辽东半岛东南岸全新世海进的认识

辽东半岛呈北东向低山丘陵地形,西临渤海,东濒黄海,半岛的东西两侧为窄长的第四纪沿海平原。为了搞清半岛东部沿海平原的第四纪海侵问题,近年来我们在东沟、庄河等地打了七个钻孔,分层取样,进行微体古生物的研究,首次发现了有孔虫及海生硅藻化石。     

Holocene palaeoceanographic changes in Barrow Strait,Canadian Arctic: foraminiferal evidence

Holocene changes in the benthic and planktic foraminiferal fauna (>63 µm) from a marine sediment core (ARC‐3 Canadian Arctic Archipelago, 74° 16.050′ N, 91° 06.380′ W, water depth 347 m) show that significant environmental and palaeoceanographic variations occurred during the last 10 ka. Foraminiferal assemblages are restricted to the ca. 4.5–10 ka interval as younger samples are mostly barren of foraminifera due to intense carbonate dissolution after ca. 4.5 ka. Foraminiferal assemblages in the ca. 4.5–10 ka interval are dominated by the benthic species Islandiella helenae and Cassidulina reniforme (57% of total), with Elphidium clavatum, Cibicides lobatulus and Buccella frigida also being common in this interval. The dominance of these species indicates a seasonal sea ice regime which is consistent with the occurrence of the sea ice diatom‐derived organic geochemical biomarker IP₂₅ throughout the core. The abundances of C. reniforme and E. clavatum decline upcore; consistent with more frequent mixing of the Barrow Strait water column during the early Holocene. It is likely that the influence of CO₂‐rich Arctic surface water masses have caused an increase in bottom water corrosivity after ca. 8.5 ka, and dissolution has been further enhanced by sea ice‐related processes after ca. 6 ka, concomitant with increased IP₂₅ fluxes. Dissolution is strongest when IP₂₅ fluxes are highest, suggesting a link between the sea ice and benthic systems. Copyright © 2010 John Wiley & Sons, Ltd.     

Microfossil evidence for salinity events in the Holocene Coorong Lagoon,South Australia

Nearly 6 m of uncompacted muddy sediment was recovered from the floor of the northern Coorong Lagoon in the core Coorong #5. Radiocarbon analyses of molluscan shells indicate that sedimentation at the core site commenced before 6830 ± 90 yr cal BP, and the presence of Pinus pollen confirms a modern age for the uppermost 0.5 m. Microfossils extracted from the core sediment samples, 2 cm slices at 10 cm intervals, included the foraminifera Ammonia sp., Elphidium excavatum and Elphidium gunteri; the ostracods Osticythere baragwanathi and Leptocythere lacustris; and charophyte oogonia. Shell fragments of the estuarine bivalve Spisula (Notospisula) trigonella in the lowermost 0.7 m of the core are evidence that these sediments were subject to some marine influence, but the absence of foraminifera and ostracods from this same interval indicates that at the core site salinity was not sufficient to support populations of these organisms. Thus, prior to 6830 ± 90 yr cal BP the Younghusband Peninsula was in place, in part isolating the northern lagoon from the Southern Ocean. The initial recorded salinity event is signified by abundant Ammonia sp. at a core depth of 5.2 m. The duration of this event was relatively brief; foraminifera were mostly absent in the immediately overlying 2 m, representing ca 700 yr of sedimentation. This observation is attributed to substantial inflow of freshwater from the River Murray. In the upper 3.0 m, Ammonia sp. was present in most core samples indicating that for most of the past 6000 years the Coorong Lagoon has been sufficiently saline to support a continuing population of this species. At a core depth of 1.3 m, the sediment sample yielded >2000 tests of Ammonia sp., and they were accompanied by maximum pre-modern numbers of E. excavatum, O. baragwanathi and oogonia. Taken together, these data signify the maximum pre-modern salinity event recorded in the core sediments, probably correlating in time with regional drought conditions at ca 3500 yr BP. Elphidium gunteri is confined to the modern sediments where it is abundant and accompanied by equally large numbers of Ammonia sp., E. excavatum, O. baragwanathi and L. lacustris. These data collectively indicate water conditions that are significantly changed from those that prevailed in the Coorong Lagoon for most of the Holocene.     

Sedimentary and foraminiferal facies in Exmouth Gulf,in arid tropical northwestern Australia

Exmouth Gulf is a major U‐shaped embayment on the northwestern coast of Western Australia, at a latitude of 22°S. Water temperatures are 18–31°C and normal oceanic salinity is maintained by strong tidal currents despite the hot, arid climate. A series of sediment grab samples were collected and analysed for particle‐size and foraminiferal diversity. Samples contained mud, quartzose fine sand and coarse carbonate sand fractions. The muddiest facies are located in the most sheltered areas of the gulf: mangrove channels, tidal flats, southwestern flanks and the deeper axial region. Quartzose fine sands probably have mixed origins which might include: southern aeolian dunes; cyclone‐related reworking of beach and near‐shore deposits; and reworked relict shelf alluvium. The shallow‐water fair‐weather wave climate may play a significant role in localised sediment dispersal and sorting along the eastern margin of the gulf. Sediment distributions within the gulf are complicated by low sedimentation rates through much of the central and western areas of the gulf, significant mixing, and possible inheritance of pre‐Holocene alluvium. The Holocene foraminiferal assemblage recorded from Exmouth Gulf is overwhelmingly dominated by benthic species: agglutinated, calcitic‐porcellaneous, and calcitic‐hyaline groups. The distribution of individual foraminiferal species shows relatively simple patterns, governed by environmental parameters. Live individuals are rare.     

Molecular fossils as a tool for tracking Holocene sea-level change in the Loch of Stenness,Orkney

Sediments deposited in the Loch of Stenness (Orkney Islands, Scotland) during the Holocene transgression, previously dated to between ~5939–5612 bp , were analysed for molecular fossils – lipids and chlorophyll pigments from primary producers – that complement conventional microfossil and lithological approaches for studying past sea-level change. While microfossil and lithological studies identified a transgression between 102 and 81 cm core depth, key molecular fossils fluctuate in occurrence and concentration between 118 and 85 cm, suggesting an earlier start to the transgression. Terrestrial lipid concentrations decreased and algal-derived, short-chain, n-alkanoic acid concentrations increased at 118 cm, indicating a disruption of the freshwater lake conditions associated with the early stages of the marine transgression. The lipid and pigment analyses provided information that complements and extends that from microfossil analysis, presenting a more complete record of Holocene sea-level changes and local vegetation changes in the Loch of Stenness. The isostatic stability of Stenness during the Holocene points towards other factors to explain the transgression, such as regional factors and/or melting of the Antarctic ice sheet (which occurred up to 3 ka).     

Foraminiferal evidence of basin submergence in part of Sundarban mangrove delta,India

Sundarban is a largest mangrove forest delta developed along the NE-SW direction covering parts of India and Bangladesh. Little work has been done on Indian part of Sundarban in respect of heterogeneity in channel morphology which could be mostly due to the effect of tilting and basin subsidence. These changes might have played a major role on development of high marshes, which offers a congenial environment for survival of Haplophragmoides wilberti, Jadammina macrescens, Trochammina inflata, and Miliammina fusca. These marsh benthonic foraminiferal assemblages provide a direct evidence of recent past sea level changes. To establish the depositional pattern and their effects rendered by merciless changing environment, 11 pit sections have been excavated along three E-W transects from Indian Sundarban. Depth of these pit sections varies from 2 to 3 m. Generally, top 20 cm sediment (in pit section W-1 to W-11) deposited under the intertidal environment, as indicated by the presence of Ammonia tepida. However, sediment below 20 cm in some of the pit sections (W-3 and W-5) exhibits fresh water signatures as indicated by the presence of Charophytes algae. In other pit sections (W-1, W-2, W-6, W-7, W-8, W-9 and W-11), the intertidal assemblage is noticed just above the upper marshes assemblage and vice versa, signifying that depositional environment is in proximity to the mangrove dominated area as indicated by the presence of marsh benthonic foraminiferal assemblage containing T. inflata, H. wilberti, Haplophragmoides sp., J. macrescens and M. fusca. Bottom sediment in most of the pit sections from south to north have different depositional environment with alternate presence of intertidal to subtidal faunal assemblages. The peculiar presence of intertidal assemblage above the upper marshes assemblages in recent sediment points towards the theory of submergence due to relative rise in the sea level. But the effect of relative sea level rise is not uniform throughout the area because of differential subsidence due to varied rate of sediment supply (0.5 to 3.3 cm/year) and eastward tilting of the basin. Based on the upper marshes benthonic foraminiferal assemblage and radiocarbon age (in W-1 at 100 cm ~?150 years age), the average subsidence rate as recorded is approximately 0.3 to 0.5 cm/year. Hence, such depositional sequence conjectures that the Indian part of Sundarban is undergoing a phase of submergence concomitant to basin subsidence.     

Anthropogenic impact on Andaman coast monitoring with benthic foraminifera,Andaman Sea,India

The concept of anthropogenic impact is extremely important to be considered while analysing the ecology of coast and shelf zones. For centuries, these zones have been the epicentres for various human activities, including urbanisation, construction of sea ports and harbours, development of natural reservoirs (including oil production and fishing), marine aquaculture, shipping, recreation and many others. Many of the activities in progress on both sides of the shoreline provide 50% or more of the gross State/UT (Union Tertiary) product for surrounding states. The data shows that land-based and atmospheric sources account for about two-thirds of the total contamination found in the marine environment, constituting 44 and 33%, respectively. The greatest anthropogenic pollution pressure undoubtedly falls on the shelf zones and coastal areas. To prove this theory, a total of 25 bottom sediment samples were collected within the depth zone of 5 fathoms from the South Andaman coastal fringe for sediment geochemistry studies and foraminiferal analysis. The samples were further analysed for heavy metal pollutants like Co, Cu, Mn, Pb and Zn. The study yielded 20 benthic foraminiferal species. Of these, five benthic species were living including Ammonia beccarii, Calcarine calcar, Elphidium crispum, Operculina complanata and Nonion deppresula. The presence of deformed specimens and the domination of Ammonia spp. are indications of a polluted environment. Sampled coral reefs had high abundances of Operculina spp. The highest counts of benthic microbiota were found in finer sediment. Species diversity is very limited along the coastal fringe of South Andaman Island in comparison with fauna from the coast of India. This first report of benthic foraminifera from South Andaman Island will allow us to assess future impacts of marine pollution because foraminiferal deformations are positively correlated to the concentrations of heavy metals (Cr, Cu, Mn, Pb and Zn).     

Holocene stratigraphic and morphological evolution of the Wandandian Creek delta,St Georges Basin,New South Wales

Subaerial exposure beside the Wandandian Creek channel during the last glacial maximum led to the development of red and orange mottling and, in some areas, produced a palaeosol over the Pleistocene land surface. Incision of the palaeo-Wandandian Creek, during the Late Pleistocene, formed a relatively deep steep-sided channel partially infilled with medium-grained fluvial sand. This palaeovalley became drowned as the post-glacial marine transgression impounded the western portion of St Georges Basin and the basal prodelta/lagoonal mud facies was deposited from ca 7 ka. The Wandandian Creek delta prograded down the palaeovalley and reached the study area ～3500 – 4000 years ago with the deposition of delta-front sandy silt and the overlying prograded sand facies. The subaerial portion of the delta is characterised by well-developed floodplains, levees, mouth bars and backswamps. Dredging in Wandandian Creek and land clearing for rural and urban development have had little long-term effect on the growth and morphology of Wandandian Creek delta.     

Glacial history and marine environmental change during the last interglacial-glacial cycle, western Spitsbergen, Svalbard

Superimposed glacial and marine sediment exposed in coastal cliffs on Brøggerhalvøya, west Spitsbergen, contain four emergence cycles (episodes D, C, B, and A) that are related to glacial-isostatic depression and subsequent recovery of the crust. Tills are found in episodes C and B; in each case glaciation began with an advance of local glaciers, followed by regional glaciation. The marine transgression following episode C deglaciation reached 70 to 80 m above sea level. Glacial-marine and sublittoral sands within episode C contain a diverse and abundant microfauna requiring marine conditions more favorable than during the Holocene. We define this interval as the Leinstranda Interglacial. Based on the fauna, sedimentology and geochronology (radiocarbon, amino acid racemization, and uranium-series disequilibrium) we conclude that the Leinstranda Interglacial occurred during isotope substage 5e. Episode B deglaciation occurred late in isotope stage 5 (c. 70 ± 10 ka ago), and was followed by a marine transgression to about 50 m above sea level. The associated foraminifera, mollusca, and vertebrate fauna require seasonally ice-free conditions similar to those of the Holocene, but less ameliorated than during the Leinstranda Interglacial. A significant influx of Atlantic water into the Norwegian Sea, augmented by a local insolation maximum late in isotope stage 5, are required to produce shallow-water conditions similar to those of the Holocene. There is no evidence for major glacial activity during the Middle Weichselian (isotope stages 4 and 3), and we conclude that ice margins were not significantly different from those of the late Weichselian, but the record for this interval is scant. The extent of ice at the Late Weichselian maximum was less than during either of the two preceding episodes (B or C). Late Weichselian deglaciation (episode A) began prior to 13 ka B.P. Oceanic and atmospheric circulation patterns conducive to large-scale glaciation of western Spitsbergen are not well understood, but those patterns that prevailed during isotope stages 4,3, 2, and 1 did not produce a major glacial advance along this coast.     

Palynological evidences on paleoclimate and paleoenvironmental changes during Holocene of Al-Hussaynia District,Central Iraq

This paper is concerned with the study of paleoclimate and paleoenvironmental changes of Hussaynia township which is located in Karbala at the center of the Mesopotamian plain during Holocene. Ten soil samples were examined to determine their content of pollens, spores, and marine organisms (dinoflagellates). These palynomorphs include: Graminidites, Palmaepollenites, Chenopodiaceae, Composita, Cyperaceae, Sphaginum sporites, Pinus pollenites, Convovolus, Artimesia, Laevigatosporites, Quercus, dinoflagellates, and fungi. The study revealed climatic and environmental changes in the area during Holocene and four climatic zones were determined in the studied sequence and correlated with other areas in and outside of Iraq. The climate was pluvial with intervening dry periods in the 10000 years?bp. The study indicated as well, some marine effects on the studied area on the commencement of Holocene due to the global transgression. This is based on the presence of marine organisms, dinoflagellate.     

Paleogeography of the Laptev Sea eastern shelf in the first half of Holocene based on faunal and palynological evidence

The Holocene paleogeography of the Laptev Sea eastern shelf is reconstructed based on mollusks, foraminifers, ostracodes, spores and pollen found for the first time. Environmental changes in the course of the postglacial (Holocene) transgression are detectable from quantitative analysis of three ostracod assemblages. Three phases of the transgression are established based on ostracode assemblages from the AMS ¹⁴C-dated core from the ancient valley of Yana River, central part of the Laptev Sea eastern shelf. After the first phase of coastal brackish-water environment (11.3–11.1 ka), shallow-water marine taxa appeared in the transitional phase (11.1–10.3 ka), and the third phase of modern sea conditions commenced 10.3 ka ago. Spore and pollen assemblages from the core indicate that the early Holocene land vegetation was dominated by tundra plant communities adapted to climatic conditions not warmer than at present. In the interval of 9.3–8.0 ka, climate was increasingly humid and warm, and forest-tundra vegetation occupied more favorable zones of the region.     

北京顺义早更新世有孔虫动物群的古生态及古环境

1975年我们报道了泥河湾盆地怀来及蔚县境内发现半咸水有孔虫化石,当时认为它们的层位可能属第四系上部,后来进一步工作证实应是泥河湾组上部沉积。1977年我们对华北平原第四纪海进海退现象作了初步报道,认为华北平原在早更新世时发生过海进(渤海海进),并引用陈方吉在北京东南发现海相介形虫资料,说明早更新世渤海海进时海水曾经到达这一地区。1978年李鼎容等在北京市顺义县早更新世地层中发现大量有孔虫化石。进一步证实北京地区早更新世确曾发生过海进,使我们解释怀来及蔚县所发现的半咸水有孔虫来源,有更多证据。这一发现,对于北京地区第四纪地层划分对比、新构造运动判别和古地理恢复有重大意义。     

Sub‐arctic Holocene climatic and oceanographic variability in Stjernsund,northern Norway: evidence from benthic foraminifera and stable isotopes

A high‐resolution record, covering 9.3–0.2 ka BP, from the sub‐arctic Stjernsund (70°N) was studied for benthic foraminiferal faunas and stable isotopes, revealing three informally named main phases during the Holocene. The Early‐ to Mid‐Holocene (9.3–5.0 ka BP) was characterized by the strong influence of the North Atlantic Current (NAC), which prevented the reflection of the Holocene Climatic Optimum (HCO) in the bottom‐water temperature. During the Mid‐Holocene Transition (5.0–2.5 ka BP), a turnover of benthic foraminiferal faunas occurred, Atlantic Water species decreased while Arctic‐Polar species increased, and the oxygen isotope record showed larger fluctuations. Those variations correspond to a period of global climate change, to spatially more heterogeneous benthic foraminiferal faunas in the Nordic Seas region, and to regionally diverging terrestrial temperatures. The Cool Late Holocene (2.5–0.2 ka BP) was characterized by increased abundances of Arctic‐Polar species and a steady cooling trend reflected in the oxygen isotopes. In this period, our record differs considerably from those on the SW Barents Sea shelf and locations farther south. Therefore, we argue that regional atmospheric cooling triggered the late Holocene cooling trend. Several cold episodes centred at ～8.3, ～7.8, ～6.5, ～4.9, ～3.9 and ～3.3 ka BP were identified from the benthic foraminiferal faunas and the δ¹⁸O record, which correlated with marine and atmospherically driven proxy records. This suggests that short‐term cold events may result from reduced heat advection via the NAC or from colder air temperatures.     

Nearshore cool-water carbonate sedimentation and provenance of Holocene calcareous strandline dunes,southeastern Australia

The southeastern coastal plain of South Australia contains a spectacular and world-renowned suite of Quaternary calcareous eolianites. This study is focused on the provenance of components in the Holocene, actively forming sector, of these carbonate eolian deposits. Research was carried out along seven transects across a lateral distance of 120 km from ～30 m water depth offshore across the beach and into the dunes. Offshore sediments were acquired via grab sampling and SCUBA. Results indicate that dunes of the southern Lacepede and Bonney coasts are composed of siliciclastic particles (mainly quartz), relict allochems, Cenozoic and limestone pieces, but dominated by Holocene invertebrate and calcareous algal biofragments. The most numerous grains are from molluscs > benthic foraminifera ≥ coralline algae, > echinoids and > bryozoans. Most of these particles originate in carbonate factories such as macroalgal forests, rocky reefs, seagrass meadows and low-relief sea-floor rockgrounds. Incorporation of Holocene carbonate skeletons into coastal dunes, however, depends on a combination of: (1) the addition of infauna from intertidal and nearshore environments; (2) the physical characteristics of different allochems and their ability to withstand bioerosion, fragmentation and abrasion; (3) the character of the wave and swell climate; and (4) the nature of eolian transport. Most eolian dune sediment is derived from nearshore and intertidal carbonate factories. This is well illustrated by the abundance of robust infaunal bivalves that inhabit the nearshore sands and virtual absence of bryozoans that are common as sediment particles in offshore water depths >15 m. Importantly, the calcareous eolianites in this cool-water, open-platform carbonate setting are not simply an allochthonous reflection of the offshore marine shelf factories, but more a product of autothonous shallow nearshore–intertidal skeletal production and modification. These findings explain the preponderance of mollusc fragments and lack of bryozoans in similar older Pleistocene calcareous eolianites up to ca 1 million years old across ～2000 km of southern Australia with implications for the older rock record.     

江苏省里下河(兴化-泰州)地区浅表沉积物特征及古地理环境演变

里下河地区浅部沉积物多为全新世中、晚期堆积,多数地区缺失全新世早期沉积。沉积物以淤泥质亚粘土、亚粘土、亚砂土,粉砂质淤泥、淤泥质粉砂、淤泥及泥炭为特征。沉积前的古地貌为四周高、中间低的碟形盆地。古气候经历了温湿—暖湿—温湿—温干的变化过程。区内曾有两次海侵,第一次海侵发生在全新世早中期,范围几乎遍及全区;第二次海侵发生在全新世晚期,规模小、范围窄、时间短,为海水沿江河倒灌、回溯形起。该区古环境自全新世以来经历了浅水海湾—古泻湖—湖沼地及平原的演变过程,最终形成现今河湖稠密的低凹平原。     

A record of Lateglacial and early Holocene environmental and ecological change from southwestern Connecticut,USA

Analyses of a sediment core from Highstead Swamp in southwestern Connecticut, USA, reveal Lateglacial and early Holocene ecological and hydrological changes. Lateglacial pollen assemblages are dominated by Picea and Pinus subg. Pinus, and the onset of the Younger Dryas (YD) cold interval is evidenced by higher abundance of Abies and Alnus viridis subsp. crispa. As climate warmed at the end of the YD, Picea and Abies declined and Pinus strobus became the dominant upland tree species. A shift from lacustrine sediment to organic peat at the YD–Holocene boundary suggests that the lake that existed in the basin during the Lateglacial interval developed into a swamp in response to reduced effective moisture. A change in wetland vegetation from Myrica gale to Alnus incana subsp. rugosa and Sphagnum is consistent with this interpretation of environmental changes at the beginning of the Holocene. Copyright © 2009 John Wiley & Sons, Ltd.     

The Littorina transgression in the southwestern Baltic Sea: new insights based on proxy methods and radiocarbon dating of sediment cores

Rößler, D., Moros, M. & Lemke, W. 2010: The Littorina transgression in the southwestern Baltic Sea: new insights based on proxy methods and radiocarbon dating of sediment cores. Boreas, 10.1111/j.1502‐3885.2010.00180.x. ISSN 0300‐9483. The Littorina transgression is one of the most pronounced environmental events in the Holocene history of the Baltic Sea. It changed the hydrographic system from the freshwater Ancylus Lake into the brackish‐marine Littorina Sea. Here, 18 cores from two western Baltic basins, Mecklenburg Bay and the Arkona Basin, were analysed. We show that, besides biological indicators, sedimentary organic carbon, C/N ratio, bulk δ¹³C isotope values and carbonate content display clearly the transition from Ancylus Lake to the Littorina Sea. The first appearances of benthic foraminifers, marine molluscs and ostracods represent the onset of brackish‐marine conditions in the bottom waters. Central Arkona Basin sediments display more abrupt shifts in geochemical parameters and microfossil records at the transition from Ancylus Lake to the Littorina Sea than those from Mecklenburg Bay. Mixing of reworked Ancylus material with Littorina Sea stage material was stronger in Mecklenburg Bay, resulting in less pronounced proxy parameter changes and older bulk material dates. Radiocarbon dating of both calcareous material (benthic foraminifers, mollusc shells) and bulk fractions at the transgression horizon shows large age discrepancies. Based on calcareous fossil dates it appears that marine waters began to enter Mecklenburg Bay c. 8000 cal. a BP. In the Arkona Basin the first marine signals are recorded approximately 800 years later, c. 7200 cal. a BP. This indicates a transgression pathway via the Great Belt into Mecklenburg Bay and then into the Arkona Basin.     

天津大直沽晚第四纪沉积物红外释光测年及环境变迁年代学

对天津大直沽ZH2钻孔晚第四纪沉积物岩芯12个样品的红外释光(IRSL)测年及沉积物记录的环境变化研究结果表明:1)细颗粒(4～11μm)多测片的红外释光(IRSL)技术对水悬浮沉积物的年龄测定有着巨大的潜力,渤海湾西岸全新世环境变化的IRSL年代可与¹⁴C年代相对比;2)大直沽ZH2孔所在地未见晚更新世海侵,并在距今约30 ka至约10 ka期间处于沉积间断状态,距今9.5 ka开始发生海侵,距今5.1 ka发生海退,距今4.4 ka海水已退出ZH2孔所在地,距今2 ka左右已有人类活动.     

Monsoonal changes inferred from the Middle to Late Holocene sediments off Landfall Island,North Andaman

In this paper, sediment texture, clay mineral composition, and δ ¹⁸O data on Globigerinoides ruber of a sediment core collected from a water depth of 250 m near Landfall Island, Bay of Bengal, is presented to understand paleoenvironmental shifts during the Mid–Late Holocene period. From the sediment core, five organic carbon-rich samples were radiocarbon dated and the reservoir-corrected ages range from 6,078 to 1,658 years BP. The marine sediment core is represented dominantly by clayey silt with incursions of coarser components that occur around 6,000, 5,400, and 3,400 years BP. The sedimentation of the coarser detritus is due to strengthened southwest monsoon (SWM) since 6,500 to 5,400 years BP. Clay minerals are represented by smectite, illite, kaolinite, and chlorite in varying amounts. High kaolinite content and K/C ratio indicate intense SWM and strong bedrock weathering from the hinterland (~6,500–5,400 years BP). Incidence of smectite (48.82 to 25.09 %) and chlorite/illite (C/I) ratio (0.56 to 0.28) indicate an overall weakened southwest monsoon since 6,000 to 2,000 years BP with a brief incursion of extremely reduced SWM around 4,400 to 4,200 years BP. This is corroborated with the oxygen isotope on G. ruber that reveals a significant shift in the isotopic values ~4,300 years BP (?3.39?‰), indicating weakening in SWM. Subsequently, fluctuations in the intensity of SWM are observed since 2,000 years to present.     

Changes in the inflow of saline water into the Bornholm Basin (SW Baltic Sea) during the past 7100 years – evidence from benthic foraminifera record

The Baltic Sea (~393 000 km²) is the largest brackish sea in the world and its hydrographic and environmental conditions are strongly dependent on the frequency of saline water inflows from the North Sea. To improve our understanding of the natural variability of the Baltic Sea ecosystem detailed reconstructions of past saline water inflow changes based on palaeoecological archives are needed. Here we present a high‐resolution study of benthic foraminiferal assemblages accompanied by sediment geochemistry (loss on ignition, total organic carbon) and other microfossil data (ostracods and cladocerans) from a well‐dated 8‐m‐long gravity core taken in the Bornholm Basin. The foraminiferal diversity in the core is low and dominated by species of Elphidium. The benthic foraminiferal faunas in the central Baltic require oxic bottom water conditions and salinities >11–12 PSU. Consequently, shell abundance peaks in the record reflect frequent saline water inflow phases. The first appearance of foraminiferal tests and ostracods in the investigated sediment core is dated to c. 6.9 cal. ka BP and attributed to the first inflows of saline and oxygenated bottom waters into the Bornholm Basin during the Littorina Sea transgression. The transgression terminated the Ancylus Lake phase, reflected in the studied record by abundant cladocerans. High absolute foraminiferal abundances are found within two time intervals: (i) c. 5.5–4.0 cal. ka BP (Holocene Thermal Maximum) and (ii) c. 1.3–0.75 cal. ka BP (Medieval Climate Anomaly). Our data also show three intervals of absent or low saline water inflows: (i) c. 6.5–6.0 cal. ka BP, (ii) c. 3.0–2.3 cal. ka BP and (iii) c. 0.5–0.1 cal. ka BP (Little Ice Age). Our study demonstrates a strong effect of saline and well‐oxygenated water inflows from the Atlantic Ocean on the Baltic Sea ecosystem over millennial time scales, which is linked to the major climate transitions over the last 7 ka.