Constraints on the magnitude of the deglacial migration of the ITCZ in the Central Equatorial Pacific Ocean

Abstract

Accurate paleo-latitudinal reconstructions of the Intertropical Convergence Zone (ITCZ) are necessary for understanding tropical hydroclimate and atmospheric circulation. Paleoclimate models and records suggest that as global temperatures increase, the ITCZ should migrate towards the warmer hemisphere. Many uncertainties remain regarding the magnitude of this migration, and few studies have focused on the Central Equatorial Pacific (CEP). Here, we use eolian dust records recovered from three locations in the CEP to address changes in dust provenance across the paleo ITCZ since the last glacial maximum (LGM). Radiogenic isotope compositions of Nd and Pb show that dust delivered to the CEP was sourced mainly from two regions: East Asia and South America. From these data we deduced that since Marine Oxygen Isotope Stage 2 (MIS2) the ITCZ has migrated north to its modern position, being displaced by as much as 7°, to as little as 2.5°, degrees. We find that the ITCZ migrated further north during the early Holocene (~ 9 kyr), reaching its position furthest north during the mid-Holocene warm interval (~7 kyr), based on an increase in South American dust at the northernmost sites.

Climate-related response of dust flux to the central equatorial Pacific over the past 150 kyr

“…Observations of ocean chemistry in the tropical Atlantic Ocean show a linear correlation between ITCZ precipitation and dissolved iron from mineral dust (Schlosser et al, 2014). Existing paleorecords confirm that sites within the ITCZ are characterized by latitudinal gradients in dust flux (McGee et al, 2007) and provenance (Xie and Marcantonio, 2012;Reimi and Marcantonio, 2016). Thus, we can use the scavenging of dust by the ITCZ to determine its position, taking into consideration that dust at the northern edge of the ITCZ will be primarily sourced from the Northern Hemisphere (NH) and that which is deposited at its southern edge will be predominately sourced from the Southern Hemisphere (SH).…”

Productivity patterns in the equatorial Pacific over the last 30,000 years

“…Of the three modes, Mode 3 has the greatest uncertainty (Figure ), but it can be interpreted as either three half‐precessional peaks at 0, 10, and 20 ka or one precessional peak at 10 ka, with a gradual increase in productivity from 25 ka to 10 ka followed by an abrupt decline at ~8 ka. The more robust productivity maximum at 10 ka coincides with the Northern Hemisphere Holocene Thermal Maximum, which fueled the Green Sahara of the African Humid Period with a mean ITCZ shifted substantially to the north both on land [ de Menocal et al ., ] and in the ocean [ Reimi and Marcantonio , ]. A similar deflection of the ITCZ in the EEEP would have promoted La Niña‐like conditions, vitalizing surface productivity, especially in the relatively nutrient‐replete conditions inferred from Mode 1 at this time.…”

The Penultimate Glacial Termination and Variability of the Pacific Intertropical Convergence Zone

“…Previous work determined that the four most dominant sources of dust to the Line Islands were three South American volcanic regions and Chinese Loess (Reimi & Marcantonio, 2016). The most northern South American source is the North Central Volcanic Zone (N-CVZ), between 14.5°S and 19.5°S, as defined by Pichat et al (2014a).…”

“…Previous studies have used dust provenance to track ITCZ position over glacial‐interglacial timescales (Abouchami et al, ; Abouchami & Zabel, ; Xie & Marcantonio, ). In the CEP, the ITCZ was found to be further south during the last glacial period than during the Holocene (Reimi & Marcantonio, ). Here, we are able to resolve dust provenance changes during the penultimate termination, consistent with the timing of Heinrich Stadial 11 (HS11) and consider whether these changes are due to movement of the ITCZ precipitation centroid (i.e., changes in the position of the interhemispheric dust transport barrier) or to decreases in the convective intensity of the ITCZ (which would allow interhemispheric leakage of dust).…”