Geological review of English coastal archaeological evidence portending multi-metre sea-level rise by 2100

Roger Higgs 

English archaeological literature, its sea-level significance hitherto underappreciated, is reviewed here from a geological (sedimentological) perspective. Five Roman-built (~300AD) waterside forts and a seaside palace (~100AD), all meticulously excavated by archaeologists, tightly dated (tree-rings, coins, pottery), and published in great detail, yield evidence proving a ~4-metre (m) sea-level rise in only ~70 years, spanning ~430-500AD (early 'Dark Ages'), following 410AD Roman abandonment of Britain. (A comparably fast 2-3m rise within 100 years is known for the MIS5e interglacial, preceding our current Holocene interglacial.) The evidence includes excavated stumps, up to 2.5m tall, of Roman Londinium's Thames-estuary-side defensive wall, its entire waterside face eroded, implying that high-spring tide rose 3m+ after 300AD, constrained to pre-500AD by other archaeological evidence. The rise equates to the geologically-based global 'Rottnest transgression' (loosely carbon-dated ~350-950AD) of the celebrated 1961 'Fairbridge Curve' of Holocene sea level; and it explains enigmatic late-5th-Century mass-migration to SE Britain of Anglo-Saxons (birth of English nationhood), their NW European coastal-plain homelands 'pinched' between the eastwardly encroaching shoreline and west-advancing Huns. The Rottnest transgression can only be explained by Antarctic ice-cliff collapse, probably reflecting a solar-driven(?) known Arctic warm spike ~400AD; the resulting 'overwarmed' Arctic sea-surface-water reached Antarctica ~30 years later by 'conveyor-belt' ocean circulation. Since 2005, anthropogenically boosted Arctic warmth has continuously exceeded the ~400AD spike, portending another decades-long, multi-metre SL rise, ending by ~2100.