BA/CA IN NEOGLOBOQUADRINA PACHYDERMA AS AN INDICATOR OF MELTWATER DISCHARGE INTO THE WESTERN ARCTIC OCEAN

Ba/Ca in the planktonic foraminifer Neogloboquadrina pachyderma sinstral can be used as an effective indicator of meltwater discharge into the surface waters of the Arctic Ocean during deglacial time. Samples from a core taken from the Mendeleyev Ridge in the western Arctic Ocean were analyzed for Ba/Ca and d¹⁸O. Ba/Ca in N. pachyderma sin. appears to reflect the barium concentration of seawater with a distribution coefficient of 0.22 ± 0.02. Two high-barium meltwater events were identified, coincident with d¹⁸O minima around 11.8 ka and 9.4 ¹⁴C ka BP. High-barium concentrations calculated for the surface ocean during deglacial time are indicative of a continental source. Reconstructed barium concentrations in meltwater discharged between 12 ka and 11.3 ¹⁴C ka BP exceed the current Mackenzie River endmember value. Excess barium may indicate increased weathering of bedrock during glaciation, leading to an increase in barium both in the dissolved and sediment load. The meltwater endmember at 9.4 ¹⁴C ka BP yields a concentration that is equivalent to the modern Mackenzie River value.

Increases in Ba/Ca in N. pachyderma sin. directly correlate with the retreat of the Laurentide Ice Sheet and the evolution of the Mackenzie River drainage basin. Expansion of the Mackenzie River drainage basin due to retreating ice caused an increase in meltwater discharge to the western Arctic Ocean, corresponding to maximum barium concentrations in the Arctic surface water at 11.8 ¹⁴C ka BP. Increased meltwater discharge may have triggered an increase in the export of freshwater from the Arctic to the North Atlantic surface waters, thus contributing to the onset of the Younger Dryas. The second meltwater event at 9.4 ¹⁴C ka BP may be the result of glacial Lake Agassiz draining through the Clearwater spillway into the Mackenzie River.