The birth of El Niño: Geoarchaeological evidence and implications     

Harold B. Rollins  James B. Richardson  Daniel H. Sandweiss 《Geoarchaeology》1986,1(1):3-15

The oceanographic phenomenon known as El Niño is the subject of intensive recent study. Any hypotheses regarding physical causes and predictability of El Niño should consider its geological history. New geoarchaeological evidence suggests that the El Niño phenomenon did not exist along the northern and central coasts of Peru before about 5000 years B.P. Molluscan faunas from archaeological sites at Pampa las Salinas and Salinas de Chao permit temporal bracketing of a major structural change in the East Pacific water mass. The boundary between the warm Panamic Province and the cold Peruvian Province, which today occurs at about 5 degrees south latitude, was some 500 km further south from at least 11,000 years B.P. to about 5000 years B.P. This conclusion is corroborated by many other lines of evidence including phosphorite distribution, timing of glacial retreat, sea level change, radiolarian, diatom and fish scale distributions, and beach ridge patterns. The present day arid coastal climate of north central Peru is probably a post-5000 year B.P. development. Hunter–gatherer populations of the area would most likely have exploited more land-based seasonal resources from grasslands and forests before 5000 years B.P., and relied less upon the diminished productivity of warm water maritime resources.  相似文献   

Sub-annual moraine formation at an active temperate Icelandic glacier     

Benjamin M.P. Chandler  Samuel J.P. Chandler  David J.A. Evans  Marek W. Ewertowski  Harold Lovell  David H. Roberts  Martin Schaefer  Aleksandra M. Tomczyk 《地球表面变化过程与地形》2020,45(7):1622-1643

This paper presents detailed geomorphological and sedimentological investigations of small recessional moraines at Fjallsjökull, an active temperate outlet of Öræfajökull, southeast Iceland. The moraines are characterized by striking sawtooth or hairpin planforms, which are locally superimposed, giving rise to a complex spatial pattern. We recognize two distinct populations of moraines, namely a group of relatively prominent moraine ridges (mean height ~1.2 m) and a group of comparatively low-relief moraines (mean height ~0.4 m). These two groups often occur in sets/systems, comprising one pronounced outer ridge and several inset smaller moraines. Using a representative subsample of the moraines, we establish that they form by either (i) submarginal deformation and squeezing of subglacial till or (ii) pushing of extruded tills. Locally, proglacial (glaciofluvial) sediments are also incorporated within the moraines during pushing. For the first time, to our knowledge, we demonstrate categorically that these moraines formed sub-annually using repeat uncrewed aerial vehicle (UAV) imagery. We present a conceptual model for sub-annual moraine formation at Fjallsjökull that proposes the sawtooth moraine sequence comprises (i) sets of small squeeze moraines formed during melt-driven squeeze events and (ii) larger push moraines formed during winter re-advances. We suggest the development of this process-form regime is linked to a combination of elevated temperatures, high surface meltwater fluxes to the bed and emerging basal topography (a depositional overdeepening). These factors result in highly saturated subglacial sediments and high porewater pressures, which induces submarginal deformation and ice-marginal squeezing during the melt season. Strong glacier recession during the summer, driven by elevated temperatures, allows several squeeze moraines to be emplaced. This process-form regime may be characteristic of active temperate glaciers receding into overdeepenings during phases of elevated temperatures, especially where their englacial drainage systems allow efficient transfer of surface meltwater to the glacier bed near the snout margin. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Interannual Variability of Antarctic Hydrographic Structure and Frontal Zones along Meridional Sections between Syowa Station and Southern Africa     

Harold Solomon  Kaoru Ushida  Takashi Suzuki 《Journal of Oceanography》2000,56(1):1-16

Six years of quasi-meridional crossings of the Antarctic Ocean from Antarctica to southern Africa between 4°W and 16°E longitude are analyzed, with emphasis on temperature and salinity distributions. Data are sparse, but (particularly in the southern part of the sections) adequate to show significant variations in the latitude/depth distributions and T-S characteristics of the principal water masses. In particular, the cross-sectional area occupied by Warm Deep Water (Weddell Deep Water) dropped by about one third in 1968. Positions of major features associated with the Antarctic Divergence varied by up to 5 degrees of latitude. The surface temperature gradient often observed at the Antarctic Divergence appears to be the surface expression of a shallow (possibly seasonal) thermocline which sometimes slopes upward to intersect the sea surface. There is a clear need for more closely spaced and consistently planned data from Antarctic cruises, particularly those on which physical oceanography is an ancillary activity. As a bare minimum, much more closely spaced surface temperature (and if possible also salinity) measurements would be useful.  相似文献   

Z     

Shannon J.P. McPherron  Harold L. Dibble  Paul Goldberg 《Geoarchaeology》2005,20(3):243-262

Paleolithic archaeologists have been recording the three‐dimensional coordinates of excavated artifacts for several decades. These data, however, have been put to limited use. Z, or absolute elevation, in particular, is seldom used in analysis despite the fact that it speaks most directly to one of the more important areas of research we have—namely, behavioral change through time. This article addresses this deficiency in two ways. First, it examines the way in which we record elevations. The point is made that the elevations returned by high‐resolution recording systems like total stations provide behavioral and site formation data that traditional recording systems are probably incapable of capturing. Second, elevation data from two Middle Paleolithic sites are used to examine changes in behavioral factors that structure the archaeological record and that apparently take place independent of changes in factors which structure the geological record. © 2005 Wiley Periodicals, Inc.  相似文献   

DISTRIBUTION OF GEORGIA TEKTITES     

Harold Povenmire 《Meteoritics & planetary science》1982,17(3):145-148

Since March, 1970, 49 field expeditions have been made by this writer to the area of Dodge County, Georgia, in an effort to determine the distribution pattern of Georgia tektites and locate new specimens. About 50 new tektites have been recovered, which represents approximately 10% of the total known specimens. The primary area of distribution is a fan-shaped area of approximately 30 by 70 kilometers. It is difficult to make any assumptions about the shape of this distribution as it is possible that these tektites have been transported by water. No correlation was found between size, shape, soil type, or elevation and tektite location.  相似文献   

Biological experiments: The viking Mars lander     

Harold P. Klein 《Icarus》1972

Biological interest in the exploration of Mars is briefly described as is the biological experiments package to be flown as part of the Viking 1975 lander payload.  相似文献   

The composition of phytoplankton within the Chesapeake Bay plume and adjacent waters off the Virginia coast,U.S.A.     

Harold G. Marshall 《Estuarine, Coastal and Shelf Science》1982,15(1):29-43

Phytoplankton composition differences were used to identify and plot the extent of the Chesapeake Bay plume over the continental shelf. Distinct but different phytoplankton assemblages were noted within the plume for March, June and October 1980. The major constituents in the plume were Skeletonema costatum, a variety of other diatoms and an unidentified ultraplankton component assumed to consist of several cyanophycean and chlorophycean species. The shelf plankton outside of the plume was mainly characterized by the coccolithophores and other phytoplankters that formed different seasonal assemblages than what was within the plume. Patchiness and fluctuations in the shape, size and extent of the plume were noted. A total of 235 species is given, with their presence within the plume and at shelf stations indicated.  相似文献   

THE GRAYTON BEACH,FLORIDA METEORITE     

Harold Povenmire 《Meteoritics & planetary science》1984,19(2):89-90

On October 30, 1983, two treasure hunters, Phillip W. Gibson, a government diver and former Apollo recovery team member, and John M. Green, M.D. were searching for Spanish armor in an ancient Indian midden, or trash site near Grayton Beach, Florida. Using metal detectors, they found an 11.3 kg heavy brown rock approximately one meter below the surface.  相似文献   

The equivalence of von Zeipel mappings and Lie transforms     

Harold Shniad 《Celestial Mechanics and Dynamical Astronomy》1970,2(1):114-120

An order independent method is used to identify the transformation obtained from Von Zeipel's method with that obtained from Lie transforms. The correspondence between the generators is given in explicit form.  相似文献   

A LARGE GEORGIA TEKTITE     

Harold Povenmire 《Meteoritics & planetary science》1980,15(1):85-86

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