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1.
Bihourly water temperatures from two, 110-day study periods are compared for a study site in the Indian River Lagoon, along the Atlantic coast of South Florida. Results of a summer study include the annual maximum temperatures in July and August, and reveal low-frequency variations of ±1–2°C superimposed onto the annual curve. The winter study shows the annual minimum temperatures in late February and low-frequency variations of ±3–4°C superimposed onto the annual curve. At the very long and the very short periodicities, thermal activity is consistently higher during the winter study. At the diurnal period, however, the temperature range during the summer study is twice that recorded during the winter study, and the time of warmest water in the diurnal cycle is shifted back between two and three hours toward mid day in the summer months. This is attributed to the relative increase in importance of heating by insolation at that time of year. Sensible and latent heat fluxes appear to damp the diurnal cycle in both records.  相似文献   

2.
Mercury distribution was examined in the sediments of Lake Baikal that were sampled within the scope of the Baikal Drilling International Project in 1996–1999. The Hg concentrations in the ancient sediments are close to those in the modern sediments with the exception of a few peak values, whose ages coincide with those of active volcanism in adjacent areas. Mercury was demonstrated to be contained in the sediments in the adsorbed Hg0 mode, predominantly in relation with organic matter. When the organic matter of the bottom sediments is decomposed in the course of lithification, Hg is retained in the sediments adsorbed on the residual organic matter, and the concentration of this element corresponds to its initial content in the bottom sediments during their accumulation. Mercury concentrations in lithologically distinct bottom sediments of Lake Baikal and its sediments as a whole depend on the climate. Sediments that were formed during warm periods of time contain more Hg than those produced during cold periods or glaciation. Periodical variations in the Hg concentrations in the bottom sediments of Lake Baikal reflect the variations in the contents of this element in the Earth’s atmosphere in the Late Cenozoic, which were, in turn, controlled by the climatic variations on the planet and, thus, can be used for detailed reconstructions of variations in the average global temperature near the planet’s surface.  相似文献   

3.
Authigenic carbonates and seep biota are archives of seepage history and record paleo-environmental conditions at seep sites. We obtained the timing of past methane release events at the northeastern slope of the South China Sea based on U/Th dating of seep carbonates and seep bivalve fragments from three sites located at 22°02′–22°09′N, 118°43′–118°52′E (water depths from 473 to 785 m). Also, we were able to reconstruct the paleo-bottom water temperatures by calculating the equilibrium temperature using the ages, the corresponding past δ18O of seawater (δ18Osw) and the δ18O of the selected samples formed in contact with bottom seawater with negligible deep fluid influence. A criterion consists of mineralogy, redox-sensitive trace elements and U/Th-isotope systematics is proposed to identify whether the samples were formed from pore water or have been influenced by deep fluid. Our results show that all methane release events occurred between 11.5 ± 0.2 and 144.5 ± 12.7 ka, when sea level was about 62–104 m lower than today. Enhanced methane release during low sea-level stands seems to be modulated by reduced hydrostatic pressure, increased incision of canyons and increased sediment loads. The calculated past bottom water temperature at one site (Site 3; water depth: 767–771 m) during low sea-level stands 11.5 and 65 ka ago ranges from 3.3 to 4.0 °C, i.e., 1.3 to 2.2 °C colder than at present. The reliability of δ18O of seep carbonates and bivalve shells as a proxy for bottom water temperatures is critically assessed in light of 18O-enriched fluids that might be emitted from gas hydrate and/or clay dehydration. Our approach provides for the first time an independent estimate of past bottom water temperatures of the upper continental slope of the South China Sea.  相似文献   

4.
Sedimentological, micropalaeontological (benthic foraminifers and dinoflagellate cysts), stable isotope data and AMS 14C datings on cores and surface samples, in addition to acoustic data, have been obtained from Voldafjorden, western Norway. Based on these data the late glacial and Holocene sedimentological processes and variability in circulation and fjord environments are outlined. Glacial marine sedimentation prevailed in the Voldafjorden between 11.0 kyr and 9.2 kyr BP (radiocarbon years). In the later part of the Allerød period, and for the rest of the Holocene, there was deposition of fine‐grained normal marine sediments in the fjord basin. Turbidite layers, recorded in core material and on acoustic profiles, dated to ca. 2.1, 6.9–7.6, ca. 9.6 and ca. 11.0 kyr BP, interrupted the marine sedimentation. The event dated to between 6.9 and 7.6 kyr BP probably corresponds to a tsunami resulting from large‐scale sliding on the continental margin off Norway (the Storegga Tsunami). During the later part of the Allerød period, Voldafjorden had a strongly stratified water column with cold bottom water and warm surface water, reaching interglacial temperatures during the summer seasons. During the Younger Dryas cold event there was a return to arctic sea‐surface summer temperatures, possibly with year‐round sea‐ice cover, the entire benthic fauna being composed of arctic species. The first strong Holocene warming, observed simultaneously in bottom and sea‐surface temperature proxies, occurred at ca. 10.1 kyr BP. Bottom water proxies indicate two cold periods, possibly with 2°C lowering of temperatures, at ca. 10.0 (PBO 1) and at 9.8 kyr BP (PBO 2). These events may both result from catastrophic outbursts of Baltic glacial lake water. The remainder of the Holocene experienced variability in basin water temperature, indicated by oxygen isotope measurements with an amplitude of ca. 2°C, with cooler periods at ca. 8.4–9.0, 5.6, 5.2, 4.6, 4.2, 3.5, 2.2, 1.2 and 0.4–0.8 kyr BP. Changes in the fjord hydrology through the past 11.3 kyr show a close correspondence, both in amplitude and timing of events, recorded in cores from the Norwegian Sea region and the North Atlantic. These data suggest a close relationship between fjord environments and variability in large‐scale oceanic circulation. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

5.
Bornyakov  S. A.  Salko  D. V.  Seminsky  K. Zh.  Demberel  S.  Ganzorig  D.  Batsaihan  T.  Togtohbayar  S. 《Doklady Earth Sciences》2017,473(1):371-374

Instrumental monitoring of rock deformation in the South Baikal geodynamic study site showed that they are realized in the form of long-term variations in different directions superimposed with short-time anomalous spikes. Analysis of the measured spatiotemporal monitoring series showed that anomalous deformations are caused by the propagation of deformation waves through the mountainous rocks. We estimated their lengths, periods, directions, and velocity of spatial migration. We found that propagation of deformation waves is accompanied by an increase in the temperature of rocks at each point of monitoring.

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6.
This paper presents the results of a high‐resolution Late‐glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire. The samples were from a core taken from the terrestrialised margin of the present lake, which represents an intermediate depth between the true littoral and the profundal. The chironomid assemblage showed a high degree of sensitivity to both broad‐scale and short‐term temperature changes. Comparison with an existing proxy temperature record (δ18O) for the site confirmed the presence of four temperature inversions within the Late‐glacial Interstadial. A mean July air temperature inference model, derived from acid, soft‐water lakes in Norway and Svalbard, was applied to the data. Despite the absence of carbonate lakes within the Norwegian training set, there was a close similarity between trends in estimated July air temperature and the δ18O trace, with a particularly strong correspondence in the periods of clay deposition. This suggests that this model is highly robust. The inferred maximum Interstadial temperature was 13.4°C, dropping initially to 7.5°C in the Loch Lomond Stadial. Temperatures reach a maximum of nearly 10°C in this period, cool for a short period before rising rapidly to 13.2°C at the start of the Holocene. These temperatures are similar to but slightly higher than those estimated for Whitrig Bog, southeast Scotland, and lower than those inferred from coleopteran‐based models for sites in South Wales. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

7.
We have compiled what we believe is the longest coherent coastal sea surface temperature record in North America. Near-surface water temperature measurements have been made almost daily at Great Harbon, Woods Hole, Massachusetts, since 1886 with remarkably few gaps. The record shows that there was no significant trend in water temperature at this site for the first 60 yr of observation. There was some cooling during the 1960s that was followed by a significant warming from 1970–2002 at a rate of 0.04°C yr?1. During the 1990s annual mean temperatures averaged approximately 1.2°C warmer than they had been on average between 1890 and 1970; winter (December, January, and February) temperatures were 1.7°C warmer and summer (June, July, and August) temperatures were 1.0°C warmer. There has not been a statistically significant decrease in the annual number of winter days below 1°C or an increase in the annual number of winter days above 5°C. The number of summer days each year with water temperature above 21°C has not increased significantly. The dates of first observations of 10°C and 20°C water in the spring have not changed sufficiently to be statistically significant. There is a weak positive correlation between annual and winter water temperature and the annual and winter North Atlantic Oscillation index, respectively, during the period of record.  相似文献   

8.
Rapid warming in mid-latitude central Asia for the past 100 years   总被引：5，自引：0，他引：5  
Surface air temperature variations during the last 100 years (1901–2003) in mid-latitude central Asia were analyzed using Empirical Orthogonal Functions (EOFs). The results suggest that temperature variations in four major sub-regions, i.e. the eastern monsoonal area, central Asia, the Mongolian Plateau and the Tarim Basin, respectively, are coherent and characterized by a striking warming trend during the last 100 years. The annual mean temperature increasing rates at each sub-region (representative station) are 0.19°C per decade, 0.16°C per decade, 0.23°C per decade and 0.15°C per decade, respectively. The average annual mean temperature increasing rate of the four sub-regions is 0.18°C per decade, with a greater increasing rate in winter (0.21°C per decade). In Asian mid-latitude areas, surface air temperature increased relatively slowly from the 1900s to 1970s, and it has increased rapidly since 1970s. This pattern of temperature variation differs from that in the other areas of China. Notably, there was no obvious warming between the 1920s and 1940s, with temperature fluctuating between warming and cooling trends (e.g. 1920s, 1940s, 1960s, 1980s, 1990s). However, the warming trends are of a greater magnitude and their durations are longer than that of the cooling periods, which leads to an overall warming. The amplitude of temperature variations in the study region is also larger than that in eastern China during different periods.  相似文献   

9.
The Laguna Lagunillas basin in the arid Andes of northern Chile exhibits a shallow aquifer and is exposed to extreme air temperature variations from 20 to ?25 °C. Between 1991 and 2012, groundwater levels in the Pampa Lagunillas aquifer fell from near-surface to ~15 m below ground level (bgl) due to severe overexploitation. In the same period, local mean monthly minimum temperatures started a declining trend, dropping by 3–8 °C relative to a nearby reference station. Meanwhile, mean monthly maximum summer temperatures shifted abruptly upwards by 2.7 °C on average in around 1996. The observed air temperature downturns and upturns are in accordance with detected anomalies in land-surface temperature imagery. Two major factors may be causing the local climate change. One is related to a water-table decline below the evaporative energy potential extinction depth of ~2 m bgl, which causes an up-heating of the bare soil surface and, in turn, influences the lower atmosphere. At the same time, the removal of near-surface groundwater reduces the thermal conductivity of the upper sedimentary layer, which consequently diminishes the heat exchange between the aquifer (constant heat source of ~10 °C) and the lower atmosphere during nights, leading to a severe dropping of minimum air temperatures. The observed critical water-level drawdown was 2–3 m bgl. Future and existing water-production projects in arid high Andean basins with shallow groundwater should avoid a decline of near-surface groundwater below 2 m bgl and take groundwater-climate interactions into account when identifying and monitoring potential environmental impacts.  相似文献   

10.
This work presents new experimental results on the kinetics of mineral dissolution in near-critical and supercritical water in a temperature range (T) from 25 to 400℃ and a constant pressure of 23 MPa. Kinetic experiments were carried out by using a flow reactor (packed bed reactor) of an open system. The dissolution rates of albite and magnetite were measured under these experimental conditions. Na, Al and Si release rates for albite dissolution in water were measured as a function of the temperature and flow velocity in the reaction system. The maximum release rates of Na, AI and Si of albite dissolution in the hydrothermal flow systems under different flow velocities were always obtained at 300℃, that is to say, the maximum albite dissolution rates in the flow systems, regardless of different flow rates, were repeatedly measured at 300℃. Results indicate a wide fluctuation in albite dissolution rates occurring close to the critical point of water. The dissolution rates increased when the temperatu  相似文献   

11.
A dark green authigenic nontronite is the major component of the Galapagos hydrothermal mounds field sediments. Oxygen isotopic compositions of the chemically purified, <0.2-μm fraction of the nontronitic clays indicate formation temperatures of 25° to 47°C, in contrast with measured in situ mounds temperatures of up to 15°C. Assuming an authigenic origin, the Fe-rich montmorillonite that dominates in the noncarbonate clay fraction of the surrounding pelagic ooze has isotopic formation temperatures of 27° to 39°C, compared with measured in situ temperatures of ca. 3.5° to 6.5°C. The higher isotopic formation temperatures calculated for the hydrothermal nontronite suggest either complex patterns of fluid circulation and nontronite precipitation presently within the mounds or a higher thermal history associated with rapid and episodic periods of deposition during the Holocene-Pleistocene. The apparent high isotopic temperature of the Fe-rich montmorillonite may reflect: (1) formation under hydrothermal conditions at spreading centers with subsequent dispersal by bottom currents, (2) a detrital origin of the mineral, or (3) a mixture of authigenic Fe-montmorillonite and detrital Al-montmorillonite in this region.  相似文献   

12.
Hydrothermal processes and the regimes of frozen soil formed in alpine regions with glaciers and lake area are complex and important for ecological environment but have not been studied in Tibet. Based on soil temperature and moisture data from October 2005 to September 2006 collected in the Nam Co lake basin, Tibetan Plateau (TP), those questions were discussed. The mean annual air temperature was −3.4°C with 8 months below 0°C. Air and soil temperature varied between −25.3~13.1°C and −10.3~8.8°C, respectively. Soil moisture variations in the active layer were small with the minimum value of 1.4%, but were influenced greatly by snowmelt, rainfall and evaporation, varying up to 53.8%. The active layer froze later, thawed earlier and was thinner, however, the lower altitude limit of permafrost is higher than that in most areas of TP. The effects of soil moisture (unfrozen water content) on soil temperature, which were estimated through proposed models, were more significant near ground surface than the other layers. The surface soil temperature decreased with snowcover, the effect of cold snow meltwater infiltration on soil thermal conditions was negligible, however, the effect of rainfall infiltration was evident causing thermal disruptions.  相似文献   

13.
Corona, C., Edouard, J.‐L., Guibal, F., Guiot, J., Bernard, S., Thomas, A. & Denelle, N. 2010: Long‐term summer (AD751–2008) temperature fluctuation in the French Alps based on tree‐ring data. Boreas, 10.1111/j.1502‐3885.2010.00185.x. ISSN 0300‐9843. On the basis of a dense tree‐ring width network (34 unpublished multi‐centennial larch chronologies), this paper attempts to reconstruct, for the first time, the summer temperatures in the French Alps (44°–45.30°N, 6.30°–7.45°E) during the last millennium. The adaptative Regional Growth Curve standardization method is applied to preserve interannual to multi‐centennial variations in this high‐elevation proxy data set. The proxies are calibrated using the June to August mean temperatures from the last revised version of the HISTALP database spanning the period AD1760–2003 and adjusted to take into account the warm bias before 1850. About 45% of the temperature variance is reconstructed. Despite the use of the newly updated meteorological data set, the reconstruction still shows colder temperatures than early instrumental measurements between 1760 and 1840. The proxy record evidences a prolonged Medieval Warm Period persisting until 1500, with warm periods that resemble 20th century conditions but also cold phases before 1000 synchronous with Swiss glacier advances. The Little Ice Age is rather mild until 1660 if compared with other Alpine reconstructions. Thereafter, summers are 0.7 °C cooler than the 1961–1990 mean until 1920. The maximum temperature amplitude over the past 1250 years is estimated to be 3 °C between the warmest (810s, 1990s) and coldest (1810s) decades. Most of the 20th century is comparable with the Medieval Warm Period.  相似文献   

14.
The initial flooding waters from twenty-four consecutive tides were examined for changes in water properties as the flood-front traversed the intertidal zone. The flood-front water temperature depended on the time of flooding as well as the sun’s insolation. On warm sunny days, the water temperature at the leading edge of the tide successively increased as the water flooded the tidal flat. In contrast, during cloudy days, and early morning and evening samplings, the flood-front water decreased during flooding. Flood-front water temperatures on warm days exceeded 34°C, some 15°C higher than the water observed in the deeper tidal channels. Flood-front salinities increased progressively across the intertidal zone regardless of local weather conditions, and were primarily controlled by mixing of surface waters with interstitial waters during the flooding process. Particulate matter concentrations were dependent on the interaction between small amplitude waves and varying intertidal bottom slope. Extreme variability in the particulate matter concentration across the tidal flat was in part caused by alternate resuspension and settling of fecal pellets composed of silty-clay aggregates which partly form the bottom sediment of the test area. The texture of the suspended particulate matter coarsens near shore, where wave resuspension became more effective on a steeper portion of the intertidal zone. *** DIRECT SUPPORT *** A01BY009 00003  相似文献   

15.
Archaea have unique glycerol dialkyl glycerol tetraether (GDGT) lipids that can be used to develop paleotemperature proxies such as TEX86. This research is to validate proposed GDGT-proxies for paleotemperature determination in the South China Sea (SCS). Samples were collected from core-top sediments (0–5 cm) in the northern SCS. Total lipids were extracted to obtain core GDGTs, which were identified and quantified using liquid chromatography-mass spectrometry (LC-MS). The abundance of isoprenoidal GDGTs (iGDGTs) ranged from 271.5 ng/g dry sediment to 1266.3 ng/g dry sediment, whereas the branched GDGTs (bGDGTs), supposedly derived from terrestrial sources, ranged from 22.2 ng/g dry sediment to 56.7 ng/g dry sediment. The TEX86-derived sea surface temperatures ranged from 20.9 °C in the coast (water depth < 160 m) to 27.9 °C offshore (water depth > 1000 m). TEX86-derived temperatures near shore (<160 m water depth) averaged 23.1 ± 2.5 °C (n = 4), which were close to the satellite-derived winter mean sea surface temperature (average 22.6 ± 1.0 °C, n = 4); whereas the TEX86-derived temperatures offshore averaged 27.4 ± 0.3 °C (n = 7) and were consistent with the satellite mean annual sea surface temperature (average 26.8 ± 0.4 °C, n = 7). These results suggest that TEX86 may record the sea surface mean annual temperature in the open ocean, while it likely records winter sea surface temperature in the shallower water.  相似文献   

16.
To assess whether reaches of the Motueka River (New Zealand) that gain water from groundwater were likely to represent significant cold-water refugia for brown trout during periods of high water temperatures, water temperature was monitored for more than 18 months in two gaining reaches of the Motueka River and three reaches that were predicted to be losing water to groundwater. These data were used to predict brown trout (Salmo trutta) growth in gaining and losing reaches. Groundwater inputs had a small effect on water temperature at the reach-scale and modelling suggests that the differences observed were unlikely to result in appreciable differences in trout growth. Several coldwater patches were identified within the study reach that were up to 3.5°C cooler than the mainstem, but these were generally shallow and were unlikely to provide refuge for adult trout. The exception was Hinetai Spring, which had a mean water temperature of close to 16°C during the period January–March, when temperatures in the mainstem regularly exceeded 19°C. Trout were observed within the cold-water plume at the mouth of Hinetai Stream, which would allow them to thermoregulate when mainstem temperatures are unfavourable while still being able to capitalise on food resources available in the mainstem.  相似文献   

17.
During 1973 and 1974 seasonal abundance and mean total length of Atlantic croaker,Micropogonias undulatus, were investigated by otter trawl at 33 stations in South Carolina estuaries in relation to bottom salinity and temperature. Relative abundance of Atlantic croaker was measured by catch per unit effort at 3°C temperature intervals and 3‰ salinity intervals. Croaker occurred over a bottom temperature range of 9.0–31.4°C while occurring most abundantly in waters above 24.0°C. No significant correlation between size and temperature was found. Croaker were collected in salinities from 0.4 to 34.4‰. High correlations of size and salinity were evident in 1973 during winter (r=0.79), summer (r=0.82), and fall (r=0.94). In 1974, correlations were significant only during fall (r=0.76).  相似文献   

18.
The oxygen isotope records of both benthic and planktonic Foraminifera in five piston cores, collected from the region between the Oyashio and Kuroshio Currents near Japan, clearly show the marked latitudinal shifts of these two currents during the past 25 kyr. Under the present hydrographic condition, a clear relationship between the sea‐surface temperature (SST) and oxygen isotope differences from benthic to planktonic Foraminifera is observed in this region. Using this relationship, we find decreased SSTs of 12–13°C (maximum 15°C) in the southernmost core site at the Last Glacial Maximum (LGM), indicating the Oyashio Current shifted southward. The SSTs at the southern two core sites abruptly increased more than 10°C at 10–11 ka, suggesting the Kuroshio Current shifted northward over these sites at 10–11 ka. In contrast, the northern two core sites have remained under the influence of the cold Oyashio Current for the past 25 kyr. With the reasonable estimate of bottom‐water temperature decrease of 2.5°C at the LGM, the SSTs estimated by this new method give exactly the same SST values calculated from Mg/Ca ratio of planktonic Foraminifera, allowing palaeosea‐surface salinities to be reconstructed. The result suggests that the ice volume effect was 1.0 ± 0.1‰ at the LGM. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

19.
The patterns of renewal of bottom waters in Lake Baikal under the influence of deep convection and intrusion of cold waters have been considered based on the data of temperature surveys of Lake Baikal conducted in 1993–2009. The volumes of the cold bottom layer with the maximums of 200–470 km3 in individual years and the values of its total cooling (−20–60 × 109 MJ) have been determined for South, Middle, and North Baikal. The renewal process is asynchronous and proceeds with different activity in these parts of the lake, which indicates that the mechanisms that cause deep convection in the context of the great latitudinal length and differences in the climate and hydrological processes manifest themselves regionally. The volume of intrusions has been determined. Its average value for the period was higher in South Baikal (20 km3) than in Middle Baikal (9.8 km3) and North Baikal (8.6 km3). The volume of the intrusions in these parts of the lake was 30–70 km3 in some years.  相似文献   

20.
《Quaternary Science Reviews》2004,23(7-8):919-934
Speleothem fluid inclusions potentially provide vital data on the paleohydrological conditions in glacial and interglacial periods. We show here that δD analyses of fluid inclusions from speleothems in three caves in the Eastern Mediterranean region (Israel) provide a basis for understanding hydrological and temperature variations in the last 140 ka. Using measured δD fluid inclusion values and temperature ranges constrained by the present-day Mediterranean Meteoric Water Line (MMWL) and the global MWL, we show a strong compatibility between the land and marine temperature records, with the highest land temperatures occurring at 120–130 ka (17–22°C) and the present (18°C) and the lowest temperatures during the LGM, about 10°C lower than present. Interglacial waters are constrained to follow the MMWL and most glacial waters also plot close to the MMWL, with a slight shift towards the MWL. However, during two remarkable brief periods at the termination of the LGM, the waters plot on the MWL, suggesting that both sharp cooling and an increase in relative humidity above the EM Sea reduced d-excess values to those of the global system.  相似文献   

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