@article {2776, title = {Identifying the Greatest Earthquakes of the Past 2000 Years at the Nehalem River Estuary, Northern Oregon Coast, USA}, journal = {Open Quaternary}, volume = {6}, year = {2020}, month = {Feb-01-2021}, abstract = {We infer a history of three great megathrust earthquakes during the past 2000 years at the Nehalem River estuary based on the lateral extent of sharp (<=3 mm) peat-mud stratigraphic contacts in cores and outcrops, coseismic subsidence as interpreted from fossil diatom assemblages and reconstructed with foraminiferal assemblages using a Bayesian transfer function, and regional correlation of 14C-modeled ages for the times of subsidence. A subsidence contact from 1700 CE (contact A), sometimes overlain by tsunami-deposited sand, can be traced over distances of 7 km. Contacts B and D, which record subsidence during two earlier megathrust earthquakes, are much less extensive but are traced across a 700-m by 270-m tidal marsh. Although some other Cascadia studies report evidence for an earthquake between contacts B and D, our lack of extensive evidence for such an earthquake may result from the complexities of preserving identifiable evidence of it in the rapidly shifting shoreline environments of the lower river and bay. Ages (95\% intervals) and subsidence for contacts are: A, 1700 CE (1.1 {\textpm} 0.5 m); B, 942{\textendash}764 cal a BP (0.7 {\textpm} 0.4 m and 1.0 m {\textpm} 0.4 m); and D, 1568{\textendash}1361 cal a BP (1.0 m {\textpm} 0.4 m). Comparisons of contact subsidence and the degree of overlap of their modeled ages with ages for other Cascadia sites are consistent with megathrust ruptures many hundreds of kilometers long. But these data cannot conclusively distinguish among different types or lengths of ruptures recorded by the three great earthquake contacts at the Nehalem River estuary.}, keywords = {Bayesian transfer function, Cascadia subduction zone, Coseismic subsidence, earthquake hazards, Paleoseismology, salt-marsh stratigraphy, Sea-level changes, tidal foraminifera and diatoms}, doi = {10.5334/oq.70}, url = {http://www.openquaternary.com/articles/10.5334/oq.70/}, author = {Nelson, Alan R. and Hawkes, Andrea D. and Sawai, Yuki and Engelhart, Simon E. and Witter, Rob and Grant-Walter, Wendy C. and Bradley, Lee-Ann and Dura, Tina and Cahill, Niamh and Horton, Ben} } @article {2758, title = {Salt marsh ecosystem restructuring enhances elevation resilience and carbon storage during accelerating relative sea-level rise}, journal = {Estuarine, Coastal and Shelf Science}, volume = {217}, year = {2019}, month = {Jan-02-2019}, pages = {56 - 68}, abstract = { Salt marshes respond to sea-level rise through a series of complex and dynamic bio-physical feedbacks. In this study, we found that sea-level rise triggered salt marsh habitat restructuring, with the associated vegetation changes enhancing salt marsh elevation resilience. A continuous record of marsh elevation relative to sea level that includes reconstruction of high-resolution, sub-decadal, marsh elevation over the past century, coupled with a lower-resolution 1500-year record, revealed that relative sea-level rose 1.5 {\textpm} 0.4 m, following local glacial isostatic adjustment (1.2 mm/yr). As sea-level rise has rapidly accelerated, the high marsh zone dropped 11 cm within the tidal frame since 1932, leading to greater inundation and a shift to flood- and salt-tolerant low marsh species. Once the marsh platform fell to the elevation favored by low-marsh Spartina alterniflora, the elevation stabilized relative to sea level. Currently low marsh accretion keeps pace with sea-level rise, while present day high marsh zones that have not transitioned to low marsh have a vertical accretion deficit. Greater biomass productivity, and an expanding subsurface accommodation space favorable for salt marsh organic matter preservation, provide a positive feed-back between sea-level rise and marsh platform elevation. Carbon storage was 46 {\textpm} 28 g C/m2/yr from 550 to 1800 CE, increasing to 129 {\textpm} 50 g C/m2/yr in the last decade. Enhanced carbon storage is controlled by vertical accretion rates, rather than soil carbon density, and is a direct response to anthropogenic eustatic sea-level rise, ultimately providing a negative feedback on climate warming. }, keywords = {14-Carbon, accretion, Carbon storage, Elevation, Salt marsh, Sea level index point, sea-level rise}, issn = {02727714}, doi = {10.1016/j.ecss.2018.11.003}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0272771418306851}, author = {Gonneea, Meagan Eagle and Maio, Christopher V. and Kroeger, Kevin D. and Hawkes, Andrea D. and Mora, Jordan and Sullivan, Richard and Madsen, Stephanie and Buzard, Richard M. and Cahill, Niamh and Donnelly, Jeffrey P.} } @article {2808, title = {Relative sea-level change in Newfoundland, Canada during the past \~{}3000 years}, journal = {Quaternary Science Reviews}, volume = {201}, year = {2018}, month = {Jan-12-2018}, pages = {89 - 110}, abstract = {Several processes contributing to coastal relative sea-level (RSL) change in the North Atlantic Ocean are observed and/or predicted to have distinctive spatial expressions that vary by latitude. To expand the latitudinal range of RSL records spanning the past \~{}3000 years and the likelihood of recognizing the characteristic fingerprints of these processes, we reconstructed RSL at two sites (Big River and Placentia) in Newfoundland from salt-marsh sediment. Bayesian transfer functions established the height of former sea level from preserved assemblages of foraminifera and testate amoebae. Age-depth models constrained by radiocarbon dates and chronohorizons estimated the timing of sediment deposition. During the past \~{}3000 years, RSL rose by \~{}3.0 m at Big River and by \~{}1.5 m at Placentia. A locally calibrated geotechnical model showed that post-depositional lowering through sediment compaction was minimal. To isolate and quantify contributions to RSL from global, regional linear, regional non-linear, and local-scale processes, we decomposed the new reconstructions (and those in an expanded, global database) using a spatio-temporal statistical model. The global component confirms that 20th century sea-level rise occurred at the fastest, century-scale rate in over 3000 years (P > 0.999). Distinguishing the contributions from local and regional non-linear processes is made challenging by a sparse network of reconstructions. However, only a small contribution from local-scale processes is necessary to reconcile RSL reconstructions and modeled RSL trends. We identified three latitudinally-organized groups of sites that share coherent regional non-linear trends and indicate that dynamic redistribution of ocean mass by currents and/or winds was likely an important driver of sea-level change in the North Atlantic Ocean during the past \~{}3000 years.}, issn = {02773791}, doi = {10.1016/j.quascirev.2018.10.012}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0277379118304980}, author = {Kemp, Andrew C. and Wright, Alexander J. and Edwards, Robin J. and Barnett, Robert L. and Brain, Matthew J. and Kopp, Robert E. and Cahill, Niamh and Horton, Benjamin P. and Charman, Dan J. and Hawkes, Andrea D. and Hill, Troy D. and van de Plassche, Orson} } @article {2773, title = {Reconstructing Common Era relative sea-level change on the Gulf Coast of Florida}, journal = {Marine Geology}, volume = {390}, year = {2017}, month = {Jan-08-2017}, pages = {254 - 269}, abstract = {To address a paucity of Common Era data in the Gulf of Mexico, we reconstructed ~ 1.1 m of relative sea-level (RSL) rise over the past ~ 2000 years at Little Manatee River (Gulf Coast of Florida, USA). We applied a regional-scale foraminiferal transfer function to fossil assemblages preserved in a core of salt-marsh peat and organic silt that was dated using radiocarbon and recognition of pollution, 137Cs and pollen chronohorizons. Our proxy reconstruction was combined with tide-gauge data from four nearby sites spanning 1913{\textendash}2014 CE. Application of an Errors-in-Variables Integrated Gaussian Process (EIV-IGP) model to the combined proxy and instrumental dataset demonstrates that RSL fell from ~ 350 to 100 BCE, before rising continuously to present. This initial RSL fall was likely the result of local-scale processes (e.g., silting up of a tidal flat or shallow sub-tidal shoal) as salt-marsh development at the site began. Since ~ 0 CE, we consider the reconstruction to be representative of regional-scale RSL trends. We removed a linear rate of 0.3 mm/yr from the RSL record using the EIV-IGP model to estimate climate-driven sea-level trends and to facilitate comparison among sites. This analysis demonstrates that since ~ 0 CE sea level did not deviate significantly from zero until accelerating continuously from ~ 1500 CE to present. Sea level was rising at 1.33 mm/yr in 1900 CE and accelerated until 2014 CE when a rate of 2.02 mm/yr was attained, which is the fastest, century-scale trend in the ~ 2000-year record. Comparison to existing reconstructions from the Gulf coast of Louisiana and the Atlantic coast of northern Florida reveal similar sea-level histories at all three sites. We explored the influence of compaction and fluvial processes on our reconstruction and concluded that compaction was likely insignificant. Fluvial processes were also likely insignificant, but further proxy evidence is needed to fully test this hypothesis. Our results indicate that no significant Common Era sea-level changes took place on the Gulf and southeastern Atlantic U.S. coasts until the onset of modern sea-level rise in the late 19th century.}, issn = {00253227}, doi = {10.1016/j.margeo.2017.07.001}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0025322716303346}, author = {Gerlach, Matthew J. and Engelhart, Simon E. and Kemp, Andrew C. and Moyer, Ryan P. and Smoak, Joseph M. and Bernhardt, Christopher E. and Cahill, Niamh} } @article {2829, title = {Relative sea-level trends in New York City during the past 1500 years}, journal = {The Holocene}, volume = {27}, year = {2017}, month = {Sep-08-2017}, pages = {1169 - 1186}, abstract = {New York City (NYC) is threatened by 21st-century relative sea-level (RSL) rise because it will experience a trend that exceeds the global mean and has high concentrations of low-lying infrastructure and socioeconomic activity. To provide a long-term context for anticipated trends, we reconstructed RSL change during the past ~1500 years using a core of salt-marsh sediment from Pelham Bay in The Bronx. Foraminifera and bulk-sediment δ13C values were used as sea-level indicators. The history of sediment accumulation was established by radiocarbon dating and recognition of pollution and land-use trends of known age in down-core elemental, isotopic, and pollen profiles. The reconstruction was generated within a Bayesian hierarchical model to accommodate multiple proxies and to provide a unified statistical framework for quantifying uncertainty. We show that RSL in NYC rose by ~1.70 m since ~575 CE (including ~0.38 m since 1850 CE). The rate of RSL rise increased markedly at 1812{\textendash}1913 CE from ~1.0 to ~2.5 mm/yr, which coincides with other reconstructions along the US Atlantic coast. We investigated the possible influence of tidal-range change in Long Island Sound on our reconstruction using a regional tidal model, and we demonstrate that this effect was likely small. However, future tidal-range change could exacerbate the impacts of RSL rise in communities bordering Long Island Sound. The current rate of RSL rise is the fastest that NYC has experienced for >1500 years, and its ongoing acceleration suggests that projections of 21st-century local RSL rise will be realized.}, keywords = {Bayesian transfer function, carbon isotope, Foraminifera, Salt marsh, sedimentation, The Bronx}, issn = {0959-6836}, doi = {10.1177/0959683616683263}, url = {http://journals.sagepub.com/doi/10.1177/0959683616683263}, author = {Kemp, Andrew C and Hill, Troy D and Vane, Christopher H and Cahill, Niamh and Orton, Philip M and Talke, Stefan A and Parnell, Andrew C and Sanborn, Kelsey and Hartig, Ellen K} } @article {2489, title = {Relative sea-level change in northeastern Florida (USA) during the last \~{}8.0~ka}, journal = {Quaternary Science Reviews}, volume = {142}, year = {2016}, month = {Jan-06-2016}, pages = {90 - 101}, abstract = {An existing database of relative sea-level (RSL) reconstructions from the U.S. Atlantic coast lacked valid sea-level index points from Georgia and Florida. This region lies on the edge of the collapsing forebulge of the former Laurentide Ice Sheet making it an important location for understanding glacio-isostatic adjustment and the history of ice-sheet melt. To address the paucity of data, we reconstruct RSL in northeastern Florida (St. Marys) over the last \~{}8.0 ka from samples of basal salt-marsh sediment that minimize the influence of compaction. The analogy between modern salt-marsh foraminifera and their fossil counterparts preserved in the sedimentary record was used to estimate paleomarsh surface elevation. Sample ages were determined by radiocarbon dating of identifiable and in-situ plant macrofossils. This approach yielded 25 new sea-level index points that constrain a \~{}5.7 m rise in RSL during the last \~{}8.0 ka. The record shows that no highstand in sea level occurred in this region over the period of the reconstruction. We compared the new reconstruction to Earth-ice models ICE 6G-C VM5a and ICE 6G-C VM6. There is good fit in the later part of the Holocene with VM5a and for a brief time in the earlier Holocene with VM6. However, there are discrepancies in model-reconstruction fit in the early to mid Holocene in northeastern Florida and elsewhere along the Atlantic coast at locations with early Holocene RSL reconstructions. The most pronounced feature of the new reconstruction is a slow down in the rate of RSL rise from approximately 5.0 to 3.0 ka. This trend may reflect a significant contribution from local-scale processes such as tidal-range change and/or change in base flow of the St. Marys River in response to paleoclimate changes. However, the spatial expression (local vs. regional) of this slow down is undetermined and corroborative records are needed to establish its geographical extent.}, keywords = {Foraminifera, Georgia, Holocene, Salt marsh, St. Marys River}, issn = {02773791}, doi = {10.1016/j.quascirev.2016.04.016}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0277379116301275http://api.elsevier.com/content/article/PII:S0277379116301275?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0277379116301275?httpAccept=text/plain}, author = {Hawkes, Andrea D. and Kemp, Andrew C. and Donnelly, Jeffrey P. and Horton, Benjamin P. and Peltier, W. Richard and Cahill, Niamh and Hill, David F. and Ashe, Erica and Alexander, Clark R.} } @article {2494, title = {Relative sea-level change in Connecticut (USA) during the last 2200 yrs}, journal = {Earth and Planetary Science Letters}, volume = {428}, year = {2015}, month = {Jan-10-2015}, pages = {217 - 229}, abstract = {We produced a relative sea-level (RSL) reconstruction from Connecticut (USA) spanning the last \~{}2200 yrs that is free from the influence of sediment compaction. The reconstruction used a suite of vertically- and laterally-ordered sediment samples <=2 cm above bedrock that were collected by excavating a trench along an evenly-sloped bedrock surface. Paleomarsh elevation was reconstructed using a regional-scale transfer function trained on the modern distribution of foraminifera on Long Island Sound salt marshes and supported by bulk-sediment δ13C measurements. The history of sediment accumulation was estimated using an age-elevation model constrained by radiocarbon dates and recognition of pollution horizons of known age. The RSL reconstruction was combined with regional tide-gauge measurements spanning the last \~{}150 yrs before being quantitatively analyzed using an error-in-variables integrated Gaussian process model to identify sea-level trends with formal and appropriate treatment of uncertainty and the temporal distribution of data. RSL rise was stable (\~{}1 mm/yr) from \~{}200 BCE to \~{}1000 CE, slowed to a minimum rate of rise (0.41 mm/yr) at \~{}1400 CE, and then accelerated continuously to reach a current rate of 3.2 mm/yr, which is the fastest, century-scale rate of the last 2200 yrs. Change point analysis identified that modern rates of rise in Connecticut began at 1850{\textendash}1886 CE. This timing is synchronous with changes recorded at other sites on the U.S. Atlantic coast and is likely the local expression of a global sea-level change. Earlier sea-level trends show coherence north of Cape Hatteras that are contrasted with southern sites. This pattern may represent centennial-scale variability in the position and/or strength of the Gulf Stream. Comparison of the new record to three existing and reanalyzed RSL reconstructions from the same site developed using sediment cores indicates that compaction is unlikely to significantly distort RSL reconstructions produced from shallow (\~{}2{\textendash}3 m thick) sequences of salt-marsh peat.}, keywords = {Atlantic Ocean, Foraminifera, Gulf Stream, Late Holocene, Salt marsh}, issn = {0012821X}, doi = {10.1016/j.epsl.2015.07.034}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0012821X15004690http://api.elsevier.com/content/article/PII:S0012821X15004690?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0012821X15004690?httpAccept=text/plain}, author = {Kemp, Andrew C. and Hawkes, Andrea D. and Donnelly, Jeffrey P. and Vane, Christopher H. and Horton, Benjamin P. and Hill, Troy D. and Anisfeld, Shimon C. and Parnell, Andrew C. and Cahill, Niamh} } @article {56, title = {Late Holocene sea- and land-level change on the U.S. southeastern Atlantic coast}, journal = {Marine Geology}, volume = {357}, year = {2014}, pages = {90-100}, abstract = {Late Holocene relative sea-level (RSL) reconstructions can be used to estimate rates of land-level (subsidence or uplift) change and therefore to modify global sea-level projections for regional conditions. These reconstructions also provide the long-term benchmark against which modern trends are compared and an opportunity to understand the response of sea level to past climate variability. To address a spatial absence of late Holocene data in Florida and Georgia, we reconstructed ~ 1.3 m of RSL rise in northeastern Florida (USA) during the past ~ 2600 years using plant remains and foraminifera in a dated core of high salt-marsh sediment. The reconstruction was fused with tide-gauge data from nearby Fernandina Beach, which measured 1.91 {\textpm} 0.26 mm/year of RSL rise since 1900 CE. The average rate of RSL rise prior to 1800 CE was 0.41 {\textpm} 0.08 mm/year. Assuming negligible change in global mean sea level from meltwater input/removal and thermal expansion/contraction, this sea-level history approximates net land-level (subsidence and geoid) change, principally from glacio-isostatic adjustment. Historic rates of rise commenced at 1850{\textendash}1890 CE and it is virtually certain (P = 0.99) that the average rate of 20th century RSL rise in northeastern Florida was faster than during any of the preceding 26 centuries. The linearity of RSL rise in Florida is in contrast to the variability reconstructed at sites further north on the U.S. Atlantic coast and may suggest a role for ocean dynamic effects in explaining these more variable RSL reconstructions. Comparison of the difference between reconstructed rates of late Holocene RSL rise and historic trends measured by tide gauges indicates that 20th century sea-level trends along the U.S. Atlantic coast were not dominated by the characteristic spatial fingerprint of melting of the Greenland Ice Sheet.}, issn = {0025-3227}, doi = {10.1016/j.margeo.2014.07.010}, url = {http://www.sciencedirect.com/science/article/pii/S0025322714002187}, author = {Kemp, Andrew C. and Bernhardt, Christopher E. and Horton, Benjamin P. and Kopp, Robert E. and Vane, Christopher H. and Peltier, W. Richard and Hawkes, Andrea D. and Donnelly, Jeffrey P. and Parnell, Andrew C. and Cahill, Niamh} } @article {2497, title = {Late Holocene sea- and land-level change on the U.S. southeastern Atlantic coast}, journal = {Marine Geology}, volume = {357}, year = {2014}, month = {Jan-11-2014}, pages = {90 - 100}, abstract = {Late Holocene relative sea-level (RSL) reconstructions can be used to estimate rates of land-level (subsidence or uplift) change and therefore to modify global sea-level projections for regional conditions. These reconstructions also provide the long-term benchmark against which modern trends are compared and an opportunity to understand the response of sea level to past climate variability. To address a spatial absence of late Holocene data in Florida and Georgia, we reconstructed ~ 1.3 m of RSL rise in northeastern Florida (USA) during the past ~ 2600 years using plant remains and foraminifera in a dated core of high salt-marsh sediment. The reconstruction was fused with tide-gauge data from nearby Fernandina Beach, which measured 1.91 {\textpm} 0.26 mm/year of RSL rise since 1900 CE. The average rate of RSL rise prior to 1800 CE was 0.41 {\textpm} 0.08 mm/year. Assuming negligible change in global mean sea level from meltwater input/removal and thermal expansion/contraction, this sea-level history approximates net land-level (subsidence and geoid) change, principally from glacio-isostatic adjustment. Historic rates of rise commenced at 1850{\textendash}1890 CE and it is virtually certain (P = 0.99) that the average rate of 20th century RSL rise in northeastern Florida was faster than during any of the preceding 26 centuries. The linearity of RSL rise in Florida is in contrast to the variability reconstructed at sites further north on the U.S. Atlantic coast and may suggest a role for ocean dynamic effects in explaining these more variable RSL reconstructions. Comparison of the difference between reconstructed rates of late Holocene RSL rise and historic trends measured by tide gauges indicates that 20th century sea-level trends along the U.S. Atlantic coast were not dominated by the characteristic spatial fingerprint of melting of the Greenland Ice Sheet.}, keywords = {florida, Foraminifera, Glacio-isostatic adjustment Greenland fingerprint, Salt marsh}, issn = {00253227}, doi = {10.1016/j.margeo.2014.07.010}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0025322714002187http://api.elsevier.com/content/article/PII:S0025322714002187?httpAccept=text/xmlhttp://api.elsevier.com/content/article/PII:S0025322714002187?httpAccept=text/plain}, author = {Kemp, Andrew C. and Bernhardt, Christopher E. and Horton, Benjamin P. and Kopp, Robert E. and Vane, Christopher H. and Peltier, W. Richard and Hawkes, Andrea D. and Donnelly, Jeffrey P. and Parnell, Andrew C. and Cahill, Niamh} } @article {98, title = {Sea-level change during the last 2500 years in New Jersey, USA}, journal = {Quaternary Science Reviews}, volume = {81}, year = {2013}, pages = {90-104}, abstract = {Relative sea-level changes during the last \~{}2500 years in New Jersey, USA were reconstructed to test if late Holocene sea level was stable or included persistent and distinctive phases of variability. Foraminifera and bulk-sediment δ13C values were combined to reconstruct paleomarsh elevation with decimeter precision from sequences of salt-marsh sediment at two sites using a multi-proxy approach. The additional paleoenvironmental information provided by bulk-sediment δ13C values reduced vertical uncertainty in the sea-level reconstruction by about one third of that estimated from foraminifera alone using a transfer function. The history of sediment deposition was constrained by a composite chronology. An age{\textendash}depth model developed for each core enabled reconstruction of sea level with multi-decadal resolution. Following correction for land-level change (1.4 mm/yr), four successive and sustained (multi-centennial) sea-level trends were objectively identified and quantified (95\% confidence interval) using error-in-variables change point analysis to account for age and sea-level uncertainties. From at least 500 BC to 250 AD, sea-level fell at 0.11 mm/yr. The second period saw sea-level rise at 0.62 mm/yr from 250 AD to 733 AD. Between 733 AD and 1850 AD, sea level fell at 0.12 mm/yr. The reconstructed rate of sea-level rise since \~{}1850 AD was 3.1 mm/yr and represents the most rapid period of change for at least 2500 years. This trend began between 1830 AD and 1873 AD. Since this change point, reconstructed sea-level rise is in agreement with regional tide-gauge records and exceeds the global average estimate for the 20th century. These positive and negative departures from background rates demonstrate that the late Holocene sea level was not stable in New Jersey.}, issn = {0277-3791}, doi = {10.1016/j.quascirev.2013.09.024}, url = {http://www.sciencedirect.com/science/article/pii/S0277379113003740}, author = {Kemp, Andrew C. and Horton, Benjamin P. and Vane, Christopher H. and Bernhardt, Christopher E. and Corbett, D. Reide and Engelhart, Simon E. and Anisfeld, Shimon C. and Parnell, Andrew C. and Cahill, Niamh} }