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Snow algae are found in snowfields across cold regions of the planet, forming highly visible red and green patches below and on the snow surface. In Antarctica, they contribute significantly to terrestrial net primary productivity due to the paucity of land plants, but our knowledge of these communities is limited. Here we provide the first description of the metabolic and species diversity of green and red snow algae communities from four locations in Ryder Bay (Adelaide Island, 68°S), Antarctic Peninsula. During the 2015 austral summer season, we collected samples to measure the metabolic composition of snow algae communities and determined the species composition of these communities using metabarcoding. Green communities were protein-rich, had a high chlorophyll content and contained many metabolites associated with nitrogen and amino acid metabolism. Red communities had a higher carotenoid content and contained more metabolites associated with carbohydrate and fatty acid metabolism. Chloromonas, Chlamydomonas and Chlorella were found in green blooms but only Chloromonas was detected in red blooms. Both communities also contained bacteria, protists and fungi. These data show the complexity and variation within snow algae communities in Antarctica and provide initial insights into the contribution they make to ecosystem functioning.

Unprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre. Warming ocean water plays a significant role in accelerating Arctic sea ice melt. Here the authors present detailed observations of warm water of Pacific origin entering and diving beneath the Arctic ocean surface, and explore the dynamical processes governing its evolution.

Antarctic sea ice is one of the largest biomes on Earth providing a critical habitat for ice algae. Measurements of primary production in Antarctic sea ice remain scarce and an observation‐based estimate of primary production has not been revisited in over 30 years. We fill this knowledge gap by presenting a newly compiled circumpolar data set of particulate and dissolved organic carbon from 362 ice cores, sampled between 1989 and 2019, to estimate sea‐ice net community production using a carbon biomass accumulation approach. Our estimate of 26.8–32.9 Tg C yr−1 accounts for at least 15%–18% of the total primary production in the Antarctic sea‐ice zone, less than a previous observation‐based estimate (63–70 Tg C yr−1 ) and consistent with recent modeled estimates. The results underpin the ecological significance of sea‐ice algae as an early season resource for pelagic food webs.

Warming of the Arctic has resulted in environmental and ecological changes, termed borealization, leading to the northward shift of temperate species. Borealization has occurred across all trophic levels, altering the structure of the food web. The onset and rate of borealization likely varies with latitude, depending on local warming and advection of warmer water into the Arctic. In order to assess latitudinal trends in food web structure in the Arctic, we analyzed stable nitrogen isotopes of specific amino acids alongside bulk stable carbon isotopes in ringed seal muscle tissue from the Canadian Arctic Archipelago (high-Arctic) and Southern Baffin Bay (mid-Arctic) from 1990 to 2016. Our results indicate a shift in food web structure in the high-Arctic that has occurred more recently when compared with the mid-Arctic. Specifically, over the past 25 years, the trophic position of ringed seals from the mid-Arctic was largely constant, whereas the trophic position of ringed seals decreased in the high-Arctic, reaching similar values observed in the mid-Arctic in 2015–2016. This suggests a potential shortening of the food chain length in the high-Arctic, possibly driven by changes in zooplankton communities feeding complexity in association with sea ice decline. This study identifies a temporal offset in the timing of borealization in the Canadian Arctic, resulting in different response of food webs to ecological changes, depending on latitude.

Climate change is altering nutrient cycling within the Arctic Ocean, having knock-on effects to Arctic ecosystems. Primary production in the Arctic is principally nitrogen-limited, particularly in the western Pacific-dominated regions where denitrification exacerbates nitrogen loss. The nutrient status of the eastern Eurasian Arctic remains under debate. In the Barents Sea, primary production has increased by 88% since 1998. To support this rapid increase in productivity, either the standing stock of nutrients has been depleted, or the external nutrient supply has increased. Atlantic water inflow, enhanced mixing, benthic nitrogen cycling, and land–ocean interaction have the potential to alter the nutrient supply through addition, dilution or removal. Here we use new datasets from the Changing Arctic Ocean program alongside historical datasets to assess how nitrate and phosphate concentrations may be changing in response to these processes. We highlight how nutrient dynamics may continue to change, why this is important for regional and international policy-making and suggest relevant research priorities for the future.

While the entire Arctic Ocean is warming rapidly, the Barents Sea in particular is experiencing significant warming and sea ice retreat. An increase in ocean heat transport from the Atlantic is causing the Barents Sea to be transformed from a cold, salinity-stratified system into a warmer, less-stratified Atlantic-dominated climate regime. Productivity in the Barents Sea shelf is fuelled by waters of Atlantic origin (AW) which are ultimately exported to the Arctic Basin. The consequences of this current regime shift on the nutrient characteristics of the Barents Sea are poorly defined. Here we use the stable isotopic ratios of nitrate (δ15N-NO3, δ18O-NO3) to determine the uptake and modification of AW nutrients in the Barents Sea. In summer months, phytoplankton consume nitrate, surface waters become nitrate depleted, and particulate nitrogen (δ15N-PN) reflects the AW nitrate source. The ammonification of organic matter in shallow sediments resupplies N to the water column and replenishes the nitrate inventory for the following season. Low δ18O-NO3 in the northern Barents Sea reveals that the nitrate in lower-temperature Arctic waters is > 80 % regenerated through seasonal nitrification. During on-shelf nutrient uptake and regeneration, there is no significant change to δ15N-NO3 or N*, suggesting that benthic denitrification does not impart an isotopic imprint on pelagic nitrate. Our results demonstrate that the Barents Sea is distinct from other Arctic shelves where benthic denitrification enriches δ15N-NO3 and decreases N*. As nutrients are efficiently recycled in the Barents Sea and there is no significant loss of N through benthic denitrification, changes to Barents Sea productivity are unlikely to alter N availability on shelf or the magnitude of N advected to the central Arctic Basin. However, we suggest that the AW nutrient source ultimately determines Barents Sea productivity and that changes to AW delivery have the potential to alter Barents Sea primary production and subsequent nutrient supply to the central Arctic Ocean.

It is widely accepted that the complexation of iron (Fe) with organic compounds is the primary factor that regulates Fe reactivity and its bioavailability to phytoplankton in the open ocean. Despite considerable efforts to unravel the provenance of the many organic ligands present in the ‘ligand soup’ much of this pool remains largely unresolved and the ligands remain grouped into either strong (L1) or weak (L2) types. The Tasman Sea and Southern Ocean are areas of particular interest as both regions are subject to Fe limitation or co-limitation and are likely to be severely affected under climate change scenarios. The predictions of dryer conditions in central Australia suggest that the Tasman Sea may be subject to changes in the intensity and frequency of atmospheric dust deposition and, in consequence, enhanced Fe deposition into the surface waters. This thesis aims to improve our knowledge of a) how natural organic ligands affect Fe solubility, chemistry, and bioavailability, and b) which forms of Fe are available to phytoplankton.Natural seawater samples (surface and profiles to 1000m) revealed that electrochemically detected HS-like material, which are thought to make up a proportion of the weaker L2 class of ligands, account for a very small fraction of the Fe-binding organic ligand pool. The distribution of HS-like material in coastal, shelf and offshore regions associated with the EAC does not exhibit a nearshore to offshore (high to low) concentration gradient, likely because of low riverine HS-like input. Higher concentrations of HS-like material were generally found at, or adjacent to, the chlorophyll maximum (Cmax). However, little correlation with chlorophyll-a (Chl-a) was observed and so these higher concentrations are more likely linked to degraded algal material and microbial activity rather than direct primary productivity. Perturbation experiments using water collected offshore in the EAC and a cold core cyclonic eddy (CCE) indicated that the in situutilisation and production of HS-like material, and its character, differ depending on the phytoplankton and microbial communities present, and reflect the biological activities of these different communities, as well as photochemical transformations. The addition of a model HS (Suwannee River fulvic acid) enhanced Chl-a concentration in both communities, particularly in the EAC, likely due to the remineralisation of Fe and other nutrients via photochemical and bacterial transformation of this material.Seawater depth profiles from the northern and southern Tasman Sea indicate Fe limitation (or co-limitation) at the stations sampled. Dissolved Fe (dFe), organic ligand concentrations and conditional stability constants were consistent with previous studies (showing the presence of mostly L2ligands) with higher ligand concentrations and conditional stability constants close to the Cmax. Ligand concentration, as previously reported, is in excess of dFe throughout the water column, although no correlation between dFe and ligand concentration was observed.Fe-enrichment experiments using two contrasting phytoplankton communities investigated how the communities respond, in terms of biomass and community structure, to inorganic Fe delivered alone or bound to an organic ligand (siderophore, saccharides, bacterial exopolymeric substances (EPS)) or dust-borne Fe from two dust samples (D1 and D2) originating from the Australian continent. Overall, Fe bound to a strong Fe-binding siderophore was much less available to both phytoplankton communities; whereas, Fe bound to bacterial EPS (lowest conditional stability constant) induced the greatest increase in overall phytoplankton biomass. Dust D1 did not have the highest rate of dFe uptake, or result in the greatest increase Chl-a, but did induce the greatest shift in community structure. Whilst one ligand (L2) was measured in most incubations, both L1 and L2 ligands were detected in the D1 and inorganic Fe incubations, indicating in situbiological production of Fe-binding ligands (i.e. siderophores or EPS) in response to Fe addition and an added ligand component from the dust. The greater response of the phytoplankton to the EPS and D1 led to further laboratory experiments.Analysis of 4 EPS isolates (1 bacterial, 1 mixed natural community, and 2 microalgal laboratory cultures) showed that both bacterial and algal EPS contain functional components known to bind Fe (uronic acid, saccharides). The bacterial EPS was made up of mainly high molecular mass components, whereas the algal EPS were of low molecular mass. Most EPS contained components that were measured as both L1 and L2 ligands, with the L1 ligands having an affinity for Fe close to that of bacterial siderophores. EPS greatly enhanced Fe solubility in seawater, however, it may also accelerate Fe(II) oxidation, and thus, Fe(II) removal from the system. Other trace elements and macronutrients were associated with the EPS that may be accessible to phytoplankton and could help to relieve nutrient limitation. Bioaccumulation experiments indicated that Fe bound to all EPS used was highly bioavailable to the Southern Ocean diatom C. simplex(50 to > 100%) relative to the bioavailability of inorganic Fe (assumed 100% bioavailable). This enhanced bioavailability was likely due to increased Fe solubility, and possible formation of more bioavailable forms of Fe.Further experiments using dust D1, and rainwater collected in the Tasman Sea, revealed that despite low fractional solubilities (< 1%), the dust represents, potentially, an important source of Fe and other vital macronutrients and trace elements. Both the rainwater and dust were associated with ligands in the L2 class that helped to maintain the solubility of Fe. Light exposure, particularly UV, can a) have a substantial effect on the Fe chemistry of the Feladen dust, lowering the conditional stability constant and altering the size distribution of both Fe and ligands (including saccharides and HS-like material), and b) improve the bioavailability of dust-borne Fe to C. simplex.The perturbation experiments in the EAC, CCE and north and south Tasman Sea demonstrated that organic ligands play an important role in regulating the nutrient dynamics of marine systems. They show that the bioavailability of Fe to phytoplankton is dependent on the various Fe species and Fe sources (i.e. inorganic Fe, organically bound, dust-borne), and that this differs between phytoplankton size fractions and from one bacterio- or phytoplankton species to another. The Tasman Sea and Southern Ocean receive, possibly increasing, periodic inputs of atmospheric dust from the source region of D1, which initiated a substantial community shift in perturbation experiments. However, the impact that dust-borne Fe will have on a natural phytoplankton community will be dependent on the duration and intensity of the dust deposition event, and the nutritive state and community structure of the resident phytoplankton. Bacterial siderophores have previously been suggested as key players in Fe biogeochemistry, however, in remote regions bacterial and algal EPS could play a significant role in the biogeochemical cycling of Fe and other nutrients, and their contribution should also be considered to further our understanding of the dynamics of Fe-limited oceans.

We used data from the Global Burden of Diseases, Injuries, and Risk Factors Study 2010 (GBD 2010) to estimate the burden of disease attributable to mental and substance use disorders in terms of disability-adjusted life years (DALYs), years of life lost to premature mortality (YLLs), and years lived with disability (YLDs). For each of the 20 mental and substance use disorders included in GBD 2010, we systematically reviewed epidemiological data and used a Bayesian meta-regression tool, DisMod-MR, to model prevalence by age, sex, country, region, and year. We obtained disability weights from representative community surveys and an internet-based survey to calculate YLDs. We calculated premature mortality as YLLs from cause of death estimates for 1980–2010 for 20 age groups, both sexes, and 187 countries. We derived DALYs from the sum of YLDs and YLLs. We adjusted burden estimates for comorbidity and present them with 95% uncertainty intervals. In 2010, mental and substance use disorders accounted for 183·9 million DALYs (95% UI 153·5 million–216·7 million), or 7·4% (6·2–8·6) of all DALYs worldwide. Such disorders accounted for 8·6 million YLLs (6·5 million–12·1 million; 0·5% [0·4–0·7] of all YLLs) and 175·3 million YLDs (144·5 million–207·8 million; 22·9% [18·6–27·2] of all YLDs). Mental and substance use disorders were the leading cause of YLDs worldwide. Depressive disorders accounted for 40·5% (31·7–49·2) of DALYs caused by mental and substance use disorders, with anxiety disorders accounting for 14·6% (11·2–18·4), illicit drug use disorders for 10·9% (8·9–13·2), alcohol use disorders for 9·6% (7·7–11·8), schizophrenia for 7·4% (5·0–9·8), bipolar disorder for 7·0% (4·4–10·3), pervasive developmental disorders for 4·2% (3·2–5·3), childhood behavioural disorders for 3·4% (2·2–4·7), and eating disorders for 1·2% (0·9–1·5). DALYs varied by age and sex, with the highest proportion of total DALYs occurring in people aged 10–29 years. The burden of mental and substance use disorders increased by 37·6% between 1990 and 2010, which for most disorders was driven by population growth and ageing. Despite the apparently small contribution of YLLs—with deaths in people with mental disorders coded to the physical cause of death and suicide coded to the category of injuries under self-harm—our findings show the striking and growing challenge that these disorders pose for health systems in developed and developing regions. In view of the magnitude of their contribution, improvement in population health is only possible if countries make the prevention and treatment of mental and substance use disorders a public health priority. Queensland Department of Health, National Health and Medical Research Council of Australia, National Drug and Alcohol Research Centre-University of New South Wales, Bill & Melinda Gates Foundation, University of Toronto, Technische Universität, Ontario Ministry of Health and Long Term Care, and the US National Institute of Alcohol Abuse and Alcoholism.

The Global Burden of Disease Study 2010 (GBD 2010) identified mental and substance use disorders as the 5th leading contributor of burden in 2010, measured by disability adjusted life years (DALYs). This estimate was incomplete as it excluded burden resulting from the increased risk of suicide captured elsewhere in GBD 2010's mutually exclusive list of diseases and injuries. Here, we estimate suicide DALYs attributable to mental and substance use disorders. Relative-risk estimates of suicide due to mental and substance use disorders and the global prevalence of each disorder were used to estimate population attributable fractions. These were adjusted for global differences in the proportion of suicide due to mental and substance use disorders compared to other causes then multiplied by suicide DALYs reported in GBD 2010 to estimate attributable DALYs (with 95% uncertainty). Mental and substance use disorders were responsible for 22.5 million (14.8-29.8 million) of the 36.2 million (26.5-44.3 million) DALYs allocated to suicide in 2010. Depression was responsible for the largest proportion of suicide DALYs (46.1% (28.0%-60.8%)) and anorexia nervosa the lowest (0.2% (0.02%-0.5%)). DALYs occurred throughout the lifespan, with the largest proportion found in Eastern Europe and Asia, and males aged 20-30 years. The inclusion of attributable suicide DALYs would have increased the overall burden of mental and substance use disorders (assigned to them in GBD 2010 as a direct cause) from 7.4% (6.2%-8.6%) to 8.3% (7.1%-9.6%) of global DALYs, and would have changed the global ranking from 5th to 3rd leading cause of burden. Capturing the suicide burden attributable to mental and substance use disorders allows for more accurate estimates of burden. More consideration needs to be given to interventions targeted to populations with, or at risk for, mental and substance use disorders as an effective strategy for suicide prevention.

Expands on previous analyses of the contribution of illicit drug use to the global burden of disease (GBD). Conducts the first assessment of the global burden of cannabis (e.g. marijuana, hashish and hash oil) dependence. Outlines the methodology used to estimate burden for this disorder specifically. Assembles data on the incidence and prevalence of cannabis use and dependence into a comprehensive disease model which adjusts for known sources of variability between studies. Investigates trends in the burden of cannabis dependence. Investigates the model used in GBD 2010 to estimate the global burden of disease attributable to cannabis dependence as a risk factor for schizophrenia. Looks at the effect on mortality. Includes data from New Zealand. Source: National Library of New Zealand Te Puna Matauranga o Aotearoa, licensed by the Department of Internal Affairs for re-use under the Creative Commons Attribution 3.0 New Zealand Licence.