Upper Wisconsinan submarine end moraines off Cape Ann,Massachusetts

Seismic profiles across the southwest end of Jeffreys Ledge, a bathymetric high north of Cape Ann, Massachusetts, reveal two end moraines. The moraines overlie upper Wisconsinan glacialmarine silty clay and are composed mostly of subaqueous ice-contact deposits and outwash. They were formed below sea level in water depths of as much as 120 m during fluctuations of a calving ice front. The moraines are late Wisconsinan in age and were formed after the Cambridge readvance, about 14,000 yr B.P., and before the Kennebunk readvance, about 13,000 yr B.P. They represent fluctuations of the ice front during overall retreat of Laurentide ice from the Gulf of Maine and New England.     

Shoreline changes along the southeastern coast of Martha's Vineyard, Massachusetts for the past 200 years

Shoreline changes since 1776, including two 30-yr periods separated by nearly 100 yr are documented from surveys, topographic maps, harbor charts, and aerial photographs for the southeastern corner of the island of Martha's Vineyard, Massachusetts (41°25′ N, 70°35′ W). From 1776 to 1969, a barrier beach has receded by more than 880 m, and average rate of 4.6 m/yr. A series of four detailed surveys from 1840 to 1886 document consistent shoreline retreat in this area of 3.1 m/yr.For the period 1938–1969, planimetry from aerial photographs and field observation indicate that more than 28 ha and nearly 3 × 10⁶ m³ of foreland composed of till have washed away. A house, located 200 m from the cliff edge of the foreland in 1938 was only 56 m from the cliff edge in July 1972.Violent storms were associated with the opening of the bay behind the barrier beach in nearly the same location in 1856, 1886, 1938, and 1954. Easterly migration of the opening results in rapid erosion of the southeastern corner of the island (Wasque Point) and eventual closing of the opening.Field observation of the 1954 opening indicates that the mechanism of failure of the barrier beach is primarily by storm tide-induced subsidence. Subsequently, strong (up to 1.2 mps) easterly currents cause migration of the opening to the east and closure within 15 yr.A summary review of evidence for changes in sea level in the past is suggested in partial explanation for the consistent shoreline retreat described in this paper.     

A 12,000-year history of vegetation and climate for Cape Cod,Massachusetts

Pollen and charcoal analysis of radiocarbon-dated sediment cores from Duck Pond in the Cape Cod National Seashore provide a continuous 12,000-yr vegetation and climate history of outer Cape Cod. A Picea-Hudsonia parkland and then a Picea-Pinus banksiana-Alnus crispa boreal forest association grew near the site between 12,000 and 10,000 yr B.P. This vegetation was replaced by a northern conifer forest of Pinus strobus-P. banksiana, and, subsequently, by a more mesophytic forest (Pinus strobus, Tsuga, Quercus, Fagus, Acer, Ulmus, Fraxinus, Ostrya) as the climate became warmer and wetter by 9500 yr B.P. By 9000 yr B.P. a Pinus rigida-Quercus association dominated the landscape. High charcoal frequencies from this and subsequent levels suggest that the pine barrens association developed during a warmer and drier climate that lasted from 9000 to about 5000 yr B.P. Increased percentages of Pinus strobus pollen indicate a return to moister and cooler conditions by about 3500 yr B.P. A doubled sedimentation rate, increased charcoal, and increased herb pollen suggest land disturbance near the pond before European settlement. These results suggest a rapid warming in the northeast in the early Holocene and support a hypothesis of a rapid sea level rise at that time. Comparison of the pollen results from Duck Pond with those from Rogers Lake, Connecticut, illustrates the importance of edaphic factors in determining the disturbance frequency and vegetation history of an area.     

Classification of paraglacial barrier systems: coastal New England, USA

The New England coast harbours a wide variety of barrier forms, which we organize into six barrier-coastline types. The barriers develop in response to the relative importance of several spatially and temporally variable parameters, particularly antecedent topography and geology, sediment abundance and size, exposure to wave and tidal energy and sea-level history. The six coastline types can also be identified in other paraglacial regions. Existing barrier-coastline classification schemes do not allow consistent subdivision of paraglacial barrier coasts. This paper presents a new scheme that is applicable to paraglacial and non-paraglacial barrier coasts alike. Aside from hydrodynamic regime, which forms the basis of the barrier classification most commonly used to date, it includes a compartmentalization factor. Sediment-starved ‘isolated’ (‘type 1’) barrier coastlines are characterized by short, widely spaced barriers. Small, localized updrift and offshore sources have provided sediment for short barriers along ‘clustered headland-separated’ (‘type 2’) barrier coastlines. Various amounts of sediment from larger updrift and offshore glaciofluvial deposits or directly from rivers have formed the longer barriers along ‘wave-dominated mainland-segmented’ (‘type 3a’), ‘mixed-energy mainland-segmented’ (‘type 3b’), ‘wave-dominated inlet-segmented’ (‘type 4a’) and ‘mixed-energy inlet-segmented’ (‘type 4b’) barrier coastlines. Geomorphic form, grain size and stratigraphy can be used to characterize individual barriers along barrier coastlines. Most paraglacial barriers form as spits, but many are transformed subsequently. Welded barriers are common along ‘type 1’ and ‘type 2’ coasts. Baymouth barriers are characteristic of ‘type 3’ coasts, and barrier islands occur exclusively along ‘type 4’ coasts. The coarsest grained barriers are located along ‘type 1’ and ‘type 2’ coasts. Progradational barrier sections are concentrated along ‘type 3’ and ‘type 4’ coasts with abundant sediment supply, but are also present along ‘type 2’ coasts. Temporary increases in sediment supply, common in paraglacial regions, result in transitions between retrogradational and progradational barrier behaviour, which may be recognized on shore-perpendicular stratigraphic cross-sections.     

Use of salt-marsh peat reefs by small juvenile lobsters on Cape Cod,Massachusetts

The habitats utilized by small juvenile (<40 mm carapace length, CL) lobsters (Homarus americanus) are poorly known. We discovered and studied an undescribed juvenile lobster habitat in Nauset Marsh, Cape Cod. Juvenile lobsters (X=26.7 mm carapace length, 6 to 72 mm, n=38) were collected from suction samples primarily 0144 01 in “peat reef” habitats during the period from August 1985 through October 1986. The reefs consisted of large blocks ofSpartina alterniflora peat that had separated from the marsh surface and fallen into adjacent subtidal marsh channels. The smallest lobsters (6 to 7 mm CL) were collected from peat reefs in October 1985, and April and July 1986. In these habitats, juvenile lobster density averaged 2.5 individuals m^?2 (range 0–5.7) in suction samples. Peat reef habitats occur in other salt marshes in the northeastern United States and may be an important nursery habitat for small juvenile lobsters.     

Radar facies of paraglacial barrier systems: coastal New England, USA

Analysis of a large data base of ground-penetrating-radar (GPR) profiles from both natural and developed paraglacial barriers along the coast of New England has allowed identification of eight reflection configurations that characterize this type of mid- to high-latitude coastal environment. Bedrock anchor points yield primarily hyperbolic configurations, whereas glacial anchor points and sediment-source areas are characterized by chaotic, parallel, and tangential-oblique configurations. Beaches and dunes produce predominantly sigmoidal oblique, hummocky, reflection-free, and bounding-surface configurations. Back-barrier sediments may yield basin-fill configurations, but generally include abundant signal-attenuating units.
The GPR data, calibrated with information from cores, were collected across swash-aligned and drift-aligned barriers in a variety of wave- and tidal-energy settings. Application of a 120-MHz antenna, as used in this study, enables portrayal of a range of sedimentary units, from individual bedforms (on single records) to entire barrier elements (using large numbers of intersecting GPR sections), at maximum vertical resolutions that vary between 0·2 m and 0·7 m.
The most important drawback of GPR in the coastal environment is attenuation of the electromagnetic (EM) signal by layers of salt-marsh peat or by brackish or salty groundwater, primarily along barrier edges. This disadvantage is offset by many benefits. Data can be collected at rates of several km per day, making GPR an excellent reconnaissance tool. A core that is used in the calibration of GPR data can be matched with great accuracy to its position on the complementary GPR record, allowing detailed correlation between lithostratigraphy and reflection configuration.     

The reproductive cycle of the bay scallop,Argopecten irradians irradians (Lamarck), in a small coastal embayment on Cape Cod,Massachusetts

The spawning activity of the bay scallop Argopecten irradians irradians (Lamarck) was monitored from May through September in a small embayment on Cape Cod, Massachusetts and compared with changes in hydrographic conditions. Spawning activity of bay scallops began in May and continued through July with some minor activity occurring during August and September. Activity was most closely related to changes in ambient temperature and occurred predominantly before the summer maximum temperature was recorded. As temperatures declined in the late summer and early fall, increased gametogenic activity was evident. A longer period of spawning activity was observed than was previously reported for New England waters.     

The role of sediment denitrification in reducing groundwater-derived nitrate inputs to Nauset Marsh estuary, Cape Cod, Massachusetts

The Nauset Marsh estuary is the most extensive (9.45 km²) and least disturbed salt marsh/estuarine system within the Cape Cod National Seashore, even though much of the 19 km² watershed area of the estuary is developed for residential or commercial purposes. Because all of the Nauset watershed is serviced by on-site individual sewage disposal systems, there is concern over the potential impact of groundwater-derived nutrients passing from these systems to the shallow receiving waters of the estuary. The purpose of this study was to determine whether denitrification (the bacterial conversion of nitrate to gaseous nitrogen) in estuarine sediments could effectively remove the nitrate from contaminated groundwater before it passed from the watershed to the estuary. Rates of denitrification were measured both in situ and in sediment cores, in areas of active groundwater discharge, in relatively pristine locations, and in areas situated down-gradient of moderate to heavily developed regions of the watershed. Denitrification rates for 47 sediment cores taken over an annual cycle at 5 stations ranged from non-detectable to 47 μmol N₂ m⁻² h⁻. Mean denitrification rates were positively correlated with sediment organic content, and varied seasonally due to changes in sediment organic content and to the effect of water temperatures on sediment oxygen penetration depths. There was no correlation between observed denitrification rates and corresponding nitrate concentrations in groundwater. A comparison of in situ denitrification rates (supported by groundwater nitrate) with denitrification rates observed in sediment cores (supported by remineralized nitrate) showed that groundwater-driven denitrification rates were small, and not in excess of denitrification rates supported by remineralized nitrate. Most of the denitrification in Nauset sediments was apparently fueled by remineralized nitrate through coupled nitrification/denitrification. Denitrification did not contribute significantly to the direct loss of nitrate from incoming groundwater at Nauset Marsh estuary. Groundwater flow was rapid, and much of it occurred in freshwater springs and seeps through very coarse, sandy, well-oxygenated sediments of limited organic content. There was little opportunity for denitrification to occur during groundwater passage through these sediments. These results have important management implications because they suggest that the majority of nitrogen from contaminated groundwater crosses the sediment/water interface and arrives at Nauset Estuary, where it is available to primary producers. Preliminary budget calculations suggest that while denitrification was not an effective mechanism for the direct removal of nitrate in contaminated groundwater flowing to Nauset Marsh estuary, it may contribute to significant nitrogen losses from the estuary itself.     

Infiltration-Driven Metamorphism in Northern New England, USA

Mineral reactions at the biotite isograd were investigated inpelitic schists, micaceous sandstones, micaceous limestones,and metaigneous rocks from three stratigraphic units over anarea of 10000 km² in north-central New England. The biotiteisograd in north-central New England represents a metamorphicdecarbonation front that affected all major rock types in eachstratigraphic unit. Pressure at the isograd was near 3500 bat the northern end of the study area and near 5500 b in thesouth. Temperature was in the range 400–450?C. Equilibriummetamorphic fluids were approximately CO₂-H₂O mixtures withX_CO2=0?04–0?07. Volumetric fluid]-rock ratios were calculatedfor more than 70 samples of all major rock types from each formationusing measured progress of the prograde reactions and the estimatedP-T-X_CO2, conditions of metamorphism. Regardless of stratigraphicunit, limestones record low values of 0–0?2, pelites andmetaigneous rocks generally record high values of 1–3,and standstones record intermediate values of 0?2–1. With exception of the limestones, all samples from the biotitezone record fluid-rock ratios significantly greater than likelyrock porosity during metamorphism. The prograde decarbonationreactions therefore were driven by infiltration of rock by reactiveaqueous fluids. The observed correlations between fluid-rockratio and rock type indicate that significant permeability contrastsoccurred during low-grade metamorphsim with permeability increasingin the order: limestones<sandstones<pelites rocks. Asa corollary, reactive fluid flow must have been channelizedwith enhanced flow in pelites and metaigneous rocks relativeto sandstones and limestones. Results of this study in north-centralNew England taken together with studies of the biotite isogradin south-central Maine (Ferry, 1984, 1986a, 1988) demonstratethat low-grade metamorphism over much of the northern Appalachianorogen was infiltration-driven.     

Vegetation Cover and Elevation in Long-Term Experimental Nutrient-Enrichment Plots in Great Sippewissett Salt Marsh,Cape Cod,Massachusetts: Implications for Eutrophication and Sea Level rise

Nitrogen inputs restructure ecosystems and can interact with other agents of ecological change and potentially intensify them. To examine the effects of nitrogen combined with those of elevation and competition, in 2005 we mapped vegetation and elevation within experimental plots that have been fertilized since 1970 in Great Sippewissett salt marsh, Cape Cod, MA, USA and compared the resulting effects on marsh vegetation. Decadal-scale chronic nutrient enrichment forced changes in cover and spatial distribution of different species. With increasing enrichment, there was a shift in species cover primarily involving loss of Spartina alterniflora and an increase in Distichlis spicata. Percent cover of near monocultures increased with nitrogen fertilization, owing mainly to the proliferation of D. spicata. The experimental fertilization prompted a shift from the short form of S. alterniflora to taller forms, hence increasing above-ground biomass, where this species managed to remain. Chronic enrichment increased upper and lower limits of the elevation range within which certain species occurred. The shift to increased cover of D. spicata was also associated with faster accretion of the marsh surface where this species was dominant, but not where S. alterniflora was dominant. Interactions among nutrient supply, elevation, and competition altered the direction of competitive success among different species of marsh plants, and forced changes in the spatial distribution and composition of the salt marsh plant communities. The results imply that there will be parallel changes in New England salt marshes owing to the widespread eutrophication of coastal waters and the increasing sea level rise. Knowing the mechanisms structuring marsh vegetative cover, and their role in modification of salt marsh accretion, may provide background with which to manage maintenance of affected coastal wetlands.     

Cosmogenic nuclide exposure ages for moraines in the Lago San Martin Valley, Argentina

At several times during the Quaternary, a major eastward-flowing outlet glacier of the former Patagonian Ice Sheet occupied the Lago San Martin Valley in Argentina (49°S, 72°W). We present a glacial chronology for the valley based on geomorphological mapping and cosmogenic nuclide (¹⁰Be) exposure ages (n = 10) of boulders on moraines and lake shorelines. There are five prominent moraine belts in the Lago San Martin Valley, associated with extensive sandar (glaciofluvial outwash plains) and former lake shorelines. Cosmogenic nuclide exposure ages for boulders on these moraines indicate that they formed at 14.3 ± 1.7 ka, 22.4 ± 2.3 ka, 34.4 ± 3.4 ka to 37.6 ± 3.4 ka (and possibly 60 ± 3.5 ka), and 99 ± 11 ka (1σ). These dated glacier advances differ from published chronologies from the Lago San Martin Valley based on ¹⁴C age determinations from organic sediments and molluscs in meltwater channels directly in front of moraines or in kettleholes within end moraine ridges. The moraine boulder ages also point to possible pre-LGM glacial advances during the last glacial cycle and a key observation from our data is that the LGM glaciers were probably less extensive in the Lago San Martin Valley than previously thought.     

Spawning densities,egg densities,size structure,and movement patterns of spawning horseshoe crabs,<Emphasis Type="Italic">Limulus polyphemus</Emphasis>, within four coastal embayments on Cape Cod,Massachusetts

Spawning densities, spawning indices, egg densities, size distributions, and movement patterns of horseshoe crabs (Limulus polyphemus) were quantified for four coastal embayments (Monomoy National Wildlife Refuge, Pleasant Bay, Nauset Estuary, and Cape Cod Bay) on Cape Cod, Massachusetts from 2000 to 2002. Spawning activity was highest from mid May through mid June, but densities varied throughout the Cape Cod region. Average spawning densities (male and female crabs combined), measured using 25-m² quadrats, were lower than 1 crab 25 m^?2, although certain locations had consistently higher densities averaging 2 to 3 crabs 25 m^?2 with individual survey densities recorded as high as 17 crabs 25 m^?2. Spawning densities during night surveys were either similar or slightly higher than day surveys, except at a few sites within Pleasant Bay. Spawning indices were considerably lower ranging from 0 to 1.3 females 25 m^?2 throughout the Cape Cod region. Spawning sex ratios varied from 1∶1.6 to 1∶3.1 (females:males) throughout the region, except within Pleasant Bay where highly male skewed ratios were observed (e.g., 1∶5.8, 3-yr average). Egg densities were low overall (<1 egg cm^?2) throughout Cape Cod and egg densities tended to be higher in deeper sediments (5–20 cm deep) compared to shallow sediments (0–5 cm deep) at most locations. Over 7,800 horseshoe crabs were tagged on Cape Cod from 2000 to 2002. Average size and size frequency distributions of tagged crabs varied among regions. Larger individuals were observed at Monomoy National Wildlife Refuge while the smallest individuals were from Cape Cod Bay. We documented an overall recapture rate of 6.7% and our tag-recapture data indicated that 62% of crabs were recaptured at the original tagging location and 70% of recaptures traveled less than 2 km from the original tagging location, providing evidence for localized populations on Cape Cod. We have observed that horseshoe crabs differ among embayments within a regional area, suggesting the potential need for management plans specific to embayments or subregions depending on the characteristics of a population.     

Mineral dissolution in the Cape Cod aquifer, Massachusetts, USA: I . Reaction stoichiometry and impact of accessory feldspar and glauconite on strontium isotopes, solute concentrations, and REY distribution

To compare relative reaction rates of mineral dissolution in a mineralogically simple groundwater aquifer, we studied the controls on solute concentrations, Sr isotopes, and rare earth element and yttrium (REY) systematics in the Cape Cod aquifer. This aquifer comprises mostly carbonate-free Pleistocene sediments that are about 90% quartz with minor K-feldspar, plagioclase, glauconite, and Fe-oxides. Silica concentrations and pH in the groundwater increase systematically with increasing depth, while Sr isotopic ratios decrease. No clear relationship between ⁸⁷Sr/⁸⁶Sr and Sr concentration is observed. At all depths, the ⁸⁷Sr/⁸⁶Sr ratio of the groundwater is considerably lower than the Sr isotopic ratio of the bulk sediment or its K-feldspar component, but similar to that of a plagioclase-rich accessory separate obtained from the sediment. The Si-⁸⁷Sr/⁸⁶Sr-depth relationships are consistent with dissolution of accessory plagioclase. In addition, solutes such as Sr, Ca, and particularly K show concentration spikes superimposed on their respective general trends. The K-Sr-⁸⁷Sr/⁸⁶Sr systematics suggests that accessory glauconite is another major solute source to Cape Cod groundwater. Although the authigenic glauconite in the Cape Cod sediment is rich in Rb, it is low in in-grown radiogenic ⁸⁷Sr because of its young Pleistocene age. The low ⁸⁷Sr/⁸⁶Sr ratios are consistent with equilibration of glauconite with seawater. The impact of glauconite is inferred to vary due to its variable abundance in the sediments. In the Cape Cod groundwater, the variation of REY concentrations with sampling depth resembles that of K and Rb, but differs from that of Ca and Sr. Shale-normalized REY patterns are light REY depleted, show negative Ce anomalies and super-chondritic Y/Ho ratios, but no Eu anomalies. REY input from feldspar, therefore, is insignificant compared to input from a K-Rb-bearing phase, inferred to be glauconite. These results emphasize that interpretation of groundwater chemistry, even in relatively simple aquifers, may be complicated by solute contributions from “exotic” accessory minerals such as glauconite. To detect such peculiarities, groundwater studies should combine the study of elemental concentration and isotopic composition of several solutes that show different geochemical behavior.     

Fluid inclusion evidence for basement decompression during Permo-Triassic extension, SE New England, USA

Abstract CO₂-bearing fluid inclusions in strongly lineated but weakly foliated late Precambrian gneisses within the Hope Valley Shear zone of Connecticut and Rhode Island are of mixed composition ( X _co2± 0.1; 7 wt% NaCl equivalent) and variable density (0.59–0.86 g/ml) and occur mainly as isolated inclusions. Also present are dilute (3 wt% NaCl equivalent) aqueous inclusions which occur on healed fractures related to greenschist facies retrograde metamorphism. Isochores for dense isolated CO₂-bearing inclusions indicate pressures of 7.5–9 kbar at 500–600° C, the estimated temperature conditions of peak metamorphism. Published ⁴⁰Ar/³⁹Ar hornblende plateau age spectra indicate cooling through about 500° C at 265 ± 5 Ma. Isochores for low-density CO₂-bearing inclusions and aqueous inclusions intersect at the conditions of retrograde metamorphism (325–400° C) and indicate pressures of 3–4 kbar. Published ⁴⁰Ar/³⁹Ar biotite plateau ages indicate cooling through about 300° C at 250 ± 5 Ma. These data define a P–T uplift curve for the region which is convex towards the temperature axis and indicate uplift rates between 0.4 and 3.3 mm/year in Permian time. Exhumation of basement gneisses was coeval with normal (west-down) motion along the regional basement–cover contact (Honey Hill–Lake Char–Willimantic fault system), and is interpreted as due to post-orogenic extensional collapse of the Alleghanian orogeny.     

The application of ground‐penetrating radar to a coastal prehistoric archaeological site,Cape Henlopen,Delaware, USA

Cape Henlopen, Delaware is a coastal spit complex located at the confluence of Delaware Bay and the Atlantic Ocean. This region was occupied by prehistoric peoples throughout the evolution of ancestral Cape Henlopen. A ground‐penetrating radar (GPR) survey was conducted at one of the prehistoric archaeological sites (7S‐D‐30B) located within the Cape Henlopen Archaeological District. The site was in a remote location in the center of a tide dominated back‐barrier marsh. Ground‐penetrating radar waves penetrated to depths of 7 m, and four major sets of reflections were observed. Three sets were interpreted to be GPR images of geomorphic units associated with the spit complex, and the fourth was identified as the GPR image of a shell midden deposit. The GPR survey was used to determine the approximate dimensions of the shell midden, including its depth below ground surface (up to 2.1 m) and horzontal extent (∼250 m²), and to establish the paleoenvironmental setting and antecedent topography of the site prior to occupation. The GPR data suggests that the shell midden was initially deposited upon an aeolian dune surface and the antecedent topography at the site included an up to 1 m deep trough located 5 m to the north of, and trending parallel to, the axis of a present‐day topographic high. This survey illustrates that GPR is a useful, noninvasive, tool that may be implemented at archaeological sites in coastal areas. It provides constraints on the environmental setting and topography of the terrain which prehistoric peoples inhabited, and it can be used in planning excavations at sites in coastal geomorphic settings. © 2000 John Wiley & Sons, Inc.     

A record of late-Holocene environmental change from southern New England, USA

Analyses of a sediment core from Little Pond, located in the town of Bolton, Massachusetts, provide new insights into the history of environmental and ecological changes in southern New England during the late Holocene. Declines in organic content and peaks in the abundance of Isoetes spores indicate reduced water depth at 2900–2600, 2200–1800, and 1200–800 calibrated years before present (cal yr BP), generally consistent with the timing of dry conditions in records from elsewhere in the northeastern United States. The Little Pond pollen record features little change over the last 3000 yr, indicating that the surrounding vegetation was relatively insensitive to these periods of drought. The 1200–800 cal yr BP dry interval, however, coincides with increased abundance of Castanea pollen, suggesting that the expansion of Castanea in southern New England may have been influenced by late-Holocene climatic variability.     

Magma sources for Mesozoic anorogenic granites of the White Mountain magma series,New England,USA

The magma sources for granitic intrusions related to the Mesozoic White Mountain magma series in northern New England, USA, are addressed relying principally upon Nd isotopes. Many of these anorogenic complexes lack significant volumes of exposed mafic lithologies and have been suspected of representing crustal melts. Sm–Nd and Rb–Sr isotope systematics are used to evaluate magma sources for 18 felsic plutons with ages ranging from about 120 to 230 Ma. The possibility of crustal sources is further examined with analyses of representative older crust including Paleozoic granitoids which serve as probes of the lower crust in the region. Multiple samples from two representative intrusions are used to address intrapluton initial isotopic heterogeneities and document significant yet restricted variations (<1 in _Nd). Overall, Mesozoic granite plutons range in _Nd [T] from +4.2 to -2.3, with most +2 to 0, and in initial ⁸⁷Sr/⁸⁶Sr from 0.7031 to 0.709. The isotopic variations are roughly inversely correlated but are not obviously related to geologic, geographic, or age differences. Older igneous and metamorphic crust of the region has much lower Nd isotope ratios with the most radiogenic Paleozoic granitoid at _Nd [180 Ma] of -2.8. These data suggest mid-Proterozoic separation of the crust in central northern New England. Moreover, the bulk of the Mesozoic granites cannot be explained as crustal melts but must have large mantle components. The ranges of Nd and Sr isotopes are attributed to incorporation of crust by magmas derived from midly depleted mantle sources. Crustal input may reflect either magma mixing of crustal and mantle melts or crustal assimilation which is the favored interpretation. The results indicate production of anorogenic granites from mantle-derived mafic magmas.     

The Functions and Values of Fringing Salt Marshes in Northern New England,USA

We compared the functions and values of fringing salt marshes to those of meadow marshes along the southern Maine/New Hampshire coast. Differences included soil organic matter content, plant species richness, and percent cover of high and low-marsh species. More sediment was trapped per unit area in fringing marshes than in meadow marshes, but this difference was not significant. Similarities included aboveground and belowground peak season biomass and the ability to dampen wave energy. Both marsh types reduced the height of waves coming onto the marsh surface by 63% only 7 m into the marsh. Fringing marshes are diverse in terms of their physical characteristics (width, length, slope, elevation, soils). Despite their small size, they are valuable components of estuaries, performing many ecological functions to the same degree as nearby meadow marshes. More effort should be made to include them in regional efforts to conserve and restore coastal habitats.     

Spatially explicit mapping of hurricane risk in New England, USA using ArcGIS

Hurricanes are one of the major natural disturbances affecting human livelihoods in coastal zones worldwide. Assessing hurricane risk is an important step toward mitigating the impact of tropical storms on human life and property. This study uses NOAA’s historical tropical cyclone database (HURDAT or ‘best-track’), geographic information systems, and kernel smoothing techniques to generate spatially explicit hurricane risk maps for New England. Southern New England had the highest hurricane risk across the region for all storm intensities. Long Island, western Connecticut, western Massachusetts, and southern Cape Cod, Martha’s Vineyard, and Nantucket had high storm probabilities and wind speeds. Results from this study suggest that these locations may be of central importance for focusing risk amelioration resources along the Long Island and New England coastlines. This paper presents a simple methodology for hurricane risk assessment that could be applied to other regions where long-term spatial storm track data exist.