scholarly journals Cenozoic sea-level and cryospheric evolution from deep-sea geochemical and continental margin records

2020 ◽  
Vol 6 (20) ◽  
pp. eaaz1346 ◽  
Author(s):  
Kenneth G. Miller ◽  
James V. Browning ◽  
W. John Schmelz ◽  
Robert E. Kopp ◽  
Gregory S. Mountain ◽  
...  
Keyword(s):  
Sea Level ◽  
Ice Sheets ◽  
Milankovitch Cycles ◽  
Continental Margins ◽  
Sea Levels ◽  
Continental Scale ◽  
Global Mean Sea Level ◽  
Thermal Subsidence ◽  
Global Mean

Using Pacific benthic foraminiferal δ18O and Mg/Ca records, we derive a Cenozoic (66 Ma) global mean sea level (GMSL) estimate that records evolution from an ice-free Early Eocene to Quaternary bipolar ice sheets. These GMSL estimates are statistically similar to “backstripped” estimates from continental margins accounting for compaction, loading, and thermal subsidence. Peak warmth, elevated GMSL, high CO2, and ice-free “Hothouse” conditions (56 to 48 Ma) were followed by “Cool Greenhouse” (48 to 34 Ma) ice sheets (10 to 30 m changes). Continental-scale ice sheets (“Icehouse”) began ~34 Ma (>50 m changes), permanent East Antarctic ice sheets at 12.8 Ma, and bipolar glaciation at 2.5 Ma. The largest GMSL fall (27 to 20 ka; ~130 m) was followed by a >40 mm/yr rise (19 to 10 ka), a slowing (10 to 2 ka), and a stillstand until ~1900 CE, when rates began to rise. High long-term CO2 caused warm climates and high sea levels, with sea-level variability dominated by periodic Milankovitch cycles.

scholarly journals Twenty-first century response of Petermann Glacier, northwest Greenland to ice shelf loss

2020 ◽  
pp. 1-11
Author(s):  
Emily A. Hill ◽  
G. Hilmar Gudmundsson ◽  
J. Rachel Carr ◽  
Chris R. Stokes ◽  
Helen M. King
Keyword(s):  
Sea Level ◽  
First Century ◽  
Ice Shelf ◽  
Ice Shelves ◽  
Sea Levels ◽  
Grounding Line ◽  
Global Mean Sea Level ◽  
Near Future ◽  
Global Mean ◽  
Large Sections

Abstract Ice shelves restrain flow from the Greenland and Antarctic ice sheets. Climate-ocean warming could force thinning or collapse of floating ice shelves and subsequently accelerate flow, increase ice discharge and raise global mean sea levels. Petermann Glacier (PG), northwest Greenland, recently lost large sections of its ice shelf, but its response to total ice shelf loss in the future remains uncertain. Here, we use the ice flow model Úa to assess the sensitivity of PG to changes in ice shelf extent, and to estimate the resultant loss of grounded ice and contribution to sea level rise. Our results have shown that under several scenarios of ice shelf thinning and retreat, removal of the shelf will not contribute substantially to global mean sea level (<1 mm). We hypothesize that grounded ice loss was limited by the stabilization of the grounding line at a topographic high ~12 km inland of its current grounding line position. Further inland, the likelihood of a narrow fjord that slopes seawards suggests that PG is likely to remain insensitive to terminus changes in the near future.

scholarly journals Variations in global mean sea level associated with the 1997-1998 ENSO event: Implications for measuring long term sea level change

1999 ◽  
Vol 26 (19) ◽  
pp. 3005-3008 ◽  
Author(s):  
R. S. Nerem ◽  
D. P. Chambers ◽  
E. W. Leuliette ◽  
G. T. Mitchum ◽  
B. S. Giese
Keyword(s):  
Sea Level ◽  
Sea Level Change ◽  
Enso Event ◽  
Mean Sea Level ◽  
Level Change ◽  
Global Mean Sea Level ◽  
Global Mean

scholarly journals On the differences between two semi-empirical sea-level models for the last two millennia

2012 ◽  
Vol 8 (4) ◽  
pp. 3551-3581 ◽  
Author(s):  
M. Vermeer ◽  
S. Rahmstorf ◽  
A. Kemp ◽  
B. Horton
Keyword(s):  
North Carolina ◽  
Sea Level Rise ◽  
Sea Level ◽  
Time Scales ◽  
Long Time ◽  
Global Mean Sea Level ◽  
Semi Empirical ◽  
The Last Two Millennia ◽  
Global Mean

Abstract. We compare hindcasts of global mean sea level over the past millennium obtained using two semi-empirical models linking temperature and sea-level rise. The models differ in that one of them includes a term for a very long-term sea-level rise component unfolding over many millennia. On short (century) time scales, both models give very similar results. Proxy sea-level reconstructions from the northern (North Carolina) and southern (New Zealand and Tasmania) hemispheres are used to test the ability of both models to reproduce the longer-term sea-level evolution. In both comparisons the model including the second term produces a markedly better fit from 1000 AD to the present. When both models are used for generating sea-level projections, they behave similarly out to 2100 AD. Further out, to 2300–2500 AD, the projections differ significantly, in no small part due to different values for the sea-level response time scale τ obtained. We conclude that careful model validation on long time scales is important before attempting multi-century projections.

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.

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

&lt;p&gt;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 ~&amp;#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.&lt;/p&gt;&lt;p&gt;Since the shortest wavelength and fastest evolving contributions to dynamic topography originate in the shallow mantle, reconstructing dynamic topography over 1&amp;#8211;10 Myr timescales requires accurate models of Earth&amp;#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 &amp;#8220;retrodictions&amp;#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.&lt;/p&gt;&lt;p&gt;By back-advecting density perturbations from an ensemble of Earth models, we demonstrate that ~&amp;#177;200 m relative sea-level changes across Australia since the Mid-Pliocene Warm Period (MPWP; &amp;#8764;3 Ma) can be tied directly to changes in dynamic topography. Significantly, after removing this signal from observed relative sea-level changes,&amp;#160; a consistent global mean sea-level during the MPWP of 12&amp;#177;8 m above present is obtained, towards the lower end of previous estimates.&lt;/p&gt;

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

&lt;p&gt;Instrumental records show that global mean sea level (GMSL) rose by approximately 15 cm in the 20&lt;sup&gt;th&lt;/sup&gt; 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.&lt;/p&gt;

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 Observational Requirements for Long-Term Monitoring of the Global Mean Sea Level and Its Components Over the Altimetry Era

2019 ◽  
Vol 6 ◽  
Author(s):  
Anny Cazenave ◽  
Ben Hamlington ◽  
Martin Horwath ◽  
Valentina R. Barletta ◽  
Jérôme Benveniste ◽  
...  
Keyword(s):  
Sea Level ◽  
Mean Sea Level ◽  
Long Term Monitoring ◽  
Global Mean Sea Level ◽  
Term Monitoring ◽  
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 Global glacier retreat: a revised assessment of committed mass losses and sampling uncertainties

2013 ◽  
Vol 7 (3) ◽  
pp. 1987-2005 ◽  
Author(s):  
S. H. Mernild ◽  
W. H. Lipscomb ◽  
D. B. Bahr ◽  
V. Radi&amp;cacute; ◽  
M. Zemp
Keyword(s):  
Sea Level ◽  
Return To Equilibrium ◽  
Ice Caps ◽  
The Past ◽  
Mass Losses ◽  
Assessment Approach ◽  
Global Mean Sea Level ◽  
Additional Losses ◽  
Global Mean

Abstract. Most glaciers and ice caps (GIC) are out of balance with the current climate. To return to equilibrium, GIC must thin and retreat, losing additional mass and raising sea level. Because glacier observations are sparse and geographically biased, there is an undersampling problem common to all global assessments. Here, we further develop an assessment approach based on accumulation-area ratios (AAR) to estimate committed mass losses and analyze the undersampling problem. We compiled all available AAR observations for 144 GIC from 1971–2010 and found that most glaciers and ice caps are farther from balance than previously believed. Accounting for regional and global undersampling errors, our model suggests that GIC are committed to additional losses of 30 &amp;pm; 11% of their area and 38 &amp;pm; 17% of their volume if the future climate resembles the climate of the past decade. These losses imply global mean sea-level rise of 163 &amp;pm; 73 mm, assuming total glacier volume of 430 mm sea-level equivalent. To reduce the large uncertainties in these projections, more long-term glacier measurements are needed in poorly sampled regions.

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