Publications
For the abstract, please click the title🖱️
21. Radiocarbon research on meltwater and carbon cycling in the polar oceans in a changing climate
19. Empowering Early Career Polar Researchers in a changing climate: Challenges and solutions
16. Carbon cycling in the East Sea (Japan Sea): A review
15. Current Status and Prospects Regarding Radiocarbon Studies in the East Sea
11. Lithogenic Particle Transport Trajectories on the Northwest Atlantic Margin
10. Lateral particle supply as a key vector in the oceanic carbon cycle
8. Collection of large benthic invertebrates in sediment traps in the Amundsen Sea, Antarctica
4. Sedimentation of particulate organic carbon on the Amundsen Shelf, Antarctica
3. Sinking particle flux in the sea ice zone of the Amundsen Shelf, Antarctica
2. Temporal and spatial variability of particle transport in the deep Arctic Canada Basin
Abstracts
Tracing freshwater sources and particle discharge in Kongsfjorden: insights from a water isotope approach
Ling Fang, Eun Jin Yang, Junho Yoo, Minkyoung Kim*
(2024, Front. Mar. Sci.)
Arctic fjords are inherently vulnerable to global warming, particularly because of the substantial freshwater influx resulting from the melting of glaciers. In this study, precipitation, river water, surface ice, and seawater samples from Kongsfjorden were collected to identify the main sources of freshwater. The dual water isotope (δ18O and δD) results and temperature–salinity profiles revealed that between 0% and 7% freshwater contributed to the fjord’s water. Furthermore, different freshwater sources for surface and deep water were identified by the dual water isotope analysis. Turbidity profiles confirmed the alter in particle discharge associated with surface runoff and subglacial discharge. Our study highlighted the sensitivity of water isotope analysis in elucidating the hydrological processes within the fjord system and demonstrated its potential for investigating the impact of meltwater on biological processes in the Arctic.
Statistical analysis of the association between El Niño and the biological carbon pump in the East Sea (Japan Sea)
Geunsoo Jang, Seunghyun Hong, Janghun Oh, Young-Il Kim, Minkyoung Kim*, Hyojung Lee*
(2024, Scientific Reports)
Understanding the impacts of climate change on oceanic carbon cycling is important from a carbon sequestration perspective. A sediment trap study focused on the biological carbon pump system in the Ulleung Basin (UB) in the southwestern part of the East Sea (Japan Sea) was conducted from 2011to 2017. Particulate organic carbon (POC) flux significantly increased by 37, 56, and 43% from 2014 to 2016 during the El Niño phase. We examined data related to water current variability, such as sea surface height, current velocity, and eddy frequency to understand their roles in particle transport. In addition, a Martin curve was employed to analyze the rate of vertical attenuation of POC flux in the UB. Current variability could be the most important factor influencing the increase in sinking-particle flux during the El Niño phase.
Mapping the evolution of marine carbon during the last deglaciation: δ13C perspectives on the deglacial ocean carbon cycle
Ling Fang, Ninglian Wang, Minkyoung Kim*
(2024, Earth-Science Reviews)
The changes in the ocean circulation and biological pump played crucial roles in the rise in atmospheric CO2 during the last deglaciation. However, our understanding remains limited regarding which processes―air-sea exchange, ocean circulation, and the biological pump―primarily influence the spatial dynamics of the oceanic carbon cycle. To address this knowledge gap, the present study compiles global stable carbon isotope (δ13C) records from various sources, including shallow and deep planktic, along with epifaunal and infaunal benthic foraminifera. The synthesis reveals a total increase of 0.37 ± 0.05 ‰ in marine δ13C values since the last glacial maximum. Of this increase, 68 ± 5 % is attributed to the response of the oceans in the southern hemisphere, while 32 ± 4 % is attributed to the northern hemisphere. By analyzing the difference between planktic and benthic foraminifera, a decreased vertical δ13C gradient (δ13Csp–sb) is observed during the last deglaciation, indicating rapid carbon exchange between surface and deep waters during deglaciation. Additionally, the offset between the epifaunal and infaunal δ13C (δ13Csb–db) provides insights into changes in productivity and bottom water oxygenation. Overall, the global synthesis suggests that the δ13C variation is largely controlled by ocean circulation in the northern hemisphere and at higher latitudes of the southern hemisphere, while primary production significantly influences subtropical regions. Furthermore, the δ13C confirms that the rise in atmospheric CO2 during the first phase of Heinrich Stadial 1 (HS1) resulted from reduced primary production in subtropical regions along with strong ventilation in the second phase of HS1. Interestingly, the δ13C variations during the Younger Dryas (YD) suggest strong ventilation without evident changes in primary production. This four-dimensional dataset provides valuable insights into the transient changes in the ocean carbon cycle during deglaciation.
Radiocarbon research on meltwater and carbon cycling in the polar oceans in a changing climate
Ling Fang, Hojung Kim, DongHui Shangguan, Minkyoung Kim*
(2024, Mar. Chem.) (MKim invited review)
Radiocarbon (14C) is a widely used tool with applications that transcend disciplinary boundaries, including the marine chemistry field. The development of 14C measurement techniques and icebreaking research vessels especially encourage and support polar research using 14C. Research examining 14C in polar oceans in the context of climate change has led to considerable insight into the marine carbon cycle. A comprehensive review of the principles, applications, progress, and challenges of 14C will undoubtedly advance related polar research. This review compiled available literature on 14C in the polar oceans and summarizes current progresses in carbon cycling, glacial and ice sheet dynamics, water circulation, and ventilation. The impact of warming induced melting sea ice and glaciers on marine biogeochemical cycles, future environmental challenges and research directions have also been summarized. The limitations of existing 14C research in polar regions can be addressed through well-designed and continuous investigation, data and sample sharing, and the development of state-of-the-art 14C measurement techniques.
Spatiotemporal variation of sterols in sediment as markers of primary production and ocean sewage dumping in the southwestern East Sea (Japan Sea)
Minkyoung Kim, Jeomshik Hwang, Daniel B. Montluçon, Negar Haghipour, Dongyoung Kim, Ho Jung Kim, Ki Young Choi, Chang Joon Kim, Chang-Keun Kang, Young-Il Kim, Timothy I. Eglinton
(2024, Mar. Pollut. Bull.)
The sedimentation of organic carbon in the Ulleung Basin, in the southwestern East Sea (Japan Sea) was investigated using radiocarbon and sterols. The accumulation rates of organic carbon and the contents of brassicasterol and dinosterol were higher on the slope than in the central basin, reflecting the surface water productivity, whereas cholesterol showed similar or higher contents in the central basin. The coprostanol concentration in surface sediments reflected the dispersion of sewage dumped in this region. The vertical distribution showed that the coprostanol concentration was the highest in the top 5-cm layer near the Korea Strait, close to one of the two dumping sites. A high coprostanol concentration was also found near the coast further north, where the content peaked at ∼10 cm depth. The vertical distribution of coprostanol helped to estimate the sediment accumulation rate at sites where radiocarbon gradient was too small or the values were too variable.
Empowering Early Career Polar Researchers in a changing climate: Challenges and solutions
Adina Moraru, Filippo Calì Quaglia, Minkyoung Kim, Adrián López-Quirós, Howard M. Huynh
(2024, PLOS Climate)
Climate change is rapidly reshaping the research landscape in the polar regions. As such, Early Career Researchers (ECRs) face increasingly daunting challenges. These challenges include international and institutional competition for funding, shifting research demands and priorities, limited data sharing, and the need for strong mentorship.....
Holocene Palaeoenvironmental and Palaeoproductivity Changes in the Western Amundsen Sea Embayment of Antarctica
Minkyoung Kim, Jae Il Lee, Young-Suk Bak, Claus-Dieter Hillenbrand, Eun Jin Yang, Daniel B. Montluçon, Negar Haghipour,
Timothy I. Eglinton, Jeomshik Hwang
(2023, JGR-Oceans)
The Amundsen Polynya (AP) on the inner and middle continental shelf of the western Amundsen Sea Embayment is the fourth largest coastal polynya around Antarctica. The AP is highly productive when it opens in austral summer, with ∼20 times greater organic carbon accumulation rates over the last few thousand years compared to those at nearby shelf sites with more persistent seasonal sea-ice cover. We examined sedimentary records at a site from the AP and another site from the outer shelf to investigate temporal variations in the depositional environment with a special focus on the timing of the AP opening since the deglaciation following the Last Glacial Maximum (LGM; ca. 23–19 cal. ka BP). In the AP region, sedimentological and biogeochemical proxy data reveal a transition from a sub-glacial to a sub-ice shelf and then seasonally open marine conditions comparable to those at present. Total organic carbon contents and diatom valve abundances during the seasonally open marine period imply that the polynya environments was reached at ca. 9.2 cal. ka BP. Since the post-LGM deglaciation, diatom productivity and assemblages in the AP region appear to have varied in association with the variation in the physical environment. Compared to the AP site, only small amounts of organic carbon accumulated on the outer shelf. Differences in the depositional environments and productivity modes between the inner and outer shelf sites have persisted since ca. 10.5 cal. ka BP.
Radiocarbon Constraints on Carbon Release From the Antarctic Ice Sheet Into the Amundsen Sea Embayment
Ling Fang and Minkyoung Kim*
(2023, JGR-Biogeosciences)
The Amundsen Sea Embayment in West Antarctica is experiencing rapid ice mass loss, resulting in biogeochemical changes via altered nutrient and organic matter supply. However, organic carbon released from melting ice has not yet been accurately quantified. In this paper, we have integrated new dissolved organic carbon (DOC) data obtained close to the melting Dotson Ice Shelf (DIS) with published radiocarbon (Δ14C) data on sinking and suspended particulate organic carbon (POC), sedimentary OC, DOC and dissolved inorganic carbon to quantify the effect of ice melt to the carbon cycle. Elevated DOC concentrations in deep water near the DIS indicate the transport of carbon sources from the ice shelf to the water column at a rate of 4.6 ± 2.0 × 1010 g C yr−1. Furthermore, Δ14C-DOC measurements suggest there is a possible dark chemoautotrophic production under the influence of meltwater input. The vertical profile of Δ14C in the sedimentary OC from the Sea Ice Zone and the edge of the DIS demonstrates the presence of aged organic carbon sources during warm episodes at ∼11.5 and 15.9 ka BP. Our study indicates that deep water is not only affected by OC discharge from meltwater but also by biological processes due to altered nutrient inputs. Limited data hampers a precise assessment of the influence of meltwater on the carbon cycle. Further sampling in front of the DIS will be beneficial to enhance our understanding of the role of Antarctic Ice Sheet melting in the downstream ecosystem.
Carbon cycling in the East Sea (Japan Sea): A review
Minkyoung Kim, Jeomshik Hwang, Guebuem Kim, Taehee Na, Tae-Hoon Kim, Jung-Ho Hyun
(2022, Frontiers in Marine Science)
The East Sea (also known as the Japan Sea; hereafter, EJS) is a semi-enclosed marginal sea surrounded by the Korean Peninsula, Russia, and the Japanese Islands. The EJS is connected to the Pacific through shallow straits. Thus, the EJS has its own thermohaline circulation and the characteristic biogeochemistry. The deep overturning circulation plays a critical role in carbon cycling including absorption of atmospheric CO2 and its sequestration into the interior of the sea. The turnover time of the deep EJS (>1000 m) is ~ hundred years and probably varies depending on physical climate forcing. Thus, the effect of climate change on oceanic processes may be more easily detected in the EJS. In this paper, we summarize the current understanding of carbon cycling in the EJS. We focus especially on the Ulleung Basin in the southwestern EJS, from which more extensive data are available. Notable features of carbon cycling in the EJS include the following: primary productivity and the export/production ratio are higher than in the adjacent Pacific; the EJS is a net sink of atmospheric CO2 and anthropogenic CO2 content is ~1% of the dissolved inorganic carbon inventory; dissolved inorganic carbon in the sea interior is mostly supplied by organic matter decomposition rather than CaCO3 dissolution and thus, the deep waters are vulnerable to acidification; N:P molar ratio of the deep waters is ~13, lower than the Redfield ratio; concentration of dissolved organic carbon is significantly higher than in the oceans; and sediment resuspension and lateral transport is an important component of sinking particulate organic carbon (POC) flux. Another important feature is the temporal trends observed for the last few decades. For example, pH, calcium carbonate saturation status, and dissolved oxygen concentration in the sea interior have decreased, whereas dissolved inorganic carbon and likely, the inventory of anthropogenic CO2 have increased. These temporal trends have an implication on better understanding of the processes occurring more slowly in the oceans. Brief suggestions for future research that will improve our understanding of carbon cycling and its variability are provided at the end of the paper.
Current Status and Prospects Regarding Radiocarbon Studies in the East Sea
Minkyoung Kim
(2022, Ocean and Polar Reseasrch (in Korean))
Together with the development of measurement techniques, radiocarbon (14C) has been increasingly used as a key tool to investigate carbon cycling and associated biogeochemistry in the ocean. In this paper, the current status of radiocarbon studies in the East Sea (Japan Sea) is reviewed. Previously, spatiotemporal distribution and change of the water masses in the East Sea from 1979 to 1999 were investigated by using the 14C in the dissolved inorganic carbon (DIC). Researches on sinking particulate organic carbon (POC) revealed that POC in the deep ocean has more complex and heterogeneous origins than we expected. In particular, since 2011, Korean researchers have been collecting sinking particle samples for more than 10 years, so it is expected that 14C of POC will provide important information to understand carbon cycling in relation to climate change. Although the quantity of 14C data published in the East Sea is still limited, the importance and the future direction of using 14C to understand the biogeochemical mechanisms of carbon cycling and its role as a carbon reservoir in the East Sea are detailed herein.
Decadal Observation and Studies in the Amundsen Sea, Antarctica: Insights from Radiocarbon Values
Minkyoung Kim
(2022, Ocean and Polar Reseasrch (in Korean))
The Amundsen Sea in West Antarctica is one of the most affected regions by climate change, but it is one of the least studied realms due to difficulties in access. Korea Polar Research Institute (KOPRI) launched a research project in the Amundsen Sea in 2010 using the icebreaker research vessel (IBRV) Araon and has been conducting various research initiatives. In this paper, previous researches derived from the Amundsen Sea Embayment by Korean researchers are introduced. Through previous studies, researchers have been able to interpret the environmental and biogeochemical changes according to the inflow Circumpolar Deep Water (CDW) and provide information for climate models. In particular, researches using radiocarbon isotopes (14C) were introduced to understand the physical and biogeochemical mechanisms of the carbon cycle in the Amundsen Sea. Opportunely, with the construction of a second icebreaker research vessel, the direction for systematic and long-term polar data acquisition can be presented.
Characteristics of sediment resuspension on a deep abyssal plain in the Eastern Tropical Pacific Ocean
Minkyoung Kim, Hyung Jeek Kim, Ara Ko, Chan Min Yoo, Se-Jong Ju, Jeomshik Hwang
(2021, Journal of Sea Research)
We examined the biogenic and lithogenic particle composition and radiocarbon content of sinking particulate organic carbon to investigate sediment resuspension and its contribution to sinking particles on the deep abyssal plain of the Eastern Tropical Pacific Ocean. Samples were collected using sediment traps from August 2011 to July 2012 at depths of 4500 and 4950 m (50 m above the seafloor); above and within the benthic nepheloid layer (BNL), respectively. Biogenic particles derived from export production were the major source of sinking particles and their flux showed a unimodal temporal distribution, with larger values between February and April. At a depth of 4500 m, the lithogenic material flux was slightly greater than, or similar to, the flux of atmospheric dust deposition. In comparison, lithogenic material and excess Mn consistently showed a greater contribution to resuspended particles at 4950 m. The lithogenic material flux was proportional to the biogenic flux. These observations imply that resuspended particles exist at a background concentration in the BNL throughout the year, and are scavenged by sinking biogenic particles, especially during the high flux period.
Sediment Trap Studies to Understand the Oceanic Carbon Cycling: Significance of Resuspended Sediments
Minkyoung Kim
(2021, The Sea (in Korean))
For several decades, sediment traps have served as one of the key tools for constraining the biological carbon pump (BCP), a process that vertically exports particulate organic carbon (POC) and associated biogenic materials from marine primary production in surface waters to the deep ocean interior. In this paper, I introduced the general methods, the current status of global sediment trap studies, and importance of it to understand the deep ocean carbon cycling. Recent studies suggest that sinking POC in the deep ocean are more complex and spatio-temporally heterogeneous than we considered. Especially researches those studied resuspended and laterally transported particles are presented. Researches that used organic (radiocarbon; 14C) and inorganic (Al) tracers to understand the oceanic POC cycling and the significance of resuspended particles are reviewed, and the importance of radiocarbon study by using MICADAS (Mini radioCarbon Dating Systems) is emphasized.
Lithogenic Particle Transport Trajectories on the Northwest Atlantic Margin
Jeomshik Hwang, Jurek Blusztajn, Liviu Giosan, Minkyoung Kim, Steven J. Manganini, Daniel Montluçon, John M. Toole, Timothy I. Eglinton
(2020, Journal of Geophysical Research)
The neodymium isotopic composition of the detrital (lithogenic) fraction (εNd‐detrital) of surface sediments and sinking particles was examined to constrain transport trajectories associated with hemipelagic sedimentation on the northwest Atlantic margin. The provenance of resuspended sediments and modes of lateral transport in the water column were of particular interest given the energetic hydrodynamic regime that sustains bottom and intermediate nepheloid layers over the margin. A large across‐margin gradient of ∼5 εNd units was observed for surface sediments, implying strong contrasts in sediment provenance, with εNd‐detrital values on the lower slope similar to those of “upstream regions” (Scotian margin) under the influence of the Deep Western Boundary Current (DWBC). Sinking particles collected at three depths at a site (total water depth, ∼3,000 m) on the New England margin within the core of the DWBC exhibited a similarly large range in εNd‐detrital values. The εNd‐detrital values of particles intercepted at intermediate water depths (1,000 and 2,000 m) were similar to each other but significantly higher than those at 3,000 m (∼50 m above the seafloor). These observations suggest that lithogenic material accumulating in the upper two traps was primarily advected in intermediate nepheloid layers emanating from the adjacent shelf, while that at 3,000 m is strongly influenced by sediment resuspension and along‐margin, southward lateral transport within the bottom nepheloid layer via entrainment in the DWBC. Our results highlight the importance of both along‐ and across‐margin sediment transport as vectors for lithogenic material and associated organic carbon transport.
Lateral particle supply as a key vector in the oceanic carbon cycle
Minkyoung Kim, Jeomshik Hwang, Timothy I. Eglinton and Ellen R. M. Druffel
(2020, Global Biogeochemical Cycles)
The export of particulate organic carbon (POC) from surface waters to the ocean interior via the biological carbon pump is largely envisioned as a vertical process. However, several lines of evidence suggest that lateral supply of aged organic matter hosted on lithogenic particles derived from sediment resuspension may also be a significant process. Despite its potential importance, lateral POC supply has not been systematically examined on a global scale. Here, we assess the contribution of resuspended sediment to sinking particulate matter in the ocean using literature data of sediment trap studies. Proportions and absolute fluxes of lithogenic material at 158 sites and available radiocarbon contents are compiled to develop a global-scale assessment. We find that lithogenic material accounts for 25±20 % of sinking particulate matter, comprising a mean flux of 67 mg m-2d-1. Lithogenic material flux generally decreased with increasing distance from the coast, and with increasing height above the seafloor. The Δ14C values of POC exhibited a linear relationship with a wt/wt ratio of lithogenic material to POC. Loadings of aged POC to lithogenic material obtained from this relationship were similar to or higher than POC content of the surface sediment in the vicinity. Based on this relationship, and the global mean of lithogenic material content of sinking particulate matter, we calculate that aged POC from sediment resuspension comprises 0.2-0.7 % of sinking particles, and 4-11 % of sinking POC intercepted by sediment traps.
Influence of Sediment Resuspension on the Biological Pump of the Southwestern East Sea (Japan Sea)
Minkyoung Kim, Young-Il Kim, Jeomshik Hwang, Ki Young Choi, Chang Joon Kim, Yeongjin Ryu, Ji-Eun Park, Kyung-Ae Park, Jae-Hyoung Park, SungHyun Nam, Negar Haghipour and Timothy I. Eglinton
(2020, Frontiers in Earth Science)
The biological carbon pump in the southwestern East Sea (Japan Sea, EJS hereafter) was investigated based on examination of sinking particulate matter samples intercepted by bottom-tethered sediment traps deployed on a mooring at three depths (500, 1000, and 2000 m) between 2011 and 2017. The total particle flux increased as the sampling depth increased, while particulate organic carbon (POC) flux was greatest at 500 m. The lithogenic material content was high at all depths, and accounted for an average of ∼42% of the particulate matter. The total particle flux at all sampling depths consistently shifted toward much higher values in 2014–2016. During this period, the POC flux at 500 m increased by 32% while net primary production (NPP) increased only slightly. Consequently, the POC flux/NPP ratio increased significantly, indicating greater biological pump efficiency than in earlier years of the study. The flux of lithogenic material derived primarily from sediment resuspension was much greater at 500 m in 2014−2016 compared with previous years, implying its potential role as a ballast mineral in enhancing particle export and transfer to the deep sea interior. The radiocarbon isotope ratio of POC was higher, and the excess Mn content values were lower at 500 m in 2014–2016, suggesting that the resuspended sediment at 500 m likely originated from a shallow region during this period, and differed in provenance from the lithogenic material intercepted at 2000 m. The period of enhanced particle flux coincided with the 2015/16 El Niño and a mesoscale warm (anticyclonic) eddy that persisted for 2 years in the study region. The East Korean Warm Current and the eddy may have facilitated the transport of resuspended particles entrained in the Korea Strait and/or the western shelf and upper slope of the basin to the study site.
Minkyoung Kim, Eun Jin Yang, Hyung Jeek Kim, Dongseon Kim, Tae-Wan Kim, Hyoung Sul La, SangHoon Lee, and Jeomshik Hwang*
Unexpectedly, in sediment traps deployed in the Antarctic Amundsen Sea to catch small sinking particles in the water, large benthic invertebrates such as long and slender worms, baby sea urchins, and small scallops were found. We suggest three hypotheses: lifting of these animals by anchor ice formation and subsequent transport by ice rafting, spending their juvenile period in a habitat underneath the sea ice and subsequent falling, or their active use of the current as a means of dispersal.
Minkyoung Kim, Eun Jin Yang, Dongseon Kim, Jin-Hyun Jeong, Hyung Jeek Kim, Jisoo Park, Jinyoung Jung, Hugh W. Ducklow, SangHoon Lee, Jeomshik Hwang*
(2019, Journal of Marine Systems)
This study examines the sinking particle flux and composition of samples collected at three sites in the western Amundsen Sea, Antarctica: a perennial sea-ice-covered area, the central region of the Amundsen Sea polynya, and close to the Dotson Ice Shelf within the polynya. Time series sediment traps were deployed for one year at depths of 400–500 m from February and March 2012. Observations from the three sites confirm previously reported findings that the majority of annual POC (particulate organic carbon) flux in the Amundsen Sea occurs during the austral summer, with much smaller POC fluxes during other seasons. In the perennial ice-covered area, sea ice diatoms were the dominant source of sinking particles. In this region, the summertime POC flux is similar to that in the central polynya. However, the POC flux exhibited large interannual variability, with the reduction in sea ice cover and sufficient insolation being critical to enhanced sinking POC flux. Within the Amundsen Sea polynya, the sinking POC flux was higher in the central region than near the Dotson Ice Shelf, consistent with spatial variability in primary production. The site near the Dotson Ice Shelf had the lowest contribution of diatoms to sinking particles and the smallest POC flux among the three sites.
Bumsoo Kim, SangHoon Lee , Minkyoung Kim , Doshik Hahm, Tae Siek Rhee, Jeomshik Hwang*
(2018, Geophysical Research Letters)
We used radiocarbon isotope ratios in dissolved inorganic carbon to assess gas exchange and water circulation in the western Amundsen Sea. Radiocarbon isotope ratios indicate that Circumpolar Deep Water enters the basin along the seafloor and that the upper layer is formed through modification of this water mass. In the Amundsen Sea Polynya, radiocarbon isotope ratios of surface water are higher than those of underlying Winter Water, implying rapid absorption of atmospheric CO2. A CO2 absorption rate of 45 mmol m−2 d−1 calculated for a site in the central polynya is higher than that near the Dotson Ice Shelf (28 mmol m−2 d−1). The turnover time of water in the Dotson Trough region of the western Amundsen Sea is estimated to be 10–30 years, based on results from a box model and radiocarbon mass balance.
Minkyoung Kim, Jeomshik Hwang*, TaeKeun Rho, Tongsup Lee, Dong-Jin Kang, Kyung-Il Chang, Suyun Noh, HuiTae Joo, Jung Hyun Kwak, Chang-Keun Kang, Kyung-Ryul Kim
(2017, Journal of Marine Systems)
This study investigates the biological pump system in the East Sea (Japan Sea) by conducting an analysis of the total particle flux, biogenic material composition, and carbon isotope ratios of sinking particles. The samples were collected for one year starting from March 2011 using time-series sediment traps deployed at depths of 1040 m and 2280 m on bottom-tethered mooring at Station EC1 (37.33°N, 131.45°E; 2300 m water depth) in the Ulleung Basin (UB), southwestern part of the East Sea. The temporal variation in the particulate organic carbon (POC) flux at 1000 m shows a good relationship with the primary production in the corresponding surface water. The ratio of POC flux at 1000 m to satellite-based primary production in the corresponding region in the UB was ~ 3%, which is comparable to the values of 2 to 5% estimated from previous studies of other part of the East Sea. The lithogenic material accounted for > 17% of the sinking particles at 1000 m and for a larger fraction of 40 to 60% at 2280 m. The radiocarbon contents of the sinking POC at both trap depths imply the additional supply of aged POC, with a much greater contribution at 2280 m. Overall, the particle flux in the deep interior of the East Sea appears to be controlled by the supply of complex sources, including aeolian input, the lateral supply of resuspended sediments, and biological production in the surface water.
Minkyoung Kim, Jeomshik Hwang*, Sang Heon Lee, Hyung Jeek Kim, Dongseon Kim, Eun Jin Yang, SangHoon Lee
(2016, Deep-Sea Research Part II)
We examined the recent history of sedimentary organic carbon (SOC) accumulation on the western Amundsen Shelf, to help characterize the biological carbon pump in the Amundsen Sea, Antarctica. Vertical sedimentary profiles (in the upper 21-cm) of SOC content, radio- and stable-carbon isotopes were obtained at four locations in the western Amundsen Sea: near the shelf break, inside the polynya near the Dotson Ice Shelf, and at both the periphery and the center of the Amundsen Sea polynya. Profiles were representative not only of various distances from the coast, but also of various summertime sea ice conditions and bottom depths. The SOC content (up to 1.1%) and the radiocarbon content were distinctly higher at the periphery and at the center of the polynya than at the other sites. The SOC and 14C contents were generally consistent with the spatial distribution of primary productivity in the surface water. A linear SOC accumulation rate of about 1.0 g C m−2 yr−1 was determined from the conventional 14C ages of bulk SOC below the surface mixed layer at the periphery and at the center of the polynya, for the time period of 3.1–4.7 kyr before present (BP). This linear SOC accumulation rate was about 20 times greater than the rates determined at the two other sites for the period of 4.6–15.7 kyr BP. Note that all values are for uncorrected 14C ages. At the center of the polynya, a sudden change in SOC accumulation rate was observed at about 16 cm depth, corresponding to 4.7 kyr BP, implying that changes (during this time period) in physical environments greatly affected primary production, SOC burial and/or supply of allochthonous particles to this site. The vertical distribution of 14C content in the sediments implies that aged organic matter, likely associated with resuspended sediments, was also being deposited inside the polynya, in addition to autochthonous biogenic particles. If our estimation of SOC accumulation is extrapolated to the western Amundsen Shelf between 110°W and 120°W, approximately 3×1010 g C yr−1 is buried on the shelf, with ~90% of SOC accumulation occurring in the Amundsen Sea polynya.
Sinking particle flux in the sea ice zone of the Amundsen Shelf, Antarctica
Minkyoung Kim, Jeomshik Hwang*, Hyung Jeek Kim, Dongseon Kim, Eun Jin Yang, Hugh W.Ducklow, Hyoung Sul La, Sang Heon Lee, Jisoo Park, SangHoon Lee
(2015, Deep-Sea Research Part I)
We have examined the flux, biogenic composition, and isotopic values of sinking particles collected by a time-series sediment trap deployed in the sea ice zone (SIZ) of the Amundsen Sea from January 2011 for 1 year. The major portion of the particle flux occurred during the austral summer in January and February when sea ice concentration was reduced to <60%. Biogenic components, dominated by opal (~78% of the biogenic components), accounted for over 75% of particle flux during this high-flux period. The dominant source of sinking particles shifted from diatoms to soft-tissued organisms, evidenced by high particulate organic carbon (POC) content (>30%) and a low bio-Si/POC ratio (<0.5) during the austral winter. CaCO3 content and its contribution to total particle flux was low (~6%) throughout the study period. Aged POC likely supplied from sediment resuspension accounted for a considerable fraction only from October to December, which was evidenced by a low radiocarbon content and relatively high (30–50%) content of the non-biogenic components. When compared with POC flux inside the Amundsen Sea polynya obtained by the US Amundsen Sea Polynya International Research Expedition (ASPIRE), the POC flux integrated over the austral summer in the SIZ was virtually identical, although the maximum POC flux was approximately half that inside the Amundsen Sea polynya. This comparatively high POC flux integrated over the austral summer in the SIZ may be caused by phytoplankton blooms persisting over a longer periods and more efficient export of organic matter potentially owing to the diatom-dominant plankton community. If this observation is a general phenomenon on the Amundsen Shelf, the role of the SIZ, compared with the polynyas, need to be examined more carefully when trying to characterize the POC export in this region.
Temporal and spatial variability of particle transport in the deep Arctic Canada Basin
Jeomshik Hwang*, Minkyoung Kim, Steven J. Manganini, Cameron P. McIntyre, Negar Haghipour, JongJin Park, Richard A. Krishfield, Robie W. Macdonald, Fiona A. McLaughlin, Timothy I. Eglinton
(2015, Journal of Geophysical Research)
To better understand the current carbon cycle and potentially detect its change in the rapidly changing Arctic Ocean, we examined sinking particles collected quasi‐continuously over a period of 7 years (2004–2011) by bottom‐tethered sediment trap moorings in the central Canada Basin. Total mass flux was very low (<100 mg m−2 d−1) at all sites and was temporally decoupled from the cycle of primary production in surface waters. Extremely low radiocarbon contents of particulate organic carbon and high aluminum contents in sinking particles reveal high contributions of resuspended sediment to total sinking particle flux in the deep Canada Basin. Station A (75°N, 150°W) in the southwest quadrant of the Canada Basin is most strongly influenced while Station C (77°N, 140°W) in the northeast quadrant is least influenced by lateral particle supply based on radiocarbon content and Al concentration. The results at Station A, where three sediment traps were deployed at different depths, imply that the most likely mode of lateral particle transport was as thick clouds of enhanced particle concentration extending well above the seafloor. At present, only 1%–2% of the low levels of new production in Canada Basin surface waters reaches the interior basin. Lateral POC supply therefore appears to be the major source of organic matter to the interior basin. However, ongoing changes to surface ocean boundary conditions may influence both lateral and vertical supply of particulate material to the deep Canada Basin.
Alkenones as tracers of surface ocean temperature and biological pump processes on the Northwest Atlantic margin
Jeomshik Hwang*, Minkyoung Kim, JongJin Park, Steven J.Manganini, Daniel B.Montluçon, Timothy I.Eglinton
(2014, Deep-Sea Research Part I)
We have examined alkenone distributions, specifically the temperature proxy U37K′, in sinking particulate organic matter (POM) intercepted at three depths by time-series sediment traps deployed between 2004 and 2007 on the Northwest Atlantic margin. The goal was to assess physical and biogeochemical processes acting upon alkenones during passage through the water column. U37K′ did not exhibit any systematic trend with increasing depth despite several-fold attenuation in alkenone flux. Because of the extensive reduction in C37 alkenone flux in the water column and more efficient alkenone degradation during the period of high alkenone flux, the temperature bias toward that of more productive seasons was reduced with increasing trap depth. The temporal variation of U37K′ and alkenone-derived temperature compared best with the satellite-derived SST at an upstream region approximately 160 km east of the mooring site with a time lag of about 30 days, suggesting this region as the dominant source of alkenone-bearing POM. The alkenone-derived temperature of core-top sediments (15 °C) at the study site was lower than the flux-weighted average alkenone-derived temperature of sinking POM at 50 m above the seafloor. This discrepancy may reflect additional supply of resuspended sediment carrying alkenones produced in cooler waters to the northeast, and transported in bottom nepheloid layers