Seawater carbonate chemistry and shell weights of Laternula elliptica, Yoldia eightsi, Nacella concinna and Liothyrella uva during experiments, 2009

Antarctic calcified macroorganisms are particularly vulnerable to ocean acidification because many are weakly calcified, the dissolution rates of calcium carbonate are inversely related to temperature, and high latitude seas are predicted to become undersaturated in aragonite by the year 2100. We examined the post-mortem dissolution rates of aragonitic and calcitic shells from four species of Antarctic benthic marine invertebrates (two bivalves, one limpet, one brachiopod) and the thallus of a limpet shell-encrusting coralline alga exposed to acidified pH (7.4) or non-acidified pH (8.2) seawater at a constant temperature of 4 C. Within a period of only 14-35 days, shells of all four species held in pH 7.4 seawater had suffered significant dissolution. Despite calcite being 35% less soluble in seawater than aragonite, there was surprisingly, no consistent pattern of calcitic shells having slower dissolution rates than aragonitic shells. Outer surfaces of shells held in pH 7.4 seawater exhibited deterioration by day 35, and by day 56 there was exposure of aragonitic or calcitic prisms within the shell architecture of three of the macroinvertebrate species. Dissolution of coralline algae was confirmed by differences in weight loss in limpet shells with and without coralline algae. By day 56, thalli of the coralline alga held in pH 7.4 displayed a loss of definition of the conceptacle pores and cracking was evident at the zone of interface with limpet shells. Experimental studies are needed to evaluate whether there are adequate compensatory mechanisms in these and other calcified Antarctic benthic macroorganisms to cope with anticipated ocean acidification. In their absence, these organisms, and the communities they comprise, are likely to be among the first to experience the cascading impacts of ocean acidification.

Wet-bulk densities, mean atomic weights, effective porosities, grain densities, and compressional-wave velocities at DSDP Leg 58 Holes

The effects of water saturation and open pore space on the seismic velocities of crystalline rocks are extremely important when comparing laboratory data to in situ geophysical observations (e.g., Dortman and Magid, 1969; Nur and Simmons, 1969; Christensen and Salisbury, 1975). The existence of fractured rocks, flow breccias and drained pillows in oceanic crustal layer 2a, for instance, may appreciably reduce seismic velocities in that layer (Hyndman, 1976). Laboratory data assessing the influence of porosity and water saturation on seismic velocities of oceanic crustal rocks would certainly aid interpretation of marine geophysical data. Igneous rocks recovered during Leg 58 of the Deep Sea Drilling Project, in the Shikoku Basin and Daito Basin in the North Philippine Sea, are extremely vesicular, as evidenced by shipboard measurements of porosities, which range from 0 to 30 per cent (see reports on Sites 442, 443, 444, and 446, this volume). Samples with this range of porosities afford an excellent opportunity to examine the influence of porosity and water saturation on seismic velocities of oceanic basalts. This paper presents compressional-wave velocities to confining pressures of 1.5 kbars for water-saturated and air-dried basalt samples from the North Philippine Sea. Samples used in this study are from sites 442, 443 and 444 in the Shikoku Basin and Site 446 in the Daito Basin. Excellent negative correlation between porosity and compressional-wave velocity demonstrates that waterfilled pore space can significantly reduce compressionalwave velocities in porous basalts. Velocities measured in air-dried samples indicate that the velocity difference between dry samples and saturated samples is small for porosities exceeding 10 per cent, and very large for lower porosities.

Dissolution index and shell weights of planktonic foraminifera

Finding the ideal deep-sea CaCO3 dissolution proxy is essential for quantifying the role of the marine carbonate system in regulating atmospheric pCO2 over millennia. We explore the potential of using the Globorotalia menardii fragmentation index (MFI) and size-normalized foraminifer shell weight (SNSW) as complementary indicators of deep-sea CaCO3 dissolution. MFI has strong correlations with bottom water [CO3]2-, modeled estimates of percent CaCO3 dissolved, and Mg/Ca in Pulleniatina obliquiloculata in core top samples along a depth transect on the Ontong Java Plateau (OJP) where surface ocean temperature variation is minimal. SNSW of P. obliquiloculata and Neogloboquadrina dutertrei have weak correlations with MFI-based percent dissolved, Mg/Ca in P. obliquiloculata shells and bottom water [CO3]2- on the OJP. In core top samples from the eastern equatorial Pacific (EEP), SNSW of P. obliquiloculata has moderate to strong correlations with both MFI-based percent CaCO3 dissolved estimates and surface ocean environmental parameters. SNSW of N. dutertrei shells shows a latitudinal distribution in the EEP and a moderately strong correlation with MFI-based percent dissolved estimates when samples from the equatorial part of the region are excluded. Our results suggest that there may potentially be multiple genotypes of N. dutertrei in the EEP which may be reflected in their shell weight. MFI-based percent CaCO3 dissolved estimates have no quantifiable relationship with any surface ocean environmental parameter in the EEP. Thus MFI acts as a reliable quantitative CaCO3 dissolution proxy insensitive to environmental biases within calcification waters of foraminifers.

Organic d13C values, kerogen atomic C/N ratios and relative weights of some kerogen pyrolysis products of ODP Hole 112-682A (Table 1)

Carbon isotopic composition of predominantly marine kerogen in latest Oligocene mudstones of the Peru Margin ODP 682A Hole shows an about 3.5? increase with decreasing age. Py-GC and elemental (C=N ratio) analysis of the kerogen plus sulphur isotopic study together with earlier knowledge on geological setting and organic geochemistry results in a better understanding of depositionary environment and allows to separation of the influence of concentration of water dissolved carbon dioxide (ce) on kerogen delta13C from that of other factors (bacterial degradation, sea surface temperature, DIC delta13C, productivity, and admixture of land plant OM). Based on this analysis, the major part of the kerogen shift is considered as a result of the latest Oligocene decrease of marine photosynthetic carbon isotopic fractionation in the Peru Margin photic zone, which in turn possibly reflects a simultaneous drop in atmospheric CO2 level. Uncertainties in the evaluation of the factors affecting the marine photosynthetic carbon isotopic fractionation and the extent of ocean-atmosphere disequilibrium do not permit calculation of the decrease of the atmospheric CO2.