107 Chase.pdf (2.4 MB)
Iron, nutrient, and phytoplankton distributions in Oregon coastal waters
journal contribution
posted on 2023-05-18, 11:19 authored by Zanna ChaseZanna Chase, van Geen, A, Kosro, PM, Marra, J, Wheeler, PAThe relationship between iron and nitrate concentrations was examined off the coast of Oregon during the upwelling season. Surface Fe and N (nitrate + nitrite) concentrations measured underway by flow injection analysis ranged from <0.3 to 20 nmol L−1 and <0.1 to 30 μmol L−1, respectively. Total dissolvable Fe concentrations, measured in unfiltered, acidified samples in surface waters and in vertical profiles, ranged from <0.3 to 300 nmol L−1. Surface water Fe and N concentrations were highly variable and uncoupled. Our observations indicate two dominant sources of Fe to Oregon coastal waters: Slope or shelf sediments and the Columbia River. Sedimentary iron, probably largely in the particulate form, appears to be added to surface waters through wind-induced vertical mixing during strong winds, through thickening of the bottom mixed layer during relaxation or downwelling favorable wind conditions, and through outcropping of shelf bottom waters during upwelling events. The existence of multiple iron sources and the generally high iron concentrations may explain why the distribution of phytoplankton, measured both remotely (by Sea-viewing Wide Field-of-view Sensor) and underway (by in vivo fluorescence), appeared to be driven primarily by physical dynamics and was not strongly linked to the distribution of iron. Nevertheless, at some offshore stations where underway Fe concentrations were <0.3 nmol L−1, underway measurements of the physiological state of phytoplankton by fast repetition rate fluorometry were consistent with mild iron stress, and cross-shelf nutrient distributions were consistent with iron regulation of the magnitude of phytoplankton blooms.
History
Publication title
Journal of Geophysical Research: OceansVolume
107Issue
C10Pagination
38.1-37.17ISSN
2169-9275Department/School
Institute for Marine and Antarctic StudiesPublisher
Amer Geophysical UnionPlace of publication
2000 Florida Ave Nw, Washington, USA, Dc, 20009Rights statement
Copyright 2002 by the American Geophysical UnionRepository Status
- Open