GGR Biennial Review: Isotope Ratio Determination in the Earth and Environmental Sciences 2008–2009

This review documents developments and applications in the field of isotope ratio determination, as reflected in the literature for the Earth and environmental sciences for the years 2008 and 2009. The emphasis is predominantly on applications, reflecting the enormous diversity of problems to which isotopic analysis can now be applied, but viewed in the context of rapid development of new analytical methodologies as significant new drivers of research output.     

GGR Critical Review of Analytical Developments in 2008–2009: An Introduction

This collection of articles represents the fourth in a series of reviews in which authors have aimed at capturing the key advances in a range of analytical fields ( Hergt et al. 2005, 2006, 2008 ). The publication period under review is 2008–2009 and the intention here is to provide readers with a summary of the most influential developments published during this period, across a broad range of topics appropriate to the Earth and environmental sciences. Most authors comment on the ways in which the emphases of research in their specific fields of examination have changed over time. All note an increase in rigour and focus on data quality. Whether advances have taken place in instrumentation, sample manipulation or data deconvolution, there are a large number of dedicated scientists out there contributing to the high quality of geochemical data employed in geological and environmental research.     

The large-scale solar magnetic field

The large-scale photospheric magnetic field, measured by the Mt. Wilson magnetograph, has been analyzed in terms of surface harmonics (P _n ^m )()cosm and P _n ^m ()sinm) for the years 1959 through 1972. Our results are as follows. The single harmonic which most often characterized the general solar magnetic field throughout the period of observation corresponds to a dipole lying in the plane of the equator (2 sectors, n = m = 1). This 2-sector harmonic was particularly dominant during the active years of solar cycles 19 and 20. The north-south dipole harmonic (n = 1, m = 0) was prominent only during quiet years and was relatively insignificant during the active years. (The derived north-south dipole includes magnetic fields from the entire solar surface and does not necessarily correlate with either the dipole-like appearance of the polar regions of the Sun or with the weak polar magnetic fields.) The 4-sector structure (n = m = 2) was prominent, and often dominant, at various times throughout the cycle. A 6-sector structure (n = m = 3) occasionally became dominant for very brief periods during the active years. Contributions to the general solar magnetic field from harmonics of principal index 4 n 9 were generally relatively small throughout this entire solar cycle with one outstanding exception. For a period of several months prior to the large August 1972 flares, the global photospheric field was dominated by an n = 5 harmonic; this harmonic returned to a low value shortly after the August 1972 flare events. Rapid changes in the global harmonics, in particular, relative and absolute changes in the contributions of harmonics of different principal index n to the global field, imply that the global solar field is not very deep or that very strong fluid flows connect the photosphere with deeper layers.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Tabulation of the harmonic coefficients of the solar magnetic fields

Tables of spherical harmonic coefficients for the global photospheric magnetic field between 1959 and 1974 are now available on microfilm. (These are the same coefficients which were used to construct the maps of the coronal magnetic atlas.)The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Estimating the timescale of fluvial response to anthropogenic disturbance using two generations of dams on the South River,Massachusetts, USA

Centuries-long intensive land-use change in the north-eastern United States provides the opportunity to study the timescale of geomorphic response to anthropogenic disturbances. In this region, forest-clearing and agricultural practices following EuroAmerican settlement led to deposition of legacy sediment along valley bottoms, including behind mill dams. The South River in western Massachusetts experienced two generations of damming, beginning with mill dams up to 6-m high in the eighteenth–nineteenth century, and followed by construction of the Conway Electric Dam (CED), a 17-m-tall hydroelectric dam near the watershed outlet in 1906. We use the mercury (Hg) concentration in upstream deposits along the South River to constrain the magnitude, source, and timing of inputs to the CED impoundment. Based on cesium-137 (¹³⁷Cs) chronology and results from a sediment mixing model, remobilized legacy sediment comprised % of the sediment load in the South River prior to 1954; thereafter, from 1954 to 1980s, erosion from glacial deposits likely dominated (63 ± 14%), but with legacy sediments still a substantial source (37 ± 14%). We also use the CED reservoir deposits to estimate sediment yield through time, and find it decreased after 1952. These results are consistent with high rates of mobilization of legacy sediment as historic dams breached in the early twentieth century, and suggest rapid initial response to channel incision, followed by a long decay in the second half of the century, that is likely dependent on large flood events to access legacy sediment stored in banks. Identifying sources of sediment in a watershed and quantifying erosion rates can help to guide river restoration practices. Our findings suggest a short fluvial recovery time from the eighteenth–nineteenth century to perturbation during the first half of the twentieth century, with subsequent return to a dominant long-term signal from erosion of glacial deposits, with anthropogenic sediment persisting as a secondary source. © 2020 John Wiley & Sons, Ltd.     

On the frequency of lake-effect snowfall in the Catskill Mountains

Meltwater from snow that falls in the Catskill/Delaware watershed in the Catskill Mountains in south-central New York contributes to reservoirs that supply drinking water to approximately nine million people in and near New York City (NYC). Using the Interactive Multisensor Snow and Ice Mapping System (IMS) 4-km snow maps from the National Oceanic and Atmospheric Administration’s National Ice Center, we identified and tracked 28 lake-effect (LE) storms that deposited snow in the Catskills (2004–2017). These storms, which generally originated from Lake Ontario, but sometimes from Lake Erie, represent an underestimate of the number of LE storms that contribute snowfall to the Catskills snowpack because snowstorms are not visible on IMS maps when they travel over already-snow-covered terrain. Using satellite, meteorological (including NEXRAD and National Weather Service Cooperative Observer Program), and reanalysis data, we identified conditions that contributed to the LE snowstorms and mapped snow-cover extent (SCE) following the storms. We show that LE snow makes an important contribution to the Catskills snowpack because of the frequency of events, even though the total amount of each event may, on average, be small. The IMS 4-km maps tend to overestimate SCE compared to MODerate-resolution Imaging Spectroradiometer and Landsat snow maps. Climate change could impact LE storms and the distribution of rain versus snow in the Catskills, which may affect future reservoir operations in the NYC Water Supply System and winter recreation in the Catskills.     

Geochemical and isotopic variations in the calc-alkaline rocks of Aeolian arc,southern Tyrrhenian Sea,Italy: constraints on magma genesis

New geochemical and isotopic data are reported for calc-alkaline (CA) volcanics of the Aeolian arc. Three main groups are recognized: the Alicudi and Filicudi volcanics in the western part of the arc; the Panarea, Salina and Lipari (henceforth termed PSL) volcanics in the central part of the arc and the Stromboli suite which makes up the eastern part of the arc. Each group is characterized by distinctive isotopic ratios and incompatible element contents and ratios. ⁸⁷Sr/⁸⁶Sr values (0.70352–0.70538) increase from west to northeast, and are well correlated with ¹⁴³Nd/¹⁴⁴Nd (Nd from +4.8 to -1.5). Pb isotope ratios are fairly high (6/4=19.15–19.54; 7/4=15.61–15.71; 8/4=38.97–39.36), with a general increase of 7/4 and 8/4 values from Alicudi to PSL islands and Stromboli. LILE contents and some incompatible element ratios (e.g. Ba/La, La/Nb, Zr/Nb, Rb/Sr) increase from the western to the central part of the arc, whereas HFSE and REE abundances decrease. Opposite variations are often observed in the volcanics toward the north-east from PSL islands. To account for these features and the decoupling observed between isotopic compositions and incompatible element abundances and ratios, it is suggested that a mantle source with affinities to the MORB source is metasomatized by slab-derived, crustal components. The proportion of crustal material entrained in the mantle source increases from Alicudi to Stromboli, according to the Sr and Nd isotope variations. It is also proposed that slab derived hydrous fluids play an important role, but which is variable in different sectors of the arc. This is attributed to the metasomatizing agent having variable fluid/melt ratios, reflecting different types of mass transfer from the subducted contaminant (probably pelagic sediments) to the mantle wedge. Thus, it is suggested that the slab derived end-member has a high hydrous fluid/melt ratio in the PSL mantle source and a correspondingly lower ratio in the Alicudi and Stromboli sources.     

Use of the Aurelia Metamorphosis Test System to detect subtle effects of selected hydrocarbons and petroleum oil

The Aurelia Metamorphosis Test System was devised to use simple Aurelia polyps as indicator organisms for the detection of subtle effects of petroleum-related hydrocarbons and of Alaskan crude petroleum oil (ACPO) on developmental processes involved in strobilation initiation, differentiation of ephyrae, and genetic modification expressed through cloning. Compounds tested were ACPO, aniline, anthracene, benzanthracene, benzene, benzo[a]pyrene, biphenyl, cresol, naphthalene, perylene, phenol and pyrene. Gross morphology of the ephyrae (patterning, numbers and appearance of structures), statolith and mematocyst numbers, and pulsing behavior were recorded using the light microscope. Selected ephyrae with teratological malformations were studied with the scanning electron microscope and swimming behavior was observed visually. The variety of subtle developmental, behavioral and genetic effects due to marine hydrocarbons detected using the Aurelia Metamorphosis Test System demonstrated that this test system could be used as an early warning system to detect subtle effects of other marine pollutants.