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41.
Julian J. Dodson Jean-Claude Dauvin R. Grant Ingram B. d’Anglejan 《Estuaries and Coasts》1989,12(2):66-81
We tested the hypothesis that the distribution and retention of larval smelt (Osmerus mordax) in the middle estuary of the St. Lawrence River is related to the maintenance of other planktonic organisms in the maximum turbidity zone (MTZ). We documented the horizontal and vertical distribution of larval smelt, macrozooplankton, and suspended particulate matter over four tidal cycles at each of three stations located along the major axis of the turbid upstream portion of the middle estuary. During summer, the turbid, warm, and low salinity waters of the two upstream stations were characterized byNeomysis americana, Gammarus sp. (principallyG. tigrinus), larval smelt,Mysis stenolepsis, andCrangon septemspinosus. The more stratified and less turbid waters of the downstream station were characterized by a coastal marine macrozooplanktonic community and the almost total absence of smelt larvae. Within the MTZ, the distribution ofN. americana coincided with the zone of longest average advective replacement times (null zone). Smelt larvae were distributed further upstream within the MTZ thanN. americana. Overall, larger larvae were distributed further upstream than smaller larvae. The relationship between turbidity and larval density at a specific time was weak (due to resuspension of sediments but not larvae), but the mechanism responsible for producing higher residence times for both sediment and larvae on a longer term basis appears the same. The daily movement and skewed nature of the null zone (due to the general cyclonic circulation of the middle estuary) defines a geographic zone over which the larval smelt population oscillates and remains despite the mean downstream velocities over the water column. 相似文献
42.
Birger Schmitz Stephen L. Ingram David T. Dockery III Gran berg 《Chemical Geology》1997,140(3-4):275-287
Mixed marine, brackish-water and terrestrial vertebrate skeletal apatite is found in the late Paleocene-early Eocene Tuscahoma and Bashi Formations of Mississippi. The co-Occurrence in these near-coastal marine deposits of skeletal apatite with different provenances offers a unique opportunity for unraveling the effects of diagenesis on apatite 87Sr/86Sr composition, with bearings on the use of this isotope pair as paleosalinity indicator. The results show that the Sr isotopes of all originally poorly ordered phases of skeletal apatite have extensively re-equilibrated with pore water with significantly lower 87Sr/86Sr ratios than late Paleocene-early Eocene seawater. For example, marine shark and ray teeth from the Bashi Formation all have clearly nonmarine 87Sr/86Sr ratios, 0.7073-0.7075, compared with a coeval seawater ratio in the range 0.7077-0.7078. However, separated shark tooth enamel, with a high original crystallinity, appears to have retained all or most of its in vivo Sr isotopic signature until the present. Here we also show that 87Sr/86Sr results on recent vertebrate skeletal material from different environments are in good agreement with expected values for respective habitat.
Earlier analyses of calcite material from the Bashi Formation indicated the existence of a shift in seawater 87Sr/86Sr to a lower value at the Paleocene-Eocene boundary. The strong influence of pore water with low, nonmarine 87Sr/86Sr on the apatite in the Bashi Formation suggests that the proposed isotopic shift may be an artifact related to diagenetic processes. 相似文献
43.
A new way of quantifying GCM water vapour feedback 总被引：1，自引：0，他引：1
William Ingram 《Climate Dynamics》2013,40(3-4):913-924
The water vapour feedback probably makes the largest contribution to climate sensitivity, and the second-largest contribution to its uncertainty, in the sense of disagreement between General Circulation Models (GCMs, the most physically detailed models of climate we have). Yet there has been no quantification of it which allows these differences to be attributed physically with the aim of constraining the true value. This paper develops a new breakdown of the non-cloud LW (longwave) response to climate change, which avoids the problems of the conventional breakdown, and applies it to a set of 4 GCMs. The basic physical differences are that temperature is used as the vertical coordinate, and relative humidity as the humidity variable. In this framework the different GCMs’ feedbacks look more alike, consistent with our understanding that their water vapour responses are physically very similar. Also, in the global mean all the feedback components have the same sign, allowing us to conveniently attribute the overall response fractionally (e.g. about 60% from the “partly-Simpsonian” component). The systematic cancellation between different feedback components in the conventional breakdown is lost, so now a difference in a feedback component actually contributes to a difference in climate sensitivity, and the differences between these GCMs in the non-cloud LW part of this can be traced to differences in formulation, mean climate and climate change response. Physical effects such as those due to variations in the formulation of LW radiative transfer become visible. Differences in the distribution of warming no longer dominate comparison of GCMs. The largest component depends locally only on the GCM’s mean climate, so it can in principle be calculated for the real world and validated. However, components dependent on the climate change response probably account for most of the variation between GCMs. The effect of simply changing the humidity variable in the conventional breakdown is also examined. It gives some of this improvement—the loss of the cancellations that leave the conventional breakdown of no use to understand differences between GCMs’ climate sensitivities—but not the link to mean climate. 相似文献
44.
Observations of the turbidity and velocity fields in the near-bottom waters of the St Lawrence estuary were obtained with a package which includes a self-recording attenuance meter and a currentmeter. The latter also measures salinity and temperature. Time series varying in length between 26 h and 26 days, and with repetition rates between one and 15 min are discussed for 3 typical open-channel and nearshore stations. A high-frequency sampling mode provides a means to observe the passage of a frontal disturbance over the bottom during the semi-diurnal cycle. With lower frequency records having lengths of one week to one month, contributions to the turbidity fluctuations due to the spring-neap oscillations, seasonal changes in run-off, and the sudden rise in solid discharge of local tributaries following storms, can be resolved. From turbidity polar diagrams, local onshore sources of particulate suspended matter can be identified. Among other advantages, it is possible from such records to time precisely the occurrence of turbidity peaks in relation to the ebb and flow velocities, to assess the importance of resuspension, and to specify exactly the time rate of change of the turbidity. On the whole, self-recording equipments provide a wealth of information unavailable from more traditional hydrocast sampling techniques. 相似文献
45.
R.Grant Ingram 《Estuarine, Coastal and Shelf Science》1983,16(3):333-338
Temperature, salinity and velocity profiles taken over a 5-day period in the St. Lawrence Estuary at the head of the Laurentian Channel are used to describe the semidiurnal tidal period isopycnal oscillations occurring in this region. The observed variation in the degree of vertical mixing over the tidal cycle is used to support the concept of nutrification of the estuarine surface waters and suggests an explanation for the quarter-diurnal variability of primary production in this region. 相似文献