Biomarker evidence for recent turf cultivation in Northeast Brazil (Lagoa do Boqueirao, RN State)

The first meter of sediment in Lagoa do Boqueirao [Rio Grande do Norte State (RN), Brazil] is characterized by low sedimentation rates over the period 1000 BC-1500 AD and a high sedimentation rate in the top 20 cm, corresponding to the last 10 years Several pentacyclic triterpene methyl ethers (PTMEs) such as taraxer-14-en-3 alpha-ol ME (crusgallin) and arbor-9(11)-en-3 beta-ol ME (cylindrin) occur in all the samples selected The major change in sedimentation rate recorded at 20 cm is accompanied by a change in PTME concentration and distribution Sediments deposited during the period 1000 BC-1500 AD contain PTMEs in low concentration (1 3 mu g/g sed), which could constitute a geochemical background of the grass that naturally developed in the catchment High PTME concentrations occur during the period 1996-2000. These result mainly from high concentrations of a compound tentatively assigned as arbor-8-en-3 beta ol ME, a potential diagenetic derivative of cylindrin The increase corresponds to the beginning of intensive cultivation of Cynodon dactylon and Zoysia japonica (arundoin and cylindrin producers), for the production of turf to cover Brazilian football stadiums and golf practices The results constitute a novel application of PTMEs to reconstruct land-use changes from lake sediment archives (C) 2009 Elsevier Ltd All rights reserve

Influence of climate changes on carbon accumulation in high Andean peatlands during the last 2 500 years

High-altitude cushion peatlands contain important records for high-resolution palaeoenvironmental studies, due to their high carbon accumulation rates and sensitivity to climatic changes. In this study, we present the paleoenvironmental history for the last 2 500 years based on the study of APA01 core, located in the headwaters of the Cachi river basin in Ayacucho. Radiocarbon dating by an accelerator mass spectroscopy (AMS) and by an elemental PDZ Europa ANCA-GSL analyzer to estimate particulated organic carbon were determined. Our results reveal changes in the peatlands during the Late Holocene. The palaeo climate varied significantly during the last 2 500 years. During the Medieval Climatic Anomaly (ACM) from around 1040 DC (Before Christ - BC, in spanish paper) to 1300 DC, the drier climate caused a slowdown in peat accumulation due to a reduced water table inducing a reduced organic matter production with a negative peak of carbon concentration. At the end of the Small Ice Age (PEH), between 1600 DC and 1890 DC, carbon accumulation showed high variability. Subsequently, the peat environment is mainly characterized by a considerable increase of carbon accumulation rates due to high sedimentation rates that is possibly related to the retreat of glaciers in the Central Andes. The recent drastic increase in the sedimentation rate and the reduction of carbon concentrations are a warning of a possible future decline of these ecosystems

Geochemistry of the earth's surface meeting GES-10

The Amazon is responsible for the higher discharge of water and sediment from continent to ocean in the world, but the Amazon basin embodies a large variety of regions with different seasonal climate, hydrological regimes and vegetation. Some of these compartments may be considered as the most critical zones because they encompass severe changes in the recent past and one of the geomorphological features mostly impacted by these changes are the Amazon floodplains. In this study we report data from a floodplain lake, Quistococha, in Peru. The sediment was dated, radiographed, described and bulk density, granulometry, mineral composition, and total organic carbon were determined. Two distinctive sedimentary depositional phases were identified. During the first one, between 6100 and 5600 cal years BP, Quistococha Lake was strongly influenced by the Amazon River constraining high sediment accumulation rates. The influence of Amazon River decreased and ceased around 5600 cal years BP, due to an avulsion of the River toward its present-day position. Between 5600 and 2600 cal years BP a gap in sedimentation is observed, probably related to the dry mid-Holocene climate conditions. The sedimentation re-started about 2600 cal years BP, now the lake is an isolated lake. (Abstract author

Hydroclimatic variability record from the Cabo Frio coast (Rio de Janeiro, Brazil) during the last 6500 yr

This study concerns a core collected in Brejo do Espinho's lagoon from Cabo Frio littoral (Brazil) submitted to dry influence of local upwelling controlled by north-cast trade winds from the South Atlantic and particularly strengthened during El Nino events. Diatoms study supported by sedimentological and isotopic analyses shows dry phases infrequent before 4000 yr, a highly variable climatic phase between 3600 and 2900 yr and from 2400 yr onward a dryness enhancement

Holocene land cover dynamics in the Curuai Floodplain inferred from lacustrine biomarkers

This study on Curuai Floodplain (Central Amazonia) sediments (last 5600 cal yr BP) focused in Rock-Eval [RE; hydrogen (HI) and oxygen (OI) indices, Tmax, S2 curve and TpS2], organic petrography and molecular biomarkers [n-alkanes, hopanes, pentacyclic triterpene methyl ethers (PTMEs) and derivatives of pentacyclic triterpenes such as des-A-lupane and aromatic derivatives] analyses. Between 5600 and 5100 cal yr BP, the environment was waterlogged and dominated by emersed plants (Paq 0.27-0.38). The influence of the Amazon River was low. Terrestrial vs aquatic ratio (T/A, similar to 0.8), CPI values (3-4) and high contents of PTME (0.22-1.54 mu g/g sed) and aromatics (21-53 mu g/g sed) indicated a strong contribution of terrestrial material and anoxic OM deposition conditions. Between 5100 and 5000 cal yr BP more humid conditions due to heavier rainfalls were observed. Early in this period, terrestrial biomarker contents (253 mu g/g sed of aromatics, Paq similar to 0.17) increased due to input of watershed erosion material. This provoked a rapid burial and good preservation of terrestrial OM (CPI 3-4.5). From 5000 cal yr BP a strong sedimentation of carbonate minerals (OI similar to 1600 mg CO2.g(-1)) masked the OM signal and affecting RE parameters. Paq (similar to 0.18), T/A ratio (similar to 0.4) and the decrease of C-31 alpha beta/C-31 beta beta hopanes (1.18) indicate increasing aquatic conditions up to 2700 cal yr BP. CPI ratio (similar to 1.2) and degraded phytoclasts suggest intense degradation during transport to the sedimentation location. The PTMEs results showed that, from 3000 yr cal BP, the Poaceae genera were different from those found at the bottom (middle-Holocene), suggesting a change of vegetation. The last 600 cal yr BP were marked by the seasonal influence of the Amazon River; during periods of low water level, the organic petrography and CPI values (similar to 1.0) evidenced OM degradation and the return of rather drier conditions