Differential uplift of three Pliocene sea level indicator sites in southern Argentina driven by upwelling asthenosphere through the Patagonian slab window

<div> Bivalve and gastropod shell beds deposited during the Early Pliocene (4.69-5.23 Ma) occur in uplifted outcrops (36 &#8211; 180 m above sea level) along the east coast of Patagonian Argentina. These rock units provide a record of sea level during a geologic period when atmospheric CO2 and temperatures were higher than today. As such, reconstructing the elevation of global mean sea level (GMSL) during this time allows us to better understand how sensitive ice sheets are to increased past and future warming. However, reconstructing GMSL from local sea level indicators is hindered by effects such as mantle dynamic topography and glacial isostatic adjustment (GIA) that cause local sea level to deviate from the global mean. Here we use geodynamic modeling to better understand this complex dynamic setting and quantify the amount of uplift along this coastline. </div><div> Despite being located on a relatively stable passive margin, significant variations in the elevation of the paleo shoreline indicators imply that the underlying convecting mantle is deforming the coastline. In particular, the subduction of the Chile Rise beginning ~18 Ma beneath Patagonia has generated a slab window underneath this region through which hot asthenosphere ascends. However, the former slab is still present deeper in the mantle, which causes a complex interplay between the downwelling slab and the upwelling asthenosphere. To quantify the effects of dynamic topography change since the Pliocene, we run 3D mantle convection simulations using the code ASPECT. We initialize our global model with a composite temperature structure derived from recent tomographic studies and a calibrated parameterization of upper mantle anelasticity. Independent estimates of pressure and temperature from thermobarometric calculations of proximal Pali-Aike xenoliths agree with the thermal structure of the tomography-based Earth model. We back-advect temperature perturbations and extract the resulting change in dynamic topography. Pairing GIA models and a suite of convection simulations in which we vary the viscosity and buoyancy structure with the observed differential paleo shoreline elevations allows us to forward model the most likely scenario for uplift along this coast. </div>

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The effect of lateral variations in Earth structure on Last Interglacial sea level

10.31223/x5sp73 ◽

2021 ◽

Author(s):

Jacqueline Austermann ◽

Mark Hoggard ◽

Konstantin Latychev ◽

Fred Richards ◽

Jerry Mitrovica

Keyword(s):

Sea Level ◽

Earth Structure ◽

Last Interglacial ◽

Level Indicator ◽

Mean Sea Level ◽

Mineral Physics ◽

Shear Wave Speed ◽

Global Mean Sea Level ◽

Lateral Variations ◽

Global Mean

It is generally agreed that the Last Interglacial (LIG; ~130-115ka) was a time when global average temperatures and global mean sea level were higher than they are today. However, the exact timing, magnitude, and spatial pattern of ice melt is much debated. One difficulty in extracting past global mean sea level from local observations is that their elevations need to be corrected for glacial isostatic adjustment (GIA), which requires knowledge of Earth’s internal viscoelastic structure. While this structure is generally assumed to be radially symmetric, evidence from seismology, geodynamics, and mineral physics indicates that large lateral variations in viscosity exist within the mantle. In this study, we construct a new model of Earth’s internal structure by converting shear wave speed into viscosity using parameterisations from mineral physics experiments and geodynamical constraints on Earth’s thermal structure. We use this 3D Earth structure, which includes both variations in lithospheric thickness and lateral variations in viscosity, to calculate the first 3D GIA prediction for LIG sea level. We find that the difference between predictions with and without lateral Earth structure can be meters to 10s of meters in the near field of former ice sheets, and up to a few meters in their far field. We demonstrate how forebulge dynamics and continental levering are affected by laterally varying Earth structure, with a particular focus on those sites with prominent LIG sea level records. Results from three 3D GIA calculations show that accounting for lateral structure acts to increase local sea level by up to ~1.5m at the Seychelles and minimally decrease it in Western Australia. We acknowledge that this result is only based on a few simulations, but if robust, this shift brings estimates of global mean sea level from these two sites into closer agreement with each other. We further demonstrate that simulations with a suitable radial viscosity profile can be used to locally approximate the 3D GIA result, but that these radial profiles cannot be found by simply averaging viscosity below the sea level indicator site.

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Developing an open-source 3D glacial isostatic adjustment modeling code using ASPECT

10.5194/egusphere-egu2020-3531 ◽

2020 ◽

Author(s):

Maaike Weerdesteijn ◽

Clinton Conrad ◽

John Naliboff ◽

Kate Selway

Keyword(s):

Open Source ◽

Sea Level ◽

Material Properties ◽

Adaptive Mesh Refinement ◽

Earth Model ◽

Surface Load ◽

Glacial Isostatic Adjustment ◽

Ice Load ◽

Isostatic Adjustment ◽

Ice Cap

Models of Glacial Isostatic Adjustment (GIA) processes are useful because they help us understand landscape evolution in past and current glaciated regions. Such models are sensitive to ice and ocean loading as well as to Earth material properties, such as viscosity. Many current GIA models assume radially-symmetric (layered) viscosity structures, but viscosity may vary laterally and these variations can have large effects on GIA modeling outputs. Here we present the potential of using ASPECT, an open-source finite element mantle-convection code that can handle lateral viscosity variations, for GIA modeling applications. ASPECT has the advantage of adaptive mesh refinement, making it computationally efficient, especially for problems such as GIA with large variations in strain rates. Furthermore, ASPECT is open-source, as will be the GIA extension, making it a valuable future tool for the GIA community.&#160;Our GIA extension is benchmarked using a similar case as in Martinec et al. (GJI, 2018), such that the performance of our GIA code can be compared to other GIA codes. In this case, a spherically symmetric, five-layer, incompressible, self-gravitating viscoelastic Earth model is used (Spada et al, GJI 2011). The surface load consists of a spherical ice cap centered at the North pole, and is applied as a Heaviside loading. The ice load remains constant with time, and thus we have not yet implemented the full sea level equation (SLE). Beyond this benchmark, we have incorporated lateral viscosity variations underneath the ice cap, to demonstrate the ability of efficiently implementing laterally-varying material properties in ASPECT.&#160;We show the possibilities, capabilities, and potential of ASPECT for GIA modeling. In the near future we will further develop the code with the sea level equation and an ocean basin, and will explore ASPECT&#8217;s current capability of using time-varying distributed surface loads. These functions will allow for modeling of GIA for realistic ice load scenarios imposed above potentially complex earth structures.

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Global ocean freshening, ocean mass increase and global mean sea level rise over 2005–2015

Scientific Reports ◽

10.1038/s41598-019-54239-2 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 5

Author(s):

William Llovel ◽

S. Purkey ◽

B. Meyssignac ◽

A. Blazquez ◽

N. Kolodziejczyk ◽

...

Keyword(s):

Sea Level ◽

Global Ocean ◽

Last Deglaciation ◽

Mean Sea Level ◽

Isostatic Adjustment ◽

Ocean Mass ◽

Grace Data ◽

Global Mean Sea Level ◽

Gravity Recovery ◽

Global Mean

AbstractGlobal mean sea level has experienced an unabated rise over the 20th century. This observed rise is due to both ocean warming and increasing continental freshwater discharge. We estimate the net ocean mass contribution to sea level by assessing the global ocean salt budget based on the unprecedented amount of in situ data over 2005–2015. We obtain the ocean mass trends of 1.30 ± 1.13 mm · yr−1 (0–2000 m) and 1.55 ± 1.20 mm · yr−1 (full depth). These new ocean mass trends are smaller by 0.63–0.88 mm · yr−1 compared to the ocean mass trend estimated through the sea level budget approach. Our result provides an independent validation of Gravity Recovery And Climate Experiment (GRACE)-based ocean mass trend and, in addition, places an independent constraint on the combined Glacial Isostatic Adjustment – the Earth’s delayed viscoelastic response to the redistribution of mass that accompanied the last deglaciation- and geocenter variations needed to directly infer the ocean mass trend based on GRACE data.

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Global Mean Sea Level: Indicator of Climate Change?

Science ◽

10.1126/science.219.4587.997 ◽

1983 ◽

Vol 219 (4587) ◽

pp. 997-997 ◽

Cited By ~ 11

Author(s):

J. HANSEN ◽

V. GORNITZ ◽

S. LEBEDEFF ◽

E. MOORE

Keyword(s):

Climate Change ◽

Sea Level ◽

Level Indicator ◽

Mean Sea Level ◽

Global Mean Sea Level ◽

Global Mean

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Exploring links between geodynamics and climate change

10.5194/egusphere-egu21-13877 ◽

2021 ◽

Author(s):

Mark Hoggard ◽

Fred Richards

Keyword(s):

Climate Change ◽

Sea Level ◽

Sedimentary Cover ◽

Ice Sheet ◽

Careful Consideration ◽

Dynamic Topography ◽

Low Carbon ◽

Level Indicator ◽

Geological Processes ◽

Warming World

Combating global climate change remains one of the greatest challenges facing humanity in the coming decades. Whilst oceanographers, ice sheet dynamicists, and atmospheric modellers all have an obvious role to play in leading efforts to tackle this problem, there remain many aspects that require careful consideration and cross-disciplinary interaction in other areas of the geosciences. In this talk, I will use selected examples to illustrate important links between geodynamics and climate change, including improving our understanding of its potential impacts and mitigation. The first concerns the role of mantle convection in influencing palaeo sea-level records and ice sheet dynamics. For example, Pliocene interglacial periods are commonly invoked as potential climatic analogues for the near-future conditions expected in our warming world, but there is considerable uncertainty over the extent to which important sea-level indicator sites have been perturbed, post-deposition, by convection-induced dynamic topography. The second link involves the growing shortage of metals that are key to the manufacture of technologies for low-carbon energy generation and storage. Tackling this shortfall requires an improvement in our ability to locate new, high-grade metal deposits, particularly those buried beneath shallow sedimentary cover. Novel geodynamical insights into the geological processes responsible for ore genesis will form a core component of narrowing the exploration search-space, and we have recently demonstrated this approach for sediment-hosted metal deposits. Through these case studies, I will show that it is primarily through developing an environment of cross-disciplinary discussion and financial support that our community is most likely to progress in understanding the potential impacts of climate change and how we may mitigate against them. Although one of the least well-studied components, the solid Earth is increasingly being recognised as a critical part of the climate system. Researchers working in topics as diverse as rock mechanics, seismology, convection modelling, and geochemistry all have a crucial role to play.

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Assessment of GRACE/GRACE Follow-On Estimates of Global Mean Ocean Mass Change

10.21203/rs.3.rs-1182933/v1 ◽

2021 ◽

Author(s):

Jae-Seung Kim ◽

Ki-Weon Seo ◽

Jianli Chen ◽

Clark Wilson

Keyword(s):

Sea Level ◽

Sea Water ◽

Ocean Dynamics ◽

Water Density ◽

Partial Explanation ◽

Steric Sea Level ◽

Isostatic Adjustment ◽

Ocean Mass ◽

Global Mean Sea Level ◽

Global Mean

Abstract Global mean sea level has increased ~3.5 mm/yr over several decades due to increases in ocean mass and changes in sea water density. Ocean mass, accounting for about two-thirds of the increase, can be directly measured by the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GFO) satellites. An independent measure is obtained by combining satellite altimetry (measuring total sea level change) and Argo float data (measuring steric changes associated with sea water density). Many previous studies have reported that the two estimates of global mean ocean mass (GMOM) change are in good agreement within stated confidence intervals. Recently, particularly since 2016, estimates by the two methods have diverged. A partial explanation appears to be a spurious variation in steric sea level data. An additional contributor may be deficiencies in Glacial Isostatic Adjustment (GIA) corrections and degree-1 spherical harmonic (SH) coefficients. We found that erroneous corrections for GIA contaminate GRACE/GFO estimates as time goes forward. Errors in GIA corrections affect degree-1 SH coefficients, and degree-1 errors may also be associated with ocean dynamics. Poor estimates of degree-1 SH coefficients are likely an important source of discrepancies in the two methods of estimating GMOM change.

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Global Mean Sea Level: Indicator of Climate Change?

Science ◽

10.1126/science.219.4587.997-a ◽

1983 ◽

Vol 219 (4587) ◽

pp. 997-998 ◽

Cited By ~ 2

Author(s):

R. ETKINS ◽

E. EPSTEIN

Keyword(s):

Climate Change ◽

Sea Level ◽

Level Indicator ◽

Mean Sea Level ◽

Global Mean Sea Level ◽

Global Mean

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Dynamic Topography Change of the Eastern United States Since 3 Million Years Ago

Science ◽

10.1126/science.1229180 ◽

2013 ◽

Vol 340 (6140) ◽

pp. 1560-1563 ◽

Cited By ~ 110

Author(s):

David B. Rowley ◽

Alessandro M. Forte ◽

Robert Moucha ◽

Jerry X. Mitrovica ◽

Nathan A. Simmons ◽

...

Keyword(s):

Sea Level ◽

Coastal Plain ◽

Mantle Convection ◽

Sedimentary Rocks ◽

Ice Sheets ◽

Glacial Isostatic Adjustment ◽

Eastern United States ◽

Dynamic Topography ◽

Isostatic Adjustment ◽

Global Sea Level

Sedimentary rocks from Virginia through Florida record marine flooding during the mid-Pliocene. Several wave-cut scarps that at the time of deposition would have been horizontal are now draped over a warped surface with a maximum variation of 60 meters. We modeled dynamic topography by using mantle convection simulations that predict the amplitude and broad spatial distribution of this distortion. The results imply that dynamic topography and, to a lesser extent, glacial isostatic adjustment account for the current architecture of the coastal plain and proximal shelf. This confounds attempts to use regional stratigraphic relations as references for longer-term sea-level determinations. Inferences of Pliocene global sea-level heights or stability of Antarctic ice sheets therefore cannot be deciphered in the absence of an appropriate mantle dynamic reference frame.

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Higher than present global mean sea level recorded by an Early Pliocene intertidal unit in Patagonia (Argentina)

Communications Earth & Environment ◽

10.1038/s43247-020-00067-6 ◽

2020 ◽

Vol 1 (1) ◽

Author(s):

Alessio Rovere ◽

Marta Pappalardo ◽

Sebastian Richiano ◽

Marina Aguirre ◽

Michael R. Sandstrom ◽

...

Keyword(s):

Sea Level ◽

Differential Gps ◽

Intertidal Environment ◽

Mean Sea Level ◽

Early Pliocene ◽

Isostatic Adjustment ◽

Strontium Isotope Stratigraphy ◽

Geological Unit ◽

Global Mean Sea Level ◽

Global Mean

AbstractReconstructions of global mean sea level from earlier warm periods in Earth’s history can help constrain future projections of sea level rise. Here we report on the sedimentology and age of a geological unit in central Patagonia, Argentina, that we dated to the Early Pliocene (4.69–5.23 Ma, 2σ) with strontium isotope stratigraphy. The unit was interpreted as representative of an intertidal environment, and its elevation was measured with differential GPS at ca. 36 m above present-day sea level. Considering modern tidal ranges, it was possible to constrain paleo relative sea level within ±2.7 m (1σ). We use glacial isostatic adjustment models and estimates of vertical land movement to calculate that, when the Camarones intertidal sequence was deposited, global mean sea level was 28.4 ± 11.7 m (1σ) above present. This estimate matches those derived from analogous Early Pliocene sea level proxies in the Mediterranean Sea and South Africa. Evidence from these three locations indicates that Early Pliocene sea level may have exceeded 20m above its present level. Such high global mean sea level values imply an ice-free Greenland, a significant melting of West Antarctica, and a contribution of marine-based sectors of East Antarctica to global mean sea level.

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Correcting Late Cenozoic Sea-Level Records for Dynamic Topography: Examples from Australia

10.5194/egusphere-egu21-12420 ◽

2021 ◽

Author(s):

Fred Richards ◽

Sophie Coulson ◽

Jacqueline Austermann ◽

Mark Hoggard ◽

Jerry Mitrovica

Keyword(s):

Sea Level ◽

Upper Mantle ◽

Ice Sheets ◽

Dynamic Topography ◽

Sea Level Changes ◽

Relative Sea Level ◽

Mean Sea Level ◽

Ice Volume ◽

Global Mean Sea Level ◽

Global Mean

Much of our understanding of ice sheet sensitivity to climatic forcing is derived from palaeoshoreline records of past sea-level. However, the present-day elevations of these sea-level markers reflect the integrated effect of both ice volume change and solid Earth processes. Accurately quantifying the latter contribution is therefore essential for making reliable inferences of past ice volume. While uncertainties associated with glacial isostatic adjustment (GIA) can be mitigated by focusing on sites far from ice sheets, the same is not true for mantle flow-driven dynamic topography, which is ubiquitous and can generate vertical motions of ~&#177;100 m on million-year timescales. As a result, improved knowledge of the spatio-temporal evolution of this transient topography is required to refine constraints on ice sheet stability and to guide modelling of future trajectories.Since the shortest wavelength and fastest evolving contributions to dynamic topography originate in the shallow mantle, reconstructing dynamic topography over 1&#8211;10 Myr timescales requires accurate models of Earth&#8217;s lithosphere and asthenosphere. Here, we construct these models by mapping upper mantle shear wave velocities from high-resolution surface wave tomographic models into thermomechanical structure using calibrated parameterisations of anelasticity at seismic frequency. Resulting numerical predictions of present-day dynamic topography are in good agreement with residual depth measurements, with particularly good fits obtained around Australia. In this region, predicted temperatures are also compatible with palaeogeotherms extracted from xenolith suites, indicating that present-day upper mantle structure is well characterised and that numerical &#8220;retrodictions&#8221; of vertical motions are more likely to be reliable. In addition, Australia is sufficiently distant from major ice sheets that uncertainty in GIA contributions to sea-level change are relatively small. These considerations, combined with new compilations of continent-wide sea-level indicators, make Australia a particularly promising location for separating out ice volume-driven global mean sea-level changes from local sea-level variations related to vertical land motions and gravitational effects.By back-advecting density perturbations from an ensemble of Earth models, we demonstrate that ~&#177;200 m relative sea-level changes across Australia since the Mid-Pliocene Warm Period (MPWP; &#8764;3 Ma) can be tied directly to changes in dynamic topography. Significantly, after removing this signal from observed relative sea-level changes,&#160; a consistent global mean sea-level during the MPWP of 12&#177;8 m above present is obtained, towards the lower end of previous estimates.

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