Description: Ocean environmental conditions can be inferred from the chemical composition of bamboo coral skeletons. The high magnesium calcite internodes of these long-living octocorals may therefore represent a potential archive for seawater properties such as salinity or temperature where instrumental time series are absent. To extend these time series into the past using a natural archive the principles of temperature and salinity signal incorporation into cold-water coral skeletal material need to be investigated. Since skeletal Na and S concentrations have been proposed as environmental proxies, we mapped the spatial distribution and concentration of these elements in two Atlantic specimens of Keratoisis grayi (family Isididae). These measurements were conducted with an electron microprobe applying a spatial resolution of 4 μm. The mean apparent distribution coefficient of Na/Ca for the two samples was within 2.5 and 2.8*10−4, while that of S shows a similar depletion relative to seawater with 3.8 and 3.6*10−3. The two elements show an inverse correlation in bamboo coral skeletons. The mean apparent distribution coefficient of Na is similar to that of abiotic calcites. This similarity can be interpreted as the absence of significant vital effects for skeletal Na/Ca. Hence it corroborates the idea that the average skeletal composition of bamboo corals holds the potential to record past seawater conditions. In contrast, it appears unlikely that the spatial variations of the element distribution of seemingly simultaneously precipitated material along growth rings are exclusively controlled by environmental factors. We further exclude Rayleigh fractionation, ion-specific pumping, and Ca/proton exchange as the driver of Na and S distribution in bamboo corals. Instead, we adapt a calcification model originally proposed for scleractinians to bamboo corals. This model can explain the observed distribution of Na and S in the skeleton by a combination of Ca/proton pumping, bicarbonate active transport, and the formation of an organic skeletal matrix. The adapted model can further be used to predict the theoretical behaviour of other elements and disentangle vital effects from external factors influencing compositional features. It is therefore a useful tool for future studies on the potential of bamboo corals as environmental archives.

Description: Strontium isotopes in various marine carbonates were determined using an “AXIOM” MC-ICP-MS in combination with a NewWave UP193 laser ablation unit. Using a modified measurement and data reduction strategy, an external reproducibility of 87Sr/86Sr ratios in carbonates of about 19 ppm (RSD) was achieved. For recent and sub-recent marine carbonates a mean radiogenic strontium isotope ratio 87Sr/86Sr of 0.709170 ± 0.000007 (2SE) was determined, which agrees well with the value of 0.7091741 ± 0.0000024 (2SE) reported for modern sea water (J. M. McArthur, D. Rio, F. Massari, D. Castrodi, T. R. Bailey, M. Thirlwall and S. Houghton, Palaeogeogr. Palaeoclimatol. Palaeoeco., 2006, 242(126), 2006). Compared to published laser-based methods, an improved accuracy and precision was achieved by applying a new data reduction protocol using the simultaneous responses of all isotopes measured. The latter is considered as a new principal approach for isotope ratio evaluation using LA-MC-ICP-MS. A major advantage of the presented method is the direct determination of the stable strontium isotope fractionation. Providing reproducible sample ablation, introduction into the plasma and stable plasma condition, this method excludes the efforts of a quantitative strontium recovery after ion chromatographic separation to avoid additional fractionation of the sample strontium due to chemical pre-treatment/separation (ion chromatography and solution preparation), and is therefore, together with the quicker sample preparation and spatially resolved analysis, advantageous when compared to published solution–nebulization bracketing-standard MC-ICP-MS methods for stable strontium isotope determination.

Description: Mg/Ca and Sr/Ca ratios were determined on a single species of planktonic foraminiferan, Globigerinoides ruber (white), collected from the Gulf of Eilat and cultured in seawater at five different salinities (32 to 44), five temperatures (18 to 30 °C) and four pH values (7.9 to 8.4). The Mg/Ca-temperature calibration of cultured G. ruber (with an exponential slope of 8 ± 3%/°C) agrees well with previously published calibrations from core-tops and sediment traps. However, the dependence of Mg/Ca on salinity (with an exponential slope of 5 ± 3%/psu) is also significant and should be included in the calibration equation. With this purpose, we calculated a calibration equation for G. ruber dependent on both temperature and salinity within the 95% confidence limits: Mg/Ca(mmol/mol)=exp[0.06(±0.02)*S(psu)+0.08(±0.02)*T(°C)−2.8(±1.0)],R2=0.95 The influence of pH on Mg/Ca ratios is negligible at ambient seawater pH (8.1 to 8.3). However, we observe a dominating pH control on shell Mg/Ca when the pH of seawater is lower than 8.0. Sr/Ca in G. ruber shows a significant positive correlation with average growth rate. Presumably, part of the variability in shell Sr/Ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions.

Description: We investigated the controls of hydrography and of scavenging on the distribution of the particle reactive radionuclides 231Pa and 230Th in the water column and in surface sediments off Southwest Africa (Angola and Cape basins). Based on a vertical section of total 230Thex concentrations in the water column we show that small differences in the salinity between the North Atlantic Deep Water (NADW) in the Angola Basin and the NADW in the Cape Basin as well as the advection of NADW associated with the Namib Col Current are reflected in total 230Thex concentrations. These variable total concentrations are believed to reflect the flow path and mixing history of NADW with the NADW in the Angola Basin being relatively older and 230Th enriched compared to the NADW in the Cape Basin. In the area investigated we found high 231Paex/230Thex ratios (231Paex/230Thex 〉 0.093) in surface sediments at the continental margin and lower ones (231Paex/230Thex 〈 0.093) in the open ocean. Such a distribution is normally interpreted to result from high particle flux at ocean margins (boundary scavenging). However, the lack of any significant depletion of dissolved 230Th and 231Pa in the water column does not indicate extensive scavenging at the continental margin. High 231Paex/230Thex ratios are constrained to shallow waters depths (〈 2000 m) only and coincide with low fractionation between 231Pa and 230Th indicating that preferential scavenging of 231Pa on opal may have caused high 231Paex/230Thex ratios in the sediments. The observed close negative correlation (r2 = 0.82) between 231Paex/230Thex ratios in sediments and water depths is believed to reflect changes in the particle composition, i.e. a decrease in opal content with water depth. In the Angola and Cape basins the total 231Paex concentrations in NADW were the highest observed so far in the Atlantic Ocean, and they are attributed to the meridional export of 231Pa from the North Atlantic. This caused the average dissolved 231Pa/230Th in the Southeast Atlantic to be about a factor 2 higher when compared to the North Atlantic (Labrador Sea). These differences in the dissolved 231Pa/230Th were not reflected in 231Pa/230Th ratios of surface sediments because the fractionation is lower in the Labrador Sea compared to the Southeast Atlantic, i.e. fractionation counteracts changes in the dissolved 231Pa/230Th. This suggests that fractionation is more important for the determination of 231Paex/230Thex ratios in sediments than the meridional export of 231Pa from the North Atlantic.

Description: The weathering of silicate minerals exposed on the continents is the largest sink of atmospheric CO2 on time scales of millions of years. The rate of this process is positively correlated with global mean temperature and atmospheric CO2 concentration, resulting in a negative feedback that stabilizes Earths’ climate (Berner, 2004). Detrital silicates derived from the physical denudation of the continents are a major component of marine sediments (Li and Schoonmaker, 2003). However, their geochemical behaviour is poorly understood and they are considered to be unimportant to the long-term carbon cycle. We show that in organic matter-rich sediments of the Sea of Okhotsk detrital silicates undergo intense weathering. This process is likely favoured by microbial activity, which lowers pore water pH and releases dissolved humic substances, and by the freshness of detrital silicates which originate from the cold, poorly weathered Amur River basin. Numerical simulations of early diagenesis show that submarine weathering rates in our study area are comparable to average continental weathering rates (Gaillardet et al., 1999). Furthermore, silicate weathering seems to be widespread in organic matter-rich sediments of continental margins, suggesting the existence of a significant CO2 sink there. These findings imply a greater efficiency of the silicate weathering engine also at low surface temperatures, resulting in a weakening of the negative feedback between pCO2, climate evolution and silicate weathering.

Description: ODP Leg 204, which drilled at Hydrate Ridge, provides unique insights into the fluid regime of an accretionary complex and delineates specific sub-seafloor pathways for fluid transport. Compaction and dewatering due to smectite–illite transition increase with distance from the toe of the accretionary prism and bring up fluids from deep within the accretionary complex to sampled depths (≤ 600 mbsf). These fluids have a distinctly non-radiogenic strontium isotope signature indicating reaction with the oceanic basement. Boron isotopes are also consistent with a deep fluid source that has been modified by desorption of heavy boron as clay minerals change from smectite to illite. One of three major horizons serves as conduit for the transport of mainly fluid. Our results enable us to evaluate fluid migration pathways that play important roles on massive gas hydrate accumulations and seepage of methane-rich fluids on southern Hydrate Ridge.

Description: Exploring the potentials of new methods in palaeothermometry is essential to improve our understanding of past climate change. Here, we present a refinement of the published δ44/40Ca-temperature calibration investigating modern specimens of planktonic foraminifera Globigerinoides sacculifer and apply this to sea surface temperature (SST) reconstructions over the last two glacial–interglacial cycles. Reproduced measurements of modern G. sacculifer collected from surface waters describe a linear relationship for the investigated temperature range (19.0–28.5 °C): δ44/40Ca [‰] = 0.22 (±0.05)∗SST [°C] −4.88. Thus a change of δ44/40Ca[‰] of 0.22 (±0.05) corresponds to a relative change of 1 °C. The refined δ44/40Camodern-calibration allows the determination of both relative temperature changes and absolute temperatures in the past. This δ44/40Camodern-calibration for G. sacculifer has been applied to the tropical East Atlantic sediment core GeoB1112 for which other SST proxy data are available. Comparison of the different data sets gives no indication for significant secondary overprinting of the δ44/40Ca signal. Long-term trends in reconstructed SST correlate strongly with temperature records derived from oxygen isotopes and Mg/Ca ratios supporting the methods validity. The observed change of SST of approximately 3 °C at the Holocene-last glacial maximum transition reveals additional evidence for the important role of the tropical Atlantic in triggering global climate change, based on a new independent palaeothermometer.

Description: Chemoherm carbonates, as well as numerous other types of methane seep carbonates, were discovered in 2004 along the passive margin of the northern South China Sea. Lithologically, the carbonates are micritic containing peloids, clasts and clam fragments. Some are highly brecciated with aragonite layers of varying thicknesses lining fractures and voids. Dissolution and replacement is common. Mineralogically, the carbonates are dominated by high magnesium calcites (HMC) and aragonite. Some HMCs with MgCO3 contents of between 30–38 mol%–extreme-HMC, occur in association with minor amounts of dolomite. All of the carbonates are strongly depleted in δ13C, with a range from − 35.7 to − 57.5‰ PDB and enriched in δ18O (+ 4.0 to + 5.3‰ PDB). Abundant microbial rods and filaments were recognized within the carbonate matrix as well as aragonite cements, likely fossils of chemosynthetic microbes involved in carbonate formation. The microbial structures are intimately associated with mineral grains. Some carbonate mineral grains resemble microbes. The isotope characteristics, the fabrics, the microbial structure, and the mineralogies are diagnostic of carbonates derived from anaerobic oxidation of methane mediated by microbes. From the succession of HMCs, extreme-HMC, and dolomite in layered tubular carbonates, combined with the presence of microbial structure and diagenetic fabric, we suggest that extreme-HMC may eventually transform into dolomites. Our results add to the worldwide record of seep carbonates and establish for the first time the exact locations and seafloor morphology where such carbonates formed in the South China Sea. Characteristics of the complex fabric demonstrate how seep carbonates may be used as archives recording multiple fluid regimes, dissolution, and early transformation events.

Description: In order to improve and extend the application of U- and Th-series isotope measurements a new technique for MIC-ICP-MS (multiple ion counting inductively coupled plasma mass spectrometry) was developed. This method uses either two (double MIC) or three (triple MIC) multipliers to measure in static mode in turn the U-isotopes 233U, 234U, 235U and 236U. For online internal standardization, mass bias correction and cross calibration of the multipliers a 233U/236U double spike was used. Applying this method the level of 1‰ 2σ internal precision is reached in less than 30 min, consuming less than 5 ng of total U. The multi-static MIC-ICP-MS method improves the precision by a factor of 5 for U isotope measurement compared with TIMS and by a factor of 2 compared with published ICP-MS methods. Repeated measurements of uranium CRM-145 (otherwise NBL 112A) were performed to test the reproducibility and accuracy of the method. An average 234U/238U value of (5.285 84 ± 0.000 87) × 10−5 or a δ234U value of −36.96 ± 0.16, respectively, was determined for CRM-145 in good agreement with reference data. Based on the precisely determined U isotope ratios we furthermore developed a combined multi-static U- and Th-measurement method. This approach extends this new MIC-ICP-MS technique to those U- and Th-series isotope systems having no constant isotope ratio for normalization (e.g., 230Th/232Th, 230Th/229Th) and is the key for new approaches to determining 226Ra/228Ra and 231Pa/233Pa. The applicability of the methods presented here is demonstrated by accurate dating of very young corals (10–350 y).