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Long-chain diols are biomarkers commonly used in the marine realm to reconstruct several environmental parameters such as sea surface temperature and salinity. However, they are also produced in lacustrine and slow-flowing river environments, a characteristic that has proved to be useful to trace past riverine inputs in coastal sedimentary records. So far, their use in lacustrine settings is sparse as their controls are not well-known. Previous studies in two lakes have shown that long-chain diol distribution is linked to changes in temperature (in a small Spanish alpine lake), but also to water column stratification (in a large deep Swiss lake). To understand the controls on i) the presence of long-chain diols in lakes, and ii) the distribution of long-chain diol isomers, surface sediments from 52 Swiss lakes were studied. Long-chain diols are present in 57% of the lakes, and machine learning (i.e., random forest model) showed that their presence is mainly controlled by mean annual air temperature, sodium and potassium concentrations and area of the lakes. Long-chain diol isomer relative distribution seems to react to temperature, nutrient (here nitrate) and oxygen concentrations in the lakes. This new insight was tested on a short sedimentary core from Lake Zurich, and compared with other biomarker proxies (based on branched and isoprenoid glycerol dialkyl glycerol tetraethers), as well as with historical record of nutrient contents and temperature. Variations in the long-chain diol index (LDI) mirror measured temperature, but also reacted to changes in nutrients and oxygenation in the lake. This study highlights the potential of long-chain diols as a proxy to trace both nutrients and temperature in lakes, potentially on geological timescales. [ABSTRACT FROM AUTHOR]

Long-chain diols are biomarkers commonly used in the marine realm to reconstruct several environmental parameters such as sea surface temperature and salinity. However, they are also produced in lacustrine and slow-flowing river environments, a characteristic that has proved to be useful to trace past riverine inputs in coastal sedimentary records. So far, their use in lacustrine settings is sparse as their controls are not well-known. Previous studies in two lakes have shown that long-chain diol distribution is linked to changes in temperature (in a small Spanish alpine lake), but also to water column stratification (in a large deep Swiss lake). To understand the controls on i) the presence of long-chain diols in lakes, and ii) the distribution of long-chain diol isomers, surface sediments from 52 Swiss lakes were studied. Long-chain diols are present in 57% of the lakes, and machine learning (i.e., random forest model) showed that their presence is mainly controlled by mean annual air temperature, sodium and potassium concentrations and area of the lakes. Long-chain diol isomer relative distribution seems to react to temperature, nutrient (here nitrate) and oxygen concentrations in the lakes. This new insight was tested on a short sedimentary core from Lake Zurich, and compared with other biomarker proxies (based on branched and isoprenoid glycerol dialkyl glycerol tetraethers), as well as with historical record of nutrient contents and temperature. Variations in the long-chain diol index (LDI) mirror measured temperature, but also reacted to changes in nutrients and oxygenation in the lake. This study highlights the potential of long-chain diols as a proxy to trace both nutrients and temperature in lakes, potentially on geological timescales.

Long chain alkyl diols (LCDs) are lipid biomarkers that occur ubiquitously in sediments. Their abundance and distributions are increasingly used as the basis of molecular proxies for environmental parameters such as sea surface temperature (SST) via the Long chain Diol Index (LDI), and upwelling intensity and nutrient conditions (parametrized as diol indices, DI-2, and Nutrient Diol Index, NDI, respectively). Their marine producers remain the subject of debate, but in cultures, they can be found within the outer wall (algaenan) of eustigmatophytes or in Proboscia diatoms. LCDs appear to be well preserved in sediments, potentially as a result of their association with algaenan and/or minerals, but little is known of their pre-depositional histories, in particular transport dynamics. Here, 15 surface continental margin sediments as well as one high-deposition-rate sediment core (50 cm, spanning the last ~30 years) were analyzed in order to evaluate the impact of organo-mineral associations, lateral transport, and hydrodynamic sorting on sedimentary LCD signals. The abundance and distribution of LCDs in bulk sediments and corresponding grain-size fractions was determined. The highest proportion of all LCD isomers is found in the fine fraction (2 – 10 µm), which also holds the highest proportion of organic matter in relation to the other grain-size fractions. However, LCDs are also found in the other fractions (sand, coarse silt, and clay), and their concentrations are not correlated with bulk organic carbon content, indicating different preservation or transport mechanisms. LDI-SST in the bulk sediment is comparable to the mean annual SST at all sites except those influenced by upwelling and characterized by strong seasonal SST gradients. To the contrary of other biomarker-related proxies (e.g., alkenones), lateral transport does not appear to strongly affect LDI-SST in size fractions, suggesting that the intimate relationship of LCD with the algaenan may counteract the influence of hydrodynamic mineral sorting processes on related proxy signals. The difference between the fraction-weighted LCD concentration and bulk sedimentary LCD concentration indicates potential release of LCD during laboratory fractionation, suggesting degradation of algaenan or dissolution of opal frustules.

• LDI-reconstructed sea water temperature is impacted by seasonality. • F C32 1,15 is influenced by sea-level changes in the Sea of Okhotsk. • 1,14-diols and opal suggest that primary productivity is controlled by sea-ice cover. • TEXL 86 -temperatures shows a 100-kyr cyclicity after 1100 ka. Long-chain diols have been detected in a wide range of environments and have been used to reconstruct past environmental changes, however only a few long-term records exist to date. Here we reconstructed past environmental changes in the central Sea of Okhotsk over the last 1.5 million years, covering the Mid-Pleistocene Transition (MPT). Sea surface temperatures (SST) reconstructed using the Long-Chain Diol Index (LDI) reflects glacial/interglacial changes. However, when compared with other organic paleothermometers (Uk′ 37 and TEXL 86) the LDI-SST is lower during interglacials and similar or higher during glacials, possibly suggesting a shift of diol production season during interglacials. The LDI-SST does not change in periodicity around the MPT as observed for the TEXL 86 , likely due to this seasonal shift. Diatom productivity, as recorded by 1,14-diols and biogenic opal content, increased during the main deglaciations with a succession from Proboscia diatoms to diatoms with a more heavily silicified shell, confirming that primary productivity in the central Sea of Okhotsk is driven by sea-ice progress and retreat. In contrast to the LDI-SST, the 1,14-diols record shows a change in periodicity around the MPT from 41- to 100-kyr cycle, suggesting an influence of orbital parameters on diatom productivity. In the central Sea of Okhotsk, the relative amount of C 32 1,15-diol (F C32 1,15), a proxy for riverine input, correlates with sea-level change with more riverine-derived material reaching the core site when the Amur River mouth is closer at lower sea-levels. In agreement, F C32 1,15 shows a change in periodicity during the MPT, with the appearance of a 100-kyr cycle. Our results show that the long chain diols can provide important paleoceanographic information in subpolar environments over long time scales, but that temperature reconstructions can be severely impacted by changes in seasonality. [ABSTRACT FROM AUTHOR]

Abstract: Via an all‐catalytic route, long‐chain diamines were prepared by the catalytic direct amination of long‐chain diols, derived from plant oils. High conversion was achieved with good selectivity, with the amount of nitrile impurities formed suppressed to a low level. From the lignocellulose‐based 5‐hydroxymethylfurfural (5‐HMF), or from bis(hydroxymethyl)furan, 2,5‐bis(aminomethyl)furan (BAMF) was generated. 5‐HMF was converted in a one‐pot, one‐step direct amination and reductive amination using ammonia. In both cases, the reaction proceeded very efficiently. In the combined amination and reductive amination, the H2 concentration is a rate‐limiting factor. Reducing the partial pressure of H2 also shortened the reaction time required significantly. Polycondensation of the long‐chain diamines with long‐chain diacids led to higher molecular weight polyamides, illustrating the quality of the diamines obtained by this synthetic approach as monomers. [ABSTRACT FROM AUTHOR]

Abstract: Via an all‐catalytic route, long‐chain diamines were prepared by the catalytic direct amination of long‐chain diols, derived from plant oils. High conversion was achieved with good selectivity, with the amount of nitrile impurities formed suppressed to a low level. From the lignocellulose‐based 5‐hydroxymethylfurfural (5‐HMF), or from bis(hydroxymethyl)furan, 2,5‐bis(aminomethyl)furan (BAMF) was generated. 5‐HMF was converted in a one‐pot, one‐step direct amination and reductive amination using ammonia. In both cases, the reaction proceeded very efficiently. In the combined amination and reductive amination, the H2 concentration is a rate‐limiting factor. Reducing the partial pressure of H2 also shortened the reaction time required significantly. Polycondensation of the long‐chain diamines with long‐chain diacids led to higher molecular weight polyamides, illustrating the quality of the diamines obtained by this synthetic approach as monomers. [ABSTRACT FROM AUTHOR]

Polar lipids of bacteria from the class Thermomicrobia are known to contain long-chain 1,2-diols instead of glycerol, although the nature of polar head groups has not been investigated. We have studied phospholipid classes of two species from the class Thermomicrobia- Sphaerobacter thermophilus and Thermomicrobia sp. WKT50.2. TLC and P-NMR analysis of polar lipids revealed that both S. thermophilus and Thermomicrobia sp. WKT50.2 contain the same set of four major phospholipid classes. Structures of the novel phospholipids in S. thermophilus were established as 2-acylalkyldiol-1- O-phosphoinositol, 2-acylalkyldiol-1- O-phosphoinositol mannoside, 2-acylalkyldiol-1- O-phospho-acylmannoside, and 2-acylalkyldiol-1- O-phosphoinositol acylmannoside. To our knowledge, this is the first report of a phospholipid with a mannose directly bound to the phosphate. We also analyzed fatty acids and long-chain 1,2-diols of S. thermophilus and Thermomicrobia sp. WKT50.2 and compared our data with available information for T. roseum. All species share a similar set of fatty acids, with 12-Me 18:0 being the major fatty acid. The major diol in S. thermophilus was identified as 13-Me 19:0 (66.2 %). The 21:0 diol was the major component both in Thermomicrobia sp. WKT50.2 (50.6 %) and in T. roseum (56.6 %). [ABSTRACT FROM AUTHOR]

Structural identities of the major phospholipid (PL-2), minor phospholipid (PL-1) and trace phospholipid (PL-0) from representative strains of the genera Thermus and Meiothermus were established. Phospholipids were quantified using phosphorus-31 nuclear magnetic resonance (P-NMR). The structures of the major phospholipid (PL-2) from Thermus filiformis MOK14.7 and Meiothermus ruber WRG6.9 were identified as 2′- O-(1,2-diacyl- sn-glycero-3-phospho)-3′- O-(α- N-acetylglucosaminyl)- N-glyceroyl alkylamine (GlcNAc-PGAA) and 2′- O-(2-acylalkyldiol-1- O-phospho)-3′- O-(α- N-acetylglucosaminyl)- N-glyceroyl alkylamine (GlcNAc-diolPGAA). Interestingly, M. ruber contained only a diacyl form of GlcNAc-PGAA (87 %), while T. filiformis contained both GlcNAc-PGAA (59 %) and GlcNAc-diolPGAA (18 %). The structures of the minor phospholipid (PL-1) were established as 2′- O-(1,2-diacyl- sn-glycero-3-phospho)-3′- O-(α-glucosaminyl)- N-glyceroyl alkylamine (GlcN-PGAA, 13 %) in T. filiformis and 2′- O-(1,2-diacyl- sn-glycero-3-phospho)-3′- O-(α-galactosaminyl)- N-glyceroyl alkylamine (GalN-PGAA, 19 %) in M. ruber. This is the first reliable discovery of phosphatidylglyceroylalkylamines modified by glucosamine or galactosamine with a free amino group. No signs of diol-based phosphatidylglyceroylalkylamines were found in PL-1 phospholipids. Similar to PL-2, trace phospholipid (PL-0) from T. filiformis contained both unsubstituted diol-based phosphatidylglyceroylalkylamine (diolPGAA) and PGAA, while M. ruber contained only free PGAA. Unlike analysis using TLC, the diol form of phosphatidylglyceroylalkylamines is clearly resolved from the diacyl form via P-NMR. [ABSTRACT FROM AUTHOR]

Abstract: Presently, upwelling is of major importance for driving primary productivity in the Arabian Sea but its intensity in the past is not well constrained. Here we used long-chain 1,14-alkane diols, specific lipids of diatoms of the genus Proboscia, as new proxies to reconstruct upwelling conditions in the Arabian Sea. Variations in the seasonal lipid fluxes were determined using sediment traps in the Somalia upwelling system deployed 80 km off the coast on the Somali continental slope (NIOP 905, 10°45.444′N / 51°56.655′E) at 1265 m water depth, 268 m above the sea floor and 270 km off the coast in the deep Somali Basin south of Socotra (NIOP 915, 10°43.068′N / 53°34.422′E), at 3047 m depth, 1000 m above the sea floor. Highest fluxes of C28 and C30 1,14-diols (up to almost 600 µg m−2 day−1) were only observed during nutricline shoaling at the onset of the Southwest monsoon (SWM), prior to massive upwelling. By contrast, fluxes of C30 1,15-diols, derived from as yet undefined biological sources, only increased marginally during the SWM and also during the Northeast monsoon (NEM), when, instead of upwelling, enhanced vertical mixing led to a second productivity pulse. Sediment core NIOP 905 taken at the continental slope site showed strong fluctuations in relative concentrations of long-chain 1,14- and 1,15-diols with time, which we quantified as the summed concentrations of C28 and C30 1,14-diols divided by the summed concentrations of C28 and C30 1,14-diols and C30 1,15-diols. This diol index follows the same trend as other upwelling intensity records from the Arabian Sea that are based on sea surface temperature reconstructions, organic carbon content, barium/aluminium ratios, and abundance and stable isotope composition of specific foraminiferal species. The diol index was relatively high during the Holocene (ca. 0.7) but much lower during the Late Glacial Maximum (ca. 0.2). It was generally low during the last Glacial but elevated values were found during the first half of marine isotope stage 3 (between 60 and ~45 ka) and at the end of marine isotope stage 5.1 (approximately 80 ka), suggesting intensified glacial upwelling. Our data shows that long chain diols are suitable proxies to reconstruct past upwelling intensities in the Arabian Sea. [Copyright &y& Elsevier]

Sedimentary processes on continental shelves are affected by complex interactions between a variety of riverine and oceanographic processes. In the shelf of the East China Sea (ECS) south of the Yangtze River estuary, we investigated source-to-sink processes relating to local riverine input as well as the effects of the Kuroshio intrusion by examining the distribution of long-chain alkyl diols in surface and core sediments. The results show that at present the main source of 1,14-diols is most likely diatoms belonging to the genus Proboscia. Most C 32 1,15-diol is produced in situ in local rivers (rather than originating from the Yangtze River) and its distribution is mainly restricted to the front of local river mouths along the coast (water depth < 50 m) due to the hydrodynamism of the nearshore circulation system. Although the sources of the 1,13- and 1,15-diols remain uncertain, principal component analysis and their distribution patterns suggest that 1,14-, 1,13- and 1,15-diols have different biological sources, and that their producers may bloom in different seasons. The long chain diol index (LDI), a proxy for sea surface temperature (SST), was used in this study to reconstruct records of SST (with a bias towards autumn temperatures) in different parts of the ECS shelf, except for shallow water areas (water depth < 50 m), which are more affected by riverine input. The diol index (DI), based on 1,14-diols, worked well as a upwelling tracer in our study area, and our results show that upwelling prevails in the ECS shelf and that zones of strengthened upwelling are present to some extent at ~28.8°N–29.6°N and ~ 27.0°N–27.8°N during the summer due to the interaction of geomorphology, monsoons, and different water masses (i.e., the Kuroshio branch and the Yangtze River diluted water). The nutrient diol index (NDI) shows potential as an indicator for nutrient concentration in the surface waters in this study area during the warm season, but further work is needed. • Local riverine input contributes significant amounts of C 32 1,15-diols to the shallow water of the ECS shelf. • Fluvial C 32 1,15-diols corrupt the LDI-based SST records in regions with a strong freshwater influence. • The DI record indicates the presence of zones of enhanced upwelling in the study area in summer. • The NDI shows potential as an indicator for nutrient concentration in the ECS shelf south of the Yangtze River Estuary. [ABSTRACT FROM AUTHOR]

• 1,13- and 1,15-diols are seasonally produced during water-column stratification. • 1,13- and 1,15-diols are likely produced by several species of eustigmatophytes. • Diatoms are unlikely to be 1,14-diol producers in Lake Geneva. Long-chain diols (LCDs) are lipids commonly found in freshwater environments. They are produced in lake waters and in low water-flow regions of rivers but their sources and the controls on their abundance are poorly constrained. To be able to use LCD as environmental proxy (e.g. for reconstructing lake temperature and as a freshwater indicator in marine systems) we need to understand the sources of these LCDs and the processes controlling their abundance and distribution. Therefore, we performed a seasonal study of suspended particulate matter in Lake Geneva, a temperate lake at the border of France and Switzerland in 2017–2018. LCDs were most abundant in lake surface water from late spring to early autumn, coinciding with the thermal stratification of the water column. Their distribution varied throughout the year, which points towards multiple producers. Incubation of lake water with 13C-labelled bicarbonate only showed uptake of inorganic carbon in LCDs during their peak seasonal abundance. An 18S rRNA gene amplicon analysis revealed that eustigmatophytes, known producers of LCDs, are present in Lake Geneva and show the same seasonal trend in abundance as the LCDs, indicating that these algae are likely the most important producers of LCDs in this lake. In combination with previous studies our results suggest that LCDs show potential to trace changes in lake water-column stratification, and validate the use of the C 32 1,15-diol as a proxy for freshwater input from rivers and lakes in marine sediments. [ABSTRACT FROM AUTHOR]

Alpine regions of the Mediterranean realm are among the most climatically sensitive areas in the world. Thus, alpine wetlands from the southern Iberian Peninsula, in the westernmost part of the Mediterranean region, are highly sensitive sensors of environmental changes. Difficulties have surfaced in separating controls by temperature and/or precipitation in previous paleoenvironmental studies from alpine environments in this area. We present a Holocene biomarker record (n -alkanes and long-chain diols) from a high elevation lake, Laguna de Río Seco (LdRS), in the south of the Iberian Peninsula, which contributes to the identification of these forcing mechanisms. The hydrological history of the area, primarily water availability and evapotranspiration, is reconstructed by means of the n- alkane record, including the indices of average chain length, portion aquatic, and carbon preference index, as well as hydrogen isotopes (δD) of aquatic (δD aq) and terrestrial (δD wax) n- alkanes. Temperatures are also estimated using the algae derived long-chain diols. We interpret δD aq and δD wax fluctuations as showing changes in the source and amount of precipitation throughout the LdRS record. An Atlantic precipitation source appears to have predominated during the early-middle Holocene, but an occasional Mediterranean influence with an isotopic enrichment in precipitation is detected in the middle-late Holocene that is likely related to the setting of the current atmospheric pattern in southeastern Iberia under the joint control of the North Atlantic Oscillation (NAO) and the Western Mediterranean dynamics, such as the Western Mediterranean Oscillation (WeMO). Our new record from LdRS is consistent with a generalized trend of a humid early-middle Holocene with low temperature variability, evolving towards an arid middle-late Holocene with abrupt temperature changes. In addition to these long-term trends during the last ∼10,500 years, two phases of climate instability, evidenced by abrupt depletions in δD aq , have been identified at the end of these periods, one between ∼6500 and 5500 cal yr BP and another in the last ∼500 years. These episodes would represent strengthened winter cold conditions that favoured the persistence of snowpack and frozen soil in the catchment, causing reduced terrestrial plant growth and low lake evaporation. According to the long-chain diol record, temperatures during these phases were relatively low, but experienced abrupt increases at the end of each period. • Algal and plant lipids reconstruct Holocene environments in South Iberia alpine wetlands. • First reconstruction of Holocene temperatures and hydrology in South Iberia alpine wetlands. • Wet climate and Atlantic precipitation sources predominate in the early-middle Holocene. • Arid climate and occasional Mediterranean moisture sources lead the middle-late Holocene. • Climate instability phases have been identified in both middle and latest Holocene. [ABSTRACT FROM AUTHOR]

• The LDI proxy is calibrated for the tropics using South China Sea surface sediments. • LDI values are negatively correlated with SST at temperatures above 27 °C. • This new LDI calibration is well correlated with archaeal lipid temperature proxies. The Long-chain Diol Index (LDI) is a palaeotemperature proxy applied to marine sediments up to Miocene in age. Recent studies have revealed that the LDI-inferred temperature yields significant errors in waters >27 °C. This necessitates further assessment of the performance of the LDI proxy in high-temperature marine regimes. For this purpose, we collected 58 surface sediment samples from the tropical South China Sea (SCS), where annual sea surface temperature (SST) ranges from 24 °C to 29 °C. The original LDI calibration yields temperatures <27 °C for these samples, and the residual between the LDI-inferred temperature and the measured SST (ΔT) increases (to >4 °C) as SST increases. This ΔT, or mis-calibration, is significantly correlated with the measured SST as the temperature increases above 27 °C. This relationship also exists in sediment trap data. We therefore re-calibrated the LDI-inferred temperature to generate a new relationship that can be applied to environments with SST >27 °C, which is beyond the range of the original LDI proxy. Both the recalibrated LDI and, for comparison, archaeal lipid temperature proxies were applied in the high-temperature SCS; the improved correlation shows the LDI recalibration could be applied to palaeo-records from tropical oceans. [ABSTRACT FROM AUTHOR]