The 7,000 BP eustatic event

Just how important was the "eustatic event" that occurred at around 7,000 years ago?  I think it was hugely important, although it has not been greatly remarked upon by researchers in the past.  If we look at the accepted eustatic sea-level rise graph for the late glacial and Holocene, an accept that it is a "smoothed" graph made from multiple data points, we see that there are two major events:

1.  the onset of catastrophic ice wastage in the northern hemisphere ice sheets at around 20,000 years ago.

2.  the 7 ka event which marks a sudden transition from rapid sea-level rise to a much slower rise.

There are also two lower-order events marked on the graph, showing short-lived meltwater release "pulses" characterised by very rapid rises of maybe 2m per century, followed to short stabilisation phases and returns to the "background" rate of rise.  There are thought to coincide with "drainage episodes" associated with the vast meltwater lakes of North America and Scandinavia which led, for very short periods, to sea-level rises of up to 4 m per decade.   See this open access article by Harrison, Smith and Glasser:

Late Quaternary meltwater pulses and sea level change
Stephan Harrison , David E. Smith and Neil F. Glasser
Jnl of Quaternary Research Volume 34, Issue1 - January 2019
Pages 1-15
https://doi.org/10.1002/jqs.3070

https://onlinelibrary.wiley.com/doi/full/10.1002/jqs.3070

The overall rate of rise from the 20 ka event to the 7 ka event, over approx 13,000 years, was 1m per century, but between the onset of the Holocene at 10,000 yrs BP and the 7 ka event, the rate of rise was around 1.4m per century.  Then, at the completion of the ice sheet wastage period, it was as if a switch was turned off, and the rate of rise through to the present day was just 8 cm per century according to some measures and just 4 cm per century according to other measures.  That is an extraordinarily small rate of rise -- well below the level of human perception, and probably so low that its effects would be drowned out by other factors such as sedimentation rates, extreme storm events, vegetation growth, and changes in coastal morphology.

From the point of view of our understanding of the evolution of the West Wales coastal zone and the submerged forest, the 7 ka event marked the beginning of peat accumulation and forest growth that seemed to last for around 2000 years before waterlogging and a slow marine transgression overwhelmed them.  As suggested in other posts, residual isostatic uplift around the Welsh coast may well have been a contributory factor in encouraging the creation of freshwater environments.

Here, by the way, is a high-resolution graph showing how well established this 7 ka event is now in the literature.  It is based on a huge number of observations and data points.

It's always fun to have a somewhat unexpected graph by way of validation of results already presented.  The graph below was created by Alan Heyworth for his 1985 thesis.  On it he plots all known c14 dates for tree remains in the blue clays and peat deposits of Wales and SW England.  I have added the sea-level curve.  But interestingly, it shows there were some peat beds and tree remains overwhelmed by the rising sea before the 7 ka event -- that would be expected.  The peat beds concerned are thin and patchy.  The great bulk of C14 dates relate to the period of very slow sea-level rise after the 7 ka event -- but there was a lag of a thousand years or so.  Again, this would be expected, for a scenario in which  salt marshes would gradually be replaced by freshwater lagoons and peat development, prior to the establishment of drier woodland conditions.