Search

The biological production of calcium carbonate (CaCO3), a process termed calcification, is a key term in the marine carbon cycle. A major planktonic group responsible for such pelagic CaCO3 production (CP) is the coccolithophores, single-celled haptophytes that inhabit the euphotic zone of the ocean. Satellite-based estimates of areal CP are limited to surface waters and open-ocean areas, with current algorithms utilising the unique optical properties of the cosmopolitan bloom-forming species Emiliania huxleyi , whereas little understanding of deep-water ecology, optical properties or environmental responses by species other than E. huxleyi is currently available to parameterise algorithms or models. To aid future areal estimations and validate future modelling efforts we have constructed a database of 2765 CP measurements, the majority of which were measured using 12 to 24 h incorporation of radioactive carbon (14C) into acid-labile inorganic carbon (CaCO3). We present data collated from over 30 studies covering the period from 1991 to 2015, sampling the Atlantic, Pacific, Indian, Arctic and Southern oceans. Globally, CP in surface waters (<20 m) ranged from 0.01 to 8398 µ mol C m -3 d -1 (with a geometric mean of 16.1 µ mol C m -3 d -1). An integral value for the upper euphotic zone (herein surface to the depth of 1 % surface irradiance) ranged from <0.1 to 6 mmol C m -2 d -1 (geometric mean 1.19 mmol C m -2 d -1). The full database is available for download from PANGAEA at https://doi.org/10.1594/PANGAEA.888182. [ABSTRACT FROM AUTHOR]

The biological production of calcium carbonate (CaCO3), a process termed calcification, is a key term in the marine carbon cycle. A major planktonic group responsible for such pelagic CaCO3 production (CP) are the coccolithophores, single-celled haptophytes that inhabit the euphotic zone of the ocean. Satellite-based estimates of areal CP are limited to open-ocean waters, with current algorithms utilising the unique optical properties of the cosmopolitan bloom-forming species Emiliania huxleyi, whereas little understanding of the optical properties and environmental responses by species other than E. huxleyi are currently available to parameterise algorithms or models. To aid future areal estimations and validate future modelling efforts we have constructed a database of 2765 CP measurements, the majority of which were measured using 12 to 24h incorporation of radioactive carbon (14C) into acid-labile inorganic carbon (CaCO3). We present data collated from over 30 studies covering the period from 1991 to 2015, sampling the Atlantic, Pacific, Indian, Arctic and Southern oceans. Globally, CP in surface waters (<20m) ranged from 0.01 to 8398μmolCm-3d-1 (with a geometric mean of 16.1μmolCm-3d-1). An integral value for the upper euphotic zone (herein surface to the depth of 1% surface irradiance) ranged from <0.1 to 6mmolCm-2d-1 (geometric mean 1.19mmolCm-2d-1). [ABSTRACT FROM AUTHOR]

Latitudinal variability in export fluxes and efficiencies (ThE) of calcite, opal, and particulate organic carbon (POC) were examined during a basin-scale Atlantic Ocean cruise. A clear relationship between integrated euphotic zone POC and calcite export combined with similarities in average ThE for calcite (0.26), opal (0.31), and POC (0.29) implies a potential association between biomineral and POC export. However, such similarity conceals substantial uncorrelated variability when ThE values are compared on regional scales, with ThE of POC often being much higher than that of calcite or opal. High-euphotic zone ThE for POC (0.3-0.4) relative to that found in deep sea sediment traps (<0.05) suggests that considerable remineralization occurs below the euphotic zone. We suggest (1) that regional variability in the mechanisms by which biominerals and POC become associated are more important in determining the efficient export of organic carbon than that of ballast materials; and (2) that, because of the preferential remineralization of POC relative to calcite/opal dissolution during subeuphotic processes, the potential for effective ballasting increases with depth in the water column. [ABSTRACT FROM AUTHOR]

Laboratory experiments were performed with the prymnessophyte Emiliania huxleyi (Lohm.) Hay and Mohler, strain 88E to quantify calcification per cell, coccolith detachment, and effects of cocolith production on optical scattering of individual cells. [sup14]C-labeled cells also were sorted using a flow cytometer and analysed for carbort incorporation into attached rocliths. The difference between the bulk and flow cytometer analyses provided a [sup14]C-based estimate of the rate of production of detached coccoliths. Coccolith production and detachment were separated in time in batch cultures, with m ost detachment happening well after calafication had stopped. Accumulation of coccoliths was maximum at the end of logarithmic growth with 50-80 coccoliths per cell (three to five complete layers of coccoliths around the cells). Net accretion rates of coccoliths were on the order of 7 coccoliths cell [sup-1]d[sup-1] for stationary phase cells. Equal numbers of coccoliths were attached and detached early in logarithmic growth, and as cells aged, the numbers of detached coccoliths exceeded the attached ones by a factor of 6. Our results demanstrate pronounced changes of forward angle fight scatter and 90° light scatter of cells as they grow logarithmically and enter stationary phase. Counts of loose coccoliths in batch cultures are constent with the detachment of coccoliths in layers rather than individual coccoliths. [ABSTRACT FROM AUTHOR]

Oceans have a fundamental role in the global climate system on account of their capacity to store and transport heat and absorb and emit tract gases, which directly or indirectly affect the earth's radiation budget. The ocean biota, in particular the phytoplankton, contribute significantly to these processes: photosynthetic carbon fixation and the downward transport of organic carbon increase the storage capacity of oceans for the major greenhouse gas, carbon dioxide. Changes in the oceanic cycling of carbon are believed to have been a major factor in the control of atmospheric carbon dioxide concentrations during the Pleistocene ice age cycles, although biological mechanisms that contribute to these changes are still not well understood.

ABSTRACT Satellite data show that the distribution of Emiliania huxleyi in the North Sea is characterized by considerable spatial patchiness as well as large annual differences in abundance within any particular area. The causes of this variability are largely unknown, and therefore unpredictable, reflecting a paucity of information on the ecophysiology of the species. [ABSTRACT FROM AUTHOR]

Observations of vertical gradients in phytoplankton community structure were made through the water column of the seasonally stratified Celtic Sea, including within the thermocline. A deep chlorophyll maximum (DCM) was located within the thermocline at all stations, coupled to the nitracline. Vertical gradients in phytoplankton community composition were routinely observed within the thermocline. The cell abundance maxima for Synechococcus occurred in the upper part of the DCM coincident with a picoeukaryote abundance minima. Picoeukaryote abundance typically increased at or just above the peak of the DCM. Diatoms were observed occasionally at the DCM peak. Pigment compositions and phytoplankton absorption spectra indicated that the different phytoplankton communities were chromatically well adapted to the spectral composition of irradiance at the depths where they occurred in the water column. Profiles of vertical eddy diffusivity revealed that timescales formixing between the phytoplankton layers within the thermocline were in excess of typical phytoplankton growth rates. The observed vertical gradients in community structure could therefore result from selection and niche partitioning of phytoplankton types on the light and nutrient gradient within the thermocline. The data further indicate that the pigments, light absorption characteristics, and cell size contribute to the phytoplankton selection process. [ABSTRACT FROM AUTHOR]

Measurements of the intra-tidal and spring-neap variation in the vertical flux of nitrate into the base of the sub-surface chlorophyll maximum (SCM) were made at the shelf edge of the Celtic Sea, a region with strong internal mixing driven by an internal tide. The neap tide daily mean nitrate flux was 1.3 (0.9-1.8, 95% confidence interval) mmol m-2 d-1. The spring tide flux was initially estimated as 3.5 (2.3-5.2, 95% confidence interval) mmol m-2 d-1. The higher spring tide nitrate flux was the result of turbulent dissipation occurring within the base of the SCM as compared to deeper dissipation during neap tides and was dominated by short events associated with the passage of internal solitons. Taking into account the likely under-sampling of these short mixing events raised the spring tide nitrate flux estimate to about 9 mmol m-2 d-1. The neap tide nitrate flux was sufficient to support substantial new production and a considerable fraction of the observed rates of carbon fixation. Spring tide fluxes were potentially in excess of the capacity of the phytoplankton community to uptake nitrate. This potential excess nitrate flux during spring tides may be utilized to support new production during the lower mixing associated with the transition toward neap tide. The shelf edge is shown to be a region with a significantly different phytoplankton community as compared to the adjacent Celtic Sea and northeast Atlantic Ocean, highlighting the role of gradients in physical processes leading to gradients in ecosystem structure. [ABSTRACT FROM AUTHOR]

Variability in the photosynthetic performance of natural phytoplankton communities, due to both taxonomic composition and the physiological acclimation of these taxa to environmental conditions, was assessed at contrasting sites within a temperate shelf sea region. Physiological parameters relating to the structure of the photosystem II (PSII) antenna and processes downstream from PSII were evaluated using a combination of fast repetition rate fluorescence, oxygen flash yields, spectral fluorescence, and 14C photosynthesis versus irradiance measurements. Parameters relating to PSII antenna structure, specifically the functional absorption cross-section (ΣPSII) and the chlorophyll to PSII reaction center ratio, varied principally as a result of spatial (horizontal) taxonomic differences. Phenotypic plasticity in the size of the PSII light-harvesting antenna appeared to be limited. In contrast, parameters related to electron transport rates (ETRs) downstream of PSII, including the maximum ETR (1τPSII), the chlorophyll-specific maximum rate of carbon fixation (P*max), and the light-saturation intensity (Ek), all decreased from the surface to the subsurface chlorophyll maximum (SCM) in stratified waters. The primary photoacclimation response to the vertical light gradient thus resulted in decreasing light-saturated carbon fixation per reaction center with increasing depth. Increases in the ratio of PSII reaction centers to carbon fixation capacity thus dominated the phenotypic response to decreased irradiance within the SCM. Perhaps counterintuitively, phytoplankton populations within fully mixed water columns, characterized by low mean irradiance, were acclimated or adapted to relatively high irradiance. [ABSTRACT FROM AUTHOR]