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Atlantic Meridional Overturning Circulation (AMOC) circulates heat and nutrients within the Atlantic Ocean. As it plays a vital role in regulating climate, precipitation, and productivity, it is imperative to gain a deeper understanding of this system of ocean currents. This endeavor is especially urgent, as recent studies have stressed the potential impact of freshwater inputs due to anthropogenic climate change on the strength of AMOC. In addition to the uncertainty associated with the claim of a slowdown or complete collapse of AMOC in the near future, questions about the geometry of AMOC remain unanswered. For instance, intra-basin variability in North Atlantic paleocirculation (231Pa/230Th) records was observed in Gherardi et al., 2005. However, it was unclear whether different sources of Glacial North Atlantic Intermediate Water (GNAIW) or different overturning depths caused this variability. Reconstructing deep ocean circulation in the eastern North Atlantic using an assortment of geochemical proxies can provide insight into the future state of AMOC, as well as the evolution of its geometry. Here we present records of benthic foraminiferal δ18O and δ13C, and sedimentary 231Pa/230Th (a kinematic proxy for AMOC strength) from International Ocean Discovery Program (IODP) expedition 397, Iberian Margin Paleoclimate, site 1586 (37°37.7108′N, 10°42.6987′W, 4691.4 mbsl). The optimal location and depth of this site allow for a meaningful comparison to available paleocirculation records in order to determine whether AMOC strength varies zonally or with depth. We find that the benthic δ13C, export of 231Pa, and inferred strength of AMOC generally increased from the LGM to the Holocene, with significant decreases during Heinrich events 1 and 2. Additionally, the 231Pa/230Th record at this deep site in the eastern basin was found to vary in a similar pattern as that of a western site of a comparable depth, more closely than that of a shallower, proximal site on the Iberian Margin (Gherardi et al., 2005). This indicates that depth differences are more of a determining factor than zonal differences in establishing AMOC strength, revealing that different overturning depths likely influenced the variability observed between eastern and western Atlantic paleocirculation records more than different GNAIW sources. 

If you wish to cite an abstract presented at AGU25, please cite as: Author(s) (2025), Title, Abstract (Final paper number, ex: AE14B-1234) presented at AGU25, 15-19 Dec. 

With the threat of rising temperatures, the Atlantic Meridional Overturning Circulation (AMOC) has been predicted to slow down or stop entirely, potentially exacerbating climate dysregulation in the Atlantic region. This project looks to the geologically recent past, to examine how much and in what way Atlantic ocean circulation has fluctuated over the last ~10,000 years. From IODP expedition 397, we processed 33 samples from site U1586, the sediment core at the greatest depth from the Iberian Margin. Stable isotope analysis of benthic foraminifera microfossils found in these sediment cores is a widely used technique for reconstructing past ocean circulation patterns; δ13C is a tracer for water masses, and δ18O is a proxy for sea temperature and land ice coverage. We searched specifically for Cibicidoides wuellerstorfi foraminifera and used mass spectrometry to find their values of δ13C and δ18O throughout the time-series. Our analyses of the stable isotopes generally indicate a warm climate and strong AMOC activity throughout the Holocene. Within the time interval 3.5-2.4 ka, stable oxygen isotope analysis shows a deep water temperature change from warmer to colder conditions. The lowest δ13C value occurs within that time interval; after δ18O values dropped at 3.5 ka, and gradually started increasing, the δ13C decreased significantly at 2.8 ka. The fact that the lowest δ13C value coincides with a 1,000 year period of deep water temperature change shown in the δ18O record suggests a link between climate change and AMOC activity in the past, and supports predictions for the impact that current climate change may have on AMOC in the future.