Bulk Sedimentary Organic Matter Research Articles

Carbon isotope fractionation in phytoplankton as a potential proxy for pH rather than for [CO2(aq)]: Observations from a carbonate lake

AbstractThe method of reconstructing paleoatmospheric CO2 levels using carbon isotope signatures of organic matter buried in sediments has been questioned due to the dubious foundation that carbon isotope fractionation during phytoplankton photosynthesis (εp) is controlled primarily by aquatic CO2 concentration ([CO2(aq)]). Consequently, what carbon isotope data from bulk sedimentary organic matter reflects is a puzzle. In this study, we determined the carbon isotope compositions of dissolved inorganic carbon and particulate organic carbon in a lake located in a carbonate area. Partial correlation analysis was employed to distinguish between direct and indirect factors in controlling εp. The results show that εp is more closely, and more steadily related with pH than with [CO2(aq)], which is in accordance with recent advances in our understanding of the physiology of carbon utilization by phytoplankton for CO2 and . Therefore, we propose that carbon isotope fractionation in phytoplankton is more suitable as a proxy of pH than of [CO2(aq)]. One advantage of this amendment is that information on , the main species of carbon uptake by phytoplankton, is likewise included. In the future, culture experiments aiming at revealing the relationship between pH and cellular carbon isotope signatures is necessary to construct a new isotope fractionation formula to couple the different effects of CO2 and , which is of critical importance to improve the understanding of carbon isotope fractionation, and to more precisely model pH and CO2.

ANNUAL AND SEASONAL DISTRIBUTION OF INTERTIDAL FORAMINIFERA AND STABLE CARBON ISOTOPE GEOCHEMISTRY, BANDON MARSH, OREGON, USA

We investigated the influence of inter-annual and seasonal differences on the distribution of live and dead foraminifera, and the inter-annual variability of stable carbon isotopes (d 13 C), total organic carbon (TOC) values and carbon to nitrogen (C/N) ratios in bulk sediments from intertidal environments of Bandon Marsh (Oregon, USA). Living and dead foraminiferal species from 10 stations were analyzed over two successive years in the summer (dry) and fall (wet) seasons. There were insignificant inter-annual and seasonal variations in the distribution of live and dead species. But there was a noticeable decrease in calcareous assemblages (Haynesina sp.) between live populations and dead assemblages, indicating that most of the calcareous tests were dissolved after burial; the agglutinated assemblages were comparable between constituents. The live populations and dead assemblages were dominated by Miliammina fusca in the tidal flat and low marsh, Jadammina macrescens, Trochammina inflata and M. fusca in the high marsh, and Trochamminita irregularis and Balticammina pseudomacrescens in the highest marsh to upland. Geochemical analyses (d 13 C, TOC and C/N of bulk sedimentary organic matter) show no significant influence of inter-annual variations but a significant correlation of d 13 C values (R = 20.820, p , 0.001), TOC values (R = 0.849, p , 0.001) and C/N ratios (R = 0.885, p , 0.001) to elevation with respect to the tidal frame. Our results suggest that foraminiferal assemblages and d 13 C and TOC values, as well as C/N ratios, in Bandon

Pelagic-benthic coupling, food webs, and organic matter degradation in the Chukchi Sea: Insights from sedimentary pigments and stable carbon isotopes

An understanding of the origin and fate of organic matter deposited on the seabed in the Chukchi Sea is critical to our understanding of how regional changes in climate will affect this highly productive ecosystem. We measured the concentrations of chlorophyll a, pheopigments, and accessory pigments in sediments at 39 stations using high-performance liquid chromatography (HPLC) to investigate the degradation pathways of chlorophyll-containing organic matter. Chlorophyll a concentrations were among the highest ever reported in marine sediments (up to 665 mg m-2). Measurements of pheopigments, including pheophytin a, pheophorbide a, and pyropheophorbide a, revealed substantial degradative processing of organic matter that began ∼ 2 weeks after ice breakup. However, the ratio of chlorophyll a to total pheopigments (Chl a : pheo) was > 1 in most stations, indicating that chlorophyll a was preserved despite grazing and senescent degradation pathways that produced accumulated pheopigments. Increased δ13C values of bulk sediment organic matter was also positively correlated to concentrations of pheophytin a (p < 0.01, r=0.46), and total pheopigment concentration was correlated to the δ13C values of the epibenthic scavenging snow crab Chionoecetes opilio (p < 0.01, r = 0.92) and the surface deposit feeding bivalves Macoma spp. (p < 0.01, r = 0.69). Based on these observations, we hypothesize that organic matter degraded by microbial and herbivorous grazing pathways produces an enriched 13C signal that is transferred to macrofaunal consumers, providing a critical source of carbon to a rich and diverse benthic food web.

Stable C and N isotope record of short term changes in water level in lakes of different morphometry: Lake Anastazewo and Lake Skulskie, central Poland

We present the stable C isotope record of the changes within the past 20yr in water level of two morphologically different lakes in central Poland. The aim was to explain the relationship between lake water level and the δ13C signature of bulk sedimentary organic matter (δ13CTOC) and to assess the potential of δ13CTOC as a paleolimnological proxy of lake level change. This was done by comparison of the fossil δ13CTOC record with instrumental data for lake level change in a shallow and small lake as well as in one large and deep basin. In both lakes the water table varied greatly between 1980 and 2000 AD. The δ13CTOC data were supplemented with δ15N and bulk geochemistry data, as well as paleoecological data. We show that δ13CTOC reacted to short term and low amplitude fluctuation in water level, but the response was highly dependent on the morphometry of the lake. In the shallow and small basin, δ13CTOC decreased along with lake level drop due to oxidation and greater input of organic matter from macrophytes colonizing the lake bottom. On the contrary, in the deep/large lake δ13CTOC decreased with increasing water level due to enhanced delivery of soil-derived OM to the lake during highstands. Our results have broad paleolimnological implications as they show that δ13CTOC cannot act as a universal paleohydrological proxy. Its interpretation for a particular lake can be ambiguous and must be supported with additional geochemical and paleocological information.

A Meta-Analysis of the Incidence of Cancers in Solid Organ Transplant Recipients

We present the stable C isotope record of the changes within the past 20 yr in water level of two morphologically different lakes in central Poland. The aim was to explain the relationship between lake water level and the δ13C signature of bulk sedimentary organic matter (δ13CTOC) and to assess the potential of δ13CTOC as a paleolimnological proxy of lake level change. This was done by comparison of the fossil δ13CTOC record with instrumental data for lake level change in a shallow and small lake as well as in one large and deep basin. In both lakes the water table varied greatly between 1980 and 2000 AD. The δ13CTOC data were supplemented with δ15N and bulk geochemistry data, as well as paleoecological data. We show that δ13CTOC reacted to short term and low amplitude fluctuation in water level, but the response was highly dependent on the morphometry of the lake. In the shallow and small basin, δ13CTOC decreased along with lake level drop due to oxidation and greater input of organic matter from macrophytes colonizing the lake bottom. On the contrary, in the deep/large lake δ13CTOC decreased with increasing water level due to enhanced delivery of soil-derived OM to the lake during highstands. Our results have broad paleolimnological implications as they show that δ13CTOC cannot act as a universal paleohydrological proxy. Its interpretation for a particular lake can be ambiguous and must be supported with additional geochemical and paleocological information.

Taxon-specific δ13C analysis of chitinous invertebrate remains in sediments from Strandsjön, Sweden

Taxon-specific stable carbon isotope (δ13C) analysis of chitinous remains of invertebrates can provide valuable information about the carbon sources used by invertebrates living in specific habitats of lake ecosystems (for example, sediments, water column, or aquatic vegetation). This is complementary to δ13C of sedimentary organic matter (SOM), which provides an integrated signal of organic matter produced in a lake and its catchment, and of diagenetic processes within sediments. In a sediment record from Strandsjon (Sweden) covering the past circa 140 years, we analyzed SOM geochemistry (δ13C, C:Natomic, organic carbon content) and δ13C of chitinous invertebrate remains in order to examine whether taxon-specific δ13C records could be developed for different invertebrate groups and whether these analyses provide insights into past changes of organic carbon sources for lacustrine invertebrates available in benthic and planktonic compartments of the lake. Invertebrate taxa included benthic chironomids (Chironomus, Chironomini excluding Chironomus, Tanytarsini, and Tanypodinae), filter-feeders on suspended particulate organic matter (Daphnia, Plumatella and Cristatella mucedo), and Rhabdocoela. δ13C of chironomid remains indicated periodic availability of 13C-depleted carbon sources in the benthic environment of the lake as δ13C values of the different chironomid taxa fluctuated simultaneously between −34.7 and −30.5 ‰ (VPDB). Daphnia and Bryozoa showed parallel changes in their δ13C values which did not coincide with variations in δ13C of chironomids, though, and a 2–3 ‰ decrease since circa AD 1960. The decrease in δ13C of Daphnia and Bryozoa could indicate a decrease in phytoplankton δ13C as a result of lower lake productivity, which is in accordance with historical information about the lake that suggests a shift to less eutrophic conditions after AD 1960. In contrast, Rhabdocoela cocoons were characterized by relatively high δ13C values (−30.4 to −28.2 ‰) that did not show a strong temporal trend, which could be related to the predatory feeding mode and wide prey spectrum of this organism group. The taxon-specific δ13C analyses of invertebrate remains indicated that different carbon sources were available for the benthic chironomid larvae than for the filter-feeding Daphnia and bryozoans. Our results therefore demonstrate that taxon-specific analysis of δ13C of organic invertebrate remains can provide complementary information to measurements on bulk SOM and that δ13C of invertebrate remains may allow the reconstruction of past changes in carbon sources and their δ13C in different habitats of lake ecosystems.

Trophodynamics and organic matter assimilation pathways in the northeast Chukchi Sea, Alaska

We analyzed trophic linkages in the northeast Chukchi Sea shelf based on the stable carbon and nitrogen isotopic analysis of 39 species collected in 2009 and 2010. To decipher organic matter assimilation pathways, benthic fauna were first categorized into nine trophic guilds based on their physical location in the seabed (epibenthic, surface, or subsurface), feeding mode (suspension feeder, deposit feeder, predator, or scavenger), and food source (suspended particulate organic matter, phytoplankton, zooplankton, sediment, microflora, meiofauna, or macrofauna). A discriminant function analysis (DFA) determined that feeding modes were predicted by stable isotope values at an overall classification success rate of 42%, although classification success of each individual guild varied from 0 to 66%. In some instances, stable isotopes classified trophic guilds incorrectly more often than correctly, suggesting high trophic redundancy in the system. A striking pattern was observed where the δ13C values of individuals in some trophic guilds, ranging from about −23 to −17‰, were substantially more 13C-enriched than representative end-members, which includes phytoplankton (−24.0‰), suspended particulate organic matter (−24.3‰), and bulk sediment organic matter (−23.3‰). In contrast, near-seafloor suspended particulate organic matter was significantly 13C-enriched compared to suspended particulate organic matter of near surface waters (p<0.05), and bulk sedimentary organic matter was more 13C-enriched than overlying phytoplankton at seven of 10 stations. This suggests the presence of an unmeasured 13C-enriched end-member that is a product of biogeochemical alteration and reworking by the sediment microbial community. Although the microbial community is difficult to quantify using bulk stable isotope analytical techniques, these results indicate it cannot be overlooked as a critical component and avenue through which large amounts of reduced carbon are assimilated by a rich and diverse arctic shelf food web.

A biomarker record of Lake El'gygytgyn, Far East Russian Arctic: investigating sources of organic matter and carbon cycling during marine isotope stages 1–3

Abstract. Arctic paleoenvironmental archives serve as sensitive recorders of past climate change. Lake El'gygytgyn (Far East Russian Arctic) is a high-latitude crater impact lake that contains a continuous sediment record influenced by neither glaciation nor glacial erosion since the time of impact 3.58 Ma ago. Prior research on sediments collected from Lake El'gygytgyn suggest times of permanent ice cover and anoxia corresponding to global glacial intervals, during which the sediments are laminated and are characterized by the co-occurrence of high total organic carbon, microscopic magnetite grains that show etching and dissolution, and negative excursions in bulk sediment organic matter carbon isotope (δ13C) values. Here we investigate the abundance and carbon isotopic composition of lipid biomarkers recovered from Lake El'gygytgyn sediments spanning marine isotope stages 1–3 to identify key sources of organic matter (OM) to lake sediments, to establish which OM sources drive the negative δ13C excursion exhibited by bulk sediment OM, and to explore if there are molecular and isotopic signatures of anoxia in the lake during glaciation. We find that during marine isotope stages 1–3, direct evidence for water column anoxia is lacking. A ~4‰ negative excursion in bulk sediment δ13C values during the Local Last Glacial Maximum (LLGM) is accompanied by more protracted, higher magnitude negative excursions in n-alkanoic acid and n-alkanol δ13C values that begin 20 kyr in advance of the LLGM. In contrast, n-alkanes and the C30 n-alkanoic acid do not exhibit a negative δ13C excursion at this time. Our results indicate that the C24, C26 and C28 n-alkanoic acids do not derive entirely from terrestrial OM sources, while the C30 n-alkanoic acid at Lake El'gygytgyn is a robust indicator of terrestrial OM contributions. Overall, our results strongly support the presence of a nutrient-poor water column, which is mostly isolated from atmospheric carbon dioxide during glaciation at Lake El'gygytgyn.

Stable isotope chemostratigraphy in lacustrine strata of the Xiagou Formation, Gansu Province, NW China

Abstract Two sections from Early Cretaceous lacustrine strata of the Xiagou Formation from the Changma Basin in Gansu Province, China, are correlated based on their carbon isotopic compositions of bulk sedimentary organic matter and carbonate, as well as carbonate oxygen-isotopic compositions. The samples were collected from fossiliferous strata, which contain well-preserved Cretaceous bird remains. The sections are primarily correlated based on a two-step increase in δ 13 C org with an overall magnitude of c. 12.5‰. The stratigraphic variations in carbon isotopes within the two lacustrine sections are correlated with global carbon isotope variations C3–C7 based on marine carbon isotope records. This correlation places the Xiagou lacustrine strata in this locality within the early Aptian Stage, specifically, the Selli Equivalent, which is associated with Ocean Anoxic Event 1a.

Carbon cycling within an East African lake revealed by the carbon isotope composition of diatom silica: a 25-ka record from Lake Challa, Mt. Kilimanjaro

The carbon cycle of a lake is a balance between supply from the atmosphere and catchment, and the net demand exerted by primary producers, minus losses back to the atmosphere and to sediment storage. Evaluating the sum of these processes and reconstructing them from sediment records of lake history requires a range of methods and a multi-proxy approach. One promising technique is to explore the carbon-isotope composition (δ13Cdiatom) of organic matter incorporated within the silica frustules of diatom algae. Here we present a 25,000-year record of δ13Cdiatom from the sediments of crater Lake Challa on the eastern flank of Mt. Kilimanjaro, and along with other proxy data we make inferences about the three major phases in the history of the lake's carbon cycle. From 25 ka to 15.8 ka years BP, δ13Cdiatom is positively correlated with the δ13C of bulk sediment organic matter (δ13Cbulk), indicating that high diatom productivity, as recorded by high % biogenic silica at this time, was preferentially removing 12C and enriching the δ13C of lake-water dissolved inorganic carbon. From 15.8 to 5.5 ka the correlation between δ13Cdiatom and δ13Cbulk breaks down, suggesting carbon supply to the lake satisfied or exceeded the demand from productivity. From 5.5 ka BP the positive correlation resumes, indicating an increase in the internal demand for carbon relative to external supply. Diatom frustule-bound carbon isotopes offer an original tool in examining long-term fluctuations in a lake's carbon budget and how the balance between supply and demand has changed through time.

The last Glacial–Interglacial transition in Patagonia, Argentina: the stable isotope record of bulk sedimentary organic matter from Laguna Potrok Aike

An investigation of stable isotope (δ13CTOC and δ15NTN) and elemental parameters (TOC, TN contents and TOC/TN ratios) of bulk organic matter (<200 μm) from sediment cores recovered from the Patagonian lake Laguna Potrok Aike (Argentina) in the framework of the ICDP deep drilling project PASADO provided insights into past changes in lake primary productivity and environmental conditions in South Patagonia throughout the last Glacial–Interglacial transition. Stratigraphically constrained cluster analyses of all proxy parameters suggest four main phases. From ca 26,100 to 17,300 cal. years BP, lacustrine phytoplankton was presumably the predominant organic matter source in an aquatic environment with low primary productivity rates. At around 17,300 cal. years BP, abrupt and distinct shifts of isotopic and elemental values indicate that the lacustrine system underwent a rapid reorganization. Lake primary productivity (phytoplankton and aquatic macrophytes) shows higher levels albeit with large variations during most of the deglaciation until 13,000 cal. years BP. The main causes for this development can be seen in improved growing conditions for primary producers because of deglacial warming in combination with expedient availability of nutrients and likely calm wind conditions. After 13,000 cal. years BP, decreased δ13CTOC values, TOC, TN contents and TOC/TN ratios indicate that the lake approached a new state with reduced primary productivity probably induced by unfavourable growing conditions for primary producers like strengthened winds and reduced nutrient availability. The steady increase in δ15NTN values presumably suggests limitation of nitrate supply for growth of primary producers resulting from a nutrient shortage after the preceding phase with high productivity. Nitrate limitation and consequent decreased lacustrine primary productivity continued into the early Holocene (10,970–8400 cal. years BP) as reflected by isotopic and elemental values.

Macrofauna regulate heterotrophic bacterial carbon and nitrogen incorporation in low-oxygen sediments

Oxygen minimum zones (OMZs) currently impinge upon >1 million km(2) of sea floor and are predicted to expand with climate change. We investigated how changes in oxygen availability, macrofaunal biomass and retention of labile organic matter (OM) regulate heterotrophic bacterial C and N incorporation in the sediments of the OMZ-impacted Indian continental margin (540-1100 m; [O(2)]=0.35-15 μmol l(-1)). In situ pulse-chase experiments traced (13)C:(15)N-labelled phytodetritus into bulk sediment OM and hydrolysable amino acids, including the bacterial biomarker D-alanine. Where oxygen availability was lowest ([O(2)]=0.35 μmol l(-1)), metazoan macrofauna were absent and bacteria assimilated 30-90% of the labelled phytodetritus within the sediment. At higher oxygen levels ([O(2)]=2-15 μmol l(-1)) the macrofaunal presence and lower phytodetritus retention with the sediment occur concomitantly, and bacterial phytodetrital incorporation was reduced and retarded. Bacterial C and N incorporation exhibited a significant negative relationship with macrofaunal biomass across the OMZ. We hypothesise that fauna-bacterial interactions significantly influence OM recycling in low-oxygen sediments and need to be considered when assessing the consequences of global change on biogeochemical cycles.

Paleoenvironmental reconstruction of a Late Quaternary lagoon system in southern Brazil (Jaguaruna region, Santa Catarina state) based on multi‐proxy analysis

AbstractThis paper provides a paleoenvironmental reconstruction of a Late Quaternary lagoon system in the Jaguaruna region of Santa Catarina state, southern Brazil. Integrated results of bulk sedimentary organic matter characterization (δ13C, δ15N and C/N), microfossil (pollen and diatom) and grain‐size analysis from three shallow cores (∼2.5 m depth) allowed us to propose an evolving paleogeographic scenario in this coastal region for the last ca. 5500 cal a BP. The lagoonal system in this area was more extensive during the mid‐Holocene than today, with a gradual and continuous lagoon–sea disconnection until the present. We add to the debate regarding relative sea‐level (RSL) variations for the Brazilian coast during the Holocene and discuss the importance of sedimentary dynamics for interpreting changes in coastal ecosystems. The multi‐proxy analysis suggests that changes in coastal ecosystems could be directly related to local sedimentary processes, which are not necessarily linked to RSL fluctuations and/or to climatic variations. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Late-glacial and Holocene palaeoenvironments in the Baltic Sea based on a sedimentary record from the Gda´n%%KERN_ERR%%sk Basin

The focus of this study was the 11.55 m long sediment core 303700-7, which was retrieved from the Gdansk Basin during a cruise of RV ‘Poseidon’ within the frame of the Russian–German Project GISEB. The core was analysed for grain size, elemental chemical composition, organic carbon and palynological spectra. The age control was based on palynostratigraphy and 7 radiocarbon datings of bulk sedimentary organic matter. These data provide a high-resolution record of climatic and marine palaeoenvironments in the Gdansk Basin for the last ca. 13 kyr, from the Bolling to late Holocene time. Sedimentation rates were estimated to vary between 0.37 and 1.62 mm yr–1. Major variations in palaeosalinity were estimated from bromine concentrations in the sediment. This method allows the first quantitative reconstruction of palaeosalinity changes in the Baltic Sea, especially profound during the Littorina and Postlittorina periods (middle to late Holocene). In addition, grain size data indicated several Littorina transgressive–regressive stages and a few episodes of increased near-bottom current activity. Our results from the Gdansk Basin are consistent with palaeoceanographic data from other deep basins of the Baltic Sea and provide new insights into the regional Holocene history.

Late Holocene Neoglacial conditions from the Lesotho highlands, southern Africa: phytolith and stable carbon isotope evidence from the archaeological site of Likoaeng

The late Holocene environmental history of the Lesotho highlands, southern Africa, is poorly understood with few detailed studies to date. At Likoaeng, Senqu Valley, Lesotho, a 3 m stratified sedimentary sequence from an open-air archaeological site records vegetation development for the period 3400–1070 cal. BP. Phytolith analyses and bulk sediment organic matter δ 13C indicate that C 4 grassland dominated the lower part of the sequence until approximately 2960 cal. BP when there was a switch to C 3 Pooid grassland (2960–2160 cal. BP). Also noted was a change from hunting mainly bovids to a dominance of fishing at the site. The change in grassland type and archaeological subsistence strategies corresponds with an episode of neoglacial cooling and the expansion of Alpine sourgrasses into lower altitudes. From 2160 to 1600 cal. BP grassland became a mix of C 3 and C 4 types and by 1600–1070 cal. BP there was a return to C 4 dominated grassland. During this latter phase there was a reversal from fishing to hunting again (and eventually some keeping of domestic livestock) at the site. These data outline the vegetation response to latitudinal shifts of frontal systems, and relatively strong atmospheric circulation variability, perhaps underpinned by variations of polar water into the Benguela Current during the late Holocene.

Alkyl amides in two organic-rich anoxic sediments: A possible new abiotic route for N sequestration

Fixed nitrogen (N) plays an integral role in global cycling; while most is recycled to refuel primary productivity, a small fraction escapes to be preserved and stabilised in sediments. Despite decades of research, the functionality and reactivity of this sequestered organic N has been poorly understood. This study was undertaken to shed light on this problem by characterising the bulk sediment organic matter using nuclear magnetic resonance (NMR), followed by molecular level analysis using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT–ICR–MS). We studied two organic-rich anaerobic sediments, one from a freshwater system and another from a marine paralic basin. Mangrove Lake, Bermuda (marine) and Mud Lake, Florida (freshwater) have been shown in past studies to contain high levels of N-containing organic matter. Our resulting multidimensional NMR data suggests the existence of a new type of amide functionality in both these lake sediments, and we investigated this further using FT–ICR–MS and gas chromatography mass spectrometry (GC–MS). FT–ICR–MS confirmed the existence of homologous series of CHNO containing compounds, whose structures are verified using GC–MS as alkyl amides. Model reactions involving naturally occurring esters and ammonia suggest the source of alkyl amides to be amidation of esters with sedimentary ammonia derived from anaerobic degradation of organic matter. This expands upon previous hypotheses for preservation of amide containing compounds that call upon biological/abiological protection of proteins and peptides or the formation of refractory nitrogenous adducts.

Comparison of lignin phenols and branched/isoprenoid tetraethers (BIT index) as indices of terrestrial organic matter in Doubtful Sound, Fiordland, New Zealand

The branched/isoprenoid tetraether (BIT) index has recently been proposed as a qualitative proxy for the relative amounts of soil and marine derived organic matter (OM) in marine sediments. We compare BIT values with lignin–phenol CuO oxidation products and bulk OM proxies in surface sediment samples from Doubtful Sound, a fjord in the southwestern end of New Zealand’s South Island, as well as in soils and leaf litter from the local pristine temperate rainforest watershed. The region has extreme rates of annual rainfall (>7 m year −1) and large mass-wasting soil and vegetation events on fjord slopes, which results in relatively high fluxes of terrestrial organic matter (OM terr) to fjord sediments. Sediments contained up to 11.4% w/w organic carbon (OC) with terrestrial to a mixture of terrestrial/marine δ 13C (−24.3‰ to −28.7‰) and C/N (14.7–36.8) signatures. BIT values ranged from 0.24 to 0.93. Lignin abundance in sediments, reported as Λ 8 values (mg 8 lignin–phenols/100 mg OC −1), ranged from 2.7 to 11.2. A weak correlation was found between concentrations of lignin phenols and BIT values ( R 2 0.313). The likely cause of the differences between the two proxies is differences in the relative amounts of soil OM (OM soil) and vegetation (intact and detrital) transported to the fjord by episodic mass-wasting events and gradual accumulation from overland (leaching by rainfall) and riverine sources. Interestingly, the BIT index correlated significantly with bulk sedimentary OM (OM sed) proxies (δ 13C, R 2 0.774) (C/N, R 2 0.629), while lignin phenol values (Λ 8) exhibited a much weaker correlation with δ 13C values ( R 2 0.320) and no correlation with C/N values ( R 2 0.005). This suggests that OM soil represents the dominant fraction of OM terr delivered to fjord sediments.

A multi-method approach for identifying meiofaunal trophic connections

Meiofauna can play an important role in the energetics of benthic communities, but determining their diet remains problematic due to their small size. In this study, the contribution of primary producers to the diet of meiofauna and to bulk and fine (<125 µm) sediment organic matter (SOM) was investigated in Papanui Inlet, southern New Zealand, using stable isotopes (δ 13 C and δ 15 N) and fatty acid analyses in the field and in a microcosm experiment. Seston did not contribute significantly to SOM of vegetated (seagrass Zostera muelleri) and unvegetated habitats, suggesting limited bentho-pelagic coupling. The contribution of different benthic primary producers to SOM and meiofaunal diet could not be determined accurately based on isotopic signatures alone due to over- lapping isotopic signatures. The high content of highly unsaturated fatty acids (HUFAs) of harpacti- coid copepods from vegetated and unvegetated sites suggested that their main food item was micro- phytobenthos (MPB), although bacterial biomarkers were twice as abundant in copepods sampled from the seagrass bed than in copepods sampled from unvegetated sediments. Isotopic and fatty acid analyses showed that the uptake of 13 C-labeled macroalgal (Enteromorpha sp.) detritus by harpacti- coid copepods in the microcosm experiment was minimal. Nematode diet could not be assessed with certainty, but seagrass detritus and MPB are likely to represent significant food sources at the vege- tated and unvegetated sites, respectively, based on the fatty-acid profile of fine SOM. This combined approach (i.e. isotopic and fatty acid analyses, field sampling and microcosms), and analysis of bulk SOM, fine SOM, and aged seagrass detritus helped circumvent limitations associated with the indi- vidual methods. The combination of approaches was still insufficient to quantify the contribution of different primary producers to meiofaunal diet, however, highlighting the difficulties associated with the study of meiofaunal trophic connections in coastal systems.

A molecular evaluation of bulk organic carbon-isotope chemostratigraphy for terrestrial correlations: An example from two Paleocene–Eocene tropical sequences

The dynamics associated with the carbon cycle and the linkage between the oceans, the atmosphere, and land plants provide an opportunity to correlate marine and terrestrial sedimentary sequences using stable isotopes of carbon ( δ 13C), but few studies have tested this approach. For instance, it has been proposed that changes in plant community (e.g., gymnosperm-dominated vs. angiosperm-dominated) could have significantly altered/amplified the carbon-isotope ratios of bulk sedimentary organic matter derived from land plants ( δ 13C TOM), compared to that of the marine carbonates ( δ 13C carbonate). Here, δ 13C TOM values in a terrestrial sequence of the Colombian tropics are compared to the composite Paleocene–Eocene δ 13C carbonate curve from Zachos et al. (2001) to evaluate the use of δ 13C TOM values as a reliable chronostratigraphic tool. Sediments of the studied terrestrial sequences were deposited in a transitional setting dominated by mudstones, coals, and small lenses of sandstones (Late Cretaceous–Middle Paleocene sediments) and in a mixture of deltaic and fluvial conditions (Late Paleocene–Early Eocene sediments). The biostratigraphic control was based on palynological zones for the region. The δ 13C TOM values for the studied terrestrial sequence show three carbon-isotope excursions, which correlate closely with those present in the marine record. The δ 13C TOM values decreased from − 24.2‰ to − 26.5‰ in sediments accumulated during Early to Middle Paleocene, increased from − 26.5‰ to − 23.8‰ during the Late Paleocene, and decreased from − 23.8‰ to − 26.5‰ near the Paleocene–Eocene boundary (52–50 Ma). Selected biomarkers indicate that most of the organic matter derived from both gymnosperms and angiosperms. Moreover, the analyses of selected biomarker ratios (CPI, Pr/Ph, P aq, and ββ/ββ + αβ hopanes) show some diagenetic transformation in the preserved organic matter. However, no correlation between diagenesis and δ 13C TOM values was detected, thus suggesting that δ 13C TOM could be correlated with δ 13C carbonate values. The close correspondence that was found between δ 13C TOM and δ 13C carbonate values (Δ 13C TOM–carbonate ~ − 27‰) provides support to the hypothesis that a tight land-plant–oceans linkage exists through geologic timescales via atmospheric carbon dioxide.

Mid‐Miocene paleoproductivity in the Atlantic Ocean and implications for the global carbon cycle

A prominent, middle Miocene (17.5–13.5 Ma) carbon isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13C depleted organic carbon in marine sediments or enhanced carbon burial in peat/lignite deposits on land. Here we test the hypothesis that the marine δ13C record reflects a change in productivity with proxy records from three Atlantic Ocean sites (Deep Sea Drilling Program Site 608 and Ocean Drilling Program Sites 925 and 1265). Our multiproxy approach is based on benthic foraminiferal accumulation rates, elemental ratios (Ba/Al and P/Al), the δ13C of bulk sedimentary organic matter, and dissolution indices. We compare these proxies to benthic foraminiferal δ13C values measured on the same samples. Our results indicate that marine paleoproductivity in the Atlantic Ocean is not related to the benthic foraminiferal δ13C excursion. A numerical box model confirms that marine productivity cannot account for the δ13C maximum. The model shows that sequestration of 1.5 × 1018 mol C in the terrestrial realm over a period of 3 Ma leads to a 0.9‰ δ13C increase in the deep ocean, which is near the observed records. Therefore, an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean's carbon pool with 13C, which is consistent with coeval lignite deposits worldwide. The δ13C values of bulk sedimentary organic matter parallel the δ13C of dissolved inorganic carbon as reflected by benthic foraminiferal δ13C values suggesting no significant change in atmospheric pCO2 levels over the investigated period.