The sedimentary record of glacial retreat, Marinelli Fjord, Patagonia: Regional correlations and climate ties

The Inland Passage of Chile comprises the most continuous latitudinal transect of ice fields, ice caps, and alpine glaciers in the Southern Hemisphere, providing an excellent natural laboratory for the study of glacial response to climate change during the Holocene. Here we report results from a marine geological investigation of Marinelli Fjord, Tierra del Fuego (54°25 S, 69°35 W) and Ainsworth Fjord, which merges with Marinelli Fjord. Data acquired during July 2005 onboard the RV/IB Nathaniel B. Palmer include high-resolution seismic data, multibeam swath bathymetry data and sediment cores. Post-cruise analyses include detailed seismic facies and lithofacies analysis and radiocarbon dating. The results indicate that a major transition in the glacimarine record from ice-proximal facies to ice-distal facies occurred in the outer basins of the fjord at 15.5 kyr to 12.5 kyr. The ice-proximal facies consists of pebbly mud with abundant laminations and is characterized by high average sedimentation rates (28 mm/yr). In contrast, an ice-distal facies is dominantly bioturbated mud with low average sedimentation rates (0.56 mm/yr). This transition marks the retreat of Marinelli Glacier from the outer basins with no evidence for glacial re-advance. Subsequently, during the mid to late-Holocene, Ainsworth Glacier retreated and exposed Ainsworth Fjord. Our results are consistent with the climatic trends for southern South America where the final deglaciation of the region ended at ~ 12.5 ka. During the Holocene, stable ice conditions persisted until the mid-1960s when Marinelli Glacier began rapidly retreating to its modern day position.