The end of moai quarrying and its effect on Lake Rano Raraku, Easter Island

We reconstruct aspects of the history of Easter Island over the last 4-5 centuries based on the study of a core from Rano Raraku Lake, situated in the crater that contains the quarry of the island's giant statues or moai. We use microfossils of plants and animals to identify five zones. The last three of these are separated by waves of immigration from South America and from the subantarctic. We argue that the first or South American wave, dated to the second half of the 14th century, may represent a visit by South American Indians. Magnetic information, pollen, diatoms, chrysophyte stomatocysts and fossil plant pigments reveal a synchronism between the South American contact and the cessation of moai quarrying. We therefore suggest that Amerindians contributed to the cultural collapse of the island. The second or subantarctic wave may reflect an early European visit to the island, possibly by Cpt. James Cook in 1774, or by Jacob Roggeveen in 1722.     

Health of red morwong, Cheilodactylus fuscus, and rock cale, Crinodus lophodon, from Sydney cliff-face sewage outfalls

Health of red morwong, Cheilodactylus fuscus and rock cale, Crinodus lophodon was assessed using histology to determine effects of the Sydney cliff outfalls on these two species. Ten individuals of each species were sampled from three outfall sites and three control sites. Benign epitheliocystis, presence of metazoan parasites, epithelial lifting, telangiectasis, haemorrhage and inflammation were found in the gills of some individuals. Hemosiderin was present in melanomacrophage aggregates in liver and spleen of some fish and also in kidneys of a few fish collected in Malabar outfall site. Hyaline droplets were present in tubular epithelium in kidney of some fish, particularly in the individuals collected from Malabar. Although for some changes there was a trend of greater prevalence at the outfall sites, there was no statistically significant difference between the fish from outfall sites and control sites. Most changes were species specific and the differences were statistically significant. This suggests problems with extrapolating results from one species to others. Greater replication, smaller range of size, chemical analysis of tissue residues as well as better knowledge of the fate of sewage and oceanographic processes would improve interpretation of any future surveys. A multidisciplinary approach would be most beneficial for pollution studies.     

A weighted-averaging regression and calibration model for inferring lakewater salinity using chrysophycean stomatocysts from lakes in western Canada

Chrysophycean stomatocysts were identified and enumerated from the surface sediments of 60 lakes located on the Interior Plateau of British Columbia. The lakes span a salinity gradient from freshwater to hypersaline (0.0–92.4 g L^–1), with the majority being fresh to hyposaline. One hundred and ten stomatocyst morphotypes, almost all of which were previously described, were identified from the lake sediments. The first axis of direct gradient analysis, which was highly significant, was essentially a salinity axis (i.e. [Ca], [Mg], [K], [Na], [SO₄], [DIC], and [Cl]). Most cysts were found to have fairly broad tolerances, with the narrowest tolerances occurring among morphotypes with the lowest salinity optima. Weighted-averaging regression and calibration techniques were used to develop an inference model to measure the relationship between measured average lakewater salinity and stomatocyst inferred salinity (apparent r²=0.80). Simple weighted-averaging produced a model with a lower bootstrapped RMSE of prediction than weighted-averaging with tolerance downweighting. These data indicate that chrysophyte stomatocysts are useful quantitative indicators of past lakewater salinity (in the freshwater to hyposaline range) in B.C. lakes, and can be used to strengthen the interpretations from diatom-inference models already developed from the same region.     

Lithium in staurolite and its petrologic significance

Natural metapelitic staurolites contain appreciable amounts of lithium. Lithium contents were determined by ion microprobe with concentrations of representative samples independently analyzed by atomic absorption spectrophotometry for calibration. Seventy-one percent of the analyzed staurolites contain >0.1 wt.% Li₂O, although the distribution is skewed to values less than 0.3 wt.%.High Li contents observed in staurolite are attributed to one or more of several factors: initiation of staurolite breakdown, lack of additional host phases for lithium (e.g. biotite), pre-metamorphic Li-rich bulk rock composition, and/or interaction of the rock with Li-rich fluids. Li content is generally not correlated with the modal amount of staurolite in the rock, rather Li values tend to reflect variable host rock Li. Lithium most likely resides in the R²⁺ tetrahedral site. Its incorporation into the structure is probably related to a coupled substitution with Al: ^ivLi ^viA_1/3 ^ivR _–1 ^{2+ vi}_–1/3 When staurolite analyses yield low R²⁺ and high Al values, the possibility of high Li should be considered after accounting for variable H.Lithium partitions into common pelitic metamorphic minerals in the order staurolite>cordierite>biotite>muscovite> garnet, tourmaline, and chloritoid. Partitioning is non-ideal in staurolite and a function of Fe content. Li in staurolite expands its stability field to a higher T relative to garnet and sillimanite, and to a lower T relative to chloritoid and Al-silicate. Analysis of staurolites for Li may provide further insight into this enigmatic mineral.     

Geologic and atmospheric input factors affecting watershed chemistry in upper michigan

The relationships between watershed variables and lakewater chemistry were examined for 53 lakes in the Upper Peninsula of Michigan to identify factors influencing lake sensitivity to atmospheric inputs. The lakes lie in three distinct geologic/geomorphic regions. Acid neutralization capacity (ANC), sulfate, and color were correlated with parameters related to atmospheric loading, watershed area and relief, hydrology, geology, and land use for the entire 53-lake set and for lower alkalinity subsets. Acid-neutralizing capacity was related to atmospheric acidic inputs and, in the southern portion of the Upper Peninsula, to the presence of mineralized groundwater inputs. In the north, ANC is correlated with hydrologic lake type and surficial deposits. Results show the highest density of acidified lakes in the northern region, which is underlain by noncalcareous sedimentary rocks. Color was related to lake size and the presence of organic soils in the watershed, whereas lake sulfate concentration was mainly influenced by atmospheric or groundwater inputs, surficial deposits, and soil type.     

Benthic nutrient remineralization in a coastal lagoon ecosystem

In situ measurements of the exchange of ammonia, nitrate plus nitrite, phosphate, and dissolved organic phosphorus between sediments and the overlying water column were made in a shallow coastal lagoon on the ocean coast of Rhode Island, U.S.A. The release of ammonia from mud sediments in the dark (20–440 μmol per m² per h) averaged ten times higher than from a sandy tidal flat (0–60 μmol per m² per h), and while mud sediments also released nitrate and phosphate, sandy sediments took up these nutrients. Fluxes of nutrients from mud sediments, but not from sandy areas, markedly increased with temperature. Ammonia release rates for mud sediments in the light (0–350 μmol per m² per h) were lower than those in the dark and it is estimated that some 25% of the ammonia released to the water column on an annual basis may be intercepted by the benthic microfloral community. Estimates of the annual net exchange of nutrients across the sediment-water interface, weighted by sediment type for the lagoon as a whole, showed a release of 450 mmol per m² of ammonia, 5 mmol per m² of phosphate, 5 mmol per m² of dissolved organic phosphorus, and an uptake of 80 mmol per m² of nitrate. Although rates of ammonia and nitrate exchange were comparable to those described for the deeper heterotrophic bottom communities of nearby Narragansett Bay, rates of benthic phosphate release were significantly lower. On an annual basis the Bay benthos released approximately 20 times more inorganic phosphate per unit area than did the lagoon benthos. As a result., the N/P ratio for the flux from the sediments was 74∶1 in the lagoon, compared with 16∶1 in “average” marine plankton and 8∶1 for the benthic flux from Narragansett Bay. The lack of remineralized phosphate in the lagoon, is reflected in water, column phosphate concentrations (always <1 μm) and water column N/P ratios (annual N/P=27) and suggests that the lagoon may show phosphate limitation rather than the nitrogen limitation commonly associated with marine systems.     

Pure path attenuation measurements of long-period Rayleigh waves across the Tibet Plateau

A method is presented to derive pure path attenuation coefficients of Rayleigh waves, in the period range 30–90 s, across the Tibet Plateau, using events located within Tibet and observed at teleseismic distances. This method uses data from 2 events and 2 stations simultaneously, these being aligned along a great circle path, and, for relatively small events, is practically free of errors due to inaccurate knowledge of the source radiation patterns.In spite of large standard errors due to the impossibility of separating effects of anclasticity from spurious effects on amplitudes such as scattering or multipathing, results seem to indicate an anelastic model of the crust and upper mantle compatible with shear velocity models derived independently, with a thick crust and in particular, a thick high Q lid and thin low Q zone consistent with a shield like upper mantle beneath Tibet.     

Reflection of the orographic patterns in the micro- and mesoclimatic conditions

In the Polish Carpathian Mountains two altitudinal profiles were chosen. Ranging from 200 to 1,000 m asl along 20°00′ and 21°30′E their spatial patterns of the topographical types in the mountains and uplands, geometric configuration of concave topographies and direction of their course are different. The effects of topography on the mesoclimatic conditions in the area investigated were analyzed by the diurnal air temperature records at the 28 meteorological stations in the years 1951 – 1970. Along the two profiles, taking the points situated at the same height asl and similar altitude, the mean extreme temperatures in the particular months, as well as the values of the first and ninth deciles of the maximum and minimum temperatures were analyzed. Special consideration was given to the spatial distribution of the minimum temperature and characteristics derived, because it reflects the influence of topography in a higher degree than the maximum temperature. Since low air temperatures are the main factor for the plant growth in the Polish Carpathians, spatial differentiation of the minimum temperature regulates the rate of development of the wild and cultivated plants during the growing season.     

Dewatering of an unvegetated muddy tidal flat during exposure—Desiccation or drainage?

An unvegetated muddy tidal flat was sampled to determine the changes in surface pore water content and salinity during exposure. Local evaporation accounted for 61% of the upper intertidal surface salinity, with evaporation rates increasing salinity as high as 2.2‰ per hour. In contrast, only 37% of the decrease in pore water content was attributed to evaporative processes. This suggests that drainage (a combination of porosity and permeability) controlled the water content rather than local evaporative conditions.