The upper ocean silicon cycle of the subarctic Pacific during the EXPORTS field campaign

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 ca...

Full description

Bibliographic Details
Published in:Elementa: Science of the Anthropocene
Main Authors: Brzezinski, Mark A., Varela, Diana E., Jenkins, Bethany D., Buck, Kristen N., Kafrissen, Sile M., Jones, Janice L.
Format: Text
Language:unknown
Published: DigitalCommons@URI 2022
Subjects:
Biological pump
Exports
Ocean Station Papa
Si cycling
Silica export
Silica production
Silicon
Pacific
Subarctic
Online Access:https://digitalcommons.uri.edu/gsofacpubs/1566
https://doi.org/10.1525/elementa.2021.00087
Description
Summary: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 mM. On average, the >5.0-mm 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 mm). 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.

Similar Items