MILLENNIAL-SCALE GLACIAL PALAEOCEANOGRAPHY OF WEST GREENLAND: GEOCHEMICAL TRACKING OF ICE SHEET BREAKUP, ADVANCE AND RETREAT

During the last glacial cycle Baffin Bay has been influenced by three major ice sheets: the Greenland, Innuitian, and Laurentide Ice Sheets (GIS, IIS, LIS). Palaeozoic carbonate-rich rocks covered by the LIS and IIS were eroded by ice streams and transported via icebergs into Baffin Bay. This resulted in distinct intervals of carbonate enrichment in the sedimentary layers, so-called “detrital carbonate events”. Specifically, in our studied core, two carbonate-enriched zones occur at ~21–38 cm, and 58–78 cm. Preliminarily ¹⁴C dates suggest that these detrital carbonate events are temporally related to the climate warming following the Younger and Older Dryas events.

Across these detrital carbonate events we observe an abrupt increase to more radiogenic osmium isotope ¹⁸⁷Os/¹⁸⁸Os (Os_i) compositions (~1.5–2.2), whereas during periods of low Ca-enrichment, the Os_i values become abruptly less radiogenic (~0.5–1.4). The Os_i compositions over the last 10 kyrs gradually decrease from ~1.3 to 1.1, which is similar to those records further south in Baffin Bay and the present day North Atlantic ocean (~1.0).

The highly radiogenic Os_i compositions observed during detrital carbonate events suggest that as well as Ca delivery via icebergs from the northern LIS and IIS, the provenance of Os, and by inference other detritus, was also sourced from the Archean/Proterozoic terrains of western Greenland, which comprise Os_i values of ~2.8. In contrast, the less radiogenic Os_i values (1.0–1.4) during lower Ca-enrichment intervals could potentially be a baseline to which values return when there is less influence from continental erosion and iceberg delivery, and more influence of oceanic Os from the Atlantic. Moreover, the least radiogenic Os_i values (0.5–0.7), which may correspond to the coldest intervals of the Dryas Events, could potentially be due to reduced weathering and/or the influx of weathered Paleocene mafic lithologies (¹⁸⁷Os/¹⁸⁸Os = 0.13–0.14) from Disko Island, the surrounding islands and the shelf, and/or from Baffin Island. In conclusion, our new osmium isotope data provide further insight into glacial advance, retreat, and sediment provenance within Baffin Bay during the past 50 kyrs, specifically during the Younger and Older Dryas Events.