A quantitative proxy of diatom dissolution with implications for biological production in the Eastern Equatorial Pacific over the past 25,000 years
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Here we present a quantitative proxy for determining opal dissolution in deep sea sediment cores. The ratio of organic carbonxalcite production in the ocean is thought to affect global climate by changing CO2 levels in the atmosphere. The diatom-dominated opal producers generate significant organic carbon and have the ability to sequester organic carbon from the atmosphere to the ocean floor. Thus using diatom accumulation rates to reconstruct diatom production is important to climate research. However, opal and organic carbon accumulation rates reflect both variable production and preservation. Separating these factors is crucial to estimating past opal and organic carbon fluxes. The Eastern Equatorial Pacific is an important area for ocean/atmosphere carbon exchange, and yields different opal accumulation records for sites influenced by Equatorial divergence and Peru upwelling; the former shows an opal accumulation rate decrease for the last glacial, and the latter shows an increase compared to the Holocene. Differential diatom preservation was diagnosed via a four-stage preservation index using the vellum of the centric diatom Azpeitia nodulifer, to determine whether these differences are related to production or preservation. These records may provide evidence supporting the ‘silica leakage’ hypothesis for enhancement of the equatorial biotic pump in the Peru upwelling system during the last glacial. We find similar dissolution records at both sites from the last glacial maximum through the Holocene, implying that production, not preservation, controlled the accumulation rates. This supports a role for silica leakage in the eastern equatorial Pacific. Additionally, we find that diatom preservation is not related to either opal accumulation rates or sediment focusing. Therefore, some other factor(s) at the in the production zone or within the water column must control the dissolution variations we observe.