排序方式: 共有33条查询结果,搜索用时 15 毫秒
11.
Amanda W. J. Demopoulos Nicole Cormier Katherine C. Ewel Brian Fry 《Estuaries and Coasts》2008,31(2):371-381
The mangrove or mud crab, Scylla serrata, is an important component of mangrove fisheries throughout the Indo-Pacific. Understanding crab diets and habitat use should
assist in managing these fisheries and could provide additional justification for conservation of the mangrove ecosystem itself.
We used multiple chemical tracers to test whether crab movements were restricted to local mangrove forests, or extended to
include adjacent seagrass beds and reef flats. We sampled three mangrove forests on the island of Kosrae in the Federated
States of Micronesia at Lelu Harbor, Okat River, and Utwe tidal channel. Samples of S. serrata and likely food sources were analyzed for stable carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S) isotopes. Scylla serrata tissues also were analyzed for phosphorus (P), cations (K, Ca, Mg, Na), and trace elements (Mn, Fe, Cu, Zn, and B). Discriminant
analysis indicated that at least 87% of the crabs remain in each site as distinct populations. Crab stable isotope values
indicated potential differences in habitat use within estuaries. Values for δ13C and δ34S in crabs from Okat and Utwe were low and similar to values expected from animals feeding within mangrove forests, e.g.,
feeding on infauna that had average δ13C values near −26.5‰. In contrast, crabs from Lelu had higher δ13C and δ34S values, with average values of −21.8 and 7.8‰, respectively. These higher isotope values are consistent with increased crab
foraging on reef flats and seagrasses. Given that S. serrata have been observed feeding on adjacent reef and seagrass environments on Kosrae, it is likely that they move in and out of
the mangroves for feeding. Isotope mixing model results support these conclusions, with the greatest mangrove ecosystem contribution
to S. serrata diet occurring in the largest mangrove forests. Conserving larger island mangrove forests (> 1 km deep) appears to support
crab foraging activities. 相似文献
12.
13.
A global mean dynamic topography and ocean circulation estimation using a preliminary GOCE gravity model 总被引:8,自引:4,他引:4
The Gravity and steady-state Ocean Circulation Explorer (GOCE) satellite mission measures Earth’s gravity field with an unprecedented
accuracy at short spatial scales. In doing so, it promises to significantly advance our ability to determine the ocean’s general
circulation. In this study, an initial gravity model from GOCE, based on just 2 months of data, is combined with the recent
DTU10MSS mean sea surface to construct a global mean dynamic topography (MDT) model. The GOCE MDT clearly displays the gross
features of the ocean’s steady-state circulation. More significantly, the improved gravity model provided by the GOCE mission
has enhanced the resolution and sharpened the boundaries of those features compared with earlier satellite only solutions.
Calculation of the geostrophic surface currents from the MDT reveals improvements for all of the ocean’s major current systems.
In the North Atlantic, the Gulf Stream is stronger and more clearly defined, as are the Labrador and the Greenland currents.
Furthermore, the finer scale features, such as eddies, meanders and branches of the Gulf Stream and North Atlantic Current
system are visible. Similar improvements are seen also in the North Pacific Ocean, where the Kuroshio and its extension are
well represented. In the Southern hemisphere, both the Agulhas and the Brazil-Malvinas Confluence current systems are well
defined, and in the Southern ocean the Antarctic Circumpolar Current appears enhanced. The results of this preliminary analysis,
using an initial GOCE gravity model, clearly demonstrate the potential of the GOCE mission. Already, at this early stage of
the mission, the resolution of the MDT has been improved and the estimated surface current speeds have been increased compared
with a GRACE satellite-only MDT. Future GOCE gravity models are expected to build further upon this early success. 相似文献
14.
15.
16.
17.
18.
Marie-Helene Cormier Daniel S. Scheirer Ken C. Macdonald 《Marine Geophysical Researches》1996,18(1):53-84
Nearly complete side-scan, bathymetry and magnetic coverage documents the evolution of the geometry of the East Pacific Rise (EPR) between 16° and 19° S since 5 Ma. Lineaments visible in SeaMARC II, H-MR1 and Sea Beam 2000 side-scan data correspond dominantly to normal fault scarps which have developed in the axial region perpendicular to the least compressive stress. Except near overlapping spreading centers (OSCs), the lineament orientations are taken to represent the perpendicular to the instantaneous Pacific-Nazca spreading direction. Their dominant orientation in the axial region is 012°, in good agreement with the prediction of the current model of relative plate motion (DeMets et al., 1994). However, the variations of the lineament azimuths with age show that there has been a small (3°–5°) clockwise change in the Nazca-Pacific relative motion since 5 Ma. There is also a distinct population of lineaments which strike counterclockwise to the ambient orientation. These discordant lineaments form somewhat coherent patterns on the seafloor and represent the past migration tracks of several left-stepping OSCs. Concurrent analysis of these discordant zones and the magnetic anomalies, reveals that up to 1 Ma, the EPR was offset by a few large, left-stepping OSCs. These OSCs were bisected into smaller OSCs by new spreading segments forming within their overlap basins. The smaller OSCs proceeded to migrate rapidly and were further bisected by newly spawned ridge segments until the present staircase of small, left-stepping OSCs was achieved. By transferring lithosphere from one plate to the other, these migration events account remarkably well for the variable spreading asymmetry in the area. Between 16° and 19° S, the present EPR is magmatically very robust, as evidenced by its inflated morphology, the profuse volcanic and hydrothermal activity observed from submerisbles and towed cameras, the geochemistry of axial basalts, and seismic and gravity data. Since 1 Ma, all the OSCs have migrated away from the shallowest, most robust section of the ridge between 17° and 17°30 S, which was previously offset by a large OSC. We propose that the switch from a presumed starved magmatic regime typically associated with large OSCs to the presently robust magmatic regime occurred when the EPR overrode a melt anomaly during its westward migration relative to the asthenosphere. The resulting increase in melt supply at 17°–17°30 S has fed the migration of axial discontinuities for this section of the southern EPR since 1 Ma. 相似文献
19.
20.
Vernon F. Cormier 《Physics of the Earth and Planetary Interiors》1981,24(4):291-301
Short-period seismograms are synthesized for PKP phases in anelastic Earth models. The synthetics were constructed using a synthetic technique valid at grazing incidence, a source-time function appropriate for deep-focus earthquakes, and an instrument response for either a short-period WWSSN or SRO seismograph. The agreement between predicted and observed amplitudes and spectral ratios requires neither a low-Qα zone at 0.2–2 Hz nor a low or negative P-velocity gradient at the bottom of the outer core. Thin low-Qα zones beneath the inner core boundary fit spectral ratio data that sample the upper 200 km of the inner core but fail to fit data that sample the lower inner core. Only a model having Qα?1?[0.003, 0.004] at 0.2–2 Hz, nearly constant with depth in the inner core, satisfies all of the spectral ratio and amplitude data. The assumption of a bulk viscosity of 10-103 Pa s for the liquid phase of a partially molten inner core combined with the observation of low shear attenuation in the inner core at frequencies less than 0.005 Hz limit the physical parameters associated with two possible attenuation mechanisms: (1) fluid flow and viscous relaxation due to ellipsoidally shaped inclusions of melt, and (2) the solid-liquid phase transformation induced by the stress change during the passage of a seismic wave. Both mechanisms require an order of 0.1% partial melt to reproduce the observed Qα?1. In the outer core, the time constant of the mechanism of phase transformation is predicted to be 104–106 s. Confirmation of small shear attenuation in the inner core in the frequency band of seismic body waves would favor the mechanism of phase transformation. 相似文献