O. van de Plassche

Submergence of coastal Connecticut 6000–3000 (14C) years B.P.

Abstract Curves of relative sea-level (RSL) change are essential to testing geophysical models of earth crustal behaviour. RSL curves, therefore, must be reliable. A 1963 RSL curve for Connecticut, showing a significantly slower submergence rate between 7000 and 3000 yrs B.P. than at other New England sites, is revised. New data indicate a rate of rise similar to the other regional curves. Two of the earlier samples were contaminated with older residual peat. This residual material points to water-level changes which, if regionally significant, are important for studying the postglacial isostatic response of the Long Island Sound region.

Mid-Holocene water-level changes in the lower Rhine-Meuse delta (western Netherlands): implications for the reconstruction of relative mean sea-level rise, palaeoriver-gradients and coastal evolution

We present a revised relative mean sea-level (MSL) curve for the Rhine-Meuse delta, western Netherlands, for the period 7900-5300 cal yr BP. The revision is based on a series of new and previously unpublished local groundwater-level index data from buried Late Glacial aeolian dunes in the lower Rhine-Meuse delta, and reinterpretation of existing data. The new index data consist of (AMS and conventional) radiocarbon dates of samples, collected from the base of peat formed on dune slopes, near Vlaardingen (21 index points), Hillegersberg (one index point), and Hardinxveld-Giessendam (10 index points). The Vlaardingen data represent the coast-nearest Rhine-Meuse delta local water-level record, which therefore is highly indicative for sea-level change. Pollen and macrofossil analysis, and dating of paired samples was carried out to assess the reliability of the groundwater-level index data. The revision of the MSL curve involves: (1) a significant (0 to >1 m) upward adjustment for the period 7900-7300 cal yr BP; (2) a downward adjustment of ≤0.25 m for the period 6650-5300 cal yr BP. The new data indirectly support the reliability of the part of the curve for the period 7300-6650 cal yr BP. A longitudinally fairly uniform river gradient of 2.5-3.0 cm/km in the lower Rhine-Meuse delta during the period 6650-5600 cal yr BP can be inferred from the data sets. A significant river gradient extended further towards the coastline than previously thought and it may be that also the revised MSL curve reflects river-gradient effects. An increased floodbasin effect (stronger intra-coastal tidal damping) seems to have developed in the lower Rhine-Meuse delta in de period 7500-6600 cal yr BP, and was probably a complex response to a major avulsion of the Rhine.

New groundwater-level rise data from the Rhine-Meuse delta – implications for the reconstruction of Holocene relative mean sea-level rise and differential land-level movements

We present new local groundwater-level rise data from two Late Glacial aeolian dunes, located near Barendrecht and Oud-Alblas in the western Rhine-Meuse delta. These data are based on AMS radiocarbon dating of terrestrial macrofossils, collected from the base of peat formed on the slopes of these dunes. This method avoids contamination of bulk peat samples by old soil carbon or younger rootlets and rhizomes, as well as the hardwater effect. The new data are used to assess the reliability of previously published groundwater-level index data based on conventional radiocarbon dating of bulk basal peat samples from the slopes of the Late Glacial aeolian dunes at Barendrecht, Hillegersberg, Bolnes and Wijngaarden, all located in the western Rhine-Meuse delta. Comparison of the new and published groundwater-level data shows no significant systematic difference between conventionally dated bulk peat samples and AMS-dated samples of terrestrial macrofossils. The new data from the dune at Barendrecht confirm the reliability of the younger than 6600 cal yr BP age-depth data from the dunes at Hillegersberg and near Bolnes. This result supports the validity of this part of the mean sea-level (MSL) curve for the western Netherlands. Consequently, the position of the groundwater-level curve for Flevoland (central Netherlands) below this MSL curve can most likely be attributed to differential land-level movement. The available data show that the groundwater-gradient effect in the western Rhine-Meuse delta became less than 5 cm/km after 6600 calyr BP. Finally, temporal correlation between temporary increases in local groundwater-level rise with known shifts of river courses in the delta plain suggests, that avulsions can explain sudden local deviations from the trend in groundwater-level rise. A general conclusion of this study is that a complex relationship exists between sea level and local delta-plain water levels.

Mid-Holocene sea-level change on the Eastern Shore of Virginia

Abstract The 1965 and 1987 curves of relative sea-level (RSL) change for the Eastern Shore of Virginia differ markedly from similar curves for Delaware, New Jersey and New England. The latter show a rapid and continuous RSL rise between 6000 and 3000 or 2000 yrs B.P., whereas the curves for the Eastern Shore of Virginia suggest a sea-level lowering between 5100 and 4400 yrs B.P. or a marked retardation between 4700 (or earlier) and 4000 yrs B.P. New radiocarbon dates on high marsh basal peat samples from the Eastern Shore of Virginia indicate, however, a mid-Holocene rate of RSL rise similar to that indicated by the other regional curves.

Sulphate reduction as a geomorphological agent in tidal marshes ('Great marshes' at Barnstable, Cape Cod, USA).

Many tidal marsh surfaces feature water-filled depressions, known as salt pans (shallow) or ponds (deeper). In the Great Marshes at Barnstable, Cape Cod, pond formation is an active process. We hypothesize that degradation of organic matter by sulphate-reducing bacteria in these peat-rich marsh deposits is the primary cause of pan and pond formation. Sulphate reduction below an actively developing pond is probably enhanced by higher temperature and salinity of the pond water. Computer simulation suggests that ponds with similar characteristics to those in the Barnstable marshes may develop by sulphate reduction. Necessary conditions are sufficiently deep percolation and diffusion of sulphate into the underlying marsh deposits, and a high decomposition rate stimulated by high water temperatures in the ponds. In areas with a high density of ponds, drainage of the ponds by headward erosion of tidal creeks may cause rapid disintegration of the marsh surface.

Sea-level variability in the northwest Atlantic during the past 1500 years: A delayed response to solar forcing?

[1] Numerical experiments with a coupled oceanatmosphere model (ECBilt) have shown that centennial variations in sea level (SL) in the northwest Atlantic may be associated with deep-ocean salinity anomalies generated by solar-forced variations in the North Atlantic overturning circulation. Here we compare simulated SL curves for the Gulf Stream region with reconstructed, late-Holocene SL records from Connecticut (USA). Simulated SL variations lag the solar forcing record by ca. 120 year. This lag is found to be robust over a small number of different experiments. The reconstructed SL curves visually match the solar forcing optimally when lagging it by ca. 125 yr. A quantitative test shows that the correlation is significant, while this result is not sensitive to dating uncertainties. The temporal response pattern of the simulated SL curves compares reasonably well with the reconstructions. INDEX TERMS: 4556 Oceanography: Physical: Sea level variations; 1650 Global Change: Solar variability; 4255 Oceanography: General: Numerical modeling; 4267 Oceanography: General: Paleoceanography; 3030 Marine Geology and Geophysics: Micropaleontology. Citation: van de Plassche, O., G. van der Schrier, S. L. Weber, W. R. Gehrels, and A. J. Wright, Sea-level variability in the northwest Atlantic during the past 1500 years: A delayed response to solar forcing?, Geophys. Res. Lett., 30(18), 1921, doi:10.1029/ 2003GL017558, 2003.

ON THE EROSIVE TRAIL OF A 14TH AND 15TH CENTURY HURRICANE IN CONNECTICUT (USA) SALT MARSHES

This paper examines if an erosive hiatus found in the peat stratigraphy and marsh-accumulation record from northwest Hammock River Marsh (HRM), Connecticut (CT) can be attributed to a 14th or a 15th century hurricane, each documented by a radiocarbon-dated overwash fan in Succotash Marsh (SM) (Rhode Island) about 90 km to the east. Given that (i) the best estimate age range for the 15th century overwash deposit in SM (1400-1440 cal AD, 2 sigma ) overlaps entirely with that for first plant growth after erosion at HRM (1390-1450 cal AD, 2 sigma ), while the best estimate age range for the 14th century overwash deposit (1290-1410 cal AD, 2 sigma ) overlaps just 10 yr, and (ii) interpretation of the available stratigraphic and sedimentary evidence from HRM suggests that a high-energy event offers the simplest explanation for the observed marsh erosion, we conclude that a plausible link exists between the 15th century hurricane and the marsh erosion in HRM. The best estimate age range for the 14th century hurricane appears to overlap for 91% with the age range for the first plant growth (1290-1400 cal AD, 2 sigma ) following marsh erosion in East River Marsh (CT), located about 12 km west of HRM. These results imply that erosive boundaries in salt-marsh peat deposits have potential as markers of past hurricane activity.

Relative sea-level rise across the Eastern Border fault (Branford, Connecticut): evidence against seismotectonic movements

Abstract Basal peat age–depth data from four salt-marsh sites located 500–1500 m south of the Eastern Border fault (EBF) near Branford, Connecticut, document an error envelope for the lower limit of relative mean high water (MHW) rise during the past 3300 yr. The long-term rate of relative lower-limit-MHW rise during the past 3000 yr (1.1 mm yr −1 ) corresponds with late Holocene rates of relative MHW rise found elsewhere in coastal Connecticut (0.9–1.2 mm yr −1 ). This result invalidates repeated claims that multiple seismotectonic lowering of a crustal block towards the south has occurred along a segment of the EBF near Branford shortly after 815 cal yr BC and during the past 1200 yr and calls for a non-tectonic interpretation of biostratigraphic evidence of local short-term sea-level variations.

Research targets 2000 years of climate‐induced sea level fluctuations

Sea level rise as a consequence of “greenhouse-induced” global warming has been a major focus of global change science for the last 2 decades. The principle approach has been to test climate-forced sea level models by comparing model results with regional or global averages of sea level rise based on multidecadal, and in a few cases, centennial tidegauge records, corrected for local crustal movements that in turn are based on millennialscale records of relative sea level change. The majority of the multi-decadal instrumental records are inherently noisy (±0.3 m) due to sub-decadal and decadal variability in ocean temperature, salinity fields,and circulation, any of which can affect density and hence local sea level. This variability is induced by atmospheric and oceanographic phenomena such as ENSO.