The upper ocean silicon cycle of the subarctic Pacific during the EXPORTS field campaign
Author:
Brzezinski Mark A.12, Varela Diana E.34, Jenkins Bethany D.5, Buck Kristen N.6, Kafrissen Sile M.34, Jones Janice L.1
Affiliation:
1. 1Marine Science Institute, University of California, Santa Barbara, CA, USA 2. 2Department of Ecology Evolution and Marine Biology, University of California, Santa Barbara, CA, USA 3. 3Department of Biology, University of Victoria, Victoria, BC, Canada 4. 4School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada 5. 5Department of Cell and Molecular Biology, Graduate School of Oceanography, University of Rhode Island, Kingston, RI, USA 6. 6College of Marine Science, University of South Florida, Tampa, FL, USA
Abstract
Diatoms are major contributors to marine primary productivity and carbon export due to their rapid growth in high-nutrient environments and their heavy silica ballast. Their contributions are highly modified in high-nutrient low-chlorophyll regions due to the decoupling of upper-ocean silicon and carbon cycling caused by low iron (Fe). The Si cycle and the role of diatoms in the biological carbon pump was examined at Ocean Station Papa (OSP) in the HNLC region of the northeastern subarctic Pacific during the NASA EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field study. Sampling occurred during the annual minimum in surface silicic acid (Si(OH)4) concentration. Biogenic silica (bSi) concentrations were low, being in the tens of nanomolar range, despite high Si(OH)4 concentrations of about 15 μM. On average, the >5.0-µm particle size fraction dominated Si dynamics, accounting for 65% of bSi stocks and 81% of Si uptake compared to the small fraction (0.6–5.0 μm). Limitation of Si uptake was detected in the small, but not the large, size fraction. Growth rate in small diatoms was limited by Fe, while their Si uptake was restricted by Si(OH)4 concentration, whereas larger diatoms were only growth-limited by Fe. About a third of bSi production was exported out of the upper 100 m. The contribution of diatoms to carbon export (9–13%) was about twice their contribution to primary productivity (3–7%). The combination of low bSi production, low diatom primary productivity and high bSi export efficiency at OSP was more similar to the dynamics in the subtropical gyres than to other high-nutrient low-chlorophyll regions.
Publisher
University of California Press
Subject
Atmospheric Science,Geology,Geotechnical Engineering and Engineering Geology,Ecology,Environmental Engineering,Oceanography
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