late Pleistocene climate in the lower reaches of the Kolyma River. Zool. Zhurn. 2003, 82, 281–300. (In Russian) [Google Scholar]
  32. Matthews, J.V.; Schweger, C.E.; Janssens, J.A. The last (Koy-Yukon) inter- glaciation in the northern Yukon: Evidence from unit 4 at Ch’ijee’s bluff, Bluefish basin. Géogr. Phys. Quat. 1990, 44, 341–352. [Google Scholar]
  33. Schirrmeister, L.; Froese, D.; Tumskoy, V.; Grosse, G.; Wetterich, S. Yedoma: Late Pleistocene Ice-Rich Syngenetic Permafrost of Beringia. In The Encyclopedia of Quaternary Science; Elias, S., Ed.; Elsevier: Amsterdam, The Netherlands, 2013; Volume 3, pp. 542–552. [Google Scholar]
  34. Froese, D.G.; Westgate, J.A.; Sanborn, P.T.; Reyes, A.V.; Pearce, N.J.G. The Klondike goldfields and Pleistocene environments of Beringia. GSA Today 2009, 19, 4–10. [Google Scholar] [CrossRef]
  35. Sher, A.V. Yedoma as a store of paleoenvironmental records in Beringida. In Beringia Paleoenvironmental Workshop, Abstracts and Program; Elias, S., Brigham-Grette, J., Eds.; Ohana Productions: Nepean, ON, Canada, 1997; pp. 92–94. [Google Scholar]
  36. Gubin, S.V. Pedogenesis–the main component of the late Pleistocene Ice Complex forming. Krioshera Zemli 2002, 6, 82–91. (in Russian). [Google Scholar]
  37. Wetterich, S.; Schirrmeister, L.; Pietrzeniuk, E. Freshwater ostracodes in Quaternary permafrost deposits in the Siberian Arctic. J. Paleolimnol. 2005, 34, 363–376. [Google Scholar] [CrossRef]
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Article Metrics

Citations

Article Access Statistics

Journal Statistics
Multiple requests from the same IP address are counted as one view.
Download PDF
Study on Interaction between Surface Water and Groundwater in Typical Reach of Xiaoqing River Based on WEP-L Model
Previous
Bragg Resonance of Water Waves by Multiple Permeable Thin Barriers over Periodic Breakwaters
Next