Award: OCE-1259776

Project Outcomes Report for NSF proposal entitled: Accomplishment Based Renewal: An iron limitation mosaic within the central California Current System. This proposal funded a major component of the Ph.D. thesis of Claire P. Till (nee Claire Parker) who is now an assistant professor at Humboldt State University. A manuscript presenting part of this research entitled "The iron limitation mosaic in the California Current system: factors governing Fe availability" by Till et al. has been submitted to the journal Limnology and Oceanography. This study provides evidence for potential Fe-limitation of diatoms off the southern coast of Oregon in July 2014, just off the shelf break near Cape Blanco in a region with moderate shelf width and river input. Since eastern boundary regions account for a disproportionally large amount of global primary production, this observation of potential Fe-limitation in a new region of the California Current System has implications for global models of primary productivity. In order to reevaluate the factors impacting Fe availability, we utilized satellite imagery to compare with historical datasets, and show that unexpected levels of Fe can often be explained by eddies, plumes of upwelled water moving offshore, or lack of recent upwelling. A multi-authored paper including many of the participants on the research cruise was recently published in Frontiers of Marine Science entitled "Diatom transcriptional and physiological responses to changes in iron bioavailability across ocean provinces" (Cohen et al., 14 Nov 2017). This interdisciplinary study investigated the response of diatom communities to variable Fe conditions through incubation experiments performed in the Fe mosaic of the California Upwelling Zone and along a natural Fe gradient in the Northeast Pacific Ocean. Through coupling gene expression of two dominant diatom taxa (Pseudo-nitzschia and Thalassiosira) with biological rate process measurements, we provided an in-depth examination of the physiological and molecular responses associated with varying Fe status. Following Fe enrichment, oceanic diatoms showed distinct differential expression of gene products involved in nitrogen assimilation, photosynthetic carbon fixation, and vitamin production compared to diatoms from low-Fe coastal sites, possibly driven by the chronic nature of Fe stress at the oceanic site. Genes of interest involved in Fe and N metabolism additionally exhibited divergent expression patterns between the two diatom taxa investigated, demonstrating that diverse diatoms may invoke alternative strategies when dealing with identical changes in their environment. We reported here several mechanisms used distinctly by coastal or oceanic diatom communities as well as numerous taxa-specific strategies for coping with Fe stress and rearranging nutrient metabolism following Fe enrichment. Other manuscripts resulting from this interdisciplinary research cruise are stilll in preparation. Last Modified: 12/07/2017 Submitted by: Kenneth W Bruland