Diatoms and their influence on the biologically mediated uptake of atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; in the Arabian Sea upwelling system

Rixen, Tim; Goyet, Catherine; Ittekkot, V.

doi:10.5194/bg-3-1-2006

Cited by 27 publications

(14 citation statements)

References 72 publications

(79 reference statements)

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“…In freshwater environments, chytrid infections modify phytoplankton composition (Holfeld, ; Ibelings et al ., ; Kagami et al ., ), impacting bloom progression and primary productivity (Gleason et al ., ; Rasconi et al ., ). In upwelling ecosystems, the decline of diatom blooms has been mainly attributed to depletion of nutrients (Barlow, ) and grazing (Rixen et al ., ). We challenge these views and propose that parasitic Fungi are partly responsible for falling marine diatom populations.…”

Section: Resultsmentioning

confidence: 97%

Fungal parasites infect marine diatoms in the upwelling ecosystem of the Humboldt current system off central Chile

Gutiérrez

Jara

Pantoja

2016

Environmental Microbiology

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This is the first report of fungal parasitism of diatoms in a highly productive coastal upwelling ecosystem, based on a year-round time series of diatom and parasitic Chytridiomycota abundance in the Humboldt Current System off Chile (36°30.80'S-73°07.70'W). Our results show co-variation in the presence of Skeletonema, Thalassiosira and Chaetoceros diatoms with attached and detached chytrid sporangia. High abundance of attached sporangia was observed during the austral spring, coinciding with a predominance of Thalassiosira and Skeletonema under active upwelling conditions. Towards the end of austral spring, a decreasing proportion of attached sporangia was accompanied by a decline in abundance of Skeletonema and Thalassiosira and the predominance of Chaetoceros, suggesting specificity and host density dependence of chytrid infection. The new findings on fungal parasitism of diatoms provide further support for the inclusion of Fungi in the current model of the role played by the marine microbial community in the coastal ocean. We propose a conceptual model where Fungi contribute to controlling the dynamics of phytoplankton populations, as well as the release of organic matter and the transfer of organic carbon through the pelagic trophic web in coastal upwelling ecosystems.

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Section: Resultsmentioning

confidence: 97%

Fungal parasites infect marine diatoms in the upwelling ecosystem of the Humboldt current system off central Chile

Gutiérrez

Jara

Pantoja

2016

Environmental Microbiology

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“…Based on the growing evidence that low concentrations of dissolved oxygen slow down the respiration of organic matter in the water column and thereby the biological oxygen consumption (Aumont et al, 2015;Cavan et al, 2017;Laufkötter et al, 2017;Thamdrup et al, 2012;Van Mooy et al, 2002), it has been hypothesized that an oxygen-related feedback mechanism stabilizes the Arabian Sea OMZ (Rixen et al, 2019a). This mechanism operates in the upper part of the OMZ, which hosts the seasonal thermocline but also affects the base of the OMZ and thereby its thickness as discussed before (Fig.…”

Section: Biological Feedback Mechanismmentioning

confidence: 96%

“…3c, Antoine et al, 1996;Naqvi, 1991). The offshore advection of upwelling-driven blooms, which increases the organic carbon export into the central Arabian Sea (Rixen et al, 2006), contributes to this eastward displacement of the OMZ, but monsoon-driven and seasonally varying physical oxygen supply mechanisms are assumed to be the main processes causing it. Numerical model studies have shown that, on an annual timescale, mesoscale eddies and filaments dominate the vertical supply of oxygen to the OMZ and the lateral transport of ventilated waters into the central and northern Arabian Sea (Resplandy et al, 2011(Resplandy et al, , 2012.…”

Section: Spatial and Temporal Variability Of The Arabian Sea Omzmentioning

confidence: 99%

“…Accordingly, the seasonal thermocline represents the main zone of respiration and, similar to soils on land, accommodates the nutrient recycling machinery of the pelagic ecosystem. Nutrient losses from the seasonal thermocline, via particle fluxes into the deep sea, denitrification, and lateral advection, must be compensated for by nutrient inputs in order to maintain the productivity (Rixen et al, 2019a). Nitrogen fixation, river discharges, and atmospheric deposition can be important nutrient sources, but in the Arabian Sea lateral inflow of water masses from the south via the cross-equatorial cell are the main source balancing nutrient losses from the seasonal thermocline (Bange et al, 2000;Gaye et al, 2013).…”

Section: Biological Feedback Mechanismmentioning

confidence: 99%

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Reviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian Ocean

et al. 2020

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Abstract. Decreasing concentrations of dissolved oxygen in the ocean are considered one of the main threats to marine ecosystems as they jeopardize the growth of higher organisms. They also alter the marine nitrogen cycle, which is strongly bound to the carbon cycle and climate. While higher organisms in general start to suffer from oxygen concentrations < ∼ 63 µM (hypoxia), the marine nitrogen cycle responds to oxygen concentration below a threshold of about 20 µM (microbial hypoxia), whereas anoxic processes dominate the nitrogen cycle at oxygen concentrations of < ∼ 0.05 µM (functional anoxia). The Arabian Sea and the Bay of Bengal are home to approximately 21 % of the total volume of ocean waters revealing microbial hypoxia. While in the Arabian Sea this oxygen minimum zone (OMZ) is also functionally anoxic, the Bay of Bengal OMZ seems to be on the verge of becoming so. Even though there are a few isolated reports on the occurrence of anoxia prior to 1960, anoxic events have so far not been reported from the open northern Indian Ocean (i.e., other than on shelves) during the last 60 years. Maintenance of functional anoxia in the Arabian Sea OMZ with oxygen concentrations ranging between > 0 and ∼ 0.05 µM is highly extraordinary considering that the monsoon reverses the surface ocean circulation twice a year and turns vast areas of the Arabian Sea from an oligotrophic oceanic desert into one of the most productive regions of the oceans within a few weeks. Thus, the comparably low variability of oxygen concentration in the OMZ implies stable balances between the physical oxygen supply and the biological oxygen consumption, which includes negative feedback mechanisms such as reducing oxygen consumption at decreasing oxygen concentrations (e.g., reduced respiration). Lower biological oxygen consumption is also assumed to be responsible for a less intense OMZ in the Bay of Bengal. According to numerical model results, a decreasing physical oxygen supply via the inflow of water masses from the south intensified the Arabian Sea OMZ during the last 6000 years, whereas a reduced oxygen supply via the inflow of Persian Gulf Water from the north intensifies the OMZ today in response to global warming. The first is supported by data derived from the sedimentary records, and the latter concurs with observations of decreasing oxygen concentrations and a spreading of functional anoxia during the last decades in the Arabian Sea. In the Arabian Sea decreasing oxygen concentrations seem to have initiated a regime shift within the pelagic ecosystem structure, and this trend is also seen in benthic ecosystems. Consequences for biogeochemical cycles are as yet unknown, which, in addition to the poor representation of mesoscale features in global Earth system models, reduces the reliability of estimates of the future OMZ development in the northern Indian Ocean.

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“…The low areal extension appears to be a consequence of the inflow of ICW because it favors the eastward retreat of the OMZ in the western Arabian Sea while it attenuates the influence of the clockwise circulation and the associated southwards expansion of the OMZ in the eastern Arabian Sea. The summer-monsoon-driven upwelling and the resulting offshore advection of blooms along filaments increase the carbon export in the central Arabian Sea (Rixen et al, 2006a) which in turn explains the low oxygen concentrations during the summer monsoon.…”

Section: Omz and Upwellingmentioning

confidence: 99%

Present past and future of the OMZ in the northern Indian Ocean

Rixen¹,

Cowie²,

Gaye³

et al. 2020

Preprint

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Abstract. Decreasing concentrations of dissolved oxygen and the resulting expansion of anaerobic ecosystems is a major threat to marine ecosystem services because it favors the formation of greenhouse gases such as methane, endangers the growth of economically important species, and increases the loss nitrate. Nitrate is one of the potential primary nutrients, which availability controls the marine productivity. The Arabian Sea and the Bay of Bengal are home to ~ 59 % of the Earth's marine sediments exposed to severe oxygen depletion and approximately 21 % of the total volume of oxygen-depleted waters (oxygen minimum zones, OMZs). The balance between physical oxygen supply and the biological oxygen consumption controlled the oxygen concentrations. In the Arabian Sea and most likely also in the Bay of Bengal the supply of oxygen sustained by mixing and advection associated with mesoscale eddies compensated the biological oxygen consumption. These steady states maintain low (hypoxic) oxygen concentrations allowing the competition between anaerobic and aerobic processes. However, due to slightly higher oxygen concentrations, the aerobic nitrite oxidization inhibits the anaerobic nitrite reduction and thus denitrification (the reduction of nitrate to N2) to become significant in the Bay of Bengal. A feedback mechanism caused by the negative influence of decreasing oxygen concentrations on the biological oxygen demand helped to maintain these steady states. Furthermore, it might have also counteracted a reduced physical oxygen supply into the Arabian Sea caused by climate-driven changes in the ocean's circulation during the last 6000 years. However, due to human-induced global changes, the OMZs in Arabian Sea and the Bay of Bengal intensified and expanded, which included also the occurrence of anoxic events on the Indian shelf. This affects benthic ecosystems, and in the Arabian Sea it seems to have initiated a regime shift within the pelagic ecosystem structure. Consequences for biogeochemical cycles are unknown, which, in addition to the poor representation of mesoscale features reduces the reliability of predictions of the future OMZ development in the northern Indian Ocean.

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Diatoms and their influence on the biologically mediated uptake of atmospheric CO<sub>2</sub> in the Arabian Sea upwelling system

Cited by 27 publications

References 72 publications

Fungal parasites infect marine diatoms in the upwelling ecosystem of the Humboldt current system off central Chile

Fungal parasites infect marine diatoms in the upwelling ecosystem of the Humboldt current system off central Chile

Reviews and syntheses: Present, past, and future of the oxygen minimum zone in the northern Indian Ocean

Present past and future of the OMZ in the northern Indian Ocean

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