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The purpose of this research is to investigate whether icebergs influenced the ocean’s circulation and contributed to significant climate changes during the last Ice Age. Previous studies have suggested that iceberg discharge from surrounding ice sheets introduced large volumes of freshwater into sensitive deep-water production locations in the North Atlantic Ocean, potentially altering ocean circulation and influencing regional and global climate. This research focused on the sequence of events approximately 40-50 thousand years ago in the central North Atlantic Ocean, utilizing a sediment core VM 30-100 PC recovered from the Mid- Atlantic Ridge. We quantified the abundance of ice-rafted debris (IRD) as an indicator of the presence of icebergs in the core sample from every cm at depths from 150-200 cm. In addition to IRD counting, we determined the relative abundance and stable oxygen isotope ratios (δ O) in the microfossil shells of the polar foraminifera species Neogloboquadrina pachyderma (N. pachy) as indicators of the surface ocean’s conditions during that time. By detecting an increase in δ O values over time it will indicate a decrease in ocean temperature, which we expect to correspond with a large abundance of N. pachy. Once IRD counting is completed, graphing the IRD concentration over depth will reveal periods of significant iceberg presence. By comparing the relative abundance of IRD and N. pachy in the samples, and by observing the δ O data, we aim to determine whether iceberg discharge preceded changes in ocean circulation or if sea-surface conditions shifted beforehand. Our hypothesis is that icebergs appeared first and disrupted ocean circulation, leading to subsequent changes in sea-surface conditions. This research will provide insight into the cause and sequence of natural variability in the climate system. We believe that there is a strong possibility that iceberg discharges played a crucial role in altering ocean circulation, thus driving significant climatic changes and contributing to the onset of the last Ice Age. 

Abundant proxy records suggest a profound reorganization of the Atlantic Meridional Overturning Circulation (AMOC) during the Last Glacial Maximum (LGM, ~21,000 y ago), with the North Atlantic Deep Water (NADW) shoaling significantly relative to the present-day (PD) and forming Glacial North Atlantic Intermediate Water (GNAIW). However, almost all previous observational and modeling studies have focused on the zonal mean two-dimensional AMOC feature, while recent progress in the understanding of modern AMOC reveals a more complicated three-dimensional structure, with NADW penetrating from the subpolar North Atlantic to lower latitude through different pathways. Here, combining²³¹Pa/²³⁰Th reconstructions and model simulations, we uncover a significant change in the three-dimensional structure of the glacial AMOC. Specifically, the mid-latitude eastern pathway (EP), located east of the Mid-Atlantic Ridge and transporting about half of the PD NADW from the subpolar gyre to the subtropical gyre, experienced substantial intensification during the LGM. A greater portion of the GNAIW was transported in the eastern basin during the LGM compared to NADW at the PD, resulting in opposite²³¹Pa/²³⁰Th changes between eastern and western basins during the LGM. Furthermore, in contrast to the wind-steering mechanism of EP at PD, the intensified LGM EP was caused primarily by the rim current forced by the basin-scale open-ocean convection over the subpolar North Atlantic. Our results underscore the importance of accounting for three-dimensional oceanographic changes to achieve more accurate reconstructions of past AMOC. 

While the Atlantic Ocean is ventilated by high-latitude deep water formation and exhibits a pole-to-pole overturning circulation, the Pacific Ocean does not. This asymmetric global overturning pattern has persisted for the past 2–3 million years, with evidence for different ventilation modes in the deeper past. In the current climate, the Atlantic-Pacific asymmetry occurs because the Atlantic is more saline, enabling deep convection. To what extent the salinity contrast between the two basins is dominated by atmospheric processes (larger net evaporation over the Atlantic) or oceanic processes (salinity transport into the Atlantic) remains an outstanding question. Numerical simulations have provided support for both mechanisms; observations of the present climate support a strong role for atmospheric processes as well as some modulation by oceanic processes. A major avenue for future work is the quantification of the various processes at play to identify which mechanisms are primary in different climate states. 

Abstract While substantial changes in thermohaline circulation related to deglacial climate variability are well established, the role of this circulation in Holocene climate variability remains uncertain. Here we use two dynamical proxies,²³¹Pa/²³⁰Th ratios and mean sortable silt size (), to reconstruct Holocene bottom water circulation at the intermediate‐depth Carolina Slope. We find no substantial change in deep current speed or²³¹Pa export at this site during the Holocene, suggesting consistent²³¹Pa export via the Deep Western Boundary Current.shows increasing millennial‐scale variability in the middle‐late Holocene, which may reflect Labrador Sea Water contribution to current speed. We conclude that deepwater export from the North Atlantic has remained remarkably stable during the Holocene, decoupled from changing rates of specific water masses, while production of these water masses varied at millennial to centennial time scales. The persistence of the large‐scale overturning may reflect the ocean's stabilizing influence on Holocene climate. 

Abstract ²³⁰Th normalization is a valuable paleoceanographic tool for reconstructing high‐resolution sediment fluxes during the late Pleistocene (last ~500,000 years). As its application has expanded to ever more diverse marine environments, the nuances of²³⁰Th systematics, with regard to particle type, particle size, lateral advective/diffusive redistribution, and other processes, have emerged. We synthesized over 1000 sedimentary records of²³⁰Th from across the global ocean at two time slices, the late Holocene (0–5,000 years ago, or 0–5 ka) and the Last Glacial Maximum (18.5–23.5 ka), and investigated the spatial structure of²³⁰Th‐normalized mass fluxes. On a global scale, sedimentary mass fluxes were significantly higher during the Last Glacial Maximum (1.79–2.17 g/cm²kyr, 95% confidence) relative to the Holocene (1.48–1.68 g/cm²kyr, 95% confidence). We then examined the potential confounding influences of boundary scavenging, nepheloid layers, hydrothermal scavenging, size‐dependent sediment fractionation, and carbonate dissolution on the efficacy of²³⁰Th as a constant flux proxy. Anomalous²³⁰Th behavior is sometimes observed proximal to hydrothermal ridges and in continental margins where high particle fluxes and steep continental slopes can lead to the combined effects of boundary scavenging and nepheloid interference. Notwithstanding these limitations, we found that²³⁰Th normalization is a robust tool for determining sediment mass accumulation rates in the majority of pelagic marine settings (>1,000 m water depth).