Abundances and d13C values of n-alkanes extracted from sediment samples of ODP Hole 116-717C

Siwalik paleosol and Bengal Fan sediment samples were analyzed for the abundance and isotopic composition of n-alkanes in order to test for molecular evidence of the expansion of C4 grasslands on the Indian subcontinent. The carbon isotopic compositions of high-molecular-weight alkanes in both the ancient soils and sediments record a shift from low d13C values (ca. -30 per mil) to higher values (ca. -22 per mil) prior to 6 Ma. This shift is similar in magnitude to that recorded by paleosol carbonate and fossil teeth, and is consistent with a relatively rapid transition from dominantly C3 vegetation to an ecosystem dominated by C4 plants typical of semi-arid grasslands. The n-alkane values from our paleosol samples indicate that the isotopic change began as early as 9 Ma, reflecting either a growing contribution of C4 plants to a dominantly C3 biomass or a decrease in water availability to C3 plants. Molecular and isotopic analyses of other compounds, including n-alcohols and low-molecular weight n-alkanes indicate paleosol organic matter contains contributions from a mixture of sources, including vascular plants, algae and/or cyanobacteria and microorganisms. A range of inputs is likewise reflected in the isotopic composition of the total organic carbon from these samples. In addition, the n-alkanes from two samples show little evidence for pedegenic inputs and we suggest the compounds were derived instead from the paleosol's parent materials. We suggest the record of vegetation in ancient terrestrial ecosystems is better reconstructed using isotopic signatures of molecular markers, rather than bulk organic carbon. This approach provides a means of expanding the spatial and temporal records of C4 plant biomass which will help to resolve possible tectonic, climatic or biological controls on the rise of this important component of the terrestrial biosphere.

Northwards and eastwards velocities extracted from a historical run (for the year 2000) of the UVic Earth System Climate Model of Weaver et al. (2001)

This study provides a theoretical assessment of the potential bias due to differential lateral transport on multi-proxy studies based on a range of marine microfossils. Microfossils preserved in marine sediments are at the centre of numerous proxies for paleoenvironmental reconstructions. The precision of proxies is based on the assumption that they accurately represent the overlying watercolumn properties and faunas. Here we assess the possibility of a syn-depositional bias in sediment assemblages caused by horizontal drift in the water column, due to differential settling velocities of sedimenting particles based on their shape, size and density, and due to differences in current velocities. Specifically we calculate the post-mortem lateral transport undergone by planktic foraminifera and a range of other biological proxy carriers (diatoms, radiolaria and fecal pellets transporting coccolithophores) in several regions with high current velocities. We find that lateral transport of different planktic foraminiferal species is minimal due to high settling velocities. No significant shape- or size-dependent sorting occurs before reaching the sediment, making planktic foraminiferal ideal proxy carriers. In contrast, diatoms, radiolaria and fecal pellets can be transported up to 500km in some areas. For example in the Agulhas current, transport can lead to differences of up to 2°C in temperature reconstructions between different proxies in response to settling velocities. Therefore, sediment samples are likely to contain different proportions of local and imported particles, decreasing the precision of proxies based on these groups and the accuracy of the temperature reconstruction.

Pb isotopes in Cenozoic sediments of ODP Site 177-1090

Nd and Pb isotopic compositions extracted from bulk deep sea sediments have been shown to be robust proxies for deep water circulation as well as weathering provenance and intensity over geologically young time scales. In this study we evaluated ten deep sea samples from Ocean Drilling Program (ODP) site 1090 ranging in age from mid Eocene to early-Miocene to test whether Pb isotopic compositions extracted from geologically older sediments record reliable seawater isotopic ratios and to evaluate the source of the extracted Pb. The sequential extraction protocol used in this study is similar to protocols reported for previous studies and produces acetic acid, hydroxylamine hydrochloride (HH) and residue fractions. Each extracted fraction was analyzed for Pb isotopes, rare earth elements (REEs), and a suite of major elements. Similar 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios are recorded from the acetic acid and HH fractions for ~70-80% of the samples, suggesting that either the acetic acid dissolves Fe-Mn oxides or multiple phases are recording the same seawater isotopic value. Several indirect tests, such as Al mass balance, comparison of Sr isotopes in HH extracts to contemporaneous seawater Sr isotopes, and comparison of Nd isotopic compositions in HH extracts to published fossil fish teeth values, provide evidence that Pb isotopic compositions measured in our bulk HH extracts record bottom water values. The relationship between Pb, Mn and Ca concentrations in HH fractions indicates that Fe-Mn oxides and a Mn-bearing carbonate are the dominant phases contributing seawater Pb. Comparison of REE patterns derived from the HH fraction and total digestions of Fe-Mn nodule standards reveals that the trivalent REEs exhibit patterns consistent with the parent archive, but Ce can be fractionated during extraction. Ratios of REEs also produce unique fields for each fraction and can be used to test the purity of the seawater signal of the extraction protocol. Finally, an initial evaluation of Pb isotopic compositions in fossil fish indicates that this archive is not suitable for bottom water Pb isotope studies.

Strontium and neodymium concentrations and isotope compositions in fossil fish teeth and pore waters at ODP Sites 130-807 and 125-786

We analyzed Nd and Sr isotopic compositions of Neogene fossil fish teeth from two sites in the Pacific in order to determine the effect of cleaning protocols and burial diagenesis on the preservation of seawater isotopic values. Sr is incorporated into the teeth at the time of growth; thus Sr isotopes are potentially valuable for chemostratigraphy. Nd isotopes are potential conservative tracers of paleocirculation; however, Nd is incorporated post-mortem, and may record diagenetic pore waters rather than seawater. We evaluated samples from two sites (Site 807A, Ontong Java Plateau and Site 786A, Izu-Bonin Arc) that were exposed to similar bottom waters, but have distinct lithologies and pore water chemistries. The Sr isotopic values of the fish teeth appear to accurately reflect contemporaneous seawater at both sites. The excellent correlation between the Nd isotopic values of teeth from the two sites suggests that the Nd is incorporated while the teeth are in chemical equilibrium with seawater, and that the signal is preserved over geologic timescales and subsequent burial. These data also corroborate paleoseawater Nd isotopic compositions derived from Pacific ferromanganese crusts that were recovered from similar water depths (Ling et al., 1997; doi:10.1016/S0012-821X(96)00224-5). This corroboration strongly suggests that both materials preserve seawater Nd isotope values. Variations in Pacific deepwater e-Nd values are consistent with predictions for the shoaling of the Isthmus of Panama and the subsequent initiation of nonradiogenic North Atlantic Deep Water that entered the Pacific via the Antarctic Circumpolar Current.

Oxygen isotope values from biogenic apatie (conodont elements and fish teeth) from the Lower Triassic Mianwali Formation (Salt Range, Pakistan)

Recovery from the end-Permian mass extinction is frequently described as delayed, with complex ecological communities typically not found in the fossil record until the Middle Triassic epoch. However, the taxonomic diversity of a number of marine groups, ranging from ammonoids to benthic foraminifera, peaked rapidly in the Early Triassic. These variations in biodiversity occur amidst pronounced excursions in the carbon isotope record, which are compatible with episodes of massive CO2 outgassing from the Siberian Large Igneous Province. Here we present a high-resolution Early Triassic temperature record based on the oxygen isotope composition of pristine apatite from fossil conodonts. Our reconstruction shows that the beginning of the Smithian substage of the Early Triassic was marked by a cooler climate, followed by an interval of warmth lasting until the Spathian substage boundary. Cooler conditions resumed in the Spathian. We find the greatest increases in taxonomic diversity during the cooler phases of the early Smithian and early Spathian. In contrast, a period of extreme warmth in the middle and late Smithian was associated with floral ecological change and high faunal taxonomic turnover in the ocean. We suggest that climate upheaval and carbon-cycle perturbations due to volcanic outgassing were important drivers of Early Triassic biotic recovery.

Neodymium isotopes from fossil fish teeth and detrital sediment, and oxygen isotopes from benthic forams from ODP Hole 119-738 B

Ephemeral polar glaciations during the middle-to-late Eocene (48-34 Ma) have been proposed based on far-field ice volume proxy records and near-field glacigenic sediments, although the scale, timing, and duration of these events are poorly constrained. Here we confirm the existence of a transient cool event within a new high-resolution benthic foraminiferal d18O record at Ocean Drilling Program (ODP) Site 738 (Kerguelen Plateau; Southern Ocean). This event, named the Priabonian oxygen isotope maximum (PrOM) Event, lasted ~140 kyr and is tentatively placed within magnetochron C17n.1n (~37.3 Ma) based on the correlation to ODP Site 689 (Maud Rise, Southern Ocean). A contemporaneous change in the provenance of sediments delivered to the Kerguelen Plateau occurs at the study site, determined from the <63 µm fraction of decarbonated and reductively leached sediment samples. Changes in the mixture of bottom waters, based on fossil fish tooth epsilon-Nd, were less pronounced and slower relative to the benthic d18O and terrigenous epsilon-Nd changes. Terrigenous sediment epsilon-Nd values rapidly shifted to less radiogenic signatures at the onset of the PrOM Event, indicating an abrupt change in provenance favoring ancient sources such as the Paleoproterozoic East Antarctic craton. Bottom water epsilon-Nd reached a minimum value during the PrOM Event, although the shift begins much earlier than the terrigenous epsilon-Nd excursion. The origin of the abrupt change in terrigenous sediment provenance is compatible with a change in Antarctic terrigenous sediment flux and/or source as opposed to a reorganization of ocean currents. A change in terrigenous flux and/or source of Antarctic sediments during the oxygen isotope maximum suggests a combination of cooling and ice growth in East Antarctica during the early late Eocene.

Strontium isotope ratios of fish teeth from ODP sites in the central North Pacific

Strontium isotopic compositions of ichthyoliths (microscopic fish remains) in deep-sea clays recovered from the North Pacific Ocean (ODP holes 885A, 886B, and 886C) are used to provide stratigraphic age control within these otherwise undatable sediments. Age control within the deep-sea clays is crucial for determining changes in sedimentation rates, and for calculating fluxes of chemical and mineral components to the sediments. The Sr isotopic ages are in excellent agreement with independent age datums from above (diatom ooze), below (basalt basement) and within (Cretaceous-Tertiary boundary) the clay deposit. The 87Sr/86Sr ratios of fish teeth from the top of the pelagic clay unit (0.7089891), indicate an Late Miocene age (5.8 Ma), as do radiolarian and diatom biostratigraphic ages in the overlying diatom ooze. The 87Sr/86Sr ratio (0.707887) is consistent with a Cretaceous-Tertiary boundary age, as identified by anomalously high iridium, shocked quartz, and sperules in Hole 886C. The 87Sr/86Sr ratios of pretreated fish teeth from the base of the clay unit are similar to Late Cretaceous seawater (0.707779-0.7075191), consistent with radiometric ages from the underlying basalt of 81 Ma. Calculation of sedimentation rates based on Sr isotopic ages from Hole 886C indicate an average sedimentation rate of 17.7 m/Myr in Unit II (diatom ooze), 0.55 m/Myr in Unit IIIa (pelagic clay), and 0.68 m/Myr in Unit IIIb (distal hydrothermal precipitates). The Sr isotopic ages indicate a period of greatly reduced sedimentation (or possible hiatus) between about 35 and 65 Ma (Eocene-Paleocene), with a linear sedimentation rate of only 0.04 m/Myr The calculated sedimentation rates are generally inversely proportional to cobalt accumulation rates and ichthyolith abundances. However, discrepancies between Sr isotope ages and cobalt accumulation ages of l0-15 Myr are evident, particularly in the middle of the clay unit IIIa (Oligocene-Paleocene).

Strontium isotope ratios and concentrations in fossil fish teeth

We analyzed 87Sr/86Sr ratios in foraminifera, pore fluids, and fish teeth for samples ranging in age from Eocene to Pleistocene from four Ocean Drilling Program sites distributed around the globe: Site 1090 in the Cape Basin of the Southern Ocean, Site 757 on the Ninetyeast Ridge in the Indian Ocean, Site 807 on the Ontong-Java Plateau in the western equatorial Pacific, and Site 689 on the Maud Rise in the Southern Ocean. Sr isotopic ratios for dated foraminifera consistently plot on the global seawater Sr isotope curve. For Sites 1090, 757, and 807 Sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values, as are values for fossil fish teeth. In contrast, pore fluid 87Sr/86Sr values at Site 689 are more radiogenic than contemporaneous seawater, and the corresponding fish teeth also record more radiogenic values. Thus, Sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values; furthermore, there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve, and the associated offset between the fish teeth and the seawater curve. These data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange Sr with its surroundings during burial and diagenesis. Therefore, Sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores, but cannot be used to fine-tune age models. In contrast to the Sr isotopic system, our Nd concentration data, combined with published isotopic and rare earth element data, suggest that fish teeth acquire Nd during early diagenesis while they are still in direct contact with seawater. The concentrations of Nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids. As a result, Nd isotopes are not altered during burial and later diagenesis. Therefore, fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater Nd isotopic compositions from the time of deposition.

Nd isotope composition of fossil fish teeth of ODP Hole 119-738B

We report an optimized method for extracting neodymium (Nd) from fossil fish teeth with a single-stage column (125 µl stem volume; LN Resin, Eichrom Industries, Darien Illinois) for isotopic analysis by multi-collector inductively coupled mass spectrometry (MC-ICMPS). Three reference materials (basalt: BCR-2, BHVO-2; phosphate: fossil bone composite) and splits of fossil fish teeth samples previously processed with existing two-stage column methods were processed using the single-stage column method. 143Nd/144Nd values of reference materials agree within error with published values, and the values for fish teeth correspond with sample splits processed with two-stage columns. Precision to ± ~0.23 epsilon-Nd was achieved for 30 ng Nd samples of reference materials, and Nd isotope measurements of fossil fish tooth sample replicates as small as 7 ng Nd were reproducible within long term instrumental uncertainty. We demonstrate the utility of the new method with the first high resolution Nd isotope record spanning the ~40.0 Ma middle Eocene Climatic Optimum, which shows an excursion of 0.65 epsilon-Nd during the peak warming at the study site (Ocean Drilling Program Leg 119, Site 738; 30 kyr sample spacing from 40.3 to 39.6 Ma). LN Resin is already used in standard methods for separating Nd, and Nd isotopes are routinely measured by MC-ICPMS with high efficiency inlet systems. Our innovation is a single, small volume LN Resin column for Nd separation. The streamlined approach results in a 10X increase in sample throughput.