Evolving the Geodetic Infrastructure to Meet New Scientific Needs (2020) / Chapter Skim
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3 Sea-Level Change
3 Sea-Level Change
Pages 25-38
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describes been validated with tide gauge data. These records show the scientific needs for understanding both absolute that climate-driven global mean sea level has risen by and relative sea-level rise.
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The latter mass. Ocean heat content change can also be measured also causes relative sea-level change due to vertical with the Argo network of profiling floats, which have land motion in response to the deformation of the minimal dependence on the geodetic infrastructure.
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Relative sea interesting. The uncorrected tide gauge record indicates level depends on global mean sea-level rise and its re- that relative sea level rose by 6.4 mm/yr since 1900, gional variations, vertical land motion, and other local mostly due to ground subsidence caused by sediment processes, such as small-scale currents, wind, waves, compaction due to groundwater withdrawal.1 After fresh water input from river estuaries, shelf bathymetry, correcting for vertical land motion, the rate of sea-level and along-shore and cross-shore sediment transport rise in that area is reduced to 1.8 mm/yr.
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GNSS measurements are also important for accurately GIA increases the volume of the ocean basins, measuring vertical land motions due to earthquakes producing a linear effect of ~–0.3 mm/yr on the (coseismic and postseismic) and local subsidence due
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Right panels: records corrected for vertical land motions. SOURCE: Woodworth et al., 2019.
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Thus, for both sea-level science validation is driven by errors in the amount of vertical and altimeter validation, it is important that the geo- land motion at the tide gauge sites. Therefore, improved detic infrastructure include the means for monitoring estimates of vertical land motion can reduce the error esvertical land motion at as many tide gauges as possible timate for the rate of sea-level rise from satellite altimetry.
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Because tide gauges only measure water level with respect to the tide gauge's anchor point (usually a pier) , all tide gauge records are inherently biased due to any vertical motion of the pier (see Figure 3.5A)
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For ocean mass distribution, monthly gravity mea• Vertical land motion accuracy at tide gauges of less surements with 300 km × 300 km spatial resolution, a than 0.5 mm/yr to minimize errors in validating stability of 15 mm water equivalent at 300 km × 300 km, satellite altimeter observations of sea-surface height. and precision in ocean mass change of 0.1 mm/decade.
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the course of a decade and the changes in surface mass The third approach involves estimating ice mass balance and glacier ice discharge with the same accuchanges from radar and laser altimetry measurements racy over all of the ice sheets, continuously, for decades
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. The land water contribution to sea-level change can also be The GRACE mass change measurements strongly estimated using global hydrological models, but these depend on the geodetic infrastructure.
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GNSS near tide gauges can be used ice mass loss may show anomalous motion and should to estimate vertical land motions, but less than 14 percent be treated carefully if used to define the reference frame. of Global Sea Level Observing System tide gauge sta It is also important to always be able to reconstruct tions are equipped with a permanent GNSS station (e.g., the TRF back in time, so that sea-level measurements Ponte et al., 2019)
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Reducing the errors in vertical land motion for the tide gauge calibration of satellite altimeter Enhancements to the Geodetic Infrastructure measurements could significantly improve the error estimates for sea-level change from satellite altimetry. • The sea-level science questions require a TRF acThe following summarizes the needs for maintaining curacy of 1 mm and drift in the origin of the TRF or enhancing the geodetic infrastructure, and related of less than 0.1 mm/yr (or less than 0.02 ppb/yr in improvements to enhance scientific returns.
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2017. • Install GNSS stations at tide gauges to achieve the New estimate of the current rate of sea level rise from a absolute vertical land motion requirement of better sea level budget approach.
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2010. Warming of global abyssal global mean thermosteric sea level rise in CMIP5 climate mod- and deep southern ocean waters between the 1990s and 2000s: els.
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