Despite clear evidence for iron limitation in the modern ocean, the sedimentary record of "paleoproductivity" has not provided a link between changes in dust flux and regional/global productivity. A scientist from Scripps Institute of Oceanography will examine the relationship between trace element chemistry and paleoproductivity through analysis of biogenic opal. Results from a pilot study wherein a newly developed technique was used to separate and purify sedimentary opal from detrital contaminants indicated that this mineral phase faithfully records dissolved oceanic concentrations of cosmic ray-produced radionuclides (10Be, 26Al) and trace elements (Fe, Mn, Ti, Zn). Thus, one sedimentary phase within the sediment column could be used to compare directly a proxy for aeolian input of micronutrients (Fe, Ti) with a proxy for production (26Al/Al ratios). As part of this project, the PI will continue to extend the pilot study using sediment cores from the Southern Ocean diatomaceaous ooze belt to provide an integrated assessment of paleoproductivity in this region. In addition, the temporal records of trace elements and cosmic nuclides will be determined in sediments from the equatorial Pacific and the southeastern Atlantic, two contrasting regions of upwelling and productivity. These areas are expected to differ in their response to global climate fluctuations and micronutrient input, thereby providing a comparison/contrast with records obtained from the Southern Ocean. It is anticipated that this study will reveal how the chemistry and biological productivity in the marine environment has changed with climate in the past.
In terms of the broader impacts, this study will document to use of biogenic opal as a recorder of dissolved trace element concentrations and cosmic ray-produced radionuclides, as well as provide the ocean science community with a new techniques for separating biogenic opal from other detritus within a sediment sample. Results from this study will be included in a new climate exhibit dedicated to how scientists use the marine sedimentary record to infer about past climate entitled Nature's Time Capsule opening in the Fall of 2006 at the Scripps Explorers Galley in the Birch Aquarium. Training and support of graduate and undergraduate students has been included in the study.
