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Comparison of organic and palynological proxies for biomass burning and vegetation
No full textContinental fire and vegetation history have been widely studied in sedimentary archives using palynological proxies (i.e. charcoal abundance and the pollen assemblage) and organic proxies (i.e. the anhydrosugars levoglucosan and it isomers, and plant-wax n-alkanes), but rarely in concert. Here, we compared palynological and organic proxies to reconstruct fire and vegetation history in a sediment core from Lake Allom on Fraser Island, Australia, covering the last 5.4 kyrs. We found that anhydrosugar and microscopic charcoal accumulation rates had similar trends, while trends in macroscopic charcoal accumulation rates were different. This was attributed to the short distance over which macroscopic charcoal is transported compared to microscopic charcoal and anhydrosugars. Furthermore, differences in fire regime and combusted types of vegetation may also explain the differences in levoglucosan and charcoal accumulation rates in lacustrine sediments. Moreover, we found that the ratios between anhydrosugars seem to be governed by combustion conditions and not by type of burned vegetation. Long chain n-alkane accumulation rates and stable isotope compositions showed similar patterns as the pollen assemblage throughout the last 5.4 kyrs, with both representing the local vegetation history. Collectively, our results showed that in the period between 5.4 and 4 ka, biomass burning was low on Fraser Island, while at 4 ka, fire occurrence started to increase, in absence of changes in vegetation and hydrology. Therefore, we suggest that increased fire activity on Fraser Island around 4 ka might have been caused by human-lit biomass burning, since aboriginals settled on Fraser Island around this time
Ligands Phantastic
No full textDFe and DFe-binding organic ligands were measured using Competing Ligand Exchange Cathodic Stripping Voltammetry (CLE-CSV) with TAC as competing ligand in the vicinity of the Ross Sea during a cruise between 20 December 2013 and 5 January 2014.
DFe-binding organic ligand concentrations were highest in the Ross Sea Polynya and the Antarctic Circumpolar Current west of the Ross Sea, in association with seasonal phytoplankton blooms.
Phytoplankton sources and sinks of DFe-binding organic ligands are probably related to seasonal differences in the stage of the bloom. In 39% of the samples, two DFe-binding organic ligand groups were distinguished based on the difference in binding strength. The distinction was especially clear in the RSP and in the West ACC (54 and 77% of the samples, respectively) where blooms occurred and much less in the East ACC and ice covered eastern part of the Ross Sea (15 and 10% of the samples, respectively)
Sediment oxygen concentrations in Iberian Margin sediments
No full textComparison of in situ and shipboard techniques to measure oxygen distribution in deep sea sediment reveals non-steady state behavior when profiles are measured shipboard. This suggest a boosting of microbial activity in the surface sediment, probably due to the exudation of highly reactive organics by in fauna due to decompression