Oregon 2100: projected climatic and ecological changes

Greenhouse climatic warming is underway and exacerbated by human activities. Future outcomes of these processes can be projected using computer models checked against climatic changes during comparable past atmospheric compositions. This study gives concise quantitative predictions for future climate, landscapes, soils, vegetation, and marine and terrestrial animals of Oregon. Fossil fuel burning and other human activities by the year 2100 are projected to yield atmospheric CO2 levels of about 600-850 ppm (SRES A1B and B1), well above current levels of 400 ppm and preindustrial levels of 280 ppm. Such a greenhouse climate was last recorded in Oregon during the middle Miocene, some 16 million years ago. Oregon’s future may be guided by fossil records of the middle Miocene, as well as ongoing studies on the environmental tolerances of Oregon plants and animals, and experiments on the biological effects of global warming. As carbon dioxide levels increase, Oregon’s climate will move toward warm temperate, humid in the west and semiarid to subhumid to the east, with increased summer and winter drought in the west. Western Oregon lowlands will become less suitable for temperate fruits and nuts and Pinot Noir grapes, but its hills will remain a productive softwood forest resource. Improved pasture and winter wheat crops will become more widespread in eastern Oregon. Tsunamis and stronger storms will exacerbate marine erosion along the Oregon Coast, with significant damage to coastal properties and cultural resources

Soil organic matter decomposition and turnover in a tropical Ultisol: evidence from δ¹³C, δ¹⁵N and geochemistry

Soil organic matter (SOM), leaf litter, and root material of an Ultisol from the tropical rainforest of Kakamega, Kenya, were analyzed for stable carbon (delta-13C) and nitrogen (delta-15N) isotopic values as well as total organic carbon (TOC) and total nitrogen (TN) contents in order to determine trends in SOM decomposition within a very well-developed soil under tropical conditions. In addition, we quantified mineralogy and chemistry of the inorganic soil fraction. Clay mineralogical variation with depth was small and the abundance of kaolin indicates intense weathering and pedoturbation under humid tropical conditions. The soil chemistry was dominated by silica, aluminium, and iron with calcium, potassium, and magnesium as minor constituents. The relative depletion of base cations compared with silica and aluminium is an indicator for intense weathering and leaching conditions over long periods of time. Depth profiles of delta-13C and delta-15N showed a distinct enrichment trend down profile with a large (average 13Delta-C = 5.0 per mil average 15Delta-N = 6.3 per mil) and abrupt offset within the uppermost 10-20 cm of the soil. Isotopic enrichment with depth is commonly observed in soil profiles and has been attributed to fractionation during decomposition. However, isotopic offsets within soil profiles that exceed 3 per mil are usually interpreted as a recent change from C4 to C3 dominated vegetation. We argue that the observed isotopic depth profiles along with data from mineralogy and chemistry of the inorganic fraction from the Kakamega Forest soil are a result of intense weathering and high organic matter turnover rates under humid tropical conditions.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

Geochemistry (delta13C, delta15N, 13C NMR) and residence times (14C and OSL) of soil organic matter from red-brown earths of South Australia: implications for soil genesis

Soil forming processes important to the development of Red-Brown Earths (duplex soils) in southeastern Australia have been investigated by a combination of techniques, including isotopic (δ13C, δ15N, 14C), spectroscopic (13C NMR, MIR), optically stimulated luminescence dating (OSL) and phytolith analyses. A distinct increase in clay content, corresponding changes in the abundance of major elements, as well as changes in organic chemistry (13C NMR), stable isotope trends (δ13C, δ15N), and phytolith abundance, are apparent in the transition from the very sandy A horizon to the clayey B horizon in three soil profiles from the Coonawarra–Padthaway region of South Australia. These structural and chemical changes between the A and the B horizons are associated with an abrupt increase in both 14C (bulk soil organic matter) and OSL burial ages of individual quartz grains. While previous interpretations have promoted the formation of duplex red-brown earths as due to clay illuviation, we propose a two-stage soil formation, which may be related to paleoclimatic changes during and after the Last Glacial Maximum. Our data suggest that a major part of the A horizon was aeolian derived and was deposited over the last 10,000 years, whereas much of the B horizon, although originally aeolian, has been extensively modified over much longer periods of time (tens of thousands of years). These results indicate the influence of different substrates (sandy versus clayey), process and time for formation as well as paleoclimatic history on the physical properties of the soil and the chemical characteristics of the organic matter within the soil profile

A cautionary tale from down under: dating the Black Creek Swamp megafauna site on Kangaroo Island, South Australia

The extinction of the Australian megafauna is presently one of the most hotly contested debates in Australian Quaternary sciences. [Roberts et al., 2001. U-series and ESR analyses of bones and teeth relating to the human burials from Skhul. Journal of Human Evolution. 49, 316-334.] proposed contentiously that the megafauna went extinct within a short time period somewhere in the range of 39,000-52,000 years ago. Being tucked away at the continental fringe, Kangaroo Island offers an ideal refuge for the megafauna for survival. Initial radiocarbon analyses of soil organic matter, ESR of teeth and OSL of quartz provided consistent age assessments, which strongly suggested that the site could be as young as 20,000 years. However, it turned out that the sediments contained extreme disequilibria in the U-decay chain, with 230Th/238U ratios in the range of 0.3 and 210Pb/238U ratios around 0.1. Furthermore, in situ laser ablation analysis revealed that uranium migrated into the teeth at a very late stage during the Holocene. Contrary to expectations, insoluble organic matter was considerably younger than the soluble fraction. After combining all analytical results, a complex geochemical history can be reconstructed, implying that organic matter and large amounts of uranium were injected into the megafauna-bearing layers around the Last Glacial Maximum. When combined U-series/ESR dates are calculated, they all turn out older than the proposed extinction window. This was confirmed by a subsequent OSL study. The Black Creek Swamp site is another example that the parametric early (EU) and linear U-uptake (LU) ESR age models, particularly when applied to teeth with high-U concentrations, may provide completely unreliable age results

Application of sedimentary and chronological analyses to refine the depositional context of a Late Pleistocene vertebrate deposit, Naracoorte, South Australia

Cave deposits of infill sediments and associated vertebrate fossils provide a valuable source of information on terrestrial palaeoenvironments, climatic conditions and palaeocommunities. In the deposits of the Naracoorte Caves World Heritage Area, such records span the last 500 ka and are renowned for their rich, diverse vertebrate assemblages. Previous research into the Grant Hall deposit of Victoria Fossil Cave suggested that it may preserve the only peak last interglacial (ca. 125 ka) faunal community within the World Heritage Area. The current work tested this existing model for the age of faunal remains from Grant Hall using multiple techniques. Physical and geochemical properties of the visually homogeneous sediments were analysed at regular intervals through the sequence to establish meaningful stratigraphic divisions and sediment provenance. Optically stimulated luminescence dating of individual quartz grains indicates that sediments accumulated in Grant Hall from 93 ± 8 to 70 ± 5 ka. Minimum ages provided by U/Th dating of fossil teeth (72.3 ± 2.2 to 38.2 ± 0.8 ka) are consistent with the luminescence chronology, and show that the deposit represents a more recent faunal accumulation than previously modelled for the site. U/Th ages on calcite straws within the deposit are significantly older than the sediments and fossil teeth (>500 to 186.4 ± 1 ka). As such they provide no further constraint on the chronology of the deposit but do indicate that speleothem deposition was active over much of the Middle Pleistocene. Sedimentary analyses resulted in the identification of five depositional units, contrasting with previous divisions which were based only on visual observation of the sedimentary sequence. Sediments within each unit are broadly classified as sandy silts with soil structures and may be indirectly derived from the lunettes of nearby Bool Lagoon, although their ultimate provenance is unknown. As a result of this work, palaeoenvironmental reconstruction based on fossil remains in the deposit may be more accurately related to prevailing climatic and environmental conditions at the time of accumulation. It also contributes to an understanding of the temporal occurrence of regional vertebrate faunas through the Late Pleistocene, reinforcing the value of developing stratigraphically constrained chronologies for cave deposits based on multiple techniques