Geoquímica de la materia particulada en hundimiento y del Los sedimentos recientes de cuenca Alfonso, Bahía de La Paz.

impreso y digita

Sensitivity of Classic and Novel Proxies to Oxygen Minimum Zone Variability of the Eastern Tropical North Pacific

Accurately recreating how Oxygen Minimum Zones (OMZs) changed through time requires the combined use of classic and novel proxy approaches. Short-term proxy trends are often deemphasized in favor of the major patterns despite having the potential to capture environmental shifts in the OMZs. To address this problem decadal-to-millennial OMZ variations were reconstructed over the last 70 kyr BP in a major OMZ—the Eastern Tropical North Pacific (ETNP). Specifically, sedimentary material collected from basinal settings with diverse levels of restriction and nutrient availability in the Gulf of California were analyzed: Alfonso, La Paz, and Pescadero. This dissertation emphasizes a broad range of classic and novel paleoredox and paleoproductivity proxies (CaCO3, C-S-Fe relationships, Ba, Cd, Cu, Mo, Mn, Ni, V, Zn, as well as U concentrations and isotope ratios). Global circulation effects on the availability of nutrients and deep-water oxygenation are the main controls for OMZ variability over glacial-interglacial time scales. Newly-generated data reveal that the ETNP OMZ achieved its peak strength during warm Marine Isotope Stages (MIS) accompanied by sea-level highstands (MIS3 and Holocene) exposed by high Mo, V, authigenic U (Uauth) and higher δ238U. Conversely, the cold sea-level lowstands (MIS4, LGM) often manifested as low Mo, V, and Fe/Al values indicating exposure of the marine basins to oxygenated waters. When it comes to submillennial variability, Heinrich events and cold Dansgaard-Oeschger phases enhanced the ventilation of the ETNP, as fingerprinted in low Mo, V, U, and lower δ238U values. The mechanisms that control decadal-to-centennial oxygen variability in the ETNP remain in the shadows but are likely influenced by solar forcing indirectly driving the intensity changes of the Pacific Walker Circulation (PWC). During the Little Ice Age, solar irradiance was at its lowest for the past millennium, which strengthened the PWC. The latter created more frequent La Niña-like conditions that enhanced upwelling of nutrient-rich waters of the west coast of North America, driving productivity and reducing bottom oxygen levels, as seen in the ETNP records. This research brings new insights into the biogeochemistry of U in OMZs, revealing the sources and causes of its isotopic fractionation and enrichment mechanisms

GEOQUÍMICA DE LA MATERIA PARTICULADA EN HUNDIMIENTO Y DE LOS SEDIMENTOS RECIENTES DE CUENCA ALFONSO, BAHÍA DE LA PAZ

vii RESUMEN La caracterización geoquímica de elementos traza en los materiales sedimentarios de las regiones de climas áridos es relativamente menor que en las zonas templadas y tropicales con mayor precipitación y escorrentía. La influencia de la composición de las rocas de la cuenca de drenaje en el material sedimentario marino (materia particulada en hundimiento - MPH y capa sedimentaria superficial) es estudiada en una de estas áreas climáticas con poca precipitación, como es el caso de la Bahía de La Paz, Golfo de California, donde los principales aportes ocurren por el paso de ciclones tropicales, lluvias esporádicas y tormentas de polvo. Se colectaron 10 muestras de roca, 15 de sedimentos aluviales y 15 de dunas en la cuenca de drenaje de la bahía. Entre los años 2005 y 2008 se obtuvieron 64 muestras de MPH con una trampa sedimentaria, así como de submuestras de un núcleo (110 mm de largo, fechado con 210Pb, obteniendose una tasa de sedimentación de 0.61 mm/año) en la parte más profunda de este cuerpo de agua (Cuenca Alfonso). En los sedimentos aluviales se observa que los elementos como As, U y P son aportados de productos de erosión de rocas marinas que presentan elevado contenido de fósforo, como las fosforitas y areniscas fosfáticas de la Formación El Cien. Esto debido a que dichas rocas fueron formadas en condiciones de surgencias con elevada productividad primaria, así como en cuencas suboxicas, lo mismo que ocurre actualmente en Cuenca Alfonso. Lo anterior es registrado en la composición de MPH mediante eventos de enriquecimiento de As (47.5 mg/kg) y U (42.8 mg/kg), concordando en algunos casos con elevados valores de Ca biogénico asociados a florecimientos planctónicos. Por otro lado, el registro histórico (núcleo sedimentario) indica algunos eventos de variación de estos elementos, especialmente el U que presenta un pico con un valor elevado (19 mg/kg) a la profundidad de núcleo de 35 mm que corresponde al año 1950. El calcio probablemente sea aportado a la cuenca mediante florecimientos planctónicos y productividad primaria, lo cual hace que concuerde con eventos reportados por otros autores durante la serie de tiempo de la trampa sedimentaria. En el núcleo, este elemento presenta un aumento gradual a partir de 1950 y su comportamiento es casi idéntico a la reconstrucción de temperatura superficial del mar (ERSST.v3b de la NOAA). viii Esto probablemente se deba a la preferencia de organismos calcáreos por condiciones más cálidas. El aporte terrígeno, estimado por medio del Sc en la materia particulada, muestra una relación positiva con ciclones tropicales, así como con rachas persistentes de viento (> 4.5 m/s) provenientes del NW. En el núcleo sedimentario se observan cambios de régimen fluvial, destacando un periodo que abarca desde 1890 hasta 1980 con elevados contenidos de este elemento

Increasing arsenic mobility in the fine fraction of the dry stream sediments of the semi-arid San Antonio gold mining district (Baja California peninsula, Mexico)

The geochemical mobility of arsenic and somemetals in the fine fraction of 20 alluvial sediment samplescollected along the thalweg of the San Antonio arroyo wasassessed in the abandoned gold mining district of the semi-arid southeastern Baja California peninsula. Acid-digestedelement concentrations were determined by treating thefine fraction of the sediments with concentrated HNO3viamicrowave heating. A separate leaching of the diluted acid-soluble As and some metals from the samples was carriedout using 1 M HCl. The most reactive As phase wasextracted from the subsamples using an ascorbic solutionof Na citrate buffered at pH 8. The high abundance ofsulphosalts (tennantite Cu12As4S13and proustite Ag3AsS3)in the sediments from the head of the arroyo changesdownstream to the predominance of arsenic trioxide (ar-senolite As2O3) and arsenate (scorodite FeAsO42H2O).Acid-digested As concentrations were always found to behigh (230–270 mg kg-1) from the San Antonio villageuntil the end of the arroyo. The concentration of reactiveAs and its relative contribution increased from low valuesof 2.3 mg kg-1and 1 %, respectively, at the upstream ofthe arroyo, to 191–220 mg kg-1and 75–89 % in themiddle and lower parts, and is probably a result of Asrelease from the mineral sulfide fraction of the tailings.Metallic contaminants exhibited different behavior, with apeak of acid-digested and diluted acid-leached concentra-tions observed in the central part of the arroyo and analmost permanent geochemical mobility

Evaluation of contribution sources for the sediments of the La Paz Lagoon, based on statistical treatment of the mineralogy of their heavy fraction and surrounding rock and drainage basin characteristics

To identify the main sources of terrigenous sediments of the La Paz Lagoon, a description of the hydrology of the drainage basins and the mineralogy of the heavy fraction of the lagoon sediments is needed. In this work, 14 terrigenous sediment samples from the arroyos (dry streams) and 55 superficial marine sediment samples were collected from the study area. The drainage basins of the prin­cipal arroyos discharging into the lagoon were defined using geomorphologic analyses on Geographic Information Systems (GIS). The sediment samples’ grain size fraction of 3.25 – 3.00 phi was obtained by sieving. The heavy minerals were separated using bromoform and the mineralogical composition was determined using a petrographic polarization microscope. Three main sedimentary provinces in the lagoon were distinguished based on principal component analysis of the heavy mineral data and the study of the surrounding regional streams. The eastern sedimentary province is characterized by the predominance of orthopyroxene, especially hypersthene, as well as a high hornblende presence. This is due to the erosion of volcanoclastic sequences of the Comondú Formation and intrusive granitic complexes of Sierra de Las Cruces. The southeastern province displays a high abundance of hornblendes (up to 81% in some stations), micas, apatite, sphene, anatase, tourmaline, chlorite, clinopyroxene and orthopyroxene. Lower contents of amphibole (up to 27.2% in some stations) and resistant garnet and zircon minerals were found, as were some soft-pink piedmontite and pale-green hypersthene. These minerals were supplied by the El Cajoncito, Los Bledales, La Palma, Cardonal and El Novillo arroyos eroding the intrusive rocks of “Granito Sierra de Las Cruces”, “Tonalita La Buena Mujer” and in a smaller extent the extrusive and non-marine rocks (tuffs, riodacites, conglomerates and sandstones) of the Comondú Formation. The predominant minerals of the northwestern province are clinopyroxene, orthopyroxene and phosphatic ooids. Relatively high abundance of olivine, hornblende, zircon, epidote and garnet were also found. These minerals are presumably supplied by the arroyos La Ardilla and other streams to the north of the El Centenario and El Comitán villages, as well as by eolian and littoral transport of the El Mogote sandbar dunes, which accumulates eroded sediments from the marine sedimentary rocks of El Cien Formation

Assessment of geochemical mobility of metals in surface sediments of the Santa Rosalía mining region, western Gulf of California

To asses the geomobility of cadmium, copper, iron, manganese, nickel, lead, and zinc in marine sediments near the Santa Rosalía copper smelter, which is located on the eastern coast of the Baja California Peninsula, sequential leaching was applied to sediment samples containing different levels of Cu: (1) uncontaminated or slightly contaminated (<55 mg kg−1 Cu); (2) moderately contaminated (55–500 mg kg−1 Cu); and (3) heavily contaminated (>500 mg kg−1 Cu). Concentrations of Cd, Cu, Fe, Mn, Ni, Pb, and Zn in four fractions of the leachate (mobile fraction F1, relatively mobile fraction F2, associated with organic matter/sulphides fraction F3, and residual fraction F4) were measured by atomic absorption spectrophotometry (AAS). The sediments with Cu concentration <500 mg kg−1 displayed prevalence of mobile acid-leachable fraction F1 and reducible fraction F2 for Cd, Cu, Mn, and Pb, whereas the relative contribution of fraction F3 was relatively low for all of the examined metals. Residual fraction F4 was highest (>65%) for Fe and Ni because both metals are associated with the crystalline matrix of natural sediments. The sediments heavily contaminated with Cu (>500 mg kg−1) had dramatically increased percentages of Cu, Mn, Pb, and Zn, ranging on average from 63 to 81%, in the residual fraction. In the case of Cu, for example, the relative abundances of this element in the different fractions of such sediments followed this sequence: residual fraction F4 (76 ± 5%) >absorbed form and carbonates fraction F1 (15 ± 5%) >Fe and Mn oxyhydroxides fraction F2 (5 ± 2%) >fraction associated with organic matter and sulphides F3 (4.5 ± 3.9%). Copper, Pb, and Zn contents in each geochemical fraction of all samples were compared with sediment-quality guideline values (“effects range low” [ERL] and “effects range medium” [ERM]) to assess their possible negative effects on biota. Copper contents in mobile fractions F1 and F2, which were moderately contaminated with Cu, were higher than ERL but lower than ERM guideline values. For heavily contaminated sediments, Zn contents of mobile fractions F1 and F2 were higher than ERL but lower than ERM guideline values. The Cu content of fraction F1 was higher than ERM guideline values, whereas for fractions F2 and F3 copper content was higher than ERL guidelines but still lower than ERM guideline values

Elevated sedimentary removal of Fe, Mn, and trace elements following a transient oxygenation event in the Eastern Gotland Basin, central Baltic Sea

info:eu-repo/semantics/publishe

Elevated sedimentary removal of Fe, Mn, and trace elements following a transient oxygenation event in the Eastern Gotland Basin, central Baltic Sea

info:eu-repo/semantics/publishe