A reconciled solution of Meltwater Pulse 1A sources using sea-level fingerprinting.

The most rapid global sea-level rise event of the last deglaciation, Meltwater Pulse 1A (MWP-1A), occurred ∼14,650 years ago. Considerable uncertainty regarding the sources of meltwater limits understanding of the relationship between MWP-1A and the concurrent fast-changing climate. Here we present a data-driven inversion approach, using a glacio-isostatic adjustment model to invert for the sources of MWP-1A via sea-level constraints from six geographically distributed sites. The results suggest contributions from Antarctica, 1.3 m (0-5.9 m; 95% probability), Scandinavia, 4.6 m (3.2-6.4 m) and North America, 12.0 m (5.6-15.4 m), giving a global mean sea-level rise of 17.9 m (15.7-20.2 m) in 500 years. Only a North American dominant scenario successfully predicts the observed sea-level change across our six sites and an Antarctic dominant scenario is firmly refuted by Scottish isolation basin records. Our sea-level based results therefore reconcile with field-based ice-sheet reconstructions.

Predicting marsh vulnerability to sea-level rise using Holocene relative sea-level data.

Tidal marshes rank among Earth's vulnerable ecosystems, which will retreat if future rates of relative sea-level rise (RSLR) exceed marshes' ability to accrete vertically. Here, we assess the limits to marsh vulnerability by analyzing >780 Holocene reconstructions of tidal marsh evolution in Great Britain. These reconstructions include both transgressive (tidal marsh retreat) and regressive (tidal marsh expansion) contacts. The probability of a marsh retreat was conditional upon Holocene rates of RSLR, which varied between -7.7 and 15.2 mm/yr. Holocene records indicate that marshes are nine times more likely to retreat than expand when RSLR rates are ≥7.1 mm/yr. Coupling estimated probabilities of marsh retreat with projections of future RSLR suggests a major risk of tidal marsh loss in the twenty-first century. All of Great Britain has a >80% probability of a marsh retreat under Representative Concentration Pathway (RCP) 8.5 by 2100, with areas of southern and eastern England achieving this probability by 2040.

Integration of shelf evolution and river basin models to simulate Holocene sediment dynamics of the Humber Estuary during periods of sea-level change and variations in catchment sediment supply.

Three modelling elements and sedimentary evidence provide an understanding of sediment characteristics, river basin processes, tidal regimes and sea-level changes to explain sediment supply to the Humber Estuary through the Holocene (the last 10,000 years). An upscaled cellular catchment model simulates water and sediment fluxes from river basins, illustrating significant variations in response to climate change, especially precipitation and vegetation changes, principally deforestation. Much of the sediment mobilised remains in stores within the catchment and only a small fraction reaches the Humber tidal system. An empirical model helps to explain sediment erosion, transport and deposition from the offshore and coastal zones through the Holocene and sea-level rise caused the transgression of the continental shelf of the North Sea. Comparison with the sediment fill of the lowlands around of the Humber estuary, that represent the extent of the estuary during the Holocene, demonstrates that most of the fill (approximately 95-98%) was derived from non-fluvial sources. A shelf evolution model, with reconstructions of sea level, palaeogeography and palaeobathymetry for 1,000 year time steps through the Holocene predicts significant changes in tidal regimes, first over wide areas of the coast as the transgression of the continental shelf progresses. The most significant changes occur with the inner reaches of the palaeo-estuaries, especially those of the Humber and the Fenland. Throughout the mid-Holocene they are characterised by significantly lower tidal ranges (MWHST approximately 2.5 m less than present) and low tidal currents. The simulated patterns of tidal currents concur with the transport of fine grain sediment from the coastal zone into the estuaries. The major tidal range changes revise estimates of late Holocene and ongoing relative sea and land level changes.