34-6 Approximating the Onset and Intensification of AMOC using changes in Bottom Current Strength at “Little” Bjӧrn Drift IODP Site U1563, Expedition 395C

Session: High latitude paleoceanographic discoveries from Scientific Ocean Drilling (IODP, ODP, DSDP). (Posters)

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Abstract:

Climate change threatens the stability of Atlantic Meridional Overturning Circulation (AMOC), which plays a crucial role in climate in the Northern Hemisphere through the redistribution of heat and nutrients. Some research shows that AMOC is slowing due to rising global temperatures, with predictions of a possible collapse by the end of the century (e.g., Rahmstorf et al., 2015; Ditlevsen and Ditlevsen, 2023). This makes the study of AMOC and the North Atlantic circulation crucial to understanding our climate future.

Site U1563, located in the Bjӧrn Drift, east of the Reykjanes Ridge off the southern coast of Iceland, is an ideal location for studying AMOC due to its proximity to the formation of North Atlantic Deep Water. At ~3.6 Ma, a 200,000-year hiatus was identified at Site U1563, above which there is an increased sedimentation rate with lithologic changes consistent with contourite deposition. The dominant lithology prior to the hiatus is carbonate ooze, which changes to silt clay, indicating a change from a warmer environment with a lower deposition rate to a cooler environment with more rapid deposition.

We present a high-resolution record of sortable silt (particles 10-63 µm) from 2.4 to 4.0 Ma at Site U1563 to determine bottom current strength and variability. Combined with XRF measurements and shipboard data, we look for signals of the onset and intensification of AMOC, and indications for Northern Hemisphere Glaciation. Toyos et al. (2020) show good correlation between Zr/Rb XRF ratios and mean sortable silt. Our record does not follow this pattern with the sortable silt record showing more variability than the Zr/Rb ratio. Kleiven et al. (2011) use magnetic susceptibility as a proxy for grain size, which correlates well with their sortable silt record. We see a stronger correlation between magnetic susceptibility and mean sortable silt at Site U1563, leading us to conclude that provenance is impacting our Zr/Rb record. This is supported by K/Fe ratios, where lower Zr/Rb ratios correlate with high K/Fe ratio, which indicates varying concentrations of Icelandic basalts and Nordic Sea components in the cold, dense water that becomes North Atlantic Deep Water. We interpret the variation in grain size as indicating that cold Nordic Deep Water did not flow continuously into the North Atlantic after flow was initiated.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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