Facies and diagenesis of organic matter in sediments at DSDP Leg 87

A series of upper Pliocene to Pleistocene sediment samples from DSDP Sites 582 and 583 (Nankai Trough, active margin off Japan) were investigated by organic geochemical methods including organic carbon determination, Rock- Eval pyrolysis, gas chromatography of extractable hydrocarbons, and kerogen microscopy. The organic carbon content is fairly uniform and moderately low (0.35 to 0.77%) at both sites, although accompanied by high sedimentation rates. The low organic matter concentrations are the result of the combined effect of several factors: low bioproductivity, oxic depositional environment, and dilution with lithogenic material. Organic petrography revealed a mixture of three maceral types: (1) fresh, green fluorescent alginites of aquatic origin probably transported by turbidites from the shelf edge, (2) gelified huminites and paniculate liptinites derived from the erosion of unconsolidated peat, and (3) highly reflecting inertinites derived from continental erosion. By a combination of organic petrography and Rock-Eval pyrolysis results, the organic matter is characterized as mainly type III kerogen with a slight tendency to a mixed type II-III. During Rock-Eval pyrolysis, a mineral matrix effect on the generated hydrocarbons was observed. The organic matter in all sediments has a low level of maturity (below 0.45% Rm) and has not yet reached the onset of thermal hydrocarbon generation according to several geochemical maturation parameters. This low maturity is in contrast to anomalously high extract yields at both sites and large hydrocarbon proportions in the extracts at Site 583. This contrast may be due to early generation of polar compounds and perhaps redistribution of hydrocarbons caused by subduction tectonics. Carbon isotope data of the interstitial hydrocarbon gases indicate their origin from bacterial degradation of organic matter, although only very few bacterially degraded maceral components were detected.

Mineralogy and stable isotopic composition of carbonates and sulfide minerals from ODP Leg 164 sites

During Ocean Drilling Program Leg 164, gas hydrates were recovered in the Blake Ridge where the top of the gas hydrate zone lies at about 200 meters below seafloor (mbsf) and the bottom-simulating reflector (BSR) is located at about 450 mbsf. There is no sedimentological discontinuity crossing the BSR. The BSR is disrupted by the salt piercement of the Cape Fear Diapir. The authigenic carbonates (dolomite and siderite) are always present in small amounts (a few weight percent) in the sediments; they are also concentrated in millimeter- to centimeter-sized nodules and layers composed of dolomite above the top of the gas hydrate reservoir, and of siderite below the BSR. In the Blake Ridge, the dolomite/siderite boundary is located near 140 mbsf. The distribution with depth of the d18O values of dolomite and siderite shows a sharp decrease from high values (maximum 7.5 per mil) in the topmost 50 m, to very low values (minimum -2.7 per mil) at 140 mbsf, and at greater depth increase to positive values within the range of 1.8 per mil to 5.0 per mil. The d13C distribution is marked by the rapid increase with greater depth from low values (-31.3 per mil to -11.4 per mil) near 50 mbsf to positive values at 110 mbsf, which remain in the range of 1.7 to 5.4 down to 700 mbsf. Diagenetic carbonates were precipitated in pore waters in which d18O and d13C values were highly modified by strong fractionation effects, both in the water and in the CO2-CH4 systems associated with the formation and dissociation of gas hydrates.

Physico-chemical parameters of sediment core PG1975-1 (09-Tik-05) from a Tundra Lake, Northeastern Siberia

The relationships between thermokarst activity, limnogeological processes and climate change in the Siberian Arctic are not well understood. The objective of this paper is to identify the factors controlling the patterns of deposition, using grain size distribution, organic content, elemental composition and mineralogical composition of a 137-cm long sediment core with a maximum age of ~10.9 cal. kyr BP from Lake El'gene-Kyuele in the tundra of northeastern Siberia. Eight fine sand layers are attributed to depositional events associated with thaw slump activity acting upon orthogonally oriented patterns of ice-wedge networks in the ice-rich permafrost on the NW margin of the lake catchment. Sr/Rb ratios, which correspond to the total feldspar and illite content, serve as high-resolution grain size proxies. The Br content relates to the total organic carbon content, and the Fe/Mn ratio reflects the degree of oxidisation. Our results indicate a relationship between repeated phases of fine sand input and retrogressive thaw slumping dependent on hydroclimate variability and orthogonally oriented ice-wedge networks within the catchment.

Effects of pCO2 and iron on the elemental composition and cell geometry of the marine diatom Pseudo-nitzschia pseudodelicatissima//(Bacillariophyceae)

Partial pressure of CO2 (pCO2) and iron availability in seawater show corresponding changes due to biological and anthropogenic activities. The simultaneous change in these factors precludes an understanding of their independent effects on the ecophysiology of phytoplankton. In addition, there is a lack of data regarding the interactive effects of these factors on phytoplankton cellular stoichiometry, which is a key driving factor for the biogeochemical cycling of oceanic nutrients. Here, we investigated the effects of pCO2 and iron availability on the elemental composition (C, N, P, and Si) of the diatom Pseudo-nitzschia pseudodelicatissima (Hasle) Hasle by dilute batch cultures under 4 pCO2 (~200, ~380, ~600, and ~800 µatm) and five dissolved inorganic iron (Fe'; ~5, ~10, ~20, ~50, and ~100 pmol /L) conditions. Our experimental procedure successfully overcame the problems associated with simultaneous changes in pCO2 and Fe' by independently manipulating carbonate chemistry and iron speciation, which allowed us to evaluate the individual effects of pCO2 and iron availability. We found that the C:N ratio decreased significantly only with an increase in Fe', whereas the C:P ratio increased significantly only with an increase in pCO2. Both Si:C and Si:N ratios decreased with increasing pCO2 and Fe'. Our results indicate that changes in pCO2 and iron availability could influence the biogeochemical cycling of nutrients in future oceans with high- CO2 levels, and, similarly, during the time course of phytoplankton blooms. Moreover, pCO2 and iron availability may also have affected oceanic nutrient biogeochemistry in the past, as these conditions have changed markedly over the Earth's history.

Seawater carbonate chemistry and larval growth response of the Portuguese oyster (Crassostrea angulata) in a laboratory experiment

Rising anthropogenic carbon dioxide (CO2) dissolving into coastal waters is decreasing the pH and carbonate ion concentration, thereby lowering the saturation state of calcium carbonate (CaCO3) minerals through a process named ocean acidification (OA). The unprecedented threats posed by such low pH on calcifying larvae of several edible oyster species have not yet been fully explored. Effects of low pH (7.9, 7.6, 7.4) on the early growth phase of Portuguese oyster (Crassostrea angulata) veliger larvae was examined at ambient salinity (34 ppt) and the low-salinity (27 ppt) treatment. Additionally, the combined effect of pH (8.1, 7.6), salinity (24 and 34 ppt) and temperature (24 °C and 30 °C) was examined using factorial experimental design. Surprisingly, the early growth phase from hatching to 5-day-old veliger stage showed high tolerance to pH 7.9 and pH 7.6 at both 34 ppt and 27 ppt. Larval shell area was significantly smaller at pH 7.4 only in low-salinity. In the 3-factor experiment, shell area was affected by salinity and the interaction between salinity and temperature but not by other combinations. Larvae produced the largest shell at the elevated temperature in low-salinity, regardless of pH. Thus the growth of the Portuguese oyster larvae appears to be robust to near-future pH level (> 7.6) when combined with projected elevated temperature and low-salinity in the coastal aquaculture zones of South China Sea.

Seawater carbonate chemistry, physiology, morphology of larval sea urchins, Strongylocentrotus purpuratus in a laboratory experiment

Ocean warming and ocean acidification, both consequences of anthropogenic production of CO2, will combine to influence the physiological performance of many species in the marine environment. In this study, we used an integrative approach to forecast the impact of future ocean conditions on larval purple sea urchins (Strongylocentrotus purpuratus) from the northeast Pacific Ocean. In laboratory experiments that simulated ocean warming and ocean acidification, we examined larval development, skeletal growth, metabolism and patterns of gene expression using an orthogonal comparison of two temperature (13°C and 18°C) and pCO2 (400 and 1100 µatm) conditions. Simultaneous exposure to increased temperature and pCO2 significantly reduced larval metabolism and triggered a widespread downregulation of histone encoding genes. pCO2 but not temperature impaired skeletal growth and reduced the expression of a major spicule matrix protein, suggesting that skeletal growth will not be further inhibited by ocean warming. Importantly, shifts in skeletal growth were not associated with developmental delay. Collectively, our results indicate that global change variables will have additive effects that exceed thresholds for optimized physiological performance in this keystone marine species.

Seasonal changes in the D/H ratio of fatty acids of pelagic microorganisms

Culture studies of microorganisms have shown that the hydrogen isotopic composition of fatty acids depends on their metabolism, but there are only few environmental studies available to confirm this observation. Here we studied the seasonal variability of the deuterium/hydrogen (D/H) ratio of fatty acids in the coastal Dutch North Sea and compared this with the diversity of the phyto- and bacterioplankton. Over the year, the stable hydrogen isotopic fractionation factor epsilon between fatty acids and water ranged between -172 per mil and -237 per mil, the algal-derived polyunsaturated fatty acid nC20:5 being the most D-depleted and nC18:0 the least D-depleted fatty acid. The D-depleted nC20:5 is in agreement with culture studies, which indicates that photoautotrophic microorganisms produce fatty acids which are significantly depleted in D relative to water. The epsilon-lipid/water of all fatty acids showed a transient shift towards increased fractionation during the spring phytoplankton bloom, indicated by increasing chlorophyll a concentrations and relative abundance of the nC20:5 PUFA, suggesting increased contributions of photoautotrophy. Time periods with decreased fractionation (less negative epsilon-lipid/water values) can be explained by an increased contribution by heterotrophy to the fatty acid pool. Our results show that the hydrogen isotopic composition of fatty acids is a useful tool to assess the community metabolism of coastal plankton.

Effects of ocean acidification on sponge communities

The effects of ocean acidification on lower invertebrates such as sponges may be pronounced because of their low capacity for acid-base regulation. However, so far, most studies have focused on calcifiers. We present the first study of the effects of ocean acidification on the Porifera. Sponge species composition and cover along pH gradients at CO2 vents off Ischia (Tyrrhenian Sea, Italy) was measured at sites with normal pH (8.1-8.2), lowered pH (mean 7.8-7.9, min 7.4-7.5) and extremely low pH (6.6). There was a strong correlation between pH and both sponge cover and species composition. Crambe crambe was the only species present in any abundance in the areas with mean pH 6.6, seven species were present at mean pH 7.8-7.9 and four species (Phorbas tenacior, Petrosia ficiformis, Chondrilla nucula and Hemimycale columella) were restricted to sites with normal pH. Sponge percentage cover decreased significantly from normal to acidified sites. No significant effect of increasing CO2 levels and decreasing pH was found on spicule form in Crambe crambe. This study indicates that increasing CO2 concentrations will likely affect sponge community composition as some demosponge species appear to be more vulnerable than others. Further research into the mechanisms by which acidification affects sponges would be useful in predicting likely effects on sessile marine communities.

Growth response of an early successional assemblage of coralline algae and benthic diatoms to ocean acidification

The sustained absorption of anthropogenically released atmospheric CO2 by the oceans is modifying seawater carbonate chemistry, a process termed ocean acidification (OA). By the year 2100, the worst case scenario is a decline in the average oceanic surface seawater pH by 0.3 units to 7.75. The changing seawater carbonate chemistry is predicted to negatively affect many marine species, particularly calcifying organisms such as coralline algae, while species such as diatoms and fleshy seaweed are predicted to be little affected or may even benefit from OA. It has been hypothesized in previous work that the direct negative effects imposed on coralline algae, and the direct positive effects on fleshy seaweeds and diatoms under a future high CO2 ocean could result in a reduced ability of corallines to compete with diatoms and fleshy seaweed for space in the future. In a 6-week laboratory experiment, we examined the effect of pH 7.60 (pH predicted to occur due to ocean acidification just beyond the year 2100) compared to pH 8.05 (present day) on the lateral growth rates of an early successional, cold-temperate species assemblage dominated by crustose coralline algae and benthic diatoms. Crustose coralline algae and benthic diatoms maintained positive growth rates in both pH treatments. The growth rates of coralline algae were three times lower at pH 7.60, and a non-significant decline in diatom growth meant that proportions of the two functional groups remained similar over the course of the experiment. Our results do not support our hypothesis that benthic diatoms will outcompete crustose coralline algae under future pH conditions. However, while crustose coralline algae were able to maintain their presence in this benthic rocky reef species assemblage, the reduced growth rates suggest that they will be less capable of recolonizing after disturbance events, which could result in reduced coralline cover under OA conditions.

Effects of ocean acidification on population dynamics and community structure of crustose coralline algae

Calcification and growth of crustose coralline algae (CCA) are affected by elevated seawater pCO2 and associated changes in carbonate chemistry. However, the effects of ocean acidification (OA) on population and community-level responses of CCA have barely been investigated. We explored changes in community structure and population dynamics (size structure and reproduction) of CCA in response to OA. Recruited from an experimental flow-through system, CCA settled onto the walls of plastic aquaria and developed under exposure to one of three pCO2 treatments (control [present day, 389±6 ppm CO2], medium [753±11 ppm], and high [1267±19 ppm]). Elevated pCO2 reduced total CCA abundance and affected community structure, in particular the density of the dominant species Pneophyllum sp. and Porolithon onkodes. Meanwhile, the relative abundance of P. onkodes declined from 24% under control CO2 to 8.3% in high CO2 (65% change), while the relative abundance of Pneophyllum sp. remained constant. Population size structure of P. onkodes differed significantly across treatments, with fewer larger individuals under high CO2. In contrast, the population size structure and number of reproductive structures (conceptacles) per crust of Pneophyllum sp. was similar across treatments. The difference in the magnitude of the response of species abundance and population size structure between species may have the potential to induce species composition changes in the future. These results demonstrate that the impacts of OA on key coral reef builders go beyond declines in calcification and growth, and suggest important changes to aspects of population dynamics and community ecology.

Effect of ocean acidification and pH fluctuations on the growth and development of coralline algal recruits, and an associated benthic algal assemblage

Coralline algae are susceptible to the changes in the seawater carbonate system associated with ocean acidification (OA). However, the coastal environments in which corallines grow are subject to large daily pH fluctuations which may affect their responses to OA. Here, we followed the growth and development of the juvenile coralline alga Arthrocardia corymbosa, which had recruited into experimental conditions during a prior experiment, using a novel OA laboratory culture system to simulate the pH fluctuations observed within a kelp forest. Microscopic life history stages are considered more susceptible to environmental stress than adult stages; we compared the responses of newly recruited A. corymbosa to static and fluctuating seawater pH with those of their field-collected parents. Recruits were cultivated for 16 weeks under static pH 8.05 and 7.65, representing ambient and 4*preindustrial pCO2 concentrations, respectively, and two fluctuating pH treatments of daily (daytime pH = 8.45, night-time pH = 7.65) and daily (daytime pH = 8.05, night-time pH = 7.25). Positive growth rates of new recruits were recorded in all treatments, and were highest under static pH 8.05 and lowest under fluctuating pH 7.65. This pattern was similar to the adults' response, except that adults had zero growth under fluctuating pH 7.65. The % dry weight of MgCO3 in calcite of the juveniles was reduced from 10% at pH 8.05 to 8% at pH 7.65, but there was no effect of pH fluctuation. A wide range of fleshy macroalgae and at least 6 species of benthic diatoms recruited across all experimental treatments, from cryptic spores associated with the adult A. corymbosa. There was no effect of experimental treatment on the growth of the benthic diatoms. On the community level, pH-sensitive species may survive lower pH in the presence of diatoms and fleshy macroalgae, whose high metabolic activity may raise the pH of the local microhabitat.

Grain counts and XRD mineralogy of turbidite sand and hemipelagic mud from ODP Leg 168 sites

Sequences of late Pliocene to Holocene sediment lap onto juvenile igneous crust within 20 km of the Juan de Fuca Ridge in northwestern Cascadia Basin, Pacific Ocean. The detrital modes of turbidite sands do not vary significantly within or among sites drilled during Leg 168 of the Ocean Drilling Program. Average values of total quartz, total feldspar, and unstable lithic fragments are Q = 35, F = 35, and L = 30. Average values of monocrystalline quartz, plagioclase, and K-feldspar are Qm = 46, P = 49, and K = 5, and the average detrital modes of polycrystalline quartz, volcanic-rock fragments, and sedimentary-rock plus metamorphic-rock fragments are Qp = 16, Lv = 43, and Lsm = 41. Likely source areas include the Olympic Peninsula and Vancouver Island; sediment transport was focused primarily through the Strait of Juan de Fuca, Juan de Fuca Channel, Vancouver Valley, and Nitinat Valley. Relative abundance of clay minerals (<2-µm-size fraction) fluctuate erratically with depth, stratigraphic age, and sediment type (mud vs. turbidite matrix). Mineral abundance in mud samples are 0%-35% smectite (mean = 8%), 18%-59% illite (mean = 40%), and 29%-78% chlorite + kaolinite (mean = 52%). We attribute the relatively low content of smectite to rapid mechanical weathering of polymictic source terrains, with little or no input of volcanic detritus from the Columbia River. The scatter in clay mineralogy probably was caused by converging of surface currents, turbidity currents, and near-bottom nepheloid clouds from several directions, as well as subtle changes in glacial vs. interglacial weathering products.

Mineral composition of sediments from ODP Leg 190 sites and DSDP Hole 31-297

This data report documents the acquisition of two new sets of normalization factors for semiquantitative X-ray diffraction analyses. One set of factors is for bulk sediment powders, and the other applies to oriented aggregates of clay-sized fractions (<2 µm). We analyzed mixtures of standard minerals with known weight percentages of each component and solved for the normalization factors using matrix singular value decomposition. The components in bulk powders include total clay minerals (a mixture of smectite, illite, and chlorite), quartz, plagioclase, and calcite. For clay-sized fractions, the minerals are smectite, illite, chlorite, and quartz. We tested the utility of the method by analyzing natural mudstone specimens from Site 297 of the Deep Sea Drilling Project, which is located in the Shikoku Basin south of Site 1177 of the Ocean Drilling Program (Ashizuri transect).