The early Holocene sea level rise

Abstract

The causes, anatomy and consequences of the early Holocene sea level rise (EHSLR) are reviewed. The rise, of ca 60m, took place over most of the Earth as the volume of the oceans increased during deglaciation and is dated at 11,650–7000 cal. BP. The EHSLR was largely driven by meltwater release from decaying ice masses and the break up of coastal ice streams. The patterns of ice sheet decay and the evidence for meltwater pulses are reviewed, and it is argued that the EHSLR was a factor in the ca 8470 BP flood from Lake Agassiz-Ojibway. Patterns of relative sea level changes are examined and it is argued that in addition to regional variations, temporal changes are indicated. The impact of the EHSLR on climate is reviewed and it is maintained that the event was a factor in the 8200 BP cooling event, as well as in changes in ocean current patterns and their resultant effects. The EHSLR may also have enhanced volcanic activity, but no clear evidence of a causal link with submarine sliding on continental slopes and shelves can yet be demonstrated. The rise probably influenced rates and patterns of human migrations and cultural changes. It is concluded that the EHSLR was a major event of global significance, knowledge of which is relevant to an understanding of the impacts of global climate change in the future.

Introduction

The early Holocene, defined here as 11,650 to 7000 calibrated years before 1950 (BP), was a time of widespread environmental change as temperatures rose rapidly at the end of the last glaciation. A notable feature of this time was the ca 60m rise in sea levels over most of the Earth, as several studies imply (e.g. Fairbanks, 1989, Bard et al., 1996). This has attracted a great deal of scientific attention in recent years and we believe that it is timely to consider the published evidence for this rise and its impacts on the environment. We review the likely causes of the sea level rise, including its effects on the decay of coastal ice streams, before outlining the nature of the rise and its effects on coastlines. We then examine its possible consequences, in particular its relationship to climate, volcanic activity and submarine sliding, before considering its impacts on Mesolithic and Neolithic cultures. In a concluding statement, the paper summarises the changes described; comments on the relevance of studies of early Holocene sea level change as a key to understanding patterns and rates of change during glacial terminations; and concludes with a brief account of the extent to which an understanding of this phase of Earth history can prepare us for Earth system responses in the foreseeable future.

In the account which follows, sea level (SL) refers to the level of the sea surface without reference to the land and relative sea level (RSL) refers to the level of the sea as observed at the coastline. All dates given here are in sidereal (calibrated) years. Where original calibrated radiocarbon dates are not given in the published accounts quoted, calibrated dates have been obtained using Calib 6.0 (Reimer et al., 2009). All dates are given as before 1950: where 2000 AD is the datum (as with some ice core records), dates have been adjusted. Locations discussed are shown in Fig. 1, Fig. 3, Fig. 5, Fig. 7.