Ocean Drilling Project Research Articles

Vivianite is a key sink for phosphorus in sediments of the Landsort Deep, an intermittently anoxic deep basin in the Baltic Sea

Phosphorus (P) is an essential nutrient for marine organisms. Its burial in hypoxic and anoxic marine basins is still incompletely understood. Recent studies suggest that P can be sequestered in sediments of such basins as reduced iron (Fe)-P but the exact phase and the underlying mechanisms that lead to its formation are unknown. In this study, we investigated sediments from the deepest basin in the Baltic Sea, the Landsort Deep (site M0063), that were retrieved during the Integrated Ocean Drilling Project (IODP) Baltic Sea Paleoenvironment Expedition 347. The record comprises the whole brackish/marine Littorina Sea stage including past intervals of extensive hypoxia in the Baltic Sea that occurred during the Holocene Thermal Maximum (HTMHI) and the Medieval Climate Anomaly (MCA1HI and MCA2HI). Various redox proxies (e.g. the presence of laminations and high Mo contents) suggest almost permanent bottom water hypoxia during the Littorina Sea stage in the Landsort Deep. The bottom waters were likely even seasonally anoxic or sulfidic during the MCA1HI and MCA2HI, and permanently sulfidic during the HTMHI. With the use of micro-analysis of sieved minerals (SEM-EDS, XRD and synchrotron-based XAS), we show that Mn- and Mg-rich vivianite crystals are present at various depths in the Littorina Sea sediments. We also have indications for vivianite in the MCA1HI, MCA2HI and HTMHI deposits. The formation of vivianite thus likely explains the high Fe-bound P fraction throughout the whole Littorina Sea stage. Shuttling of Fe and Mn from the shelves into the basin and high inputs of P in settling organic matter are likely key drivers for vivianite formation. Our study shows that vivianite can likely form in near-surface sediments under a broad range of bottom water redox conditions, varying from hypoxic and anoxic to sulfidic.

Miocene to Pleistocene osmium isotopic records of the Mediterranean sediments

In the late Miocene the Mediterranean Sea experienced a salinity crisis and thick sequences of evaporites precipitated across the deep and marginal basins. In this study we report Os isotopic records from Deep Sea Drilling Project and Ocean Drilling Project cores in the Mediterranean: the Balearic Sea (Site 372), the Tyrrhenian Sea (Site 654), the Ionian Basin (Site 374), and the Florence Rise (Sites 375–376), as well as Integrated Ocean Drilling Project Site U1387 in Gulf of Cadiz, North Atlantic. Pliocene-Pleistocene sediments at all sites show 187Os/188Os values close to that of the coeval ocean water, indicating that the Mediterranean was connected to the North Atlantic. Evaporitic sediments deposited during the latest Miocene, however, have 187Os/188Os values significantly lower than coeval ocean water values. The offset of the Mediterranean evaporite 187Os/188Os is attributed to limited exchange with the North Atlantic during the Messinian salinity crisis. The source of unradiogenic Os is likely to be weathering of ultramafic rocks (ophiolites) cropping out in the Mediterranean's drainage basins. Based on a box model we estimated the amount of unradiogenic Os and the Atlantic-Mediterranean exchange rate to explain this offset. Os isotopic ratios of the pre-evaporite sediments in the western Mediterranean are almost identical to that of the coeval ocean water. In contrast, equivalent sediments from the Florence Rise have significantly lower 187Os/188Os values. The offset in the Os isotopic ratio on the Florence Rise is attributed either to limited water exchange between eastern and western Mediterranean or to local effects associated with exhumation of the Troodos ophiolites (Cyprus).

Expansion and diversification of high-latitude radiolarian assemblages in the late Eocene linked to a cooling event in the southwest Pacific

Abstract. The long-term cooling trend from middle to late Eocene was punctuated by several large-scale climate perturbations that culminated in a shift to "icehouse" climates at the Eocene–Oligocene transition. We present radiolarian micro-fossil assemblage and foraminiferal oxygen and carbon stable isotope data from Deep Sea Drilling Project (DSDP) sites 277, 280, 281, and 283 and Ocean Drilling Project (ODP) Site 1172 to identify significant oceanographic changes in the southwest Pacific through this climate transition (~ 40–30 Ma). We find that the Middle Eocene Climatic Optimum at ~ 40 Ma, which is truncated but identified by a negative shift in foraminiferal δ18O values at Site 277, is associated with a small increase in radiolarian taxa with low-latitude affinities (5 % of total fauna). In the early late Eocene at ~ 37 Ma, a positive oxygen isotope shift at Site 277 is correlated with the Priabonian Oxygen Isotope Maximum (PrOM). Radiolarian abundance, diversity, and preservation increase within this cooling event at Site 277 at the same time as diatom abundance. A negative δ18O excursion above the PrOM is correlated with a late Eocene warming event (~ 36.4 Ma). Radiolarian abundance and diversity decline within this event and taxa with low-latitude affinities reappear. Apart from this short-lived warming event, the PrOM and latest Eocene radiolarian assemblages are characterised by abundant high-latitude taxa. High-latitude taxa are also abundant during the late Eocene and early Oligocene (~ 38–30 Ma) at DSDP sites 280, 281, 283 and 1172 and are associated with very high diatom abundance. We therefore infer a northward expansion of high-latitude radiolarian taxa onto the Campbell Plateau in the latest Eocene. In the early Oligocene there is an overall decrease in radiolarian abundance and diversity at Site 277, and diatoms are scarce. These data indicate that, once the Antarctic Circumpolar Current was established in the early Oligocene (~ 30 Ma), a frontal system similar to present day developed, with nutrient-depleted Subantarctic waters bathing the area around DSDP Site 277, resulting in a more restricted siliceous plankton assemblage.

Changes to the Marine Geology Editorial Team in 2015

The microstructures, mineralogy and chemistry of four representative samples collected from cores extracted from the Japan Trench during Integrated Ocean Drilling Project Expedition 343, the Japan Trench Fast Drilling Project (JFAST) have been studied using optical microscopy, TEM, SEM, XRF, XRD and microprobe analyses. The samples provide a transect from relatively undeformed marine sediments in the hanging wall, to the undeformed footwall material, crossing the thrust interface between the Pacific and North American plate, where the fault slipped during the March 2011 Tohoku-Oki earthquake. Our preliminary results suggest that the low strength of JFAST fault gouge material is caused by the high amount of clay minerals (~ 60% smectite, ~ 14 illite). Clay minerals in the décollement (gouge) sample are partly replaced by newly formed manganese oxide, which precipitated from hydrothermal fluids. Dauphine twins were found in quartz grains of the décollement sample suggesting local high stress possible during seismic loading. Other microstructures cannot be assigned unambiguously to co-seismic or a-seismic faulting processes. The observed scaly clay fabric is consistent with observations in many other plate-boundary fault zones. Significant grain size reduction was found in the fault (décollement) zone sample. But a change in lithology of the fault material cannot be ruled out. Microstructures typical for a-seismic deformation like dissolution–precipitation features (e.g. dissolved grain boundaries, mineral alteration) occur in all JFAST core samples, but more frequently in the décollement sample.

Co-seismic and/or a-seismic microstructures of JFAST 343 core samples from the Japan Trench

Abstract The microstructures, mineralogy and chemistry of four representative samples collected from cores extracted from the Japan Trench during Integrated Ocean Drilling Project Expedition 343, the Japan Trench Fast Drilling Project (JFAST) have been studied using optical microscopy, TEM, SEM, XRF, XRD and microprobe analyses. The samples provide a transect from relatively undeformed marine sediments in the hanging wall, to the undeformed footwall material, crossing the thrust interface between the Pacific and North American plate, where the fault slipped during the March 2011 Tohoku-Oki earthquake. Our preliminary results suggest that the low strength of JFAST fault gouge material is caused by the high amount of clay minerals (~ 60% smectite, ~ 14 illite). Clay minerals in the decollement (gouge) sample are partly replaced by newly formed manganese oxide, which precipitated from hydrothermal fluids. Dauphine twins were found in quartz grains of the decollement sample suggesting local high stress possible during seismic loading. Other microstructures cannot be assigned unambiguously to co-seismic or a-seismic faulting processes. The observed scaly clay fabric is consistent with observations in many other plate-boundary fault zones. Significant grain size reduction was found in the fault (decollement) zone sample. But a change in lithology of the fault material cannot be ruled out. Microstructures typical for a-seismic deformation like dissolution–precipitation features (e.g. dissolved grain boundaries, mineral alteration) occur in all JFAST core samples, but more frequently in the decollement sample.

Iron Fertilization of the Subantarctic Ocean During the Last Ice Age

John H. Martin, who discovered widespread iron limitation of ocean productivity, proposed that dust-borne iron fertilization of Southern Ocean phytoplankton caused the ice age reduction in atmospheric carbon dioxide (CO2). In a sediment core from the Subantarctic Atlantic, we measured foraminifera-bound nitrogen isotopes to reconstruct ice age nitrate consumption, burial fluxes of iron, and proxies for productivity. Peak glacial times and millennial cold events are characterized by increases in dust flux, productivity, and the degree of nitrate consumption; this combination is uniquely consistent with Subantarctic iron fertilization. The associated strengthening of the Southern Ocean's biological pump can explain the lowering of CO2 at the transition from mid-climate states to full ice age conditions as well as the millennial-scale CO2 oscillations.

Warming of surface waters in the mid‐latitude North Atlantic during Heinrich events

During the six Heinrich events of the last 70 kyr, episodic calving from the circum‐Atlantic ice sheets released large numbers of icebergs into the North Atlantic. These icebergs and associated meltwater flux are hypothesized to have led to a shutdown of Atlantic Meridional Overturning Circulation and severe cooling in large parts of the Northern Hemisphere. However, due to the limited availability of high‐resolution records, the magnitude of sea surface temperature (SST) changes related to the impact of Heinrich events on the midlatitude North Atlantic is poorly constrained. Here we present a record of ‐based SSTs derived from sediments of Integrated Ocean Drilling Project Site U1313, located at the southern end of the ice‐rafted debris (IRD) belt in the midlatitude North Atlantic (41°N). We demonstrate that all six Heinrich events are associated with a rapid warming of surface waters by 2–4°C in a few thousand years. The presence of IRD leaves no doubt about the simultaneous timing and correlation between rapid surface water warming and Heinrich events. We argue that this warming in the midlatitude North Atlantic is related to a northward expansion of the subtropical gyre during Heinrich events. As a wide range of studies demonstrated that in the central IRD belt Heinrich events are associated with low SSTs, these results thus identify an antiphased (seesaw) pattern in SSTs during Heinrich events between the midlatitude (warm) and northern North Atlantic (cold). This highlights the complex response of surface water characteristics in the North Atlantic to Heinrich events that is poorly reproduced by freshwater hosing experiments and challenges the widely accepted view that, within the IRD belt of the North Atlantic, Heinrich events coincide with periods of low SSTs.

Palaeoceanographic changes in the North Atlantic during the Mid‐Pleistocene Transition (MIS 31–19) as inferred from planktonic foraminiferal and calcium carbonate records

Marine sediments from the Integrated Ocean Drilling Project (IODP) Site U1314 (56.36°N, 27.88°W), in the subpolar North Atlantic, were studied for their planktonic foraminifera, calcium carbonate content, and Neogloboqudrina pachyderma sinistral (sin.) δ13C records in order to reconstruct surface and intermediate conditions in this region during the Mid‐Pleistocene Transition (MPT). Variations in the palaeoceanography and regional dynamics of the Arctic Front were estimated by comparing CaCO3 content, planktonic foraminiferal species abundances, carbon isotopes and ice‐rafted debris (IRD) data from Site U1314 with published data from other North Atlantic sites. Site U1314 exhibited high abundances of the polar planktonic foraminifera N. pachyderma sin. and low CaCO3 content until Marine Isotope Stage (MIS) 26, indicating a relatively southeastward position of the Arctic Front (AF) and penetration of colder and low‐salinity surface arctic water‐masses. Changing conditions after MIS 25, with oscillations in the position of the AF, caused an increase in the northward export of the warmer North Atlantic Current (NAC), indicated by greater abundances of non‐polar planktonic foraminifera and higher CaCO3. The N. pachyderma sin. δ13C data indicate good ventilation of the upper part of the intermediate water layer in the eastern North Atlantic during both glacial and interglacial stages, except during Terminations 24/23, 22/21 and 20/1. In addition, for N. pachyderma (sin.) we distinguished two morphotypes: non‐encrusted and heavily encrusted test. Results indicate that increases in the encrusted morphotype and lower planktonic foraminiferal diversity are related to the intensification of glacial conditions (lower sea‐surface temperatures, sea‐ice formation) during MIS 22 and 20.

Isotope fractionation during Ca exchange on clay minerals in a marine environment

In order to interpret marine porewater profiles it is mandatory to understand the behavior of calcium (Ca) and its isotopes during cation exchange in marine sediments. It has been proposed that the exchange of adsorbed Ca2+ for ammonium, which is a product of organic matter decomposition, results in the releases of light Ca from clay minerals into the porewater (Teichert et al., 2009). In order to investigate the effect of ammonium on Ca isotope fractionation, experiments with clay mineral separates (illites, montmorillonite, kaolinite) and natural marine sediments from the North Atlantic (Integrated Ocean Drilling Project Site U1306A) in artificial seawater were carried out at different temperatures (4, 14, 21°C) and ammonium concentrations (100, 140, 180mM).The results of the adsorption experiments, carried out in artificial seawater, show that during adsorption of Ca2+ the light Ca isotopes are favored over the heavier Ca isotopes. This effect is most prominent for the illite samples (1000lnα=−0.82 to −1.15) and kaolinite sample (1000lnα=−1.23 to −2.76), whereas montmorillonite and the natural marine sediments show smaller degrees of fractionation from the fluid in the range of −0.46 to +0.06‰. Determination of the desorbed Ca2+ is based on the adsorbed Ca2+ left on the exchanger and reveals that the desorbed Ca2+ has a significantly different isotopic signature from the surrounding fluid. In general, the degree of Ca isotope fractionation is dependent on the ammonium concentration, and does not show significant influence of temperature. Modeling the Ca2+ desorption induced by ammonium adsorption demonstrates, that according to the prevailing mineralogy and porewater:sediment ratio, desorbed Ca2+ has the potential to shift the porewater isotopy by up to −2.5‰ and needs to be considered when interpreting Ca isotope porewater profiles.

Ice-sheet collapse and sea-level rise at the Bølling warming 14,600 years ago

Past sea-level records provide invaluable information about the response of ice sheets to climate forcing. Some such records suggest that the last deglaciation was punctuated by a dramatic period of sea-level rise, of about 20 metres, in less than 500 years. Controversy about the amplitude and timing of this meltwater pulse (MWP-1A) has, however, led to uncertainty about the source of the melt water and its temporal and causal relationships with the abrupt climate changes of the deglaciation. Here we show that MWP-1A started no earlier than 14,650 years ago and ended before 14,310 years ago, making it coeval with the Bølling warming. Our results, based on corals drilled offshore from Tahiti during Integrated Ocean Drilling Project Expedition 310, reveal that the increase in sea level at Tahiti was between 12 and 22 metres, with a most probable value between 14 and 18 metres, establishing a significant meltwater contribution from the Southern Hemisphere. This implies that the rate of eustatic sea-level rise exceeded 40 millimetres per year during MWP-1A.

Revised taxonomy and stratigraphy of Middle Miocene calcareous nannofossils of the Paratethys

The taxonomy of Paratethyan Middle Miocene calcareous nannofossils is reviewed and revised. Two new species, Syracosphaera croatica and Syracosphaera horvati, are proposed. Comparative study of coeval Neogene nannofossils from NHM and ODP (Ocean Drilling Project) reference collections give differences and similarities between the investigated areas (first occurrence, theirmorphology and dimensions). Other studies data on taxonomy are reviewed including palaeoecological and biostratigraphic applications.

The East Greenland rifted volcanic margin

The Palaeogene North Atlantic Igneous Province is among the largest igneous provinces in the world and this review of the East Greenland sector includes large amounts of information amassed since previous reviews around 1990.
 The main area of igneous rocks extends from Kangerlussuaq (c. 67°N) to Scoresby Sund (c. 70°N), where basalts extend over c. 65 000 km2 , with a second area from Hold with Hope (c. 73°N) to Shannon (c. 75°N). In addition, the Ocean Drilling Project penetrated basalt at five sites off South-East Greenland. Up to 7 km thickness of basaltic lavas have been stratigraphically and chemically described and their ages determined. A wide spectrum of intrusions are clustered around Kangerlussuaq, Kialeeq (c. 66°N) and Mesters Vig (c. 72°N). Layered gabbros are numerous (e.g. the Skaergaard and Kap Edvard Holm intrusions), as are under- and oversaturated syenites, besides small amounts of nephelinite-derived products, such as the Gardiner complex (c. 69°N) with carbonatites and silicate rocks rich in melilite, perovskite etc. Felsic extrusive rocks are sparse. A single, sanidine-bearing tuff found over an extensive area of the North Atlantic is thought to be sourced from the Gardiner complex.
 The province is famous for its coast-parallel dyke swarm, analogous to the sheeted dyke swarm of ophiolites, its associated coastal flexure, and many other dyke swarms, commonly related to central intrusive complexes as in Iceland. The dyke swarms provide time markers, tracers of magmatic evolution and evidence of extensional events. A set of dykes with harzburgite nodules gives unique insight into the Archaean subcontinental lithosphere.
 Radiometric dating indicates extrusion of huge volumes of basalt over a short time interval, but the overall life of the province was prolonged, beginning with basaltic magmas at c. 60 Ma and continuing to the quartz porphyry stock at Malmbjerg (c. 72°N) at c. 26 Ma. Indeed, activity was renewed in the Miocene with the emplacement of small volumes of basalts of the Vindtoppen Formation to the south of Scoresby Sund.
 Although the basalts were extruded close to sea level, this part of East Greenland is a plateau raised to c. 2 km, but the timing of uplift is controversial. Superimposed on the plateau is a major dome at Kangerlussuaq.
 East Greenland presents a rich interplay between magmatic and tectonic events reflecting the birth of the North Atlantic Ocean. It was active over a much longer period (36 Ma) than other parts of the province (5 Ma in the Hebrides, Northern Ireland and the Faroe Islands) and contains a wider range of products, including carbonatites, and felsic rocks tend to be granitic rather than syenitic. As expected, there are many similarities with Iceland, the present-day expression of activity in the province. Differences are readily explained by higher production rates and the thicker lithospheric lid during the early stages of development in East Greenland. The igneous and related activity clearly results from plate-tectonic factors, but the relationship is not understood in detail. In particular, the nature of the underlying mantle processes, primarily the presence or absence of a plume, is still not resolved.

Submarine landslide potential near the megasplay fault at the Nankai subduction zone

We investigate the mechanics of slope failures on the Nankai accretionary complex offshore Japan in the vicinity of a major out-of-sequence thrust fault (termed the “megasplay”). Incorporating laboratory-measured shear strength of slope sediments sampled during Integrated Ocean Drilling Project (IODP) Expeditions 315 and 316 with local seafloor slope angles from bathymetric data and constraints on in-situ effective stress conditions from drilling, we find that slopes in the study area are stable and submarine landslides are not expected to occur under static conditions. In order to assess the possibility of slope failure triggered by coseismic rupture of the megasplay fault, we use empirical relations for strong ground motion attenuation from earthquakes with M w 6–9. We find that the slope sediments should be stable based on computations from one model, developed from a catalog of worldwide subduction zone earthquakes ( Youngs et al., 1997). However, using a different model developed primarily from a catalog of crustal earthquakes in Japan ( Kanno et al., 2006), we find that slopes should be unstable for earthquakes 8 ≤ M w ≤ 9, and possibly unstable for events with 6 ≤ M w < 8, depending on the proximity of rupture to the seafloor. Considering limitations of the models and geologic observations of slope failure recurrence, the true slope stability is likely to be in between the predictions of the two models, and we suggest that it may be modulated by long-term pore pressure fluctuations.

Coccolithophore estimates of paleotemperature and paleoproductivity changes in the southeast Pacific over the past ∼27 kyr

We provide high‐resolution sea surface temperature (SST) and paleoproductivity data focusing on Termination 1. We describe a new method for estimating SSTs based on multivariate statistical analyses performed on modern coccolithophore census data, and we present the first downcore reconstructions derived from coccolithophore assemblages at Ocean Drilling Project (ODP) Site 1233 located offshore Chile. We compare our coccolithophore SST record to alkenone‐based SSTs as well as SST reconstructions based on dinoflagellates and radiolaria. All reconstructions generally show a remarkable concordance. As in the alkenone SST record, the Last Glacial Maximum (LGM, 19–23 kyr B.P.) is not clearly defined in our SST reconstruction. After the onset of deglaciation, three major warming steps are recorded: from 18.6 to 18 kyr B.P. (∼2.6°C), from 15.7 to 15.3 kyr B.P. (∼2.5°C), and from 13 to 11.4 kyr B.P. (∼3.4°C). Consistent with the other records from Site 1233 and Antarctic ice core records, we observed a clear Holocene Climatic Optimum (HCO) from ∼8–12 kyr B.P. Combining the SST reconstruction with coccolith absolute abundances and accumulation rates, we show that colder temperatures during the LGM are linked to higher coccolithophore productivity offshore Chile and warmer SSTs during the HCO to lower coccolithophore productivity, with indications of weak coastal upwelling. We interpret our data in terms of latitudinal displacements of the Southern Westerlies and the northern margin of the Antarctic Circumpolar Current system over the deglaciation and the Holocene.

Late Pliocene changes in the North Atlantic Current

During the late Pliocene global climate changed drastically as the Northern Hemisphere glaciation (NHG) intensified. It remains poorly understood how the North Atlantic Current (NAC) changed in strength and position during this time interval. Such changes may alter the amount of northward heat transport and therefore have a large impact on climate in the circum-North Atlantic region and the growth of Northern Hemisphere ice sheets. Using the alkenone biomarker we reconstructed orbitally resolved sea surface temperature (SST) and productivity records at Integrated Ocean Drilling Project (IODP) Expedition 306 Site U1313 during the late Pliocene and early Pleistocene, 3.68–2.45 million years ago (Ma). Before 3.1 Ma, SSTs in the mid-latitude North Atlantic were up to 6 °C higher than the present and surface water productivity was low, indicating that an intense NAC transported warm, nutrient-poor surface waters northwards. Starting at 3.1 Ma, surface water characteristics changed drastically as the NHG intensified. During glacial periods at the end of the late Pliocene and beginning of the Pleistocene, SSTs decreased and surface water productivity in the mid-latitude North Atlantic increased, reflecting a weakened influence of the NAC at our site. At the same time the increase in surface productivity suggests that the Arctic Front (AF) reached down into the mid-latitudes. We propose that during the intensification of the NHG the NAC had an almost pure west to east flow direction in glacials and did not penetrate into the higher latitudes. The diminished northward heat transport would have led to a cooling of the higher latitudes, which may have encouraged the growth of large continental ice sheets in the Northern Hemisphere.

Retrogressive failures recorded in mass transport deposits in the Ursa Basin, Northern Gulf of Mexico

Clay‐rich mass transport deposits (MTDs) in the Ursa Basin, Gulf of Mexico, record failures that mobilized along extensional failure planes and transformed into long runout flows. Failure proceeded retrogressively: scarp formation unloaded adjacent sediment causing extensional failure that drove successive scarp formation updip. This model is developed from three‐dimensional seismic reflection data, core and log data from Integrated Ocean Drilling Project (IODP) Expedition 308, and triaxial shear experiments. MTDs are imaged seismically as low‐amplitude zones above continuous, grooved, high‐amplitude basal reflections and are characterized by two seismic facies. A Chaotic facies typifies the downdip interior, and a Discontinuous Stratified facies typifies the headwalls/sidewalls. The Chaotic facies contains discontinuous, high‐amplitude reflections that correspond to flow‐like features in amplitude maps: it has higher bulk density, resistivity, and shear strength, than bounding sediment. In contrast, the Discontinuous Stratified facies contains relatively dim reflections that abut against intact pinnacles of parallel‐stratified reflections: it has only slightly higher bulk density, resistivity, and shear strength than bounding sediment, and deformation is limited. In both facies, densification is greatest at the base, resulting in a strong basal reflection. Undrained shear tests document strain weakening (sensitivity = 3). We estimate that failure at 30 meters below seafloor will occur when overpressure = 70% of the hydrostatic effective stress: under these conditions soil will liquefy and result in long runout flows.

Steryl ethers in a Valanginian claystone: Molecular evidence for cooler waters in the central Pacific during the Early Cretaceous?

Coring on Shatsky Rise by Ocean Drilling Project Leg 198 recovered sediments rich in organic matter (> 2.0% C org) from three time intervals: the Early Aptian, corresponding to oceanic anoxic event (OAE 1a), the Valanginian and the Berriasian. Episodes of enhanced sequestration of organic matter during the Valanginian are well documented in the Tethyan realm, notably those associated with a positive δ 13C isotopic excursion and with changes in plankton assemblages, including a demise in nannoconids. The δ 13C excursion has been previously reported in the Pacific but the occurrence of Valanginian sediments rich in organic matter (> 1% C org) is unprecedented. A distinctive feature of the biomarker composition of these Valanginian sediments at Shatsky Rise is the presence of a suite of steryl ethers, which extends the temporal record of these compounds from the Neogene to the Early Cretaceous. The biological source of steryl ethers remains enigmatic, although the sedimentary occurrences of these compounds in Quaternary and Neogene environments characterized by cool water, high seasonal productivity, and/or nutrient enrichment by upwelling, in combination with their liquid crystal properties, raise the possibility that they may represent storage lipids, akin to wax esters and triacylglycerols. Prior occurrences of steryl ethers suggest that their presence in the Valanginian may reflect an oceanic environment characterized by upwelling, consistent with the likely position of Shatsky Rise within the equatorial divergence zone of the Pacific during the Early Cretaceous. Alternatively, or in addition, the appearance of these compounds may represent a biological response to cooler temperatures, and thereby augment evidence for global cooling during the Early Valanginian, consistent with independent paleontological evidence for contemporaneous, upwelling-induced increases in productivity in the Western Atlantic.

Chikyu: The First Three Years of Operation

Three years have passed since the completion of the Chikyu, a state-of-the-art scientific drilling vessel. As the main platform of the Integrated Ocean Drilling Program (IODP), the Chikyu explores the mysteries of planet Earth. The Chikyu aims to achieve scientific breakthroughs in the mechanism of great earthquakes, the origins of life, the past and future of the Earth's global climate, and drilling into the mantle. The Chikyu is the first science research vessel to be equipped with the Riser Drilling System, and she also has shipboard research laboratories on four dedicated decks with a total area of 2,300 m2. These laboratories have an extensive array of cutting-edge equipment used to conduct physical, chemical and biological analyses of recovered cores, pore water and boreholes. After the first dry-docking from March to May 2006, the Chikyu successfully performed shakedown drilling operations off Japan's Shimokita Peninsula, and then again off Kenya and the Northwest Australian Continental Shelf. The Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), a complex multiyear ocean drilling project implemented as part of the Integrated Ocean Drilling Program, began the Chikyu's involvement with IODP drilling. NanTroSEIZE is a multiple-expedition project involving teams of some of the top scientists from all around the world. NanTroSEIZE attempts for the first time to drill, sample, and instrument the earthquake-causing, or seismogenic, portion of a plate subduction zone. The Chikyu successfully completed the first three Stage 1 NanTroSEIZE expeditions in 2007 and 2008. This paper describes the Chikyu's operations over the past three years.

Wildfire and abrupt ecosystem disruption on California's Northern Channel Islands at the Ållerød–Younger Dryas boundary (13.0–12.9 ka)

Sedimentary records from California's Northern Channel Islands and the adjacent Santa Barbara Basin (SBB) indicate intense regional biomass burning (wildfire) at the Ållerød–Younger Dryas boundary (∼13.0–12.9 ka) (All age ranges in this paper are expressed in thousands of calendar years before present [ka]. Radiocarbon ages will be identified and clearly marked “ 14C years”.). Multiproxy records in SBB Ocean Drilling Project (ODP) Site 893 indicate that these wildfires coincided with the onset of regional cooling and an abrupt vegetational shift from closed montane forest to more open habitats. Abrupt ecosystem disruption is evident on the Northern Channel Islands at the Ållerød–Younger Dryas boundary with the onset of biomass burning and resulting mass sediment wasting of the landscape. These wildfires coincide with the extinction of Mammuthus exilis [pygmy mammoth]. The earliest evidence for human presence on these islands at 13.1–12.9 ka (∼11,000–10,900 14C years) is followed by an apparent 600–800 year gap in the archaeological record, which is followed by indications of a larger-scale colonization after 12.2 ka. Although a number of processes could have contributed to a post 18 ka decline in M. exilis populations (e.g., reduction of habitat due to sea-level rise and human exploitation of limited insular populations), we argue that the ultimate demise of M. exilis was more likely a result of continental scale ecosystem disruption that registered across North America at the onset of the Younger Dryas cooling episode, contemporaneous with the extinction of other megafaunal taxa. Evidence for ecosystem disruption at 13–12.9 ka on these offshore islands is consistent with the Younger Dryas boundary cosmic impact hypothesis [Firestone, R.B., West, A., Kennett, J.P., Becker, L., Bunch, T.E., Revay, Z.S., Schultz, P.H., Belgya, T., Kennett, D.J., Erlandson, J.M., Dickenson, O.J., Goodyear, A.A., Harris, R.S., Howard, G.A., Kloosterman, J.B., Lechler, P., Mayewski, P.A., Montgomery, J., Poreda, R., Darrah, T., Que Hee, S.S., Smith, A.R., Stich, A., Topping, W., Wittke, J.H. Wolbach, W.S., 2007. Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and Younger Dryas cooling. Proceedings of the National Academy of Sciences 104, 16016–16021.].

New equations for density, entropy, heat capacity, and potential temperature of a saline thermal fluid

A set of fitted polynomial equations for calculating the physical variables density, entropy, heat capacity and potential temperature of a thermal saline fluid for a temperature range of 0–374 °C, pressure range of 0.1–100 MPa and absolute salinity range of 0–40 g/kg is established. The freshwater components of the equations are extracted from the recently released tabulated data of freshwater properties of Wagner and Pruß [2002. The IAPWS formulation 1995 for the thermodynamic properties of ordinary water substance for general and scientific use. Journal of Physical and Chemical Reference Data 31, 387–535]. The salt water component of the equation is based on the near-linear relationship between density, salinity and specific heat capacity and is extracted from the data sets of Feistel [2003. A new extended Gibbs thermodynamic potential of seawater. Progress in Oceanography 58, 43–114], Bromley et al. [1970. Heat capacities and enthalpies of sea salt solutions to 200 °C. Journal of Chemical and Engineering Data 15, 246–253] and Grunberg [1970. Properties of sea water concentrates. In: Third International Symposium on Fresh Water from the Sea, vol. 1, pp. 31–39] in a temperature range 0–200 °C, practical salinity range 0–40, and varying pressure and is also calibrated by the data set of Millero et al. [1981. Summary of data treatment for the international high pressure equation of state for seawater. UNESCO Technical Papers in Marine Science 38, 99–192]. The freshwater and salt water components are combined to establish a workable multi-polynomial equation, whose coefficients were computed through standard linear regression analysis. The results obtained in this way for density, entropy and potential temperature are comparable with those of existing models, except that our new equations cover a wider temperature—(0–374 °C) than the traditional (0–40 °C) temperature range. One can apply these newly established equations to the calculation of in-situ or onboard density, specific volume (therefore, the porosity), and potential temperature change that are usually measured on shipboard by the Ocean Drilling Project (ODP) and other hydrothermal-fluid studies.