Fertilisation of an Ocean Desert by Volcanic Eruption
I-I Lin,1* Yuan-Hui Li,2 Jingfeng Wu,3 Chuanmin Hu,4 Chi-Wei Hwang,1,6
D. Allen Chu,5 George T. F. Wong,6 Dong S. Ko,7 Jen-Ping Chen1
1
Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan.
2
Department of Oceanography, School of Ocean and Earth Science and Technology,
University of Hawaii, USA. 3International Arctic Research Center, University of Alaska,
Fairbanks, USA.4College of Marine Sciences, University of South Florida, St. Petersburg,
Florida, 33701, USA. 5Goddard Earth Sciences and Technology Center, NASA Goddard
Space Flight Center, Greenbelt, Maryland, USA. 6Research Centre for Environmental
Change, Academia Sinica, Taipei, Taiwan. 7Naval Research Laboratory, Stennis Space
Center, Mississippi, USA.
*To whom correspondence should be addressed. Email: iilin@as.ntu.edu.tw
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Nitrogen fixation by the N2 fixer phytoplankton in the extensive Low Nutrient
Low Productivity (LNLP) oceans plays a critical role in the global nitrogen, carbon,
and biogeochemical cycling, thus impacting the climate. The supply of key nutrients
such as iron and phosphorus through volcanic eruption to promote N2 fixation is an
issue which has long been postulated but awaiting definitive evidence. On May 10 2003,
the Anatahan volcano in the Northern Mariana Islands erupted for its first time in the
recorded history. Using five types of satellite data and numerical modelling, here we
present evidence on the stimulation of biogeochemical responses from fallout of the
Anatahan eruption in the western North Pacific subtropical gyre, a well-known LNLP
ocean desert on the earth. Results show doubling of biological activities in a week after
the eruption. Spectral analyses further suggest the species involved include the primary
N2 fixer, Trichodesmium. This seminal work presents a valid basis for the rapid and
effective fertilisation in the LNLP oceans by volcanic eruption.
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The fertilisation potential of volcanic aerosols to promote nitrogen fixation (1-4) in the
low nutrient low productivity oceans and its impact on climate is a subject at its infancy
(5-11). N2 fixation in the vast LNLP Oceans on Earth (including the Earth’s largest biomes,
the subtropical North Pacific Ocean and the subtropical/tropical Atlantic) plays a key role in
global nitrogen, and carbon-biogeochemical cycling, thus is a critical component in the
earth’s climate system (1-4). In these oligotrophic waters, N2 fixation is considered to be
limited by the availability of essential nutrients such as iron and phosphorus (12,13).
Research on the supply of these nutrients has been focused on desert dust for few decades
(14-16). Nutrient supply from volcanic eruption has long been proposed (7), especially
laboratory study has suggested its rapid fertilisation potential (8). However, real world
evidence is lacking. For example, the influence of the Miyake-jima volcano on the water
south of Kuroshio was assessed for more than a year in 2000-2001. The identified primary
nutrient was ammonium sulphate and no promotion on N2 fixation was reported throughout
the study period (6).
In the evening of 10 May 2003, the Anatahan volcano (146E, 16N) in the Northern
Mariana Islands (Figure 1a) erupted for its first time in the recorded history (17-18). Its
location is in the midst of the western North Pacific Subtropical Gyre (WNPSG), a
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well-known oligotrophic ocean desert on the earth (19). Throughout the year in this water,
the nutrients are predominantly undetectable in the top 100m together with surface
chlorophyll-a (chl-a) concentration as low as ~0.05 mgm-3 (19). In a week after the eruption,
evident enhancement of biological activities was detected by NASA’s Moderate Resolution
Imaging Spectroradiometer (MODIS) ocean colour sensor (20). Using multiple satellite data
together with numerical modelling, this work documents this un-precedent volcanic event
and provides early evidence to report that N2 fixation can indeed be promoted in the LNLP
ocean desert through nutrient inputs from volcanic ash. The 5 types of satellite data used are
MODIS aerosol and ocean colour data, TOPEX/Poseidon and JASON-1 altimetry sea
surface height anomaly (SSHA) data, Tropical Rainfall Measuring Mission/Microwave
Imager (TMI) sea surface temperature (SST) data, and QuikSCAT sea surface wind vectors
while the numerical model used is the US Naval Research Lab’s East Asian Seas
Nowcast/Forecast System (EASNFS), a data assimilating, full-physics ocean model (20).
As illustrated in Fig. 1b, before the volcanic eruption the WNPSG was characterised by
the typical marine atmospheric condition of low aerosol loading with aerosol optical depth
(AOD) < 0.1. Immediately after the eruption on 11 May 2003, MODIS-derived AOD
abruptly increased to 1.0-2.0, nearly a 20-fold increase of aerosol loading at the downwind of
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the island (Fig. 1c). As also clearly depicted in the corresponding MODIS true colour image,
a large plume of volcanic ash was found to spread westward across approximately 500 km
over the WNPSG from the Mt. Anatahan (Fig. 1a). Correspondently, before the eruption the
MODIS ocean colour image depicts the typical WNPSG oligotrophic ocean condition with
Chlorophyll-a (Chl-a) concentration of about ~0.05 mgm-3 (Fig. 2a). Five days after the
eruption on 15 May, the first-available cloud-free MODIS Chl-a image illustrates a
well-defined ‘bloom-like’ patch in the area of 144-146.5∘ E, and 16.5-17.5∘ N (Fig. 2b),
co-located at the ash plume location (Fig. 1a). As the Chl-a image alone is not sufficient to
show that the ‘bloom-like’ patch is indeed a phytoplankton bloom, additional information
using the MODIS fluorescence line height (FLH) at 678nm band is used. This is because the
Chl-a image uses the blue/green band ratio to estimate the Chl-a concentration (20) but
non-living particles like suspended volcanic ash in the water can also cause a decrease in the
blue/green ratio and therefore a false increase in the estimated Chl-a (8,21). As such, the
MODIS FLH information is used to aid the interpretation because among all water
constituents (including phytoplankton, coloured dissolved organic matter, detritus, and other
non-living particles), only phytoplankton has the local peak at 678 nm (22-23). It has been
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found that the FLH signal is effective in delineating phytoplankton blooms in complex
waters (23).
As depicted in Fig. 2d, an elevated FLH signal is also detected in the ‘bloom-like’ patch
(boxed region in Fig. 2b), confirming enhancement of biological activities after the eruption.
However, the magnitude of the FLH increase is smaller than that of the standard Chl-a image
(Fig. 2b). As shown in Fig. 2d, the FLH value is ~ 0.002-0.005mWcm-2μm-1sr-1 in ambient
oligotrophic water and ~0.005-0.014mWcm-2μm-1sr-1 in the bloom patch, indicating an
around doubling in the biological activities. In contrast, the standard Chl-a image shows a
2-15 times increase in biological activities, from the ambient Chl-a of ~ 0.05-0.07mgm-3 to
Chl-a of ~ 0.1-1mgm-3 in the patch, suggesting a false amplification in Chl-a increase due to
the presence of suspended volcanic ash. On 17 May 2003, the next-available MODIS cloud
free Chl-a image reveals that the patch elongated towards northeast at the location between
145.-147.∘ E, and 16.5-18.5∘ N (Fig. 2c). The corresponding flow field from the EASNFS
also shows NE dispersion, supporting the elongated pattern of the bloom (Fig. 3e). Similar to
the situation on 15 May, the FLH image depicts a 2-3 times increase in the biological
activities (Fig. 2e) while the standard Chl-a image reveals the up to 10 times false increase
situation (Fig. 2c). These results suggest that indeed increase in the biological activities is
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found after the eruption and based on the FLH signal, the increase is about 2-3 folds after one
week from the eruption. In the beginning of June 2003, the bloom patch had mostly
disappeared.
To rule out the possibility of the observed bloom patch being fuelled by nutrient supply
from subsurface ocean through wind mixing or upwelling (24-25), the ambient wind, SST,
and altimetry SSHA maps are examined. As depicted in Fig. 3a, the bloom area is dominated
by positive SSHA of ~ 10 cm, indicating a clear down-welling condition (24). Consistent
observations are also found in the corresponding SST and sea surface wind that during the
bloom period, the SST is dominated by warm SST of ~ 29∘ C (Fig. 3c), and weak easterly
winds of around 5-7 m/s (Fig. 3d). In addition, one can see in Fig. 3b that little (≦ 10 nM)
nutrient (P and N) is detectable in the top 100 m of the water column (28). Therefore the
chance of the observed bloom being fuelled by nutrient supply from deeper ocean is slim.
As reported in Wade et al. (2005) (17), soon after the eruption there was a
well-organised field campaign by the US National Science Foundation’s MARGINS team to
the Anatahan to collect eruption samples for major and trace element analyses. Iron and
phosphorus were found together with silica and other elements (see sup_Table 1 in the
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support online material) (17). It would thus be interesting to examine whether the observed
bloom is associated with the N2 fixation species like Trichodesmium (26). Therefore,
MODIS ocean colour spectra of the normalised water-leaving radiance were analysed and
compared with the known Trichodesmium spectra (27). Also, as suggested by Duggen et al.
(8), spectra from suspended volcanic ash in the water are often associated with significant
raise in the 555nm band. Thus to avoid taking spectra from regions dominant by the volcanic
ash, each pixel is screened and only spectra without such possible contamination are used.
The screened spectra are then compared with the reference oligotrophic ocean background
spectra outside the bloom and the well-known reference Trichodesmium spectra from the
Atlantic (27). As in Fig. 4, the spectra in the reference region outside the bloom (in black and
locations depicted as black box in Fig. 2e) clearly depict the oligotrophic blue water
condition peak in the 412nm band. The reference Trichodesmium spectra are evidently
different from the oligotrophic reference spectra and are characterised by a clear single peak
at 490nm (green spectra in Fig. 4). Comparing with the observed spectra in various parts of
the bloom patch (red spectra in Fig. 4, location depicted by black arrows in Figs. 2d and 2e),
they are found in close similarity with the reference Trichodesmium spectra, in both shape
and the peak location (Fig. 4). This result provides further evidence to suggest that through
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the supply of the Anatahan volcanic ash, enhancement of biological activities through N2
fixation can be promoted in the WNPSG.
In summary, we present evidences to show that volcanic eruption promotes algal
growth in one of the most oligotrophic waters of the ocean. We observed a factor of two
increases in biological activities within 5 days after the volcanic eruption. Circumstantial
conditions are identified that such fertilisation took place in the presence of down-welling,
warm SST (~ 29∘C) and weak wind (~ 5-7 m/s) conditions. In addition, the ocean colour
spectra from the bloom patch were found to match with the spectra of the well-known N2
fixer, Trichodesmium. Our observation supports the hypothesis that N2 fixation in the
present-day oligotrophic North Pacific gyre is limited by the availability of Fe (1,9) and that
an increase in atmospheric dust loading during glacial time may enhance ocean uptake of
atmospheric CO2 and cool the climate (9,10,16). Our observation that volcanic activities can
influence oceanic biological production implies that the intensified rates of volcanic eruption
have a potential to initiate global cooling independent of altered global aridity (9,10,16) and
provide a negative feedback for tectonically-related global warming during the geologic past
(11).
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References and Notes
1.
D. Karl et al., Nature 388, 533 (1997).
2.
P. G. Falkowski, R. T. Barber, V. Smetacek, Science, 281, 200 (1998).
3.
D. Capone et al., Glob. Biogeochem. Cycles 19, 10.1029/2004GB002331 (2005).
4.
C. Deutsch, J. L. Sarmiento, D. M. Sigman, N. Gruber, J. P. Dunne, Nature 445, 163
(2007).
5.
R. C. Bay, N. Bramall, P. B. Price, Proc. Natl. Acad. Sci.USA 101, 6341 (2004).
6.
M. Uematsu et al., Geophys. Res. Lett. 31, 10.1029/2003GL018790 (2004).
7.
T. D. Jickells et al., Science 308, 67 (2005).
8.
S. Duggen, P. Croot, U. Schacht, L. Hoffmann, Geophys. Res. Lett. 34,
10.1029/2006GL027522 (2007).
9.
W. S. Broecker, G. Henderson, Paleoceanogr. 13, 352 (1998).
10. J. H. Martin, R. Gordon, Deep-Sea Res. Part A. 35, 177 (1988).
11. R. A. Berner, A. C. Lasaga, R. M. Garrels, Am. J. Sci. 283, 641 (1983).
12. J. Wu, W. Sunda, E. A. Boyle, D. M. Karl, Science 289, 759 (2000).
13. M. M. Mills, C. Ridame, M. Davey, J. L. Roche, J. L., R. J. Gelder, Nature 429, 292
(2004).
14. I. Fung et al., Glob. Biogeochem. Cycles 14, 281 (2000).
15. K. S. Johnson et al., Glo. Biogeochem. Cycles 17, 10.1029/2002GB002004 (2003).
16. N. Mahowald. et al. J. Geophys. Res. 104, 15895 (1999).
17. J. A. Wade et al., J. Volcanol. & Geotherm. Res. 146, 139 (2005).
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18. S. Nakada et al., J. Volcanol. & Geotherm. Res. 146, 226 (2005).
19. D. M. Karl, Ecosystems 2, 181 (1999).
20. see support online material.
21. H. Claustre et al., Geophys. Res. Lett. 29, 10.1029/2001GL014056 (2002).
22. C. Hu, F. E. Muller-Karger, C. Taylor, K. L. Carder, C. Kelble, E. Johns, C. Heil, Remote
Sens. Environ. 97, 311 (2005).
23. A. Gilerson, J. Zhou, S. Hlaing, I. Ioannou, J. Schalles, B. Gross, F. Moshary, S. Ahmed,
Opt. Express. 15, 15702 (2007).
24. C. Wilson, V. J. Coles, J. Geophys. Res. 110, 10.1029/2004JC002724 (2005).
25. I. I. Lin, W. T. Liu, C. C. Wu, G. T. F. Wong, C. Hu, Z. Chen, W. D. Liang, Y. Yang, K. K.
Liu, Geophys. Res. Lett. 30, 10.1029/2003GL017141 (2003).
26. D. G. Capone, J. P. Zehr, H. W. Paerl, B. Bergman, E. J. Carpenter, Science 276, 1221
(1997).
27. A. Subramaniam, C. W. Brown, R. R. Hood, E. J. Carpenter, E. J., D. G. Capone,
Deep-Sea Res. II 49, 107 (2002).
28. S. Levitus, M. E. Conkright, J. L. Reid, R. G., Najjar, A. Mantyla, Prog. Oceanog. 31,
245 (1993).
29. Thanks to NASA and Remote Sensing Systems for data provision, to G. C. Gong for
helpful discussion. This work is primarily supported by the National Science Council,
Taiwan through NSC 95-2611-M-002-024-MY3 and 97-2111-M-002-014-MY3.
Additional supports are given to Wong through NSC 96-2611-M-001-003-MY3, and to
Wong and Lin through a thematic research grant titled ‘Atmospheric Forcing on Ocean
Biogeochemistry (AFOBi)’ by the Academia Sinica, Taiwan.
11
30. Correspondence and requests for materials should be addressed to Dr. I-I Lin (email:
iilin@as.ntu.edu.tw).
12
Fig. 1: (a): MODIS true colour image showing the volcanic plume erupted (in the red box;
140-150°E, 15-20°N) from Anatahan on 11 May 2003. The box location is depicted in the
geographical map below. (b)-(d): MODIS AOD images of the box; (b) 6-8 May 2003 (before
eruption), (c) 11 May 2003 (during eruption), and (d) 14-19 May 2003 (after eruption).
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Fig. 2: (a)-(c): MODIS chl-a images on (a) 7-9 May 2003 (i.e., pre-eruption), (b) 15 May
2003 (5 days after the eruption), and (c) 17 May 2003 (7 days after the eruption). (d)-(e):
MODIS FLH images of the boxed region in (b) and (c), respectively. Black arrows in (d) and
(e) depict the locations where the bloom spectra in Fig. 4 are from while the black box in (e)
depicts the location where the reference background spectra in Fig. 4 are from.
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Fig. 3: (a) Sea surface height anomaly from the TOPEX/Poseidon and JASON-1 satellite
altimetry measurements for 1 cycle between 10 and 19 May 2003 (location depicted in the
boxed region from the map of Fig. 1a). (b) Climatological depth-nitrate profile in May. (c)
Corresponding SST map from the TRMM microwave imager on 15-17 May. (d)
Corresponding QuikSCAT ocean surface wind speed and direction on 15-17 May. (e)
Corresponding surface current field from NRL’s EASNFS prediction on 16 May.
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Fig. 4: (a) MODIS ocean colour spectra for a: reference oligotrophic ocean background
spectra (in black) (location depicted by black square in Fig. 2e, b: reference Trichodesmium
spectra from the Atlantic (in green) (location see the green box of sup_Fig. 1 in the support
online material), c: spectra from various parts of the bloom patch (red spectra, locations see
arrows in Figs. 2d and 2e).
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Support Online Material
1. Details of the 5 types of satellite data used:
The satellite data used are introduced as follows: 1. true colour and Aerosol Optical Depth
(AOD) data from the MODIS (Moderate Resolution Imaging Spectroradiometer) sensors of
the NASA/Terra and Aqua satellites (Kaufman et al. 2002). The AOD data is from the daily,
1 degree spatial resolution level 3 data. 2. Chlorophyll-a concentration and ocean colour
spectra (in normalized water-leaving radiance) from the MODIS Sensor (Carder et al. 1999).
The daily, 4km resolution level 2 data is used. 3. Sea surface height anomaly (SSHA) data
from the 10-day cycle data of the TOPEX/Poseidon and JASON-1 altimetry missions (Fu et
al. 1994). 4. The sea surface temperature (SST) data from the Tropical Rainfall Measuring
Mission (TRMM) Microwave Imager (Wentz et al. 2000). The daily, 0.25 degree data is used.
5. The ocean surface wind vector data from the NASA/Quick Scatterometer (QuikSCAT)
(Liu et al. 1998). The daily, 0.25 degree data is used.
References:
K. L. Carder et al., J. Geophys. Res., 104, 5403 (1999).
L. L. Fu et al., J. Geophys. Res., 99, 24369 (2000).
Y. J. Kaufman, D. Tanre´, O. Boucher, Nature, 419, 215 (2002).
W. T. Liu, W Tang, P. S. Polito, Geophys. Res. Lett. 25, 761 (1998).
F. J. Wentz, C Gentemann, D. Smith, D. Chelton, Science, 288, 847 (2000).
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2. Support online figure 1:
Sup_Fig. 1: Supplementary figure showing the Atlantic Trichodesmium bloom reported by
Subramaniam et al. (2002) (27), green box depicts the location where the reference
Trichodesmium spectra in Fig. 4 were taken (After Subramaniam et al. 2002).
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2. Support online Table 1
Sup_Table 1: Part of the Table 1 from Wade et al. (2005) (17) showing the major and trace
element analyses from the Anatahan samples.
19