Showing papers on "Holocene climatic optimum published in 1988"

Vegetational history of Carbury Bog (Co. Kildare, Ireland) during the last 850 years and a test of the temperature indicator value of 2H/1H measurements of peat samples in relation to historical sources and meteorological data

Abstract: SUMMARY A palynological study of contiguous samples of the upper 128 cm of Carbury Bog, Co. Kildare, Ireland, showed details of the fluctuating human impact on the vegetation during the last c. 850 years. During the period of c. 1130–1440 A.D. the landscape around Carbury Bog was still dominated by forest. During the second half of the 15th century there was a considerable reduction of the forested area, reflected in the pollen diagram. The commercial exploitation of the forest during the 17th century resulted in almost complete deforestation. The pollen records for the 18th century vegetation show a rise in the curves of Pinus, Fraxinus and Fagus as a consequence of planting of these trees. Apart from pollen many other palynomorphs (‘Types’, a.o. fungal spores and rhizopods) were recorded. The spectrum of Types appeared to be comparable with the Type spectrum of continental raised bogs. The results of the macrofossil analysis in combination with the indicator values of some Types were used in a detailed reconstruction of the local vegetation succession and the changes in hydrological and trophic conditions. The disappearance of Sphagnum imbricatum during the late medieval period possibly was caused by the increased influx of dust, as a consequence of man's impact on the environment around the bog. The recent importance of S. magellanicum as a peat forming species is possibly the effect of an increased atmospheric deposition of nitrate. Parallel to the analysis of micro- and macrofossils a sample series from the same monolith was analysed for the ratio of the stable isotopes 2H and 1H. Theoretically the 2H/1H ratio in cellulose of peat-forming plants should be indicative for palaeotemperatures, but, apart from a temperature dependent signal, this ratio is also strongly related to specific characteristics in the isotopic behaviour of different peat forming species. The overall fractionation is a complex function of climatic and plant-physiological parameters. In the present study the results of the 2H/1H measurements were compared with Lamb's palaeoclimatic data derived from historical sources and meteorology. The 2H/1H ratios of Carbury Bog appeared to be negatively correlated with the medieval climatic optimum, the Little Ice Age and the subsequent phase of warming climate. There is an obvious relationship between the 2H/1H ratio and the local succession of peat forming taxa and, as a consequence, with strictly local hydrological and trophic conditions. The present study shows that a climatic signal in the 2H/1H ratio of peat samples is completely dominated by the direct effects of the spectrum of plants. In addition, the variation in the duration of the growing season in different climatic periods may have had a considerable influence on the 2H/1H ratio of the peat-forming plants.

Late Holocene sea level indicators from twelve atolls in the central and eastern Tuamotus (Pacific Ocean)

Abstract: New sea-level data for the late Holocene period are reported from twelve atolls of the Tuamotu archipelago: Faaite, Hikueru, Marokau, Hao, Amanu, Tatakoto, Pukarua, Nukutavake, Vairaatea, Tureia, Nukutipipi, and Hereheretue. The data come from coral conglomerate outcrops, coral colonies in growth position, in situ reef framework and marine notches; they give consistent results, and their ages are controlled by 29 radiocarbon datings. The Holocene MSL remained 0.8±0.2 m higher than at present, from before 4000 years BP until at least 1500 years BP, then dropped gradually to the present level. This pattern is very similar to that reported from the northwest Tuamotus, suggesting the absence of measurable differential vertical movements over a distance greater than 1300 km during the late Holocene. Effects of the 1983 cyclones on reef morphology are reported from some atolls and radiocarbon dates of some storm-generated reef blocks are given.

Weather, Climate and Human Affairs: A Book of Essays and Other Papers

Abstract: 1. Introduction Part 1: Studies of Climatic History and its Effects on Human Affairs and Environment 2. The Earth's Restless Climate 3. Climate and History in Northern Europe and Everywhere Else in the Last Thousand Years 4. Climate and Life During the Middle Ages, Studied Especially in the Mountains of Europe 5. The Climate Theory of Race in Sixteenth- and Seventeenth- Century Literature and its Modern Implications 6. Climate in Historical Times and Transgressions of the Sea, Storm Floods and Other Coastal Changes 7. Some Aspects of the Little Ice Age and Other Periods of Cold, Disturbed Climate 8. Studies of the Little Ice Age: I, The Great Storms and Data Available for Establishing Details of the Period 9. Studies in the Little Ice Age: II, Changes in the Winds and Ocean Currents in the North-East Atlantic Region 10. Climate and Human, Animal and Crop Diseases, an Example: the Great Irish Potato Famine of the 1840s and some Lessons for Today 11. The Recent Increase of Storminess in and Around the North Sea Region and Related Changes Since the Twentieth-Century Climatic Optimum 12. Drought in Africa: the Climatic Background to a Threatening Problem of Today's World Part 2: Climate and Weather Changes, Causes and Mechanisms 13. Causes and Time-Scales of Climatic Change 14. An Outline of the World's Wind Circulation and Weather Systems, and their Part in Variations of Weather and Climate, with Notes of some Relationships to Birds and the Living World 15. Christmas to New Year Weather as an Indicator of the Tendency of the Large-Scale Wind Circulation and Climate 16. Fronts and their Life History 17. Volcanoes and climate: An Updated Assessment Part 3: Conclusion: What of the Future 18. The Future of the Earth: Greenhouse or Refrigerator

Monte Verde, South-Central Chile: Stratigraphy, Climate Change, and Human Settlement

Abstract: Two sedimentary units are recognized by means of stratigraphic and sedimentological analyses at Monte Verde, a late Pleistocene archeological site with stone tools and well-preserved wood artifacts and botanical remains, that lies southwest of Lago Llanquihue and north of the Golfo de Reloncavi in the southern end of the Chilean Central graben. the geological evidence shows that at no time after 33,000 yr B.P., and perhaps since the first Llanquihue advance (before 56,000 yr B.P.), was the Monte Verde area covered by ice. Influences of two glacial advances at 20,000 and 15,000-14,500 yr B.P. are recognized at the site; effects of the Varas Interstade, however, are not identified. Rapid climatic change took place after the end of the Llanquihue Glaciation. It was shortly interrupted by a cool, wet period around 10,000 yr B.P., after which a well-documented Hypsithermal (8270-4750 yr B.P.) accompanied by pyroclastic vulcanism followed. The evidence indicates that around 13,000 yr B.P. 1) the site occupants settled on the sandy point bars and beaches of the old creek channel and 2) the area was habitated during cool and wet conditions similar to those that prevail in the area today. Evidence for reconstruction of the paleo-environment and climate of the terminal Pleistocene and the preliminary implications of these findings for understanding the human occupation at Monte Verde are discussed.

Holocene history of the Bugaboo glacier, British Columbia

Abstract: Sequences of tills, buried paleosols, wood, and tephra in moraines provide a fairly complete record of Holocene fluctuations of the Bugaboo glacier in British Columbia. The oldest till known to be exposed in the lateral moraines, apparently associated with an end moraine of the regionally known Crowfoot advance, is overlain by Mazama tephra, and is possibly early Holocene, but probably latest Pleistocene, in age. A paleosol incorporating the tephra and capping this till developed during early to middle Holocene time; it represents the warm and/or dry Altithermal interval. Subsequent (Neoglacial) advances deposited tills after 3.39 ka but before 3.07 ka, in the period ca. 2.5-1.9 ka, and in the period from ca. 0.9 ka to the nineteenth century. Recessional intervals are marked by paleosols and a former moraine gully, now filled. Results of the Bugaboo glacier study increase the resolution of known Neoglacial history in the Canadian Cordillera and generally demonstrate the usefulness of lateral-moraine stratigraphy.

Thermal Conditions Both of the Upper and Lower Limits of the Fagus crenata Forest Zone, and Changes in Summer Temperature from the Latest Pleistocene to the Middle Holocene in Japan

Abstract: The Fagus forest zone dominated by Fagus crenata streches over the Japanese Archipelago from the southwestern part of Hokkaido to Kyushu. The thermal conditions of its upper and lower limits of distribution are examined by a new method inferred from multiple regression analysis of mountainous meteorological data. The vertical distribution of the Fagus forest zone is strictly affected by the temperature during the summer, rather than by the warmth index and annual mean temperature. The summer temperature, which is represented by the mean of monthly mean temperatures for July and August, shows 16.8°C for the upper limit and 21.0°C for the lower limit of the Fagus forest zone.Using both the thermal conditions of the Fagus forest zone described above and the history of migration of the Fagus forest zone indicated by pollen stratigraphies of many sites in Japan, the changes in summer temperature from the latest Pleistocene to the middle Holocene (from 12, 000y.B.P. to 3, 000y.B.P.) are discussed, as follows (Fig. 7);The summer temperature during the latest Pleistocene from 12, 000y.B.P. to 10, 000y.B.P. was estimated to be between 3°C and 7°C lower than at present. Through the period from 9, 500y.B.P. to 6, 000y.B.P., the summer temperature at each site was higher than at present, showing the early phase of the Hypsithermal. Every site was warmer than at present during the period from 6, 000y.B.P. to 4, 500y.B.P.. Although the exact age of the warmest phase of each site could not be specified, the summer temperature during the climax phase of the Hypsithermal rose to 1° and/or 2.5°C higher than at present. The period between 4, 500y.B.P. and 3, 000y.B.P. was the end of the Hypsithermal, and a decrease in summer temperature was shown at every site, though some sites were still warmer than at present.

Holocene coastal changes in Rio de Janeiro state, Brazil

Abstract: Evidence of Holocene sea-level changes along the Rio de Janeiro State Coast, and for the evolution of coastal lagoons and barriers in response to these sea- level movements, has been examined using stratigraphical and micropalaeontological techniques, radiocarbon dating and published data. Present-day diatom death assemblages have been studied in order to facilitate the interpretation of fossil assemblages, which has inter aha permitted the development of a simple statistical technique for the evaluation of the allochthonous diatom component. Modern lagoonal tide- gauge data have been used to establish a relationship between lagoonal water levels and tidal levels on the open coast. Evidence is presented which indicates that barriers which were previously believed to date from the mid-Holocene formed during the 'Last' Interglacial. The history of true Holocene barriers has been shown to be relatively complex, with some barriers having migrated by over-stepping and others by continous shoreface retreat. The published Holocene sea-level maximum for Rio de Janeiro State of -t- 4.8 m at 5100 BP is considered to be in error (approximately 3.0 m too high at this time) and a maximum Holocene sea level of -t- 3.0 m at c. 4000 BP is preferred. The evidence for sea-level maxima in other parts of Brazil at 5150 BP and for the migration of the geoid surface during the Holocene is questioned and shown to require further study. It is tentatively suggested that there may be evidence for an interglacial sea-level high at c. 35000 BP in Rio de Janeiro State.

Sea Level of the Two Stages in the Late Holocene Deduced from the Deposits of the Coastal Low Land in the Subsided Region of the Southern Shikoku Island

Abstract: 完新世堆積物についての各種分析 の うち, 近年, 珪藻 化石分析 の精密化が進み, 堆積環境 の復元を場所に よっ ては102年 のオーダーで論ず るこ とが できる ようにな っ た (鹿島, 1985a, 1986). また, FeS2 (黄鉄鉱)-S含 有 量分 析の適用 に よって, 海成 層 と淡 水成層の 識 別をか な り明確 に行 なえる ことが分 かってきた (白神, 1985, 1986). これ らの分 析手法 を用 いて, 完新世におけ る各 地の海水準に関す る資料を蓄積 してい くことは, と りわ け縄 文海進以後 の微小な海水準 変化の議論に, きわめて 有 意義 と思わ れる. 筆者 らは, 高知県春野町の海岸低地において, 2本 の 試錐を 行 な う機 会を得, オ ール コアサ ンプルを 採取 し た. 本調査地が, 吉川 (1968) の指摘す る沈降帯 に位置 す るとい う前提をふ まえつつ, 完新世後半 におけ る二 つ の時期 の相対的海水準を報告 し, 資料蓄積 の一 助 とした い.