Climate change and control of the southeastern Bering Sea pelagic ecosystem     

George L. Hunt Jr.  Phyllis Stabeno  Gary Walters  Elizabeth Sinclair  Richard D. Brodeur  Jeffery M. Napp  Nicholas A. Bond   《Deep Sea Research Part II: Topical Studies in Oceanography》2002,49(26)

We propose a new hypothesis, the Oscillating Control Hypothesis (OCH), which predicts that pelagic ecosystem function in the southeastern Bering Sea will alternate between primarily bottom-up control in cold regimes and primarily top-down control in warm regimes. The timing of spring primary production is determined predominately by the timing of ice retreat. Late ice retreat (late March or later) leads to an early, ice-associated bloom in cold water (e.g., 1995, 1997, 1999), whereas no ice, or early ice retreat before mid-March, leads to an open-water bloom in May or June in warm water (e.g., 1996, 1998, 2000). Zooplankton populations are not closely coupled to the spring bloom, but are sensitive to water temperature. In years when the spring bloom occurs in cold water, low temperatures limit the production of zooplankton, the survival of larval/juvenile fish, and their recruitment into the populations of species of large piscivorous fish, such as walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus) and arrowtooth flounder (Atheresthes stomias). When continued over decadal scales, this will lead to bottom-up limitation and a decreased biomass of piscivorous fish. Alternatively, in periods when the bloom occurs in warm water, zooplankton populations should grow rapidly, providing plentiful prey for larval and juvenile fish. Abundant zooplankton will support strong recruitment of fish and will lead to abundant predatory fish that control forage fish, including, in the case of pollock, their own juveniles. Piscivorous marine birds and pinnipeds may achieve higher production of young and survival in cold regimes, when there is less competition from large piscivorous fish for cold-water forage fish such as capelin (Mallotus villosus). Piscivorous seabirds and pinnipeds also may be expected to have high productivity in periods of transition from cold regimes to warm regimes, when young of large predatory species of fish are numerous enough to provide forage. The OCH predicts that the ability of large predatory fish populations to sustain fishing pressure will vary between warm and cold regimes.The OCH points to the importance of the timing of ice retreat and water temperatures during the spring bloom for the productivity of zooplankton, and the degree and direction of coupling between zooplankton and forage fish. Forage fish (e.g., juvenile pollock, capelin, Pacific herring [Clupea pallasii]) are key prey for adult pollock and other apex predators. In the southeastern Bering Sea, important changes in the biota since the mid-1970s include a marked increase in the biomass of large piscivorous fish and a concurrent decline in the biomass of forage fish, including age-1 walleye pollock, particularly over the southern portion of the shelf. Populations of northern fur seals (Callorhinus ursinus) and seabirds such as kittiwakes (Rissa spp.) at the Pribilof Islands have declined, most probably in response to a diminished prey base. The available evidence suggests that these changes are unlikely the result of a decrease in total annual new primary production, though the possibility of reduced post-bloom production during summer remains. An ecosystem approach to management of the Bering Sea and its fisheries is of great importance if all of the ecosystem components valued by society are to thrive. Cognizance of how climate regimes may alter relationships within this ecosystem will facilitate reaching that goal.  相似文献   

A numerical model of trace-element coprecipitation in a physicochemical calcification system: Application to coral biomineralization and trace-element ‘vital effects’     

Daniel J. Sinclair  Michael J. Risk 《Geochimica et cosmochimica acta》2006,70(15):3855-3868

A mixed equilibrium/kinetic steady-state numerical model of coral calcification has been developed to test whether a physicochemical calcification mechanism is able to account for recent geochemical observations, in particular correlated trace-element variations presented in a companion paper [Sinclair, D.J., 2005. Correlated trace-element ‘vital effects’ in tropical corals: a new tool for probing biomineralization chemistry. Geochim. Cosmochim. Acta69 (13), 3265-3284]. The model simulates trace-element partitioning from a CaCO₃ supersaturated extracellular calcifying fluid (ECF) which has been modified by enzymatic input of Ca²⁺ and removal of 2H⁺ by CaATPase. CO₂ input is modelled as a diffusion process, while the ECF is continuously replenished by fresh seawater, which is the sole source of minor and trace-elements (TEs). Trace-element species fully equilibrate in the ECF, and selected trace-element species kinetically compete with Ca²⁺ or at the surface of the growing crystal. Each simulation is run to steady-state, and results are presented for a grid of CaATPase ion pumping rates and seawater replenishment rates. The dominant feature of the model output occurs when CaATPase ion pumping is high while seawater replenishment rates are low. At this point, CO₂ diffusion reaches its maximum, C input becomes limiting, buffering capacity is reduced and the pH of the system rises dramatically; significantly affecting the TE composition of the skeleton. At more modest pumping rates, the model reproduces the relative amplitudes of trace-element variations and slopes of the mutually positive correlations between B, Sr and U observed by Sinclair [Sinclair, D.J., 2005. Correlated trace-element ‘vital effects’ in tropical corals: a new tool for probing biomineralization chemistry. Geochim. Cosmochim. Acta69 (13), 3265-3284], but does not reproduce the negative correlations with Mg. The best fit between model and observation occurs when the coral simultaneously increases ion pumping and seawater replenishment rates: a strategy which allows rapid calcification while avoiding dangerously high pH variations. The model predicts that calcification occurs at only moderate pH elevations (8.3-8.4) with seasonal TE variations being explained by a shift of only 0.3 pH units. The model does not reproduce the full amplitude of diurnal pH variations observed recently. Sensitivity tests show that the model output is relatively insensitive to changes in the composition of the fluid from which the ECF is drawn (such as might occur if photosynthesis or active C transport mechanisms significantly modify the penultimate fluid source). Further research, however, is needed to establish the consequences of active transport of TEs and anions to the calcifying site.  相似文献   

Geostatistical investigation of the Kutcho Creek chrysotile deposit,Northern British Columbia   总被引：1，自引：0，他引：1  

A. J. Sinclair  L. J. Werner 《Mathematical Geosciences》1978,10(3):273-288

The Kutcho Creek asbestos deposit, owned by Cassiar Asbestos Corporation Ltd., has been sampled by two major exploratory programs that have provided two sets of grade data—one from the horizontal direction (wall readings) and one from the vertical direction (diamond drill cores). These data (percentage chrysotile by volume) were divided into well-defined groups on the basis of location and sample continuity, and experimental variograms for percentage of fiber content were calculated for each group. Horizontal data were all oriented in directions roughly parallel to the trend of an elongate serpentinite zone containing local centers rich in chrysotile veinlets. Spherical variogram models fitted to horizontal and vertical data sets are as follows: Vertical: $$\begin{gathered} \gamma (h) = 0.27 m^2 + 0.44 m^2 [(3h/70) - (h^3 /85,750)] h \leqslant a \hfill \\ \gamma (h) = 0.71 m^2 h \geqslant a \hfill \\ \end{gathered}$$ Horizontal: $$\begin{gathered} \gamma (h) = 0.27 m^2 + 1.20 m^2 [(h/60) - (h^3 /729,000)] h \leqslant a \hfill \\ \gamma (h) = 1.47 m^2 h \geqslant a \hfill \\ \end{gathered}$$ Wherem is the mean value of data used in the construction of a variogram,h is a lag (sample spacing), anda is the range over which the grade is autocorrelated. These two one-dimensional models can be combined to a two-dimensional model with the form γ(h)=γ(r)+γ(x) where γ(r) is an isotropic component (equivalent to the vertical model above) and γ(x) is a zonal component in the horizontal direction (equivalent to the difference between the horizontal and vertical models above). This general model describes data throughout the entire serpentinite zone in a satisfactory manner but, of course, does not contain information in the third dimension, and, thus, cannot be used as a basis for grade and tonnage calculations and corresponding error estimates. Nevertheless, the analysis has illustrated the potential of variogram analysis for such tonnage and grade calculations. Furthermore, the study has provided limiting two-dimensional information on the geometry of chrysotile-rich zones within the serpentinite belt, information that can be used to advantage in planning future exploratory drilling.  相似文献   

Tectonic evolution of the Himalaya constrained by detrital ⁴⁰Ar–³⁹Ar, Sm–Nd and petrographic data from the Siwalik foreland basin succession, SW Nepal     

A. G. Szulc  Y. Najman†  H. D. Sinclair  M. Pringle‡  M. Bickle§  H. Chapman§  E. Garzanti¶  S. Andò¶  P. Huyghe&#;  J-L. Mugnier&#;  T. Ojha  P. DeCelles† 《Basin Research》2006,18(4):375-391

⁴⁰Ar–³⁹Ar dating of detrital white micas, petrography and heavy mineral analysis and whole‐rock geochemistry has been applied to three time‐equivalent sections through the Siwalik Group molasse in SW Nepal [Tinau Khola section (12–6 Ma), Surai Khola section (12–1 Ma) and Karnali section (16–5 Ma)]. ⁴⁰Ar–³⁹Ar ages from 1415 single detrital white micas show a peak of ages between 20 and 15 Ma for all the three sections, corresponding to the period of most extensive exhumation of the Greater Himalaya. Lag times of less than 5 Myr persist until 10 Ma, indicating Greater Himalayan exhumation rates of up to 2.6 mm year^?1, using one‐dimensional thermal modelling. There are few micas younger than 12 Ma, no lag times of less than 6 Myr after 10 Ma and whole‐rock geochemistry and petrography show a significant provenance change at 12 Ma indicating erosion from the Lesser Himalaya at this time. These changes suggest a switch in the dynamics of the orogen that took place during the 12–10 Ma period whereby most strain began to be accommodated by structures within the Lesser Himalaya as opposed to the Greater Himalaya. Consistent data from all three Siwalik sections suggest a lateral continuity in tectonic evolution for the central Himalayas.  相似文献   

Exhumation of the Pyrenean orogen: implications for sediment discharge   总被引：3，自引：1，他引：2  

Morris  Sinclair  & Yell 《Basin Research》1998,10(1):69-85

Apatite fission track analyses of 21 samples from the central and eastern Pyrenees are modelled to generate time–temperature plots for the post 110±10 °C cooling history over the 40–10 Ma time interval. Modelled thermal histories have been converted into exhumation plots through the application of the present-day geothermal gradient in the Pyrenees. The documented geology of the Pyrenees allows us to assume no significant extensional unroofing and subvertical exhumation trajectories, thus enabling exhumation to be translated into erosional denudation. Maps of denudation have been constructed for six, 5-Myr time intervals. Denudation varied with a 20–50-km length scale, and does not appear to have been related to the major structural zones of the mountain belt. Spatially averaged denudation rates for the six time intervals ranged from 34 to 61 mm kyr^?1 assuming the present-day geothermal gradient. Maximum rates of 240 mm kyr^?1 occurred in the interval 35–30 Ma, in the region of the Querigut-Millas massif. Assuming the denudation resulted primarily from erosion, the denudation maps can be used to calculate sediment discharge through time to the neighbouring foreland basins. Using a series of rectangular drainage basins with a 2:1 aspect ratio (based on modern linear mountain belts) and a location of the main drainage divide based on the mean present-day position, it is possible to evaluate the potential for spatial and temporal variations in sediment discharge as a function of denudation. The results show along-strike variations in sediment discharge between drainage basins of 500%, and temporal variations from individual basins of >300%. A comparison of total sediment discharge per year to the Ebro and Aquitaine basins, assuming a fixed drainage divide, shows that the discharge to the south is likely to have been between 1.5 and 2.8 times greater than to the north.  相似文献   

Geostatistical ore reserve estimation | M. David, 1977. Elsevier,Amsterdam, 364 pp., Dfl. 110.00, $ 44.95     

A.J. Sinclair 《Earth》1978,14(1):84-85

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Subsidence and exhumation of the Mesozoic Qiangtang Basin: Implications for the growth of the Tibetan plateau     

Jiawei Zhang  Hugh D. Sinclair  Yalin Li  Chengshan Wang  Cristina Persano  Xinyu Qian  Zhongpeng Han  Xiang Yao  Yaoyao Duan 《Basin Research》2019,31(4):754-781

The subsidence and exhumation histories of the Qiangtang Basin and their contributions to the early evolution of the Tibetan plateau are vigorously debated. This paper reconstructs the subsidence history of the Mesozoic Qiangtang Basin with 11 selected composite stratigraphic sections and constrains the first stage of cooling using apatite fission track data. Facies analysis, biostratigraphy, palaeo‐environment interpretation and palaeo‐water depth estimation are integrated to create 11 composite sections through the basin. Backstripped subsidence calculations combined with previous work on sediment provenance and timing of deformation show that the evolution of the Mesozoic Qiangtang Basin can be divided into two stages. From Late Triassic to Early Jurassic times, the North Qiangtang was a retro‐foreland basin. In contrast, the South Qiangtang was a collisional pro‐foreland basin. During Middle Jurassic‐Early Cretaceous times, the North Qiangtang is interpreted as a hinterland basin between the Jinsha orogen and the Central Uplift; the South Qiangtang was controlled by subduction of Meso‐Tethyan Ocean lithosphere and associated dynamic topography combined with loading from the Central Uplift. Detrital apatite fission track ages from Mesozoic sandstones concentrate in late Early to Late Cretaceous (120.9–84.1 Ma) and Paleocene–Eocene (65.4–40.1 Ma). Thermal history modelling results record Early Cretaceous rapid cooling; the termination of subsidence and onset of exhumation of the Mesozoic Qiangtang Basin suggest that the accumulation of crustal thickening in central Tibet probably initiated during Late Jurassic–Early Cretaceous times (150–130 Ma), involving underthrusting of both the Lhasa and Songpan–Ganze terranes beneath the Qiangtang terrane or the collision of Amdo terrane.  相似文献   

Reviews     

J. E. Robinson  D. Marsal  Roberto Potenza  A. J. Sinclair  P. C. Sylvester-Bradley  D. F. Merriam 《Mathematical Geology》1971,3(4):383-391

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Temporal occurrence of ichthyoplankton in relation to hydrographic and biological variables at a fixed station in the St Lawrence Estuary     

Y. de Lafontaine  M. Sinclair  M.I. El-Sabh  C. Lassus  R. Fournier 《Estuarine, Coastal and Shelf Science》1984,18(2):177-190

Spring to autumn temporal distributions of ichthyoplankton and other oceanographic variables were measured at three nearshore stations in the lower St Lawrence Estuary in 1977 and 1978. The seasonal occurrence of various species of fish eggs and larvae was similar from one year to the next. Inshore-offshore gradients in abundance of eggs and larvae of different species appeared to be primarily related to the spawning location of each species. The semidiurnal variability was considerably less than the week-to-week variability in all physical and biological variables measured. The weekly variability is predominantly a function of spatiotemporal interactions, due to the geographic displacement of different water masses and their associated plankton in relation to the neap-spring tidal cycle. The timing and duration of spawning for each common species, inferred from ichthyoplankton distributions, suggest a unique combination of spawning and hatching times, ensuring a succession in the occurrence of larvae through time. Results of the temporal and spatial distributions of the different species of ichthyoplankton are discussed in terms of reduced competitive interactions. The relationship between ichthyoplankton distributions and the plankton production cycle in the St Lawrence Estuary is discussed in comparison with other areas.  相似文献   

Relationships between air mass properties and mesoscale rainfall in New Zealand's Southern Alps     

D. S. Wratt  M. J. Revell  M. R. Sinclair  W. R. Gray  R. D. Henderson  A. M. Chater 《Atmospheric Research》2000,52(4)

This paper identifies relationships between air mass properties and mesoscale rainfall when moist air blows over New Zealand's Southern Alps from the Tasman Sea. Around 50% of the variance in six-hourly rain volumes summed across three separate cross-mountain raingauge transects and in six-hourly rain volume spilling across the alpine divide are statistically explained by the following properties of the approaching air mass: relative humidity, wind velocity normal to the mountains, air mass stability and synoptically induced upward motion. These factors also explain about 25% (r≈0.5) of the variance in the downwind distance reached by the spillover rainfall. For the highest 10% of six-hourly rainfalls, spillover distance and magnitude are negatively correlated with the 700 or 500 hPa temperature. Multiple linear regression equations suitable for predicting rainfall intensity and spillover are developed. A progression is described in the magnitude and depth of vertical motion and resulting condensation rates over the mountains as the properties of the incoming air mass evolve through a storm. These changes, together with greater downwind advection of ice particles compared to raindrops, explain the observed statistical relationships between the air mass properties and mountain rainfall.  相似文献