Stratigraphy and ice sheet dynamics of the greater Lake Melville region

Abstract

This quantitative reanalysis reviews the high-fidelity record of ice-sheet dynamics and ensuing sediment supply to the greater Lake Melville region of Labrador, Canada. The environment is strategically located close to a major ice divide of the Quebec-Labrador Dome (QLD) of the Laurentide Ice Sheet. More than 5000 km of acoustic records are examined along with multibeam bathymetric data acquired over the last 2 decades. Findings reveal a thin (1125 m), low-angle (0.15°–0.21°) ice stream once emanated from the eastern sector of the QLD, which likely over-deepened Cartwright Saddle, a major trough on the Labrador Shelf. Modeled-ice velocities during glaciation are 2500 ± m/yr, allowing the ice sheet to discharge 10,000± icebergs each year into the North Atlantic. The ice stream's flux may have caused a drawdown of the QLD, shifting the ice divide into Lake Melville's drainage basin. After deglaciation began ∼10.4 kyr BP, the ice stream had thinned to ∼820 ± 20 m, reducing ice stream ice velocities to ∼820 ± 50 m/yr. Vertical ablation of the ice sheet proceeded at rates of ∼0.17 m/yr and ice-marginal retreat was on the order of 140 ± m/yr (190 ± m/yr if stillstand pauses are excluded), which resulted in complete deglaciation of the 250 km-long basin in approximately 2500 years. The ice stream delivered, on average, 50 Mt/yr of deglacial sediment between 9 and 8 kyr BP; sediment loads associated with the six largest submarine moraines range 44–64 Mt/yr, delivered by a freshwater discharge 5-fold larger than for modern conditions. With 94 Gt of subglacial and deglacial sediment deposited in Lake Melville, the regional deglacial sediment yield is 300 t/km2/yr, perhaps ∼430 t/m2/yr if terrestrial deglacial deposits are included. Our findings confirm the existence of a Lake Melville ice stream during the Last glacial episode and highlight future research opportunities for empirical and modeling studies directed towards an understanding of ice-sheet dynamics.