Marine Particulate Organic Matter Research Articles

Temperature is a better predictor of stable carbon isotopic compositions in marine particulates than dissolved CO2 concentration

The stable carbon isotopic composition of marine particulate organic matter (δ13CPOM) varies with source and environmental conditions. Dissolved carbon dioxide (CO2) concentration is thought to influence δ13CPOM more than temperature, but this relationship is poorly constrained in marginal seas. Here we present δ13CPOM, hydrographic and carbonate system variables at the deep chlorophyll maxima of the southern Yellow Sea in late summer 2017. We find δ13CPOM values varied between stable and cyclonic gyre regions, but indicated autochthonous organic matter production and were more strongly correlated with temperature than dissolved CO2 concentration throughout. We find that the relationship between temperature and δ13CPOM was independent of CO2 concentration, whereas the relationship between δ13CPOM and CO2 concentration was dependent on temperature also being correlated with CO2 concentration. We suggest that temperature is the primary determinant of marine δ13CPOM due to temperature-dependent metabolism in phytoplankton, irrespective of inorganic carbon acquisition mode.

Assessing the sources and dynamics of organic matter in a high human impact bay in the northern Beibu Gulf: Insights from stable isotopes and optical properties

Severe human activities in coastal areas have greatly impacted the sources and biogeochemical behaviors of organic matter (OM), including particulate OM (POM) and dissolved OM (DOM). However, few studies have incorporated the indices of POM and DOM to address this issue. Here, a dataset of the combination of stable isotopes of carbon and nitrogen in POM and the optical properties of DOM was presented in Xi Bay, a semi-enclosed bay with a highly developing industrial port in Beibu Gulf, South China, to reveal the origin, distribution, and fate of OM during the rainy season. In the upper bay, depleted δ13C suggested that particulate organic carbon (POC) mainly originated from terrestrial sources. However, the negative relationship between chromophoric DOM (CDOM) and particulate nitrogen (PN) suggested that bacterial-mediated decomposition of POM may be the primary source of CDOM. The negative correlation between humic-like fluorescent components (C1 and C2) and salinity suggested that those two components were mainly affected by terrestrial input. The significant correlation between the protein-like component (C3) and Chl a suggested that C3 was mainly derived from phytoplankton production in the upper bay. In the lower bay, the increase of δ13C values indicated an increased contribution of marine POC. The high levels of CDOM may be due to the decomposition of marine (fresh) POM. However, the low levels of C1 and C2 might be affected by dilution with seawater, and the increased levels of the protein-like C3 were due to enhanced primary production. In addition, the enhancement of δ15N values in both the upper and lower bays indicated serious nitrogen pollution in the bay. This study highlights that biological production fueled by excess nutrients is the dominant OM dynamic process in the bay with high human impact in Beibu Gulf.

Seasonal variations in biochemical (biomolecular and amino acid) compositions and protein quality of particulate organic matter in the Southwestern East/Japan Sea

The biochemical compositions of marine particulate organic matter (POM) can provide significant information to understanding the physiological conditions of phytoplankton and food quality for their potential consumers. We investigated the seasonal variations in biomolecular and amino acid (AA) compositions of the bulk POM in the southwestern East/Japan Sea from four different sampling months (February, April, August, and October) in 2018. In terms of the biomolecular composition of the POM, overall carbohydrates (CHO) were predominant among three biomolecules accounting for 48.6% followed by lipids (LIP; 35.5%) and proteins (PRT; 15.9%) in the East/Japan Sea. However, markedly seasonal differences in the biomolecular composition of POM were found from February to October, which could be due to seasonally different conditions favorable to phytoplankton growth. Dominant AA constituents to trace POM lability were glycine (GLY), alanine (ALA), and glutamic acid (GLU), suggesting that our POM was the mixtures of decomposing and fresher materials. Furthermore, the significantly negative correlation between the proportion of total essential amino acids (EAAs) and PRT composition (r = -0.627, p< 0.01) was probably reflected by nutrient availability to phytoplankton partitioning EAAs or non-essential AAs (NEAAs). The different biomolecular compounds under un- or favorable growth conditions for phytoplankton could determine the nutritional quality of POM as potential prey as well as degradation status of POM. Therefore, the biochemical compositions of phytoplankton-originated POM hold important ecological implications in various marine ecosystems under ongoing climate changes.

Biocatalytic quantification of α-glucan in marine particulate organic matter.

Marine algae drive the marine carbon cycle, converting carbon dioxide into organic material. A major component of this produced biomass is a variety of glycans. Marine α‐glucans include a range of storage glycans from red and green algae, bacteria, fungi, and animals. Although these compounds are likely to account for a high amount of the carbon stored in the oceans they have not been quantified in marine samples so far. Here we present a method to extract and quantify α‐glucans (and compare it with the β‐glucan laminarin) in particulate organic matter from algal cultures and environmental samples using sequential physicochemical extraction and enzymes as α‐glucan‐specific probes. This enzymatic assay is more specific and less susceptible to side reactions than chemical hydrolysis. Using HPAEC‐PAD to detect the hydrolysis products allows for a glycan quantification in particulate marine samples down to a concentration of ≈2 µg/L. We measured glucans in three cultured microalgae as well as in marine particulate organic matter from the North Sea and western North Atlantic Ocean. While the β‐glucan laminarin from diatoms and brown algae is an essential component of marine carbon turnover, our results further indicate the significant contribution of starch‐like α‐glucans to marine particulate organic matter. Henceforth, the combination of glycan‐linkage‐specific enzymes and chromatographic hydrolysis product detection can provide a powerful tool in the exploration of marine glycans and their role in the global carbon cycle.

Contribution of deep-sourced carbon from hydrocarbon seeps to sedimentary organic carbon: Evidence from radiocarbon and stable isotope geochemistry

Sulfate-driven anaerobic oxidation of methane (AOM) limits the release of methane from marine sediments and promotes the formation of carbonates close to the seafloor in seepage areas along continental margins. It has been established that hydrocarbon seeps are a source of methane, dissolved inorganic carbon, and dissolved organic carbon to marine environments. However, questions remain about the contribution of deep-sourced carbon from hydrocarbon seeps to the sedimentary organic carbon pool. In this study, we analyzed carbon quantity, radiocarbon content (as percent modern carbon, pMC), stable carbon isotopic compositions (as δ13C) of organic matter enclosed within seep carbonates from the Gulf of Mexico and the South China Sea to assess if sediment organic matter may be used as a proxy for methane seepage intensity. The δ13C values of organic matter (δ13Corg) exhibited a large range from −81.4‰ to −23.9‰. Radiocarbon contents of the carbonate-bound organic matter in seep carbonates ranged from 6% to 28% pMC, suggesting organic matter of the carbonates is a mixture of marine particulate organic matter (δ13C = −22‰ VPDB and 90% modern carbon) and biomass resulting from methane oxidation (assumed to have 0% modern carbon). Assuming constant productivity in the marine photic zone, it is proposed that seepage intensity and duration are the most important factors controlling the contribution of methane-derived carbon to the sedimentary column. This study reinforces the potential for using δ13C values of organic carbon to discern methane-rich environments in ancient sedimentary environments where authigenic carbonate is not present and to constrain the record of AOM through Earth history.

Different food particle sources in the pearl oyster Pinctada margaritifera and its epibionts

Suspended bivalve culture (e.g. longlines) transfers benthic biomass - including bivalves and various epibionts - toward the water column, creating strong trophic interactions with the planktonic compartment. Trophic interactions are of central interest for ecologists, yet not well understood in coastal lagoon food webs, especially in tropical areas. Using stable isotope (SI) analyses, this study explored the trophic relationships between marine particulate organic matter (POM), pearl oysters and epibionts, in two contrasted production areas in French Polynesia. Different size classes of POM (0.7–2 µm, 2–20 µm, 20–80 µm, 80–250 µm and >250 µm) were well discriminated both by their δ13C and δ15N signature and results showed a low dietary overlap between pearl oysters and epibionts, likely due to assimilation of large particles in greater proportion by pearl oysters. Pearl oyster diet may vary in time in relation with variations of the basal trophic resource and selective feeding, such that their isotopic signature is more variable compared with that of epibionts. Pearl oysters and epibionts might alter nutrient cycling in a different way as reflected by their different tissue C:N.

Climate-Associated Changes in Mercury Sources in the Arctic Fjord Sediments

Despite the large climatic fluctuations in the Arctic over the Holocene, the dominant mercury (Hg) sources and the potential changes in Hg sources associated with the climate remain unclear. Here, we use Hg isotopes to reconstruct changes in Hg sources and processes in two Svalbard fjord sediment cores spanning the Holocene. The Hg isotope ratios of the fjord sediment cores are similar to bedrock and Hg bound to terrestrial total organic carbon (TOC) but different from other sediment cores influenced by atmospheric Hg drawdowns via the sinking of marine particulate organic matter. The absence of significant Hg and TOC relationships indicates that bedrock erosion caused by glacier dynamics is the major Hg source to the fjord sediment rather than those bound to marine and terrestrial TOC. Measurable shifts in Hg sources are observed at regional cooling (4.3 ka) and during the Medieval Warm Period in the late Holocene. The negative shift in δ202Hg (by −0.5‰) at 4.3 ka from baseline (∼10 ka) is consistent with the rapid increase in glacier-mediated physical and chemical erosions of bedrock. The significant positive shifts in δ202Hg (by 0.5‰) in the late Holocene are explained by enhanced input of atmospheric Hg and its drawdown via the sinking of marine particulate organic matter and some anthropogenic influence, which suppressed the positive Δ199Hg and Δ200Hg shifts. This study suggests that Hg isotope ratios measured in sedimentary archives can be used to decipher climate and other local to global changes modifying Hg sources in the Arctic.

Cyclic di-GMP Is Integrated Into a Hierarchal Quorum Sensing Network Regulating Antimicrobial Production and Biofilm Formation in Roseobacter Clade Member Rhodobacterales Strain Y4I

Microbial biofilms associated with marine particulate organic matter carry out transformations that influence local and regional biogeochemical cycles. Early microbial colonizers are often hypothesized to “set the stage” for biofilm structure, dynamics, and function via N-acyl homoserine lactone (AHL)-mediated quorum sensing (QS). Production of AHLs, as well as antimicrobials, contributes to the colonization success of members of the Roseobacter clade. One member of this group of abundant marine bacteria, Rhodobacterales sp. Y4I, possesses two QS systems, phaRI (QS1) and pgaRI (QS2). Here, we characterize mutants in both QS systems to provide genetic evidence that the two systems work in hierarchical fashion to coordinate production of the antimicrobial indigoidine as well as biofilm formation. A mutation in pgaR (QS2) results in decreased expression of genes encoding both QS systems as well as those governing the biosynthesis of indigoidine. In contrast, mutations in QS1 did not significantly influence gene expression of QS2. Addition of exogenous AHLs to QS1 and QS2 mutants led to partial restoration of indigoidine production (45–60% of WT) for QS1 but not QS2. Mutational disruptions of QS1 had a more pronounced effect on biofilm development than those in QS2. Finally, we demonstrate that c-di-GMP levels are altered in QS and indigoidine biosynthesis Y4I mutants. Together, these results indicate that pgaRI (QS2) is at the top of a regulatory hierarchy governing indigoidine biosynthesis and that the global regulatory metabolite, c-di-GMP, is likely integrated into the QS circuitry of this strain. These findings provide mechanistic understanding of physiological processes that are important in elucidating factors driving competitiveness of Roseobacters in nature.

Linking a Latitudinal Gradient in Ocean Hydrography and Elemental Stoichiometry in the Eastern Pacific Ocean

AbstractA past global synthesis of marine particulate organic matter (POM) suggested latitudinal variation in the ratio of surface carbon (C): nitrogen (N): phosphorus (P). However, this synthesis relied on compiled datasets that may have biased the observed pattern. To demonstrate latitudinal shifts in surface C:N:P, we combined hydrographic and POM observations from 28°N to 69°S in the eastern Pacific Ocean (GO‐SHIP line P18). Both POM concentrations and ratios displayed distinct biome‐associated changes. Surface POM concentrations were relatively low in the North Pacific subtropical gyre, increased through the Equatorial Pacific, were lowest in the South Pacific subtropical gyre, and increased through the Southern Ocean. Stoichiometric elemental ratios were systematically above Redfield proportions in warmer regions. However, C:P and N:P gradually decreased across the Southern Ocean despite an abundance of macro‐nutrients. Here, a size‐fraction analysis of POM linked increases in the proportion of large plankton to declining ratios. Subsurface N* values support the hypothesis that accumulated remineralization products of low C:P and N:P exported POM helps maintain the Redfield Ratio of deep nutrients. We finally evaluated stoichiometric models against observations to assess predictive accuracy. We attributed the failure of all models to their inability to capture shifts in the specific nature of nutrient limitation. Our results point to more complex linkages between multinutrient limitation and cellular resource allocation than currently parameterized in models. These results suggest a greater importance of understanding the interaction between the type of nutrient limitation and plankton diversity for predicting the global variation in surface C:N:P.

Resource Utilization of Three Copepods Along Salinity Gradient in the Seomjin River Estuary, Revealed by Stable Isotope Analysis

Estuaries are one of the most productive regions in ecosystems and serve as important nursery and recruitment habitats for various living resources. However, information on the trophic dynamics of estuarine copepods along the salinity gradient is not well known. Here, we investigated resource partitioning among three copepods, Pseudodiaptomus japonicus, Sinocalanus tenellus, and Tortanus dextrilobatus in the Seomjin River estuary of the Korea using stable carbon and nitrogen isotope analyses. Among the three copepods, S. tenellus showed the lowest δ13C values, while the highest δ13C values were observed in T. dextrilobatus. Stable Isotope Analysis in R (SIAR) showed that S. tenellus fed mainly on terrestrial particulate organic matter (POM), while the contribution of marine POM was relatively high in the diet of T. dextilobatus. In contrast, P. japonicus showed relatively high trophic flexibility between terrestrial and marine POM. Thus, the Stable Isotope Bayesian Ellipses in R (SIBER) showed no dietary niche overlap among the three copepods. Therefore, we suggest that the coexistence of S. tenellus, P. japonicus, and T. dextrilobatus in the Seomjin River estuary can be closely associated with species-specific differences in resource utilization along the salinity gradient.

Structure and seasonal variability in fish food webs in a small macrotidal estuary (Canche estuary, Eastern English Channel) based on stable carbon and nitrogen isotope analysis

Estuaries are highly important nursery habitats for a range of fish species because they provide refuge and food, especially for juveniles. However, the importance of specific salinity zones and adjacent shallow marine habitats (subtidal and surf zones) for fish feeding is not well understood, particularly in small macrotidal estuaries. Using the example of the Canche estuary, which is considered a reference for small macrotidal estuaries in France, we investigated the structure and seasonal variability in fish food webs based on stable carbon and nitrogen isotope analysis. Our results provide a new vision of the Canche estuary, which has been considered a major feeding ground for all marine fish that spend time there. Based on δ13C results, our results revealed that organic matter of terrestrial origin has little influence on functioning of the Canche food web, except for flounders in the upstream area of the estuary. Conversely, microphytobenthos and marine particulate organic matter contribute most to the food web of fish in the estuary. Our study also revealed that some fish species visit the estuary for reasons other than feeding, such as to avoid predation or because they are carried by the tide. This work confirmed the suitability of using stable isotopes to trace fish fidelity to feeding grounds less than 10 km apart.

Oceanographic transport along frontal zones forms carbon, nitrogen, and oxygen isoscapes on the east coast of New Zealand: Implications for ecological studies

Characterizing the spatial distribution of δ18O in seawater and δ15N and δ13C in marine particulate organic matter pools can be useful in identifying isotopic discriminators of major water masses and serve as a baseline for food web and other ecological studies. Nevertheless, we do not know how isoscapes of δ18O, δ15N and δ13C are distributed and interact with mesoscale (10–100 km) physical oceanographic features for large parts of the global ocean. Here samples and measurements were collected during research cruises in the austral summer of 2017/18 and 2018/19 along the east coast of the South Island of New Zealand. The physical structure of the water column, δ18O of seawater, and δ15N and δ13C of suspended particulate organic matter were analyzed. Interannual differences in inferred circulation, oceanographic features, and the interaction of Subtropical and Subantarctic water masses in the study area were described. The relationships between nutrient concentrations, physical oceanographic variables and δ18O, δ15N and δ13C isoscapes were investigated by running linear models with all combination of variables, then averaging the most parsimonious ones that best fit the data. Results demonstrate that different environments along the east coast are connected via northward transport of Subtropical Water near the surface and Subantarctic Mode Water at depth (220–500 m). The northward transport of modified STW was associated with nutrient inputs and deepening of the maximum fluorescence depth. The spatial distribution of isotopic values had minimal temporal variability and was primarily linked to patterns of nutrient input (δ15N), coastal productivity (δ13C) and water mass type (δ18O). δ15N values demonstrated significant spatial variation, while δ18O displayed distinct values among depths. The present study was the first to resolve the distribution of δ15N and δ13C isotopes at a regional scale along the east coast of the South Island of New Zealand, δ18O in New Zealand waters, and to investigate the extent to which these distributions were influenced by patterns in physical oceanography. Average values of δ18O, δ15N and δ13C for different fishery management areas and depths are presented to support future ecological studies along Southeast New Zealand.

Different Biochemical Compositions of Particulate Organic Matter Driven by Major Phytoplankton Communities in the Northwestern Ross Sea.

Marine particulate organic matter (POM) largely derived from phytoplankton is a primary food source for upper trophic consumers. Their biochemical compositions are important for heterotrophs. Especially, essential amino acids (EAAs) in phytoplankton are well known to have impacts on the survival and egg productions of herbivorous zooplankton. To estimate the nutritional quality of POM, the biochemical compositions [biomolecular and amino acid (AA) compositions] of POM were investigated in the northwestern Ross Sea during the late austral summer in 2018. Carbohydrates (CHO) accounted for the highest portion among different biomolecules [CHO, proteins (PRT), and lipids (LIP)] of POM. However, the higher contribution of PRT and lower contribution of CHO were observed in the southern section of our study area compared to those in the northern section. The spatial distribution of total hydrolyzable AAs in POM was considerably influenced by phytoplankton biomass, which indicates that the main source of particulate AA was generated by phytoplankton. Our results showed that the relative contribution of EAA to the total AAs was strongly associated with EAA index (EAAI) for determining protein quality. This result indicates that higher EAA contribution in POM suggests a better protein quality in consistency with high EAAI values. In this study, variations in the biochemical compositions in POM were principally determined by two different bloom-forming taxa (diatoms and Phaeocystis antarctica). The southern region dominated majorly by diatoms was positively correlated with PRT, EAA, and EAAI indicating a good protein quality, while P. antarctica-abundant northern region with higher CHO contribution was negatively correlated with good protein quality factors. Climate-driven environmental changes could alter not only the phytoplankton community but also the physiological conditions of phytoplankton. Our findings could provide a better understanding for future climate-induced changes in the biochemical compositions of phytoplankton and consequently their potential impacts on higher trophic levels.

Carbon and nitrogen isotopes to distinguish sources of sedimentary organic matter in a Caribbean estuary

ABSTRACT Carbon and nitrogen stable isotope compositions (δ13C and δ15N) of organic matter (OM) and total organic carbon to total nitrogen ratio (Corg/TN) in a sediment core collected in Sagua estuary (Cuba), were investigated to elucidate the origin of the Sedimentary OM (SOM) and changes in its main sources, over the last 100 years. Results showed almost constant values in the elemental and isotope composition of SOM from 1908 to 1970 with an abrupt change after 1970. From 1970 to 2005, δ13C increased from -21.2 up to -19.3 ‰, while δ15N declined from 1.5 to values close to 0 ‰. The output of the mass-balance model for the identification of OM sources indicated that δ13C and Corg/TN values are generally influenced by marine Particulate OM (POM) sources. Between 1900 and 1970, the main OM source in sediments was marine POM (>85 %), with freshwater POM contributing ca. 15%. Since 1970, the establishment of the Alacranes Dam determined drastic environmental changes influencing the OM sources in the area. Mixing models pointed to seagrasses (79 %) as the main contributors to SOM in the first period, while since 1973 onward, the contribution of human-derived sources such as fertilizers and urban discharges became greater. This information can provide baseline data for the environmental management of the Sagua watershed.

Sources of particulate organic matter in the Chukchi and Siberian shelves: clues from carbon and nitrogen isotopes

The stable isotopic composition (δ13C and δ15N) and carbon/nitrogen ratio (C/N) of particulate organic matter (POM) in the Chukchi and East Siberian shelves from July to September, 2016 were measured to evaluate the spatial variability and origin of POM. The δ13CPOC values were in the range of −29.5‰to −17.5‰ with an average of −25.9‰±2.09‰, and the δ15NPN values ranged from 3.9‰ to 13.1‰ with an average of 8.0‰±1.6‰. The C/N ratios in the East Siberian shelf were generally higher than those in the Chukchi shelf, while the δ13C and δ15N values were just the opposite. Abnormally low C/N ratios ( 10‰) values were observed in the Wrangel Island polynya, which was attributed to the early bloom of small phytoplankton. The contributions of terrestrial POM, bloom-produced POM and non-bloom marine POM were estimated using a three end-member mixing model. The spatial distribution of terrestrial POM showed a high fraction in the East Siberian shelf and decreased eastward, indicating the influence of Russian rivers. The distribution of non-bloom marine POM showed a high fraction in the Chukchi shelf with the highest fraction occurring in the Bering Strait and decreased westward, suggesting the stimulation of biological production by the Pacific inflow in the Chukchi shelf. The fractions of bloom-produced POM were highest in the winter polynya and gradually decreased toward the periphery. A negative relationship between the bloom-produced POM and the sea ice meltwater inventory was observed, indicating that the net sea ice loss promotes early bloom in the polynya. Given the high fraction of bloom-produced POM, the early bloom of phytoplankton in the polynyas may play an important role on marine production and POM export in the Arctic shelves.

Nutrient ratios in marine particulate organic matter are predicted by the population structure of well-adapted phytoplankton.

A common assumption of a constant nitrogen-to-phosphorus ratio (N:P) of 16:1 in marine particulate organic matter (POM) appears to be invalidated by observations of major spatial variations in N:P. Two main explanations have been proposed. The first attributes the N:P variability to changes in the community composition of well-adapted phytoplankton. The second proposes that variability arises from physiological acclimation involving intracellular adjustments of nutrient allocation under nutrient deficiency. Using a model of phytoplankton physiology, observational datasets, and a review of laboratory culture results, we assess the mechanistic basis of N:P variability. We find that the taxonomic composition of well-adapted phytoplankton best explains observed variations in POM N:P. Furthermore, we show that acclimation to nutrient deficiency may be safely neglected when considering the effects of ecology on POM N:P. These findings provide insight into the controls on global variability in POM composition and average phytoplankton physiological performance in the oceans.

Sources of organic matter in an atypical phytoplankton rich coral ecosystem, Marquesas Islands: composition and properties

The purpose of this work is to characterize several potential sources of organic matter (OM) in the Marquesas Islands, French Polynesia, and to understand how these sources contribute to OM pools. Stable isotope (δ 13 C and δ 15 N) and fatty acid (FA) compositions of OM potential sources (algal turf, benthic macroalgae, detrital terrestrial plants (DTP), phytoplankton) and OM pools (sediment (SOM) and particulate organic matter (POM)) were studied in coastal areas in Nuku Hiva Island. Isotope compositions of marine POM (δ 13 C = − 22.5 ± 0.8 ‰; δ 15 N = 12.1 ± 1.1 ‰) and SOM (δ 13 C = − 19.1 ± 0.9 ‰; δ 15 N = 14.4 ± 0.5 ‰) highlighted that OM sources at the base of the local food web had unusually high δ 15 N values. Potential FA markers of diatoms and/or cyanobacteria (20:5ω3 and 16:1ω7) were found in these two OM pools. In addition, coastal SOM also displayed FA markers of bacteria, macroalgae and terrestrial plants. For marine POM, potential macroalgae FA markers were recorded (18:2ω6 and 16:2ω4). The stable isotope mixing model highlighted the major contribution of phytoplankton to the coastal SOM (62%), followed by benthic macroalgae (32%), whereas marine POM was mainly composed of a mixture of algal turf and phytoplankton in similar averaged proportions (38%) but presenting wide variations. Our results as a whole strongly suggest that pelagic-benthic coupled processes drive the characteristics and properties of OM sources.

PALYNOLOGY AND CHEMOSTRATIGRAPHY OF MIDDLE TRIASSIC SUCCESSIONS IN NORTHERN SWITZERLAND (WEIACH, BENKEN, LEUGGERN) AND SOUTHERN GERMANY (WEIZEN, FREUDENSTADT)

New Anisian to Ladinian palynology, palynofacies and stable carbon isotope records are reported for the Middle Triassic from deep Swiss wells (Weiach, Benken, Leuggern), well B3/13 (Weizen, S-Germany) and the type area of the Freudenstadt Formation in southern Germany. A wide spectrum of moderately to well-preserved palynomorphs represent a high Middle Triassic plant diversity. Based on the distribution of diverse spore-pollen assemblages five Anisian Palynozones (A–E) and two Ladinian ones (F, G) are differentiated. Throughout these Palynozones the occurrence of spores and pollen, assigned to plant groups so far known only from the Palaeozoic, shed a new light on the evolution of plant assemblages during the Triassic. The comparison of Palynozones A–G with palynostratigraphic schemes from the central part of the Germanic Basin and from the Tethyan realm demonstrate the regional variability of marker species ranges – especially for the Anisian. n agreement with the lithological record, two prominent transgressive events (Lower Muschelkalk, Upper Muschelkalk) are indicated by increased abundances of marine particulate organic matter in palynofacies data. Marginal marine influence is documented at the base of the studied interval, comprising the Buntsandstein and the base of the Lower Muschelkalk. Carbonate carbon isotopes data show a negative shift at the boundary between lower and middle Muschelkalk. Coincidently, a prominent change in relative abundances of climate-sensitive plant groups (e.g. Triadispora spp. vs. Pteridophytes) indicate a change to relatively dryer climatic conditions during the middle Muschelkalk.

Sample acidification has a predictable effect on isotopic ratios of particulate organic matter along the Chilean coast.

Stable isotopes of carbon and nitrogen have proved to be valuable tools for researchers working across the different subfields of ecology. However, the chemical pretreatment of samples prior to analytical determination of stable isotope ratios can influence the results, and therefore conclusions regarding the ecology of the taxon or system under study. Here, we determined the effect of vapor acidification with concentrated HCl on the δ13 C and δ15 N values of particulate organic matter (POM), which are commonly used as baselines for studies of trophic ecology, or to understand oceanographic patterns. Samples of marine POM were obtained along a large-scale latitudinal gradient (ca 3000 km) along the Chilean coast, along with a range of oceanographic variables thought to potentially influence inorganic carbon at each sampling location. A random subset of 50 samples was divided into two parts: one acidified by HCl fumigation treatment, and the other acting as a control. We compared paired differences in δ13 C and δ15 N values measured by continuous flow isotope ratio mass spectrometry and used a model selection approach to examine which oceanographic factor best explained shifts in values following acid treatment. Acidification resulted in statistically significant reductions in both δ13 C and δ15 N values, but the effect was relatively small. The model that best explained the differences between acidified and non-acidified δ13 C values included depth, salinity and sea-surface temperature at the sampling point. A regression of acidified on non-acidified δ13 C values shows that the treatment effect was strongest on samples more depleted in 13 C. The differences between δ13 C and δ15 N values in acidified and non-acidified samples are linear and predictable. This implies that the nature of the POM and its possible alteration during the acid treatment are important factors that support the reliable determination of the values of δ13 C and δ15 N of POM.

Simultaneous determination of neutral sugars, alditols and anhydrosugars using anion-exchange chromatography with pulsed amperometric detection: Application for marine and atmospheric samples

An improved high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) method is described for the simultaneous determination of neutral sugars (hexoses, pentoses and deoxysugars), alditols and anhydrosugars commonly found in atmospheric and marine samples. The method uses a CarboPac MA1 column, at a flow rate of 0.3 mL min−1, and a NaOH gradient (250–700 mM). The proposed method applies a temperature gradient (from 25 to 28 °C) to the column for the first 30 min of the analysis, followed by a constant temperature at 28 °C until the end of the analysis. These analytical conditions allowed the separation of 15 out of 17 carbohydrates in 75 min with resolution factors better than 0.5 for the critical pairs levoglucosan/arabitol, galactosan/arabinose, arabinose/mannose and glucose/xylose.The application of this method to field samples revealed that anhydrosugars represented 53% of total neutral carbohydrates (TCHO) in total suspended atmospheric particles (TSP), whereas they were detected for the first time in marine particulate organic matter (POM) and high-molecular-weight dissolved organic matter (HMWDOM) samples accounting 2% and 3% of TCHO, respectively. Levoglucosan and/or galactosan were the major anhydrosugars in all samples however, their concentrations are undoubtedly underestimated because hydrolysis was applied to the marine samples prior to the HPAEC-PAD analysis. Despite this underestimation, their presence in the marine samples clearly indicates possible terrestrial input most likely via atmospheric deposition as these compounds are considered terrestrial burring biomass tracers. Finally, deoxysugars were also detected for the first time in the TSP sample representing 1% of TCHO, while alditols accounted for 0.4% and 0.3% of TCHO in POM and HMWDOM, respectively.