Indian Ocean salinity build-up primes deglacial ocean circulation recovery.

The Indian Ocean provides a source of salt for North Atlantic deep-water convection sites, via the Agulhas Leakage, and may thus drive changes in the ocean's overturning circulation1-3. However, little is known about the salt content variability of Indian Ocean and Agulhas Leakage waters during past glacial cycles and how this may influence circulation. Here we show that the glacial Indian Ocean surface salt budget was notably different from the modern, responding dynamically to changes in sea level. Indian Ocean surface salinity increased during glacial intensification, peaking in glacial maxima. We find that this is due to rapid land exposure in the Indonesian archipelago induced by glacial sea-level lowering, and we suggest a mechanistic link via reduced input of relatively fresh Indonesian Throughflow waters into the Indian Ocean. Using climate model results, we show that the release of this glacial Indian Ocean salinity via the Agulhas Leakage during deglaciation can directly impact the Atlantic Meridional Overturning Circulation and global climate.

Diversity aboard a Tudor warship: investigating the origins of the Mary Rose crew using multi-isotope analysis.

The great Tudor warship, the Mary Rose, which sank tragically in the Solent in 1545 AD, presents a rare archaeological opportunity to research individuals for whom the precise timing and nature of death are known. A long-standing question surrounds the composition of the Tudor navy and whether the crew were largely British or had more diverse origins. This study takes a multi-isotope approach, combining strontium (87Sr/86Sr), oxygen (δ18O), sulfur (δ34S), carbon (δ13C) and nitrogen (δ15N) isotope analysis of dental samples to reconstruct the childhood diet and origins of eight of the Mary Rose crew. Forensic ancestry estimation was also employed on a subsample. Provenancing isotope data tentatively suggests as many as three of the crew may have originated from warmer, more southerly climates than Britain. Five have isotope values indicative of childhoods spent in western Britain, one of which had cranial morphology suggestive of African ancestry. The general trend of relatively high δ15N and low δ13C values suggests a broadly comparable diet to contemporaneous British and European communities. This multi-isotope approach and the nature of the archaeological context has allowed the reconstruction of the biographies of eight Tudor individuals to a higher resolution than is usually possible.

Upper limits on the extent of seafloor anoxia during the PETM from uranium isotopes.

The Paleocene Eocene Thermal Maximum (PETM) represents a major carbon cycle and climate perturbation that was associated with ocean de-oxygenation, in a qualitatively similar manner to the more extensive Mesozoic Oceanic Anoxic Events. Although indicators of ocean de-oxygenation are common for the PETM, and linked to biotic turnover, the global extent and temporal progression of de-oxygenation is poorly constrained. Here we present carbonate associated uranium isotope data for the PETM. A lack of resolvable perturbation to the U-cycle during the event suggests a limited expansion of seafloor anoxia on a global scale. We use this result, in conjunction with a biogeochemical model, to set an upper limit on the extent of global seafloor de-oxygenation. The model suggests that the new U isotope data, whilst also being consistent with plausible carbon emission scenarios and observations of carbon cycle recovery, permit a maximum ~10-fold expansion of anoxia, covering <2% of seafloor area.

Ocean mixing and ice-sheet control of seawater 234U/238U during the last deglaciation.

Seawater 234U/238U provides global-scale information about continental weathering and is vital for marine uranium-series geochronology. Existing evidence supports an increase in 234U/238U since the last glacial period, but the timing and amplitude of its variability has been poorly constrained. Here we report two seawater 234U/238U records based on well-preserved deep-sea corals from the low-latitude Atlantic and Pacific Oceans. The Atlantic 234U/238U started to increase before major sea-level rise and overshot the modern value by 3 per mil during the early deglaciation. Deglacial 234U/238U in the Pacific converged with that in the Atlantic after the abrupt resumption of Atlantic meridional overturning. We suggest that ocean mixing and early deglacial release of excess 234U from enhanced subglacial melting of the Northern Hemisphere ice sheets have driven the observed 234U/238U evolution.

The oceanic budgets of nickel and zinc isotopes: the importance of sulfidic environments as illustrated by the Black Sea.

Isotopic data collected to date as part of the GEOTRACES and other programmes show that the oceanic dissolved pool is isotopically heavy relative to the inputs for zinc (Zn) and nickel (Ni). All Zn sinks measured until recently, and the only output yet measured for Ni, are isotopically heavier than the dissolved pool. This would require either a non-steady-state ocean or other unidentified sinks. Recently, isotopically light Zn has been measured in organic carbon-rich sediments from productive upwelling margins, providing a potential resolution of this issue, at least for Zn. However, the origin of the isotopically light sedimentary Zn signal is uncertain. Cellular uptake of isotopically light Zn followed by transfer to sediment does not appear to be a quantitatively important process. Here, we present Zn and Ni isotope data for the water column and sediments of the Black Sea. These data demonstrate that isotopically light Zn and Ni are extracted from the water column, probably through an equilibrium fractionation between different dissolved species followed by sequestration of light Zn and Ni in sulfide species to particulates and the sediment. We suggest that a similar, non-quantitative, process, operating in porewaters, explains the Zn data from organic carbon-rich sediments.This article is part of the themed issue 'Biological and climatic impacts of ocean trace element chemistry'.

The terrestrial uranium isotope cycle.

Changing conditions on the Earth's surface can have a remarkable influence on the composition of its overwhelmingly more massive interior. The global distribution of uranium is a notable example. In early Earth history, the continental crust was enriched in uranium. Yet after the initial rise in atmospheric oxygen, about 2.4 billion years ago, the aqueous mobility of oxidized uranium resulted in its significant transport to the oceans and, ultimately, by means of subduction, back to the mantle. Here we explore the isotopic characteristics of this global uranium cycle. We show that the subducted flux of uranium is isotopically distinct, with high (238)U/(235)U ratios, as a result of alteration processes at the bottom of an oxic ocean. We also find that mid-ocean-ridge basalts (MORBs) have (238)U/(235)U ratios higher than does the bulk Earth, confirming the widespread pollution of the upper mantle with this recycled uranium. Although many ocean island basalts (OIBs) are argued to contain a recycled component, their uranium isotopic compositions do not differ from those of the bulk Earth. Because subducted uranium was probably isotopically unfractionated before full oceanic oxidation, about 600 million years ago, this observation reflects the greater antiquity of OIB sources. Elemental and isotope systematics of uranium in OIBs are strikingly consistent with previous OIB lead model ages, indicating that these mantle reservoirs formed between 2.4 and 1.8 billion years ago. In contrast, the uranium isotopic composition of MORB requires the convective stirring of recycled uranium throughout the upper mantle within the past 600 million years.

Conscious and anaesthetised Göttingen mini-pigs as an in-vivo model for buccal absorption - pH-dependent absorption of metoprolol from bioadhesive tablets.

The potential of buccal mucosa as a site for systemic absorption has attracted increased attention in recent years creating a need for new predictive in-vivo models. The aim of this study was to evaluate anaesthetised and conscious Göttingen mini-pigs as a model for buccal drug absorption by testing pH-dependent absorption of metoprolol from a solid dosage form. Buccal tablets buffered to pH 6.2 and pH 8.9, oral liquid and intravenous injection were tested in four conscious and anaesthetised Göttingen mini-pigs in a non-randomised cross-over study. Blood samples were collected and processed before analysis by ultra-performance liquid chromatography with tandem mass spectrometry detection. An ex-vivo flow retention model was applied to study release and retention of the bioadhesive buccal tablets. The Tmax obtained from the two buccal conscious groups (55 ± 5 and 35 ± 5 min) were significantly different to the buccal anaesthetised groups (120 ± 0 and 165 ± 15 min) for buccal tablet pH 6.2 and pH 8.9, respectively. Also, the absolute bioavailability from the anaesthetised buccal tablet pH 8.9 (20.7 ± 4.0%) had a significant increase compared to all other buccal tablet groups. In conclusion, this study showed a pH-dependent absolute bioavailability of metoprolol when administrated as bioadhesive buccal tablets to anaesthetised mini-pigs. The anaesthesia was found to delay the time to reach maximal plasma concentration of metoprolol as compared to the conscious pig model when administrated as buccal tablets.

In vitro, ex vivo and in vivo examination of buccal absorption of metoprolol with varying pH in TR146 cell culture, porcine buccal mucosa and Göttingen minipigs.

This work studied the buccal absorption of metoprolol in vitro, ex vivo and in vivo as a function of buffered pH at 7.4, 8.5, 9.0 and 9.5. Permeability studies showed a correlation (r(2)=0.92) between in vitro TR146 cell culture and ex vivo porcine buccal mucosa in a modified Ussing chamber. A higher apparent permeability was observed at higher pH values, i.e. the more compound that was unionised the higher the permeability. In vivo studies were conducted in anaesthetised Göttingen mini-pigs. A clear influence of pH on the absorption was seen and a significant higher absolute bioavailability was obtained after buccal dosing (58-107%) compared to oral (3%) administration, ranging 58-107% and 3%, respectively. Macroscopically, no local toxic effects were observed by visual inspection of mini-pig cheeks. A very clear level C in vitro in vivo correlation (r(2)=0.98) was obtained between the observed in vitro permeabilities and the bioavailability observed in vivo, suggesting that the two in vitro models have good predictive power for drug delivery, which could be a useful tool for future formulation developments intended for buccal delivery.

Spatial and temporal distribution of Pu in the Northwest Pacific Ocean using modern coral archives.

Historical (239)Pu activity concentrations and (240)Pu/(239)Pu atom ratios were determined in skeletons of dated modern corals collected from three locations (Chuuk Lagoon, Ishigaki Island and Iki Island) to identify spatial and temporal variations in Pu inputs to the Northwest Pacific Ocean. The main Pu source in the Northwest Pacific is fallout from atmospheric nuclear weapons testing which consists of global fallout and close-in fallout from the former US Pacific Proving Grounds (PPG) in the Marshall Islands. PPG close-in fallout dominated the Pu input in the 1950s, as was observed with higher (240)Pu/(239)Pu atom ratios (>0.30) at the Ishigaki site. Specific fallout Pu contamination from the Nagasaki atomic bomb and the Ivy Mike thermonuclear detonation at the PPG were identified at Ishigaki Island from the (240)Pu/(239)Pu atom ratios of 0.07 and 0.46, respectively. During the 1960s and 1970s, global fallout was the major Pu source to the Northwest Pacific with over 60% contribution to the total Pu. After the cessation of the atmospheric nuclear tests, the PPG again dominated the Pu input due to the continuous transport of remobilised Pu from the Marshall Islands along the North Equatorial Current and the subsequent Kuroshio Current. The Pu contributions from the PPG in recent coral bands (1984 onwards) varied over time with average estimated PPG contributions between 54% and 72% depending on location.

Temporal record of Pu isotopes in inter-tidal sediments from the northeastern Irish Sea.

A depth profile of (239)Pu and (240)Pu specific activities and isotope ratios was determined in an inter-tidal sediment core from the Esk Estuary in the northeastern Irish Sea. The study site has been impacted with plutonium through routine radionuclide discharges from the Sellafield nuclear reprocessing plant in Cumbria, NW England. A pronounced sub-surface maximum of ~10 k Bq kg(-1) was observed for (239+240)Pu, corresponding to the peak in Pu discharge from Sellafield in 1973, with a decreasing trend with depth down to ~0.04 k Bq kg(-1) in the deeper layers. The depth profile of (239+240)Pu specific activities together with results from gamma-ray spectrometry for (137)Cs and (241)Am was compared with reported releases from the Sellafield plant in order to estimate a reliable sediment chronology. The upper layers (1992 onwards) showed higher (239+240)Pu specific activities than would be expected from the direct input of annual Sellafield discharges, indicating that the main input of Pu is from the time-integrated contaminated mud patch of the northeastern Irish Sea. The (240)Pu/(239)Pu atom ratios ranged from ~0.03 in the deepest layers to >0.20 in the sub-surface layers with an activity-weighted average of 0.181. The decreasing (240)Pu/(239)Pu atom ratio with depth reflects the changing nature of operations at the Sellafield plant from weapons-grade Pu production to reprocessing spent nuclear fuel with higher burn-up times in the late 1950s. In addition, recent annual (240)Pu/(239)Pu atom ratios in winkles collected during 2003-2008 from three stations along the Cumbrian coastline showed no significant spatial or temporal differences with an overall average of 0.204, which supports the hypothesis of diluted Pu input from the contaminated mud patch.