Haptophyte Species Research Articles

Testing the alkenone D/H ratio as a paleo indicator of sea surface salinity in a coastal ocean margin (Mozambique Channel)

Reconstructing past ocean salinity is important for assessing paleoceanographic change and therefore past climatic dynamics. Commonly, sea water salinity reconstruction is based on planktonic foraminifera oxygen isotope values combined with sea surface temperature reconstruction. However, the approach relies on multiple proxies, resulting in rather large uncertainty and, consequently, relatively low accuracy of salinity estimates. An alternative tool for past ocean salinity reconstruction is the hydrogen isotope composition of long chain (C37) alkenones (δDalkenone). Here, we have applied δDalkenone to a 39ka sedimentary record from the Eastern South African continental shelf in the Mozambique Channel, close to the Zambezi River mouth. Despite changes in global seawater δD related to glacial – interglacial ice volume effects, no clear changes were observed in the δDalkenone record throughout the entire 39ka. The BIT index record from the same core, which provides information on relative contributions of soil organic matter (OM) vs. marine input, indicates high soil OM input during the glacial and low input during the Holocene. This suggests a more pronounced freshwater influence at the core location during the glacial, resulting in alkenones depleted in D during that time, thereby explaining the lack of a clear glacial-interglacial alkenone δD shift. The correlation between the BIT index and δDalkenone during the glacial period suggests that increased continental runoff potentially changed the growth conditions of the alkenone-producing haptophytes, promoting coastal haptophyte species with generally more enriched δDalkenone values. We therefore suggest that the application of δDalkenone for reconstructing past salinity in coastal settings may be complicated by changes in the alkenone-producing haptophyte community.

Alkenone distribution in Lake Van sediment over the last 270 ka: influence of temperature and haptophyte species composition

Fossil long-chain alkenones have been used for several decades to reconstruct past ocean surface water temperatures and gained recent interest as a paleotemperature proxy for continental lake settings. However, factors besides temperature can affect alkenone distributions in haptophyte algae, and alkenone compositions can differ between haptophyte species. Alkenone-biosynthesizing haptophyte algae are genetically much more diverse in lakes than in the marine realm, and species-level variations in alkenone compositions could have implications for alkenone paleothermometry. Here, we performed a paired analysis of alkenone distributions and haptophyte species compositions using ancient DNA in up to 270 ka-old sediments of Lake Van in Turkey to reveal a possible species-effect on fossil alkenone distributions and paleotemperature estimates. The same predominant haptophyte in Lake Van today prevailed also since the last ∼100 ka. However, a calibration of alkenone paleotemperature especially in the oldest analyzed intervals is complicated due to a more complex haptophyte species composition predominated by a haptophyte (LVHap_6), which is phylogenetically different from sequences recovered from currently existing lakes including Lake Van and from haptophyte species existing in culture. The predominance of LVHap_6 coincided with the presence of alkenone MeC38:3 and relatively high MeC37:3/4 (2.4) and MeC38:4/5 ratios (3.0). Uk37 index values in the sediment core over the last 270 ka reflect relative changes in past temperature and are additionally linked to haptophyte species composition. A sustained period of high salinity, as indicated by pore-water salinity measurements, could potentially have triggered the succession of haptophytes as sources of alkenones in Lake Van.

Occurrence of extended chain length C41 and C42 alkenones in hypersaline lakes

The chain length of long chain alkenones (LCAs) in ocean and lake sediments commonly ranges from C37 to C39. Alkenones >C40 are extremely rare: C41 and C42 alkenones have only been reported in a Cretaceous black shale (Cenomanian, ca. 95Ma) from the Blake Bahama Basin, western North Atlantic (DSDP Leg 76, site 534). The significance of these exceptionally long chain alkenones is, however, unclear. We have conducted a systematic survey of LCAs in surface sediments from 12 lakes with a wide range of salinity (0.7–146.3g/l) from arid northwestern China. They showed a general trend of increasing maximum chain length with increasing salinity. In particular, C41 and C42 LCAs occurred only in the surface sediments of hypersaline lakes (113.6–146.3g/l), but were absent from lakes with lower salinity, indicating that these compounds may be produced by an unknown haptophyte species living in hypersaline environments.

Rapid adaptation of some phytoplankton species to osmium as a result of spontaneous mutations

To understand the vulnerability of individual species to anthropogenic contamination, it is important to evaluate the different abilities of phytoplankton to respond to environmental changes induced by pollution. The ability of a species to adapt, rather than its initial tolerance, is the basis for survival under rapidly increasing levels of anthropogenic contamination. High doses of osmium (Os) cause massive destruction of diverse phytoplankton groups. In this study, we found that the coastal chlorophyte Tetraselmis suecica and the continental chlorophyte Dictyosphaerium chlorelloides were able to adapt to a lethal dose of Os. In these species, Os-resistant cells arose as a result of rare spontaneous mutations (at rates of approximately 10(-6) mutants per cell division) that occurred before exposure to Os. The mutants remained in the microalgal populations by means of mutation-selection balance. The huge size of phytoplankton populations ensures that there are always enough Os-resistant mutants to guarantee the survival of the population under Os pollution. In contrast, we observed that neither a haptophyte species from open ocean regions nor a cyanobacterium from continental freshwater were able to adapt to the lethal Os dose. Adaptation of phytoplankton to Os contamination is relevant because industrial activities are leading to a rapid increase in Os pollution worldwide.

The influence of salinity on D/H fractionation in alkenones from saline and hypersaline lakes in continental North America

We present a preliminary assessment of the hydrogen isotopic composition of individual alkenones (C37–39 di-, tri- and tetra-unsaturated methyl- and ethyl-ketones) purified from surface lake sediment from sites spanning a range of salinities from 20 to 133ppt. Combining these measurements with measurements of the hydrogen isotopic composition of modern lake water, we estimate the magnitude of D/H fractionation across our sample set and observe reduced sensitivity to salinity compared to observations from Emiliania huxleyi and Gephyrocapsa oceanica. This lends support to the hypothesis that D/H fractionation during biosynthesis is less sensitive to changes in salinity in alkenone producers from continental interior sites than in producers from open marine environments. We also observe stronger correlations between the tetra-unsaturated alkenone δD values with water δD values, and associated α values with salinity than we do for the di- and tri-unsaturated compounds, and suggest that this may result from increased number of lacustrine haptophyte species producing the di- and tri-unsaturated as compared to the tetra-unsaturated.

Vertical and horizontal controls of a haptophyte thin layer in the Bay of Biscay, France

Investigations into the phytoplankton of the Bay of Biscay in July 2006 revealed an extensive bloom of an unidentified haptophyte species. High-resolution sampling techniques identified the region in the vicinity of the mouth of the Loire estuary as an area of high (106–107cellsl−1) cell densities of the haptophyte in a thin sub-surface layer. This organism dominated the phytoplankton population regionally. Measurements of the vertical distribution of horizontal shear showed that the population, located at ca. 20m depth, was confined to a layer lying between two density discontinuities with high shear. Physical measurements indicated that the population was being advected southeastwards, along the coast. Seaward spreading of the population was also noted during the survey. Horizontal diffusion could be derived from the changes in the offshore gradient in the population's distribution with time, with estimates of Kx, the horizontal diffusion coefficient, of the order of 100m2s−1. The magnitude of horizontal dispersion is compared with that of horizontal advective flux, vertical dispersion and growth.

454 Pyrosequencing to Describe Microbial Eukaryotic Community Composition, Diversity and Relative Abundance: A Test for Marine Haptophytes

Next generation sequencing of ribosomal DNA is increasingly used to assess the diversity and structure of microbial communities. Here we test the ability of 454 pyrosequencing to detect the number of species present, and assess the relative abundance in terms of cell numbers and biomass of protists in the phylum Haptophyta. We used a mock community consisting of equal number of cells of 11 haptophyte species and compared targeting DNA and RNA/cDNA, and two different V4 SSU rDNA haptophyte-biased primer pairs. Further, we tested four different bioinformatic filtering methods to reduce errors in the resulting sequence dataset. With sequencing depth of 11000–20000 reads and targeting cDNA with Haptophyta specific primers Hap454 we detected all 11 species. A rarefaction analysis of expected number of species recovered as a function of sampling depth suggested that minimum 1400 reads were required here to recover all species in the mock community. Relative read abundance did not correlate to relative cell numbers. Although the species represented with the largest biomass was also proportionally most abundant among the reads, there was generally a weak correlation between proportional read abundance and proportional biomass of the different species, both with DNA and cDNA as template. The 454 sequencing generated considerable spurious diversity, and more with cDNA than DNA as template. With initial filtering based only on match with barcode and primer we observed 100-fold more operational taxonomic units (OTUs) at 99% similarity than the number of species present in the mock community. Filtering based on quality scores, or denoising with PyroNoise resulted in ten times more OTU99% than the number of species. Denoising with AmpliconNoise reduced the number of OTU99% to match the number of species present in the mock community. Based on our analyses, we propose a strategy to more accurately depict haptophyte diversity using 454 pyrosequencing.

Production and temperature sensitivity of long chain alkenones in the cultured haptophyte Pseudoisochrysis paradoxa

The alkenone unsaturation index (U37K or U37K′) serves as a critical tool for reconstructing temperature in marine environments. Lacustrine haptophyte algae are genetically distinct from their ubiquitous and well studied marine counterparts, and the unknown species-specific genetic imprints on long chain alkenone production by lacustrine species have hindered the widespread application of the U37K temperature proxy to lake sediment records. The haptophyte Pseudoisochrysis paradoxa produces alkenones but its U37K calibration has never been determined. It has an alkenone fingerprint abundant in tetraunsaturated alkenones, a hallmark of lacustrine environments. We present here the first calibration of the U37K index to temperature for a culture of P. paradoxa. We found that the U37K index accurately captured the alkenone response to temperature whereas the U37K′ index failed to do so, with U37K′ values below 0.08 projecting to two different temperature values. Our results add a fifth species-specific U37K calibration and provide another line of evidence that different haptophyte species require different U37K calibrations. The findings also highlight the necessary inclusion of the C37:4 alkenone when reconstructing temperatures from P. paradoxa-derived alkenone records.

Spectral fluorometric characterization of Haptophyte dynamics using the FluoroProbe: an application in the eastern English Channel for monitoring Phaeocystis globosa

In this study, we examined the possibility of using the FluoroProbe for monitoring the dynamics of the Haptophyte Phaeocystis globosa in the coastal waters of the eastern English Channel. The FluoroProbe was recalibrated by recording a new fingerprint for P. globosa and the use of this new fingerprint was tested through a series of laboratory and in situ experiments. The annual dynamics of P. globosa estimated using the FluoroProbe and by flow cytometry were similar. A strong relationship was found between the FluoroProbe estimates of P. globosa biomass expressed in terms of chlorophyll a equivalent per litre (eq. m gL 21 ) and flow cytometric cell counts (r ¼ 0.889, P , 0.001, n ¼ 121). The FluoroProbe can be used to detect the flagellated cells as well as the colonial cells of P. globosa but not to distinguish these two cell types in mixed assemblages. The use of the new fingerprint recorded for P. globosa improved the detection of Isochrysis sp .T his suggests the possibility of using the FluoroProbe to monitor Haptophytes other than P. globosa by calibrating the device with species representative of the region of interest. However, it is important to note that the detection of P. globosa at the species level was possible in the eastern English Channel because it was the only Haptophyte species present with a biomass sufficient to be detected by the FluoroProbe. In areas where several Haptophyte species are simultaneously present, their discrimination will be impossible and in such situations the FluoroProbe can be used to monitor the dynamics of the combined Haptophyte group.

Platychrysis moestrupii sp. nov. (Prymnesiophyceae): a new dimorphic, sand-dwelling haptophyte species from southeastern Australia

Grant B., Waller R.F. and Wetherbee R. 2011. Platychrysis moestrupii sp. nov. (Prymnesiophyceae): a new dimorphic, sand-dwelling haptophyte species from southeastern Australia. Phycologia 50: 608–615. DOI: 10.2216/11-14.1A marine prymnesiophyte, Platychrysis moestrupii sp. nov., is described. Clonal cultures were established from field samples collected during the summer of 2009 from Stewart's Bay, Tasmania, Australia. Cells of P. moestrupii have two distinct morphologies, a motile swimming phase and an adhesive benthic phase. Motile cells are oblong to cylindrical with a posterior rounded protuberance and are 50–65 µm long and 20–25 µm wide. The cells possess two equal to subequal homodynamic flagella and a flexible noncoiling haptonema (8–10 µm long). Benthic cells are irregularly discoid with a diameter of 50–65 µm and are adherent to the substrate. Cells possess scales of two types, both of which are elliptical and 300 by 500 nm. Distal scales are unique amongst Platychrysis and have a marginal series of hair-like spines, a loculate peripheral margin and an internal structure that appears aveolate. Phylogenetic analysis based on the nuclear encoded SSU ribosomal sequence places P. moestrupii with other Platychrysis taxa, although the internal topology of this clade is poorly resolved.

Phylogenetic diversity and evolutionary relatedness of alkenone-producing haptophyte algae in lakes: Implications for continental paleotemperature reconstructions

Alkenones have been found in an increasing number of lakes around the world, making them a promising new tool for continental paleoclimate reconstruction. However, individual lakes may harbor different species of haptophyte algae with different sensitivities to temperature variations, thus presenting a significant challenge to the use of lacustrine alkenones for paleotemperature reconstructions. To explore the extent of lacustrine haptophyte diversity, we conducted the first comprehensive phylogenetic and geochemical survey of lacustrine alkenone producers. We sampled 15 alkenone-containing lake surface sediments from a variety of geographic locales and inferred identities of environmental sequences using 18S ribosomal RNA (rRNA) gene-based phylogenies. For two lakes, BrayaSø in southwest Greenland and Tso Ur on the Tibetan Plateau, we also analyzed both surface and downcore sediments to characterize haptophyte populations through time. In parallel with phylogenetic analyses, we determined the alkenone distributions (including C 37/C 38 ratios, and the presence/absence of C 38 methyl ketones and C 40 compounds) in all the samples. The resulting alkenone profiles from this study do not all align with traditional “marine” versus “coastal/lacustrine” alkenone profiles. Additionally, our genetic data indicate the presence of multiple haptophyte species from a single lake sediment sample; these distinct haptophyte populations could not be discerned from the alkenone profiles alone. These results show that alkenone profiles are not a reliable way to assess the haptophyte algae in lakes and that DNA fingerprinting is a preferred approach for species identification. Although closely related haptophyte species or subspecies may not warrant different temperature calibrations, our results emphasize the importance of genetic data for inferring haptophyte identities and eventually selecting alkenone–temperature calibrations for paleoclimate reconstructions.

Change of the unsaturation degree of alkenone and alkenoate during acclimation to salinity change in Emiliania huxleyi and Gephyrocapsa oceanica with reference to palaeosalinity indicator

Laboratory cultured strains of Emiliania huxleyi EH2 (identical to NIES-837) and Gephyrocapsa oceanica GO1 (NIES-838) were grown at 20oC under various salinity conditions ranging from 15‰ to 34‰, and were analyzed for long-chain (C37 C39) alkenones and (C37 C38) alkyl alkenoates. In both E. huxleyi EH2 and G. oceanica GO1, there were no tetra-unsaturated (C37:4) alkenones, which were frequently identifi ed at low salinity waters in literatures. The alkenone unsaturation index (U37) in E. huxleyi clearly changed under lower salinities such as 27‰ and 32‰, while the values in G. oceanica were almost constant in various salinities. From these results, the U37 variations affected by salinity should be paid attention in paleotemperature reconstruction from natural samples that E. huxleyi predominates, especially in lower saline environments. Interestingly, our culture experiments also showed that the alkenone chain-length ratio (K37/K38) for E. huxleyi and G. oceanica increased with decreasing salinities, although the ranges of these variations were small. These results suggest that the K37/K38 values were affected by the cellular and physiological factors in a single haptophyte cell, although this value varies mainly depending on the changes of haptophyte species and/or strains in natural environments. Hence, we suggest that the K37/K38 ratio can be more reliable as a paleosalinity indicator. * Department of Natural History Sciences, Faculty of Science, Hokkaido University, N10W8, Kita-ku, Sapporo 060-0810, Japan a corresponding author; Tel: +81-11-706-2733 Fax: +81-11-746-0394 e-mail: sawadak@mail.sci.hokudai.ac.jp ** Graduate School of Life and Environmental Sciences, University of Tsukuba, Japan 1-1-1 Tennoudai, Tsukuba 305-8572, Japan

Climatic and environmental controls on the occurrence and distributions of long chain alkenones in lakes of the interior United States

Long chain alkenones (LCA) are temperature-sensitive lipids with great potential for quantitative reconstruction of past continental climate. We conducted the first survey for alkenone biomarkers from 55 different lakes in the Northern Great Plains and Nebraska Sand Hills of the United States. Among those surveyed, we found 13 lakes that contain LCAs in the surface sediments. The highest concentrations of alkenones in sediments are found in cold (mean annual air temperature ∼11 °C versus 17 °C in our warmest sites), brackish to mesosaline (salinity = 8.5–9.7 g/L), and alkaline (pH = 8.4–9.0) lakes with high concentrations of sodium and sulfate. The dynamics of stratification and nutrient availability also appear to play a role in LCA abundance, as early spring mixing promotes a bloom of alkenone-producing haptophytes. Four of the alkenone-containing sites contain the C 37:4 alkenone; however, we discovered an unprecedented lacustrine alkenone distribution in a cluster of lakes, with a total absence of C 37:4 alkenone. We attribute this unusual composition to a different haptophyte species and show that the sulfate:carbonate ratio may control the occurrence of these two distinct populations. We created a new in-situ temperature calibration for lacustrine sites that contain C 37:4 using a water-column calibration from Lake George, ND and show that U 37 K is linearly correlated to lake water temperature ( R 2 = 0.74), but U 37 K ′ is not. A number of lakes contain an unidentified compound series that elutes close to the LCAs, highlighting the importance of routine GC–MS examination prior to using lacustrine LCAs for paleotemperature reconstructions.

Growth rates and pigment patterns of haptophytes isolated from estuarine waters

Eleven haptophyte species were isolated over a two year period (2001–2002) from the Nervion River estuary (Biscay Bay) and batch cultured under non-axenic, isothermal (18 °C), isohaline (30 psu) conditions at three different light levels (60, 110 and 350 µmol photons m − 2 s − 1 ). The variation pattern of growth rate with light intensity was different among species. In all cases growth rates were maxima at 350 µmol photons m − 2 s − 1 and ranged from 0.93 divisions d − 1 in Chrysochromulina throndsenii, the slower growing species at the highest light studied, to 2.23 divisions d − 1 in Pleurochrysis roscoffensis, the faster one at the three light intensities tested. Differences in growth rate were less acute between cultures growing at 60 and 110 µmol photons m − 2 s − 1 but large species-specific differences were observed between 110 and 350 µmol photons m − 2 s − 1 . Based on the occurrence of chl c-type pigments and fucoxanthin and its derivatives, the isolated species belonged to six of the eight pigment types known in Haptophyta. Most haptophytes isolated could be unequivocally distinguished from other algal groups based on pigment composition. Chlorophyll c- and fucoxanthin-type pigment ratios normalized to chl a showed a decrease with the increase in light intensity and growth rate. The observed decrease in pigment ratios were more marked for the fucoxanthin pool than for the chlorophyll c-pool. The intensity of the changes were highly species-specific reflecting both differences in the pigment composition of the different components of the light harvesting protein complexes as well as the balance between them and the reaction centre complexes.

DNA and lipid molecular stratigraphic records of haptophyte succession in the Black Sea during the Holocene

Previous studies suggest that the coccolithophorid haptophyte Emiliania huxleyi entered the Black Sea ~ 3400 yrs ago and since then a coccolith ooze defined as Unit I has developed. Unit I sediments contain long-chain alkenones derived from E. huxleyi whereas the alkenone distribution of the deeper coccolith-free sapropel (Unit II) is rather unusual. Alkenone-derived past sea surface temperature (SST) estimates suggest a large difference between Unit II and Unit I, which is likely a result of unusual biological precursors of the alkenones in Unit II. Here, we report a high-resolution stratigraphic analysis of ancient haptophyte DNA to establish the Holocene succession of haptophytes as sources of the alkenones in the Black Sea. Haptophytes related to brackish Isochrysis spp. were the initial sources of alkenones, and appeared immediately after the onset of sapropel deposition (~ 7550 yrs before present [a BP]). As salinity increased, Isochrysis-related haptophytes were slowly replaced by a complex suite of E. huxleyi strains as sources of alkenones. Our paleogenetic data showed that E. huxleyi colonized the Black Sea shortly after the onset of sapropel deposition, ~ 4000 yrs earlier than previously recognized based on their preserved coccoliths. E. huxleyi strains were the most likely source of the previously reported abundant and unusual C 36 di-unsaturated “Black Sea alkenone”. Strong haptophyte species and strain-specific effects were observed on the level of unsaturation of alkenones which resulted in spurious alkenone-derived SST estimates before 5250 a BP. In contrast, from ~ 5250 a BP onwards a relatively stable haptophyte assemblage dominated by a different suite of E. huxleyi strains yielded robust alkenone-SST values and indicated a gradual cooling from 19 °C to ~ 15 °C at the top of the record (~ 450 a BP).

Haptophytes of the Nervión River estuary, northern Spain

Abstract The meso-macrotidal Nervión River estuary in northern Spain was sampled monthly from March to September 2002 and 2003 to study species composition and abundance of haptophytes in the phytoplankton. From natural samples and uni-algal cultures, 17 haptophyte species were identified using light and electron microscopy. The species were found across a wide range of temperatures and salinities. The most frequently occurring haptophytes in the estuary were species of the genus Chrysochromulina; however, Isochrysis galbana reached highest abundances. Chrysochromulina lanceolata and Phaeocystis globosa were occasionally present at high abundances. Another bloom-forming species, Prymnesium parvum, was recorded only once. Of the genera identified, eight species belonged to Chrysochromulina, two to Prymnesium and the rest of the genera were represented by one species only. The majority of the species were recorded for the first time in the Cantabrian Sea and one of them for the first time in the Atlantic Ocean.

Effect of imbalanced nutrients and immigration on Prymnesium parvum community dominance and toxicity: results from in-lake microcosm experiments

Prymnesium parvum, a haptophyte species, forms harmful blooms, including those that have caused severe fish kills in Texas, USA, over the past 6 yr. We studied P. parvum dynamics using in situ microcosm experiments at Lake Possum Kingdom, Texas, during 3 seasons (fall 2004, winter and spring 2005). Experimental treatments included full and partial nutrient enrichment (encompass- ing nitrogen (N) and phosphorus (P) deficient treatments), P. parvum immigration and combinations of these factors. In the control and N and P deficient treatments, P. parvum populations dominated the community, but only in the N deficient treatments did P. parvum experience a significant growth in the population. In contrast, when nutrients were not limiting, P. parvum tended to lose its competitive edge to other taxa such as chlorophytes, euglenophytes and diatoms, which then dominated the com- munity. Population growth of P. parvum was also stimulated through immigration, but only during the winter experiment, a period of the year when bloom initiation is common. This finding suggests that movement into the water column may be an important process leading to P. parvum bloom initiation. Toxicity of P. parvum to fish was also affected by the nutrient changes: during conditions of no nutrient addition P. parvum was most toxic; intermediate toxicity was observed under N and P deficient conditions, and full nutrient enrichments resulted in nearly non-toxic conditions.

PULSED‐FIELD GEL ELECTROPHORESIS ANALYSIS OF GENOME SIZE AND STRUCTURE INPAVLOVA GYRANSANDDIACRONEMASP. (HAPTOPHYTA)1

Information regarding genome size and structure is a prerequisite for selecting model organisms and for facilitating the most efficient study of their chromosomal DNA. The goal of this study was to identify future candidates for complete‐genome‐sequencing projects among economically or evolutionarily important species of haptophyte algae. Using pulsed‐field gel electrophoresis (PFGE), we identified relatively small genomes and chromosome sizes in two haptophyte species from the class Pavlovophyceae,Pavlova gyransButcher andDiacronemasp. The basal position of Pavlovophyceae in the Haptophyta; the key position of this group in the chromalveolates; and their economic and potential biomedical importance, ease of culturing, and small genome size make these taxa ideal models for complete‐genome sequencing.

Calibration of alkenone unsaturation index with growth temperature for a lacustrine species, Chrysotila lamellosa (Haptophyceae)

Although long chain alkenones (LCKs) occur widely in lacustrine sediments, their origin is not clear. Here, we report a lacustrine source, the non-calcifying species Chrysotila lamellosa Anand (Haptophyceae), collected and isolated from an inland saline water body, Lake Xiarinur (Inner Mongolia, China). Its alkenone pattern is similar to those of coastal marine strains of C. lamellosa,but the relationship between U 37 K ′ index and culture temperature for the lacustrine species is quite different from that of the coastal species. A significant feature of the alkenones in this strain of C. lamellosa is a lack of C 38 methyl alkenones, which might be used to distinguish the species from the marine haptophyte species Emiliania huxleyi and Gephyrocapsa oceanica. The higher C 38 tetraunsaturated compound abundance might be another important feature for distinguishing the C. lamellosa alkenone producer from the coastal species Isochrysis galbana. This alkenone distribution pattern has been detected in many lakes, which suggests that C. lamellosa or a closely related species might be a very common alkenone precursor in lacustrine systems. We examined U 37 K ′ and U 37 K values for C. lamellosa as a function of culture temperature in a batch culture experiment. The calibration for U 37 K ′ vs. culture temperature ( T) was U 37 K ′ = 0.0011 × T 2 - 0.0157 × T + 0.1057 ( n = 14 , r 2 = 0.99 ) from 10 °C to 22 °C or U 37 K ′ = 0.0257 × T - 0.2608 ( n = 9 , r 2 = 0.97 ) from 14 °C to 22 °C. U 37 K vs. culture temperature was U 37 K = 0.0377 × T - 0.5992 ( n = 14 , r 2 = 0.98 ) from 10 °C to 22 °C. Our experiments show that the alkenone unsaturation index ( U 37 K ′ ) is strongly controlled by culture temperature and can be used for palaeoclimate reconstruction.

Unusual C 35 and C 36 alkenones in a paleoceanographic benchmark strain of Emiliania huxleyi

Our specimen of the cultured Emiliania huxleyi strain (CCMP1742, also known as NEPCC55a) that provides the benchmark for U 37 K ′ -based paleothermometry has started producing, for reasons yet unclear, major amounts of three new alkenones identified as ω15,22-C 35 methyl ketone, ω15,22-C 36 ethyl ketone and ω16,23-C 36 methyl ketone. Comparison of these structures with those established now by the same OsO 4 derivatization method applied to the di-unsaturated C 37, C 38 and C 39 alkenones typically found in this organism provides insight into the possible pathway for their biosynthesis. Isothermal batch culture experiments also show the content and composition of these new compounds change systematically and quite significantly in cells when subjected to environmental conditions such as nutrient depletion, variation in light availability and prolonged darkness. Alkenones of similarly unusual short-chain length are evident in suspended particulate materials from present day surface waters in the Ligurian Sea (Mediterranean) and in two different Holocene time horizons (Unit I and Unit II deposits) in Black Sea sediments. However, the positions of the double bonds are different from those that we now report in our culture, implying a different biosynthetic sequence. These alkenones are most likely derived from another, as yet unknown, haptophyte species. If this other organism accounts for all documented occurrences of these compounds in natural samples, then either it has a capacity for growth over a remarkably wide salinity range or surface water salinity in the early Holocene Black Sea may not have been as low as is currently believed.