(2015) 'Sea-level rise due to polar ice-sheet mass loss during past warm periods. ', Science., 349 (6244). aaa4019.Further information on publisher's website: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.

We assess the relationship between temperature and global sea-level (GSL) variability over the Common Era through a statistical metaanalysis of proxy relative sea-level reconstructions and tide-gauge data. GSL rose at 0.1 ± 0.1 mm/y (2σ) over 0–700 CE. A GSL fall of 0.2 ± 0.2 mm/y over 1000–1400 CE is associated with ∼0.2 °C global mean cooling. A significant GSL acceleration began in the 19th century and yielded a 20th century rise that is extremely likely (probability P≥0.95) faster than during any of the previous 27 centuries. A semiempirical model calibrated against the GSL reconstruction indicates that, in the absence of anthropogenic climate change, it is extremely likely (P=0.95) that 20th century GSL would have risen by less than 51% of the observed 13.8±1.5 cm. The new semiempirical model largely reconciles previous differences between semiempirical 21st century GSL projections and the process model-based projections summarized in the Intergovernmental Panel on Climate Change’s Fifth Assessment Report.

Analysis of more than 1200 radiocarbon dated samples that constrain relative sealevels in Great Britain over the past 16 000 yr provides estimates of current land-level changes (negative of relative sea-level change). Maximum relative land uplift occurs in central and western Scotland, ca. 1.6 mm yr −1 , and maximum subsidence is in southwest England, ca. 1.2 mm yr −1 . Sediment consolidation, arising from autocompaction as the sediment accumulates and from land drainage, increases the subsidence in areas with thick sequences of Holocene sediments, with an average effect equivalent to at least an extra ca. 0.2 mm yr −1 land subsidence, but more in parts of southeast England, 0.5-1.1 mm yr −1 . Modelled changes in tidal range during the mid-to late Holocene in eastern England suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified. The effect is most significant for large coastal lowlands, the Fenland and Humber (ca. 0.5 and 0.6 mm yr −1 ), that were tidal embayments during the mid-to late Holocene.

Past earthquake rupture models used to explain paleoseismic estimates of coastal subsidence during the great A.D. 1700 Cascadia earthquake have assumed a uniform slip distribution along the megathrust. Here we infer heterogeneous slip for the Cascadia margin in A.D. 1700 that is analogous to slip distributions during instrumentally recorded great subduction earthquakes worldwide. The assumption of uniform distribution in previous rupture models was due partly to the large uncertainties of then available paleoseismic data used to constrain the models. In this work, we use more precise estimates of subsidence in 1700 from detailed tidal microfossil studies. We develop a 3‐D elastic dislocation model that allows the slip to vary both along strike and in the dip direction. Despite uncertainties in the updip and downdip slip extensions, the more precise subsidence estimates are best explained by a model with along‐strike slip heterogeneity, with multiple patches of high‐moment release separated by areas of low‐moment release. For example, in A.D. 1700, there was very little slip near Alsea Bay, Oregon (~44.4°N), an area that coincides with a segment boundary previously suggested on the basis of gravity anomalies. A probable subducting seamount in this area may be responsible for impeding rupture during great earthquakes. Our results highlight the need for more precise, high‐quality estimates of subsidence or uplift during prehistoric earthquakes from the coasts of southern British Columbia, northern Washington (north of 47°N), southernmost Oregon, and northern California (south of 43°N), where slip distributions of prehistoric earthquakes are poorly constrained.

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We present new sea-level reconstructions for the past 2100 y based on salt-marsh sedimentary sequences from the US Atlantic coast. The data from North Carolina reveal four phases of persistent sea-level change after correction for glacial isostatic adjustment. Sea level was stable from at least BC 100 until AD 950. Sea level then increased for 400 y at a rate of 0.6 mm/y, followed by a further period of stable, or slightly falling, sea level that persisted until the late 19th century. Since then, sea level has risen at an average rate of 2.1 mm/y, representing the steepest century-scale increase of the past two millennia. This rate was initiated between AD 1865 and 1892. Using an extended semiempirical modeling approach, we show that these sea-level changes are consistent with global temperature for at least the past millennium.climate | ocean | late Holocene | salt marsh C limate and sea-level reconstructions encompassing the past 2,000 y provide a preanthropogenic context for understanding the nature and causes of current and future changes. Hemispheric and global mean temperature have been reconstructed using instrumental records supplemented with proxy data from natural climate archives (1, 2). This research has improved understanding of natural climate variability and suggests that modern warming is unprecedented in the past two millennia (1). In contrast, understanding of sea-level variability during this period is limited and the response to known climate deviations such as the Medieval Climate Anomaly, Little Ice Age, and 20th century warming is unknown. We reconstruct sea-level change over the past 2100 y using new salt-marsh proxy records and investigate the consistency of reconstructed sea level with global temperature using a semiempirical relationship that connects sea-level changes to mean surface temperature (3, 4). The new sea level proxy data constrain a multicentennial response term in the semiempirical model. Results and DiscussionSea-Level Data. Salt-marsh sediments and assemblages of foraminifera record former sea level because they are intrinsically linked to the frequency and duration of tidal inundation and keep pace with moderate rates of sea-level rise (5, 6). We developed transfer functions using a modern dataset of foraminifera (193 samples) from 10 salt marshes in North Carolina, USA (7). Transfer functions are empirically derived equations for quantitatively estimating past environmental conditions from paleontological data (8). The transfer functions were applied to foraminiferal assemblages preserved in 1 cm thick samples from two cores of salt-marsh sediment (Sand Point and Tump Point, North Carolina; Fig. 1) to estimate paleomarsh elevation (PME), which is the tidal elevation at which a sample formed with respect to its contemporary sea level (9). Unique vertical errors were calculated by the transfer functions for each PME estimate and were less than 0.1 m. Composite chronologies were developed using Accelerator Mass Spectrometry (AMS) 14 C (conventional, high-precision, and bo...

The response of mangroves to high rates of relative sea level rise (RSLR) is poorly understood. We explore the limits of mangrove vertical accretion to sustained periods of RSLR in the final stages of deglaciation. The timing of initiation and rate of mangrove vertical accretion were compared with independently modeled rates of RSLR for 78 locations. Mangrove forests expanded between 9800 and 7500 years ago, vertically accreting thick sequences of organic sediments at a rate principally driven by the rate of RSLR, representing an important carbon sink. We found it very likely (>90% probability) that mangroves were unable to initiate sustained accretion when RSLR rates exceeded 6.1 millimeters per year. This threshold is likely to be surpassed on tropical coastlines within 30 years under high-emissions scenarios.