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A changing climate is altering many ocean properties that consequently will modify marine productivity. Previous phytoplankton manipulation studies have focused on individual or subsets of these properties. Here, we investigate the cumulative e ects of multi-faceted change on a subantarctic diatom Pseudonitzschia multiseries by concurrently manipulating five stressors (light/nutrients/CO 2 /temperature/iron) that primarily control its physiology, and explore underlying reasons for altered physiological performance. Climate change enhances diatom growth mainly owing to warming and iron enrichment, and both properties decrease cellular nutrient quotas, partially o setting any e ects of decreased nutrient supply by 2100. Physiological diagnostics and comparative proteomics demonstrate the joint importance of individual and interactive e ects of temperature and iron, and reveal biased future predictions from experimental outcomes when only a subset of multi-stressors is considered. Our findings for subantarctic waters illustrate how composite regional studies are needed to provide accurate global projections of future shifts in productivity and distinguish underlying species-specific physiological mechanisms.A n ongoing major challenge is to grasp how climate-changemediated alteration of environmental conditions will influence biota across different scales, from organismal health to community structure 1,2 . Oceanographers have employed climate-change models 3,4 , time-series observations 5 and manipulation experiments 6 to understand the biological ramifications of global change. Phytoplankton manipulation studies reveal how alteration of individual properties, such as CO 2 , affects physiology 2,6,7 . However, the validity of such singleparameter findings 6,8,9 , in the context of complex ocean change 1,2 , is challenged by research that reveals interactive effects between multi-stressors on phytoplankton physiology 10,11 . We need to diagnose and understand the physiological mechanisms that underpin interconnected responses to multi-stressors, which together set the cumulative response of phytoplankton species to changing conditions 4,6,8 .Understanding the combined effects, across the global ocean, of complex change on phytoplankton physiology requires a gradualist approach 12,13 . Individual provinces will encounter different permutations of multi-faceted change 14 , and each is characterized by a range of resident phytoplankton groups (termed biomes 5 ). Earth System models provide a framework of projections of regional change 14 that stimulate improved experimental design to understand the biological effects of oceanic change. In return, a new generation of manipulation studies must deliver estimates of the combined effects of complex change on many phytoplankton species, and distinguish the underlying mechanisms that underpin these physiological outcomes.Here, we target subantarctic diatoms, which are ubiquitous and bloom-formers 15 . We experimentally manipulate a representative species 6,15 (Pseudonitzschi...

Research into natural mass‐dependent stable isotope fractionation of cadmium has rapidly expanded in the past few years. Methodologies are diverse with MC‐ICP‐MS favoured by all but one laboratory, which uses thermal ionisation mass spectrometry (TIMS). To quantify the isotope fractionation and correct for instrumental mass bias, double‐spike techniques, sample‐calibrator bracketing or element doping has been used. However, easy comparison between data sets has been hampered by the multitude of in‐house Cd solutions used as zero‐delta reference in different laboratories. The lack of a suitable isotopic reference material for Cd is detrimental for progress in the long term. We have conducted a comprehensive round‐robin assay of NIST SRM 3108 and the Cd isotope offsets to commonly used in‐house reference materials. Here, we advocate NIST SRM 3108 both as an isotope standard and the isotopic reference point for Cd and encourage its use as ‘zero‐delta’ in future studies. The purity of NIST SRM 3108 was evaluated regarding isobaric and polyatomic molecular interferences, and the levels of Zn, Pd and Sn found were not significant. The isotope ratio 114Cd/110Cd for NIST SRM 3108 lies within ∼ 10 ppm Da−1 of best estimates for the Bulk Silicate Earth and is validated for all measurement technologies currently in use.

The stable isotope composition of radiogenic and natural elements provides a powerful tool for unraveling element sources and biogeochemical processes in the marine environment. Depending on the element, trace element isotope ratios can (1) narrow possible sources of the element in a sample and/or (given a temporal history boundary condition) constrain the time the when the element departed the ocean surface (e.g., Pb, Nd), (2) provide information on redox processes that the element is directly or indirectly involved in (e.g., Fe, Mo, Tl), (3) indicate the extent of biological uptake and/or ocean mixing of the element (e.g., Cd, Zn).However, these trace metals occur at picomolar to nanomolar concentrations, and precise stable isotope measurements require 100-1000 times more sample than required for concentration determination. AbstractWe report data on the isotopic composition of cadmium, copper, iron, lead, zinc, and molybdenum at the GEOTRACES IC1 BATS Atlantic intercalibration station. In general, the between lab and within-lab precisions are adequate to resolve global gradients and vertical gradients at this station for Cd, Fe, Pb, and Zn. Cd and Zn isotopes show clear variations in the upper water column and more subtle variations in the deep water; these variations are attributable, in part, to progressive mass fractionation of isotopes by Rayleigh distillation from biogenic uptake and/or adsorption. Fe isotope variability is attributed to heavier crustal dust and hydrothermal sources and light Fe from reducing sediments. Pb isotope variability results from temporal changes in anthropogenic source isotopic compositions and the relative contributions of U.S. and European Pb sources. Cu and Mo isotope variability is more subtle and close to analytical precision. Although the present situation is adequate for proceeding with GEOTRACES, it should be possible to improve the within-lab and between-lab precisions for some of these properties.

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Biological vectors are important for redistribution of nutrients in many ecological systems. While availability of iron (Fe) to phytoplankton limits pelagic productivity in the Southern Ocean, biomagnification within marine food webs can lead to high concentrations of Fe in the diet of seabirds and marine mammals. We investigated patterns in concentrations of the micronutrients Fe, Co, Zn and Mn, and the toxins Cd and As, in the guano of oceanic, coastal and predatory seabirds and in faeces of 2 species of marine mammals that congregate to breed in the sub-Antarctic Auckland Islands. We found that much of the variability in concentrations of Fe, Co, Zn and Mn among species could be explained by foraging behaviour and by trophic position. We observed concentrations of Fe to be 8 orders of magnitude higher in the guano of predators and coastal foragers than in the sub-Antarctic mixed layer. High concentrations of As and Cd were associated with organic matter sources from macroalgae. Analyses of the molar ratio Fe:Al indicated that Fe within food webs supporting seabirds has likely been extensively recycled from its lithogenic source. Patterns in Fe:N among species indicated that Fe is concentrated 2 to 4 orders of magnitude in the guano of seabirds compared to limiting conditions for phytoplankton growth in sub-Antarctic waters. These data highlight the potential role of seabirds and marine mammals in the redistribution of micronutrients in the Southern Ocean and their likely role as key nutrient vectors in the ecosystem, particularly around the sub-Antarctic islands during the breeding season.Seabirds such as the albatross Diomedea epomophora are important nutrient vectors in the Southern Ocean.

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Iron, phosphate, and nitrate are essential nutrients for phytoplankton growth, and hence, their supply into the surface ocean controls oceanic primary production. Here we present a GEOTRACES zonal section (GP13; 30–33°S, 153°E–150°W) extending eastward from Australia to the oligotrophic South Pacific Ocean gyre outlining the concentrations of these key nutrients. Surface dissolved iron concentrations are elevated at >0.4 nmol L−1 near continental Australia (west of 165°E) and decreased eastward to ≤0.2 nmol L−1 (170°W–150°W). The supply of dissolved iron into the upper ocean (<100 m) from the atmosphere and vertical diffusivity averaged 11 ± 10 nmol m−2 d−1. In the remote South Pacific Ocean (170°W–150°W), atmospherically sourced iron is a significant contributor to the surface dissolved iron pool with average supply contribution of 23 ± 17% (range 3% to 55%). Surface water nitrate concentrations averaged 5 ± 4 nmol L−1 between 170°W and 150°W, while surface water phosphate concentrations averaged 58 ± 30 nmol L−1. The supply of nitrogen into the upper ocean is primarily from deeper waters (24–1647 μmol m−2 d−1) with atmospheric deposition and nitrogen fixation contributing <1% to the overall flux along the eastern part of the transect. The deep water N:P ratio averaged 14.5 ± 0.5 but declined to <1 above the deep chlorophyll maximum (DCM) indicating a high N:P assimilation ratio by phytoplankton leading to almost quantitative removal of nitrate. The supply stoichiometry for iron and nitrogen relative to phosphate at and above the DCM declines eastward leading to two biogeographical provinces: one with diazotroph production and the other without diazotroph production.