34-8 Grain-size Sensitivity of IRD Reconstructions Across the Mid-Pleistocene Transition: A study from North Atlantic IODP Site U1564

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

Presenting Author:

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Abstract:

There is ongoing debate over how ice‐rafted debris (IRD) in deep‐sea sediments relates to ice‐sheet dynamics, driven largely by inconsistent size‐fraction definitions and methodological differences used to quantify IRD. These discrepancies can yield divergent reconstructions across studies, complicating intercomparison and synthesis. Moreover, IRD signals may reflect multiple, non‐exclusive processes, including variability in iceberg flux, debris load per iceberg, and spatially variable melt rates along iceberg trajectories, underscoring the need for a robust and standardized operational definition of IRD.

Here, we investigate sediments from IODP Site U1564 (Gardar Drift) spanning the Mid‐Pleistocene Transition (MPT; ~1.25–0.7 Ma), a period marked by a fundamental shift in climate variability from dominant 41‐kyr to 100‐kyr cycles. We quantify sieved weight percentages across a range of coarse fractions commonly used in prior IRD studies (125 μm–2 mm), with additional separations at 63 μm, 125 μm, 250 μm, and 2 mm, allowing systematic evaluation of how size thresholds influence inferred IRD variability.

We further plan to count lithic grains >150 μm to directly compare grain counts with weight‐based estimates and to evaluate consistency between methods. These results will be placed in the context of published North Atlantic IRD records that employ alternative approaches. By explicitly assessing methodological and size‐fraction sensitivities, this study provides a foundation for standardizing IRD reconstructions and improving quantitative interpretations of iceberg discharge and Northern Hemisphere ice‐sheet behavior across the Mid‐Pleistocene Transition.

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

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