Coccolithophore Bloom Research Articles

Dissolved inorganic carbon dynamics and air‐sea carbon dioxide fluxes during coccolithophore blooms in the northwest European continental margin (northern Bay of Biscay)

We report a data set of dissolved inorganic carbon (DIC) obtained during three cruises in the northern Bay of Biscay carried out in June 2006, May 2007, and May 2008. During these cruises, blooms of the coccolithophore Emiliania huxleyi occurred, as indicated by patches of high reflectance on remote sensing images, phytoplankton pigment signatures, and microscopic examinations. Total alkalinity showed a nonconservative behavior as a function of salinity due to the cumulative effect of net community calcification (NCC) on seawater carbonate chemistry during bloom development. The cumulative effect of NCC and net community production (NCP) on DIC and the partial pressure of CO2 (pCO2) were evaluated. The decrease of DIC (and increase of pCO2) due to NCC was overwhelmingly lower than the decrease of DIC (and decrease of pCO2) due to NCP (NCC:NCP ≪ 1). During the cruises, the northern Bay of Biscay acted as a sink of atmospheric CO2 (on average ∼−9.7 mmol C m−2 d−1 for the three cruises). The overall effect of NCC in decreasing the CO2 sink during the cruises was low (on average ∼12% of total air‐sea CO2 flux). If this is a general feature in naturally occurring phytoplankton blooms in the North Atlantic Ocean (where blooms of coccolithophores are the most intense and recurrent), and in the global ocean, then the potential feedback on increasing atmospheric CO2 of the projected decrease of pelagic calcification due to thermodynamic CO2 “production” from calcification is probably minor compared to potential feedbacks related to changes of NCP.

Coccolithophore dynamics in non‐bloom conditions during late summer in the central Iceland Basin (July‐August 2007)

Measurements of primary production (PP), calcification (CF), and coccolithophore abundance were made during late summer (July‐August 2007) in the Iceland Basin. Low numbers of coccolithophore cells and detached coccoliths (< 1 × 103 cells mL−1 and 1‐15 × 103 coccoliths mL−1, respectively) indicated a non‐bloom community, with Emiliania huxleyi as the dominant coccolithophore in terms of abundance, coccolithophore organic biomass, and cell calcite. PP ranged from 0.1 to 2 [mol C m−3 d−1, while CF ranged from 10 to 250 [mol C m−3 d−1, with both typically decreasing with depth. Coccolithophores were estimated to contribute 10‐20% toward total chlorophyll a, phytoplankton carbon, and PP within the euphotic zone. In these non‐bloom conditions, ~ 30‐60% of the total calcite in the water column was present as detached coccoliths rather than whole cells. Both cell numbers and variability in cell‐normalized CF controlled the magnitude of total CF, and hence both physiological limits to cell CF and growth, as well as mortality factors, need to be taken into account when examining oceanic coccolithophore communities. Combining cell‐normalized CF with an estimate of coccolith calcite gave coccolith production rates (0.4‐1.8 h−1) similar to those reported in the literature for laboratory cultures of E. huxleyi. None of the factors currently associated with coccolithophore blooms (irradiance, mixed‐layer depth, nitrate, phosphate, or calcite saturation) showed a clear correlation with community or cellular CF. Hence, although mortality is likely to control cell numbers, other factors such as trace metal (iron) availability may influence coccolithophore physiology in the central Iceland Basin during late summer.

Biogeochemical study of a coccolithophore bloom in the northern Bay of Biscay (NE Atlantic Ocean) in June 2004

The present paper synthesizes data obtained during a multidisciplinary cruise carried out in June 2004 at the continental margin of the northern Bay of Biscay. The data-set allows to describe the different stages of a coccolithophore bloom dominated by Emiliania huxleyi. The cruise was carried out after the main spring phytoplankton bloom that started in mid-April and peaked in mid-May. Consequently, low phosphate (PO 4 < 0.2 μM) and silicate (DSi < 2.0 μM) concentrations, low partial pressure of carbon dioxide (pCO 2) and high calcite saturation degree in surface waters combined with thermal stratification, probably favoured the blooming of coccolithophores. During the period of the year our cruise was carried out, internal tides induce enhanced vertical mixing at the continental shelf break leading to the injection of inorganic nutrients to surface waters that probably trigger the bloom. The bloom developed as the water-column stratified and as the water mass was advected over the continental shelf, following the general residual circulation in the area. The most developed phase of the bloom was sampled in a remote sensed high reflectance (HR) patch over the continental shelf that was characterized by low chlorophyll-a (Chl-a) concentration in surface waters (<1.0 μg L −1), high particulate inorganic carbon (PIC) concentration (∼8 μmol L −1) and coccolithophore abundance up to 57 × 10 6 cells L −1. Transparent exopolymer particles (TEP) concentrations ranged between 15 and 75 μg C L −1 and carbon content of TEP represented up to 26% of the particulate organic carbon (POC; maximum concentration of 15.5 μmol L −1 in the upper 40 m). Integrated primary production (PP) ranged between 210 and 680 mg C m −2 d −1 and integrated calcification (CAL) ranged between 14 and 140 mg C m −2 d −1, within the range of PP and CAL values previously reported during coccolithophore blooms in open and shelf waters of the North Atlantic Ocean. Bacterial protein production (BPP) measurements in surface waters (0.3–0.7 μg C L −1 h −1) were much higher than those reported during early phases of coccolithophore blooms in natural conditions, but similar to those during peak and declining coocolithophorid blooms reported in mesocosms. Total alkalinity anomalies with respect to conservative mixing (ΔTA) down to −49 μmol kg −1 are consistent with the occurrence of biogenic precipitation of calcite, while pCO 2 remained 15–107 μatm lower than atmospheric equilibrium (372 μatm). The correlation between ΔTA and pCO 2 suggested that pCO 2 increased in part due to calcification, but this increase was insufficient to overcome the background under-saturation of CO 2. This is related to the biogeochemical history of the water masses due to net carbon fixation by the successive phytoplankton blooms in the area prior to the cruise, hence, the investigated area remained a sink for atmospheric CO 2 despite calcification.

Coccolithophore bloom detection in the north east Atlantic using SeaWiFS: Algorithm description, application and sensitivity analysis

Coccolithophores are the largest source of calcium carbonate in the oceans and are considered to play an important role in oceanic carbon cycles. Current methods to detect the presence of coccolithophore blooms from Earth observation data often produce high numbers of false positives in shelf seas and coastal zones due to the spectral similarity between coccolithophores and other suspended particulates. Current methods are therefore unable to characterise the bloom events in shelf seas and coastal zones, despite the importance of these phytoplankton in the global carbon cycle. A novel approach to detect the presence of coccolithophore blooms from Earth observation data is presented. The method builds upon previous optical work and uses a statistical framework to combine spectral, spatial and temporal information to produce maps of coccolithophore bloom extent. Validation and verification results for an area of the north east Atlantic are presented using an in situ database ( N = 432) and all available SeaWiFS data for 2003 and 2004. Verification results show that the approach produces a temporal seasonal signal consistent with biological studies of these phytoplankton. Validation using the in situ coccolithophore cell count database shows a high correct recognition rate of 80% and a low false-positive rate of 0.14 (in comparison to 63% and 0.34 respectively for the established, purely spectral approach). To guide its broader use, a full sensitivity analysis for the algorithm parameters is presented.

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.

Chalk‐Ex—Fate of CaCO3 particles in the mixed layer: Evolution of patch optical properties

The fate of particles in the mixed layer is of great relevance to the global carbon cycle as well as to the propagation of light in the sea. We conducted four manipulative field experiments called “Chalk‐Ex” in which known quantities of uniform, calcium carbonate particles were injected into the surface mixed layer. Since the production term for these patches was known to high precision, the experimental design allowed us to focus on terms associated with particle loss. The mass of chalk in the patches was evaluated using the well‐calibrated light‐scattering properties of the chalk plus measurements from a variety of optical measurements and platforms. Patches were surveyed with a temporal resolution of hours over spatial scales of tens of kilometers. Our results demonstrated exponential loss of the chalk particles with time from the patches. There was little evidence for rapid sinking of the chalk. Instead, horizontal eddy diffusion appeared to be the major factor affecting the dispersion of the chalk to concentrations below the limits of detection. There was unequivocal evidence of subduction of the chalk along isopycnals and subsequent formation of thin layers. Shear dispersion is the most likely mechanism to explain these results. Calculations of horizontal eddy diffusivity were consistent with other mixed layer patch experiments. Our results provide insight into the importance of physics in the formation of subsurface particle maxima in the sea, as well as the importance of rapid coccolith production and critical patch size for maintenance of natural coccolithophore blooms in nature.

Environmental factors controlling the Barents Sea spring‐summer phytoplankton blooms

We provide an analysis of the seasonal change of the physical forcing factors and their impact on the timing and intensity of phytoplankton blooms in the Barents Sea, with emphasis on the different functional groups that can be distinguished (coccolithophores and other phytoplankton groups) using satellite remote sensing algorithms. Our analyses are based on an integration of satellite derived products and historical hydrographic data. There is a significant phase shift between the peaks of the diatom bloom in May to the coccolithophore bloom in August. Light and nutrient variability, driven by the large seasonal changes of solar irradiance and mixed layer depth in the Barents Sea, are the major environmental factors controlling these phytoplankton blooms. Based on previous field campaigns that identified Emiliana huxleyi as the most predominant species of coccolithophores in the Barents Sea, we conclude that the high concentration of calcite retrieved by ocean color satellites in summer is a result of bloom‐forming coccolithophores of this species. A strong correlation between calcite concentration and wind speed squared (r2 = 0.8) was found during the peak of the bloom. We suggest that this correlation is an indication of CO2 fertilization resulting from regionally enhanced uptake of atmospheric CO2.

Space monitoring of pollution of the Russian sector of the Azov-Black Sea basin in 2008

Technology of space monitoring of the state of water bodies and results of its application for studying the Azov-Black Sea basin in 2008 are considered. Based on the processing of more than 1000 satellite images and ground-based station data, basic characteristic features of the marine environmental pollution are determined which are connected with suspension dispersion, phytoplankton and algae growth, ship dumping of oil products (more than 62 oil patches were revealed), etc. The influence of dynamic structures in the coastal zone on the spatiotemporal distribution of the sea surface pollution parameters, and their contribution to mechanisms of water purification and self-purification are estimated. In particular, new data are obtained about the evolution of “Caucasian anticyclones,” about the dates of intensification of the Main Black Sea Current, and about features of coccolithophore bloom in the abyssal area of the Black Sea, etc.

DMS air/sea flux and gas transfer coefficients from the North Atlantic summertime coccolithophore bloom

Dimethylsulfide (DMS) atmospheric and oceanic concentrations and eddy covariance air/sea fluxes were measured over the N. Atlantic Ocean during July 2007 from Iceland to Woods Hole, MA, USA. Seawater DMS levels north of 55°N ranged from 3 to 17 nM, with variability related to the satellite‐derived distributions of coccoliths and to a lesser extent, chlorophyll. For the most intense bloom region southwest of Iceland, DMS air/sea fluxes were as high as 300 μmol m−2 d−1, larger than current model estimates. The observations imply that gas exchange coefficients in this region are significantly greater than those estimated using most gas transfer parameterizations. South of 55°N, DMS levels were lower and the gas transfer coefficients were similar to those observed in other regions of the ocean. The data suggest that DMS emissions from the bloom region may be significantly larger than current estimates. The anomalous gas exchange coefficients likely reflect strong near‐surface, water column DMS gradients influenced by physical and biological processes.

Investigation of the variations in the water leaving polarized reflectance from the POLDER satellite data over two biogeochemical contrasted oceanic areas

The biogeochemical characterization of marine particles suspended in sea water, is of fundamental importance in many areas of ocean science. Previous studies based on theoretical calculations and field measurements have demonstrated the importance of the use of the polarized light field in the retrieval of the suspended marine particles properties. However, because of the weakness of the water leaving polarized signal and of the limited number of appropriate spatial sensors, such measurements have never been exploited from space. Here we show that the marine polarized remote sensing reflectance, as detected from the POLarization and Directionality of the Earth's Reflectances (POLDER) sensor, can be measured from space over bright waters and in absence of aerosols. This feasibility study is carried out over two oceanic areas characterized by different nature of the bulk particulate assemblage: the Barents sea during an intense coccolithophore bloom, and the Rio de la Plata estuary waters dominated by suspended sediments. The retrieved absolute values of the degree of polarization, P, its angular pattern, and its behavior with the scattering level are consistent with theory and field measurements. Radiative transfer simulations confirm the sensitivity of the POLDER-2 P values to the nature of the particulate assemblage. These preliminary results are very promising for the assessment of the bulk particle composition from remote sensing of the polarized signal, at least over highly scattering waters.

Development and validation of a molecular technique for the analysis of archived formalin-preserved phytoplankton samples permits retrospective assessment of Emiliania huxleyi communities

Abstract The coccolithophores, particularly the species Emiliania huxleyi (Lohmann) Hay & Mohler, account for the bulk of global calcium carbonate production and as such play a fundamental role in global CO 2 cycling and the carbonate chemistry of the oceans. To evaluate the response of this functional group to the effects of climate change, we undertook a feasibility study to determine whether a retrospective approach could be used on archived coccolithophore datasets. We demonstrate for the first time a technique for the extraction of E. huxleyi nucleic acids from archived formalin-fixed samples of the long-term Continuous Plankton Recorder. Molecular analysis of a nine year old formalin-fixed sample reveals the presence of a diverse population of E. huxleyi genotypes within a developing coccolithophore bloom. In addition, E. huxleyi sequences were amplified from a number of formalin-fixed samples, the earliest of which was collected in August 1972. This molecular assay promises the possibility of studying global variations in the distribution and genetic make-up of E. huxleyi communities over extensive periods of time.

Patrick Michael Holligan: a short biography

Our understanding of the role of marine phytoplankton in the global biogeochemical cycles of carbon and sulphur, particularly the rates and variability of primary production and calcification, phytoplankton activity and ecology in the subsurface chlorophyll maximum, and the use of satellite remote sensing to detect coccolithophore blooms, has progressed substantially through research initiated, led and undertaken by Patrick M. Holligan. The enthusiasm and commitment of Patrick’s colleagues for both this special issue and the symposium on “Marine Plankton: From Cells to Ecosystems” held in his honour in April 2008 at Plymouth, UK are testament to the high esteem in which he is held within the international scientific community. His expertise as a scientific leader, teacher and writer has inspired students and collaborators over more than three decades. In particular, his chairmanship during the early 1990s of the Planning Committee for the “Land-Ocean Interactions in the Coastal Zone” (LOICZ) project led to the establishment of a new core project within the International Geosphere-Biosphere Programme (IGBP). As the first Head of the School of Ocean and Earth Science (SOES), University of Southampton (1998– 2002), Patrick had responsibility for substantial expansion of the School, including 13 new academic appointments. As one of the first UK Principal Investigators to propose an open-ocean latitudinal time-series study, he helped initiate the development of the Atlantic Meridional Transect (AMT) programme (www.amt-uk. org), and as the President of the Council of the Sir Alister Hardy Foundation for Ocean Science (SAHFOS), he guided the transition to a new Directorship of the Continuous Plankton Recorder programme. Patrick gained an MA in Botany from Christs College, Cambridge in 1966. He then moved to the Department of Botany at the University of Leeds where he completed his PhD in 1970 on “Carbohydrate metabolism in the fungus Dendryphiella salina“ under the supervision of David Jennings. During the first year of his PhD, Patrick assisted Ed Drew in some research on acclimations by seaweeds to changes in light intensity and quality that required summer fieldwork in Malta. It was here that Patrick practised his self-taught skills in scuba diving, met John Woods for the first time, acted as a guinea pig for behavioural research into the effects of nitrogen narcosis, and developed a serious interest in the marine environment. While doing his PhD, Patrick also met and married his wife, Sue. Patrick then undertook a postdoctoral appointment (1969–1973) with David Lewis in the Department of Botany at the University of Sheffield to work on the physiology of higher plants infected by rust fungi. In 1973, Patrick joined the staff at the Marine Biological Association (MBA) in Plymouth UK as a Research Scientist, despite his only “marine” credentials being research on a marine fungus and his hobby of scuba diving. He sought external advice from David Cushing and Tim Wyatt at Lowestoft and from Jack Talling at Windermere about developing a new research programme on marine phytoplankton and then, over morning coffee, met Robin Pingree, a physicist with an interest in biology who had come from the Institute of Oceanographic Sciences (IOS), Wormley, UK to work

Effects of acidification and primary production on coccolith weight: Implications for carbonate transfer from the surface to the deep ocean

The coccolithophores are not only an important group of oceanic primary producers; they are also one of the main carbonate producers in the ocean. Because the calcium carbonate plates (coccoliths) secreted by these unicellular algae are so small and light (a few picograms each), they cannot be directly weighed, with the result that very little is known about the effect of primary production and dissolution on the coccoliths. Using a new method that allows a rapid estimate of the weight of discrete coccoliths, we analyzed the effect of dissolution. The results of two acidification experiments, using cultured and fossil coccoliths, indicate that acidification does not change significantly the weight and size of coccoliths. On the basis of these experiments, we identify four parameters for identifying the effects of dissolution on a coccolith assemblage. These parameters were applied in samples from two sediment trap time series taken at the same tropical Atlantic site (EUMELI), but separated by 2000 m water depth. There was no evidence of increased dissolution with water depth between 250 and 2500 m. This is indicative of the absence of dissolution of coccoliths between the photic zone and the lysocline. Other studies have identified supra‐lysoclinal dissolution, and we propose that most of this takes place in the photic zone and possibly in the guts of grazers. Most of the coccolith weight changes observed over the duration of trap deployment were related to the occurrence of two coccolithophore blooms which resulted in significant increases in average coccolith weight of the dominant coccolithophore species during the blooms. Changes in growth rate and cell density appear to have a significant effect on the weight of coccoliths. To test this observation, we cultured E. huxleyi at different P and N concentrations. This test confirmed that coccoliths weigh more when coccolithophore production is highest. An important consequence for the carbon pump is that during higher primary production events the coccoliths will increase the ballasting of the aggregates in which they are carried to the seafloor, increasing the rate and amount of organic matter sequestered into the deep sea.

Modeling coccolithophores in the global oceans

Abstract Coccolithophores are important ecological and geochemical components of the global oceans. A global three-dimensional model was used to simulate their distributions in a multi-phytoplankton context. The realism of the simulation was supported by comparisons of model surface nutrients and total chlorophyll with in situ and satellite observations. Nitrate, silica, and dissolved iron surface distributions were positively correlated with in situ data across major oceanographic basins. Global annual departures were +18.9% for nitrate (model high), +5.4% for silica, and +45.0% for iron. Total surface chlorophyll was also positively correlated with satellite and in situ data sets across major basins. Global annual departures were −8.0% with Sea-viewing Wide Field-of-view Sensor (SeaWiFS) (model low), +1.1% with Aqua, and −17.1% with in situ data. Global annual primary production estimates were within 1% and 9% of estimates derived from SeaWiFS and Aqua, respectively, using a common primary production algorithm. Coccolithophore annual mean relative abundances were 2.6% lower than observations, but were positively correlated across basins. Two of the other three phytoplankton groups, diatoms and cyanobacteria, were also positively correlated with observations. Distributions of coccolithophores were dependent upon interactions and competition with the other phytoplankton groups. In this model, coccolithophores had a competitive advantage over diatoms and chlorophytes by virtue of a greater ability to utilize nutrients and light at low values. However, their higher sinking rates placed them at a disadvantage when nutrients and light were plentiful. In very low nutrient conditions, such as the mid-ocean gyres, coccolithophores were unable to compete with the efficient nutrient utilization capability and low sinking rate of cyanobacteria. Comparisons of simulated coccolithophore distributions with satellite-derived estimates of calcite concentration and coccolithophore blooms showed some agreement, but also areas of departure. Vast blooms observed in the North Atlantic were well-represented by the model. However, model coccolithophores were nearly absent in the North Pacific, while calcite estimates suggested widespread abundance in summer. In situ observations supported the satellite calcite, suggesting a deficiency in the model. New satellite estimates of phytoplankton groups indicated good agreement of diatoms in one case, and poor agreement in general in another. Comparisons of phytoplankton group primary production with other models showed wide disparity. The divergence among models and satellite estimates is common for such an emerging field of research. The quantitative comparisons with in situ observations are encouraging, but disparities with model and satellite estimates suggested that further research is needed.

Nutrient and phytoplankton dynamics in the Queen Charlotte Islands (Canada) during the summer upwelling seasons of 2001–2002

The Queen Charlotte Islands, Canada, lie at the northern extreme of the coastal upwelling system of the eastern North Pacific Ocean (51-54°N). In this study, the first observations of spatial and inter-annual patterns in nutrient inventories, chlorophyll (Chl) a and phytoplankton assemblages are reported and related to oceanographic conditions in near-shore waters of the island archipelago. Stronger and more persistent upwelling in 2002 coincided with higher nutrient and Chl a standing stocks compared to 2001 and a higher proportion of diatoms. Dinoflagellates were more prevalent in 2001, including several potentially harmful species. At sub-seasonal scales, Chl a concentrations were greatest during downwelling conditions and smallest during upwelling conditions. On the west coast, weak water column stratification, high relative proportions of diatoms and large nutrient inventories accompanied upwelling-favourable conditions, whereas on the east coast, there was no direct relationship between the Bakun Upwelling Index and water column stability. According to redundancy analysis, variability in species composition was best explained by sea surface temperature, the depth of the euphotic zone and nutrient inventories. The east coast supported blooms of coccolithophores within protected bays, confirming previous satellite observations that showed bright patches in these areas. The data illustrate that moderate upwelling can have an important influence on near-shore algal standing stocks and species composition at the northern extreme of the upwelling system off the west coast of North America, and that topographical complexity may be important for the development of phytoplankton blooms.

Identification of coccolithophore blooms in the SE Atlantic Ocean off Namibia by satellites and in-situ methods

Sporadic occurrences of milky turquoise waters visible in true colour satellite imagery in the Benguela upwelling system off Namibia are characterized by high reflectances due to enhanced scattering properties. Previous opinion was that the features are due to increased reflectances by elemental sulphur (S 0) resulting from upwelling or eruptions of hydrogen sulphide-enriched waters. In March/April 2003, a remotely sensed offshore plume was identified as a coccolithophore bloom for the first time in this region, followed by satellite imagery and intensively investigated using ship-borne measurements. Different methods were applied such as high-performance liquid chromatography (HPLC) pigment analysis, electronic disperse X-ray analysis, scanning electronic microscopy as well as spectral particle absorption and reflectance measurements. Ocean colour satellite data of the SeaWiFS and MERIS sensors were used to investigate the blooms. The SeaWiFS coccolithophore algorithm identified the bloom in March 2003. MERIS-derived spectral reflectances which were in a good agreement with in-situ measurements were used to study the occurrence of blooms in the first half of the year 2004. The observed offshore plumes can be optically divided into two groups. Far offshore the plumes are dominated by coccolithophores Emiliania huxleyi (Type-C) increasing the reflectance by scattering. Directly outside the active upwelling area the spectral shape of reflectance is affected by absorbing phytoplankton, but the magnitude is the result of scattering by coccolithophores and possibly diatom frustules. The coccolithophore bloom water was characterized by high calcite content, the occurrence of the marker pigment 19′- hexanoyloxyfucoxanthin as well as by a double maximum in the blue spectral range of the specific absorption of phytoplankton. The coccolithophore bloom develops as a phytoplankton succession during a low wind period in a stable stratified water body with a shallow top layer under high solar radiation with the starting conditions of low silicate and high N/P ratios. In the area off Namibia the sporadic occurrence of milky turquoise water may have two different causes. The features nearshore are due to sulphur discolouration but the further offshore plumes are caused by coccolithophores. The occurrence of coccolithophores is not as sporadic as the blooms which are visible in satellite data. These results improve the interpretation of milky turquoise water identified by ocean colour satellite data in the SE Atlantic Ocean off Namibia because they verified the occurrence of coccolithophores in that region for the first time with different methods.

Coccolithophore bloom size variation in response to the regional environment of the subarctic North Atlantic

Several environmental/physical variables derived from satellite and in situ data sets were used to understand the variability of coccolithophore abundance in the subarctic North Atlantic. The 7-yr (1997–2004) time-series analysis showed that the combined effects of high solar radiation, shallow mixed layer depth ( 89% of the coccolithophore variation. The June 1998 bloom, which was associated with high light intensity, unusually high sea-surface temperature, and a very shallow mixed layer, was found to be one of the most extensive (>995,000 km2) blooms ever recorded. There was a pronounced sea-surface temperature shift in the mid-1990s with a peak in 1998, suggesting that exceptionally large blooms are caused by pronounced environmental conditions and the variability of the physical environment strongly affects the spatial extent of these blooms. Consequently, if the physical environment varies, the effects of these blooms on the atmospheric and oceanic environment will vary as well.

Seasonal and interannual variability of calcite in the vicinity of the Patagonian shelf break (38°S–52°S)

The timing and duration of coccolithophore blooms along the Patagonian shelf break, as well as insights on the mechanisms that drive and maintain these blooms, were analyzed using time series of chlorophyll chl a, calcite, and sea‐surface temperature (SST) derived from remote sensing data (SeaWiFS and AVHRR) and historic hydrographic data. The seasonal variability and succession of phytoplankton groups respond to light intensity and nutrient supply within the mixed layer due to seasonal changes in stratification. The early spring bloom is diatom‐dominated and starts in September under nutrient‐rich Malvinas waters when the mixed layer begins to shallow (&lt;80 m), and peaks around November with mixed layer depths (MLD) less than 40 m. After nutrient depletion from the spring bloom, a coccolithophore bloom begins in November when the MLD is less than 40 m, and peaks in January when the MLD reaches its minimum (18 m) and PAR reaches its maximum intensity.

Enhanced terrestrial weathering/runoff and surface ocean carbonate production during the recovery stages of the Paleocene‐Eocene thermal maximum

The carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the Paleocene‐Eocene thermal maximum (PETM) (circa 55 Ma). The rapid release of large quantities of carbon into the ocean‐atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion (CIE). The brevity (120–220 kyr) of the PETM reflects the rapid enhancement of negative feedback mechanisms within Earth's exogenic carbon cycle that served the dual function of buffering ocean pH and reducing atmospheric greenhouse gas levels. Detailed study of the PETM stratigraphy from Ocean Drilling Program Site 690 (Weddell Sea) reveals that the CIE recovery period, which postdates the CIE onset by ∼80 kyr, is represented by an expanded (∼2.5 m thick) interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate. Collectively, the micropaleontological and sedimentological changes preserved within the CIE recovery interval reflect a transient state when ocean‐atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths. A prominent peak in the abundance of the clay mineral kaolinite is associated with the CIE recovery interval, indicating that continental weathering/runoff intensified at this time as well (Robert and Kennett, 1994). Such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering/runoff and carbonate precipitation helped sequester carbon during the PETM recovery period (e.g., Dickens et al., 1997; Zachos et al., 2005).

Productivity changes in the Bering Sea during the late Quaternary

Changes in biological productivity of the Bering Sea have been evaluated for the late Quaternary based on biogenic opal, calcium carbonate, and microfossils in two piston cores. Biological productivity increased during Marine Isotope Stage (MIS) 1 after the last glaciation. During the last deglaciation, two pronounced peaks of calcium carbonate content were observed at ca. 2400 m water depth, which can be explained by the ‘‘CaCO3 compensation hypothesis’’ and coccolithophore blooms. Simultaneous with the CaCO3 peaks, oxygen-poor deep water was apparently distributed in the Aleutian Basin based on benthic foraminiferal assemblages. The low-O2 events seem to be related to deep-water circulation and/or elevated productivity in the northwest Pacific. After the CaCO3 peak events, biogenic opal contents and diatoms increased gradually, associated with enhanced vertical mixing with an inflow of the Alaskan Stream through the eastern Aleutian Arc passes. r 2005 Elsevier Ltd. All rights reserved.