Deglaciation Of Fennoscandia Research Articles

Human-mediated introduction of geoengineering earthworms in the Fennoscandian arctic

It is now well established that European earthworms are re-shaping formerly glaciated forests in North America with dramatic ecological consequences. However, few have considered the potential invasiveness of this species assemblage in the European arctic. Here we argue that some earthworm species (Lumbricus rubellus, Lumbricus terrestris and Aporrectodea sp.) with great geomorphological impact (geoengineering species) are non-native and invasive in the Fennoscandian arctic birch forests, where they have been introduced by agrarian settlers and most recently through recreational fishing and gardening. Our exploratory surveys indicate no obvious historical dispersal mechanism that can explain early arrival of these earthworms into the Fennoscandian arctic: that is, these species do not appear to establish naturally along coastlines mimicking conditions following deglaciation in Fennoscandia, nor were they spread by early native (Sami) cultures. The importance of anthropogenic sources and the invasive characteristics of L. rubellus and Aporrectodea sp. in the arctic is evident from their radiation outwards from abandoned farms and modern cabin lawns into adjacent arctic birch forests. They appear to outcompete previously established litter-dwelling earthworm species (i.e. Dendrobaena octaedra) that likely colonized the Fennoscandian landscape rapidly following deglaciation via hydrochory and/or dispersal by early Sami settlements. The high geoengineering earthworm biomasses, their recognized ecological impact in other formerly glaciated environments, and their persistence once established leads us to suggest that geoengineering earthworms may pose a potent threat to some of the most remote and protected arctic environments in northern Europe.

Deglaciation of Fennoscandia

Abstract To provide a new reconstruction of the deglaciation of the Fennoscandian Ice Sheet, in the form of calendar-year time-slices, which are particularly useful for ice sheet modelling, we have compiled and synthesized published geomorphological data for eskers, ice-marginal formations, lineations, marginal meltwater channels, striae, ice-dammed lakes, and geochronological data from radiocarbon, varve, optically-stimulated luminescence, and cosmogenic nuclide dating. This is summarized as a deglaciation map of the Fennoscandian Ice Sheet with isochrons marking every 1000 years between 22 and 13 cal kyr BP and every hundred years between 11.6 and final ice decay after 9.7 cal kyr BP. Deglaciation patterns vary across the Fennoscandian Ice Sheet domain, reflecting differences in climatic and geomorphic settings as well as ice sheet basal thermal conditions and terrestrial versus marine margins. For example, the ice sheet margin in the high-precipitation coastal setting of the western sector responded sensitively to climatic variations leaving a detailed record of prominent moraines and other ice-marginal deposits in many fjords and coastal valleys. Retreat rates across the southern sector differed between slow retreat of the terrestrial margin in western and southern Sweden and rapid retreat of the calving ice margin in the Baltic Basin. Our reconstruction is consistent with much of the published research. However, the synthesis of a large amount of existing and new data support refined reconstructions in some areas. For example, the LGM extent of the ice sheet in northwestern Russia was located far east and it occurred at a later time than the rest of the ice sheet, at around 17–15 cal kyr BP. We also propose a slightly different chronology of moraine formation over southern Sweden based on improved correlations of moraine segments using new LiDAR data and tying the timing of moraine formation to Greenland ice core cold stages. Retreat rates vary by as much as an order of magnitude in different sectors of the ice sheet, with the lowest rates on the high-elevation and maritime Norwegian margin. Retreat rates compared to the climatic information provided by the Greenland ice core record show a general correspondence between retreat rate and climatic forcing, although a close match between retreat rate and climate is unlikely because of other controls, such as topography and marine versus terrestrial margins. Overall, the time slice reconstructions of Fennoscandian Ice Sheet deglaciation from 22 to 9.7 cal kyr BP provide an important dataset for understanding the contexts that underpin spatial and temporal patterns in retreat of the Fennoscandian Ice Sheet, and are an important resource for testing and refining ice sheet models.

Investigating the mechanisms leading to the deglaciation of past continental northern hemisphere ice sheets with the CLIMBER–GREMLINS coupled model

A coupling procedure between a climate model of intermediate complexity (CLIMBER-2.3) and a 3-dimensional thermo-mechanical ice-sheet model (GREMLINS) has been elaborated. The resulting coupled model describes the evolution of atmosphere, ocean, biosphere, cryosphere and their mutual interactions. It is used to perform several simulations of the Last Deglaciation period to identify the physical mechanisms at the origin of the deglaciation process. Our baseline experiment, forced by insolation and atmospheric CO 2, produces almost complete deglaciation of past northern hemisphere continental ice sheets, although ice remains over the Cordilleran region at the end of the simulation and also in Alaska and Eastern Siberia. Results clearly demonstrate that, in this study, the melting of the North American ice sheet is critically dependent on the deglaciation of Fennoscandia through processes involving switches of the thermohaline circulation from a glacial mode to a modern one and associated warming of the northern hemisphere. A set of sensitivity experiments has been carried out to test the relative importance of both forcing factors and internal processes in the deglaciation mechanism. It appears that the deglaciation is primarily driven by insolation. However, the atmospheric CO 2 modulates the timing of the melting of the Fennoscandian ice sheet, and results relative to Laurentide illustrate the existence of threshold CO 2 values, that can be translated in terms of critical temperature, below which the deglaciation is impeded. Finally, we show that the beginning of the deglaciation process of the Laurentide ice sheet may be influenced by the time at which the shift of the thermohaline circulation from one mode to the other occurs.

Glacial isostatic adjustment in Fennoscandia for a laterally heterogeneous earth

Glaciation and deglaciation in Fennoscandia during the last glacial cycles has significantly perturbed the Earth’s equilibrium figure. Changes in the Earth’s solid and geoidal surfaces due to external and internal mass redistributions are recorded in sequences of ancient coastlines, now either submerged or uplifted, and are still visible in observations of present-day motions of the surface and glacially induced anomalies in the Earth’s gravitational field. These observations become increasingly sophisticated with the availability of GPS measurements and new satellite gravity missions. Observational evidence of the mass changes is widely used to constrain the radial viscosity structure of the Earth’s mantle. However, lateral changes in earth model properties are usually not taken into account, as most global models of glacial isostatic adjustment assume radial symmetry for the earth model. This simplifying assumption contrasts with seismological evidence of significant lateral variations in the Earth’s crust and upper mantle throughout the Fennoscandian region. We compare predictions of glacial isostatic adjustment based on an ice model over the Fennoscandian region for the last glacial cycle for both radially symmetric and fully 3-D earth models. Our results clearly reveal the importance of lateral variations in lithospheric thickness and asthenospheric viscosity for glacially induced model predictions. Relative sea-level predictions can differ by up to 10–20m, uplift rate predictions by 1–3mmyr−1 and free-air gravity anomaly predictions by 2–4mGal when a realistic 3-D earth structure as proposed by seismic modelling is taken into account.

New trends in global tectonics

The last 3.0 Ma represents a period of extraordinarily active geodynamic forces leading to a drastically changed land relief and hypsographic mass distribution. This linked to the initiation of Quaternary-typ ice ages. Sub-crustal phase transition may generate abrupt loss in lithospheric ridigity. Nappe thrusting is another important factor in mega-tectonics; its rates and processes need clarification, however. Intra-plate seismotectonics have become an important issue, and much is to be learned. At the deglaciation of Fennoscandia when the rate of uplift was in the order of tens of centimeters per year, the seismic activity was very intense. There seems to be an interrelation between Earth's rate of rotation and the temporal and spatial distribution of earthquakes.

Flexural rigidity of Fennoscandia inferred from the postglacial uplift

The Earth's response to glacial loading/unloading offers exceptional promise for the study of the physical properties of the lithosphere. In particular, tilting of paleoshorelines is very sensitive to the lithosphere rigidity. To determine the flexural rigidity, the isostatic response to deglaciation in Fennoscandia is modeled using an Earth model with a layered mantle viscosity overlain by an elastic lithosphere. The flexural rigidity and asthenosphere viscosity is allowed to vary to get a match between theoretical and observed present rate of uplift and tilting of paleoshorelines. Five different ice thickness models are used. For a relatively thin ice (2500 m in central areas) the resulting flexural rigidity is more or less uniform over Fennoscandia, with a value of 1023 N m (elastic thickness te ≈ 20 km). This is regarded as minimum for the flexural rigidity of central Fennoscandia. The pattern of the present rate of uplift and the tilts of the paleoshorelines of the area also sets an upper bound of the flexural rigidity, 2.5 × 1025 N m (te ≈ 110 km) in more central areas of Fennoscandia. The flexural rigidity at the western coast of Norway does not seem to exceed 1023 N m (te ≈ 50 km). The most likely glacier model gives a flexural rigidity of 1023 N m (te ≈ 20 km) at the Norwegian coast, increasing to above 1024 N m (te ≈ 50 km) in central parts of Fennoscandia.

Viscosity and thickness of the asthenosphere detected from the Fennoscandian uplift

The earth's response to the deglaciation in Fennoscandia is modelled using a layered viscous model with an elastic lithosphere. The modelled tilting of palaeoshorelines at particular locations peripheral to the former ice load and the pattern of the present rate of uplift consistent with the observations strongly suggest a low-viscosity asthenosphere. Earth models without a low-viscosity asthenosphere give significant mismatch to the present rate of uplift, and are unable to mimic the observed tilting of palaeoshorelines. Models with a viscosity of the lower mantle of 1.0–2.0 × 10 21 Pa s, and a viscosity of the upper mantle of 0.7–1.0 × 10 21 Pa s overlain by low-viscosity asthenosphere with a thickness ranging from 25 to 100 km, fit equally well with the observations. It is suggested strongly that the asthenosphere has a thickness of less than 150 km and a viscosity of less than 7.0 × 10 19 Pa s.

Glaciofluvial canyons and their relation to the Late Weichselian deglaciation in Fennoscandia

Glaciofluvial canyons and their relation to the Late Weichselian deglaciation in Fennoscandia

The present rate of uplift of Fennoscandia implies a low‐viscosity asthenosphere

ABSTRACTThe rate of displacement in Fennoscandia has been intensively discussed for many years. It is now widely accepted to be an isostatic response of the glacial history of the area.The Earth's present response to deglaciation in Fennoscandia is simulated using a three‐dimensional (3D), viscoelastic model in which the asthenosphere and mantle viscosity are allowed to vary so that the maximum rate of present uplift matches its observed value. The deglaciation history is considered to be known, and the C14‐datings are converted to sidereal years. The pattern of the present uplift gives a firm match with the observed data when a low‐viscosity asthenosphere is introduced. Assuming a 15,000 years load cycle, i.e. the glacier was applied to the surface for 15,000 years before the melting started, the best fitting earth viscosity model is a 1024 Nm lithosphere overlying a 75 km‐thick 2.0 × 1019 Pas asthenosphere and a 1.2 × 1021 Pas mantle. The simulations suggest a remaining maximum uplift of 40 m.

Geoidal-eustatic changes induced by the deglaciation of fennoscandia

Relative sea level changes in Fennoscandia have long been known to be a result of processes connected to the last glaciation. The post-glacial sea level changes have commonly been thought of as a result of global variations of the ocean water volume and isostatic movements (connected to the deglaciation). However, changes of the ice loads bring about gravimetric changes, and resulting eustatic changes will vary significantly over the globe. The importance of the geoid changes related to the deglaciation in Fennoscandia is illustrated by theoretical simulations, which show that the resulting sea level movements differ significantly over the globe. During a fast deglaciation there is not a worldwide rise in sea level due to increased volume of ocean water, but in the region near the former glacier there may actually be a fall in sea level. By simulations of the deglaciation history it is also shown that the associated sea level history varies even within a small area, and may differ by up to 20–30 m from the Barents Sea to central Scandinavia. This is really a significant difference, compared to the overall pattern of sea level change of 100 m for the last 15 ka. Thus no eustatic curve is valid globally.