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181.
Alexander M. Heyng Christoph Mayr Andreas Lücke Holger Wissel Bernd Striewski 《Journal of Paleolimnology》2014,51(4):485-497
Isotopic records of aquatic cellulose are becoming increasingly important for palaeohydrological reconstructions, but widespread application of this climate proxy is hampered by minerogenic contamination that affects oxygen isotope measures in cellulose. Few records of isotopes in aquatic cellulose are available from palaeoclimate archives in the Southern Hemisphere. In this study, we used a new bulk cellulose extraction method and determined the oxygen (δ18O) and carbon (δ13C) isotope values in cellulose from a Holocene lake sediment core segment (7.2–1.1 cal ka BP) from Lake Pupuke, Auckland, New Zealand. Isotope values from modern, potential sources of sedimentary cellulose revealed the aquatic origin of the cellulose extracted from the core, and hence enabled inference of past lake water δ18O values from the δ18O of measured cellulose in the core. A shift to a more positive water balance in the lake was identified around 2.8 cal ka BP by a decrease in inferred lake water δ18O values. At that time, greater epilimnetic primary productivity is indicated by the higher δ13C values of sedimentary cellulose. Greater divergence between the δ13C values of cellulose and bulk organic matter suggests stronger stratification of the lake, likely caused by greater freshwater input. We discuss a possible link to a solar minimum that occurred at that time. 相似文献
182.
Evaluating Light Availability,Seagrass Biomass,and Productivity Using Hyperspectral Airborne Remote Sensing in Saint Joseph’s Bay,Florida 总被引:1,自引:0,他引:1
Victoria J. Hill Richard C. Zimmerman W. Paul Bissett Heidi Dierssen David D. R. Kohler 《Estuaries and Coasts》2014,37(6):1467-1489
Seagrasses provide a number of critical ecosystem services, including habitat for numerous species, sediment stabilization, and shoreline protection. Ariel photography is a useful tool to estimate the areal extent of seagrasses, but recent innovations in radiometrically calibrated sensors and algorithm development have allowed identification of benthic types and retrieval of absolute density. This study demonstrates the quantitative ability of a high spatial resolution (1 m) airborne hyperspectral sensor (3.2 nm bandwidth) in the complex coastal waters of Saint Joseph’s Bay (SJB). Several benthic types were distinguished, including submerged and floating aquatic vegetation, benthic red algae, bare sand, and optically deep water. A total of 23.6 km2 of benthic vegetation was detected, indicating no dramatic change in vegetation area over the past 30 years. SJB supported high seagrass density at depths shallower than 2 m with an average leaf area index of 2.0?±?0.6 m2 m?2. Annual seagrass production in the bay was 13,570 t C year?1 and represented 41 % of total marine primary production. The effects of coarser spatial resolution were investigated and found to reduce biomass retrievals, underestimate productivity, and alter patch size statistics. Although data requirements for this approach are considerable, water column optical modeling may reduce the in situ requirements and facilitate the transition of this technique to routine monitoring efforts. The ability to quantify not just areal extent but also productivity of a seagrass meadow in optically complex coastal waters can provide information on the capacity of these environments to support marine food webs. 相似文献
183.
Dominik Höyng Fernando Mazo D’Affonseca Peter Bayer Edson Gomes de Oliveira José Alexandre J. Perinotto Fábio Reis Holger Weiß Peter Grathwohl 《Environmental Earth Sciences》2014,71(7):3081-3094
The Guarani aquifer system (GAS) represents one of the biggest aquifers in the world and is the most relevant groundwater resource in South America. For the first time, by combining field and laboratory measurements, a high-resolution aquifer analog model of fluvial–aeolian sediments of the GAS in São Paulo State (Brazil) is constructed. Three parallel sections of frontal outcrops, 28 m × 5.8 m, and two parallel sections of lateral outcrops, 7 m × 5.8 m, are recorded during open-pit mining of sandy sediments and describe in detail the three-dimensional distribution of the local lithofacies and hydrofacies. Variations of hydraulic conductivity, K, and porosity, n, are resolved on the centimeter scale, and the most permeable units of the fluvial–aeolian facies association are identified. The constructed aquifer analog model shows moderate hydraulic heterogeneity and a mean K value of 1.36 × 10?4 m/s, which is greater than the reported range of K values for the entire GAS in São Paulo State. The results suggest that the examined sedimentary unit constitutes a relevant portion of the GAS in São Paulo State in the context of groundwater extraction and pollution. Moreover, the constructed aquifer analog is considered an ideal basis for future numerical model experiments, aiming at in-depth understanding of the groundwater flow and contaminant transport patterns at this GAS portion or at comparable fluvial–aeolian facies associations. 相似文献
184.
Holger Pedersen 《Meteoritics & planetary science》2013,48(6):1091-1095
Several pallasites are known to have formed strewn fields with multiple fragments. Therefore, it seems possible that the famous Krasnojarsk pallasite—the Pallas Iron of 687 kg—could have been accompanied by one or more additional fragments that had not been recovered due to incomplete observations from the overgrown and remote place of fall. During a survey for literature accounts of distant fragments in such a hypothetical strewn field, a report of native iron was found, dating to 1847. The fragments of nickel‐free iron—amounting to at least a few kg—had been recovered 1836–1843 during placer gold mining north of the Angara River. The position of these finds is coincident with Burovaya, Murozhna, and Uderei, the three known fragments of the pseudometeorite Angara, all collected in 1885. 相似文献
185.
Stefan Hagemann Holger Göttel Daniela Jacob Philip Lorenz Erich Roeckner 《Climate Dynamics》2009,32(6):767-781
For the fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC), the recent version of the coupled
atmosphere/ocean general circulation model (GCM) of the Max Planck Institute for Meteorology has been used to conduct an ensemble
of transient climate simulations These simulations comprise three control simulations for the past century covering the period
1860–2000, and nine simulations for the future climate (2001–2100) using greenhouse gas (GHG) and aerosol concentrations according
to the three IPCC scenarios B1, A1B and A2. For each scenario three simulations were performed. The global simulations were
dynamically downscaled over Europe using the regional climate model (RCM) REMO at 0.44° horizontal resolution (about 50 km),
whereas the physics packages of the GCM and RCM largely agree. The regional simulations comprise the three control simulations
(1950–2000), the three A1B simulations and one simulation for B1 as well as for A2 (2001–2100). In our study we concentrate
on the climate change signals in the hydrological cycle and the 2 m temperature by comparing the mean projected climate at
the end of the twenty-first century (2071–2100) to a control period representing current climate (1961–1990). The robustness
of the climate change signal projected by the GCM and RCM is analysed focussing on the large European catchments of Baltic
Sea (land only), Danube and Rhine. In this respect, a robust climate change signal designates a projected change that sticks
out of the noise of natural climate variability. Catchments and seasons are identified where the climate change signal in
the components of the hydrological cycle is robust, and where this signal has a larger uncertainty. Notable differences in
the robustness of the climate change signals between the GCM and RCM simulations are related to a stronger warming projected
by the GCM in the winter over the Baltic Sea catchment and in the summer over the Danube and Rhine catchments. Our results
indicate that the main explanation for these differences is that the finer resolution of the RCM leads to a better representation
of local scale processes at the surface that feed back to the atmosphere, i.e. an improved representation of the land sea
contrast and related moisture transport processes over the Baltic Sea catchment, and an improved representation of soil moisture
feedbacks to the atmosphere over the Danube and Rhine catchments. 相似文献