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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]

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]

Abstract: We have made daily measurements of phytoplankton pigments, size-fractionated (<2 and >2-μm) carbon fixation and chlorophyll-a concentration during four Atlantic Meridional Transect (AMT) cruises in 2003–04. Surface rates of carbon fixation ranged from <0.2-mmolCm−3 d−1 in the subtropical gyres to 0.2–0.5-mmolCm−3 d−1 in the tropical equatorial Atlantic. Significant intercruise variability was restricted to the subtropical gyres, with higher chlorophyll-a concentrations and carbon fixation in the subsurface chlorophyll maximum during spring in either hemisphere. In surface waters, although picoplankton (<2-μm) represented the dominant fraction in terms of both carbon fixation (50–70%) and chlorophyll-a (80–90%), nanoplankton (>2-μm) contributions to total carbon fixation (30–50%) were higher than to total chlorophyll-a (10–20%). However, in the subsurface chlorophyll maximum picoplankton dominated both carbon fixation (70–90%) and chlorophyll-a (70–90%). Thus, in surface waters chlorophyll-normalised carbon fixation was 2–3 times higher for nanoplankton and differences in picoplankton and nanoplankton carbon to chlorophyll-a ratios may lead to either higher or similar growth rates. These low chlorophyll-normalised carbon fixation rates for picoplankton may also reflect losses of fixed carbon (cell leakage or respiration), decreases in photosynthetic efficiency, grazing losses during the incubations, or some combination of all these. Comparison of nitrate concentrations in the subsurface chlorophyll maximum with estimates of those required to support the observed rates of carbon fixation (assuming Redfield stoichiometry) indicate that primary production in the chlorophyll maximum may be light rather than nutrient limited. [Copyright &y& Elsevier]

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]

A Natural Resource Georges Bank is situated to the east of Cape Cod and Nantucket, between the Gulf of Maine and the edge of the continental shelf. The bank, as [...]

Abstract: The aims of the Atlantic Meridional Transect (AMT) programme [www.amt-uk.org] are to quantify the nature and causes of ecological and biogeochemical variability in the planktonic ecosystems of the Atlantic Ocean, and to assess the effects of this variability on biological carbon cycling and air–sea exchange of radiatively active gases and aerosols. Marine and atmospheric data have been collected twice a year along a 13,500km transect in the Atlantic Ocean between 50°N and 52°S since 1995. The cruise track enables biogeochemical measurements to be made within the poorly studied North and South Atlantic oligotrophic gyres as well as within equatorial and coastal upwelling regions. The range of ecosystems sampled during AMT has facilitated the calibration and validation of newly developed optical, microbiological, molecular and analytical techniques and provided a testbed for comparative ecology and the development of atmospheric and oceanographic models. This paper describes the rationale and methodology of the programme. Upper-ocean measurements of density, nitrate and chlorophyll a (Chl a) are presented to illustrate seasonal, inter-annual and decadal variability in hydrography. Seasonal distributions of dissolved nitrous oxide (N2O) and methane (CH4) are used to derive estimates of the sea–air flux of these gases in the South Atlantic Gyre. Observations made during AMT and published since 2000 are reviewed, and the key findings are highlighted. The extent to which the programme aims have been achieved is discussed and improvements for the future suggested. [Copyright &y& Elsevier]

Abstract: Recent measurements of surface coccolithophore calcification from the Atlantic Ocean (50°N–50°S) are compared to similar measurements from other oceanic settings. By combining the different data sets of surface measurements, we examine general and regional patterns of calcification relative to organic carbon production (photosynthesis) and other characteristics of the phytoplankton community. Generally, surface calcification and photosynthesis are positively correlated, although the strength of the relationship differs between biogeochemical provinces. Relationships between surface calcification, chlorophyll-a and calcite concentrations are also statistically significant, although again there is considerable regional variability. Such variability appears unrelated to phytoplankton community composition or hydrographic conditions, and may instead reflect variations in coccolithophore physiology. The contribution of inorganic carbon fixation (calcification) to total carbon fixation (calcification plus photosynthesis) is ∼1–10%, and we estimate a similar contribution from coccolithophores to total organic carbon fixation. However, these contributions vary between biogeochemical provinces, and occasionally coccolithophores may account for >20% of total carbon fixation in unproductive central subtropical gyres. Combining surface calcification and photosynthetic rates with standing stocks of calcite, particulate organic carbon, and estimated phytoplankton carbon allows us to examine the fates of these three carbon pools. The relative turnover times vary between different biogeochemical provinces, with no clear relationship to the overall productivity or phytoplankton community structure found in each province. Rather, interaction between coccolithophore physiology (coccolith production and detachment rates), species diversity (cell size), and food web dynamics (grazer ecology) may control the composition and turnover times of calcite particles in the upper ocean. [Copyright &y& Elsevier]

Abstract: Photosynthetic electron transport directly generates the energy required for carbon fixation and thus underlies the aerobic metabolism of aquatic systems. We determined photosynthetic electron turnover rates, ETRs, from ca. 100 FRR fluorescence water-column profiles throughout the subtropical and tropical Atlantic during six Atlantic Meridional Transect cruises (AMT 6, May–June 1998, to AMT 11, September–October 2000). Each FRR fluorescence profile yielded a water-column ETR-light response from which the maximum electron turnover rate , effective absorption (σ PSII) and light saturation parameter (E k) specific to the concentration of photosystem II reaction centres (RCIIs) were calculated. and E k increased whilst σ PSII decreased with mixed-layer depth and the daily integrated photosynthetically active photon flux when all provinces were considered together. These trends suggested that variability in maximum ETR can be partly attributed to changes in effective absorption. Independent bio-optical measurements taken during AMT 11 demonstrated that σ PSII variability reflects taxonomic and physiological differences in the phytoplankton communities. and E k, but not σ PSII, remained correlated with mixed-layer depth and daily integrated photosynthetically active photon flux when data from each oceanic province were considered separately, indicating a decoupling of electron turnover and carbon fixation rates within each province. Comparison of maximum ETRs with 14C-based measurements of P max further suggests that light absorption and C fixation are coupled to differing extents for the various oligotrophic Atlantic provinces. We explore the importance of quantifying RCII concentration for determination of ETRs and interpretation of ETR-C fixation coupling. [Copyright &y& Elsevier]