Number Of Coccoliths Research Articles

Coccolithophore response to changes in surface water conditions south of Iceland (ODP Site 984) between 130 and 56 ka

Quantitative coccolithophore analyses were performed using sediments from Ocean Drilling Program (ODP) Site 984, located south of Iceland close to the modern location of the Polar Front, to reconstruct climatically induced variations in surface water conditions from 130 to 56 ka, spanning the end of Marine Isotope Stage (MIS) 6 to the beginning of MIS 3. For this purpose, changes in the coccolith assemblages (e.g., abundances, accumulation rates, composition, diversity and preservation, as well as coccolith carbonate) and variations in sizes and morphotypes of Gephyrocapsa muellerae and Emiliania huxleyi were investigated.The coccolith assemblages were generally of low diversity and were mostly dominated by G. muellerae throughout most of the record. Two intervals of relatively warm surface water expansion (MIS 5e, 5a) were identified by increased coccolith numbers, coccolith accumulation rates (CAR), and highest coccolith carbonate content, and interpreted to be associated with the expansion of the relatively warm Irminger Current (IC). The low coccolith numbers and low CAR during the interval MIS 5d to 5b point to much lower sea-surface temperatures and the decreased influence of the warm IC. Furthermore, MIS 5c is notable due to the absence of E. huxleyi accompanied by lowest species diversity, which suggest either cooler or less productive surface water conditions during this time interval.Another intriguing result of this research is the observed significant increase in the mean length of the G. muellerae distal shield (> 15%) from the beginning of MIS 5e to MIS 4. Furthermore, E. huxleyi occurs almost exclusively as Type B/C throughout MIS 5 and is particularly characterized by a considerable proportion of strongly calcified types during MIS 5a. Emiliania huxleyi Type A is first determined in MIS 5a and became the dominant morphotype during MIS 4. In addition, E. huxleyi (> 4 μm) commonly occurred during MIS 5e and 5a, during intervals of warmer surface waters. It seems likely, that E. huxleyi as well as G. muellerae went through various adaptations during MIS 5, which may have led to a global step in the exchange in dominance between the two species at the end of MIS 5, recorded in most ocean basins.

Continental influence on the fertilization of marine waters during the late quaternary in the south of the Brazilian continental margin

This study sought to understand the role of continental influence on ocean productivity along the late Quaternary based on the comparison between continental palynomorphs and paleoproductivity proxies from the marine sediment core SIS188. Retrieved from the slope of the Pelotas Basin at a depth of 1,514 m, the core documents the time interval between 47.8 and 7.4 cal ka BP, including the Marine Isotope Stages (MIS) 3, 2 and 1. The palynological content found in the core SIS188 indicates a typical flora of the southern Brazil highlands, which is at the same latitude as the core. Thus, continental input sources, such as wind-borne dust and discharges from the Mampituba and Araranguá rivers, would more likely account for the palynological content than the Brazilian Coastal Current (BCC). During the glacial intervals (MIS 3 and MIS 2), paleoproductivity (indicated by the proxies coccolith numbers, N Ratio, and TOC content) suggest the intensification of upwelling and transport of wind dust, the latter of which may have transported pollen grains to the core region. There is a concentration decrease of continental palynomorphs at the end of MIS 2, which is accentuated during MIS 1 when the sea level is higher. Paleoproductivity was high during MIS 1, especially from the Holocene onwards, although the concentration of continental-derived palynomorphs decreases sharply, showing that the rise in sea level interferes with the fertilization of marine waters far from the coast by continental input.

Vliyaniye sluchayev tsveteniya kokkolitoforid na bioopticheskiye kharakteristiki vod Chernogo morya po dannym nablyudeniy v 2012 i 2017 godakh

This paper presents and discusses the results of optical and biological measurements performed during the coccolithophore blooms. This study uses data of measurements from a stationary oceanographic platform (near the Southern coast of Crimea, 44°23' N, 33°59' E) in July 2012 (7–16 July) and in May 2017 (24–31 May), and data obtained during the R/V “Professor Vodyanitsky” expedition to the northern part of the Black Sea in June 2017 (14–30 June). Observation periods coincided with intensive blooms of coccolithophore. The measurements of the Secchi disk depth, light beam attenuation coefficient and reflectance coefficient, as well as biological determinations of the coccolithophore cells number in water samples, are considered and analyzed. In addition to field data, satellite information on the sea reflectance and backscattering are used. The beam attenuation coefficient, reflectance coefficient, backscattering coefficient and coccolithophore concentrations were increased as compared with no bloom period. The Secchi disk depth was abnormally low. The number of coccolithophore cells, according to biological data, varied from 150 thousand cells/L to 1.7 million cells/L and averaged 0.6 ± 0.4 million cells/L. According to these data, the estimated concentration of shed coccoliths was (1.46 ± 0.42) 1011 m-3 . The average coccolith concentrations calculated from satellite data were (1.29 ± 0.23) 1011 m-3 in July 2012, (1.32 ± 0.12) 1011 m-3 in May 2017, and (2.37 ± 0.69) 1011 m-3 in June 2017. During blooms, high variability was observed not only in optical properties, but also in biological properties, and the relationship between their spatial distribution was weak. From the optical point of view, the indicator of bloom is the number of coccoliths, not cells, which can lead to an incorrect description of the biological situation.

Caracterización de las asociaciones de cocolitóforos en las cuencas offshore del Pacífico colombiano

This study was conducted on coccolithophores recovered from 39 piston-core samples taken offshore Chocó and Tumaco basins, on the Colombian Pacific. Qualitative and quantitative analyses of the coccoliths showed changes in the relative abundances and the state of preservation in the two basins. The examined sediments were characterized by the coccoliths Gephyrocapsa oceanica, Gephyrocapsamuellerae, Gephyrocapsa <3 μm, Emiliania huxleyi, Calcidiscus leptoporus and Helicosphaera carteri, which presented abundances higher than 2 %. We also identified a minority assemblage (<2%) constituted by Ceratolithus spp., Coccolithus pelagicus, Florisphaera profunda,Helicosphaera princei, Helicosphaera sellii, Helicosphaera wallichii and Pontosphaera spp. together with reworked specimens of Reticulofenestra spp, Sphenolithus spp. and Discoaster spp. The recovery of E. huxleyi as part of the assemblage indicates that the studied sediments are younger than the biozone NN21, covering an age range of Middle Pleistocene (Ionian). The number of coccoliths per gram (cc/g) was calculated, demonstrating an average of 5.7x106 cc/g and 1.2x107 cc/g for Chocó and Tumaco basins, respectively. In order to interpret the causes of this variance, we performed a multivariate redundancy analysis (RDA), showing that the distance to the coastline is the controlling factor of the fluctuations of the relative abundances and distribution of the coccoliths in both basins.

Paleoceanographic evolution of the Japan Sea over the last 460 kyr – A coccolithophore perspective

Abstract Changes in the intensity of the influx of the Tsushima Warm Current (TWC) in the south-central part of the Japan Sea (JS), or East Sea in Korean, were reconstructed for the last 460 kyr at IODP Site U1427 using the composition and abundance of the coccolithophore assemblage. In addition, the recent distribution of coccolithophore taxa in the JS and the East China Sea was assessed using electron microscopy. Coccolithophore assemblages, dominated by Emiliania huxleyi and Gephyrocapsa species, and coccolith abundance reveal a strong relationship between sea level and ocean variability over the last five glacial/interglacial cycles, in good agreement with planktic foraminiferal data. Three different circulation modes based on calcareous nannofossil and foraminifera TWC indicators were proposed for the JS. Coccolith production was low and TWC indicators (i.e., Gephyrocapsa oceanica, Calcidiscus leptoporus s.l., and Helicosphaera carteri) absent due to the isolation of the JS during glacials in response to global sea level falls (Mode 1). In contrast, coccolith abundance and TWC indicators reach a maximum due to the most intense TWC flow through the Tsushima Strait during interglacials (Mode 3). Intermediate conditions (Mode 2) are characterized by moderate/high coccolith numbers, presence of TWC coccolith indicators, and rare TWC planktic foraminifera indicators. This mode resulted in intermittent variations in the contribution of the TWC and East China Sea coastal water due to relatively low sea level stands (ca. −90 m to −20 m). Coccoliths dominated the carbonate sequence prior to MIS 8 and were major contributors to the total carbonate of the sediment at Site U1427, suggesting high coccolithophore productivity and a bloom-type environment during MIS 11 and 9. These changes in the carbonate chemistry caused by glacio-eustacy in the JS at the northwest margin of the Pacific Ocean should be considered in future paleoceanographic and paleoclimate models.

Coccolith arrangement follows Eulerian mathematics in the coccolithophore Emiliania huxleyi.

BackgroundThe globally abundant coccolithophore, Emiliania huxleyi, plays an important ecological role in oceanic carbon biogeochemistry by forming a cellular covering of plate-like CaCO3 crystals (coccoliths) and fixing CO2. It is unknown how the cells arrange different-sized coccoliths to maintain full coverage, as the cell surface area of the cell changes during daily cycle.MethodsWe used Euler’s polyhedron formula and CaGe simulation software, validated with the geometries of coccoliths, to analyze and simulate the coccolith topology of the coccosphere and to explore the arrangement mechanisms.ResultsThere were only small variations in the geometries of coccoliths, even when the cells were cultured under variable light conditions. Because of geometric limits, small coccoliths tended to interlock with fewer and larger coccoliths, and vice versa. Consequently, to sustain a full coverage on the surface of cell, each coccolith was arranged to interlock with four to six others, which in turn led to each coccosphere contains at least six coccoliths.ConclusionThe number of coccoliths per coccosphere must keep pace with changes on the cell surface area as a result of photosynthesis, respiration and cell division. This study is an example of natural selection following Euler’s polyhedral formula, in response to the challenge of maintaining a CaCO3 covering on coccolithophore cells as cell size changes.

Coccolithophore variability across Marine Isotope Stage 11 in the Pacific sector of the Southern Ocean and its potential impact on the carbon cycle

AbstractProxy‐based reconstructions of past changes in the marine biological carbon pumps are limited, especially in the Southern Ocean. This work provides new insights into the productivity variations in the Pacific sector of the Southern Ocean. We present new data derived from three sediment cores that show glacial/interglacial coccolithophore variability across Marine Isotope Stage 11 (MIS 11). The cores were retrieved during R/V Polarstern cruise PS75 from the Subantarctic Zone and Polar Front Zone at the western flank of the East Pacific Rise and in the vicinity of the Antarctic‐Pacific Ridge. Coccolithophore assemblages were overwhelmingly dominated by the species Gephyrocapsa caribbeanica and small Gephyrocapsa. Total numbers of coccoliths, coccolith accumulation rates, coccolith fraction (CF; <20 μm fraction) Sr/Ca data, and temperature‐corrected CF Sr/Ca records consistently showed an increase in coccolithophore productivity during Termination V (MIS 12‐11 boundary), highest productivity throughout MIS 11 (~424–374 kyr), and a decrease during late MIS 11 in all the cores. We end with a discussion of back‐calculated coccolith calcification rate in the surface ocean and its potential contribution to changes in the concentration of atmospheric CO2.

Physiology regulates the relationship between coccosphere geometry and growth phase in coccolithophores

Abstract. Coccolithophores are an abundant phytoplankton group that exhibit remarkable diversity in their biology, ecology and calcitic exoskeletons (coccospheres). Their extensive fossil record is a testament to their important biogeochemical role and is a valuable archive of biotic responses to environmental change stretching back over 200 million years. However, to realise the full potential of this archive for (palaeo-)biology and biogeochemistry requires an understanding of the physiological processes that underpin coccosphere architecture. Using culturing experiments on four modern coccolithophore species (Calcidiscus leptoporus, Calcidiscus quadriperforatus, Helicosphaera carteri and Coccolithus braarudii) from three long-lived families, we investigate how coccosphere architecture responds to shifts from exponential (rapid cell division) to stationary (slowed cell division) growth phases as cell physiology reacts to nutrient depletion. These experiments reveal statistical differences in coccosphere size and the number of coccoliths per cell between these two growth phases, specifically that cells in exponential-phase growth are typically smaller with fewer coccoliths, whereas cells experiencing growth-limiting nutrient depletion have larger coccosphere sizes and greater numbers of coccoliths per cell. Although the exact numbers are species-specific, these growth-phase shifts in coccosphere geometry demonstrate that the core physiological responses of cells to nutrient depletion result in increased coccosphere sizes and coccoliths per cell across four different coccolithophore families (Calcidiscaceae, Coccolithaceae, Isochrysidaceae and Helicosphaeraceae), a representative diversity of this phytoplankton group. Building on this, the direct comparison of coccosphere geometries in modern and fossil coccolithophores enables a proxy for growth phase to be developed that can be used to investigate growth responses to environmental change throughout their long evolutionary history. Our data also show that changes in growth rate and coccoliths per cell associated with growth-phase shifts can substantially alter cellular calcite production. Coccosphere geometry is therefore a valuable tool for accessing growth information in the fossil record, providing unprecedented insights into the response of species to environmental change and the potential biogeochemical consequences.

Comparison of living and surface sediment coccolithophore assemblages in the Pacific sector of the Southern Ocean

This study examined recent coccolith surface sediment assemblages across the Pacific sector of the Southern Ocean (from Punta Arenas, Chile to Wellington, New Zealand). Twenty five stations located within 44.4°S to 65.4°S and 80.1°W to 174.5°E were selected in order to assess if and how the surface sediment assemblages reflect the present-day coccolithophore community and surface- water oceanographic conditions. The highest numbers of coccoliths in the surface sediments are reached near the East Pacific Rise and close to the Subtropical Front, at the New Zealand Margin (>6x109 coccoliths/g of sediment). The dominant taxa are Emiliania huxleyi (including types A, B, B/C and C), Calcidiscus leptoporus, Gephyrocapsa spp. (including G. muellerae, G. oceanica and G. ericsonii), Umbellosphaera tenuis and Coccolithus braarudii. Despite the recognition of species morphotypes being hampered by carbonate dissolution at some locations, we observed that numbers generally decrease southward until almost a monospecific and sporadic record of E. huxleyi (types B/C and C) and C. leptoporus south of the Polar Front occurs. The recent coccolithophore distribution was compared to already published living coccolithophore distributions (i.e., water column samples collected at the same specific locations) showing a fairly similar pattern. Combining the numbers of cells/l and coccoliths/g of sediment, different coccolithophore assemblages were established coincidentwith areas bounded by the major surface oceanographic fronts, i.e. the Subantarctic Zone and the Polar Front Zone.

Extant coccolithophores from the western equatorial Indian Ocean off Tanzania and coccolith distribution in surface sediments

Living coccolithophores and coccoliths from surface sediments were investigated in the western equatorial Indian Ocean off Tanzania, from the coast and Pemba Channel to the open ocean. In total, 49 plankton samples from 8 stations and 20 surface sediment samples collected in February 2008 were analysed. Coccolithophore standing stock ranged from barren up to almost 23,000 coccospheres/l in the upper water column and the living community comprised 47 different taxa in total. In addition, six more species were only found as detached coccoliths. Coccolithophore numbers were generally low and only Florisphaera profunda, Gephyrocapsa oceanica, and Emiliania huxleyi were numerically important (>5,000 coccospheres/l). Two distinct depth-related assemblages were identified. The upper photic zone (down to about 50m) in the Pemba Channel was dominated by G. oceanica and can be related to slightly increased nutrient conditions. In contrast, the upper photic zone community in the open ocean (down to about 70m) is characterised by high numbers of Umbellosphaera irregularis, typically indicating oligotrophic stratified waters, high sea-surface temperatures and strong water stratification. The lower photic-zone flora in the whole study area is generally dominated by F. profunda and accompanying species. A total of 40 species were identified in the surface sediments and total coccolith numbers vary drastically from <1000 to 18,200 x 106 coccoliths/g of sediment. The absolute numbers are much lower near-shore and strikingly enhanced further offshore mainly due to heavy dilution by fine-grained terrigenous sediments. Nevertheless, the occurrence of species in the plankton communities compares well to those of the surface sediment assemblages although plankton samples are from just one season. This points to an excellent preservation potential in this area, which can be explained by high supply of clay-rich sediments and a therefore rapid burial of the coccoliths in shelf and upper slope sediments.

Phosphorus availability modifies carbon production in Coccolithus pelagicus (Haptophyta)

The coccolithophore Coccolithus pelagicus (Wallich) Schiller fixes CO2 into particulate organic carbon (POC) through photosynthesis and into particulate inorganic carbon (PIC) in the form of calcite. To examine the role of phosphorus (P) availability in the production of POC and PIC, C. pelagicus subsp. braarudii (Gaarder) Geisen et al. was grown in semi-continuous cultures at three initial phosphate concentrations (P-replete, 1, and 0.5μM [P]). Reduced P-availability (1 and 0.5μM [P]) decreased POC production, while PIC production only decreased when phosphate concentrations became growth limiting (0.5μM [P]). This decrease has not been observed previously in batch cultures, highlighting the inadequacy of the batch culture approach with regard to determining carbon production. The reduction in growth rate by 50% at 0.5μM [P] was accompanied by a doubling in cell volume (and POC). PIC production was halved, resulting in a lowered PIC to POC ratio. The average number of coccoliths per cell (and PIC content) remained the same among treatments, despite the significant change in cell size. Our data suggest that POC production in C. pelagicus is more sensitive towards a moderate reduction in phosphorus availability than PIC production. Once phosphorus availability limits cell division, however, phosphorus resources are invested into POC rather than PIC production. This reduces cell density and sinking rates, indicating that coccoliths do not act as ballast for reaching deeper nutrient-rich layers under nutrient limitation.

Cell geometry records the physiological responses of coccolithophores to Paleogene climate change

The physiology and ecology of the calcifying marine phytoplankton group coccolithophores are expected to be susceptible to future changes in environmental conditions forced by increasing atmospheric carbon dioxide and temperature (e.g., Fabry et al., 2008). A key trait of the physiological state of a phytoplankton cell is cell size (e.g., Finkel et al., 2007), which we have captured from exquisitely preserved fossil coccospheres in biometric measurements of coccolith length, coccosphere size and number of coccoliths per coccosphere (Fig. 1). Our exquisitely preserved calcareous microfossils are obtained from sites where post-depositional alteration of the calcite is virtually absent. Typically these sites contain hemipelagic, clay-rich lithologies with high sedimentation rates that rapidly encapsulate calcareous microfossils, isolating them within an impermeable matrix (Bown et al., 2008). These sediments contain a remarkably high diversity of fossil coccolithophores and an unusually high abundance of intact coccospheres, where the original spherical-subspherical cell covering of coccoliths is completely preserved, instead of the typical disarticulation into loose coccoliths. The pristine preservation of fragile and taxonomically important central-area structures in coccoliths combined with the preservation of very small (<3μm)coccolithsenablesustostudycoccospheregeometry across a wide variety of Paleogene taxa at species level. We present material from Tanzania (Nicholas et al., 2006), New Jersey (Miller et al., 1998) and Californian (John et al., 2008) continental shelf environments, where the shallow water depth minimized water-column disaggregation and dissolution and the shelf setting promoted high sedimentation rates. The thick sequence of clay-rich oozes at deep-sea Labrador Sea site ODP 647A (Firth, 1989) has also yielded diverse coccospheres that illustrate a high-latitude North Atlantic Eocene assemblage. Intact fossil coccospheres can be interpreted on a cellular level through analogy with the cellular geometry of their modern counterparts (Gibbs et al., 2013). This facilitates an unprecedented insight into the cellular physiology of cells that are millions of years old and its link to population-level responses to climate change. Our biometric data (following Fig. 1; Gibbs et al., 2013 and Henderiks, 2008) reveals the cellular growth and calcification response of more than 30 coccolithophore species to long-term variability in sea-surface conditions during the Paleogene greenhouse interval, between 66 and 34 million years ago. Cell geometry from abundant coccospheres of the common Paleogene genera

Chronological and paleoceanographic constraints ofMiocene toPliocene ‘mud sea’ in theRyukyuIslands (southwesternJapan) based on calcareous nannofossil assemblages

AbstractTheCenozoic sedimentary succession inOkinawa‐jima, including the upperMiocene toPleistocene siliciclastic deposits (ShimajiriGroup) and thePleistocene reef to shelf deposits (RyukyuGroup), suggests a drastic paleoceanographic change from a ‘mud sea’ to a ‘coral sea.’ To delineate the paleoceanographic evolution of the mud sea, we quantified the stratigraphic distribution of the calcareous nannofossil assemblages from theShimajiriGroup in a 2119.49 m‐deep well (NanjoR1ExploratoryWell) drilled in southernOkinawa‐jima (RyukyuIslands, southwesternJapan). Four lateMiocene andPliocene datum planes were found in the studied interval: the first occurrence ofAmaurolithusspp. (7.42 Ma), the last occurrence ofDiscoaster quinqueramus(5.59 Ma), the first occurrence ofCeratolithus rugosus(5.12 Ma), and the last occurrence ofReticulofenestra pseudoumbilicus(3.70 Ma). The calcareous nannofossil assemblages from theTomigusukuFormation and the lower part of theYonabaruFormation are characterized by a lower total number of coccoliths and abundantSphenolithus abiesthat is associated, at times, with commonDiscoasterspp. Overall, these suggest the existence of oligotrophic conditions between 5.3 and &gt;8.3 Ma. The total number of coccoliths increased and smallReticulofenestraspp. became more common in the middle part of theYonabaru Formation, suggesting that eutrophic conditions were present between 3.5 and 5.3 Ma. The rare occurrence of calcareous nannofossils in the upper part of theYonabaruFormation indicates a return to oligotrophic conditions at 3.5 Ma. Micropaleontological evidence suggests that these oceanographic changes were likely caused by local tectonic movement (shallowing of the sedimentary basin in which theShimajiriGroup was deposited).

Influence of changing carbonate chemistry on morphology and weight of coccoliths formed by &amp;lt;i&amp;gt;Emiliania huxleyi&amp;lt;/i&amp;gt;

Abstract. The coccolithophore Emiliania huxleyi is a marine phytoplankton species capable of forming small calcium carbonate scales (coccoliths) which cover the organic part of the cell. Calcification rates of E. huxleyi are known to be sensitive to changes in seawater carbonate chemistry. It has, however, not yet been clearly determined how these changes are reflected in size and weight of individual coccoliths and which specific parameter(s) of the carbonate system drive morphological modifications. Here, we compare data on coccolith size, weight, and malformation from a set of five experiments with a large diversity of carbonate chemistry conditions. This diversity allows distinguishing the influence of individual carbonate chemistry parameters such as carbon dioxide (CO2), bicarbonate (HCO3−), carbonate ion (CO32−), and protons (H+) on the measured parameters. Measurements of fine-scale morphological structures reveal an increase of coccolith malformation with decreasing pH suggesting that H+ is the major factor causing malformations. Coccolith distal shield area varies from about 5 to 11 μm2. Changes in size seem to be mainly induced by varying [HCO3−] and [H+] although influence of [CO32−] cannot be entirely ruled out. Changes in coccolith weight were proportional to changes in size. Increasing CaCO3 production rates are reflected in an increase in coccolith weight and an increase of the number of coccoliths formed per unit time. The combined investigation of morphological features and coccolith production rates presented in this study may help to interpret data derived from sediment cores, where coccolith morphology is used to reconstruct calcification rates in the water column.

Conflicting coccolithophore and geochemical evidence for productivity levels in the Eastern Mediterranean sapropel S1

Abstract The cyclic development of anoxic conditions in the eastern Mediterranean deep sea waters is one of the most fascinating research topics in paleoceanographic studies. In combination with bottom water stagnation, enhanced primary production is a common explanation for the deposition of organic-rich layers (sapropels). This is supported by extensive evidence from both geochemical and micropaleontological studies. The correspondence of recent sapropel layers with peaks of the lower photic zone coccolithophore species Florisphaera profunda has been interpreted as a proxy for the development of a deep chlorophyll maximum (DCM), due to the pycnocline/nutricline shallowing into the lower part of the photic zone. We present millennial-scale data for coccolithophore assemblages from sediments across the most recent sapropel (S1), in the ODP Hole 964B drilled in the Ionian Sea. Relative and absolute abundances of taxa are compared with selected elemental composition of the bulk sediments. The Mn/Al and Ba/Al profiles are used to determine the original thickness of the S1 interval, and show that the upper part of S1 was affected by post-depositional oxidation of organic matter. The Nannofossil Accumulation Rate, defined by the number of coccoliths·cm− 2·kyr− 1, suggests that there is no evidence of increased productivity within most of the sapropel layer. In fact, coccolithophore production was at its minimum in the lower part. Minimum coccolith concentrations are reached despite the increase in F. profunda in both relative and absolute abundance. We suggest that the DCM deduced from the increased productivity of this species did not significantly contribute to the putative overall increased primary productivity during the deposition of most of the sapropel layer. Within the upper oxidized part of S1, coccolith accumulation was at least five times higher than in the lower part. This period of high coccolith productivity finds a counterpart in the increase of the Ba/Al ratio. The total concentration of coccoliths is again controlled by the amount of E. huxleyi, but it is also supported by concomitant increases in all the other groups, suggesting that coccolithophore productivity increased throughout the year and through the total vertical extent of the photic zone. At site 964, this is apparently the only moment when coccolithophores contributed substantially to the increased primary productivity generally assumed for the S1 layer.

Comparison of different preparation and analysis techniques for quantitative coccolith studies focusing on biogeographic patterns of species

The scanning ElectronMicroscope (SEM) and the PetrographicMicroscope (Light Microscope, LM) are devices which both are used in routine analysis of coccolithophore assemblages, but comparisons and/or combinations of quantitative data from both sources are difficult. In this paper a comparison is made between the results obtainedwith the Flores and Sierro settling technique (1997) for LMand the Andruleit filtration technique (1996) for SEM, considering their advantages and drawbacks. Twenty-six surface sediment samples from the SouthAtlantic and Southeast Pacificwere studied.All the taxa distinguished were reduced to fourteen groups accounting for 100%. The biogeographical patterns of coccolithophorid species and species groups determined using both techniques are highly comparable, although the trends in relative and absolute numbers are not always identical. In particular, the numbers of coccoliths per gram of sediment are higher in the case of the filtration technique/SEM-technique than for the settling technique/LMtechnique and an approach is introduced to estimate LM values using SEM counts with a linear regression equation. The results obtained allow different methodologies to be compared for the study of current coccolithophore biogeography.

Changes in palaeoceanography and palaeoecology during Marine Isotope Stage (MIS) 5 in the eastern North Atlantic (ODP Site 980) deduced from calcareous nannoplankton observations

Calcareous nannoplankton analyses on late quaternary sediments from the eastern North Atlantic ODP Site 980 (55°29′N, 14°42′W) provide detailed insight into palaeoceanographic and palaeoclimatic changes that occurred throughout the Termination II and the adjacent interglacial of the Marine Isotope Stage (MIS) 5. This study presents the development of the coccolith assemblage throughout the interglacial MIS 5 towards the beginning of the glacial MIS 4 in the vicinity of the Rockall Plateau and investigates and characterises the impact of climatic and environmental variations on the coccolith assemblage distribution between 135 and 65 ky. In general, the coccolith assemblage is dominated by Gephyrocapsa muellerae and Emiliania huxleyi, whilst significant changes in palaeoceanographic and palaeoclimatic conditions are mainly shown by variations of subordinate species. A drastic increase in coccolith accumulation rates and a change from a less to a higher diverse species assemblage indicate a rapid increase in surface water temperatures during the onset of MIS 5 from c. 127.5 ky on. Highest coccolith numbers, high numbers of taxa and a large diversity indicate highest coccolithophore primary productivity and peak interglacial conditions during MIS 5.5, which are due to the high influence of relatively warm surface water to this region. Coccolith numbers peak again around 120 ky and decline afterwards but stay above glacial levels. The two cooling events of MIS 5.4 and 5.2 interrupt the generally warm conditions and are indicated by lowered coccolith numbers, a drop of thermophile species and a reduction of the species diversity. Decreasing coccolith numbers and a slightly reduced diversity indicate that environmental conditions deteriorated towards the onset of MIS 4. The analysis of the coccolith assemblage reveals that not only the stadial events MIS 5.4 and 5.2 are characterised by colder conditions, but furthermore confirms the upcoming notion that MIS 5.5 was terminated by a slight short-term cooling of the surface water which occurred around 124 ky.

Light scattering by coccoliths detached from Emiliania huxleyi.

We used in situ radiance/irradiance profiles to retrieve profiles of the spectral backscattering coefficient for all particles in an E. huxleyi coccolithophore bloom off the coast of Plymouth, UK. At high detached coccolith concentrations the spectra of backscattering all showed a minimum near approximately 550 to 600 nm. Using flow cytometry estimates of the detached coccolith concentration, and assuming all of the backscattering (over and above the backscattering by the water itself) was due to detached coccoliths, we determined the upper limit of the backscattering cross section (sigma(b)) of individual coccoliths to be 0.123+/-0.039 microm(2)/coccolith at 500 nm. Physical models of detached coccoliths were then developed and the discrete dipole approximation was used to compute their average backscattering cross section in random orientation. The result was 0.092 microm(2) at 500 nm, with the computed sigma(b) displaying a spectral shape similar to the measurements, but with less apparent increase in backscattering toward the red. When sigma(b) is computed on a per mole of calcite, rather than a per coccolith basis, it agreed reasonably well with that determined for acid-labile backscattering at 632 nm averaged over several species of cultured calcifying algae. Intact coccolithophore cells were taken into account by arguing that coccoliths attached to coccolithophore cells (forming a "coccosphere") backscatter in a manner similar to free coccoliths in random orientation. Estimating the number of coccoliths per coccosphere and using the observed number of coccolithophore cells resulted is an apparent backscattering cross section at 500 nm of 0.114+/-0.013 microm(2)/coccolith, in satisfactory agreement with the measured backscattering.

Coccolithophore size rules — Reconstructing ancient cell geometry and cellular calcite quota from fossil coccoliths

Algal cell size exerts a fundamental influence on the stable isotopic fractionation during photosynthesis and biocalcification, as well as the incorporation of trace elements in coccolith calcite by calcifying haptophytes (the coccolithophores). Therefore, it is important to evaluate the influence of ancient coccolithophore cell size on coccolithophorid-derived geochemical proxies that are applied in paleoceanographic studies. However, in contrast to planktonic foraminifera, for which cell size may be directly estimated from their fossilized calcite shells, the reconstruction of ancient coccolithophore cell dimensions appears hampered because the sediment record is dominated by single coccoliths, rather than intact coccospheres — the armor of multiple interlocking calcite platelets that surround live cells. Solving this apparent problem, this paper presents quantitative constraints on coccolith size, coccosphere and cell diameters, for three main Cenozoic genera of coccolithophore ( Reticulofenestra, Cyclicargolithus and Coccolithus) through detailed biometry of rarely fossilized coccospheres of middle Eocene to early Miocene age. Together, these taxa are most dominant in Cenozoic deep-sea sediments, providing an exquisitely detailed record of their evolution and the bulk of biogenic carbonate burial through time. Accurate estimates of coccolithophore cell size can be made by relatively simple size measurements of individual coccoliths in fossil assemblages, since coccolith size is strongly linearly correlated to both coccosphere- and cell diameter. Additional general coccolith ‘size rules’ are confirmed by the morphometric data: (1) coccolith thickness increases with size, (2) elliptical placoliths are more circular at larger size, and (3) the number of coccoliths per coccosphere is rather invariable within the investigated Cenozoic genera. The latter observation offers better control on (minimum) estimates of cellular calcite quota in the ancestors of today's prolific bloom-forming species Emiliania huxleyi, Gephyrocapsa spp. and Coccolithus pelagicus.

Pleistocene fluctuations in the northern Benguela Current system as revealed by coccolith assemblages

Late Pleistocene coccolith data of ODP Site 1082 from the eastern South Atlantic off Namibia were analysed to document spatial and temporal changes in surface–ocean circulation, upwelling intensity, and associated productivity. The studied site is located on the continental slope close to prominent oceanographic features such as the coastal upwelling mixing area, the open-oceanic realm, and the warm-water regime of the Angola Current. Highest numbers of total coccoliths up to >30×10 9 coccoliths g −1 sediment were observed during relatively warm periods characterised by decreased upwelling intensity. These elevated numbers of coccoliths are due to higher surface water temperatures and document a domain probably influenced by lower nutrient concentrations in an area where oceanic and filamentous water mix. In contrast, low numbers of coccoliths during glacial periods probably characterise time intervals of enhanced upwelling accompanied by a broad filamentous mixing area. Coccoliths of the genus Gephyrocapsa are the most abundant taxa in samples of Site 1082. Their occurrences are characterised by abrupt changes in the investigated time interval. In addition, Calcidiscus leptoporus, Pseudoemilinia lacunosa, and Reticulofenestra asanoi contribute a common part of the assemblage. Coccoliths account for more than half of the carbonate, with peak contribution of up to >80% in the interval 560 to 280 ka when Gephyrocapsa caribbeanica is the major CaCO 3 producer. Increased carbonate accumulation during this time interval point to an overall weakening of the coastal upwelling intensity accompanied by a reduction of the mixing zone influencing the site location during this event.