Estimating the long-term sea-level contribution from shelf mass loading on the Norwegian shelf using hydrographic in-situ data, satellite altimetry and GRACE

Future sea-level rise on shallow continental shelves differs in one important aspect from open ocean sea-level rise: the local steric effect, that is the change in the water column height due to changes in sea water density, plays a minor role compared to the much deeper open ocean. Instead, the bulk of oceanic sea-level rise on continental shelves arises from an increase in ocean water mass that is being imported from the open ocean – the so-called shelf mass loading (SML). This redistribution is mainly driven by thermal expansion of water masses below shelf depth and magnifies as the subsurface ocean layers continue to warm.   Few studies have tried to detect SML as the signal is only expected to become dominant over decadal to multidecadal periods given the large natural variability in shallow regions. Here, we combine hydrographic data from a section crossing the Norwegian shelf, with observations of total sea-level change from altimetry and estimates of mass changes from GRACE gravity missions to estimate the strength of SML over the past decades. We compare the residual of total sea level (from altimetry) and steric height (from hydrography) with GRACE estimates from three different solutions. Over the common period (2002 -2020), both estimates show a consistently higher trend over the shallow shelf area compared to the deep ocean. We estimate the shelf mass contribution in the order of 0.5 – 1.0 mm/yr, depending on the GRACE solution selected.