Evidence of minimal carbon sequestration in the productive Amundsen Sea polynya

Lee, Sang Hoon; Hwang, Jeomshik; Ducklow, Hugh W.; Hahm, Doshik; Lee, Sang H.; Kim, Dong-Seon; Hyun, Jung‐Ho; Park, Jisoo; Ha, Ho Kyung; Kim, Tae‐Wan; Yang, Eun Jin; Shin, Hyoung Chul

doi:10.1002/2017gl074646

Cited by 37 publications

(35 citation statements)

References 49 publications

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“…In this way, the magnitude of deep-DOC consumption in the water column can be calculated. We estimated the fractions of fresh-DOC and deep-DOC as follows: where Δ 14 C deep = −492 ± 20‰ (mean value of CDW previously reported at 54°S, 176°W and 55.6°S, 84.7°E 25,26 ) and Δ 14 C fresh = −149 ± 10‰ from surface water DIC values 24 . Taking the surface sample at ASP-2014 with a Δ 14 C value of −285‰ as an example, we calculated that it contained 39% deep-DOC (25 ± 4 μM) and 61% fresh-DOC (39 ± 5 μM).…”

Section: Doc Cycling In the Amundsen Sea Previous Studies Have Repormentioning

confidence: 99%

Removal of Refractory Dissolved Organic Carbon in the Amundsen Sea, Antarctica

Fang

Lee

et al. 2020

Sci Rep

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the removal mechanism of refractory deep-ocean dissolved organic carbon (deep-Doc) is poorly understood. the Amundsen Sea polynya (ASp) serves as a natural test basin for assessing the fate of deep-Doc when it is supplied with a large amount of fresh-Doc and exposed to strong solar radiation during the polynya opening in austral summer. We measured the radiocarbon content of Doc in the water column on the western Amundsen shelf. the radiocarbon content of Doc in the surface water of the ASP reflected higher primary production than in the region covered by sea ice. The radiocarbon measurements of DOC, taken two years apart in the ASP, were different, suggesting rapid cycling of Doc. the increase in Doc concentration was less than expected from the observed increase in radiocarbon content from those at the greatest depths. Based on a radiocarbon mass balance, we show that deep-Doc is consumed along with fresh-Doc in the ASp. our observations imply that water circulation through the surface layer, where fresh-Doc is produced, may play an important role in global Doc cycling.The concentration of dissolved organic carbon (DOC) in the deep ocean (>1000 m, hereafter deep-DOC) is vertically uniform, but varies horizontally from ~34 to 48 μmol kg −1 (ref. 1 ). The 14 C ages of deep-DOC range from ~4000 yr in the North Atlantic to ~6500 yr in the North Pacific 2-6 . The old 14 C ages, together with its resistance to bacterial consumption 7 , imply that deep-DOC is refractory. A decrease in deep-DOC concentration of ~29% along the deep water circulation path is consistent with a very slow consumption rate 8 . Bacterial degradation, photochemical degradation, and adsorption to particles have been demonstrated as potential removal mechanisms 8-13 . However, the removal processes of deep-DOC are still not clearly understood.The Amundsen Sea in the west Antarctic is characterized by a relatively broad and deep continental shelf and extensive perennial sea ice cover 14 (Fig. 1). Circumpolar Deep Water (CDW) flows onto the Amundsen Shelf along the seafloor [15][16][17] . A part of the intruding CDW mixes with the overlying water to form modified CDW (MCDW). In the surface layer above ~400 m, water flows north, northwest, and off the shelf in general 18,19 . The western Amundsen Sea harbors a highly productive polynya, the Amundsen Sea Polynya (ASP) [20][21][22] . Peak annual production can be as high as ~3 gC m −2 d −1 with an average annual production of 105 gC m −2 yr −1 (ref. 22 ). High primary production in summer supplies considerable DOC (fresh-DOC) to the euphotic layer 20 . Deep-DOC supplied to the surface layer of the Amundsen Sea via CDW intrusion and mixing with the overlying water is subjected to biogeochemical processes such as the addition of extensive fresh-DOC 20 and microbial 23 and/or photochemical degradation 10 . The turnover time of the waters in the western Amundsen Sea embayment was suggested to be a few decades based on the 14 C content of dissolved inorganic carbon (DIC) 24 . Because of this unique enviro...

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Section: Doc Cycling In the Amundsen Sea Previous Studies Have Repormentioning

confidence: 99%

Removal of Refractory Dissolved Organic Carbon in the Amundsen Sea, Antarctica

Fang

Lee

et al. 2020

Sci Rep

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“…The export flux of C org formed by a Phaeocystis bloom is twofold slower than that formed by a diatom bloom (DeJong et al, 2017), and thus the contribution of P. antarctica cells to total export flux below the photic zone declines dramatically (Reigstad and Wassmann, 2007). Indeed, in the ASP, most photosyntheticallyproduced particulate organic carbon (POC) (>95%) exported from the surface layer is converted to suspended POC and/or dissolved carbon within the top 400 m of the water column (Ducklow et al, 2015;Lee et al, 2017). In addition, direct rate measurement conducted in this study also demonstrated that, despite high primary production (110 mmol C m −2 d −1 ) in the Phaeocystis-dominated water column of the ASP, benthic C org mineralization (average, 2.1 mmol C m −2 d −1 ) accounted for only 1.9% of primary production, which was strikingly lower than that measured in other less productive polar regions (Kim et al, 2016).…”

Section: Organic Substrates Control Spatial Distribution Of Planctomymentioning

confidence: 99%

“…Due to the inflow of warm circumpolar deep water (CDW), glaciers near the Amundsen Sea (AS) are undergoing the highest rates of melting and thinning on the Antarctic continent (Rignot, 2008;Jenkins et al, 2010;Jacobs et al, 2011). Consequently, as global warming continues, the heat flux intensity of the CDW may stimulate ice melting, which results in changes in phytoplankton productivity and community composition (Deppeler and Davidson, 2017), thereby regulating the function of the ASP in carbon sequestration (Thoma et al, 2008;Lee et al, 2017). The composition and metabolic activities of benthic microbial communities are ultimately determined by the quality and quantity of the organic matter supplied from the overlying water column (Franco et al, 2007;Bienhold et al, 2012;Ruff et al, 2014;Hoffmann et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

A Unique Benthic Microbial Community Underlying the Phaeocystis antarctica-Dominated Amundsen Sea Polynya, Antarctica: A Proxy for Assessing the Impact of Global Changes

et al. 2020

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Polynyas in the polar seas are regarded as windows through which ecosystem responses associated with global climate changes are to be noticed. However, little information is available on benthic microbial communities in the Amundsen Sea polynya (ASP), where environmental changes due to global warming are occurring rapidly, from which future climate change-induced ecosystem responses could be assessed. We performed high-throughput sequencing of 16S rRNA genes and quantitative PCR in combination with biogeochemical analyses and metabolic rate measurements to determine the composition, diversity and controls of major microbial communities in sediments of the ASP. A large fraction of the sequenced benthic microbial community (40% on average) in the polynya was uniquely affiliated with the phylum Planctomycetes, whereas Thaumarchaeota (51% on average) predominated in non-polynya areas. The relative abundance of Planctomycetes correlated significantly with organic carbon (C org) content in the polynya sediment underlying the Phaeocystis-dominated water column. These results suggest that Planctomycetes comprise a major bacterial group utilizing relatively recalcitrant C org produced primarily by Phaeocystis blooms. In contrast, the predominance of chemolithoautotrohic Thaumarchaeota in the sea-ice zone was attributed to low C org supply due to low primary productivity in the ice-covered water column. The Planctomycetes-dominated microbial communities in the ASP is in stark contrast to that Proteobacteria (Delta-and Gamma-proteobacteria) occupy ecological niches as primary mineralizers of organic materials in most benthic systems in the Southern Ocean, where organic materials in the sediments mostly originate from diatom blooms. Given that microbial communities respond quickly to environmental changes,

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“…Carbon fixed by phytoplankton in the water column is transferred to higher trophic levels, and finally, is exported from the system to the deep ocean [7]. However, intriguingly, in the Amundsen Sea dominated by P. antarctica , most of the organic carbon from primary production does not reach the sediment; instead, it is actively recycled and mineralized in the water column via microbial loop [8–11]. Indeed, higher heterotrophic bacterial production, accounting for ca.…”

Section: Introductionmentioning

confidence: 99%

Genomic and metatranscriptomic analyses of carbon remineralization in an Antarctic polynya

Kim

Lee

et al. 2019

Microbiome

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Background Polynyas in the Southern Ocean are regions of intense primary production, mainly by Phaeocystis antarctica . Carbon fixed by phytoplankton in the water column is transferred to higher trophic levels, and finally, to the deep ocean. However, in the Amundsen Sea, most of this organic carbon does not reach the sediment but is degraded in the water column due to high bacterial heterotrophic activity. Results We reconstructed 12 key bacterial genomes from different phases of bloom and analyzed the expression of genes involved in organic carbon remineralization. A high correlation of gene expression between the peak and decline phases was observed in an individual genome bin-based pairwise comparison of gene expression. Polaribacter belonging to Bacteroidetes was found to be dominant in the peak phase, and its transcriptional activity was high (48.9% of the total mRNA reads). Two dominant Polaribacter bins had the potential to utilize major polymers in P. antarctica , chrysolaminarin and xylan, with a distinct set of glycosyl hydrolases. In the decline phase, Gammaproteobacteria (Ant4D3, SUP05, and SAR92), with the potential to utilize low molecular weight-dissolved organic matter (LMW-DOM) including compatible solutes, was increased. The versatility of Gammaproteobacteria may contribute to their abundance in organic carbon-rich polynya waters, while the SAR11 clade was found to be predominant in the sea ice-covered oligotrophic ocean. SAR92 clade showed transcriptional activity for utilization of both polysaccharides and LMW-DOM; this may account for their abundance both in the peak and decline phases. Ant4D3 clade was dominant in all phases of the polynya bloom, implicating the crucial roles of this clade in LMW-DOM remineralization in the Antarctic polynyas. Conclusions Genomic reconstruction and in situ gene expression analyses revealed the unique metabolic potential of dominant bacteria of the Antarctic polynya at a finer taxonomic level. The information can be used to predict temporal community succession linked to the availability of substrates derived from the P. antarctica bloom. Global warming has resulted in compositional changes in phytoplankton from P. antarctica to diatoms, and thus, repeated parallel studies in various polynyas are required to predict global warming-related changes in carbon remineralization. Electronic supplementary material The online version of this article (10.1186/s40168-019-0643-4) contains supplementary material, which is available to authorized users.

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Evidence of minimal carbon sequestration in the productive Amundsen Sea polynya

Cited by 37 publications

References 49 publications

Removal of Refractory Dissolved Organic Carbon in the Amundsen Sea, Antarctica

Removal of Refractory Dissolved Organic Carbon in the Amundsen Sea, Antarctica

A Unique Benthic Microbial Community Underlying the Phaeocystis antarctica-Dominated Amundsen Sea Polynya, Antarctica: A Proxy for Assessing the Impact of Global Changes

Genomic and metatranscriptomic analyses of carbon remineralization in an Antarctic polynya

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