Search

A site representative of the oligotrophic North Pacific subtropical gyre (NPSG) alkenone content and composition, in a study of Station ALOHA, on suspended particulate materials and sinking particulate materials, are examined. It is found that each year, the sediment trap records documented pronounced alkenone export events in winter and summer seasons.

Isorenieratane, a molecular fossil derived from the brown strain of the green sulfur bacteria Chlorobiaceae, is ubiquitous in the organic carbon-rich, argillaceous, fossiliferous Peterborough Member (Callovian, UK) of the Oxford Clay Formation, indicating a temporal overlap of the euphotic and sulfidic zone in the water column. The presence of euxinic conditions in the water column is inconsistent with the abundant benthic fauna in that formation, which indicates bottom-water oxygenation. These conflicting geochemical and paleontological data suggest intermittent euxinia during deposition. The duration of oxic-dysoxic events can be estimated by considering the life mode, life span, and colonization time of the benthic fauna incorporated in these sedimentary rocks. As previously proposed, the preservation of sedimentary organic matter, based on Rock-Eval parameters, is directly related to the frequency and/or duration of oxic bottom-water conditions. Keywords: green sulfur bacteria, biofacies, Oxford Clay Formation, Peterborough Member, anoxia, isorenieratane.

Nitrous oxide is a trace gas which is increasing in concentration in the atmosphere. Its biogeochemical cycle has been closely scrutinized, but the nature and magnitude of sources and sinks are still being debated. Dual-isotope measurements of nitrous oxide were taken from the water column of the subtropical North Pacific Ocean. Nitrous oxide is depleted in (super15)N and (super18)O within the lower-euphotic and upper-aphotic zones, consistent with predictions of a near-surface isotopically depleted oceanic nitrous oxide source.

Sample introduction systems have been developed to significantly extend existing isotope ratio monitoring gas chromatography/mass spectrometry techniques to allow the simultaneous determination of the concentration and stable carbon isotopic ratio of methane from low-concentration aqueous and gaseous samples. These systems, along with improvements to the basic analytical system, are used with 1-50 nM water samples and 45 ppb-250 ppm (v/v) gas samples. The detection limit of the technique is 200 pmol of C[H.sub.4] in either aqueous or gaseous samples. The precision of isotopic measurements of replicate samples is [less than or equal to]0.8% for water and 0.9% [per thousand] when 200-pmol gas samples are analyzed, the latter improving to less than 0.1% [per thousand] with 4-nmol or larger gas samples.

Compound‐specific isotope analyses (CSIA) and multivariate "isotope fingerprinting" track biosynthetic sources and reveal trophic interactions in food webs. However, CSIA have not been widely applied in the study of marine symbioses. Here, we exposed a reef coral (Montipora capitata) in symbiosis with Symbiodiniaceae algae to experimental treatments (autotrophy, mixotrophy, heterotrophy) to test for trophic shifts and amino acid (AA) sources using paired bulk (δ13C, δ15N) and AA‐CSIA (δ13CAA, δ15NAA). Treatments did not influence carbon or nitrogen trophic proxies, thereby not supporting nutritional plasticity. Instead, hosts and symbionts consistently overlapped in essential‐ and nonessential‐δ13CAA (11 of 13 amino acids) and trophic‐ and source‐δ15NAA values (9 of 13 amino acids). Host and symbiont trophic‐δ15NAA values positively correlated with a plankton end‐member, indicative of trophic connections and dietary sources for trophic‐AA nitrogen. However, mass balance of AA‐trophic positions (TPGlx–Phe) revealed heterotrophic influences to be highly variable (1–41% heterotrophy). Linear discriminant analysis using M. capitata mean‐normalized essential‐δ13CAA with previously published values (Pocillopora meandrina) showed similar nutrition isotope fingerprints (Symbiodiniaceae vs. plankton) but revealed species‐specific trophic strategies. Montipora capitata and Symbiodiniaceae shared identical AA‐fingerprints, whereas P. meandrina was assigned to either symbiont or plankton nutrition. Thus, M. capitata was 100% reliant on symbionts for essential‐δ13CAA and demonstrated autotrophic fidelity and contrasts with trophic plasticity reported in P. meandrina. While M. capitata AA may originate from host and/or symbiont biosynthesis, AA carbon is Symbiodiniaceae‐derived. Together, AA‐CSIA/isotope fingerprinting advances the study of coral trophic plasticity and are powerful tools in the study of marine symbioses. [ABSTRACT FROM AUTHOR]

Mercury isotopic compositions of amphipods and snailfish from deep-sea trenches reveal information on the sources and transformations of mercury in the deep oceans. Evidence for methylmercury subjected to photochemical degradation in the photic zone is provided by odd-mass independent isotope values (?199Hg) in amphipods from the Kermadec Trench, which average 1.57? (±0.14, n = 12, SD), and amphipods from the Mariana Trench, which average 1.49?(±0.28, n = 13). These values are close to the average value of 1.48? (±0.34, n = 10) for methyl-mercury in fish that feed at ~500-m depth in the central Pacific Ocean. Evidence for variable contributions of mercury from rainfall is provided by even-mass independent isotope values (?200Hg) in amphipods that average 0.03? (±0.02, n = 12) for the Kermadec and 0.07? (±0.01, n = 13) for the Mariana Trench compared to the rainfall average of 0.13 (±0.05, n = 8) in the central Pacific. Mass-dependent isotope values (d202Hg) are elevated in amphipods from the Kermadec Trench (0.91 ±0.22?, n = 12) compared to the Mariana Trench (0.26 ±0.23?, n = 13), suggesting a higher level of microbial demethylation of the methyl-mercury pool before incorporation into the base of the foodweb. Our study suggests that mercury in the marine foodweb at ~500 m, which is predominantly anthropogenic, is transported to deep-sea trenches primarily in carrion, and then incorporated into hadal (6,000-11,000-m) food webs. Anthropogenic Hg added to the surface ocean is, therefore, expected to be rapidly transported to the deepest reaches of the oceans. [ABSTRACT FROM AUTHOR]

Sponges are ecologically important components of many marine ecosystems and are abundant benthic fauna on coral reefs. Mycale grandis is an alien invasive sponge found on many partially degraded shallow water coral ecosystems in Hawai'i. Mycale grandis is known to compete spatially with dominant native reef building coral such as Montipora capitata and Porites compressa. Since its appearance in the late 1990s, M. grandis has established itself in a number of coral reef ecosystems around the main Hawaiian Islands. Within south Kāne'ohe Bay, sponge coverage in 2014–2017 ranged from 2.1% on fringing reefs to 32.3% within the mangrove habitat along the northern edge of Coconut Island, which is similar to coverage found in 2006–2007 surveys. Sponges are prolific filter feeders and pump seawater for the dual purpose of obtaining resources and removing metabolic wastes, and thus process large amounts of water in their environment. Mycale grandis pumps 0.0027 L seawater s–1 L–1 sponge, equivalent to 115 times its own volume per day. These pumping rates were combined with biomass estimates, depth, and circulation parameters in south Kāne'ohe Bay to show that M. grandis can cycle a substantial amount of the overlying water column and therefore has the potential to influence the biogeochemistry of overlying reef water in south Kāne'ohe Bay. [ABSTRACT FROM AUTHOR]

Many sponges host abundant and active microbial communities that may play a role in the uptake of dissolved organic matter (DOM) by the sponge holobiont, although the mechanism of DOM uptake and metabolism is uncertain. Bulk and compound-specific isotopic analysis of whole sponge, isolated sponge cells, and isolated symbiotic microbial cells of the shallow water tropical Pacific sponge Mycale grandis were used to elucidate the trophic relationships between the host sponge and its associated microbial community. δ15N and δ13C values of amino acids in M. grandis isolated sponge cells are not different from those of its bacterial symbionts. Consequently, there is no difference in trophic position of the sponge and its symbiotic microbes indicating that M. grandis sponge cell isolates do not display amino acid isotopic characteristics typical of metazoan feeding. Furthermore, both the isolated microbial and sponge cell fractions were characterized by a similarly high ΣV value—a measure of bacterial-re-synthesis of organic matter calculated from the sum of variance among individual δ15N values of trophic amino acids. These high ΣV values observed in the sponge suggest that M. grandis is not reliant on translocated photosynthate from photosymbionts or feeding on water column picoplankton, but obtains nutrition through the uptake of amino acids of bacterial origin. Our results suggest that direct assimilation of bacterially synthesized amino acids from its symbionts, either in a manner similar to translocation observed in the coral holobiont or through phagotrophic feeding, is an important if not primary pathway of amino acid acquisition for M. grandis. [ABSTRACT FROM AUTHOR]