Sea level budget over 2003–2008: A reevaluation from GRACE space gravimetry, satellite altimetry and Argo

Abstract

From the IPCC 4th Assessment Report published in 2007, ocean thermal expansion contributed by ∼ 50% to the 3.1 mm/yr observed global mean sea level rise during the 1993-2003 decade, the remaining rate of rise being essentially explained by shrinking of land ice. Recently published results suggest that since about 2003, ocean thermal expansion change, based on the newly deployed Argo system, is showing a plateau while sea level is still rising, although at a reduced rate (∼ 2.5 mm/yr). Using space gravimetry observations from GRACE, we show that recent years sea level rise can be mostly explained by an increase of the mass of the oceans. Estimating GRACE-based ice sheet mass balance and using published estimates for glaciers melting, we further show that ocean mass increase since 2003 results by about half from an enhanced contribution of the polar ice sheets -compared to the previous decade -and half from mountain glaciers melting. Taking also into account the small GRACE-based contribution from continental waters (b 0.2 mm/yr), we find a total ocean mass contribution of ∼ 2 mm/yr over 2003-2008. Such a value represents ∼ 80% of the altimetry-based rate of sea level rise over that period. We next estimate the steric sea level (i.e., ocean thermal expansion plus salinity effects) contribution from: (1) the difference between altimetry-based sea level and ocean mass change and (2) Argo data. Inferred steric sea level rate from (1) (∼ 0.3 mm/yr over [2003][2004][2005][2006][2007][2008] agrees well with the Argo-based value also estimated here (0.37 mm/yr over [2004][2005][2006][2007][2008]. Furthermore, the sea level budget approach presented in this study allows us to constrain independent estimates of the Glacial Isostatic Adjustment (GIA) correction applied to GRACE-based ocean and ice sheet mass changes, as well as of glaciers melting. Values for the GIA correction and glacier contribution needed to close the sea level budget and explain GRACE-based mass estimates over the recent years agree well with totally independent determinations.

On the origins of Earth rotation anomalies: New insights on the basis of both “paleogeodetic” data and Gravity Recovery and Climate Experiment (GRACE) data

“…They accept as a reasonable estimate for the GIA-related mass rate correction over the oceans, a value of À1.0 mm yr À1 which is approximately a factor of 2 smaller in magnitude than the value delivered by the ICE-5G (VM2) model listed here in Table 1 and discussed more fully by Peltier [2009]. The Peltier [2009] value has previously been accepted by Cazenave et al [2009] as being required to achieve closure of the budget. Although Leuliette and Miller [2009] claim that they also achieve closure of the budget using a value for the GIA correction of À1.0 mm yr À1 , a value attributed to Paulson et al [2007], it will be clear that their own analysis would be markedly improved if they were to employ the ICE-5G(VM2) value for the GIA correction.…”

“…As shown explicitly in section 5, the action of such modern ice sheet melting has a significant impact on Earth rotation. Models of modern land ice melting such as those constrained by GRACE itself [e.g., Cazenave et al, 2009;Peltier, 2009] for the polar regions and by Meier et al [2007] for the small ice sheets and glaciers, must be shown to pass the test provided by the GRACE observations. However, the ICE-5G (VM2) model, and the modest improvements to it that are currently under construction, are precisely the models required to filter ice age influence from these modern space geodetic observations.…”

“…It will be observed that the latter effect is extremely important. According to Cazenave et al [2009], if the altimetric correction to the TOPEX/POSEIDON global rate of sea level rise measurement is taken to be approximately À0.30 mm yr À1 (see Table 1), as first described by Peltier [2001], then the average rate of increase in the thickness of an equivalent layer of water over the ocean basins must be close to À1.90 mm yr À1 in order to establish closure of the sea level budget. Their analysis could be construed to deliver an independent estimate of what the GRACE correction for GIA must be in order that the sea level budget, as observed over the GRACE era, be closed.…”

What Can be Expected from the GRACE-FO Laser Ranging Interferometer for Earth Science Applications?

“… Quantification of the increase or decrease of the ice and snow masses in the polar or large glacier areas has been achieved by scientists who were able to demonstrate a strong correlation between the climatic phenomenon ENSO / La Nina, the rainfall patterns in West Antarctica and the reduction of ice mass there (Sasgen et al 2010).  Monitoring of global mean eustatic sea-level variations as a consequence of mass re-distribution between continents and ocean basins for the partitioning of observed sea-level changes into mass and temperature contributions (Cazenave et al 2009), as well as the regional re-distribution of water masses in response to time-variable surface winds that are tightly connected to time-variations of hemispheric current systems such as the Antarctic Circumpolar Current (Bergmann and Dobslaw (2012)).  Observation of changes in the solid Earth following large earthquakes, such as Sumatra-Andaman (2004), Chile (2010) and Fukushima (2011, Wang et al 2012).…”

Estimates of twenty-first century sea-level changes for Norway

“…Cazenave et al 2009;Milne et al 2009;Church et al 2011) and efforts are underway to improve projections of the contributions of ice to future sea-level change (e.g. www.ice2sea.eu).…”