ALBERT

Description: We determine the contribution of glacial isostatic adjustment (GIA) to future relative sea level change for the North American coastline between Newfoundland and Texas. We infer GIA model parameters using recently compiled and quality assessed databases of past sea-level changes, including new databases for the United States Gulf coast and Atlantic Canada. At 13 cities along this coastline, we estimate the GIA contribution to range from a few centimeters (e.g. 3[−1 − 9]cm, Miami) to a few decimeters (e.g. 18[12 − 22]cm, Halifax) for the period 2085-2100 relative to 2006-2015 (1- σ ranges given). We provide estimates of uncertainty in the GIA component using two different methods; the more conservative approach produces total ranges (1- σ confidence) that vary from 3to16cm for the cities considered. Contributions from ocean steric and dynamic changes as well as those from changes in land ice are also estimated to provide context for the GIA projections. When summing the contributions from all three processes at the 13 cities considered along this coastline, using median or best-estimate values, the GIA signal comprises ≈ 5 − 38 % of the total depending on the adopted climate forcing and location. The contributions from ocean dynamic/steric changes and ice mass loss are similar in amplitude but with spatial variation that approximately cancels, resulting in GIA dominating the net spatial variability north of 35 ∘ N).

Description: ABSTRACT We present an expanded training set of salt-marsh foraminifera for reconstructing Holocene relative sea-level change from 12 sites in New Jersey that represent varied physiographic environments. Seven groups of foraminifera are recognized, including four high- or transitional-marsh assemblages and a low-salinity assemblage. A weighted-averaging transfer function trained on this dataset was applied to a dated core from Barnegat Bay to reconstruct sea level with uncertainties of ± 14% of tidal range. We evaluate the transfer function using seven tests. (1) Leave-one-site-out cross validation suggests that training sets of salt-marsh foraminifera are robust to spatial autocorrelation caused by sampling along transects. (2) Segment-wise analysis shows that the transfer function performs best at densely sampled elevations and overall estimates of model performance are over optimistic. (3) Dissimilarity and (4) non-metric multi-dimensional scaling evaluated the analogy between modern and core samples. The closest modern analogues for core samples were drawn from six sites demonstrating the necessity of a multi-site training set. (5) Goodness-of-fit statistics assessed the validity of reconstructions. (6) The transfer function failed a test of significance because of the unusual properties of some cores selected for sea-level reconstruction. (7) Agreement between reconstructed sea level and tide-gauge measurements demonstrates the transfer function's utility. Copyright © 2013 John Wiley & Sons, Ltd.

Description: We examined the use of δ 13 C, TOC and C/N geochemistry of sedimentary organic matter to reconstruct former sea levels and paleoenvironments in the absence of suitable microfossil data. The modern distribution of δ 13 C, TOC and C/N of 33 vegetation and 74 surface sediment samples collected from four coastal wetlands in the Thames Estuary and Norfolk, UK are described. The δ 13 C, TOC and C/N geochemistry of sediments varied in relation to the input of in situ vascular vegetation versus allochthonous particulate organic matter and algae, which was controlled primarily by tidal inundation. We reviewed published and unpublished studies to produce an English database of vegetation ( n  = 257) and sediment ( n  = 132) δ 13 C, TOC and C/N geochemistry. Four elevation-dependent environments in the database had statistically distinct δ 13 C, TOC and C/N values: (1) tidal flat/low marsh (δ 13 C: −24.9 ± 1.2‰; TOC: 3.6 ± 1.7%; C/N: 9.9 ± 0.8); (2) middle marsh/high (δ 13 C: −26.2 ± 1.0‰; TOC: 9.8 ± 6.7%; C/N: 12.1 ± 1.8); (3) reed swamp (δ 13 C: −27.9 ± 0.7‰: TOC: 36.5 ± 11.5%; C/N: 13.9 ± 1.2); and (4) fen carr (δ 13 C: −29.0 ± 0.6‰; TOC: 41.6 ± 5.7%; C/N: 17.4 ± 3.1). The δ 13 C, TOC and C/N geochemistry database was applied to a Holocene sediment core collected from the Thames Estuary to produce three new sea-level index points and one limiting date, illustrating the utility of δ 13 C, TOC and C/N values to reconstruct Holocene relative sea levels. Copyright © 2015 John Wiley & Sons, Ltd.

Description: Tidal constituents and datums are computed on a high resolution grid of the northwestern Atlantic Ocean, including the Gulf of Mexico and the Caribbean Sea. A global model is used to determine tidal parameters on a grid with a nominal resolution of 800 × 800. The global model includes self-attraction and loading, drag in shallow marginal seas, and internal tide drag in the deep ocean. Simulations are performed at 1000 year intervals during the Holocene (10,000 calibrated years before present (10 ka)) in combination with changes in bathymetry and coastline location derived from a glacial isostatic adjustment model. The global model results are then used to force a regional barotropic tidal model. The regional model uses an unstructured finite element grid, with very high resolution at the coastline. The model results reveal significant variations in tidal constituent amplitudes throughout the Holocene. In the northwestern Atlantic, semi-diurnal components show a strong amplification at around 9 ka while in the Gulf of Mexico, the response is much more muted. Variations in diurnal tidal parameters are found to be less significant than semi-diurnal parameters throughout the model domain. Changes in tidal range, of great relevance to changes in relative sea level (RSL), are also investigated throughout the Holocene. The overall structure is similar to the patterns observed in the M2 tide, with peak increases of 200–300%, relative to present-day, being observed along the east coast of the United States from 9 to 8 ka. Finally, the high spatial resolution of the regional model allows for the investigation of tidal changes at spatial scales (e.g., individual bays) much smaller than in previous studies.

Description: We investigated use of δ 13 C in bulk organic sediment to define the botanical origin of samples preserved in coastal sediment as a means to reconstruct relative sea level in New Jersey, USA. Modern transects at three sites demonstrated that low and high salt-marsh floral zones dominated by C 4 species ( Spartina alterniflora and Spartina patens ) were associated with sediment δ 13 C values between −18.9‰ and −15.8‰ and occurred from mean tide level (MTL) to mean higher high water (MHHW). Brackish transitional settings vegetated by Phragmites australis with Iva fructescens and Typha sp. (C 3 species) and freshwater upland samples (C 3 species) were characterized by bulk sediment δ 13 C values of −27.0‰ to −22.0‰ and existed above MHHW. Parallel transects at one site suggested that intra-site variability was not discernible. The utility of δ 13 C values for reconstructing relative sea level in New Jersey is limited by an inability to differentiate between brackish sediments related to sea level and freshwater upland samples. To facilitate this distinction in a 4.4 m core, we used a multi-proxy approach (δ 13 C values with presence or absence of agglutinated foraminifera) to recognize indicative meanings for four sample types. Sediment with δ 13 C values greater than −18.9‰ was derived from a vegetated salt-marsh and formed between MTL and MHHW. Sediment with δ 13 C values less than −22.0‰ and containing agglutinated foraminifera formed in a brackish transitional zone between MHHW and highest astronomical tide (HAT). This is the narrowest elevational range of the four sample types and most precise sea-level indicator. Sediment with δ 13 C values less than −22.0‰ and lacking foraminifera can only constrain the upper bound of former sea level. Samples with intermediate values (−22.0‰ to −18.9‰) formed between MTL and HAT. Using these indicative meanings and radiocarbon dates, we suggest that a transition from brackish to salt-marsh δ 13 C values recorded in the core took approximately 350 years (from 1800 to 1450 cal. a BP). Copyright © 2011 John Wiley & Sons, Ltd.

Description: [1]  Tides in the Delaware Bay (USA) have been modeled from 7000 years before present (7 ka) to the present day and for selected future sea-level rise scenarios (100 years, 300 years). Historic bathymetries were constructed through use of glacial isostatic adjustment models and a very high spatial resolution (〈 100 m) was used at the shoreline. Future bathymetries were obtained by extrapolating these glacial isostatic adjustment models and applying an additional eustatic sea-level rise. It was found that tides in the lower bay have remained fairly constant through time but that tides in the upper bay have increased steadily from about 4 ka to the present day; a nearly 100% increase in total. The future runs demonstrated spatially complex behavior with tidal-range changes of up to 10%.

Description: Prenatal exposure to chlorpyrifos (CPF), an organophosphate insecticide, is associated with neurobehavioral deficits in humans and animal models. We investigated associations between CPF exposure and brain morphology using magnetic resonance imaging in 40 children, 5.9–11.2 y, selected from a nonclinical, representative community-based cohort. Twenty high-exposure children (upper tertile of CPF concentrations in umbilical cord blood) were compared with 20 low-exposure children on cortical surface features; all participants had minimal prenatal exposure to environmental tobacco smoke and polycyclic aromatic hydrocarbons. High CPF exposure was associated with enlargement of superior temporal, posterior middle temporal, and inferior postcentral gyri bilaterally, and enlarged superior frontal gyrus, gyrus rectus, cuneus, and precuneus along the mesial wall of the right hemisphere. Group differences were derived from exposure effects on underlying white matter. A significant exposure × IQ interaction was derived from CPF disruption of normal IQ associations with surface measures in low-exposure children. In preliminary analyses, high-exposure children did not show expected sex differences in the right inferior parietal lobule and superior marginal gyrus, and displayed reversal of sex differences in the right mesial superior frontal gyrus, consistent with disruption by CPF of normal behavioral sexual dimorphisms reported in animal models. High-exposure children also showed frontal and parietal cortical thinning, and an inverse dose–response relationship between CPF and cortical thickness. This study reports significant associations of prenatal exposure to a widely used environmental neurotoxicant, at standard use levels, with structural changes in the developing human brain.

Description: Stratigraphic evidence is found for two coseismic subsidence events that underlie a floodplain 20 km south of Padang, West Sumatra along the Mentawai segment (0.5°S–0.3°S) of the Sunda subduction zone. Each earthquake is marked by a sharp soil-mud contact that represents a sudden change from mangrove to tidal flat. The earthquakes occurred about 4000 and 3000 cal years B.P. based on radiocarbon ages of detrital plant fragments and seeds. The absence of younger paleoseismic evidence suggests that late Holocene relative sea level fall left the floodplain too high for an earthquake to lower it into the intertidal zone. Our results point to a brief, few thousand year window of preservation of subsidence events in tidal-wetland stratigraphic sequences, a result that is generally applicable to other emergent coastlines of West Sumatra.

Description: We investigated use of δ 13 C in bulk organic sediment to define the botanical origin of samples preserved in coastal sediment as a means to reconstruct relative sea level in New Jersey, USA. Modern transects at three sites demonstrated that low and high salt-marsh floral zones dominated by C 4 species ( Spartina alterniflora and Spartina patens ) were associated with sediment δ 13 C values between −18.9‰ and −15.8‰ and occurred from mean tide level (MTL) to mean higher high water (MHHW). Brackish transitional settings vegetated by Phragmites australis with Iva fructescens and Typha sp. (C 3 species) and freshwater upland samples (C 3 species) were characterized by bulk sediment δ 13 C values of −27.0‰ to −22.0‰ and existed above MHHW. Parallel transects at one site suggested that intra-site variability was not discernible. The utility of δ 13 C values for reconstructing relative sea level in New Jersey is limited by an inability to differentiate between brackish sediments related to sea level and freshwater upland samples. To facilitate this distinction in a 4.4 m core, we used a multi-proxy approach (δ 13 C values with presence or absence of agglutinated foraminifera) to recognize indicative meanings for four sample types. Sediment with δ 13 C values greater than −18.9‰ was derived from a vegetated salt-marsh and formed between MTL and MHHW. Sediment with δ 13 C values less than −22.0‰ and containing agglutinated foraminifera formed in a brackish transitional zone between MHHW and highest astronomical tide (HAT). This is the narrowest elevational range of the four sample types and most precise sea-level indicator. Sediment with δ 13 C values less than −22.0‰ and lacking foraminifera can only constrain the upper bound of former sea level. Samples with intermediate values (−22.0‰ to −18.9‰) formed between MTL and HAT. Using these indicative meanings and radiocarbon dates, we suggest that a transition from brackish to salt-marsh δ 13 C values recorded in the core took approximately 350 years (from 1800 to 1450 cal. a BP). Copyright © 2011 John Wiley & Sons, Ltd.

Description: Soil ice content impacts winter vadose zone hydrology. It may be possible to estimate changes in soil ice content with a sensible heat balance (SHB) method, using measurements from heat pulse (HP) sensors. Feasibility of the SHB method is unknown because of difficulties in measuring soil thermal properties in partially frozen soils. The objectives of this study were (i) to examine the SHB method for determining in situ ice content, and (ii) to evaluate the required accuracy of HP sensors for use in the SHB method. Heat pulse sensors were installed in a bare field to measure soil temperatures and thermal properties during freezing and thawing events. In situ soil ice contents were determined at 60-min intervals with SHB theory. Sensitivity of the SHB method to temperature, heat capacity, thermal conductivity, and time step size was analyzed based on numerically produced soil freezing and thawing events. The in situ ice contents determined with the SHB method were sometimes unrealistically large or even negative. Thermal conductivity accuracy and time step size were the key factors contributing to SHB errors, while temperature and heat capacity accuracy had less influence. Ice content estimated with a 15-min SHB time step was more accurate than that estimated with a 60-min time step. Sensitivity analysis indicated that measurement errors in soil temperature and thermal conductivity should be less than ±0.05°C and ±20%, respectively, but the error in the soil heat capacity could vary by ±50%. Thus, improving the accuracy of thermal conductivity measurements and using short time steps are required to accurately estimate soil ice contents with the SHB method.