Search

Records of the spatial and temporal variability of Arctic Ocean sea ice are of significance for understanding the causes of the dramatic decrease in Arctic sea-ice cover of recent years. In this context, the newly developed sea-ice proxy IP25, a mono-unsaturated highly branched isoprenoid alkene with 25 carbon atoms biosynthesized specifically by sea-ice associated diatoms and only found in Arctic and sub-Arctic marine sediments, has been used to reconstruct the recent spatial sea-ice distribution. The phytoplankton biomarkers 24S-brassicasterol and dinosterol were determined alongside IP25 to distinguish ice-free or permanent ice conditions, and to estimate the sea-ice conditions semi-quantitatively by means of the phytoplankton-IP25 index (PIP25). Within our study, for the first time a comprehensive data set of these biomarkers was produced using fresh and deep-frozen surface sediment samples from the Central Arctic Ocean proper (>80°N latitude) characterised by a permanent ice cover today and recently obtained surface sediment samples from the Chukchi Plateau/Basin partly covered by perennial sea ice. In addition, published and new data from other Arctic and sub-Arctic regions were added to generate overview distribution maps of IP25 and phytoplankton biomarkers across major parts of the modern Arctic Ocean. These comprehensive biomarker data indicate perennial sea-ice cover in the Central Arctic, ice-free conditions in the Barents Sea and variable sea-ice situations in other marginal seas. The low but more than zero values of biomarkers in the Central Arctic supported the low in-situ productivity there. The PIP25 index values reflect modern sea-ice conditions better than IP25 alone and show a positive correlation with spring/summer sea ice. When calculating and interpreting PIP25 index as a (semi-quantitative) proxy for reconstructions of present and past Arctic sea-ice conditions from different Arctic/sub-Arctic areas, information of the source of phytoplankton biomarkers and the possible presence of allochthonous biomarkers is needed, and the records of the individual biomarkers always should be considered as well.

To determine how and what kind of marine-sourced biomarkers are transported and deposited on land by tsunami, we collected and analyzed samples of the 2011 Tohoku-oki tsunami deposits and the underlying and overlying soil at Sendai and Odaka, in northeast Japan. Characteristic hydrocarbons, such as short-chain n-alkanes, pristane, and phytane, were detected only in soil layers 0–2 cm below the tsunami deposits at both sites. Dinosterol originated from dinoflagellates was detected in a mud layer overlying sand deposits in Odaka. Such characteristic biomarkers were not detected in soil layers deeper than 2 cm beneath the tsunami deposits at either site, and none was found in the surface soil layer overlying the tsunami deposit in Odaka. Therefore, it is probable that the biomarkers were transported and deposited by the tsunami. The sand layer was highly permeable and low in clay or organic matter to which biomarkers could bind. Any biomarkers deposited with the sand probably leached into the underlying soil or were found in sediments richer in clay and organic matter such as tsunamigenic mud. Sediment samples were collected more than 2 years after the tsunami, indicating that the marine-sourced biomarkers were preserved for at least 2 years in the soil. In addition, a comparative analysis of sediment samples collected earlier indicated that characteristic biomarkers did not remain in the sand layer 3 months after the tsunami. These findings show the potential of using biomarkers as proxies to identify marine-sourced deposits on coastal land.

Methoxylated (MeO-) and hydroxylated (OH-) polybrominated diphenyl ethers (PBDEs) in marine environments have been of increasing concern due to their potential ecological toxicities and worldwide occurrence. However, few reports have been referred to their occurrence and distributions in marine sediments despite large numbers of studies on marine organisms have been reported. In the present paper, nine MeO-BDEs, ten OH-BDEs and three phytoplankton biomarkers (PBs) of brassicasterol, dinosterol and alkenones have been measured in surface sediments from the East China Sea. 6-MeO-BDE47, 2'-MeO-BDE68 and 6-OH-BDE47 were predominant congeners, ranging from 5.2 to 599.5 pg g(-1)dw, 5.2 to 562.4 pg g(-1)dw, and 11.4 to 129.1 pg g(-1)dw, respectively. Their spatial patterns all presented a seaward increasing trend and higher levels of these compounds were mainly concentrated in the outer shelf influenced by the Kuroshio Current. The patterns further prove that these ortho-substituted MeO-BDEs and OH-BDEs in marine sediments are natural compounds. Furthermore, alkenones also presented a seaward increasing trend. Statistical analysis shows that there are significant correlations between MeO-BDEs, OH-BDEs and alkenones, impling the potential of coccolithophorids for producing these natural compounds and their global distribution, especially in open oceans. Comparison between TOC and the ratio of 6-MeO-BDE47/6-OH-BDE47 suggests that TOC should be a potential controlling factor of the conversion between MeO-BDE and OH-BDE pairs.

The South China Sea (SCS) is one of the largest marginal seas in the world and it plays an important role in regional climate change and carbon cycles. However, mechanisms of glacial–interglacial phytoplankton productivity changes remain under-studied, especially for the southeastern SCS. In this study, the productivity record for the southeastern SCS (core MD972142) over the last 185 kyr was generated using multiple biomarkers, including C37 alkenones (C37:2 + C37:3), brassicasterol, dinosterol, and alkyl diols (C30 + C32) as productivity proxies for haptophytes, diatoms, dinoflagellates, and eustigmatophytes (and diatoms), respectively. All biomarker contents indicate higher individual as well as total phytoplankton productivities during peak glacials than during interglacials. Our records afford a better constraint on spatial pattern of glacial productivity changes, which suggest that both the southeastern and northern SCS glacial productivity increases were controlled by the stronger East Asian winter monsoon (EAWM), which brought more nutrients to the surface through stronger mixing of nutrient-rich deep waters. Biomarker ratios reveal a relatively stable phytoplankton community structure (PCS), but relative diatom productivity was higher during glacials. The PCS record is consistent with stronger EAWM forcing during glacials, which supplied nutrients to the surface with relatively stable composition. The decrease of C37 alkenones during the last 120 kyr is likely a global phenomenon, which could be related to the evolution of the haptophytes. In the SCS, this trend was also likely caused by changes of subsurface nutrient supply to the SCS, which significantly modulated the PCS by a gradual decrease of haptophyte contribution to total phytoplankton in the northern and southeastern SCS since MIS 5.

Ocean warming can modify the phytoplankton biomass on decadal scales. Significant increases in sea surface temperature (SST) and rainfall in the northwest of Australia over recent decades are attributed to climate change. Here, we used four biomarker proxies (TEX86 index, long‐chain n‐alkanes, brassicasterol, and dinosterol) to reconstruct approximately 60‐year variations of SST, terrestrial input, and diatom and dinoflagellate biomass in the coastal waters of the remote Kimberley region. The results showed that the most significant increases in SST and terrestrial input occurred since 1997, accompanied by an abrupt increase in diatom and dinoflagellate biomasses. Compared with the results before 1997, the average TEX86H temperature during 1997–2011 increased approximately 1°C, rainfall increased 248.2 mm, brassicasterol and dinosterol contents increased 8.5 and 1.7 times. Principal component analysis indicated that the warming SST played a more important role in the phytoplankton increase than increased rainfall and river discharge.

Phytoplankton productivity and community structure in marginal seas have been altered significantly during the past three decades, but it is still a challenge to distinguish the forcing mechanisms between climate change and anthropogenic activities. High time-resolution biomarker records of two 210Pb-dated sediment cores (#34: 28.5°N, 122.272°E; CJ12-1269: 28.861 9°N, 122.515 3°E) from the Min-Zhe coastal mud area were compared to reveal changes of phytoplankton productivity and community structure over the past 100 years. Phytoplankton productivity started to increase gradually from the 1970s and increased rapidly after the late 1990s at Site #34; and it started to increase gradually from the middle 1960s and increased rapidly after the late 1980s at Site CJ12-1269. Productivity of Core CJ12-1269 was higher than that of Core #34. Phytoplankton community structure variations displayed opposite patterns in the two cores. The decreasing D/B (dinosterol/brassicasterol) ratio of Core #34 since the 1960s revealed increased diatom contribution to total productivity. In contrast, the increasing D/B ratio of Core CJ12-1269 since the 1950s indicated increased dinoflagellate contribution to total productivity. Both the productivity increase and the increased dinoflagellate contribution in Core CJ12-1269 since the 1950–1960s were mainly caused by anthropogenic activities, as the location was closer to the Changjiang River Estuary with higher nutrient concentration and decreasing Si/N ratios. However, increased diatom contribution in Core #34 is proposed to be caused by increased coastal upwelling, with higher nutrient concentration and higher Si/N ratios.

We present a 3000-yr rainfall reconstruction from the Galapagos Islands that is based on paired biomarker records from the sediment of El Junco Lake. Located in the eastern equatorial Pacific, the climate of the Galapagos Islands is governed by movements of the Intertropical Convergence Zone (ITCZ) and the El Nino-Southern Oscillation (ENSO). We use a novel method for reconstructing past ENSO- and ITCZ-related rainfall changes through analysis of molecular and isotopic biomarker records representing several types of plants and algae that grow under differing climatic conditions. We propose that δD values of dinosterol, a sterol produced by dinoflagellates, record changes in mean rainfall in El Junco Lake, while δD values of C34 botryococcene, a hydrocarbon unique to the green alga Botryococcus braunii, record changes in rainfall associated with moderate-to-strong El Nino events. We use these proxies to infer changes in mean rainfall and El Nino-related rainfall over the past 3000 yr. During periods in which the inferred change in El Nino-related rainfall opposed the change in mean rainfall, we infer changes in the amount of ITCZ-related rainfall. Simulations with an idealized isotope hydrology model of El Junco Lake help illustrate the interpretation of these proxy reconstructions. Opposing changes in El Nino- and ITCZ-related rainfall appear to account for several of the largest inferred hydrologic changes in El Junco Lake. We propose that these reconstructions can be used to infer changes in frequency and/or intensity of El Nino events and changes in the position of the ITCZ in the eastern equatorial Pacific over the past 3000 yr. Comparison with El Junco Lake sediment grain size records indicates general agreement of inferred rainfall changes over the late Holocene.

Hydroxylated (OH-) and methoxylated (MeO-) polybrominated diphenyl ethers (PBDEs) have caused much concern because of their potential toxicity and worldwide distribution. These compounds are recently suggested to originate from the natural process in the ocean. However, their source remains highly controversial. In this study, we analyzed the contents of nine MeO-BDEs, ten OH-BDEs, and phytoplankton biomarkers (PBs) in two sediment cores collected from the East China Sea (ECS). The detection of 6-MeO-BDE-47, 2'-MeO-BDE-68, and 6-OH-BDE-47 have been reported since the 1920s, prior to the production of PBDEs. Significant relations were found between MeO/OH-BDEs and indicators of marine organic matters. The similar down-core variations and significant correlations between MeO/OH-BDEs and PBs suggest the possibility that phytoplankton produced these natural compounds. Laboratory incubation further demonstrates that phytoplanIcton can produce Me0-BDE5. Comparisons between the content ratios of 6-MeO-BDE-47/2'-MeO-BDE-68 and brassicasterol/dinosterol indicate that the signature of MeO-BDE5 is controlled by the phytoplankton community structure. (C) 2014 Elsevier Ltd. All rights reserved.

The study provides one of the first lines of evidence showing linkages between Antarctic phytoplankton abundance and composition in response to ENSO, based on historical reconstruction of sediment biomarkers. In addition to sediment biomarkers, field measured and remote sensing data of phytoplankton abundance were also recorded from Prydz Bay, Eastern Antarctica. Community structure of field measured phytoplankton showed significant El Nino/La Nina-related succession during 1990 to 2002. In general, the number of algae species decreased during El Nino and La Nina years compared to normal years. Austral summer monthly variation of remotely sensed chlorophyll-a (Chl-a), particulate organic carbon (POC), and sea surface temperature (SST) indicated that ENSO impacted the timing of phytoplankton blooms during 2007 to 2011. Phytoplankton blooms (indicated by Chl-a and POC) preceded the increases in SST during El Nino years, and lagged behind the SST increases during La Nina years. Stratigraphic record of marine sedimentary lipid (brassicasterol, dinosterol and alkenones) biomarkers inferred that the proportions of different algae (diatoms, dinoflagellates and haptophytes) changed significantly between El Nino and La Nina events. The relative proportion of diatoms increased, with that of dinoflagellates being decreased during El Nino years, while it was reversed during La Nina years.

A variety of lipid biomarkers were identified in sediments from El Junco Lake, Galapagos and their sources investigated for potential use in paleoclimate applications. A series of unusual sterols was also found, including 4α-methylgorgostanol, reported in only four species of dinoflagellates to date. We also tentatively assigned 22,23-methylene-4α-methyl-24-ethylcholest-5-en-3β-ol, the mass spectrum of which matched a sterol found in resting cysts of the dinoflagellate Peridinium umbonatum. In addition, we identified the novel sterol 4α,22,23,24-tetramethyl-5α-cholest-22E-en-3β-ol. Based on the unique sterol distribution, we hypothesize that a dinoflagellate from the genus Peridinium was the primary source of dinosterol and the novel sterols throughout the sediment record. The source specificity and abundance throughout the 3.7 m of recovered sediment make dinosterol an excellent target for hydrogen isotope analysis for use as a paleohydrological proxy in future studies. The abundant C30 and C32 1,ω20-diols and keto-ols, C29 9,10-diol and C29 1,ω9,ω10-triol likely derive from the ferns Azolla microphylla and Cyathea weatherbyana, while sources of the C30 1,ω16-diol and keto-ol, C32 1,ω18-diol and keto-ol, and the C30–C32 n-alken-1-ols are likely limited to aquatic microalgae. Due to their source specificity, these diol, triol, keto-ol, and n-alkenol biomarkers present further tools for studying past environmental and climatic change.

Sterols, a group of stable lipid compounds, are often used as biomarkers in marine biogeochemical studies to indicate sources of organic matter. In this study, sterols in 13 species of major bloom-forming algae in China, which belong to Dinophyceae, Bacillariophyceae, Ulvophyceae, and Pelagophyceae, were analyzed with gas chromatography-mass spectrometry (GC-MS) to test their feasibility in representing different types of harmful algal blooms (HABs). It was found that (24Z)-stigmasta-5,24-dien-3β-ol (28-isofucosterol) was a major sterol component in green-tide forming macroalga Ulva prolifera. In bloom-forming dinoflagellates Alexandrium spp., Prorocentrum micans and Scrippsiella trochoidea, (22E)-4α,23-dimethyl-5α-ergost-22-en-3β-ol (dinosterol) was detected in addition to cholest-5-en-3β-ol (cholesterol), (22E)-ergosta-5,22-dien-3β-ol, (22E)-stigmasta-5,22-dien-3β-ol and other minor sterol components. In brown-tide forming pelagophyte Aureococcus anophagefferens, (24E)-24-propylcholesta-5,24-dien-3β-ol ((24E)-24-propylidenecholesterol) and (24Z)-24-propylcholesta-5,24-dien-3β-ol ((24Z)-24-propylidenecholesterol) were detected together with cholesterol, (22E)-stigmasta-5,22-dien-3β-ol, stigmast-5-en-3β-ol and campest-5-en-3β-ol. Among the selected bloom-forming diatoms, Chaetoceros sp. and Pseudo-nitzschia spp. only produced cholesterol, while Cylindrotheca closterium produced solely (22E)-ergosta-5,22-dien-3β-ol. Sterol content in four bloom-forming algal species correlates well with their biomass or abundance. It's proposed that 28-isofucosterol could serve as a promising biomarker for green algae in green-tide studies. Dinosterol and (24Z)-24-propylidenecholesterol can be used as potential biomarkers to represent bloom-forming dinoflagellates and pelagophytes, while (22E)-ergosta-5,22-dien-3β-ol is not a good indicator for diatoms.

Dinoflagellates are key species in marine environments, but they remain poorly understood in part because of their large, complex genomes, unique molecular biology, and unresolved in-group relationships. We created a taxonomically representative dataset of dinoflagellate transcriptomes and used this to infer a strongly supported phylogeny to map major morphological and molecular transitions in dinoflagellate evolution. Our results show an early-branching position of Noctiluca, monophyly of thecate (plate-bearing) dinoflagellates, and paraphyly of athecate ones. This represents unambiguous phylogenetic evidence for a single origin of the group's cellulosic theca, which we show coincided with a radiation of cellulases implicated in cell division. By integrating dinoflagellate molecular, fossil, and biogeochemical evidence, we propose a revised model for the evolution of thecal tabulations and suggest that the late acquisition of dinosterol in the group is inconsistent with dinoflagellates being the source of this biomarker in pre-Mesozoic strata. Three distantly related, fundamentally nonphotosynthetic dinoflagellates, Noctiluca, Oxyrrhis, and Dinophysis, contain cryptic plastidial metabolisms and lack alternative cytosolic pathways, suggesting that all free-living dinoflagellates are metabolically dependent on plastids. This finding led us to propose general mechanisms of dependency on plastid organelles in eukaryotes that have lost photosynthesis; it also suggests that the evolutionary origin of bioluminescence in nonphotosynthetic dinoflagellates may be linked to plastidic tetrapyrrole biosynthesis. Finally, we use our phylogenetic framework to show that dinoflagellate nuclei have recruited DNA-binding proteins in three distinct evolutionary waves, which included two independent acquisitions of bacterial histone-like proteins.

Climate changes as well as the inherent properties of phytoplankton have important and complex effects on the ecology and biogeochemical cycles of the oceans. Dinoflagellates are often dominant groups in harmful algae blooms (HABs) and red tides, while the impact of environmental changes on chemical composition in typical dinoflagellates is currently unclear, which limits our understanding of the role of dinoflagellates in planktonic trophodynamics in the changing ocean. Here, we investigated the responses of elemental stoichiometry and sterol contents in three dinoflagellate species (Prorocentrum donghaiense, Prorocentrum minimum and Karenia mikimotoi) to changes in temperatures (15, 20 and 25 °C), N:P supply ratios (molar ratios 10:1, 24:1 and 63:1) and growth phases (exponential and stationary growth phases) in batch culture experiments. Both dinosterol and brassicasterol were produced by all the three species, but the cellular contents of dinosterol were up to 10 times higher than brassicasterol. Overall, growth phase changes showed the most pronounced effects, while warming and nutrient deficiency had moderate effects on the ratios of particulate organic nitrogen and carbon (PON:POC) and sterol contents. Our observations imply that under future ocean scenarios (warming and imbalanced N:P supply ratios), PON:POC may decrease but carbon-normalized sterol contents may increase in the three species. Such parallel changes in PON:POC and sterol contents may influence the dinoflagellate-grazer relationship and have significant consequences for ecological functions of the future ocean.

A high-resolution molecular organic geochemical study of core MD05-2904 reveals changes in the productivity and community structure of paleo-phytoplankton during the last 260 ka in the northern South China Sea (SCS). Multiple biomarkers, including C37 alkenones, dinosterol, brassicasterol and C30 diols, are used as representatives of haptophytes, dinoflagellates, diatoms and eustigmatophytes, respectively. The abundances and mass accumulation rates of biomarkers indicate that phytoplankton productivity was relatively higher during glacial periods than during interglacial periods. However, the phytoplankton community structure, inferred from the relative abundance of biomarkers, does not display any evident glacial/interglacial cycles. In agreement with previous studies, our results also suggest a linkage between the increased paleo-productivity and the enhanced East Asian winter monsoon in the glacial northern SCS. The relatively stable PCS may reflect a lack of sensitivity of the phytoplanktonic groups to variations of nutrient composition on glacial/interglacial and shorter time scales. A long-term decrease in the C37 alkenone abundance since MIS 5 might have been related to the increasing influence of the northward intrusion of Antarctic Intermediate Water and/or sub-Antarctic Mode Water on the SCS thermocline waters. Moreover, the evolution of alkenone producers and changes in the coccolithophore genera on C37 alkenones might also have contributed to the long-term decrease in the C37 alkenone abundance.

Studies of spatial and temporal changes in modern and past sea-ice occurrence may help to understand the processes controlling the recent decrease in Arctic sea-ice cover. Here, we determined concentrations of IP25, a novel biomarker proxy for sea ice developed in recent years, phytoplankton-derived biomarkers (brassicasterol and dinosterol) and terrigenous biomarkers (campesterol and β-sitosterol) in the surface sediments from the Kara and Laptev seas to estimate modern spatial (seasonal) sea-ice variability and organic-matter sources. C25-HBI dienes and trienes were determined as additional palaeoenvironmental proxies in the study area. Furthermore, a combined phytoplankton-IP25 biomarker approach (PIP25 index) is used to reconstruct the modern sea-ice distribution more quantitatively. The terrigenous biomarkers reach maximum concentrations in the coastal zones and estuaries, reflecting the huge discharge by the major rivers Ob, Yenisei and Lena. Maxima in phytoplankton biomarkers indicating increased primary productivity were found in the seasonally ice-free central part of the Kara and Laptev seas. Neither \{IP25\} nor PIP25, however, shows a clear and simple correlation with satellite sea-ice distribution in our study area due to the complex environmental conditions in our study area and the transportation process of sea-ice diatom in the water column. Differences in the diene/IP25 and triene/IP25 ratios point to different sources of these \{HBIs\} and different environmental conditions. The diene/IP25 ratio seems to correlate positively with sea-surface temperature, while negatively with salinity distributions.

Three methods are presented on how to purify acetylated sterols, acetylated triterpenols and individual alkenones for hydrogen isotope analysis from marine and lacustrine sediments using reverse-phase high performance liquid chromatography (RP-HPLC). The main advantages over previous HPLC methods are reduced operator time, increased automation and the ability to simultaneously purify multiple target compounds from a sample. These gains are achieved primarily by acetylating compounds prior to purification rather than after, and also by using a fraction collector with semi-preparatory rather than analytic configuration. The effectiveness of the method is demonstrated for (i) dinosterol and taraxerol in sediment from the brackish pond Poza del Diablo, Galapagos, (ii) for di- and tri-unsaturated C37 and C38 alkenones in cultured Emiliania huxleyi, (iii) for brassicasterol, and di-, tri- and tetra-unsaturated C37 alkenones in sediment from Manito Lake, Saskatchewan, Canada, and (iv) for brassicasterol, dinosterol and di-, tri- and tetra-unsaturated C37 alkenones in sediment from the Great Salt Lake, Utah. The purification process yields 80–90% recoveries and results in no measurable hydrogen isotope alteration.

The ecological environment in the East China Sea (ECS) and the Yellow Sea (YS) has changed significantly due to sea-level rising and the Kuroshio incursion since the last deglaciation. In this study, biomarker records of core F10B from the mud area southwest off Cheju Island (MSWCI) were generated to evaluate phytoplankton productivity and community structure changes in response to environmental evolution during the last 14 kyr. The contents of diatom, dinoflagellate and haptophyte biomarkers (brassicasterol, dinosterol and C-37 alkenones) display similar trends, with increasing phytoplankton productivity during the last 14 kyr due to the increased influences of the Kuroshio, and especially due to the eddy-induced upwelling during the late Holocene. On the other hand, the contents of terrestrial biomarkers (C-28 +C-30 +C-32 n-alkanols) and terrestrial organic matter (TOM) proxies (TMBR' and BIT) all reveal decreasing TOM input into the area around the sampling site for the 14 kyr, mostly due to sea-level rising. Phytoplankton biomarker ratios reveal a shift from a haptophyte-dominated community at 6.2-2.5 kyr BP to a diatom-dominated community at 2.5-1.45 kyr BP, likely caused by a stronger cold eddy circulation system at 2.5-1.45 kyr BP in the MSWCI.

The Yellow Sea (YS) environmental and ecological changes during the Holocene are driven by the interactions between the Yellow Sea Warm Current (YSWC), the East Asian Winter Monsoon (EAWM) and the Kuroshio Current (KC). We report marine biomarker records of brassicasterol, dinosterol and C37 alkenones in core ZY1 and core ZY2 from the South Yellow Sea (SYS) to reconstruct the spatial/temporal variations and possible mechanisms of phytoplankton primary productivity and community structure changes during the Mid-late Holocene. The contents of the corresponding biomarkers in the two cores are similar, and they also reveal broadly similar temporal trends. From 6 kyr to 3 kyr, the biomarker contents in the two cores were relatively low with small oscillations, followed by a distinct increase at about 3 kyr indicating productivity increases caused by a stronger EAWM. The alkenone/brassicasterol ratio (A/B) is used as a community structure proxy, which also showed higher values in both cores since 3 kyr, indicating increased haptophyte contribution to total productivity. It is proposed that the YS community structure has been mainly influenced by the YSWC, with stronger YSWC influences causing an increase in haptophyte contribution since 3 kyr. Some differences of the biomarker records between ZY2 and ZY1 suggest spatial variations in response to YSWC and KC forcing. When the KC was intensified during the periods of 6–4.2 kyr and 1.7–0 kyr, the YSWC extended eastward, exerting more influence on core ZY1. On the other hand, when the KC weakened during 4.2–1.7 kyr, the YSWC extended westward, exerting more influence on the ZY2.

The many lakes present among the inactive dunes of the Nebraska Sand Hills are unique ecosystems that formed under particular conditions of local and regional geomorphology, hydrology and climate. They offer an exceptional opportunity to study the inter-relations between hydrology, microbial diversity, and biogeochemistry in comparatively closely-spaced bodies of water ranging in pH from neutral to alkaline. We analyzed for lipid biomarkers in the surficial sediments of six Sand Hills lakes, including alkanes, alkenes, alkanols, phytol, sterols, hopanoids, tetrahymanol, and phospholipid fatty acids. Overall, these biomarkers exist in significantly lower concentrations in the alkaline lakes of the Sand Hills than in ordinary neutral lakes. More specifically, microbial functional groups can be identified in the lake sediments on the basis of the biomarkers for which we analyzed. The presence of eukaryotic phototrophs is indicated by the detection of phytadienes, phytol, phytanol, diatomsterol, dinosterol, and polyunsaturated fatty acids. The detection of short-chain wax esters suggests the presence of anoxygenic autotrophic sulfur bacteria (purple and green sulfur bacteria). The phospholipid fatty acid (PLFA) profiles indicate the presence of sulfate-reducing bacteria in the sediment. Tetrahymanol and polyunsaturated fatty acids in the sediments suggest the presence of bacterivorous ciliates and phototrophic sulfur bacteria, which probably live at the chemocline. Our results reveal that there are unique and integrated ecosystems within the Sand Hills lakes that are defined by the close interactions between regional hydrology, geochemistry, and microbiology.

In this paper discusses the aquatic environment at Lake Kizaki, central Japan, during the last ca. 60 years and describes the importance of laminated sediments in environmental analyses. The flux of total algal carbon increased between 1965 and 1996 while the BSi flux, which can be used in diatom production, showed a larger increase between 1960 and 1998 than typically occurs on average. The flux of dinosterol, an indicator of dinoflagellate production, also increased from 1966 to 1998, and the sedimentary dinoflagellate record correlated with observations of freshwater red tides caused by dinoflagellate blooms. Parallel laminated sediment was determined to have appeared between 1960 and 1995, corresponding to a period of high total algal carbon levels and BSi fluxes. For lamina formation and its preservation process, the thickness of the oxygen-poor layer depended on excessive total algal production during stagnant periods and appeared to be important because nutrients were diffused and accumulated in the oxygen-poor layer from bottom sediments. This could result in diatom blooms at the next overturn period. The development of the thick oxygen-poor layer appeared to be triggered primarily by the presence of excessive nutrients generated by human activities. In general, the occurrence of laminated sediments can provide a useful tool for understanding the eutrophic state in Lake Kizaki.

Herein, lipid biomarker analysis is applied to surface sediments from the southeastern Niger Delta region for the quantitative determination of aliphatic lipids, steroids and triterpenoids in order to differentiate between natural (autochthonous vs. allochthonous) and anthropogenic organic matter (OM) inputs to this deltaic environment. This ecosystem, composed of the Cross, Great Kwa and Calabar Rivers, is receiving new attention due to increased human and industrial development activities and the potential effects of these activities impacting its environmental health. While the presence of low molecular weight n -alkanes ( 22 ) and the fossil biomarkers pristane and phytane in all samples, are indicative of a minor petroleum related input, the total extractable organic component of the surface sediments of these rivers remains predominantly of a natural origin as characterized by the variety and predominance of lipid classes that are mainly derived from the epicuticular waxes of vascular plants and include n -alkanes, n -alkanols, n -alkan-2-ones, n -alkanoic acids, steroids and triterpenoids. In addition, recent OM inputs from microorganisms are indicated by the presence of lower molecular weight n -alkanoic acids (C max = 16), while the major triterpenoids of the sediments, taraxerol and friedelin, and the major sterol, sitosterol, indicate recent OM inputs from vascular plants. Plankton-derived sterols, such as fucosterol and dinosterol, are also found in sediments from the Cross and Great Kwa Rivers and likely originate from autochthonous primary productivity. Furthermore, the coprosterols coprostanol and 24-ethylcoprostanol are present in most samples and indicate measurable anthropogenic contributions from domestic untreated sewage inputs and agricultural run-off, respectively. Of the three rivers studied, the Cross River system was excessively influenced by human and industrial development activities, including drivers such as urbanization and population center growth, land-use change to support agricultural production and animal husbandry, and petroleum exploration and production. These influences were found to be regionally specific as controlled by point sources of pollution based on the relative distributions measured and on the fact that the molecular characteristics of sedimentary OM were not distributed smoothly along a gradient.

We used a multiple-proxy palaeoecological method to reconstruct a 100 yr time series showing coastal eutrophic processes and phytoplankton responses. Total organic carbon, total nitrogen, diatom frustules, dinoflagellate cysts, brassicasterol and dinosterol were extracted from chronologic sediment cores in Sishili Bay, a polluted area in China. The cores showed that eutrophication occurred during about 1975 to 1985, which corresponds to increased human activity associated with China's economic development since 1978. During eutrophication, the biomass of diatoms and dinoflagellates increased, and dominant species shifted abruptly. The small, heavily silicified diatoms Cyclotella stylorum and Paralia sulcata gradually took the place of the large dominant diatom Coscinodiscus radiatus, while dinoflagellates displayed a progressive in crease since 1975. Compared to changes in temperature and rainfall during 1950 to 2010, increased fertilizer use, marine aquaculture and sewage discharge showed a better match to the increasing trend in biomass, species shift and nutrient concentration. Altered nutrient supply ratios caused by increased nitrogen inputs play an important role in the shifts in diatom and dinoflagellate assemblages.

Biomarkers including brassicasterol, dinosterol and alkenone in sediments are used as indicators to reconstruct changes to the phytoplankton community in surface and sub-aerial sediments of Prydz Bay, Antarctica. The results indicate that the biomarker records in surface and core sediment samples changed with time and space. The total content of phytoplankton biomarkers ranges from 391.0-1 470.6 ng•g -1 . The phytoplankton biomass has increased in Prydz Bay over the past 100 years. This variation may be mainly related with climate change in the region. The total biomarker contents in surface sediments from 5 stations in Prydz Bay are in the range of 215.8-1 294.3 ng•g -1 . The phytoplankton biomass in Prydz Bay is higher than that outside of the bay. This is similar to the distributions of chlorophyll a , organic carbon and biogenic silica in surface waters determined through in situ investigation. Such consistency indicates a coupling between the bottom of the ocean and biogeochemical processes in the upper water.

The distribution of free sterols in a sulfur-rich lacustrine sediment of Miocene age deposited in the ancient crater lake of the Nordlinger Ries (southern Germany) was investigated and compared with the corresponding distributions of esterified and kerogen-bound sterols. The three fractions exhibited the same suite of principal sterols, with 4α,24-dimethyl-5α- cholestan-3β-ol, dinosterol and dinostanol displaying the highest concentrations and relative abundances. The distributions of sterols, steroidal ketones, n-alkanols and isoprenoid alcohols suggest a prevalent deposition of autochthonous aquatic organic matter under saline conditions. In particular, the high abundance of 4α,24-dimethyl-5α-cholestan-3-one, dinosterone and dinostanone and the corresponding 4-methyl sterols indicates the importance of dinoflagellate productivity in this former crater lake and its significant contribution to the sedimentary lipids in the Nordlinger Ries sediment. The similarity in structures and relative abundance of the major 4-methyl sterols and the corresponding steroidal ketones suggest that they are biosynthetically linked.

Geological records of past sea ice, such as those contained in Arctic marine sediments, offer an opportunity to strengthen our understanding of long-term sea ice variability, provided unambiguous paleo-sea ice proxies can be developed. One such recently proposed proxy is IP25, a highly branched isoprenoid alkene biosynthesized exclusively by sea-ice dwelling diatoms (Haslea spp.), which is well preserved in marine sediments and could be used to reconstruct past changes in spring sea-ice extent. However, little is known about regional-scale controls on IP25 production in sea ice, limiting its wider applicability as a paleo-sea-ice proxy. To address this issue we examined the distributions of IP25 and the marine productivity biomarkers dinosterol and brassicasterol in a suite of surface sediment samples distributed across the Arctic. We find a statistically significant, logarithmic relationship between IP25 and spring sea ice cover in sediment samples from arctic and subarctic sites in the Pacific (n = 96, R2 = 0.67, P

Suspended particles in the West Pacific surface water were collected during the KX08-973 Cruise(Nov.14,2008 ~ Jan.19,2009).Four kinds of phytoplankton lipids biomarkers,i.e.Brassicasterol,Dinosterol,C37-Alkenone,and 1,15-C30 alkyl-diol,corresponding to diatoms,dinoflagellates,coccolithophores,and Eustigmatophytes algae were collected by organic geochemistry method.The variability and influencing factors of the phytoplankton biomass and communities structure were studied according to their distribution.The results show that the obtained biomass are correlated well with the Chl-a,indicating the validation of biomarker lipids to the reconstruction of the ocean productivity.The biomass distribution has distinct regional differentiation,highest in Yangtze River estuary and related shelf areas,followed by the area off eastern New Guinea and the zone off eastern Philippines,with the lowest in the pelagic.Fluvial transport,ocean currents,regional landform configurations and resuspension of the shelf sediment are the main factors effecting the phytoplanktons biomass distribution.As the result of competition for nutrient,the phytoplanktons biomass is dominated by diatom,with dinoflagellate,coccolithophores and Eustigmatophytes as minor contributors.The data obtained from the present research can be applied not only to modern marine ecological investigation,but also for paleoceanographic reconstruction.

This chapter reviews the sterol compositions reported for the different classes of microalgae. For a few major phyla such as the green microalgae, diatoms, dinoflagellates and haptophytes a sufficiently large number of species (over 100 in the case of diatoms) have been analysed for sterols allowing some generalisations to be made and characteristic features to be identified. In many other algal classes there is a paucity of sterol data available as only a few species have been analysed. These compositions are discussed in terms of taxonomic groupings and from the viewpoint of the various steps involved in sterol biosynthesis that introduce specific double bonds or alkylate the sterol side-chain. Green microalgae are shown to have a variety of compositions including some with simple distributions of sterols dominated by the C29 sterol 24-ethylcholest-5-en-3β-ol (sitosterol) more commonly associated with higher plants. In other green algae a predominance of Δ7-unsaturated sterols is found dominated by 24-methylcholesta-5,7,22E-dien-3β-ol (ergosterol). Diatoms contain a surprising diversity of sterol distributions with over 40 sterols identified. Common sterols include 24-methylcholesta-5,22E-dien-3β-ol, 24-methylenecholesterol and cholesterol. Some diatom genera display distinctive distributions such as Amphora which contains high contents of the C29 sterol 24-ethylcholesta-5,22E-dien-3β-ol. A number of unusual sterols have been found in smaller amounts in a few species including 4-methylsterols and the C30 sterol gorgosterol. Sterols with a methyl group at C-23 are also surprisingly common showing that this feature is not unique to dinoflagellate sterols. Many dinoflagellates contain mixtures of 4-methylsterols including the C30 sterol 4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol (dinosterol), as well as related 5α(H)-stanols. A few genera contain unusual sterols such as Amphidinium and Karenia species which contain Δ8(14)-unsaturated sterols. Haptophytes, in contrast, usually have simple sterol distributions, often dominated by 24-methylcholesta-5,22E-dien-3β-ol also found in diatoms.

On, Zeki Bora/0000-0002-8684-3476; On, Zeki Bora/0000-0002-8684-3476; Akcer On, Sena/0000-0002-0708-8629 WOS: 000385855900012 Lake Salda, located in south-western Anatolia, is characterized by the presence of living stromatolites and by a low diversity of both phytoplankton and zooplankton due to high pH and magnesium concentration. The most abundant, free sedimentary lipids of the uppermost five centimetres of the lake sediments were studied as potential environmental biomarkers, and proxies based on glycerol dialkyl glycerol tetraethers (GDGT) were tested in this extreme environment. Dinosterol and tetrahymanol are potentially relevant biomarkers for the dinoflagellate Peridinium cinctum and ciliates, respectively. C-20: 1 and C-25: 2 highly branched isoprenoid (HBI) alkenes, and n-C-17 alkane and n-C-17: 1 alkene are considered to represent, respectively, diatoms and Cyanobacteria, that are involved in the formation of stromatolites. Crenarchaeol is assumed to be derived mainly from Thaumarchaeota thriving in the lake. Allochthonous organic material is represented by long-chain n-alkanes and n-alkanols derived from land plant leaf waxes, as well as branched GDGTs produced by soil bacteria. The latter may also be produced partly in the water column and/or the surface sediment of the lake. Branched GDGT-derived lake calibrations for water pH provide estimates close to observations, but estimated lake water/air temperature are lower than observed values. TEX86 (tetraether index of tetraethers consisting of 86 carbons), a proxy based on isoprenoid GDGTs, potentially allows estimating mean annual lake surface temperature. Interestingly, C-22 to C-25 1,2 diols, which have a yet unknown origin, were found for the first time in lake sediments. This study represents the first investigation of sedimentary lipid distribution in an alkaline and magnesium-rich lake in Anatolia, and provides a basis for future biomarker-based paleoenvironmental reconstruction of Lake Salda. Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK) [113Y408] We would like to thank Kadir Eris, Dursun Acar, Bedri Kurtulus, Iliya Danladi Bauchi, Huseyin Caldirak, Burak Yalamaz and Rana Salihoglu for field work and sample preparation. Namik Cagatay is thanked for making lab facilities available at the ITU-EMCOL. Stefan Schouten, Simon Belt, and Wael Skeff are acknowledged for their help in compound identification. We are thankful to the Yesilova chamber of agriculture for providing soil pH data. Sena Akcer-On was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) project no. 113Y408.

We present two new methods for purifying dinosterol (4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol) from sediments for the purpose of hydrogen isotope analysis via gas chromatography–isotope ratio mass spectrometry (GC–IRMS). The first method uses reversed phase-high performance liquid chromatography (RP-HPLC) to purify dinosterol from structurally similar 4α-methyl sterols that co-elute on GC analysis. Dinosterol purified from sedimentary sterol/alcohol fractions using this RP-HPLC method demonstrated an average yield of 80%. A very large isotope effect was observed during RP-HPLC purification, with a 560‰ range in δD value between the first and last 5% of a cholesterol standard, which is four times that during normal phase-HPLC (NP-HPLC) purification. However, we show that dinosterol recombined from 3–4 min of eluent during RP-HPLC purification yields highly reproducible and unbiased isotope values. Due to a larger isotope effect and lower sterol recovery during RP-HPLC, NP-HPLC purification is recommended for samples that do not contain 4α-methyl sterols that co-elute with dinosterol during GC. However, for samples that contain a variety of 4α-methyl sterols, RP-HPLC is more likely to yield baseline resolution of dinosterol. In the second method presented, RP-HPLC purification is preceded by NP-HPLC purification. Using this two step procedure, baseline resolution between dinosterol and all other compounds present was achieved for all samples with an average yield of 60% and, in many cases, dinosterol was purified from all other sedimentary lipids. For samples that contain a variety of 4α-methyl sterols and sitostanol concentration > 2× that of dinosterol, the two step purification method is recommended, as neither NP-HPLC or RP-HPLC alone is likely to yield baseline resolution of dinosterol.

Lepidodinium chlorophorum is a green-pigmented dinoflagellate with an aberrant, tertiary plastid of chlorophyte ancestry rather than the typical red algal, secondary endosymbiont found in the vast majority of photosynthetic dinoflagellates. To date, only one published study exists on the galactolipids of L. chlorophorum, with nothing known about other lipid classes, including sterols. Our objectives were to examine the sterol composition of L. chlorophorum to determine if it produces any unique sterols with the potential to serve as biomarkers, and to compare it to members of the Chlorophyceae to determine if it has inherited any signature green algal sterols from its chlorophyte-derived endosymbiont. We have found that L. chlorophorum produces 6 sterols, all with a 4α-methyl substituent and none of which are known to occur in the Chlorophyceae. Rather, the sterols produced by L. chlorophorum place it within a group of dinoflagellates that have the common dinoflagellate sterols, dinosterol and dinostanol, as part of their sterol composition.

The dinoflagellate genus Pyrocystis includes a small number of marine species, which spend the majority of their life cycles as nonmotile cells within a carbohydrate sheath, and which are found ubiquitously throughout the world's oceans. The biochemistry of this model dinoflagellate genus has been widely studied due to its ability to bioluminesce. However, Pyrocystis has been comparatively understudied with respect to its lipid biochemistry, in particular that of sterols. To date, examination of the sterols of Pyrocystis has focused primarily upon Pyrocystis lunula, which produces cholesterol and 4,24-dimethyl-5α-cholestan-3β-ol as its predominant sterols, while it lacks the common dinoflagellate sterol, dinosterol. We have examined the sterol composition of the two other commercially available species of Pyrocystis, Pyrocystis fusiformis and Pyrocystis noctiluca. Pyrocystis noctiluca possesses dinosterol as its most abundant sterol, while P. fusiformis possesses dinosterol and 4,24-dimethyl-5α-cholestan-3β-ol as the predominant sterols, placing it at an intermediate position between P. lunula and P. noctiluca, as based on sterol composition. The potential limitations of the dinoflagellate sterol biomarker dinosterol are also explored in this study due to its notable absence in P. lunula.

Recent studies have shown that ancient plankton DNA can be recovered from Holocene lacustrine and marine sediments, including from species that do not leave diagnostic microscopic fossils in the sediment record. Therefore, the analysis of this so-called fossil plankton DNA is a promising approach for refining paleoecological and paleoenvironmental information. However, further studies are needed to reveal whether DNA of past plankton is preserved beyond the Holocene. Here, we identified past eukaryotic plankton members based on 18S rRNA gene profiling in eastern Mediterranean Holocene and Pleistocene sapropels S1 (~9 ka), S3 (~80 ka), S4 (~105 ka), and S5 (~125 ka). The majority of preserved ~400- to 500-bp-long 18S rDNA fragments of microalgae that were studied in detail (i.e. from haptophyte algae and dinoflagellates) were found in the youngest sapropel S1, whereas their specific lipid biomarkers (long-chain alkenones and dinosterol) were also abundant in sediments deposited between 80 and 124 ka BP. The late-Pleistocene sediments mainly contained eukaryotic DNA of marine fungi and from terrestrial plants, which could have been introduced via the river Nile at the time of deposition and preserved in pollen grains. A parallel analysis of Branched and Isoprenoid Tetraethers (i.e. BIT index) showed that most of the organic matter in the eastern Mediterranean sediment record was of marine (e.g. pelagic) origin. Therefore, the predominance of terrestrial plant DNA over plankton DNA in older sapropels suggests a preferential degradation of marine plankton DNA.

To quantify changes in organic carbon inputs and preservation, sediments from the Northern Chukchi Sea spanning the last 9000 years of the Holocene period were collected during the HOTRAX expedition and analyzed. The multi-proxy approach included molecular organic markers, bulk carbon and isotope measurements plus more recent approaches to terrestrial carbon estimation (the BIT index of Branched and Isoprenoid Tetraethers). The upper 1100 cm of the core, corresponding to the last 7.4 ka, showed a relatively stable total organic carbon content of 1.13–1.38% which decreased below 1100 cm to 0.6%. C:N ratios ranged from 8.4 to 10.83 over the Holocene time period examined. The distribution of n-alcohols and n-alkanes revealed major contributions from long-chain n-alcohols and n-alkanes while minimal contributions were seen from short-chain n-alkanes. The majority of the total fatty acids was comprised of saturated and monounsaturated fatty acids with short-chain and long-chain saturated fatty acids present in similar concentrations throughout most of the core and monounsaturated fatty acids decreasing down-core. Total sterol concentrations showed considerable inputs from marine sterols, C28Δ5,22, C28Δ5,24(28) and dinosterol, as well as C29Δ5, typically considered a terrestrial marker. The BIT indices for core sediments ranged from 0.021 to 0.216 with minor changes seen in older sequences. Overall, organic biomarkers indicate marine sources as the more dominant input of organic matter with lower but continual contributions from terrestrial sources at this location during the Holocene. The remarkable consistency among multiple molecular organic markers of both marine and terrestrial origin over the Holocene period encompassed by the core suggests that sinking material or surface sediments were heavily influenced by bottom currents or other mixing processes prior to their deposition.

This paper reports on the spatial distribution patterns and investigates the controlling mechanisms of phytoplankton biomarkers (brassicasterol for diatoms, alkenones for haptophytes, dinosterol for dinoflagellates) and terrestrial biomarkers (odd C number long-chain (C 27 + C 29 + C 31 ) n -alkanes) in surface sediments from the southern Yellow Sea (SYS). The contents of the phytoplankton biomarkers in the SYS surface sediments reveals a clear spatial pattern, with low values near the coasts and increased values seaward, caused by higher phytoplankton primary productivity and low sedimentation rates in the basin. The contents of terrestrial biomarkers show high values in the northern part of the study areas off the Shandong Peninsula and Jiangsu coast, caused by inputs of materials from the modern Huanghe River and the old Huanghe delta, respectively. The results also indicate that biomarker ratios offer the best approach for reconstructing marginal sea C cycles, as these proxies can be used to estimate the contributions of both terrestrial and marine organic matter and to reconstruct paleoproductivity and paleoecological changes in the SYS.

Revealing of the sources and distributions of sedimentary organic matter in the East China Sea (ECS) is important for understanding its carbon cycle, which has significant temporal and spatial variability due to the influences of recent climate changes and anthropogenic activities. In this study, we report the contents of both terrestrial and marine biomarkers including ∑C27+C29+C31 n-alkanes (38.6–580 ng/g), C37 alkenones (5.6–124.6 ng/g), brassicasterol (98–913 ng/g) and dinosterol (125–1521 ng/g) from the surface sediments in the Changjiang River Estuary (CRE) and shelf areas of the ECS. Several indices based on biomarker contents and ratios are calculated to assess the spatial distributions of both terrestrial and marine organic matter in the ECS surface sediments, and these results are compared with organic matter distribution patterns revealed by the δ13C (−20.1‰ to −22.7‰) and C/N ratio (5–7.5) of total organic matter. The contents of terrestrial biomarkers in the ECS surface sediments decrease seaward, controlled mostly by Changjiang River (CR) inputs and surface currents; while higher contents of the two marine biomarkers (brassicasterol and dinosterol) occur in upwelling areas outside the CRE and in the Zhejiang–Fujian coastal zone, controlled mostly by marine productivity. Four proxies, fTerr(δ13C) (the fraction of terrestrial organic matter in TOC estimated by TOC δ13C), odd-alkanes (∑C27+C29+C31 n-alkanes), 1/Pmar-aq ((C23+C25+C29+C31)/(C23+C25) n-alkanes) and TMBR (terrestrial and marine biomarker ratio) (C27+C29+C31 n-alkanes)/((C27+C29+C31) n-alkanes+(brassicasterol+dinosterol+alkenones)), reveal a consistent pattern showing the relative contribution of terrestrial organic matter (TOM) is higher in the CRE and along the Zhejiang–Fujian coastline, controlled mostly by CR inputs and currents, but the TOM contribution decreases seaward, as the influences of the CR discharge decrease.

Previous studies have indicated that the Yellow Sea underwent significant environmental changes during the Holocene, but many questions remain concerning the timing of the establishment of the modern circulation system, which would have major implications for the Yellow Sea ecosystem and carbon cycle. In this study, marine and terrestrial biomarkers were analyzed in Core YE-2 from a muddy area in the southern Yellow Sea to reconstruct Holocene environmental and phytoplankton community change. The content of three individual marine phytoplankton biomarkers (alkenones, brassicasterol and dinosterol) all display a similar trend, and their total contents during the early Holocene (362 ng/g) were lower than those during the mid-late Holocene (991 ng/g). On the other hand, the contents of terrestrial biomarkers (C27+C29+C31n-alkanes) during the early Holocene (1 661 ng/g) were about three times higher than those during the mid-late Holocene (499 ng/g). Our biomarker results suggest that the modern circulation system of the Yellow Sea was established by 5–6 ka, and resulted in higher marine productivity and lower terrestrial organic matter inputs. Biomarker ratios were used to estimate shifts in phytoplankton community structure in response to mid-Holocene (5–6 ka) environmental changes in the Yellow Sea, revealing a transition from a dinoflagellate-diatom dominant community structure during the early Holocene to a coccolithophore-dominant dominant community structure during the mid-late Holocene.

We tested the use of hydrogen isotopic ratios (δD) of lipids in marine lake sediments from the Micronesian Republic of Palau against the instrumental record of the last century to assess their capacity to record past hydrological changes of the Western Pacific Warm Pool. δD values of the algal lipid biomarker dinosterol (δD Dino ) and the more generic palmitic acid (δD PA ) were found to be sensitive indicators of the intensity of regional precipitation, as recorded by the Southern Oscillation Index (SOI). The observed sensitivity is caused by the combined effect of: 1) The amount effect in tropical precipitation; 2) Dilution of the isotopically heavy saline surface waters with light precipitation; 3) A salinity effect on the biosynthetic D/H fractionation between lipid and lake water. Both lake water δD (δD Lake ) and δD Dino could be expressed as a quadratic function of either precipitation or lake water salinity. δD Dino values were used to reconstruct past hydrological changes of the region. Long-term variations in the strength and sign of the El Nino - Southern Oscillation (ENSO) since the Little Ice Age (LIA, ∼1450–1850 A.D.) and during the early Holocene (∼7–9 kyr BP) appeared to dominate decadal variability, and indicate very dry conditions during the LIA. Early Holocene δD Dino values were on average ∼10‰ higher than those of recent centuries, which we interpret as a result of millennial scale hydrologic and water mass changes on a global level. The similar ∼35‰ range of δD changes during the early Holocene and last several centuries imply a similar range of decadal-centennial hydrologic variability during those two climate regimes. Our results indicate that a correlation exists between solar irradiance levels and tropical Pacific climate.

Relatively few well-dated and high-resolution paleoclimate records of the past few centuries presently exist from tropical East Africa. Here, we examine the bulk and molecular geochemical records of two varved sediment cores from Lake Malawi, which together provide a continuous record of environmental variability in East Africa of the last 730 years. We observe a number of changes in the aquatic ecosystem of Lake Malawi, which are likely attributed to both natural climatic forcing and anthropogenic activities. Biomarkers of dinoflagellates (dinosterol) and bacterivorous ciliates (tetrahymanol) display increased accumulation rates from ~ 1900 AD to the present, while a simultaneous decrease in accumulation rates of diatom biomarkers (isololiolide/loliolide) is observed. Increased accumulation rates of retene, a compound derived from conifers, are also noted since ~ 1930 AD and likely reflect increased soil erosion due to deforestation of the Lake Malawi watershed. Spectral analysis of the high-resolution TOC record indicates a periodicity of 204 years, similar to the 206 year cycle noted in 14C and 10Be records, suggesting a link between East African climate and solar forcing.

The hydrogen isotope ratio of the dinoflagellate sterol dinosterol (4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol) was measured in suspended particles and surface sediments from the Chesapeake Bay estuary in order to evaluate the influence of salinity on hydrogen isotope fractionation. D/H fractionation was found to decrease by 0.99 ± 0.23‰ per unit increase in salinity over the salinity range 10–29 PSU, a similar decrease to that observed in a variety of lipids from hypersaline ponds on Christmas Island (Kiribati). We hypothesize that the hydrogen isotopic response to salinity may result from diminished exchange of water between algal cells and their environment, lower growth rates and/or increased production of osmolytes at high salinities. Regardless of the mechanism, the consistent sign and magnitude of dinosterol δD response to changing salinity should permit qualitative to semi-quantitative reconstructions of past salinities from sedimentary dinosterol δD values.

article i nfo Organic geochemical analyses of marine surface sediments from the continental margins of East Greenland and West Spitsbergen provide for a biomarker-based estimate of recent sea ice conditions in the northern North Atlantic. By means of the sea ice proxy IP25 and phytoplankton derived biomarkers (e.g. brassicasterol and dinosterol) we reconstruct sea ice and sea surface conditions, respectively. The combination of IP25 with a phytoplankton marker (in terms of a phytoplankton marker-IP25 index; PIP25) proves highly valuable to properly interpret the sea ice proxy signal as an under- or overestimation of sea ice coverage can be circumvented. A comparison of this biomarker-based assessment of the sea ice distribution in the study area with (1) modern remote sensing data and (2) numerical modelling results reveal a good agreement between organic geochemical, satellite and modelling observations. The reasonable simulation of modern sea ice conditions by means of a regional ocean-sea ice model demonstrates the feasibility to effectively integrate the complex atmospheric and oceanic circulation features as they prevail in the study area. The good correlation between modelled sea ice parameters and the biomarker-based estimate of sea ice coverage substantiates that linking proxy and model data occurs to be a promising concept in terms of a cross-evaluation. This combinatory approach may provide a first step towards quantitative sea ice reconstructions by means of IP25. Future IP25 studies on marine surface sediments from the Arctic realm, however, are recommended to extend and validate this new attempt of using IP25 in combination with a phytoplankton marker as a quantitative measure for sea ice reconstructions.

Due to the increasing evidences on dinoflagellate contribution to mucilage phenomena in the Mediterranean Sea, this study was aimed at identifying biochemical and/or genetic markers that could help in relating Gonyaulax fragilis growth with mucilage formation when microscope identification was difficult. The biochemical characterization considered the fatty acid and sterol composition of cultured strains and mucilage samples. The cultured algae displayed the typical fatty acid pattern of dinoflagellates as the 18:0 was the prevalent saturated fatty acid (SFA), 18:1n-7 and 18:1n-9 were the major monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) were dominated by 18:5n-3 and 22:6n-3. Two groups of sterols were identified in algal cells: desmethylsterols, dominated by cholesterol and β-sitosterol, and 4α-methylsterols, having dinosterol as the prevailing sterol. The mucilage lipid pattern was characterized by low amounts of PUFAs and appeared deeply influenced by environment dynamics; however, the 20:5n-3/22:6n-3 ratio

The motile cells of the autotrophic dinoflagellates Peridinium umbonatum var. inaequale, Akashiwo sanguinea, Scrippsiella tinctoria, and Prorocentrum micans commonly contain five major sterols: cholesterol, 4-methylcholestan-3-ol, 4,24-dimethylcholestan-3-ol, dinosterol, and dinostanol. The motile cell of the heterotrophic dinoflagellate Protoperidinium crassipes contains cholesterol, 4,24-dimethylcholestan-3-ol, dinosterol, dinostanol, and 4-tetramethylcholestan-3-ol as major free sterols. The dinosterol concentrations of heterotrophic dinoflagellates are about 4-12 times higher than those of autotrophic species, suggesting that the heterotrophic dinoflagellate is an important source of dinosterol in some sediments. 4-Tetramethylcholestan-3-ol has not been reported in cultured samples of other heterotrophic dinoflagellates. The difference in 4-methyl sterol composition in heterotrophic dinoflagellates may be related to the feeds used during the culture experiment. The resting cyst of P. umbonatum var. inaequale contains 4-methylcholestan-3-ol, 4,24-dimethylcholestan-3-ol, dinosterol, dinostanol, and C31Δ^[5.22]-sterol as major free sterols. The C31Δ^[5.22]-sterol has not been reported in cultured samples of motile cells from dinoflagellates. This compound might be produced during the resting stage, and thus may serve as a potential biomarker for the resting cysts of dinoflagellates.

Recent work has shown that paleoenvironmental genomics, i.e. the application of genomic tools to analyze preserved DNA in sedimentary records, is a promising approach to reconstruct the diversity of past planktonic communities. This provides information about past ecological and environmental changes. A major advantage of this approach is that individual species, including those that did not leave other characteristic markers, can be identified. In this study, we determined which dinoflagellate marker (i.e. 18S rDNA, dinosterol or dinocysts) provided the most detailed information about the late-Holocene succession of dinoflagellates in an Antarctic Fjord (Ellis Fjord, Vestfold Hills). The preserved rDNA revealed two intervals in the 2750-year-old sediment record. The dinoflagellate diversity was the highest until approximately 1850 cal yr bp and included phylotypes related to known dinosterol producers. A lower concentration of dinosterol in sediments

Molecular organic biomarkers together with trace element composition were investigated in sediments east of Barrow Canyon in the western Arctic Ocean to determine sources and recycling of organic carbon in a continuum from the shelf to the basin. Algal biomarkers (polyunsaturated and short-chain saturated fatty acids, 24-methylcholesta-5,24(28)-dien-3β-ol, dinosterol) highlight the substantial contribution of organic matter from water column and sea-ice primary productivity in shelf environments, while redox markers such as acid volatile sulfide (AVS), Mn, and Re indicate intense metabolism of this material leading to sediment anoxia. Shelf sediments also receive considerable inputs from terrestrial organic carbon, with biomarker composition suggesting the presence of multiple pools of terrestrial organic matter segregated by age/lability or hydrodynamic sorting. Sedimentary metabolism was not as intense in slope sediments as on the shelf; however, sufficient labile organic matter is present to create suboxic and anoxic conditions, at least intermittently, as organic matter is focused towards the slope. Basin sediments also showed evidence for episodic delivery of labile organic carbon inputs despite the strong physical controls of water depth and sea-ice cover. Principal components analysis of the lipid biomarker data was used to estimate fractions of preserved recalcitrant (of terrestrial origin) and labile (of marine origin) organic matter in the sediments, with ranges of 12–79%, 14–45%, and 37–66% found for the shelf, slope, and basin cores, respectively. On average, the relative preserved terrestrial organic matter in basin sediments was 56%, suggesting exchange of organic carbon between nearshore and basin environments in the western Arctic.

Bulk geochemical parameters and organic matter biomarkers in a short, high resolution gravity core (Lake Valencia, Venezuela) were examined to reconstruct anthropogenic impacts on the lake’s conditions. During the period of ca. 1840–1990, sedimentary organic matter was characterized by high contents of total organic C (TOC) and total N (TN), low TOC/TN values as well as relatively enriched δ13C and δ15N signals, suggesting a primary autochthonous (algae and macrophytes) organic matter origin. The occurrence of large amounts of C23 and C25 relative to C29 and C31 n-alkanes indicated substantial inputs from submerged/floating macrophytes. The variations of C32 15-keto-ol, tetrahymanol, diploptene, C32 bishomohopanol, 2-methylhopane, dinosterol and isoarborinol concentrations over the investigated period record changes in the planktonic community structure, including Botryococcus braunii, bacteriavore ciliates, cyanobacteria, Eustigmatophytes and dinoflagellates. A principal shift occurred in the 1910s when cyanobacteria and dinoflagellates became more abundant at the expense and decline of B. braunii and Eustigmatophytes, likely related to increasing anthropogenic activity around the lake. A second shift (less obvious) occurred in the 1960s when cyanobacteria became the sole predominant planktonic class, coinciding with further deterioration of lake conditions.

Using multiple geochemical proxies including specific biomarkers (dinosterol, phytol, stigmasterol and b-sitosterol) measured in a high-sedimentation rate core collected from the inner shelf (depth � 45 m) off Goa (India), we reconstruct surface productivity, which is mainly controlled by the monsoon upwelling in this region, during the last ca. 700 a. Surface productivity appears to have varied in tandem with the Konkan-Goa rainfall and sunspot activity during the instrumental period (last 250 a). The productivity proxies also covary with the total solar irradiance reconstructed for the period beyond the instrumental era, within the considerable uncertainty of the age model. This suggests that solar forcing may control coastal upwelling intensity and biological productivity in the eastern Arabian Sea on decadal to centennial timescales. During the late Anthropocene (last ca. 50 a), steep increases in all four biomarkers indicate greatly enhanced productivity in response to high solar irradiance as well as anthropogenic inputs of nutrients. Copyright # 2008 John Wiley & Sons, Ltd.

The interconnected Icaraí and Jurujuba embayments, set within the lower south-eastern portion of Guanabara Bay, SE-Brazil, have been subject to the direct input of domestic effluents and other associated contaminants from human activities in their watersheds. This study addresses the composition of carbon, nitrogen and molecular steroid markers of surface sediments (n = 24) and a short core (L = 47 cm), in order to evaluate the impact by sewage, the contribution between allochthonous and autochthonous derived organic matter and eutrophication of the embayments. Coprostanol concentrations revealed, when compared to other regions in Guanabara Bay, high contamination by sewage close to the point of sewage discharge in Icaraí embayment. In contrast, the more enclosed and eutrophic Jurujuba embayment exhibited a larger contribution of autochthonous organic matter, as shown by the combination of cholesterol, dinosterol and, partially, also brassicasterol. The presence of stigmasterol and b-sitosterol also indicated a minor contribution of organic matter from terrestrial plants, as revealed by principal component analysis. The sedimentary record of the Jurujuba embayment exhibited highest concentrations of all sterol markers in the top layer, corroborating the recent increase in the accumulation of sewage, plankton derived organic carbon and also eutrophication. Trend in degradation of organic matter was evidenced by sterol/stanol ratios and the behavior of dinosterol indicated that the embayment has been dominated by the accumulation of phytoplankton derived organic matter since earlier times.As enseadas de Icaraí e Jurujuba, localizadas na porção sudoeste da Baía de Guanabara, são sujeitas a impactos ambientais decorrentes da ocupação humana nas suas bacias de drenagem. No presente trabalho foi determinada a composição elementar (C e N) e molecular (esteróides) da matéria orgânica em amostras de sedimentos superficiais (n = 24) e de um testemunho curto (c = 47 cm) nas enseadas. As concentrações de coprostanol, em comparação com outras áreas da Baía de Guanabara, indicaram elevado nível de contaminação por esgotos nas estações mais próximas ao ponto de lançamento de efluentes, na Enseada de Icaraí. A Enseada de Jurujuba, mais enclausurada e eutrófica, apresentou uma maior contribuição de matéria orgânica autóctone, conforme evidenciado pelos marcadores colesterol, dinosterol, e parcialmente, também , brassicasterol. A presença de estigmasterol e b-sitosterol indicaram leve contribuição de matéria orgânica oriunda de vegetação terrestre, conforme revelou a análise por componentes principais. No registro sedimentar, foram observados maiores teores de matéria orgânica e esteróis na camada superior, corroborando a acumulação recente de esgotos e de matéria orgânica fitoplanctônica, como conseqüência do processo de eutrofização do sistema. A presença de processos de degradação da matéria orgânica foi evidenciada pelas razões entre esteróis/estanóis, e o perfil do dinosterol indicou que na Enseada predomina o acúmulo de material fitoplanctônico anteriormente ao processo de eutrofização.

Abundances and isotopic compositions of sterols and of total organic carbon in surface sediments were measured at 18 stations in the Ross Sea, Antarctica. Ten sterols, 5α-cholestan-3β-ol (cholestanol), cholest-5-en-3β-ol (cholesterol), cholest-5,22E-dien-3β-ol, 24-methyl-5α-cholest-22E-en-3β-ol (brassicastanol), 24-methyl-cholest-5,22E-dien-3β-ol (brassicasterol), 24-ethyl-5α-cholestan-3β-ol (sitostanol), 24-ethyl-cholest-5-en-3β-ol (sitosterol), 24-ethyl-cholest-5,22E-dien-3β-ol (stigmasterol), 4α,23,24-trimethyl-5α-cholestan-3β-ol (dinostanol), and 4α,23,24-trimethyl-5α-cholest-22E-en-3β-ol (dinosterol), are most widely distributed. Polytopic vector analysis of the variations in abundance resolved four sources for these compounds: an assemblage of phytoplankton characteristic of the Ross Sea Polynya, diatoms and associated consumers, zooplankton, and processes associated with heterotrophic dinoflagellates. Concentrations of stanols were strongly correlated with those of dinosterol and dinostanol. Concentrations of total organic carbon (TOC) ranged from 0.1% to 1.2% and were lowest on crests and banks and higher in basins. The mole fraction of organic carbon occurring as sterols ranged from 3 to 1100 ppm. Values were lowest at stations with anomalously old TOC (estimated from regional variations in the radiocarbon age of acid-insoluble organic carbon), thus pointing to weathering and redistribution of surface sediments as important factors in the differential degradation of sterols and TOC. The difference in first order rate constants for the degradation of these materials is ca. 0.002 yr−1. Stigmasterol and the C27 sterols were significantly enriched in 13C relative to other sterols. The abundance of 13C in TOC at four western stations was 4‰ higher than elsewhere. Abundances of 13C in all sterols at these stations is also 4‰ higher than elsewhere, indicating enrichment of 13C in the entire biological community. Independent observations of P CO 2 in surface waters, together with known relationships between isotopic fractionation and the concentration of dissolved CO2, show that the isotopic zonation in organic carbon is due entirely to dynamic drawdown of CO2 in western surface waters. At those locations, late melting of ice produces salinity gradients that inhibit mixing of CO2 from deeper waters.

Total organic carbon (TOC), total nitrogen (TN), stable isotopes (δ13C and δ15N), lipids and biogenic silica (BSi) from a high-resolution sediment core east of Hong Kong span the interval from 1925 to 2001. Organic matter (OM) within this core (E2) is derived from both marine phytoplankton and terrestrial material as deduced from the range of values of δ13Corg (− 24.0‰ to − 22.4‰) and δ15N (2.9‰ to 5.3‰) and lipid biomarkers. Diatom and dinoflagellate productivity which is reflected in the biogenic silica (BSi) and dinosterol concentrations respectively, increased gradually starting in 1940 and accelerated after 1965, especially between 1980 and 2000, indicating that algal blooms and/or red tides caused by eutrophication increased during this time. The abundance of coprostanol, which reflects domestic sewage discharge, and the terrestrial biomarkers (long-chain fatty acids and fatty alcohols and sitosterol) exhibit similar temporal changes with the primary production, showing that the enhanced eutrophication resulted from increased anthropogenic activities in the northern coastal waters of the South China Sea (SCS) in recent decades.

International audience; Selected lipid biomarkers were analyzed in modern aerobic surface sediments from the tropical NE Atlantic off the Mauritanian coast, in the frame of the JGOFS EUMELI program. This paper explores how sedimentary molecular proxies record productivity and vascular plant inputs. Dry weight-normalized concentrations and TOC-normalized concentrations of biomarkers poorly matched the gradient of higher-plant inputs and of primary productivity. In contrast, mass accumulation rates of long-chain n-alkanols and n-fatty acids (80-710 and 210-1750 μg m- 2 yr- 1, respectively) showed good agreement with dust inputs transported between 15 and 24°N by NE trade winds, whereas long-chain n-alkanes showed a distinct pattern. At the coastal site, n-alkanols and n-fatty acids predominated over long-chain n-alkanes. Cross-shelf changes in proportions of n-fatty acids and n-alkanols relative to n-alkanes point to an increased degradation of terrigeneous waxes when going offshore. The cross-shelf C/N ratio poorly registered vascular plant inputs, most probably because denitrification influenced C/N values at the eutrophic site. Mass accumulation rates of phytoplanktonic biomarkers declined from the eutrophic to the oligotrophic site, reflecting the primary productivity variation. Mass accumulation rates of highly branched isoprenoid hydrocarbons, C37 n-alkenones, n-alkyl diols and dinosterol varied from 3 to 410, 9 to 1600, 12 to 360 and 7 to 320 μg m- 2 yr- 1, respectively. They target the productivity of Haslea-type diatoms, coccolithophorids, eustigmatophytes and dinoflagellates. While the results encourage the development of molecular proxies of palaeoproductivity and of palaeophytocommunities, progress is still needed to deconvolute the impact of degradation on mass accumulation rates and to move towards quantitative calibrations.