Spatial variability of late Holocene and 20th century sea-level rise along the Atlantic coast of the United States

Engelhart, Simon E.; Horton, Benjamin P.; Douglas, Bruce C.; Peltier, W. R.; Törnqvist, Torbjörn E.

doi:10.1130/g30360a.1

Cited by 169 publications

(132 citation statements)

References 38 publications

(51 reference statements)

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“…Typically, a near monotonic rise is observed during the majority of the time period covered (e.g., see the New Jersey and Delaware RSL records). Inter-locality differences in the mean rate of this rise occurs due to the location of each with respect to the peripheral bulge [Clark et al, 1978;Engelhart et al, 2009], with those sites which lie on the peak of the bulge showing a greater rate of RSL rise compared with those located further from the peak. Given that the global mean sea-level change due to meltwater addition has been only a few meters since 7 ka (and zero within data uncertainty over the last ≈2000 years) [Masson-Delmotte et al, 2013;Lambeck et al, 2014], it is clear that GIA, specifically peripheral bulge subsidence, is a significant contributor to Holocene RSL rise for the stretch of North American coastline considered here.…”

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confidence: 99%

The contribution of glacial isostatic adjustment to projections of sea‐level change along the Atlantic and Gulf coasts of North America

et al. 2016

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We determine the contribution of glacial isostatic adjustment (GIA) to future relative sea-level change for the North American coastline between Newfoundland and Texas. We infer GIA model parameters using recently compiled and quality-assessed databases of past sea-level changes, including new databases for the United States Gulf Coast and Atlantic Canada. At 13 cities along this coastline, we estimate the GIA contribution to range from a few centimeters (e.g., 3 [−1 to 9] cm Miami) to a few decimeters (e.g., 18 [12][13][14][15][16][17][18][19][20][21][22] cm, Halifax) for the period 2085-2100 relative to 2006-2015 (1− ranges given). We provide estimates of uncertainty in the GIA component using two different methods; the more conservative approach produces total ranges (1− confidence) that vary from 3 to 16 cm for the cities considered. Contributions from ocean steric and dynamic changes as well as those from changes in land ice are also estimated to provide context for the GIA projections. When summing the contributions from all three processes at the 13 cities considered along this coastline, using median or best-estimate values, the GIA signal comprises 5-38% of the total depending on the adopted climate forcing and location. The contributions from ocean dynamic/steric changes and ice mass loss are similar in amplitude but with spatial variation that approximately cancels, resulting in GIA dominating the net spatial variability north of 35 ∘ N.

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Section: Datamentioning

confidence: 99%

The contribution of glacial isostatic adjustment to projections of sea‐level change along the Atlantic and Gulf coasts of North America

et al. 2016

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“…GPS observations are the net effect of complex processes from which GIA must be isolated. iii) Grinsted et al (2) wrongly claim that a 4-mm/y sea-level rise from NC tide-gauge data was identified by Engelhart et al (1). No NC tide gauges were used in that study.…”

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confidence: 92%

“…Late Holocene (past 2 ka) GIA rates are estimated from geological data and permanent global positioning system (GPS) stations or predicted from GIA models. We used a linear trend fitted to the regional, compaction-free, RSL reconstructions compiled by Engelhart et al (1) for the past 2 ka (excluding data since AD 1900) as a GIA estimate. Similarly, GIA models also attribute all RSL changes during the past 2 ka to linear GIA and have zero eustatic (e.g., meltwater) contribution.…”

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confidence: 99%

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Reply to Grinsted et al.: Estimating land subsidence in North Carolina

Kemp¹,

Horton²,

Donnelly³

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Reconstructions and observations of relative sea level (RSL) must be corrected for vertical land movements from glacial isostatic adjustment (GIA) to facilitate comparisons among regions and identify deviations from background rates. Late Holocene (past 2 ka) GIA rates are estimated from geological data and permanent global positioning system (GPS) stations or predicted from GIA models. We used a linear trend fitted to the regional, compaction-free, RSL reconstructions compiled by Engelhart et al.(1) for the past 2 ka (excluding data since AD 1900) as a GIA estimate. Similarly, GIA models also attribute all RSL changes during the past 2 ka to linear GIA and have zero eustatic (e.g., meltwater) contribution.Grinsted et al. (2) contend that the approximately 1 mm/y GIA correction we applied to North Carolina (NC) RSL reconstructions (3) was too small, but their arguments are ill-founded and also misrepresent published results from Engelhart et al.(1, 4) that were co-authored by Horton and Peltier.i) Peltier's GIA model ICE-5G VM2 predicts subsidence of approximately 1.3 mm/y for NC during the past 2 ka (2). However, this model does not fit Holocene RSL reconstructions from the US mid-Atlantic coast and systematically overpredicts subsidence rates because of mantle lateral heterogeneity and/or tectonic effects (4). Geological data implicitly account for these factors. ii) Grinsted et al. (2) assert from the work of Engelhart et al.(1) that GPS observations indicate a greater rate of subsidence in NC than ICE-5G. The paper does not state this, and no NC measurements were reported (1). Rather, it concluded that GPS uncertainties are currently too large to confidently identify regional trends on the US mid-Atlantic coast because of the shortness of the time series. The nearest reported trend (Charleston, SC) was 1.6 ± 1.7 mm/y (5). GPS observations are the net effect of complex processes from which GIA must be isolated. iii) Grinsted et al. (2) wrongly claim that a 4-mm/y sea-level rise from NC tide-gauge data was identified by Engelhart et al. (1).No NC tide gauges were used in that study. NC gauges at Oregon Inlet, Cape Hatteras, and Beaufort record rates of 2.55 to 3.46 mm/y (with uncertainty up to ±1.1 mm/y). Our reconstruction of RSL from NC was consistent with regional tide-gauge measurements (3). The same GIA rate applied to both datasets, so consistency was necessarily preserved. Following GIA correction (∼1 mm/y), the NC reconstruction was also consistent with global tide-gauge compilations (3). iv) The larger GIA correction (1.3 ± 0.5 mm/y) proposed by Grinsted et al. (2) accumulates to as much as 1.6 m over 2 ka (being up to 0.8 mm/y greater than ours). To reconcile this GIA rate with the thickness and age of salt-marsh peat on the US Atlantic coast (1, 4) requires eustatic sealevel fall of the same magnitude (2). This contradicts IPCC AR4 and the archeological data used by Grinsted et al. (6).We applied a GIA rate of 1 mm/y and showed the effect of a ±0.15 mm/y range (3), which adequately spanned the uncer...

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“…To assess the uncertainty of the subsidence adjustment, we can look at several alternative estimates of the subsidence rate, and this is done by Engelhart et al (2). Global modeling of glacial isostasy (3) gives a rate of subsidence of approximately 1.3 mm/y.…”

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confidence: 99%

Comment on the subsidence adjustment applied to the Kemp et al. proxy of North Carolina relative sea level

Grinsted¹,

Jevrejeva²,

Moore³

2011

Proc. Natl. Acad. Sci. U.S.A.

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et al.(1) presented a new salt-marsh proxy record of relative sea level (RSL) from North Carolina (NCRSL). The salt marsh is slowly subsiding as a result of glacial isostatic adjustment (GIA), and the NCRSL record needs to be adjusted to remove this vertical land movement from the sea level record. Kemp et al. (1) corrected for a constant subsidence rate of approximately 1 mm/y. This is a "geologic" estimate based on sea level index points, which are determined from linear fits to data from other North American RSL proxy records. Thus, the geologic method implicitly assumes that the entire trend is a result of subsidence and leaves no room for any millennial-scale climatedriven changes in sea level. It is therefore not surprising that the adjusted RSL record has a preindustrial trend near zero.To assess the uncertainty of the subsidence adjustment, we can look at several alternative estimates of the subsidence rate, and this is done by Engelhart et al. (2). Global modeling of glacial isostasy (3) gives a rate of subsidence of approximately 1.3 mm/y. Direct GPS measurements indicate an even higher rate of subsidence of the regional proglacial forebulge (2). Finally, local tide gauge records have a 20th century rate of sea level rise of close to 4 mm/y (2), or approximately 2 mm/y higher than the global mean rate of sea level rise. To summarize, all these alternative estimates point to a substantially greater rate of subsidence than the 1 mm/y geologic estimate. We therefore question the zero-trend assumption used in the geologic estimates. We prefer the midrange correction from modeled GIA (3), which incorporates many lines of evidence and additionally includes nonlinear terms. Until the disagreement in subsidence rate has been resolved, the uncertainty must be gauged from the spread in alternative estimates, which is clearly much greater than the 2σ estimate of 0.1 mm/y in the study of Kemp et al. (1). In Fig. 1, we tentatively use an uncertainty of 0.5 mm/y, which accumulates to 1 m over 2,000 y. The impact of a greater rate of subsidence is that the adjusted NCRSL has a negative preindustrial trend with a pronounced Little Ice Age minimum rather than being a record of predominantly rising sea level (Fig. 1).We emphasize that the salt marsh record is an exceptional dataset on past sea level, but that great care must be taken to consider uncertainty in land movement that accumulates remorselessly over time, as we highlight here. Many of the primary conclusions of the work of Kemp et al. (1) were unaffected by a slightly greater subsidence correction, and the 20th century rate of rise is still exceptional. Hind-casts from semiempirical models (1,4,5) are consistent with the North Carolina salt-marsh proxy for a millennium (Fig. 1), but uncertainties are too large before that date.

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Spatial variability of late Holocene and 20th century sea-level rise along the Atlantic coast of the United States

Cited by 169 publications

References 38 publications

The contribution of glacial isostatic adjustment to projections of sea‐level change along the Atlantic and Gulf coasts of North America

The contribution of glacial isostatic adjustment to projections of sea‐level change along the Atlantic and Gulf coasts of North America

Reply to Grinsted et al.: Estimating land subsidence in North Carolina

Comment on the subsidence adjustment applied to the Kemp et al. proxy of North Carolina relative sea level

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