18Relative sea-level changes during the last ~2500 years in New Jersey, USA were reconstructed to test if 19 late Holocene sea level was stable or included persistent and distinctive phases of variability. 20Foraminifera and bulk-sediment δ 13 C values were combined to reconstruct paleomarsh elevation with 21 decimeter precision from sequences of salt-marsh sediment at two sites using a multi-proxy approach. 22The history of sediment deposition was constrained by a composite chronology. An age-depth model 23 developed for each core enabled reconstruction of sea level with multi-decadal resolution. Following 24 correction for land-level change (1.4mm/yr), four successive and sustained (multi-centennial) sea-level 25 trends were objectively identified and quantified using error-in-variables change point analysis to account 26 for age and sea-level uncertainties. From at least 500BC to 250AD sea-level fell at 0.11mm/yr. The 27 second period saw sea-level rise at 0.62mm/yr from 250AD to 733AD. Between 733AD and 1850AD sea 28 level fell at 0.12mm/yr. The reconstructed rate of sea-level rise since ~1850AD was 3.1mm/yr and 29 represents the most rapid period of change for at least 2500 years. This trend began between 1830AD and 30 1873AD and its onset is synchronous with other locations on the U.S. Atlantic coast. Since this change 31 point, reconstructed sea-level rise is in agreement with regional tide-gauge records and exceeds the global 32 average estimate for the 20 th century. These positive and negative departures from background rates 33 demonstrate that the late Holocene sea level was not stable in New Jersey. 34 35

Carbon (C) standing stocks, C mass balance, and soil C burial in tidal freshwater forested wetlands (TFFW) and TFFW transitioning to low‐salinity marshes along the upper estuary are not typically included in “blue carbon” accounting, but may represent a significant C sink. Results from two salinity transects along the tidal Waccamaw and Savannah rivers of the U.S. Atlantic Coast show that total C standing stocks were 322–1,264 Mg C/ha among all sites, generally shifting to greater soil storage as salinity increased. Carbon mass balance inputs (litterfall, woody growth, herbaceous growth, root growth, and surface accumulation) minus C outputs (surface litter and root decomposition, gaseous C) over a period of up to 11 years were 340–900 g C · m−2 · year−1. Soil C burial was variable (7–337 g C · m−2 · year−1), and lateral C export was estimated as C mass balance minus soil C burial as 267–849 g C · m−2 · year−1. This represents a large amount of C export to support aquatic biogeochemical transformations. Despite reduced C persistence within emergent vegetation, decomposition of organic matter, and higher lateral C export, total C storage increased as forests converted to marsh with salinization. These tidal river wetlands exhibited high N mineralization in salinity‐stressed forested sites and considerable P mineralization in low‐salinity marshes. Large C standing stocks and rates of C sequestration suggest that TFFW and oligohaline marshes are considerably important globally to coastal C dynamics and in facilitating energy transformations in areas of the world in which they occur.

The ridge and slough landscape of the Florida Everglades consists of a mosaic of linear sawgrass ridges separated by deeper-water sloughs with tree islands interspersed throughout the landscape. We used pollen assemblages from transects of sediment cores spanning sawgrass ridges, sloughs, and ridge-slough transition zones to determine the timing of ridge and slough formation and to evaluate the response of components of the ridge and slough landscape to climate variability and 20th-century water management. These pollen data indicate that sawgrass ridges and sloughs have been vegetationally distinct from one another since initiation of the Everglades wetland in mid-Holocene time. Although the position and community composition of sloughs have remained relatively stable throughout their history, modern sawgrass ridges formed on sites that originally were occupied by marshes. Ridge formation and maturation were initiated during intervals of drier climate (the Medieval Warm Period and the Little Ice Age) when the mean position of the Intertropical Convergence Zone shifted southward. During these drier intervals, marsh taxa were more common in sloughs, but they quickly receded when precipitation increased. Comparison with regional climate records suggests that slough vegetation is strongly influenced by North Atlantic Oscillation variability, even under 20th-century water management practices.

Tree islands are centers of biodiversity within the Florida Everglades, USA, but the factors controlling their distribution, formation, and development are poorly understood. We use pollen assemblages from tree islands throughout the greater Everglades ecosystem to reconstruct the timing of tree island formation, patterns of development, and response to specific climatic and environmental stressors. These data indicate that fixed (teardrop‐shaped) and strand tree islands developed well before substantial human alteration of the system, with initial tree island vegetation in place between 3500 and 500 calibrated years before present (cal yr BP), depending on the location in the Everglades wetland. Tree island development appears to have been triggered by regional‐ to global‐scale climatic events at 2800 cal yr BP, 1600–1500 cal yr BP, 1200–1000 cal yr BP (early Medieval Warm Period), and 500–200 cal yr BP (Little Ice Age). These periods correspond to drought intervals documented in Central and South America and periods of southward displacement of the Intertropical Convergence Zone. The records indicate a coherence of climate patterns in both subtropical North America and the Northern Hemisphere Neotropics. Water management practices of the 20th century altered plant communities and size of tree islands throughout the Everglades. Responses range from loss of tree islands due to artificially long hydroperiods and deep water to expansion of tree islands after flow reductions. These data provide evidence for the rapidity of tree island response to specific hydrologic change and facilitate prediction of the response to future changes associated with Everglades restoration plans.