Geoarchaeological evidence for multidecadal natural climatic variability and ancient Peruvian fisheries

Understanding the influence of natural climatic variability on modern fisheries is complicated by over a century of industrial fishing. Archaeological data provide unique opportunities for assessing precolonial and preindustrial fisheries. Records show that anchoveta-vs sardine-dominated fisheries correlate with 20th-century climate change in the Pacific Basin and are linked to multidecadal climatic variability. The “anchovy regime” is characterized by cooler conditions and lower frequency El Niño/Southern Oscillation (ENSO) events, while the “sardine regime” is associated with warmer conditions and higher frequency ENSO. Fish remains excavated at Lo Demás, an Inca-period (ca. A.D. 1480–1540) fishing site at 13°25′S on the Peruvian coast, document a shift from an anchoveta-to a sardine-dominated fishery at about A.D. 1500. This shift correlates with records for increasing ENSO frequency at the same time. Middle and late Holocene sites have archaeofish assemblages that also suggest regime changes. Here we show that changes in fish regimes can result from natural variability and we support the potential role of archaeological assemblages in tracking multidecadal climate change in the Pacific Basin throughout the Holocene (0–11,500 cal yr B.P.).     

Combining stochastic facies and fractal models for representing natural heterogeneity

Sedimentary deposits are often characterized by various distinct facies, with facies structure relating to the depositional and post-depositional environments. Permeability (k) varies within each facies, and mean values in one facies may be several orders of magnitude larger or smaller than those in another facies. Empirical probability density functions (PDFs) of log(k) increments from multi-facies structures often exhibit properties well modeled by the Levy PDF, which appears unrealistic physically. It is probable that the statistical properties of log(k) variations within a facies are very different from those between facies. Thus, it may not make sense to perform a single statistical analysis on permeability values taken from a mix of distinct facies. As an alternative, we employed an indicator simulation approach to generate large-scale facies distributions, and a mono-fractal model, fractional Brownian motion (fBm), to generate the log(k) increments within facies. Analyses show that the simulated log(k) distributions for the entire multi-facies domain produce apparent non-Gaussian log(k) increment distributions similar to those observed in field measurements. An important implication is that Levy-like behavior is not real in a statistical sense and that rigorous statistical measures of the log(k) increments will have to be extracted from within each individual facies. Electronic Publication     

Lunar periods as grouping variables for temporally fixed sampling regimes in a tidally dominated estuary

The complex interaction of a daily temporally fixed sampling design with seasonal, tidal, and diurnal cycles can result in serious aliasing and reduced usefulness of estuarine data. The choice of appropriate sampling windows for data grouping and analysis of tidally influenced data is complex and must take into account both solar and lunar influences and their interactions in order to represent actual estuarine conditions. A fixed modulus for grouping or time-series analysis introduces errors. Grouping data by calendar month can be misleading since calendar months may have as many as three or as few as one spring tide. Daily measurements of salinity and water clarity at a fixed time of day were analyzed to illustrate the effects of aliasing. Although the length of synodical (lunar) months is also variable, a seasonally adjusted grouping variable based on solar and synodical month (MO-DAY), created to partially correct for aliasing, was found to be an efficient way to remove short-term cycles for the identification of long-term trends, episodic events, and spatial patterns.     

The historical record of metal enrichment in two Florida estuaries

Historical profiles of metal accumulation have been generated for the lower St. Johns River and Hillsborough Bay, Florida, in cores representing approximately 50 yr of sediment and metal accumulation. These profiles demonstrate that Cd, Pb, and Zn are enriched in these Florida estuarine sediments. Pb enrichment has decreased since the mid 1970s because of reduced use of leaded gasoline. In the St. Johns River, most metals exhibit a trend of increasing enrichment with time. Cd enrichment significantly decreased between 1970 and 1975 as a result of reduced discharges into the river and control of aquatic vegetation. In Hillsborough Bay, enrichment factors for most metals are relatively high and show little change downcore. Cr, Cu, and Ni border on enrichment and Pb, Cd, and Zn are enriched. The results of this study are consistent with other studies of surficial-sediment metal concentration in other Florida estuaries.     

Comment: On the need for validation of the Jones et al. temperature trends with respect to urban warming

The Jones et al. hemispheric and global temperature trends and the methodology used to detect and correct for urban heat island effects are examined in detail. The results of this review suggest that there is still the possibility of significant urban warming bias remaining in the hemispheric and global averages. The actual extent of any such bias is unknown but warrants full investigation, since undetected and/or uncorrected urban warming could account for some of the hemispheric and global warming reported by Jones et al. Several research activities are suggested for resolving this uncertainty, including the rigorous application of urban warming correction factors to the data set used by Jones et al. and the development of geographically representative rural temperature series.Office of Technology Assessment, United States Congress, Washington, D.C. 20510, U.S.A. The views expressed are those of the author and not necessarily those of the OTA, Technology Assessment Board, or U.S. Congress. The article is based on independent research of the author and not on work conducted for the OTA.     

Oxygen-isotope geochemistry of metamorphosed,massive sulfide deposits of the Flin Flon — Snow Lake belt,Manitoba

Oxygen-isotope compositions have been measured for whole-rock and mineral samples of host and hydrothermally altered rocks from three massive sulfide deposits, Centennial (CL), Spruce Point (SP), and Anderson Lake (AL), in the Flin Flon — Snow Lake belt, Manitoba. Wholerock ¹⁸O values of felsic metavolcanic, host rocks (+8.5 to +16.1) are higher than those of altered rocks from the three deposits. The ¹⁸O values of altered rocks are lower in the chlorite zone and muscovite zone-I (CL=+ 5.3; SP=+5.4 to +8.3; AL= +3.7 to +5.9) than in the gradational zone (CL= +9.9 to +11.7; SP= +8.4 to +9.8; AL= + 6.6 to +7.7). Muscovite schist (Muscovite Zone-II) enveloping the Anderson Lake ore body has ¹⁸O values of +7.2 to +8.3. Quartz, biotite, muscovite, and chlorite separated from the altered rocks have lower ¹⁸O values compared to the same minerals separated from the host rocks. However, isotopic fractionation between mineral-pairs is generally similar in both host and altered rocks.It is interpreted that differences in the oxygen-isotope compositions of the altered and host rocks were produced prior to metamorphism, during hydrothermal alteration related to ore-deposition. Isotopic homogenization during metamorphism occurred on a grain-to-grain scale, over no more than a few meters. The whole-rock ¹⁸O values did not change significantly during metamorphism. The generally lower ¹⁸O values of altered rocks, the Cu-rich nature of the ore and the occurrence of the muscovite zone-II at Anderson Lake are consistent with the presence of higher temperature hydrothermal fluids at Anderson Lake than at the Centennial and Spruce Point deposits.     

Paleomagnetic evidence for clockwise rotation of the northern arm of Sulawesi,Indonesia

Paleomagnetic results from the northern arm of Sulawesi show that the arm has been subjected to a clockwise rotation of more than 90° and that its rotational motion began no later than the middle Miocene. The mean direction showing a normal polarity at the Eocene to the early Miocene isD = 98.0° andI = 6.9°. A declination value ofD = 50.1° obtained from Miocene rocks indicates a transition stage of the rotational motion. The datum from Plio-Pleistocene volcanics isD = ?4.6° andI = ?9.3°. This suggests that the rotational motion terminated before the initiation of volcanic activity during the Plio-Pleistocene.