Amino acid geochronology of foraminifera test from north Queensland margin

In this study, we demonstrate the utility of amino acid geochronology based on single-foraminiferal tests in Quaternary sediment cores from the Queensland margin, Australia. The large planktonic foraminifer Pulleniatina obliquiloculata is ubiquitous in shelf, slope, and basin sediments of north Queensland as well as pantropical oceans. Fossil tests are resistant to dissolution, and retain substantial concentrations of amino acids (2-4 nmol/mg of shell) over hundreds of thousands of years. Amino acid D and L isomers of aspartic acid (Asp) and glutamic acid (Glu) were separated using reverse phase chromatography, which is sensitive enough to analyze individual foraminifera tests. In all, 462 Pulleniatina tests from 80 horizons in 11 cores exhibit a systematic increase in D/L ratios down core. D/L ratios were determined in 32 samples whose ages are known from AMS 14C analyses. In all cases, the Asp and Glu D/L ratios are concordant with 14C age. D/L ratios of equal-age samples are slightly lower for cores taken from deeper water sites, reflecting the sensitivity of the rate of racemization to bottom water temperature. Beyond the range of 14C dating, previously identified marine oxygen-isotope stage boundaries provide approximate ages of the sediments up to about 500,000 years. For this longer time frame, D/L ratios also vary systematically with isotope-correlated ages. The rate of racemization for Glu and Asp was modeled using power functions. These equations can be used to estimate ages of samples from the Queensland margin extending back at least 500,000 years. This analytical approach provides new opportunities for geochronological control necessary to understand fundamental sedimentary processes affecting a wide range of marine environments.

Rare earth elements of ROV sample GeoB12338-2 from the Makran accretionary complex

Authigenic carbonates forming at an active methane-seep on the Makran accretionary prism mainly consist of aragonite in the form of microcrystalline, cryptocrystalline, and botryoidal phases. The d13Ccarbonate values are very negative (-49.0 to -44.0 per mill V-PDB), agreeing with microbial methane as dominant carbon source. The d18Ocarbonate values are exclusively positive (+ 3.0 to + 4.5 per mill V-PDB) and indicate precipitation in equilibrium with seawater at bottom water temperatures. The content of rare earth elements and yttrium (REE + Y) determined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and solution ICP-MS varies for each aragonite variety, with early microcrystalline aragonite yielding the highest, cryptocrystalline aragonite intermediate, and later botryoidal aragonite the lowest REE + Y concentrations. Shale-normalised REE + Y patterns of different types of authigenic carbonate reflect distinct pore fluid compositions during precipitation: Microcrystalline aragonite shows high contents of middle rare earth elements (MREE), reflecting REE patterns ascribed to anoxic pore water. Cryptocrystalline aragonite exhibits a seawater-like REE + Y pattern at elevated total REE + Y concentrations, indicating higher concentrations of REEs in pore waters, which were influenced by seawater. Botryoidal aragonite is characterised by seawater-like REE + Y patterns at initial growth stages followed by an increase of light rare earth elements (LREE) with advancing crystal growth, reflecting changing pore fluid composition during precipitation of this cement. Conventional sample preparation involving micro-drilling of carbonate phases and subsequent solution ICP-MS does not allow to recognise such subtle changes in the REE + Y composition of individual carbonate phases. To be able to reconstruct the evolution of pore water composition during early diagenesis, an analytical approach is required that allows to track the changing elemental composition in a paragenetic sequence as well as in individual phases. High-resolution analysis of seep carbonates from the Makran accretionary prism by LA-ICP-MS reveals that pore fluid composition not only evolved in the course of the formation of different phases, but also changed during the precipitation of individual phases.

Medem Channel profiles based on stand-alone model simulation and corrections with nudging

State-of-the-art process-based models have shown to be applicable to the simulation and prediction of coastal morphodynamics. On annual to decadal temporal scales, these models may show limitations in reproducing complex natural morphological evolution patterns, such as the movement of bars and tidal channels, e.g. the observed decadal migration of the Medem Channel in the Elbe Estuary, German Bight. Here a morphodynamic model is shown to simulate the hydrodynamics and sediment budgets of the domain to some extent, but fails to adequately reproduce the pronounced channel migration, due to the insufficient implementation of bank erosion processes. In order to allow for long-term simulations of the domain, a nudging method has been introduced to update the model-predicted bathymetries with observations. The model-predicted bathymetry is nudged towards true states in annual time steps. Sensitivity analysis of a user-defined correlation length scale, for the definition of the background error covariance matrix during the nudging procedure, suggests that the optimal error correlation length is similar to the grid cell size, here 80-90 m. Additionally, spatially heterogeneous correlation lengths produce more realistic channel depths than do spatially homogeneous correlation lengths. Consecutive application of the nudging method compensates for the (stand-alone) model prediction errors and corrects the channel migration pattern, with a Brier skill score of 0.78. The proposed nudging method in this study serves as an analytical approach to update model predictions towards a predefined 'true' state for the spatiotemporal interpolation of incomplete morphological data in long-term simulations.

Carbon and nitrogen content of marine pore waters

We have developed sampling methods and an analytical system to determine the concentration of dissolved organic C (DOC) in marine pore waters. Our analytical approach is a modification of recently developed high-temperature, Pt-catalyzed oxidation methods; it uses Chromatographic trapping of the DOC-derived CO2 followed by reduction to CH4 and flame ionization detection. Sampling experiments with nearshore sediments indicate that pore-water separation by whole-core squeezing causes artificially elevated DOC concentrations, while pore-water recovery by sectioning and centrifugation does not appear to introduce DOC artifacts. Results from a set of northwestern Atlantic continental slope cores suggest that net DOC production accounts for >50% of the organic C that is recycled at the sediment-water interface.

Apatite fission track analytical data for samples from ODP Leg 152

We test a new approach to understanding the tectonic evolution of passive margins by using fission-track analysis on detrital apatites from sediments deposited offshore East Greenland. These apatites have not undergone postdepositional track annealing and therefore reflect provenance. The apatites preserve a component of the source rocks' thermal history that otherwise may not be retained within the present-day outcrop. Fission-track derived denudational histories from samples at Ocean Drilling Program drill sites offshore East Greenland at lat 63°N are compared with data from the onshore Singertat Complex. Previous apatite fission-track studies and geomorphic mapping of the East Greenland coast have shown that locally up to 6 km of denudation may have occurred, implying significant tectonic or magmatic activity starting as much as 30 m.y. after breakup at 56 Ma. In contrast, apatite fission-track data presented here record <2 km of Cenozoic denudation in southeast Greenland, probably driven by magmatic underplating at the time of breakup. Large-magnitude, postrift denudation of East Greenland is restricted to the area around Kangerdlugssuaq (68°N). The timing (<40-50 Ma) and magnitude are in accord with revised plume track models suggesting that the Iceland plume crossed the margin here during the late Eocene.