Climate simulations of major estuarine watersheds in the Mid-Atlantic region of the US

To better understand the implications of anthropogenic climate change for three major Mid-Atlantic estuaries (the Chesapeake Bay, the Delaware Bay, and the Hudson River Estuary), we analyzed the regional output of seven global climate models. The simulation given by the average of the models was generally superior to individual models, which differed dramatically in their ability to simulate twentieth-century climate. The model average had little bias in its mean temperature and precipitation and, except in the Lower Chesapeake Watershed, was able to capture the twentieth-century temperature trend. Weaknesses in the model average were too much seasonality in temperature and precipitation, a shift in precipitation’s summer maximum to spring and winter minimum to fall, interannual variability that was too high in temperature and too low in precipitation, and inability to capture the twentieth-century precipitation increase. There is some evidence that model deficiencies are related to land surface parameterizations. All models warmed over the twenty-first century under the six greenhouse gas scenarios considered, with an increase of 4.7 ± 2.0°C (model mean ± 1 standard deviation) for the A2 scenario (a medium-high emission scenario) over the Chesapeake Bay Watershed by 2070–2099. Precipitation projections had much weaker consensus, with a corresponding increase of 3 ± 12% for the A2 scenario, but in winter there was a more consistent increase of 8 ± 7%. The projected climate averaged over the four best-performing models was significantly cooler and wetter than the projected seven-model-average climate. Precipitation projections were within the range of interannual variability but temperature projections were not. The implied research needs are for improvements in precipitation projections and a better understanding of the impacts of warming on streamflow and estuarine ecology and biogeochemistry.     

A comprehensive model inter-comparison study investigating the water budget during the BALTEX-PIDCAP period

Summary A comparison of 8 regional atmospheric model systems was carried out for a three-month late summer/early autumn period in 1995 over the Baltic Sea and its catchment area. All models were configured on a common grid using similar surface and lateral boundary conditions, and ran in either data assimilation mode (short term forecasts plus data assimilation), forecast mode (short term forecasts initialised daily with analyses) or climate mode (no re-initialisation of model interior during entire simulation period). Model results presented in this paper were generally post processed as daily averaged quantities, separate for land and sea areas when relevant. Post processed output was compared against available analyses or observations of cloud cover, precipitation, vertically integrated atmospheric specific humidity, runoff, surface radiation and near surface synoptic observations. The definition of a common grid and lateral forcing resulted in a high degree of agreement among the participating model results for most cases. Models operated in climate mode generally displayed slightly larger deviations from the observations than the data assimilation or forecast mode integration, but in all cases synoptic events were well captured. Correspondence to near surface synoptic quantities was good. Significant disagreement between model results was shown in particular for cloud cover and the radiative properties, average precipitation and runoff. Problems with choosing appropriate initial soil moisture conditions from a common initial soil moisture field resulted in a wide range of evaporation and sensible heat flux values during the first few weeks of the simulations, but better agreement was shown at later times. Received September 8, 2000 Revised April 3, 2001     

Platinum-group elements (Ir,Pd, Pt and Rh) in road-deposited sediments in two urban watersheds,Hawaii

This study represents the first detailed investigation of platinum-group elements (PGEs) in road-deposited sediment (RDS) in Hawaii, USA. Thirty-three sample locations, in two urban watersheds in Honolulu, Oahu, Hawaii were sampled. The <63 μm fraction of RDS was digested with aqua regia, followed by matrix separation with Dowex AG50-X8 cation exchange resin. PGEs were analyzed with inductively coupled plasma-mass spectrometry (ICP-MS) equipped with a desolvating nebulizer. Concentrations of Rh, Pd and Pt in residential streets reached 64, 105 and 506 ng/g, respectively. Maximum enrichment ratios, computed as RDS concentrations relative to baseline values, exceeded 400, indicating a significant anthropogenic signal with the sequence Rh > Pt > Pd. Iridium concentrations were uniformly low <1 ng/g, and enrichment ratios support a geogenic source. Significant interelement PGE correlations (Pd–Pt–Rh), combined with the magnitude of PGE pair-wise ratios (Pt/Pd, Pt/Rh and Pd/Rh), and relative percentages comparable to European RDS and roadside soil in Indiana, USA all suggest an automobile source. Attrition of PGE-loaded automobile catalytic converters and subsequent loss to the environment by exhaust emissions explains the significant environmental signal of PGEs in road environments of Hawaii. Further PGE work is required to quantify urban transport paths as PGEs are known to bioaccumulate, cause cellular damage and may have detrimental human health effects.     

RARE EARTH ELEMENT ABUNDANCES IN SEPARATED PHASES OF MAYO BELWA,AN ENSTATITE ACHONDRITE

Separated fractions from the Mayo Belwa aubrite have been analysed for the rare earth elements (REE). The data show no ytterbium anomalies but the feldspar and magnetic fractions show complementary europium anomalies. The separated phases together account for the total REE abundances in the bulk meteorite which are about 0.5 times chondritic. The REE content of the feldspar is greater than that of the bulk meteorite. The partition coefficients for the REE between feldspar and orthopyroxene are about 10 times (in favour of the feldspar) those of the nearest equivalent terrestrial feldspar/orthopyroxene pairs, implying that the distribution of the REE which would result from equilibrium co-crystallisation from a single liquid has been disturbed by a later event. This occurred more recently than 4.33 b.y. ago and resulted in a redistribution of the REE between the feldspar and a REE enriched residue. However, the REE patterns of the minerals are very like those of terrestrial equivalents and appear to be the result of igneous cumulus processes on a parent body rather than condensation of dust from a nebular gas.     

The Tuxtuac,Mexico, Meteorite,an LL5 Chondrite Fall

Abstract— The Tuxtuac meteorite fell in Zacatecas state, Mexico, on 16 October 1975, at 1820 hours. Two partly crusted masses, weighing 1924 g and 2340 g, were recovered. The stone is an ordinary chondrite, LL5, with olivine Fa₃₀ and 19.22 weight % total iron. The silicates contain numerous voids and a froth-like mesostasis is present within some chondrules. Metal phases present are kamacite (5.7–6.4% Ni, 6–7% Co) and high nickel metal (taenite 37–41% Ni, 1.7 ± 0.3% Co; tetrataenite 47–52% Ni, 0.8–1.4% Co). The stone is unusual for an LL-group chondrite in that it exhibits neither large-scale brecciation features nor dark veins.     

The Julesburg (L3) meteorite

Abstract— The Julesburg chondrite, a single stone weighing 57.9 kg, was found in 1983 in Sedgewick County, Colorado, USA. It contains abundant chondrules and chondrule fragments but little fine-grained matrix. The olivine composition ranges from Fa₁ to Fa₂₅ but a frequency plot of olivine compositions is strongly peaked at Fa₂₃. The low-Ca pyroxenes range from Fs₃ to Fs₂₈ and show no dominant composition. The abundance of clearly defined chondrules, the heterogeneity of the silicates and the presence of glass within chondrules indicate a type 3 chondrite, refined by thermoluminescence data to 3.6. The total iron content of 20.46% is indicative of an L-group stone. The low noble gas retention ages indicate that this meteorite was outgassed late in its history. This is supported by petrographic evidence of brecciation and shock. Aluminum-rich spinels within chondrules and inclusions contain up to 2.6% ZnO which suggests that they formed in a volatile-rich environment.     

Magmatic evolution of Late Cenozoic volcanic rocks of the Lau Ridge,Fiji

Three main groups of lavas are exposed on islands of the Lau Ridge: the Lau Volcanic Group (LVG), 14.0–5.4 Ma, are predominantly andesite; Korobasaga Volcanic Group (KVG), 4.4–2.4 Ma, are predominantly basalt and Mago Volcanic Group (MVG), 2.0–0.3 Ma, are basalt-hawaiite. LVG and KVG lavas are mostly medium-K tholeiitic rocks with high LILE/HFSE ratios characteristic of islands ares, while MVG lavas are ne-normative alkalic rocks with high LILE and HFSE, characteristic of ocean island basalts. LVG lavas have high ?_Nd (+8.0–+8.4) and low ⁸⁷Sr/⁸⁶Sr (0.70273–0.70349) similar to N-MORB, whereas KVG lavas have slightly more radiogenic values (?_Nd=+7.5?+8.4; ⁸⁷Sr/⁸⁶Sr=0.70323-0.70397). MVG lavas form an isotopically distinct group having lower ?_Nd (+4.6–+4.9) and (⁸⁷Sr/⁸⁶Sr ranging from 0.70347–0.70375). LVG lavas were erupted in a primary oceanic island arc (Vitiaz arc) during the Miocene. Basaltic lavas were derived by approximately 19% partial melting of mantle wedge peridotite with only minor subduction component. Andesites and dacites were produced by low-pressure plagioclase-pyroxene-titanomagnetite dominated crystal fractionation. KVG lavas were erupted during the period immediately prior to or during the initial stages of rifting in the Lau Basin, and, like LVG lavas, show significant chemical differences at the northern and southern ends of the Lau Ridge. Lavas at the northern end (type (ii)) appear to be derived from a more depleted source than LVG but with a greater amount of subduction component. Those at the southern end (type (i)) probably came from a slightly more enriched source with less subduction component. MVG basalts and hawaiites were derived from an enriched mantle with little or no subduction input. The hawaiites (type (i)) could not have been derived from the basalts (type (ii)), and the two magma types must have come from different sources, indicating mantle heterogeneity. The lack of subduction influence indicates the MVG lavas are tectonically unrelated to the present-day Tonga arc, and the lack of depletion indicators suggests they have tapped a different (new?) part of the mantle wedge. This may reflect introduction of sub-Pacific mantle through the present Tonga-Lau subduction system.     

Regional climate changes drive increased scaled-chrysophyte abundance in lakes downwind of Athabasca Oil Sands nitrogen emissions

Several limnological and paleolimnological investigations have linked enhanced atmospheric nitrogen (N) deposition to nutrient enrichment and increased primary production. The Athabasca Oil Sands Region (AOSR) in northeast Alberta, Canada is a significant source of N emissions, particularly since development intensified during the 1990s, and recent paleolimnological investigations provide evidence of increased lake production in adjacent areas subject to enhanced N deposition. The AOSR, however, has also experienced atmospheric warming since ca. AD 1900, and therefore the relative effects of nutrient deposition and climate changes on lake production remain unclear. We undertook a factorial-design paleolimnological assessment of 16 lakes in northwest Saskatchewan to quantify changes in abundance and species composition of scaled chrysophytes over the past 100 years. Study sites included both N-limited and P-limited lakes within control regions, as well as lakes that receive enhanced N deposition from the AOSR. We hypothesized that a change in algal communities within N-limited AOSR-impacted lakes, without concurrent changes in the other lake groups, would suggest AOSR-derived N as a driver of enhanced primary production. Instead, marked increases in concentrations of scaled chrysophytes, mainly Mallomonas crassisquama, occurred in the recent sediments in cores from all four lake groups (N-limited vs. P-limited, impacted vs. control), suggesting that regional climate change rather than N deposition was the paramount process enhancing chrysophyte production. Because chrysophyte abundances tended to be higher in deep, lower-pH lakes, and chrysophyte time series were fit best by lake-specific generalized additive models, we infer that climate effects may have been mediated by additional catchment and/or lake-specific processes.     

A Social–Ecological Systems Approach to Assessing Conservation and Fisheries Outcomes in Fijian Locally Managed Marine Areas

Locally managed marine areas (LMMAs) are often recommended as a strategy to achieve conservation and fisheries management, though few studies have evaluated their performance against these objectives. We assessed the effectiveness of eight periodically harvested closures (PHCs), the most common form of management within Fijian LMMAs, focusing on two outcomes: protection of resource units and biodiversity conservation. Of the eight PHCs, only one provided biodiversity benefits, whereas three were moderately successful in protecting resource units (targeted fish biomass). Protection of resource units was more likely when PHCs were harvested less frequently, less recently, and when total fish biomass in open areas was lower. Our findings further suggest that monitoring, enforcement, and clearly defined boundaries are critical, less frequent harvesting regimes are advised, and culturally appropriate management incentives are needed. Although PHCs have some potential to protect resource units, they are not recommended as a single strategy for broad-scale biodiversity conservation.