Relative sea-level trends in New York City during the past 1500 years

Abstract

foraminifera, salt marsh, Bayesian transfer function, carbon isotope, The Bronx, sedimentation Abstract: New York City is at risk from 21st century relative sea-level rise because it is likely to experience a regional trend that exceeds the global mean and has high concentrations of low-lying infrastructure and socio economic activity. To provide a long-term context for anticipated future trends, we reconstructed relative sea-level change during the past ~1500 years using a sediment core from a salt marsh at Pelham Bay in The Bronx. Foraminifera and bulk sediment δ13C values were used as sea level indicators, while the history of sediment accumulation was established by radiocarbon dating of plant macrofossils 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 comprised of three modules (calibration, chronology, and process) to accommodate multiple proxies and to provide a unified statistical framework for quantifying uncertainty. We show that relative sea level in New York City rose by ~1.70 m since ~575 CE, of which ~0.38 m occurred after 1850 CE. The rate of relative sea level rise increased markedly between 1852 CE and 1911 CE, which coincides with other reconstructions along the U.S. Atlantic coast. A regional tidal model was used to investigate the possible influence of tidal-range change in Long Island Sound on our reconstruction and we demonstrate that this effect was likely small. However, future tidal-range change could http://mc.manuscriptcentral.com/holocene approximately mean high water (MHW) and mean higher high water (MHHW; e.g., van de Plassche, 1991;Redfield, 1972; Johnson and York, 1915). At the boundary between the salt marsh and surrounding, upland forest is a narrow vegetative zone dominated by Phragmites australis. This zone is found above the MHHW tidal datum. Peat forming in this environment is typically a black, amorphous organic matrix that hosts the rhizomes of Phragmites australis plants (e.g., Niering et al., 1977). Through time these rhizomes are commonly flattened and degraded, resulting in a homogenized peat. The halotype of Phragmites found on and around modern salt marshes in the northeastern United States is invasive, although native haloptypes existed prior to European colonization in this region (Saltonstall, 2002). Elsewhere this uppermost zone of marine influence may also be occupied by Schoeneplectus spp., Typha spp., and/or Iva fructescens. We estimated the great diurnal tidal range (mean lower low water, MLLW to MHHW) at the site to be 2.44 m using the VDatum Harbor and Long Island Sound. METHODS Core collection and levelingThe sediment beneath the Pelham Bay salt marsh was described from hand-driven cores collected along two transects ( Figure 1C, D). Core PBA-4 was selected for detailed analysis because it included the thickest accumulation of peat and was therefore anticipated to provide the longest RSL record and adequate materia...

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