Karin F. Helmens

The Last Interglacial-Glacial cycle in NE Fennoscandia: a nearly continuous record from Sokli (Finnish Lapland)

Abstract Boreholes from the Sokli basin in Finnish Lapland have recovered a unique sequence of diamicts interlayered with fine-grained sediments that are rich in fossils. The diamicts are interpreted as till beds deposited by the Fennoscandian Ice-Sheet. The fine-grained intercalations seem to represent a series of warm stages that include one interglacial and three interstadials. The interglacial is characterized by a mixed taiga pollen assemblage and corresponds to a distinct diatom gyttja bed. The interstadials show progressively colder floras from open birch forest to arctic forest limit to shrub tundra. Their sediments comprise gyttja interlayered with wood and sand (interstadial 1); sands grading into sandy gyttja (interstadial 2); and sands overlain by laminated silt and clay (interstadial 3). The interstadial 2 and 3 deposits are underlain by diamict and are interpreted as deglaciation sequences. Silts with a tundra pollen assemblage separate the interglacial and interstadial 1 deposits. Luminescence dating evidence indicates that the interglacial bed most probably represents the NW European mainland Eemian Interglacial (marine isotope stage (MIS) 5e). The interstadial 1, 2 and 3 deposits are tentatively correlated with the Early Weichselian Brorup and Odderade Interstadials and an interstadial of Middle Weichselian age, respectively (MIS 5c, 5a and 3, respectively). The correlation implies that the easternmost part of the ice-divide zone of the Fennoscandian continental ice-sheet was deglaciated during part of MIS 3.

Present-day temperatures in northern Scandinavia during the last glaciation

Scandinavia is generally considered to have been covered extensively with ice throughout marine isotope stages (MIS) 4–2 between 75 and 10 ka. Here we present evidence for ice-free, warm conditions in the central area of the Scandinavian glaciations during MIS 3. Our multiproxy data obtained from a lacustrine sequence in northern Fin-land reveal not only significant response in the northeastern sector of the Scandinavian Ice Sheet to warming during the early part of MIS 3, but also indicate rapid climate warming to present-day temperatures in this ice-free period. New climate-model simulations for interstadial conditions in MIS 3 confirm the high mean July temperatures northeast of the Scandinavian Ice Sheet in response to the high insolation values and the presence of the ice sheet during MIS 3.

Plant macrofossil evidence for an early onset of the Holocene summer thermal maximum in northernmost Europe

Holocene summer temperature reconstructions from northern Europe based on sedimentary pollen records suggest an onset of peak summer warmth around 9,000 years ago. However, pollen-based temperature reconstructions are largely driven by changes in the proportions of tree taxa, and thus the early-Holocene warming signal may be delayed due to the geographical disequilibrium between climate and tree populations. Here we show that quantitative summer-temperature estimates in northern Europe based on macrofossils of aquatic plants are in many cases ca. 2 °C warmer in the early Holocene (11,700–7,500 years ago) than reconstructions based on pollen data. When the lag in potential tree establishment becomes imperceptible in the mid-Holocene (7,500 years ago), the reconstructed temperatures converge at all study sites. We demonstrate that aquatic plant macrofossil records can provide additional and informative insights into early-Holocene temperature evolution in northernmost Europe and suggest further validation of early post-glacial climate development based on multi-proxy data syntheses.

Optical dating of a late quaternary sediment sequence from Sokli, Northern Finland

Optical Dating of a Late Quaternary Sediment Sequence from Sokli, Northern Finland Interstadial and non-glacial stadial sediments collected in boreholes from Sokli in northeastern Finland have been dated by optically stimulated luminescence on quartz and feldspar grains. The quartz OSL ages follow stratigraphic order, with one exception, and support the litho- and biostratigraphical correlation with the NW European mainland climate-stratigraphy and the marine oxygen-isotope stages. Feldspar IRSL dates generally overestimate the age, probably due to incomplete bleaching. The data show that during the last glacial cycle north-eastern Finland was not glaciated until MIS 5b, around 90 ka. Interstadial conditions occurred around ~94 ka (MIS 5c), ~74-80 ka (MIS 5a) and 42-54 ka (MIS 3). The OSL ages have large standard errors mainly due to small sample sizes, relatively poor luminescence characteristics and uncertainties in dose-rate determinations.

The Quaternary glacial record of the Colombian Andes

The onset of glaciations in the Colombian Andes as recorded by the start of glaciofluvial sedimentation in the inter-montane Bogota basin is dated near the Gauss/Matuyama polarity reversal at 2.6 Ma; episodes of increased glacial activity occurred since ca. 0.8 Ma. Moraines and till beds in the higher parts of the Andes record a series of glacier fluctuations of Late Quaternary age. Radiocarbon dates of organic-rich sediments and palaeosols found associated with glacial landforms/deposits in mountain ranges exceeding 3600 m altitude in the Eastern Cordillera, in combination with evidence provided by the radiocarbon-dated palaeosol sequence in the region, place glacial events between probably 43 ka and 38 ka, 36 to 31 ka, 23.5 to 19.5 ka, 18.0 to 15.5 ka 13.5 to 12.5 ka, and most probably 11 to 10 ka (radiocarbon years BP). Independent chronologies for the glacial and palynological records of the Eastern Cordillera suggest a close match between stadials characterised by low upper Andean forest limits and glacier advances in the surrounding high-mountain ranges. Major glacier advances during the Middle Weichselian seem to have responded to cool and humid climatic conditions. The Late Weichselian Glacial Maximum (LGM) is recorded as a two-fold glaciation maximum just before 19.5 and 15.5 ka, with glaciers advancing some 1200 to 1100 m below their present limits; during the cooling events, the forest limit was depressed by 1100 to 900 m, implying a drop in mean annual temperature of ca. 8 to 6 °C, respectively. Interstadial conditions prevailed around 18 ka, when temperatures rose considerably to values up to 4 °C higher than during the preceding and following stadial periods. Mountain ranges below 4000 m altitude were deglaciated at ca. 12.5 ka following a Late-glacial advance of cirque glaciers. Younger Dryas cooling is well-registered in the palynological record; glaciers in the highest parts of the Andes seem to have responded to the cooling by extending to elevations some 700 m lower than at present. The glacial record registers a high climatic variability in the northern Tropical Andes during the Late Quaternary period.

Erratum to: Evaluating environmental drivers of Holocene changes in water chemistry and aquatic biota composition at Lake Loitsana, NE Finland

This study presents a detailed analysis of geochemical and biotic proxies in a lake sediment profile to assess the effects of local and regional environmental drivers on the Holocene development of Lake Loitsana, situated in the northern boreal forest of NE Finland. Multi-proxy studies, in particular those that include a detailed plant macrofossil record, from the part of the northern boreal zone of Fennoscandia which has not been affected by treeline fluctuations, are scarce and few of these records date back to the earliest part of the Holocene. A 9-m sediment sequence of gyttja overlying silts representing the last c. 10,700 cal year, allowed for a high-resolution study with emphasis on the early to mid-Holocene lake history. The lacustrine sediments were studied using lithology, loss-on-ignition and C/N ratios, micro- and macro-fossils of aquatic and wetland taxa, diatoms, chironomids and accelerator mass spectrometry 14C dating on terrestrial plant macrofossils. Our study shows that the local development at Loitsana was complex and included a distinct glacial lake phase and subsequent drainage, a history of fluvial input affected by nearby wetland expansion, and lake infilling in an eventual esker-fed shallow lake. Enhanced trophic conditions, due to morphometric eutrophication, are recorded as Glacial Lake Sokli drained and open water conditions became restricted to a relatively small Lake Loitsana depression. pH appears to have been stable throughout the Holocene with a well-buffered lake due to the local carbonatite bedrock (Sokli Carbonatite Massif). The fossil assemblage changes are best explained by a complex mixture of drivers, including water-body conditions (i.e. depth, turbidity and turbulence), rate of sediment input, and the general infilling of the lake, highlighting the need to carefully evaluate the possible influence of such local factors as palaeoenvironmental conditions are reconstructed based on aquatic proxies.

Glaciations in North and South America from the Miocene to the Last Glacial Maximum

Improved dating methods have increased our ability to more precisely determine the timing and durations of glaciations. Utilizing glacial and loess deposits, we have compared glaciations that occurred in North and South America in order to determine whether events are synchronous or not, to explore forcing mechanisms, and to compare glaciations with cold periods of the Marine Oxygen Isotope stages and the loess/paleosol records of China. Stratigraphic sections containing a variety of glacial deposits, some with interbedded volcanics, as well as loess deposits, were used in reconstructing the glacial history. The major problems included fragmentary sections, missing evidence, and limited detailed age estimates. Dating methods utilized included radiocarbon, K–Ar, Ar–Ar, fission track, paleomagnetic polarity interpretation, and luminescence techniques (China). In North America, the best evidence for Late Cenozoic glaciations is in southeastern Alaska, the Pacific Coastal Mountains, and northwestern Canada, in South America, in the Patagonian Andes and forelands of Argentina, and in the Bogotá basin of Colombia. Four Miocene-Pliocene (Gilbert and Gauss Chrons) and Pliocene–Pleistocene (Gauss/Matuyama Chrons) glaciations have been identified in southern South America, whereas only one mountain Pliocene and one Pliocene– Pleistocene glaciations have been identified in northwest America. This may be the result of the near-coeval volcanic activity which preserved till deposits under basaltic lava flows. Major tectonic uplift in the northern Andes suggests the absence of terrain high enough to support glaciers in the Bogotá mountains during the Miocene-Pliocene. During the Early and Late Pleistocene (Matuyama Chron) there are ten glacial advances recognized in either North or South America. Five appear to be roughly synchronous. During the Jaramillo Chron the greatest glaciation occurred in Patagonia whereas the Jaramillo glaciation in northwestern Canada was not a major event. At least three Middle Pleistocene (Brunhes Chron) glaciations are represented in both North and South America. In southern South America, subsequent glaciations are less extensive than the previous. The opposite is true in northern South America and North America where younger glaciations appear to be more extensive. This may indicate the impact of local factors such as

Comparison of quantitative Holocene temperature reconstructions using multiple proxies from a northern boreal lake

Four biotic proxies (plant macrofossils, pollen, chironomids and diatoms) are employed to quantitatively reconstruct variations in mean July air temperatures (Tjul) at Lake Loitsana (northern Finland) during the Holocene. The aim is to evaluate the robustness and biases in these temperature reconstructions and to compare the timing of highest Tjul in the individual reconstructions. The reconstructed Tjul values are evaluated in relation to local-scale/site-specific processes associated with the Holocene lake development at Loitsana as these factors have been shown to significantly influence the fossil assemblages found in the Lake Loitsana sediments. While pollen-based temperatures follow the classical trend of gradually increasing early-Holocene Tjul with a mid-Holocene maximum, the aquatic/wetland assemblages reconstruct higher-than-present Tjul already during the early Holocene, that is, at the peak of summer insolation. The relatively low early-Holocene July temperatures recorded by the pollen are the result of site-specific factors possibly combined with a delayed response of the terrestrial ecosystem compared with the aquatic ecosystem. Our study shows that all reconstructions are influenced at least to some extent by local factors. This finding stresses the need to evaluate quantitatively reconstructed climate values against local lake development and highlights the benefit of using multi-proxy data in Holocene climate reconstructions.

The Glacial Record of Northern South America

The Bogota basin and direct surroundings (eastern Andes in Colombia) holds a long sedimentary sequence that reaches from the present into the Miocene. Palaeo-botanical data indicates tectonic uplift by some 2,000 m during the Late Miocene–Pliocene that probably precluded sufficiently high enough terrain to support glaciers during the time period preceding the Quaternary. The first mountain glaciation as recorded by glaciofluvial sedimentation in the Bogota basin is dated by fission-track and magnetic polarity dating at ca. 2.6 Ma, whereas a shift towards more extensive glaciations occurred after ca. 0.8 Ma. Moraines preserved in the Bogota mountains record a series of glacial events for the time interval ca. 43 to 12.5 ka BP. Equilibrium Line Altitude (ELA) depression by ca. 1,300 m is reconstructed for the early Last Glacial Maximum (LGM; ca. 20 ka BP).

Chinese Loess/Paleosol Record

The loess/paleosol sequence of north central China is probably the most complete record of Quaternary climate change derived from terrestrial deposits in the world. Alternating loess units (utilizing grain-size differences) which indicate cold periods and paleosols which indicate warm periods, record 37 major climatic cycles over the past 2.6 Ma. The Eastern Hemisphere loess/paleosol climate records are compared to the Western Hemisphere glaciations in order to record similarities of climate change intervals over a wider area by comparing Marine Isotope Stage (MIS) records. Results indicate that even though there are many uncertainties in timing of glaciations, there are major equivalent synchronous climate intervals represented in both areas.