Palaeoenvironmental evolution of the Baltic Sea basin during the Last Interglacial (Eemian, Mikulino stages): a review

Abstract. Through detailed investigations, three sequences of marine and associated deposits in the south-west Baltic area are shown to represent the Eemian interglacial transgression. Pollen analyses and foraminiferal and ostracod analyses are combined to provide the evolution of relative sea-level change. An independent chronology is established by correlation of the pollen record with that from the Bispingen laminated lake deposits in north Germany. Additional published sites from the area are included in a wider reconstruction of events. Ostracod analyses indicate that freshwater lakes initially existed in the basin prior to the marine inundation. This was followed by an early marine transgression. In the south-west Baltic the first marine ingression took place at the base of regional pollen zone E3, with fully marine conditions established in E4 continuing into the lower part of E5. The regression of the sea during zone E6 was followed by freshwater deposition in E7. The linking of the sequences in the south-west Baltic demonstrates that the Eemian transgression occurred both through northern Germany and through the Danish belts–Kattegat seaway, indicating that connections to the North Sea and North Atlantic were present in the area during the maximum interglacial sea-level highstand.

Eemian sea-level highstand in the eastern Baltic Sea linked to long-duration White Sea connection

A multiproxy study of Eemian Stage sediments in two core records, Licze and Obrzynowo, in the Gulf of Gdańsk area of northern Poland, shows that the brackish‐marine interglacial conditions were determined partly by regional environmental changes and partly by local changes of the river outflow from the Vistula into the southern Baltic Sea. Correlation of the sediments with the Eemian is based on pollen analysis of the Obrzynowo record, showing the presence of regional pollen zones (RPAZ) E2–E6, combined with previously published pollen analyses from Licze (RPAZ E1–E7). A floating chronology is established on the basis of correlation with the annually laminated Bispingen sequence. Diatoms, foraminifera and ostracods are used as marine environmental proxies at both sites. An indication of marine conditions as early as pollen zone E1 or E2 at Licze and close to the E2–E3 boundary at Obrzynowo reflects the rapid relative sea‐level rise in the area, which proceeded through ∼3000 years. A major salinity increase c. 1100 years after the beginning of the Eemian (early pollen zone E4) at both sites may be related to the opening of the Danish Straits. The Obrzynowo site became isolated from the sea at c. 3500 years (early pollen zone E5), whereas marine conditions continued at Licze until c. 7000 years, that is, throughout pollen zone E5. Gradually shallower water after c. 5000 years presumably resulted from progradation of the rivers combined with isostatic rebound of the area before final isolation from the sea at c. 7000 years.

Dinoflagellate cysts were studied in 42 samples from the surface sediments of the White Sea. The total concentration of dinocysts varies from single cysts to 25 000 cyst/g of dry sediments, which reflects the biological productivity in the White Sea waters and the regional particular features of the sedimentation processes. The highest concentrations are observed in silts; they are related to the regions of propagation of the highly productive Barents Sea waters in the White Sea. Generally, the spatial distribution of dinocysts species in the surface sediments corresponds to the distribution of the major types of water masses in the White Sea. The cysts of the relatively warm-water species (Operculodinium centrocarpum, Spiniferites sp.) of North Atlantic origin that dominate in the sediments indicate an intensive intrusion of the Barents Sea water masses to the White Sea along with hydrological dwelling conditions in the White Sea favorable for the development of these species during their vegetation period. The cold-water dinocyst assemblage (Islandinium minutum, Polykrikos sp.) is rather strictly confined to the inner parts of shallow-water bays, firstly, those adjacent to the Onega and Severnaya Dvina river mouths.

Past environmental changes in the Baltic area are discussed on the basis of foraminifera and ostracods as well as pollen and spores in marine sediments in cliff sections at Ristinge Klint, Langeland, southern Denmark. The sediment succession represents Jessen & Milthers' (1928) pollen zones d–g or Andersen's (1961, 1975) zones E2–E5, and a correlation with the annually laminated Bispingen sequence indicates that the sequence spans about 3400 years. Marine conditions seem to have occurred at c. 300–365 years after the beginning of the Eemian Interglacial, close to fully marine conditions developing by c. 2500 years. This early date of the marine ingression pre‐dates that of most previous studies in the region by several hundred years, but it postdates the initial marine ingression in the easternmost Baltic. A marked change in salinity at c. 650 years after the beginning of the Eemian was presumably caused by an opening of the Danish Belts. An indication of a major alteration in current activity is registered at c. 3000 years after the beginning of the interglacial. The recognition of the relative timing of these events may be significant for the understanding of the opening of connections between the North Sea, the Baltic and the White Sea.

The Chinese mitten crab Eriocheir sinensis penetrated West European rivers early in the 20th century. It has recently been caught in the White Sea (Northern Dvina River estuary). In 1957 the transportation of eggs of the Pacific pink salmon, Oncorhynchus gorbuscha, from the Far East to the White Sea, began. As a result of a successful acclimatisation, the catches of pink salmon in the White Sea now add up to some hundred tons per year. The steelhead Parasalmo mykiss, native to the northern Pacific Ocean, has become one of the most important species of aquaculture in the White and Barents Seas. Natural populations of steelhead, registered in the Barents Sea, have not been found in the White Sea area yet.

Comprehensive studies of diatoms and palynomorphs from the White Sea sediments revealed the following features of the composition of their assemblages. The species composition of the marine plankton diatoms and dinoflagellate cysts in the sediments reflects the features of the high-latitude position of the sea and the impact of the Arctic and North Atlantic water masses on hydrological regime of the White Sea. The spatial distribution of plankton species in the surface sediments (both diatoms and dinoflagellate cysts) matches the distribution of the main types of water masses in the White Sea. The characteristic property of the diatom and dinoflagellate cyst assemblages is the presence, in high concentrations, of relatively warmwater species typical for the Atlantic water masses. Diatom algae, aquatic palynomorphs, and the grain size of surface sediments from bays of the White Sea were investigated in a program dedicated to the study of marginal filters (MF) in the Northern Dvina, the Onega, and the Kem’ Rivers.

SummaryInvestigations have been made of Late‐Weichselian and Flandrian deposits in Blelham Tarn, Lancashire and other parts of its basin. Pollen and diatom analyses have been made of several cores and samples taken from the inflows. Pollen analysis has been used as a basis for chronology. The vegetational history of the region and past diatom flora of the tarn and ‘kettle‐hole’ are discussed. During the Late‐Weichselian, in pollen zones I and III, the vegetation was dominated by herbs of open habitats, whilst in pollen zone II birch woodland developed. The diatom flora consisted mainly of non‐planktonic forms with Fragilaria spp. dominant. In the Early‐Flandrian (pollen zones IV–VI) birch woodland developed and was succeeded by a mixed oak forest. Differences are shown in the pollen spectra from the ‘kettle‐hole’, marginal and open water regions of the tarn. The planktonic/non‐planktonic (P/NP) diatom ratio slowly increased in the tarn. However, dominance was retained by the non‐planktonic forms. This increase in P/NP ratio did not occur in the ‘kettle‐hole’ region. A new diatom variety Melosira distans var. blelhamensis appeared in the flora. At the opening of pollen zone VIIa Alnus rapidly increased, and for the first time planktonic diatoms became dominant in the open waters of the tarn. In littoral regions non‐planktonic forms, in particular Achnanthes minutissima var. cryptocephala, remained dominant. Sphagnum‐sedge peat accumulated in the ‘kettle‐hole’. Diatoms are scarce in this peat. During the Late‐Flandrian (pollen zone VIIb to the present day) the local vegetation was an older mixed oak forest. However, more open vegetational conditions gradually developed as shown by the increase in herbaceous pollen. Dominance was held in the open waters by the planktonic diatoms. The littoral regions favoured the growth of Achnanthes minutissima var. cryptocephala. Sphagnum‐sedge peat continued to accumulate in the ‘kettle‐hole’. Other limnological aspects considered include the tarn's trophic condition, productivity, alkalinity, the transparency of its waters and tarn level changes. In the past the tarn covered a much wider area. Field evidence shows that man has interfered with the drainage system.

Marine sediments from river sections in the Mezen River drainage, northwest Russia, have been analysed for dinoflagellate cysts, foraminifers and molluscs. The sediments were dated by pollen analysis and by reference to the local sea‐level history, and are Late Saalian to late Eemian (c. 133 to 119.5 kyr in age). The Late Saalian deglaciation was characterized by Arctic conditions, but a few centuries into the Eemian the Gulf Stream system carried warm Atlantic water into the region. At 129.8 kyr BP there was a marked increase in the influx of Atlantic water, and the advection of warm Atlantic water was stronger and probably penetrated further eastwards than at present. The molluscs, dinoflagellate cysts and foraminifers reflect conditions warmer than present and that the optimum temperature occurred at the time of the early Eemian global sea‐level rise. Around 128 kyr BP, the eustatic sea‐level rise was curbed by isostatic rebound and accompanying regression and constriction of marine passages to the White Sea. Local, low‐saline, stratified basins developed and characterized the next five to six millennia.

Discussions on the age and the depositional environments of the Veldhoven Formation and its members are persistent in Belgium and the Netherlands. Uncertainties on stratigraphy and the constructive process of sediment accumulation continue today as a result of lack of data on this succession within the Roer Valley Rift System. The present study provides new information on the bio- and lithostratigraphy and facies from two boreholes based on dinoflagellate cyst taxa. The results were correlated by gamma-ray logs towards other key boreholes in the region and show a good consistency for stratigraphy and depositional environments for the members of the Veldhoven Formation. After marginal to restricted marine conditions in the latest Rupelian (early Oligocene), the start of deposition of the Veldhoven Formation marked the transition towards a higher sea level, expressed by increased glauconite contents and gamma-ray values. The Voort Member in the lower part of the Veldhoven Formation has an early to late Chattian (Late Oligocene) age and comprises predominantly shallow marine (fluctuating restricted to open marine) conditions. The lithology in the lower part of this unit is often very clayey but is coarsening upward into sands. The superjacent Wintelre Member has a latest Chattian to early Aquitanian (early Miocene) age. This member is distinct by its clayey nature which is expressed by relatively high gamma-ray values. Earlier studies suggest a deeper marine facies for the Wintelre Member compared to the Someren and Voort members. However, the dinoflagellate cyst assemblages in this unit are mostly dominated by a single genus indicating a restricted marine setting, including salinities that deviate from normal marine conditions, most probably due to minor ventilation by narrow or lack of connection to the Atlantic Ocean. A glacio-eustatic sea-level fall around the Oligocene/Miocene boundary limited the sea coverage to the strongest subsiding areas, where deposition of the Wintelre Member is recorded, while non-deposition or erosion occurred in the surrounding highs, hence creating an isolated (sub)basin. The superjacent Someren Member was deposited during the late Aquitanian to middle Burdigalian and consists of shallow to open marine clayey fine sands. Increasing clay contents indicate a gradual development towards a higher sea level, which coincide with upward increasing gamma-ray values. The biostratigraphic results of this study suggest that no major hiatuses are present in the differentially subsiding blocks of the Roer Valley Rift System during the late Oligocene to early Miocene.

At Tornskov 4 km north of Løgumkloster, south Jutland, a Quaternary marine deposit was found at 27-95 m below the surface. The marine deposit is covered by glacial deposits, which contain a dislocated fragment of the marine deposit. Tertiary deposits occur below 107 m. The deposits were investigated with pollen analysis. Re-deposited pollen is very frequent below 77 m. The layers at 27-77 m correspond to a major part of an interglacial succession beginning with Betula-Pinus dominance, and continuing with Alnus-Pinus dominance. Picea, Quercus, Ulmus, Carpinus, Abies, Corylus, Taxus and other trees and shrubs are represented with rather low frequencies. The interglacial marine deposit at Tornskov is contemporaneous with the interglacial marine deposit at Inder Bjergum near Ribe, and with deposits of the interglacial Holstein Sea in north Germany and the northern Netherlands, in which there is a similar vegetational development. Pollen diagrams typical of the Holsteinian Interglacial are also known from fresh-water deposits in north Germany, the Netherlands and Poland. The interglacial fresh-water deposits at Harreskov, Starup and Ølgod in western Jutland belong to another, presumably older interglacial stage.

Marine and continental deposits from the Tjörnes area in northern Iceland were studied to obtain their pollen/spore content. Six Pollen Zones (PZ) were defined in the Early Pliocene Tjörnes beds and the Early Pleistocene Breidavík Group. The pollen is most diverse during the deposition of the lowest Tapes Zone (PZ 1) and the lower part of the overlying Mactra Zone (PZ 2). Local pollen from marshland, levee and foothill forests was deposited on a large coastal plain. The pollen spectrum reflects transgression and deepening during the second part of the Mactra Zone (PZ 3) and the lower part of the Serripes Zone (PZ 4). Gymnosperm pollen derived from the higher inland plateau increases in PZ 3. This background pollen was of minor importance during periods with an extensive coastal plain (PZ 1, 2, 4, 6). PZ 5 did not yield sufficient pollen for analysis. The pollen analysis allowed refinement of the sea‐level variations based on sedimentology and molluscs. Pollen of warmth‐demanding plants is recorded throughout the Tjörnes beds and the Early Pleistocene interglacial deposits. Warmth‐loving species indicate summers 8°C warmer than today during deposition of the Tapes Zone, and at least 5°C warmer during the rest of the Tjörnes beds. The Pliocene vegetation of Iceland matches well that of the present‐day western European maritime temperate climate. The drastic cooling at the onset of the Quaternary led to a marked vegetation impoverishment, already noticeable in the Early Pleistocene Breidavík Group.

Palynology of late Quaternary coastal sediments, Perak, Malaysia

Upper Vendian rocks of the East European Platform (EEP) are characterized by the presence of the White Sea fossil biota, which colonized the region from the southeastern White Sea area to the Central Urals [1]. The White Sea biota includes ecological assemblages of the Avalon (Newfoundland), Ediacara (South Australia), and Nama (Namibia) types, each related to certain environmental conditions [2]. In 2006, we found a previously unknown and morphologically diverse assemblage of carbonaceous macroscopic fossils in the fine-grained aluminosiliciclastic rocks of the Perevalok Formation (Sylvitsa Group) in the Central Urals. Together with the organic-walled macrofossils from the rocks of the Lyamtsa Formation (Valdai Group) in the southeastern White Sea area, the carbonaceous fossils from the Perevalok Formation represent a new (fourth) ecological assemblage of the White Sea fossil biota. The ecological assemblage is older than 557‐558 Ma [3, 4] and includes macroscopic microbial colonies, multicellular and coenocytic eukaryotic macroalgae. In the Late Vendian history of the EEP, this assemblage predated the appearance of the world’s most diverse soft-bodied assemblage, which was found in the overlying rocks of the White Sea area (Verkhovka and Erga formations) and Central Urals (Chernokamen Formation) [1, 2, 5]. The carbonaceous fossils are confined to a thick (200‐400 m) transgressive sequence at the base of the Upper Vendian succession in the southeastern White Sea area and Central Urals (Fig. 1). The lower part of the sequence (laminated mudstones with layers of volcanic tuffs) is gradually replaced upsection by thinly interbedded siltstones and mudstones with rare layers of wave-bedded sandstones. The sequence was formed by the advance and periodic retreat of storm-dominated coastal depositional setting into subaqueous muddy planes with relatively quiet sedimentation in the course of oscillating wane in transgression. Fossiliferous intervals contain thin laminae of phosphorites and organic matter and mark the peak of shallow-water transgression over the platform. In the southeastern White Sea area, this sequence correlates with the Lyamtsa Formation and lower part of the Verkhovka Formation; in the Central Urals, with the upper part of the Staropechny and Perevalok formations [6, 7] (Fig. 1).

High-elevation paleoenvironmental change during MIS 6–4 in the central Rockies of Colorado as determined from pollen analysis