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

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

<p>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 ~±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.</p><p>Since the shortest wavelength and fastest evolving contributions to dynamic topography originate in the shallow mantle, reconstructing dynamic topography over 1–10 Myr timescales requires accurate models of Earth’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 “retrodictions” 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.</p><p>By back-advecting density perturbations from an ensemble of Earth models, we demonstrate that ~±200 m relative sea-level changes across Australia since the Mid-Pliocene Warm Period (MPWP; ∼3 Ma) can be tied directly to changes in dynamic topography. Significantly, after removing this signal from observed relative sea-level changes,  a consistent global mean sea-level during the MPWP of 12±8 m above present is obtained, towards the lower end of previous estimates.</p>

Global Mean Sea-level Changes in the Last Two Millennia

2021 ◽  
Author(s):  
Nidheesh Gangadharan ◽  
Hugues Goosse ◽  
David Parkes ◽  
Heiko Goelzer
Keyword(s):  
Thermal Expansion ◽  
Sea Level ◽  
Ice Sheets ◽  
Sea Level Changes ◽  
Contributing Factors ◽  
Mean Sea Level ◽  
Global Mean Sea Level ◽  
The Individual ◽  
Instrumental Records ◽  
Global Mean

<p>Instrumental records show that global mean sea level (GMSL) rose by approximately 15 cm in the 20<sup>th</sup> Century, with estimates of contributing factors suggesting the major components are ocean thermal expansion and melting of continental ice sheets and glaciers. However, little is known about the individual contributions to GMSL changes over the preindustrial common era (PCE) and the potential differences in the mechanisms controlling those changes between different time periods. Here, we describe the GMSL changes in the PCE by comparing proxy-based reconstructions with estimates derived from model experiments. The ocean thermal expansion is estimated on the basis of Coupled (Paleoclimate) Model Intercomparison Project (CMIP/PMIP) experiments. The contributions of ice sheets and glaciers are based on simulations with an ice-sheet model (IMAU-ICE) and a global glacier model (The Open Global Glacier Model), respectively. We also describe the thermal expansion response in the different ocean basins over the last millennium. The findings provide new insights on the current anthropogenic warming and sea-level rise in a wider context.</p>

scholarly journals Modelling ice sheet evolution and atmospheric CO<sub>2</sub> during the Late Pliocene

2019 ◽  
Author(s):  
Constantijn J. Berends ◽  
Bas de Boer ◽  
Aisling M. Dolan ◽  
Daniel J. Hill ◽  
Roderik S. W. van de Wal
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Mean Sea Level ◽  
Late Pliocene ◽  
Proxy Records ◽  
Global Mean Sea Level ◽  
Global Mean

Abstract. In order to investigate the relation between ice sheets and climate in a warmer-than-present world, recent research has focussed on the Late Pliocene, 3.6 to 2.58 million years ago. It is the most recent period in Earth history when such a climate state existed for a significant duration of time. Marine Isotope Stage (MIS) M2 (~ 3.3 Myr ago) is a strong positive excursion in benthic oxygen records in the middle of the otherwise warm and relatively stable Late Pliocene. However, the relative contributions to the benthic δ18O signal from deep-ocean cooling and growing ice sheets are still uncertain. Here, we present results from simulations of the late Pliocene with a hybrid ice-sheet–climate model, showing a reconstruction of ice sheet geometry, sea-level and atmospheric CO2. Initial experiments simulating the last four glacial cycles indicate that this model yields results which are in good agreement with proxy records in terms of global mean sea level, benthic oxygen isotope abundance, ice core-derived surface temperature and atmospheric CO2 concentration. For the Late Pliocene, our results show an atmospheric CO2 concentration during MIS M2 of 233–249 ppmv, and a drop in global mean sea level of 10 to 25 m. Uncertainties are larger during the warmer periods leading up to and following MIS M2. CO2 concentrations during the warm intervals in the Pliocene, with sea-level high stands of 8–14 m above present-day, varied between 320 and 400 ppmv, lower than indicated by some proxy records but in line with earlier model reconstructions.

Thermosteric Effects on Interannual and Long-term Global Mean Sea Level Changes

2006 ◽  
Vol 80 (5) ◽  
pp. 240-247 ◽  
Author(s):  
J. L. Chen ◽  
C. R. Wilson ◽  
B. D. Tapley ◽  
X. G. Hu
Keyword(s):  
Sea Level ◽  
Sea Level Changes ◽  
Mean Sea Level ◽  
Global Mean Sea Level ◽  
Global Mean

scholarly journals Challenges and research priorities to understand interactions between climate, ice sheets and global mean sea level during past interglacials

2019 ◽  
Vol 219 ◽  
pp. 308-311 ◽  
Author(s):  
Emilie Capron ◽  
Alessio Rovere ◽  
Jacqueline Austermann ◽  
Yarrow Axford ◽  
Natasha L.M. Barlow ◽  
...  
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Research Priorities ◽  
Mean Sea Level ◽  
Global Mean Sea Level ◽  
Global Mean

scholarly journals Kinematics of global mean thermosteric sea level during 1993–2019

2021 ◽  
Vol 11 (1) ◽  
pp. 75-82
Author(s):  
H. Bâki İz
Keyword(s):  
Time Series ◽  
Sea Level ◽  
Temperature Gradients ◽  
Sea Surface ◽  
Sea Level Changes ◽  
Mean Sea Level ◽  
Mean Sea Surface ◽  
Global Mean Sea Level ◽  
Global Sea Level ◽  
Global Mean

Abstract Because oceans cover 71% of Earth’s surface, ocean warming, consequential for thermal expansion of sea water, has been the largest contributor to the global mean sea level rise averaged over the 20 th and the early 21 st century. This study first generates quasi-observed monthly globally averaged thermosteric sea level time series by removing the contributions of global mean sea level budget components, namely, Glaciers, Greenland, Antarctica, and Terrestrial Water Storage from satellite altimetry measured global sea level changes during 1993–2019. A baseline kinematic model with global mean thermosteric sea level trend and a uniform acceleration is solved to evaluate the performance of a rigorous mixed kinematic model. The model also includes coefficients of monthly lagged 60 yearlong cumulative global mean sea surface temperature gradients and control variables of lunisolar origins and representations for first order autoregressive disturbances. The mixed kinematic model explains 94% (Adjusted R 2)1 of the total variability in quasi-observed monthly and globally averaged thermosteric time series compared to the 46% of the baseline kinematic model’s Adjusted R 2. The estimated trend, 1.19±0.03 mm/yr., is attributed to the long-term ocean warming. Whereas eleven statistically significant (α = 0.05) monthly lagged cumulative global mean sea surface temperature gradients each having a memory of 60 years explain the remainder transient global mean thermosteric sea level changes due to the episodic ocean surface warming and cooling during this period. The series also exhibit signatures of a statistically significant contingent uniform global sea level acceleration and periodic lunisolar forcings.

On the recent global mean sea level changes: Trend extraction and El Niño's impact

2013 ◽  
Vol 345 (4) ◽  
pp. 167-175 ◽  
Author(s):  
Mahdi Haddad ◽  
Habib Taibi ◽  
Si Mohammed Mohammed Arezki
Keyword(s):  
Sea Level ◽  
Sea Level Changes ◽  
Mean Sea Level ◽  
Trend Extraction ◽  
Global Mean Sea Level ◽  
Global Mean

scholarly journals The land-ice contribution to 21st-century dynamic sea level rise

Ocean Science ◽  
2014 ◽  
Vol 10 (3) ◽  
pp. 485-500 ◽  
Author(s):  
T. Howard ◽  
J. Ridley ◽  
A. K. Pardaens ◽  
R. T. W. L. Hurkmans ◽  
A. J. Payne ◽  
...  
Keyword(s):  
Sea Level ◽  
21St Century ◽  
Sea Level Change ◽  
Sea Level Changes ◽  
Mean Sea Level ◽  
Ice Melt ◽  
Level Change ◽  
Global Mean Sea Level ◽  
Global Mean ◽  
Dynamic Sea Level

Abstract. Climate change has the potential to influence global mean sea level through a number of processes including (but not limited to) thermal expansion of the oceans and enhanced land ice melt. In addition to their contribution to global mean sea level change, these two processes (among others) lead to local departures from the global mean sea level change, through a number of mechanisms including the effect on spatial variations in the change of water density and transport, usually termed dynamic sea level changes. In this study, we focus on the component of dynamic sea level change that might be given by additional freshwater inflow to the ocean under scenarios of 21st-century land-based ice melt. We present regional patterns of dynamic sea level change given by a global-coupled atmosphere–ocean climate model forced by spatially and temporally varying projected ice-melt fluxes from three sources: the Antarctic ice sheet, the Greenland Ice Sheet and small glaciers and ice caps. The largest ice melt flux we consider is equivalent to almost 0.7 m of global mean sea level rise over the 21st century. The temporal evolution of the dynamic sea level changes, in the presence of considerable variations in the ice melt flux, is also analysed. We find that the dynamic sea level change associated with the ice melt is small, with the largest changes occurring in the North Atlantic amounting to 3 cm above the global mean rise. Furthermore, the dynamic sea level change associated with the ice melt is similar regardless of whether the simulated ice fluxes are applied to a simulation with fixed CO2 or under a business-as-usual greenhouse gas warming scenario of increasing CO2.

scholarly journals Modelling ice sheet evolution and atmospheric CO<sub>2</sub> during the Late Pliocene

2019 ◽  
Vol 15 (4) ◽  
pp. 1603-1619 ◽  
Author(s):  
Constantijn J. Berends ◽  
Bas de Boer ◽  
Aisling M. Dolan ◽  
Daniel J. Hill ◽  
Roderik S. W. van de Wal
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Mean Sea Level ◽  
Late Pliocene ◽  
Proxy Records ◽  
Global Mean Sea Level ◽  
Global Mean

Abstract. In order to investigate the relation between ice sheets and climate in a warmer-than-present world, recent research has focussed on the Late Pliocene, 3.6 to 2.58 million years ago. It is the most recent period in Earth's history when such a warm climate state existed for a significant duration of time. Marine Isotope Stage (MIS) M2 (∼3.3 Myr ago) is a strong positive excursion in benthic oxygen records in the middle of the otherwise warm and relatively stable Late Pliocene. However, the relative contributions to the benthic δ18O signal from deep ocean cooling and growing ice sheets are still uncertain. Here, we present results from simulations of the Late Pliocene with a hybrid ice-sheet–climate model, showing a reconstruction of ice sheet geometry, sea level and atmospheric CO2. Initial experiments simulating the last four glacial cycles indicate that this model yields results which are in good agreement with proxy records in terms of global mean sea level, benthic oxygen isotope abundance, ice-core-derived surface temperature and atmospheric CO2 concentration. For the Late Pliocene, our results show an atmospheric CO2 concentration during MIS M2 of 233–249 ppmv and a drop in global mean sea level of 10 to 25 m. Uncertainties are larger during the warmer periods leading up to and following MIS M2. CO2 concentrations during the warm intervals in the Pliocene, with sea-level high stands of 8–14 m above the present day, varied between 320 and 400 ppmv, lower than indicated by some proxy records but in line with earlier model reconstructions.

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