Penultimate Deglacial Dust Fluxes in the Equatorial Pacific: Implications for ITCZ Movement and a Common Mechanism for Glacial Terminations

Abstract:

The position of the Intertropical Convergence Zone (ITCZ) has been hypothesized to play a role in linking the climate of the poles and in predicating important changes in ocean overturning, particularly on deglacial timescales. The position of the ITCZ has also been linked to changes in equatorial upwelling strength, marine productivity, terrestrial aridity and even the collapse of civilizations.

One method of tracking the paleo-position of the ITCZ is through the quantification of ²³⁰Th_xs,0-normalized ²³²Th concentrations in marine sediments which acts as proxy for dust flux. Because the ITCZ is an efficient scavenger of atmospheric particulates, changes in the latitude of maximum dust flux can yield insight into variations in ITCZ position. Previous studies have used this technique to reconstruct the movement of the ITCZ during the last deglaciation at low resolution, but no studies have attempted to resolve the movement of the ITCZ during Termination II (Marine Isotope Stage 6-5) or during the ensuing glacial inception (MIS 5-4). Termination II is a time interval of particular interest because of its potential to yield information about the similarities of deglacial transitions despite different orbital configurations.

We present high-resolution (sub millennial) proxy records of dust flux, marine productivity and thermocline upwelling from 150-60 kyr at two sites in the central equatorial Pacific (cruise MGL-1208). These records provide the first evidence of an abrupt climatic shift during the deglaciation with timing similar to that of Heinrich Event 11 (H11). We evaluate the interpretation of this event both as a northern hemisphere increase in aeolian dust abundance concomitant with H11, and as a signature of an ITCZ shift during the deglaciation. We compare our data sets to existing records of the last deglaciation and infer large-scale similarities between Terminations I and II.