Glacial isostatic adjustment, relative sea level history and mantle viscosity: reconciling relative sea level model predictions for the U.S. East coast with geological constraints

Abstract. During the last glacial maximum, a large ice sheet covered Scandinavia, which depressed the earth's surface by several 100 m. In northern central Europe, mass redistribution in the upper mantle led to the development of a peripheral bulge. It has been subsiding since the begin of deglaciation due to the viscoelastic behaviour of the mantle. We analyse relative sea-level (RSL) data of southern Sweden, Denmark, Germany, Poland and Lithuania to determine the lithospheric thickness and radial mantle viscosity structure for distinct regional RSL subsets. We load a 1-D Maxwell-viscoelastic earth model with a global ice-load history model of the last glaciation. We test two commonly used ice histories, RSES from the Australian National University and ICE-5G from the University of Toronto. Our results indicate that the lithospheric thickness varies, depending on the ice model used, between 60 and 160 km. The lowest values are found in the Oslo Graben area and the western German Baltic Sea coast. In between, thickness increases by at least 30 km tracing the Ringkøbing-Fyn High. In Poland and Lithuania, lithospheric thickness reaches up to 160 km. However, the latter values are not well constrained as the confidence regions are large. Upper-mantle viscosity is found to bracket [2–7] × 1020 Pa s when using ICE-5G. Employing RSES much higher values of 2 × 1021 Pa s are obtained for the southern Baltic Sea. Further investigations should evaluate whether this ice-model version and/or the RSL data need revision. We confirm that the lower-mantle viscosity in Fennoscandia can only be poorly resolved. The lithospheric structure inferred from RSES partly supports structural features of regional and global lithosphere models based on thermal or seismological data. While there is agreement in eastern Europe and southwest Sweden, the structure in an area from south of Norway to northern Germany shows large discrepancies for two of the tested lithosphere models. The lithospheric thickness as determined with ICE-5G does not agree with the lithosphere models. Hence, more investigations have to be undertaken to sufficiently determine structures such as the Ringkøbing-Fyn High as seen with seismics with the help of glacial isostatic adjustment modelling.

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Holocene relative sea-level changes and glacial isostatic adjustment of the U.S. Atlantic coast

10.31223/osf.io/ecb5g ◽

2019 ◽

Author(s):

Simon Engelhart ◽

W. Peltier ◽

Benjamin Horton

Keyword(s):

Sea Level ◽

Atlantic Coast ◽

Glacial Isostatic Adjustment ◽

Sea Level Changes ◽

Relative Sea Level ◽

Isostatic Adjustment ◽

The U.S

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Relative sea-level data from the SEAMIS database compared to ICE-5G model predictions of glacial isostatic adjustment

Data in Brief ◽

10.1016/j.dib.2019.104600 ◽

2019 ◽

Vol 27 ◽

pp. 104600 ◽

Cited By ~ 2

Author(s):

Thomas Mann ◽

Maren Bender ◽

Thomas Lorscheid ◽

Paolo Stocchi ◽

Matteo Vacchi ◽

...

Keyword(s):

Sea Level ◽

Glacial Isostatic Adjustment ◽

Relative Sea Level ◽

Isostatic Adjustment ◽

Level Data ◽

Model Predictions

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Holocene relative sea-level changes and glacial isostatic adjustment of the U.S. Atlantic coast

Geology ◽

10.1130/g31857.1 ◽

2011 ◽

Vol 39 (8) ◽

pp. 751-754 ◽

Cited By ~ 85

Author(s):

S.E. Engelhart ◽

W.R. Peltier ◽

B.P. Horton

Keyword(s):

Sea Level ◽

Atlantic Coast ◽

Glacial Isostatic Adjustment ◽

Sea Level Changes ◽

Relative Sea Level ◽

Isostatic Adjustment ◽

The U.S

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Lithosphere and upper-mantle structure of the southern Baltic Sea estimated from modelling relative sea-level data with glacial isostatic adjustment

Solid Earth Discussions ◽

10.5194/sed-5-2483-2013 ◽

2013 ◽

Vol 5 (2) ◽

pp. 2483-2507

Author(s):

H. Steffen ◽

G. Kaufmann ◽

R. Lampe

Keyword(s):

Baltic Sea ◽

Sea Level ◽

Upper Mantle ◽

Glacial Isostatic Adjustment ◽

Relative Sea Level ◽

Southern Baltic Sea ◽

Lithospheric Thickness ◽

Isostatic Adjustment ◽

Mantle Viscosity ◽

Ice Model

Abstract. During the last glacial maximum, a large ice sheet covered Scandinavia, and the Earth's surface was depressed by several 100 m. Beyond the limit of this Fennoscandian ice sheet, mass redistribution in the upper mantle led to the development of peripheral bulges around the glaciated region. These once uplifted areas subside since the begin of deglaciation due to the viscoelastic behavior of the mantle. Parts of this subsiding region are located in northern central Europe in the coastal parts of Denmark, Germany and Poland. We analyze relative sea-level (RSL) data of these regions to determine the lithospheric thickness and radial mantle viscosity structure for distinct regional RSL subsets. We load a one-dimensional Maxwell-viscoelastic earth model with a global ice-load history model of the last glaciation. We test two commonly used ice histories, RSES from the Australian National University and Ice-5G from the University of Toronto. Our results indicate that the lithospheric thickness varies, depending on the ice model used, between 60 and 160 km. The lowest values are found in the Oslo Graben area and the western German Baltic Sea coast. In between, thickness increases by at least 30 km tracing the Fyn High. In Poland, lithospheric thickness values up to 160 km are reached. However, the latter values are not well constrained due to a low number of RSL data from the Polish area. Upper-mantle viscosity is found to bracket [2–7] × 1020 Pa s when using Ice-5G. Employing RSES much higher values of 2 × 1021 Pa s yield for the southern Baltic Sea, which suggests a revision of this ice-model version. We confirm that the lower-mantle viscosity in Fennoscandia can only be poorly resolved. The lithospheric structure inferred partly supports structural features of regional and global lithosphere models based on thermal or seismological data. While there is agreement in eastern Europe and southwest Sweden, the structure in an area from south of Norway to northern Germany shows large discrepancies for two of the tested models. It thus remains challenging to sufficiently determine the Fyn High as seen with seismics with the help of glacial isostatic adjustment modelling.

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Inferring mantle viscosity through data assimilation of relative sea level observations in a glacial isostatic adjustment model

10.5194/egusphere-egu21-1261 ◽

2021 ◽

Author(s):

Reyko Schachtschneider ◽

Jan Saynisch-Wagner ◽

Volker Klemann ◽

Meike Bagge ◽

Maik Thomas

Keyword(s):

Data Assimilation ◽

Sea Level ◽

Glacial Isostatic Adjustment ◽

Layer Model ◽

Relative Sea Level ◽

Isostatic Adjustment ◽

Mantle Viscosity ◽

Level Data ◽

The Time Domain ◽

Spectral Finite Element

We suggest to apply data assimilation in glacial isostatic adjustment (GIA) to constrain the mantle viscosity structure based on sea level observations. We apply the Parallel Data Assimilation Framework (PDAF) to assimilate sea level data into the time-domain spectral-finite element code VILMA in order to obtain better estimates of the mantle viscosity structure. In a first step, we reduce to a spherically symmetric earth structure and prescribe the glaciation history. A particle filter is used to propagate an ensemble of models in time. At epochs when observations are available, each particle's performance is estimated and the particles are resampled based on their performance to form a new ensemble that better resembles the true viscosity distribution.Using this algorithm, we show the ability to recover mantle viscosities from a set of synthetic relative sea level observations. Those synthetic observations are obtained from a reference run with a given viscosity structure that defines the target viscosity values in our experiments. The viscosity estimation is applied to a three-layer model with an elastic lithosphere and two mantle layers, and to a multi-layer model with a smoother viscosity profile. We use various subsets of realistic observation locations (e.g. only observations from Fennoscandia) and show that it is possible to obtain the target viscosity values in those cases. We also vary the time from which observations are available to evolve the test cases towards a realistic scenario for the availability of relative sea level observations. The most relevant cases start at 26.5ka BP and at 10ka BP as they mark the beginning of the maximum glaciation and the end of deglaciation with a larger amount of observations following, respectively, and end at present day.

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Holocene relative sea-level changes and glacial isostatic adjustment of the U.S. Atlantic coast

Quaternary International ◽

10.1016/j.quaint.2012.08.393 ◽

2012 ◽

Vol 279-280 ◽

pp. 207

Author(s):

Benjamin Horton

Keyword(s):

Sea Level ◽

Atlantic Coast ◽

Glacial Isostatic Adjustment ◽

Sea Level Changes ◽

Relative Sea Level ◽

Isostatic Adjustment ◽

The U.S

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Comparing a thermo-mechanical Weichselian ice sheet reconstruction to GIA driven reconstructions: aspects of earth response and ice configuration

Solid Earth Discussions ◽

10.5194/sed-5-2345-2013 ◽

2013 ◽

Vol 5 (2) ◽

pp. 2345-2388 ◽

Cited By ~ 1

Author(s):

P. Schmidt ◽

B. Lund ◽

J-O. Näslund

Keyword(s):

Sea Level ◽

Ice Sheet ◽

Younger Dryas ◽

Slow Phase ◽

Glacial Isostatic Adjustment ◽

Relative Sea Level ◽

Isostatic Adjustment ◽

Earth Models ◽

Uplift Rates ◽

Best Fit

Abstract. In this study we compare a recent reconstruction of the Weichselian ice-sheet as simulated by the University of Main ice-sheet model (UMISM) to two reconstructions commonly used in glacial isostatic adjustment (GIA) modeling: ICE-5G and ANU (also known as RSES). The UMISM reconstruction is carried out on a regional scale based on thermo-mechanical modelling whereas ANU and ICE-5G are global models based on the sea-level equation. The Weichselian ice-sheet in the three models are compared directly in terms of ice volume, extent and thickness, as well as in terms of predicted glacial isostatic adjustment in Fennoscandia. The three reconstructions display significant differences. UMISM and ANU includes phases of pronounced advance and retreat prior to the last glacial maximum (LGM), whereas the thickness and areal extent of the ICE-5G ice-sheet is more or less constant up until LGM. The final retreat of the ice-sheet initiates at earliest time in ICE-5G and latest in UMISM, while ice free conditions are reached earliest in UMISM and latest in ICE-5G. The post-LGM deglaciation style also differs notably between the ice models. While the UMISM simulation includes two temporary halts in the deglaciation, the later during the Younger Dryas, ANU only includes a decreased deglaciation rate during Younger Dryas and ICE-5G retreats at a relatively constant pace after an initial slow phase. Moreover, ANU and ICE-5G melt relatively uniformly over the entire ice-sheet in contrast to UMISM which melts preferentially from the edges. We find that all three reconstructions fit the present day uplift rates over Fennoscandia and the observed relative sea-level curve along the Ångerman river equally well, albeit with different optimal earth model parameters. Given identical earth models, ICE-5G predicts the fastest present day uplift rates and ANU the slowest, ANU also prefers the thinnest lithosphere. Moreover, only for ANU can a unique best fit model be determined. For UMISM and ICE-5G there is a range of earth models that can reproduce the present day uplift rates equally well. This is understood from the higher present day uplift rates predicted by ICE-5G and UMISM, which results in a bifurcation in the best fit mantle viscosity. Comparison of the uplift histories predicted by the ice-sheets indicate that inclusion of relative sea-level data in the data fit can reduce the observed ambiguity. We study the areal distributions of present day residual surface velocities in Fennoscandia and show that all three reconstructions generally over-predict velocities in southwestern Fennoscandia and that there are large differences in the fit to the observational data in Finland and northernmost Sweden and Norway. These difference may provide input to further enhancements of the ice-sheet reconstructions.

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Late Holocene sea-level changes and isostasy in western Denmark

Quaternary Research ◽

10.1016/j.yqres.2006.05.004 ◽

2006 ◽

Vol 66 (2) ◽

pp. 288-302 ◽

Cited By ~ 42

Author(s):

W. Roland Gehrels ◽

Katie Szkornik ◽

Jesper Bartholdy ◽

Jason R. Kirby ◽

Sarah L. Bradley ◽

...

Keyword(s):

Salt Marsh ◽

Sea Level ◽

Salt Marshes ◽

Late Holocene ◽

Glacial Isostatic Adjustment ◽

Sea Level Changes ◽

Relative Sea Level ◽

Isostatic Adjustment ◽

Tidal Embayment ◽

Made In

AbstractCores and exposed cliff sections in salt marshes around Ho Bugt, a tidal embayment in the northernmost part of the Danish Wadden Sea, were subjected to 14C dating and litho- and biostratigraphical analyses to reconstruct paleoenvironmental changes and to establish a late Holocene relative sea-level history. Four stages in the late Holocene development of Ho Bugt can be identified: (1) groundwater-table rise and growth of basal peat (from at least 2300 BC to AD 0); (2) salt-marsh formation (0 to AD 250); (3) a freshening phase (AD 250 to AD 1600?), culminating in the drying out of the marshes and producing a distinct black horizon followed by an aeolian phase with sand deposition; and (4) renewed salt-marsh deposition (AD 1600? to present). From 16 calibrated AMS radiocarbon ages on fossil plant fragments and 4 calibrated conventional radiocarbon ages on peat, we reconstructed a local relative sea-level history that shows a steady sea-level rise of 4 m since 4000 cal yr BP. Contrary to suggestions made in the literature, the relative sea-level record of Ho Bugt does not contain a late Holocene highstand. Relative sea-level changes at Ho Bugt are controlled by glacio-isostatic subsidence and can be duplicated by a glacial isostatic adjustment model in which no water is added to the world's oceans after ca. 5000 cal yr BP.

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Parameters controlling mid-Holocene highstand in Glacial Isostatic Adjustment modelling

10.5194/egusphere-egu21-4224 ◽

2021 ◽

Author(s):

Tanghua Li ◽

Stephen Chua ◽

Nicole Khan ◽

Patrick Wu ◽

Benjamin Horton

Keyword(s):

Southeast Asia ◽

Sea Level ◽

Late Holocene ◽

Ice Sheets ◽

Thickness Variation ◽

Glacial Isostatic Adjustment ◽

Lithospheric Thickness ◽

Isostatic Adjustment ◽

Mantle Viscosity ◽

Open Questions

Holocene relative sea-level (RSL) records from regions distal from ice sheets (far-field) are commonly characterized by a mid-Holocene highstand, when RSL reached higher than present levels. The magnitude and timing of the mid-Holocene highstand varies spatially due to hydro-isostatic processes including ocean syphoning and continental levering. While there are open questions regarding the timing, magnitude and source of ice-equivalent sea level in the middle to late Holocene.Here, we compare Glacial Isostatic Adjustment (GIA) model predictions to a standardized database of sea-level index points (SLIPs) from Southeast Asia where we have near-complete Holocene records. The database has more than 130 SLIPs that span the time period from ~9.5 ka BP to present. We investigate the sensitivity of mid-Holocene RSL predictions to GIA parameters, including the lateral lithospheric thickness variation, mantle viscosity (both 1D and 3D), and deglaciation history from different ice sheets (e.g., Laurentide, Fennoscandia, Antarctica).We compute gravitationally self-consistent RSL histories for the GIA model with time dependent coastlines and rotational feedback using the Coupled Laplace-Finite Element Method. The preliminary results show that the timing of the highstand is mainly controlled by the deglaciation history (ice-equivalent sea level), while the magnitude is dominated by Earth parameters (e.g., lithospheric thickness, mantle viscosity). We further investigate whether there is meltwater input during middle to late Holocene and whether the RSL records from Southeast Asia can reveal the meltwater source, like Antarctica.

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