Sea level during MIS 9: Evidence from the Nar Valley, north Norfolk, UK

Efforts to identify appropriate geological analogues for the Holocene have prompted previous interglacial periods as a fitting choice. However, there is room for substantial improvements to our knowledge of past inter- and intra-interglacial sea level fluctuations. Studies that provide information on relative sea level movements during previous interglacial periods facilitate an understanding of the link between changes in climatological parameters, ice sheet response and resultant changes in sea level and afford more accurate prediction of sea level changes that could occur in the future. An interglacial lithological sequence from the Nar Valley area of north Norfolk, UK represents a marine transgression that occurred during marine isotope stage 9. The aim of this project was to provide an account of the nature of this marine transgression; in terms of its rapidity and whether any oscillations in sea level occurred. In order to do so, the project used foraminifera as a palaeoenvironmental indicator of water depth and, subsequently, sea level. Collating evidence from four study sites tracked this marine transgression over an elevation range of 20 metre and suggested a transgression initially characterised by oscillations of very small magnitudes that initiated to the west of the Nar Valley. As the transgression tracked eastwards, it was characterised by a smooth and somewhat gradual progression through the Nar Valley from west to east where, at its greatest extent, marine conditions persisted as far inland as a site at Bradmoor Hill. The maximum elevation of the marine transgression is estimated to have been 23 metres OD, with fully estuarine conditions established across most of the Nar Valley. This transgression appears to have been absent of any sizeable sea level oscillations, suggesting that MIS 9 serves as an appropriate analogue for the Holocene in terms of sea level change. The smooth nature of the transgression provides no evidence to suggest rapid changes in sea level occurred as a result of unstable ice sheets. This suggestion has important implications for better constraining the upper and lower bounds of predictions of future sea level change.This project forms part of the NERC-funded project ‘Using interglacials to assess future sea-level scenarios’ (iGlass). Core material used in the study was provided by members of the iGlass consortium