Estudio paleoclimático del afloramiento ecuatorial del Océano Pacífico durante los últimos 160.000 años a partir de biomarcadores moleculares

Caducat el període d'embargament de l'article de la revista: Quirós-Collazos, L., Calvo, E., Schouten, S., van der Meer, M. T. J., Rodrigo-Gámiz, M., Pena, L. D., et al. (2020). Controls on primary productivity in the Eastern Equatorial Pacific, east of the Galapagos Islands, during the penultimate deglaciation. Paleoceanography and Paleoclimatology, 35, e2019PA003777. https://doi.org/10.1029/2019PA003777The present PhD thesis is focused on the paleoclimatic reconstruction of the Pacific Ocean equatorial upwelling conditions, east of the Galapagos Islands, over the last 160.000 years. This region is of great interest to understand climate dynamics within the context of current global change, as it plays a key role in global biogeochemical cycles, especially the carbon cycle, being one of the areas with largest CO2 fluxes from the ocean to the atmosphere. In addition, studies covering the recent decades have shown that tropical regions play a key role in regulating global climate, since they control the transfer of thermal energy from low to high latitudes. This study is based on the analysis of molecular biomarkers in the marine sediment core ODP 1240, which was obtained during Leg 202 of the Ocean Drilling Program. The main analysed compounds were the long-chain ketones, known as C37 alkenones, the 24-methylcholesta-5,22-dien-3ß-ol, known as brassicasterol, long-chain n-alkanes, glycerol dialkyl glycerol tetraethers (GDGTs) and 1,14-alkyl diols. The UK'37 and TEXH86 indexes were obtained from the analyses of the mentioned biomarkers to assess their suitability as temperature proxies to reconstruct sea surface conditions at the eastern Pacific upwelling on a glacial-interglacial time scale. They reflect variations in the mean annual surface temperature at the study area and track the warming and cooling trends typical of glacial-interglacial variations, although with certain peculiarities associated with each proxy. The UK'37 derived record shows a special sensitivity to periods with La Niña-like seasonal conditions, when the upwelling was more intense and sea surface temperatures in this area were colder. On the other hand, the TEXH86 index shows a tendency to overestimate the cooling of surface waters during glacial periods, as it has been also observed in similar reconstructions in this and other tropical regions. This might be due to the combined influence of changes in surface temperature and in ammonium oxidation rates of the Thaumarchaeotas that synthesize GDGTs and proliferate in the upper water column. Paleoclimatic information provided by other records nearby indicate that changes in oceanic denitrification linked to the supply of oxygen through subsurface and intermediate waters could have a regulating effect on the availability of ammonium in surface water. This, in turn, would have led to changes in the relative abundance of the GDGTs synthesized by Thaumarchaeotas, causing a glacial cooling overestimation through the TEXH86 index. The high resolution that characterizes the ODP 1240 core has allowed gaining a more in-depth knowledge on the millennial-scale climatic variability of this region. In particular, the changes in primary production during the penultimate deglaciation have been studied. This deglaciation, known as Termination II, can be used as a laboratory to understand climate dynamics during periods of rapid global warming. The results show that phytoplankton production was enhanced by an increasing influence of nutrient-rich Southern Ocean-sourced waters and by enhanced atmospheric dust inputs, which would have served as an additional source of iron to the study region. These processes culminated during the development of the Heinrich Event 11 in the North Atlantic, at a time when the highest increase in primary productivity of Termination II was recorded in the eastern equatorial Pacific upwelling. The results of this thesis highlight the relationships between global dynamics of biogeochemical cycles and those of the eastern equatorial Pacific, as well as the role played by high to low latitude teleconnections.La presente tesis doctoral se centra en la reconstrucción de las condiciones paleoclimáticas del afloramiento ecuatorial del Océano Pacífico, al este de las Islas Galápagos, a lo largo de los últimos 160.000 años. Esta región es de gran interés para comprender las dinámicas del clima dentro del contexto de cambio global actual. Se trata de una región que juega un papel clave en los ciclos biogeoquímicos globales, en especial el del carbono, pues es una de las zonas que presenta mayor flujo de CO2 del océano a la atmósfera, además de ejercer un papel clave en el clima global regulando la transferencia de energía térmica de las bajas a las altas latitudes. Este estudio se ha realizado a partir del análisis de biomarcadores moleculares en el testigo sedimentario ODP 1240, obtenido durante la campaña 202 del Ocean Drilling Program. Los principales compuestos analizados son las cetonas de cadena larga (alquenonas C37), el 24-metilcolesta-5,22-dien-3ß-ol (brasicasterol), n-alcanos de cadena larga, tetraéteres de glicerol dialquil glicerol (GDGTs) y alquil dioles 1,14. A partir de estos biomarcadores se han obtenido los índices UK'37 y TEXH86 y se ha evaluado su utilidad como indicadores de temperatura para reconstruir las condiciones de las aguas superficiales del afloramiento del Pacífico oriental a escala glacial-interglacial. Éstos reflejan las variaciones en la temperatura superficial media anual de la zona y registran el calentamiento y enfriamiento típicos de las variaciones glacial-interglacial, aunque con ciertos matices asociados con cada indicador. El registro derivado del UK'37 muestra sensibilidad a los períodos con unas condiciones de estacionalidad similares a las de La Niña, cuando el afloramiento fue más intenso y las temperaturas superficiales del mar en esta zona fueron más frías. Por otro lado, se ha observado que, durante los glaciales, el índice TEXH86 tiende a sobreestimar el enfriamiento de las aguas superficiales, tal y cómo se ha observado en reconstrucciones similares de ésta y otras regiones tropicales. Esto se debería a la influencia combinada de los cambios en la temperatura superficial y las variaciones en las tasas de oxidación de amonio sobre las Thaumarchaeotas que sintetizan los GDGTs y que proliferan en la parte superficial de la columna de agua. La información paleoclimática aportada por otros registros de la zona indica que los cambios en la desnitrificación oceánica vinculados al aporte de oxígeno a través de las aguas subsuperficiales e intermedias pudo tener un efecto regulador sobre la disponibilidad de amonio en superficie. Esto, a su vez, habría provocado cambios en la abundancia relativa de los GDGTs sintetizados por las Thaumarchaeotas, causando una sobreestimación del enfriamiento estimado durante los glaciales por parte del índice TEXH86. La alta resolución que caracteriza al testigo ODP 1240 ha permitido estudiar las variaciones climáticas de esta región a escala milenaria. En concreto, se han estudiado los cambios en la productividad primaria ocurridos durante la penúltima deglaciación, la Terminación II, un período que resulta interesante como laboratorio para conocer las dinámicas del clima en períodos de rápido calentamiento global. Los resultados muestran que la producción de fitoplancton se vio favorecida por la creciente influencia de aguas procedentes del Océano Austral ricas en nutrientes y por un aumento de las deposiciones de polvo atmosférico que habrían aportado hierro a la zona de estudio. Estos procesos experimentaron su mayor expresión durante el desarrollo del Evento Heinrich 11 en el Atlántico Norte, cuando en el afloramiento del Pacífico ecuatorial se registró el mayor aumento de productividad primaria de la Terminación II. Los resultados de esta tesis ponen de manifiesto la relación que existe entre las dinámicas globales de los ciclos biogeoquímicos y las del Pacífico ecuatorial oriental, y el papel el papel que juegan las teleconexiones de alta a baja latitudLa present tesi doctoral se centra en la reconstrucció de les condicions paleoclimàtiques de l'aflorament equatorial de l'Oceà Pacífic, a l'est de les Illes Galápagos, al llarg dels darrers 160.000 anys. Aquesta regió és de gran interès per comprendre les dinàmiques del clima dins el context de canvi global actual. Es tracta d'una regió que té un paper clau en els cicles biogeoquímics globals, especialment el del carboni, ja que és una de les zones que presenta un major flux de CO2 de l'oceà a l'atmosfera. A més, els estudis de les darreres dècades han anat posant de manifest que les regions tropicals exerceixen un paper clau com a reguladores del clima global, atès que regulen la transferència d'energia tèrmica de les baixes a les altes latituds. Aquest estudi s'ha realitzat a partir de l'anàlisi de biomarcadors moleculars en el testimoni sedimentari ODP 1240, obtingut durant la campanya (del anglès, Leg) 202 del programa ODP (del anglès, Ocean Drilling Program). Els principals compostos analitzats han estat les cetones de cadena llarga denominades alquenones C37, el 24-metilcolesta-5,22-dien-3β-ol conegut com a brasicasterol, n-alcans de cadena llarga, tetraèters de glicerol dialquil glicerol (GDGTs) i alquil diols 1,14. A partir d'aquests biomarcadors, a la primera part d'aquesta tesi s'han obtingut els índexs UK'37 i TEXH86. i se n'ha avaluat la seva utilitat com a indicadors de temperatura per reconstruir les condicions de les aigües superficials de l'aflorament del Pacífic oriental a escala glacial-interglacial. Aquests reflecteixen les variacions en la temperatura superficial mitjana anual de la zona i enregistren l'escalfament i el refredament típics de les variacions glacial-interglacial, encara que amb certs matisos associats amb cada indicador. El registre derivat de l'UK'37 mostra una sensibilitat especial als períodes on predominen condicions d'estacionalitat similars a les de La Niña, quan l'aflorament va ser més intens i les temperatures superficials del mar en aquesta zona varen ser més fredes. Per la seva banda, s'ha observat que, durant els glacials, l'índex TEXH86. té tendència a sobreestimar el refredament de les aigües superficials, tal com s'ha observat en reconstruccions semblants realitzades en aquesta i d’altres regions tropicals. Això seria degut a la influència combinada dels canvis en la temperatura superficial i de les variacions en les taxes d'oxidació d'amoni sobre les Thaumarchaeotes que sintetitzen els GDGTs i que proliferen a la part superficial de la columna d'aigua (aproximadament per sobre dels 50 m de profunditat). La interpretació d'aquests registres dins del context paleoclimàtic dels darrers 160.000 anys és el que conforma la segona part d'aquesta tesi. La informació paleoclimàtica que aporten altres registres de la zona indica que els canvis en la desnitrificació oceànica vinculats amb l'aportació d'oxigen a través de les aigües subsuperficials i intermèdies hauria tingut un efecte regulador sobre la disponibilitat d'amoni en superfície. Això, alhora, hauria provocat canvis en l'abundància relativa dels GDGTs sintetitzats per les Thaumarchaeotes, causant una sobreestimació del refredament estimat per a les èpoques glacials per part de l'índex TEXH86 A la tercera part d’aquesta tesi, l’alta resolució que caracteritza el testimoni ODP 1240 ha permès aprofundir en l’estudi de les variacions climàtiques d’aquesta regió a escala mil·lenària. En concret s'han estudiat els canvis en la productivitat primària esdevinguts durant la penúltima deglaciació, coneguda com a Terminació II, un període menys estudiat que la Terminació I, la deglaciació més recent, i que resulta interessant com a laboratori per conèixer les dinàmiques del clima en períodes de ràpid escalfament global. Els resultats mostren que la producció de fitoplàncton es va veure afavorida per la influència creixent d'aigües procedents de l'Oceà Austral riques en nutrients i per un augment de les deposicions de pols atmosfèrica que haurien suposat una font addicional de ferro a la zona d'estudi. La major expressió d’aquests processos va tenir lloc durant el desenvolupament de l'Esdeveniment Heinrich 11 a l'Atlàntic Nord, quan a l'aflorament del Pacífic equatorial oriental es va enregistrar el major augment de productivitat primària de la Terminació II. Els resultats d'aquesta tesi fan palesa la relació que hi ha entre les dinàmiques globals dels cicles biogeoquímics i les del Pacífic equatorial oriental, i el paper que hi juguen els vincles entre les altes i baixes latituds.Postprint (published version

Rare earth elements and Nd isotopes as tracers of modern ocean circulation in the central Mediterranean Sea

Seawater rare earth element (REE) concentrations and Nd isotopic composition (εNd) are increasingly applied as valuable tracers of oceanographic processes such as water mass mixing and lithogenic inputs to seawater. However, their measurements are basically lacking in the Mediterranean Sea water column. This study analyzes 9 seawater stations around the central Mediterranean Sea to clarify the relative importance of external sources, vertical (biogeochemical) processes and lateral water mass transport in controlling REE and εNd distributions. Concentrations of REE do not show nutrient-like profiles with depth, likely indicative of relatively young waters with limited accumulation of remineralized REE. Light REE (LREE) present a non-conservative behavior, which largely peak at surface waters and rapidly decrease with depth. The negative correlation of surface LREE enrichment with offshore distance highlights the influence of continental input from the western Italian coast to the Tyrrhenian surface waters. In contrast to other regions with reported boundary exchange, this process does not modify the εNd values here. On the other side, distributions of dissolved heavy REE (HREE) and εNd display a conservative behavior that can be explained by mixing of western- (MAW and WMDW) and eastern- (LIW and EMDW) originated waters. We test this hypothesis with an Optimum Multi-Parameter Analysis (OMPA) including HREE and εNd parameters. Even though the limited data set, consistent results of water mass fractions are obtained for the four main water masses although with some particularities. While LIW takes on major importance when considering HREE in the model, EMDW fractions are preferentially detected with εNd. This latter finding implies a noticeable deep water flux across the Sicily Strait into the Western Mediterranean that was not clearly evidenced before

Mapping human impacts to support sustainable uses of marine ecosystems in the Mediterranean sea

European Geosciences Union (EGU) General Assembly, 23-27 May 2022, Vienna, AustriaLocal and global anthropogenic pressures due to climate change and to local uses and activities are exerting significant cumulative impacts to greater extents of the oceans and seas. Coastal ecosystems are particularly threatened by the intensity and coexistence of several marine uses and pressures, including sewage and urban constructions, tourism, ship traffic, fisheries and aquaculture. Assessment of pressures and the identification of mitigation measures are key urgent actions, as already highlighted by the EU Marine Strategy Framework Directive and the United Nations Sustainable Development Goal 14. The aim of this work, developed within the Interreg-Med project SHAREMED, is to systematize existing knowledge on threats and pollution, including those of transboundary origin, for long term strategies and common action marine spatial planning, jointly developed with stakeholders. The quest is to assess coexisting environmental threats, and their propagation in space and time, at proper spatial and temporal scales, according to the type and action of each stressor (i.e. global vs. local). Cumulative pressures are tackled within a dedicated Atlas comprising three sub-basinsins of the Mediterranean Sea: the North Adriatic Sea, the Sicilian Channel and the North-Western region. The Atlas integrates information generated at the best available resolutions by 1) in-situ sampling, 2) remote observations, 3) numerical models, and 4) focusing on target ecosystems and habitat forming species. These sub-basins are subjected to multiple local and larger scale (e.g. climate) pressures that propagate in space and time, and across political boundaries, that need to be addressed through coordinated actions, based on evidence-rooted common understanding. Interactions with relevant Stakeholders, solicited through an online survey, and meetings, were used to select target ecosystems and to identify the key relevant pressures. The Atlas is based on open-access databases and portals, literature reviews and from ad-hoc model simulations concerning marine heatwaves, ship traffic, oil pollution, marine litter and fishing efforts. We will present the main preliminary results and needs and gaps in observations related to marine ecosystems threatsPeer reviewe

Comparison of the Eastern Equatorial Pacific UK'37, TEX86 and Globigerinoides ruber derived sea temperatures: Insights from Termination II

5th Past Global Changes (PAGES) Ocean Sciences Meeting, 9-13 May 2017, ZaragozaThe Subtropical Front (STF) separates warm and saltier subtropical waters from the cold, less saline and nutrient-rich subantarctic waters of the Southern Ocean. Determining its past north-south movements is crucial, for instance, to understand the role of such frontal systems on ocean productivity of the subantarctic region, as opposed to increased Fe availability. Three marine cores were recovered south of New Zealand, along a latitudinal transect crossing the modern STF. We have analysed long chain alkenones, as markers of coccolithophore productivity and past sea surface temperatures, n-alkanes and n-alcohols, as proxies for continental input and dust-derived iron and long chain diols as tracers of diatom productivity. Reconstructed SST changes show a 3-4°C temperature gradient during the Holocene between the core locations, while during the last glacial period no temperature gradient existed, with 8-9°C recorded at all three sites. This suggests a northward displacement of the STF during the cold glacial climate and the prevalence of subantarctic waters at the core sites, between 47 and 50.5°S. An increased productivity and continental input during the glacial and early deglaciation suggest that both Fe fertilization and equatorward migration of fronts likely drove the biological productivity of the region. The SST evolution will also be complemented with a temperature reconstruction based on the relative distribution of isoprenoid GDGTs, the TEXH86 index, which in this region, we believe may record deeper temperatures than coccolithophoresPeer Reviewe

Phytoplankton response to changes in the chemistry of the Eastern Equatorial Pacific waters during Termination II

12th International Conference on Paleoceanography (ICP12), 29 August - 2 September 2016, UtrechtResearch on the physical and biological processes controlling the transitions from glacial to interglacial periods has mostly focused on the most recent Termination (TI). However, studying previous deglaciations should provide further insights into the mechanisms involved during these transitions. In this study, we focus on the penultimate deglaciation in the Eastern Equatorial Pacific (EEP), a strategic location under the influence of upwelled nutrient-rich waters and a tight link with the Southern Ocean (SO) through the advection of intermediate waters. We present a multiproxy record of surface ocean productivity, dust inputs and thermocline conditions across TII(110¿ 150 kyr BP). These new records will allow us to assess responses of the phytoplankton community to changes in the surface water chemistry. Our records suggest enhanced dust input and high primary productivity during the end of the penultimate glacial maximum. A prominent peak in diatom production at the middle of the transition points to the arrival of Si-rich waters to the EEP, which would have promoted the growth of these organisms. The coincidence of this peak with a minimum in the ¿13C signal of deep thermocline dwelling foraminifera from the same core, used as a proxy for the influence of subantarctic sourced waters, suggests that a silicic acid leakage from the SO through intermediate waters occurred during the TII, similar to what was reported in this area for TI (Calvo et al., 2011, PNAS)Peer Reviewe

Ocean productivity across the subtropical front over the last deglaciation

5th Past Global Changes (PAGES) Ocean Sciences Meeting, 9-13 May 2017, ZaragozaThe Subtropical Front (STF) separates warm and saltier subtropical waters from the cold, less saline and nutrient-rich subantarctic waters of the Southern Ocean. Determining its past north-south movements is crucial, for instance, to understand the role of such frontal systems on ocean productivity of the subantarctic region, as opposed to increased Fe availability. Three marine cores were recovered south of New Zealand, along a latitudinal transect crossing the modern STF. We have analysed long chain alkenones, as markers of coccolithophore productivity and past sea surface temperatures, n-alkanes and n-alcohols, as proxies for continental input and dust-derived iron and long chain diols as tracers of diatom productivity. Reconstructed SST changes show a 3-4°C temperature gradient during the Holocene between the core locations, while during the last glacial period no temperature gradient existed, with 8-9°C recorded at all three sites. This suggests a northward displacement of the STF during the cold glacial climate and the prevalence of subantarctic waters at the core sites, between 47 and 50.5°S. An increased productivity and continental input during the glacial and early deglaciation suggest that both Fe fertilization and equatorward migration of fronts likely drove the biological productivity of the region. The SST evolution will also be complemented with a temperature reconstruction based on the relative distribution of isoprenoid GDGTs, the TEXH86 index, which in this region, we believe may record deeper temperatures than coccolithophoresPeer Reviewe

SHAREMED: Sharing and enhancing capabilities to address environmental threats in the NW Mediterranean Sea

International Symposium Human Health & the Ocean in a Changing World, 2-3 December 2020, Monte-Carlo, MonacoThe new Interreg Med project, SHAREMED (6MED_4.1_SP_006), "Sharing and enhancing capabilities to address environmental threats in the Mediterranean Sea" is aimed to engage stakeholders and authorities, and jointly define state-of-the-art and regional strategies for common marine environmental trends. Among them, focus is taken on the prevention and mitigation of the impacts of HABs in the Mediterranean, plankton diversity changes, pollution, eutrophication, weather and climate change. This presentation will summarize how SHAREMED is working to increase the capability of authorities and the scientific community to observe, assess and address the environmental biological and physical parameters through multidisciplinary research in a coordinated way in the NW Mediterranea

Distribution and sources of organic matter in size-fractionated nearshore sediments off the Barcelona city (NW Mediterranean)

14 pages, 10 figures, 2 tablesContinental shelves are recognized to play a key role in the biogeochemical cycle of carbon, linking terrestrial and marine carbon reservoirs. In this study we investigate the physical and biogeochemical processes that control the source, transport and fate of organic carbon (OC) in the continental shelf off Barcelona city, in the NW Mediterranean Sea. Surface sediment samples were collected from depths of 10–40 m during late summer and autumn 2012. Grain size and biogeochemical parameters such as OC, its stable isotope δC, total nitrogen (TN) and OC/TN ratios were analysed in size-fractionated sediments. The influence of environmental factors over the study area was determined using hydrological and oceanographic time series, together with video images of the Barcelona coast line and nearshore region. We have found a wide range of OC contents, from 0.13 to 8.68%, depending on water depth and sediment particle size. The highest OC concentration was always found in the clay fraction (63 μm) that contained terrestrial plant debris. Wave activity, discharge of the Besòs River and the “Espigó de Ginebra” outfall were the main mechanisms controlling the sorting of sediments by their grain size and thus the distribution of OC in the inner shelf off Barcelona. In addition, we observed that the organic matter in clay particles was progressively degraded seawards, probably because these particles remain suspended in the water column much more time compared to those that are heavier and, therefore, they are exposed for longer time periods to oxygenated conditions. Both OC/TN ratios and δC values found suggest that the organic matter preserved was predominantly land supplied.This research has been supported by the project PERSEUS (FP7-OCEAN-2011-3-287600) and the Coastal Ocean Observatory (COO, ICM-CSIC), and the Generalitat de Catalunya through a Consolidated Research Groups grant (2014 SGR 1068). [...] AS is supported by a “Ramon y Cajal” contract from MICINN and RD is supported by the JAE Programme from the CSICPeer Reviewe