Late Holocene record of sedimentologic and paleooceanographic events in western Guaymas Basin, Gulf of California

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Mary McGann1, Charles K Paull2, Juan Carlos Herguera3, John Arthur Barron4, Roberto Gwiazda5, Krystle Anderson5, Eve M Lundsten5, Brian D Edwards1 and David W Caress5, (1)USGS Pacific Coastal and Marine Science Center, Menlo Park, CA, United States, (2)Monterey Bay Aquarium Research Institute, Watsonville, CA, United States, (3)CICESE Center for Scientific Research and Higher Education, Oceanography, Ensenada, Mexico, (4)USGS Western Regional Offices Menlo Park, Menlo Park, CA, United States, (5)Monterey Bay Aquarium Res Inst, Moss Landing, CA, United States
Transects of ≤1.5 m-long vibracores obtained with MBARI’s ROV Doc Ricketts reveal late Holocene sedimentologic and paleooceanographic events in western Guaymas Basin, Gulf of California (GOC) (~26.87°N, 111.338°W). Cores were located where layered near-seafloor sediments and subtle bedforms occur in 1793 to 1863 m water depths on the SW flank of the basin using detailed bathymetry and chirp profiles. Color banding was observed in the cores and gamma-density, XRF, grain size, and stable isotope data show that most of the banding is attributed to distal deposition from two turbidities. Distinctive white bands ~4 cm thick are present in three cores dispersed across ~300 m. The white bands are diatom oozes composed primarily of Thalassiothrix longissima as well as lesser abundances of Fragilariopsis doliolus and are probably a result of aggregations of Thalassiothrix-dominated mats that settle through the water column and accumulate on the seafloor. An AMS14C date taken ~3 cm above the white band in one core suggests this event occurred shortly before cal AD 1290±30. The core sites were most likely located beneath an important oceanographic front between nutrient-rich and oligotrophic water masses, probably as the result of well-mixed upper intermediate and surface waters in the mid-GOC and better-stratified tropical waters to the south. This implies the existence of a deeper mixed layer to the N in the mid GOC region most likely controlled by equatorial La Niña events fueled by stronger and more persistent NW winds along the GOC. A substantial reduction in diatom abundance evident by low specimen counts and lack of white bands following this mat-forming event seem to correlate with an abrupt decline in biosiliceous productivity and increases in the abundance of tropical diatoms and silicoflagellates in core MD02-2517 (887 m water depth; western Guaymas Basin slope) at the end of the Medieval Climate Anomaly and transition to the Little Ice Age (~AD 1200-1300).