Contrasting effects of temperature and winter mixing on the seasonal and inter-annual variability of the carbonate system in the Northeast Atlantic Ocean

Future climate change as a result of increasing atmospheric CO2 concentrations is expected to strongly affect the oceans, with shallower winter mixing and consequent reduction in primary production and oceanic carbon drawdown in low and mid-latitudinal oceanic regions. Here we test this hypothesis by examining the effects of cold and warm winters on the carbonate system in the surface waters of the Northeast Atlantic Ocean for the period between 2005 and 2007. Monthly observations were made between the English Channel and the Bay of Biscay using a ship of opportunity program. During the colder winter of 2005/2006, the maximum depth of the mixed layer reached up to 650 m in the Bay of Biscay, whilst during the warmer (by 2.6 a± 0.5 a°C) winter of 2006/2007 the mixed layer depth reached only 300 m. The inter-annual differences in late winter concentrations of nitrate (2.8 ± 1.1 μmol l−1) and dissolved inorganic carbon (22 a± 6 μmol kg−1, with higher concentrations at the end of the colder winter (2005/2006), led to differences in the dissolved oxygen anomaly and the chlorophyll <i>α</i>-fluorescence data for the subsequent growing season. In contrast to model predictions, the calculated air-sea CO2 fluxes (ranging from +3.7 to ĝ̂'4.8 mmol mĝ̂'2 d−1) showed an increased oceanic CO2 uptake in the Bay of Biscay following the warmer winter of 2006/2007 associated with wind speed and sea surface temperature differences. ©Author(s) 2010. CC Attribution 3.0 License

Temporal variability in the nutrient biogeochemistry of the surface North Atlantic: 15 years of ship of opportunity data

Ocean biological processes play an important role in the global carbon cycle via the production of organic matter and its subsequent export. Often, this flux is assumed to be in steady state; however, it is dependent on nutrients introduced to surface waters via multiple mechanisms, some of which are likely to exhibit both intra‐annual and interannual variability leading to comparable variability in ocean carbon uptake. Here we test this variability using surface (5 m) inorganic nutrient concentrations from voluntary observing ships and satellite‐derived estimates of chlorophyll and net primary production. At lower latitudes, the seasonality is small, and the monthly averages of nitrate:phosphate are lower than the canonical 16:1 Redfield ratio, implying nitrogen limitation, a situation confirmed via a series of nutrient limitation experiments conducted between Bermuda and Puerto Rico. The nutrient seasonal cycle is more pronounced at higher latitudes, with clear interannual variability. Over a large area of the midlatitude North Atlantic, the winters of 2009/2010 and 2010/2011 had nitrate values more than 1μmol L−1 higher than the 2002–2017 average, suggesting that during this period, the system may have shifted to phosphorus limitation. This nitrate increase meant that, in the region between 31° and 39° N, new production calculated from nitrate uptake was 20.5g C m−2 in 2010, more than four times higher than the median value of the whole observing period. Overall, we suggest that substantial variability in nutrient concentrations and biological carbon uptake occurs in the North Atlantic with interannual variability apparent over a number of different time scales

Seasonality and spatial heterogeneity of the surface ocean carbonate system in the northwest European continental shelf

In 2014–5 the UK NERC sponsored an 18 month long Shelf Sea Biogeochemistry research programme which collected over 1500 nutrient and carbonate system samples across the NW European Continental shelf, one of the largest continental shelves on the planet. This involved the cooperation of 10 different Institutes and Universities, using 6 different vessels. Additional carbon dioxide (CO2) data were obtained from the underway systems on three of the research vessels. Here, we present and discuss these data across 9 ecohydrodynamic regions, adapted from those used by the EU Marine Strategy Framework Directive (MSFD). We observed strong seasonal and regional variability in carbonate chemistry around the shelf in relation to nutrient biogeochemistry. Whilst salinity increased (and alkalinity decreased) out from the near-shore coastal waters offshore throughout the year nutrient concentrations varied with season. Spatial and seasonal variations in the ratio of DIC to nitrate concentration were seen that could impact carbon cycling. A decrease in nutrient concentrations and a pronounced under-saturation of surface pCO2 was evident in the spring in most regions, especially in the Celtic Sea. This decrease was less pronounced in Liverpool Bay and to the North of Scotland, where nutrient concentrations remained measurable throughout the year. The near-shore and relatively shallow ecosystems such as the eastern English Channel and southern North Sea were associated with a thermally driven increase in pCO2 to above atmospheric levels in summer and an associated decrease in pH. Non-thermal processes (such as mixing and the remineralisation of organic material) dominated in winter in most regions but especially in the northwest of Scotland and in Liverpool Bay. The large database collected will improve understanding of carbonate chemistry over the North-Western European Shelf in relation to nutrient biogeochemistry, particularly in the context of climate change and ocean acidification

Chemical aspects of ocean acidification monitoring in the ICES marine area

It is estimated that oceans absorb approximately a quarter of the total anthropogenic releases of carbon dioxide to the atmosphere each year. This is leading to acidification of the oceans, which has already been observed through direct measurements. These changes in the ocean carbon system are a cause for concern for the future health of marine ecosystems. A coordinated ocean acidification (OA) monitoring programme is needed that integrates physical, biogeochemical, and biological measurements to concurrently observe the variability and trends in ocean carbon chemistry and evaluate species and ecosystems response to these changes. This report arises from an OSPAR request to ICES for advice on this matter. It considers the approach and tools available to achieve coordinated monitoring of changes in the carbon system in the ICES marine area, i.e. the Northeast Atlantic and Baltic Sea. An objective is to measure long-term changes in pH, carbonate parameters, and saturation states (Ωaragonite and Ωcalcite) in support of assessment of risks to and impacts on marine ecosystems. Painstaking and sensitive methods are necessary to measure changes in the ocean carbonate system over a long period of time (decades) against a background of high natural variability. Information on this variability is detailed in this report. Monitoring needs to start with a research phase, which assesses the scale of short-term variability in different regions. Measurements need to cover a range of waters from estuaries and coastal waters, shelf seas and ocean-mode waters, and abyssal waters where sensitive ecosystems may be present. Emphasis should be placed on key areas at risk, for example high latitudes where ocean acidification will be most rapid, and areas identified as containing ecosystems and habitats that may be vulnerable, e.g. cold-water corals. In nearshore environments, increased production resulting from eutrophication has probably driven larger changes in acidity than CO2 uptake. Although the cause is different, data are equally required from these regions to assess potential ecosystem impact. Analytical methods to support coordinated monitoring are in place. Monitoring of at least two of the four carbonate system parameters (dissolved inorganic carbon (DIC), total alkalinity (TA), pCO2, and pH) alongside other parameters is sufficient to describe the carbon system. There are technological limitations to direct measurement of pH at present, which is likely to change in the next five years. DIC and TA are the most widely measured parameters in discrete samples. The parameter pCO2 is the most common measurement made underway. Widely accepted procedures are available, although further development of quality assurance tools (e.g. proficiency testing) is required. Monitoring is foreseen as a combination of low-frequency, repeat, ship-based surveys enabling collection of extended high quality datasets on horizontal and vertical scales, and high-frequency autonomous measurements for more limited parameter sets using instrumentation deployed on ships of opportunity and moorings. Monitoring of ocean acidification can build on existing activities summarized in this report, e.g. OSPAR eutrophication monitoring. This would be a cost-effective approach to monitoring, although a commitment to sustained funding is required. Data should be reported to the ICES data repository as the primary data centre for OSPAR and HELCOM, thus enabling linkages to other related datasets, e.g. nutrients and integrated ecosystem data. The global ocean carbon measurement community reports to the Carbon Dioxide Information Analysis Center (CDIAC), and it is imperative that monitoring data are also reported to this database. Dialogue between data centres to facilitate an efficient “Report-Once” system is necessary

Impact of combined 18F-FDG PET/CT in head and neck tumours

To compare the interobserver agreement and degree of confidence in anatomical localisation of lesions using 2-[fluorine-18]fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography (PET)/computed tomography (CT) and 18F-FDG PET alone in patients with head and neck tumours. A prospective study of 24 patients (16 male, eight female, median age 59 years) with head and neck tumours was undertaken. 18F-FDG PET/CT was performed for staging purposes. 2D images were acquired over the head and neck area using a GE Discovery LS™ PET/CT scanner. 18F-FDG PET images were interpreted by three independent observers. The observers were asked to localise abnormal 18F-FDG activity to an anatomical territory and score the degree of confidence in localisation on a scale from 1 to 3 (1=exact region unknown; 2=probable; 3=definite). For all 18F-FDG-avid lesions, standardised uptake values (SUVs) were also calculated. After 3 weeks, the same exercise was carried out using 18F-FDG PET/CT images, where CT and fused volume data were made available to observers. The degree of interobserver agreement was measured in both instances. A total of six primary lesions with abnormal 18F-FDG uptake (SUV range 7.2–22) were identified on 18F-FDG PET alone and on 18F-FDG PET/CT. In all, 15 nonprimary tumour sites were identified with 18F-FDG PET only (SUV range 4.5–11.7), while 17 were identified on 18F-FDG PET/CT. Using 18F-FDG PET only, correct localisation was documented in three of six primary lesions, while 18F-FDG PET/CT correctly identified all primary sites. In nonprimary tumour sites, 18F-FDG PET/CT improved the degree of confidence in anatomical localisation by 51%. Interobserver agreement in assigning primary and nonprimary lesions to anatomical territories was moderate using 18F-FDG PET alone (kappa coefficients of 0.45 and 0.54, respectively), but almost perfect with 18F-FDG PET/CT (kappa coefficients of 0.90 and 0.93, respectively). We conclude that 18F-FDG PET/CT significantly increases interobserver agreement and confidence in disease localisation of 18F-FDG-avid lesions in patients with head and neck cancers

Mechanisms for a nutrient-conserving carbon pump in a seasonally stratified, temperate continental shelf sea

Continental shelf seas may have a significant role in oceanic uptake and storage of carbon dioxide (CO2) from the atmosphere, through a ‘continental shelf pump’ mechanism. The northwest European continental shelf, in particular the Celtic Sea (50°N 8°W), was the target of extensive biogeochemical sampling from March 2014 to September 2015, as part of the UK Shelf Sea Biogeochemistry research programme (UK-SSB). Here, we use the UK-SSB carbonate chemistry and macronutrient measurements to investigate the biogeochemical seasonality in this temperate, seasonally stratified system. Following the onset of stratification, near-surface biological primary production during spring and summer removed dissolved inorganic carbon and nutrients, and a fraction of the sinking particulate organic matter was subsequently remineralised beneath the thermocline. Water column inventories of these variables throughout 1.5 seasonal cycles, corrected for air-sea CO2 exchange and sedimentary denitrification and anammox, isolated the combined effect of net community production (NCP) and remineralisation on the inorganic macronutrient inventories. Overall inorganic inventory changes suggested that a significant fraction (>50%) of the annual NCP of around 3 mol-C m–2 yr–1 appeared to be stored within a long-lived organic matter (OM) pool with a lifetime of several months or more. Moreover, transfers into and out of this pool appeared not to be in steady state over the one full seasonal cycle sampled. Accumulation of such a long-lived and potentially C-rich OM pool is suggested to be at least partially responsible for the estimated net air-to-sea CO2 flux of ∼1.3 mol-C m–2 yr–1 at our study site, while providing a mechanism through which a nutrient-conserving continental shelf pump for CO2 could potentially operate in this and other similar regions

A study of gas exchange during the transition from deep winter mixing to spring bloom in the bay of biscay measured by continuous observation from a ship of opportunity

Monitoring from ships of opportunity allows a wide range of parameters to be measured; thereby extending the coverage of operational oceanographic studies. Observation of dissolved oxygen using new sensors offers an effective way of monitoring changes in biological production. The limits of the application were tested following the transition from winter storms to the spring bloom (2007). Calculation of dissolved nitrogen enables changes in gas saturation due to physical and biological processes to be separated. By combining these measurements with data from numerical models and Argo floats the critical role of subsurface processes in determining rates of change at the surface can be assesse

Low salinity intrusions in the western English Channel

Low salinity (<35) surface waters (LSSW) at the southern entrance to the western English Channel (48.5°N, 5.1°W, near Ushant) were observed in late winter (March–April) in three successive years (2002–04) during near continuous ship of opportunity operations. The source of the LSSW is the northward spreading plumes from the Loire (47.5°N, 2.5°W) and Gironde (45.6°N, 1.2°W) along the French Atlantic coast. Fastest plume travel times were associated with northeasterly winds, consistent with Ekman theory. Differences between years in the mean winter (January–March) combined river discharges (D) was consistent with the minimum salinities (Smin) of the LSSW (2004: D=4211 m3 s?1, Smin=33.68; 2003: D=3630 m3 s?1, Smin=33.90; 2002: D=1579 m3 s?1, Smin=34.53). Winter mean (1905–74) salinity is otherwise 35.33 near Ushant.The LSSW intruded into the western English Channel in each year, suggesting a common phenomenon. The low salinity intrusion was freshest (mean=35.11±0.21) and most penetrative (reaching 50.7°N, 1.0°W by the end of the year) in 2003 on account of (1) entering on a spring tide giving greater tidal excursion into the western English Channel and (2) intrusion favourable winds (southwesterly/southeasterly) acting on the longer term residual flow. Less penetration occurred in 2004 when the arrival of the LSSW coincided with a neap tide followed by intrusion-resistant northwesterly winds, resulting in a less saline (mean=35.20±0.23) intrusion. In 2004, transport tended to be offshore to at least 100 km from the French Atlantic coast (47°N, 4.8°W–48°N, 4.7°W). In 2002, the lower volume of plume water relative to the other years produced a more saline intrusion (mean=35.25±0.12). Prevailing westerly winds may have pushed this intrusion northwards beyond the route of the ferry, making it difficult to assess the true extent of the intrusion in 2002. A link of the LSSW to phases of the winter North Atlantic Oscillation index from a literature search of the last 84 years was inconclusive

Phytoplankton distribution and survival in the thermocline

Observations of the vertical structure of density, concentrations of chlorophyll a and nitrate, and turbulent dissipation rates were made over a period of 25 h in a well-stratified shelf region in the Western English Channel, between neap and spring tides. Maximum turbulent dissipation at the base of the thermocline occurred almost 5 h after maximum tidal currents. This turbulence aids phytoplankton growth by supplying bottom-layer nutrients into the subsurface chlorophyll maximum but reduces phytoplankton concentrations in the thermocline by mixing cells from the base of the subsurface maximum into the bottom mixed layer. The turbulent dissipation observations were used to estimate an average nitrate flux into the thermocline of 2.0 (0.8–3.2, 95% confidence interval) mmol m22d21, which is estimated to have been capable of supporting new phytoplankton growth at a rate of 160 (64–256)mg C m22 d21. Turbulent entrainment of carbon from the base of the subsurface biomass maximum into the bottom mixed layer was observed to be 290 (120–480) mg C m22 d21. This apparent excess export from the chlorophyll maximum is suggested to be a feature of the spring-neap cycle, with export dominating as the tidal turbulence increases toward spring tides and erodes the base of the thermocline. The observed rate of carbon export into the bottom mixed layer could account for as much as 25% of the gross annual primary production in stratifying shelf seas. Such turbulent losses, combined with grazing losses and low light levels, suggest that phytoplankton need to be highly adapted to environmental conditions within the thermocline in order to survive

A uniform, quality controlled Surface Ocean CO2 Atlas (SOCAT)

A well documented, publicly available, global data set of surface ocean carbon dioxide (CO2) parameters has been called for by international groups for nearly two decades. The Surface Ocean CO2 Atlas (SOCAT) project was initiated by the international marine carbon science community in 2007 with the aim of providing a comprehensive, publicly available, regularly updated, global data set of marine surface CO2, which had been subject to quality control (QC). Many additional CO2 data, not yet made public via the Carbon Dioxide Information Analysis Center (CDIAC), were retrieved from data originators, public websites and other data centres. All data were put in a uniform format following a strict protocol. Quality control was carried out according to clearly defined criteria. Regional specialists performed the quality control, using state-of-the-art web-based tools, specially developed for accomplishing this global team effort. SOCAT version 1.5 was made public in September 2011 and holds 6.3 million quality controlled surface CO2 data points from the global oceans and coastal seas, spanning four decades (1968–2007). Three types of data products are available: individual cruise files, a merged complete data set and gridded products. With the rapid expansion of marine CO2 data collection and the importance of quantifying net global oceanic CO2 uptake and its changes, sustained data synthesis and data access are priorities