A global compilation of coccolithophore calcification rates

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 µmol C m−3 d−1 (with a geometric mean of 16.1 µmol 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

Coccolithophore ecology in the tropical and subtropical Atlantic Ocean: New perspectives from the Atlantic Meridional Transect (AMT) programme

Coccolithophore species composition was determined in 199 samples collected from the upper 300 m of the Atlantic Ocean, spanning temperate, tropical and subtropical waters in both hemispheres during four Atlantic Meridional Transect (AMT) cruises over the period 2003 to 2005. Of the 171 taxa observed, 140 consistently represented less than 5% of total cell numbers, and were classed as rare. Multivariate statistical techniques were used on the common taxa to assess variability in community composition vertically in the water column, horizontally across hydrographic provinces (subtropical gyres, equatorial waters, temperate waters), and temporally between cruises. Sharper gradients of statistical dissimilarity in species composition occurred vertically over a few tens of metres than horizontally over hundreds of kilometres. Three floral groups were identified from analysis of the depth of normalised abundance maxima in the subtropical gyres and equatorial waters: the upper euphotic zone (UEZ, >10% surface irradiance); the lower euphotic zone (LEZ, 10-1% surface irradiance); and the sub-euphotic zone (SEZ, <1% surface irradiance). The LEZ includes the deep chlorophyll maximum (DCM) and nutricline, and was characterised by species such as Emiliania huxleyi and Gephyrocapsa ericsonii which were also abundant at higher latitudes. It is suggested that this pattern reflects similarities in the light (and inorganic nutrient) conditions between the LEZ and temperate waters. The SEZ is below the depth where light is thought to be sufficient to support photosynthesis, suggesting that deep-dwelling species such as Florisphaera profunda and Gladiolithus spp. may be mixotrophic or phagotrophic, although conclusive proof will need to be gained experimentally. Mixotrophy could also be an important nutritional strategy for species abundant (Umbellosphaera spp., holococcolithophores) in the UEZ where inorganic nutrient concentrations are depleted and limiting to growth, although other nutritional strategies, such as the use of organic nutrients, are also possible. Statistical differences were also found in the species composition between the different cruises, with high levels of similarity for similar timed cruises (May or September-October). Few individual taxa showed significant variability in abundance over the time-span of sampling, except species such as E. huxleyi and G. ericsonii at higher latitudes. In subtropical and equatorial waters, high levels of species richness and low levels of species dominance remained throughout the sampling period indicating that seasonal fluctuations reflected differences in the whole coccolithophore community rather than in just one or a few species. Multivariate analyses of the taxa classified as rare also indicated some level of temporal, as well as vertical, zonation. Such insights into coccolithophore ecology and community composition provide important new perspectives that require innovative research to fully understand their impact on ocean biogeochemistry

Internal tidal mixing as a control on continental margin ecosystems

We show that a breaking internal tide at a shelf edge is a fundamental control on the structural and functional properties of ecosystems. Contrasts in vertical mixing of nitrate between the shelf and the open ocean correspond with horizontal and vertical changes in phytoplankton communities, with largest cells found in surface waters at the shelf edge. Intense fishing activity is commonly seen at continental shelf edges, targeting spawning fish stocks. We suggest that the internal tide, a globally ubiquitous physical process at steep shelf edge bathymetry, supports shelf edge fisheries by providing large-celled phytoplankton for first-feeding fish larvae. The repeatability of the internal tide removes fish from the need to time spawning with a spring bloom. Also, with large phytoplankton cells dominating particulate organic carbon export, the internal tides could be an important influence on spatial and temporal variability in patterns of global carbon sequestration in deep water and sediments. Citation: Sharples, J., C. M. Moore, A. E. Hickman, P. M. Holligan, J. F. Tweddle, M. R. Palmer, and J. H. Simpson (2009), Internal tidal mixing as a control on continental margin ecosystems, Geophys. Res. Lett., 36, L23603, doi:10.1029/2009GL040683

Benthic-pelagic exchange of microalgae at a tidal flat. 2: taxonomic analysis

Benthic-pelagic exchange of diatoms over a tidal cycle has been examined using a combination of field measurements and annular flume experiments. The relative contribution of benthic and planktonic species to water-column abundance and biomass has been estimated using taxonomic counts, and cell volume to carbon conversions. In June, peaks in chlorophyll a (chl a) biomass occurred either side of the high-water slack period, which corresponded with increased abundance of benthic diatoms, as well as the large centric diatom Coscinodiscus spp. In numerical terms, benthic diatoms accounted for, on average, 15 to 42% of total diatom abundance over the flood-ebb period, while Coscinodiscus spp. accounted for 12 to 17% in June and 3% in late August. Because of the large size of planktonic forms (e.g., Coscinodiscus spp., Rhizosolenia spp., Biddulphia spp.) compared with the small benthic Nitzschia and Navicula species, the contribution of benthic diatoms was significantly lower in terms of biomass. The average contribution of benthic diatoms to total diatom carbon was &lt;1% in June, but up to 25% in late August. In contrast, the relative contribution of Coscinodiscus spp. was ~90% in June and 73 to 80% in late August. The flume experiments confirmed that, in addition to increased benthic abundance in response to stepwise increases in current velocity, the large centric diatom Coscinodiscus spp. was also resuspended from sediments at high current velocities. At low current velocities, these cells rapidly sank to the seabed, the rate probably enhanced by deposition of sand grains out of the water column. Ecological implications related to water-column biomass and production, macro-infauna diet, and composition of benthic chl a are discussed

Dimethylsulphide and dimethylsulphoniopropionate in the Northeast atlantic during the summer coccolithophore bloom

Concentrations of dimethylsulphide (DMS) and dissolved and particulate pools of its precursor, dimethylsulphoniopropionate (DMSP), were surveyed at the time of the summer bloom of coccolithophores in the Northeast Atlantic. The average DMS concentration was 12 nmol dm-3 (n = 158, range 1.06-93.8 nmol dm-3, sn - 1 = 12.4). Statistically significant positive correlations between particulate DMSP and chlorophyll were found for samples from areas where coccolithophores accounted for 50% or more of the total carbon biomass. In these areas correlations between DMS and chlorophyll were not as strong but still significant. An estimate of the flux of DMS from the Northeast Atlantic in June–July (721 nmol m-2 h-1) is of the same order as estimates for the southern North Sea at the same time of year (646 nmol m-2 h-1). The data provide strong evidence for the importance of coccolithophores in the emission of DMS to the atmosphere. Comparison of flux data with budgets for airborne sulphur in Europe, reported by the European Monitoring and Evaluation Programme (EMEP), suggests that in summer the Northeast Atlantic may be a source of the sulphur deposited on adjacent land areas not strongly affected by anthropogenic sulphur sources. The overall results are discussed in relation to present knowledge of the global distribution of coccolithophores