[MIS08-18] Deglacial productivity changes reflect XRF Br fueled by Cordilleran Ice Sheet dynamics
Keywords:Paleoproductivity, XRF Br, Meltwater, Cordilleran Ice Sheet, Gulf of Alaska, Deglaciation
We found that δ18O of both -Neogloboquadrina pachyderma (sinistral) and Globigerina bulloides gradually decreased at ~16.7 cal ka BP and then sharply decreased at 14.8 cal ka BP, corresponding to the onset of the Bølling-Allerød. Before the onset of the Bølling-Allerød, there were three pronounced IRD (ice-rafted debris) layers at ~16.49, ~16.17 and ~15.65 cal ka BP, suggesting that gradual warming conditions might have caused multistep collapses of the coastal ice lobes of the CIS. However, lower TOC, higher organic carbon/total nitrogen ratios during this period indicate lower primary productivity. Probably, lower temperatures, increased water turbidity, and increased stratification should be the key variables for suppressing primary productivity.
During the Bølling-Allerød (14.8–13.0 cal ka BP) and the early Holocene (Preboreal, 11.7–10.8 cal ka BP), both foraminiferal δ18O records decreased, with exhibited prominent peaks up to 1.9 ‰ and 1.88 ‰ at 14.57 cal ka BP, and 1.93‰ and 1.65‰ at 14.14 cal ka BP (may reflect two discrete episodes of very high meltwater input) for N. pachyderma (sinistral) and G.bulloides, respectively, suggesting that increased temperature and low salinity, and due to the abrupt warming during this period triggered rapid decay of the CIS and discharges of meltwater. The fact that XRF Br counts are highly correlated with TOC contents in our core supports that Br counts can be used as a proxy of productivity. The high-resolution Br counts and TOC data showed high productivity at 14.8–13.0 cal ka BP and 11.7–10.8 cal ka BP corresponding to the regional expressions of Bølling-Allerød and Preboreal, respectively.