Description: Tracing the origin of nutrients is a fundamental goal of food web research but methodological issues associated with current research techniques such as using stable isotope ratios of bulk tissue can lead to confounding results. We investigated whether naturally occurring delta C-13 patterns among amino acids (delta C-13(AA)) could distinguish between multiple aquatic and terrestrial primary production sources. We found that delta C-13(AA) patterns in contrast to bulk delta C-13 values distinguished between carbon derived from algae, seagrass, terrestrial plants, bacteria and fungi. Furthermore, we showed for two aquatic producers that their delta C-13(AA) patterns were largely unaffected by different environmental conditions despite substantial shifts in bulk delta C-13 values. The potential of assessing the major carbon sources at the base of the food web was demonstrated for freshwater, pelagic, and estuarine consumers; consumer delta C-13 patterns of essential amino acids largely matched those of the dominant primary producers in each system. Since amino acids make up about half of organismal carbon, source diagnostic isotope fingerprints can be used as a new complementary approach to overcome some of the limitations of variable source bulk isotope values commonly encountered in estuarine areas and other complex environments with mixed aquatic and terrestrial inputs.

Description: The unabated rise in anthropogenic CO2 emissions is predicted to strongly influence the ocean's environment, increasing the mean sea-surface temperature by 4°C and causing a pH decline of 0.3 units by the year 2100. These changes are likely to affect the nutritional value of marine food sources since temperature and CO2 can influence the fatty (FA) and amino acid (AA) composition of marine primary producers. Here, essential amino (EA) and polyunsaturated fatty (PUFA) acids are of particular importance due to their nutritional value to higher trophic levels. In order to determine the interactive effects of CO2 and temperature on the nutritional quality of a primary producer, we analyzed the relative PUFA and EA composition of the diatom Cylindrotheca fusiformis cultured under a factorial matrix of 2 temperatures (14 and 19°C) and 3 partial pressures of CO2 (180, 380, 750 μatm) for 〉250 generations. Our results show a decay of ∼3% and ∼6% in PUFA and EA content in algae kept at a pCO2 of 750 μatm (high) compared to the 380 μatm (intermediate) CO2 treatments at 14°C. Cultures kept at 19°C displayed a ∼3% lower PUFA content under high compared to intermediate pCO2, while EA did not show differences between treatments. Algae grown at a pCO2 of 180 μatm (low) had a lower PUFA and AA content in relation to those at intermediate and high CO2 levels at 14°C, but there were no differences in EA at 19°C for any CO2 treatment. This study is the first to report adverse effects of warming and acidification on the EA of a primary producer, and corroborates previous observations of negative effects of these stressors on PUFA. Considering that only ∼20% of essential biomolecules such as PUFA (and possibly EA) are incorporated into new biomass at the next trophic level, thepotential impacts of adverse effects of ocean warming and acidification at the base of the food web may be amplified towards higher trophic levels, which rely on them as source of essential biomolecules.

Description: Burial of organic carbon in marine sediments has a profound influence in marine biogeochemical cycles and provides a sink for greenhouse gases such as CO2 and CH4. However, tracing organic carbon from primary production sources as well as its transformations in the sediment record remains challenging. Here we examine a novel but growing tool for tracing the biosynthetic origin of amino acid carbon skeletons, based on naturally occurring stable carbon isotope patterns in individual amino acids (δ13CAA). We focus on two important aspects for δ13CAA utility in sedimentary paleoarchives: first, the fidelity of source diagnostic of algal δ13CAA patterns across different oceanographic growth conditions, and second, the ability of δ13CAA patterns to record the degree of subsequent microbial amino acid synthesis after sedimentary burial. Using the marine diatom Thalassiosira weissflogii, we tested under controlled conditions how δ13CAA patterns respond to changing environmental conditions, including light, salinity, temperature, and pH. Our findings show that while differing oceanic growth conditions can change macromolecular cellular composition, δ13CAA isotopic patterns remain largely invariant. These results emphasize that δ13CAA patterns should accurately record biosynthetic sources across widely disparate oceanographic conditions. We also explored how δ13CAA patterns change as a function of age, total nitrogen and organic carbon content after burial, in a marine sediment core from a coastal upwelling area off Peru. Based on the four most informative amino acids for distinguishing between diatom and bacterial sources (i.e., isoleucine, lysine, leucine and tyrosine), bacterially derived amino acids ranged from 10 to 15 % in the sediment layers from the last 5000 years, and up to 35 % during the last glacial period. The greater bacterial contributions in older sediments indicate that bacterial activity and amino acid resynthesis progressed, approximately as a function of sediment age, to a substantially larger degree than suggested by changes in total organic nitrogen and carbon content. It is uncertain whether archaea may have contributed to sedimentary δ13CAA patterns we observe, and controlled culturing studies will be needed to investigate whether δ13CAA patterns can differentiate bacterial from archeal sources. Further research efforts are also needed to understand how closely δ13CAA patterns derived from hydrolyzable amino acids represent total sedimentary proteineincous material, and more broadly sedimentary organic nitrogen. Overall, however, both our culturing and sediment studies suggest that δ13CAA patterns in sediments will represent a novel proxy for understanding both primary production sources, and the direct bacterial role in the ultimate preservation of sedimentary organic matter.

Description: [1]  Different proxies for sea surface temperature (SST) often exhibit divergent trends for deglacial warming in tropical regions, hampering our understanding of the phase relationship between tropical SSTs and continental ice volume at glacial terminations. To reconcile divergent SST trends, we report reconstructions of two commonly used paleothermometers (the foraminifera G . ruber Mg/Ca and the alkenone unsaturation index) from a marine sediment core collected in the southwestern tropical Indian Ocean encompassing the last 37,000 years. Our results show that SSTs derived from the alkenone unsaturation index (U K’ 37 ) are consistently warmer than those derived from Mg/Ca by ~2-3 °C except for the Heinrich Event 1. In addition, the initial timing for the deglacial warming of alkenone SST started at ~15.6 ka, which lags behind that of Mg/Ca temperatures by 2.5 kyr. We argue that the discrepancy between the two SST proxies reflects seasonal differences between summer and winter rather than post-depositional processes or sedimentary biases. The U K’ 37 SST record clearly mimics the deglacial SST trend recorded in the North Atlantic region for the earlier part of the termination, indicating the early deglacial warming trend attributed to local summer temperatures was likely mediated by changes in the Atlantic Meridional Overturning Circulation at the onset of the deglaciation, In contrast, the glacial to interglacial SST pattern recorded by G . ruber Mg/Ca probably reflects cold season SSTs. This indicates that the cold season SSTs was likely mediated by climate changes in the southern hemisphere, as it closely tracks the Antarctic timing of deglaciation. Therefore our study reveals that the tropical southwestern Indian Ocean seasonal SST was closely linked to climate changes occurring in both hemispheres. The austral summer and winter recorded by each proxy is further supported with seasonal SST trends modeled by AOGCMs for our core site. Our interpretation that the alkenone and Mg/Ca SSTs are seasonally biased may also explain similar proxy mismatches observed in other tropical regions at the onset of the last termination.

Description: Author(s): Britta Johansen, Christian Uhrenfeldt, Arne Nylandsted Larsen, Thomas Garm Pedersen, Hans Ulrik Ulriksen, Peter Kjær Kristensen, Jesper Jung, Thomas Søndergaard, and Kjeld Pedersen We present measurements of the collinear optical transmission through arrays of β -Sn nanoparticles on fused silica substrates. The particles are cylinders or squares with side lengths of 120–520 nm, and heights of 26–118 nm placed in square-periodic arrays fabricated by electron-beam lithography. By... [Phys. Rev. B 84, 113405] Published Mon Sep 12, 2011

Description: The haptophyte Prymnesium parvum is known to cause massive fish kills during its blooms. The toxicity of P. parvum is attributed to its ability to produce prymnesins, a group of supersized ladder-frame polyether compounds. This group of toxins can be further divided into three different types (A-, B- and C- type), which present further diversity in terms of number and chemical structure of derivatives. In the present study, we used nine P. parvum strains representing all three types of prymnesins to elucidate the molecular mechanisms involved in prymnesin biosynthesis. Due to the polyketide nature of prymnesins, particular attention was paid to polyketide synthase genes (PKSs). The transcriptomes of all nine P. parvum strains were screened for the presence of PKS genes. A mean of 25 contigs containing multi-modular type I PKS ketosythase (KS) domains were found per strain, which were subsequently used to assess the evolutionary history of prymnesin production. The phylogenetic analysis of the KS domains showed that, compared to KS transcripts from other organisms, they form distinct clades as well as clades corresponding to each prymnesin type. In addition, a comparative transcriptomic analysis of all strains revealed the presence of candidate genes involved in the biosynthesis of specific prymnesin derivatives. The current study will contribute to a better understanding of the mechanisms of toxin production in P. parvum in order to develop efficient tools for monitoring purposes.

Description: An external standard of goniodomin A (GDA) was prepared from a strain of Alexandrium pseudogonyaulax originating from New Zealand and its chemical structure was confirmed by nuclear magnetic resonance (NMR) spectroscopy. Using the GDA standard, an ultra-performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) method in selected reaction monitoring (SRM) mode was developed for separation and quantification of GDA. This method was successfully applied to planktonic field samples collected during an oceanographic expedition conducted with R/V Uthörn along the Danish west coast, Limfjord and Kattegat in June 2016. In addition, this method was used to characterize goniodomin (GD) profiles of 17 A. pseudogonyaulax strains from the coastal North Sea and from Limfjord. Highest GDA levels were found in Limfjord (up to 590 ng NT−1 m−1), but GDA was also detected in the North Sea appearing at the latitude of Sylt Island northwards and in Kattegat from the eastern mouth of Limfjord down to the Kiel Bight, but at lower abundances than within Limfjord. This is the first reported detection of GDA in planktonic field samples. Chemical analysis of 17 strains of A. pseudogonyaulax revealed that all strains were producers of GDA (5–35 pg cell−1) as well as in most cases minor amounts (0.01–0.07 pg cell−1, expressed as GDA equivalents) of goniodomin B (GDB).