High concentrations of plastic hidden beneath the surface of the Atlantic Ocean

Concern over plastic pollution of the marine environment is severe. The mass-imbalance between the plastic litter supplied to and observed in the ocean currently suggests a missing sink. However, here we show that the ocean interior conceals high loads of small-sized plastic debris which can balance and even exceed the estimated plastic inputs into the ocean since 1950. The combined mass of just the three most-littered plastics (polyethylene, polypropylene, and polystyrene) of 32–651 µm size-class suspended in the top 200 m of the Atlantic Ocean is 11.6–21.1 Million Tonnes. Considering that plastics of other sizes and polymer types will be found in the deeper ocean and in the sediments, our results indicate that both inputs and stocks of ocean plastics are much higher than determined previously. It is thus critical to assess these terms across all size categories and polymer groups to determine the fate and danger of plastic contamination

Observing climate change trends in ocean biogeochemistry: when and where

Understanding the influence of anthropogenic forcing on the marine biosphere is a high priority. Climate change-driven trends need to be accurately assessed and detected in a timely manner. As part of the effort towards detection of long-term trends, a network of ocean observatories and time series stations provide high quality data for a number of key parameters, such as pH, oxygen concentration or primary production (PP). Here, we use an ensemble of global coupled climate models to assess the temporal and spatial scales over which observations of eight biogeochemically relevant variables must be made to robustly detect a long-term trend. We find that, as a global average, continuous time series are required for between 14 (pH) and 32 (PP) years to distinguish a climate change trend from natural variability. Regional differences are extensive, with low latitudes and the Arctic generally needing shorter time series (<~30 years) to detect trends than other areas. In addition, we quantify the ‘footprint’ of existing and planned time series stations, that is the area over which a station is representative of a broader region. Footprints are generally largest for pH and sea surface temperature, but nevertheless the existing network of observatories only represents 9–15% of the global ocean surface. Our results present a quantitative framework for assessing the adequacy of current and future ocean observing networks for detection and monitoring of climate change-driven responses in the marine ecosystem

Downward particle flux in the open ocean: future global opportunities and insights from time-series measurements at the pap sustained observatory in the northeast atlantic

The Joint Global Ocean Flux Study (JGOFS) started in 1987 and stimulated massive integration of efforts to measure and understand the processes of downward flux in the ocean. A small number of sustained observatories have persisted from this time in the belief that a key to gaining this understanding is by prolonged time-series observations. The sustained observatory over the Porcupine Abyssal Plain (PAP-SO) in the Northeast Atlantic is one such site which has provided nearly continuous measurements of downward flux at a depth of 3000m since 1989. This was using sediment traps but, in order to understand the data, we have exploited a wide range of other approaches such as optical methods, drifting sediment traps in the upper 1000m, chemical variables near the surface and computational modelling. Insights are also gained from the Continuous Plankton Recorder (CPR), satellite observations and various climatic indices. This presentation draws together these measurements to quantify and understand flux at 3000m. Seasonal and interannual variability is large but after 30 years of observation, explanations are now possible. In addition, some of the conclusions identify major and surprising features about the ways ecosystems in one year may be influenced by their structure and function in previous years. At the same time as these time-series observations have been in progress, major new developments have taken place globally and at PAP-SO to provide additional and alternative means to asses flux. The sediment trap has significant advantages as well as uncertainties which have been described previously. The new era of approaches using, for instance, BGC Argo, the Carbon Flux Explorer and a variety of other optical techniques offer what may be a quantum leap in our understanding of downward particle flux now and how it is changing in response to changes in the global climate. This presentation will give a personal and optimistic view of the opportunities which are now developing to quantify and understand this crucially important process

Can neap-spring tidal cycles modulate biogeochemical fluxes in the abyssal near-seafloor water column?

Before particulate matter that settles as ‘primary flux’ from the interior ocean is deposited into deep-sea sediments it has to traverse the benthic boundary layer (BBL) that is likely to cover almost all parts of the seafloor in the deep seas. Fluid dynamics in the BBL differ vastly from fluid dynamics in the overlying water column and, consequently, have the potential to lead to quantitative and compositional changes between primary and depositional fluxes. Despite this potential and the likely global relevance very little is known about mechanistic and quantitative aspects of the controlling processes. Here, results are presented for a sediment-trap time-series study that was conducted on the Porcupine Abyssal Plain in the abyssal Northeast Atlantic, with traps deployed at 2, 40 and 569 m above bottom (mab). The two bottommost traps were situated within the BBL-affected part of the water column. The time series captured 3 neap and 4 spring tides and the arrival of fresh settling material originating from a surface-ocean bloom. In the trap-collected material, total particulate matter (TPM), particulate inorganic carbon (PIC), biogenic silica (BSi), particulate organic carbon (POC), particulate nitrogen (PN), total hydrolysable amino acids (AA), hexosamines (HA) and lithogenic material (LM) were determined. The biogeochemical results are presented within the context of time series of measured currents (at 15 mab) and turbidity (at 1 mab). The main outcome is evidence for an effect of neap/spring tidal oscillations on particulate-matter dynamics in BBL-affected waters in the deep sea. Based on the frequency-decomposed current measurements and numerical modelling of BBL fluid dynamics, it is concluded that the neap/spring tidal oscillations of particulate-matter dynamics are less likely due to temporally varying total free-stream current speeds and more likely due to temporally and vertically varying turbulence intensities that result from the temporally varying interplay of different rotational flow components (residual, tidal, near-inertial) within the BBL. Using information from previously published empirical and theoretical relations between fluid and biogeochemical dynamics at the scale of individual particle aggregates, a conceptual and semi-quantitative picture of a mechanism was derived that explains how the neap/spring fluid-dynamic oscillations may translate through particle dynamics into neap/spring oscillations of biogeochemical aggregate decomposition (microbially driven organic-matter breakdown, biomineral dissolution). It is predicted that, during transitions from neap into spring tides, increased aggregation in near-seafloor waters and/or reduced deposition of aggregates at the seafloor coincides with reduced biogeochemical particulate-matter decomposition in near-seafloor waters. By contrast, during transitions from spring into neap tides, enhanced biogeochemical particulate-matter decomposition in near-seafloor waters is predicted to coincide with increased deposition of particulate matter at the seafloor. This study suggests that, in addition to current speed, the specifics and subtleties of the interplay of different rotational flow components can be an important control on how the primary flux from the interior ocean is translated into the depositional flux, with potential implications for sedimentary carbon deposition, benthic food supply and possibly even the sedimentary records of environmental change

AtlantOS Deliverable 3.8: OceanSITES Networking Report

During the course of AtlantOS, our ability to provide biogeochemical (BGC) time series and Eulerian data which is of sufficient quality and quantity to approach basin-scale capacity has improved in a major way in some areas but has declined or not progressed in others. Indeed, the increased coordination achieved through AtlantOS has both increased our capacity to collectively further a basin-scale operation, and revealed new challenges in implementation. These outcomes are synthesised in this report to improve future planning for Eulerian capacities in BGC observation. Areas of significant progress 1. Development of capacity for emerging BGC variables 2. Establishment of a system for developing “Best practice” recording. 3. Transatlantic MOU with Canada 4. Data management and dissemination The ways to address the areas in which progress has not been made are conceptually simple but practically demanding. In all cases this needs to be carried out at the global scale and therefore under the auspices of OceanSITES. A coherent system which can provide data of sufficient quality and quantity to address societal needs cannot be achieved in isolation by any one Nation state or by Europe and must not be restricted by discipline. It will become self-evident that such an integrated approach will lead to a system which performs at a much higher level than the sum of its component parts. With continuous pressure from the European Commission, further and additional support from member states, continuing political and scientific dialogue with South Atlantic countries and strong management encouragement at all levels, the establishment of an effective eulerian observatory network is anticipated within the coming decade

Are all sediment traps created equal? An intercomparison study of carbon export methodologies at the PAP-SO site

Sinking particulate flux out of the upper ocean is a key observation of the ocean’s biological carbon cycle. Particle flux in the upper mesopelagic is often determined using sediment traps but there is no absolute standard for the measurement. Prior to this study, differing neutrally-buoyant sediment trap designs have not been deployed simultaneously, which precludes meaningful comparisons between flux data collected using these designs. The aim of the study was to compare a suite of modern methods for measuring sinking carbon flux out of the surface ocean. This study compared samples from two neutrally buoyant drifting sediment trap designs, and a surface tethered drifting sediment trap, which collected sinking particles alongside other methods for sampling particle properties, including in situ pumps and 234Th radionuclide measurements. Samples were collected at the Porcupine Abyssal Plain Sustained Observatory (PAP-SO) site in the Northeast Atlantic Ocean (49°N, 16.5°W). Neutrally-buoyant conical traps appeared to collect lower absolute fluxes than neutrally-buoyant, or surface-tethered cylindrical traps, but compositional ratios of sinking particles indicated collection of similar material when comparing the conical and cylindrical traps. In situ pump POC:234Th ratios generally agreed with trap ratios but conical trap samples were somewhat depleted in 234Th, which along with sinking particle size distribution data determined from gel traps, may imply under-sampling of small particles. Cylindrical trap POC fluxes were of similar magnitude to 234Th-derived POC fluxes while conical POC fluxes were lower. Further comparisons are needed to distinguish if differences in particle flux magnitude are due to conical versus cylindrical trap designs. Parallel analytical determinations, conducted by different laboratories, of replicate samples for elemental fluxes and gel trap particle size distributions were comparable. This study highlights that the magnitude of particle fluxes and size spectra may be more sensitive than the chemical composition of particle fluxes to the instrumentation used. Only two deployments were possible during this study so caution should be taken when applying these findings to other regions and export regimes. We recommend that multiple methodologies to measure carbon export should be employed in field studies, to better account for each method’s merits and uncertainties. These discrepancies need further study to allow carbon export fluxes to be compared with confidence across laboratory, region and time and to achieve an improved global understanding of processes driving and controlling carbon export

Attenuation of sinking particulate organic carbon flux through the mesopelagic ocean

The biological carbon pump, which transports particulate organic carbon (POC) from the surface to the deep ocean, plays an important role in regulating atmospheric carbon dioxide (CO2) concentrations. We know very little about geographical variability in the remineralization depth of this sinking material and less about what controls such variability. Here we present previously unpublished profiles of mesopelagic POC flux derived from neutrally buoyant sediment traps deployed in the North Atlantic, from which we calculate the remineralization length scale for each site. Combining these results with corresponding data from the North Pacific, we show that the observed variability in attenuation of vertical POC flux can largely be explained by temperature, with shallower remineralization occurring in warmer waters. This is seemingly inconsistent with conclusions drawn from earlier analyses of deep-sea sediment trap and export flux data, which suggest lowest transfer efficiency at high latitudes. However, the two patterns can be reconciled by considering relatively intense remineralization of a labile fraction of material in warm waters, followed by efficient downward transfer of the remaining refractory fraction, while in cold environments, a larger labile fraction undergoes slower remineralization that continues over a longer length scale. Based on the observed relationship, future increases in ocean temperature will likely lead to shallower remineralization of POC and hence reduced storage of CO2 by the ocean

Prokaryotic niche partitioning between suspended and sinking marine particles

Suspended particles are major organic carbon substrates for heterotrophic microorganisms in the mesopelagic ocean (100–1000 m). Nonetheless, communities associated with these particles have been overlooked compared with sinking particles, the latter generally considered as main carbon transporters to the deep ocean. This study is the first to differentiate prokaryotic communities associated with suspended and sinking particles, collected with a marine snow catcher at four environmentally distinct stations in the Scotia Sea. Amplicon sequencing of 16S rRNA gene revealed distinct prokaryotic communities associated with the two particle‐types in the mixed‐layer (0–100 m) and upper‐mesopelagic zone (mean dissimilarity 42.5% ± 15.2%). Although common remineralising taxa were present within both particle‐types, gammaproteobacterial Pseudomonadales and Vibrionales, and alphaproteobacterial Rhodobacterales were found enriched in sinking particles up to 32‐fold, while Flavobacteriales (Bacteroidetes) favoured suspended particles. We propose that this niche‐partitioning may be driven by organic matter properties found within both particle‐types: K‐strategists, specialised in the degradation of complex organic compounds, thrived on semi‐labile suspended particles, while generalists r‐strategists were adapted to the transient labile organic contents of sinking particles. Differences between the two particle‐associated communities were more pronounced in the mesopelagic than in the surface ocean, likely resulting from exchanges between particle‐pools enabled by the stronger turbulence

Molecular-level evidence of early lipid transformations throughout oceanic depths

Our understanding of lipid biogeochemistry of the ocean’s interior is still in its infancy. Here we focus on early lipid transformation and the formation of lipid degradation products in the NE Atlantic Ocean (49.0°N, 16.5°W). We employed high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), a method that allows observation and elemental composition assignment of thousands of lipids in a single sample. Using these data, we infer molecular-level changes that occur during lipid transformation in the oceanic water column to shed new light on early lipid transformation processes and the formation of lipid decomposition intermediates, here termed CHO compounds (i.e., lipid-derived species that contain carbon, hydrogen and oxygen in their molecular formula). We considered the distribution of molecular rings and/or double bonds (DBE), H/C and O/C ratios, molecular diversity based on the number of mass spectral signals for monoisotopic species, and carbon number in CHO molecules. Data are elaborated for the four ocean zones, the epipelagic, mesopelagic, bathypelagic and abyssal. The highest molecular diversity characterizes CHO compounds associated with the epipelagic zone, which is explained by numerous and diverse planktonic communities inhabiting the epipelagic and by the effects of both biotic and abiotic processes on lipid transformation. Lipid transformations include crosslinking (condensation), partial degradation or fragmentation, double bond reduction, oxidation, hydrogenation, dehydrogenation and cyclization. Crosslinking likely results in a unimodal distribution of carbon number of CHO compounds, in contrast to cell lipids (referred to as Reported lipids based on the Lipid Maps Database), which have a bimodal distribution of carbon number. CHO compounds that appear to be formed by fragmentation (decrease of the number of C atoms) and ring/double bond reduction were more stable to further transformation and remained longer in the water column, i.e., these compounds were transferred deeper into the water column. Low unsaturation and fast transport to depth promotes CHO compound preservation in the water column. Dehydrogenation leads to increased unsaturation (average DBE up to 21.3), condensation, and cyclization, resulting in high molecular weight compounds with a high degree of unsaturation. Our data demonstrate that lipids with cyclic structures are more refractory than those with acyclic structures. The formation of aromatic structures is not a significant process during early lipid transformation in the oceanic water column