Seasonal variation of pteropods from the Western Arabian Sea sediment trap

Mohan, Rahul; Verma, Kamlesh; Mergulhao, Lina P.; Sinha, D. K.; Shanvas, S.; Guptha, M.V.S.

doi:10.1007/s00367-006-0035-1

Cited by 22 publications

(13 citation statements)

References 32 publications

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“…Overall, the organic carbon export flux in the Arabian Sea during spring‐intermonsoon was found to be low compared to monsoon (Buesseler et al, ). Results of organic carbon measured from shallow sediment traps deployed at ~900 m water depth in the western Arabian Sea (16° 20′N 60° 18.8′E) also showed low organic carbon flux ~0.83 mmol m −2 d −1 (Mohan et al, ). A possible mechanism for such reduced export flux, though remineralization at this trap depth is significant, could be due to lack of diatom group of phytoplankton in this season, which could be able to ballast to deeper depth, caused by occurrence of nutrient poor oligotrophic conditions in the photic zone (Gauns et al, ).…”

Section: Discussionmentioning

confidence: 99%

²³⁴Th‐Based Carbon Export Flux Along the Indian GEOTRACES GI02 Section in the Arabian Sea and the Indian Ocean

Anand

Rengarajan

Sarma

2018

Global Biogeochemical Cycles

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234Th (t1/2 = 24.1 d), present in seawater, is a naturally occurring particle‐reactive radionuclide formed through the radioactive decay of its parent, 238U (t1/2 = 4.47 × 109 years). The 234Th:238U disequilibrium is exploited to quantify fluxes of elements moving out of the euphotic zone by attaching on to sinking particles. Under the Indian GEOTRACES programme, high‐resolution sampling in the upper 300 m depth was carried out at 11 stations in the Arabian Sea and the Indian Ocean during April–May 2014 from 17°N to 16°S along 65°E transect to estimate the 234Th‐based particulate organic carbon (POC) export flux from the upper ocean. Average 234Th fluxes integrated to 100 m depth were 2,612 and 1,968 dpm m−2 d−1 for the Arabian Sea and the Indian Ocean, respectively. The estimated POC export fluxes ranged from negligible to 9.0 mmol m−2 d−1, and the 234Th‐based POC export efficiencies were <2 to 5%. For the same season, the Arabian Sea and the Bay of Bengal showed highly contrasting carbon export trends (mean: 4.0 and 0.8 mmol C m−2 d−1, respectively). The modeled POC export fluxes from in situ and satellite‐derived primary production are higher than the 234Th‐based values for the Laws and Dunne models and are comparable for the Henson model. The modeled POC fluxes that depend on surface temperature and primary production could be further refined for the seasonal cycle in biological productivity and associated differences in trophic structure, grazing intensity, recycling efficiency, high bacterial activity, and associated dissolved organic carbon (DOC) export.

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Section: Discussionmentioning

confidence: 99%

²³⁴Th‐Based Carbon Export Flux Along the Indian GEOTRACES GI02 Section in the Arabian Sea and the Indian Ocean

Anand

Rengarajan

Sarma

2018

Global Biogeochemical Cycles

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“…Because of their sensitivity to ocean acidification, there has been a significant increase in research on this group over the past decades, including incubation experiments, studies on natural CO 2 gradients, and descriptions of the genetic variability within natural populations (see Manno et al, 2017). The impact of predicted future conditions on live specimens has been assessed using wide variety of parameters, including calcification (Comeau et al, 2009(Comeau et al, , 2010Maas et al, 2018;Moya et al, 2016), shell degradation (Bednaršek et al, 2012b;Bergan et al, 2017;Lischka and Riebesell, 2012), metabolic rates (Lischka and Riebesell, 2017;Maas et al, 2011;Seibel et al, 2012), respiration (Comeau et al, 2010;Maas et al, 2018;Moya et al, 2016), and gene expression patterns (Koh et al, 2015;Maas et al, 2015Maas et al, , 2018Moya et al, 2016;Thabet et al, 2017). Generally, previous studies have found that as the aragonite saturation state decreases, pteropod calcification rates decrease (Comeau et al, 2010(Comeau et al, , 2009Lischka and Riebesell, 2012).…”

Section: Understanding Natural Pteropod Variabilitymentioning

confidence: 99%

Determining how biotic and abiotic variables affect the shell condition and parameters of <i>Heliconoides inflatus</i> pteropods from a sediment trap in the Cariaco Basin

Oakes

Sessa

2020

Biogeosciences

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Abstract. Pteropods have been nicknamed the “canary in the coal mine” for ocean acidification because they are predicted to be among the first organisms to be affected by changing ocean chemistry. This is due to their fragile, aragonitic shells and high abundances in polar and subpolar regions where the impacts of ocean acidification are most pronounced. For pteropods to be used most effectively as indicators of ocean acidification, the biotic and abiotic factors influencing their shell formation and dissolution in the modern ocean need to be quantified and understood. Here, we measured the shell condition (i.e., the degree to which a shell has dissolved) and shell characteristics, including size, number of whorls, shell thickness, and shell volume (i.e., amount of shell material) of nearly 50 specimens of the pteropod species Heliconoides inflatus sampled from a sediment trap in the Cariaco Basin, Venezuela, over an 11-month period. The shell condition of pteropods from sediment traps has the potential to be altered at three stages: (1) when the organisms are live in the water column associated with ocean acidification, (2) when organisms are dead in the water column associated with biotic decay of organic matter and/or abiotic dissolution associated with ocean acidification, and (3) when organisms are in the closed sediment trap cup associated with abiotic alteration by the preservation solution. Shell condition was assessed using two methods: the Limacina Dissolution Index (LDX) and the opacity method. The opacity method was found to capture changes in shell condition only in the early stages of dissolution, whereas the LDX recorded dissolution changes over a much larger range. Because the water in the Cariaco Basin is supersaturated with respect to aragonite year-round, we assume no dissolution occurred during life, and there is no evidence that shell condition deteriorated with the length of time in the sediment trap. Light microscope and scanning electron microscope (SEM) images show the majority of alteration happened to dead pteropods while in the water column associated with the decay of organic matter. The most altered shells occurred in samples collected in September and October when water temperatures were warmest and when the amount of organic matter degradation, both within the shells of dead specimens and in the water column, was likely to have been the greatest. The hydrographic and chemical properties of the Cariaco Basin vary seasonally due to the movement of the Intertropical Convergence Zone (ITCZ). Shells of H. inflatus varied in size, number of whorls, and thickness throughout the year. There was not a strong correlation between the number of whorls and the shell diameter, suggesting that shell growth is plastic. H. inflatus formed shells that were 40 % thicker and 20 % larger in diameter during nutrient-rich, upwelling times when food supply was abundant, indicating that shell growth in this aragonite-supersaturated basin is controlled by food availability. This study produces a baseline dataset of the variability in shell characteristics of H. inflatus pteropods in the Cariaco Basin and documents the controls on alteration of specimens captured via sediment traps. The methodology outlined for assessing shell parameters establishes a protocol for generating similar baseline records for pteropod populations globally.

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“…Pteropod shell condition has been used to visually assess the extent of shell dissolution in both modern and fossil samples (Gerhardt et al, 2000;Gerhardt & Henrich, 2001). In the modern ocean, the condition of pteropod shells in sediment traps have been used to monitor carbonate chemistry (Meinecke & Wefer, 1990;Mohan et al, 2006), with the notion that shell dissolution is indicative of aragonite undersaturated waters between the sea surface and the depth of the sediment trap (Almogi-Labin et al, 1986;Gerhardt et al, 2000). In the fossil record, shell condition has been used to assess the impact of dissolution on the growth of living pteropods and their subsequent alteration during burial.…”

Section: Introductionmentioning

confidence: 99%

Degradation of Internal Organic Matter is the Main Control on Pteropod Shell Dissolution After Death

Oakes

Peck

Manno

et al. 2019

Global Biogeochemical Cycles

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The potential for preservation of thecosome pteropods is thought to be largely governed by the chemical stability of their delicate aragonitic shells in seawater. However, sediment trap studies have found that significant carbonate dissolution can occur above the carbonate saturation horizon. Here we present the results from experiments conducted on two cruises to the Scotia Sea to directly test whether the breakdown of the organic pteropod body influences shell dissolution. We find that on the timescales of 3 to 13 days, the oxidation of organic matter within the shells of dead pteropods is a stronger driver of shell dissolution than the aragonite saturation state of seawater. Three to four days after death, shells became milky white and nano scanning electron microscope images reveal smoothing of internal surface features and increased shell porosity, both indicative of aragonite dissolution. These findings have implications for the interpretation of the condition of pteropod shells from sediment traps and the fossil record, as well as for understanding the processes controlling particulate carbonate export from the surface ocean.

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Seasonal variation of pteropods from the Western Arabian Sea sediment trap

Cited by 22 publications

References 32 publications

²³⁴Th‐Based Carbon Export Flux Along the Indian GEOTRACES GI02 Section in the Arabian Sea and the Indian Ocean

²³⁴Th‐Based Carbon Export Flux Along the Indian GEOTRACES GI02 Section in the Arabian Sea and the Indian Ocean

Determining how biotic and abiotic variables affect the shell condition and parameters of <i>Heliconoides inflatus</i> pteropods from a sediment trap in the Cariaco Basin

Degradation of Internal Organic Matter is the Main Control on Pteropod Shell Dissolution After Death

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Seasonal variation of pteropods from the Western Arabian Sea sediment trap

Cited by 22 publications

References 32 publications

234Th‐Based Carbon Export Flux Along the Indian GEOTRACES GI02 Section in the Arabian Sea and the Indian Ocean

234Th‐Based Carbon Export Flux Along the Indian GEOTRACES GI02 Section in the Arabian Sea and the Indian Ocean

Determining how biotic and abiotic variables affect the shell condition and parameters of &lt;i&gt;Heliconoides inflatus&lt;/i&gt; pteropods from a sediment trap in the Cariaco Basin

Degradation of Internal Organic Matter is the Main Control on Pteropod Shell Dissolution After Death

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²³⁴Th‐Based Carbon Export Flux Along the Indian GEOTRACES GI02 Section in the Arabian Sea and the Indian Ocean

²³⁴Th‐Based Carbon Export Flux Along the Indian GEOTRACES GI02 Section in the Arabian Sea and the Indian Ocean

Determining how biotic and abiotic variables affect the shell condition and parameters of <i>Heliconoides inflatus</i> pteropods from a sediment trap in the Cariaco Basin