Ecosistemes marins i costaners

28 pages, 5 figuesLa Mediterrània és una mar semitancada i que pateix una gran pressió a causa de l’activitat humana vora la costa, dos aspectes que la fan especialment vulnerable al canvi climàtic. Les observacions pluridecennals mostren que la mar catalana s’està escalfant a una velocitat de 0,3ºC per decenni i que el nivell del mar augmenta gairebé quatre centímetres per decenni, i els models apunten que gairebé la meitat d’aquests canvis han estat causats per l’escalfament global d’origen antropogènic. Aquests canvis progressius, juntament amb episodis puntuals de sobreescalfament a l’estiu o amb un augment de les tempestes de tardor, tenen efectes en els ecosistemes marins. Les comunitats de coral·ligen dels fons litorals, formades sobretot per organismes sèssils i de creixement lent, experimenten episodis de mortaldats massives dels quals els costa molt recuperar-se. L’extensió dels alguers de Posidonia és sensible a la temperatura i a les variacions del nivell del mar. A l’ecosistema pelàgic, els models preveuen un increment de la producció primària bruta del fitoplàncton que no es veu reflectida en un augment de la productivitat planctònica neta perquè també s’incrementa la respiració. Tant entre els organismes sèssils com en els que es poden moure (vàgils), s’observa un desplaçament cap al nord d’algunes espècies habituals al litoral català, mentre que la presència d’espècies termòfiles vingudes de més al sud augmenta. Els hiverns suaus, la poca pluviositat i els estius càlids afavoreixen els eixams de meduses a les platges. A més, algunes algues tòxiques es poden veure afavorides per aigües més càlides i més estratificades. Alguns d’aquests canvis constitueixen amenaces per als serveis de què els ecosistemes marins proveeixen la societat: referents culturals, recursos econòmics directes (turisme i pesca), protecció pel que fa a l’erosió, la captura i l’emmagatzemament de CO2 atmosfèric, o l’aprofitament farmacèutic i industrial de la riquesa genètica i metabòlica. Malauradament, els agents climàtics actuen sinèrgicament i en la mateixa direcció que molts altres agents antròpics. Recomanem, doncs, que els esforços de mitigació de l’escalfament global vagin acompanyats d’esforços de millora i de regulació d’activitats d’impacte ambiental com ho són algunes arts de pesca, la pol·lució, l’explotació recreativa o la construcció. Es fa imprescindible, també, dissenyar i aplicar estratègies d’inversió en recerca i monitoratge i en protecció d’hàbitats singularsPeer Reviewe

Acidificación oceánica: una visión a través de paleoreconstrucciones

Ponencia presentada en: VI Congreso Internacional de la Asociación Española de Climatología celebrado en Tarragona del 8 al 11 de octubre de 2008.[ES]Una buena parte del CO2 emitido a la atmósfera por las actividades humanas está siendo absorbido por los océanos, provocando su progresiva acidificación, con consecuencias nocivas para los organismos marinos, sobretodo para aquellos que construyen un esqueleto de carbonato de calcio. Para entender mejor la magnitud de este problema medioambiental, es necesario conocer como ha oscilado el pH marino en el pasado, a diferentes escalas de tiempo y en diferentes localidades. Dado que los registros instrumentales de pH existentes son muy recientes y escasos, los pH pretéritos deben reconstruirse a partir de indicadores indirectos (proxies) de archivos adecuados. Un proxy geoquímico muy prometedor es la composición isotópica de boro en fósiles biogénicos de carbonato que, de hecho, representa el único método práctico para determinar, de manera cuantitativa, las variaciones de pH marino en el pasado. En esta comunicación presentamos y discutimos la base teórica de este proxy y algunas de las reconstrucciones de paleo-pH publicadas hasta el momento.[EN]A large part of CO2 emitted by human activities in the atmosphere is being absorbed by the oceans, leading to a progressive acidification, with detrimental effects on marine organisms, particularly those that build a skeleton of calcium carbonate. To better understand the magnitude of this environmental problem, it is necessary to know how seawater pH has oscillated in the past, at different timescales and locations. Because instrumental records of seawater pH exceeding a couple of decades are not yet available, past variations of pH need to be reconstructed using indirect indicators or proxies in suitable archives. A very promising geochemical proxy is the isotopic composition of boron in fossil biogenic carbonates which is, so far, the only practical method to quantitatively determine seawater pH variations back through time. In this communication, we present and discuss the theoretical grounds of this proxy and some of the paleo-pH reconstructions published so far.Este trabajo forma parte del proyecto ROMIAT (CTM2006-01957/MAR), financiado por el Ministerio de Educación y Ciencia, y es una de las actividades del Grup de Recerca en Biogeoquímica Marina i Canvi Global (2005SGR00021), financiado por la Generalitat de Catalunya. E.C. agradece un contrato Ramón y Cajal

Increased reservoir ages and poorly ventilated deep waters inferred in the glacial Eastern Equatorial Pacific

Consistent evidence for a poorly ventilated deep Pacific Ocean that could have released its radiocarbon-depleted carbon stock to the atmosphere during the last deglaciation has long been sought. Such evidence remains lacking, in part due to a paucity of surface reservoir age reconstructions required for accurate deep-ocean ventilation age estimates. Here we combine new radiocarbon data from the Eastern Equatorial Pacific (EEP) with chronostratigraphic calendar age constraints to estimate shallow sub-surface reservoir age variability, and thus provide estimates of deep-ocean ventilation ages. Both shallow- and deep-water ventilation ages drop across the last deglaciation, consistent with similar reconstructions from the South Pacific and Southern Ocean. The observed regional fingerprint linking the Southern Ocean and the EEP is consistent with a dominant southern source for EEP thermocline waters and suggests relatively invariant ocean interior transport pathways but significantly reduced air–sea gas exchange in the glacial southern high latitudes

Increased reservoir ages and poorly ventilated deep waters inferred in the glacial Eastern Equatorial Pacific.

Consistent evidence for a poorly ventilated deep Pacific Ocean that could have released its radiocarbon-depleted carbon stock to the atmosphere during the last deglaciation has long been sought. Such evidence remains lacking, in part due to a paucity of surface reservoir age reconstructions required for accurate deep-ocean ventilation age estimates. Here we combine new radiocarbon data from the Eastern Equatorial Pacific (EEP) with chronostratigraphic calendar age constraints to estimate shallow sub-surface reservoir age variability, and thus provide estimates of deep-ocean ventilation ages. Both shallow- and deep-water ventilation ages drop across the last deglaciation, consistent with similar reconstructions from the South Pacific and Southern Ocean. The observed regional fingerprint linking the Southern Ocean and the EEP is consistent with a dominant southern source for EEP thermocline waters and suggests relatively invariant ocean interior transport pathways but significantly reduced air-sea gas exchange in the glacial southern high latitudes.We acknowledge funding by the Spanish Ministry of Economy and Competitiveness through grants CTM2009-08849 (ACDC Project) and CTM2012-32017 (MANIFEST Project). M. de la Fuente was funded by a FPI studentship (BES-2010-039700) from the Spanish Government, and L. Skinner acknowledges support from NERC grant NE/L006421/1.This is the final version. It first appeared at http://www.nature.com/ncomms/2015/150703/ncomms8420/full/ncomms8420.html

Interdcadal climate variability in the Coral Sea since 1708 A.D.

Low resolution (5-year) Sr/Ca and δ18O samples, extending back to 1708 A.D., were analysed from a Porites coral core collected from Flinders Reef, an offshore reef on the Queensland Plateau in the western Coral Sea (17.5° S, 148.3° E). Using the Sr/C

Calcification reduction and recovery in native and non-native Mediterranean corals in response to ocean acidification

10 páginas, 7 figuras, 2 tablas.In recent years, some of the ramifications of the ocean acidification problematic derived from the anthropogenic rising of atmospheric CO2 have been widely studied. In particular, the potential effects of a lowering pH on tropical coral reefs have received special attention. However, only a few studies have focused on testing the effects of ocean acidification in corals from the Mediterranean Sea, despite the fact that this basin is especially sensitive to increasing atmospheric CO2. In this context, we investigated the response to ocean acidification of the two zooxanthellate coral species capable of constituting the main framework of the community, the endemic Cladocora caespitosa and the non-native Oculina patagonica. To this end, we examined the response of both species to pCO2 concentrations expected by the end of the century, 800 ppm, vs the present levels. Calcification rate measurements after 92 days of exposure to low pH conditions showed the same negative response in both species, a decrease of 32–35% compared to corals reared under control conditions. In addition, we detected in both species a correlation between the calcification rate of colonies in control conditions and the degree of impairment of the same colonies at low pH. Independent of species, faster growing colonies were more affected by decreased pH. After this period of decreased pH, we conducted a recovery experiment, in which corals reared in the acidic treatment were brought back to control conditions. In this case, normal calcification rates were reached in both species. Overall, our results suggest that O. patagonica and C. caespitosa will both be affected detrimentally by progressive ocean acidification in the near future. They do not display differences in response between native and non-native species but do manifest differential responses depending on calcification rate, pointing to a role of the coral genetics in determining the response of corals to ocean acidification.Financial support for this study was provided by the Spanish Ministry of Economy and Competitiveness through projects CTM2006-01957/MAR, CTM2009-08849/MAR, CGL2010-18466 and a FPI studentship (BES-2007-16537) to J.M. This work is a contribution from the Marine Biogeochemistry and Global Change research group, funded by Generalitat de Catalunya (Catalan Government) through grant 2009SGR142. [RH]Peer reviewe

Millennial surface water dynamics in the Ría de Vigo during the last 3000 years as revealed by coccoliths and molecular biomarkers

13 pages, 7 figures, 2 tables.-- Printed version published Mar 10, 2005.A combined study of coccolith assemblages and biomarkers in a gravity core collected from the Ría de Vigo (NW Spain) allowed us to reconstruct the paleoenvironmental conditions for the last 3000 years. The quantitative distribution of coccolithophore species points to three different intervals within the core, dated by AMS radiocarbon measurements. The first interval (ca. 975 BC–252 AD), characterized by high abundances of Calcidiscus leptoporus and Gephyrocapsa muellerae, is thought to represent moderate water temperatures, suggesting a transition from a warmer to a cooler period. The second interval (ca. 252–1368 AD), characterized by the dominance of Coccolithus pelagicus, Helicosphaera carteri and Syracosphaera spp., and a high concentration of hexacosanol linked to terrestrial input, is interpreted as having been a humid period with fluvial input. The third interval (ca. 1368 AD–1950) is characterized by a high abundance of Gephyrocapsa oceanica, high alkenone values and low values of hexacosanol, and is thought to represent a period dominated by oceanic conditions within the Ría.Taking into account the ocean–atmospheric system affecting the region studied, here we propose an alternation in the mean state of North Atlantic Oscillation (NAO) at millennial time scales. A well-developed upwelling system and an active Ría–ocean connection during the warmer interval I suggest a NAO+ phase influenced by a Hypsithermal period. The occurrence of the humid and relatively warm interval II is consistent with a negative phase in the NAO, as well as a relative restriction in ocean–Ría exchange. Interval III, which was drier and more productive, again suggests the dominance of a positive phase in the NAO, with a more intense oceanic connection and more energized upwelling.Research grants ABRUMIS REN2003-08642-C02-02/CLI, BTE2002-04670 (Ministerio de Ciencia y Tecnología) and SA088/04 (Junta de Castilla y León) supported this study.Peer reviewe