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Abstract Marine dissolved organic carbon (DOC) is highly depleted in radiocarbon and thus inferred to be largely refractory to removal processes that operate on less than millennial timescales. However, a growing number of reports have shown that a large fraction of marine DOC can be effectively removed during circulation through submarine hydrothermal systems. What is not clear, however, is whether the DOC that remains in hydrothermal fluids is remnant non-reactive DOC from recharged seawater, or DOC that has been largely produced in the subsurface. We collected and characterized warm (∼65 °C) hydrothermal fluids from deep (18, 40, 73, 200 m) within the basalt-hosted basement of the Juan de Fuca Ridge flank in the Northeast Pacific Ocean. DOC concentrations in hydrothermal fluids were 9 to 18 μM, much lower than measured in local deep seawater (37.5 μM). DOC Δ 14 C values of −683‰ to −856‰ were much lower than the Δ 14 C-dissolved inorganic carbon (DIC) values of −880‰ to −918‰, while DOC δ 13 C values of −23.6‰ to −27.0‰ were much heavier than that of the particulate organic carbon (POC) pool (∼ − 34 ‰), suggesting that biological production in the subsurface is not a primary source of DOC. Rather, our data suggest that isotopically enriched DOC are selectively removed from recharged seawater, leaving DOC that is very isotopically depleted in the basaltic basement fluids. Despite the removal of 50–75% of DOC in the subsurface, nuclear magnetic resonance (NMR) functional group analyses indicate that aromatic compounds were added to basaltic basement fluids during passage through the deep subseafloor and may partly contribute to the depleted 14C DOC in the ridge-flank basement fluids. Highlights • Isotopically enriched dissolved organic carbon removed in basaltic basement. • Aromatic carbon is added to fluids during passage through the basaltic subseafloor. • Carbon isotopic data suggest biological production not a primary contributor to DOC. [ABSTRACT FROM AUTHOR]

The nitrogen isotope ratio of algae, which suspended particles and nitrate in the water column, was used to track spatial variations in the marine nitrogen cycle in the Mediterranean Sea. It is observed that N2 fixation represents a significant fraction of the annual fixed N supply to subtropical surface waters.

Abstract: Nuclear magnetic resonance (NMR) spectroscopy shows that > 50% of the carbon in marine high molecular weight dissolved organic matter (HMWDOM) from surface waters is a compositionally well-defined family of acylated polysaccharides that is conserved across ocean basins. However, acid hydrolysis of HMWDOM, followed by chromatographic analysis, recovers only 10–20% of the carbon as neutral, amino and acidic sugars. Most carbohydrate in HMWDOM therefore remains uncharacterized. Here, we use acid hydrolysis followed by Ag+ and Pb2+ cation exchange chromatography to separate HMWDOM hydrolysis products for characterization using 1-D and 2-D NMR spectroscopy. In addition to neutral sugars identified in past studies, we find 3-O-methylglucose, 3-O-methylrhamnose, 2-O-methylrhamnose and 2-O-methylfucose. We also find 3-deoxysugars to be present, although their complete structures could not be determined. Methyl sugars are widely distributed in plant and bacterial structural carbohydrates, such as cell wall polysaccharides, and their presence in HMWDOM suggests that structural carbohydrates may contribute to DOM in surface seawater. We find most HMWDOM carbohydrate is not depolymerized by acid hydrolysis and that the non-hydrolyzable component includes 6-deoxysugars. [Copyright &y& Elsevier]

We report the structure determination (RP-18 HPLC, UV–vis, MS, 1H NMR) of the purified 132(S)–OH methyl bacteriopheophorbide a allomer isolated from a coastal salt pond sediment (Salt Pond, MA, USA). This compound, which occurs with its pheophytin counterpart, is a new bacteriochlorophyll a molecular fossil and may be an intermediate in the formation of some ETIO porphyrins previously isolated from ancient sediments. [Copyright &y& Elsevier]

This study focuses on the chemical characterization of high molecular-weight dissolved organic matter (HMW DOM) isolated from the Middle Atlantic Bight in April 1994 and March 1996. Using proton nuclear magnetic resonance spectroscopy (1HNMR) and monosaccharide analysis we compared both spatial and temporal variations in the chemical structure of HMW DOM across this region. Our analyses support the presence of at least two compositionally distinct components to HMW DOM. The major component is acyl polysaccharide (APS), a biopolymer rich in carbohydrates, acetate and lipid, accounting for between 50% and 80% of the total high molecular-weight dissolved organic carbon (HMW DOC) in surface samples. APS is most abundant in fully marine, surface-water samples, and is a product of autochthonous production. Organic matter with spectral properties characteristic of humic substances is the second major component of HMW DOM. Humic substances are most abundant (up to 49% of the total carbon) in samples collected from estuaries, near the coast, and in deep water, suggesting both marine and perhaps terrestrial sources. Radiocarbon analyses of neutral monosaccharides released by the hydrolysis of APS have similar and modern (average 71‰) Δ14C values. Radiocarbon data support our suggestion that these sugars occur as part of a common macromolecule, with an origin via recent biosynthesis. Preliminary radiocarbon data for total neutral monosaccharides isolated from APS at 300 and 750 m show this fraction to be substantially enriched relative to total HMW DOC and DOC. The relatively enriched radiocarbon values of APS at depth suggest APS is rapidly transported into the deep ocean. [Copyright &y& Elsevier]

We report the isolation and structure determination [RP-18 HPLC, UV-Vis, MS, 1H NMR, and two-dimensional 1H NMR (COSY and ROESY)] of two novel C(132)–OH bacteriopheophytin a allomers from a coastal salt pond sediment (Salt Pond, MA, USA). These allomers are formed by oxidative transformation of bacteriochlorophyll a and/or bacteriopheophytin a, and may play, through fossilization, an important role as intermediates on the formation of some ETIO porphyrins isolated early from sediments. [Copyright &y& Elsevier]

The high molecular weight fraction of dissolved organic matter in a suite of lakes, rivers, seawater, and marine sediment interstitial water samples was collected by ultrafiltration and characterized by molecular level and spectroscopic techniques. Proton nuclear magnetic resonance spectra of all samples show a high degree of similarity, with major contributions from carbohydrates, bound acetate, and lipids. Molecular level analyses of neutral sugars show seven monosaccharides, rhamnose, fucose, arabinose, xylose, mannose, glucose, and galactose, to be abundant, and to occur in comparable relative amounts in each sample. Previous studies have emphasized the distinctive composition of dissolved humic substances in fresh and marine waters, and have attributed these differences to sources and transformations of organic matter unique to each environment. In contrast we find a large fraction of freshwater high molecular weight dissolved organic matter (HMWDOM; > 1kD) to be indistinguishable from marine HMWDOM in bulk and molecular-level chemical properties. Aquatic HMWDOM is similar in chemical composition to biologically derived acylated heteropolysaccharides isolated from marine algal cultures, suggesting a biological source for some fraction of persistent HMWDOM. High molecular weight DOC contributes 51 ± 26% of the total DOC, and monosaccharides 18 ± 8% of the total HMWDOC in our freshwater samples. These contributions are on average higher and more variable, but not significantly different than for surface seawater (30% and 16% respectively). Biogeochemical processes that produce, accumulate, and recycle DOM may therefore share important similarities and be broadly comparable across a range of environmental settings. [Copyright &y& Elsevier]

The southeast subtropical Pacific Ocean was sampled along a zonal transect between the coasts of Chile and Easter Island. This remote area of the world’s ocean presents strong gradients in physical (e.g., temperature, density and light), chemical (e.g., salinity and nutrient concentrations) and microbiological (e.g., cell abundances, biomass and specific growth rates) properties. The goal of this study was to describe the phosphorus (P) dynamics in three main ecosystems along this transect: the upwelling regime off the northern Chilean coast, the oligotrophic area associated with the southeast subtropical Pacific gyre and the transitional area in between these two biomes. We found that inorganic phosphate (Pi) concentrations were high and turnover times were long (>210 nmol l −1 and >31 d, respectively) in the upper water column, along the entire transect. Pi uptake rates in the gyre were low (euphotic layer integrated rates were 0.26 mmol m −2 d −1 in the gyre and 1.28 mmol m −2 d −1 in the upwelling region), yet not only driven by decreases in particle mass or cell abundance (particulate P- and cell- normalized Pi uptake rates in the euphotic layer were ∼1–4 times and ∼3–15 times lower in the gyre than in the upwelling, respectively). However these Pi uptake rates were at or near the maximum Pi uptake velocity (i.e., uptake rates in Pi amended samples were not significantly different from those at ambient concentration: 1.5 and 23.7 nmol l −1 d −1 at 50% PAR in the gyre and upwelling, respectively). Despite the apparent Pi replete conditions, selected dissolved organic P (DOP) compounds were readily hydrolyzed. Nucleotides were the most bioavailable of the DOP substrates tested. Microbes actively assimilated adenosine-5′-triphosphate (ATP) leading to Pi and adenosine incorporation as well as Pi release to the environment. The southeast subtropical Pacific Ocean is a Pi-sufficient environment, yet DOP hydrolytic processes are maintained and contribute to P-cycling across the wide range of environmental conditions present in this ecosystem. [ABSTRACT FROM AUTHOR]

The Mid-Atlantic Bight (MAB) is a highly productive continental shelf region on the eastern North American coast and a potential sight for the export of organic carbon to the open ocean. The dynamics of dissolved organic carbon (DOC) in the MAB were studied during three cruises in April 1994, March 1996 and August 1996 in order to characterize DOC distributions on the shelf, estimate inventories of DOC on the shelf and quantify DOC transport. There were clear spatial and temporal trends in DOC distributions. Concentrations of DOC were greater inshore than offshore and increased southward along the shelf. The total DOC inventory on the shelf during the March and April cruises was estimated at ∼5.88×1012 g C and this increased by 0.4×1012 g C (7%) in August. A simple mass balance of DOC input and export in the MAB resulted in total export of 18.7–19.6×1012g C yr−1. Up to 67% of this carbon is recycled oceanic DOC that is refractory with respect to MAB seawater residence times, ∼4% is introduced through estuaries, sediments and rainwater and at least 29% of the exported shelf DOC (4.1–7.4×1012 g C yr−1) is produced on the shelf. Net ecosystem production of DOC in the MAB is estimated to be between 10% and 18% of MAB primary productivity estimates. Our data supports the hypothesis that the MAB as a whole is net autotrophic for the periods of study and that DOC is an important component in ocean margin carbon budgets. [Copyright &y& Elsevier]

Global environmental changes are challenging the structure and functioning of ecosystems. However, a mechanistic understanding of how global environmental changes will affect ecosystems is still lacking. The complex and interacting biological and physical processes spanning vast temporal and spatial scales that constitute an ecosystem make this a formidable problem. A unifying framework based on ecological theory, that considers fundamental and realized niches, combined with metabolic, evolutionary, and climate change studies, is needed to provide the mechanistic understanding required to evaluate and forecast the future of marine communities, ecosystems, and their services. Marine ecosystems are changing and the services they provide are threatened by global environmental changes. Environmental changes can provoke evolution of species, affecting both the realized and fundamental niches of species. Environmental change can drive evolution, but evolution can also affect environmental conditions. There is a need for a unifying framework that combines studies of evolution, metabolism, and climate change. That framework should be based on ecological theory, on the study of the realized and fundamental niche dynamics, their spatial and temporal dynamics, and their potential response to environmental changes. [ABSTRACT FROM AUTHOR]

Ocean acidification (OA) threatens coral reef ecosystems by slowing calcification and enhancing dissolution of calcifying organisms and sediments. Nevertheless, multiple factors have been shown to modulate OA's impact on calcification, including the nutritional status of the coral host. In three separate experiments, we exposed juveniles of the Atlantic golf ball coral, Favia fragum , to elevated CO 2 and varied nutritional (light or feeding) conditions. Juveniles reared from planulae larvae were significantly larger and produced more CaCO 3 when fed, regardless of CO 2 level. However, corals subjected to elevated CO 2 produced less CaCO 3 per mm 2 regardless of feeding condition. Additionally, unfed corals reared under elevated light levels exhibited lower chlorophyll a and higher total lipid content, but light had no significant effect on coral calcification. Conversely, elevated CO 2 had a significant, negative affect on calcification, regardless of light condition but no detectable effect on physiological tissue parameters. Our results indicate that the sensitivity of juvenile F. fragum calcification to OA was neither modulated by light nor by feeding, despite physiological indications of enhanced nutritional status. This suggests that corals do not necessarily divert energy to maintain calcification under high CO 2 , even when they have the energetic resources to do so. [ABSTRACT FROM AUTHOR]

Abstract: Plant wax lipids and lignin phenols are the two most common classes of molecular markers that are used to trace vascular plant-derived OM in the marine environment. However, their 13C and 14C compositions have not been directly compared, which can be used to constrain the flux and attenuation of terrestrial carbon in marine environment. In this study, we describe a revised method of isolating individual lignin phenols from complex sedimentary matrices for 14C analysis using high pressure liquid chromatography (HPLC) and compare this approach to a method utilizing preparative capillary gas chromatography (PCGC). We then examine in detail the 13C and 14C compositions of plant wax lipids and lignin phenols in sediments from the inner and mid shelf of the Washington margin that are influenced by discharge of the Columbia River. Plant wax lipids (including n-alkanes, n-alkanoic (fatty) acids, n-alkanols, and n-aldehydes) displayed significant variability in both δ13C (−28.3‰ to −37.5‰) and Δ14C values (−204‰ to +2‰), suggesting varied inputs and/or continental storage and transport histories. In contrast, lignin phenols exhibited similar δ13C values (between −30‰ and −34‰) and a relatively narrow range of Δ14C values (−45‰ to −150‰; HPLC-based measurement) that were similar to, or younger than, bulk OM (−195‰ to −137‰). Moreover, lignin phenol 14C age correlated with the degradation characteristics of this terrestrial biopolymer in that vanillyl phenols were on average ∼500years older than syringyl and cinnamyl phenols that degrade faster in soils and sediments. The isotopic characteristics, abundance, and distribution of lignin phenols in sediments suggest that they serve as promising tracers of recently biosynthesized terrestrial OM during supply to, and dispersal within the marine environment. Lignin phenol 14C measurements may also provide useful constraints on the vascular plant end member in isotopic mixing models for carbon source apportionment, and for interpretation of sedimentary records of past vegetation dynamics. [Copyright &y& Elsevier]

Abstract: We targeted the warm, subsurface waters of the Eastern Mediterranean Sea (EMS) to investigate processes that are linked to the chemical composition and cycling of dissolved organic carbon (DOC) in seawater. The apparent respiration of semi-labile DOC accounted for 27 ± 18% of oxygen consumption in EMS mesopelagic and bathypelagic waters; this value is higher than that observed in the bathypelagic open ocean, so the chemical signals that accompany remineralization of DOC may thus be more pronounced in this region. Ultrafiltered dissolved organic matter (UDOM) collected from four deep basins at depths ranging from 2 to 4350m exhibited bulk chemical (1H-NMR) and molecular level (amino acid and monosaccharide) abundances, composition, and spatial distribution that were similar to previous reports, except for a sample collected in the deep waters of the N. Aegean Sea that had been isolated for over a decade. The amino acid component of UDOM was tightly correlated with apparent oxygen utilization and prokaryotic activity, indicating its relationship with remineralization processes that occur over a large range of timescales. Principal component analyses of relative mole percentages of monomers revealed that oxygen consumption and prokaryotic activity were correlated with variability in amino acid distributions but not well correlated with monosaccharide distributions. Taken together, this study elucidates key relationships between the chemical composition of DOM and heterotrophic metabolism. [Copyright &y& Elsevier]

Abstract: A major fraction of particulate organic carbon (POC) in the deep ocean remains molecularly uncharacterized. In an effort to determine the chemical characteristics and source(s) of sinking POC, we studied a nonhydrolyzable fraction of sinking POC using 13C NMR (nuclear magnetic resonance) spectroscopy and analytical pyrolysis. 13C NMR spectra and products from analytical pyrolysis of the nonhydrolyzable fraction exhibit a strongly aliphatic character that is distinct from that of bulk POC. The aliphatic nature of this fraction is consistent with its low stable carbon isotope values. We hypothesize that the nonhydrolyzable fraction derives to a significant extent from a refractory component of organisms that selectively accumulates, resulting in its manifestation as a major part of POC sinking to the deep ocean and in underlying sediments. [Copyright &y& Elsevier]