The average radiocarbon (14C) age of dissolved organic carbon (DOC) in the deep ocean ranges from 4000-6500 14C years. However, the data set used to estimate this range is based on only a few sites in the world ocean. For this reason, a scientist from the University of California, Irvine will participate in three CLIVAR Repeat Hydrography cruises to collect water samples from six detailed profiles in the Pacific and Atlantic Oceans for which there is no data (P6-along 32°S in the South Pacific, A10 along 30°S in the South Atlantic, and A20 along 50°W in the North Atlantic). Seawater samples will be analyzed by accelerator mass spectrometry to determine the 14C signatures of DOC. In addition, the black carbon from DOC will be isolated and analyzed for 14C and 13C signatures. With the data set, the scientist plans to test the following three hypotheses: (1) 14C of bulk DOC in the South Pacific Ocean is intermediate between values in the Southern Ocean and those in the North Pacific, and these 14C ages can be used to determine the timescale of DOC cycling in deep waters of the Pacific; (2) 14C levels in bulk DOC of the Atlantic Ocean are highest in the north (43°N), lower in the equatorial region (10°N) and lowest in the South Atlantic (30°S), and reflects the timescale of DOC cycling as deep water travels south in the western Atlantic; and (3) black carbon constitutes a significant amount of DOC in open ocean water, and its 14C age is greater than 20,000 14C years.
The proponent will help high school teachers prepare science curricula for their classes and teaches a short course called "Radiocarbon in Ecology and Earth System Science" during the summer. She currently serves on the board for the Florida Center for Ocean Science Education Excellence and aids in the development of college level web-based educational classes. One graduate and two undergraduate students will be supported and trained as part of this project.
We collected samples for dissolved organic and inorganic radiocarbon (DOC, DIC) and for black carbon (BC) in DOC. We have made most of the 14C measurements for the DOC and DIC samples, and are now measuring the BC samples. A new technique has been developed that extracts DOC out of seawater and measures the concentration and 14C levels in black carbon. We have increased the numbers of measurements available in the ocean to about double the number of measurements in 2010. We seek to understand the cycling of DOC in the world ocean, the largest pool of organic carbon in the oceans. In particular, we want to reveal why the DOC is 4000-7000 14C years in the deep ocean. Implications for DOC cycling in the world ocean are being analyzed and will be reported in a paper submitted to Geophysical Research Letters during 2014. Several other papers have been published as a part of this research program. Broader impacts of this research include participation of a graduate student and postdoctoral who participated in several research cruises as the sole representatives of our laboratory. A specialist in our group both trained several undergraduate students, as well as participated on two research cruises to collect the samples, as a part of this research program.
