Particle Flux and Remineralization at Hawaii Ocean Time-Series Station ALOHA: Development of a New Estimation Method Based on 230Th and 231Pa

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ABSTRACTOCE-0117922In this project, researchers at the Woods Hole Oceanographic Institution will develop a technique independent of sediment traps for determining particle flux throughout the oceanic water column. It is based on the known rate of production of 230Th and 231Pa from decay of U isotopes dissolved in seawater and is similar in concept to the use of 234Th to determine export flux from the euphotic zone. Particles of various size ranges will be sampled by large- volume (1000-2000 liters), in-situ filtration and analyzed for the two radionuclides and for their major components (organic matter, carbonate, opal, aluminosilicate). The whole water column will be sampled, but a major emphasis will be on remineralization of organic matter in the mesopelagic zone (~150 - 1500m), where there is a large decrease of the flux with depth but where direct measurement of the flux with sediment traps is difficult and subject to large errors. The Hawaii Ocean Time-series (HOT) Station ALOHA is the site chosen for this initial study because it is remote from the complicating effects of ocean margins and because of the logistical ease and the supporting data provided by the ongoing time-series program. The proposed method is made feasible by the recent development of high-sensitivity analytical methods for measurement of 230Th and 231Pa in small samples by inductively-coupled plasma mass spectrometry (ICP-MS). If the concept proves in this project to be successful, the method could be applied to other oceanic areas and could be extended to a variety of specific elements and compounds.