Summer phytoplankton blooms in the oligotrophic North Pacific Subtropical Gyre: Historical perspective and recent observations

Dore, John E.; Letelier, Ricardo M.; Church, Matthew J.; Lukas, Roger; Karl, David M.

doi:10.1016/j.pocean.2007.10.002

Cited by 196 publications

(257 citation statements)

References 124 publications

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“…Although aperiodic phytoplankton blooms have been observed by satellite remote sensing of the North Pacific Subtropical Gyre (NPSG) (24,25), we currently lack a comprehensive understanding of their origins, dynamics, and fates (24,26). Summer blooms detected via shipboard measurements are not always detected by satellites, and even large stochastic increases in symbiont-containing diatoms (increases of up to 10 4 -to 10 5 -fold relative to nonbloom concentrations) do not always reach the arbitrary 0.15 mg of chl a·m −3 threshold that is used to define a bloom based on satellite remote sensing of ocean color (27).…”

Section: Discussionmentioning

confidence: 99%

Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation

Karl

Church

Dore

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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271

308

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The atmospheric and deep sea reservoirs of carbon dioxide are linked via physical, chemical, and biological processes. The last of these include photosynthesis, particle settling, and organic matter remineralization, and are collectively termed the "biological carbon pump." Herein, we present results from a 13-y (1992-2004) sediment trap experiment conducted in the permanently oligotrophic North Pacific Subtropical Gyre that document a large, rapid, and predictable summertime (July 15-August 15) pulse in particulate matter export to the deep sea (4,000 m). Peak daily fluxes of particulate matter during the summer export pulse (SEP) average 408, 283, 24.1, 1.1, and 67.5 μmol·m −2 ·d −1 for total carbon, organic carbon, nitrogen, phosphorus (PP), and biogenic silica, respectively. The SEP is approximately threefold greater than mean wintertime particle fluxes and fuels more efficient carbon sequestration because of low remineralization during downward transit that leads to elevated total carbon/PP and organic carbon/PP particle stoichiometry (371:1 and 250:1, respectively). Our long-term observations suggest that seasonal changes in the microbial assemblage, namely, summertime increases in the biomass and productivity of symbiotic nitrogen-fixing cyanobacteria in association with diatoms, are the main cause of the prominent SEP. The recurrent SEP is enigmatic because it is focused in time despite the absence of any obvious predictable stimulus or habitat condition. We hypothesize that changes in day length (photoperiodism) may be an important environmental cue to initiate aggregation and subsequent export of organic matter to the deep sea. Approximately half of the photosynthesis on Earth is attributable to microscopic, single-celled phytoplankton that inhabit the sea (1). Within the marine environment, most (∼90%) of the photosynthetic carbon fixation takes place in the low-biomass, low-nutrient open ocean gyres that are grossly undersampled relative to coastal habitats (2, 3). A small but variable (typically <15% for open ocean ecosystems) portion of the organic matter produced in the sunlit (euphotic) zone is exported to the deeper, dark regions of the ocean by gravitational settling of living and nonliving particulate organic matter (POM). Most of the exported POM undergoes microbial decomposition before reaching the seabed. This POM remineralization process creates a deep sea reservoir of inorganic nutrients, including dissolved inorganic carbon (DIC), nitrate (NO 3 − ), and phosphate (PO 4 3− ). The resupply of these deep sea nutrients to the euphotic zone via turbulent diffusion and upwelling sustains surface ocean productivity over long time scales.The term "carbon pump" (4) is used to describe the oceanic processes that collectively sustain the large ∼272 μmol C·kg −1 global mean surface-to-deep sea increase of DIC in the ocean. The carbon pump ultimately sets the limit for carbon dioxide (CO 2 ) exchange between the ocean and the atmosphere (4). A stated goal of the seminal paper by Volk and Hoffert (4...

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Section: Discussionmentioning

confidence: 99%

Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation

Karl

Church

Dore

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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271

308

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“…An excess of phosphate (PO 4 3Ϫ ) over NO 3 Ϫ , relative to the 16:1 Redfield N:P, exists in the subsurface waters at Station ALOHA (32,33). If this excess P, combined with high light due to stratification, sufficiently stimulates nitrogen (N 2 ) fixation by photosynthetic cyanobacteria in the surface layer, N limitation of net community production may be alleviated and there can be a net biological sequestration of DIC (15,32,33). It has recently been suggested that deliberate fertilization of the surface ocean with PO 4 3Ϫ at sites like Station ALOHA might enhance the net removal of atmospheric CO 2 to the deep sea via this mechanism (32).…”

Section: Discussionmentioning

confidence: 99%

Physical and biogeochemical modulation of ocean acidification in the central North Pacific

Dore

Lukas

Sadler

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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Atmospheric carbon dioxide (CO2) is increasing at an accelerating rate, primarily due to fossil fuel combustion and land use change. A substantial fraction of anthropogenic CO2 emissions is absorbed by the oceans, resulting in a reduction of seawater pH. Continued acidification may over time have profound effects on marine biota and biogeochemical cycles. Although the physical and chemical basis for ocean acidification is well understood, there exist few field data of sufficient duration, resolution, and accuracy to document the acidification rate and to elucidate the factors governing its variability. Here we report the results of nearly 20 years of time-series measurements of seawater pH and associated parameters at Station ALOHA in the central North Pacific Ocean near Hawaii. We document a significant long-term decreasing trend of ؊0.0019 ؎ 0.0002 y ؊1 in surface pH, which is indistinguishable from the rate of acidification expected from equilibration with the atmosphere. Superimposed upon this trend is a strong seasonal pH cycle driven by temperature, mixing, and net photosynthetic CO2 assimilation. We also observe substantial interannual variability in surface pH, influenced by climate-induced fluctuations in upper ocean stability. Below the mixed layer, we find that the change in acidification is enhanced within distinct subsurface strata. These zones are influenced by remote water mass formation and intrusion, biological carbon remineralization, or both. We suggest that physical and biogeochemical processes alter the acidification rate with depth and time and must therefore be given due consideration when designing and interpreting ocean pH monitoring efforts and predictive models.carbon cycle ͉ climate change ͉ CO2 ͉ pH ͉ Station ALOHA W hen gaseous CO 2 is dissolved in seawater, it reacts to form carbonic acid (H 2 CO 3 ), which undergoes a series of reversible dissociation reactions that release hydrogen (H ϩ ) ions:The concentration of H ϩ (in mol kg Ϫ1 seawater) approximates its activity and determines the acidity of the solution. Acidity is commonly expressed on a logarithmic scale as pH:The addition of CO 2 therefore acidifies seawater and lowers its pH. Over the past 250 years, the mean pH of the surface global ocean has decreased from Ϸ8.2 to 8.1, which is roughly equivalent to a 30% increase in [H ϩ ] (1-3). This acidification of the sea is driven by the rapidly increasing atmospheric CO 2 concentration, which results from fossil fuel combustion, deforestation, and other human activities. Models predict that surface ocean pH may decline by an additional 0.3-0.4 during the 21st century (3, 4); over time, turbulent mixing, subduction, and advection are expected to transport anthropogenic CO 2 from the seasonally mixed layer into the ocean interior, lowering the pH of these deeper waters as well (4). Crucial marine biogeochemical processes may be altered, and many marine organisms may be negatively impacted by such pH reductions (2, 3, 5). As ocean CO 2 accumulates, seawater becomes more corrosive ...

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“…In the ocean, cyanobacterial diazotrophs generally show a consistent pattern in depth with higher abundances in the upper euphotic zone (Goebel et al, 2010;Moisander et al, 2010). Recurring summer blooms of these diazotrophs are reported in the North Pacific subtropical gyre (Dore et al, 2008) usually related to shallow mixing conditions that ensure the solar energy needed for nitrogen fixation. A recent study showed that the UCYN-A symbiosis appeared largely restricted to the upper water column, where N/P ratios were o16 (Krupke et al, 2014a).…”

Section: Distribution Of a Prymnesiophyte-ucyn-a Symbiosis Am Cabellomentioning

confidence: 98%

Global distribution and vertical patterns of a prymnesiophyte–cyanobacteria obligate symbiosis

et al. 2015

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A marine symbiosis has been recently discovered between prymnesiophyte species and the unicellular diazotrophic cyanobacterium UCYN-A. At least two different UCYN-A phylotypes exist, the clade UCYN-A1 in symbiosis with an uncultured small prymnesiophyte and the clade UCYN-A2 in symbiosis with the larger Braarudosphaera bigelowii. We targeted the prymnesiophyte-UCYN-A1 symbiosis by double CARD-FISH (catalyzed reporter deposition-fluorescence in situ hybridization) and analyzed its abundance in surface samples from the MALASPINA circumnavigation expedition. Our use of a specific probe for the prymnesiophyte partner allowed us to verify that this algal species virtually always carried the UCYN-A symbiont, indicating that the association was also obligate for the host. The prymnesiophyte-UCYN-A1 symbiosis was detected in all ocean basins, displaying a patchy distribution with abundances (up to 500 cells ml − 1 ) that could vary orders of magnitude. Additional vertical profiles taken at the NE Atlantic showed that this symbiosis occupied the upper water column and disappeared towards the Deep Chlorophyll Maximum, where the biomass of the prymnesiophyte assemblage peaked. Moreover, sequences of both prymnesiophyte partners were searched within a large 18S rDNA metabarcoding data set from the Tara-Oceans expedition around the world. This sequence-based analysis supported the patchy distribution of the UCYN-A1 host observed by CARD-FISH and highlighted an unexpected homogeneous distribution (at low relative abundance) of B. bigelowii in the open ocean. Our results demonstrate that partners are always in symbiosis in nature and show contrasted ecological patterns of the two related lineages.

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Summer phytoplankton blooms in the oligotrophic North Pacific Subtropical Gyre: Historical perspective and recent observations

Cited by 196 publications

References 124 publications

Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation

Predictable and efficient carbon sequestration in the North Pacific Ocean supported by symbiotic nitrogen fixation

Physical and biogeochemical modulation of ocean acidification in the central North Pacific

Global distribution and vertical patterns of a prymnesiophyte–cyanobacteria obligate symbiosis

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