Exploring the Carbonate Production/Dissolution Paradox in the Mid-Bruhnes of the Southern Ocean Using Coupled Records of Biological and Chemical Dynamics

HR: 16:15h
AN: PP54A-02 INVITED [Abstracts]
TI: Exploring the Carbonate Production/Dissolution Paradox in the Mid-Bruhnes of the Southern Ocean Using Coupled Records of Biological and Chemical Dynamics
AU: * Flores, J
EM: flores@usal.es
AF: Universidad de Salamanca, Departamento de Geolog｛, Salamanca, 37008 Spain
AU: Filippelli, G M
AF: Indiana University - Purdue University Indianapolis, Department of Geology, Indianapolis, IN 46202-5132 United States
AU: Sierro, F J
AF: Universidad de Salamanca, Departamento de Geolog｛, Salamanca, 37008 Spain
AU: Latimer, J
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109 United States
AU: Murray, R W
AF: Boston University, Department of Earth Sciences, Boston, MA 02215 United States
AB: The Mid-Brunhes event, an interval including MIS 9 to 11, is considered one of the warmest during the Pleistocene. This interval is also characterized by generally high carbonate concentrations (and presumably high productivity) with punctuated intervals of high dissolution in the deep ocean. The paradox of high carbonate production and high dissolution in certain intervals might be linked to nutrient available, ocean geochemistry, and upwelling. To explore this situation in the Southern Ocean, we examined calcareous nannofossil and geochemical proxies in order to estimate the degree of dissolution in the calcareous nannofossil assemblages, and examine primary production of these organisms and their relationship with surface water dynamics. In ODP Site 1089 (Cape Basin, Atlantic Ocean) the MIS 9 to 11 is characterized, as in the whole ocean, by the dominance of Gephyrocapsa caribbeanica (a small but robust and well-calcified placolith). Although the record of calcareous nannofossil is continuous, we observed fluctuations in the degree of preservation in the calcareous nannofossil assemblages, particularly periods of high to moderate dissolution during interglacial periods. Conversely, glacials are characterized by moderate to good calcareous nannofossil preservation. During Terminations IV and V we observed maxima in calcareous nannofossil accumulation, but with moderate preservation, indicating that maxima in calcareous nannofossil production occur during Terminations. One potential explanation is related to ocean geochemical mass balances and upwelling dynamics. The geochemical data from this site show that the P/Ti ratio, a paleoproductivity and P mass balance proxy, and Sr concentrations, a nannofossil production proxy, also show peaks during Terminations IV and V-thus, high production from nutrients coincides with high carbonate dissolution. In a coupled biological, chemical, and oceanographic model, low sea levels during glacials result in a basin dominance of the shelf-basin fractionation, with generally high nutrient delivery to the deep sea and increased carbonate production. During termination, the shelf reservoir of nutrients and carbonates begins to increase, but perhaps ocean stratification is diminished with higher upwelling causing greater productivity, with high dissolution the result of a switch in alkalinity with the termination. Basin production then decreases with the increase of nutrient apportionment to the shelves during higher interglacial sea levels.
DE: 4835 Inorganic marine chemistry
DE: 4850 Organic marine chemistry
DE: 3344 Paleoclimatology
DE: 3030 Micropaleontology
DE: 1635 Oceans (4203)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting