Using ocean models to predict spatial and temporal variation in marine carbon isotopes

Natural-abundance stable isotope ratios provide a wealth of ecological information relating to food web structure, trophic level, and location. The correct interpretation of stable isotope data requires an understanding of spatial and temporal variation in the isotopic compositions at the base of the food web. In marine pelagic environments, accurate interpretation of stable isotope data is hampered by a lack of reliable, spatio-temporally distributed measurements of baseline isotopic compositions. In this study, we present a relatively simple, process-based carbon isotope model that predicts the spatio-temporal distributions of the carbon isotope composition of phytoplankton (here expressed as δ13CPLK) across the global ocean at one degree and monthly resolution. The model is driven by output from a coupled physics-biogeochemistry model, NEMO-MEDUSA, and operates offline; it could also be coupled to alternative underlying ocean model systems. Model validation is challenged by the same lack of spatio-temporally explicit data that motivates model development, but predictions from our model successfully reproduce major spatial patterns in carbon isotope values observed in zooplankton, and are consistent with simulations from alternative models. Model predictions represent an initial hypothesis of spatial and temporal variation in carbon isotopic baselines in ocean areas where a few data are currently available, and provide the best currently available tool to estimate spatial and temporal variation in baseline isotopic compositions at ocean basin to global scales

Quantifying carbon fluxes from primary production to mesopelagic fish using a simple food web model

An ecosystem-based flow analysis model was used to study carbon transfer from primary production (PP) to mesopelagic fish via three groups of copepods: detritivores that access sinking particles, vertical migrators, and species that reside in the surface ocean. The model was parameterized for 40°S to 40°N in the world ocean such that results can be compared with recent estimates of mesopelagic fish biomass in this latitudinal range, based on field studies using acoustic technologies, of ∼13 Gt (wet weight). Mesopelagic fish production was predicted to be 0.32% of PP which, assuming fish longevity of 1.5 years, gives rise to predicted mesopelagic fish biomass of 2.4 Gt. Model ensembles were run to analyse the uncertainty of this estimate, with results showing predicted biomass >10 Gt in only 8% of the simulations. The work emphasizes the importance of migrating animals in transferring carbon from the surface ocean to the mesopelagic zone. It also highlights how little is known about the physiological ecology of mesopelagic fish, trophic pathways within the mesopelagic food web, and how these link to PP in the surface ocean. A deeper understanding of these interacting factors is required before the potential for utilizing mesopelagic fish as a harvestable resource can be robustly assessed

The stable isotope composition of organic and inorganic fossils in lake sediment records: current understanding, challenges, and future directions

This paper provides an overview of stable isotope analysis (H, C, N, O, Si) of the macro and microscopic remains from aquatic organisms found in lake sediment records and their application in (palaeo)environmental science. Aquatic organisms, including diatoms, macrophytes, invertebrates, and fish, can produce sufficiently robust remains that preserve well as fossils and can be identified in lake sediment records. Stable isotope analyses of these remains can then provide valuable insights into habitat-specific biogeochemistry, feeding ecology, but also on climatic and hydrological changes in and around lakes. Since these analyses focus on the remains of known and identified organisms, they can provide more specific and detailed information on past ecosystem, food web and environmental changes affecting different compartments of lake ecosystems than analyses on bulk sedimentary organic matter or carbonate samples. We review applications of these types of analyses in palaeoclimatology, palaeohydrology, and palaeoecology. Interpretation of the environmental ‘signal’ provided by taxon-specific stable isotope analysis requires a thorough understanding of the ecology and phenology of the organism groups involved. Growth, metabolism, diet, feeding strategy, migration, taphonomy and several other processes can lead to isotope fractionation or otherwise influence the stable isotope signatures of the remains from aquatic organisms. This paper includes a review of the (modern) calibration, culturing and modeling studies used to quantify the extent to which these factors influence stable isotope values and provides an outlook for future research and methodological developments for the different examined fossil groups

Rare earth element geochemistry and taphonomy of terrestrial vertebrate assemblages

Most taphonomic analyses of vertebrate remains have focused upon physical processes. Chemical processes only rarely are addressed, leaving a large untapped store of quantitative taphonomic information contained within the bones themselves. In this paper, the rare earth element (REE) signature of fossil bones in terrestrial deposits is shown to be controlled by the early diagenetic environment. Thus, bones fossilized in different early diagenetic environments may be separated by their distinct REE signatures. Furthermore, the variation of REE patterns developed in individual bones within an assemblage is controlled by sedimentologic and taphonomic processes. Hence, the degree of mixing and reworking (relative time and space averaging) of vertebrate elements within a particular assemblage may be determined from the REE patterns of the interred bones. REE geochemistry represents a new and powerful taphonomic tool

Rare earth element geochemistry and taphonomy of terrestrial vertebrate assemblages

Most taphonomic analyses of vertebrate remains have focused upon physical processes. Chemical processes only rarely are addressed, leaving a large untapped store of quantitative taphonomic information contained within the bones themselves. In this paper, the rare earth element (REE) signature of fossil bones in terrestrial deposits is shown to be controlled by the early diagenetic environment. Thus, bones fossilized in different early diagenetic environments may be separated by their distinct REE signatures. Furthermore, the variation of REE patterns developed in individual bones within an assemblage is controlled by sedimentologic and taphonomic processes. Hence, the degree of mixing and reworking (relative time and space averaging) of vertebrate elements within a particular assemblage may be determined from the REE patterns of the interred bones. REE geochemistry represents a new and powerful taphonomic tool

A geochemical method to trace the taphonomic history of reworked bones in sedimentary settings

Rare earth element (REE) signatures can be used to identify the original mode of deposition of fossil bones and teeth that have been reworked. This new technique may resolve the notoriously difficult problem of assessing the amount of transport or reworking undergone by fossil bones and teeth on the basis of physical parameters, such as degree of abrasion. Different REE signals characterize different pore-water environments. Bones and teeth, composed of apatite, incorporate REEs rapidly during early diagenesis, and the REE signature in the bone is controlled by that of the surrounding pore waters. Reworked bones and teeth may show REE traces suggesting early-diagenetic pore-water conditions different from those indicated by in situ sedimentary or geochemical evidence. This situation is demonstrated in a case study from the Rhaetian (latest Triassic) of southwest England, where different bone beds are compared. In one case, the original environmental setting of reworked bone is traced by matching REE traces with contemporaneous unreworked bone assemblages in neighboring areas

Rare earth elements in Solnhofen biogenic apatite: geochemical clues to the palaeoenvironment

Rare earth element (REE) concentrations in biogenic apatite samples (coprolite, bone and soft-tissue) were used to investigate the environment of deposition of the celebrated Solnhofen fossil Lagerstätten. The measured REE patterns are similar between different localities, lithologies (flinz, fäule) and levels in the Upper Solnhofen Plattenkalk, suggestive of a stable REE supply during deposition. The behaviour of cerium in the Solnhofen samples implies that bottom water conditions were not anoxic, and variations in the cerium anomaly can be explained by differences in burial rate. These results provide further geochemical support for current depositional models [Barthel, K.W., 1978. Solnhofen: Ein Blick in die Erdgeschichte. Ott Verlag, Thun.; Barthel, K.W., Swinburne, N.H.M., Conway Morris, S., 1990, Solnhofen. A Study in Mesozoic Palaeontology. Cambridge Univ. Press, Cambridge.] that propose that extra-basinal processes are responsible for the interbedded nature of the Solnhofen deposits, rather than intra-basinal processes such as water turnover events

The long–term survival of bone: the role of bioerosion

Fossil bones (N = 350) spanning more than 350 million years, and covering a wide range of depositional environments, were studied to compare the distribution of microbial destruction features in fossil bones with previously published data sets of bones of archaeological age. The distribution of bioerosion in fossil bones is very different from that found in bone from archaeological sites. Fossil bones typically show little or no bioerosion. Under normal conditions, if a bone is to survive into the fossil record, then rapid bioerosion must be prevented (or halted). This conclusion suggests that early post mortem processes,such as the mode of death, influence the potential of any bone to survive into deep time