Measuring Global Mean Sea Level Changes With Surface Drifting Buoys

Abstract We propose to establish a new ocean observing system for monitoring global and regional mean sea-level changes. This system will consist of a global array of thousands of water-following drifting buoys tracked by a global navigation satellite system—such as the Global Positioning System (GPS)—which will continuously provide the geographical positions and the height of the sea surface along the buoys' trajectories. The sea-level height data collected in this way, averaged over regional basins and the global ocean, will provide daily measures of regional and global mean sea levels. An essential climate variable, mean sea level is an intrinsic measure of climate change, integrating the thermal expansion of the ocean's waters and additions to the ocean's mass from melting terrestrial ice. The realization of this new system requires that standardized vertical position measurements with controlled accuracy be acquired and regularly transmitted from relatively small and expendable drifting buoys, which constitutes a technological challenge, yet one with a clear path for being met. The development and implementation of this ocean shot concept will ultimately provide an independent, resilient, sustainable, and economical observational system to quantify natural and anthropogenic sea-level changes, augmenting the existing satellites and tide gauge observing systems.

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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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Global Mean Sea-level Changes in the Last Two Millennia

10.5194/egusphere-egu21-1951 ◽

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

Instrumental records show that global mean sea level (GMSL) rose by approximately 15 cm in the 20th 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.

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

Journal of Geodesy ◽

10.1007/s00190-006-0055-7 ◽

2006 ◽

Vol 80 (5) ◽

pp. 240-247 ◽

Cited By ~ 2

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

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Kinematics of global mean thermosteric sea level during 1993–2019

Journal of Geodetic Science ◽

10.1515/jogs-2020-0121 ◽

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.

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

Comptes Rendus Geoscience ◽

10.1016/j.crte.2013.03.002 ◽

2013 ◽

Vol 345 (4) ◽

pp. 167-175 ◽

Cited By ~ 7

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

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

Ocean Science ◽

10.5194/os-10-485-2014 ◽

2014 ◽

Vol 10 (3) ◽

pp. 485-500 ◽

Cited By ~ 8

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.

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