Resumen del producto

The biological pump in the ocean plays an important role in the global carbon cycle. A substantial portion of carbon is exported and preserved on continental margins, areas that support 10 to 15% of the total production of chlorophyll across the ocean with a contribution of more than 40% of the global organic carbon export to the ocean floor. Reconstruction of past primary productivity (PP) in areas of high biological activity is important to understand how climate change affects the global carbon cycle in different timescales. Burial rates of organic carbon (Corg) and biogenic opal (BSi) were measured in a core couplet GC31/PC08 from the Magdalena margin, SW of the Peninsula of Baja California, in order to estimate changes in PP during the last 50,000 years. During the late Holocene (period between 3,000 years ago and today), the burial rate of BSi and Corg was lower than in the marine isotope stages 2 and 3 (occurred in the periods 29,000 to 14,000 and 57,000 to 29,000 years ago, respectively), including the last glacial maximum (27,000 to 18,000 years ago), suggesting that PP was greater in the latter two stages than in the most recent part of the record. In the marine isotope stage 3, the burial rate of BSi and Corg showed important oscillations coupled with DO cycles (rapid climate fluctuations that occurred in Greenland during the last glacial period with a quasi-periodically recurrence time of 1,470 years) indicating that PP in the region responds to millennial-scale global climate forcing. Our study in Baja California suggests that, in coherence with evidences from other sites along the northeast Pacific margin, the variability of the Oxygen Minimum Zone (OMZ) in the northeast Pacific is more largely controlled by changes in productivity rather than by ventilation changes of the water column, as it was the prevalent view.

Palabras clave: oceanic paleoproductivity; paleoclimate; global climate change; carbon export; carbon-silica burial rates; millennial cycles; marine isotope stages

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