Low light adaptation and export production in the deep chlorophyll maximum layer in the northern Indian Ocean

AbstractThroughout the open ocean, a minimum in dissolved iron concentration (dFe) overlaps with the deep chlorophyll maximum (DCM), which marks the lower limit of the euphotic zone. Maximizing light capture in these dim waters is expected to require upregulation of Fe-bearing photosystems, further depleting dFe and possibly leading to co-limitation by both iron and light. However, this effect has not been quantified for important phytoplankton groups like Prochlorococcus, which contributes most of the productivity in the oligotrophic DCM. Here, we present culture experiments with Prochlorococcus strain MIT1214, a member of the Low Light 1 ecotype isolated from the DCM in the North Pacific subtropical gyre. Under a matrix of iron and irradiance matching those found at the DCM, the ratio of Fe to carbon in Prochlorococcus MIT1214 cells ranged from 10–40 × 10−6 mol Fe:mol C and increased with light intensity and growth rate. These results challenge theoretical models predicting highest Fe:C at lowest light intensity, and are best explained by a large photosynthetic Fe demand that is not downregulated at higher light. To sustain primary production in the DCM with the rigid Fe requirements of low-light-adapted Prochlorococcus, dFe must be recycled rapidly and at high efficiency.

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Deep chlorophyll maximum and primary productivity in Indian Ocean sector of the Southern Ocean: Case study in the Subtropical and Polar Front during austral summer 2011

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/j.dsr2.2015.01.004 ◽

2015 ◽

Vol 118 ◽

pp. 240-249 ◽

Cited By ~ 16

Author(s):

S.C. Tripathy ◽

S. Pavithran ◽

P. Sabu ◽

H.U.K. Pillai ◽

D.R.G. Dessai ◽

...

Keyword(s):

Indian Ocean ◽

Southern Ocean ◽

Primary Productivity ◽

Austral Summer ◽

Polar Front ◽

Deep Chlorophyll Maximum ◽

Chlorophyll Maximum ◽

Indian Ocean Sector ◽

Ocean Sector

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Contribution of Rhizosolenia eriensis and Cyclotella spp. to the Deep Chlorophyll Maximum of Sproat Lake, British Columbia, Canada

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f90-013 ◽

1990 ◽

Vol 47 (1) ◽

pp. 128-135 ◽

Cited By ~ 10

Author(s):

Leland J. Jackson ◽

John G. Stockner ◽

Paul J. Harrison

Keyword(s):

Spatial Separation ◽

Deep Chlorophyll Maximum ◽

Nitrogen And Phosphorus ◽

Low Light ◽

Temporal And Spatial Distribution ◽

Neutral Buoyancy ◽

Chlorophyll Maximum ◽

Centric Diatoms ◽

Temporal And Spatial ◽

Lake Fertilization

Experimental fertilization of Sproat Lake with nitrogen and phosphorus greatly increased the abundance of two centric diatoms: Cyclotella spp. and Rhizosolenia eriensis. A decrease in sinking rates to neutral buoyancy at 17.5–22.5 m, an area of high nutrients and low light, coupled with sedimentation estimates of 106–107 celis∙m−2∙d−1, provide strong evidence that diatoms contribute to the formation of a seasonal deep chlorophyll maximum (DCM). The position of the Sproat Lake DCM, occurring at or just above the 1% light depth, appears to be largely determined by the light regime. R. eriensis bloomed and sank out of the mixed layer early in the spring before lake fertilization began. Immediately after fertilization, concentrations of nitrate and phosphate were elevated for 1 h only in the top 1 m of the water column. Most R. eriensis cells were well below 1 m and benefited little from the nutrient addition because of temporal and spatial separation. Cyclotella spp. occurred in the upper epilimnion and bloomed later in the year and consequently benefited (by large density increases) from fertilization. It is important to consider the temporal and spatial distribution of phytoplankton in determining which species will increase in abundance as a result of areal fertilization.

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Vertical Patterns of Early Summer Chlorophyll a Concentration in the Indian Ocean with Special Reference to the Variation of Deep Chlorophyll Maximum

Journal of Marine Biology ◽

10.1155/2012/801248 ◽

2012 ◽

Vol 2012 ◽

pp. 1-6 ◽

Cited By ~ 4

Author(s):

Gang Li ◽

Qiang Lin ◽

Guangyan Ni ◽

Pingping Shen ◽

Yanzhi Fan ◽

...

Keyword(s):

Indian Ocean ◽

Special Reference ◽

Chlorophyll A ◽

Early Summer ◽

Deep Chlorophyll Maximum ◽

Sampling Protocol ◽

The Real ◽

Chlorophyll Maximum ◽

The Indian Ocean ◽

Routine Sampling

Vertical patterns of early summer chlorophylla(Chla) concentration from the Indian Ocean are presented, as well as the variations of depth and size-fractioned Chlain the deep chlorophyll maximum (DCM). A total of 38 stations were investigated from 12 April to 5 May 2011, with 8 discrete-depth samples (7 fixed and 1 variable at real DCM) measured at each station. Depth-integrated Chlaconcentration (∑Chl a) varied from 11.5 to 26.8 mg m−2, whereas Chlacontent at DCM ranged from 0.17 to 0.57 μg L−1with picophytoplankton (<3 μm) accounting for 82% to 93%. The DCM depth varied from 55.6 to 91 m and shoaled latitudinally to northward. Moreover, our results indicated that the∑Chl acould be underestimated by up to 9.3% with a routine sampling protocol of collecting samples only at 7 fixed depths as the real DCM was missed. The underestimation was negatively correlated to the DCM depth when it varied from 55.6 to 71.3 m (r=−0.63,P<0.05) but positively correlated when it ranged from 75.8 to 91 m (r=0.68,P<0.01). This indicates that in the Indian Ocean the greater the departure of the DCM from 75 m depth, the greater the underestimation of integrated Chlaconcentration that could occur if the real DCM is missed.

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Siderophores as an iron source for Prochlorococcus in deep chlorophyll maximum layers of the oligotrophic ocean

10.1101/2021.11.13.468467 ◽

2021 ◽

Author(s):

Shane L Hogle ◽

Thomas Hackl ◽

Randelle M Bundy ◽

Jiwoon Park ◽

Brandon Satinsky ◽

...

Keyword(s):

Trace Metal ◽

Iron Uptake ◽

Global Ocean ◽

Deep Chlorophyll Maximum ◽

Iron Stress ◽

Selective Force ◽

Low Light ◽

Selective Pressures ◽

Chlorophyll Maximum ◽

Content Variation

Prochlorococcus is one of the most abundant photosynthesizing organisms in the oligotrophic oceans. Gene content variation among Prochlorococcus populations in separate ocean basins often mirrors the selective pressures imposed by the region's distinct biogeochemistry. By pairing genomic datasets with trace metal concentrations from across the global ocean, we show that the genomic capacity for siderophore-mediated iron uptake is widespread in low-light adapted Prochlorococcus populations from iron-depleted regions of the oligotrophic Pacific and S. Atlantic oceans: Prochlorococcus siderophore consumers were absent in the N. Atlantic ocean (higher iron flux) but constituted up to half of all Prochlorococcus genomes from metagenomes in the N. Pacific (lower iron flux). Prochlorococcus siderophore consumers, like many other bacteria with this trait, also lack siderophore biosynthesis genes indicating that they scavenge exogenous siderophores from seawater. Statistical modeling suggests that the capacity for siderophore uptake is endemic to remote ocean regions where atmospheric iron fluxes are the smallest, particularly at deep chlorophyll maximum and primary nitrite maximum layers. We argue that abundant siderophore consumers at these two common oceanographic features could be a symptom of wider community iron stress, consistent with prior hypotheses. Our results provide a clear example of iron as a selective force driving the evolution of Prochlorococcus.

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