Fire and vegetation change during the Early Pleistocene in southeastern Australia     

J. M. Kale Sniderman  Simon G. Haberle 《第四纪科学杂志》2012,27(3):307-317

Early Pleistocene vegetation in upland southeastern Australia included diverse rainforests and sclerophyll forests, which alternated on precessional timescales. The nature and timing of transitions between these biomes, and the role of fire in maintaining or driving transitions between them, are uncertain. Here we present a high‐resolution pollen record from Stony Creek Basin, a small Early Pleistocene palaeolake in southeastern Australia. The pollen record documents a pattern of vegetation change, over ca. 10 ka at ca. 1590–1600 ka, between sclerophyll forests, dominated by Eucalyptus, Callitris (Cupressaceae) or Casuarinaceae, and rainforests dominated by either angiosperms or conifers of the family Podocarpaceae. Transitions between these biomes typically occurred within ca. 1–2 ka. The associated charcoal record suggests that greatest biomass combustion occurred when local vegetation was dominated by Eucalyptus, and the least biomass combustion occurred when local vegetation was dominated by Podocarpaceae. However, local fires burnt in both sclerophyll and angiosperm‐dominated rainforest vegetation, at least once every several centuries. Fire was very rare (less than about one fire per millennium) only when the local vegetation was rainforest dominated by Podocarpaceae. This suggests that fire was an irregular presence in both sclerophyll‐ and angiosperm‐dominated rainforest biomes during the late Neogene, though was largely absent in Podocarpaceae‐dominated rainforests. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The Cap Roux MPA (Saint-Raphael, French Mediterranean): changes in fish assemblages within four years of protection     

Seytre  Catherine; Francour  Patrice 《ICES Journal of Marine Science》2009,66(1):180-187

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Holocene environmental change in South Georgia: Evidence from lake sediments     

Jacqueline Birnie 《第四纪科学杂志》1990,5(3):171-187

The Holocene environmental history of South Georgia is important because of the island's location in the Southern Westerlies in an oceanic zone of the world devoid of high resolution terrestrial records. This is the first attempt to interpret a palaeoenvironmental record from lake sediments in South Georgia. It is based on a wide variety of analyses undertaken on cores from two lakes. Both are in the same, unglaciated, drainage basin, but one is at 80 m above sea-level and near the altitudinal limit for vegetation growth, whereas the other is at 25 m and within the zone of continuous vegetation cover. Results from both lakes indicate shifts of vegetation boundaries, which, together with evidence for changing biotic productivity within the lakes themselves, are interpreted as indicating climatic changes. Radiocarbon dates on the main changes identify a climatic optimum, beginning before 5620 ± 290 ¹⁴C yr BP, and ending at around 4815 ± 330 ¹⁴C yr BP, when conditions in the upper part of the catchment were more conducive to plant growth than they are today. The record obtained from the lower lake was shorter, but indicates two periods of harsher climate relative to the present since 4000 yr BP. This interpretation of the lake evidence agrees with other dated evidence of environmental change from peat sections, glacial stratigraphy and geomorphology in South Georgia. Together the work allows an overall reconstruction of environmental change in the Holocene.  相似文献   

广西钦州湾百年来红树林演变的有机碳同位素和孢粉示踪及其影响因素   总被引：1，自引：0，他引：1  

夏鹏  孟宪伟  平爱平  李珍 《海洋学报》2015,37(3):77-85

气候变化和人类活动制约下的红树林演变是一种长时间尺度效应,而沉积物则是记录这种响应的最佳档案。采用古生态学研究思路,选择有效的示踪参数是解读这一档案的有效途径。本文通过广西钦州湾红树林区1根柱状沉积物中有机碳同位素(δ13C)、C/N分析和孢粉鉴定,以沉积物中的红树林源有机碳贡献和红树植物孢粉组合为示踪参数,在210Pb年龄框架构建的基础上,通过对比研究红树林源有机碳贡献和红树孢粉组合特征,揭示百年来钦州湾红树林兴衰和群落演替规律;进而重塑其红树林演变历史:兴盛期(1864-1918年)、衰退期(1918-1968年)和低谷期(1968-2007年),这与土地替代、遥感分析和现场勘测数据较为吻合。结合气候变化和人类活动资料,发现钦州湾红树林的近期衰退主要源于人类活动的影响,尤其是虾塘围垦;而与气候变化关系不大。  相似文献   

Macrobenthos relative to the oxygen minimum zone on the East Indian margin,Bay of Bengal          下载免费PDF全文

Akkur V. Raman  Rayaroth Damodaran  Lisa A. Levin  Thiruchitrambalam Ganesh  Yannamani K. V. Rao  Sateesh Nanduri  Rakhesh Madhusoodhanan 《Marine Ecology》2015,36(3):679-700

The Bay of Bengal remains one of the least studied of the world's oxygen minimum zones (OMZs). Here we offer a detailed investigation of the macrobenthos relative to oxygen minimum zone [OMZ – DO (dissolved oxygen), concentration <0.5 ml·1^?1] at 110 stations off the North East Indian margin (16⁰ and 20⁰ N) featuring coastal, shelf and slope settings (10–1004 m). Macrobenthos (>0.5 mm) composition, abundance and diversity were studied in relation to variations in depth, dissolved oxygen, sediment texture and organic carbon. Using multivariate procedures powered by SIMPROF analysis we identified distinct OMZ core sites (depth 150–280 m; DO 0.37 ml·1^?1) that exhibited dense populations of surface‐feeding polychaetes (mean 2188 ind. m^?2) represented by spionids and cossurids (96%). Molluscs and crustaceans were poorly represented except for ampeliscid amphipods. The lower OMZ sites (DO > 0.55 ml·l^?1) supported a different assemblage of polychaetes (cirratulids, amphinomids, eunicids, orbinids, paraonids), crustaceans and molluscs, albeit with low population densities (mean 343 ind. m^?2). Species richness [E(S₁₀₀)], diversity (Margalef d; H’) and evenness (J’) were lower and dominance was higher within the OMZ core region. Multiple regression analysis showed that a combination of sand, clay, organic carbon, and dissolved oxygen explained 62–78% of the observed variance in macrobenthos species richness and diversity: E(S₁₀₀) and H’. For polychaetes, clay and oxygen proved important. At low oxygen sites (DO <1 ml·l^?1), depth accounted for most variance. Residual analysis (after removing depth effects) revealed that dissolved oxygen and sediment organic matter influenced 50–62% of residual variation in E(S₁₀₀), H’ and d for total macrofauna. Of this, oxygen alone influenced up to ~50–62%. When only polychaetes were evaluated, oxygen and organic matter explained up to 58–63%. For low oxygen sites, organic matter alone had the explanatory power when dominance among polychaetes was considered. Overall, macrobenthic patterns in the Bay of Bengal were consistent with those reported for other upwelling margins. However, the compression of faunal gradients at shallower depths was most similar to the Chile/Peru margin, and different from the Arabian Sea, where the depth range of the OMZ is two times greater. The Bay of Bengal patterns may take on added significance as OMZs shoal globally.  相似文献   

Macrobenthic polychaete assemblages of the continental shelf and upper slope off the west coast of the South Island,New Zealand     

P. K. Probert  G. B. Read  S. L. Grove  A. A. Rowden 《新西兰海洋与淡水研究杂志》2013,47(5):971-984

Polychaete assemblages are described from replicate box‐core samples collected in summer 1983 at 18 stations on the continental shelf and upper slope (28–943 m) off the west coast of the South Island, New Zealand, south‐eastern Tasman Sea (c. 41–43°S, 169–172°E). Three main station groupings were identified by multivariate analysis: (1) inner shelf sandy stations characterised by Prionospio australiensis, Aricidea (Acesta) sp., Magelona cf. dakini, Paraprionospio aff. pinnata, Aglaophamus sp., Heteromastus filiformis, and Magelona sp.; (2) middle to outer shelf muddy stations characterised by Levinsenia cf. gracilis, Prionospio australiensis, Paraprionospio coora, Aglaophamus verrilli, and Auchenoplax mesos; and (3) upper slope sandy mud or mud stations characterised by Prionospio ehlersi. A combination of water depth and sediment clay content provided the best correlation with the biotic pattern. Spionidae was the most abundant family (49% of polychaete individuals), which may reflect the scope for opportunistic species in a shelf environment characterised by a high input of terrigenous sediment and episodic upwelling.  相似文献   

Effects of beach nourishment on sediments and benthic assemblages     

Colosio F  Abbiati M  Airoldi L 《Marine pollution bulletin》2007,54(8):1197-1206

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Sediment records as archives of the Late Pleistocene-Holocene hydrological change in the alluvial Narmada River basin, western India     

Alpa Sridhar  L.S. Chamyal 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(2):195-202

The rivers of western India are monsoon dominated and have been so throughout the late Quaternary. Sediment accumulation in these river basins has been controlled by climatic and tectonic changes over a time span from the Late Pleistocene to the recent. The lithofacies assemblages associated with the various sediment archives in the Narmada basin range from the boulders of the alluvial fans to overbank fines on the alluvial plains. Estimates, based on clast size, of stream power and competence, bed shear stress and discharge reveal that hydrological conditions during the Late Pleistocene (∼90 ka) were comparable to the present day. The size of the transported clasts and the thickness of the accumulated sediment indicate the influence of basin subsidence rather than an increase in discharge. Discharge estimates based on sedimentary structures preserved in the alluvial-plain facies suggest that the channel had a persistent flow, with a low width-depth ratio and large meander wavelength. The hydrological changes during the Holocene are more pronounced where the early Holocene is marked by a high-intensity hydrological regime that induced erosion and incision of the earlier sediments. The mid-Holocene stream channel was less sinuous and had a higher width-depth ratio and a higher meander amplitude in comparison with the present-day channel. Palaeo-fluvial reconstructions based on the sediment archives in the alluvial reach of the river basin are important tools in understanding the long-term hydrological changes and the intricate fluvial architecture preserved in the Narmada River basin ensures scope for detailed studies to identify phases of weak and enhanced hydrological regimes.  相似文献   

川北若尔盖高原表土孢粉的特征及其与现代植被的关系   总被引：1，自引：0，他引：1  

蔡遥  王燕  蒋复初  李朝柱 《中国区域地质》2010,(5):707-712

通过对若尔盖高原不同植被带34个表土样的孢粉分析,研究了各植被带的表土孢粉组合与现代植被的关系。结果显示：表土孢粉组合基本上能够反映出现代植被的整体特征,与现代植被带在空间分布、建群种和优势种属方面基本相同,但不完全等于植被组成,影响其差异的原因可能是人类活动、孢粉保存、孢粉产量、外来孢粉和孢粉鉴定。表土花粉的代表性因种属的不同而各有差异。乔木花粉中,松属具有超代表性,云杉属代表性较好,而桦木属不具有超代表性;草本花粉中,菊科具较好的代表性,蒿属和藜科等具代表性,而禾本科和莎草科具低代表性;蕨类孢子具等代表性。  相似文献   

海洋风暴沉积的微体生物研究进展          下载免费PDF全文

陈敏  戚洪帅  沈林南  张爱梅  王承涛  方琦 《应用海洋学学报》2022,41(3):516-523

微体生物和它们的化石在研究现代风暴和古风暴沉积方面是一个很好和有效的指标。本文综述了国内外近几十年来有关海洋风暴沉积研究中微体生物的应用。目前主要的研究成果集中在对古风暴层有孔虫、硅藻的研究上,而孢粉方面的研究较少。应用微体化石揭示地质历史时期古风暴的发生频率已较为成熟。但未来需提高古风暴重建的可靠性、准确性和精确性,以及探讨微体化石记录与风暴强度之间的相关关系。有关现代风暴过程中微体生物的研究稍显逊色,研究程度较低。了解现代风暴过程中不同沉积环境下微体生物的沉积特征、面貌,它们的形成和保存机制等将成为未来的研究热点和方向。  相似文献