Radionuclides measured on 21 water bottle profiles during POLARSTERN cruise ANT-XXIV/3

Drake Passage is a major route for many water masses from the strong Antarctic Circumpolar Current. During the ANTXXIV-3 expedition (in 2008) the vertical distributions of dissolved and size-fractionated particulate 231Pa and thorium isotopes (230Th, 232Th and 234Th) were investigated in order to better define the scavenging regimes and the effects of the oceanic circulation on the fate of particulate material and on the Pa-Th distributions in the water column. The reversible scavenging-model applied to both 230Th and 234Th, in the upper 1500 m depth, gives estimates of the particle dynamics (settling velocities S~ 500-1300 m/y, adsorption and desorption rate constants of 0.1-0.4 1/y and 1-6 1/y respectively). Particulate 234Th/230Th activity ratio shows a depth dependence, with decreasing ratio with increasing depth in agreement with previous studies, but no relationship with particle size was found. 231Pa and thorium isotope fractionation and partition coefficients were investigated with particle size vs depth and latitude and appear to vary horizontally following a North-South gradient. This suggests that both radionuclides are mostly bound to the fine suspended particles. At Drake Passage, the 230Thxs distribution is controlled by a southward upwelling of deep water (clearly visible on the vertical section of total 230Thxs, defined as dissolved + particulate concentrations) and reversible-scavenging processes (linear increase of 230Thxs with increasing depth) with North of the Southern ACC Front, higher settling velocities and less adsorption/desorption cycles, than South of it. Distributions of dissolved and total 231Paxs also reflect the influence of the North-South upwelling but somehow this effect appears to be limited to the upper 1500 m depth of the water column. Below this depth, 231Paxs vertical profiles exhibit contrasted concentrations, with some high dissolved activities in the deep water of the stations in the northern part of the ACC and not South of the ACC. These N-S differences in dissolved 231Paxs were attributed to the different origins and scavenging history of the deep Pacific waters flowing across Drake Passage. Here at North, radionuclides-rich deep water originates from the Central Pacific, while at South, deep water derives from the Southern Pacific in which the observed low radionuclides concentrations are attributed to high opal abundance. South of the Drake Passage, high dissolved and particulate activities of 230Th and 232Th confirmed the intrusion of 230Th-rich Weddell Sea Deep Water (WSDW) close to the Antarctic Peninsula.

Sulfate and methane concentrations measured in pore water of sediment core GeoB13809-1 and GeoB13849-1

Several previous studies have shown that submarine mass-movements can profoundly impact the shape of pore water profiles. Therefore, pore water geochemistry and diffusion models were proposed as tools for identifying and dating recent (max. several thousands of years old) mass-transport deposits (MTDs). In particular, sulfate profiles evidentially indicate transient pore water conditions generated by submarine landslides. After mass-movements that result in the deposition of sediment packages with distinct pore water signatures, the sulfate profiles can be kink-shaped and evolve into the concave and linear shape with time due to molecular diffusion. Here we present data from the RV METEOR cruise M78/3 along the continental margin off Uruguay and Argentina. Sulfate profiles of 15 gravity cores are compared with the respective acoustic facies recorded by a sediment echosounder system. Our results show that in this very dynamic depositional setting, non-steady state profiles occur often, but are not exclusively associated with mass-movements. Three sites that show acoustic indications for recent MTDs are presented in detail. Where recent MTDs are identified, a geochemical transport/reaction model is used to estimate the time that has elapsed since the perturbation of the pore water system and, thus, the timing of the MTD emplacement. We conclude that geochemical analyses are a powerful complementary tool in the identification of recent MTDs and provide a simple and accurate way of dating such deposits.

Sediment and pore water chemistry of cores 214 and 755 recovered during Meteor M72/1 and POSEIDON cruise POS317/2, northwestern Black Sea

High-resolution sedimentary records of major and minor elements (Al, Ba, Ca, Sr, Ti), total organic carbon (TOC), and profiles of pore water constituents (SO42-, CH4, Ca2+, Ba2+, Mg2+, alkalinity) were obtained for two gravity cores (core 755, 501 m water depth and core 214, 1686 m water depth) from the northwestern Black Sea. The records were examined in order to gain insight into the cycling of Ba in anoxic marine sediments characterized by a shallow sulfate-methane transition (SMT) as well as the applicability of barite as a primary productivity proxy in such a setting. The Ba records are strongly overprinted by diagenetic barite (BaSO4) precipitation and remobilization; authigenic Ba enrichments were found at both sites at and slightly above the current SMT. Transport reaction modeling was applied to simulate the migration of the SMT during the changing geochemical conditions after the Holocene seawater intrusion into the Black Sea. Based on this, sediment intervals affected by diagenetic Ba redistribution were identified. Results reveal that the intense overprint of Ba and Baxs (Ba excess above detrital average) strongly limits its correlation to primary productivity. These findings have implications for other modern and ancient anoxic basins, such as sections covering the Oceanic Anoxic Events for which Ba is frequently used as a primary productivity indicator. Our study also demonstrates the limitations concerning the use of Baxs as a tracer for downward migrations of the SMT: due to high sedimentation rates at the investigated sites, diagenetic barite fronts are buried below the SMT within a relatively short period. Thus, 'relict' barite fronts would only be preserved for a few thousands of years, if at all.

Experimental data of CO2, CO3, Omega calcite saturation, pH values, alpha and epsilon fractionation factors, and Dd18O calctite-water

The oxygen isotopic composition (d18O) of calcium carbonate of planktonic calcifying organisms is a key tool for reconstructing both past seawater temperature and salinity. The calibration of paloeceanographic proxies relies in general on empirical relationships derived from field experiments on extant species. Laboratory experiments have more often than not revealed that variables other than the target parameter influence the proxy signal, which makes proxy calibration a challenging task. Understanding these secondary or "vital" effects is crucial for increasing proxy accuracy. We present data from laboratory experiments showing that oxygen isotope fractionation during calcification in the coccolithophore Calcidiscus leptoporus and the calcareous dinoflagellate Thoracosphaera heimii is dependent on carbonate chemistry of seawater in addition to its dependence on temperature. A similar result has previously been reported for planktonic foraminifera, supporting the idea that the [CO3]2- effect on d18O is universal for unicellular calcifying planktonic organisms. The slopes of the d18O/[CO3]2- relationships range between -0.0243 per mil/(µmol/kg) (calcareous dinoflagellate T. heimii) and the previously published -0.0022 per mil/(µmol/kg) (non-symbiotic planktonic foramifera Orbulina universa), while C. leptoporus has a slope of -0.0048 per mil/(µmol/kg). We present a simple conceptual model, based on the contribution of d18O-enriched [HCO3]- to the [CO3]2- pool in the calcifying vesicle, which can explain the [CO3]2- effect on d18O for the different unicellular calcifiers. This approach provides a new insight into biological fractionation in calcifying organisms. The large range in d18O/[CO3]2- slopes should possibly be explored as a means for paleoreconstruction of surface [CO3]2-, particularly through comparison of the response in ecologically similar planktonic organisms.