Oxygen isotopic composition of early Eocene fishapatite from hole 913 B, ODP Leg 151: An indicator of the early Norwegian-Greenland Sea paleosalinity

• Main Authors: Andreasson, F., Schmitz, B., Spiegler, Dorothee
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1996
• Subjects: Greenland; Greenland Basin; Lofoten; Lofoten Basin; Greenland Sea; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/30992/; https://oceanrep.geomar.de/id/eprint/30992/1/sr151_33.pdf

Fish-apatite (teeth and bone fragments) of early Eocene age from Ocean Drilling Program Hole 913B (Greenland Basin) was analyzed, in the absence of biogenic calcite, for stable isotopic (δ1 8θco,2~, δ13C) composition to determine paleosalinity. Comparisons are made with isotopic results for early Eocene fish-apatite from Deep Sea Drilling Project (DSDP) Hole 550 (northeastern Atlantic) and the R0snaεs Clay Formation (Denmark). These two sites represent fully marine and semimarine conditions, respectively. The δ^Ocα,2- values of the fish-apatite from Hole 913B are 4.3%o to 8.1%c more negative than the fish-apatite values from DSDP Hole 550, and 1.9%o to 6.1%o more negative than the values from the R0snses Clay Formation. The results indicate reduced salinity in the early Eocene Greenland Basin relative to the open ocean. Using the present salinity/ δ'8O relationship in the North Atlantic, the salinity in the Greenland Basin was 22 ppt to 28 ppt. The reduced salinity is in agreement with an isolated early Eocene Greenland Basin, as suggested in earlier geophysical and paleontological studies. It is also likely that other parts of the Norwegian-Greenland Sea, such as the Lofoten Basin, exhibited brackish water conditions. Because of similar oxygen-isotopic composition of fish-apatite and excellently preserved foraminifer tests in the samples from the R0snaεs Clay Formation as well as DSDP Hole 550, we consider the fish-apatite δ1 8θco,2 - t o be a reliable instrument for paleosalinity determination. It is possible that the fish-apatite was exposed to diagenesis and isotopic reequilibration shortly after deposition on the seafloor. This should not, however, reduce the possibility of using δ1 8θco,2 - as an indicator of paleosalinity, because both δ1 8θ and salinity usually are very similar in the uppermost pore water and the overlying water mass. The fish-apatite δ13C values may support that early diagenesis has affected the original isotopic signal. The values seem to be related to the organic carbon content of the ...