Magnetic response of marine sediments to climate variations over the last 40 ka in the western equatorial Pacific.

Magnetic properties from marine sediment cores, combined with other proxies, make it possible to study climatic variations. The type, concentration and grain size of magnetic minerals can be used as proxies of precipitation and deep oceanic circulation changes.  

In this study, we focus on core MD01-2385 retrieved on the northwest margin of Papua-New Guinea, in the western equatorial Pacific Ocean. This area is located in the Indo-Pacific Warm Pool (IPWP), which is a major source of heat and moisture to the atmosphere and plays an important role on global climate. The western Indo-Pacific climate is complex, being affected by the El Nino-Southern Oscillation (ENSO) and the Australian-Indonesian monsoon.

 

Core MD01-2385 was dated using ¹⁴C. The studied interval covers the last 40 ka with an average sedimentation rate of 30 cm/ka. We took samples every 2 cm (time resolution ~ 70 years). Magnetic granulometry proxies (ARM/SIRM and Karm/K) show a gradual decrease in grain size from the last glacial-interglacial transition (~17 ka) before a stabilization with fine grains from 8 ka. The records show variations associated with Heinrich events and the Younger Dryas. In the ~40 to 13 ka interval, the ARM/SIRM ratio is correlated with the d18O curve from EPICA-EDML ice cores (Antartica), whereas over the last 13 ka the ARM/SIRM ratio appears correlated to d18O curve of the NGRIP ice cores (Greenland).This observation suggests a stronger climatic influence of the Southern Hemisphere than the Northern Hemisphere in this region from 40 to 13 ka, followed since 13 ka by a period in which remote climatic influences originate from northern high latitudes.

Our magnetic results were combined with geochemical analyses carried out by Yu et al. (2023) on the same core (Rb/Sr ratio, chemical index of alteration (CIA), and the smectite/(illite + chlorite) ratio). These data indicate that heinrichs events (HS) are associated, in this region, with lower precipitation (Yu et al., 2023) and also correspond to lower magnetic concentrations, suggesting a dominant physical weathering in northwest Papua-New Guinea.

An interval with coarse magnetic grains and glass shards was dated at ~ 25 ka, suggesting the recording of a volcanic eruption during HS2. It could be the Oruanui supereruption from Taupo volcano, in New Zealand, dated at ~25.5 ka.