کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5780017 | 1634698 | 2017 | 10 صفحه PDF | دانلود رایگان |
- A â¼560Â yr history of C14, Pb, and Pb isotopes in the deep North Atlantic Ocean was reconstructed.
- Deep-ocean Pb increased by â¼5 fold due to the intrusion of anthropogenic Pb.
- Deep-ocean ÎC14 increased by â¼40â° due to the intrusion of bomb-radiocarbon.
- Approx. 25 yr of transit time is estimated for 14C and Pb by comparing the data to the surface ocean record.
- Model suggests that mixing is as important as advection in the transport of these tracers.
Deep-ocean, ÎC14, Pb concentrations, and Pb isotopes were reconstructed from a deep-sea coral Enallopsammia rostrata from 1410 m depth off of Bermuda. Our high-resolution time series is created from closely spaced radial cross sections, with samples taken from the center of concentric coral growth bands that we show to be the oldest portion of the section. Prebomb radiocarbon ages from the coral demonstrate that the vertical growth rate of the coral is linear, and the age of the coral is estimated to be 560-630 yr old based on the growth rate. Using this age model to reconstruct ÎC14 in deep seawater, we first detect bomb radiocarbon at the coral growth site around 1980, and show that ÎC14 increased from â80±1â° (average 1930-1979) to a plateau at â39±3â° (1999-2001). Pb/Ca of the coral ranges between 1.1-4.5 nmol/mol during the 16th and 17th centuries, and Pb isotope ratios (206Pb/207Pb = 1.21, 208Pb/207Pb = 2.495) in this period agree with pre-anthropogenic values found in the pelagic sediments of the North Atlantic Ocean basin. Coral Pb/Ca is slightly elevated to 6.2±0.9 nmol/mol between the 1740s and the 1850s and then increases to 25.1±0.2 nmol/mol in the 1990s. The increase in coral Pb/Ca is accompanied by a decrease in coral 206Pb/207Pb and 208Pb/207Pb, indicating that the increase was caused by the infiltration of anthropogenic Pb to the coral growth site. Comparing our data to the surface coral ÎC14 and Pb records from Bermuda reveals a time scale of tracer transport from the surface ocean to the coral growth site. Some characteristic features, e.g., the bomb-derived ÎC14 increase, appear in the deep ocean approximately 25 yr later than the surface, but the overall increase of ÎC14 and Pb in the deep ocean is smaller and slower than the surface, showing the importance of mixing during the transport of these tracers.
Journal: Earth and Planetary Science Letters - Volume 458, 15 January 2017, Pages 223-232