Beschreibung: An important tool for deep-sea temperature reconstruction is Mg/Ca paleothermometry applied to benthic foraminifera. Foraminifera of the genus Melonis appear to be promising candidates for temperature reconstructions due to their wide geographical and bathymetric distribution, and their infaunal habitat, which was suggested to reduce secondary effects from carbonate ion saturation (Δ[CO3 2−]). Here, we make substantial advances to previous calibration efforts and present new multi-lab Mg/Ca data for Melonis barleeanum and Melonis pompilioides from more than one hundred core top samples spanning in situ bottom temperatures from −1 to 16 °C, coupled with morphometric analyses of the foraminifer tests. Both species and their morphotypes seem to have a similar response of Mg/Ca to growth temperature. Compilation of new and previously published data reveals a linear dependence of temperature on Mg/Ca, with a best fit of Mg/Ca (mmol/mol) = 0.113 ± 0.005 ∗ BWT (°C) + 0.792 ± 0.036 (r2 = 0.81; n = 120; 1σ SD). Salinity, bottom water Δ[CO3 2−], and varying morphotypes have no apparent effect on the Mg/Ca-temperature relationship, but pore water Δ[CO3 2−] might have had an influence on some of the samples from the tropical Atlantic.

Beschreibung: Clay- and silt-size mineral assemblages are described from eight piston cores from the fiords and shelf on the western margin of Baffin Bay, Arctic Canada. Radiocarbon dates indicate that all the cores extend back in time to the last local glacial/interglacial transition (i.e. 8–10 ka); four extend back to between 10 and 12 ka, and HU77-021-156, located on the Southeast Baffin Island shelf, includes the entire late Foxe glacial stage. Silt- and clay-size particles constitute ca 40 and 55%, respectively, by weight of the bulk sediment. The clay-size fraction is dominated by mica; feldspars and quartz are the main constituents of the silt fraction. The fiord sediments are mainly composed of local mineralogies, but on the shelf, and at times in the fiords, exotic mineral species occur. The most important of these are detrital carbonates, derived from erosion of the Paleozoic basins in Arctic Canada and/or northwest Greenland. Both calcite and dolomite occur; calcite is the major carbonate mineral in the “southern” cores, whereas dolomite is the most abundant in cores north of 66°N. Higher inputs of carbonate species occur during regional deglaciation, 7–10 ka, and during the last 5 ka (probably reflecting increased iceberg production from northwest Greenland). Thus variations in the precentages of the carbonate minerals indicate significant shifts in Late Quaternary glacial-sediment source areas and oceanographic regimes.

Beschreibung: In the North Atlantic we define H-0 as a Heinrich-like event which occurred during the Younger Dryas chron. On the SE Baffin shelf prior to 11 ka, surface water productivity was reasonably high, as measured by the numbers of diatom and planktic foraminifera per gram, but an abrupt increase in detrital carbonate (DC-0 event) (from approximately 15% up to 50% carbonate by weight) occurred at 11 ± 14C ka and continued to circa 10 ka. These deposits, 2–6 m thick, are dominated by detrital calcite and silt- and clay-sized sediments. During this event (DC-0/H-0), ice extended onto the inner shelf but did not reach the shelf break and probably originated from a center over Labrador-Ungava. As a consequence, the pattern of ice-rafted debris and sediment provenance shown by H-O in the North Atlantic is different from that during H-1 (14.5 ka) or H-2 (20 ka) when the ice sheet extended along the axis of Hudson Strait and may have reached the shelf break; for example, there is no concrete evidence for DC-O is cores on the floor of the Labrador Sea due east of Hudson Strait (HU75-55,-56), but H-O has been noted in cores off Newfoundland and west of Ireland. A coeval carbonate event to DC-0, but this one dominated by dolomite, occurs in HU82-SU5 on the west side of Davis Strait with a source either from northern Baffin Bay or Cumberland Sound. Although other sources for North Atlantic detrital carbonate cannot be totally excluded, our evidence suggests that H-0 represents the expression of glaciological instability of the Laurentide Ice Sheet within the general region of Hudson Strait and probably to the north (Cumberland Sound and northernmost Baffin Bay). There is one younger DC event, dated circa 8.4 ka, present in sediments along the Labrador margin and in Hudson Strait, which represents the final collapse of the ice sheet within Hudson Strait and Hudson Bay.