Walter C. Dudley

Stable isotopic composition of coccoliths

Oxygen isotope analyses of coccoliths from eight coccolithophore species grown in laboratory culture indicate that biological fractionation occurs during the formation of calcium carbonate. Cultures of coccolithophores, including species not previously grown in the laboratory were maintained at various temperatures ranging from 12–28°C. Over this range of temperature, oxygen isotope values for Emiliania huxleyi, Gephyrocapsa oceanica, and Crenalithus sessilis are found to be 1‰ enriched in 18O relative to calcium carbonate precipitated under equilibrium conditions. Coccoliths of Calcidiscus leptoporus, Umbilicosphaera sibogae, U. hulburtiana, Syracosphaera pulchra, and Cricosphaera carterae were found to be 2.5‰ depleted in 18O relative to equilibrium. These findings help clarify previously reported equivocal oxygen isotope data derived from sedimentary calcareous nannofossils and reveal the importance of species-specific isotopic fractionation.

Quaternary surface-water stable isotope signal from calcareous nannofossils at DSDP Site 593, southern Tasman Sea

Oxygen isotope values from calcareous nannofossils in four cores spanning the Quaternary from DSDP Site 593 in Tasman Sea are compared with the δ18O signal of planktonic and benthic foraminifers from the same samples. The classic mid-late Quaternary isotope stages are exhibited with stage 12 particularly well developed. When δ18O values of nannofossils are adjusted for coccolithophore vital effects they indicate larger (by 1–6°C) surface to bottom paleotemperature gradients and greater (by 1–3°C) changes in mean sea-surface temperature between full glacial and interglacial conditions than do δ18O values from planktonic foraminifers. Along with the foraminifers, the nannofossils record a bimodal distribution of δ18O between the early and mid-late Quaternary, indicating a significant change in global ice budget. The δ13C of nannofossils also shows a bimodal distribution, but is opposite to that for the foraminifers. Nannofossil δ18O values record a shift of ∼ −0.8‰ at isotope stage 8 corresponding to a major reduction in abundance of the previously dominant gephyrocapsids. A shift in δ13C of ∼ −1.5‰ also occurs at stage 8, and a shift in δ13C of ∼ +1.2‰ at around stage 14. The δ18O shift in nannofossils is at least a Pacific-wide phenomenon; the δ13C shifts are possibly global. The δ13C signal of nannofossils exhibits an antipathetic relationship to that of benthic foraminifers back to isotope stage 18 but no significant correlation beyond this level to the base of the Quaternary. This is interpreted as reflecting local productivity dominating global influences on δ13C since stage 18 at DSDP Site 593. The difference between nannofossil and benthic foraminifer δ13C signals (Δ13C) tends to be maximum during glacial stages and minimum during interglacials throughout the section, showing a strong correlation with the nannofossil δ18O signal. The increased partitioning of 13C between surface and bottom waters during the glacial periods may indicate heightened productivity in surface waters in the southern Tasman Sea at these times.

STABLE ISOTOPIC VARIATION IN PTEROPODS AND ATLANTIDS FROM NORTH PACIFIC SEDIMENT TRAPS

Abstract To determine their usefulness in paleoenvironmental studies and to better understand isotopic equilibrium in biogenic aragonite, carbon and oxygen isotopic analyses were performed on six species of pteropod and two species of atlantid collected with free drifting sediment traps from the North Pacific Ocean. Where the depth habitat of a species is constrained enough to permit estimation of the ambient temperature and water δ18O, the isotopic compositions of the shells are close to aragonite-water 18O equilibrium with the ambient water. None of the fauna are in 13C equilibrium with the dissolved bicarbonate. Assuming aragonite-water equilibrium fractionation, the δ18O values of the shells provide reasonable average depths of shell growth. The distribution is as follows: (1) “shallow-water” species ( 125 m) — L. bulimoides (small). The 18O variation within specimens of C. columnella, a large, easily sectioned species, is complex with no clear record of seasonality. However, some minor seasonal effects are observed. The δ 13 C values within specimens consistently show a 1–2‰ decrease from the caudal septum to the aperture, perhaps reflecting increased incorporation of metabolic CO2 with age.

Palaeotectonic implications of increased late Eocene-early Oligocene volcanism from South Pacific DSDP sites

Late Eocene-early Oligocene (42–35 Myr) sediments cored at two DSDP sites in the south-west Pacific contain evidence of a pronounced increase in local volcanic activity, particularly in close association with the Eocene–Oligocene boundary. This pulse of volcanism is coeval with that in New Zealand and resulted from the development of an Indo- Australian / Pacific Plate boundary through the region during the late Eocene. The late Eocene / earliest Oligocene was marked by widespread volcanism and tectonism throughout the Pacific and elsewhere, and by one of the most important episodes of Cenozoic climatic cooling.

The influence of non-equilibrium isotope fractionation on the Quaternary calcareous nannofossil stable isotope signal in the southwest Pacific Ocean, DSDP Site 594

Oxygen and carbon isotope values from calcareous nannofossils in the mid-late Quaternary (Brunhes) interval of core from DSDP Site 594 off eastern South Island, New Zealand are compared with the δ18O and δ13C signal of planktic and benthic foraminifers from the same samples. Nannofossil δ18O values appear strongly affected by non-equilibrium fractionation, in agreement with previous in-vitro studies. The nannofossil δ18O and δ13C signals show a strong down-core cross-correlation and a significant positive linear correlation. This is interpreted as the result of kinetic isotope effects producing non-equilibrium fractionation of both18O and13C. A previously reported isotope stage ⅞ carbon-shift appears to be related mainly to a Pacific-wide reduction in the abundance of gephyrocapsids rather than to any significant change in the partitioning of carbon isotopes. The strong correlation between nannofossil δ18O and δ13C can also be interpreted as being influenced by increased productivity during glacial intervals and decreased productivity during interglacials in subantarctic waters.

The δ13C content of calcareous nannofossils as an indicator of Quaternary paleoproductivity in the Southwest Pacific region

Abstract The δ13C signal from calcareous nannofossils in marine sediments may provide a valuable new tool for measuring the 13C content of ocean surface waters in the past. Measurements of Quaternary nannofossils from Deep Sea Drilling Project Site 593 on Challenger Plateau, off western New Zealand, indicate that the difference in the δ13C of nannofossils and benthic foraminifers, defined as Δ13C, is strongly correlated (r = +0.78) with the δ18O climatic signal, and has promise as an indicator of local paleoproductivity. The isotopic data suggest that, compared with interglacial episodes, there was a general increase in the productivity of surface waters in the southern Tasman Sea during glacial episodes, possibly as a result of intensification of ocean circulation patterns and upwelling currents in the region.

An examination of hazard communication logs and public response during the 1946 and 1960 tsunamis that impacted Hilo, Hawaii

Abstract This paper examines communication methods used to inform the vulnerable community of Hilo, Hawaii of the impending tsunamis that struck in 1946 and 1960. These tsunamis caused tragic loss of life and enormous economic damage in Hilo and along the shores of the Hawaiian Island chain. Over 12 h notice of a possible large tsunami was given in 1960 and the siren warning system sounded more than 4 h prior to the event. The government agencies knew there was a tsunami alert and the media were broadcasting warnings. However, the 1960 tsunami took the lives of 61 people in Hilo only 14 years after 96 people were killed during the 1946 event. In order to discover why so many people perished, government agency logs recorded during the 1960 tsunami were examined and personal accounts from survivors of both the 1946 and 1960 tsunamis were analysed. Contributing to the tragic loss of life was a lack of communication between government agencies in addition to media inaccuracies and a public that was not educated in tsunami safety. Effective tsunami mitigation can only be accomplished through continual tsunami awareness education for the public, media and emergency personnel, and with accurate and timely tsunami warnings.