Flandrian sea-level changes in west Lancashire and their implications for the ‘Hillhouse Coastline’

A relative sea-level curve for the Flandrian Stage has been drawn, based on twenty-three index points from west Lancashire and three from north Cheshire. Twenty-two of the points derive from a restricted area flanking the River Ribble, and one from Morecambe Bay. Evidence for sea-level changes comes from detailed stratigraphic and pollen analyses on material selected for radiocarbon assays. Eleven periods of marine transgression are recognised in northwest England, and these are compared with periods of marine transgression elsewhere in northwest Europe. The evidence for the ‘Hillhouse Coastline’ is considered in relation to the periods of marine transgression established in northwest England.     

Middle and late Holocene sea-levels along the Israel Mediterranean coast — evidence from ancient water wells

During the course of a study of historical water wells along the Israeli shore, which has been in progress since 1984, an innovative method for investigating sea-level fluctuations was developed. Eighteen ancient water wells were re-dug, 14 by the author, and four by archaeologists. Most of the re-dug wells are found at archaeological sites located a very short distance inland from the present shoreline. Evidence of ancient ground-water levels found in the wells directly reflects on historic eustatic sea-level changes, and the rate at which the end of the post-glacial transgression advanced. A critical question concerns the durability and life span of these wells, as the true age is very important for the accurate reconstruction of a sea-level curve. The Pre-Pottery Neolithic well of Atlit-Yam, which is the oldest known well in the world (ca. 8000 yr old), enabled the most accurate sea-level reconstruction for early Holocene times. Sea-level rise during that period of the Atlit-Yam site was of the order of 20 mm yr⁻¹ at the beginning, slowing to 6–8 mm yr⁻¹ at the abandonment of this site at ca. 7.5 ka BP, when it was flooded by the advancing and rising sea. After reaching its present level, sea-level fluctuations for the past 2.5 millennia were not greater than 1.5 to 2 m. © 1997 John Wiley & Sons, Ltd.     

Recent accretion in mangrove ecosystems based on137Cs and210Pb

Accretion rates were measured in fringe and basin mangrove forests in river and tidally dominated sites in Terminos Lagoon, Mexico, and a basin mangrove forest in Rookery Bay, Florida, USA. Accretion rates were determined using the radionuclides²¹⁰Pb and¹³⁷Cs. Consolidation-corrected accretion rates for the Rookery Bay cores, ranged from 1.4 to 1.7 mm yr^?1, with an average rate of 1.6 mm yr^?1. Rates at the Mexico sites ranged from 1.0 to 4.4 mm yr^?1, with an average of 2.4 mm yr^?1. Determination of rates in these mangrove forests was greatly affected by the consolidation corrections which decreased the apparent accretion rate by over 50% in one case. Accretion rates at basin sites compare favorably with a reported 1.4 to 1.6 mm yr^?1 rate of sea-level rise, indicating little or no subsidence at inland locations. Accretion rates in fringe sites are generally greater than basin sites, indicating greater subsidence rates in these sediments over longer time intervals.     

Rates and causes of recent global sea-level rise inferred from long tide gauge data records

Tide gauge data at seven sites of the Permanent Service for Mean Sea Level (PSMSL), with information for relative sea-level during the past 140–200 yr, were analyzed to examine the rates and causes of the global sea-level rise (GSLR) during the twentieth century. By subtracting linear trends for relative sea-level rise during the past 100 yr from the observed data, we get the apparent GSLRs of ∼1 mm yr⁻¹ for five sites around the Baltic Sea and Brest. The rate for San Francisco is significantly larger than this, with an optimum value ∼2 mm yr⁻¹. The spatial difference of ∼1 mm yr⁻¹ between these sites is reasonably explained by the recent melting of the Greenland ice sheet with an equivalent sea-level rise of ∼1 mm yr⁻¹. The predicted relative sea-level change for this melting scenario is 0.5 mm yr⁻¹ at sites around the Baltic Sea and Brest, and 1.5 mm yr⁻¹ for San Francisco. The residuals between observations and predictions, ∼0.5 mm yr⁻¹ at all sites, may be contributed by thermal expansion of seawater and/or other melting sources. These results suggest the rate of twentieth-century GSLR to be 1.5 mm yr⁻¹.     

Late Pleistocene raised beaches of coastal Estremadura,central Portugal

We present new stratigraphic, sedimentological, and chronological data for a suite of tectonically raised beaches dating to Marine Isotope Stages 5, 4, and 3 along the Estremadura coast of west-central Portugal. The beach deposits are found in association with ancient tidal channels and coastal dunes, pollen bearing mud and peat, and Middle Paleolithic archaeological sites that confirm occupation of the coastal zone by Neanderthal populations. The significance of these deposits is discussed in terms of the archaeological record, the tectonic and geomorphic evolution of the coast, and correlation with reconstructions of global climate and eustatic sea-level change. Direct correlation between the Estremadura beach sections is complicated by the tectonic complexity of the area and the age of the beach deposits (which are near or beyond the limit of radiocarbon dating). Evidence from multiple sites dated by AMS radiocarbon and optical luminescence methods suggests broad synchroneity in relative sea-level changes along this coast during Marine Isotope Stage 3. Two beach complexes with luminescence and radiocarbon age control date to about 35 ka and 42 ka, recording a rise in relative sea level around the time of Heinrich Event 4 at 39 ka. Depending on assumptions about eustatic sea level at the time they were deposited, we estimate that these beaches have been uplifted at rates of 0.4–4.3 mm yr^?1 by the combined effects of tectonic, halokinetic, and isostatic processes. Uplift rates of 1–2 mm yr^?1 are likely if the beaches represent sea level stands at roughly 40 m below modern, as suggested by recent eustatic sea level reconstructions. Evidence from coastal bluffs and the interior of the study area indicates extensive colluvial, fluvial, and aeolian sedimentation beginning around 31 ka and continuing into the Holocene. These geomorphic adjustments are related to concomitant changes in climate and sea level, providing context that improves our understanding of Late Pleistocene landscape change and human occupation on the western Iberian margin.     

Late Holocene sea-level changes and isostatic crustal movements in Atlantic Canada

It has long been recognised that sea levels along the shores of Atlantic Canada have been rising rapidly during the Holocene in response to isostatic crustal movements. New sea-level data for the Bay of Fundy coast of southern New Brunswick (Little Dipper Harbour) and the Atlantic coast of Nova Scotia (Chezzetcook Inlet) show that late Holocene average rates of sea-level rise in these areas have been 1.0 and 2.5 m per 1000 yr, respectively. Numerical model calculations suggest that the high rates of sea-level rise are due to crustal subsidence produced by the combined effects of Laurentide ice loading (forebulge collapse) and ocean loading of the Scotian shelf. Although ice loading is the dominant contributor to the regional sea-level pattern, ocean loading is also important, contributing up to 40% of the total crustal subsidence in some areas. Tide gauges record rates of sea-level rise during the 20^th century that are 0.7–1.9 mm/yr higher than late Holocene trends, with the highest residuals occurring in the Bay of Fundy.     

香港及其邻近海域海洋沉积物研究

香港及其邻近海域的表层沉积物以粘土质粉砂为主,测得的全新世沉积物最大厚度为17.8m,全新世平均沉积速率为0.81mm/a;维多利亚港因后期的潮流作用改造,全新世沉积很薄。第四纪沉积层中有5次海进及5次海退过程,体现了第四纪以来香港及其邻近海域的环境演变过程。香港海域的沉积环境与珠江密切有关,珠江不仅塑造了香港的5层陆相地层,同时为现代香港水域的潮流通道奠定了基础。     

Development and carbon sequestration of tropical peat domes in south-east Asia: links to post-glacial sea-level changes and Holocene climate variability

Tropical peatlands of SE-Asia represent a significant terrestrial carbon reservoir of an estimated 65 Gt C. In this paper we present a comprehensive data synthesis of radiocarbon dated peat profiles and 31 basal dates of ombrogenous peat domes from the lowlands of Peninsular Malaysia, Sumatra and Borneo and integrate our peatland data with records of past sea-level and climate change in the region. Based on their developmental features three peat dome regions were distinguished: inland Central Kalimantan (Borneo), Kutai basin (Borneo) and coastal areas across the entire region. With the onset of the Holocene the first peat domes developed in Central Kalimantan as a response to rapid post-glacial sea-level rise over the Sunda Shelf and intensification of the Asian monsoon. Peat accumulation rates in Central Kalimantan strongly declined after 8500 cal BP in close relation to the lowering rate of the sea-level rise and possibly influenced by the regional impact of the 8.2 ka event. Peat growth in Central Kalimantan apparently ceased during the Late Holocene in association with amplified El Niño activity as exemplified by several truncated peat profiles. Peat domes from the Kutai basin are all younger than ～8300 cal BP. Peat formation and rates of peat accumulation were driven by accretion rates of the Mahakam River and seemingly independent of climate. Most coastal peat domes, the largest expanse of SE-Asian peatlands, initiated between 7000 and 4000 cal BP as a consequence of a Holocene maximum in regional rainfall and the stabilisation and subsequent regression of the sea-level. These boundary conditions induced the highest rates of peat accumulation of coastal peat domes. The Late Holocene sea-level regression led to extensive new land availability that allowed for continued coastal peat dome formation until the present. The time weighted mean Holocene peat accumulation rate is 0.54 mm yr^?1 for Central Kalimantan, 1.89 mm yr^?1 for Kutai and 1.77 mm yr^?1 for coastal domes of Sumatra and Borneo. The mean Holocene carbon sequestration rates amount to 31.3 g C m^?2 yr^?1 for Central Kalimantan and 77.0 g C m^?2 yr^?1 for coastal sites, which makes coastal peat domes of south-east Asia the spatially most efficient terrestrial ecosystem in terms of long term carbon sequestration.     

Slip rates on the Helike Fault, Gulf of Corinth, Greece: new evidence from geoarchaeology

Palaeoseismological and archaeological analysis of a trench enabled us to estimate the Holocene slip rates on the East Helike Fault, flanking the south-western Gulf of Corinth. We recognized two major fault strands within the trench: the ‘north fault’ controls a succession of three colluvial wedges and the deposition of a 2.7 m thick sedimentary sequence. The ‘south fault’ controls the deposition of a 2.9-m thick brownish-red colluvium. Based on colluvial stratigraphy, radiocarbon dating of the sediments suggests that the slip rate was c. 0.3 mm yr⁻¹ from 10 250 to c. 1400 bp , when it increased dramatically to c. 2.0 mm yr⁻¹ after a strong earthquake event near 1400 bp . The faster slip rate evidently increased the sedimentation rate.     

Submerged upper Holocene beachrock on San Salvador Island,Bahamas: implications for recent sea-level history

Sedimentological, petrographic and radiometric data from a submerged beachrock on San Salvador Island, Bahamas, provide new information about the Late Holocene sea-level history in this area.At French Bay, on the southern shore of the island, samples of beachrock collected at a depth of 1 m below low tide level yielded an average ¹⁴C age of 965 ± 60 years before present. These samples further display a well developed fenestral porosity and present an early generation of low Mg calcite meniscus cement. These features characterize intertidal and supratidal settings; they are not consistent with the present beachrock position and the reported Late Holocene sea-level history in the Bahamas. A 1.5–2m low stand of the sea about 1000 years ago would best explain the observed particularities of the French Bay beachrock.This example from San Salvador shows that the smooth trend of Late Holocene sea-level rise proposed by previous workers might be overprinted by high frequency, low amplitude fluctuations. Recognition of these fluctuations is fundamental when calculating rates of sea-level rise and evaluating the coastal response to a marine transgression. Correspondence to: P. Kindler     

Holocene sea-level changes along the North Carolina Coastline and their implications for glacial isostatic adjustment models

We have synthesized new and existing relative sea-level (RSL) data to produce a quality-controlled, spatially comprehensive database from the North Carolina coastline. The RSL database consists of 54 sea-level index points that are quantitatively related to an appropriate tide level and assigned an error estimate, and a further 33 limiting dates that confine the maximum and minimum elevations of RSL. The temporal distribution of the index points is very uneven with only five index points older than 4000 cal a BP, but the form of the Holocene sea-level trend is constrained by both terrestrial and marine limiting dates. The data illustrate RSL rapidly rising during the early and mid Holocene from an observed elevation of ?35.7 ± 1.1 m MSL at 11062–10576 cal a BP to ?4.2 m ± 0.4 m MSL at 4240–3592 cal a BP.We restricted comparisons between observations and predictions from the ICE-5G(VM2) with rotational feedback Glacial Isostatic Adjustment (GIA) model to the Late Holocene RSL (last 4000 cal a BP) because of the wealth of sea-level data during this time interval. The ICE-5G(VM2) model predicts significant spatial variations in RSL across North Carolina, thus we subdivided the observations into two regions. The model forecasts an increase in the rate of sea-level rise in Region 1 (Albemarle, Currituck, Roanoke, Croatan, and northern Pamlico sounds) compared to Region 2 (southern Pamlico, Core and Bogue sounds, and farther south to Wilmington). The observations show Late Holocene sea-level rising at 1.14 ± 0.03 mm year^?1 and 0.82 ± 0.02 mm year^?1 in Regions 1 and 2, respectively. The ICE-5G(VM2) predictions capture the general temporal trend of the observations, although there is an apparent misfit for index points older than 2000 cal a BP. It is presently unknown whether these misfits are caused by possible tectonic uplift associated with the mid-Carolina Platform High or a flaw in the GIA model. A comparison of local tide gauge data with the Late Holocene RSL trends from Regions 1 and 2 support the spatial variation in RSL across North Carolina, and imply an additional increase of mean sea level of greater than 2 mm year^?1 during the latter half of the 20th century; this is in general agreement with historical tide gauge and satellite altimetry data.     

Dating faulted alluvial fans with cosmogenic 10Be in the Gurvan Bogd mountain range (Gobi-Altay, Mongolia): climatic and tectonic implications

The Gurvan Bogd mountain range is a fault system characterized by strong earthquakes (M ∼ 8) separated by long periods of quiescence. Further to the previous works in the area, our study provides new data concerning the tectonic and climatic processes in the Gobi-Altay. To quantify the slip rates along the faults, we dated offset alluvial fans analysing the in situ produced ¹⁰Be along profiles at depth. The slip rates along the Bogd strike–slip fault and its associated thrust faults over the Upper Pleistocene–Holocene period are 0.95 ± 0.29 mm yr⁻¹ and comprised between 0.12 ± 0.02 and 0.13 ± 0.02 mm yr⁻¹, respectively. The surfaces ages account for a cyclic formation of the fans over the past ∼360 ka, in correlation with the terminations of the marine isotope stages 2, 6, 8 and 10.     

Holocene stratigraphy and depositional history of the Narragansett Bay System, Rhode Island, U.S.A.

ABSTRACT An extensive seismic reflection survey has been used to gain further knowledge of Holocene stratigraphy and depositional history in the Narragansett Bay System (NBS). The early Holocene stream-dissected surface beneath the NBS is interpreted as having been flooded by the Holocene sea in a manner suggested by Oldale & O'Hara's (1980) sea-level-rise curve. The sea initially is believed to have penetrated the pre-NBS East Passage trunk valley about 9000 yr BP and subsequently spread landward via the trunk valley and its branches. The Holocene sediments display stratigraphic relationships that differ spatially. At passage mouths, the basal unconformity is inferred to be covered over with some 3 m of paralic and 5 m of marine sands and silts separated, by a transgressive unconformity. In contrast the interior sequences reveal (a) a valley section up to more than 15 m thick in which the regressional unconformity is overlain by probable lower fluvial and/or estuarine sand-silt facies that commonly grades upward to an estuarine silt-clay facies and (b) an interfluve section in which a basal transgressive unconformity is blanketed by an estuarine nearshore sand-silt facies that locally may change upward to a silt-clay facies. Primarily Holocene silt-clay accretion, produced by sedimentation processes associated with net non-tidal estuarine circulation, infilled the evolving NBS. Depositional bodies, lenticular in shape and comprised of 12 m or more of sediment, developed in lowlands near Gould Island (?9000 yr BP), in Upper Narragansett Bay (?7500 yr BP), around Hope Island (?7500 yr BP) and in Mt Hope Bay (?6250 yr BP) with an average minimal sedimentation rate of 1.6–2.2 mm yr^-1. Silt-clay deposition, commonly gas-bearing, has buried the basal relief in most of the NBS upper and middle portions except for middle East Passage. A comparison of NBS sedimentation with that of Chesapeake, Delaware and Hudson Estuaries shows that the estuaries to the south have accumulated more sediment over a slightly longer period yet, with the exception of the higher rate in the Hudson Estuary, the sedimentation rates appear to be similar.     

Submerged archaeological sites along the Ionian coast of southeastern Sicily (Italy) and implications for the Holocene relative sea-level change

Precise measurements of submerged archaeological markers in the Siracusa coast (Southeastern Sicily, Italy) provide new data on relative sea-level change during the late Holocene. Four submerged archaeological sites have been studied and investigated through direct observations. Two of them are Greek archaic in age (2.5–2.7 ka) and are now 0.98–1.48 m below sea level; the other two developed during the Bronze age (3.2–3.8 ka) and are now 1.03–1.97 m below sea level. These archaeological data have been integrated with information derived from a submerged speleothem collected in a cave located along the Siracusa coast at − 20 m depth. The positions of the archaeological markers have been measured with respect to present sea level, corrected for tide and pressure at the time of surveys. These data were compared with predicted sea-level rise curves for the Holocene using a glacio-hydro-isostatic model. The comparison with the curve for the southeastern Sicily coast yields a tectonic component of relative sea-level change related to regional uplift. Uplift rates between 0.3 and 0.8 mm/yr have been estimated.     

A new Late Holocene sea-level record from the Mississippi Delta: evidence for a climate/sea level connection?

A detailed relative sea-level (RSL) record was constructed for the time interval 600–1600 AD, using basal peat to track sea level and containing 16 sea-level index points that capture ～60 cm of RSL rise. The study area is in the Mississippi Delta where the spring tidal range is ～0.47 m, the impact of ocean currents on sea-surface topography is limited, and crustal motions are well constrained. Age control was obtained by AMS ¹⁴C dating and most ages represent weighted means of two subsamples. Sample elevations were determined by combining differential GPS measurements with optical surveying. All index points were plotted as error boxes using 2σ confidence intervals for the ages, plus all vertical errors involved in sampling and surveying, as well as the indicative range of the samples. A striking clustering of sea-level index points between ～1000 and ～1200 AD suggests a possible acceleration in the rate of RSL rise. Removal of the long-term trend (0.60 mm yr^?1) allows for the possibility of a sea-level oscillation with a maximum amplitude of ～55 cm. However, given the size of the error boxes the possibility that oscillations did not occur cannot be entirely ruled out. Comparison of the new RSL record with various proxy climate records suggests that sea level in this area may have responded to hemispheric temperature changes, including the Medieval Warm Period and the Little Ice Age. However, given the error margins associated with this reconstruction, it is stressed that this causal mechanism is tentative and requires corroboration by high-resolution sea-level reconstructions elsewhere.     

A relative sea-level history for Arviat,Nunavut, and implications for Laurentide Ice Sheet thickness west of Hudson Bay

Thirty-six new and previously published radiocarbon dates constrain the relative sea-level history of Arviat on the west coast of Hudson Bay. As a result of glacial isostatic adjustment (GIA) following deglaciation, sea level fell rapidly from a high-stand of nearly 170 m elevation just after 8000 cal yr BP to 60 m elevation by the mid Holocene (~ 5200 cal yr BP). The rate of sea-level fall decreased in the mid and late Holocene, with sea level falling 30 m since 3000 cal yr BP. Several late Holocene sea-level measurements are interpreted to originate from the upper end of the tidal range and place tight constraints on sea level. A preliminary measurement of present-day vertical land motion obtained by repeat Global Positioning System (GPS) occupations indicates ongoing crustal uplift at Arviat of 9.3 ± 1.5 mm/yr, in close agreement with the crustal uplift rate inferred from the inferred sea-level curve. Predictions of numerical GIA models indicate that the new sea-level curve is best fit by a Laurentide Ice Sheet reconstruction with a last glacial maximum peak thickness of ~ 3.4 km. This is a 30–35% thickness reduction of the ICE-5G ice-sheet history west of Hudson Bay.     

Geological constraints on glacio-isostatic adjustment models of relative sea-level change during deglaciation of Prince Gustav Channel,Antarctic Peninsula

The recent disintegration of Antarctic Peninsula ice shelves, and the associated accelerated discharge and retreat of continental glaciers, has highlighted the necessity of quantifying the current rate of Antarctic ice mass loss and the regional contributions to future sea-level rise. Observations of present day ice mass change need to be corrected for ongoing glacial isostatic adjustment, a process which must be constrained by geological data. However, there are relatively little geological data on the geometry, volume and melt history of the Antarctic Peninsula Ice Sheet (APIS) after Termination 1, and during the Holocene so the glacial isostatic correction remains poorly constrained. To address this we provide field constraints on the timing and rate of APIS deglaciation, and changes in relative sea-level (RSL) for the north-eastern Antarctic Peninsula based on geomorphological evidence of former marine limits, and radiocarbon-dated marine-freshwater transitions from a series of isolation basins at different altitudes on Beak Island. Relative sea-level fell from a maximum of c. 15 m above present at c. 8000 cal yr BP, at a rate of 3.91 mm yr^?1 declining to c. 2.11 mm yr^?1 between c. 6900–2900 cal yr BP, 1.63 mm yr^?1 between c. 2900–1800 cal yr BP, and finally to 0.29 mm yr^?1 during the last c. 1800 years. The new Beak Island RSL curve improves the spatial coverage of RSL data in the Antarctic. It is in broad agreement with some glacio-isostatic adjustment models applied to this location, and with work undertaken elsewhere on the Antarctic Peninsula. These geological and RSL constraints from Beak Island imply significant thinning of the north-eastern APIS by the early Holocene. Further, they provide key data for the glacial isostatic correction required by satellite-derived gravity measurements of contemporary ice mass loss, which can be used to better assess the future contribution of the APIS to rising sea-levels.     

Latest Miocene to Quaternary horizontal and vertical displacement rates during simultaneous contraction and extension in the Southern Apennines orogen, Italy

Foreland contraction and hinterland extension in the Southern Apennines orogen of Italy produced a complex spatial and temporal pattern of vertical and horizontal displacement. Remarkably, Late Miocene to mid-Pleistocene foreland migration of the contractional front at ∼16 mm yr⁻¹ was not accompanied by uplift and the frontal thrust belt remained at or below sea level. Only following a mid-Pleistocene reduction in horizontal displacement did the frontal thrust belt and foreland begin uplift at ∼0.5 mm yr⁻¹, a rate that increased to ∼1 mm yr⁻¹ after 125 ka. Although the extensional hinterland experienced net subsidence during formation of the Tyrrhenian basin, an extensional transition zone adjacent to the frontal thrust belt records sustained uplift at ∼0.3 mm yr⁻¹. The interaction of preexisting crustal structure and deep tectonic processes resulted in time-integrated displacement rates suggesting steady-state deformation for periods of 10⁶ years. Displacement rate changes were abrupt and occurred over intervals of 10⁵ years or less.     

Late Holocene sea-level changes and isostasy in western Denmark

Cores and exposed cliff sections in salt marshes around Ho Bugt, a tidal embayment in the northernmost part of the Danish Wadden Sea, were subjected to ¹⁴C dating and litho- and biostratigraphical analyses to reconstruct paleoenvironmental changes and to establish a late Holocene relative sea-level history. Four stages in the late Holocene development of Ho Bugt can be identified: (1) groundwater-table rise and growth of basal peat (from at least 2300 BC to AD 0); (2) salt-marsh formation (0 to AD 250); (3) a freshening phase (AD 250 to AD 1600?), culminating in the drying out of the marshes and producing a distinct black horizon followed by an aeolian phase with sand deposition; and (4) renewed salt-marsh deposition (AD 1600? to present). From 16 calibrated AMS radiocarbon ages on fossil plant fragments and 4 calibrated conventional radiocarbon ages on peat, we reconstructed a local relative sea-level history that shows a steady sea-level rise of 4 m since 4000 cal yr BP. Contrary to suggestions made in the literature, the relative sea-level record of Ho Bugt does not contain a late Holocene highstand. Relative sea-level changes at Ho Bugt are controlled by glacio-isostatic subsidence and can be duplicated by a glacial isostatic adjustment model in which no water is added to the world's oceans after ca. 5000 cal yr BP.     

Accretion rates and sediment accumulation in Rhode Island salt marshes

In order to test the assumption that accretion rates of intertidal salt marshes are approximately equal to rates of sea-level rise along the Rhode Island coast,²¹⁰Pb analyses were carried out and accretion rates calculated using constant flux and constant activity models applied to sediment cores collected from lowSpartina alterniflora marshes at four sites from the head to the mouth of Narragansett Bay. A core was also collected from a highSpartina patens marsh at one site. Additional low marsh cores from a tidal river entering the bay and a coastal lagoon on Block Island Sound were also analyzed. Accretion rates for all cores were also calculated from copper concentration data assuming that anthropogenic copper increases began at all sites between 1865 and 1885. Bulk density and weight-loss-on-ignition of the sediments were measured in order to assess the relative importance of inorganic and organic accumulation. During the past 60 yr, accretion rates at the eight low marsh sites averaged 0.43±0.13 cm yr^?1 (0.25 to 0.60 cm yr^?1) based on the constant flux model, 0.40±0.15 cm yr^?1 (0.15 to 0.58 cm yr^?1) based on the constant activity model, and 0.44±0.11 cm yr^?1 (0.30 to 0.59 cm yr^?1) based on copper concentration data, with no apparent trend down-bay. High marsh rates were 0.24±0.02 (constant flux), 0.25±0.01 (constant activity), and 0.47±0.04 (copper concentration data). The cores showing closest agreement between the three methods are those for which the excess²¹⁰Pb inventories are consistent with atmospheric inputs. These rates compare to a tide gauge record from the mouth of the bay that shows an average sea-level rise of 0.26±0.02 cm yr^?1 from 1931 to 1986. Low marshes in this area appear to accrete at rates 1.5–1.7 times greater than local relative sea-level rise, while the high marsh accretion rate is equal to the rise in sea level. The variability among the low marsh sites suggests that marshes may not be poised at mean water level to within better than ±several cm on time scales of decades. Inorganic and organic dry solids each contributed about 9% by volume to low marsh accretion, while organic dry solids contributed 11% and inorganic 4% to high marsh accretion. Water/pore space accounted for the majority of accretion in both low and high marshes. If water associated with the organic component is considered, organic matter accounts for an average of 91% of low marsh and 96% of high marsh accretion. A dramatic increase in the organic content at a depth of 60 to 90 cm in the cores from Narragansett Bay appears to mark the start of marsh development on prograding sand flats.