Seafloor habitats across geological boundaries in Disko Bay, central West Greenland

In this paper we describe seafloor terrain of nearly the entire Disko Bay region and provide scientific baseline information about surface geology and sedimentary environments that can support the seafloor management plan in Greenland. Our study utilized multiple datasets of multibeam bathymetry and backscatter, seismic profiles and ground-truthing consisting of video footage from drop camera and benthic video sled, as well as sediment samples from grab and corers. Our results revealed that the key geological units in Disko Bay characterize the scale of geomorphic features, which in turn affects the distribution and complexity of habitat zones. The NE sub-region is underlain by Cretaceous sandstone and characterized by large-scale landforms, mainly vast flat areas draped by glacial lineations, bedrock ridges and pockmark fields. This setting promotes less topographically complex habitats, i.e. coarse plain, muddy/sandy plain with dropstones, and muddy plain. The SW sub-region is characterized by Precambrian Gneiss and Paleoproterozoic metasedimentary rocks with complex system of small-scale geomorphic features, such as cross-cutting channels. This results in topographically complex habitats in the area, such as rocky bank, coarse rugged terrain, and rocky slopes. Two distinctive habitat areas, associated with potential gas seeps, i) southern pockmark field and ii) western zoanthid-sponge wall, were discovered at the geological boundary separating the two sub-regions. Our study highlights the importance of seafloor habitat mapping and analyses by providing fundamental geophysical knowledge necessary to comply with long-term sustainable use of marine resources in Greenland

Tracking the provenance of Greenland-sourced, Holocene aged, individual sand-sized ice-rafted debris using the Pb-isotope compositions of feldspars and 40Ar/39Ar ages of hornblendes

The provenance of sand-sized ice-rafted debris (IRD) sourced from Greenland is currently difficult to determine. Such knowledge, if it could be ascertained with a high degree of certainty, could be applied to the Greenland-proximal marine records to improve both our understanding of modern-day spatial patterns of iceberg rafting and the past history of the Greenland Ice Sheet (GIS). Recent studies have highlighted the utility of the Pb-isotope composition of individual sand-sized feldspars and the 40Ar/39Ar ages of individual sand-sized hornblendes in this regard. However, before any such provenance toolkit can be applied to the palaeo-record, it is necessary first to determine whether this approach can be used to track the sources of known recent Greenland-proximal IRD deposition. To this end we present new records of the Pb-isotope composition and the 40Ar/39Ar ages of individual sand-sized grains of feldspars and hornblendes, respectively, from modern Greenland glacifluvial and fjord sands and Holocene to modern Greenland-proximal marine sediments. These new data demonstrate that sand-sized feldspars and hornblendes glacially eroded by the GIS exhibit distinct intra- and inter-tectonic terrane differences in their Pb-isotope compositions and ages and that these differences are clearly expressed in the geochemistry and geochronology of sand-sized IRD deposited in marine sediments around Greenland. Although overlap exists between some Greenland-proximal IRD ‘source fields’ defined by these data, our approach has the potential to both better understand spatial patterns of Greenland-derived IRD in the modern day as well as during past episodes of iceberg calving

Paleocurrent reconstruction of the deep Pacific inflow during the middle Miocene : reflections of East Antarctic Ice Sheet growth

Today the deep western boundary current (DWBC) east of New Zealand is the most important route for deep water entering the Pacific Ocean. Large-scale changes in deep water circulation patterns are thought to have been associated with the development of the East Antarctic Ice Sheet (EAIS) close to the main source of bottom water for the DWBC. Here we reconstruct the changing speed of the southwest Pacific DWBC during the middle Miocene from ∼15.5-12.5 Ma, a period of significant global ice accumulation associated with EAIS growth. Sortable silt mean grain sizes from Ocean Drilling Program Site 1123 reveal variability in the speed of the Pacific inflow on the timescale of the 41 kyr orbital obliquity cycle. Similar orbital period flow changes have recently been demonstrated for the Pleistocene epoch. Collectively, these observations suggest that a strong coupling between changes in the speed of the deep Pacific inflow and high-latitude climate forcing may have been a persistent feature of the global thermohaline circulation system for at least the past 15 Myr. Furthermore, long-term changes in flow speed suggest an intensification of the DWBC under an inferred increase in Southern Component Water production. This occurred at the same time as decreasing Tethyan outflow and major EAIS growth between ∼15.5 and 13.5 Ma. These results provide evidence that a major component of the deep thermohaline circulation was associated with the middle Miocene growth of the EAIS and support the view that this time interval represents an important step in the development of the Neogene icehouse climate

Century- to milliennial-scale sedimentological-geochemical records of glacial-Holocene sediment variations from the Barra Fan (NE Atlantic).

The Barra Fan, located at the continental margin of NW Scotland, offers a unique possibility to retrieve records of exceptional high resolution to obtain climate records on a century-millennial timescale. We used a sedimentological-geochemical approach to examine the sediment variations that reflect the palaeoceanography and climate history of the area. Inorganic chemistry combined with micropalaeontology reveals trends and changes in NE Atlantic palaeoceanography and northwest European climate at the sub-Milankovitch frequency. This study builds on results from two British Geological Survey cores and one giant piston core (Core 57/-11/59, Core 56/-10136 and Images Core MD95-2006) that were obtained during the NEAPACC (NE Atlantic Palaeoceanography, Special Topic NERC) phase. Geochemical records of lithogenic input fluctuate rapidly and their patterns parallel sea surface temperature and particle size records. The cold periods are characterized by increased clay input compared to the warm periods. The Younger Dryas period and other prominent periods such as the equivalent of Heinrich Event 1, show extremely expanded sections up to several metres in thickness. Enhancement of accumulation rates in the glacial section is due to the influence of downslope sedimentation, meltwater deposition; and large-scale currents redistributing the sediment along the upper slope. The radiochemical tracer (excess Th-230) shows that major shifts in terrigenous sediment supply were extremely rapid over the last 15 ka. The shifts in terrigenous supply occurred over time-spans of less than a century. Century-scale events of lithogenic input can be visually correlated to other North Atlantic climate records such as the GISP2 Greenland ice core delta(18)O record for the last 15 ka, although the resolution of radiocarbon dating of these events in the sediments is not sufficiently precise to verify that the visual correlations are correct. The particle flux and biogenic records show sawtooth-shaped cycles opposite to the Dansgaard-Oeschger cycles.</p

(Table 1) Age comparison between the GPTS and ODP Site 181-1123 age model for each chron base within the Middle Miocene section

Today the deep western boundary current (DWBC) east of New Zealand is the most important route for deep water entering the Pacific Ocean. Large-scale changes in deep water circulation patterns are thought to have been associated with the development of the East Antarctic Ice Sheet (EAIS) close to the main source of bottom water for the DWBC. Here we reconstruct the changing speed of the southwest Pacific DWBC during the middle Miocene from ~15.5-12.5 Ma, a period of significant global ice accumulation associated with EAIS growth. Sortable silt mean grain sizes from Ocean Drilling Program Site 1123 reveal variability in the speed of the Pacific inflow on the timescale of the 41 kyr orbital obliquity cycle. Similar orbital period flow changes have recently been demonstrated for the Pleistocene epoch. Collectively, these observations suggest that a strong coupling between changes in the speed of the deep Pacific inflow and high-latitude climate forcing may have been a persistent feature of the global thermohaline circulation system for at least the past 15 Myr. Furthermore, long-term changes in flow speed suggest an intensification of the DWBC under an inferred increase in Southern Component Water production. This occurred at the same time as decreasing Tethyan outflow and major EAIS growth between ~15.5 and 13.5 Ma. These results provide evidence that a major component of the deep thermohaline circulation was associated with the middle Miocene growth of the EAIS and support the view that this time interval represents an important step in the development of the Neogene icehouse climate