Benthic biomass size spectra in shelf and deep-sea sediments

The biomass distributions of marine benthic metazoans (meio- to macro-fauna, 1 ?g–32 mg wet weight) across three contrasting sites were investigated to test the hypothesis that allometry can consistently explain observed trends in biomass spectra. Biomass (and abundance) size spectra were determined from observations made at the Faroe–Shetland Channel (FSC) in the Northeast Atlantic (water depth 1600 m), the Fladen Ground (FG) in the North Sea (150 m), and the hypoxic Oman Margin (OM) in the Arabian Sea (500 m). Observed biomass increased with body size as a power law at FG (scaling exponent, b = 0.16) and FSC (b = 0.32), but less convincingly at OM (b = 0.12 but not significantly different from 0). A simple model was constructed to represent the same 16 metazoan size classes used for the observed spectra, all reliant on a common detrital food pool, and allowing the three key processes of ingestion, respiration and mortality to scale with body size. A micro-genetic algorithm was used to fit the model to observations at the sites. The model accurately reproduces the observed scaling without needing to include the effects of local influences such as hypoxia. Our results suggest that the size-scaling of mortality and ingestion are dominant factors determining the distribution of biomass across the meio- to macrofaunal size range in contrasting marine sediment communities. Both the observations and the model results are broadly in agreement with the "metabolic theory of ecology" in predicting a quarter power scaling of biomass across geometric body size classes

Report of the SNOMS Project 2006 to 2012, SNOMS SWIRE NOCS Ocean Monitoring System. Part 1: Narrative description

The ocean plays a major role in controlling the concentration of carbon dioxide (CO2) in the atmosphere. Increasing concentrations of CO2 in the atmosphere are a threat to the stability of the earth’s climate. A better understanding of the controlling role of the ocean will improve predictions of likely future changes in climate and the impact of the uptake of CO2 itself on marine eco-systems caused by the associated acidification of the ocean waters. The SNOMS Project (SWIRE NOCS Ocean Monitoring System) is a ground breaking joint research project supported by the Swire Group Trust, the Swire Educational Trust, the China Navigation Company (CNCo) and the Natural Environment Research Council. It collects high quality data on concentrations of CO2 in the surface layer of the ocean. It contributes to the international effort to better quantify (and understand the driving processes controlling) the exchanges of CO2 between the ocean and the atmosphere. In 2006 and 2007 a system that could be used on a commercial ship to provide data over periods of several months with only limited maintenance by the ships crew was designed and assembled by NOCS. The system was fitted to the CNCo ship the MV Pacific Celebes in May 2007. The onboard system was supported by web pages that monitored the progress of the ship and the functioning of the data collection system. To support the flow of data from the ship to the archiving of the data at the Carbon Dioxide Information Analysis Center (CDIAC in the USA) data processing procedures were developed for the quality control and systematic handling of the data. Data from samples of seawater collected by the ships crew and analysed in NOC (730 samples) have been used to confirm the consistency of the data from the automated measurement system on the ship. To examine the data collected between 2007 and 2012 the movements of the ship are divided into 16 voyages. Initially The Celebes traded on a route circum-navigating the globe via the Panama and Suez Canals. In 2009 the route shifted to one between Australia and New Zealand to USA and Canada. Analysis of the data is an on going process. It has demonstrated that the system produces reliable data. Data are capable of improving existing estimates of seasonal variability. The work has improved knowledge of gas exchange processes. Data from the crew-collected-samples are helping improve our ability to estimate alkalinity in different areas. This helps with the study of ocean acidification. Data from the 9 round trips in the Pacific are currently being examined along with data made available by the NOAA-PMEL laboratory forming time series from 2004 to 2012. The data from the Pacific route are of considerable interest. One reason is that the data monitors variations in the fluxes of CO2 associated with the current that flows westwards along the equator. This is one of the major natural sources of CO2 from the ocean into the atmosphere

Seasonal and inter-annual variability in nutrient supply in relation to mixing in the Bay of Biscay

Post-print

Nitrogen fixation in the western English Channel (NE Atlantic Ocean)

In temperate Atlantic waters (18.8 to 20.1°C), biological nitrogen fixation has beendemonstrated by 2 independent measurements: 15N-N2 incorporation and nifH identification in theDNA and expressed messenger RNA (mRNA). At 2 stations in the western English Channel, bulkwaters were incubated with 15N-N2. At the high levels of particulate nitrogen (?11.5 ?mol N l–1),absolute fixation rates of 18.9 ± 0.01 and 20.0 nmol N l–1d–1 were determined. While a caveat mustaccompany the magnitude of the rates presented due to the limited number of data, the presence andactivity of diazotrophic organisms in these waters is of ecological significance and may affect currentattitudes to nitrogen and carbon budgets. In particular, our estimate of the rate of N fixation(0.35 mmol N m–2 d–1) is comparable to that of denitrification rates in UK shelf seas. Molecular analysisidentified a diversity of expressed nifH genes, and 21 different prokaryotic nifH transcripts wereidentified

Modelling sedimentary biogeochemical processes in a high nitrate, UK estuary (the Gt. Ouse) with emphasis on the nitrogen cycle

The description, calibration and application of a reaction-diffusion model of early diagenesis is presented. Unlike previous models it has been developed for a temperate latitude estuary (upper and lower Gt. Ouse, UK) impacted by high nitrate concentrations (annual mean 700 mM). Five variables, O2, NO-3, NH4+, SO4= and S=, are modelled from the steady state distributions of bulk total organic carbon (TOC). Different representations of the first order rate constant, k, for TOC mineralisation are tested. Use of separate k values for individual mineralisation pathways is the only way to reproduce the data but at the cost of 1) increasing the degrees of freedom in the model and 2) conceptual simplicity. This casts doubt over the universal applicability of diagenetic models in high NO3- environments. Underestimation of the observed ammonium fluxes leads to the inclusion of dissimilatory nitrate reduction to ammonium (DNRA) into a diagenetic model for the first time. Use of an empirical temperature function successfully simulates rates of denitrification and DNRA. It is concluded that temperature is an important control in partitioning nitrate reduction into DNRA and denitrification in the Gt. Ouse sediments. This temperature effects implies that during an extended warm summer in temperature estuaries receiving high nitrate inputs, nitrate reduction may contribute to, rather than counteract a eutrophication event. A literature review showing that DNRA can account for up to 100% of the nitrate reduction in different locations around the world, means that diagenetic models of the nitrogen cycle in coastal areas should include DNRA. A parameter sensitivity analysis (PSA) reveals a highly non linear model response to parameter changes of ±50%. The variability in model response among the sites in the Gt. Ouse highlights the importance of accounting for differences in 1) the relative contributions of oxic, suboxic and anoxic mineralization to total organic carbon mineralization; 2) rates of oxygen consumption and 3) oxygen penetration depths.</p

Modelling sedimentary biogeochemical processes in a high nitrate, UK estuary (the Gt. Ouse) with emphasis on the nitrogen cycle

The description, calibration and application of a reaction-diffusion model of early diagenesis is presented. Unlike previous models it has been developed for a temperate latitude estuary (upper and lower Gt. Ouse, UK) impacted by high nitrate concentrations (annual mean 700 mM). Five variables, O2, NO-3, NH4+, SO4= and S=, are modelled from the steady state distributions of bulk total organic carbon (TOC). Different representations of the first order rate constant, k, for TOC mineralisation are tested. Use of separate k values for individual mineralisation pathways is the only way to reproduce the data but at the cost of 1) increasing the degrees of freedom in the model and 2) conceptual simplicity. This casts doubt over the universal applicability of diagenetic models in high NO3- environments. Underestimation of the observed ammonium fluxes leads to the inclusion of dissimilatory nitrate reduction to ammonium (DNRA) into a diagenetic model for the first time. Use of an empirical temperature function successfully simulates rates of denitrification and DNRA. It is concluded that temperature is an important control in partitioning nitrate reduction into DNRA and denitrification in the Gt. Ouse sediments. This temperature effects implies that during an extended warm summer in temperature estuaries receiving high nitrate inputs, nitrate reduction may contribute to, rather than counteract a eutrophication event. A literature review showing that DNRA can account for up to 100% of the nitrate reduction in different locations around the world, means that diagenetic models of the nitrogen cycle in coastal areas should include DNRA. A parameter sensitivity analysis (PSA) reveals a highly non linear model response to parameter changes of ±50%. The variability in model response among the sites in the Gt. Ouse highlights the importance of accounting for differences in 1) the relative contributions of oxic, suboxic and anoxic mineralization to total organic carbon mineralization; 2) rates of oxygen consumption and 3) oxygen penetration depths.</p

Report of the SNOMS Project 2006 to 2012, SNOMS SWIRE NOCS Ocean Monitoring System. Part 1: Narrative description

The ocean plays a major role in controlling the concentration of carbon dioxide (CO2) in the atmosphere. Increasing concentrations of CO2 in the atmosphere are a threat to the stability of the earth’s climate. A better understanding of the controlling role of the ocean will improve predictions of likely future changes in climate and the impact of the uptake of CO2 itself on marine eco-systems caused by the associated acidification of the ocean waters. The SNOMS Project (SWIRE NOCS Ocean Monitoring System) is a ground breaking joint research project supported by the Swire Group Trust, the Swire Educational Trust, the China Navigation Company (CNCo) and the Natural Environment Research Council. It collects high quality data on concentrations of CO2 in the surface layer of the ocean. It contributes to the international effort to better quantify (and understand the driving processes controlling) the exchanges of CO2 between the ocean and the atmosphere. In 2006 and 2007 a system that could be used on a commercial ship to provide data over periods of several months with only limited maintenance by the ships crew was designed and assembled by NOCS. The system was fitted to the CNCo ship the MV Pacific Celebes in May 2007. The onboard system was supported by web pages that monitored the progress of the ship and the functioning of the data collection system. To support the flow of data from the ship to the archiving of the data at the Carbon Dioxide Information Analysis Center (CDIAC in the USA) data processing procedures were developed for the quality control and systematic handling of the data. Data from samples of seawater collected by the ships crew and analysed in NOC (730 samples) have been used to confirm the consistency of the data from the automated measurement system on the ship. To examine the data collected between 2007 and 2012 the movements of the ship are divided into 16 voyages. Initially The Celebes traded on a route circum-navigating the globe via the Panama and Suez Canals. In 2009 the route shifted to one between Australia and New Zealand to USA and Canada. Analysis of the data is an on going process. It has demonstrated that the system produces reliable data. Data are capable of improving existing estimates of seasonal variability. The work has improved knowledge of gas exchange processes. Data from the crew-collected-samples are helping improve our ability to estimate alkalinity in different areas. This helps with the study of ocean acidification. Data from the 9 round trips in the Pacific are currently being examined along with data made available by the NOAA-PMEL laboratory forming time series from 2004 to 2012. The data from the Pacific route are of considerable interest. One reason is that the data monitors variations in the fluxes of CO2 associated with the current that flows westwards along the equator. This is one of the major natural sources of CO2 from the ocean into the atmosphere

Control of the diffusive boundary layer on benthic fluxes: a model study

A simple, steady state, reaction-diffusion diagenesis model is used to quantify the possible error associated with benthic flux measurements which neglect the presence of the diffusive boundary layer (DBL). Model application is restricted to non-bioturbated, fine-grained sediments in which oxygen consumption is dominated (~65% of the consumption budget) by organic carbon degradation, oxygen penetration depths are low (<0.5 cm) and solute exchange across the sediment-water interface (SWI) is diffusive. The effect of different thicknesses of the DBL is tested on sediments with different organic carbon reactivities (k = 1, 5, 10, 20, 40 yr–1). When imposing the range of DBL thicknesses observed in nature (0.01 to 0.1 cm) on the model, the model simulates lower oxygen fluxes (by up to 22% for k = 40 yr–1) across the SWI compared to fluxes simulated in the absence of a DBL. Greater reactivity increases the impact of the DBL by lowering the oxygen penetration depth. Changes in the DBL directly influence oxygen fluxes and aerobic mineralisation by changing the diffusion path length to a relatively thin oxic sediment layer. The changes in anaerobic processes are small (<8% for denitrification and <3% for sulphate reduction) and, together with the associated solute fluxes (nitrate, sulphate, ammonium) across the SWI, occur in response to changes in porewater oxygen concentrations induced by the DBL, rather than by direct interactions with the DBL. Changes included a 380% increase in nitrate influxes and a 90% reduction in nitrate effluxes. Rates of nitrification decreased by up to 18%. Thicker DBLs also decreased the organic carbon degradation rate by a maximum of 22%, implicating the DBL as a factor in organic carbon preservation for highly reactive sediments. Measurements of near-bed currents in a macro-tidal estuary (Southampton Water, UK) suggest that the observed range in DBL thicknesses can exist for up to 31% of the time (sampling period: 3 to 4 mo). The presence of these DBL thicknesses in such a dynamic environment, makes it is reasonable to assume that the establishment of the DBL may be widespread. Consequently, it is only reasonable to neglect the DBL over sediments in which aerobic mineralisation is dominant, when organic reactivity is low