Ba, Si, U, Al, Sc, La, Th, C and C/C in a sediment core in the western subarctic Pacific as proxies of past biological production

A sediment core covering the last 145 kyrs was collected in the western subarctic Pacific (WSAP), and analyzed for Ba, U, Al, Sc, La, Yb, Th, biogenic opal (Opal) and organic carbon (C_org) as well as its isotopic ratio (δ¹³C). This study examined the change of past biological production in WSAP with multiple proxies, together with understanding the relation between Loess from the Asian continent and the biological production. The Loess content was estimated from the metal components, Al, Sc, La, Yb and Th. In this high latitude core (50°N), the Loess content was generally high during the glacial periods, but it was also high even in some interglacial periods. The excess amount of Ba relative to the detrital material composition, Ba_ex, showed the best correlation with the Vostok δD (r = 0.72, p < 0.001), indicating that the biological production was lower in the glacial periods than in the interglacials. This corroborates the pervasive correlation between Ba_ex in the polar region, WSAP and the Antarctic Sea, and Antarctic temperature, combined with previous research. This correlation might be explained by the stratification caused by cooling. In addition, the time variations of Ba_ex in WSAP were similar to those of Ba_ex in the Okhotsk Sea and of other proxies (C_org and Opal) in both the Okhotsk and the Bering Sea, indicating the spatial homogeneity of Ba_ex in WSAP including proximal marginal seas. The Opal content was more weakly correlated with the Vostok δD (r = 0.46, p < 0.001) than Ba_ex, reflecting that Opal in WSAP including proximal marginal seas was spatially heterogeneous compared to Ba_ex. While both the C_org content and U_ex, the excess amount of U relative to the detritus composition, were not positively correlated with the Vostok δD, they behaved similarly in the sediments. The positive correlation between δ¹³C and the Vostok δD (r = 0.42, p < 0.001), between δ¹³C and Ba_ex (r = 0.60, p < 0.001) and between δ¹³C and Opal (r = 0.36, p < 0.01) indicates that δ¹³C in WSAP may give some information on the phytoplankton growth rate. There was not a significant correlation between the spatially homogeneous Ba_ex in WSAP and Loess (r = − 0.16, p > 0.01), suggesting that the increase of biological production with the increase of Loess supply during the glacial periods did not occur.     

莱州湾E孔中更新世末期以来的地球化学特征

对1994年在莱州湾沿岸所取的E孔(37°07'N,118°55'E,孔深为821m)岩心进行了地球化学研究.用等离子光谱法测量了9个常量元素、15个微量元素和碳酸钙的含量.结果表明,(1)E孔大部分常量元素、微量元素含量、尤其元素特征比值(Mn/Fe,Sr/Ba,Sr/Ca,Ti/Al)在地层分界处都有明显变化,可作为该区第四纪地层划分的重要指标;(2)常量元素含量变化主要受宿主矿物控制,主要反映物质来源,同时也反映沉积作用和沉积环境,Fe,Al,Ca,Mg,Mn,Ti对物源和环境反映较为敏感;(3)微量元素在中更新世末期、最后间冰期、最后冰期和全新世四个不同沉积时期分布特征不同,尤其在气候“冷期”和“暖期”有不同分布规律;大多数微量元素含量变化旋回曲线之“波谷”对应着沙层沉积,有6个沙层代表“暖期”沉积,1个沙层代表“冷期”沉积;(4)E孔在冰期低海面时期风成粉砂沉积中碳酸钙含量偏高,间冰期时海侵沙层中碳酸钙的含量偏低,碳酸钙含量变化与粒度和沉积物类型有关,对气候、环境和地层划分有良好的指示.     

Geochemistry and environment evolution of Core E in the Laizhou Bay since last stage of Middle Pleistocene

IwrincrIONOn the evolution of palcoenvironment, salt-water encroachmnt and the distributionof subsurface brine in the LaizhOu Bay area, many researches had been carried out, and muchknowledge abeut the gcolOgical features in this area since Late QUaternary was aCquired' ) (H8nand Wu, l992; Han and Meng, l994; Wen et al. l989). However there was IittIe studyon the sediment geOChemical characteristics since Quaternary. In this Paper, the element strati-graphic characteristics and evolut…     

Paleoceanographic records in the Chukchi Basin, western Arctic Ocean during the late Quaternary

The late Quaternary paleoceanographic changes in the western Arctic Ocean are revealed by quantitative studies of foraminiferal abundance, ice-rafted detritus (IRD) and its mineralogical and petrological compositions, planktonic Neogloboquadrina pachyderma (sin.) (Nps)-δ¹⁸O and -δ¹³C, biogenic and non-biogenic components in Core M03 token from the Chukchi Basin during the Second Chinese National Arctic Expedition cruise. Seven IRD events appeared at MIS 7, 5, 3 and 1. These IRD were carried in massive icebergs, which were exported to the Beaufort Sea through the M'Clure Strait Ice Stream, Canadian Arctic Archipelago, and then transported into the Chukchi Basin by the Beaufort Gyre. Low IRD deposition occurred during the glacial times when more extended ice cover and weakened Beaufort Gyre, while the open water condition and the intensified Beaufort Gyre during interglacial periods favored the IRD deposition. Therefore, the IRD events not only indicate the provenance of coarser detritus and ice export events, but also reflect the evolutionary histories of the Beaufort Gyre and North American ice sheet. Seven light Nps-δ¹⁸O and -δ¹³C excursions could respond to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines, but was irrelevant to the warm Atlantic water and freshwater inputs. Whereas, the heavy Nps-δ¹⁸O and -δ¹³C values separately reflect the lessened Arctic freshwater and Pacific water, and well-ventilated surface water from the continental shelf and halocline water. Variations of CaCO₃ content and planktonic foraminiferal abundance during the interglacial and glacial periods can demonstrate the incremental or diminishing input of the Atlantic water, while the total organic carbon (TOC) and opal contents increased and decreased during the glacial and interglacial periods, respectively, which could be related to the TOC degradation, opal dissolution and redox conditions of interface between the bottom water and sediments.     

Significant features of the calendar of the late Pleistocene glacial cycles

Comparison of the δD deuterium record in the ice cores at the Antarctic Vostok and Dome C stations with the δ¹⁸ oxygen isotope in bottom oceanic sediments has elucidated the boundaries of glacial cycles in the late Pleistocene and revealed their inner symmetry: the longer the cycles, the more distant they were from the interglacial that occurred approximately 400 kyr ago. The symmetry is also manifested in the reversal of the sawtooth sequence of the cycles in that period. Wavelet analysis shows that symmetry was induced by amplitude modulation of climate oscillations on the precession and obliquity time scales and by frequency modulation on the scales of the eccentricity of the Earth’s orbital motion around the Sun.     

越南岸外上升流区48万年来高分辨率的生源组分记录及其古海洋学意义

南海西部越南岸外MD05-2901孔沉积物分析显示,该孔覆盖氧同位素1-12期,底界年龄约为48万年。生源组分记录显示表层古生产力冰期高、间冰期低,体现间冰期海平面下降、陆源物质输入增强的影响。生产力在末次冰期达到最高,体现末次盛冰期海陆差异增强,东北风发育对生产力提高的促进作用。碳酸钙含量变化呈现冰期早期含量低、冰消期和间冰期含量高的趋势。其冰消期的高值在MIS1/2、MIS3/4和MIS5/6分界处,与浮游有孔虫碳同位素低值对应,揭示该地区的碳酸钙沉积旋回是“稀释旋回”。同时碳酸钙含量变化领先于同一地区浮游有孔虫氧同位素的变化,证明低纬海区碳酸钙泵作用对大气二氧化碳浓度和温度有影响。滤波分析结果显示碳同位素存在23 ka的岁差周期和偏心率长周期,生源组分的含量变化显示出典型的岁差周期,体现南海季风环流的轨道响应,证明低纬热带过程是调节气候变化的重要因素。     

Paleoceanographic records and sea ice extension history on the slope of the northern Bering Sea over the last 100 ka B.P.

1Introduction TheBeringSea,locatedinthesub-arcticNorth Pacific,playsanimportantroleininfluencingtheevo- lutionaryprocessoftheglobalclimaticsystembecause itsseasonalseaiceisformedinrelativelowerlatitudes (Takahashi,1999).ItisalsoasinkofatmosphericCO2, whichisoriginatedfromtheeffectivebiologicalpump inthissea.Particulatefluxdatameasuredinthesea overthelast10aindicatethattheorganic/inorganic carbonratiowasalwaysgreaterthan1,whichexplains thattheBeingSeaoccupiesasignificantpositionin theproces…     

Geochemical changes of the terrigenous sediments in the southern South China Sea and their paleoenvironmental implications during the last 31 ky

Fifty-six subsamples of the 86GC core were collected from the southern South China Sea continental slope. Major and trace elements, including rare earth elements (REEs), of detrital matters in these sediments were measured. The patterns of chondrite normalized REEs and the discrimination plots based on major and trace elements, respectively, indicate that the terrigenous sediments around this area had been supplied with one dominating provenience during the last 31 ky. The co-operation of sea level changes with the East Asian winter monsoon-related rainfall and sea water circulations should be the main mechanism causing the geochemical characteristics variations. Higher ratios of Al/Ti and some other elements to Ti, except P/Ti and Mn/Ti, are present during the last glacial sea-level low stand and the winter monsoon periods owing to increased fluvial input of material with low Ti content from the Mekong River, followed by strengthened chemical weathering intensity, causing higher Al₂O₃ and most other elements contents. The elemental patterns imply general warm and very humid climate in the tropical areas during the last glacial times; however, the climate since the last deglaciation was very changeable, especially during the Holocene. Even so, it can still be certain that the climate during the early part (29–24 ky B.P.) of the last glacial maximum was much worse than during other stages. Additionally, it is very likely that the 8 k cold event and the Younger Dryas event have been impressed in the geochemical record of this core.     

Late quaternary organic carbon cycles and paleoproductivity in the Labrador Sea

Accumulation rates of (marine) organic carbon and estimates of paleoproductivity from organic carbon data indicate distinct late Quaternary glacial/interglacial cycles at Ocean Drilling Program (ODP) Site 646. During the last 240,000 years, surface-water productivity was significantly higher in the northern Labrador Sea during interglacial than during glacial times (70 to 170 gC/m²/yr vs. 30 to 70 gC/m²/yr). The reduced glacial productivity is probably caused by a closed sea-ice cover dominating the northern Labrador Sea during glacial intervals.     

东海陆架HY126EA1孔有孔虫壳体的氧、碳同位素记录

东海陆架HY126EA1孔有孔虫壳体氧同位素组成具有明显的阶段性变化.通过与深海氧同位素组成曲线对比,可将氧同位素组成变化分为5期,分别对应着冰消期、末次冰期极盛期、末次冰期间冰段、末次冰期初期和末次间冰期.碳同位素组成的变化与氧同位素组成的变化基本一致.δ18O和δ13C的相关性在不同气候期存在明显差异,主要受陆源水和海水交换复杂程度的控制.     

Radiocarbon-derived sedimentation rates in the Gulf of Mexico

Sedimentation rates were determined for the northern Gulf of Mexico margin sediments at water depths ranging from 770 to 3560 m, using radiocarbon determinations of organic matter. Resulting sedimentation rates ranged from 3 to 15 cm/kyr, decreasing with increasing water depth. These rates agree with long-term sedimentation rates estimated previously using stratigraphic methods, and with estimates of sediment delivery rates by the Mississippi River to the northern Gulf of Mexico, but are generally higher by 1–2 orders of magnitude than those estimated by ²¹⁰Pb_xs methods. Near-surface slope sediments from 2737 m water depth in the Mississippi River fan were much older than the rest. They had minimum ¹⁴C ages of 16–27 kyr and δ¹³C values ranging from −24‰ to −26.5‰, indicating a terrestrial origin of organic matter. The sediments from this site were thus likely deposited by episodic mass wasting of slope sediment through the canyon, delineating the previously suggested main pathway of sediment and clay movement to abyssal Gulf sediments.     

南海西沙海槽83PC柱状沉积物组成特征及其古环境意义

为了解南海北部末次间冰期以来的沉积环境演化,分析了西沙海槽83PC柱状沉积物的浮游有孔虫氧碳同位素、碳酸钙、有机碳和粒度组成。浮游有孔虫的δ18 O值具有冰期-间冰期旋回特征,记录了海平面的升降和古气候的变化,而海平面变化控制了沉积物的碳酸钙和有机碳含量。冰期,海平面下降,陆源物质输入增多,带来了大量的碎屑物质和陆源有机质,沉积物具有低碳酸钙含量和高有机碳含量;间冰期,海平面上升,陆源物质输入减少,碎屑物质的稀释作用减弱,沉积物具有高碳酸钙含量和低有机碳含量。南海北部83PC柱状沉积物记录了末次间冰期以来的多次海平面升降旋回,还记录了气候变冷事件以及低碳酸钙沉积事件,其中,150、510、660和740cm处的低碳酸钙含量和相对重δ18 O值记录了全球性气候变冷事件,而冰后期的低碳酸钙沉积事件,则主要反映了季风降雨的增强,出现了洪水高发期,陆源碎屑物质对碳酸钙沉积的稀释作用明显增强。     

白令海DSDP188站氧同位素3期以来的古海洋与古气候记录

白令海南部DSDP188站沉积物生源组分分析显示,该地区表层生产力在MIS3早、晚期(3.3和3.1)以及MIS2期增加,而其他时期表层生产力相应降低,并且表层生产力的变化没有显示明显的冰期与间冰期旋回。沉积物的C/N比值反映了有机碳的混合来源,说明该地区表层生产力可能受陆源营养物质输入的影响。该站位沉积物的非生源组分分析显示,MIS3早、晚期陆源物质输入量增加,反映洋流加强和气候变化。MIS2出现两次陆源物质输入量的增加,显示了洋流和气候的波动。MIS3和末次冰消期碳屑丰度增加,但MIS2降低,指示MIS3和MIS1陆地天然火灾概率大,而MIS2天然火灾概率低,反映间冰期比冰期更容易发生天然火灾。     

DISCOVERY OF DIATOM ASSEMBLAGES FROM DEEP-SEA BASIN IN THE SOUTH CHINA SEA AND THEIR GEOLOGICAL IMPLICATION

Of the diatoms from sediments of the South China Sea, mainly composed of planktonic species of tropical and subtropical zones, 36 genera and 86 species are identified. Based on the changes in diatom numbers and the appearance of diatom assemblages, six diatom zones are distinguished in Core V, reflecting six phases of paleoclimatc, paleo-watertemperature and paleogeography. According to the Quaternary climatic division, these zones represent hot weather and warm weather as a whole, and they are separately equal to postglacial period, the Holocene; Wurm glacial period; Riss-Wurm interglacial period; and Riss glacial period, the Late Pleistocene.     

东海陆架晚第四纪沉积物化学成分及物源示踪

东海陆架EA1孔和EA5孔沉积物化学成分变化范围较大。与东海陆架表层沉积物相比，钻孔沉积物的Si,Al,Mg,Mn,Ti,P,Ba,Zr,Co,Ni,Cu,Zn,Cr明显偏高，而Fe,Na,Ca,Sr,Li,U明显偏低，与全球大陆地壳化学组成相比，钻孔沉积物的Si,Li,Rb,Ba,Th,Zr,Hf,Cu,Zn,Pb偏高，而Al,Na,Ca,Mg,Fe,Mn,Ti,P,Sr,U,Co,Ni,V,Cr偏低，钻孔沉积物的化学成分在垂向上具有明显变化，主要受岩性和沉积环境的控制，钻孔沉积物中元素的富集因子（EF）均小于10，接近于1，表明钻孔沉积物主要来自大陆地壳，一些元素因分异或外来物质加入而富集，一些元素则因分异带出而亏损，钻孔沉积物源区的DF值判别表明，钻孔沉积物与现代黄河，长江沉积物均有亲缘关系，可能是在末次冰期最盛期，由于气候带南移，干旱区域扩大，在古长江搬运沉积物中类似现今黄河沉积物的干旱组分明显增加，从而导致了地球化学示踪结果的长江与黄河双重性，或者说古气候的变化导致了古长江搬运物质成分的变化。     

Paleoceanography of the central sea of Okhotsk during the middle Pleistocene (350–190 ka) as inferred from micropaleontological data

The distribution of diatoms, radiolarians, planktonic and benthic foraminifers, and sediment components in the fraction >0.125 mm was analyzed in the core obtained from the central Sea of Okhotsk within the frameworks of the Russian-German KOMEX project. The core section characterizes the period 190–350 ka, which corresponds to marine-isotopic stages (MIS) 7 to 10. During glacial MIS 10 and MIS 8, the basin accumulated terrigenous material lacking microfossils or containing them in low abundance, which reflects, along with their composition, heavy sea-ice conditions, suppressed bioproductivity, and bottom environments aggressive toward calcium carbonate. Interglacial MIS 9 was characterized by elevated bioproductivity with accumulation of diatomaceous ooze during the climatic optimum (328 to 320 ka). The water exchange with the Pacific was maximal from 328 to 324 ka ago. Environments became moderate and close to the present-day ones at the end of the optimum exhibiting the possible existence of a dichothermal layer with substantial amounts of the surface Pacific water still flowing into the basin. Similar to interglacial MIS 5e and MIS 1, the “old” Pacific water determined near-bottom environments in the central Sea of Okhotsk during that period, although the influx of terrigenous material was higher, probably reflecting a more humid climate of the region. Slight warming marked the terminal MIS 8 (approximately 260 ka ago). The paleoceanographic situation during interglacial MIS 7 was highly variable: from warm-water to almost glacial. The main climatic optimum of MIS 7 occurred within 220–210 ka, when the subsurface stratification increased and the dichothermal layer developed. Bottom environments during the studied time interval, except for the optimum of interglacial MIS 9, resembled those characteristic of glacial periods: the actively formed “young” Okhotsk water displaced the “old” Pacific deep water.     

Temporal variation in mass fluxes and the major components of sinking particles in Sagami Bay, off Japan

Sinking particles were collected using time-series sediment traps deployed at 350 and 20 mab at Site SB (34° 58.5’N, 139° 20.9’E, 1544 m depth) near the center of Sagami Bay, off Japan with high time resolutions of 5-8 days (March 1997 to August 1998) and 3-4.5 days (March 1998 to August 1998), respectively. The major components (CaCO₃, OM, opal, and clay) of these sinking particles and surface bottom sediments were determined using a stepwise leaching method combined with gravimetry. Average total mass fluxes were 1480, 5560 and 3068 mg/m²/year at 350 mab, at 20 mab, and in the surface sediments, respectively, indicating an enhanced collection of sinking particles at 20 mab. Clay was the dominant component and biogenic components (opal+OM+CaCO₃) were dominated mainly by opal and secondly by OM. On average, opal and CaCO₃ contents decreased gradually as clay content increased with increasing depth from 350 mab-20 mab and in the surface sediments, indicating dissolution of opal and CaCO₃ through sinking, rebound, resuspension or sedimentation processes. Thirteen total mass flux peaks at 17--40-day intervals were observed at 350 mab during the period from March 1997 to August 1998 except for winter, while eight peaks were observed at 20 mab for the period from March 1998 to August 1998. Two types of total mass peaks can be distinguished: one with a clear increase in biogenic flux (opal+OM+CaCO₃) and little or no increase in clay flux and termed a bloom type (B-type), and the other with a clear increase in clay flux, little increase in biogenic flux and termed a resuspension type (R-type). Some R-type peaks, but not all, coincided with total mass flux peaks observed at the mouth of Tokyo Bay and suggested the possibility of the effect of particulate materials transported from Tokyo Bay to site SB. The enormously large peak observed at 20 mab in late May 1998 and that at 350 mab in early June 1998 were considered to be due to some physical perturbations from an earthquake swarm near site SB during the period from April to June 1998. The 17--40-day periodicity was associated clearly with the change in biogenic flux dominated by opal flux and is thought to reflect the periodicity of biological productivity dominated by diatoms in the euphotic zone of Sagami Bay.     

南海东北部晚更新世以来沉积环境演变的矿物-地球化学记录

对南海东北部69柱(20°07.10'N,118°49.0'E)沉积物岩心进行碎屑矿物-地球化学特征研究,结果表明,以孔深165cm为界可划分出晚更新世末次冰期沉积和全新世冰后期沉积,这一地层划分结果与根据浮游有孔虫氧、碳同位素分析得出的结果是一致的.末次冰期时自生黄铁矿和硫元素高度富集,钠与铝、镁与铝和钠与钾的比值均较高,重矿物和SiO₂含量较高,CaCO₃含量较低,反映当时是一种相对闭塞的缺氧环境,气候干寒,化学风化作用较弱,以机械风化作用为主;研究区主要接受粒径较粗的硅质沉积;陆源物质的稀释作用可能是造成碳酸盐含量相对较低的主要原因.冰后期褐铁矿出现高含量,钠与铝、镁与铝和钠与钾的比值均降低,Al₂O₃和CaCO₃含量增高,反映沉积环境渐变为开放的氧化环境,气候转变为化学风化作用较强的湿热气候;研究区以接受较细粒的铝硅酸盐沉积为主,冰消期时还出现了碳酸盐保存高峰事件.     

Core-based reconstruction of paleoenvironmental conditions in the southern Drake Passage (West Antarctica) over the last 150 ka

A deep-sea sediment core (GC98-06) from the southernmost Drake Passage, West Antarctica, shows late Quaternary depositional environments distinctly different from sedimentary drifts commonly found along the southwestern Pacific margin of the Drake Passage. The chronology of the core has been inferred using geochemical tracers of paleoproductivity and diatom biostratigraphy, and represents the paleoceanographic conditions in a continental rise setting during the last 150,000 years. Three dominant sediment types associated with distinct sedimentary processes have been identified using textural/compositional analyses: (1) hemipelagic mud (interglacial sediments) deposited from pelagic settling of bioclasts, meltwater plumes, and ice-rafted detritus; (2) terrigenous mud (glacial sediments) delivered by turbid meltwater plumes; and (3) massive muds marking the boundaries from interglacial to glacial periods. The succession of the sedimentary facies in core GC98-06 is interpreted to reflect temporal changes in environmental conditions prevailing on the continental rise of the southern Drake Passage in the course of successive climatic stages over the last 150 ka: from the bottom upward, these are glacial, interglacial, glaciation, glacial, and interglacial episodes. Variability in sediment flux and diatom abundance seem to have been related to changes in glacial advance, sea-ice extent, and specific sedimentary environments, collectively influenced by mid- to late Quaternary climatic changes.     

Sediment dynamics in the Eurasian Arctic Ocean during the last deglaciation — The clay mineral group smectite perspective

This study focuses on sedimentological investigations of sediment cores recovered during the international Arctic′91, expeditions with the German research ice breaker RV “Polarstern” to the European sector of the Arctic Ocean. Here, we deduce the last glacial/interglacial changes in transport mechanism and sedimentation from the clay mineral group smectite. We choose the smectites as an example of how sediment mineralogy can be linked with particular source regions (the Kara and Laptev seas), distinct transport mechanism (sea ice and surface currents) and sedimentation processes. Smectite contents in Arctic sediments discussed for two time slices, including the Last Glacial Maximum (LGM), and the last deglaciation (Termination I), reveal the highest variability subsequent to the retreat of the Eurasian ice sheets. Our results show that smectite anomalies in the Eurasian Basin are associated with distinct meltwater pulses and occurred around 13.5–13.0 ¹⁴C ka B.P. Compelling evidence is provided that these anomalies are deduced from sea-ice entrained sediments from the eastern Kara Sea that entered the Arctic Ocean after ice-sheet break-up and eventually flooding of the Kara Sea. We propose that smectite anomalies in sediments of the eastern Arctic Ocean can be utilized to identify deglacial events and to help decipher configurations of the Eurasian ice sheets. The identification of smectite maxima along the modern sea-ice edge in the Eurasian Basin further indicates biologically enhanced sedimentation from melting sea ice allowing the reconstruction of seasonally open water in the region. Hence, considering the poor preservation conditions of primary paleoceanographic proxies in the Arctic Ocean, the clay mineral contents, particularly the smectite group, may be one alternative tool for paleoclimatic reconstruction in the Eurasian Basin.