Systematic changes in circumpolar dust transport to the Subantarctic Pacific Ocean over the last two glacial cycles

Abstract

The input of the soluble micronutrients iron (Fe) and/or manganese (Mn) by mineral dust stimulates net primary productivity in the Fe/Mn-deficient Southern Ocean. This mechanism is thought to increase carbon export, thus reducing atmospheric CO 2 during the Pleistocene glacial cycles. Yet, relatively little is known about changes in the sources and transport pathways of Southern Hemisphere dust over glacial cycles. Here, we use the geochemical fingerprint of the dust fraction in marine sediments and multiisotope mixture modeling to identify changes in dust transport to the South Pacific Subantarctic Zone (SAZ). Our data show that dust from South America dominated the South Pacific SAZ during most of the last 260,000 a with maximum contributions of up to ∼70% in the early part of the glacial cycles. The enhanced dust-Fe fluxes of the latter parts of the glacial cycles show increased contributions from Australia and New Zealand, but South American dust remains the dominant component. The systematic changes in dust provenance correspond with grain size variations, consistent with the circumpolar transport of dust by the westerly winds. Maximum contributions of dust from more proximal sources in Australia and New Zealand (up to ∼63%) paired with a finer dust grain size indicate reduced westerly wind speeds over the South Pacific SAZ during deglacial and peak interglacial intervals. These quantitative dust provenance changes provide source-specific dust-Fe fluxes in the South Pacific SAZ and show how their systematic changes in magnitude and timing influence the Southern Ocean dust-Fe feedback on glacial-interglacial to millennial time scales.

Alaskan Glacial Dust Is an Important Iron Source to Surface Waters of the Gulf of Alaska

“…Dust fluxes from these locations to the Southern Ocean may be underappreciated during the LGM, a time interval when we know dust fluxes were large to some parts of the Southern Ocean (Martinez‐Garcia et al., 2014). Indeed, recent work suggests large dust fluxes to the subantarctic Pacific Ocean from South America, but also from New Zealand and Australia during the last two glacial cycles (Struve et al., 2022).…”

A Cost Model for Ocean Iron Fertilization as a Means of Carbon Dioxide Removal That Compares Ship‐ and Aerial‐Based Delivery, and Estimates Verification Costs

“…Aerial application has yet to be tried for OIF. Nonetheless, a major source of iron to the open ocean is air‐borne aeolian dust (Hooper et al., 2019; Jickells et al., 2005; Moore & Braucher, 2008; Struve et al., 2022), thus aerial delivery better mimics natural processes of iron delivery than ship‐based methods. Recent well‐documented examples of large scale phytoplankton blooms from natural Fe‐fertilization events due to volcanos (Duggen et al., 2010; Hamme et al., 2010; Watson, 1997) and wild‐fires also resulted in delivery of iron from the atmosphere.…”

“…It was first proposed in the 1980s (Martin & Fitzwater, 1988; Martin & Gordon, 1988). Coincident with the recognition of iron as a limiting nutrient in the modern ocean was paleoclimate analysis indicating that iron supply, primarily as wind‐blown aeolian dust delivered from the continents to the open ocean, was one of several factors that controlled atmospheric CO 2 concentrations during the glacial‐interglacial periods of the past several hundred thousand years (Lamy et al., 2014; Martin, 1990; Martínez‐García et al., 2014; Struve et al., 2022). Combined, these factors led to the hypothesis that active addition of Fe to Fe‐limited regions of the ocean, often referred to as high nitrate, low chlorophyll (HNLC), could stimulate enough additional phytoplankton growth that the resultant export of newly fixed CO 2 into the deep ocean could be an effective means of CDR for the mitigation of anthropogenic GHG‐induced global warming.…”

A cost model for ocean iron fertilization as a means of carbon dioxide removal that compares ship- and aerial-based delivery, and estimates verification costs.

“…Aerial application has yet to be tried for OIF. Nonetheless, a major source of iron to the open ocean is air-borne aeolian dust (Hooper et al, 2019;Jickells et al, 2005;Moore & Braucher, 2008;Struve et al, 2022) , thus aerial delivery better mimics natural processes of iron delivery than ship-based methods. Recent welldocumented examples of large scale phytoplankton blooms from natural Fe-fertilization events due to volcanos (Duggen et al, 2010;Hamme et al, 2010;Watson, 1997) and wild-fires also resulted in delivery of iron from the atmosphere.…”