Correction to: Microphysics and Optical Attenuation in Fog: Observations from Two Coastal Sites

Boundary-Layer Meteorology -     

Ledgers and landscapes: Indicators of rural landscape change in southern New Zealand, 1878–1919

Our objective was to develop and calibrate numerical measures to represent the timing and magnitude of landscape change between 1878, and 1919 using information in a stock and station agency's ledgers. Relative expenditures on fencing materials peaked in the 1880s, were lowest in the early 1900s, and rose to one‐fifth of annual expenditures from 1914 onwards. In contrast, relative expenditures on soil preparation, cropping and harvesting grew steadily after 1879, peaked in 1900, and declined from then until 1919. This research found that periods of intensive landscape investment between 1878 and 1919 were separated by longer intervals of landscape maintenance.     

Stable isotopic evidence in support of active microbial methane cycling in low-temperature diffuse flow vents at 9°50′N East Pacific Rise

A unique dataset from paired low- and high-temperature vents at 9°50′N East Pacific Rise provides insight into the microbiological activity in low-temperature diffuse fluids. The stable carbon isotopic composition of CH₄ and CO₂ in 9°50′N hydrothermal fluids indicates microbial methane production, perhaps coupled with microbial methane consumption. Diffuse fluids are depleted in ¹³C by ∼10‰ in values of δ¹³C of CH₄, and by ∼0.55‰ in values of δ¹³C of CO₂, relative to the values of the high-temperature source fluid (δ¹³C of CH₄ =−20.1 ± 1.2‰, δ¹³C of CO₂ =−4.08 ± 0.15‰). Mixing of seawater or thermogenic sources cannot account for the depletions in ¹³C of both CH₄ and CO₂ at diffuse vents relative to adjacent high-temperature vents. The substrate utilization and ¹³C fractionation associated with the microbiological processes of methanogenesis and methane oxidation can explain observed steady-state CH₄ and CO₂ concentrations and carbon isotopic compositions. A mass-isotope numerical box model of these paired vent systems is consistent with the hypothesis that microbial methane cycling is active at diffuse vents at 9°50′N. The detectable ¹³C modification of fluid geochemistry by microbial metabolisms may provide a useful tool for detecting active methanogenesis.     

A sustained +21 m sea-level highstand during MIS 11 (400 ka): direct fossil and sedimentary evidence from Bermuda

A small, protected karstic feature exposed in a limestone quarry in Bermuda preserved abundant sedimentary and biogenic materials documenting a transgressive phase, still-stand, and regressive phase of a sea-level in excess of 21.3 m above present during Marine Isotope Stage (MIS) 11 (400 ka) as determined by U/Th dating and amino acid racemization. Cobbles and marine sediments deposited during the high-energy transgressive phase exhibit rim cements indicating a subsequent phreatic environment. This was succeeded stratigraphically by a still-stand deposition of fine calcareous lagoonal sediments containing bioclasts of red algae and benthic and planktonic foraminifera that was intensely burrowed by marine invertebrates, probably upogebiid shrimp, that could not be produced under any condition other than sustained marine submergence. Overlying this were pure carbonate beach sands of a low-energy regressive phase containing abundant remains of terrestrial and marine vertebrates and invertebrates. The considerable diversity of this fauna along with taphonomic evidence from seabird remains indicates deposition by high run-up waves over a minimum duration of months, if not years. The maximum duration has yet to be determined but probably did not exceed one or two thousand years. The most abundant snails in this fauna are two species indicative of brackish water and high-tide line showing that a Ghyben-Herzberg lens must have existed at > + 20 m. The nature of these sediments and fossil accumulation is incompatible with tsunami deposition and, given the absence of evidence for tectonic uplift of the Bermuda pedestal or platform, provide proof that sea-level during MIS 11 exceeded +20 m, a fact that has widespread ramifications for geologists, biogeographers, and human demographics along the world's coastlines.     

Hydrothermal alteration of late- to post-tectonic Lyon Mountain Granitic Gneiss, Adirondack Mountains, New York: Origin of quartz–sillimanite segregations, quartz–albite lithologies, and associated Kiruna-type low-Ti Fe-oxide deposits

Quartz–sillimanite segregations, quartz–albite lithologies (Ab_95–98), and Kiruna‐type low‐Ti iron‐oxide deposits are associated with late‐ to post‐tectonic (c. 1055 Ma) leucogranites of Lyon Mountain Gneiss (LMG) in the Adirondack Mountains, New York State. Most recent interpretations of these controversial features, which are global in occurrence, favour hydrothermal origins in agreement with results presented here. Field relations document that quartz–sillimanite veins and nodules cut, and therefore post‐date, emplacement of host LMG leucogranites. Veins occur in oriented fracture networks, and aligned trains of nodules are interpreted as disrupted early veins. Late dykes of leucogranite cut veins and nodules demonstrating formation prior to terminal magmatism. Veins and nodules consist of sillimanite surrounded by quartz that commonly embays wall‐rock feldspar indicating leaching of Na and K from LMG feldspar by acidic hydrothermal fluids. Subsequent, and repeated, ductile flow disrupted earlier veins into nodular fragments but produced little grain shape fabric. Geochemical and petrographic studies of quartz–albite rock indicate that it formed through metasomatic replacement (albitization) of LMG microperthite by sodic hydrothermal fluids that resulted in diagnostic checkerboard albite. Low‐Ti iron‐oxide ores are commonly associated with the quartz–albite sub‐unit, and it is proposed that hydrothermal fluids related to albitization transported Fe as well. The regional extent of sodic alteration suggests large quantities of surface‐derived hydrothermal fluids. Fluid inclusion and oxygen isotope data are consistent with high temperature, regionally extensive fluids consisting primarily of evolved surface‐derived brines enriched in Na and Cl. Quartz–sillimanite veins and nodules, which are significantly more localised phenomena and require acidic fluids, were most likely formed from local magmatic fluids in the crystallizing carapaces of LMG plutons.     

Geotechnical analysis of paleoseismic shaking using liquefaction features: a major updating

A new methodology is proposed for the geotechnical analysis of strength of paleoseismic shaking using liquefaction effects. The proposed method provides recommendations for selection of both individual and regionally located test sites, provides techniques for validation of field data for use in back-analysis, and presents a recently developed energy-based solution to back-calculate paleoearthquake magnitude and strength of shaking. The proposed method allows investigators to qualitatively assess the influence of post-earthquake density change and aging. The proposed method also describes how the back-calculations from individual sites should be integrated into a regional assessment of paleoseismic parameters.     

The Ground Water Recharge and Pollution Potential of Dry Wells in Pima County, Arizona

This paper summarizes a study to estimate the potential for dry-well drainage of urban runoff to recharge and pollute ground water in Tucson, Arizona. We selected three candidate dry wells for study. At each site we collected samples of runoff, dry-well sediment, vadose-zone sediment, perched ground water, and ground water. Water content data from vadose-zone samples suggest that dry-well drainage has created a transmission zone for water movement at each site. Volatile organic compounds, while undetected in runoff samples, were present in dry-well sediment, perched ground water at one site, and ground water at two sites. The concentrations of volatile organics (toluene and ethylbenzene) in the water samples were less than the corresponding EPA human health criteria. Pesticides were detected only in runoff and dry-well sediment. Lead and chromium occurred in runoff samples at concentrations above drinking water standards. Nickel, chromium, and zinc concentrations were elevated in vadose-zone samples at the commercial site. Of the metals, only manganese, detected at the residential site, exceeded Secondary Drinking Water Standards in ground water. It is concluded that the three dry wells examined during this study are currently not a major source of ground water pollution.     

The contribution of magnetospheric currents toSq

Since the discovery of the magnetosphere, it has been known that the currents flowing in the magnetosphere contribute toSq, the regular daily variation in the earth's surface magnetic field. The early models, however, were not very accurate in the vicinity of the earth. The magnetospheric contribution toSq has therefore been recalculated by direct integration over the three major magnetospheric current systems; magnetopause, tail and ring. The finite electrical conductivity of the earth, which increases the horizontal and decreases the vertical components of the magnetospheric field at the earth's surface, has been taken into account. The magnetospheric currents are found to contribute 12 nanotesla to the day to night difference in the mid-latitudeSq pattern for steady, quiet magnetospheric conditions. They also contribute to the annual variation in the surface field and must be considered an important source of the observed day to day variation in theSq pattern.     

Ar/Ar dating of Apollo 12 regolith: Implications for the age of Copernicus and the source of nonmare materials

Twenty-one 2–4 mm rock samples from the Apollo 12 regolith were analyzed by the ⁴⁰Ar/³⁹Ar geochronological technique in order to further constrain the age and source of nonmare materials at the Apollo 12 site. Among the samples analyzed are: 2 felsites, 11 KREEP breccias, 4 mare-basalt-bearing KREEP breccias, 2 alkali anorthosites, 1 olivine-bearing impact-melt breccia, and 1 high-Th mare basalt. Most samples show some degree of degassing at 700–800 Ma, with minimum formation ages that range from 1.0 to 3.1 Ga. We estimate that this degassing event occurred at 782 ± 21 Ma and may have been caused by the Copernicus impact event, either by providing degassed material or by causing heating at the Apollo 12 site. ⁴⁰Ar/³⁹Ar dating of two alkali anorthosite clasts yielded ages of 3.256 ± 0.022 Ga and 3.107 ± 0.058 Ga. We interpret these ages as the crystallization age of the rock and they represent the youngest age so far determined for a lunar anorthosite. The origin of these alkali anorthosite fragments is probably related to differentiation of shallow intrusives. Later impacts could have dispersed this material by lateral mixing or vertical mixing.