Seasonal Variability of Phytoplankton Biomass Revealed by Satellite and BGC‐Argo Data in the Central Tropical Indian Ocean

Hu, Qifan; Chen, Xiaoyan; He, Xianqiang; Bai, Yan; Zhong, Qingwen; Gong, Fang; Zhu, Qiankun; Pan, Delu

doi:10.1029/2021jc018227

Cited by 4 publications

(12 citation statements)

References 65 publications

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“…The gradient criterion (-1 mmol/kg/m) was chosen based on the accuracy of 8 mmol/kg of oxygen sensor, the vertical resolution of 2 m, and the 5-point slope calculation (i.e., the slope was determined in an 8-m layer, where the change in the oxygen concentration that exceeded the sensor accuracy was considered reliable). Monthly averaged sea-surface wind stress and Ekman pumping velocity (EPV) data were observed by the ASCAT sensor on the Metop-A satellite (Hu et al, 2022) and provided by NOAA (https://coastwatch.pfeg.noaa.gov/). The satellite data were for the period October 2009-January 2022 and had a horizontal resolution 0.25°×0.25°.…”

Section: Data Processingmentioning

confidence: 99%

“…Wind-driven Ekman pumping causes vertical transport of the water mass. Positive EPV corresponds to the upward transportation of seawater (upwelling), and thus the uplift of thermocline and pycnocline and oxycline; conversely, negative EPV corresponds to downward transportation of seawater (downwelling), and the depression of thermocline, pycnocline and oxycline (Williams and Follows, 2003;McCreary et al, 2009;Hu et al, 2022). We selected an isotherm of 21.4°C as the thermocline indicator as this was the temperature closest to the bottom depth of the oxycline in the Arabian Sea.…”

Section: Seasonal Cycles Of the Thermoclinementioning

confidence: 99%

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Spatiotemporal variations of the oxycline and its response to subduction events in the Arabian Sea

Zhou

Chen

et al. 2023

Front. Mar. Sci.

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The Arabian Sea is a significant hypoxic region in world’s oceans, characterized by the most extensive oxygen minimum zones (OMZs). Both physical and biological processes can alter the vertical and horizontal distribution of dissolved oxygen within the upper ocean and affect the spatial and temporal distribution of hypoxia within the OMZ. To identify the key physical and biological factors influencing the boundaries of oxycline, we analyzed an extensive dataset collected from the biogeochemical-Argo (BGC-Argo) floats during the period of 2010–2022. In particular, we investigated the impact of physical subduction events on the oxycline. Our results shows that the upper boundary of the oxycline deepened in summer and winter, and seemed to be controlled by the mixed layer depth. In contrast, it was shallower during spring and autumn, mainly regulated by the deep chlorophyll maximum. The lower boundary of the oxycline in the western Arabian Sea was predominantly controlled by regional upwelling and downwelling, as well as Rossby waves in the eastern Arabian Sea. Subduction patches originated from the Arabian Sea High Salinity Water (ASHSW) were observed from the BGC-Argo data, which were found to deepen the lower boundary of the oxycline, and increase the oxygen inventory within the oxycline by 8.3%, leading to a partial decrease in hypoxia levels.

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Section: Data Processingmentioning

confidence: 99%

Section: Seasonal Cycles Of the Thermoclinementioning

confidence: 99%

Spatiotemporal variations of the oxycline and its response to subduction events in the Arabian Sea

Zhou

Chen

et al. 2023

Front. Mar. Sci.

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“…Below the surface mixed layer of the seasonally and permanently stratified regions, covering over 70% of the global ocean, resides an understudied subsurface community which satellites cannot see (Cullen, 2015;Cornec et al, 2021). This community can contribute a significant portion of the total water column phytoplankton biomass and production (Bouman et al, 2020;Zhuang et al, 2020;Arteaga et al, 2022;Cox et al, 2023) and can have contrasting phenology to surface communities (Brewin et al, 2022;Hu et al, 2022). Subsurface phytoplankton often forms a deep or subsurface chlorophyll maximum (DCM or SCM) (Cornec et al, 2021), and blooms often occur for longer periods compared to surface communities (Ross et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

“…Utilising the increasing wealth of data provided from autonomous platforms, such as Biogeochemical-Argo (BGC-Argo) floats, will complement satellite data and improve our ability to monitor phytoplankton at depth (Cornec et al, 2021;Hu et al, 2022). Recently, a model was developed to partition the vertical structure of phytoplankton biomass into two communities, a surface community which can be seen by a satellite and a subsurface community below the mixed-layer, hidden from satellite observations (Brewin et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

Climate variability shifts the vertical structure of phytoplankton in the Sargasso Sea

Viljoen,

Sun,

Brewin

2024

Preprint

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Marine phytoplankton are essential to ocean biogeochemical cycles. Yet, how climate variability is impacting phytoplankton vertical structure remains unclear. Here, we apply a conceptual model that partitions a profile of phytoplankton into two communities – one in the surface mixed layer and one in the subsurface below – to 33 years of data in the Sargasso Sea. Seasonally, the surface community alters their carbon-to-chlorophyll ratio without changing their carbon biomass, whereas the chlorophyll-a and carbon of the subsurface community covaries with no change in their carbon-to-chlorophyll ratio. At the multidecadal scale, climate variability influences these two communities differently. Over the last decade, subsurface phytoplankton biomass has increased in response to warming. In contrast, the surface phytoplankton has altered their carbon-to-chlorophyll without modifying their carbon biomass. Given that satellites can only view the surface ocean, sustained subsurface monitoring is required to understand fully how phytoplankton are responding to climate change.

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“…Multiple physical forcing has been proved to strengthen or disturb the vertical stratification, resulting the fluctuations of different biogeochemical processes. For instance, the "barrier layer", the layer between the bottoms of the mixed layer and of the isothermal layer, limits the phytoplankton growth; and wind-induced upwelling modulates the thermocline depth and associated subsurface blooms (Zhang H. et al, 2021;Hu et al, 2022). In addition, highly variable current systems in the equatorial IO (e.g., Equatorial Undercurrent (EUC)) redistribute vast amounts of heat, saltwater, nutrients, and oxygen (Schott et al, 2009;Huang et al, 2022), thus giving rise to significant ecosystem changes.…”

Section: Introductionmentioning

confidence: 99%

Different behaviors of organic matter under physical-biological controls in the eastern Indian Ocean

Zhang

et al. 2023

Front. Mar. Sci.

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Marine organic matter (OM) pools are the key to understanding biogeochemical cycles and carbon storage, especially under ongoing ocean warming. The tropical eastern Indian Ocean (IO) is ideal for unraveling marine OM pools for being one of the least understood ocean basins in terms of its complex physical and biogeochemical dynamics. So far, OM transformation and export remain underexplored and enigmatic in the IO. Here, we integrated in situ observations and incubation experiments in the Central IO (CIO) and Bay of Bengal (BoB). A large OM pool was found in the CIO, where we emphasized the prominent contribution of production in the deep euphotic layer, with physical forcing seasonally playing a supporting role. The dissolved organic matter (DOM)-degradation experiment results revealed high efficiency of in situ DOM consumption in the BoB, whereas dark carbon fixation by ammonia-oxidizing microorganisms was considered an alternative strategy in the euphotic CIO. Water mixing was found to highly influence the OM pools in the mesopelagic waters in the tropical eastern IO, but active microbial respiration could also regulate the OM degradation in the CIO. Our results emphasized the heterogeneity of OM pools between the BoB and CIO, and stated their different regulators of carbon reservoir considering an ocean warming scenario.

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Seasonal Variability of Phytoplankton Biomass Revealed by Satellite and BGC‐Argo Data in the Central Tropical Indian Ocean

Cited by 4 publications

References 65 publications

Spatiotemporal variations of the oxycline and its response to subduction events in the Arabian Sea

Spatiotemporal variations of the oxycline and its response to subduction events in the Arabian Sea

Climate variability shifts the vertical structure of phytoplankton in the Sargasso Sea

Different behaviors of organic matter under physical-biological controls in the eastern Indian Ocean

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