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Los cocolitofóridos son fitoplancton calcificante unicelular cosmopolita involucrado en importantes ciclos biogeoquímicos globales. Esta tesis doctoral se centra en los impactos del calentamiento del océano y la acidificación sobre la morfología y la calcificación de los cocolitofóridos, con especial atención a la especie cosmopolita y dominante Emiliania huxleyi. El estudio incluye experimentos de temperatura usando cepas de E. huxleyi aisladas en el noroeste del océano Pacífico, y el análisis de muestras de agua colectadas a lo largo de un transecto que cubre aguas del Golfo de California y del margen NE del oceáno Pacífico. Este tipo de trabajo es oportuno dado que el calentamiento global y el rápido aumento del CO2 antropogénico en la atmósfera tienen consecuencias notables en el medio marino. Para aclarar discrepancias que aparecen en la literatura sobre la respuesta de la calcificación a los cambios de temperatura, comparamos tres cepas de E. huxleyi cultivadas bajo condiciones no limitantes de nutrientes ni de luz, a 10, 15, 20 y 25 ºC de temperatura. Las tres cepas mostraron tasas de crecimiento similares en función de la temperatura, con un óptimo en los 20–25 ºC. Se correlacionaron positivamente con la temperatura: la tasa de producción de cocolitos y de elementos particulados (carbono inorgánico particulado (PIC), carbono orgánico particulado (POC), nitrógeno particulado total (TPN)), la masa y tamaño del cocolito, el ancho del ciclo de elementos del tubo de los cocolitos, el número de cocolitos en la cocosfera, la masa de la cocosfera, y la velocidad de hundimiento y la relación PIC : POC de las células individuales. La correlación entre la producción de PIC y la masa/tamaño del cocolito apoya la noción de que la masa del cocolito se puede usar como proxy para la producción de PIC en muestras de sedimentos. Encontramos que los cocolitos incompetos no se deben a la escasez de tiempo a altas producciones de PIC. Las temperaturas de crecimiento subóptimas a, Coccolithophores are cosmopolitan unicellular calcifying phytoplankton involved in important biogeochemical global cycles. This PhD thesis focuses on the impacts of ocean warming and acidification on the morphology and calcification of coccolithophores, with special attention to the cosmopolitan and dominant species Emiliania huxleyi. The study includes temperature experiments using three strains of E. huxleyi isolated in the NW Pacific Ocean, and the analysis of water samples collected along a transect covering the Gulf of California and NE Pacific margin waters. This type of work is timely since global warming and the rapid increase in anthropogenic atmospheric CO2 have remarkable consequences on the marine environment. To clarify discrepancies featuring in the literature about the calcification response to temperature changes, we compared three strains of E. huxleyi grown under non-limiting nutrient and light conditions, at 10, 15, 20 and 25 ºC of temperature. All three strains displayed similar growth rate versus temperature relationships, with an optimum at 20–25 ºC. Over the sub-optimum to optimum temperature range (10–25 ºC), elemental production (particulate inorganic carbon (PIC), particulate organic carbon (POC), total particulate nitrogen (TPN)), coccolith mass, coccolith size, width of the tube element cycle, number of attached coccoliths per coccosphere, coccosphere mass, individual sinking velocity, individual cell PIC : POC ratio, and coccolith production rate, were positively correlated with temperature. The correlation between PIC production and coccolith mass/size supports the notion that coccolith mass can be used as a proxy for PIC production in sediment samples. We found that incompleteness of coccoliths is not due to time shortage at high PIC production. Sub-optimal growth temperatures lead to an increase in the percentage of malformed coccoliths in a strain-specific fashion. The PIC : POC ratio showed a minimum at optimum growth temperature in

It has long since been noted that minor element (Me) partitioning into biogenic carbonates is sometimes different from Me partitioning into inorganically precipitated carbonates. The prime example is the partitioning coefficient, which might be lower or even higher than the one of inorganically precipitated carbonate. Such a difference is usually termed “vital effect” and is seen as indicative of a biologically modified minor element partitioning. Over the last three decades interest in conceptual biomineralization models compatible with minor element and isotope fractionation has been steadily increasing. However, inferring features of a biomineralization mechanism from Me partitioning is complicated, because not all partitioning coefficients show vital effects in every calcium carbonate producing organism. Moreover, the partitioning coefficient is not the only aspect of Me partitioning. Other aspects include polymorph specificity and rate dependence. Patellogastropod limpets are ideally suited for analysing Me partitioning in terms of biomineralization models, because they feature both aragonitic and calcitic shell parts, so that polymorph specificity can be tested. In this study, polymorph-specific partitioning of the minor elements Mg, Li, B, Sr, and U into shells of the patellogastropod limpet Patella caerulea from within and outside a CO2 vent site at Ischia (Italy) was investigated by means of LA-ICP-MS. The partitioning coefficients of U, B, Mg, and Sr (in aragonite) differed from the respective inorganic ones, while the partitioning coefficients of Li and Sr (in calcite) fell within the range of published values for inorganically precipitated carbonates. Polymorph specificity of Me partitioning was explicable in terms of inorganic precipitation in the case of Sr and Mg, but not Li and B. Seawater carbon chemistry did not have the effect on B partitioning that was expected on the basis of data on inorganic precipitates and foraminifera. Carbon chemistry did

Barium (Ba) incorporated in the calcite of many foraminiferal species is proportional to the concentration of Ba in seawater. Since the open ocean concentration of Ba closely follows seawater alkalinity, foraminiferal Ba ∕ Ca can be used to reconstruct the latter. Alternatively, Ba ∕ Ca from foraminiferal shells can also be used to reconstruct salinity in coastal settings in which seawater Ba concentration corresponds to salinity as rivers contain much more Ba than seawater. Incorporation of a number of minor and trace elements is known to vary (greatly) between foraminiferal species, and application of element ∕ Ca ratios thus requires the use of species-specific calibrations. Here we show that calcite Ba ∕ Ca correlates positively and linearly with seawater Ba ∕ Ca in cultured specimens of two species of benthic foraminifera: Heterostegina depressa and Amphistegina lessonii. The slopes of the regression, however, vary two- to threefold between these two species (0.33 and 0.78, respectively). This difference in Ba partitioning resembles the difference in partitioning of other elements (Mg, Sr, B, Li and Na) in these foraminiferal taxa. A general trend across element partitioning for different species is described, which may help develop new applications of trace elements in foraminiferal calcite in reconstructing past seawater chemistry.

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 0.5 μM [P]). Reduced P-availability (1 and 0.5 μM [P]) decreased POC production, while PIC production only decreased when phosphate concentrations became growth limiting (0.5 μM [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 0.5 μM [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.

The shallow water benthic foraminifer Amphistegina lessonii was grown in seawater of variable Li and Ca concentration and shell Li/Ca was determined by means of LA-ICPMS. Shell Li/Ca is positively correlated to seawater Li/Ca only when the Li concentration of seawater is changed. If the seawater Ca concentration is changed, shell Li/Ca remains constant. This indicates that Li does not compete with Ca for incorporation in the shell of A. lessonii. A recently proposed calcification model can be applied to divalent cations (e.g., Mg and Sr), which compete for binding sites of ion transporters and positions in the calcite lattice. By contrast, the transport pathway of monovalent cations such as Li is probably diffusion based (e.g., ion-channels), and monovalent cations do not compete with Ca for a position in the calcite lattice. Here we present a new model for Li partitioning into foraminiferal calcite which predicts our experimental results and should also be applicable to other alkali metals.

Biological activity introduces variability in element incorporation during calcification and thereby decreases the precision and accuracy when using foraminifera as geochemical proxies in paleoceanography. This so-called ‘vital effect’ consists of organismal and environmental components. Whereas organismal effects include uptake of ions from seawater and subsequent processing upon calcification, environmental effects include migration- and seasonality-induced differences. Triggering asexual reproduction and culturing juveniles of the benthic foraminifer Ammonia tepida under constant, controlled conditions allow environmental and genetic variability to be removed and the effect of cell-physiological controls on element incorporation to be quantified. Three groups of clones were cultured under constant conditions while determining their growth rates, size-normalized weights and single-chamber Mg/Ca and Sr/Ca using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Results show no detectable ontogenetic control on the incorporation of these elements in the species studied here. Despite constant culturing conditions, Mg/Ca varies by a factor of ~ 4 within an individual foraminifer while intra-individual Sr/Ca varies by only a factor of 1.6. Differences between clone groups were similar to the intra-clone group variability in element composition, suggesting that any genetic differences between the clone-groups studied here do not affect trace element partitioning. Instead, variability in Mg/Ca appears to be inherent to the process of bio-calcification itself. The variability in Mg/Ca between chambers shows that measurements of at least 6 different chambers are required to determine the mean Mg/Ca value for a cultured foraminiferal test with a precision of ≤ 10%.