Neogene overflow of Northern Component Water at the Greenland-Scotland Ridge

[ 1] In the North Atlantic Ocean, flow of North Atlantic Deep Water (NADW), and of its ancient counterpart Northern Component Water (NCW), across the Greenland-Scotland Ridge (GSR) is thought to have played an important role in ocean circulation. Over the last 60 Ma, the Iceland Plume has dynamically supported an area which encompasses the GSR. Consequently, bathymetry of the GSR has varied with time due to a combination of lithospheric plate cooling and fluctuations in the temperature and buoyancy within the underlying convecting mantle. Here, we reassess the importance of plate cooling and convective control on this northern gateway for NCW flow during the Neogene period, following Wright and Miller ( 1996). To tackle the problem, benthic foraminiferal isotope data sets have been assembled to examine delta C-13 gradients between the three major deep water masses (i.e., Northern Component Water, Southern Ocean Water, and Pacific Ocean Water). Composite records are reported on an astronomical timescale, and a nonparametric curve-fitting technique is used to produce regional estimates of delta C-13 for each water mass. Confidence bands were calculated, and error propagation techniques used to estimate % NCW and its uncertainty. Despite obvious reservations about using long-term variations of delta C-13 from disparate analyses and settings, and despite considerable uncertainties in our understanding of ancient oceanic transport pathways, the variation of NCW through time is consistent with independent estimates of the temporal variation of dynamical support associated with the Iceland Plume. Prior to 12 Ma, delta C-13 patterns overlap and % NCW cannot be isolated. Significant long-period variations are evident, which are consistent with previously published work. From 12 Ma, when lithospheric cooling probably caused the GSR to submerge completely, long-period delta C-13 patterns diverge significantly and allow reasonable % NCW estimates to be made. Our most robust result is a dramatic increase in NCW overflow between 6 and 2 Ma when dynamical support generated by the Iceland Plume was weakest. Between 6 and 12 Ma a series of variations in NCW overflow have been resolved.