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Holocene climate reconstructions from tandem trace-element and stable-isotope composition of ostracodes from Coldwater Lake, North Dakota, U.S.A. (1997)

Xia, J. ; Haskell, B. J. ; Engstrom, D. R. ; [et al.]

Springer

Journal of paleolimnology 17 (1997), S. 85-100

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ISSN: 1573-0417

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Geosciences

Notes: Abstract The geochemistry of ostracode shells and bulk carbonates in a 19-meter sediment core documents at century-scale resolution the evolution of water chemistry in Coldwater Lake, North Dakota, providing a continuous paleohydrologic record of Holocene climate change in the northern Great Plains. A combination of δ18O, δ13C, Mg/Ca and Sr/Ca in ostracode calcite aided by Sr/Ca in bulk carbonates are used to constrain the paleoclimatic reconstructions. A fresh-water phase in the early Holocene, indicated by the absence of Candona rawsoni and low concentrations of Sr/Ca in bulk carbonate, was followed by a sharp increase in salinity between 10 800 and 8900 yr B.P. The climate was predominately dry during the late part of the early Holocene and most of the middle Holocene (8900–5000 yr B.P.), when the lake was very sensitive and recorded a series of dry and wet oscillations. Maximum salinity occurred around 5500 yr B.P. and was followed by a gradual decrease between 5000 and 2400 yr B.P. From 2400 yr B.P. the δ18O, Mg/Ca, and Sr/Ca in the ostracodes indicate generally wet conditions interrupted by a series of lesser salinity and temperature oscillations lasting until 600 yr B.P. Ostracode geochemistry indicates that a warm and dry climate returned at about the time of the Little Ice Age (600–150 yr B.P.). Ostracode δ13C shows a ong-term increasing trend during the Holocene, which suggests that lake productivity and atmospheric CO2 exchange made greater contributions to the hypolimnetic carbon pool as the lake became shallower with time.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1007921328712

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Water quality and sediment geochemistry in lakes of Yunnan Province, southern China (1997)

Whitmore, T. J. ; Brenner, M. ; Jiang, Z. ; [et al.]

Springer

Environmental geology 32 (1997), S. 45-55

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ISSN: 1432-0495

Keywords: Key words China ; Sediment ; Water quality ; Yunnan ; Lakes ; Isotopes

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences

Notes: Abstract Yungui Plateau lakes in southwestern China are economically important, although few have been studied previously. Water and sediments of 24 lakes throughout Yunnan Province were sampled in October 1994. We describe the chemical and physical characteristics of Yunnan lakes, and address effects of regional geology and human influences on water quality and sediment type. Water quality differs between deep Yunnan lakes of tectonic origin and shallow solution basins. Shallow lakes generally have higher nutrient concentrations and appear to be more susceptible to riparian disturbance than deeper lakes. Shallow lakes with high macrophyte standing crops, nevertheless, exhibit nutrient-poor waters. Principal ions Ca2+, Mg2+, and HCO3 – reflect regional carbonate geology, except in Cheng Hai, which is a sodium bicarbonate lake. Specific conductance and δ18O are positively correlated, indicating that evaporation concentrates both solutes and 18O. Large, shallow lakes in southeastern Yunnan exhibit 18O-enriched waters because of substantial evaporation, whereas small, deep lakes are 18O-depleted. Lake waters are 18O-depleted in small, shallow basins that receive substantial rainwater input relative to their small volumes. 18O enrichment in Cheng Hai suggests that a recent 5-m water-level decline in this lake was caused by increased evaporation or diversion of freshwater inflow. Yunnan watersheds have undergone substantial deforestation, agricultural cultivation, soil erosion, and industrialization. Limnetic nutrient concentrations indicate that human activities have affected water quality. Organic matter content is low in sediments because of increased non-carbonate, clastic sediment yield from watersheds. Environmental policies are needed to balance ecological contraints with economic activities that impact water quality.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s002540050192

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