Cycling of Vitamin B12 in the Ocean

ABSTRACT OCE-035199 The organic regulation of primary production in the ocean is not well understood, despite the fact that more than 65 species of phytoplankton are known to be auxotrophic for vitamin B12, meaning they require exogenous supplies for growth. While a major research effort has been directed in the last 10 years to understand the importance of trace metals and other inorganic micronutrients on phytoplankton production, the role of organic growth factors such vitamin B12 has been overlooked. The lack of clear understanding of the cycling of vitamin B12 in the marine environment has also hindered the understanding of methane production, the formation of organic chelators (which may control the bioavailability of some bioactive trace metals such as cobalt), and phytoplankton assemblage shifts (from vitamin-requiring to non-vitamin-requiring species) observed in some regions of the world ocean. Unfortunately, the lack of availability for a quantifying B12 in a quick and reliable technique has hindered the progress of vitamin B12 studies in the marine environment. In this study, researchers at SUNY at Stony Brook have developed a new method for the direct determination of vitamin B12 in seawater by pre-concentration using solid phase extraction, quantification using reversed phase HPLC with gradient elution, and detection by UV-visible absorption. By using this new technique the researchers will study the marine cycling of vitamin B12 in various biogeochemical provinces. This information is needed to evaluate the importance of this vitamin in the marine environment, as well as to validate previous studies carried out using the bioassay technique. The field study sites have been selected to give the maximum amount of information about the cycling of vitamin B12 in a broad range of marine environments (Southern Ocean, Sargasso Sea, upwelling regions of central and Baja California, the Cariaco Basin and a coastal environment). These B12 measurements will be interpreted using a suite of analyses to determine the dominant phytoplankton groups in the water being sampled, as well as analyses of DOC, POC, PON, chlorophyll a, inorganic nutrients and bacterial biomass. The determination of B12 cycling in contrasting oceanographic regimes will not only provide a better understanding of the processes influencing the "biological pump" but also of methane in the world ocean. Therefore, the application of this new vitamin B12 method has the potential to play a vital role in furthering our understanding of how the carbon sequestration capacity of the ocean could be enhanced.