Magnetic hysteresis properties and rotational hysteresis losses of synthetic stress-controlled titanomagnetite (Fe_2.4Ti_0.6O₄) particles—II. Rotational hysteresis losses     

R. Keller  & E. Schmidbauer 《Geophysical Journal International》1999,138(2):334-342

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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   

近1000年来西格陵兰荷尔斯泰因斯堡港生物硅指示的海洋生产力变化   总被引：1，自引：1，他引：0  

沙龙滨  李冬玲  刘焱光  吴彬  吴燕妮  Knudsen Karen Luise  李中乔  徐皓 《海洋学报(英文版)》2020,39(9):78-85

We analyzed the biogenic silica(BSi) content and produced a diatom-based summer sea-surface temperature(SST) reconstruction for sediment core GC4 from the Holsteinsborg Dyb, West Greenland. Our aim was to reconstruct marine productivity and climatic fluctuations during the last millennium. Increased BSi content and diatom abundance suggest relatively high marine productively during the interval of AD 1000–1400, corresponding in time to the Medieval Warm Period(MWP). The summer SST reconstruction indicates relatively warm conditions during AD 900–1100, followed by cooling after AD 1100. An extended cooling period during AD 1400–1900 is characterized by prolonged low in reconstructed SST and high sea-ice concentration. The BSi values fluctuated during this period, suggesting varying marine productivity during the Little Ice Age(LIA).There is no significant correlation between the BSi content and SST during the last millennium, suggesting that the summer SST has little influence on marine productively in the Holsteinsborg Dyb. A good correspondence between the BSi content and the element Ti counts in core GC4 suggests that silicate-rich meltwater from the Greenland ice sheet was likely responsible for changes in marine productively in the Holsteinsborg Dyb.  相似文献   

Scleractinian Corals of the Arctic and High Latitudes of the North Atlantic Ocean     

Keller  N. B.  Oskina  N. S.  Savilova  T. A. 《Oceanology》2019,59(4):552-555

Oceanology - Only two species of scleractinian corals were found in the high latitudes of the Arctic Ocean west of the Barents Sea: Lophelia pertusa (Linné, 1758) and Flabellum macandrewi...  相似文献   

Habitat temperature ranges of azooxantellate scleractinian corals in the World Ocean     

N. B. Keller  N. S. Os’kina 《Oceanology》2008,48(1):77-84

Based on the study of the scleractinian azooxantellate corals sampled during many marine expeditions of Russian research vessels in the Pacific, Indian, and Atlantic oceans, habitat temperature ranges of their species were first estimated with compiling of temperature series according to the growing thermophility. The temperature series compiled for these oceanic basins consist of 35, 17 and 10 species, respectively. The confinement of scleractinian species to particular water masses is revealed. These data are thought to be useful for reconstructing ecological and oceanological characteristics in the past geological epochs, since coral species exist for millions years. For example, the temperature series established for scleractinian species may be used for reconstructing water temperatures in Cenozoic oceans and, probably, for determining geological ages for some coral species.  相似文献   

北大西洋北部中全新世以来古海洋环境记录     

冉莉华  蒋辉  EIRíKSSON Jón 《海洋通报》2008,27(5)

利用主成分分析法对冰岛北部陆架 MD99-2275 孔中全新世以来沉积物硅藻数据进行研究发现,5 000 - 3 000 a B.P.,冰岛北部陆架表层古海水温度逐渐上升,来自印明格暖流的北大西洋暖水对该区域的影响有所增强.自 3 000 a B.P.以来,表层海水温度开始稳步下降,北大西洋暖水水团的影响逐步减弱,而来自东格陵兰寒流和东冰岛海流的极地冷水水团的影响显著加强.在晚全新世气候逐渐变冷的过程中,发生了几次短期而显著的气候变冷事件,分别出现在 3 000 - 2 600 a B.P.,1 300 - 1 000 a B.P.及 600- 200 a B.P..该中晚全新世古海洋环境记录与格陵兰冰芯(GSIP2)氧同位素气候记录存在良好的对应关系,也与冰岛北部陆架其他海水温度记录有较好的一致性.而冰岛北部陆架区域海底地形的复杂性和海流分布的差异性,以及所采用研究方法的不同则导致该区域各古海水温度记录之间也存在一定的差异性.  相似文献   

Morphology and sedimentary processes in and around Tortugas and Agassiz Sea Valleys,southern Straits of Florida     

Larry L. Minter  George H. Keller  Thomas E. Pyle 《Marine Geology》1975,18(2):47-69

Continuous seismic reflection profiling and new bathymetry data in the southern Straits of Florida over an area dominated by the Tortugas and Agassiz Valley systems have allowed a more detailed analysis of the morphology and sedimentary processes active in this region. Four dives in the submersible DSV “Alvin” supplement the seismic and bathymetric data.The continental slope in the study area can be divided into two physiographic provinces: (I) an irregular topography controlled by the Florida Escarpment west of Tortugas Valley; and (II) the remainder of the continental slope which contains the majority of features under investigation. Seismic data indicate that the valleys are being filled shoreward of 290 fathoms (530 m) by a wedge of prograding sediments derived from the Florida shelf.The morphology of the two valley systems reflects probable differences of origin. Tortugas Valley appears to have originated coincident with the eastern terminus of the Florida Escarpment and province-I-type topography. The Agassiz valleys may have an origin associated with jointing patterns observed by divers aboard DSV “Alvin”. Current meter readings and bottom photographs from “Alvin” indicate that currents are relatively sluggish and not very effective in the transport of sediment within the valleys. An area of undulations west of Pourtales Terrace was investigated and concluded to be erosional in origin.Slumping appears to have played a large part in shaping many features in the study area. The bottom morphology and sediment distribution on the continental slope and in the axis of the Straits of Florida suggest that bottom currents are active in shaping the entire area.  相似文献   

Exploring the past through lynchet landscapes in the Vosges Mountains and the Lorraine Plateau (France)     

Benjamin Keller  Robin Vincent  Dominique Schwartz  Damien Ertlen 《Geoarchaeology》2024,39(3):300-319

Lynchets are ridges formed by erosion and sediment accumulation downstream of agricultural plots and offer valuable insights into past agricultural activity. These microtopographies cover vast areas and serve as indicators of historical changes in land use. As a result, their ubiquity across Europe makes them particularly interesting. In this study, we propose a geoarchaeological approach to analyze six lynchets, four in the Vosges Mountains and two on the Lorraine Plateau (France). The lynchets can be considered soil archives with no stratigraphic organization or chronological sequence from bottom to top, making it difficult to determine the age of the lynchets and identify changes in land use over time. To this end, we propose the analysis of historical and geo-historical archives combined with the “pedosedimentary” archives of lynchets through charcoal identification and dating combined with near-infrared spectroscopy to determine the age, vegetation, and past land use changes associated with lynchet landscapes. By combining these multiple data sources, we are better able to show the chronological development of these ancient agricultural systems and uncover valuable information on landscape history. Charcoal dating suggests a higher frequency of fires from the Middle Ages. The dating aligns with the regional dynamics of anthropogenic fires, indicating a potential use of fire for cultural purposes. We also demonstrate the difficulty of extrapolating the dating of a lynchet to the entire lynchet system. Our results highlight the difficulties of interpreting the formation and dating of lynchets and the lynchet system on the sole basis of charcoal analysis. However, we highlight the value of applying pedoanthracology to lynchets to determine the dynamics of land use change in former fields.  相似文献