Acoustic thermometry data compared with two ocean models: the importance of Rossby waves and ENSO in modifying the ocean interior     

John L. Spiesberger  Harley E. Hurlburt  Mark Johnson  Mark Keller  Steven Meyers  Jim O'Brien 《Dynamics of Atmospheres and Oceans》1998,26(4):209-240

An interpretation is made of interannual changes in acoustic travel time between Oahu and seven receivers at distances of 3000–4000 km. Measurements were made in late 1983, and over two 5-month intervals between 1987 and 1989. Previous publications demonstrated that these changes stem from variations in temperature. Two hydrodynamic ocean models are used to identify plausible oceanic features that could cause these variations. They are from the Naval Research Laboratory and the Florida State University at (1/8)° and (1/6)° resolution, respectively, and are forced with different interannual wind sets for more than a decade. Modelled El Niño's and La Niña's generate poleward travelling Kelvin waves on the eastern boundary of the Pacific. These excite Rossby waves that propagate westward at mid-latitudes. Rossby waves are the dominant model features which affect the modelled acoustic travel times, and hence section-averaged temperatures in the eastern North Pacific. These waves yield travel times whose standard deviations and rates of changes are similar to the measurements. In the observations, some sections separated by less than 500 km exhibit trends in heat content with opposite signs. Similar variability can be explained with modelled Rossby waves. Model wavelengths less than 500 km, eddies, and seasonal cycles induced by seasonal winds yield travel times that are two orders of magnitude too small to account for the data.  相似文献   

Breaking waves in deep water: measurements and modeling of energy dissipation     

Ticona Rollano  Fadia  Brown  Adam  Ellenson  Ashley  Özkan-Haller  H. Tuba  Thomson  Jim  Haller  Merrick C. 《Ocean Dynamics》2019,69(10):1165-1179

Ocean Dynamics - In the presence of strong winds, ocean surface waves dissipate significant amounts of energy by breaking. Here, breaking rates and wave-following turbulent dissipation rate...  相似文献   

The impact of different rainfall products on landscape modelling simulations     

Christopher J. Skinner  Nadav Peleg  Niall Quinn  Tom J. Coulthard  Peter Molnar  Jim Freer 《地球表面变化过程与地形》2020,45(11):2512-2523

Rainfall products can contain significantly different spatiotemporal estimates, depending on their underlying data and final constructed resolution. Commonly used products, such as rain gauges, rain gauge networks, and weather radar, differ in their information content regarding intensities, spatial variability, and natural climatic variability, therefore producing different estimates. Landscape evolution models (LEMs) simulate the geomorphic changes in landscapes, and current models can simulate timeframes from event level to millions of years and some use rainfall inputs to drive them. However, the impact of different rainfall products on LEM outputs has never been considered. This study uses the STREAP rainfall generator, calibrated using commonly used rainfall observation products, to produce longer rainfall records than the observations to drive the CAESAR-Lisflood LEM to examine how differences in rainfall products affect simulated landscapes. The results show that the simulation of changes to basin geomorphology is sensitive to the differences between rainfall products, with these differences expressed linearly in discharges but non-linearly in sediment yields. Furthermore, when applied over a 1500-year period, large differences in the simulated long profiles were observed, with the simulations producing greater sediment yields showing erosion extending further downstream. This suggests that the choice of rainfall product to drive LEMs has a large impact on the final simulated landscapes. The combination of rainfall generator model and LEMs represents a potentially powerful method for assessing the impacts of rainfall product differences on landscapes and their short- and long-term evolution. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

A GIS method to identify flat surfaces and restore relict fluvial long-profiles from terrace remnants gives new clues on how large basins respond to endorheic–exorheic transitions (Duero basin,Iberian Peninsula)     

Laura Rodríguez-Rodríguez  Loreto Antón  Raimon Pallàs  Daniel García-Castellanos  Ivone Jiménez-Munt  Candela Pastor-Martín 《地球表面变化过程与地形》2020,45(4):1013-1027

Fluvial terraces are used as geomorphic indicators for deciphering long-term landscape evolution. Knowing the distribution of fluvial terraces is essential for establishing former river profiles and their tectonic significance, for studying climate-modulated processes of terrace development, or for defining fluvial network adjustments in response to sudden base-level changes like those produced by fluvial captures. Multiple methods for automatic map production have been proposed based on the comparison of morphometric indices with those of the modern river course. Here we propose an alternative method to identify flat surfaces and scarps separating them from digital elevation models without setting comparisons with a modern river course and thus fully applicable to study flat landforms whatever their origin. Its application to the low-relief landscape of the Cenozoic Duero basin has allowed the improvement of previous geomorphological maps and the analysis of fluvial network adjustments in response to a sudden base-level fall after the opening of the Neogene endorheic basin towards the Atlantic Ocean. Reconstructed terrace long-profiles suggest an initial episode of fast vertical incision followed by a period of repeated planation–aggradation–incision with the formation of 14 to 13 unpaired terrace levels. Changes observed in the pattern of terrace profiles are discussed with regard to changes in regional tectonics and base-level variations. © 2019 John Wiley & Sons, Ltd.  相似文献   

New evidence of sea‐level lowstands and paleoenvironment during MIS 6 and 4 in the Cantabrian coastal karst: the Cobiheru cave (North Iberia)          下载免费PDF全文

Daniel Ballesteros  Laura Rodríguez‐Rodríguez  Saúl González‐Lemos  Santiago Giralt  Diego Jaime Álvarez‐Lao  Luna Adrados  Montserrat Jiménez‐Sánchez 《地球表面变化过程与地形》2017,42(11):1704-1716

The geomorphological evolution of the Cobiheru Cave shows the influence of the non‐carbonate coastal mountain ranges on coastal karst evolution, as well as the temporal distribution of the cold‐adapted fauna sites in the Cantabrian Coast. Geomorphological observation and uranium/thorium (U/Th) dating lead to the construction of an evolution model. The model comprises two episodes of cave deposition occurring at c. 60–70 and 130–150 ka, linked to cold climate conditions, global sea‐level lowstands and the erosion of alluvial fans that covered the karst. Moreover, the comparison between the Cobiheru record and some raised beaches identified in previous studies sets the beginning of the sea‐level lowering in the Cantabrian Sea during the marine isotope stages (MIS) 5–4 transition. Two palaeoenvironments are inferred based on finding Equus ferus and Elona quimperiana. A wet deciduous forest would have developed on the emerged marine terrace of the Cobiheru Cave since at least the Middle Pleistocene, and an open landscape with scarce vegetation would have been present at c. 65 ka. The erosional event identified in the Cobiheru Cave helps to understand the temporal distribution of cold‐adapted mammals located in the Asturias region. The probable sites of cold‐adapted fauna developed in caves and alluvial fans would have disappeared after 65 ka. Therefore, palaeontological and palaeoclimate research based on cold‐adapted mammals suggests the occurrence of an hiatus in the palaeontological record prior to 50 ka. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

An integrated process-based model of flutes and tool marks in deep-water environments: Implications for palaeohydraulics,the Bouma sequence and hybrid event beds     

Jeff Peakall  Jim Best  Jaco H. Baas  David M. Hodgson  Michael A. Clare  Peter J. Talling  Robert M. Dorrell  David R. Lee 《Sedimentology》2020,67(4):1601-1666

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Holocene carbon storage and testate amoeba community structure in treed peatlands of the western Hudson Bay Lowlands margin,Canada     

Marissa A. Davies  Jim W. Mclaughlin  Maara S. Packalen  Sarah A. Finkelstein 《第四纪科学杂志》2023,38(1):92-106

The Hudson Bay Lowlands (HBL) stores a significant proportion of the northern peatland carbon pool, and constraints on the factors controlling local-scale variation are needed to better predict soil carbon stocks. We investigated two treed peatland sites, a fen and a bog, to understand how local ecohydrological factors impacted long-term carbon storage. Ecohydrological conditions were reconstructed using quantitative water table depth reconstructions from testate amoebae (TA) and broad peat type classifications. We also linked these factors and carbon storage to changes in TA community structure through the investigation of morphological and functional traits. Both sites have high rates of peat vertical accretion during the warmer Middle Holocene. A shift to a drier, Sphagnum-dominated habitat after 7400 cal a bp at the bog site, however, led to lower apparent carbon accumulation rates (aCARs) than at the fen site. aCARs decreased with the transition to a cooler Late Holocene climate at both sites. Both sites have higher total carbon masses (kg m⁻²) than other more open and younger HBL localities, demonstrating the potential importance of treed peatlands in regional carbon storage. Shifts in the frequency of TA traits corresponded to changing ecohydrological conditions and provided insights into the role of TA in carbon storage.  相似文献   

A late Ordovician (Hirnantian) karstic surface in a submarine channel,recording glacio‐eustatic sea‐level changes: Meifod,central Wales     

Patrick J. Brenchley  Jim D. Marshall  David A. T. Harper  Caroline J. Buttler  Charlie J. Underwood 《Geological Journal》2006,41(1):1-22

The growth and decay of the end‐Ordovician Gondwanan glaciation is globally reflected by facies changes in sedimentary sequences, which record a major eustatic fall and subsequent rise in the Hirnantian Stage at the end of the Ordovician. However, there are different reported estimates of the magnitude and pattern of sea‐level change. Particularly good evidence for end‐Ordovician sea‐level change comes from a sequence at Meifod in central Wales, which has a karstified limestone unit within a channel incised into marine shelf sediments. Pre‐glacial (Rawtheyan) mudstones have a diverse fauna suggesting a mid‐to‐deep‐shelf water depth of c. 60 m. The channel, 20 m deep, was incised into these mudstones and partially filled with a mixture of fine sand and detrital carbonate. The taphonomy of bioclasts and intraclasts indicates that many had a long residence time on the sea floor or suffered diagenesis after shallow burial before being resedimented into the channel. The presence of carbonates on the Welsh shelf is atypical and they are interpreted as having accumulated as patches during a minor regression prior to the main glacio‐eustatic fall. Comparison of the carbon stable‐isotopic values of the bioclast material with the global isotopic record confirms that most of the material is of Rawtheyan age, but that some is Hirnantian. The resedimented carbonates lithified rapidly and formed a limestone, several metres thick, in the deepest parts of the channel. As sea‐level fell, this limestone was exposed and eroded into karstic domes and pillars with a relief of over 2 m. The overall, glacio‐eustatic, sea‐level fall is estimated to be in excess of 80 m. A succeeding sea‐level rise estimated to be 40–50 m is recorded in the laminated crust that mantles the karstic domes and pillars. The crust is formed of encrusting bryozoans, associated cystoids, crinoid holdfasts and clusters of the brachiopod Paromalomena, which is normally associated with mid‐shelf environments. Fine sands buried the karst topography and accumulated to fill the channel. In the sandstones at the base of the channel there is a Hirnantia fauna, while in the sandstones high in the channel‐sequence there is cross‐stratification characteristic of mid‐shoreface environments. This would indicate a fall of sea‐level of c. 30 m. The subsequent major transgression marking the end of the glaciation is not recorded at the Meifod locality, but nearby exposures of mudstones suggest a return to mid‐to‐deep‐shelf environments, similar to those that prevailed before the Hirnantian regression. The Meifod sequence provides strong evidence for the magnitude of the Hirnantian sea‐level changes and by implication confirm larger estimates for the size of the ice sheets. Smaller oscillations in relative sea‐level seen at Meifod may be local phenomena or may reflect eustatic changes that have not been widely reported elsewhere. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献