Long-term river discharge and multidecadal climate variability inferred from varved sediments, southwest Alaska

2011 ◽  
Vol 76 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Claire A. Kaufman ◽  
Scott F. Lamoureux ◽  
Darrell S. Kaufman
Keyword(s):  
Grain Size ◽  
Early 19Th Century ◽  
Varve Thickness ◽  
Hydroclimate Variability ◽  
Varved Sediment ◽  
Daily Discharge ◽  
Multidecadal Climate Variability ◽  
Instrumental Period ◽  
Annual Discharge

AbstractSedimentological analyses of 289 years (AD 1718–2006) of varved sediment from Shadow Bay, southwest Alaska, were used to investigate hydroclimate variability during and prior to the instrumental period. Varve thicknesses relate most strongly to total annual discharge (r2 = 0.75, n = 43, p < 0.0001). Maximum annual grain size depends most strongly on maximum spring daily discharge (r2 = 0.63, n = 43, p < 0.0001) and maximum annual daily discharge (r2 = 0.61, n = 43, p < 0.0001), while varve thickness is poorly correlated with maximum annual grain size (r2 = 0.004, n = 287, p = 0.33). Relations between varve thickness and annual climate variables (temperature, precipitation, North Pacific (NP) and Pacific Decadal Oscillation (PDO) indices) are insignificant. On multidecadal timescales, however, regime shifts in varve thickness and total annual discharge coincide with shifts in NP and PDO indices. Periods with increased varve thickness and total annual discharge were associated with warm PDO phases and a strengthened Aleutian Low. The varve-inferred record of PDO suggests that any periodicity in the PDO varied over time, and that the early 19th century marked a transition to a more frequent or detectable shifts.

A High Effective and Low-Cost Modifier for Hypereutectic Al-Si Alloys

2013 ◽  
Vol 721 ◽  
pp. 282-286
Author(s):  
Guang Hui Qi
Keyword(s):  
Grain Size ◽  
Master Alloy ◽  
Low Cost ◽  
Environment Pollution ◽  
Casting Method ◽  
Good Future ◽  
Primary Si ◽  
Average Grain Size ◽  
Master Alloys

In order to settle environment pollution and provide a high effective and low-cost modifier for refining the primary Si in hypereutectic Al-Si alloys, Al-Fe-P master alloys containing 2.0~5.0% phosphorus have been invented by casting method. The Al-Fe-P master alloys can be conveniently produced and an excellent modification can be obtained by adding 0.3~0.8wt% Al-Fe-P master alloy in Al-Si alloys containing 12%-25% Si at a relatively lower modifying temperature. The number of primary Si increases obviously and the average grain size of primary Si decreases largely, less than 50μm. Furthermore Al-Fe-P master alloys have many advantages, such as low cost, convenient operation technology, no pollution, stable and long-term modification effect, easy storage and etc. Al-Fe-P master alloys have overcome the shortages of current modifier and have a good future for hypereutectic Al-Si alloy modification.

scholarly journals Land use influences on acidification and recovery of freshwaters in Galloway, south-west Scotland

2001 ◽  
Vol 5 (3) ◽  
pp. 451-458 ◽  
Author(s):  
R. C. Helliwell ◽  
R. C. Ferrier ◽  
L. Johnston ◽  
J. Goodwin ◽  
R. Doughty
Keyword(s):  
Surface Waters ◽  
Chemical Recovery ◽  
Dry Period ◽  
Sulphur Deposition ◽  
South West ◽  
Recovery From Acidification ◽  
Long Term Trends ◽  
Acid Status ◽  
Annual Discharge

Abstract. The long term response of surface waters to changes in sulphur deposition and afforestation is investigated for three upland river systems in the Galloway region of south-west Scotland. From 1984-1999, these rivers exhibited a statistically significant decline in non-marine sulphate concentrations in response to reduced acid deposition. This reduction in non-marine sulphate was, however, insufficient to induce a pH recovery over the period. A statistically significant increase in river pH was observed between 1956-1970 (0.05 yr-1) when subsidised agricultural lime payments were at a maximum. In 1976, this subsidy ceased and surface waters have progressively acidified. In addition, climatic change is found to influence long-term trends in pH. Mean annual pH was greatest during a dry period between 1969-1973 when total annual discharge was low. Thereafter, pH declined gradually in response to higher rainfall and increased total annual discharge. Overall, surface waters draining the afforested catchments of the Rivers Cree and Bladnoch are more acid than those draining the moorland catchment of the Luce. These results indicate that in afforested catchments, current reductions in sulphur emissions have not led to an observed improvement in the acid status of surface waters. Forestry, therefore, represents a confounding factor with regard to chemical recovery from acidification in this region. Keywords: acidification, afforestation, deposition, rivers, lochs, non-marine sulphate, pH

scholarly journals Analyses of Monthly Discharges in Slovakia Using Hydrological Exploratory Methods

Proceedings ◽  
2018 ◽  
Vol 7 (1) ◽  
pp. 18
Author(s):  
Mária Ďurigová ◽  
Dominika Ballová ◽  
Kamila Hlavčová
Keyword(s):  
Change Points ◽  
Hydrological Data ◽  
Pettitt Test ◽  
The Mean ◽  
Monthly Discharge ◽  
Meteorological Elements ◽  
The Relationship ◽  
Annual Discharge ◽  
Hydrological Regimes

Detailed analyses of hydrological data are necessary in order to prove changes in their character. This article focuses on an analysis of the average monthly discharges of 14 stage-discharge gauging stations in Slovakia. The measured period is from 1931 to 2016. The approaches used are hydrological exploration methods, which were created by hydrologists to describe the behavior of hydrological time series. The methods are used to identify a change-point using an analysis of any residuals, the Pettitt test, and an analysis of the relationship between the mean annual discharge deviations from the long-term annual discharge and the deviations of the average monthly discharge from the long-term average monthly discharge. A considerable number of change-points were identified in the 1970s and 1980s. The results of the analyses show changes in the hydrological regimes, but to confirm the accuracy of the outcomes, it is also necessary to examine other hydrological and meteorological elements such as, e.g., precipitation and the air temperature.

Anomalous early 20th century sedimentation in proglacial Green Lake, British Columbia, Canada

2006 ◽  
Vol 43 (6) ◽  
pp. 671-678 ◽  
Author(s):  
Brian Menounos
Keyword(s):  
British Columbia ◽  
Air Temperature ◽  
Laminated Sediments ◽  
Annual Maximum ◽  
Coast Mountains ◽  
Varve Thickness ◽  
Green Lake ◽  
Daily Discharge ◽  
Temperature Records ◽  
Temperature Proxy

Annually laminated sediments were recovered from Green Lake, a proglacial lake in the southern Coast Mountains in British Columbia, to examine their potential as a temperature proxy. Varve thickness is moderately correlated with temperature anomalies (A.D. 1900–1994) and annual maximum mean daily discharge of Lillooet River (A.D. 1930–1999), but these relations are not stable through time. Following A.D. 1977, the relation between varve thickness and annual maximum mean daily discharge is stronger. Prior to A.D. 1977, varve thickness is correlated with March to October air temperature, which controls the intensity and duration of glacier runoff. Varve thickness is weakly correlated with reconstructed air temperature records for North America and the Northern Hemisphere for the period A.D. 1600–1976. Less extensive glacier cover may explain the lack of a clear temperature signal in the varved sediment record prior to A.D. 1600 and following A.D. 1977. The period of highest lake sedimentation, from A.D. 1920 to 1945, coincides with rapid retreat of glaciers in the watershed. The lack of a similar level of sedimentation in the varve chronology suggests that glacier recession during the period 1920–1945 was higher than at any time in the past 600 years.

scholarly journals Rainfall-runoff modelling and palaeoflood hydrology applied to reconstruct centennial scale records of flooding and aquifer recharge in ungauged ephemeral rivers

2010 ◽  
Vol 7 (6) ◽  
pp. 9631-9660 ◽  
Author(s):  
G. Benito ◽  
B. A. Botero ◽  
V. R. Thorndycraft ◽  
M. Rico ◽  
Y. Sánchez-Moya ◽  
...  
Keyword(s):  
Return Period ◽  
Stream Flow ◽  
Rainfall Runoff ◽  
Aquifer Recharge ◽  
Flood Duration ◽  
Ephemeral Rivers ◽  
Daily Discharge ◽  
And Storage ◽  
Large Floods

Abstract. In this study we propose a multi-source data approach for quantifying long-term flooding and aquifer recharge in ungauged ephemeral rivers. The methodology is applied to the Buffels River, at 9000 km2 the largest ephemeral river in Namaqualand (NW South Africa), a region with scarce stream flow records limiting research investigating hydrological response to global change. Daily discharge and annual flood series (1965–2006) were estimated from a distributed rainfall-runoff hydrological model (TETIS) using rainfall gauge records located within the catchment. The model was calibrated and validated with data collected during a two year monitoring programme (2005–2006) at two stream flow stations, one each in the upper and lower reaches of the catchment. In addition to the modelled flow records, non-systematic flood data were reconstructed using both sedimentary and documentary evidence. The palaeoflood record identified at least 25 large floods during the last 700 yr; with the largest events reaching a minimum discharge of 255 m3 s−1 (450 yr return period) in the upper basin, and 510 m3 s−1 (100 yr return period) in the lower catchment. Since 1925 AD, the flood hydrology of the Buffels River has been characterised by a decrease in the magnitude and frequency of extreme events, with palaeoflood discharges five times greater than the largest modelled floods during the period 1965–2006. Large floods generated the highest hydrograph volumes, however their contribution to aquifer recharge is limited as this depends on other factors such as flood duration and storage capacity of the unsaturated zone prior to the flood. Floods reaching flows associated with 5–10 yr return periods (120–140 m3 s−1) and flowing for 12 days are able to fully saturate the Spektakel aquifer in the lower Buffels River basin.

scholarly journals Long-term decrease in Asian monsoon rainfall and abrupt climate change events over the past 6,700 years

2021 ◽  
Vol 118 (30) ◽  
pp. e2102007118
Author(s):  
Bao Yang ◽  
Chun Qin ◽  
Achim Bräuning ◽  
Timothy J. Osborn ◽  
Valerie Trouet ◽  
...  
Keyword(s):  
Asian Summer Monsoon ◽  
Low Frequency ◽  
Northern China ◽  
Human Migration ◽  
The Tibetan Plateau ◽  
Drying Trend ◽  
Asian Summer ◽  
Second Millennium Bce ◽  
Instrumental Period

Asian summer monsoon (ASM) variability and its long-term ecological and societal impacts extending back to Neolithic times are poorly understood due to a lack of high-resolution climate proxy data. Here, we present a precisely dated and well-calibrated tree-ring stable isotope chronology from the Tibetan Plateau with 1- to 5-y resolution that reflects high- to low-frequency ASM variability from 4680 BCE to 2011 CE. Superimposed on a persistent drying trend since the mid-Holocene, a rapid decrease in moisture availability between ∼2000 and ∼1500 BCE caused a dry hydroclimatic regime from ∼1675 to ∼1185 BCE, with mean precipitation estimated at 42 ± 4% and 5 ± 2% lower than during the mid-Holocene and the instrumental period, respectively. This second-millennium–BCE megadrought marks the mid-to late Holocene transition, during which regional forests declined and enhanced aeolian activity affected northern Chinese ecosystems. We argue that this abrupt aridification starting ∼2000 BCE contributed to the shift of Neolithic cultures in northern China and likely triggered human migration and societal transformation.

scholarly journals CONCEPT FOR INFERRING THE LITTORAL DRIFT TREND

1976 ◽  
Vol 1 (15) ◽  
pp. 71
Author(s):  
Masatoaro Hattori ◽  
Takasuke Suzuki
Keyword(s):  
Grain Size ◽  
Coastal Zones ◽  
Littoral Drift ◽  
Beach Sediment ◽  
Sediment Properties ◽  
Term Trend ◽  
Transport Direction ◽  
Environmental Consideration ◽  
Prevailing Direction

To infer the rate and prevailing direction of littoral transport along a given coast is of prime importance in the functional and rational designing of coastal structures as well as in the environmental consideration of coastal zones. Many efforts have been made to develop the inferring method from field evidences such as 1) coastal landforms and shore configurations in the vicinity of existing structures1'~°', 2) alongshore variations in beach and bed sediment properties V)~12)j 3) statistical analysis of incident wave properties 13)~16)/ 4) movements of natural or artificial tracers 17)-20)^ an(j so on_ Among these evidences, the alongshore variations of indigeneous beach materials have served as a powerfull, practical and economical tool in the inference of general trend of littoral transport. Properties of beach sediment, such as grain size of sand and volume and shape of gravels, indicate some progressive trends with alongshore distance from supply sources2D. Thus the littoral transport direction along a given coast is inferable from variations in beach sediment properties. However, inferring criteria of prevailing direction from variations in various beach sediment properties have not yet been fully established. For example, the prevailing direction of littoral transport should be defined to be alongshore component of intergrated vector of littoral transport during several years or decades along a given coast. But this direction is often confused with the alongshore dislocating or traveling direction of beach sediment, which is indicated by the variations. It has also been concluded simply that the variation series obtained from backshore samples show a long-term trend of littoral transport, whereas those from foreshore indicate a short-term trend such as seasonal changes. In this inferring procedure any considerations have never been paid on differences in grain size of beach materials (sand and gravels) and in wave conditions during the period of field study. Rate or intensity of littoral transport has scarcely been inferred from the variation series of beach sediment properties even quantitatively. To solve these problems, the present study proposed a new concept on the basis of field evidences obtained on the Enshu Coast, Central Japan.

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