Influence of Seasonal Variability in Flux Attenuation on Global Organic Carbon Fluxes and Nutrient Distributions.

The biological carbon pump is a key component of the marine carbon cycle. This surface-to-deep flux of carbon is usually assumed to follow a simple power law function, which imposes that the surface export flux is attenuated throughout subsurface waters at a rate dictated by the parameterization exponent. This flux attenuation exponent is widely assumed as constant.

Detection of climate change-driven trends in phytoplankton phenology.

The timing of the annual phytoplankton spring bloom is likely to be altered in response to climate change. Quantifying that response has, however, been limited by the typically coarse temporal resolution (monthly) of global climate models. Here, we use higher resolution model output (maximum 5 days) to investigate how phytoplankton bloom timing changes in response to projected 21st century climate change, and how the temporal resolution of data influences the detection of long-term trends.

Big in the benthos: Future change of seafloor community biomass in a global, body size-resolved model.

Deep-water benthic communities in the ocean are almost wholly dependent on near-surface pelagic ecosystems for their supply of energy and material resources. Primary production in sunlit surface waters is channelled through complex food webs that extensively recycle organic material, but lose a fraction as particulate organic carbon (POC) that sinks into the ocean interior. This exported production is further rarefied by microbial breakdown in the abyssal ocean, but a residual ultimately drives diverse assemblages of seafloor heterotrophs.

Estimating Oceanic Primary Production Using Vertical Irradiance and Chlorophyll Profiles from Ocean Gliders in the North Atlantic.

An autonomous underwater vehicle (Seaglider) has been used to estimate marine primary production (PP) using a combination of irradiance and fluorescence vertical profiles. This method provides estimates for depth-resolved and temporally evolving PP on fine spatial scales in the absence of ship-based calibrations. We describe techniques to correct for known issues associated with long autonomous deployments such as sensor calibration drift and fluorescence quenching.

Dominant oceanic bacteria secure phosphate using a large extracellular buffer.

The ubiquitous SAR11 and Prochlorococcus bacteria manage to maintain a sufficient supply of phosphate in phosphate-poor surface waters of the North Atlantic subtropical gyre. Furthermore, it seems that their phosphate uptake may counter-intuitively be lower in more productive tropical waters, as if their cellular demand for phosphate decreases there. By flow sorting (33)P-phosphate-pulsed (32)P-phosphate-chased cells, we demonstrate that both Prochlorococcus and SAR11 cells exploit an extracellular buffer of labile phosphate up to 5-40 times larger than the amount of phosphate required to replicate their chromosomes.

Elemental composition of natural populations of key microbial groups in Atlantic waters.

Intracellular carbon (C), nitrogen (N) and phosphorus (P) content of marine phytoplankton and bacterioplankton can vary according to cell requirements or physiological acclimation to growth under nutrient limited conditions. Although such variation in macronutrient content is well known for cultured organisms, there is a dearth of data from natural populations that reside under a range of environmental conditions. Here, we compare C, N and P content of Synechococcus, Prochlorococcus, low nucleic acid (LNA) content bacterioplankton and small plastidic protists inhabiting surface waters of the North and South subtropical gyres and the Equatorial Region of the Atlantic Ocean.

Comparable light stimulation of organic nutrient uptake by SAR11 and Prochlorococcus in the North Atlantic subtropical gyre.

Subtropical oceanic gyres are the most extensive biomes on Earth where SAR11 and Prochlorococcus bacterioplankton numerically dominate the surface waters depleted in inorganic macronutrients as well as in dissolved organic matter. In such nutrient poor conditions bacterioplankton could become photoheterotrophic, that is, potentially enhance uptake of scarce organic molecules using the available solar radiation to energise appropriate transport systems. Here, we assessed the photoheterotrophy of the key microbial taxa in the North Atlantic oligotrophic gyre and adjacent regions using (33)P-ATP, (3)H-ATP and (35)S-methionine tracers.

Mixotrophic basis of Atlantic oligotrophic ecosystems.

Oligotrophic subtropical gyres are the largest oceanic ecosystems, covering >40% of the Earth's surface. Unicellular cyanobacteria and the smallest algae (plastidic protists) dominate CO(2) fixation in these ecosystems, competing for dissolved inorganic nutrients. Here we present direct evidence from the surface mixed layer of the subtropical gyres and adjacent equatorial and temperate regions of the Atlantic Ocean, collected on three Atlantic Meridional Transect cruises on consecutive years, that bacterioplankton are fed on by plastidic and aplastidic protists at comparable rates.

Comparison of phosphate uptake rates by the smallest plastidic and aplastidic protists in the North Atlantic subtropical gyre.

The smallest phototrophic protists (<3 μm) are important primary producers in oligotrophic subtropical gyres - the Earth's largest ecosystems. In order to elucidate how these protists meet their inorganic nutrient requirements, we compared the phosphate uptake rates of plastidic and aplastidic protists in the phosphate-depleted subtropical and tropical North Atlantic (4-29°N) using a combination of radiotracers and flow cytometric sorting on two Atlantic Meridional Transect cruises. Plastidic protists were divided into two groups according to their size (<2 and 2-3 μm).

Management of hepatocellular carcinoma in the age of liver transplantation.

Hepatocellular carcinoma is one of the most frequently encountered malignancies worldwide. Its association with cirrhosis increases the difficulty of diagnosis and therapy. Different approaches, ranging from medical treatment to highly complex ablative and surgical therapies, including liver resection and transplantation have significantly improved the outcome of this disease.

Assessing amino acid uptake by phototrophic nanoflagellates in nonaxenic cultures using flow cytometric sorting.

Biologically available concentrations of individual dissolved amino acids in the open ocean are generally <1 nM. Despite this, the microbial turnover of amino acids is usually measured in hours indicating high demand. It is thought that the majority of uptake is due to bacterioplankton, although protists, particularly phototrophic protists, are also expected to take up amino acids.

Spatially implicit plankton population models: Transient spatial variability.

Ocean plankton models are useful tools for understanding and predicting the behaviour of planktonic ecosystems. However, when the regions represented by the model grid cells are not well mixed, the population dynamics of grid cell averages may differ from those of smaller scales (such as the laboratory scale). Here, the 'mean field approximation' fails due to 'biological Reynolds fluxes' arising from nonlinearity in the fine-scale biological interactions and unresolved spatial variability.

A single-center experience with liver transplantation for Wilson's disease.

Wilson's disease is an inherited disorder of copper metabolism, presenting with prominent hepatic and neurologic manifestations. There is an established place for liver transplantation in the presence of liver disease, while the indication for neurologic manifestations is debated. Between 1993 and 2005, 11 patients were liver transplanted for Wilson's disease at our institution.

Polycystic liver and kidney disease: post-transplant kidney function in patients receiving pre-emptive kidney transplantation.

The aim of the study is to evaluate the changes in kidney function after pre-emptive kidney transplantation in patients with polycystic liver and kidney disease (PLKD) and to establish whether pre-emptive kidney transplantation is warranted. Between 1998 and 2006, five patients with severe anatomical changes in both native kidneys but only mild alteration of the clearance function received combined liver and kidney transplantation. Preoperatively, Technetium-99m mercaptoacetyltriglycine (Tc99m MAG3) scintigraphy was used to evaluate separately the function of each native kidney.

Climate-driven range expansion of a critically endangered top predator in northeast Atlantic waters.

Global climate change is driving rapid distribution shifts in marine ecosystems; these are well established for lower trophic levels, but are harder to quantify for migratory top predators. By analysing a 25-year sightings-based dataset, we found evidence for rapid northwards range expansion of the critically endangered Balearic shearwater Puffinus mauretanicus in northeast Atlantic waters. A 0.

The significance of nitrification for oceanic new production.

The flux of organic material sinking to depth is a major control on the inventory of carbon in the ocean. To first order, the oceanic system is at equilibrium such that what goes down must come up. Because the export flux is difficult to measure directly, it is routinely estimated indirectly by quantifying the amount of phytoplankton growth, or primary production, fuelled by the upward flux of nitrate.

Extreme spatial variability in marine picoplankton and its consequences for interpreting Eulerian time-series.

A high-resolution mesoscale spatial survey of picoplankton in the Celtic Sea, using flow cytometry, reveals cell concentrations of Synechococcus spp. cyanobacteria and heterotrophic bacteria that vary up to 50-fold over distances as short as 12 km. Furthermore, the range of abundances is comparable to that typically found on seasonal scales at a single location.

Radiofrequency thermal ablation of hepatocellular carcinoma before liver transplantation--a clinical and histological examination.

Background: Radiofrequency ablation (RFA) of hepatocellular carcinoma (HCC) is an optional treatment for patients awaiting liver transplantation (LTX). The study evaluates the efficacy of RFA in the explanted liver and its effect on patient outcome.

Material And Method: Forty-seven patients underwent RFA and were listed for transplant between January 1998 and May 2003.

An outcome comparison between primary liver transplantation and retransplantation based on the pretransplant MELD score.

Survival after liver retransplantation (RLTX) is worse than after primary liver transplantation (LTX). We studied retrospectively the 2-year outcome in 44 patients who received RLTX more than 30 days after the primary transplant and in 669 after LTX performed between December 1993 and October 1999, focusing on the relation between the model for end-stage liver disease (MELD) score immediately pretransplant and post-transplant survival. A 2-year survival for RLTX was inferior to LTX (65.