IRD, benthic foraminifera and stable isotopic record of northern Sargasso Sea sediments

New geochemical proxy data from Bermuda Rise piston cores reveal ocean and climate conditions in the northern Sargasso Sea during marine isotope stage 3. Using ?18O on the planktonic foraminifer Globigerinoides ruber, we can correlate explicitly with every stadial/interstadial change in Greenland ice between ~32 and 58 ka. These data suggest repetitive changes of ~4°C in the annual average sea surface temperature (SST), with maximum cooling comparable to or greater than SST during glacial maximum conditions. The extent of SST depression is about the same for typical stadial events and for Heinrich events 4 and 5, which we have identified on the Bermuda Rise by traces of ice rafting. Benthic foraminiferal d13C decreases during every stadial event, consistent with reduced production of the deepest component of North Atlantic Deep Water and shoaling of its interface with Antarctic Bottom Water. This interpretation is supported by benthic Cd/Ca data from the climate cycle associated with interstadial 8.

(Table 2) Salinity in bays of the White Sea

Analysis of contribution of micronodules of sand and silt size to chemical composition of various types of pelagic sediments, as well as use of published data indicate that in some types of bottom sediments micronodules are the principal carriers of manganese and nickel. These elements appear to constitute smaller fractions of colloidal iron and manganese hydroxides, as well as terrigenous material.

K-Ar dating of altered deep-sea igneous rocks from DSDP Legs 2, 34, and 35

In an attempt to establish criteria for obtaining reliable K-Ar dates, conventional K-Ar studies of several Deep Sea Drilling Project sites were undertaken. K-Ar dates of these rocks may be subject to inaccuracies as the result of sea-water alteration. Inaccuracies may also result from the presence of excess radiogenic 40Ar trapped in rapidly cooled rocks at the time of their formation. The results obtained for DSDP Leg 34 basalts indicate that lowering of K-Ar dates, which is related to potassium addition by weathering, is a major cause of uncertainty in obtaining reliable K-Ar dates for deep-sea rocks. It could not be determined if the potassium addition to the basalts occurred at the time of formation, t_o, or continuously from t_o to the present. Calculations show that sediment cover is not a significant barrier to the diffusion of potassium into the basalt. 40Ar loss contributes, at least in part, to the lowering of the K-Ar date in rocks that have added potassium. The meaning of the K-Ar results obtained for DSDP Legs 35 and 2 basalts could not be unambiguously established. Because of the problems involved, caution must be used in interpreting the meaning of conventional K-Ar dates for deep-sea rocks.