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 δ13C 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 δ13C 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 δ13C 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, δ13C 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 δ13C 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.

[1] V-shaped lineations in the bathymetry and in the free-air gravity field surrounding Iceland result from crustal thickness variations caused by temporal variations in melt production rate at the Mid-Atlantic Ridge. We have studied the record of V-shaped ridges in the basins surrounding Iceland by plotting the shortwavelength component of the gravity field in terms of age versus distance from Iceland. The V-shaped ridge gravity signal is obscured by crustal segmentation and by sediment more than 1-2 km thick. The best V-shaped ridge record is found in the unsegmented part of the Irminger Basin, where Oligocene-Recent Vshaped ridges occur with a primary periodicity of 5-6 Myr and a secondary periodicity of 2-3 Myr. Vshaped ridge records from the Iceland Basin and from east of the Kolbeinsey Ridge to the north of Iceland correlate with the record from the Irminger Basin but are less complete. A record of uplift of the GreenlandIceland-Faroes Ridge based on paleoceanographic data is correlated with the gravity record of V-shaped ridges. There is less decisive evidence for V-shaped ridges in crust of Eocene age. The observation that Vshaped ridges propagate up to 1000 km from Iceland is compatible with a model in which the Iceland Plume head spreads out from the plume stalk below a depth of $100 km, as suggested by geochemical arguments and studies of mantle rheology. Time-dependent flow in the plume head probably results from time-dependent flow up the plume stalk from deep below Iceland. These pulses may have triggered jumps in location of the spreading axis observed in the Icelandic geological record.Components: 9806 words, 15 figures.

Abstract. Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high ( >  800 ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene ( ∼  50  Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 ×  CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP – the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.

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[1] The Icelandic mantle plume generated maximum uplift in early Paleogene times. The Faroe-Shetland basin, which fringes the North Atlantic margin of Europe, was close to the center of early Paleogene Icelandic plume activity. Three-dimensional seismic reflection data from the Faroe-Shetland basin reveal sedimentary geometries that allow a phase of transient uplift to be accurately reconstructed and quantified. Close to the Paleocene/Eocene boundary (circa 56 Ma), rapid uplift resulted in fluvial incision into marine sediments. This unconformity was buried by nonmarine sediments, recording the decay of transient uplift. Relief on the unconformity was $550 m, constraining the minimum amount of surface uplift. Some 60 m of this uplift can be attributed to the isostatic response to erosional unloading. Tectonic uplift of over 490 m peaked and decayed within 3 Ma. Rates of waterloaded tectonic subsidence following peak uplift are several times greater than maximum expected postrift subsidence rates. The amplitude and duration of this transient effect is best explained by a mantle convective phenomenon. We suggest that a region of hot plume material flowed laterally beneath the lithosphere, producing transient uplift which decayed when plume material was advected farther away. Our analysis suggests that under certain circumstances, stratigraphic records can yield valuable quantitative information about aspects of mantle convective circulation.

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