RRS James Cook Cruise 87, 31 May - 18 Jun 2013. The Twilight Cruise to the Porcupine Abyssal Plain Sustained Observatory

The Twilight Zone is that depth zone in the ocean between 100 and 1000m depth where a tremendous amount of activity takes place. Much of the material containing carbon which sinks out of the upper sunlit or "Euphotic" zone is broken down in the twilight zone and then mixes back up to the surface in the winter. If it manages to sink further, this carbon is lost for periods of centuries. The main factor that affects this sedimentation process and the rate of destruction of the sinking particles is the structure and function of the biological community living near the sea surface and in the twilight zone beneath. This is because the planktonic plants and animals living there both generate and destroy particles. The Porcupine Abyssal Plain sustained observatory (PAP) is a heavily instrumented area of the open ocean 350 miles southwest of Ireland and in a water depth of 4800m. The instruments measure a wide variety of properties of the environment above the water, within it and on the seabed and much of the data is transmitted in real time to land via satellite

RV Meteor Cruise 108, 06 - 24 Jul 2014. Cruise to the Porcupine Abyssal Plain sustained observatory

The Porcupine Abyssal Plain Observatory is a sustained, multidisciplinary observatory in the North Atlantic coordinated by the National Oceanography Centre, Southampton. For over 20 years the observatory has provided key time-series datasets for analysing the effect of climate change on the open ocean and deep-sea ecosystems. As is normally the case during cruises which are needed to refurbish the observatory, a wide range of other activities were carried out during the cruise. The main mooring of the observatory broke in December 2013 during the horrendous winter storms which destroyed a number of Met Office moorings around the UK. However we were fortunate that the break occurred just below the main sensor frame and as a result we were able to recover it along with the massive Ocean Data Acquisition System (ODAS) buoy after it had drifted towards Ireland. We were therefore able to recover all of the sensors and, most importantly, the data stored in them. Prior to Meteor cruise 108 they were all refurbished and were deployed during M108 along with some additional sensors. In addition we recovered a set of sediment traps which had been collecting sinking material in the lower part of the water column for the previous 12 months and a new set was deployed. Furthermore some entirely novel research was carried out on the distribution and characteristics of marine snow particles in the top few hundred meters of the water column. These are inanimate particles which are the principle vehicles by which material sinks out of the upper sunlit zone down to the abyss, taking carbon down with them and out of contact with the atmosphere for centuries. We used optical methods to characterise their distribution and collected samples using the Marine Snow catcher thereby providing material for a variety of experiments with colleagues from Bremen. The Bathysnap time-lapse camera system which had been taking photos of the seabed at 4800m was recovered to give an assessment of the behaviour of the benthic animals and how the seabed appearance changes in response to deposition of material. A new module was deployed. Temporal variability of the water column and seabed fauna - a task which is difficult or impossible to do autonomously was assessed using nets and cores

RRS Discovery Cruise DY032, 20 Jun - 07 Jul 2014. Cruise to the Porcupine Abyssal Plain sustained observatory

The Porcupine Abyssal Plain Observatory is a sustained, multidisciplinary observatory in the North Atlantic coordinated by the National Oceanography Centre, Southampton. For over 20 years the observatory has provided key time-series datasets for analysing the effect of climate change on the open ocean and deep-sea ecosystems. As is normally the case during cruises which are needed to refurbish the observatory, a wide range of other activities were carried out during the cruise. The main mooring Ocean Data Acquisition System (ODAS) buoy had ceased transmitting data in March 2015, so a high priority was to recover the buoy and its stored data and this was successfully achieved. In addition, we recovered a set of sediment traps which had been collecting sinking material in the lower part of the water column for the previous 12 months and deployed a new set. These are the autonomous systems, but as is usually the case with our trips to PAP, we carried out various other activities and in this case we investigated the degradation of particles as they sink. Our colleagues from MIO in France carry out sophisticated interrogation using radiolabelling. The Bathysnap time-lapse camera system which had been taking photos of the seabed at 4800m was recovered to give an assessment of the behaviour of the benthic animals and how the seabed appearance changes in response to deposition of material. A new module was deployed. Temporal variability of the water column and seabed fauna - a task which is difficult or impossible to do autonomously was assessed using nets and cores

RRS Discovery Cruise DY077, 14 Apr - 01 May 2017. Cruise to the Porcupine Abyssal Plain sustained observatory

The Discovery slipped moorings in Southampton at 0830h GMT on Friday 14th April 2017 after an uneventful mobilisation apart from the discovery that on opening one of the sealed boxes of mooring rope for the PAP#1 mooring, it was found to be empty. Discovery arrived at PAP at 2005h for our first station, a CTD rosette cast to 100m. The Discovery left the site at 1645h on Friday 28th April, somewhat earlier than expected due to a predicted storm which did indeed cause some difficulties for the ship during the return to the UK coming alongside at Portland at 1100h on Monday 1st May to exchange personnel and equipment. Moorings were slipped at 0800h on 2nd May followed by equipment trials and a final docking at Southampton NOC at 2000h on 2nd May. The Porcupine Abyssal Plain Observatory is a sustained, multidisciplinary observatory in the North Atlantic coordinated by the National Oceanography Centre, Southampton. For over 20 years the observatory has provided key time-series datasets for analysing the effect of climate change on the open ocean and deep-sea ecosystems. More information on PAP can be found in NOCs website at: http://projects.noc.ac.uk/pap/ where the most current data can be found: http://projects.noc.ac.uk/pap/pap-april-2017 PAP is one of the 23 fixed-point open ocean observatories included in the Europe-funded project FixO3, coordinated by Professor Richard Lampitt at NOC: http://www.fixo3.eu/ This 4-year project started in September 2013 with the aim to integrate the open ocean observatories operated by European organizations and is a collaboration of 29 partners from 10 different countries

RRS Discovery Cruise 217, 27 Sep-22 Oct 1995. The biology, chemistry and physics of the Goban Spur on the European continental slope of the northeast Atlantic

Discovery Cruise 217 was one of a series of cruises to the continental slope southwest of the UK in support of an EEC MAST programme "OMEX'"(Ocean Margin Exchange). The overall objectives of the programme are "to measure and to model exchange processes at the ocean margins..." and permanent repeat stations were established on the Goban Spur (around 49°N 12°W) in 1993 to address these. Discovery 217 focused primarily on the biological and chemical processes of the upper water column and the flux of particulate material associated with these processes. In spite of a number of technical problems associated with scientific equipment and significant losses of time due to poor weather, most of the original objectives were successfully met and the results will make a major contribution to the overall programme

Feeding and egg production of Oithona similis in the North Atlantic

Although cyclopoids of the genus Oithona are considered the most abundant copepods in the marine environment, there is still very little information about what sustains their population and almost constant reproduction rate throughout the year. Feeding and egg production rate (EPR) of O. similis were measured at coastal and oceanic stations during 3 cruises in the North Atlantic between April and November 2002. O. similis ingested ciliates preferentially to other components of the nano- and microplankton (herein nano-microplankton), which only became a more important component of the copepod diet when the abundance of the former decreased to low concentrations. EPR did not show significant seasonal differences, with 2.13 ± 0.67 eggs female–1 d–1 in spring, 1.61 ± 0.32 eggs female–1 d–1 in summer and 1.60 ± 0.15 eggs female–1 d–1 in winter. The ingestion rates measured at many oceanic stations and in winter were often too low to sustain EPR. Egg production efficiency (GGE) >100% indicated that sustained EPR might have relied, particularly in winter, on alternative food sources such as a more carnivorous diet and/or on the faecal pellets of euphausids

Quantifying carbon fluxes from primary production to mesopelagic fish using a simple food web model

An ecosystem-based flow analysis model was used to study carbon transfer from primary production (PP) to mesopelagic fish via three groups of copepods: detritivores that access sinking particles, vertical migrators, and species that reside in the surface ocean. The model was parameterized for 40°S to 40°N in the world ocean such that results can be compared with recent estimates of mesopelagic fish biomass in this latitudinal range, based on field studies using acoustic technologies, of ∼13 Gt (wet weight). Mesopelagic fish production was predicted to be 0.32% of PP which, assuming fish longevity of 1.5 years, gives rise to predicted mesopelagic fish biomass of 2.4 Gt. Model ensembles were run to analyse the uncertainty of this estimate, with results showing predicted biomass >10 Gt in only 8% of the simulations. The work emphasizes the importance of migrating animals in transferring carbon from the surface ocean to the mesopelagic zone. It also highlights how little is known about the physiological ecology of mesopelagic fish, trophic pathways within the mesopelagic food web, and how these link to PP in the surface ocean. A deeper understanding of these interacting factors is required before the potential for utilizing mesopelagic fish as a harvestable resource can be robustly assessed

Links between surface productivity and deep ocean particle flux at the Porcupine Abyssal Plain sustained observatory

In this study we present hydrography, biogeochemistry and sediment trap observations between 2003 and 2012 at Porcupine Abyssal Plain (PAP) sustained observatory in the Northeast Atlantic. The time series is valuable as it allows for investigation of the link between surface productivity and deep ocean carbon flux. The region is a perennial sink for CO2, with an average uptake of around 1.5 mmol m?2 day?1. The average monthly drawdowns of inorganic carbon and nitrogen were used to quantify the net community production (NCP) and new production. Seasonal NCP and new production were found to be 4.57 ± 0.85 mol C m?2 and 0.37 ± 0.14 mol N m?2, respectively. The C : N ratio was high (12) compared to the Redfield ratio (6.6), and the production calculated from carbon was higher than production calculated from nitrogen, which is indicative of carbon overconsumption. The export ratio and transfer efficiency were 16 and 4 %, respectively, and the site thereby showed high flux attenuation. Particle tracking was used to examine the source region of material in the sediment trap, and there was large variation in source regions, both between and within years. There were higher correlations between surface productivity and export flux when using the particle-tracking approach, than by comparing with the mean productivity in a 100 km box around the PAP site. However, the differences in correlation coefficients were not significant, and a longer time series is needed to draw conclusions on applying particle tracking in sediment trap analyses

Links between deep-sea respiration and community dynamics

It has been challenging to establish the mechanisms that link ecosystem functioning to environmental and resource variation, as well as community structure, composition and compensatory dynamics. A compelling hypothesis of compensatory dynamics, known as 'zero-sum' dynamics, is framed in terms of energy resource and demand units, where there is an inverse link between the number of individuals in a community and the mean individual metabolic rate. However, body-size energy distributions that are non-uniform suggest a niche advantage at a particular size class, which suggests a limit to which metabolism can explain community structuring. Since 1989, the composition and structure of abyssal seafloor communities in the northeast Pacific and northeast Atlantic have varied inter-annually with links to climate and resource variation. Here, for the first time, class and mass-specific individual respiration rates were examined along with resource supply and time series of density and biomass data of the dominant abyssal megafauna, echinoderms. Both sites had inverse relationships between density and mean individual metabolic rate. We found fourfold variation in echinoderm respiration over inter-annual timescales at both sites, which were linked to shifts in species composition and structure. In the north-eastern Pacific, the respiration of mobile surface deposit feeding echinoderms was positively linked to climate-driven particulate organic carbon fluxes with a temporal lag of about one year, respiring about 1-6% of the annual particulate organic carbon flux

Vertical imbalance in organic carbon budgets is indicative of a missing vertical transfer during a phytoplankton bloom near South Georgia (COMICS)

The biological carbon pump, driven principally by surface production and sinking of organic matter to deep water and its subsequent remineralization to CO2 maintains atmospheric CO2 around 200 ppm lower than it would be if the ocean were abiotic. One important driver of the magnitude of this effect is the depth to which organic matter sinks before it is remineralised, a parameter we have limited confidence in measuring given the difficulty involved in balancing sources and sinks in the ocean's interior. This imbalance is due, in part, to our inability to measure respiration directly and our reliance on radiotracer-based proxies. One solution to these problems might be a temporal offset in which organic carbon accumulates in the mesopelagic zone (100–1000 m depth) early in the productive season prior to it being consumed later, a situation which could lead to a net apparent sink occurring if a steady state assumption is applied as is often the approach. In this work, we develop a novel accounting method to address this issue, independent of respiration measurements, by estimating fluxes into and accumulation within distinct vertical layers in the mesopelagic. We apply this approach to a time series of measurements of particle sinking velocities and interior organic carbon concentrations made during the declining phase of a large diatom bloom in a low-circulation region of the Southern Ocean downstream of South Georgia. Our data show that the major export event led to a significant accumulation of organic matter in the upper mesopelagic (100–200 m depth) which declined over several weeks, implying that temporal offsets need to be considered when compiling budgets. However, even when accounting for this accumulation, a mismatch in the vertically resolved organic carbon budget remained, implying that there are likely widespread processes that we do not yet understand that redistribute material vertically in the mesopelagic