Search

Ocean Sciences Meeting 2020. San Diego, 16-21 Febrero 2020, Thin layers of phytoplankton (TLP) are a particular case of blooms characterized by high cell densities within a narrow depth interval. Despite TLP may play an important role in the formation of harmful algae blooms (HABs), we have a limited understanding about the mechanisms responsible for their formation in the Rías Baixas (NW Spain), one of the main producers of cultured mussels in the world. In this investigation we studied the spatial and temporal variability of TLP by means of high-frequency observations of thermohaline properties, turbulent mixing, horizontal currents, inorganic nutrients, phytoplankton biomass and composition, and primary production in the Rías Baixas in summer 2018. Sharp changes in phytoplankton distribution were observed during the three-weeks cruise, when hydrographic properties rapidly evolve from downwelling to upwelling conditions. The formation of a TLP, centered at the 14.3ºC isotherm, was associated with the upwelling of cold nutrient-replete waters, which which evolved to a subsurface chlorophyll maximum at the end of the cruise. Phytoplankton composition in the TLP was dominated by an assemblage of diatoms, including Pseudo-nitzschia species, Leptocylindrus danicus, Thalassionema nitzschioides, Chaetoceros lorenzianum and Cerataulina pelagica. A net accumulation rate of 0.72 d-1, which resulted from the combination of physical and biological processes, was derived from the temporal evolution of chlorophyll-a at the TLP. This value was within the range of phytoplankton net growth rates derived from 14C-primary production measurements for the same period [0.09-1.03]. Although other biological loss terms, such as zooplankton grazing and cells sinking, should be considered, this preliminary analysis indicates that in situ growth may account by itself for the phytoplankton biomass accumulation observed in the thin layer

Poster.-- Encontros IIM Primeira fase, 12 de decembro de 2019

V Encuentro de Oceanografía Física 2018 (EOF), Vigo (Spain), 20-22th June 2018, The Galician Rias, located in NW Iberia, are highly productive coastal ecosystems due to the influence of upwelling events occurring seasonally during spring-summer. Thus, a series of phytoplankton blooms occur in the Rias along the year. However, the mechanism of formation and the persistence of some of these blooms are poorly understood. Thin layers of phytoplankton (TLP) are a particular case of phytoplankton blooms that occur when large numbers of photosynthetic cells are located within a narrow depth interval. They have been recurrently observed in the Galician Rias, sometimes related to the occurrence of harmful algal bloom species. The analysis of the dataset collected weekly by the INTECMAR (Instituto Tecnolóxico para o control do medio mariño de Galicia) showed that two major events of TLP were observed, in May 2012 and June 2013, extending over several stations, throughout the Rias of Vigo, Pontevedra and Arousa. In this study we used a 3D ocean circulation model of the southern Galician Rias coupled to a biogeochemical model in order to reproduce the oceanographic conditions during these events. Our mail goal was to investigate the possible drivers responsible for the formation of the observed TLPs. The model was able to reproduce the formation of the blooms, their approximate horizontal extension and their time evolution, although the modeled chlorophyll fields were smoother, with lower concentrations and more vertically spread maximums, than observed. In both events, the bloom formation was associated with strong surface haline stratification within the Rias. The source of the freshwater driving this stratification during the 2013 event was associated with the northward advection of the river Miño plume, whereas in 2012 it was associated with local river discharges. These results demonstrate the utility of modeling approaches for the study of the dynamics of TLPs in this ecosystem, This is a contribution to the REMEDIOS project (CTM 2016-75451-C2-1-R) funded by Ministerio de Economía y Competitividad

1 poster.-- VI International Symposium on Marine Sciences, Vigo (Spain), 20-22th June 2018, The Galician Rías, located in the NW of the Iberian Peninsula, are a highly productive ecosystem under the influence ofthe Coastalupwelling. This region sustains an important shellfish activity, which every year is threatened by episodes of harmfulphytoplankton. Aparticular caseof microalgae bloom, named thin layers of phytoplankton (TLP),occurs whenhigh-celldensities are locatedwithin a narrow depth interval.These featuresare believed to play an important role in the sudden formation and maintenance of harmful algae blooms. Previousanalysis of the dataset collected by the INTECMAR monitoring program (http://www.intecmar.org) in the Galician Rías, weekly between 2012-2015, showed that the occurrence of TLP was higher between May and July,associated with the base of shallow pycnoclines(Mouriño et al., this issue).Despite this evidence, the mechanisms responsible for the formation of TLP in the Galician Rías remains unknown. Here we investigate the environmental conditions favorable for the formation of TLP in the Galician Ríasduring the period of 2012-2015. For that we first built a database containing the meteorological and hydrographic information corresponding to the INTECMAR weekly sampling. Statistical procedures based on principal component and cluster analysis were usedto investigate the relationship between theoccurrence of TLP and the favorable environmental conditions, This is a contribution to the REMEDIOS project (CTM 2016-75451-C2-1-R) funded by Ministerio de Economía y Competitividad

1 póster presentado en ECSA54 coastal systems under change: tuning assessment and management tools, 12-16 May 2014, Sesimbra, Portugal

1 poster presented at the European Geosciences Union General Assembly 2012, Vienna, Austria, 22 – 27 April 2012, Trying to find a set of parameters to properly reproduce the biogeochemical dynamics of the region of study is a major concern in biogeochemical ocean modelling. Model parameters are constant values introduced in the equations that calculate the time and space evolution of the state variables of the biogeochemical model. A good set of parameters allows for a better representation of the biological and chemical processes in the system, and thus to model results more approximated to reality. However, it is not a straightforward task, because many parameters are not well constrained in the literature, or they may be unknown or vary considerably between different regions. Usually, the approach to find the appropriate values is running several simulations, after some sensitivity test to individual parameters, until a satisfactory result is obtained. This may be very time consuming and quite subjective. A more systematic way to find this set of parameters has arisen over the last years by using mathematical optimization techniques. The basic principle under optimization is to minimize the difference between an observed and a simulated data series by using a cost function. We have applied an optimization technique to find an appropriate set of parameters for modelling the biogeochemical dynamics of the western Iberian shelf, off the Atlantic coast of Portugal and Galicia (NW Spain), which is characterized by a conspicuous seasonal upwelling. The ocean model is a high resolution 3D regional configuration of ROMS coupled to a N2PZD2 biogeochemical model. Results using the a priori parameters and the optimized parameters are compared and discussed. The study is the result of a multidisciplinary collaborative effort between the University of Aveiro ocean modelling group (Portugal), the ETHZ (Switzerland) and the IIM-CSIC Vigo oceanography group (Spain), Fundação para a Ciência e a Tecnologia (FCT) for funding this PhD research (SFRH/BD/33388/2008).

International audience

279 pages, This doctoral dissertation is structured in six chapters and two appendices. From this point the reader is warned about the independent numbering in each chapter, both for sections and subsections as well as for figures and tables, that is, the numbering restarts at the beginning of each chapter. Chapter I is divided into two parts. On the one hand, the topic of the doctoral dissertation is introduced in a general way to put in context the different research studies that are part of it. This introduction presents the key concepts on climate change and ocean acidification necessary to approach the reading of the following chapters. On the other hand, the main and secondary objectives that are addressed in the next chapters are detailed. Chapter II develops the construction of a global and seasonal climatology of total alkalinity. The chapter details for the first time in the thesis the use of neural networks. This methodology is used throughout the manuscript, highlighting the peculiarities associated with each study in each of the chapters where it is applied. This chapter has been published in Earth System Science Data: https://doi.org/10.5194/essd-11-1109-2019 Chapter III describes the development of a total dissolved inorganic carbon climatology. In general terms, a methodology similar to that of chapter II is used, although with certain relevant nuances such as the inclusion of a new database. In this chapter, a pCO2 climatology is also generated in a secondary way to evaluate the consistency between the two climatologies previously generated in this thesis. This chapter has been published in Earth System Science Data: https://doi.org/10.5194/essd-12-1725-2020., Chapter IV completely changes the scale of the previous two chapters and focuses on the study of sweater CO2 chemistry system on a regional scale. Specifically, neural networks are used to generate time series of total alkalinity and pH at various locations in the Ría de Vigo. From the time series, the magnitude of seasonal variability and interannual trends for these variables are analyzed. This chapter has been published in Biogeosciences Discussions: https://doi.org/10.5194/bg-2021-33, 2021 Chapter V contains an analysis of the variability of the hydrogen ion concentration and the aragonite saturation state in the Ría de Vigo. This analysis is carried out from the time series of these variables that are constructed thanks to the study developed in chapter IV. Chapters II to V are structured in the same way as a typical scientific article, thus containing an introduction, methodology, results, discussion and conclusions about each study. Finally, chapter VI summarizes the main conclusions derived from the complete work shown through this doctoral thesis. It is worth noting the inclusion of two appendices in the final part of the thesis. Appendix I details the meaning of each of the acronyms, abbreviations and symbols used throughout the manuscript. Appendix II contains a summary of the doctoral dissertation in Spanish