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At least 253 records · Page 14Linked to original sources
USGS2009

Forest rodents provide directed dispersal of Jeffrey pine seeds

Some species of animals provide directed dispersal of plant seeds by transporting them nonrandomly to microsites where their chances of producing healthy seedlings are enhanced. We investigated whether this mutualistic interaction occurs between granivorous rodents and Jeffrey pine ( Pinus jeffreyi ) in the eastern Sierra Nevada by comparing the effectiveness of random abiotic seed dispersal with the dispersal performed by four species of rodents: deer mice ( Peromyscus maniculatus ), yellow-pine and long-eared chipmunks ( Tamias amoenus and T. quadrimaculatus ), and golden-mantled ground squirrels ( Spermophilus lateralis ). We conducted two caching studies using radio-labeled seeds, the first with individual animals in field enclosures and the second with a community of rodents in open forest. We used artificial caches to compare the fates of seeds placed at the range of microsites and depths used by animals with the fates of seeds dispersed abiotically. Finally, we examined the distribution and survival of naturally establishing seedlings over an eight-year period. Several lines of evidence suggested that this community of rodents provided directed dispersal. Animals preferred to cache seeds in microsites that were favorable for emergence or survival of seedlings and avoided caching in microsites in which seedlings fared worst. Seeds buried at depths typical of animal caches (5–25 mm) produced at least five times more seedlings than did seeds on the forest floor. The four species of rodents differed in the quality of dispersal they provided. Small, shallow caches made by deer mice most resembled seeds dispersed by abiotic processes, whereas many of the large caches made by ground squirrels were buried too deeply for successful emergence of seedlings. Chipmunks made the greatest number of caches within the range of depths and microsites favorable for establishment of pine seedlings. Directed dispersal is an important element of the population dynamics of Jeffrey pine, a dominant tree species in the eastern Sierra Nevada. Quantifying the occurrence and dynamics of directed dispersal in this and other cases will contribute to better understanding of mutualistic coevolution of plants and animals and to more effective management of ecosystems in which directed dispersal is a keystone process.

Ecology↗
USGS2009

Interannual variation of carbon fluxes from three contrasting evergreen forests: The role of forest dynamics and climate

Interannual variation of carbon fluxes can be attributed to a number of biotic and abiotic controls that operate at different spatial and temporal scales. Type and frequency of disturbance, forest dynamics, and climate regimes are important sources of variability. Assessing the variability of carbon fluxes from these specific sources can enhance the interpretation of past and current observations. Being able to separate the variability caused by forest dynamics from that induced by climate will also give us the ability to determine if the current observed carbon fluxes are within an expected range or whether the ecosystem is undergoing unexpected change. Sources of interannual variation in ecosystem carbon fluxes from three evergreen ecosystems, a tropical, a temperate coniferous, and a boreal forest, were explored using the simulation model STANDCARB. We identified key processes that introduced variation in annual fluxes, but their relative importance differed among the ecosystems studied. In the tropical site, intrinsic forest dynamics contributed ?? 30% of the total variation in annual carbon fluxes. In the temperate and boreal sites, where many forest processes occur over longer temporal scales than those at the tropical site, climate controlled more of the variation among annual fluxes. These results suggest that climate-related variability affects the rates of carbon exchange differently among sites. Simulations in which temperature, precipitation, and radiation varied from year to year (based on historical records of climate variation) had less net carbon stores than simulations in which these variables were held constant (based on historical records of monthly average climate), a result caused by the functional relationship between temperature and respiration. This suggests that, under a more variable temperature regime, large respiratory pulses may become more frequent and high enough to cause a reduction in ecosystem carbon stores. Our results also show that the variation of annual carbon fluxes poses an important challenge in our ability to determine whether an ecosystem is a source, a sink, or is neutral in regard to CO 2 at longer timescales. In simulations where climate change negatively affected ecosystem carbon stores, there was a 20% chance of committing Type II error, even with 20 years of sequential data. ?? 2009 by the Ecological Society of America.

Ecology↗
USGS2009

Multi-state succession in wetlands: a novel use of state and transition models

The complexity of ecosystems and mechanisms of succession are often simplified by linear and mathematical models used to understand and predict system behavior. Such models often do not incorporate multivariate, nonlinear feedbacks in pattern and process that include multiple scales of organization inherent within real-world systems. Wetlands are ecosystems with unique, nonlinear patterns of succession due to the regular, but often inconstant, presence of water on the landscape. We develop a general, nonspatial state and transition (S and T) succession conceptual model for wetlands and apply the general framework by creating annotated succession/management models and hypotheses for use in impact analysis on a portion of an imperiled wetland. The S and T models for our study area, Water Conservation Area 3A South (WCA3), Florida, USA, included hydrologic and peat depth values from multivariate analyses and classification and regression trees. We used the freeware Vegetation Dynamics Development Tool as an exploratory application to evaluate our S and T models with different management actions (equal chance [a control condition], deeper conditions, dry conditions, and increased hydrologic range) for three communities: slough, sawgrass ( Cladium jamaicense ), and wet prairie. Deeper conditions and increased hydrologic range behaved similarly, with the transition of community states to deeper states, particularly for sawgrass and slough. Hydrology is the primary mechanism for multi-state transitions within our study period, and we show both an immediate and lagged effect on vegetation, depending on community state. We consider these S and T succession models as a fraction of the framework for the Everglades. They are hypotheses for use in adaptive management, represent the community response to hydrology, and illustrate which aspects of hydrologic variability are important to community structure. We intend for these models to act as a foundation for further restoration management and experimentation which will refine transition and threshold concepts.

Florida↗
USGS2012

Allowable levels of take for the trade in Nearctic songbirds

The take of Nearctic songbirds for the caged-bird trade is an important cultural and economic activity in Mexico, but its sustainability has been questioned. We relied on the theta-logistic population model to explore options for setting allowable levels of take for 11 species of passerines that were subject to legal take in Mexico in 2010. Because estimates of population size necessary for making periodic adjustments to levels of take are not routinely available, we examined the conditions under which a constant level of take might contribute to population depletion (i.e., a population below its level of maximum net productivity). The chance of depleting a population is highest when levels of take are based on population sizes that happen to be much lower or higher than the level of maximum net productivity, when environmental variation is relatively high and serially correlated, and when the interval between estimation of population size is relatively long (≥5 years). To estimate demographic rates of songbirds involved in the Mexican trade we relied on published information and allometric relationships to develop probability distributions for key rates, and then sampled from those distributions to characterize the uncertainty in potential levels of take. Estimates of the intrinsic rate of growth (r) were highly variable, but median estimates were consistent with those expected for relatively short-lived, highly fecund species. Allowing for the possibility of nonlinear density dependence generally resulted in allowable levels of take that were lower than would have been the case under an assumption of linearity. Levels of take authorized by the Mexican government in 2010 for the 11 species we examined were small in comparison to relatively conservative allowable levels of take (i.e., those intended to achieve 50% of maximum sustainable yield). However, the actual levels of take in Mexico are unknown and almost certainly exceed the authorized take. Also, the take of Nearctic songbirds in other Latin American and Caribbean countries ultimately must be considered in assessing population-level impacts.

Ecological Applications↗
USGS2014

Demography of a reintroduced population: moving toward management models for an endangered species, the whooping crane

The reintroduction of threatened and endangered species is now a common method for reestablishing populations. Typically, a fundamental objective of reintroduction is to establish a self-sustaining population. Estimation of demographic parameters in reintroduced populations is critical, as these estimates serve multiple purposes. First, they support evaluation of progress toward the fundamental objective via construction of population viability analyses (PVAs) to predict metrics such as probability of persistence. Second, PVAs can be expanded to support evaluation of management actions, via management modeling. Third, the estimates themselves can support evaluation of the demographic performance of the reintroduced population, e.g., via comparison with wild populations. For each of these purposes, thorough treatment of uncertainties in the estimates is critical. Recently developed statistical methods - namely, hierarchical Bayesian implementations of state-space models - allow for effective integration of different types of uncertainty in estimation. We undertook a demographic estimation effort for a reintroduced population of endangered whooping cranes with the purpose of ultimately developing a Bayesian PVA for determining progress toward establishing a self-sustaining population, and for evaluating potential management actions via a Bayesian PVA-based management model. We evaluated individual and temporal variation in demographic parameters based upon a multi-state mark-recapture model. We found that survival was relatively high across time and varied little by sex. There was some indication that survival varied by release method. Survival was similar to that observed in the wild population. Although overall reproduction in this reintroduced population is poor, birds formed social pairs when relatively young, and once a bird was in a social pair, it had a nearly 50% chance of nesting the following breeding season. Also, once a bird had nested, it had a high probability of nesting again. These results are encouraging considering that survival and reproduction have been major challenges in past reintroductions of this species. The demographic estimates developed will support construction of a management model designed to facilitate exploration of management actions of interest, and will provide critical guidance in future planning for this reintroduction. An approach similar to what we describe could be usefully applied to many reintroduced populations.

Ecological Applications↗
USGS2014

Managing the whole landscape: Historical, hybrid, and novel ecosystems

The reality confronting ecosystem managers today is one of heterogeneous, rapidly transforming landscapes, particularly in the areas more affected by urban and agricultural development. A landscape management framework that incorporates all systems, across the spectrum of degrees of alteration, provides a fuller set of options for how and when to intervene, uses limited resources more effectively, and increases the chances of achieving management goals. That many ecosystems have departed so substantially from their historical trajectory that they defy conventional restoration is not in dispute. Acknowledging novel ecosystems need not constitute a threat to existing policy and management approaches. Rather, the development of an integrated approach to management interventions can provide options that are in tune with the current reality of rapid ecosystem change.

Frontiers in Ecology and the Environment↗
USGS2014

A synopsis of short-term response to alternative restoration treatments in sagebrush-steppe: the SageSTEP project

The Sagebrush Steppe Treatment Evaluation Project (SageSTEP) is an integrated long-term study that evaluates ecological effects of alternative treatments designed to reduce woody fuels and to stimulate the herbaceous understory of sagebrush steppe communities of the Intermountain West. This synopsis summarizes results through 3 yr posttreatment. Woody vegetation reduction by prescribed fire, mechanical treatments, or herbicides initiated a cascade of effects, beginning with increased availability of nitrogen and soil water, followed by increased growth of herbaceous vegetation. Response of butterflies and magnitudes of runoff and erosion closely followed herbaceous vegetation recovery. Effects on shrubs, biological soil crust, tree cover, surface woody fuel loads, and sagebrush-obligate bird communities will take longer to be fully expressed. In the short term, cool wet sites were more resilient than warm dry sites, and resistance was mostly dependent on pretreatment herbaceous cover. At least 10 yr of posttreatment time will likely be necessary to determine outcomes for most sites. Mechanical treatments did not serve as surrogates for prescribed fire in how each influenced the fuel bed, the soil, erosion, and sage-obligate bird communities. Woody vegetation reduction by any means resulted in increased availability of soil water, higher herbaceous cover, and greater butterfly numbers. We identified several trade-offs (desirable outcomes for some variables, undesirable for others), involving most components of the study system. Trade-offs are inevitable when managing complex natural systems, and they underline the importance of asking questions about the whole system when developing management objectives. Substantial spatial and temporal heterogeneity in sagebrush steppe ecosystems emphasizes the point that there will rarely be a “recipe” for choosing management actions on any specific area. Use of a consistent evaluation process linked to monitoring may be the best chance managers have for arresting woodland expansion and cheatgrass invasion that may accelerate in a future warming climate.

Rangeland Ecology and Management↗
USGS1968

Chronology of intrusion, volcanism, and ore deposition at Bingham, Utah

Potassium-argon dates for major igneous rock types in the Bingham mining district, Utah, range from 39 to 32 m.y. and suggest that:(1) Plutonism, volcanism, and hydrothermal activity were sequential stages in a magmatic history of about 7 m.y. duration.(2) Latitic volcanic rocks, in part, postdate emplacement of the Last Chance and Bingham stocks.(3) Sulfide mineralization and hydrothermal alteration followed emplacement of the monzonitic stocks and extrusion of at least the earliest units in the volcanic sequence; the time interval between intrusion and alteration was probably less than 1 m.y.(4) The rhyolites of Shaggy Peak, which may represent terminal differentiation products in a comagmatic series, are the youngest igneous rocks in the area.

Utah↗
USGS2024

Best practices for incorporating climate change science into Department of the Interior analyses, consultations, and decision making

The purpose of this document is to provide technical guidance, practical application examples, and resource lists for those who conduct, manage, and/or interpret technical workflows within the Department of the Interior. This document is intended to support implementation of Department of the Interior policy 526 DM 1 and establish best practices for using climate change science to inform analysis, consultation, and decision making. The Earth’s climate is an interconnected system that distributes energy, heat, and water around the planet. Due to human-driven increases in long-lived greenhouse gases, the Earth’s climate is now changing. For Departmental decision-making purposes, assuming a static, unchanging baseline climate is no longer consistent with current knowledge about the climate system. There are uncertainties about future climate and how resources or assets (RoAs) will respond to new conditions. To depict the possibilities, the global climate science community develops scenarios and models to explore how future climate may respond to socioeconomic and technological development in the world. Principles for informing policy development, planning and decisions, and regulatory processes using climate change science must: 1) consider the effects of future climate change, 2) characterize the risks, and 3) characterize the uncertainties. Best practices include: Use multiple scenarios to assess risks from a range of plausible societal pathways. When constraints prevent the use of multiple scenarios or if decision makers are risk averse, ensure that the chosen scenario considers higher risk outcomes. This is particularly important for large investments or irreversible decisions and reduces the chances of overconfident decision making. Use multiple climate models within each scenario to account for the range of outcomes due to model uncertainty. Do not rely solely on a single model or an ensemble average. Use relevant climate data . Use a time-period for model projections of the future climate change consistent with the relevant timeframe of the policy, action, or decision being considered. Historical observations are useful for understanding past conditions and climate trends for the next several years, but not beyond the next decade. Consult with climate data and modeling experts to assess which data and model resources are most appropriate for any given application. Clearly describe key analysis uncertainties (including with any climate observations, models, and scenarios used), and how they were addressed in the analysis and/or decision process. This ensures transparency and learning among analysts and decision makers.

Report↗
USGS2007

Dietary and spatial overlap between sympatric ursids relative to salmon use

We hypothesized that there would be minimal dietary overlap between sympatric brown bears ( Ursus arctos ) and American black bears ( U. americanus ) relative to salmon ( Oncorhynchus spp.) utilization when alternative foods (e.g., fruits) are abundant. To maximize the chance that we would reject this hypothesis, we examined the diets of brown and black bears known to have visited salmon streams. Species, sex, and individual identification of bears visiting salmon streams were determined by DNA analysis of hair and feces collected in 2002-2004 along those streams. Diets were estimated from fecal residues and stable isotope analyses of hair. Assimilated diets of brown bears were 66.0% (SD = 16.7%) salmon , 13.9% (SD = 7.5%) terrestrial animal matter, and 20.1% (SD = 17.2%) plant matter. Assimilated diets of black bears were 8.0% (SD = 5.4%) salmon , 8.4% (SD = 9.7%) terrestrial animal matter, and 83.6% (SD = 7.7%) plant matter. Male and female brown bears did not differ in either the proportion of dietary salmon, terrestrial animal matter, or plant matter. The relative amounts of fruit residues in the feces of brown bears (87.0%, SD = 15.2%) and black bears (91.8%, SD = 7.2%) did not differ. Both sexes of brown bears visited salmon streams and consumed significant amounts of salmon, but only male American black bears visited streams and then consumed minimal amounts of salmon. Thus, brown bears were largely carnivorous and black bears were largely herbivorous and frugivorous. This reduced dietary overlap relative to salmon and fruit use is understandable in light of the concentrated, defendable nature of salmon in small streams, the widely dispersed, non-defendable nature of abundant fruits, the dominance of brown over black bears, the higher energy requirement of the larger brown bear, and, therefore, the differing ability of the species to efficiently exploit different food resources.

Ursus↗
USGS2019

The influence of body size, condition, and age on recruitment of four Alaskan brown bear populations

Recruitment of brown bear ( Ursus arctos ) offspring into a population is the product of initial cub production and subsequent survival and is a critical component of overall population status and trend. We investigated the relationship between maternal body size, body condition, and age (as a surrogate for gained experience) and recruitment of dependent offspring (≥1 yr old) in 4 Alaska, USA (2014–2017), brown bear populations using logistic regression. Body size alone was our top predictor of the presence of offspring and appeared in all top models. Our data suggest that bear size is the primary driver of productivity across all 4 study populations, with larger bears having a greater chance of being observed with offspring. The effect of body condition was likely confounded by the increased energetic costs of supporting cubs through time and had a negative relationship with recruitment. Age (experience) was positively related to recruitment. Understanding the relative importance of body size, body condition, and age on the recruitment of offspring provides insights into life-history trade-offs female bears must manage as they strive to meet the nutritional costs of cub production and rearing, while minimizing risks to themselves and their offspring. Further assessment of long-term longitudinal studies of brown bears that assess the lifetime reproductive output of individuals would be highly informative to further assess the effect of experience on recruitment and to support the management of brown bear populations for recovery, conservation, sustained yield, and ecosystem function.

Alaska↗
USGS2006

Using role analysis to plan for stakeholder involvement: a Wyoming case study

Prior to implementing laws and policies regulating water, wildlife, wetlands, endangered species, and recreation, natural resource managers often solicit public input. Concomitantly, managers are continually seeking more effective ways to involve stakeholders. In the autumn of 1999, the Wyoming Game and Fish Department sought to develop a state management plan for its portion of the Yellowstone grizzly bear (Ursus arctos horribilis) population if it was removed from the federal threatened species list. A key aspect of developing this plan was the involvement of federal, state, and local agencies, representatives from nongovernmental organizations, and citizens. Wyoming wildlife managers asked researchers from the United States Geological Survey to demonstrate how the Legal-Institutional Analysis Model could be used to initiate this process. To address these needs, we conducted similar workshops for a group of state and federal managers or staffers and a broad group of stakeholders. Although we found similarities among the workshop groups, we also recorded differences in perspective between stakeholder groups. The managers group acknowledged the importance of varied stakeholders but viewed the grizzly bear planning process as one centered on state interests, influenced by state policies, and amenable to negotiation. The other workshops identified many stakeholders and viewed the decision process as diffuse, with many opportunities for entry into the process. These latter groups were less certain about the chance for a successful negotiation. We concluded that if these assumptions and differences were not reconciled, the public involvement effort was not likely to succeed.

Wildlife Society Bulletin↗
USGS2010

Factors influencing nesting success of king eiders on northern Alaska's Coastal Plain

King eider (Somateria spectabilis) populations have declined markedly in recent decades for unknown reasons. Nest survival is one component of recruitment, and a female's chance of reproductive success increases with her ability to choose an appropriate nesting strategy. We estimated variation in daily nest survival of king eiders at 2 sites, Teshekpuk and Kuparuk, Alaska, USA, 2002-2005. We evaluated both a priori and exploratory competing models of nest survival that considered importance of nest concealment, seclusion, and incubation constancy as strategies to avoid 2 primary egg predators, avian (Larus spp., Stercorarius spp., and Corvus corax) and fox (Alopex lagopus). We used generalized nonlinear techniques to examine factors affecting nest survival rates and information-theoretic approaches to select among competing models. Estimated nest survival, accounting for a nest visitation effect, varied considerably across sites and years (0.21-0.57); however, given our small sample size, much of this variation maybe attributable to sampling variation (??process = 0.007, 95% CI: 0.003-0.070). Nest survival was higher at Kuparuk than Teshekpuk in all years; however, due to the correlative nature of our data, we cannot determine the underlying causes with any certainty. We found mixed support for the concealed breeding strategy, females derived no benefit from nesting in areas with more willow (Salix spp.; measure of concealment) except that the observer effect diminished as willow cover increased. We suggest these patterns are due to conflicting predation pressures. Nest survival was not higher on islands (measure of seclusion) or with increased incubation constancy but was higher post-fox removal, indicating that predator control on breeding grounds could be a viable management option. Nest survival was negatively affected by our nest visitations, most likely by exposing the nest to avian scavengers. We recommend precautions be taken to limit the effects of nest visits in future studies and to consider them as a possible negative bias in estimated nest survival. Future models of the impacts of development within the breeding grounds of king eider should consider the influence of humans in the vicinity of nests.

Journal of Wildlife Management↗
USGS1975

Weights, growth, and survival of timber wolf pups in Minnesota

Weights, growth rates, canine tooth lengths, and survival data were obtained from 73 wild wolf ( Canis lupus ) pups that were 8 to 28 weeks old when live-trapped in three areas of northern Minnesota from 1969 to 1972. Relative weights of wild pups are expressed as percentages of a standard weight curve based on data from captive pups of similar age. These relative weights varied greatly within litters, between litters, and between years; extremes of 31 to 144 percent of the standard were observed. Growth rates ranging from 0.05 to 0.23 kilograms per day were observed, and similar variations in general development and in replacement and growth of canine teeth were noted. Survival data based on radio-tracking and tag returns indicated that pups with relative weights less than 65 percent of standard have a poor chance of survival, whereas pups of at least 80 percent of standard weight have a high survivability. Pups born in 1972 were especially underweight, probably a result of declining white-tailed deer ( Odocoileus virginianus ) densities in the interior of the Superior National Forest study area.

Minnesota↗
USGS1987

Spatial relations between sympatric coyotes and red foxes in North Dakota

Spatial relations between coyotes ( Canis latrans ) and red foxes ( Vulpes vulpes ) on a 360-km2 area in North Dakota were studied during 1977-78. Coyote families occupied large (mean = 61.2 km2), relatively exclusive territories that encompassed about one-half of the study area. Fox families occupied much smaller (mean = 11.9 km2), relatively exclusive, territories that overlapped perimeters of coyote territories and/or encompassed area unoccupied by coyotes. No fox family lived totally within a coyote territory, but 3 fox families lived within the 153.6-km2 home range of an unattached yearling male coyote. Both coyotes and foxes, from families with overlapping territories, tended to use their overlap areas less than was expected by amount of overlap. Encounters between radio-equipped coyotes and foxes from families with overlapping territories occurred less often than was expected by chance. Foxes living near coyotes exhibited considerable tenacity to their territories, and no monitored fox was killed by coyotes during 2,518 fox-days of radio surveillance. A hypothesis for coyote-induced fox population declines, based largely on fox avoidance mechanisms, is presented.

North Dakota↗
USGS1997

Capture-recapture analysis of a wintering black-capped chickadee population in Connecticut, 1958-1993

We investigated the dynamics of a wintering population of Black-capped Chickadees ( Parus atricapillus ) using data from a long-term capture-recapture study. Goodness-of-fit and likelihood-ratio tests indicated that the standard Jolly-Seber model was inadequate for the data, so we explored different parameterizations of a model in which survival probability for new captures differed from that of previously marked birds. One possible explanation for the lower local survival rate of new captures is that some of the birds were transients that had no chance of being recaptured. Average survival probability over the entire period was 0.62, and the estimated fraction of transients among unmarked birds was 0.27. We found evidence that chickadee survival rates were lower in years immediately following establishment of the Tufted Titmouse ( Parus bicolor ) as a territorial species (after 1967) than during years immediately preceding this event. We found no evidence that chickadee survival rates were lower in the years immediately following establishment of territorial raptors (after 1984) than during preceding years. Evidence suggested a long-term decline in survival probability from 1959 to 1991.

The Auk↗
USGS2016

Applications for General Purpose Command Buffers: The Emergency Conjunction Avoidance Maneuver

A case study is presented for the use of Relative Operation Sequence (ROS) command buffers to quickly execute a propulsive maneuver to avoid a collision with space debris. In this process, a ROS is custom-built with a burn time and magnitude, uplinked to the spacecraft, and executed in 15 percent of the time of the previous method. This new process provides three primary benefits. First, the planning cycle can be delayed until it is certain a burn must be performed, reducing team workload. Second, changes can be made to the burn parameters almost up to the point of execution while still allowing the normal uplink product review process, reducing the risk of leaving the operational orbit because of outdated burn parameters, and minimizing the chance of accidents from human error, such as missed commands, in a high-stress situation. Third, the science impacts can be customized and minimized around the burn, and in the event of an abort can be eliminated entirely in some circumstances. The result is a compact burn process that can be executed in as few as four hours and can be aborted seconds before execution. Operational, engineering, planning, and flight dynamics perspectives are presented, as well as a functional overview of the code and workflow required to implement the process. Future expansions and capabilities are also discussed.

Conference Paper↗
USGS1989

Geochemical expression of early diagenesis in middle Eocene-lower Oligocene pelagic sediments in the southern Labrador Sea, Site 647, ODP Leg 105

Geochemical analyses of the middle Eocene through lower Oligocene lithologic Unit IIIC (260-518 meters below sea floor [mbsf]) indicate a relatively constant geochemical composition of the detrital fraction throughout this depositional interval at Ocean Drilling Program (ODP) Site 647 in the southern Labrador Sea. The main variability occurs in redox-sensitive elements (e.g., iron, manganese, and phosphorus), which may be related to early diagenetic inability in anaerobic pore waters during bacterial decomposition of organic matter. Initial preservation of organic matter was mediated by high sedimentation rates (36 m/m.Y.). High iron (Fe) and manganese (Mn) contents are associated with carbonate concretions of siderite, manganosiderite, and rhodochrosite. These concretions probably formed in response to elevated pore-water alkalinity and total dissolved carbon dioxide (CO2) concentrations resulting from bacterial sulfate reduction, as indicated by nodule stable-isotope compositions and pore-water geochemistry. These nodules differ from those found in upper Cenozoic hemipelagic sequences in that they are not associated with methanogenesis. Phosphate minerals (carbonate-fluorapatite) precipitated in some intervals, probably as the result of desorption of phosphorus from iron and manganese during reduction. The bulk chemical composition of the sediments differs little from that of North Atlantic Quaternary abyssal red clays, but may contain a minor hydrothermal component. The silicon/ aluminum (Si/Al) ratio, however, is high and variable and probably reflects original variations in biagenic opal, much of which is now altered to smectite and/or opal CT. An increase in the sodium/potassium (Na/K) ratio in the upper Eocene corresponds to the beginning of coarser-grained feldspar flux to the site, possibly marking the onset of more vigorous deep currents. Although the Site 647 cores provide a nearly complete high-resolution, high-latitude Eocene-Oligocene record, the high sedimentation rate and somewhat unusual diagenetic conditions have led to variable alteration of benthic foraminifers and fine-fraction carbonate and have overprinted the original stable-isotope records. Planktonic foraminifers are less altered, but on the whole, there is little chance of sorting out the nature and timing of environmental change on the basis of our stable-isotope analyses.

Proceedings of the Ocean Drilling Program: Scienti↗