https://repository.kopri.re.kr/handle/201206/11917 2026-03-16T16:29:36Z https://repository.kopri.re.kr/handle/201206/13554 Title: Ross Sea Dissolved Organic Matter Optical Properties During an Austral Summer: Biophysical Influences Authors: D'Sa, Eurico J.; Kim, Hyun-Cheol; Ha, Sun-Yong; Joshi, Ishan Abstract: The Ross Sea, one of the most productive regions in the Southern Ocean, plays a significant role in deep water formation and carbon cycling. Dissolved organic carbon (DOC) concentrations and chromophoric dissolved organic matter (CDOM) absorption and fluorescence (FDOM) properties were studied in conjunction with biophysical properties during austral summer. Elevated values of both DOC (mean 47.82 +/- 5.70 mu M) and CDOM (absorption coefficient at 325 nm, a(cdom)325: mean 0.31 +/- 0.18 m(-1)) observed in the upper shelf waters in the southwest (SW), north of the Ross Ice Shelf (RIS), the northwest and along a transect inward of the shelf break, suggested in situ production and accumulation linked to the productive spring/summer season. However, regional differences were observed in CDOM with a(cdom)325 higher (0.63 +/- 0.19 m(-1)) and its spectral slope S275-295 lower (24.06 +/- 2.93 mu m(-1)) in the SW compared to other regions (0.25 +/- 0.08 m(-1) and 28.92 +/- 2.67 mu m(-1), respectively). Similarly, the specific UV absorption coefficient or SUVA(254) determined at 254 nm was greater (1.85 +/- 0.55 m(2) mg(-1) C) compared to other regions (1.07 +/- 0.24 m(2) mg(-1) C), indicating CDOM of greater molecular weight and aromaticity in the SW. Phytoplankton absorption spectra indicated the shallow mixed layer of SW Ross Sea to be dominated by diatoms (e.g., Fragilariopsis spp.), a preferential food source for grazers such as the Antarctic krill, which in large numbers have been shown to enhance CDOM absorption, a likely source in the SW. Excitation-emission matrix (EEM) fluorescence combined with parallel factor analysis (PARAFAC) retrieved one protein-like and two humic-like FDOM fractions commonly observed in the global ocean. In contrast to a(cdom)325 which was uncorrelated to DOC, we observed weak but significant positive correlations between the humic-like FDOM with salinity and DOC, high value of the biological index parameter BIX and an instance of increasing FDOM with depth at a location with sinking organic matter, suggesting autochthonous production of FDOM. The absorption budget showed a relatively higher contribution by CDOM (70.7 +/- 18.3%) compared to phytoplankton (22.5 +/- 15.2%) absorption coefficients at 443 nm with implications to ocean color remote sensing. This first study of DOM optical properties provides additional insights on carbon cycling in the Ross Sea. 2021-10-27T00:00:00Z https://repository.kopri.re.kr/handle/201206/13615 Title: Phytoplankton Bloom Changes under Extreme Geophysical Conditions in the Northern Bering Sea and the Southern Chukchi Sea Authors: Park, Jinku; Lee, sungjae; Jo, Young-Heon; Kim, Hyun-cheol Abstract: The northern Bering Sea and the southern Chukchi Sea are undergoing rapid regional biophysical changes in connection with the recent extreme climate change in the Arctic. In particular, since observations began in the 1970s, the ice concentration in 2018 was the lowest due to the unusually warm southerly wind in winter, which continued in 2019. We analyzed the characteristics of spring phytoplankton biomass distribution under such extreme environmental conditions in the two years. Our results show that higher phytoplankton biomass during late spring compared to the 18-year average was observed in the Bering Sea in both years. Their spatial distribution is closely related to the open water extent following winter-onset sea ice retreat in association with dramatic atmospheric conditions. However, despite a similar level of shortwave heat flux, the 2019 springtime biomass in the Chukchi Sea is lower than that in 2018, and instead, the bloom in 2019 was delayed to summer. We confirmed that this difference in bloom timing in the Chukchi Sea is due to the seawater property changes determined by the combination of the modulation of the northward oceanic heat flux caused by the disturbance of the enlarged sea ice in winter and the higher surface net shortwave heat flux than usual. 2021-10-09T00:00:00Z https://repository.kopri.re.kr/handle/201206/13635 Title: Feasibility Study on Estimation of Sea Ice Drift from KOMPSAT-5 and COSMO-SkyMed SAR Images Authors: Park, Jeong-Won; Kim, Hyun-cheol; Korosov, Anton; Demchev, Denis; Zecchetto, Stefano; Kim, Seung Hee; Kwon, Young-Joo; Han, Hyangsun; Hyun, Chang-Uk Abstract: Estimating the sea ice drift field is of importance in both scientific study and activities in the polar ocean. Ice motion is being tracked at large scale (10 km and larger) on a daily basis; however, a higher resolution product is desirable for more reliable monitoring of rapid changes in sea ice. The use of wide-swath SAR has been extensively studied; yet, recent high-resolution X-band SAR sensors have not been tested enough. We examine the feasibility of KOMPSAT-5 and COSMO-SkyMed for retrieving sea ice motion by using the dataset of the MOSAiC expedition. The ice drift match-ups extracted from consecutive SAR image pairs and buoys for more than seven months in the central Arctic were used for a performance evaluation and validation. In addition to individual tests for KOMPSAT-5 and COSMO-SkyMed, a cross-sensor combination of two sensors was tested to overcome the drawback, a relatively long revisit time of high-resolution SAR. The experimental results show that higher accuracies are achievable from both single- and cross-sensor configurations of high-resolution X-band SARs compared to wide-swath C-band SARs, and that sub-daily monitoring is feasible from the cross-sensor approach. 2021-10-01T00:00:00Z https://repository.kopri.re.kr/handle/201206/13649 Title: Retrieval of daily sea ice thickness from AMSR2 passive microwave data using ensemble convolutional neural networks Authors: Chi, Junhwa; Kim, Hyun-Cheol Abstract: Recently, measurement of sea ice thickness (SIT) has received increasing attention due to the importance of thinning ice in the context of global warming. Although altimeter sensors onboard satellite missions enable continuous SIT measurements over larger areas compared to in situ observations, these sensors are inadequate for mapping daily Arctic SIT because of their small footprints. We exploited passive microwave data from AMSR2 (Advanced Microwave Scanning Radiometer 2) by incorporating a state-of-the-art deep learning (DL) approach to address this limitation. Passive microwave data offer better temporal resolutions than those from a single altimeter sensors, but are rarely used for SIT estimations due to their limited physical relationship with SIT. In this study, we proposed an ensemble DL model with different modalities to produce daily pan-Arctic SIT retrievals. The proposed model determined the hidden and unknown relation- ships between the brightness temperatures of AMSR2 channels and SITs measured by CryoSat-2 (CS2) from the extended input features defined by our feature augmentation strategy. Although AMSR2-based SITs agreed well with CS2-derived gridded SIT values, they had similar uncertainties and errors in the CS2 SIT measurements, particularly for thin ice. However, based on quantitative validations using long-term unseen data and IceBridge data, the proposed retrieval model con- sistently generated SITs from AMSR2 at 25 km spatial resolution, regardless of time and space. 2021-08-18T00:00:00Z