57-1 Tracking Iceberg Delivery Pathways and Circulation Shifts Across the Mid-Pleistocene Transition at IODP Site U1564 (Gardar Drift): An Integrated Geochemical and Petrographic Provenance Approach

Abstract:

The Mid-Pleistocene Transition (MPT ~1.25–0.7 Ma) marks a fundamental climate reorganization from 41-kyr to 100-kyr cycles. While ice-rafted debris (IRD) records track Northern Hemisphere ice-sheet calving, understanding the spatial routing and shifting currents that steered these icebergs remains a challenge. We investigate variations in iceberg delivery routes and surface current pathways across the MPT by integrating high-resolution X-ray fluorescence (XRF) core-scanning data with manual lithic grain petrography at IODP Site U1564 (Gardar Drift, 2208 m water depth).

Preliminary Principal Component Analysis (PCA) of bulk elemental data reveals distinct geochemical clusters reflecting sediment source regions. PC1 (64%) isolates heavy basaltic (Icelandic) and detrital carbonate IRD from Laurentide sources, alongside coarse crystalline basement IRD. PC2 (24%) captures a detrital silicate/basaltic mineral continuum depleted in biogenic fractions, while PC3 (6%) and PC4 (3%) isolate pure biogenic carbonate and Laurentide-derived detrital carbonate, respectively. Downcore variations in key elemental ratios—specifically K/Ti (felsic vs. basaltic provenance), Ca/Sr (detrital carbonate tracking Laurentide discharge), and Ti/Al (Icelandic inputs)—demonstrate pronounced orbital pacing.

Preliminary results suggest that during critical MPT intervals, including super-interglacial MIS 31 (~1.07 Ma), systematic provenance shifts occurred between distal continental and proximal Icelandic inputs. These fingerprints record major front migrations relative to the "Nordic Heat Pump," providing crucial empirical benchmarks for ice-sheet models and North Atlantic legacy reconstructions.

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