北冰洋西部晚第四纪浮游有孔虫氧碳同位素记录的海冰形成速率

北冰洋西部晚第四纪浮游有孔虫Neogloboquadrina pachyderma(sin.)(Nps)壳体的δ18O和δ13C与浮游有孔虫丰度和筏冰碎屑含量的综合研究表明,MIS 7晚期以来,Nps的δ18O和δ13C值出现7次明显的偏轻,可能与海冰形成速率的提高造成轻同位素卤水的生产和下沉相关.偏轻的Nps δ18O和δ13C值对应于极低的浮游有孔虫丰度和筏冰碎屑含量,因此这些轻值与温暖的大西洋水和淡水的输入无关,应当指示进入北冰洋的大西洋水减弱和楚科奇海陆架水的大量减少.相反,Nps δ18O的重值则反映输入北冰洋的淡水和太平洋水的减少;Nps δ13C的重值指示来自陆架流通性更好的表层和盐跃层水向北冰洋的输送.     

Modern river discharge and pathways of supplied material in the Eurasian Arctic Ocean: evidence from mineral assemblages and major and minor element distribution

Clay-mineral, heavy-mineral, and elemental distributions in sediments from the Arctic Ocean and the adjacent Laptev and Kara seas can be attributed to the geology of the hinterland and the transport of terrigenous material by rivers onto the shelves. Kara Sea sediments are characterized by increased contents of smectite and elevated Ni/Al-, Ti/Al-, and Cr/Al ratios. In the western Laptev Sea sediments are enriched in smectite and clinopyroxene and increased in Ti/Al-, Cr/Al-, and Ca/Al ratios. The composition of the sediments reflects suspended matter input from the large trap basalt of the Putoran Mountains. The eastern Laptev Sea sediments display increased illite and amphibole contents as well as a chemical composition similar to average shale. This composition is due to the discharge from the Lena and Yana rivers, which drain a large catchment area consisting of sedimentary Mesozoic and Paleozoic rocks. Material from the eastern Laptev Sea is transported by ocean currents and sediment-laden sea ice along the Transpolar Drift into the central Arctic Ocean. This is indicated by similar values of Ti/Al-, Cr/Al-, Rb/Al-, and K/Al ratios as well as increased concentrations of amphibole and illite, determined in sediments from the Lomonosov Ridge. A minor input from the Beaufort Sea into the central Arctic Ocean is suggested from increased Ca/Al ratios and increased contents of opaque minerals.     

Clay-mineral distribution in surface sediments of the Eurasian Arctic Ocean and continental margin as indicator for source areas and transport pathways — a synthesis

Clay-mineral distributions in the Arctic Ocean and the adjacent Eurasian shelf areas are discussed to identify source areas and transport pathways of terrigenous material in the Arctic Ocean. The main clay minerals in Eurasian Arctic Ocean sediments are illite and chlorite. Smectite and kaolinite occur in minor amounts in these sediments, but show strong variations in the shelf areas. These two minerals are therefore reliable in reconstructions of source areas of sediments from the Eurasian Arctic. The Kara Sea and the western part of the Laptev Sea are enriched in smectite, with highest values of up to 70% in the deltas of the Ob and Yenisey rivers. Illite is the dominant clay mineral in all the investigated sediments except for parts of the Kara Sea. The highest concentrations with more than 70% illite occur in the East Siberian Sea and around Svalbard. Chlorite represents the clay mineral with lowest concentration changes in the Eastern Arctic, ranging between 10 and 25%. The main source areas for kaolinite in the Eurasian Arctic are Mesozoic sedimentary rocks on Franz-Josef Land islands. Based on clay-mineral data, transport of the clay fraction via sea ice is of minor importance for the modern sedimentary budget in the Arctic basins.     

Manganese-rich brown layers in Arctic Ocean sediments: Composition, formation mechanisms, and diagenetic overprint

We present inorganic geochemical analyses of pore waters and sediments of two Late Quaternary sediment cores from the western Arctic Ocean (southern Mendeleev Ridge, RV Polarstern Expedition ARK-XXIII/3), focussing on the composition and origin of distinct, brown-colored, Mn-rich sediment layers. Carbonate enrichments occur in association with these layers as peaks in Ca/Al, Mg/Al, Sr/Al and Sr/Mg, suggesting enhanced input of both ice-rafted and biogenic carbonate. For the first time, we show that the Mn-rich layers layers are also consistently enriched in the scavenged trace metals Co, Cu, Mo and Ni. Distinct bioturbation patterns, specifically well-defined brown burrows into the underlying sediments, suggest these metal enrichments formed close to the sediment-water interface. The geochemical signature of these metal- and carbonate-rich layers most probably documents formation under warmer climate conditions with an intensified continental hydrological cycle and only seasonal sea ice cover. Both rivers and sea ice delivered trace metals to the Arctic Ocean, while enhanced seasonal productivity exported reactive organic matter to the sea floor. The coeval deposition of organic matter, Mn (oxyhydr)oxides and trace metals triggered intense diagenetic Mn cycling at the sediment-water interface. These processes resulted in the formation of Mn and trace metal enrichments, and the degradation of labile organic matter. With the onset of cooler conditions, reduced riverine runoff and/or a solid sea ice cover terminated the input of riverine trace metal and fresh organic matter, resulting in deposition of grayish-yellowish, metal-poor sediments. Oxygen depletion of Arctic bottom waters under these cooler conditions is not supported by our data, and did not cause the sedimentary Mn distribution. While the original composition and texture of the brown layers resulted from specific climatic conditions and corresponding diagenetic processes, pore water data show that diagenetic Mn redistribution is still affecting the organic-poor deeper sediments. Given persistent steady state conditions, purely authigenic Mn-rich brown layers may form, while others may be partly or completely dissolved. The degree of diagenetic Mn redistribution largely depends on the depositional environment, the Mn and organic matter availability, and apparently affected the Co/Mo ratios of Mn-rich layers. Thus, brown Arctic layers are not necessarily synchronous features, and should not be correlated across the Arctic Ocean without additional age control.     

Deglacial to postglacial palaeoenvironments of the Celtic Sea: lacustrine conditions versus a continuous marine sequence

Recent work on the last glaciation of the British Isles has led to an improved understanding of the nature and timing of the retreat of the British?Irish Ice Sheet (BIIS) from its southern maximum (Isles of Scilly), northwards into the Celtic and Irish seas. However, the nature of the deglacial environments across the Celtic Sea shelf, the extent of subaerial exposure and the existence (or otherwise) of a contiguous terrestrial linkage between Britain and Ireland following ice retreat remains ambiguous. Multiproxy research, based on analysis of 12 BGS vibrocores from the Celtic Deep Basin (CDB), seeks to address these issues. CDB cores exhibit a shell‐rich upward fining sequence of Holocene marine sand above an erosional contact cut in laminated muds with infrequent lonestones. Molluscs, in situ Foraminifera and marine diatoms are absent from the basal muds, but rare damaged freshwater diatoms and foraminiferal linings occur. Dinoflagellate cysts and other non‐pollen palynomorphs evidence diverse, environmentally incompatible floras with temperate, boreal and Arctic glaciomarine taxa co‐occurring. Such multiproxy records can be interpreted as representing a retreating ice margin, with reworking of marine sediments into a lacustrine basin. Equally, the same record may be interpreted as recording similar conditions within a semi‐enclosed marine embayment dominated by meltwater export and deposition of reworked microfossils. As assemblages from these cores contrast markedly with proven glaciomarine sequences from outside the CDB, a glaciolacustrine interpretation is favoured for the laminated sequence, truncated by a Late Weichselian transgressive sequence fining upwards into fully marine conditions. Reworked rare intertidal molluscs from immediately above the regional unconformity provide a minimum date c. 13.9 cal. ka BP for commencement of widespread marine erosion. Although suggestive of glaciolacustrine conditions, the exact nature and timing of laminated sediment deposition within the CDB, and the implications this has on (pen)insularity of Ireland following deglaciation, remain elusive.     

Behavior of Hydrocarbons in the Mouth Parts of Arctic Rivers

The paper reviews data (acquired in 2007–2016) on aliphatic and polycyclic aromatic hydrocarbons in comparison with data on concentrations of lipids, C_org, and chlorophyll a in the water and bottom sediments the river–sea geochemical barrier (for the Northern Dvina, Ob, Yenisei, and Lena rivers). It was established that the concentrations of anthropogenic hydrocarbons decrease and these compounds precipitate like other organic compounds and particulate matter, where riverine and marine waters mix. Relatively pure water flows in the pelagic zones of seas. In spite of low temperatures in the Arctic, anthropogenic hydrocarbons transform so rapidly that natural compounds dominate in the water and bottom sediments: autochthonous in the seawater and allochthonous in the bottom sediments.     

Provenance and sea-ice transportation of Mid-Pliocene and Quaternary sediments, Yermak Plateau, Arctic Ocean (ODP Site 911)

In this study, the clay and heavy mineral analysis of ODP Site 911 sediments is used to investigate the sources and transport mechanisms (sea ice and oceanic currents) of sediments in the Arctic Ocean during the Mid to Late Pliocene (3.10–2.78 Myr) and upper Quaternary (800 kyr to the present). The time period between 3.10 and 3.00 Myr is characterized by a decreasing smectite and increasing illite content, which is interpreted as reflecting cooling conditions. At the beginning of the Mid-Pliocene Global Warmth period at ∼3.00 Myr, the smectite content shows an abrupt increase. This change can also be seen as a drop in the amount of kaolinite and TOC. After 3.00 Myr the kaolinite and TOC values start to increase, probably indicating high rates of reworked glacially eroded matter. During the Pleistocene, smectite shows a lower and illite a higher fluctuation level compared with the Pliocene. This might be due to reigning glacial conditions during the Pleistocene, when the freshwater input was much lower than during the Pliocene. During the Pliocene, the fluctuating heavy minerals might reflect changes in freshwater input from the great Siberian rivers, which would have led to changes in the supply of terrigenous material delivered to the shelf by the rivers. The heavy mineral fluctuation also reflects changes in the amount of sea-ice formation, which correlates with climate variations and the freshwater input from the continent. Based on the composition of the clay and heavy mineral groups in this study, the most likely transportation path is the Siberian branch of the Transpolar Drift.     

中国海域表层沉积物分布规律及沉积分异模式

中国海域拥有宽广的大陆架，同时还有陆坡和深海盆，有众多河流入海并输入巨量的陆源物质，沉积物记录了海陆变迁、环流变化、海平面升降、物质输送和气候变化等环境信息。沉积物的粒度特征可以反映沉积动力、物质来源和搬运距离等，可以通过沉积物粒度组成、参数及各种图解来研究沉积环境的变化。前人对中国海域表层沉积物的粒度分布特征展开了大量的研究，取得了丰富的研究成果，但这些研究多集中在某一海域或区域，缺乏对整个中国海域的表层沉积物类型的宏观系统认识。本文基于中国地质调查局“1：100万海洋区域地质调查项目”获取了中国海域4300个海底表层沉积物样品，通过沉积物粒度分析，结合前人已发表资料，对中国海域表层沉积物的沉积类型特征、物质来源和运移模式等开展了系统的研究。本文把浅海和半深海沉积物按照含砾石和不含砾石主要划分出5个和7个沉积物类型，深海沉积物主要划分了9个沉积类型，研究结果表明：中国海域表层沉积物沉积类型多样、来源复杂，主要受控于物质来源、水动力条件和地形地貌的变化，在东部海域总体呈现“大江大河-宽缓陆架-残留慢速沉积”的条带状沉积分异模式，而在南部海域呈现的是“短源性河流-多类型陆架-重力流快速沉积”的环带状沉积分异模式。本文的结果对研究中国海域沉积物的宏观分布规律提供了基础资料，对理解海洋沉积动力过程具有重要意义，同时沉积物粒度的特征对海底砂矿分布也具有指示意义。     

Trace metals in sediments from the inner continental shelf of the western Beaufort Sea

Increased development and changing climate have enhanced global interest in the Arctic Ocean and adjacent seas. Using a large, 3-yr data base, we have determined the distribution of trace metals in sediments from the inner shelf of the western Beaufort Sea. Metal concentrations in these sediments reflect pristine conditions, consistent with those for most coastal areas in the Arctic and with predictions based on average continental crust. Geographic variations in metal values are primarily related to sediment grainsize distribution. However, grain-size patterns are a complex function of several variables including source areas, ice and water movement, as well as physical and chemical weathering. Future identification of any metal contamination in Beaufort Sea sediments will be simplified by understanding the predictable natural patterns.     

Cryosphere as a temporal sink and source of microplastics in the Arctic region

Microplastics (MPs) pollution has become a serious environmental issue of growing global concern due to the increasing plastic production and usage. Under climate warming, the cryosphere, defined as the part of Earth’s layer characterized by the low temperatures and the presence of frozen water, has been experiencing significant changes. The Arctic cryosphere (e.g., sea ice, snow cover, Greenland ice sheet, permafrost) can store and release pollutants into environments, making Arctic an important temporal sink and source of MPs. Here, we summarized the distributions of MPs in Arctic snow, sea ice, seawater, rivers, and sediments, to illustrate their potential sources, transport pathways, storage and release, and possible effects in this sentinel region. Items concentrations of MPs in snow and ice varied about 1–6 orders of magnitude in different regions, which were mostly attributed to the different sampling and measurement methods, and potential sources of MPs. MPs concentrations from Arctic seawater, river/lake water, and sediments also fluctuated largely, ranging from several items of per unit to >40,000 items m^?3, 100 items m^?3, and 10,000 items kg^?1 dw, respectively. Arctic land snow cover can be a temporal storage of MPs, with MPs deposition flux of about (4.9–14.26) × 10⁸ items km^?2 yr^?1. MPs transported by rivers to Arctic ocean was estimated to be approximately 8–48 ton/yr, with discharge flux of MPs at about (1.65–9.35) × 10⁸ items/s. Average storage of MPs in sea ice was estimated to be about 6.1×10¹⁸ items, with annual release of about 5.1×10¹⁸ items. Atmospheric transport of MPs from long-distance terrestrial sources contributed significantly to MPs deposition in Arctic land snow cover, sea ice and oceanic surface waters. Arctic Great Rivers can flow MPs into the Arctic Ocean. Sea ice can temporally store, transport and then release MPs in the surrounded environment. Ocean currents from the Atlantic brought high concentrations of MPs into the Arctic. However, there existed large uncertainties of estimation on the storage and release of MPs in Arctic cryosphere owing to the hypothesis of average MPs concentrations. Meanwhile, representatives of MPs data across the large Arctic region should be mutually verified with in situ observations and modeling. Therefore, we suggested that systematic monitoring MPs in the Arctic cryosphere, potential threats on Arctic ecosystems, and the carbon cycle under increasing Arctic warming, are urgently needed to be studied in future.     

Organic carbon isotope ratios (δ13C) of Arctic Amerasian Continental shelf sediments

Organic matter origins are inferred from carbon isotope ratios ('¹³C) in recent continental shelf sediments and major rivers from 465 locations from the north Bering-Chukchi-East Siberian-Beaufort Sea, Arctic Amerasia. Generally, there is a cross-shelf increase in '¹³C, which is due to progressive increased contribution seaward of marine-derived organic carbon to surface sediments. This conclusion is supported by the correlations between sediment '¹³C, OC/N, and '¹⁵N. The sources of total organic carbon (TOC) to the Amerasian margin sediments are primarily from marine water-column phytoplankton and terrigenous C₃ plants constituted of tundra taiga and angiosperms. In contrast to more temperate regions, the source of TOC from terrigenous C₄ and CAM plants to the study area is probably insignificant because these plants do not exist in the northern high latitudes. The input of carbon to the northern Alaskan shelf sediments from nearshore kelp community (Laminaria solidungula) is generally insignificant as indicated by the absence of high sediment '¹³C values (-16.5 to -13.6‰) which are typical of the macrophytes. Our study suggests that the isotopic composition of sediment TOC has potential application in reconstructing temporal changes in delivery and accumulation of organic matter resulting from glacial-interglacial changes in sea level and environments. Furthermore, recycling and advection of the extensive deposits of terrestrially derived organic matter from land, or the wide Amerasian margin, could be a mechanism for elevating total CO₂ and pCO₂ in the Arctic Basin halocline.     

Evolution in sea ice from 1978 to 2012

In this paper, the intra-annual and interannual variability of the sea ice is analysed over the period 1979–2012 from the data and images facilitated by the “National Snow and Ice dates Center”. These data are related to the annual average temperature. The annual average of the marine ice surface area (1979–2012) is very similar in both poles, although its temporary evolution is opposed in both hemispheres. In the Arctic Ocean there is an abrupt reduction of the surface area of the ice during this period. As opposed to it, the marine seas surrounding the Antarctic show an increase of the extension of the ice, especially in the last 15 years, with a maximum value in 2012. With respect to the total of the marine ice over the period 1979–2012, there is an overall deficit balance, because the reduction of the Arctic ice is greater than the increase of the Antarctic ice.     

Marine ice-rafting as a new type of sedimentogenesis in the Arctic and novel approaches to studying sedimentary processes

Research on sedimentogenesis and geochemistry of the Arctic Ocean over the last 10–20 years has allowed direct (in situ) studies to be made for all types of sedimentary matter that mix together and form the bottom deposit. Contrary to common knowledge, river sediment turned out to be insignificant; instead, more important is the dispersed sedimentary matter (suspension) from the atmosphere, cryosphere (snow, ice), marine water, riverine water, biosphere (plankton and benthos), and anthroposphere (all types of pollutants), supplemented by the endogenic mater supplied from spreading zone of the Gakkel Ridge. The mixture is dominated by sedimentary material discharged from sea ice; hence, this type of sedimentogenesis is referred to as the ice-rafted marine sedimentogenesis.Application of new methods and tools (including satellites, remote hydrooptical, hydrophysical, and hydroacoustic survey, etc.) and in situ analyses produced measurements of content, composition, and characteristics of all types of dispersed sedimentary matter, its fluxes (mg/m²/year), vectors of movement, and rates for different segments of the Arctic Ocean; observations were carried out continuously on different time scale, from hours–days to seasons and dozens of years. It is a new approach to the study of sedimentary matter that opens up new possibility for a 4D quantitative sedimentology.     

白令海与西北冰洋表层沉积物中四醚膜类脂物研究及其生态和环境指示意义

通过对中国第3次和第4次北极考察在白令海和西北冰洋采集的65个表层样沉积物中生物标记物四醚膜类脂物(GDGTs)的研究,发现西北冰洋表层沉积物中类异戊二烯和支链GDGTs的浓度分布大致以楚科奇海和波弗特海的陆坡为界线,呈现南高北低的特征,这一特征主要与水体生产力和陆源有机质的输入量有关.基于GDGTs的陆源输入指数BIT显示,从楚科奇海北部到高纬度区的阿尔法脊,陆源有机质的相对比例明显增加,与有机碳稳定同位素等结果一致,表明BIT可以用来指示北极陆源有机质输入量的变化.应用前人TEXL86-SST方程估算的研究区表面海水温度SST与现代年均SST和夏季平均SST的相关性较差,原因可能与陆源输入的类异戊二烯GDGTs干扰以及低的古菌生产力有关.从季节性海冰覆盖区到永久性海冰覆盖区,基于支链GDGTs的环化指数CBT明显升高,可能反映了CBT对海冰覆盖状况的响应,但其响应机制还不清楚.基于支链GDGTs的环化指数CBT和甲基化指数MBT估算的北极陆地年均大气温度和土壤pH差异较大,可能是由表层沉积物的来源复杂以及混合作用造成的.     

Huge Ice‐age lakes in Russia

During an early phase of the Last Ice Age (Weichselian, Valdaian), about 90 000 yr ago, an ice sheet formed over the shallow Barents and Kara seas. The ice front advanced on to mainland Russia and blocked the north‐flowing rivers (Yenissei, Ob, Pechora, Dvina and others) that supply most of the freshwater to the Arctic Ocean. The result was that large ice‐dammed lakes were formed between the ice sheet in the north and the continental water divides to the south. Here we present reconstructions and calculations of the areas and volumes of these lakes. The lake on the West Siberian Plain was nearly twice as large as the largest lake on Earth today. The well‐mapped Lake Komi in northeast Europe and a postulated lake in the White Sea Basin would also rank before the present‐day third largest lake. The lakes overflowed towards the south and thus the drainage of much of the Eurasian continent was reversed. The result was a major change in the water balance on the continent, decreased freshwater supply to the Arctic Ocean, and increased freshwater flow to the Aral, Caspian, Black and Baltic seas. A sudden outburst of the lakes' water to the Arctic Ocean when the ice sheet thinned is postulated. Copyright © 2001 John Wiley & Sons, Ltd.     

Distribution of clay minerals in surface sediments from the eastern Barents and south-western Kara seas

Surface samples from the eastern Barents and south-western Kara seas have been analysed for clay mineralogy. Transport paths, the role of regional sources and local bedrock outcrops and the influence of hydrodynamic and glacigenous processes for clay distribution on the shelves are discussed in relation to central Arctic Ocean deep sea and sea ice sediments. Franz Josef Land and Novaya Zemlya show significantly different clay mineral associations. Although smectite concentrations are fairly high, Franz Josef Land can be excluded as a source for central Arctic sea ice sediments, which are relatively rich in smectite. In the Kara Sea, smectite concentrations in coastal sediments surpass even the Franz Josef Land concentrations. The large cyclonic gyre in the eastern Barents Sea between Novaya Zemlya and Franz Josef Land, which serves as a mixing zone between Arctic and North Atlantic water, is apparently reflected within the smectite distribution pattern. With the exception of Franz Josef Land, the area of investigation is typically low in kaolinite. In particular, coastal areas and areas north of Novaya Zemlya, influenced by the inflow of Arctic waters, show the lowest kaolinite concentrations. A high kaolinite occurrence within the Nansen Basin is most probably related to Franz Josef Land and emphasizes the importance of long-range downslope transport of sediments across the continental slope. The surface water circulation pattern in close interaction with local outcrops onshore Novaya Zemlya and locally restricted occurrences within the eastern Barents Sea significantly alter the illite dispersal pattern. Illite concentrations are lowest around Franz Josef Land. Chlorite is generally low in the area of investigation. Submarine outcrops and important chlorite occurrences onshore Novaya Zemlya bias its distribution pattern.     

格陵兰海海冰外缘线变化特征分析

格陵兰海作为北冰洋的边缘海之一,容纳了北极输出的海冰,其海冰外缘线的变化既受北极海冰输出量的影响,也受局地海冰融化和冻结过程的影响。利用2003年1月到2011年6月AMSR-E卫星亮温数据反演的海冰密集度产品,对格陵兰海海冰外缘线的变化特征进行了分析。结果表明,格陵兰海海冰外缘线不仅存在一年的变化周期,还存在比较显著的半年变化周期,与海冰在春秋两季向岸收缩有关。格陵兰海冬季的海冰外缘线极大值呈逐年下降的趋势,体现了北极增暖导致的冬季海冰范围减小;而夏季海冰外缘线离岸距离的极小值呈上升趋势,表明夏季来自北冰洋的海冰输出量增大。2003—2004年是格陵兰海夏季海冰融化最严重的2年。2007年北冰洋夏季海冰覆盖范围达到历史最小;而格陵兰海夏季的最小海冰范围最大,表明2007年北冰洋海冰的输出量大于其他年份。此外,夏季格陵兰岛冰雪融化形成的地表径流对海冰外缘线有一定的影响。对海冰外缘线影响最大的不是格陵兰海的局地风场,而是弗拉姆海峡(Fram Strait)区域的经向风,它直接驱动了北冰洋海冰向格陵兰海的输运,进而对格陵兰海海冰外缘线的分布产生滞后的影响。     

A 10,000 yr B.P. extensive ice shelf over Viscount Melville Sound,Arctic Canada

Late Wisconsinan age glacial landforms and deposits indicate that an ice shelf of at least 60,000 km² flowed northwestward into Viscount Melville Sound, probably from the M'Clintock Dome of the Laurentide Ice Sheet. The ice shelf overlapped coastal areas and laid Winter Harbour Till up to 125 m above present sea level on the southern coast of Melville Island, to 135 m on Byam Martin Island, to possibly 90 m on the northeast tip of Banks Island, and to 150 m on the north coast of Victoria Island. The contemporary sea level was 50 to 100 m higher than present (it now rises eastward). A maximum age of 10,340 ± 150 yr B.P. for the till, and thus the ice-shelf advance, is provided by shells in marine sediments which underlie it, whereas a minimum age of 9880 ± 150 yr B.P. is provided by overlying shells that postdate the ice advance. The major advance of shelf ice into Viscount Melville Sound may be the result of the rapid disintegration of the M'Clintock Dome while the climate ameliorated in the western Arctic.     

History of sedimentation rates in the sea-ice sedimentation zone during the last 130 ka

Based on literature and our data, analysis of sedimentation rates during the last glacial/interglacial cycle (during the last 130 ka) is given for the Norwegian-Greenland Basin, the Arctic Ocean, Bering and Okhotsk seas, as well as a number of seas in the Southern Ocean. Sedimentation rates in the studied zone are controlled by the development of continental ice sheets, sea ice covers, and biogenic sedimentation, which, in turn, depends on climate variations.     

Retreat of the Smith Sound Ice Stream in the Early Holocene

Nares Strait, a major connection between the Arctic Ocean and Baffin Bay, was blocked by coalescent Innuitian and Greenland ice sheets during the last glaciation. This paper focuses on the events and processes leading to the opening of the strait and the environmental response to establishment of the Arctic‐Atlantic throughflow. The study is based on sedimentological, mineralogical and foraminiferal analyses of radiocarbon‐dated cores 2001LSSL‐0014PC and TC from northern Baffin Bay. Radiocarbon dates on benthic foraminifera were calibrated with ΔR = 220±20 years. Basal compact pebbly mud is interpreted as a subglacial deposit formed by glacial overriding of unconsolidated marine sediments. It is overlain by ice‐proximal (red/grey laminated, ice‐proximal glaciomarine unit barren of foraminifera and containing >2 mm clasts interpreted as ice‐rafted debris) to ice‐distal (calcareous, grey pebbly mud with foraminifera indicative of a stratified water column with chilled Atlantic Water fauna and species associated with perennial and then seasonal sea ice cover) glacial marine sediment units. The age model indicates ice retreat into Smith Sound as early as c. 11.7 and as late as c. 11.2 cal. ka BP followed by progressively more distal glaciomarine conditions as the ice margin retreated toward the Kennedy Channel. We hypothesize that a distinct IRD layer deposited between 9.3 and 9 (9.4–8.9 1σ) cal. ka BP marks the break‐up of ice in Kennedy Channel resulting in the opening of Nares Strait as an Arctic‐Atlantic throughflow. Overlying foraminiferal assemblages indicate enhanced marine productivity consistent with entry of nutrient‐rich Arctic Surface Water. A pronounced rise in agglutinated foraminifers and sand‐sized diatoms, and loss of detrital calcite characterize the uppermost bioturbated mud, which was deposited after 4.8 (3.67–5.55 1σ) cal. ka BP. The timing of the transition is poorly resolved as it coincides with the slow sedimentation rates that ensued after the ice margins retreated onto land.