ALBERT

Description: This review is intended to cover the principal developments that have occurred within the last six years in the paleomagnetic study of marine sediments. Recent work utilizing the reflecting-light microscope indicates that detrital high-temperature Fe-Ti oxides are probably responsible for most of the magnetic remanence in marine sediments. These minerals possess a spectrum of coercivities that makes it necessary to use alternating-field—demagnetization techniques to isolate stable components. It is possible to use the standard magnetic stratigraphy for the last 4 m.y. of earth history derived from terrestrial lavas. Using the ages of the magnetic boundaries from this time scale it is possible by extrapolation and interpolation to better determine the ages of the major events. The ages of these events in increasing age are Jaramillo, 0.87 to 0.92 m.y.; Olduvai, 1.71 to 1.86 m.y.; Kaena, 2.82 to 2.90 m.y.; Mammoth, 3.0 to 3.085 m.y.; Cochiti, 3.72 to 3.82 m.y.; Nunivak, 3.97 to 4.14 m.y.; ‘c’ event of the Gilbert series, 4.33 to 4.65 m.y. Through the use of long cores from the central Pacific and through correlation using fossil datums, it has been possible to extend the magnetic stratigraphy back to the upper middle Miocene to magnetic epoch 5. It is concluded that very short magnetic events are probably short-term excursions of the field and not true magnetic events. It is shown that the field of the earth averages to an axial-dipole field within a period of 27,000 years and that the field over the last two million years has acted as a geocentric axial dipole. The evidence shows that when reversals of the dipole occur, the values of the reversed inclination are not significantly different from the normal values. The use of magnetic stratigraphy in marine geology has opened up a new era in study of sedimentary processes and evolution of marine organisms.

Description: In a previous paper (Iselin 1936) the writer considered that the temperature and salinity of the main thermocline layer (400–1200 meters) in the Sargasso Sea were mainly determined by vertical turbulence. At that time special significance was attached to the very consistent temperature‐salinity correlation at mid‐latitude stations from the western North Atlantic. Thus, when plotted on a temperature‐salinity diagram, the great majority of the modern observations fell along a narrow and slightly curving path connecting the characteristics of the superficial layer with those of deep water. The fact that in the main thermocline the temperature‐salinity correlation was somewhat fresher than a pure mixture of deep water and surface‐water was thought to result from the inflow of relatively large volumes of subantarctic intermediate water which appeared to enter the Sargasso Sea in two ways. First, this low‐salinity layer seemed to penetrate northward across the Northern Equatorial Current at mid‐depths and second, a considerable volume of it was observed leaving the Florida Straits to be, discharged into the Sargasso Sea along the southern edge of the Gulf Stream. In short, lt was considered that the negative salinity‐anomalies brought to the Sargasso Sea by the subantarctic intermediate layer more than counteracted the positive anomalies arriving at similar depths from the westward flow of water carrying Mediterranean characteristics.