High‐resolution chronology of 24 000‐year long cores from two lakes in the Polar Urals, Russia, correlated with palaeomagnetic inclination records with a distinct event about 20 000 years ago

Based on radiocarbon dating, a tephra horizon, varve counts and palaeomagnetism, detailed age models covering the last ~24 k cal a bp, have been developed for the stratigraphy in the lakes Bolshoye Shchuchye and Maloye Shchuchye in the Polar Ural Mountains, Russia. The inclination curves from these lakes show nearly identical palaeomagnetic secular variations in the studied cores from both lakes, allowing for a precise correlation between the cores. A large and very distinct inclination deviation, named the Bolshoye Shchuchye Event, was identified in all cores retrieved from both lakes. It lasted over a period of 1245 years, from 20 470 to 19 225 cal a bp. The well-dated palaeomagnetic inclination graph offers a new possibility to correlate archives in this part of the Arctic for the last ~24 k cal a bp, probably also over longer distances. The sedimentation rate shows the same trend in all cores from both lakes, including high input during the Last Glacial Maximum and gradually lowering after ~18 k cal a bp to lower and stable Holocene values.publishedVersio

Abrupt high-latitude climate events and decoupled seasonal trends during the Eemian

The Eemian (the Last Interglacial; ca. 129-116 thousand years ago) presents a testbed for assessing environmental responses and climate feedbacks under warmer-than-present boundary conditions. However, climate syntheses for the Eemian remain hampered by lack of data from the high-latitude land areas, masking the climate response and feedbacks in the Arctic. Here we present a high-resolution (sub-centennial) record of Eemian palaeoclimate from northern Finland, with multi-model reconstructions for July and January air temperature. In contrast with the mid-latitudes of Europe, our data show decoupled seasonal trends with falling July and rising January temperatures over the Eemian, due to orbital and oceanic forcings. This leads to an oceanic Late-Eemian climate, consistent with an earlier hypothesis of glacial inception in Europe. The interglacial is further intersected by two strong cooling and drying events. These abrupt events parallel shifts in marine proxy data, linked to disturbances in the North Atlantic oceanic circulation regime.Peer reviewe

Rapid climate changes during the Lateglacial and the early Holocene as seen from plant community dynamics in the Polar Urals, Russia

A detailed, well-dated record of pollen and sedimentary ancient DNA (sedaDNA) for the period 15 000–9500 cal a bp describes changes at Lake Bolshoye Shchuchye in the Polar Ural Mountains, located far east of the classical Lateglacial sites in western Europe. Arctic tundra rapidly changed to lusher vegetation, possibly including both dwarf (Betula nana) and tree birch (B. pubescens), dated in our record to take place 14 565 cal a bp, coincident with the onset of the Bølling in western Europe; this was paralleled by increased summer temperatures. A striking feature is an early decline in Betula pollen and sedaDNA reads 300 years before the onset of the Younger Dryas (YD) in western Europe. Given the solid site chronology, this could indicate that the YD cooling started in Siberia and propagated westwards, or that the vegetation reacted to the inter-Allerød cooling at 13 100 cal a bp and did not recover during the late Allerød. During the YD, increases in steppe taxa such as Artemisia and Chenopodiaceae suggest drier conditions. At the onset of the Holocene, the vegetation around the lake reacted fast to the warmer conditions, as seen in the increase of arboreal taxa, especially Betula, and a decrease in herbs such as Artemisia and Cyperaceae.publishedVersio

Non-synchronous deposition of North Atlantic Ash Zone II in Greenland ice cores, and North Atlantic and Norwegian Sea sediments: an example of complex glacial-stage tephra transport

Tephra provides regional chronostratigraphical marker horizons that can link different climate archives with highly needed accuracy and precision. The results presented in this work exemplify, however, that the intermittent storage of tephra in ice sheets and during its subsequent iceberg transport, especially during glacial stages, constitutes a potential source of serious error for the application of tephrochronology to Nordic Seas and North Atlantic sediment archives. The peak shard concentration of the rhyolitic component of the North Atlantic Ash Zone II (NAAZ-II) tephra complex, often used to correlate marine and ice core records in Marine Isotope Stage (MIS) 3, is shown to lag the eruption event by ca. 100–400 years in some North Atlantic and Norwegian Sea cores. While still allowing for a correlation of archives on millennial timescales, this time delay in deposition is a major obstacle when addressing the lead–lag relationship on short timescales (years to centuries). A precise and accurate determination of lead–lag relationships between archives recording different parts of the climate system is crucial in order to test hypotheses about the processes leading to abrupt climate change and to evaluate results from climate models. Copyright # 2011 John Wiley & Sons, Ltd

Forcing of late Pleistocene ice volume by spatially variable insolation

Changes in Earth's orbit have been dubbed a pacemaker of Quaternary glacial-interglacial climate variability. However, the significance of latitudinally varying insolation as a dynamical forcing of late Pleistocene climate changes remains unclear. Here we use a model-free state-space reconstruction method to quantify the strength of the dynamical influence of locally varying summer energy on global ice volume, with orbitally independent age assignments. Our empirical approach suggests that integrated summer insolation at specific latitudes was a significant driver of ice volume during the past 800,000 years. Summer energy impact on ice volume is detected in a continuous latitudinal band at 50-90°N, consistent with the role of summer melting of Northern Hemisphere ice sheets predicted by Milankovitch theory. Insolation forcing at southern mid-latitudes strongly covaries with the canonical Milankovitch forcing, and coincides with the subtropical front and the mid-latitude westerlies, the modulation of which has been implicated in Quaternary climate changes. In contrast, the dynamics of summer energy forcing in the Northern Hemisphere south of the extent of ice sheets is different, possibly capturing ice volume sensitivity to latitudinal insolation gradients. Our results show that the importance of external forcing on late Pleistocene ice ages cannot be fully accounted for by a unique insolation forcing time series. The global ice volume response to spatially variable summer energy encompasses a range of physical processes that operate at different times of the year, including forcing signals with a wide spectrum of obliquity-to-precession frequency ratios

Eurasian Ice Sheet collapse was a major source of Meltwater Pulse 1A 14,600 years ago

Rapid sea-level rise caused by the collapse of large ice sheets is a threat to human societies. In the last deglacial period, the rate of global sea-level rise peaked at more than 4 cm yr−1 during Meltwater Pulse 1A, which coincided with the Bølling warming event some 14,650 years ago. However, the sources of the meltwater have proven elusive, and the contribution from Eurasian ice sheets has been considered negligible. Here, we present a regional carbon-14 calibration curve for the Norwegian Sea and recalibrate marine 14C dates linked to the Eurasian Ice Sheet retreat. We find that marine-based sectors of the Eurasian Ice Sheet collapsed at the Bølling transition and lost an ice volume of 4.5–7.9 m sea-level equivalents (SLE) over 500 years. During peak melting, 3.3–6.7 m SLE of ice was lost, potentially explaining up to half of Meltwater Pulse 1A. A mean meltwater flux of 0.2 Sv over 300 years was injected into the Norwegian Sea and the Arctic Ocean at a time when proxy evidence suggests vigorous Atlantic meridional overturning circulation. Our reconstruction shows that massive marine-based ice sheets can collapse in as little as 300–500 years

High‐resolution chronology of 24 000‐year long cores from two lakes in the Polar Urals, Russia, correlated with palaeomagnetic inclination records with a distinct event about 20 000 years ago

Based on radiocarbon dating, a tephra horizon, varve counts and palaeomagnetism, detailed age models covering the last ~24 k cal a bp, have been developed for the stratigraphy in the lakes Bolshoye Shchuchye and Maloye Shchuchye in the Polar Ural Mountains, Russia. The inclination curves from these lakes show nearly identical palaeomagnetic secular variations in the studied cores from both lakes, allowing for a precise correlation between the cores. A large and very distinct inclination deviation, named the Bolshoye Shchuchye Event, was identified in all cores retrieved from both lakes. It lasted over a period of 1245 years, from 20 470 to 19 225 cal a bp. The well-dated palaeomagnetic inclination graph offers a new possibility to correlate archives in this part of the Arctic for the last ~24 k cal a bp, probably also over longer distances. The sedimentation rate shows the same trend in all cores from both lakes, including high input during the Last Glacial Maximum and gradually lowering after ~18 k cal a bp to lower and stable Holocene values

Multidisciplinary investigation of a shallow near–shore landslide, Finneidfjord, Norway

The 1996 landslide near Finneidfjord, Norway, involved the displacement of c. 1 x 106 m3 of sediment. Failure initiated offshore and developed in a retrogressive manner, back-stepping 100 – 150 m inland, and removing a 250 m long section of the main North-South highway. The landslide caused the loss of four human lives, and may have been triggered by human activity (e.g., blasting for road works and/or placement of fill along the shore). Acquisition of an extensive and multi-disciplinary data set, including high-resolution swath bathymetry, 2D/3D seismic data, multiple short (up to 6 m) and two long (12 m and 14 m, respectively) sediment cores, and in situ Free-Fall Piezocone Penetrometer (FF-CPTU) profiles complemented with geotechnical laboratory data, has afforded detailed analysis of both the landslide morphology and stratigraphic controls. Using regional 2D parametric sub-bottom profiler (TOPAS) profiles and a targeted decimetre-resolution 3D Chirp seismic volume (950 m x 140 m), we focus on post-failure material transport/deposition, correlating the failure plane against one of several regionally extensive packets of high–amplitude, composite reflections. In seismic reflection data, the slide plane lies within a distinct, thin (< 0.5 m) stratigraphic bed of lower acoustic impedance than the background sedimentation (indicated by high amplitude reverse-polarity top reflection), which is extensively deformed or completely scoured by motion of the overlying material. Within the body of the landslide, two different flow facies are identified. Inversion of these broadband (1.5 – 13.0 kHz) seismic data has allowed the calculation of remote physical properties (using acoustic quality factor, Q), affording a depth and spatial assessment of the relationship between morphology and grain size. These remote physical properties have been correlated against high-resolution geotechnical data from core logs and FF-CPTU profiles, identifying the slide plane as a weak, laminated, clay-rich bed. This combined geophysical/geotechnical assessment of the landslide morphology and internal architecture supports previous work indicating a complex, multi-stage failure. These combined data illustrate how seafloor stability is strongly influenced by shallow subsurface structure, with the geotechnical properties and lateral continuity of stratified beds acting as a primary control on slide plane depth and failure probability