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11.
Alexandre Forest Simon Bélanger Makoto Sampei Hiroshi Sasaki Catherine Lalande Louis Fortier 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(1):125-142
Surface concentrations and vertical fluxes of particulate organic carbon (POC) were assessed in the Amundsen Gulf (southeastern Beaufort Sea, Arctic Ocean) over the years 2004 to 2006 by using ocean color remote-sensing imagery and sequential sediment traps moored over the ca. 400 m isobath. Environmental conditions (sea ice, wind) and oceanographic variables (temperature, salinity, fluorescence and currents) were investigated to explain the variability of POC data. Annual downward POC fluxes in 2004, 2005 and 2006 cumulated, respectively, to 3.3, 4.2 and 6.0 g C m?2 yr?1 at ～100 m depth, and to 1.3, 2.2 and 3.3 g C m?2 yr?1 at ～210 m depth. The fraction of settling POC attributable to autochthonous processes occurring at or next to ice break-up was estimated to be 75–84% of the 100 m annual fluxes and to be 61–75% of the 210 m fluxes. Over the three ice-reduced seasons, distinct scenarios between ice conditions, surface POC pools and vertical POC export at 100 m were identified: (1) in 2004, despite a normal ice break-up, a weak primary production was measured and low vertical fluxes were collected as old ice moved across the region; (2) in 2005, a lengthened ice-free period allowed an extended season of surface POC production near-shore, while an intermediate increase of vertical fluxes was recorded offshore; and (3) in 2006, a late ice melt gave rise to a pulsed ice edge bloom and to large vertical fluxes also associated with extra ice-flushed material. Linear regressions of vertical POC fluxes against satellite-derived surface POC concentrations suggested that the pelagic POC retention in the upper 100 m of the Amundsen Gulf ranged from ca. 70% to 90% depending on the timing of ice cover melt. Regardless of the inter-annual variability, the estimated fraction of the surface POC reservoir reaching the 210 m water depth was reduced to ～5%. Therefore, as the Arctic Ocean warms up, our results support the expectation that the increasing extent of the seasonal ice zone will promote the POC pathways that benefit pelagic webs rather than benthic communities. 相似文献
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We present a method for constraining key properties of the climate system that are important for climate prediction (climate
sensitivity and rate of heat penetration into the deep ocean) by comparing a model's response to known forcings over the twentieth
century against climate observations for that period. We use the MIT 2D climate model in conjunction with results from the
Hadley Centre's coupled atmosphere–ocean general circulation model (AOGCM) to determine these constraints. The MIT 2D model,
which is a zonally averaged version of a 3D GCM, can accurately reproduce the global-mean transient response of coupled AOGCMs
through appropriate choices of the climate sensitivity and the effective rate of diffusion of heat anomalies into the deep
ocean. Vertical patterns of zonal mean temperature change through the troposphere and lower stratosphere also compare favorably
with those generated by 3-D GCMs. We compare the height–latitude pattern of temperature changes as simulated by the MIT 2D
model with observed changes, using optimal fingerprint detection statistics. Using a linear regression model as in Allen and
Tett this approach yields an objective measure of model-observation goodness-of-fit (via the residual sum of squares weighted
by differences expected due to internal variability). The MIT model permits one to systematically vary the model's climate
sensitivity (by varying the strength of the cloud feedback) and rate of mixing of heat into the deep ocean and determine how
the goodness-of-fit with observations depends on these factors. This provides an efficient framework for interpreting detection
and attribution results in physical terms. With aerosol forcing set in the middle of the IPCC range, two sets of model parameters
are rejected as being implausible when the model response is compared with observations. The first set corresponds to high
climate sensitivity and slow heat uptake by the deep ocean. The second set corresponds to low sensitivities for all magnitudes
of heat uptake. These results demonstrate that fingerprint patterns must be carefully chosen, if their detection is to reduce
the uncertainty of physically important model parameters which affect projections of climate change.
Received: 19 April 2000 / Accepted: 13 April 2001 相似文献
13.
Øyvind Breivik Arthur A. Allen Christophe Maisondieu Jens-Christian Roth Bertrand Forest 《Ocean Dynamics》2012,62(5):741-752
The leeway of 20-ft containers in typical distress conditions is established through field experiments in a Norwegian fjord
and in open-ocean conditions off the coast of France with a wind speed ranging from calm to 14 m s−1. The experimental setup is described in detail, and certain recommendations were given for experiments on objects of this
size. The results are compared with the leeway of a scaled-down container before the full set of measured leeway characteristics
are compared with a semianalytical model of immersed containers. Our results are broadly consistent with the semianalytical
model, but the model is found to be sensitive to choice of drag coefficient and makes no estimate of the crosswind leeway
of containers. We extend the results from the semianalytical immersion model by extrapolating the observed leeway divergence
and estimates of the experimental uncertainty to various realistic immersion levels. The sensitivity of these leeway estimates
at different immersion levels are tested using a stochastic trajectory model. Search areas are found to be sensitive to the
exact immersion levels, the choice of drag coefficient, and somewhat less sensitive to the inclusion of leeway divergence.
We further compare the search areas, thus, found with a range of trajectories estimated using the semianalytical model with
only perturbations to the immersion level. We find that the search areas calculated without estimates of crosswind leeway
and its uncertainty will grossly underestimate the rate of expansion of the search areas. We recommend that stochastic trajectory
models of container drift should account for these uncertainties by generating search areas for different immersion levels
and with the uncertainties in crosswind and downwind leeway reported from our field experiments. 相似文献
14.
Sensitivity of climate change projections to uncertainties in the estimates of observed changes in deep-ocean heat content 总被引：1，自引：0，他引：1
The MIT 2D climate model is used to make probabilistic projections for changes in global mean surface temperature and for thermosteric sea level rise under a variety of forcing scenarios. The uncertainties in climate sensitivity and rate of heat uptake by the deep ocean are quantified by using the probability distributions derived from observed twentieth century temperature changes. The impact on climate change projections of using the smallest and largest estimates of twentieth century deep ocean warming is explored. The impact is large in the case of global mean thermosteric sea level rise. In the MIT reference (“business as usual”) scenario the median rise by 2100 is 27 and 43 cm in the respective cases. The impact on increases in global mean surface air temperature is more modest, 4.9 and 3.9 C in the two respective cases, because of the correlation between climate sensitivity and ocean heat uptake required by twentieth century surface and upper air temperature changes. The results are also compared with the projections made by the IPCC AR4’s multi-model ensemble for several of the SRES scenarios. The multi-model projections are more consistent with the MIT projections based on the largest estimate of ocean warming. However, the range for the rate of heat uptake by the ocean suggested by the lowest estimate of ocean warming is more consistent with the range suggested by the twentieth century changes in surface and upper air temperatures, combined with the expert prior for climate sensitivity. 相似文献
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KTB-Research Group Black Forest 《Geophysical Journal International》1987,89(1):325-332
Summary. The unified seismic exploration program, consisting of 345 km of deep reflection profiling, a 200 km refraction profile, an expanding spread profile and near-surface high resolution reflection meaasurements, revealed a strongly differentiated crust beneath the Black Forest. The highly reflective lower crust contains numerous horizontal and dipping reflectors at depths of 13-14 km down to the crust-mantle boundary (Moho). The Moho appears as a flat horizontal first order discontinuity at a relatively shallow level of 25–27 km above a transparent upper mantle. From modelling of synthetic near-vertical and wide-angle seismograms using the reflectivity method the lower crust is supposed to be composed of laminae with an average thickness of about 100 m and velocity differences of greater than 10% increasing from top to bottom. The upper crust is characterised by mostly dipping reflectors, associated with bivergent underthrusting and accretion tectonics of Variscan age and with extensional faults of Mesozoic age. A bright spot at 9.5 km depth is characterised by low velocity material suggesting a fluid trap. It appears on all of the three profiles in the centre of the intersection region. The upper crust seems to be decoupled from the lowest crust by a relatively transparent zone which is' also identified as a low-velocity zone. This low velocity channel is situated directly above the laminated lower crust. The laminae in the Rhinegraben area are displaced vertically to greater depths indicating an origin before Tertiary rift formation and a subsidence of the whole graben wedge. 相似文献
18.
Forest R. Schenck Torrance C. Hanley R. Edward Beighley A. Randall Hughes 《Estuaries and Coasts》2018,41(3):896-907
Phenotypic variation within species can have community- and ecosystem-level effects. Such variation may be particularly important in ecosystem engineers, including many invasive species, because of the strong influence of these species on their surrounding communities and environment. We combined field surveys and glasshouse experiments to investigate phenotypic variation within the invasive common reed, Phragmites australis, among four estuarine source sites along the east coast of North America. Field surveys revealed variation in P. australis height and stem density among source sites. In a glasshouse environment, percent germination of P. australis seeds also varied across source sites. To test the degree to which phenotypic variation in P. australis reflected genetic or environmental differences, we conducted a glasshouse common garden experiment assessing the performance of P. australis seedlings from the four source sites across a salinity gradient. Populations maintained differences in morphology and growth in a common glasshouse environment, indicating a genetic component to the observed phenotypic variation. Despite this variation, experimentally increased porewater salinity consistently reduced P. australis stem density, height, and biomass. Differences in these morphological metrics are important because they are correlated with the impacts of invasive P. australis on the ecological communities it invades. Our results indicate that both colonization and spread of invasive P. australis will be dependent on the environmental and genetic context. Additional research on intraspecific variation in invasive species, particularly ecosystem engineers, will improve assessments of invasion impacts and guide management decisions in estuarine ecosystems. 相似文献
19.
Certain complex processes are most effectively modeled not on the macro-scale, but from the bottom-up, by simulating the decisions of individual entities, or agents. This study uses an agent-based modeling (ABM) approach to simulate residential dynamics in an area of Boston that has increasingly experienced gentrification in the past decades. The model is instantiated using basic empirical data and uses simple decision-making rules, differentiated into four classes, to simulate the process of residential dynamics. The model employs the consumption explanation of the cause of gentrification, which emphasizes the choices of individuals drawn to urban amenities, while testing the production explanation, which suggests that major investments from the public and private sphere attract and explain gentrification. Verification shows that the processes in the model work according to its construction, simulates complexity and emergent phenomena, and may be a valuable explanatory tool for understanding and learning about some processes underlying gentrification. 相似文献
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