The decline and fate of an iron-induced subarctic phytoplankton bloom.
Iron supply has a key role in stimulating phytoplankton blooms in high-nitrate low-chlorophyll oceanic waters. However, the fate of the carbon fixed by these blooms, and how efficiently it is exported into the ocean's interior, remains largely unknown. Here we report on the decline and fate of an iron-stimulated diatom bloom in the Gulf of Alaska. The bloom terminated on day 18, following the depletion of iron and then silicic acid, after which mixed-layer particulate organic carbon (POC) concentrations declined over six days. Increased particulate silica export via sinking diatoms was recorded in sediment traps at depths between 50 and 125 m from day 21, yet increased POC export was not evident until day 24. Only a small proportion of the mixed-layer POC was intercepted by the traps, with more than half of the mixed-layer POC deficit attributable to bacterial remineralization and mesozooplankton grazing. The depletion of silicic acid and the inefficient transfer of iron-increased POC below the permanent thermocline have major implications both for the biogeochemical interpretation of times of greater iron supply in the geological past, and also for proposed geo-engineering schemes to increase oceanic carbon sequestration.
Boyd
Philip W
PW
NIWA Centre for Chemical and Physical Oceanography, Department of Chemistry, University of Otago, PO Box 56, Dunedin, 9003, New Zealand. p.boyd@niwa.co.nz
Law
Cliff S
CS
Wong
C S
CS
Nojiri
Yukihiro
Y
Tsuda
Atsushi
A
Levasseur
Maurice
M
Takeda
Shigenobu
S
Rivkin
Richard
R
Harrison
Paul J
PJ
Strzepek
Robert
R
Gower
Jim
J
McKay
Mike
M
Abraham
Edward
E
Arychuk
Mike
M
Barwell-Clarke
Janet
J
Crawford
William
W
Crawford
David
D
Hale
Michelle
M
Harada
Koh
K
Johnson
Keith
K
Kiyosawa
Hiroshi
H
Kudo
Isao
I
Marchetti
Adrian
A
Miller
William
W
Needoba
Joe
J
Nishioka
Jun
J
Ogawa
Hiroshi
H
Page
John
J
Robert
Marie
M
Saito
Hiroaki
H
Sastri
Akash
A
Sherry
Nelson
N
Soutar
Tim
T
Sutherland
Nes
N
Taira
Yosuke
Y
Whitney
Frank
F
Wong
Shau-King Emmy
SK
Yoshimura
Takeshi
T
D000413:Alaska; D002244:Carbon / Q000378:metabolism; D003081:Cold Climate; D017377:Diatoms / Q000254:growth & development / Q000502:physiology; D007501:Iron / Q000032:analysis / Q000378:metabolism*; D009792:Oceans and Seas; D010839:Phytoplankton / Q000254:growth & development / Q000502:physiology*; D012623:Seawater / Q000382:microbiology*; D012824:Silicic Acid; D012822:Silicon Dioxide; D013997:Time Factors
D012824:Silicic Acid; D002244:Carbon; D012822:Silicon Dioxide; D007501:Iron