Carbon export in Eastern Tropical Pacific controlled by micronutrient transport from upwelling or aeolian dust?

Abstract

We present excess-Ba (i.e., biogenic barium) and lithogenic flux derived from aluminum data from a sediment trap moored at 4950 m below sea level at a station (10.5°N, 131.2°W) in the Eastern Tropical Pacific (ETP) from 2003 to 2013 to explore the relationships between carbon export and micronutrient delivery in the ocean. The ETP is a high nutrient low chlorophyll (HNLC) region despite being an active upwelling region. Upwelling intensity that affects CO2 outgassing and nutrient transport from deep ocean to surface is influenced by Pacific decadal oscillation (PDO) on decadal scales. Upwelling was suppressed between 2003 to 2007 during a positive PDO phase and enhanced between 2008 to 2013 during a negative PDO phase. Excess-Ba – interpreted as export production – follows particulate organic carbon and sea surface temperature minimum seen with PDO phase in general. Seasonal carbon export has an outstanding correlation with lithogenic flux derived from Al (r = 0.95). However, carbon export has a lower correlation with dry dust deposition from satellite than that of lithogenic flux derived from Al, showing discrepancy between in-situ and satellite data for aeolian dust. We compared production proxies with upwelling and dust indicators to interpret sources of micronutrients in ETP: upwelling, aeolian dust, or both. The results show carbon export following PDO upwelling intensity with close relationship to dry dust deposition. Therefore, upwelling controls the carbon export trend by impacting nutrient supply and dust enhances the production magnitude. This study will contribute to the scientific community a better understanding of how climate change could affect oceanic carbon source and sink, and the impact of desertification that increases aeolian dust and atmospheric circulation change that impacts upwelling.