한국해양학회지:바다 (The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY)

  • 제29권1호
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  • Pages.14-27
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  • 2024
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  • 1226-2978(pISSN)
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  • 2671-8820(eISSN)
한국해양학회 (The Korean Society of Oceanography)
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서해 중부 태안반도 북부 해역의 장안사퇴 표층퇴적물 분포 특성

Distribution Patterns of Surface Sediments of the Jangan Linear Sand Ridge off the Northern Taean Peninsula, in the Mid-west Coast of Korea

  • 장태수 (전남대학교 지구환경과학부) ;
  • 이은일 (포항공과대학교 기후변화및대응기술연구소) ;
  • 변도성 (국립해양조사원) ;
  • 이화영 (국립해양조사원) ;
  • 백승균 (지마텍(주))
  • TAE SOO CHANG (Faculty of Earth and Environmental Sciences, Chonnam National University) ;
  • EUNIL LEE (Pohang University of Science and Technology) ;
  • DO-SEONG BYUN (Korea Hydrographic and Oceanographic Agency) ;
  • HWAYOUNG LEE (Korea Hydrographic and Oceanographic Agency) ;
  • SEUNG-GYUN BAEK (Research Center, Gematek Co. Ltd.)
  • 투고 : 2021.12.30
  • 심사 : 2023.12.25
  • 발행 : 2024.02.29
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초록

빈사 상태의 대륙붕 사퇴와는 달리, 연안 사퇴는 활동성이 높으며 주변 해양환경변화에 민감하게 반응하기 때문에 해저지형변화의 관점에서 관심의 대상이다. 대산항에서 불과 5 km 떨어진 장안사퇴는 지난 20여 년 동안 격심한 해저지형변화를 겪어오고 있다. 이러한 해저지형변화의 원인을 밝히기 위해서는 사퇴의 특성을 이해하는 것이 중요하다. 이러한 맥락에서 이 연구는 장안사퇴와 주변해역의 퇴적물 분포 양상을 이해하고자, 그랩식 채니기를 사용하여 총 227점의 퇴적물을 획득하고 체질-피펫방식의 입도분석을 수행하였다. 또한 1997년의 입도자료와 비교를 통해 지난 25년 동안의 퇴적물 입도 변화를 조사하였다. 장안사퇴의 중심부는 평균 입도 2-3∅의 중립사 내지는 세립사로 이루어졌으며, 사퇴의 골은 -2-6∅의 자갈과 니사질역으로 구성된다. 사퇴의 능선 퇴적물은 양호한 분급의 정규분포를 보인 반면에 사퇴의 기저 퇴적물은 불량한 분급과 주로 자갈퇴적물에 소량의 세립 퇴적물이 혼합된 양(+)의 왜도를 나타낸다. 사퇴의 중심부 퇴적물은 소량의 잔자갈의 혼합된 음(-)의 왜도를 보인다. 1997-2021년 동안 장안사퇴의 퇴적물은 전반적으로 0.5∅정도 조립해진 것으로 보이며, 겨울철 고파랑의 영향으로 세립질 퇴적물이 제거되었거나 해사채취 시 부유사의 제거로 설명할 수 있다. 표층퇴적물의 공간분포 양상을 미루어 볼 때 잔류 자갈 위에 30 m에 달하는 사퇴 본체가 놓인 것으로 추정된다. 사퇴 비대칭성, 기저면의 노출과 재동이 심한 잔류 자갈의 존재는 장안사퇴가 퇴적물 공급이 충분하지 않음을, 따라서 침식 상태에 놓여 있음을 시사한다.

Unlike the shelf sand ridges moribund in motion, nearshore sand ridges are highly mobile, sensitive to changes in ocean environments, thereby becoming of particular interest with respect to morphological changes. About 5 km off the Daesan port, the Jangan Sand Ridge has been undergoing severe subsea morphological change over the past two decades. Understanding the nature of sand ridges is critical to elucidate the causes of morphological changes. In this context, this study aims at understanding the characteristics and distribution patterns of surface sediments of the ridge and its vicinity. For this purpose, 227 sediment samples were acquired using a grab-sampler, the grain sizes being analysed by the sieve-pipette method. In addition, comparison of grain sizes in sediments between 1997 and 2021 was made in order to investigate the 25-years change in sediment composition. Surface sediments along the ridge axis are fine to medium sands with 2-3 phi in mean grain size, whereas, in the trough of ridge, the sediments are composed of gravels and muddy sandy gravels with mean sizes of -2 to -6 phi. Sediments in the crest of the ridge are well-sorted with normal distribution, on the other hand, the basal sediments are poorly-sorted and positively skewed. Along the ridge crest, the sediments are negatively skewed. From 1997 to 2021, the ridge sediments became largely coarser about 0.5 phi. Such coarsening trend in mean grain size can be explained either by elimination of fine sediments during high waves in winter or elimination of fines suspended during sand mining activities in the past. Spatial distribution pattern of surface sediments shows that ca. 30 m thick of the sand ridge itself overlies the thin relict gravels. The strong asymmetry of sand ridge, the exposure of ridge base, and reworked gravel lags suggest that Jangan sand ridge is probably sediment-deficit and hence erosive in nature at present.

키워드

과제정보

이 연구는 국립해양조사원의 2021-2022년 "연안 해저특이지형(태안반도 북부해역) 변화 연구(I, II)"의 지원을 받아 수행되었습니다. 장안사퇴와 주변해역의 시료채취에 도움을 준 국립해양조사원 '황해로' 선장님과 승조원들께 특별히 감사드립니다. 또한 현장조사와 입도분석을 기꺼이 함께해준 전남대 연안지질·퇴적학 실험실 학생들에게 고마움을 전합니다. 특별히 논문에 사용된 그림 작업을 도와주고 정리해준 임세린(박사과정) 학생에게 감사드립니다. 끝으로 저자들이 미처 발견하지 못한 부분을 꼼꼼하게 읽고 건설적인 비평을 해주신 심사위원과 편집위원께 감사드립니다.

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