The development and application of nutrient and carbonate system proxies in the deep sea coral Desmophyllum dianthus

• Main Author: Anagnostou, Eleni
• Format: Text
• Language: unknown
• Published: No Publisher Supplied 2011
• Subjects: New Zealand; North Atlantic; Northwest Atlantic
• Online Access: https://dx.doi.org/10.7282/t3js9ptf; https://rucore.libraries.rutgers.edu/rutgers-lib/33378/

Deep sea corals are a promising paleoceanographic archive because they offer the potential for high temporal resolution and precise absolute dating. This thesis presents the first rigorous development and calibration of geochemical proxies for phosphate, barium, carbonate ion, and pH, recorded as phosphorus to calcium (P/Ca), barium to calcium (Ba/Ca), uranium to calcium (U/Ca) ratios and boron isotopes (δ11B), respectively, in the skeleton of the deep sea coral Desmophyllum dianthus (D. dianthus). The δ11B proxy was applied for the first time to a modern coral located within the deep mixed layer of the South Chatham Rise (New Zealand), showing a change in ocean pH as a result of anthropogenic CO2 emissions, in approximate agreement with atmospheric and surface ocean CO2 measurements from this region. The P/Ca, Ba/Ca, and U/Ca proxies were applied to corals dated to 15.4ka and Heinrich 1 (~16.5ka) to reconstruct the history of phosphate, barium, and carbonate ion concentrations at intermediate depths in the northwest Atlantic. The results demonstrate that dissolved phosphate increased and carbonate ion decreased during cold periods, previously characterized by reduced deep water convection and increased meltwater input. This suggests the presence of a nutrient rich and corrosive intermediate southern source water mass (SSW) at 40oN in west Atlantic, in agreement with previous radiocarbon reconstructions. Coral Ba measurements suggest a contemporaneous increase in the North Atlantic dissolved Ba inventory compared to Holocene. Calculations of the mixing ratio between northern and SSW following the 15.4ka event suggest that SSW was the dominant water mass in northwest Atlantic. The 15ka event occurred within ~100y, the life span of the coral. The initial success of these new geochemical tools is encouraging for the utility of D. dianthus as a geochemical paleoceanographic archive. With further development, these proxies could be used to reconstruct aspects of water mass mixing and biogeochemical processes in intermediate-to-deep waters of the Atlantic and Southern Oceans, locations where D. dianthus is most abundant.