Lago Verde is a fresh-water maar found on the lower slopes of San Martin volcano, at the Sierra de Los Tuxtlas, Mexico, currently the northernmost remnant of the tropical rain forest in America. 210Pb and 137Cs analyzed in a sediment core were used to reconstruct the historical fluxes of Ag, Cd, Cu, Pb, Hg and Zn to the site during the last ∼ 150 yr. The 210Pbxs-derived sediment accumulation rates, the magnetic susceptibility, C/N ratios and δ13C data evidenced background conditions at the lake until 1960s, when enhanced erosion related to the clearing of large forested areas at Los Tuxtlas promoted higher accumulation rates of a heavier and more magnetic sedimentary material. Recent sediments from Lago Verde were found enriched by Pb (26-fold natural concentration level [NCLs]) and moderately enriched by Cd>Cu>Zn and Hg (6-, 5-, 4- and 4-fold corresponding NCLs, respectively). The fluxes of Cu, Hg, Pb and Zn have significantly increased since 1940s, with peak ratios of total modern to pre-industrial fluxes of 11, 11, 19 and 49, respectively. The lake occupies a relatively pristine, non-industrialized basin, and therefore the increased metal fluxes might be related to long-distance aeolian transport of trace metals.

Formation of annually laminated sediments in Summit Lake, White Pass, British Columbia is controlled by runoff generated by snowpack and glacier melt and major rainfall events. The 700-yr varve record is divided into two subannual series (early and late) based on sedimentological criteria and sedimentary structures within each varve. A comparison of recent subannual laminae with nearby meteorological records supports the interpretation they are formed by river discharge events generated by major snow and glacier melt events and large late-summer rainfall events. A significant correlation exists between the late subannual thickness series and the size of the largest rainfall events in late summer. The long record indicates there was an abrupt increase in the thickness and frequency of major rainfall-induced sedimentary events at the end of the seventeenth century. In addition, the frequency of laminae generated by early runoff events also increased. However, early subannual varve thickness component remains statistically the same as the thickness prior to the end of the seventeenth century. This suggests the change in varve thickness at this time is due to increases in major late-summer rainfall frequency rather than increased sediment availability caused by regional Little Ice Age glacier advances.

Coupled records of Sr/Ca and oxygen isotope ratios (δ18O) of coral skeletons have been used to produce quantitative estimates of paleo-sea surface temperature (SST) and δ18O of surface seawater that can in some cases be converted to sea surface salinity (SSS). Two fossil corals from Kikai Island in the subtropical northwestern Pacific, a location affected by East Asian summer and winter monsoons, were analyzed to investigate differences between mid-Holocene and present-day SST and SSS. At 6180 cal yr BP, SSTs were roughly the same as today, both in summer and winter; δ18Oseawater and SSS values were higher both in summer (+ 0.5‰, +1.1 psu) and in winter (+ 0.2‰, + 0.6 psu) than modern values. At 7010 cal yr BP, SSTs were slightly cooler both in summer and winter (−0.8 and −0.6 °C), whereas δ18Oseawater and SSS had higher values in summer (+ 0.3‰, + 0.6 psu) and in winter (+ 0.8‰, + 1.9 psu) than present-day values. These results are consistent with other marine records for the mid-Holocene of the low and midlatitudes in the northwestern Pacific. Such regional conditions indicate that the East Asian summer and winter monsoons were more intense in the mid-Holocene, which was likely a function of the mid-Holocene insolation regime.

A high-resolution, well-dated dinoflagellate cyst record from a lagoon of the southeastern Swedish Baltic Sea reveals climate and hydrological changes during the Holocene. Marine dinoflagellate cysts occurred initially at about 8600 cal yr BP, indicating the onset of the Littorina transgression in the southeastern Swedish lowland associated with global sea level rise, and thus the opening of the Danish straits. Both the species diversity and the total accumulation rates of dinoflagellate cysts continued to increase by 7000 cal yr BP and then decreased progressively. This pattern reveals the first-order change in local sea level as a function of ice-volume-equivalent sea level rise versus isostatic land uplift. Superimposed upon this local sea level trend, well-defined fluctuations of the total accumulation rates of dinoflagellate cysts occurred on quasi-1000- and 500-yr frequency bands particularly between 7500 and 4000 cal yr BP, when the connection between the Baltic basin and the North Atlantic was broader. A close correlation of the total accumulation rates of dinoflagellate cysts with GISP2 ice core sea-salt ions suggests that fluctuations of Baltic surface conditions during the middle Holocene might have been regulated by quasi-periodic variations of the prevailing southwesterly winds, most likely through a system similar to the dipole oscillation of the modern North Atlantic atmosphere.

Late glacial scenarios of ice retreat and biogeography databases constrain the dispersal routes of obligate freshwater fishes into Atlantic Canada and Maine. Evidence indicates glacial ice covered the present-day mainland and offshore islands at 18,000 14C yr before present. Possible refugia for extirpated freshwater fishes were the exposed outer edge of the Grand Banks (east), exposed Georges Bank (south-Atlantic Refugium), and the Mississippi Refugium in the west. It is improbable that the region was recolonized from the offshore refugia. Rather, fishes recolonized from the east via the upper St. Lawrence River valley into the upper Saint John River, Maine (Lake Madawaska) from 11,000 to 12,000 14C yr BP. The short period of entry resulted in the low diversity of obligate freshwater species in the region. Lake Madawaska was breached and dispersal continued into the remainder of the region after 8000 14C yr BP. By 6000 14C yr BP, access routes to the east along low-lying coastal zones were blocked by rising sea levels, which isolated Prince Edward Island, Cape Breton Island, and most probably Nova Scotia. Natural dispersal across the region appeared complete by this time.

At least two episodes of glacial erosion of the Chukchi margin at water depths to ∼ 450 m and 750 m have been indicated by geophysical seafloor data. We examine sediment stratigraphy in these areas to verify the inferred erosion and to understand its nature and timing. Our data within the eroded areas show the presence of glaciogenic diamictons composed mostly of reworked local bedrock. The diamictons are estimated to form during the last glacial maximum (LGM) and an earlier glacial event, possibly between OIS 4 to 5d. Both erosional events were presumably caused by the grounding of ice shelves originating from the Laurentide ice sheet. Broader glaciological settings differed between these events as indicated by different orientations of flutes on eroded seafloor. Postglacial sedimentation evolved from iceberg-dominated environments to those controlled by sea-ice rafting and marine processes in the Holocene. A prominent minimum in planktonic foraminiferal δ18O is identified in deglacial sediments at an estimated age near 13,000 cal yr BP. This δ18O minimum, also reported elsewhere in the Amerasia Basin, is probably related to a major Laurentide meltwater pulse at the Younger Dryas onset. The Bering Strait opening is also marked in the composition of late deglacial Chukchi sediments.

In the central Great Plains of North America, loess stratigraphy suggests that climate during the late Pleistocene was cold and dry. However, this record is discontinuous, and there are few other records of late-Pleistocene conditions. Cobb Basin, located on the northern edge of the Nebraska Sand Hills, contains lacustrine sediments deposited during Marine Isotope Stage 3, beginning approximately 45,000 cal yr BP and continuing for at least 10,000 yr. The lake was formed by a dune dam blockage on the ancient Niobrara River, and its deposits contain a diatom record that indicates changes through time in lake depth driven by changes in effective moisture. During the earliest stages of lake formation, the climate was arid enough to mobilize dunes and emplace dune sand into a blocking position within the Niobrara streambed. Diatom assemblages suggest that lake-level was shallow at formation, increased substantially during a wet interval, and then became shallow again, as arid conditions resumed. By about 27,000 cal yr BP the lake was filled, and a shallow ephemeral river occupied the basin.

Constancy in predator/prey ratio (PPR) is a controversial issue in ecological research. Published reports support both constancy and inconstancy of the ratio in animal communities. Only a few studies, however, specifically address its course through time. Here we study the course of predator/prey ratio in communities of large Plio-Pleistocene mammals in Italy. After controlling for taphonomic biases, we find strong support for PPR inconstancy through time. Extinction, dispersal events, and differences in body size trends between predators and their prey were found to affect the ratio, which was distributed almost bimodally. We suggest that this stepwise dynamic in PPR indicates changes in ecosystem functioning. Prey richness was controlled by predation when PPR was high and by resources when PPR was low.

Vegetation inherited from a Pliocene subtropical climate evolved through obliquity oscillations and global cooling leading to modern conditions. An integrated, highly time-resolved record of pollen and stable isotopes (δ18O and δ13C of Globigerina bulloides) was obtained to understand vegetation responses to Early Pleistocene climate changes. Continental and marine responses are compared in the Central Mediterranean region with a particular consideration of environmental changes during anoxic events.

Pollen data illustrate vegetation dynamics as follows: [1] development of mesothermic elements (warm and humid conditions); [2] expansion of mid- and high-altitude elements (cooler but still humid conditions); and [3] strengthening of steppe and herb elements (cooler and dry conditions). These successions correlate with precession. δ18O variations recorded by Globigerina bulloides define two cycles (MIS 43-40) related to obliquity. At northern low- to mid-latitudes, the pollen signal records temperature and wetness changes related to precession even during global climate changes induced by obliquity. This may result in unexpected increasing wetness during glacial periods, which has to be considered specific to the Central and Eastern Mediterranean region. Lastly, an analysis of anoxic events reveals that enhanced runoff is indicated by increasing frequency of the riparian trees Liquidambar and Zelkova.

Relict soils provide insights into Quaternary soil formation and erosion on the Edwards Plateau of central Texas and into soil-forming processes in karst terranes. Late Quaternary climate-driven soil erosion produced a mosaic of thick and thin soils on the Edwards Plateau landscape. Thick soils on uplands of the Edwards Plateau are interpreted to be relicts of a formerly more extensive soil cover that was eroded during the late Pleistocene to middle Holocene. The relict, thick soils are silicate-rich and most commonly overlie the relatively silicate-poor Cretaceous Edwards Limestone, which supports the idea that the thick soils did not form from weathering of the underlying limestone. Other potential sources of silicates for the relict soils include dust, alluvial sediments, and the Del Rio Clay, a stratigraphically higher but locally eroded clay-rich unit. Here we investigate the geographic distribution, texture, clay-sized mineralogy, rare earth element geochemistry, and neodymium isotope composition of the relict soils. We have found that the relict, thick soils are deeply weathered soils that occur dominantly over the Edwards Limestone and have a high clay content and a neodymium isotope composition that is similar to that of the Del Rio Clay. Thus, we propose that in situ weathering of the Del Rio Clay, along with partial weathering of the upper portion of the underlying Edwards Limestone produced thick chert- and clay-rich soils over resistant limestone. In areas like the Edwards Plateau, where pure limestones are interbedded with clay-rich strata, the overlying clay-rich strata must be considered as a possible silicate source to soils on pure limestone bedrock.

In this study we utilize marine shell samples from two levels of historically uplifted sessile mollusk assemblages and raised wave-cut benches to evaluate the marine reservoir correction (ΔR) for the Pacific coast of central Japan. Elevation measurements of the uplifted marine shells indicate that the lower assemblage emerged during the 1923 Taisho Kanto earthquake (M7.9), whereas uplift of the upper assemblage is most likely but less confidently ascribed to the 1703 Genroku Kanto earthquake (M8.2). Radiocarbon dating of carefully selected samples from the upper and lower assemblages yielded very similar ΔR values of 82 ± 33 and 77 ± 32 yr, respectively. We regard the former ΔR value as a representative and more reliable value given the uncertainty in correlation of the upper assemblage with the 1703 earthquake. This result is consistent with previously reported ΔR values for the Pacific coast of south-central Japan and areas around the Sea of Japan that are influenced by warm ocean currents. Radiocarbon dating of coseismically uplifted shells can aid in estimating marine reservoir ages in the tectonically active Japan Islands.

Many Northern Hemisphere paleoclimatic records, including ice cores, speleothems, lake sediments, ocean cores and glacier chronologies, indicate an abrupt cooling event about 8200 cal yr BP. A new well-dated series of sediment cores taken from Brown's Lake, a kettle in Northeast Ohio, shows two closely spaced intervals of loess deposition during this time period. The source of loess is uncertain; however, it is likely from an abandoned drainage and former glacial lake basin located to the north of the stagnant ice topography that gave rise to the kettle lake. Strong visual stratigraphy, loss on ignition data and sediment grain size analyses dated with 3 AMS radiocarbon dates place the two intervals of loess deposition between 8950 and 8005 cal yr BP. The possibility of a two-phase abrupt climate change at this time is a finding that has been suggested in other research. This record adds detail to the spatial extent and timing as well as possible structure of the 8.2-ka abrupt climate change event.

Isotopic and pollen results from a marl lake (White Lake) in the Mid-Atlantic region of USA indicate the coupling of climate and vegetation changes. Oxygen isotopes of calcite from this site show multiple oscillations at millennial and centennial scales, including the Younger Dryas with 3‰ negative shifts in δ18O at 12.4–11.4 ka (1 ka = 1000 cal yr BP) and three cold events of magnitude 1–2‰ shifts during the Bølling–Allerød warm period (BOA) at 14.3–12.4 ka. Pollen data from the same core show nearly synchronous, close correspondence with isotope-inferred climate shifts, indicating rapid forest response to deglacial climate oscillations in southern New England. A plateau-like BOA is similar to other records around the North Atlantic Ocean.

To aid interpreting the source area of charcoal in lake-sediment records, we compare charcoal deposition from an experimental fire to predictions from a particle dispersal model. This provides both a theoretical framework for understanding how lake sediments reflect fire history and a foundation for simulating sediment-charcoal records. The dispersal model captures the two-dimensional patterns in the empirical data (predicted vs. observed r2 = 0.67, p < 0.001). We further develop the model to calculate the potential charcoal source area (PCSA) for several classes of fires. Results suggest that (1) variations in airborne charcoal deposition can be explained largely by the size of PCSAs relative to fire sizes and (2) macroscopic charcoal travels many kilometers, longer than suggested by dispersal data from experimental fires but consistent with dispersal data from uncontrolled fires.