Seawater carbonate chemistry, thickness and carbonate elemental composition of the test of juvenile sea urchins in a laboratory experiment

Continuous anthropogenic CO2 emissions to the atmosphere and uptake by the oceans will cause a reduction of seawater pH and saturation state (Omega) of CaCO3 minerals from which marine calcifiers build their shells and skeletons. Sea urchins use the most soluble form of calcium carbonate, high-magnesium calcite, to build their skeleton, spines and grazing apparatus. In order to highlight the effects of increased pCO2 on the test thickness and carbonate elemental composition of juvenile sea urchins and potential differences in their responses linked to the diet, we performed a laboratory experiment on juvenile Paracentrotus lividus, grazing on calcifying (Corallina elongata) and non-calcifying (Cystoseira amentacea, Dictyota dichotoma) macroalgae, under different pH (corresponding to pCO2 values of 390, 550, 750 and 1000 µatm). Results highlighted the importance of the diet in determining sea urchin size irrespectively of the pCO2 level, and the relevance of macroalgal diet in modulating urchin Mg/Ca ratio. The present study provides relevant clues both in terms of the mechanism of mineral incorporation and in terms of bottom-up processes (algal diet) affecting top-down ones (fish predation) in rocky subtidal communities

(Table 1) Consolidation test for sediments of ODP Leg 130 sites

Consolidation tests were performed on 19 samples of calcareous ooze from the Ontong Java Plateau, obtained during Ocean Drilling Program Leg 130. Rebound curves from consolidation tests on Ontong Java Plateau samples yield porosity rebounds of 1%-4% for these sediments at equivalent depths up to 1200 mbsf. The exception is a radiolarian-rich sample that has 6% rebound. A rebound correction derived from the porosity rebound vs. depth data has been combined with a correction for pore-water expansion to correct the shipboard laboratory porosity data to in-situ values. Comparison of the laboratory porosity data corrected in this manner with the downhole log data shows good agreement.

Morphometric measurements throughout ontogeny of selected planktic foraminiferal test species

Development plays an important part in shaping adult morphology and morphological disparity, yet its influence on evolutionary processes is seldom explored because of a lack of preservation of ontogenetic stages in the fossil record. By preserving their entire ontogenetic history within their test, and with the advent of high-resolution imaging techniques, planktic foraminifera allow us to investigate the influence of developmental constraints on disparity. Using Synchrotron radiation X-ray tomographic microscopy (SRXTM), we reconstruct the ontogenetic progression of seven species across several of the major morphotypic groups of planktic foraminifera, including morphotypes of a species exhibiting high phenotypic plasticity and closely related pseudo-cryptic sister-taxa. We show differences in growth patterns between the globigerinid species, which appear more tightly regulated within the framework of isometry from the neanic stage, and the globorotaliid species, whose adult stages present allometric trends. Morphological change through ontogeny results in a change in surface area to volume ratios. Different metabolic processes therefore dominate at different stages of ontogeny, changing the vulnerability of the organism to environmental influences over growth, from factors affecting diffusion rates in the juvenile to those affecting energy supply in the adult. These findings identify some of the parameters within which evolutionary mechanisms have to act.

(Table 1) Sample characteristics, test consolidations and calculated elastic parameters of ODP Sites 194-1193 and 194-1196

This study is based on rock mechanical tests of samples from platform carbonate strata to document their petrophysical properties and determine their potential for porosity loss by mechanical compaction. Sixteen core-plug samples, including eleven limestones and five dolostones, from Miocene carbonate platforms on the Marion Plateau, offshore northeast Australia, were tested at vertical effective stress, sigma1', of 0-70 MPa, as lateral strain was kept equal to zero. The samples were deposited as bioclastic facies in platform-top settings having paleo-water depths of <10-90 m. They were variably cemented with low-Mg calcite and five of the samples were dolomitized before burial to present depths of 39-635 m below sea floor with porosities of 8-46%. Ten samples tested under dry conditions had up to 0.22% strain at sigma1' = 50 MPa, whereas six samples tested saturated with brine, under drained conditions, had up to 0.33% strain. The yield strength was reached in five of the plugs. The measured strains show an overall positive correlation with porosity. Vp ranges from 3640 to 5660 m/s and Vs from 1840 to 3530 m/s. Poisson coefficient is 0.20-0.33 and Young's modulus at 30 MPa ranged between 5 and 40 GPa. Water saturated samples had lower shear moduli and slightly higher P- to S-wave velocity ratios. Creep at constant stress was observed only in samples affected by pore collapse, indicating propagation of microcracks. Although deposited as loose carbonate sand and mud, the studied carbonates acquired reef-like petrophysical properties by early calcite and dolomite cementation. The small strains observed experimentally at 50 MPa indicate that little mechanical compaction would occur at deeper burial. However, as these rocks are unlikely to preserve their present high porosities to 4-5 km depth, further porosity loss would proceed mainly by chemical compaction and cementation.

(Appendix) Stable carbon and oxygen isotopes, and Mg/Ca ratios of foraminifera from ODP Hole 154-925A

To better understand the links between the carbon cycle and changes in past climate over tectonic timescales we need new geochemical proxy records of secular change in silicate weathering rates. A number of proxies are under development, but some of the most promising (e.g. palaeoseawater records of Li and Nd isotope change) can only be employed on such large samples of mono-specific foraminifera that application to the deep sea sediment core archive becomes highly problematic. "Dentoglobigerina" venezuelana presents a potentially attractive target for circumventing this problem because it is a typically large (> 355 ?m diameter), abundant and cosmopolitan planktic foraminifer that ranges from the early Oligocene to early Pliocene. Yet considerable taxonomic and ecological uncertainties associated with this taxon must first be addressed. Here, we assess the taxonomy, palaeoecology, and ontogeny of "D." venezuelana using stable isotope (oxygen and carbon) and Mg/Ca data measured in tests of late Oligocene to early Miocene age from Ocean Drilling Program (ODP) Site 925, on Ceara Rise, in the western equatorial Atlantic. To help constrain the depth habitat of "D." venezuelana relative to other species we report the stable isotope composition of selected planktic foraminifera species within Globigerina, Globigerinoides, Paragloborotalia and Catapsydrax. We define three morphotypes of "D." venezuelana based on the morphology of the final chamber and aperture architecture. We determine the trace element and stable isotope composition of each morphotype for different size fractions, to test the validity of pooling these morphotypes for the purposes of generating geochemical proxy datasets and to assess any ontogenetic variations in depth habitat. Our data indicate that "D." venezuelana maintains a lower thermocline depth habitat at Ceara Rise between 24 and 21 Ma. Comparing our results to published datasets we conclude that this lower thermocline depth ecology for the Oligo-Miocene is part of an Eocene-to-Pliocene evolution of depth habitat from surface to sub-thermocline for "D." venezuelana. Our size fraction data advocate the absence of photosymbionts in "D." venezuelana and suggest that juveniles calcify higher in the water column, descending into slightly deeper water during the later stages of its life cycle. Our morphotype data show that d18O and d13C variation between morphotypes is no greater than within-morphotype variability. This finding will permit future pooling of morphotypes in the generation of the "sample hungry" palaeoceanographic records.

Foraminifera Mg/Ca, test weight and XDX for sediment core WIND28K

A record of deep-sea calcite saturation (D[CO3**-2]), derived from X-ray computed tomography-based foraminifer dissolution index, XDX, was constructed for the past 150 ka for a core from the deep (4157 m) tropical western Indian Ocean. G. sacculifer and N. dutertrei recorded a similar dissolution history, consistent with the process of calcite compensation. Peaks in calcite saturation (~15 µmol/kg higher than the present-day value) occurred during deglaciations and early in MIS 3. Dissolution maxima coincided with transitions to colder stages. The mass record of G. sacculifer better indicated preservation than did that of N. dutertrei or G. ruber. Dissolution-corrected Mg/Ca-derived SST records, like other SST records from marginal Indian Ocean sites, showed coolest temperatures of the last 150 ka in early MIS 3, when mixed layer temperatures were ~4°C lower than present SST. Temperatures recorded by N. dutertrei showed the thermocline to be ~4°C colder in MIS 3 compared to the Holocene (8 ka B.P.).