Abrupt deglaciation events and Holocene palaeoceanography from high-resolution cores,Cartwright Saddle,Labrador Shelf,Canada

The uppermost Quaternary sediments in Cartwright Saddle, Labrador Shelf, are acoustically laminated, with reflectors that can be traced over long distances. Two piston cores from the saddle record changes in sediment and meltwater delivery from the northeast margin of the Laurentide Ice Sheet (LIS) during deglaciation. Variations in sediment properties indicate a similar history of sediment accumulation over the last 12 kyr. The temporal sampling interval reaches decadal resolution in the last deglacial period 7–9 ka. Analyses of total carbonate content, sediment magnetic variables, foraminiferal species and stable isotope measurements on planktic foraminifers show that abrupt changes occurred ca. 10.9, 9.2, 8.8, 7.9 and 7 ka (with 450 yr correction). There was no distinct change in sediment character during much of the Younger Dryas chronozone. In the δ¹⁸O record, the 8.8 ka event is a dramatic 1‰ shift toward lower values, which we associate with the Noble Inlet glacial event within Hudson Strait. We do not see the pronounced low δ¹⁸O event at 7.1 ka reported off Nova Scotia, but surprisingly, neither the Nova Scotia records nor other records in the Labrador Sea capture the impressive 8.8 ka change. Serious consideration must be given to the final collapse of the LIS as the cause of the 8.2 cal. ka cold event recorded in Greenland and northwest Europe. Copyright © 1999 John Wiley & Sons, Ltd.     

Relationship between aboveground and belowground biomass ofSpartina alterniflora (Smooth Cordgrass)

Aboveground and belowground biomass ofSpartina alterniflora were harvested during the period of peak aerial biomass from six sites along a latitudinal gradient ranging from Georgia to Nova Scotia. An equation relating live aboveground to live belowground biomass for short-form plants was formulated, using data collected in Delaware marshes. When data from the other sites were substituted into the equation, the mean live belowground biomass it predicted was within 15% of the value determined by harvesting at four of the five sites. At all sites, short-form plant live belowground biomass was concentrated in the upper 10 cm. Dead belowground biomass was located mostly in the top 15 cm in southern marshes, but was more evenly distributed with depth in northern marshes. Results were more ambiguous for tall-form plants, probably because of greater spatial variability in biomass distribution, and greater seasonal biomass dynamics.     

Alternative kinetic models for the interpretation of amino acid enantiomeric ratios in Pleistocene mollusks: Examples from California, Washington, and Florida

Alternative kinetic models for amino acid racemization in Pleistocene molluscan samples are compared by examination of results for samples from marine Pleistocene deposits in California, Washington, and Florida. Linear kinetic models previously have been applied to the Florida samples [Mitterer, R.M. (1975). Earth and Planetary Science Letters 28, 275–282.] because these kinetics were observed in laboratory pyrolysis experiments with the particular genus involved (Mercenaria). Nonlinear kinetic models, extrapolated from deep-sea foraminifera racemization kinetics, are applied to samples of Protothaca and Saxidomus from California and Washington and seem more consistent with their local chronologic and stratigraphic control. Average or effective diagenetic temperatures can be estimated by each of these models if reliably dated samples are available. Linear models applied to such samples from California and Florida suggest average diagenetic temperatures that are cooler (by as much as 10°C) than would be inferred from available paleoclimatic records. Nonlinear kinetic models yield estimates of average diagenetic temperatures that are more consistent with these records: full-glacial (i.e., approximately 18,000 yr BP) temperature reductions of between 2 and 6°C are inferred for coastal California and southern Florida. The nonlinear kinetic model is used to expand (by a factor of 2.5 to 3.0) the time scale proposed by Mitterer (1975) for five marine Pleistocene units of Florida.     

Deglaciation environments and evidence for glaciers of Younger Dryas age in Nova Scotia, Canada

The start of deglaciation is recorded in the Minas Basin region of Nova Scotia by the deltaic, glaciofluvial and glaciomarine sediments of the Five Islands Formation. Shell dates on bottomset beds of a delta at Spencers Island range from 14,300 to 12,600^{, 14}C yearsB.P. The time of complete deglaciation of Nova Scotia is still unknown; the uncertainty is at least partially due to evidence for a climatic oscillation at the end of the Late Wisconsinan. Peat beds were deposited during the interval between 12,700 and 10,500 B.P. They overlie previous glacial and fluvial deposits and are overlain by deposits of various origins. Pollen in these peat beds records the migration of spruce into the region indicating climatic warming, and a subsequent deterioration of climate is recorded by the return of tundra-like flora. The peat beds are truncated by a variety of deposits, including fluvial gravel and sand, lacustrine sand, silt and clay, and diamictons. Periglacial landforms and structures have been observed in some of these deposits. At Collins Pond, on the shore of Chedabucto Bay, a diamicton overlying a peat bed is characterized by strong fabrics parallel to the trend of other ice-flow landforms in the region. The evidence suggests that at least some of these deposits are glacigenic, indicating that glaciers were active in Nova Scotia until about 10,000 B.P.     

Tsunami impact to Washington and northern Oregon from segment ruptures on the southern Cascadia subduction zone

This paper explores the size and arrival of tsunamis in Oregon and Washington from the most likely partial ruptures of the Cascadia subduction zone (CSZ) in order to determine (1) how quickly tsunami height declines away from sources, (2) evacuation time before significant inundation, and (3) extent of felt shaking that would trigger evacuation. According to interpretations of offshore turbidite deposits, the most frequent partial ruptures are of the southern CSZ. Combined recurrence of ruptures extending ~490 km from Cape Mendocino, California, to Waldport, Oregon (segment C) and ~320 km from Cape Mendocino to Cape Blanco, Oregon (segment D), is ~530 years. This recurrence is similar to frequency of full-margin ruptures on the CSZ inferred from paleoseismic data and to frequency of the largest distant tsunami sources threatening Washington and Oregon, ~M _w 9.2 earthquakes from the Gulf of Alaska. Simulated segment C and D ruptures produce relatively low-amplitude tsunamis north of source areas, even for extreme (20 m) peak slip on segment C. More than ~70 km north of segments C and D, the first tsunami arrival at the 10-m water depth has an amplitude of <1.9 m. The largest waves are trapped edge waves with amplitude ≤4.2 m that arrive ≥2 h after the earthquake. MM V–VI shaking could trigger evacuation of educated populaces as far north as Newport, Oregon for segment D events and Grays Harbor, Washington for segment C events. The NOAA and local warning systems will be the only warning at greater distances from sources.     

Genetic differentiation and speciation in the estuarine isopodsCyathura polita andCyathura burbancki

We investigated the electrophoretically detectable variation at nine protein loci in seven populations ofCyathura polita and one population of the closely relatedC. burbancki from the Atlantic coast of North America. The average proportion of the genome heterozygous per individual \((\bar H)\) inC. polita ranges from about 0% in New Brunswick and Massachusetts to 9.3% in a Georgia population. \(\bar H\) in the population ofC. burbancki was 2.6%. On the basis of our results,C. polita can be separated into two geographic forms,northern (New Brunswick, Massachusetts, and Maryland) andsouthern (Georgia and Florida). The genetic distances between the southern and northernC. polita are similar to the genetic distances reported between species of several other invertebrate groups. Our genetic data support the idea that the northern and southern forms ofC. polita andC. burbancki comprise a triad of species that diverged from each other 2–3 million years ago. Since we know nothing about the genetic structure of populations ofCyathura between Georgia and Maryland, this interpretation must be considered preliminary.     

Time series and postglacial forest ecology

Forest ecology suffers from a lack of long-term community records. Preserved pollen data are richer in such information than is generally realized. By applying suitable statistical techniques to pollen records, one can learn much about competition, succession, and population dynamics in past tree communities. In this study, preserved pollen records from Everitt Lake, Nova Scotia, are analyzed as time series. Time domain studies reveal the post-fire responses of individual tree taxa. Correlograms yield models of past forest succession patterns. The models explain some effects of changing fire frequency, thus suggesting mechanisms by which fire, competition, and climate combine to produce long-term forest composition changes. Frequency domain studies suggest relationships between disturbance cycles, stand composition, and forest mosaics. Fire frequencies are seen to be highest where fire-dependent species abound and most regular where tree stands have uniform, not mixed, composition.     

Climatic Regionalization and the Spatio-Temporal Occurrence of Extreme Single-Year Drought Events (1500–1998) in the Interior Pacific Northwest, USA

Tree-ring records from western juniper (Juniperus occidentalis var. occidentalis Hook.) growing throughout the interior Pacific Northwest identify extreme climatic pointer years (CPYs) (i.e., severe single-year droughts) from 1500–1998. Widespread and extreme CPYs were concentrated in the 16th and early part of the 17th centuries and did not occur again until the early 20th century. The 217-yr absence of extreme CPYs may have occurred during an extended period of low variance in the Pacific Decadal Oscillation. We mapped climatic boundaries for the interior Pacific Northwest based on the location of sites with similar precipitation variability indices. Three regions, the Northwest (based on chronologies from nine sites), the Southwest (four sites), and the East (five sites) were identified. Our results suggest that western juniper radial growth indices have substantial interannual variability within the northwestern range of the species (central Oregon), particularly when compared with western juniper growing in its eastern range (eastern Oregon, southeastern Idaho, and northern Nevada) and southwestern range (southern Oregon and northeast California). We suspect that the substantial differences in the variability of western juniper radial growth indices are linked to the influence of ENSO events on winter/spring precipitation amounts.     

Uranium content and distribution in whole-coal samples,Sydney coalfield (Upper carboniferous), nova scotia,Canada

Uranium-poor bituminous coal-channel samples (mean and standard deviation 0.51±0.99 ppm) from the Sydney Coalfield in Nova Scotia show top and bottom enrichment trends as are known from German, British and American coals of Upper Carboniferous age (Breger and Schopf, 1955; Francis, 1961; Gluskoter et al., 1977). The trends appear to be related to sedimentary processes rather than to secondary geochemical enrichment effects on the coal.     

Occurrence of juvenile Atlantic menhanden,Brevoortia tyrannus,in the Annapolis River,Nova Scotia

This is the first report of juvenile (age 0+) Atlantic menhadens, Brevoortia tyrannus, in the Annapolis River, Nova Scotia. Juvenile Atlantic menhaden were incidentally collected during a 3-yr study of the effects of the STRAFLO hydro-power turbine at Annapolis Royal on alosine fishes. Length distribution and time of capture of collected fish suggest that Atlantic menhaden may spawn in the Bay of Fundy.     

Horsetails (equisetum) as indirect indicators of gold mineralization

The alleged reputation of the horsetail (Equisetum) as an accumulator of gold was studied by analysis of a number of specimens from various localities, mainly from Nova Scotia. None of the samples had appreciable gold concentrations but with one exception, all the specimens collected from auriferous ground had high concentrations of arsenic ranging up to 738 μg/g dry mass. To a lesser extent this was also true for antimony. The evidence tends to refute the previous belief that horsetails accumulate gold, but does show that the genus is not only tolerant of arseniferous ground but is also an arsenic accumulator. Because of the common geochemical association of gold and arsenic, it is suggested that analysis of horsetails for arsenic may be a useful prospecting tool where geologic or other evidence suggests the possible presence of auriferous ground.     

Review of factors affecting the distribution and abundance of waterfowl in shallow-water habitats of Chesapeake Bay

Long-term trends of waterfowl populations in Chesapeake Bay demonstrate the importance of shallow-water habitats for waterfowl species. Although recent increases in field feeding by geese and swans lessened the importance of shallow-water areas for these species, most duck species depend almost exclusively on shallow-water habitats. Many factors influenced the distribution and abundance of waterfowl in shallow-water habitats. Habitat degradation resulted in the decline in numbers of most duck species and a change in distribution of some species. Increased numbers of mallards (Anas platyrhynchos) in recent decades probably resulted from release programs conducted by the Maryland Department of Natural Resources and private individuals. Studies of food habits since 1885 showed a decline in submerged-aquatic vegetation in the diet of some species, such as the canvasback (Aythya valisineria), and an increase in the proportions of invertebrates in the diet. Diversity of food organisms for many waterfowl species has declined. Surveys of vegetation and invertebrates in the Chesapeake Bay generally reflect a degradation of shallow-water habitat. Human population increases in the Chesapeake Bay watershed directly and indirectly affected waterfowl distribution and abundance. The increase of exotic plant and invertebrate species in the bay, in most cases, benefited waterfowl populations. Increased contaminants have reduced the quality and quantity of habitat, although serious attempts to reverse this trend are underway. The use of shallow-water habitats by humans for fishing, hunting, boating, and other recreational and commercial uses reduced the use of shallow-water habitats by waterfowl. Humans can lessen the adverse influences on the valuable shallow-water habitats by restricting human population growth near these habitats and improving the water quality of the bay tributaries. Other affirmative actions that will improve these areas for waterfowl include greater restrictions on boat traffic in shallow-water habitats and establishing more sanctuaries in shallow-water areas that have complete protection from human disturbance. *** DIRECT SUPPORT *** A01BY074 00013     

Isotopic signatures of otoliths and the stock structure of canary rockfish along the Washington and Oregon coast

Canary rockfish are one of the commercially important rockfish species along the US Pacific coast. Yet little is known about their life history and stock structure. In this study 120 canary rockfish otoliths were collected from waters off the Washington and Oregon coast and subjected to stable O and C isotope (δ¹⁸O and δ¹³C) analyses. One powder sample was taken from the nucleus of each otolith, and the other from the 5th annual ring. Data from otolith nuclei can provide information on the natal sources and spawning stock separations, while data from age-1 to age-5 may indicate changes in fish habitat. Overall the δ¹⁸O values in otoliths of canary rockfish ranged from −0.2‰ to +1.7‰, whereas δ¹³C values of the same samples ranged from −5.4‰ to −1.4‰. The isotopic data and correlation of δ¹⁸O versus δ¹³C did not show clear separation between Washington and Oregon samples, similar to those for a previous study on yelloweye rockfish from the same region. These results suggest that canary rockfish may belong to a single spawning stock or population along the Washington and Oregon coast.     

Reconstruction of recent sea-level change using testate amoebae

Proxy-based sea-level reconstructions place the instrumentally observed rates of recent sea-level rise in a longer term context by providing data that extend the instrumental sea-level record into past centuries. This paper presents the first sea-level reconstructions based on analyses of testate amoebae, to test their ability to produce high-precision reconstructions of past sea level. We present two reconstructions for the past 100 yr from sites in Maine (USA) and Nova Scotia (Canada) based on short cores from salt marshes, and modern training data from North America and the United Kingdom. These are compared with tide-gauge records and reconstructions based on foraminifera from the same cores. The reconstructions show good agreement with both the tide-gauge data and the foraminifera-based reconstructions. The UK data perform well in predicting known elevations of North American surface samples and produce sea-level reconstructions very similar to those based on the North American data, suggesting the methodology is robust across large geographical areas. We conclude that testate amoebae have the potential to provide robust, higher precision sea-level reconstructions for the past few centuries if modern transfer functions are improved and core sites are located within the main zone of testate amoebae occurrence on the salt marsh.     

Effects of mesoscale physical processes on thin zooplankton layers at four sites along the west coast of the U.S.

Within the coastal marine environment, populations of phytoplankton, zooplankton, bacteria, viruses, and aggregations of marine snow are frequently concentrated beneath the surface in discrete, vertically thin layers. Thin layers range in vertical dimension from a few centimeters to three meters, and have been observed to extend horizontally for kilometers. They appear in the water column episodically and can persist for days. We present some of the results of an investigation of four coastal sites along the west coast of the United States to assess frequency of occurrence of thin layers of zooplankton. Our study sites included coastal sites near East Sound, Washington; Cape Perpetua, Oregon; Monterey Bay, California; and Santa Barbara, California. At each site, we collected several, weeks-long time series of hydrography, current velocity, and acoustic backscatter due to mesozooplankton. Our results show that thin layers were common features at all four sites. Across all study sites, a change in the predominant physical regime, usually precipitated by a change in the wind pattern, corresponded with an absence of thin Zooplankton layers. In order to make a first-order prediction about when thin layers have the possibility of occurring in a coastal environment, we found it useful to examine regional wind and circulation patterns and to determine how they affect stratification in each local environment.     

Hatching,estuarine transport,and distribution of larval and early juvenile Atlantic tomcod,Microgadus tomcod,in the Hudson River

Atlantic tomcod larvae, hatching in late February and early March 1975 and 1976 into a regime of accelerating river flows, were moved rapidly downriver from milepoint 42–54 (MP 0 is the estuary mouth) to the most seaward reaches of the estuary. This resulted in a spatiotemporal distribution markedly different from that of other Hudson River fish species. Peak tomcod density on posthatch sampling dates was observed most frequently at the George Washington Bridge station (MP 11). Correlation between movements of the 1.0‰ salt front and movements of the age-0 tomcod population was high (r=0.82); and may have been enhanced by high freshwater flows. The population epicenter was always seaward of the 1.0‰ salt front and mean distance between the two was 16–17 km. Moved by tidal and freshwater flows, the tomcod population oscillated between MP 0 and MP 43 during March–May 1973–1976. Location of the population epicenter after mid march was predicted (r²=0.76) to be seaward of the Tappan Zee Bridge (MP 30) when freshwater flows were greater than 450 m³ s^?1. During flow regimes greater than 1,290 m³ s^?1, the epicenter was predicted to be seaward of the George Washington Bridge (MP 11). An optimum-allocation sampling design for age-0 tomcod showed that 58% of the total effort from mid March to early June should be directed to the river region between MP 0 and MP 24, a region largely ignored in previous studies. *** DIRECT SUPPORT *** A01BY066 00013     

Impact of high herbivore densities on introduced smooth cordgrass,Spartina alterniflora,invading San Francisco Bay,California

Spartina alterniflora, smooth cordgrass, invading San Francisco Bay, California (USA), is attacked by high densities of a plant hopper, Prokelisia marginata, and a mirid bug, Trigonotylus uhleri. Both herbivores are sap-feeders. We investigated the impact of these herbivores on S. alterniflora's growth rate, vegetative spread, and seed production by manipulating herbivore densities in the field and in a greenhouse. Herbivore densities in the field peaked in early fall, with P. marginata averaging more than 300 individuals per mature culm of S. alterniflora (about 100,000 per m²) and T. uhleri densities exceeding 10 per culm (about 3,000 per m²). Field reductions of herbivore densities by approximately 70% with insecticidal soap did not result in greater vegetative growth rates or lateral spread of plants; plants grew vigorously with the highest densities of insects. In the greenhouse study, conducted with seedlings, herbivory significantly reduced plant mass and tiller number in some but not all replicate herbivory treatments. In both field and greenhouse, there were significant differences between some clones' growth rates independent of herbivory. Inflorescence production in the field was not affected by reduced-herbivory treatments. Seed set was low under conditions of both natural and reduced herbivory, averaging 0.4%. Despite densities of P. marginata and T. uhleri that are much higher than typically observed in areas where S. alterniflora is native, herbivory by these particular insects appears to have little impact and in unlikely to limit S. alterniflora’s spread through San Francisco Bay. *** DIRECT SUPPORT *** A01BY070 00009     

Composition,abundance, biomass,and production of macrofauna in a New England estuary: Comparisons among eelgrass meadows and other nursery habitats

Quantitative suction sampling was used to characterize and compare the species composition, abundance, biomass, and secondary production of macrofauna inhabiting intertidal mud-flat and sand-flat, eelgrass meadow, and salt-marsh-pool habitats in the Nauset Marsh complex, Cape Cod, Massachusetts (USA). Species richness and abundance were often greatest in eelgrass habitat, as was macroinvertebrate biomass and production. Most striking was the five to fifteen times greater rate of annual macrofaunal production in eelgrass habitat than elsewhere, with values ranging from approximately 23–139 g AFDW m² yr^?1. The marsh pool containing widgeon grass (Ruppia maritima) supported surprisingly low numbers of macroinvertebrates, probably due to stressfully low dissolved oxygen levels at night during the summer. Two species of macroinvertebrates, blue mussels (Mytilus edulis) and to a lesser extent bay scallops (Argopecten irradians), used eelgrass as “nursery habitat.” Calculations showed that macroinvertebrate production is proportionally much greater than the amount of primary production attributable to eelgrass in the Nauset Marsh system, and that dramatic changes at all trophic levels could be expected if large changes in seagrass abundance should occur. This work further underscores the extraordinarily large impact that seagrass can have on both the structure and function of estuarine ecosystems. *** DIRECT SUPPORT *** A01BY070 00006     

Petrology and Isotopic Composition of a Grenvillian Basement Fragment in the Northern Appalachian Orogen: Blair River Inlier, Nova Scotia, Canada

Mesoproterozoic metaplutonic rocks in northern Cape Breton Island,Nova Scotia, occur in a tectonic inlier within the Appalachianorogen. Although they have been multiply metamorphosed and variablydeformed, the petrology and geochemistry of these rocks provideinsight into the tectonomagmatic evolution of easternmost Laurentia.Anorthosite, syenite, and granitoid plutons (1100–980Ma) intruded the Sailor Brook and Polletts Cove River gneisses.New Nd isotopic data are presented from a biotite-rich partof the Sailor Brook gneiss (