Rapid sea-level rise in the North Atlantic Ocean since the first half of the nineteenth century

Abstract

A high-resolution late-Holocene sea-level record is produced from salt-marsh deposits at Viðarhó lmi in Snaefellsnes, western Iceland. The stratigraphy of Viðarhó lmi saltmarsh is documented using detailed descriptions of ten exposed sections and numerous hand-drilled cores. Fossil foraminifera are used as proxy sea-level indicators in an exposed section of salt-marsh peat. The agglutinated foraminifera Jadammina macrescens and Paratrochammina (Lepidoparatrochammina) haynesi are most useful as sea-level indicators because of their narrow vertical extent on the marsh surface and their good preservation in the peaty marsh deposits. We collected compaction-free sea-level index points from salt-marsh peat directly overlying the bedrock surface to establish the pre-industrial millennial-scale trend of sea-level rise and evaluate effects of autocompaction on the stratigraphy. The chronology of the sea-level reconstruction is based on tephra stratigraphy, AMS 14 C, 137 Cs, Pb and palaeomagnetic analyses. The main tephra layer visible in the stratigraphy of Viðarhó lmi salt marsh is the Landnám (settlement) layer, previously dated to AD 8759/6. A sea-transported pumice layer was correlated to the 'Mediaeval Layer' of AD 1226/27. Our reconstruction indicates that relative sea level along the coast of western Iceland has risen by about 1.3 m since c. AD 100. The detrended sea-level record shows a slow rise between AD 100 and 500, followed by a slow downward trend reaching a lowstand in the first half of the nineteenth century. This falling trend is consistent with a steric change estimated from reconstructions of sea-surface and sea-bottom temperatures from shelf sediments off Northern Iceland. The sea-level record shows a marked recent rise of about 0.4 m that commenced AD 18209/20 as dated by palaeomagnetism and Pb produced by European coal burning. This rapid sea-level rise is interpreted to be related to global temperature rise. The rise has continued up to the present day and has also been measured, since 1957, by the Reykjavik tide gauge.

Evidence for Century-Timescale Acceleration in Mean Sea Levels and for Recent Changes in Extreme Sea Levels

“…Figure 3 presents a compilation of findings from western Greenland (Long et al 2010), northern Spain (Leorri et al 2008), Tasmania (Gehrels et al in prep. ), Iceland (Gehrels et al 2006), New Zealand (Gehrels et al 2008), Connecticut (Donnelly et al 2004), North Carolina (Kemp et al 2009) and Nova Scotia (Gehrels et al 2005) (the individual papers may be consulted for analysis details, see also Woodworth et al 2009a andMitchum et al 2010). Most of the saltmarsh records contain a rapid acceleration or 'inflexion' as indicated in this schematic compilation.…”

Sea-level changes in Iceland and the influence of the North Atlantic Oscillation during the last half millennium

“…The lithostratigraphy of the marsh is detailed in Gehrels et al (2006) and mainly comprises sandy peat (Fig. 2).…”

“…In September 2009 we cleaned and re-sampled the upper 60 cm of section 3A of Gehrels et al (2006) using monolith tins driven into the cleaned sediment surface. The lithostratigraphy of the marsh is detailed in Gehrels et al (2006) and mainly comprises sandy peat (Fig.…”

“…1, 2). This is the same section where monoliths for the Gehrels et al (2006) (Ingólfsson, 1998). Mean tidal range at Viðarhólmi is 2.1 m, mean sea level (MSL) is 0.12 m above the Iceland geodetic datum and the highest astronomical tides reach ~2.1 m above MSL (Gehrels et al, 2006).…”

“…In a previous paper Gehrels et al (2006) reconstructed a 2000-yr record from this site using foraminifera (Fig. 1), and identified a single acceleration in sea level that was dated to the beginning of the nineteenth century.…”