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Daniel W. Sadler1([email protected]), Karin M. Björkman1, Matthew J. Church1, Tara M. Clemente1, Susan E. Curless1, David G. Foley2, Allison A. Fong1, Lance A. Fujieki1, Eric M. Grabowski1, Thomas K. Gregory1, David M. Karl1, Ricardo M. Letelier3, Paul J. Lethaby1, Roger Lukas1, Claire Mahaffey1,
Stacy Maenner1, Patricia M. McAndrew1, Christopher L. Sabine4, Fernando Santiago-Mandujano1, Blake V. Watkins1
AbstractA central objective of the Hawaii Ocean Time-series (HOT) program is to understand how physical processes influence ocean biogeochemistry. Integration of satellite remote sensing technologies and moorings with monthly shipboard measurements is beginning to provide insight into both spatial and temporal dynamics in upper ocean processes. Using satellite derived ocean color we observed and then sampled a 200 km wide, spatially coherent region of enhanced chlorophyll concentration in the immediate vicinity of Station ALOHA. Analyses of satellite derived sea surface altimetry and surface currents suggested the feature was associated with an eddy traveling south-west towards Station ALOHA. To assess the influence of such events on upper ocean biogeochemistry, we conducted a transect from the approximate center of the region of enhanced chlorophyll towards its western edge. Samples were collected from the upper ocean (0-125 m) for determination of soluble reactive phosphorus (SRP), nitrate+nitrite (N+N), silicic acid (Si) and dissolved inorganic carbon concentrations (DIC), as well as measurements of plankton community structure based on flow cytometry and epi-fluorescence microscopy. Generally these measurements revealed that depth-integrated inventories of SRP and N+N were elevated relative to their respective seasonal climatologies at Station ALOHA, driven by an apparent shoaling of the nutricline associated with the eddy feature. A moored pCO2 sensor clearly showed the bloom passing through Station ALOHA and revealed this feature to be an unseasonable sink for CO2. Based on microscopic analyses, the bloom consisted of large diatoms supported in part by increased abundances of nitrogen-fixing bacteria. Similar diatom-diazotroph blooms appear to be a regular occurrence during the summertime months throughout the subtropical North Pacific. As a result, understanding the spatial characteristics of this eddy may provide insight into the physical and biogeochemical conditions that favor the regular, summertime accumulation of similar plankton assemblages in the subtropical North Pacific Ocean.
1School of Ocean and Earth Science and Technology, Department of Oceanography, University of Hawaii2Pacific Fisheries Environmental Laboratory, National Oceanic and Atmospheric Administration3College of Oceanic and Atmospheric Sciences, Oregon State University4Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration
Station ALOHA Blooms: Biogeochemical Characteristics of a Large Plankton Bloom in the Oligotrophic North Pacific Ocean
Diatoms and associated endosymbiotic bacteria found in the bloom. The micrographs in the top panels are stained with DAPI while the micrographs in the bottom panels show phycoerytherin auto-fluorescence of the heterocysts. The endosymbiotic bacteria are 20 - 50 microns long.
The bloom was sampled along a transect from the center of the high chlorophyll region, NW past Station ALOHA. The map to the left shows the position of Station ALOHA, the two moorings and the stations sampled.
The map below shows the extent of the feature relative to the Hawaiian Islands.
158.5o
W 158o
W 157.5o
W
21.5o
N
22o
N
22.5o
N
23o
N
Oahu
Station ALOHA
WHOTS
MOSEAN
157o
W 156o
W158o
W
22o
N
21o
N
23o
N
pCO2 Signature at HALE-ALOHA
A pCO2 sensor aboard the MOSEAN HALE-ALOHA buoy provided a nearly continuous stream of surface water and atmospheric pCO2. The record shows seawater pCO2 reduced by 15 ppm during the bloom and that it took nearly 1 month for the ocean to re-equilibrate with atmospheric CO2. The system is operated by the NOAA PMEL CO2 group. Data and additional information can be found at:www.pmel.noaa.gov/co2/moorings/hot/hot_main.htm
pCO2 Along Transect
350352
354
356
358360
362
0 10 20 30 40 50 60 70 80 90 100Distance from Center of Bloom (km)
pC
O2
of S
eaw
ater
(
µatm
)
Direct measurements of dissolved inorganic carbon and alkalinity were used to calculate pCO2 along the cruise track. pCO2 was lowest in the center of the bloom and highest at the end of the transect.
Depth Profiles of Temperature (Blue), Nitrate (Purple), Oxygen (Red) and Chloropigment (Green) from CTD instrumentation. Panel A is from the station occupied at the center of the bloom (0 km). Panel B is from the station occupied outside the bloom (98 km). Panel C is from Station ALOHA in July, 2004 and is included to show the properties when a bloom is not present.
200
150
100
50
0
Pre
ssur
e (d
bars
)
Center of Bloom
200
150
100
50
0
Pre
ssur
e (d
bars
)
Outside Bloom
0 0.2 0.4 0.6 0.8Chloropigment (µg/l)
180 190 200 210 220Oxygen ( µmol/kg)
0 0.1 0.2 0.3 0.4 0.5Nitrate (µmol/l)
18 20 22 24 26200
150
100
50
0
Temperature (Deg C)
Pre
ssur
e (d
bars
)
Station ALOHA, July 2004
A
B
C
ALOHA
June 19 June 26
August 7
July 3
July 31 July 24 July 17
July 10
Temporal development of a sea surface height anomaly viewed weekly from June 19 to August 7, 2005. Geostrophic currents deduced from these images indicate an anticyclonic flow field coincident with the high chlorophyll region shown in the center panel. Using altimetry, the path of the eddy can be tracked back to waters 1300 km east of Station ALOHA in January, 2005.
Frequency of Seasonal Blooms at Station ALOHA
Depth integrated (0-60 m) concentrations of silicic acid, biogenic silica and fucoxanthin. Each point represents the average and standard deviation for 17 years of each property binned by season. Note that the peak concentration of biogenic silica and fucoxanthin, indicators of diatom biomass, occurs during the summer, when the concentration of silicic acid is low.
Particulate Carbon and Chlorophyll were generally higher within the bloom than the historical data from Station ALOHA. The periodicity of these time series indicates that bloom-like conditions may occur annually.
While this study was able to sample the concentrated feature close to the Hawaiian Islands, the large, amorphous, feature to the NE, seen in the satellite image in the lower, left corner of this poster, may be more representative of the yearly blooms detected in the biogeochemical signature at Station ALOHA
Sprin
g
Sum
mer Fa
ll
Win
ter
Fu
co
xan
thin
(µg
m
-2)
800
1000
1200
1400
Bio
ge
nic
Si
(µm
ol S
i m
-2)
2000
3000
4000
Si(
OH
) 4(m
mo
l S
i m
-2)
70
75
80
85
90
95
Year
89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 Distance from Center of Bloom (km)
Part
icu
late
Car
bo
n(m
mo
l m-2
)
100
200
300
400
500 0-125 m
0-125 m 0-125 m
Year
89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 Distance from Center of Bloom (km)
Ch
la (m
g m
-2)
10
20
30
40
0 20 40 60 80 100
0 20 40 60 80 100
0-125 m
OSF36F-03
Sea Surface Height Anomaly (cm)
0 10 20 30-10-20-30
Den
sity
(kg
/m3 )
Phosphate
0 10 20 30 40 50 60 70 80 90 10024.5
24
23.5
23
nm
ol/
kg
10
20
30
40
50
60
70
Den
sity
(kg
/m3 )
Chlorophyll
0 10 20 30 40 50 60 70 80 90 10024.5
24
23.5
23
µg/k
g
0.10.20.30.40.50.60.70.80.9
Den
sity
(kg
/m3 )
0 10 20 30 40 50 60 70 80 90 10024.5
24
23.5
23
nm
ol/
kg
0
100
150
200
250
50
Nitrate
Sections measured along the transect of the bloom of chlorophyll, phosphate, silica and nitrate. Nutrient and chlorophyll concentrations viewed along isopycnal surfaces are higher near the center of the bloom and decrease along the transect.
Distance from Center of Bloom (km)
Den
sity
(kg
/m3 )
0 10 20 30 40 50 60 70 80 90 10024.5
24
23.5
23
µmo
l/kg
0.35
0.75
0.95
1.15
0.55
Silica
MarineMicrobiologyInitiative
July 19-26
The authors thank the officers and crew of the R/V Melville for providing a safe and productive cruise. Financial support for this project came from the National Science Foundation and the Marine Microbiology Initiative of the Gordon and Betty Moore Foundation.
Diatomic Diatoms
Profiling the ExtremesTransect Across the Bloom
Bloom Tracking from SpaceGradients in the Bloom
