The origin of sub-surface source waters define the sea-air flux of methane in the Mauritanian Upwelling, NW Africa

Concentrations and flux densities of methane were determined during a lagrangian study of an advective filament in the permanent upwelling region off western Mauritania. Newly upwelled waters were dominated by the presence of North Atlantic Central Water and surface CH4 concentrations of 2.2 ± 0.3 nmol L-1 were largely in equilibrium with atmospheric values, with surface saturations of 101.7 ± 14%. As the upwelling filament aged and was advected offshore, CH4 enriched South Atlantic Central Water from intermediate depths of 100 to 350m was entrained into the surface mixed layer of the filament following intense mixing associated with the shelf break. Surface saturations increased to 198.9 ± 15% and flux densities increased from a mean value over the shelf of 2.0 ± 1.1 µmol m-2d-1 to a maximum of 22.6 µmol m-2d-1. Annual CH4 emissions for this persistent filament were estimated at 0.77 ± 0.64 Gg which equates to a maximum of 0.35% of the global oceanic budget. This raises the known outgassing intensity of this area and highlights the importance of advecting filaments from upwelling waters as efficient vehicles for air-sea exchange

AMT30 Cruise Report

In a break with tradition the 30th AMT cruise, the first since the COVID pandemic hit in 2020, departed Port Stanley on the 20th February 2023 and headed north, arriving in Southampton on 30th March. Onboard were teams from Plymouth Marine Laboratory, the National Oceanography Centre, UK Universities of Exeter, Heriot-Watt, East Anglia, Liverpool and Oxford, the Scottish Association for Marine Science, National Aeronautics and Space Administration, Michigan State University, University of Lisbon, Centre for Scientific Research and Higher Education of Ensenada and the University of Pretoria. Operations onboard included the measurement of core AMT variables in the maintenance of the now 28 year time series; Optical and atmospheric observations in support of NASA and the European Space Agency satellites; Deployment of 14 ARGO floats for the UK MetOffice and the NOC; and the recovery of the NOC - SOG sediment trap mooring in the South Atlantic gyre. AMT’s oceanography training program continued with places occupied by six PhD students from UK, US and South African universities alongside opportunities provided by POGO in the sponsorship of a research fellow from Mexico. The whole of the scientific complement would like to extend their gratitude to Captain Stewart Mackay and his officers and crew who supported our activities throughout with dedication and extreme professionalism. Our thanks are also extended to the team from NMF (Tom Ballinger, Andy Cotmore and Nick Harker) who ensured the delivery of all scientific activities My particular thanks as always to Glen Tarran and Christina Devereux who assisted in ways too numerous to mention here. Now in its 28th year the AMT is a multidisciplinary program which undertakes biological, chemical and physical oceanographic research during an annual voyage throughout the Atlantic Ocean. AMT objectives have evolved to enable the maintenance of a continuous set of observations, whilst addressing global issues that are raised throughout the most recent IPCC assessment and UK environmental strategy. AMT objectives are to: (1) quantify the nature and causes of ecological and biogeochemical variability in planktonic ecosystems; (2) quantify the effects of this variability on nutrient cycling, on biogenic export and on air-sea exchange of climate active gases; (3) construct a multi-decadal, multidisciplinary ocean time-series which is integrated within a wider “Pole-to-pole” observatory concept; (4) provide essential sea-truth validation for current and next generation satellite missions; (5) provide essential data for global ecosystem model development and validation and; (6) provide a valuable, highly sought after training arena for the next generation of UK and International oceanographers

A generalized stoichiometric model of C3, C2, C2+C4, and C4 photosynthetic metabolism.

The goal of suppressing photorespiration in crops to maximize assimilation and yield is stimulating considerable interest among researchers looking to bioengineer carbon-concentrating mechanisms into C3 plants. However, detailed quantification of the biochemical activities in the bundle sheath is lacking. This work presents a general stoichiometric model for C3, C2, C2+C4, and C4 assimilation (SMA) in which energetics, metabolite traffic, and the different decarboxylating enzymes (NAD-dependent malic enzyme, NADP-dependent malic enzyme, or phosphoenolpyruvate carboxykinase) are explicitly included. The SMA can be used to refine experimental data analysis or formulate hypothetical scenarios, and is coded in a freely available Microsoft Excel workbook. The theoretical underpinnings and general model behaviour are analysed with a range of simulations, including (i) an analysis of C3, C2, C2+C4, and C4 in operational conditions; (ii) manipulating photorespiration in a C3 plant; (iii) progressively upregulating a C2 shuttle in C3 photosynthesis; (iv) progressively upregulating a C4 cycle in C2 photosynthesis; and (v) manipulating processes that are hypothesized to respond to transient environmental inputs. Results quantify the functional trade-offs, such as the electron transport needed to meet ATP/NADPH demand, as well as metabolite traffic, inherent to different subtypes. The SMA refines our understanding of the stoichiometry of photosynthesis, which is of paramount importance for basic and applied research

The influence of ocean acidification on nitrogen regeneration and nitrous oxide production in the North-West European shelf sea

The assimilation and regeneration of dissolved inorganic nitrogen, and the concentration of N2O, was investigated at stations located in the NW European shelf sea during June/July 2011. These observational measurements within the photic zone demonstrated the simultaneous regeneration and assimilation of NH4+, NO2− and NO3−. NH4+ was assimilated at 1.82–49.12 nmol N L−1 h−1 and regenerated at 3.46–14.60 nmol N L−1 h−1; NO2− was assimilated at 0–2.08 nmol N L−1 h−1 and regenerated at 0.01–1.85 nmol N L−1 h−1; NO3− was assimilated at 0.67–18.75 nmol N L−1 h−1 and regenerated at 0.05–28.97 nmol N L−1 h−1. Observations implied that these processes were closely coupled at the regional scale and nitrogen recycling played an important role in sustaining phytoplankton growth during the summer. The [N2O], measured in water column profiles, was 10.13 ± 1.11 nmol L−1 and did not strongly diverge from atmospheric equilibrium indicating that sampled marine regions where neither a strong source nor sink of N2O to the atmosphere. Multivariate analysis of data describing water column biogeochemistry and its links to N-cycling activity failed to explain the observed variance in rates of N-regeneration and N-assimilation, possibly due to the limited number of process rate observations. In the surface waters of 5 further stations, Ocean Acidification (OA) bioassay experiments were conducted to investigate the response of NH4+ oxidising and regenerating organisms to simulated OA conditions, including the implications for [N2O]. Multivariate analysis was undertaken which considered the complete bioassay dataset of measured variables describing changes in N-regeneration rate, [N2O] and the biogeochemical composition of seawater. While anticipating biogeochemical differences between locations, we aimed to test the hypothesis that the underlying mechanism through which pelagic N-regeneration responded to simulated OA conditions was independent of location and that a mechanistic understanding of how NH4+ oxidation, NH4+ regeneration and N2O production responded to OA could be developed. Results indicated that N-regeneration process responses to OA treatments were location specific; no mechanistic understanding of how N-regeneration processes respond to OA in the surface ocean of the NW European shelf sea could be developed