Geolipid, pollen and diaton stratigraphy in postglacial lacustrine sediments

As part of our continuing investigation of specific compounds as organic matter indicators in lake bottoms, we have examined geolipids, pollen and diatoms in sediments from different periods in the postglacial history of Heart Lake, New York. Sediment core sections representing the major watershed vegetation periods were extracted for unbound and bound fatty acids, hydrocarbons and alcohols. Fatty acids constitute most of the extracted material. Minor decreases in unsaturated acids with depth indicate little degradation of organic matter in these sediments. The dominant unbound n-alkanoic acid in the core sections is either C22 or C24, but bound fractions contain few long chain acids and are dominated by n-C16. Nearly all the hydrocarbons are found in the unbound fraction. The ratio of C29/C17 n-alkanes increases from the bottom of the core to near the top as watershed forests have matured and lake productivity has diminished, but drops since European settlement of the region. Organic degradation in this lake bottom is mild, and input indicators appear to be well preserved.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25021/1/0000448.pd

Lessons Learned From the United States Ocean Observatories Initiative

The Ocean Observatories Initiative (OOI) is a United States National Science Foundation-funded major research facility that provides continuous observations of the ocean and seafloor from coastal and open ocean locations in the Atlantic and Pacific. Multiple cycles of OOI infrastructure deployment, recovery, and refurbishment have occurred since operations began in 2014. This heterogeneous ocean observing infrastructure with multidisciplinary sampling in important but challenging locations has provided new scientific and engineering insights into the operation of a sustained ocean observing system. This paper summarizes the challenges, successes, and failures experienced to date and shares recommendations on best practices that will be of benefit to the global ocean observing community

Better Regional Ocean Observing Through Cross-National Cooperation: A Case Study From the Northeast Pacific

The ocean knows no political borders. Ocean processes, like summertime wind-driven upwelling, stretch thousands of kilometers along the Northeast Pacific (NEP) coast. This upwelling drives marine ecosystem productivity and is modulated by weather systems and seasonal to interdecadal ocean-atmosphere variability. Major ocean currents in the NEP transport water properties such as heat, fresh water, nutrients, dissolved oxygen, pCO2, and pH close to the shore. The eastward North Pacific Current bifurcates offshore in the NEP, delivering open-ocean signals south into the California Current and north into the Gulf of Alaska. There is a large and growing number of NEP ocean observing elements operated by government agencies, Native American Tribes, First Nations groups, not-for-profit organizations, and private entities. Observing elements include moored and mobile platforms, shipboard repeat cruises, as well as land-based and estuarine stations. A wide range of multidisciplinary ocean sensors are deployed to track, for example, upwelling, downwelling, ocean productivity, harmful algal blooms, ocean acidification and hypoxia, seismic activity and tsunami wave propagation. Data delivery to shore and observatory controls are done through satellite and cell phone communication, and via seafloor cables. Remote sensing from satellites and land-based coastal radar provide broader spatial coverage, while numerical circulation and biogeochemical modeling complement ocean observing efforts. Models span from the deep ocean into the inland Salish Sea and estuaries. NEP ocean observing systems are used to understand regional processes and, together with numerical models, provide ocean forecasts. By sharing data, experiences and lessons learned, the regional ocean observatory is better than the sum of its parts

TOC, carbonate and bitumen concentrations of DSDP Holes 64-477 and 64-478 (Table 1)

The bitumens of a selection of subsurface sediments from Guaymas Basin, Gulf of California, have been analyzed in order to assess the hydrothermal effects on the organic matter and to better delineate the processes influencing the generation, deposition, and alteration of the hydrothermal petroleums at the seabed. Although the thermally generated subsurface bitumens are generally rich in polar/asphaltic materials, as are the seabed oils, the hydrocarbon transformations parallel the extent of hydrothermal alteration as reflected in the downcore mineralogy at DSDP Sites 477 and 478. At Site 477, a progressive change from n-alkane- to aromatic hydrocarbon-dominated patterns in the high resolution gas chromatography-resolvable fractions of the bitumens accompanies decreases in organic carbon and bitumen yields with depth. These transformations are indicative of sequential hydrothermal alteration of the sediments with depth, due to increasing temperature and/or progressive passage of hydrothermal fluid through the sedimentary column. The polycyclic aromatic hydrocarbon (PAH) distributions undergo extensive transformations (e.g. dealkylation) consistent with hydrothermal alterations, are dominant at depth, and have the broadest range as thermal maturation indices. The aliphatic and aromatic components of the seabed oils can be transported to the seabed independently as a result of their generation under different temperature or depth regimes and sequentially over time during pyrolysis. The concentrations of the parent PAH in the thermally altered subsurface bitumens are comparable to those in the seabed oils. The differential dissolution of the more soluble aromatics and selective solidification/condensation of the higher molecular weight PAH out of the high-temperature fluids exiting at the seabed (chimneys) result in aromatic distributions of the oils significantly skewed towards the larger components [e.g. benzo(ghi)perylene] relative to the subsurface bitumens. Comparison of the downcore hydrocarbon distributions with those in the seabed petroleums support the contention that the hydrothermal oils are mixtures of pyrolysates from different depths or thermal regimes and are significantly altered by differential solubilization during transport and at the seabed

The Influence of Growth Rate on ²H/¹H Fractionation in Continuous Cultures of the Coccolithophorid <i>Emiliania huxleyi</i> and the Diatom <i>Thalassiosira pseudonana</i>

<div><p>The hydrogen isotope (²H/¹H) ratio of lipids from phytoplankton is a powerful new tool for reconstructing hydroclimate variations in the geologic past from marine and lacustrine sediments. Water ²H/¹H changes are reflected in lipid ²H/¹H changes with R² > 0.99, and salinity variations have been shown to cause about a 1‰ change in lipid δ²H values per unit (ppt) change in salinity. Less understood are the effects of growth rate, nutrient limitation and light on ²H/¹H fractionation in phytoplankton. Here we present the first published study of growth rate effects on ²H/¹H fractionation in the lipids of coccolithophorids grown in continuous cultures. <i>Emiliania huxleyi</i> was cultivated in steady state at four growth rates and the δ²H value of individual alkenones (C_37:2, C_37:3, C_38:2, C_38:3), fatty acids (C_14:0, C_16:0, C_18:0), and 24-methyl cholest-5,22-dien-3β-ol (brassicasterol) were measured. ²H/¹H fractionation increased in all lipids as growth rate increased by 24‰ to 79‰ (div d^-1)^-1. We attribute this response to a proportional increase in the fraction of NADPH from Photosystem I (PS1) of photosynthesis relative to NADPH from the cytosolic oxidative pentose phosphate (OPP) pathway in the synthesis of lipids as growth rate increases. A 3-endmember model is presented in which lipid hydrogen comes from NADPH produced in PS1, NADPH produced by OPP, and intracellular water. With published values or best estimates of the fractionation factors for these sources (α_PS1 = 0.4, α_OPP = 0.75, and α_H2O = 0) and half of the hydrogen in a lipid derived from water the model indicates α_lipid = 0.79. This value is within the range measured for alkenones (α_alkenone = 0.77 to 0.81) and fatty acids (α_FA = 0.75 to 0.82) in the chemostat cultures, but is greater than the range for brassicasterol (α_{brassicasterol} = 0.68 to 0.72). The latter is attributed to a greater proportion of hydrogen from NADPH relative to water in isoprenoid lipids. The model successfully explains the increase in ²H/¹H fractionation in the sterol 24-methyl-cholesta-5,24(28)-dien-3β-ol from marine centric diatom <i>T</i>. <i>pseudonana</i> chemostat cultures as growth rate increases. Insensitivity of α_FA in those same cultures may be attributable to a larger fraction of hydrogen in fatty acids sourced from intracellular water at the expense of NADPH as growth rate increases. The high sensitivity of α to growth rate in <i>E</i>. <i>huxleyi</i> lipids and a <i>T</i>. <i>pseudonana</i> sterol implies that any change in growth rate larger than ~0.15 div d^-1 can cause a change in δ²H_lipid that is larger than the analytical error of the measurement (~5‰), and needs to be considered when interpreting δ²H_lipid variations in sediments.</p></div

Concentration of lipids as a function of growth rate in <i>E</i>. <i>huxleyi</i> cultures.

<p>Concentrations presented in ng lipid per mL of culture media. (A) Alkenones and brassicasterol. (B) Fatty acids.</p

Organic geochemical comparison of Cretaceous green and black claystones at DSDP Hole 75-530A

Three pairs of Upper Cretaceous black shales and adjacent green claystones from Hole 530A were analyzed to compare types and amounts of organic matter and lipids and to seek information about their environments of deposition. The organic-carbon-rich black shales have C/N ratios nearly seven times those of the organic-carbon-lean green claystones. The lipid content of organic matter in the black shales is about ten times less than in adjacent green layers. Organic matter in both types of rocks is thermally immature, and distributions of alkanoic acids, alkanols, sterols, and alkanes contain large amounts of terrigenous components. Pristane/phytane ratios of less than one suggest that younger Turonian sediments were laid down under anoxic conditions, but ratios greater than one suggest that older Turonian Cenomanian deposits accumulated in a more oxic environment. Closely bedded green and black layers have very similar types of lipid distributions and differ primarily in concentrations, although black shales contain somewhat larger amounts of terrigenous lipid components. Geochemical and stratigraphic evidence suggests much of the organic matter in these samples originated on the African continental margin and was transported to the Angola Basin by turbidity flow. Rapid reburial of organic-carbon-rich sediments led to formation of the black shales

Fractionation factor for C₃₇ alkenones as a function of growth rate in <i>E</i>. <i>huxleyi</i> and <i>G</i>. <i>oceanica</i> cultures.

<p>The presented results are from the following sources: <i>E</i>. <i>huxleyi</i> data: continuous cultures from this study (solid green circles), batch cultures from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141643#pone.0141643.ref010" target="_blank">10</a>] (open brown circles) and [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141643#pone.0141643.ref036" target="_blank">36</a>] (open blue circles). <i>G</i>. <i>oceanica</i> data: batch cultures from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141643#pone.0141643.ref010" target="_blank">10</a>] (open brown squares) and [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141643#pone.0141643.ref023" target="_blank">23</a>] (open purple squares). All data are from C₃₇ methyl alkenones. The C_37:2 and C_37:3 alkenones were measured and plotted separately in this study, whereas they were combined and measured together in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141643#pone.0141643.ref010" target="_blank">10</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141643#pone.0141643.ref023" target="_blank">23</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141643#pone.0141643.ref036" target="_blank">36</a>].</p

Concentration of lipids as a function of growth rate in <i>T</i>. <i>pseudonana</i> cultures.

<p>Concentrations presented in 10⁻¹⁵ g (fg) cell^-1. Open symbols represent estimates from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0141643#pone.0141643.ref037" target="_blank">37</a>]. Best fit lines in are curved owing to the log scale of the y-axis. The purpose of fitting lines to 3 data points is to demonstrate the positive slope for FAs and negative slope for 24-methyl-cholesta-5,24(28)-dien-3β-ol.</p