Development of a multi-method chronology spanning the Last Glacial Interval from Orakei maar lake, Auckland, New Zealand

Abstract

Northern New Zealand is an important site for understanding Last Glacial Interval (LGI) paleoclimate dynamics, since it is influenced by both tropical and polar climate systems which have varied in relative strength and timing of associated changes. The Auckland Volcanic Field maar lakes preserve these climatic influences on the regional paleoenvironment, as well as past volcanic eruptions, in their sedimentary infill. The sediment sequence infilling Orakei maar lake is continuous, laminated, high-resolution and provides a robust archive from which to investigate the dynamic nature of the northern New Zealand climate system over the LGI. Here we present the chronological framework for the Orakei maar sediment sequence. Our chronology was developed combining Bayesian age modelling of combined radiocarbon ages, tephrochronology of known-age rhyolitic tephra marker layers, 40Ar/39Ar-dated eruption age of a local basaltic volcano, luminescence dating (using post infrared-infrared stimulated luminescence, or pIR-IRSL), and the timing of the Laschamp paleomagnetic excursion. We also investigated the application of meteoric (cosmogenic) Beryllium-10 variability to improve the age-depth model by complementing relative paleointensity measurements. However, the results were apparently influenced by some unaccounted catchment process and unable to reach satisfactory interpretation, apart from confirming the presence of the Laschamp excursion, and therefore the 10Be data are not used in the production of the final age model. We have integrated our absolute chronology with tuning of the relative paleointensity record of the Earth’s magnetic field to a global reference curve (PISO-1500). The maar-forming phreatomagmatic eruption of the Orakei maar is now dated to > 130,120 yr (95 % confidence range 128,665 to 131,560 yr). Our new chronology facilitates high-resolution paleoenvironmental reconstruction for northern New Zealand spanning the last ca. 130,000 years for the first time as most NZ records that spall all or parts of the LGI are fragmentary, low-resolution and poorly dated. Providing this chronological framework for LGI climate events inferred from the Orakei sequence is of paramount importance in the context of identification of leads and lags in different components of the Southern Hemisphere climate system as well as identification of Northern Hemisphere climate signals.