Modern Planktonic Foraminifera

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SCOR/IGBP working group on modern planktonic foraminifera kicked off

Changes in the diameter of specimens from the Mediterranean morphotype are more pronounced than those observed in the Caribbean morphotype. The interval between Upward in the section, the diameter presents a size decreasing trend up to Porosity Figure 7f showed lower values than those from the Caribbean morphotype. Values oscillated between 4 and The curve shows large oscillations during MIS 2 with a maximum peak at During MIS1, values remain more stable.

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Different from the Caribbean morphotype, small pore densities in the Mediterranean morphotype Figure 7h did not present an inverse pattern with large pore densities. This parameter exhibits large fluctuations along the whole studied interval. Twenty-six planktonic foraminifera species were recognized in the analyzed samples. Typically, cold and nutrient-rich water species such as Turborotalita quinqueloba,Neogloboquadrina pachyderma and left-coiling Globorotalia truncatulinoides were more abundant during the glacial period MIS2.

SCOR/IGBP working group on modern planktonic foraminifera kicked off

On the other hand, warm-water species such as O. In the Orbulina universa plot, the red bars correspond to the Caribbean morphotype and the yellow ones to the Mediterranean morphotype.

In the Globigerinodes ruber plot, the red bars correspond to the white morphotype and the yellow ones to the pink morphotype. For T. Downcore paleo-sst reconstruction and correlation with fossil orbulina universa samples. Summer, winter and mean annual SSTs for each analyzed sample are plotted in Figure 9 , representing mean values for the m water depth. This depth range was the one that yielded the highest correlation between the modern temperature obtained by the CTD device and the reconstructed paleotemperatures of the calibration dataset.

Therefore, we consider only these results to evaluate the correlation between paleotemperatures and the morphometric parameters of O. Mean summer SST during this interval is From then on, temperatures drop, reaching a minimum value at Since Mean summer SST through during the Holocene is No significant correlations were found between summer SST m and shell diameter or porosity, neither for the Caribbean Figure 10 nor for the Mediterranean morphotype Figure Also, no correlation was found between large pore- or small pore- density and paleo-SST.

Orbulina universa morphotypes occurrence at the Western South Atlantic. Orbulina universa morphotypes are related to different hydrographic provinces and trophic conditions. On the other hand, Sargasso and Caribbean morphotypes seem to be specially related to stratified oligotrophic waters. In our study, both Mediterranean and Caribbean morphotypes specimens occur together in almost all the samples modern and fossil.

Even though De Vargas et al.

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Morphometric characteristics of Mediterranean and Sargasso morphotypes are very similar, making it difficult to separate them. However, Sargasso morphotype occurrence is unlikely in our study area, once its higher abundance has been reported to highly oligotrophic regions of the ocean De Vargas et al. The co-occurrence of Mediterranean and Caribbean morphotypes can be explained by the oceanographic characteristics of the area. The main oceanographic influence in the region comes from the Brazil Current BC Piola and Matano, which transports warm and oligotrophic waters, enabling the occurrence of the Caribbean morphotype both in modern and fossil samples.

On the other hand, there is also the influence of the PPW that reaches the study area during winter under the influence of SW winds - Pimenta et al. Both bring colder and nutrient rich waters enabling the occurrence of the Mediterranean morphotype. Moreover, proxy data i. Laprida et al. Under colder conditions, a northward migration of the Confluence region would have favored the occurrence of the Mediterranean morphotype in our fossil samples.

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  • Correlation between orbulina universa morphometric parameters and surface waters thermohaline indexes in modern samples. Large pore density is the only parameter that shows a significant correlation with temperature and salinity Caribbean morphotype.

    Planktonic Foraminifera in the water column

    Previous studies have shown an association between pore density and porosity which is affected by the pores density and dissolved oxygen concentration and temperature. In fact, several studies relate higher porosity and shell diameter in O. Moreover, some studies have related higher pore density to a lower dissolved oxygen concentration Schiebel and Hemleben, As gas dissolution in water is less efficient at higher temperatures, the number of pores in the shells increase to compensate the oxygen deficiency.

    The opposite situation occurs when the gas dissolution is higher, and the shells show lower porosities and less pores. Therefore, water temperature and oxygen concentration effects overlap. Nonetheless, in our samples the correlation found between pore density and water temperature is negative. It is possible that previous work results have been influenced by the fact that the existence of different morphotypes of O. Still, lab studies conducted by Bijma et al. Thus, the mechanisms which define these shell morphometric parameters are still not quite understood. Nonetheless, the authors did not establish a relationship between porosity and environmental conditions, but with genetic components.

    However, Morard et al. Nevertheless, the morphometric parameters related to the genotypes and its relationship with temperature are not addressed. Surprisingly, shell diameter did not show significant correlation with water temperature in our study area. This may have happened because the morphometry changes do not depend only on temperature, but also on other factors, such as nutrient availability.

    Besides, shell diameter and water temperature do not exhibit a linear relation. Each species has a temperature range that leads to its maximum diameter, but environmental disturbances interfere in shell size. At frontal zones, as at the BMC, shell diameters use to be smaller Schmidt et al. The fossil samples did not show any significant correlation between morphometric parameters and SST.

    This may have happened because carbonate fossil shells may have undergone dissolution processes. That would lead to an error of porosity estimate, as it takes into account the large and small pore diameters.

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    However, porosity did not show significant correlation with thermohaline indexes in modern samples either. On the other hand, these processes would not affect pore density estimates, that show negative correlation with temperature for the modern samples, but not for the fossil samples. There is also the possibility that other genotypes do exist in the fossil record and are yet not known Morard et al. They could have temperature water preference different from the modern ones. If that is the case, individuals with the same morphometric characteristics would be classified as the same morphotype even if they have different environmental preferences, making it difficult to recognize a correlation between the two groups of variables.

    Unfortunately, studies considering the O.

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    Another explanation for the absence of correlation are errors associated with the SST estimates. However, MAT use can be limited by the small number of modern analogs found for the fossil samples set. Therefore, part of the Equatorial Atlantic was added to the calibration dataset, allowing the obtainment of a SST curve consistent with previous knowledge for the LGM at the Southwestern Atlantic e. Another possible source of error in MAT reconstructions is related to the choice of the water depth temperature range considered in the calibration dataset Telford et al.

    After testing three different depth ranges, we decided to use the m range which was the one that yielded the best correlations between the modern and reconstructed temperatures. Still, we recognize that while recent fauna may better reflect present conditions at the m depth range, past changes in the upper thermal structure very likely happened. Thus, intrinsic errors of the method could have diminished the correlation between SST and morphometric parameters. Another hypothesis is that other factors, such as nutrient availability, play an important role in the morphotypes distribution.

    Planktonic foraminifera

    Currently, the main contributor to enhance nutrient availability at the area is the PPW. Furthermore, samples were collected in autumn and spring, while the extremes of PPW seasonal migration occur in summer when it is restricted to the mouth proximity and in winter when it reaches its farther north position.

    Thus, it is possible that planktonic samples represent conditions in which temperature and salinity changes were more relevant that the nutrient availability fluctuations. On the other hand, during the last 32 kyr, nutrient availability changed significantly. During the LGM, with the lower global sea level and the modification of La Plata river mouth position, PPW influence was more intense, enhancing productivity of the affected area Gu et al. In addition, the BMC, another high productivity area, has migrate to the north during Holocene Voigt et al.

    Therefore, fossil samples could represent distinct and more complex oceanographic conditions compared to current configuration. Two O. Significant negative correlations were obtained between large pore density and temperature and salinity for the Caribbean morphotype in modern samples. For the Mediterranean morphotype, this correlation was only significant for temperature.

    None correlation was found between temperature and shells diameter, although it is a common proxy used in paleoceanographic researches. In fossil samples obtained in core SIS none correlation was observed, so their value as a source of paleoceanographic information should be seen with caution. Hypothesis to explain this apparent incongruence include errors in SST estimates using MAT, the existence of genotypes in the recent geological past that are distinct from the modern ones and the possible difference between the current oceanographic conditions and the paleoceanographic conditions during the last 32 kyr.

    Increasing the Southwest Atlantic dataset is central to understand the relationship between morphometric parameters of the O. They are also grateful to Dr Sandro M.

    Muelbert and three anonymous reviewers for important suggestions and to Prof.

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