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The rate of carbon fixation by phytoplankton in marine surface waters is often tied to the supply of growth-limiting nutrients such as iron (Fe). While average cellular requirements and ratios for various elements are well known in the literature, especially through laboratory culture work, the plasticity of these relationships in natural plankton communities has been less explored. To gauge how changes in the biological availability of dissolved Fe might influence cellular nutrient ratios of marine phytoplankton (and thus their physiology), we carried out incubation assays during a research expedition off the east coast of New Zealand. Trace-metal clean collection of plankton communities were amended with a continuum of concentrations of either Fe (as FeCl3) or desferroxamine B (to reduce bioavailable Fe) and then maintained for 72 h under in situ conditions. Along with standard assays (Fv/Fm, chlorophyll, nutrient drawdown), we measured elemental ratios in the bulk community by inductively coupled plasma mass spectrometry and within individual plankton using synchrotron X-ray fluorescence. Our observations demonstrate that changes in the physiological ecology of the community (biomass, photosynthetic efficiency) were mirrored in changes in elemental ratios, including a 3-fold change in Fe stoichiometry and a 13-fold change in Zn stoichiometry when Fe-replete and Fe-depleted communities were compared. We present this information in consideration of the hypothesis that flexibility in elemental quotas influences the interactions between nutrient availability and planktonic physiological status, subsequently altering C flow through marine surface waters.

We present velocity-resolved reverberation results for five active galactic nuclei. We recovered velocity-delay maps using the maximum entropy method for four objects: Mrk 335, Mrk 1501, 3C 120, and PG 2130+099. For the fifth, Mrk 6, we were only able to measure mean time delays in different velocity bins of the Hß emission line. The four velocity-delay maps show unique dynamical signatures for each object. For 3C 120, the Balmer lines show kinematic signatures consistent with both an inclined disk and infalling gas, but the He II ¿4686 emission line is suggestive only of inflow. The Balmer lines in Mrk 335, Mrk 1501, and PG 2130+099 show signs of infalling gas, but the He II emission in Mrk 335 is consistent with an inclined disk. We also see tentative evidence of combined virial motion and infalling gas from the velocity-binned analysis of Mrk 6. The maps for 3C 120 and Mrk 335 are two of the most clearly defined velocity-delay maps to date. These maps constitute a large increase in the number of objects for which we have resolved velocity-delay maps and provide evidence supporting the reliability of reverberation-based black hole mass measurements.

Diatom blooms play a central role in supporting foodwebs and sequestering biogenic carbon to depth. Oceanic conditions set bloom initiation, whereas both environmental and ecological factors determine bloom magnitude and longevity. Our study reveals another fundamental determinant of bloom dynamics. A diatom spring bloom in offshore New Zealand waters was likely terminated by iron limitation, even though diatoms consumed <1/3 of the mixed-layer dissolved iron inventory. Thus, bloom duration and magnitude were primarily set by competition for dissolved iron between microbes and small phytoplankton versus diatoms. Significantly, such a microbial mode of control probably relies both upon out-competing diatoms for iron (i.e., K-strategy), and having high iron requirements (i.e., r-strategy). Such resource competition for iron has implications for carbon biogeochemistry, as, blooming diatoms fixed three-fold more carbon per unit iron than resident non-blooming microbes. Microbial sequestration of iron has major ramifications for determining the biogeochemical imprint of oceanic diatom blooms. Citation: Boyd, P. W., et al. (2012), Microbial control of diatom bloom dynamics in the open ocean, Geophys. Res. Lett., 39, L18601.

Background: Whilst outdoor activities and mobility are believed to be beneficial for older care home residents, UK best practice guidance is based on occupational therapy-led expert consensus. This thesis reports research which aimed to provide theory-driven explanations about residents’ occupational engagement in the gardens and outdoor spaces of UK care homes. Method: A systematic mapping review was used to identified gaps in the evidence base, which informed the research to be undertaken. A multi-phase, realist theory development cycle incorporated: identification of initial context, mechanism and outcome (CMO) components guided by the review literature and expert stakeholder consultation; CMO configuration (CMOc) using data from non-participant observations, Dementia Care Mapping (DCM) values, plus characteristics questionnaires; theory refinement which involved using a retroductive approach to triangulate and synthesise observational and staff focus group data and finally, theory articulation, in which the overall findings were interpreted in the context of the broader literature and substantive theories to produce a middle-range theory for further testing. Results: Contextual barriers to residents’ outdoor use were reported frequently in the mapping review articles, but explanations about why or how these operated as such were largely absent. A realist approach was selected to address this. Observational data provided by 50 residents and 35 care staff from three care homes, plus questionnaire data indicated that residents’ outdoor use was influenced primarily by the practice context rather than by intrinsic resident mechanisms. Data from three focus groups (14 staff) confirmed that staff reasoning about supporting outdoor use was characterised by risk aversion, which was partly a consequence of organisational and building design constraints. A middle-range theory posited that cognitive dissonance about outdoor use was experienced by a particular staff referenc