Distribusi Foraminifera di Laut Halmahera dari Glasial Akhir Sampai Resen

Mikrofauna foraminifera telah banyak digunakan sebagai proksi dalam penelitian paleoseanografi dan Perubahan iklim purba. Kelimpahan dan komposisi kimia cangkang foraminifera merekam berbagai informasi yang dapat diinterpretasi berkaitan dengan Perubahan lingkungan berdasarkan parameter-parameter paleoseanografi. Paleoseanografi Laut Halmahera sangat penting untuk dikaji karena berpengaruh terhadap dinamika iklim Indonesia dan iklim global. Perubahan-Perubahan parameter oseanografi tersebut mempengaruhi sirkulasi arus global dan interaksi antara air-udara yang berperan terhadap penyebaran uap air ke lintang tinggi. Oleh karena itu tujuan penelitian ini adalah mempelajari distribusi foraminifera untuk rekonstruksi Perubahan paleoseanografi di Laut Halmahera dan sekitarnya. Data foraminifera ini didukung dengan pemodelan umur dan rekonstruksi isotop stratigrafi berdasarkan analisis d18O G. ruber dan C14 radiokarbon dating. Hasil penelitian menunjukkan bahwa kelimpahan foraminifera di Laut Halmahera sangat dipengaruhi oleh iklim global. Kelimpahan foraminifera terutama didominasi oleh G. ruber, G. bulloides, P. obliqueloculata, N. dutertrei, dan G. menardii dari jenis planktonic. Sedangkan jenis bentik didominasi oleh Bulimina spp., Bolivinita quadrilatera, Bolivina spp., dan Uvigerina spp. Biozonasi foraminifera menunjukkan korelasi yang sangat baik dengan data ?18O dan mencerminkan Perubahan – Perubahan iklim di masa lalu yang terjadi sejak 50.000 tahun yang lalu antara lain glasial akhir yang berlangsung sejak zona 1 - 4b, LGM (subzone 4b), deglasiasi (subzona 4c), kondisi seperti YD dari bumi bagian utara atau ACR dari bumi bagian selatan pada awal zona 5, interglasial (pertengahan zona 5), dan Mid Holosen Maksimum pada pertengahan subzona 5a. Kata kunci: Distribusi foraminifera, paleoseanografi, isotop oksigen, Perubahan iklim global, Laut Halmahera. Microfauna foraminifera has been widely used as a potential proxy for paleoceanography and paleoclimatological changes. Its assemblages and its test geochemical composition preserve important data that could interprete various oceanographic parameters related to the paleoenvironmental changes. The paleoceanography dynamic of Halmahera sea is very important to be studied due to its great impact to Indonesian and global climate. The changes of its oceanographic parameters influence the thermohaline circulation and the air-sea interaction that contribute to the water favour distribution to the high latitudes. Therefore this research purpose is to analyze the foraminiferal distribution in order to reconstruct the paleoceanography changes of Halmahera sea and surrounded. This foraminiferal study is supported by the age model reconstruction and isotope stratigraphy analysis based on d18O G. ruber and 14C dating. The result suggests that foraminiferal assemblage was influenced by global climate changes. Planktonic foraminifera is dominated by G. ruber, G. bulloides, P. obliqueloculata, N. dutertrei, and G. menardii. Benthic foraminifera is dominated by Bulimina spp., Bolivinita quadrilatera, Bolivina spp., and Uvigerina spp. Foraminiferal biozonation indicates coherent correlation with ?18O record, and reflects global paleoclimatic changes that occurred since the 50 ka BP. Those paleoclimatic changes are last glacial (zone 1 - subzone 4b), LGM (zone 4b), deglaciation that was started from subzone 4c, condition of YD like of Northern Hemisphere climate or ACR like of the Southern Hemisphere climate (the beginning of zone 5), interglacial (middle of zone 5), and Mid Holocene Maximum at the middle of subzone 5a

Holocene evolution of summer winds and marine productivity in the tropical Indian Ocean in response to insolation forcing: data-model comparison

The relative abundance of <i>Globigerinoides bulloides</i> was used to infer Holocene paleo-productivity changes on the Oman margin and at the southern tip of India. Today, the primary productivity at both sites reaches its maximum during the summer season, when monsoon winds result in local Eckman pumping, which brings more nutrients to the surface. On a millennium time-scale, however, the % <i>G. bulloides</i> records indicate an opposite evolution of paleo-productivity at these sites through the Holocene. The Oman Margin productivity was maximal at ~9 ka (boreal summer insolation maximum) and has decreased since then, suggesting a direct response to insolation forcing. On the contrary, the productivity at the southern tip of India was minimum at ~9 ka, and strengthened towards the present. <br><br> Paleo-reconstructions of wind patterns, marine productivity and foraminifera assemblages were obtained using the IPSL-CM4 climate model coupled to the PISCES marine biogeochemical model and the FORAMCLIM ecophysiological model. These reconstructions are fully coherent with the marine core data. They confirm that the evolution of particulate export production and foraminifera assemblages at our two sites were directly linked with the strength of the upwelling. Model simulations at 9 ka and 6 ka BP show that the relative evolution between the two sites since the early Holocene can be explained by the weakening but also the southward shift of monsoon winds over the Arabian Sea during boreal summer

Climate variability during MIS 20–18 as recorded by alkenone-SST and calcareous plankton in the Ionian Basin (central Mediterranean)

This study shows the first Mediterranean high-resolution record of alkenone-derived sea surface temperature (SST) in the marine sediments outcropping at the Ideale section (IS) (southern Italy, central Mediterranean) from late marine isotope stage (MIS) 20 - through early MIS 18. The SST pattern evidences glacial-interglacial up to submillennial-scale temperature variation, with lower values (~13 °C) in late MIS 20 and substage 19b, and higher values (up to 21 °C) in MIS 19c and in the interstadials of MIS 19a. The SST data are combined with the new calcareous plankton analysis and the available, chronologically well-constrained carbon and oxygen isotope records in the IS. The multi-proxy approach, together with the location of the IS near the Italian coasts, the lower circalittoral-upper bathyal depositional setting, and high sedimentation rate allow to document long-and short-term paleoenvironmental modifications (sea level, rainfall, inorganic/organic/fresh water input to the basin), as a response to regional and global climate changes. The combined proxies reveal the occurrence of a terminal stadial event in late MIS 20 (here Med-HTIX), and warm-cold episodes (here Med-BATIX and Med-YDTIX) during Termination IX (TIX), which recall those that occurred through the last termination (TI). During these periods and the following ghost sapropel layer (insolation cycle 74, 784 ka) in the early MIS 19, high frequency internal changes are synchronously recorded by all proxies. The substage MIS 19c is warm but quite unstable, with several episodes of paleoenvironmental changes, associated with fluctuating tropical-subtropical water inflow through the Gibraltar Strait, variations of the cyclonic regime in the Ionian basin, and the southward shift of westerly winds and winter precipitation over southern Europe and Mediterranean basin. Three high-amplitude millennial-scale oscillations in the patterns of SST and calcareous plankton key taxa during MIS 19a are interpreted as linked to changes in temperature as well as in salinity due to periodical water column stratification and mixing. The main processes involved in the climate variability include changes in oceanographic exchanges through the Gibraltar Strait during modulations of Atlantic meridional overturning circulation and/or variations in atmospheric dynamics related to the influence of westerly and polar winds acting in the paleo-Ionian basin. A strong climate teleconnection between the North Atlantic and Mediterranean is discussed, and a prominent role of atmospheric processes in the central Mediterranean is evidenced by comparing data sets at the IS with Italian and extra-Mediterranean marine and terrestrial records

Modern relationships between microscopic charcoal in marine sediments and fire regimes on adjacent landmasses to refine the interpretation of marine paleofire records: An Iberian case study

Marine microcharcoal records provide invaluable information to understand changes in biomass burning and its drivers over multiple glacial and interglacial cycles and to evaluate fire models under warmer climates than today. However, quantitative reconstructions of burnt area, fire intensity and frequency from these records need calibration studies of the current fire-microcharcoal relationship. Here, we present the analysis of microcharcoal concentration and morphology in 102 core-top sediment samples collected in the Iberian margin and the Gulf of Cádiz. We show that microcharcoal concentrations are influenced by the water depth or the distance from the river mouth. At regional scale, the mean microcharcoal concentrations and microcharcoal elongation (length to width ratio) show a marked latitudinal variation in their distribution, primarily controlled by the type of burnt vegetation in the adjacent continent. High microcharcoal concentrations in marine sediments represent rare, large and intense fires in open Mediterranean woodlands. Based on these results, the increasing trend of microcharcoal concentrations recorded since 8 ka in the well-known marine sedimentary core MD95-2042 off the Iberian margin indicates the occurrence of large and infrequent fires of high intensity due to the progressive degradation of the Mediterranean forest and the expansion of shrublands

The ACER pollen and charcoal database: a global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard–Oeschger (D–O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D–O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73–15 ka) with a temporal resolution better than 1000 years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U∕230Th, optically stimulated luminescence (OSL), 40Ar∕39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft AccessTM at https://doi.org/10.1594/PANGAEA.870867

The ACER pollen and charcoal database: A global resource to document vegetation and fire response to abrupt climate changes during the last glacial period

This is the final version of the article. Available from Copernicus Publications via the DOI in this record.Quaternary records provide an opportunity to examine the nature of the vegetation and fire responses to rapid past climate changes comparable in velocity and magnitude to those expected in the 21st-century. The best documented examples of rapid climate change in the past are the warming events associated with the Dansgaard-Oeschger (D-O) cycles during the last glacial period, which were sufficiently large to have had a potential feedback through changes in albedo and greenhouse gas emissions on climate. Previous reconstructions of vegetation and fire changes during the D-O cycles used independently constructed age models, making it difficult to compare the changes between different sites and regions. Here, we present the ACER (Abrupt Climate Changes and Environmental Responses) global database, which includes 93 pollen records from the last glacial period (73-15ka) with a temporal resolution better than 1000years, 32 of which also provide charcoal records. A harmonized and consistent chronology based on radiometric dating (14C, 234U/230Th, optically stimulated luminescence (OSL), 40Ar/39Ar-dated tephra layers) has been constructed for 86 of these records, although in some cases additional information was derived using common control points based on event stratigraphy. The ACER database compiles metadata including geospatial and dating information, pollen and charcoal counts, and pollen percentages of the characteristic biomes and is archived in Microsoft Access™ at https://doi.org/10.1594/PANGAEA.870867.The members of the ACER project wish to thank the QUEST-DESIRE (UK and France) bilateral project, the INQUA International Focus Group ACER and the INTIMATE-COST action for funding a suite of workshops to compile the ACER pollen and charcoal database and the workshop on ACER chronology that allow setting the basis for harmonizing the chronologies. Josué M. Polanco-Martinez was funded by a Basque Government postdoctoral fellowship (POS_2015_1_0006) and Sandy P. Harrison by the ERC Advanced Grant GC2.0: unlocking the past for a clearer future

Early Ipswichian (last interglacial) sea level rise in the channel region : Stone Point Site of Special Scientific Interest, Hampshire, England

Constraining the speed of sea level rise at the start of an interglacial is important to understanding the size of the ‘window of opportunity’ available for hominin migration. This is particularly important during the last interglacial when there is no evidence for significant hominin occupation anywhere in Britain. There are very few finer grained fossiliferous sequences in the Channel region that can be used to constrain sea level rise and they are preserved only to the north of the Channel, in England. Of these, the sequence at Stone Point SSSI is by far the most complete. Data from this sequence has been previously reported, and discussed at a Quaternary Research Association Field Meeting, where a number of further questions were raised that necessitated further data generation. In this paper, we report new data from this sequence – thin section analysis, isotopic determinations on ostracod shells, new Optical Stimulated Luminescence ages and Amino Acid Recem analyses. These show early sea level rise in this sequence, starting during the pre-temperate vegetation zone IpI, but no early warming. The implications of this almost certainly last interglacial sequence for the human colonisation of Britain and our understanding of the stratigraphic relationship of interglacial estuarine deposits with their related fluvial terrace sequences is explored

High resolution compressional wave velocity measurements in Pleistocene sediments of the Ceara Rise (western equatorial Atlantic): implications for orbital driven sedimentary cycles

International audienceCores from Ocean Drilling Program Sites 927 and 928, retrieved in water depths of 3315 m and 4012 m on the northern ßank of the Ceara Rise, were examined to provide continuous time series of compressional-wave velocity for the Pleistocene (0-1.2 Ma), to evaluate the responses of these records to climate change in the time and frequency domain and to study the effect of carbonate dissolution on P-wave velocity changes. Comparisons with other high-resolution sediment physical property measurements (GRAPE density, magnetic susceptibility) and sedimentological parameters (CaCO 3 content, coarse fraction) demonstrate that velocity changes at Sites 927 and 928 are the result of glacial/interglacial changes in coarse-fraction grain size, with velocity increasing as grain size increases during interglacial periods. The grain-size distribution in turn is controlled by carbonate productivity and dissolution changes. This signal, however, is diluted by abundant input of Þne-grained terrigenous sediments from the Amazon Fan that contain magnetic minerals and thus lead to an inverse relationship between velocity and magnetic susceptibility. Spectral analysis of P-wave velocity and related parameters reveals that spectral energy is concentrated at orbital frequencies in the precession, obliquity, and eccentricity band, and, therefore, conÞrms the potential of velocity records as a paleoceanographic tool. Marked differences between variance density spectra of the velocity and preservation index records at Site 927 indicate that velocity changes in sediments deposited well above the present lysoclineÑapart from the dilution effectÑmost probably reßect foraminifer productivity changes. At Site 928, enhanced dissolution close to the lysocline affects the velocity time series and leads to maxima of concentration in variance density between obliquity and precessional frequency bands