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

Abstract

High resolution paleoclimate records from low latitudes are critical for understanding the role of the tropics in transmitting and generating feedbacks for high-latitude climate change on glacial-interglacial and millennial timescales. Here we present three new records of 230 Th xs,0normalized 232 Th-derived dust fluxes from the central equatorial Pacific spanning the last 150 kyr at millennial-resolution. All three dust flux records share the "sawtooth" pattern characteristic of glacial-interglacial cycles in ice volume, confirming a coherent response to global climate forcing on long timescales. These records permit a detailed examination of millennial variability in tropical dust fluxes related to abrupt perturbations in oceanic and atmospheric circulation. Increases in dust flux in association with at least six of the longest Greenland stadials provide evidence that abrupt, high-latitude climate oscillations influenced the atmospheric aerosol load in the equatorial Pacific, with implications for both direct and indirect effects on the tropical energy balance. Our latitudinal transect of cores captures shifts in the position of the Intertropical Convergence Zone (ITCZ) in response to variations in the interhemispheric thermal gradient associated with cooling in Greenland and bipolar seesaw warming in Antarctica. These observations demonstrate that changes in the energy and hydrologic balance of the tropics were repeated features of the penultimate deglaciation, last glacial inception and last glacial cycle, and highlight the role of the tropical atmosphere as a dynamic and responsive component of Earth's climate system.

Barium Concentrations as a Proxy for Equatorial Pacific Productivity During the Past 140,000 Years

“…The bioBa was estimated by subtracting the lithogenic Ba from the total Ba. Lithogenic Ba contents were calculated using thorium concentrations in the same samples (Jacobel et al, 2017). Our results…”

“…(2): bioBa flux = (bioBa) * 230 Th-derived sediment Mass Accumulation Rate Eq. (2) where the 230 Th-derived sediment Mass Accumulation Rate is given for the same sample intervals in Jacobel et al (2017).…”

“…The detrital fraction of Ba was estimated assuming that the Ba/Th ratio of the sediments is same as the Ba/Th ratio of average upper crust (51.4, i.e., 550 ppm for Ba and 10.7 ppm for Th, Taylor and McLennan, 1985). Therefore, bioBa concentration can be derived by using equation (1) where the 232 Th concentration is given for the samples at the same depths in Jacobel et al (2017).…”

“…Over the past 140 kyr, there is a positive relationship between productivity and warm interglacial periods which, in turn, are anti-correlated with dust fluxes determined by Jacobel et al (2017 …”

“…The authigenically-derived portion of the total barium, thought to be correlated with export production, is denoted as the biogenically-derived barium (bioBa). Using accumulation rates derived by Jacobel et al (2017), we found bioBa accumulation rates that ranged from about 0.5 to 1.0 mg cm -2 kyr -1 . For this research, the following hypotheses were tested:…”