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Abstract: We determined the distribution of lipids (n-alkanes and n-alkan-2-ones) in present-day peat-forming plants in the Roñanzas Bog in northern Spain. Consistent with the observation of others, most Sphagnum (moss) species alkanes maximized at C23, whereas the other plants maximized at higher molecular weight (C27 to C31). We show for the first time that plants other than seagrass and Sphagnum moss contain n-alkan-2-ones. Almost all the species analysed showed an n-alkan-2-one distribution between C21 and C31 with an odd/even predominance, maximizing at C27 or C29, except ferns, which maximized at lower molecular weight (C21–C23). We also observed that microbial degradation can be a major contributor to the n-alkan-2-one distribution in sediments as opposed to a direct input of ketones from plants. [Copyright &y& Elsevier]

Abstract: The n-alkane components of sediments were measured in 530 samples taken from a 107m-long core in the Padul Basin (Andalusia, Spain) covering from the Lower Pleistocene (ca. 1Ma) to the mid-Holocene (ca. 4.5kaB.P.). We show that the relative percentages of the high molecular weight n-alkanes (C27, C29 and C31) are useful tools to reconstruct the ancient vegetation and palaeoclimatological evolution of this basin. On the basis of these proxies, we distinguished twelve long-term climatic periods linked to alternating dry/humid scenarios: 6 Dry Episodes alternating with 5 Humid Episodes were interpreted in the Pleistocene record, together with a final Episode covering the Holocene. Dry scenarios produced the recession of forests and the development of grasses, whereas the inverse pattern was interpreted during humid phases. The good correlation with the Guadix-Baza Basin record showed that, in most cases, dry periods coexisted with warm conditions, while humid ones were linked to temperate-colder conditions. Only during the last long-term Dry Episode of the Pleistocene, which coincided with the end of the Last Glacial Period, did low temperatures concur. The relative percentages of the high molecular weight n-alkanes also indicate rapid changes in vegetation produced by short-scale arid cycles during the last Glacial Period (<100kaB.P.), which are linked to the Heinrich Events and Younger Dryas. This interpretation has been confirmed by previous pollen analysis performed in the Padul Basin. Likewise, a correlation was observed with Marine Isotope Stages (MIS). These results show that vegetation responds to long-term cycles (orbital scale) and millennial-scale global cycles. Therefore, climatic variations in the Padul Basin responded to global climatic changes, although with local climatic effects. Good correspondence was also observed with elemental, isotopic and other molecular organic proxies, thereby amplifying the palaeoclimatological knowledge of the Padul Basin during the Pleistocene, especially in some spans that were previously unclear. [Copyright &y& Elsevier]

• Based on alkane indices, three geochemical units (GU) were identified. • GUs represent major contribution of aquatic macrophytes or terrestrial plants. • Paleoenvironmental episodes (PE) produced oscillations in the marsh water level. • PEs were related to sea level and climatic changes, and recent tectonics. • Emersion led to increased amounts of short-chain and branched fatty acids. We reconstructed the paleoenvironmental conditions of the Mazarrón Basin during MIS 7 and MIS 1 based on their alkane and fatty acid contents, their mineralogy and the fossil content of an amino-acid-dated sediment sequence. The n- alkane and fatty acid indices proved to be excellent paleoenvironmental proxies for studying the paleo-hydrogeological and paleoclimatological evolution of this marshland. Three geochemical units (GUs) were identified from the abundance of the C 25 n -alkane and the ACL, TAR HC and P aq values, confirming the importance of phases with terrestrial plant input or aquatic macrophyte predominance. These GUs were used to define three paleoenvironmental episodes (PEs) during MIS 7. In PE7.1, the contribution of algal and aquatic macrophytes predominated in a temporarily flooded saline muddy plain. In PE7.2, the major contribution was from aquatic macrophytes (flooded marsh), although it was marked by episodes of emersion with greater terrestrial contribution. At the top of the MIS 7 record (PE7.3), there was a significant reduction in the water depth, with the main input deriving from terrestrial plants in a muddy alluvial plain. Six PEs were established during MIS 1 (Holocene), of which three predominately received organic matter derived from aquatic macrophytes, while the major contribution in the other three came from terrestrial plants. The two sets of PEs were linked to episodes of increased and decreased water level, respectively. This interpretation is consistent with the characteristics of the sediment facies, with PE1.1, 1.3 and 1.5 corresponding to a marsh with deeper water and a greater input of detrital materials, and PE1.2, 1.4 and 1.6 to a shallow environment with carbonates and gypsum deposits. Direct marine influence was limited, so the oscillations in the water level in the marsh were likely to be more related to climatic changes (drier/wetter phases) and recent tectonics than to large changes in sea level. Emersion led to degradation of the organic matter and enrichment in short-chain and branched saturated fatty acids. [ABSTRACT FROM AUTHOR]