Comparison of 15 evaporation methods applied to a small mountain lake in the northeastern USA

Few detailed evaporation studies exist for small lakes or reservoirs in mountainous settings. A detailed evaporation study was conducted at Mirror Lake, a 0.15 km² lake in New Hampshire, northeastern USA, as part of a long-term investigation of lake hydrology. Evaporation was determined using 14 alternate evaporation methods during six open-water seasons and compared with values from the Bowen-ratio energy-budget (BREB) method, considered the standard. Values from the Priestley–Taylor, deBruin–Keijman, and Penman methods compared most favorably with BREB-determined values. Differences from BREB values averaged 0.19, 0.27, and 0.20 mm d⁻¹, respectively, and results were within 20% of BREB values during more than 90% of the 37 monthly comparison periods. All three methods require measurement of net radiation, air temperature, change in heat stored in the lake, and vapor pressure, making them relatively data intensive. Several of the methods had substantial bias when compared with BREB values and were subsequently modified to eliminate bias. Methods that rely only on measurement of air temperature, or air temperature and solar radiation, were relatively cost-effective options for measuring evaporation at this small New England lake, outperforming some methods that require measurement of a greater number of variables. It is likely that the atmosphere above Mirror Lake was affected by occasional formation of separation eddies on the lee side of nearby high terrain, although those influences do not appear to be significant to measured evaporation from the lake when averaged over monthly periods.     

Hydrogen and carbon isotopic ratios of the cellulose nitrate and saponifiable lipid fractions prepared from annual growth rings of a California redwood

The $\text{D}\text{H}$ and ${}^{13}\text{C}{}^{12}$C ratios of the cellulose nitrate and saponifiable lipid fractions prepared from eleven annual growth rings of a California redwood were determined. The $\text{D}\text{H}$ ratios of the two fractions are related to one another for the annual rings in the sapwood portion of the tree, but not for those in the heartwood or in the wood undergoing the transition from sapwood to heartwood. No relationship was observed between the ${}^{13}\text{C}{}^{12}$ ratios of the two fractions. These results suggest that analysis of the hydrogen isotopic composition of the saponifiable lipid fractions in plants will provide information useful for climatic reconstruction provided the initial isotopic record has not been changed by subsequent physiological or diagenetic processes.     

Elasticity of orthoenstatite

Elastic constants of orthoenstatite have been determined from Brillouin-scattering measurements. They are c₁₁ = 2.247, c₂₂ = 1.779, c₃₃ = 2.136, c₄₄ = 0.776, c₅₅ = 0.759, c₆₆ = 0.816, c₂₃ = 0.527, c₃₁ = 0.541 and c₁₂ = 0.724 Mbar. Each elastic constant is uniquely defined by the data. Acoustic velocities measured for two directions ultrasonically on the same samples are within 1% of those determined from Brillouin-scattering spectra.     

Barrier-island genesis: evidence from the central atlantic shelf,eastern U.S.A.

Since most barrier systems appear to have retreated into their present positions from further out on the continental shelf, the continental shelf is a logical place in which to investigate barrier genesis. The Middle Atlantic Bight of North America, one of the best known shelf sectors, does not appear to contain any drowned barriers. Instead, a series of terraces bear on their surfaces a discontinuous carpet of lagoonal sediments beneath a discontinuous sand sheet formed by erosional barrier retreat. Scarps separating terraces are the lower shorefaces of stillstand barriers whose superstructures were destroyed when shoreface retreat resumed. Thus the “origin” of most barriers is that they have retreated in from the position of their immediate predecessors. Barrier genesis, in the classic sense of large-scale, coastwise spit progradation or mainland-beach detachment, could only have occurred at Late Wisconsin lowstand, when the sense of sea-level displacement was reversed. The relative roles of coastwise spit progradation and mainland-beach detachment depend on coastal relief and slope, with steep, rugged coasts favoring spit progradation at the expense of mainland-beach detachment. Since most major barrier systems form on flat coastal plains, it would appear that mainland-beach detachment is the more important mode of barrier formation.During stillstands or periods of reduction in the rate of sea-level rise, coasts can more nearly approach their climax configuration, in which the shoreline is relatively straight, and the shoreface is well developed and of maximum possible slope. Coastal adjustments during such periods may require localized mainland-beach detachment and coastwise spit progradation, in order to attain such a configuration.     

Age and intensity of thermal events by fission track analysis: The Ries impact crater

A thermal event reduces the number of previously registered fission tracks in a mineral dependent upon the track retention properties of the individual mineral. Apatite, sphene and zircon have retention properties over a wide range of temperatures (from 100° to 550°C); apatite data reveal information at lowest temperatures while sphene and zircon data are useful for higher temperatures.Thermal events within this temperature range of 100°C to about 550°C are suitable for study with this technique. The age of the event is determined from samples in which the fission tracks are completely erased, while minerals containing partially removed (erased) tracks provide information on the temperatures occurring during the thermal event.As a test case, the analysis of the temperatures developed by the meteorite impact which produced the Ries crater at 14.7 m.y. ago is presented.     

The Nazca Group of south-central Peru: Age,source, and regional volcanic and tectonic significance

The Nazca Group, exposed east of Nazca, Peru, consists of a lower part composed of conglomerate and finer-grained clastic strata and an upper part made up of at least seven ash-flow sheets (cooling units or ignimbrites), collectively known as the Nazca Tuff. These tuffs were erupted between about 22 and 18 m.y. ago from a vent area in the vicinity of Pampa Galeras now marked by a collapse caldera. The early Miocene age of the Nazca Tuff provides additional evidence for a major pulse of largely pyroclastic felsic volcanism throughout the central Andes during the early Miocene. Recognition of the Pampa Galeras caldera supports the idea that many of these rocks were erupted from vent areas of the collapse-caldera type located near the eastern margin of the Coastal batholith.The Nazca Group overlies a major erosional surface cut on the Coastal batholith and its envelope that can be traced southward to the Chilean border. This surface is a continuation of the post-Incaic erosional surface to the north, which is overlain by conglomerate and radiometrically dated volcanic rock of late Eocene age. The post-Incaic surface therefore represents a major episode of regional uplift and pedimentation that followed early Tertiary orogeny. The absence of volcanic rocks of late Eocene/early Oligocene age overlying the Coastal batholith near Nazca and in southern Peru may reflect a general absence of post-Incaic volcanism in this portion of the Andes possibly related to differences in the angle of subduction and/or restriction of volcanic and volcaniclastic rocks of this age to depositional basins east of the batholith.     

Stability of titanian clinohumite: Experiments and thermodynamic analysis

Reversed hydrothermal experiments on a natural titanoclinohumite [Ti-Cl; approximate formula Mg_7.5FeTi_0.5O₁₆(OH)] show that it breaks down at 475°±11° C (3.5 kbar), 620°±11° C (14 kbar) and 675°±8° C (21 kbar) to the assemblage olivine +ilmenite+vapor. An internal-consistency analysis of the data yields _r G _s ^/0 (298 K, 1 bar)=36,760±3,326 cal (mole Ti-Cl)^–1. _r S _s ^/0 (298 K, 1 bar)=34.14±5.91 cal deg^–1(mole Ti-Cl)^–1. Linear correlation coefficient r _G–S 1.0. A solution model that accounts for TiO₂-M(OH)₂ and F-OH substitution shows that the results for our nearly F-free Ti-Cl are in reasonable agreement with the unreversed breakdown experiments of Mer-rill et al. (1972) on a F-bearing Ti-Cl.Because fluorine is necessary to stabilize Ti-Cl under mantle conditions, we suggest that Ti-Cl is much more likely to be a storage device for fluorine than for water in the mantle.