Non-closure of the global mean sea level budget since 2016: contributions of altimetry and Argo
Event: 2022 Ocean Surface Topography Science Team Meeting
Session: Science I: Climate data records for understanding the causes of global and regional sea level variability and change
Presentation type: Type Oral
Contribution: PDF file
The global mean sea level (GMSL) changes result from the sum of the steric and ocean mass global mean changes. Assessing the GMSL budget allows to cross-validate the consistency and stability of the observing systems involved. Many independent studies have shown that the GMSL budget is closed within uncertainties over the 1993-2016 time period. However, the sea level budget appears no longer closed after 2016 when using Jason-3 altimetry, Argo and GRACE/GRACE Follow-On gravimetric data. This non-closure may result from errors in one or several components of the sea level budget (altimetry-based GMSL, Argo-based steric sea level or GRACE-based ocean mass). We have investigated possible sources of errors affecting Jason-3 and Argo data. Concerning altimetry data, comparisons of Jason-3 GMSL time series with other altimetry missions show agreement within 0.4 mm/yr of standard uncertainty over 2016-2020. However, the comparisons of Jason-3 wet tropospheric correction with other altimetry missions and with climate data records show that Jason-3 radiometer is likely to drift. Such drift could be responsible for about 30 % of the non-closure of the budget. Concerning Argo in-situ data, a good agreement is found between all available thermosteric products. However, a decrease in the global mean halosteric sea level is observed since 2016 with strong discrepancies between the different data providers. A halosteric decrease corresponds to a salinity increase which is in contradiction with the global freshening of the oceans. This non-physical behaviour is attributed to uncorrected salinity measurement drifts and is responsible for about 40 % of the budget non-closure. Given that the halosteric component is expected to be negligible in global average, this spurious contribution should be neglected in the budget. The budget closure is significantly improved by taking into account a Jason-3 radiometer drift and assessing the sea level budget using only the thermosteric and ocean mass components. The remaining budget residual trends could be due to potential errors in the other components (i.e. thermosteric component based on Argo in-situ data, global mean ocean mass component based on GRACE and GRACE Follow-On satellite gravimetric data, missing physical contribution) that should be further investigated.