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Kay I. Ohshima - One of the best experts on this subject based on the ideXlab platform.
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strong biological carbon uptake and carbonate chemistry associated with dense shelf water outflows in the cape darnley polynya east antarctica
Marine Chemistry, 2020Co-Authors: Kan Murakami, Daisuke Hirano, Daiki Nomura, Gen Hashida, Shinichiro Nakaoka, Yujiro Kitade, Toru Hirawake, Kay I. OhshimaAbstract:Abstract Formation of dense shelf water (DSW) in coastal Polynyas (open water or thin sea-ice cover) in the sea-ice zone around Antarctica supplies Antarctic Bottom Water (AABW) through overflow down the continental slope. In coastal Polynyas, atmospheric carbon dioxide (CO2) is absorbed by the ocean in the early spring because of active primary production, and DSW formation is an important process for transporting this carbon from the sea surface to the deep ocean. However, there have been few quantitative evaluations of carbon consumption by active primary production and transport in coastal Polynyas. Here, we examined the carbon dynamics in the Cape Darnley polynya (CDP), East Antarctica during austral summer 2009, by using carbonate system parameters combined with oceanographic mooring data. The partial pressure of CO2 in the CDP surface water was lower than that of the atmosphere and the mean and standard deviation of sea−air CO2 flux was estimated as −6.5 ± 6.9 mmol C m−2 d−1 (a negative value indicates absorption of atmospheric CO2 by the ocean). Vertical profiles of dissolved inorganic carbon (DIC) concentration showed that concentrations in the bottom layer near the ocean floor were lower (by about 20 μmol kg−1) than those in the ambient water (e.g., modified Circumpolar Deep Water, mCDW). The low-DIC in the shelf water was maintained by the strong biological uptake of carbon imported from high-DIC mCDW within the water column. Therefore, low-DIC DSW overflowed down the continental slope, and low-DIC concentrations were maintained through an export pathway to the continental shelf. The annual production of dissolved organic carbon and particulate organic carbon on the shelf was estimated as 0.7 × 1011–1.5 × 1011 mol C using the data for the DIC of DSW and current velocity data from a mooring in the CDP. Our results provide quantitative estimates for the potential role of carbon consumption by the active primary production and carbon transport by dense water formation in Antarctic coastal Polynyas.
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winter water formation in coastal Polynyas of the eastern chukchi shelf pacific and atlantic influences
Journal of Geophysical Research, 2018Co-Authors: Daisuke Hirano, Kay I. Ohshima, Yasushi Fukamachi, Eiji Watanabe, Andrew R Mahoney, Hajo Eicken, Motoyo Itoh, Daisuke SimizuAbstract:Water properties and formation processes of Alaskan Coastal Winter Water (ACWW) over the eastern Chukchi shelf along the Alaska coast, the so-called Barrow Canyon pathway, are examined using data from moorings, atmospheric reanalysis, satellite-derived sea-ice production (SIP), and a numerical tracer experiment. Along this pathway, Pacific Winter Water (PWW) can be modified to produce ACWW through SIP accompanied by production of cold, saline polynya water in the coastal Polynyas, upwelling of warm Atlantic Water (AW), and mixing processes on the shelf. Three different types of ACWW are formed: (i) a mixture of AW and PWW, (ii) a mixture of AW and polynya water, and (iii) hypersaline polynya water. The northeasterly winds, correlated with the north-south atmospheric pressure gradient between Beaufort High and Aleutian Low, are common triggers of polynya SIP episodes and AW upwelling in the Barrow Coastal Polynya (BCP). Due to the dual impact of northeasterly winds, PWW modification processes in the BCP are more complicated than what occurs elsewhere in the Chukchi Polynya. The impact of AW upwelling on the ACWW formation is most prominent in the BCP, usually centered along the coast. All types of ACWW are thought to be basically transported westward or northwestward with the Chukchi slope current and/or Beaufort Gyre and finally contribute to maintenance of the lower halocline layer especially over the Chukchi Borderland, Northwind Ridge, and southern Canada Basin. Even in the Pacific sector of the Arctic Ocean, ACWW properties are strongly influenced by both Atlantic-origin and Pacific-origin waters.
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sea ice production in antarctic coastal Polynyas estimated from amsr2 data and its validation using amsr e and ssm i ssmis data
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2017Co-Authors: Sohey Nihashi, Kay I. Ohshima, Takeshi TamuraAbstract:Antarctic coastal Polynyas are very high sea-ice production areas. The resultant large amount of brine rejection leads to the formation of dense water. The dense water forms Antarctic bottom water, which is the densest water in the global overturning circulation and a key player in climate change as a significant sink for heat and carbon dioxide. In this study, an algorithm was developed that uses Advanced Microwave Scanning Radiometer 2 (AMSR2) data (2012–present) to detect polynya area and estimates thin ice thickness by a method similar to that used to develop the algorithm for Advanced Microwave Scanning Radiometer for EOS (AMSR-E) data. Landfast sea-ice areas were also detected using AMSR2 data. Ice production in the Polynyas was estimated by a heat flux calculation using AMSR2 sea-ice data. In four major Polynyas, AMSR2 ice production was compared with AMSR-E (2003–2011) ice production through comparison of them with Special Sensor Microwave Imager (SSM/I) and Special Sensor Microwave Imager/Sounder (SSMIS) ice production. The comparison confirmed that the ice production from AMSR-E/2 data, which have higher spatial resolution than SSM/I-SSMIS data, can be used to analyze time series covering more than 10 years. For example, maps of annual ice production based on AMSR-E/2 data revealed detailed changes of the Mertz Polynya, where the ice production decreased significantly after the Mertz Glacier Tongue calving in 2010. Continuous monitoring of the coastal Polynyas by the AMSR series sensors is essential for climate-change-related analyses in the Antarctic Ocean.
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global view of sea ice production in Polynyas and its linkage to dense bottom water formation
Geoscience Letters, 2016Co-Authors: Kay I. Ohshima, Sohey Nihashi, Katsushi IwamotoAbstract:Global overturning circulation is driven by density differences. Saline water rejected during sea-ice formation in Polynyas is the main source of dense water, and thus sea-ice production is a key factor in the overturning circulation. Due to difficulties associated with in situ observation, sea-ice production and its interannual variability have not been well understood until recently. Methods to estimate sea-ice production on large scales have been developed using heat flux calculations based on satellite microwave radiometer data. Using these methods, we present the mapping of sea-ice production with the same definition and scale globally, and review the polynya ice production and its relationship with dense/bottom water. The mapping demonstrates that ice production rate is high in Antarctic coastal Polynyas, in contrast to Arctic coastal Polynyas. This is consistent with the formation of Antarctic Bottom Water (AABW), the densest water mass which occupies the abyssal layer of the global ocean. The Ross Ice Shelf polynya has by far the highest ice production in the Southern Hemisphere. The Cape Darnley polynya (65°E–69°E) is found to be the second highest production area and recent observations revealed that this is the missing (fourth) source of AABW. In the region off the Mertz Glacier Tongue (MGT), the third source of AABW, sea-ice production decreased by as much as 40 %, due to the MGT calving in early 2010, resulting in a significant decrease in AABW production. The Okhotsk Northwestern polynya exhibits the highest ice production in the Northern Hemisphere, and the resultant dense water formation leads to overturning in the North Pacific, extending to the intermediate layer. Estimates of its ice production show a significant decrease over the past 30–50 years, likely causing the weakening of the North Pacific overturning. These regions demonstrate the strong linkage between variabilities of sea-ice production and bottom/intermediate water formation. The mapping has also provided surface boundary conditions and validation data of heat- and salt-flux associated with sea-ice formation/melting for various ocean and coupled models.
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mapping of sea ice production in the arctic coastal Polynyas
Journal of Geophysical Research, 2011Co-Authors: Takeshi Tamura, Kay I. OhshimaAbstract:[1] High ice production in coastal Polynyas over the continental shelves in the Arctic Ocean is responsible for the formation of cold saline water, which contributes to the maintenance of the Arctic Ocean halocline. The accurate detection of coastal Polynyas, including an estimate of thin ice thickness, is essential for the estimation of sea ice production. This paper presents an algorithm that estimates thin ice thickness using Special Sensor Microwave/Imager (SSM/I) data in the Arctic Ocean. Detection and estimation of sea ice thicknesses of <0.15 m are based on the SSM/I 85 and 37 GHz polarization ratios (PR85 and PR37) through a comparison with sea ice thicknesses estimated from the advanced very high resolution radiometer (AVHRR) data in the three different Arctic coastal Polynyas. Thus, for the entire Arctic Ocean, the algorithm can be used for the detection of coastal Polynyas and for the estimation of sea ice production through combination with heat-flux calculation. This study provides the first circumpolar mapping of sea ice production in coastal Polynyas over the entire Arctic Ocean. High ice production is confined to the major Arctic coastal Polynyas, with the highest ice production rate being in the North Water Polynya. This study also presents the interannual variability of sea ice production in the 10 major coastal Polynyas from 1992 to 2007. In general, interannual variability in sea ice production has good correlation with polynya extent rather than surface air temperature. The mapping also provides surface heat- and salt- flux conditions in the ice-covered region, which have not been well understood to date.
Takeshi Tamura - One of the best experts on this subject based on the ideXlab platform.
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coastal Polynyas winter oases for subadult southern elephant seals in east antarctica
Scientific Reports, 2018Co-Authors: Sophie Bestley, Sara Labrousse, G D Williams, Takeshi TamuraAbstract:Antarctic coastal Polynyas are regions of persistent open water and are thought to be key bio-physical features within the sea-ice zone. However, their use by the upper trophic levels of ecosystems remains unclear. A unique bio-physical dataset recorded by southern elephant seals reveals that East Antarctic Polynyas are a key winter foraging habitat for male seals. During their post-moult trips from Isles Kerguelen to the Antarctic continental shelf, a total of 18 out of 23 seals visited 9 different Polynyas, spending on average 25 ± 20% (up to 75%) of their total trip time inside Polynyas. Changes in seal foraging and diving behaviours are observed inside Polynyas as compared to outside Polynyas. Two polynya usages by seals are observed for the inactive and active polynya phases, pointing to different seasonal peaks in prey abundance. During the active polynya phase, we link seal foraging behaviour to changes in the physical stability of the water-column, which likely impact the seasonal biological dynamics within Polynyas.
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sea ice production in antarctic coastal Polynyas estimated from amsr2 data and its validation using amsr e and ssm i ssmis data
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2017Co-Authors: Sohey Nihashi, Kay I. Ohshima, Takeshi TamuraAbstract:Antarctic coastal Polynyas are very high sea-ice production areas. The resultant large amount of brine rejection leads to the formation of dense water. The dense water forms Antarctic bottom water, which is the densest water in the global overturning circulation and a key player in climate change as a significant sink for heat and carbon dioxide. In this study, an algorithm was developed that uses Advanced Microwave Scanning Radiometer 2 (AMSR2) data (2012–present) to detect polynya area and estimates thin ice thickness by a method similar to that used to develop the algorithm for Advanced Microwave Scanning Radiometer for EOS (AMSR-E) data. Landfast sea-ice areas were also detected using AMSR2 data. Ice production in the Polynyas was estimated by a heat flux calculation using AMSR2 sea-ice data. In four major Polynyas, AMSR2 ice production was compared with AMSR-E (2003–2011) ice production through comparison of them with Special Sensor Microwave Imager (SSM/I) and Special Sensor Microwave Imager/Sounder (SSMIS) ice production. The comparison confirmed that the ice production from AMSR-E/2 data, which have higher spatial resolution than SSM/I-SSMIS data, can be used to analyze time series covering more than 10 years. For example, maps of annual ice production based on AMSR-E/2 data revealed detailed changes of the Mertz Polynya, where the ice production decreased significantly after the Mertz Glacier Tongue calving in 2010. Continuous monitoring of the coastal Polynyas by the AMSR series sensors is essential for climate-change-related analyses in the Antarctic Ocean.
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mapping of sea ice production in the arctic coastal Polynyas
Journal of Geophysical Research, 2011Co-Authors: Takeshi Tamura, Kay I. OhshimaAbstract:[1] High ice production in coastal Polynyas over the continental shelves in the Arctic Ocean is responsible for the formation of cold saline water, which contributes to the maintenance of the Arctic Ocean halocline. The accurate detection of coastal Polynyas, including an estimate of thin ice thickness, is essential for the estimation of sea ice production. This paper presents an algorithm that estimates thin ice thickness using Special Sensor Microwave/Imager (SSM/I) data in the Arctic Ocean. Detection and estimation of sea ice thicknesses of <0.15 m are based on the SSM/I 85 and 37 GHz polarization ratios (PR85 and PR37) through a comparison with sea ice thicknesses estimated from the advanced very high resolution radiometer (AVHRR) data in the three different Arctic coastal Polynyas. Thus, for the entire Arctic Ocean, the algorithm can be used for the detection of coastal Polynyas and for the estimation of sea ice production through combination with heat-flux calculation. This study provides the first circumpolar mapping of sea ice production in coastal Polynyas over the entire Arctic Ocean. High ice production is confined to the major Arctic coastal Polynyas, with the highest ice production rate being in the North Water Polynya. This study also presents the interannual variability of sea ice production in the 10 major coastal Polynyas from 1992 to 2007. In general, interannual variability in sea ice production has good correlation with polynya extent rather than surface air temperature. The mapping also provides surface heat- and salt- flux conditions in the ice-covered region, which have not been well understood to date.
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thickness and production of sea ice in the okhotsk sea coastal Polynyas from amsr e
Journal of Geophysical Research, 2009Co-Authors: Sohey Nihashi, Takeshi Tamura, Kay I. Ohshima, Yasushi Fukamachi, Seiichi SaitohAbstract:[1] From comparisons with thickness of sea ice from Advanced Very High Resolution Radiometer (AVHRR) and ice-profiling sonar data we have developed an Advanced Microwave Scanning Radiometer-EOS (AMSR-E) thin ice thickness algorithm for the Sea of Okhotsk. This algorithm can estimate ice thickness of ≤0.2 m without snow using the polarization ratio of AMSR-E brightness temperature at a 36.5 GHz channel from a linear relationship with AVHRR ice thickness. When a snow cover exists on the thin ice surface, as occurred a few times in each winter, it is shown that the algorithm cannot detect the thin ice. Sea ice and dense shelf water (DSW) production in coastal polynya are estimated on the basis of heat flux calculation with the daily AMSR-E ice thickness for three winters (December–March) of 2002–2003 to 2004–2005. The ice production is largest in the northwest shelf (NWS) polynya which accounts for ∼45% of the sum of ice production in major coastal Polynyas. The ice production in major coastal Polynyas would cover the maximum ice area of the Okhotsk Sea if the average ice thickness is assumed to be 1 m. Variability of the ice production is mainly modulated by air temperature. In the NWS polynya, which is the main DSW production area, the annual DSW formation rate is estimated to be ∼0.36 Sv.
Sophie Bestley - One of the best experts on this subject based on the ideXlab platform.
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coastal Polynyas winter oases for subadult southern elephant seals in east antarctica
Scientific Reports, 2018Co-Authors: Sophie Bestley, Sara Labrousse, G D Williams, Takeshi TamuraAbstract:Antarctic coastal Polynyas are regions of persistent open water and are thought to be key bio-physical features within the sea-ice zone. However, their use by the upper trophic levels of ecosystems remains unclear. A unique bio-physical dataset recorded by southern elephant seals reveals that East Antarctic Polynyas are a key winter foraging habitat for male seals. During their post-moult trips from Isles Kerguelen to the Antarctic continental shelf, a total of 18 out of 23 seals visited 9 different Polynyas, spending on average 25 ± 20% (up to 75%) of their total trip time inside Polynyas. Changes in seal foraging and diving behaviours are observed inside Polynyas as compared to outside Polynyas. Two polynya usages by seals are observed for the inactive and active polynya phases, pointing to different seasonal peaks in prey abundance. During the active polynya phase, we link seal foraging behaviour to changes in the physical stability of the water-column, which likely impact the seasonal biological dynamics within Polynyas.
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Bio-physical characterisation of Polynyas as a key foraging habitat for juvenile male southern elephant seals (Mirounga leonina) in Prydz Bay, East Antarctica
PLoS ONE, 2017Co-Authors: Veda Malpress, Sophie Bestley, Sara Labrousse, Stuart Corney, Dirk Welsford, Michael Sumner, Mark A. HindellAbstract:Antarctic coastal Polynyas are persistent open water areas in the sea ice zone, and regions of high biological productivity thought to be important foraging habitat for marine predators. This study quantified southern elephant seal (Mirounga leonina) habitat use within and around the Polynyas of the Prydz Bay region (63˚E– 88˚E) in East Antarctica, and examined the bio-physical characteristics structuring Polynyas as foraging habitat. Output from a cli-matological regional ocean model was used to provide context for in situ temperature-salin-ity vertical profiles collected by tagged elephant seals and to characterise the physical properties structuring Polynyas. Biological properties were explored using remotely-sensed surface chlorophyll (Chl-a) and, qualitatively, historical fish assemblage data. Spatially gridded residence time of seals was examined in relation to habitat characteristics using generalized additive mixed models. The results showed clear polynya usage during early autumn and increasingly concentrated usage during early winter. Bathymetry, Chl-a, surface net heat flux (representing polynya location), and bottom temperature were identified as significant bio-physical predictors of the spatio-temporal habitat usage. The findings from this study confirm that the most important marine habitats for juvenile male southern elephant seals within Prydz Bay region are Polynyas. A hypothesis exists regarding the seasonal evolution of primary productivity, coupling from surface to subsurface productivity and supporting elevated rates of secondary production in the upper water column during summer autumn. An advancement to this hypothesis is proposed here, whereby this bio-physical coupling is likely to extend throughout the water column as it becomes fully convected during autumn-winter, to also promote pelagic-benthic linkages important for benthic foraging within Polynyas.
Eun Jin Yang - One of the best experts on this subject based on the ideXlab platform.
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a unique benthic microbial community underlying the phaeocystis antarctica dominated amundsen sea polynya antarctica a proxy for assessing the impact of global changes
Frontiers in Marine Science, 2020Co-Authors: Hyeyoun Cho, Jong-geol Kim, Chung Yeon Hwang, Sanghoon Kang, Katrin Knittel, Ayeon Choi, Sunghan Kim, Sungkeun Rhee, Eun Jin YangAbstract: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 (Corg) content in the polynya sediment underlying the Phaeocystis-dominated water column. These results suggest that Planctomycetes comprise a major bacterial group utilizing relatively recalcitrant Corg produced primarily by Phaeocystis blooms. In contrast, the predominance of chemolithoautotrohic Thaumarchaeota in the sea-ice zone was attributed to low Corg 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 Gammaproteobacteria) 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, and that global climate change is proceeding rapidly in the ASP, our results suggest that any modifications in the Planctomycetes-dominated microbial communities will provide valuable insight into changes in organic matter transport to the seafloor that may result from shifts in planktonic communities from Phaeocystis to diatoms associated with climate change.
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Genomic and metatranscriptomic analyses of carbon remineralization in an Antarctic polynya
BMC, 2019Co-Authors: So-jeong Kim, Eun Jin Yang, Sanghoon Lee, Jong-geol Kim, Soo-je Park, Joo-han Gwak, Man-young Jung, Won-hyung Chung, Jisoo Park, Jinyoung JungAbstract:Abstract 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
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light availability rather than fe controls the magnitude of massive phytoplankton bloom in the amundsen sea Polynyas antarctica
Limnology and Oceanography, 2017Co-Authors: Jisoo Park, Eun Jin Yang, Sanghoon Lee, Fedor I Kuzminov, Benjamin Bailleul, Paul G Falkowski, Maxim Y GorbunovAbstract:Amundsen Sea Polynyas are among the most productive, yet climate-sensitive ecosystems in the Southern Ocean and host massive annual phytoplankton blooms. These blooms are believed to be controlled by iron fluxes from melting ice and icebergs and by intrusion of nutrient-rich Circumpolar Deep Water, however the interplay between iron effects and other controls, such as light availability, has not yet been quantified. Here, we examine phytoplankton photophysiology in relation to Fe stress and physical forcing in two largest Polynyas, Amundsen Sea Polynya (ASP) and Pine Island Polynya (PIP), using the combination of high-resolution variable fluorescence measurements, fluorescence lifetime analysis, photosynthetic rates, and Fe-enrichment incubations. These analyses revealed strong Fe stress in the ASP, whereas the PIP showed virtually no signatures of Fe limitation. In spite of enhanced iron availability in the PIP, chlorophyll biomass remained ∼ 30–50% lower than in the Fe-stressed ASP. This apparent paradox would not have been observed if iron were the main control of phytoplankton bloom in the Amundsen Sea. Long-term satellite-based climatology records revealed that the ASP is exposed to significantly higher solar irradiance levels throughout the summer season, as compared to the PIP region, suggesting that light availability controls the magnitude of phytoplankton blooms in the Amundsen Sea. Our data suggests that higher Fe availability (e.g., due to higher melting rates of ice sheets) would not necessarily increase primary productivity in this region. Furthermore, stronger wind-driven vertical mixing in expanding ice-free areas may lead to reduction in light availability and productivity in the future.
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pelagic ciliate communities within the amundsen sea polynya and adjacent sea ice zone antarctica
Deep-sea Research Part Ii-topical Studies in Oceanography, 2016Co-Authors: Yong Jiang, Qian Liu, Eun Jin Yang, Min Wang, Taewan Kim, Kyoungho Cho, Sanghoon LeeAbstract:Abstract Polynyas, areas of open water surrounded by sea ice, are sites of intense primary production and ecological hotspots in the Antarctic Ocean. This study determined the spatial variation in communities of pelagic ciliates in an Amundsen Sea polynya (ASP) and adjacent sea ice zones (SIZ) during austral summer from February to March 2012, and the results were compared with biotic and abiotic environmental factors. The species number, abundance and biomass were higher in the ASP than SIZ. Canonical analysis indicated that the communities in the ASP were distinct from those under the sea ice. The pelagic ciliate community structure was closely correlated with environmental variability. Several primary environmental variables, both alone and in combination, were found to affect community spatial patterns. The ciliate biomasses in the ASP and SIZ areas were both significantly correlated with total and nano-Chl a. This analysis of the ciliated microzooplankton communities associated with high primary production provides new insights into the roles of ciliates in biogeochemical cycles in high-latitude Polynyas. Additionally, our findings provide detailed data on the composition, distribution, and structure of polynya ciliate communities in the Amundsen Sea.
Seelye Martin - One of the best experts on this subject based on the ideXlab platform.
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ross sea Polynyas response of ice concentration retrievals to large areas of thin ice
Journal of Geophysical Research, 2007Co-Authors: R Kwok, Seelye Martin, Josefino C Comiso, Robert DruckerAbstract:[1] For a 3-month period between May and July of 2005, we examine the response of the Advanced Microwave Scanning Radiometer (AMSR-E) Enhanced NASA Team 2 (NT2) and AMSR-E Bootstrap (ABA) ice concentration algorithms to large areas of thin ice of the Ross Sea Polynyas. Coincident Envisat Synthetic Aperture Radar (SAR) coverage of the region during this period offers a detailed look at the development of the Polynyas within several hundred kilometers of the ice front. The high-resolution imagery and derived ice motion fields show bands of polynya ice, covering up to ∼105 km2 of the Ross Sea, that are associated with wind-forced advection. In this study, ice thickness from AMSR-E 36 GHz polarization information serves as the basis for examination of the response. The quality of the thickness of newly formed sea ice (<10 cm) from AMSR-E is first assessed with thickness estimates derived from ice surface temperatures from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument. The effect of large areas of thin ice in lowering the ice concentration estimates from both NT2/ABA approaches is clearly demonstrated. Results show relatively robust relationships between retrieved ice concentrations and thin ice thickness estimates that differ between the two algorithms. These relationships define the approximate spatial coincidence of ice concentration and thickness isopleths. Using the 83% (ABA) and 91% (NT2) isopleths as polynya boundaries, we show that the computed coverage compares well with that using the estimated 10-cm thickness contour. The thin ice response characterized here suggests that in regions with Polynyas, the retrieval results could be used to provide useful geophysical information, namely thickness and coverage.
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the areas and ice production of the western and central ross sea Polynyas 1992 2002 and their relation to the b 15 and c 19 iceberg events of 2000 and 2002
Journal of Marine Systems, 2007Co-Authors: Seelye Martin, Robert Drucker, R KwokAbstract:Abstract For 1992–2002, the paper investigates the heat loss and area of three Polynyas in the western and central Ross Sea. These are the Ross Sea Polynya (RSP) and the much smaller Terra Nova Bay and McMurdo Sound Polynyas. The importance of these Polynyas is that their associated salt rejection contributes to the formation of the High Salinity Shelf Water (HSSW) that is crucial to the Antarctic Bottom Water formation. The study divides into two parts, 1992–1999, when there was negligible iceberg activity, and 2000–2002, when major icebergs calved and interacted with the Polynyas. To retrieve the ice thicknesses and heat fluxes within the Polynyas, the paper uses an algorithm based on the ratio of the vertically and horizontally polarized Special Sensor Microwave/Imager (SSM/I) 25-km resolution 37-GHz channels, combined with meteorological data. Because of sidelobe contamination, the ice shelf and icebergs are masked. Our results show that for the Polynyas, and consistent with other observations, their mean winter area is about 30,000 km 2 and their combined ice production is about 500 km 3 y − 1 . We also find that the polynya ice production approximately equals the ice export. This is in contrast to the Weddell Sea, where the polynya ice production equals about 6% of the ice export. For the years 2000 and 2002, the calving of large icebergs directly affect the ice production by inhibiting the ice production off the shelf due to piling up of first year ice upwind of the bergs and by generating new Polynyas downwind of the bergs. The period 1992–2001 exhibits an upward trend in polynya productivity. The decadal increase in the ice production suggests that the observed HSSW salinity decrease in the western Ross Sea is not due to the Polynyas, but is rather due to a change in the properties of the water flowing into the Ross.
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improvements in the estimates of ice thickness and production in the chukchi sea Polynyas derived from amsr e
Geophysical Research Letters, 2005Co-Authors: Seelye Martin, Robert Drucker, R Kwok, Benjamin HoltAbstract:For January-March 2003, we use 12.5-km resolution Advanced Microwave Scanning Radiometer (AMSR) data for the first time in a comparison with Synthetic Aperture Radar (SAR) and Special Sensor Microwave/Imager (SSM/I) data to study two Chukchi coast Polynyas, one consisting of many, the other of only a few 25-km SSM/I pixels. Within these Polynyas, the ice thicknesses are derived separately from the SMM/I 37-GHz and AMSR 36-GHz channels; the heat fluxes are derived by combining thicknesses with meteorological data. Comparison with ScanSAR data shows that for the large polynya, because AMSR provides better resolution of the surrounding coastline and first-year ice, the AMSR heat losses are greater than the SSM/I; for the small polynya, AMSR measures its variability even when its area is order of a single SSM/I pixel. This means that AMSR permits more accurate calculation of polynya heat losses, yielding the potential of improved estimates of Arctic polynya productivity.
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estimation of the thin ice thickness and heat flux for the chukchi sea alaskan coast polynya from special sensor microwave imager data 1990 2001
Journal of Geophysical Research, 2004Co-Authors: Seelye Martin, Robert Drucker, R Kwok, Benjamin HoltAbstract:[1] One of the largest Arctic Polynyas occurs along the Alaskan coast of the Chukchi Sea between Cape Lisburne and Point Barrow. For this polynya, a new thin ice thickness algorithm is described that uses the ratio of the vertically and horizontally polarized Special Sensor Microwave/Imager (SSM/I) 37-GHz channels to retrieve the distribution of thicknesses and heat fluxes at a 25-km resolution. Comparison with clear-sky advanced very high resolution radiometer data shows that the SSM/I thicknesses and heat fluxes are valid for ice thicknesses less than 10–20 cm, and comparison with several synthetic aperture radar (SAR) images shows that the 10-cm ice SSM/I ice thickness contour approximately follows the SAR polynya edge. For the twelve winters of 1990–2001, the ice thicknesses and heat fluxes within the polynya are estimated from daily SSM/I data, then compared with field data and with estimates from other investigations. The results show the following: First, our calculated heat losses are consistent with 2 years of over-winter salinity and temperature field data. Second, comparison with other numerical and satellite estimates of the ice production shows that although our ice production per unit area is smaller, our polynya areas are larger, so that our ice production estimates are of the same order. Because our salinity forcing occurs over a larger area than in the other models, the oceanic response associated with our forcing will be modified. INDEX TERMS: 4540 Oceanography: Physical: Ice mechanics and air/sea/ice exchange processes; 3360 Meteorology and Atmospheric Dynamics: Remote sensing; 4504 Oceanography: Physical: Air/sea interactions (0312); 4572 Oceanography: Physical: Upper ocean processes; 4207 Oceanography: General: Arctic and Antarctic oceanography; KEYWORDS: Chukchi Sea, coastal polynya, remote sensing
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the production of ice and dense shelf water in the okhotsk sea Polynyas
Journal of Geophysical Research, 1998Co-Authors: Seelye Martin, Robert Drucker, Kohji YamashitaAbstract:This paper examines the ice and dense water production in the Okhotsk Sea coastal Polynyas for the 1990–1995 winters. The dominant Polynyas occur on the northwest and northern shelves and in Shelikhov Bay. We use an algorithm developed for the special sensor microwave/imager (SSM/I) to derive for each polynya the area and composition of thin ice and open water and a heat flux algorithm to derive the ice and brine production. Historic oceanographic observations show that the northwest shelf is the only North Pacific region where the σϑ = 26.8 potential density surface outcrops to the surface and is also that part of the Okhotsk shelf where the densest water is observed to occur. In support of these observations, we find that the northwest shelf polynya is the dominant ice and brine producer, contributing on average about 55% of the total production. Shelikhov Bay is the second largest producer with about 25% of the total; this region has been previously neglected by both oceanographic and remote sensing studies. Using a combination of two dense water production models, we find that the 6 year average dense water production lies between 0.2–0.4 Sv. The ice and brine production for the dominant northwest shelf vary interannually by a factor of 3, while the production from all the northern Polynyas varies by factor of 2. The source of the variability for the northwest shelf comes from the fact that the southwest-to-northeast trend of the coastline and the mean winter geostrophic wind velocities are roughly parallel, which means that small variations in the wind direction yield large changes in the ice production.
