Coccolithophores and the Continuous Plankton Recorder Survey

Samples historically collected and analysed by the Continuous Plankton Recorder (CPR) survey were used to describe the distribution of coccolithophores (class Prymnesiophyceae) in the north-east Atlantic and the North Sea. In the routine CPR analysis, members of this group are simply identified as ‘coccolithophores’ and not to any further taxonomic level. From this analysis, the 200-m depth contour marked a point of distinct transition between high coccolithophore occurrence (off the shelf) and low coccolithophore occurrence (on the shelf). Thirty-three CPR samples that had been collected between 1979–1992, were re-examined and the coccolithophores identified to a more detailed taxonomic level. Among the species identified was the bloom-forming coccolithophore, Emiliania huxleyi. Thus archived CPR samples could potentially be re-analysed to assess regional, seasonal and decadal changes in the occurrence of this species

Patterns of phytoplankton size structure and productivity in contrasting open-ocean environments

A total of 94 vertical profiles of size-fractionated chlorophyll a concentration and primary production rate were obtained along a meridional transect from the United Kingdom to the Falkland Islands (50°N to 50°S) during 4 cruises carried out in April and October 1996 and in April and October 1997. This data set allowed us to characterize the patterns of phytoplankton size-structure and productivity in temperate, oligotrophic, upwelling and equatorial regions. On average, picophytoplankton (0.2 to 2 µm) accounted for 56 and 71% of the total integrated carbon (C) fixation and autotrophic biomass, respectively. Enhanced biomass and productivity contributions by nano- and microplankton took place in the temperate regions and in the upwelling area off Mauritania. Small (<2 µm in diameter) phytoplankton cells should not be regarded as a background, relatively invariant component of the microbial community, given that most of the latitudinal variability in total photoautotrophic biomass and production was driven by changes in the picophytoplankton. In temperate regions and in the upwelling area off Mauritania, small (<2 µm) and large (>2 µm) phytoplankton accounted for a proportion of total biomass that was similar to their shares of productivity. In the oligotrophic and equatorial regions, in contrast, large phytoplankton tended to account for a fraction of the total production that was significantly higher than their share of the biomass. We found that the equatorial upwelling causes an increase in phytoplankton biomass and productivity without altering the typical size structure found in less productive regions such as the subtropical gyres. In the oligotrophic ocean, significant changes in C fixation rates take place without accompanying variations in the magnitude of the phytoplankton standing stocks or the size structure of the microbial community

Effect of multipath and antenna diversity in MIMO-OFDM systems with imperfect channel estimation and phase noise compensation

The effect of phase noise in multiple-input–multiple-output systems employing orthogonal frequency division multiplexing is analyzed in a realistic scenario where channel estimation is not perfect, and the phase noise effects are only partially compensated. In particular, the degradation in terms of SNR is derived and the effects of the receiver and channel parameters are considered, showing that the penalty is different for different receiver schemes. Moreover it depends on the channel characteristics and on the channel estimation error. An analytical expression is used to evaluate the residual inter-channel interference variance and therefore the degradation. The effects of multipath and antenna diversity are shown to be different for the two types of linear receivers considered, the zero-forcing scheme and the minimum mean squared error receiver.This work has been partly funded by projects “MACAWI” TEC2005-07477-C02-02 and “MULTI-ADAPTIVE” TEC2008-06327-C03-02.Publicad

The North Sea: Satellite Colour Atlas

Satellite imagery of the North Sea from the Coastal Zone Color Scanner (CZCS)shows complex seasonal changes in the optical and biological properties of surface waters,features which have not been resolved, hitherto, through direct observations from ships. Selectedscenes for the period 1979-1986, presented as single band (channel 3), colour composite(channels 1 + 2 + 3) and chlorophyll (channels 1/3 or 2/3) images, are used to demonstrate therelative surface distributions between February and October of suspended sediments, coccolitho-phores and plant pigments. Comparisons are made also with sea surface temperature imagesfrom the Advanced Very High Resolution Radiometer (AVHRR). Quantitative evaluation ofthe CZCS data is restricted by a lack of contemporary in situ optical and biological measurements.However, chlorophyll and Secchi disc distributions, determined by measurements from researchships have been compared qualitatively with images from the Southern Bight (13 May 1986) andfor the east central North Sea (24 August 1984 and 24 October 1985). Mini series of CZCS imagesare presented to show the annual coccolithophore blooms, the development of the spring bloomin 1980 in the eastern and north western parts of the North Sea, advection and mixing processesin the Skagerrak, June 1983 and summer chlorophyll distributions in the German Bight

Day-night variation of intertidal flat sediment properties in relation to sediment stability

The majority of investigations that have measured sediment properties related to intertidal sediment stability have been undertaken during daylight subaerial exposure periods. As a consequence, models based upon such data represent only partially the intertidal flat surface conditions within any 24 h period.In this contribution, a comparison is made between surface sediment properties related to sediment stability measured during six consecutive (day/night), semi-diurnal subaerial exposure periods, at three stations on an intertidal sand flat in late March 1999. The study site was selected on the basis of its suitability for sampling and data collection at night, with special regard to safety and logistics. Seawater temperatures ranged from 4.1 to 9.6 [deg]C, and salinities from 33.9 to 34.8.Eleven parameters related to intertidal flat sediment stability were measured, or derived. These variables included the critical erosion shear stress ([tau]c), chlorophyll a, phaeopigment, and colloidal carbohydrate content, mean grain size and settling velocity of the surface (0-1 mm) sediment fraction. Bed elevation was described using an acretion/erosion parameter (AEP) (West and West 1991), whilst additional physical terms included ambient seawater salinity and temperature, as well as tidal range and wind speed, during the preceding immersion periods. One-way ANOVA was used to detect significant differences between day- and night-time emersion periods; similarly, principal components analysis (PCA) was applied to detect continuous variation between properties.The results show a high degree of temporal and spatial variability between day- and night-time intertidal flat variables, the PCA differentiating clearly between day and night conditions. Surface sediments across the intertidal flat exhibited varying degrees of biostabilisation. The maximum biostabilisation coefficient (18) was recorded at night in high microalgal biomass areas; the minimum (5) occurred during both day and night, in areas with lower microalgal biomass. All surface sediment parameters varied rhythmically between day- and night-time. Significant differences were found between day- and night-time biostabilisation coefficients, however, differences between day- and night-time [tau]c values were not detected. It is suggested that sediment stability at night is enhanced in high microalgal biomass areas as a result of degradation products from bound extra-cellular polysaccharides (EPS) not easily detected using standard extraction procedure

Phytoplankton growth of the chlorophyll maximum in the Atlantic Ocean

The presence of a subsurface chlorophyll maximum is a ubiquitous feature of CTD profiles collected from the oligotrophic oceanic gyres in the Atlantic Ocean. Various mechanisms that control the position of the chlorophyll maximum differ widely. Previous studies have indicated that chlorophyll maximum is an important site of seasonal new production in this area. A wide range of measurements of both the phytoplankton community and hydrographic environment were made during Atlantic Meridional Transect (AMT) cruise 14 (April, 2004). Additionally, use of fast repetition rate (FRR) fluorescence technique to provide high-resolution vertical profiles of physiological properties of phytoplankton is explored. Vertical distributions of chlorophyll, light, nitrate, dissolved oxygen and photosynthetic parameters varied across the thermocline. These variations are interpreted in a regional context and compared with estimates of population size structure and the C/Chl a ratio. The community found in the chlorophyll maximum was physiologically distinct from the surface community and optimized for light harvesting and photosynthesis at low light levels. The physio - biological environment in the nutrient-rich equatorial upwelling region and the oligotrophic subtropical gyre is also compared.<br/

Microalgal mediation of ripple mobility

The interaction between physical and biological factors responsible for the cessation of ripple migration on a sandy intertidal flat was examined during a microalgal bloom period in late winter/early spring, as part of a wider study into the biostabilisation of intertidal sediments. Ripple positions and ripple geometry were monitored, and surface sediment was sampled, at weekly intervals over a 5-week period. Ripples remained in the same position for at least 4 weeks, during which time there was a progressive reduction in bedform height (smoothing) and deposition of some 1.5 cm sediment, mainly in the ripple troughs (surface levelling). The mean chlorophyll a (chl a) sediment content was 6.0 µg gDW?1 (DW: dry weight) (0–1 mm depth fraction), with a maximum value of 7.4 µg gDW?1 half way through the bloom. Mean colloidal-S carbohydrate (S: saline extraction) content was 131 µg GE gDW?1 (GE: glucose equivalent) (0–1 mm), with a maximum of 261 µg GE gDW?1 towards the end of the bloom. Important accessory pigments were peridinin (indicative of dinophytes) and fucoxanthin (diatoms). Stepwise multiple regression showed that peridinin was the best predictor of chl a. For the first time, in situ evidence for the mediation of (wave) ripple migration by microalgae is provided. Results indicate that diatoms, and quite possibly dinophytes, can have a significant effect on intertidal flat ripple mobility on a temporal scale of weeks. In addition, microalgal effects appear capable of effecting a reduction in bed roughness on a spatial scale of up to 10?2 m, with a subsequent reduction in bottom stress and bed erodability. It is suggested that a unique combination of environmental conditions, in conjunction with the microalgal bloom(s), promoted the initial cessation of ripple movement, and that stationary-phase, diatom-derived extracellular polymeric substances (EPS) (and possibly dinophyte-derived EPS) may have prolonged the condition. It is reasonable to suppose that ripple stabilisation by similar processes may have contributed to ripple mark preservation in the geological record. A conceptual model of sandy intertidal flat processes is presented, illustrating two conditions: (i) a low EPS/microalgae sediment content with low ripple stabilisation and preservation potential; and (ii) a high EPS/microalgae content with higher preservation potential.<br/