Nonlinear meridional scale interaction in baroclinic instability

Baroclinic instability of a zonal flow with latitudinal structure is examined using a nonlinear quasi-geostrophic, two-level β-plane model. An initially small perturbation with the structure of the linearly most unstable mode is allowed to grow to finite amplitude through nonlinear interaction. Because of latitudinal asymmetries of the basic zonal flow, a spectrum of meridional modes is generated in the perturbation. The time evolution of zonal wind and perturbation meridional structures, and their Fourier meridional mode spectra are examined. The radius of deformation is an important meridional scale in both the zonal flow and perturbation. This is especially true during the barotropic decay phase of the baroclinic wave. Time series of energy conversion terms show there is no energy accumulation.     

Vertical cloud structure of Jupiter's Equitorial Plumes

A model for the vertical cloud structure of Jupiter's Equitorial Plumes is deduced based on an analysis of Voyager images of the equitorial region in the 6190Å methane band and the 6000-Å continuum, and ground-based 8900-Å methane band images of Jupiter. A computer code that represents scattering and absorption from aerosol and gas layers was applied to a heirarchy of increasingly complex model aerosol structures to match the observations in the three wavelengths. The observations are consistent with a model for the vertical cloud structure of the equitorial region that consists of four aerosol layers. A high-altitude haze layer (HAL) with optical depth τ = 1 uniformly blankets the equitorial region at an altitude between 100 and 250 mbar. Below that, a middle-level cloud layer between 400 and 800 mbar contains the well-known Equatorial Plumes. The Plume clouds are optically thick (τ ≥ 12), bright clouds with single scattering albedo $\text{ω}\text{= 0.997}$. They are probably composed of ammonia ice. The darker ($\text{ω}\text{= 0.990}$) interplume regions contain optically thinner clouds (2 ≤ τ ≤ 5) at the same altitude as the Plumes. An opaque cloud deck between 4000 and 6000 mbar, which is probably composed of water, forms the lowest model layer. In addition to these three layers, a thin forward scattering haze layer above 100 mbar was included in the models for consistency with previous work (Tomasko et al., 1978). We conclude that the vertical structure of the Equatorial Plume clouds is consistent with the hypothesis (Hunt et al., 1981) that the Plumes are caused by upwelling at the ammonia condensation level produced by bouyancy due to latent heat release from the condensation of water clouds nearly three scale heights below the Plumes.     

High-precision 40Ar/39Ar sanidine geochronology of ignimbrites in the Mogollon-Datil volcanic field,southwestern New Mexico

⁴⁰Ar/³⁹Ar age spectra have been obtained from 85 sanidine separates from 36 ignimbrites and one rhyolitic lava in the latest Eocene-Oligocene Mogollon-Datil volcanic field of southwestern New Mexico. Of the 97 measured age spectra, 94 yield weighted-mean plateau ages each giving single-spectrum 1 precision of±0.25%–0.4% (±0.07–0.14 Ma). Replicate plateau age determinations for eight different samples show within-sample 1 precisions averaging ±0.25%. Plateau ages from multiple (n=3–8) samples of individual ignimbrites show 1 within-unit precision of ±0.1%–0.4% (±0.04–0.13 Ma). This within-unit precision represents a several-fold improvement over published K-Ar data for the same ignimbrites, and is similar to the range of precisions reported from single-crystal laser fusion studies. A further indication of the high precision of unit-mean ⁴⁰Ar/³⁰Ar ages is their close agreement with independently established stratigraphic order. Two samples failed to meet plateau criteria, apparently due to geologic contamination by older feldspars. Effects of minor contamination are shown by six other samples, which yielded slightly anomalous plateau ages. ⁴⁰Ar/³⁹Ar plateau ages permit resolution of units differing in age by 0.5% (0.15 Ma) or less. This high resolution, combined with paleomagnetic studies, has helped to correlate ignimbrites among isolated ranges and has allowed development of an integrated timestratigraphic framework for the volcanic field. Mogollon-Datil ignimbrites range in age from 36.2 to 24.3 Ma. Ignimbrite activity was strongly episodic, being confined to four brief (<2.6 m.y.) eruptive episodes separated by 1–3 m.y. gaps. Ignimbrite activity generally tended to migrate from the southeast toward the north and west.     

Trace-element and Sr,Nd, Pb,and O isotopic composition of Pliocene and Quaternary alkali basalts of the Patagonian Plateau lavas of southernmost South America

The Pliocene and Quaternary Patagonian alkali basalts of southernmost South America can be divided into two groups. The cratonic basalts erupted in areas of Cenozoic plateau volcanism and continental sedimentation and show considerable variation in ⁸⁷Sr/⁸⁶Sr (0.70316 to 0.70512), ¹⁴³Nd/¹⁴⁴Nd (_Nd) and ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios (18.26 to 19.38, 15.53 to 15.68, and 38.30 to 39.23, respectively). These isotopic values are within the range of oceanic island basalts, as are the Ba/La, Ba/Nb, La/Nb, K/Rb, and Cs/Rb ratios of the cratonic basalts. In contrast, the transitional basalts, erupted along the western edge of the outcrop belt of the Pliocene and Quaternary plateau lavas in areas that were the locus of earlier Cenozoic Andean orogenic arc colcanism, have a much more restricted range of isotopic composition which can be approximated by ⁸⁷Sr/⁸⁶Sr=0.7039±0.0004, _Nd, ²⁰⁶Pb/²⁰⁴Pb=18.60±0.08, ²⁰⁷Pb/²⁰⁴Pb=15.60±0.01, and ²⁰⁸Pb/²⁰⁴Pb=38.50±0.10. These isotopic values are similar to those of Andean orogenic are basalts and, compared to the cratonic basalts, are displaced to higher ⁸⁷Sr/⁸⁶Sr at a given ¹⁴³Nd/¹⁴⁴Nd and to higher ²⁰⁷Pb/²⁰⁴Pb at a given ²⁰⁸Pb/²⁰⁴Pb. The transitional basalts also have Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios higher than the cratonic and oceanic island basalts, although not as high as Andean orogenic are basalts. In contrast to the radiogenic isotopes, ¹⁸O values for both groups of the Patagonian alkali basalts are indistinguishable and are more restricted than the range reported for Andean orogenic are basalts. Whole rock ¹⁸O values calculated from mineral separates for both groups range from 5.3 to 6.5, while measured whole rock ¹⁸O values range from 5.1 to 7.8. The trace element and isotopic data suggest that decreasing degrees of partial melting in association with lessened significance of subducted slabderived components are fundamental factors in the west to east transition from arc to back-arc volcanism in southern South America. The cratonic basalts do not contain the slab-derived components that impart the higher Ba/La, Ba/Nb, La/Nb, Cs/Rb, ⁸⁷Sr/⁸⁶Sr at a given ¹⁴³Nd/¹⁴⁴Nd, ²⁰⁷Pb/²⁰⁴Pb at a given ²⁰⁸Pb/²⁰⁴Pb, and ¹⁸O to Andean orogenic arc basalts. Instead, these basalts are formed by relatively low degrees of partial melting of heterogeneous lower continental lithosphere and/or asthenosphere, probably due to thermal and mechanical pertubation of the mantle in response to subduction of oceanic lithosphere below the western margin of the continent. The transitional basalts do contain components added to their source region by either (1) active input of slab-derived components in amounts smaller than the contribution to the mantle below the arc and/or with lower Ba/La, Ba/Nb, La/Nb, and Cs/Rb ratios than below the arc due to progressive downdip dehydration of the subducted slab; or (2) subarc source region contamination processes which affected the mantle source of the transitional basalts earlier in the Cenozoic.     

Place-based or sector-based adaptation? A case study of municipal and fishery policy integration

Place-based adaptation planning is an approach to address cross-sectoral and multi-level governance concerns as well as to build local adaptive capacity in vulnerable resource-dependent communities facing the adverse impacts of climate change. In contrast, sector-based adaptation planning focuses on addressing climate change impacts on individual economic sectors (e.g. fisheries or forestry) or sub-sectors (such as lobsters or timber). Yet, linking sectoral approaches with local adaptation policies is challenging. More effort is needed to identify opportunities for complementary adaptation strategies and policy integration to foster multiple benefits. In this article, we use a case study of fishery sector resources and municipal adaptation planning in Nova Scotia to demonstrate how meaningful entry points could catalyse policy integration and lead to co-benefits across multiple levels and stakeholder groups. Drawing on a fisheries systems and fish chain framework, we identify and assess several entry points for policy integration across sector- and place-based adaptation domains within coastal habitats, as well as harvesting, processing, and marketing sectors. The analysis highlights the multiple benefits of integrating local municipal adaptation plans with multi-scale resource sectors especially towards monitoring ecosystem changes, protecting essential infrastructure, and securing local livelihoods.

POLICY RELEVANCE

Climate change is having a growing impact on coastal communities around the world, with consequences for sea-level rise, critical habitats, essential infrastructure, and multiple economic sectors and industries. This Canadian case study demonstrates how municipal adaptation initiatives can be complementary to sector-based adaptation at both local and regional levels through various entry points across commodity production chains. Policy integration across place-based and sector-based adaptation processes should lead to multiple benefits such as conserving marine biodiversity, protecting essential infrastructure, and securing livelihoods. Our analysis, which focuses specifically on the fishery sector and coastal communities, shows that these co-benefits may arise particularly in such coastal-marine systems and provide policy lessons to terrestrial systems and other sectors.     

Induction of Metamorphosis in the Asian Shore Crab <Emphasis Type="Italic">Hemigrapsus sanguineus</Emphasis>: Effects of Biofilms and Substratum Texture

Since its initial invasion in the late 1980s, the Asian shore crab Hemigrapsus sanguineus has spread over 650 km along the Atlantic Coast of the United States. Larvae of this species can live in the water column for over 3 weeks, which provides ample time for transport to new locations. Previous research on the settlement and metamorphosis of H. sanguineus showed that postlarvae (megalopae) accelerate metamorphosis in response to very specific water-soluble cues. However, the response to substratum cues appears to be much broader. The experiments presented here were designed to test the metamorphic response to biofilms and substratum texture. We found that nylon mesh with pore size of 100 and 1,000 μm had a greater effect on mean time to metamorphosis than 10 and 2,000 μm mesh. Results also showed a positive response to natural rock substrata, and this response was most pronounced when megalopae were exposed to substrata with rough texture. In addition, we found that a combination of a textured surface and a natural biofilm accelerated metamorphosis more than either an abiotic substratum or a smooth surface covered with natural biofilm. A final experiment compared the effect of textural cues to that of a water-soluble cue found in exudate from adult H. sanguineus. Results indicated that both types of cue-induced metamorphosis to the same extent.     

Pairing paleolimnological inference models with mechanistic water column models enhances assessment of lake water quality

Reconciliation of paleolimnology inference models with hindcasts from mechanistic water column models aided the reconstruction of past relationships for total phosphorus/dissolved oxygen and acid neutralizing capacity/pH in highly polluted lake ecosystems in New York State. Pre-disturbance Onondaga Lake, Syracuse, NY, was shown to have experienced seasonal hypolimnetic anoxia even under oligotrophic (<10 ug l^?1) phosphorus levels. In the Adirondack Mountains of New York State the paired modeling confirmed that, while many lakes have the potential to eventually recover from acidification by atmospheric deposition, approximately 30% likely experienced naturally acidic conditions (pH < 6) prior to increases in industrial emissions. Comparison between the model results illuminated areas of individual model inadequacy, improved understanding of lake ecology, and increased confidence in the ability of predictive water column models to accurately develop restoration scenarios representing improved conditions. The work presented here is the first such comparison modeling for total phosphorus, dissolved oxygen, and acid neutralizing capacity. The technique remains to be more widely applied geographically and extended to less heavily stressed lake systems. Because a fossil inference and mechanistic hindcast should independently lead to similar results, comparison modeling is a potentially powerful tool for examining past interactions between ecosystem structure and ecosystem functioning.     

Faulting parameters of earthquakes in the New Madrid, Missouri, region

The advent of high-resolution digital seismic recording and advances in computer technology enable the combination of traditional regional seismic network observations with direct seismogram modeling to improve estimates of small earthquake faulting geometry, depth, and size. We illustrate a combined modeling approach using observations from three earthquakes that occurred within the environs of the New Madrid Seismic Zone: two Missouri earthquakes from September 26, 1990 and May 4, 1991; and the southern Illinois earthquake of February 5, 1994. We also re-examine the faulting geometry for two events from the 1960s that are inconsistent with the current estimate of the regional stress field. Based on direct modeling of the long-period seismograms associated with these events, we revise earlier estimates of the earthquake parameters for the March 3, 1963 and July 21, 1967 Missouri earthquakes. Comparing the new and revised results with existing earthquake mechanisms in the region, we find that tension-axes are generally aligned in a N-S to NW-SE direction, while the compression-axes trend in a NE to E direction. An interesting exception to this pattern are the March 3, 1963 and two nearby earthquakes that lie within a well-defined 30-km long left step in seismicity near New Madrid.     

Sinkholes formed by piping into buried channels

Piping-induced sinks in flood-irrigated alfalfa fields on the distal part of a compound alluvial fan in California's Central Valley lack discharge conduits. It is suggested that all inflow and sediment are dispersed underground in former distributary channels that are now buried.