Millennial-scale variations of late Pleistocene radiolarian assemblages in the Bering Sea related to environments in shallow and deep waters

Itaki, Takuya,Kim, Sunghan,Rella, Stephan F.,Uchida, Masao,Tada, Ryuji,Khim, Boo-Keun Elsevier 2012 Deep-sea research. Part II, Topical studies in oce Vol.61 No.-

<P><B>Abstract</B></P><P>A high-resolution record of the radiolarian assemblage from 60 to 10ka was investigated using a piston core (PC-23A) obtained from the northern slope of the Bering Sea. Faunal changes based on the 29 major radiolarian taxa demonstrated that the surface and deep water conditions in the Bering Sea were related to the orbital and millennial-scale climatic variations known as glacial–interglacial and Dansgaard–Oeschger (D–O) cycles, respectively. During interstadial periods of the D–O cycles, the assemblage was characterized by increases in the high-latitude coastal species <I>Rhizoplegma boreale</I> and the upper-intermediate water species <I>Cycladophora davisiana</I>, while the sea-ice related species <I>Actinomma boreale</I> and <I>A. leptodermum</I> and many deep-water species such as <I>Dictyophimus crisiae</I> and <I>D. hirundo</I> tended to be reduced. This trend was more apparent in two laminated intervals at 15–13.5 and 11.5–11ka, which were correlated with well-known ice-sheet collapse events that occurred during the last deglaciation: melt-water pulse (MWP)-1A and MWP-1B, respectively. The radiolarian faunal composition in these periods suggests that oceanic conditions were different from today: (1) surface water was affected by increased melt-water discharge from continental ice-sheet, occurring at the same time as an abrupt increase in atmospheric temperature, (2) upper-intermediate water (ca. 200–500m) was well-ventilated and organic-rich, and (3) lower-intermediate water (ca. 500–1000m) was oxygen-poor. Conversely, the sea-ice season might have been longer during stadial periods of the D–O cycles and the last glacial maximum (LGM) compared to the interstadial periods and the earliest Holocene. In these colder periods, deep-water species were very abundant, and this corresponded to increases in the oxygen isotope value of benthic foraminifera. Our findings suggest that the oxygen-rich water was present in the lower-intermediate layer resulting from intensified ventilation.</P>

Intermediate water circulation of the Okhotsk Sea during the last 20 kyr : evidence from radiolarian fossil record

Takuya Itaki,Boo-Keun Khim,Ken Ikehara 대한지질학회 2007 대한지질학회 학술대회 Vol.2007 No.0

Response of the Bering Sea to 11-year solar irradiance cycles during the Bølling-Allerød : KHIM ET. AL.; 11-YEAR SOLAR CYCLE IN BOLLING-ALLEROD

Katsuki, Kota,Itaki, Takuya,Khim, Boo-Keun,Uchida, Masao,Tada, Ryuji American Geophysical Union 2014 Geophysical research letters Vol.41 No.8

베링해 중부 대륙사면 지역의 지난 65,000년 동안 탄산염 함량 변화와 Dansgaard-Oeschger 사건들

김성한,김부근,Takuya Itaki,신혜선 한국해양과학기술원 2008 Ocean and Polar Research Vol.30 No.3

A piston core (MR06-04 PC23A) collected from the northern continental slope in the central Bering Sea has recorded the high-resolution millennial-scale variation of calcium carbonate (CaCO3) content during the last 65 kyr. An estimation of the age of the core sediments was carried out by using the lithologic correlation of the deglacial laminated layers with a neighboring core (HLY02023JPC), complementing the last appearance datum of both Lychnocanoma nipponica sakaii (54 kyr) and Amphimelissa setosa (85 kyr). The probable age of core MR06-04 PC23A was approximately younger than 65 kyr. Two distinct events of a significant increase of CaCO3 in the deglacial laminated sediments clearly correspond to MWP1A and MWP1B in the Bering Sea (Gorbarenko et al. 2005) and to T1ANP and T1BNP in the North Pacific (Gorbarenko 1996). These pronounced peaks of CaCO3 contents result from the elevated carbonate production in the surface water and the subsequent weakened dilution due to terrestrial input, along with an enhanced oxygen minimum zone. The CaCO3 contents are low (~2%) during the last glacial period mainly because of a low carbonate production caused by an expanded sea-ice cover and an increased dilution by terrigenous particles due to their closer distance to the continent during the sea-level low stand. The occurrence of seven distinct CaCO3 peaks in core MR06-04 PC23A is remarkable during MIS 3 and MIS 4, and they most likely correlate to the short-term millennial Dansgaard-Oeschger events.

Correlation between faunal transitions of benthic foraminifera and ballasting of particulate organic carbon by siliceous plankton during the Holocene off San-in district, southwestern Japan

Takata, Hiroyuki,Itaki, Takuya,Ikehara, Ken,Khim, Boo-Keun E. Arnold Distributed in North America by Cambridg 2018 The Holocene Vol.28 No.3

High Organic Carbon Deposition in the Northern Margin of the Aleutian Basin (Bering Sea) before the Last Deglaciation

김부근,김성한,Masao Uchida,Takuya Itaki 한국해양과학기술원 2010 Ocean science journal Vol.45 No.4

High-resolution geochemical, isotope and elemental data from core PC23A in the northern margin of the Aleutian Basin (Bering Sea) were used to reconstruct distinct paleoceanographic features of the last deglaciation (pre-Boreal[PB], Bølling-Allerød[BA], Younger Dryas[YD]). The PB and BA intervals are characterized by increased siliceous (diatom) and calcareous (coccolithophores and foraminifers) productivity represented by high biogenic opal and CaCO3 contents, respectively. The enhanced productivity can plausibly be attributed to an elevated sea-surface nutrient supply from increased melt-water input and enhanced Alaskan Stream injection under warm, restricted sea-ice conditions. High Corg/N ratios and low δ13C values of sediment organic matter during the PB and BA intervals reflect the contribution of terrestrial organic matters. The PB and BA intervals were also identified by laminated sediment layers of core PC23A, characterized by high Mo/Al and Cd/Al ratios, indicating that the bottom water condition remained anoxic. High δ15N values during the same period were attributed mainly to the increased nutrient utilization and subsequent denitrification of seawater nitrate. Part of high δ15N values may also be due to incorporation of inorganic nitrogen in the clay minerals. It is worthy of note that high total organic carbon (TOC) deposition occurred approximately 3,000 years before onset of the last deglaciation. Simultaneous high Corg/N ratios and low δ13C values clearly suggest that the high TOC content should be related to terrestrial organic carbon input. Low δ15N values during the high TOC interval also confirm the contribution of terrigenous organic matter. Although abundant calcareous phytoplankton production under cold, nutrient-poor conditions represented by Baex data was reported for high TOC deposition preceding the last deglaciation in an earlier study of the Okhotsk Sea, the main reason for the enhanced TOC deposition in the Bering Sea is an increased terrigenous input from the submerged continental shelves (Beringia) with a sea-level rise; this is further supported by Al enrichment of bulk sediments during the high TOC deposition.

Correlation of TL layers for the synchronous paleoceanographic events in the East Sea (Sea of Japan) during the Late Quaternary

김부근,Ryuji Tada,박유현,박장준,Yoshiki Kido,Takuya Itaki,Ken Ikehara 한국지질과학협의회 2009 Geosciences Journal Vol.13 No.2

TL layers (i.e., dark mud layers), either thin or thick, as determined by the L* values with lithologic observation, are distinct paleoceanographic signatures in the East Sea (Sea of Japan), which were formed in response to the global eustatic sea-level fluctuations between interglacials and glacials during the Late Quaternary. These lithologic markers were consistently correlated among the three sediment cores (MD01-2407, 05GCRP21, and KR05-09PC1) collected from the Oki Ridge of the southern Yamato Basin, the South Korea Plateau of the northern Ulleung Basin, and the Matsumae Plateau of the northeastern Japan Basin, respectively. Reconstruction of age models for cores 05GCRP and KR05-09PC1 was aided in a good way by the AMS 14C ages of planktonic foraminifera and identification of the tephra layers, and mainly by lithostratigraphic correlation with TL layers of well-dated core MD01-2407, based on the L* values. The correlation of TL layers among the three sediment cores was remarkable, indicating that the East Sea (Sea of Japan) experienced the synchronous and basin-wide scale paleoceanographic events during the Late Quaternary. Our study exemplifies the significant usefulness of these lithologic markers for further Late Quaternary paleoceanographic investigation.

Land—sea linkage of Holocene paleoclimate on the Southern Bering Continental Shelf

Katsuki, Kota,Khim, Boo-Keun,Itaki, Takuya,Harada, Naomi,Sakai, Hideo,Ikeda, Tomonori,Takahashi, Kozo,Okazaki, Yusuki,Asahi, Hirofumi SAGE Publications 2009 The Holocene Vol.19 No.5

<P>Detailed diatom records within surface and core sediments from the Southern Bering Continental Shelf (SBCS) reveal that the Holocene evolution of sea-ice distribution is associated with low pressure patterns. Holocene sea-ice distribution over the SBCS was mainly controlled by the location of the Aleutian Low. The corresponding paleoceanographic and paleoclimate conditions can be divided into three stages: (1) the early Holocene (before 7000 cal. yr BP) was characterized by extensive sea-ice distribution under two low-pressure cells, which covered the western Bering Sea and the Gulf of Alaska, respectively. (2) Between 3000 and 7000 cal. yr BP, the low-pressure system over the Gulf of Alaska became weak, causing total sea-ice mass over the SBCS to retreat. (3) In the past 3000 years, prevailing southwesterly winds over the SBCS due to the developing Aleutian Low have reduced further sea-ice cover on the SBCS. These paleoclimatic changes were probably a response to ENSO variation. The timings of water mass exchanges on the SBCS coincided with sea-level change along the Alaskan Peninsula. As a result, subsequent morphologic alterations have also influenced the paleoceanographic condition of the SBCS. The effect of the surface coastal water and bottom marine water on the SBCS intensified about 6000 cal. yr BP when sea level increased.</P>

베링해 중부 지역의 마지막 빙하기 이후 고생산성의 고해상 변화

Kim, Sung-Han,Khim, Boo-Keun,Shin, Hye-Sun,Uchida, Masao,Itaki, Takuya,Ohkushi, Kenichi 한국해양학회 2009 바다 Vol.14 No.3

베링해 중부 지역에서 획득된 피스톤 코아 PC23A의 퇴적물에서 오팔과 총유기탄소의 함량을 측정하고 집적률을 계산하여 마지막 빙하기 이후의 고생산성 변화를 살펴보았다. 코아 PC23A의 연대는 부유성 유공충의 AMS $^{14}C$ 탄소연대와 방산충 L. nipponica sakaii의 마지막 출현 기준에 의해서 결정되어있으며, 코아 최하단부가 약 61,000년 전으로 계산되었고, 코아 상부는 일부 손실된 것으로 판단된다. 오팔과 총유기탄소 함량은 마지막 빙하기 동안 각각 1-10%, 0.2-1.0%의 범위에서 변동하였으며, 각각 5%와 0.7%의 평균값을 보였다. 반면, 후빙기 동안에 오팔과 총유기탄소 함량은 5-22%, 0.8-1.2%의 범위에서 변동하였으며, 평균값은 각각 8%와 1.0%로 증가된 값을 보여주었다. 마찬가지로 오팔과 총유기탄소의 집적률도 마지막 빙하기($1gcm^{-2}kyr^{-1}$, $0.2gcm^{-2}kyr^{-1}$)동안 보다 후빙기 동안(>$5gcm^{-2}kyr^{-1}$, >$1gcm^{-2}kyr^{-1}$)에 증가하였다. 후빙기 동안 증가된 생산성은 온난한 기후에서 해빙의 발달이 미비하고 높아진 해수면 조건에서 주변 육상으로부터 융빙수의 유입 증가와 남쪽으로부터 알라스카 해류 유입의 증가에 의하여 영양염 공급이 충분한 환경에서 규조류가 번성하였기 때문이다. 반면, 마지막 빙하기 동안에는 낮아진 해수면으로 인하여 알라스카 해류의 유입이 감소하여 영양염의 공급이 제한되고, 낮은 수온과 추운 기후로 인해 광범위하게 발달한 해빙에 의해서 생산성이 감소되었다. Paleoproductivity changes in the central part of the Bering Sea since the last glacial period were reconstructed by analyzing opal and total organic carbon (TOC) content and their mass accumulation rate (MAR) in sediment core PC23A. Ages of the sediment were determined by both AMS $^{14}C$ dates using planktonic foraminifera and Last Appearance Datum of radiolaria (L. nipponica sakaii). The core-bottom age was calculated to reach back to 61,000 yr BP. and some of core-top was missing. Opal and TOC contents during the last glacial period varied in a range of 1-10% and 0.2-1.0%, and their average values are 5% and 0.7%, respectively. In contrast, during the last deglaciation, opal and TOC contents varied from 5 to 22% and from 0.8 to 1.2%, respectively, with increasing average values of 8% and 1.0%. Opal and TOC MAR were low ($1gcm^{-2}kyr^{-1}$, $0.2gcm^{-2}kyr^{-1}$) during the last glacial period, but they increased (>5 and >$1gcm^{-2}kyr^{-1}$) during the last deglaciation. High diatom productivity during the last deglaciation was most likely attributed to the elevated nutrient supply to the sea surface resulting from increased melt water input from the nearby land and enhanced Alaskan Stream injection from the south under the restricted sea-ice and warm condition during the rising sea level. On the contrary, low productivity during the last glacial period was mainly due to decreased Alaskan Stream injection during the low sea-level condition as well as to extensive development of sea ice under low-temperature seawater and cold environment.

Temporal variation of calcium carbonate contents and their paleoceanographic significance in the East Sea (Sea of Japan) during the last 200 kyr

Boo-Keun Khim,Yoshiki Kido,Ken Ikehara,Yu Hyeon Park,Jang Jun Bahk,Ryuji Tada,Tomo Irino,Takuya Itaki 대한지질학회 2007 대한지질학회 학술대회 Vol.2007 No.0