Radiocarbon dating is the most widely used dating technique in the world. Recent advances in Accelerator Mass Spectrometry (AMS) and sample preparation techniques have reduced the sample-size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes. Today, it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates. The production of 14 C in the atmosphere varies through time due to changes in the Earth's geomagnetic field intensity and in its concentration, which is regulated by the carbon cycle. As a result of these two variables, a radiocarbon age is not equivalent to a calendar age. Four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12,000 calendar years before present. This paper presents high precision paired 230 Th/ 234 U/ 238 U and 14 C age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12,000 to 50,000 years before present. We developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years, taking full account of combined errors in input ages and calibration uncertainties. Our radiocarbon calibration program is publicly accessible at: http://www.radiocarbon.LDEO.columbia.edu/ along with full documentation of the samples, data, and our statistical calibration model. r

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Paired carbon-14 ( 14 C) and thorium-230( 230 Th) ages were determined on fossil corals from the Huon Peninsula, Papua New Guinea. The ages were used to calibrate part of the 14 C time scale and to estimate rates of sea-level rise during the last deglaciation. An abrupt offset between the 14 C and 230 Th ages suggests that the atmospheric 14 C/ 12 C ratio dropped by 15 percent during the latter part of and after the Younger Dryas (YD). This prominent drop coincides with greatly reduced rates of sea-level rise. Reduction of melting because of cooler conditions during the YD may have caused an increase in the rate of ocean ventilation, which caused the atmospheric 14 C/ 12 C ratio to fall. The record of sea-level rise also shows that globally averaged rates of melting were relatively high at the beginning of the YD. Thus, these measurements satisfy one of the conditions required by the hypothesis that the diversion of meltwater from the Mississippi to the St. Lawrence River triggered the YD event.

Emerged coral reef terraces on the Huon Peninsula in New Guinea were reported in a reconnaissance dating study by Veeh and Chappell 1970. Age definition achieved was not good for several important terraces, and we report here a series of new 230Th/234U dates, which further clarify the history of late Quaternary eustatic sea level fluctuations. More than 20 reef complexes are present, ranging well beyond 250,000 yr old: we are concerned with the seven lowest complexes. Major reef-building episodes dated by 30Th/234U are reef complex I at 5–9 ka (kilo anno = 1000 yr), r.c. IIIb at 41 ka (four dates), r.c. IV at 61 ka (four dates), r.c. V at 85 ka (two dates), r.c. VI at 107 ka (two dates), and r.c. VII at 118–142 ka. Complex II was previously dated by 14C at 29 ka: this age has not yet been confirmed, and may be only a lower limit. The reef crests were built during or immediately before intervals of sea level maxima, when rates of rising sea level and tectonic uplift briefly coincided. The culmination of each reef-building episode was only a few thousand years in duration, and multiple dates from the same reef complex generally group within the statistical errors of the individual dates.Several methods can be used to estimate the altitude of each sea level maximum relative to present sea level. The least complicated is to calculate mean tectonic uplift rate for each profile of the terraces, and use the mean rate to calculate the tectonic displacement of each dated reef complex on that profile. The difference between the present altitude of a reef complex and its calculated tectonic uplift gives the paleosea level at the time the reef grew. We estimate uplift rates for six surveyed sections by calibrating against published paleosea level estimates from Barbados and elsewhere, viz 125 ka, paleosea at +6 m; 103 ka, −15 m; 82 ka, −13 m. For each section the individual uplift rates for reefs V, VI, and VIIb are within 5% of their section means. Using the mean rates. paleosea level estimates for reef crests II, IIIB, and IV are made for each section. Consistency of estimates between sections is good, giving −28 m for the 60 ka paleosea level, around −38 m for the 42 ka level and −41 m for the 28 ka level (if the age is older the paleosea level would be lower. Using the mean uplift rates, the 82 ka and 103 ka paleosea levels are also estimated for each section: all individual estimates are plotted graphically, and a sea level curve drawn. The reef stratigraphy indicates sea level lowerings between each dated reef crest: the crests probably represent the interstadials of the Wisconsin (Würm, Weichsel) Glaciation, and intervening lower levels correspond to stadials. Since the last time of eustatic sea level higher than the present (about 125 ka), five sea level maxima occurred at roughly 20-ka intervals, none being as high as the present.

Analysis of 41 ERS 1 synthetic aperture radar images and simultaneous ground measurements of discharge for three large braided rivers indicates that the area of active flow on braided river floodplains is primarily a function of discharge. A power law correlation is found between satellite‐derived effective width We and discharge Q, where We is the water surface area within a braided reach divided by the reach length. Synthetic values of We and Q generated from a cellular automata model of stream braiding display a similar power law correlation. Power functions that are fit through plots of We and Q represent satellite‐derived rating curves that can subsequently be used to estimate instantaneous river discharge from space, with errors ranging from tens to hundreds of cubic meters per second. For ungaged rivers, changes in relative discharge can be determined from satellite data alone to determine the shape and timing of annual flows in glacierized basins. Absolute discharge can probably be estimated within a factor of 2. More accurate estimates will require either (1) one or more ground measurements of discharge acquired simultaneously with a satellite image acquisition, or (2) successful parameterization of known morphologic controls such as total sinuosity ∑P, valley slope, bank material and stability, and braid channel hydraulic geometry. Values of total sinuosity ∑P derived from satellite imagery and field measurements from two rivers of braid channel width, depth, velocity, water surface slope, and bed material grain size indicate that while the shape of satellite‐derived We‐Q rating curves may be influenced by all of these variables, the sensitivity of flow area to changing discharge is most dependent upon the degree of braiding. Efforts to monitor river discharge from space will be most successful for intensely braided rivers with high values of total sinuosity. Subsampling of existing daily discharge records from the Iskut River suggests that satellite return times of about 1 week are sufficient for approximating the shape and timing of the seasonal hydrograph in large, glacierized basins. Although errors are large, the presented technique represents the only currently available way to estimate discharge in ungauged braided rivers.

The Argentine Sierras Pampeanas are reverse fault‐bounded mountain blocks of Precambrian to Paleozoic basement rocks in the foreland of the central Andes. Uplift in the northernmost Sierras Pampeanas fault blocks of Sierra de Quilmes, Sierra Cumbres Calchaquíes, and Sierra Aconquija started about 7 Ma and became pronounced between 4 and 3.4 Ma. The movements culminated after 2.9 Ma, when the conformable Mio/Pliocene Santa María Group was overthrusted, faulted, and folded in the course of principal basement uplift. These movements created climate and base level conditions that resulted in the formation of five pediment levels in the deformed basin strata between 2.5 and 0.3 Ma. Tectonically induced base level changes in the piedmont resulted in three tectonism‐related pediment surfaces between 2.5 and 0.6 Ma, which attest to the neotectonic activity in the Andean foreland. The chronology of young tectonic uplift contradicts models in which early uplift between 20 and 13 Ma is due to the interaction between high topography on the subducting Nazca Plate and the South American craton. In conjunction with the principal uplift of the adjacent Puna Plateau the northernmost Sierras Pampeanas are better explained by E‐W compressional stresses superposed on a thinned lithosphere and inherited zones of structural weakness that facilitated uplift.

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Emerged late Quaternary coral reefs show that on the lo3 to IO5 years time scale the western part of the central New Hebrides arc is divided into several semi-independent uplifted blocks. The blocks are separated by tectonic discontinuities, oriented approximately normal to the arc trend, across which tilt directions or uplift change suddenly. However, none of the blocks is tilted in a direction normal to the arc trend of N20"W. Two of the discontinuities, across Santo and Malekula Islands, occur near the places where ridges on the north and south flanks of the d'Entrecasteaux fracture zone, a major bathymetric feature on the underthrusting plate, intersect the arc. Each of these tectonic discontinuities approximately coincides with one end of the rupture zone inferred .for a shallow thrust-type earthquake sequence in 1965. The discontinuity across Santo also nearly coincides with the south end of the rupture zone inferred for another earthquake sequence in [1973][1974]