ABSTRACT:

Robust chronologies for marine sediment cores are critical to understanding glacial and deglacial abrupt climate changes. Here we combine two classic tools for age model development, benthic d¹⁸O alignment and planktonic radiocarbon ages, to develop state-of-the-art age models for the intermediate North and South Atlantic, deep Atlantic, intermediate and deep Pacific, and deep Indian Oceans. Collectively, these age models are constrained by 776 planktonic radiocarbon dates from 61 cores. We also construct regional benthic d¹⁸O stacks using these radiocarbon age models and data from 252 cores. The stacks reveal differences of up to 4000 yr in the regional timing of the start of Termination 1, with the intermediate South Atlantic responding first at 18.5 kyr BP (95% CI: 17.7 – 19.0 kyr BP) and the deep Indian responding last at 14.5 kyr BP (95% CI: 14.3 – 14.8 kyr BP). The termination onset occurs at 17.5 kyr BP in both the deep Atlantic and deep Pacific stacks, but the deep Pacific lags the deep Atlantic by up to ~1700 yr during the middle of the termination. Diachronous regional d¹⁸O responses suggest that data compilations based on the assumption of synchronous benthic d¹⁸O change may have significant chronological errors. Radiocarbon-dated regional d¹⁸O chronologies also improve our ability to compare paleoceanographic proxy records with LGM and deglacial model simulations and with well-dated proxy records from ice cores, speleothems, and corals.

The high-latitude North Atlantic is an especially critical region for reconstructing deglacial climate responses and the interactions between climate and Atlantic Meridional Overturning Circulation (AMOC). However, AMOC changes also affect surface reservoir age, creating uncertainties of up to 2000 years in ¹⁴C ages during Heinrich Stadial 1 (HS1). We address this key uncertainty with a comparison of high- and low-latitude deep North Atlantic records that yields a continuous record of high-latitude North Atlantic reservoir ages for the last 40 kyr. Our reconstruction reveals reservoir ages of >1000 ¹⁴C yr from 18.5-16.5 kyr BP. Increased reservoir ages clearly precede HS1 ice-rafted debris (IRD) and suggest early weakening of the AMOC caused by the first deglacial melting event at 19 kyr BP. We also observe a rapid decrease in reservoir ages coincident with the 16 kyr BP IRD peak. We propose that this shift was caused by extreme North Atlantic stratification that allowed surface waters to equilibrate with the atmosphere, thus indicating severe weakening of the AMOC triggered by ice rafting at 16 kyr BP.