The role of megatides and relative sea level in controlling the deglaciation of the British–Irish and Fennoscandian ice sheets

Abstract

Key external forcing factors have been proposed to explain the collapse of ice sheets, including atmospheric and ocean temperatures, subglacial topography, relative sea level and tidal amplitudes. For past ice sheets it has not hitherto been possible to separate relative sea level and tidal amplitudes from the other controls to analyse their influence on deglaciation style and rate. Here we isolate the relative sea level and tidal amplitude controls on key ice stream sectors of the last British-Irish and Fennoscandian ice sheets using published glacial isostatic adjustment models, combined with a new and previously published palaeotidal models for the NE Atlantic since the Last Glacial Maximum (22 ka BP). Relative sea level and tidal amplitude data are combined into a sea surface elevation index for each ice stream sector demonstrating that these controls were potentially important drivers of deglaciation in the western British Irish Ice Sheet ice stream sectors. In contrast, the Norwegian Channel Ice Stream was characterized by falling relative sea level and small tidal amplitudes during most of the deglaciation. As these simulations provide a basis for observational field testing we propose a means of identifying the significance of sea level and tidal amplitudes in ice sheet collapse.

Trough geometry was a greater influence than climate-ocean forcing in regulating retreat of the marine-based Irish-Sea Ice Stream

“…Scourse et al, 1990), and in advancing from the topographic constriction of St George's Channel it spread out as a piedmontlike lobe. This low gradient, thin-ice and wide calving margin configuration likely rendered an over-extended ISIS vulnerable to rapid retreat perhaps conditioned by accelerated calving but driven by factors such as glaci-eustatic changes, a warmer sea surface, a megatidal regime and/or increasing air temperature leading to hydrofracturing (Haapaniemi et al, 2010;Scourse et al, 2009Scourse et al, , 2018Pollard et al, 2015). Notwithstanding limits imposed by uncertainties of the modeled chronology, the ISIS advance and retreat back to the south coast of Ireland by ca.…”

A rapid rise in relative sea level ~9–7 cal ka bp along the SW Cumbria coast, NW England

“…1–4; Tables 1 and 3) reflects a near simultaneous event of MHWS reaching sustained elevations of −5 to −4 m OD before the marine transgression. With a tidal range similar to today (Scourse et al ., 2018) this places the Mean Tide Level at least at ~−9 m OD. King levelled the lowest tree site at Ravenglass (Andrews et al ., 1973, their table 1) at – 5 m OD suggesting that high spring tides reached no higher than ≤ −5.2 m, while the tree embedded in peat at 0.4–0.7 m OD (Fig.…”

“…1B) is 10.75 m with mean range of 7.6 m; the mean low water spring tide (MLWS) at Barrow dock is −3.74 m OD and the mean high tide spring tide (MHWS) is 4.77 m OD. The actual tidal ranges during the early and mid‐Holocene are unresolved, although modeling (Scourse et al ., 2018) indicates the area was under the influence of megatides during deglaciation and later at 9000 cal a bp.…”

Late Quaternary sea‐level change and evolution of Belfast Lough, Northern Ireland: new offshore evidence and implications for sea‐level reconstruction

“…The (M)DoC calculation assumes that the wave regime and tidal range have not changed throughout the examined period. Palaeo‐tide modelling around the British Isles (Scourse et al, ) suggests that a meso‐tidal regime has persisted in the area since c. 16 kas bp . Despite these caveats, and because there is a lack of primary limiting dates, the reconstruction presented using the DoC is an important step forward in constraining RSL.…”