Mass accumulation rates, age, sedimentation rate and bulk density at the East Pacific Rise

The rate at which hydrothermal precipitates accumulate, as measured by the accumulation rate of manganese, can be used to identify periods of anomalous hydrothermal activity in the past. From a preliminary study of Sites 597 and 598, four periods prior to 6 Ma of anomalously high hydrothermal activity have been identified: 8.5 to 10.5 Ma, 12 to 16 Ma, 17 to 18 Ma, and 23-to-27 Ma. The 18-Ma anomaly is the largest and is associated with the jump in spreading from the fossil Mendoza Ridge to the East Pacific Rise, whereas the 23-to-27-Ma anomaly is correlated with the birth of the Galapagos Spreading Center and resultant ridge reorganization. The 12-to-16-Ma and 8.5-to-10.5-Ma anomalies are correlated with periods of anomalously high volcanism around the rim of the Pacific Basin and may be related to other periods of ridge reorganization along the East Pacific Rise. There is no apparent correlation between periods of fast spreading at 19°S and periods of high hydrothermal activity. We thus suggest that periods when hydrothermal activity and crustal alteration at mid-ocean ridges are the most pronounced may be periods of large-scale ridge reorganization.

(Table 2) Age determination of harp seals (Pagophilus groenlandicus) from the Barents Sea - comparison of methods

Lower jaws (containing the teeth), eyes, and skin samples were collected from harp seals (Pagophilus groenlandicus) in the southeastern Barents Sea for the purpose of comparing age estimates obtained by 3 different methods, the traditional technique of counting growth layer groups (GLGs) in teeth and 2 novel approaches, aspartic acid racemization (AAR) in eye lens nuclei and telomere sequence analyses as a proxy for telomere length. A significant correlation between age estimates obtained using GLGs and AAR was found, whereas no correlation was found between GLGs and telomere length. An AAR rate (k Asp) of 0.00130/year ± 0.00005 SE and a D-enantiomer to L-enantiomer ratio at birth (D/L 0 value) of 0.01933 ± 0.00048 SE were estimated by regression of D/L ratios against GLG ages from 25 animals (12 selected teeth that had high readability and 13 known-aged animals). AAR could prove to be useful, particularly for ageing older animals in species such as harp seals where difficulties in counting GLGs tend to increase with age. Age estimation by telomere length did not show any correlation with GLG ages and is not recommended for harp seals.