NE Atlantic surface water mass changes over the last 15 kyr

摘要

Planktic foraminiferal faunas (> 150 mu m) and stable isotopes from the last 15 kyr were studied in kasten core 13078#16 from the Porcupine Abyssal Plain, NE Atlantic (48 degrees 49.91 N. 16 degrees 29.94W, water depth 4844 m) in order to document changes in surface waters The faunas were dominated (>80%) by four species: Neogioboquadrina incompta (= N. pachyderma dextral), Globigerina bulloides, N. pachyderma (= N. pachyderma sinistral) and Globorotatia inflata and their abundances; fluctuated strongly over the last 15 kyr. Other species, G truncatulinoides (right and left-coiling forms) and Globigerinoides ruber (white), had low abundances (typically <6%). The polar species N pachyderma dominated (similar to 60%) the terminal glacial interval when surface conditions were cold, decreased to 25-35% during the deglaciation and remained low (<2%) throughout the Holocene The relative abundance of N. incompta increased over the last 15 kyr and shows an inverse relationship with N. pachyderma. The increase in delta C-13 values of G bulloides, G inflata and G truncatuhnoides over the last 15 kyr is consistent with the whole ocean shift due to the expansion of the terrestrial biosphere, indicating that the upper oceanic delta C-13 values did not change significantly during this time. Between the deglaciation and the Holocene, the negative shift (similar to 1.056) in delta O-18 values of G inflata and G. truncatulinoides equates to the global ice volume shift suggesting that there was no significant warming of the deeper surface waters or that the species migrated to occupy a similar temperature water mass during this time. In contrast, the negative shift (similar to 1.7 parts per thousand) in delta O-18 values of G bulloides corresponds to a local shift of 0.7 parts per thousand. equivalent to a -3 degrees C warming of surface waters. Between 10 kyr and 5 kyr, the positive 6180 increases in G. inflata and C truncatulinoides suggest a decrease in deeper surface water temperatures in the order of 1.0-1.5 degrees C, a change not evident in the shallow surface water delta O-18 record of G bulloides. Water mass stratification changes, revealed by the Delta delta O-18 G(trancatulinoides) G (bullodes) records, suggest that the waters of the upper water column were more mixed during the last deglaciation than during the Holocene, and that there was a trend towards increasing water stratification over the last 15 kyr with a peak at similar to 4 kyr. Intervals ofenhanced carbonate dissolution at similar to 12-8.5 kyr and similar to 4 kyr previously reported are not clearly reflected in changes in solution-susceptible planktic foraminiferal species, such as G. ruber.