A critical examination of the role of marine snow and zooplankton faecal pellets in removing ocean surface microplastic

Numerical simulations and emissions estimates of plastic in and to the ocean consistently over-predict the surface inventory, particularly in the case of microplastic (MP), i.e. fragments less than 5 mm in length. Sequestration in the sediments has been both predicted and, to a limited extent, observed. It has been hypothesized that biology may be exporting a significant fraction of surface MP by way of marine snow aggregation and zooplankton faecal pellets. We apply previously published data on MP concentrations in the surface ocean to an earth system model of intermediate complexity to produce a first estimate of the potential global sequestration of MP by marine aggregates, including faecal pellets. We find a MP seafloor export potential of between 7.3E3-4.2E5 metric tons per year, or about 0.06-8.8% of estimated total annual plastic ocean pollution rates. We find that presently, aggregates alone would have the potential to remove most existing surface ocean MP to the seafloor within less than 2 years if pollution ceases. However, the observed accumulation of MP in the surface ocean, despite this high potential rate of removal, suggests that detrital export is an ineffective pathway for permanent MP removal. We theorize a prominent role of MP biological fouling and de-fouling in the rapid recycling of aggregate-associated MP in the upper ocean. We also present an estimate of how the potential detrital MP sink might change into the future, as climate change (and projected increasing MP pollution) alters the marine habitat. The polar regions, and the Arctic in particular, are projected to experience increasing removal rates as export production increases faster than MP pollution. Northern hemisphere subtropical gyres are projected to experience slowing removal rates as stratification and warming decrease export production, and MP pollution increases. However, significant uncertainty accompanies these results

The global biological microplastic particle sink

Every year, about four percent of the plastic waste generated worldwide ends up in the ocean. What happens to the plastic there is poorly understood, though a growing body of evidence suggests it is rapidly spreading throughout the global ocean. The mechanisms of this spread are straightforward for buoyant larger plastics that can be accurately modelled using Lagrangian particle models. But the fate of the smallest size fractions (the microplastics) are less straightforward, in part because they can aggregate in sinking marine snow and faecal pellets. This biologically-mediated pathway is suspected to be a primary surface microplastic removal mechanism, but exactly how it might work in the real ocean is unknown. We search the parameter space of a new microplastic model embedded in an earth system model to show that biological uptake can significantly shape global microplastic inventory and distributions and even account for the budgetary “missing” fraction of surface microplastic, despite being an inefficient removal mechanism. While a lack of observational data hampers our ability to choose a set of “best” model parameters, our effort represents a first tool for quantitatively assessing hypotheses for microplastic interaction with ocean biology at the global scale

Zooplankton grazing of microplastic can accelerate global loss of ocean oxygen

Global warming has driven a loss of dissolved oxygen in the ocean in recent decades. We demonstrate the potential for an additional anthropogenic driver of deoxygenation, in which zooplankton consumption of microplastic reduces the grazing on primary producers. In regions where primary production is not limited by macronutrient availability, the reduction of grazing pressure on primary producers causes export production to increase. Consequently, organic particle remineralisation in these regions increases. Employing a comprehensive Earth system model of intermediate complexity, we estimate this additional remineralisation could decrease water column oxygen inventory by as much as 10% in the North Pacific and accelerate global oxygen inventory loss by an extra 0.2–0.5% relative to 1960 values by the year 2020. Although significant uncertainty accompanies these estimates, the potential for physical pollution to have a globally significant biogeochemical signal that exacerbates the consequences of climate warming is a novel feedback not yet considered in climate research

Study of analysis methods to monitor sporulation during fermentation of Bacillus subtilis to produce endospores

Bacterial endospores, mainly of Bacillus subtilis, B. atrophaeus or Geobacillus stearothermophilus, are used as biological indicator for the validation of sterilization processes in various industrial processes and applications. Commonly used spores for sterilization studies are spores of B. subtilis, due to their high degree of resistance to chemical and physical treatments, reproducible inactivation response, and ease of use. To prevent falsified results in the validation of sterilization processes, theses spores must have high and comparable D-values as well as a homogeneous distribution of the resistance within every charge. The main influence on the resistance properties is the fermentation process, which lead to the necessity of well-defined methods and analytics of the spore formation for the production process. To produce suspensions containing homogeneously equipped spores, a reproducible fed batch fermentation strategy with optimized concentrations of media components has been developed (VLB; data not yet published). To increase spore resistance, different influence factors such as fermentation time, temperature and composition of sporulation media were investigated. A systematic screening of fermentation capabilities towards optimal spore formation, production and efficiency was performed. A collection of commonly used sterilization-recommended B. subtilis strains was evaluated by applying a set of different molecular biological techniques and classical microbiological assays. Quantitative real time PCR was used to study transcriptomic changes during the sporulation; here major sporulation events (e.g., sigma factors; from Stuelke, Joerg, SubtiWiki) were studied. MALDI-TOF-TOF analyses were conducted to follow changes in the protein spectra (Momo et al, 2013) from during initiation of sporulation until maturation of the dormant spore. The EloTrace® System (Junne et al, 2010) allowed us to characterize the morphological and physiological of the transition of the sporulating cultures using an electro-optical approach. Established and reproducible methods for measuring spore resistance were used to determine batch-specific resistance properties to selected sterilization methods (hydrogen peroxide or UV-C radiation treatments; Raguse et al, 2016)

Seawater carbonate chemistry and mass fluxes and elemental composition of particulate export in KOSMOS mesocosm experiments (2010-2014)

Diatoms account for up to 40% of marine primary production and require silicic acid to grow and build their opal shell. On the physiological and ecological level, diatoms are thought to be resistant to, or even benefit from, ocean acidification. Yet, global-scale responses and implications for biogeochemical cycles in the future ocean remain largely unknown. Here we conducted five in situ mesocosm experiments with natural plankton communities in different biomes and find that ocean acidification increases the elemental ratio of silicon (Si) to nitrogen (N) of sinking biogenic matter by 17 ± 6 per cent under pCO2 conditions projected for the year 2100. This shift in Si:N seems to be caused by slower chemical dissolution of silica at decreasing seawater pH. We test this finding with global sediment trap data, which confirm a widespread influence of pH on Si:N in the oceanic water column. Earth system model simulations show that a future pH-driven decrease in silica dissolution of sinking material reduces the availability of silicic acid in the surface ocean, triggering a global decline of diatoms by 13–26 per cent due to ocean acidification by the year 2200. This outcome contrasts sharply with the conclusions of previous experimental studies, thereby illustrating how our current understanding of biological impacts of ocean change can be considerably altered at the global scale through unexpected feedback mechanisms in the Earth system

Enhanced silica export in a future ocean triggers global diatom decline

Diatoms account for up to 40% of marine primary production(1,2) and require silicic acid to grow and build their opal shell(3). On the physiological and ecological level, diatoms are thought to be resistant to, or even benefit from, ocean acidification(4-6). Yet, global-scale responses and implications for biogeochemical cycles in the future ocean remain largely unknown. Here we conducted five in situ mesocosm experiments with natural plankton communities in different biomes and find that ocean acidification increases the elemental ratio of silicon (Si) to nitrogen (N) of sinking biogenic matter by 17 +/- 6 per cent under p(CO2) conditions projected for the year 2100. This shift in Si:N seems to be caused by slower chemical dissolution of silica at decreasing seawater pH. We test this finding with global sediment trap data, which confirm a widespread influence of pH on Si:N in the oceanic water column. Earth system model simulations show that a future pH-driven decrease in silica dissolution of sinking material reduces the availability of silicic acid in the surface ocean, triggering a global decline of diatoms by 13-26 per cent due to ocean acidification by the year 2200. This outcome contrasts sharply with the conclusions of previous experimental studies, thereby illustrating how our current understanding of biological impacts of ocean change can be considerably altered at the global scale through unexpected feedback mechanisms in the Earth system

Simulating the carbon cycle in a high latitude shelf sea (North Sea) — evidence for decoupled carbon and nutrient cycles

For the first time, the carbon budget of the North Sea, a Northwest European shelf sea, has been assessed using a three–dimensional coupled biogeochemical model resolving the carbon cycle. Simulations for the years 2001/2002 are thoroughly validated against high resolution field data sets from the same period. The results indicate that the North Sea acts as a significant sink for atmospheric CO2. The uptake of CO2 is balanced by an export of carbon into the deep waters of the North Atlantic, confirming observations suggesting the efficient removal of CO2 from the atmosphere via the continental shelf pump mechanism. The simulated net community production (NCP) and net primary production (NPP) reveal the biological controls of this transport: despite the higher NPP in the southern North Sea, NCP, i.e. net carbon fixation, and the NCP/NPP ratio are small because of high remineralization of organic matter in the continuously mixed water column. In contrast, in the surface layers of the northern North Sea, NCP, net carbon fixation and the NCP/NPP ratio are high because of the high export of organic matter into the deeper layer of the seasonally stratified system, preventing organic matter remineralization in the surface layer. The implementation of overflow production releasing semi–labile dissolved organic carbon under nutrient limited conditions enables the model to reproduce the observed pCO2 and DIC drawdown during summer. This decoupling of carbon fixation from the control of nutrient uptake via a fixed C/N ratio is essential for a realistic simulation of the magnitude of the air–sea flux of CO2, and thus the carbon cycle of the North Sea