Biogeochemical variations at the Porcupine Abyssal Plain sustained Observatory in the northeast Atlantic Ocean, from weekly to inter-annual timescales

We present high-resolution autonomous measurements of carbon dioxide partial pressure p(CO2) taken in situ at the Porcupine Abyssal Plain sustained Observatory (PAP-SO) in the northeast Atlantic (49° N, 16.5° W; water depth of 4850 m) for the period 2010–2012. Measurements of p(CO2) made at 30 m depth on a sensor frame are compared with other autonomous biogeochemical measurements at that depth (including chlorophyll a fluorescence and nitrate concentration data) to analyse weekly to seasonal controls on p(CO2) flux in the inter-gyre region of the North Atlantic. Comparisons are also made with in situ regional time series data from a ship of opportunity and mixed layer depth (MLD) measurements from profiling Argo floats. There is a persistent under-saturation of CO2 in surface waters throughout the year which gives rise to a perennial CO2 sink. Comparison with an earlier data set collected at the site (2003–2005) confirms seasonal and inter-annual changes in surface seawater chemistry. There is year-to-year variability in the timing of deep winter mixing and the intensity of the spring bloom.The 2010–2012 period shows an overall increase in p(CO2) values when compared to the 2003–2005 period as would be expected from increases due to anthropogenic CO2 emissions. The surface temperature, wind speed and MLD measurements are similar for both periods of time. Future work should incorporate daily CO2 flux measurements made using CO2 sensors at 1 m depth and the in situ wind speed data now available from the UK Met Office Buoy

Visually Impaired OLder people's Exercise programme for falls prevenTion (VIOLET): a feasibility study

This study aims to conduct a mixed methods feasibility study to inform the design and conduct of a future definitive RCT of an adapted exercise programme to prevent falls by reducing fear of falling among older people with visual impairment (OPVI). The research questions are: can an existing exercise programme be adapted for OPVI and successfully delivered in the community; is it feasible to conduct an RCT of this intervention and what are the features of a future definitive trial? We propose to: (i) Adapt an existing exercise programme with the full involvement of OPVI and practitioners; (ii) Run a feasibility study in 2 sites to test our proposed measures, trial processes and recruitment; explore acceptability of the intervention; fidelity of and compliance with the intervention. Two stakeholder panels will be established including OPVI aged 60 and over from Newcastle Society for Blind People (NSBP) and Visibility in Glasgow, practitioners and researchers. They will work together to adapt the FaME programme, which is known to be effective in reducing falls in frequent fallers, so that the methods are acceptable for OPVI, whilst retaining the effective components of the exercise. The panels will meet 4 times to adapt the intervention and contribute to decisions on outcome measures and data collection. During this time we will identify OPVI wishing to act as expert stakeholders in the subsequent WPs. OPVI aged 60+ will be recruited from low vision clinics and voluntary organisations and randomised into the intervention or comparator arm. Those in the comparator arm will receive no intervention, but will be offered it after final data collection. The core components of the adapted exercise programme aim to strengthen leg muscles and retrain balance. However, the detail of the methods and timing will be decided by the stakeholder panel. The programme is likely to run once a week over 12 weeks, with each session lasting up to one hour. The final form of delivery will be one of the outcomes of the PPI work in WP1. Participants will be provided with instructions and equipment to do the exercises at home if they wish. The intervention will be delivered by exercise instructors engaged by Health Works, Newcastle and Visibility, Glasgow, in venues agreed with participants. The final primary outcome of the future RCT will be decided by the responsiveness to change, participant burden and participant feedback from this study. The likely candidate primary outcome is fear of falling (Short FES-I scale). The main secondary outcomes will be: activity avoidance; balance/falls risk; number of falls; quality of life; loneliness; depression; adherence to exercise programme; self-reported home exercising. An estimate of cost effectiveness and cost utility of the intervention will be undertaken. In-depth interviews with a sample of OPVI will be conducted to explore their reasons for taking part/not taking part; factors that facilitate/hinder them from participating in exercise groups; their experiences of the recruitment and randomisation process and views on the outcome measures; their experience of the adapted intervention. The interviews will highlight site specific issues to consider for the definitive RCT. Structured interviews will be undertaken with commissioners and practitioners to explore their perspectives on the application of the intervention

Deep ocean particle flux in the Northeast Atlantic over the past 30 years: carbon sequestration is controlled by ecosystem structure in the upper ocean

The time series of downward particle flux at 3000 m at the Porcupine Abyssal Plain Sustained Observatory (PAP-SO) in the Northeast Atlantic is presented for the period 1989 to 2018. This flux can be considered to be sequestered for more than 100 years. Measured levels of organic carbon sequestration (average 1.88 gm−2 y−1) are higher on average at this location than at the six other time series locations in the Atlantic. Interannual variability is also greater than at the other locations (organic carbon flux coefficient of variation = 73%). We find that previously hypothesised drivers of 3,000 m flux, such as net primary production (NPP) and previous-winter mixing are not good predictors of this sequestration flux. In contrast, the composition of the upper ocean biological community, specifically the protozoan Rhizaria (including the Foraminifera and Radiolaria) exhibit a close relationship to sequestration flux. These species become particularly abundant following enhanced upper ocean temperatures in June leading to pulses of this material reaching 3,000 m depth in the late summer. In some years, the organic carbon flux pulses following Rhizaria blooms were responsible for substantial increases in carbon sequestration and we propose that the Rhizaria are one of the major vehicles by which material is transported over a very large depth range (3,000 m) and hence sequestered for climatically relevant time periods. We propose that they sink fast and are degraded little during their transport to depth. In terms of atmospheric CO2 uptake by the oceans, the Radiolaria and Phaeodaria are likely to have the greatest influence. Foraminifera will also exert an influence in spite of the fact that the generation of their calcite tests enhances upper ocean CO2 concentration and hence reduces uptake from the atmosphere

Reconciliation of the carbon budget in the ocean’s twilight zone

Photosynthesis in the surface ocean produces approximately 100 gigatonnes of organic carbon per year, of which 5 to 15 per cent is exported to the deep ocean1, 2. The rate at which the sinking carbon is converted into carbon dioxide by heterotrophic organisms at depth is important in controlling oceanic carbon storage3. It remains uncertain, however, to what extent surface ocean carbon supply meets the demand of water-column biota; the discrepancy between known carbon sources and sinks is as much as two orders of magnitude4, 5, 6, 7, 8. Here we present field measurements, respiration rate estimates and a steady-state model that allow us to balance carbon sources and sinks to within observational uncertainties at the Porcupine Abyssal Plain site in the eastern North Atlantic Ocean. We find that prokaryotes are responsible for 70 to 92 per cent of the estimated remineralization in the twilight zone (depths of 50 to 1,000 metres) despite the fact that much of the organic carbon is exported in the form of large, fast-sinking particles accessible to larger zooplankton. We suggest that this occurs because zooplankton fragment and ingest half of the fast-sinking particles, of which more than 30 per cent may be released as suspended and slowly sinking matter, stimulating the deep-ocean microbial loop. The synergy between microbes and zooplankton in the twilight zone is important to our understanding of the processes controlling the oceanic carbon sink

Acoustic and optical variations during rapid downward motion episodes in the deep north-western Mediterranean Sea

An Acoustic Doppler Current Profiler (ADCP) was moored at the deep-sea site of the ANTARES neutrino telescope near Toulon, France, thus providing a unique opportunity to compare high-resolution acoustic and optical observations between 70 and 170 m above the sea bed at 2475 m. The ADCP measured downward vertical currents of magnitudes up to 0.03 m s-1 in late winter and early spring 2006. In the same period, observations were made of enhanced levels of acoustic reflection, interpreted as suspended particles including zooplankton, by a factor of about 10 and of horizontal currents reaching 0.35 m s-1. These observations coincided with high light levels detected by the telescope, interpreted as increased bioluminescence. During winter 2006 deep dense-water formation occurred in the Ligurian subbasin, thus providing a possible explanation for these observations. However, the 10-20 days quasi-periodic episodes of high levels of acoustic reflection, light and large vertical currents continuing into the summer are not direct evidence of this process. It is hypothesized that the main process allowing for suspended material to be moved vertically later in the year is local advection, linked with topographic boundary current instabilities along the rim of the 'Northern Current'.Comment: 30 pages, 7 figure

Large deep-sea zooplankton biomass mirrors primary production in the global ocean

The biological pump transports organic carbon produced by photosynthesis to the meso- and bathypelagic zones, the latter removing carbon from exchanging with the atmosphere over centennial time scales. Organisms living in both zones are supported by a passive flux of particles, and carbon transported to the deep-sea through vertical zooplankton migrations. Here we report globally-coherent positive relationships between zooplankton biomass in the epi-, meso-, and bathypelagic layers and average net primary production (NPP). We do so based on a global assessment of available deep-sea zooplankton biomass data and large-scale estimates of average NPP. The relationships obtained imply that increased NPP leads to enhanced transference of organic carbon to the deep ocean. Estimated remineralization from respiration rates by deep-sea zooplankton requires a minimum supply of 0.44 Pg C y(-1) transported into the bathypelagic ocean, comparable to the passive carbon sequestration. We suggest that the global coupling between NPP and bathypelagic zooplankton biomass must be also supported by an active transport mechanism associated to vertical zooplankton migration