Lipid biomarker signatures as tracers for harmful cyanobacterial blooms in the Baltic Sea

The recent proliferation of harmful cyanobacterial blooms (cyanoHABs) in the Baltic and other marginal seas poses a severe threat for the health of infested ecosystems as e.g. the massive export and decay of cyanobacterial biomass facilitates the spread of bottom water hypoxia. There is evidence that cyanoHABs occurred repeatedly in the Baltic Sea but knowledge of their spatiotemporal distribution and the cyanobacteria that contributed to them is limited. In this study, we examined representatives of the major bloom-forming heterocystous cyanobacteria (i.e. Aphanizomenon, Dolichospermum (formerly Anabaena) and Nodularia) to establish lipid fingerprints that allow tracking these environmentally important diazotrophs in the modern and past Baltic Sea. The distribution of normal and mid-chain branched alkanes, fatty acid methyl esters, bacteriohopanepolyols and heterocyst glycolipids permitted a clear chemotaxonomic separation of the different heterocystous cyanobacteria but also indicated a close phylogenetic relationship between representatives of the genera Aphanizomenon and Dolichospermum. Compared to the discontinuous nature of phytoplankton surveys studies, the distinct lipid profiles reported here will allow obtaining detailed spatiotemporal information on the frequency and intensity of Baltic Sea cyanoHABs as well as their community composition using the time-integrated biomarker signatures recorded in surface and subsurface sediments. As heterocystous cyanobacteria of the genera Aphanizomenon, Dolichospermum and Nodularia are generally known to form massive blooms in many brackish as well as lacustrine systems worldwide, the chemotaxonomic markers introduced in this study may allow investigating cyanoHABs in a great variety of contemporary environments from polar to tropical latitudes.Peer reviewe

A large-scale transcontinental river system crossed West Antarctica during the Eocene

Extensive ice coverage largely prevents investigations of Antarctica’s unglaciated past. Knowledge about environmental and tectonic development before large-scale glaciation, however, is important for understanding the transition into the modern icehouse world. We report geochronological and sedimentological data from a drill core from the Amundsen Sea shelf, providing insights into tectonic and topographic conditions during the Eocene (~44 to 34 million years ago), shortly before major ice sheet buildup. Our findings reveal the Eocene as a transition period from &gt;40 million years of relative tectonic quiescence toward reactivation of the West Antarctic Rift System, coinciding with incipient volcanism, rise of the Transantarctic Mountains, and renewed sedimentation under temperate climate conditions. The recovered sediments were deposited in a coastal-estuarine swamp environment at the outlet of a &gt;1500-km-long transcontinental river system, draining from the rising Transantarctic Mountains into the Amundsen Sea. Much of West Antarctica hence lied above sea level, but low topographic relief combined with low elevation inhibited widespread ice sheet formation.</jats:p

Life and death in the Chicxulub impact crater: a record of the Paleocene–Eocene Thermal Maximum

latitudes, with sea surface temperatures at some localities exceeding the 35 ∘C at which marine organisms experience heat stress. Relatively few equivalent terrestrial sections have been identified, and the response of land plants to this extreme heat is still poorly understood. Here, we present a new record of the PETM from the peak ring of the Chicxulub impact crater that has been identified based on nannofossil biostratigraphy, an acme of the dinoflagellate genus Apectodinium, and a negative carbon isotope excursion. Geochemical and microfossil proxies show that the PETM is marked by elevated TEXH86-based sea surface temperatures (SSTs) averaging ∼37.8 ∘C, an increase in terrestrial input and surface productivity, salinity stratification, and bottom water anoxia, with biomarkers for green and purple sulfur bacteria indicative of photic zone euxinia in the early part of the event. Pollen and plants spores in this core provide the first PETM floral assemblage described from Mexico, Central America, and the northern Caribbean. The source area was a diverse coastal shrubby tropical forest with a remarkably high abundance of fungal spores, indicating humid conditions. Thus, while seafloor anoxia devastated the benthic marine biota and dinoflagellate assemblages were heat-stressed, the terrestrial plant ecosystem thrived

ICDP workshop on the Lake Tanganyika Scientific Drilling Project: a late Miocene–present record of climate, rifting, and ecosystem evolution from the world's oldest tropical lake

The Neogene and Quaternary are characterized by enormous changes in global climate and environments, including global cooling and the establishment of northern high-latitude glaciers. These changes reshaped global ecosystems, including the emergence of tropical dry forests and savannahs that are found in Africa today, which in turn may have influenced the evolution of humans and their ancestors. However, despite decades of research we lack long, continuous, well-resolved records of tropical climate, ecosystem changes, and surface processes necessary to understand their interactions and influences on evolutionary processes. Lake Tanganyika, Africa, contains the most continuous, long continental climate record from the mid-Miocene (∼10 Ma) to the present anywhere in the tropics and has long been recognized as a top-priority site for scientific drilling. The lake is surrounded by the Miombo woodlands, part of the largest dry tropical biome on Earth. Lake Tanganyika also harbors incredibly diverse endemic biota and an entirely unexplored deep microbial biosphere, and it provides textbook examples of rift segmentation, fault behavior, and associated surface processes. To evaluate the interdisciplinary scientific opportunities that an ICDP drilling program at Lake Tanganyika could offer, more than 70 scientists representing 12 countries and a variety of scientific disciplines met in Dar es Salaam, Tanzania, in June 2019. The team developed key research objectives in basin evolution, source-to-sink sedimentology, organismal evolution, geomicrobiology, paleoclimatology, paleolimnology, terrestrial paleoecology, paleoanthropology, and geochronology to be addressed through scientific drilling on Lake Tanganyika. They also identified drilling targets and strategies, logistical challenges, and education and capacity building programs to be carried out through the project. Participants concluded that a drilling program at Lake Tanganyika would produce the first continuous Miocene–present record from the tropics, transforming our understanding of global environmental change, the environmental context of human origins in Africa, and providing a detailed window into the dynamics, tempo and mode of biological diversification and adaptive radiations.© Author(s) 2020. This open access article is distributed under the Creative Commons Attribution 4.0 License

Heterocyte glycolipid diketones: A novel type of biomarker in the N2-fixing heterocytous cyanobacterium Microchaete sp.

International audienceThe heterocyte (heterocyst) glycolipid (HG) content of heterocytous (heterocystous) cyanobacteria canprincipally be separated into two different types. In the first type, the aglycone moiety attached to thesugar headgroup exclusively contains hydroxyl functionalities resulting in the formation of HG diolsand HG triols. In the second type, one of the hydroxyl groups is replaced by a ketone functionality givingrise to HG keto-ols and HG keto-diols. In the N2-fixing heterocytous cyanobacterium Microchaetesp. PCC7126 both types of HGs were dominant and consisted primarily of two structural isomers each of theHG28diol and HG28keto-ol. In addition to these well-characterized HGs,Microchaetesp. PCC 7126 alsocontained a yet undescribed type of HG that based on comparison of retention times, molecular weightand mass spectrometry consisted of a hexose headgroup attached to an aglycone moiety with 28 carbonatoms at which two instead of one ketone functionalities were attached. Hence, the novel HG structurewas identified as HG28diketone. This study thus provides further evidence for the large structural diver-sity of HGs, which allows chemotaxonomic profiling of heterocytous cyanobacteria and in turn studyingthe community composition of these important diazotrophs in the geological rock record

Effect of water depth on the TEX86 proxy in volcanic lakes of northeastern China

The TEX(86 )index, based on the distribution of isoprenoid glycerol dialkyl glycerol tetraethers (iGDGTs), has been widely applied for reconstructing past sea surface temperature (SST). However, its successful application in lacustrine environments has been limited to certain large lakes in which aquatic Thaumarchaeota are thought be the dominant iGDGT producers. In small lakes, multiple factors, such as iGDGTs from soil and non-thaumarchaeotal sources, could complicate the use of TEX86 as a temperature proxy (Powers et al., 2010). Here we investigate iGDGTs from surface sediments and suspended particulate matter (SPM) in a series of small volcanic lakes (areas: similar to 0.1-8.2 km(2)) from three main volcanic fields of northeastern China. The iGDGT distribution patterns from surface sediments of these lakes differ significantly from those of surrounding soils, global marine sediments, as well as cultured Group I.1 a and Group I.1b Thaumarchaeota, suggesting a substantial contribution of autochthonous non-thaumarchaeotal sources. Interestingly, however, the correlation between TEX86 values in the SPM samples and in situ water temperatures remain strong and display temperature sensitivity similar to previously published linear calibrations from global marine and lake sediments. Our results suggest that the in situ TEX86-temperature relationship is little affected by the non-thaumarchaeotal iGDGT sources in these lakes. However, the TEX86-inferred temperatures from surface sediments show increasingly colder offsets relative to air temperatures with increasing lake depth, which can be explained by the observed increase in iGDGTs production and decrease in water temperatures in water column as depth increases. Our results thus suggest that TEX86 values in the sediments of these volcanic lakes are affected by both temperature and lake depth, and when temperature can be constrained independently or remains constant over a given period of time, have potential application as a lake level proxy in deep volcanic lakes. (C) 2019 Elsevier Ltd. All rights reserved

Temperature induced changes in the heterocyst glycolipid composition of N2 fixing heterocystous cyanobacteria

We investigated the effect of temperature on the heterocyst glycolipid (HG) composition of the diazotrophic heterocystous cyanobacteria Anabaena sp. strain CCY9613 and Nostoc sp. strain CCY9926 grown at 9, 12, 16, 20 and 24 °C. Both strains contained an overall similar composition of heterocyst glycolipids, with 1-(O-hexose)-3,25-hexacosanediols (HG26 diols) and 1-(O-hexose)-3-keto-25-hexacosanols (HG26 keto-ols) dominating minor quantities of 1-(O-hexose)-3,27-octacosanediols (HG28 diols) and 1-(O-hexose)-3-keto-27-octacosanols (HG28 keto-ols). The relative proportion of HG diols vs. HG keto-ols increased with increasing growth temperature, which was quantitatively expressed as HGI26 (heterocyst glycolipid index of 26 carbons). Values of the index decreased from 0.30 to 0.12 in Nostoc CCY9926 and from 0.18 to 0.10 in Anabaena CCY9613 over the temperature interval investigated. Likewise, HGI28 (heterocyst glycolipid index of 28 carbons) values decreased from 0.33 to 0.10 in Nostoc CC9926 and from 0.12 to 0.07 in Anabaena CCY9613 with increasing temperature. Our results thus provide the first evidence that changes in the composition of the heterocyst cell envelope as a function of temperature occur systematically in different heterocystous cyanobacteria and may constitute a mechanism for allowing optimum N2 fixation by regulating the rate of gas diffusion into the heterocyst

Glycerol dialkyl glycerol tetraethers (GDGT) lipids and CARD-FISH data from suspended particulate matter from the central Baltic Sea

During expedition EMB201 in the Baltic Sea we investigated the local producers of glycerol dialkyl glycerol tetraethers (GDGT) and their thriving depth by a combined 16S rRNA gene amplicon sequencing/ CARD-FISH and lipidomic approach. Water samples were taken in December 2018 by a pump-CTD, a giant water sampler and with Niskin bottles at the surface, suboxic and sulfidic zones of the Landsort Deep, Fårö Basin and East Gotland Basin. This data set contains the CARD-FISH and lipidomics data, while the 16S rRNA gene sequencing data is available on ENA. Cell abundance was analysed in an aliquot of 40 ml filtered (pore size 0.22 micro m) sea water fixed with particle-free formaldehyde. Archaeal cells on the filters were specifically hybridized via catalysed reporter deposition-fluorescence in situ hybridization (CARD-FISH) using the Cren537 probe. Cells on the hybridized filter were counter-stained with 40,6-diamidin-2-phenylindol (DAPI). For lipid analysis, 150–600 L sea water were filtered with a flow rate of 1.5 L min-1 on pre-ashed, 142-mm-diameter, 0.7µm pore size glass fibre GF/F filters, and frozen at –20 °C. The filters were lyophilized before different extraction methods were used to obtain intact and core GDGTs by ultra-sonification in different solvent mixtures. The combined supernatants were phase separated before analysis by high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS2) for intact polar lipids and by high performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry (HPLC APCI-MS; ThermoScientific) for core GDGTs

Fractional abundances of biomarkers from IODP Hole 350-U1437B

The dataset comprises fractional abundances of individual isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) and C37 alkenones of samples from the past 1 Ma at Site 350-U1437 relevant for the calculation of the TEX86 (tetraether index based on glycerol dialkyl glycerol tetraethers consisting of 86 carbon atoms), methane index (MI), branched and isoprenoid tetraether index (BIT), and the unsaturated ketone index (UK'37), respectively. The ketone-bearing fractions were measured on an Agilent 7980 GC coupled to an Agilent 5975 MS (Agilent, Germany). The polar fractions were analyzed by high performance liquid chromatography coupled to mass spectrometry (HPLC/MS) using an Alliance 2690 HPLC (Waters, UK) and a Quattro LC triple quadrupole MS (Micromass, UK) to measure glycerol dialkyl glycerol tetraethers (GDGTs)

Biomarker and XRF scanning data from IODP Site 350-U1437B: a study of paleoceanographic and paleoclimatic changes in the Northwest Pacific Ocean over the past 1 Ma

Sediment core U1437B was drilled during International Ocean Discovery Program Expedition 350 in 2014. The aim of this study was to infer information on the paleoclimatic and paleoceanographic evolution of the Northwest Pacific Ocean and adjacent East Asian continent over the past 1 Ma. For this, 174 freeze-dried and homogenized sediment samples from Site U1437 Hole B were extracted using a solvent mixture of dichloromethane:methanol (93:7, v:v) at elevated temperature (75° ) and pressure (50 bar) using a Büchi Speed Extractor (Büchi, Switzerland). Total lipid extracts were desulfurized and an aliquot with an added standard mixture was measured on an Agilent 7980 gas chromatograph (GC) coupled to an Agilent 5975 mass spectrometer (MS) to quantify long- chain n-alkanes, n-alcohols, and nonacosan-10-ol. Another aliquot of the total lipid extracts was separated into apolar, ketone and polar fractions using column chromatography. The ketone-bearing fractions were subsequently measured on an Agilent 7980 GC coupled to an Agilent 5975 MS (Agilent, Germany). The polar fractions were analyzed by high performance liquid chromatography coupled to mass spectrometry (HPLC/MS) using an Alliance 2690 HPLC (Waters, UK) and a Quattro LC triple quadrupole MS (Micromass, UK) to measure glycerol dialkyl glycerol tetraethers (GDGTs). Total organic carbon contents were determined on 200 mg decarbonized sediment powder using an ELTRA CS- 580A elemental analyzer. Additionally, sections 350-U1437B-1H-1A to 17F-4A, comprising the uppermost 120 m of Hole B and corresponding to the past 1 Ma, were scanned using an ITRAX micro-X-ray fluorescence (XRF) core scanner at Kochi Core Center, Japan. XRF spectra were generated every 2 cm with an exposure time of 60 sec. The X-ray beam was generated with a 3 kW Mo tube run at 30 kV and 55 mA. Sea surface temperature estimates calculated from the unsaturated ketone index (UK'37) and GDGT- based tetraether index (TEX86) as well as GDGT-based methane index (MI) and branched and isoprenoid tetraether index (BIT) values are reported in Dataset S1. Dataset S2 contains summed concentrations of long-chain n-alkanes, n-alcohols and nonacosan-10- ol, as well as mass accumulation rates of TOC and C37 alkenones, which were calculated using linear sedimentation rates, alkenone or TOC contents, and dry bulk densities from shipboard measurements (Tamura et al., 2015). Fractional abundances of individual GDGTs and C37 ketones are reported in Dataset S3. Dataset S4 comprises ratios of selected elements calculated from XRF scanning measurements on core sections of the uppermost 120 meters below seafloor of Site U1437 Hole B