A 14‐ka Record of Dust Input and Phytoplankton Regime Changes in the Subtropical NE Pacific: Oceanic and Terrestrial Processes Linked by Teleconnections at Suborbital Scales

Abstract

We study shifts in phytoplankton proxies linked to terrigenous inputs and teleconnections in a core from Soledad Basin, Gulf of Ulloa, NW Mexico, spanning the end of the deglaciation and the Holocene. We used biogenic opal (% opal), organic carbon (% total organic carbon [TOC]), and inorganic carbon (% CaCO3) as proxies of productivity and opal/TOC and CaCO3/TOC ratios as proxies of nutrient uptake and C‐export by siliceous and carbonate organisms. We reconstructed terrestrial inputs and identified authigenic gypsum. Based on opal/TOC and CaCO3/TOC ratios, we found periodic changes of ~0.5, 1.1–1.8 ka cycle in phytoplankton proxies exporting siliceous and carbonate skeletal debris to the sediments. An increase in carbonate organisms occurred during 14–8.7 ka, corresponding to reduced El Niño–Southern Oscillation (ENSO)‐like variability, in parallel to the northward displacement of the Intertropical Convergence Zone (ITCZ) and an overall negative phase of the Pacific Decadal Oscillation (PDO). An increase in siliceous organisms occurred between 6 and 3 ka, coincident with strong ENSO‐like conditions, southern migration of ITCZ, and less intense but more frequent positive PDO‐hydrological variability. Grain size analyses show significant amounts of fine fraction (dust <6.6 μm) present during the early‐ to mid‐Holocene in agreement to extreme weather on land, with episodes of eolian and fluvial transport to the sea. The ENSO‐like variations influenced biological C‐export producers on a scale of 1.1–1.8 ka, but PDO‐related variability is uncertain. We suggest that Holocene drivers for phytoplankton successions are changes in insolation, ITCZ migration, California Current upwelling, nutrient inputs by advection, and terrestrial sources.

Comparisons between marine productivity and terrestrial input records in the Gulf of California over the last 28 ka

“…The CaCO 3 /TOC average ratio of 0.3 is below the oceanic average of 0.5 (Pichevin et al ., 2014). The opal/TOC average ratio of 1.9 is higher than the ocean average (oceanic Redfield ratio = 1) (Brzezinski, 1985), which is higher than neighbouring sites in the California Current, between 0.15 and 1.10 (Arellano‐Torres et al ., 2019), and within calculated ratios in the GC between 2.10 and 4.7 (Pichevin et al ., 2014). High opal/TOC ratios found between 25–22 ka and the interstadial B/A event, suggest that primary productivity and C‐export were facilitated by siliceous organisms (i.e.…”

“…In areas under humid conditions, riverine input can transport bigger particles in suspension (>10 µm) and ultimately deposit them in marine environments (Ratmeyer et al ., 1999; Rea, 1994). Thus, the premise is that each sedimentary component has a polynomial distribution determined by deposition mechanisms and transport that can help us to reconstruct environmental conditions in regions with intense material delivery to the ocean (Arellano‐Torres et al ., 2019; Pichevin et al ., 2005; Ratmeyer et al ., 1999; Sun et al ., 2002).…”

“…The finer and medium particle sizes (0.6–2.8 and 3.3–11 μm) are within the average range of dust particles transported by high altitude winds from deserts (Arellano‐Torres et al ., 2019; Pichevin et al ., 2005), although we cannot exclude riverine sources transporting these fine sizes. The region surrounding the GC is an arid location where most of the terrigenous input is wind‐transported from the deserts (Douglas et al ., 2007; Van Andel, 1964).…”

“…6). We calculated the CaCO 3 /TOC and opal/TOC ratios to determine the role of calcareous and siliceous phytoplankton organisms to export carbon to the ocean floor (Arellano‐Torres et al ., 2019; Pichevin et al ., 2014). The CaCO 3 /TOC average ratio of 0.3 is below the oceanic average of 0.5 (Pichevin et al ., 2014).…”

Middle to Late Holocene Sea Surface Temperature and Productivity Changes in the Northeast Pacific

“…Satellite based diatom and coccolithophore concentrations and data for PCM00‐78C/PCM00‐78K were downloaded from the Pangaea database (Bracher et al., 2017; O’Mara et al., 2019a). Data for EW0408‐85JC, ODP1019, TN062‐O550, GC41/PC14, and Temp12K were downloaded from the NOAA Paleoclimate database (Addison et al., 2012a, 2017; Arellano‐Torres et al., 2018; Barron et al., 2003b; Kaufman, 2020; Praetorius et al., 2017).…”