TY - JOUR

T1 - Oxygen isotope analysis of diatom silica and authigenic calcite from Lake Pinarbasi, Turkey

AU - Leng, M.

AU - Barker, P.

AU - Greenwood, P.

AU - Roberts, N.

AU - Reed, J.

N1 - Apr Oxygen isotope analysis of diatom silica and authigenic calcite from Lake Pinarbasi, Turkey Times Cited: 29

PY - 2001/4

Y1 - 2001/4

N2 - There is increasing interest in the 18O/16O ratio of diatom silica, particularly for lakes where carbonates are absent. Here we compare the 18O/16O ratios preserved in diatom silica and authigenic calcite from an open, spring-fed, freshwater lake core from Turkey which spans marine oxygen isotope stage 3. The two sets of isotope data show contrasting trends in spite of their mutual dependence on the water 18O/16O ratio and lake-water temperature. The most likely explanation for this divergence is difference in seasonality of biological productivity mediated by the strongly continental climate of the Anatolian plateau. Diatom silica and authigenic calcite are precipitated from solutes in the lake-water at different times of the year. Diatom productivity follows a well-defined seasonal cycle, peaking first and most importantly in the spring and then in the autumn. The precipitation of calcite follows productivity by all forms of photosynthetic organisms that deplete CO2 but in most lakes this occurs during the summer months. The 18Ocalcite curve shows mean summer temperature maxima at ca. 30–35 and ca. 58 ka BP while the intervening data represent a period of relatively cool summers. The 18Odiatom curve shows bipolar results (15–20 and 29–33), which suggests that at least two discrete sources or processes contributed to the oxygen composition of the diatoms but probably involved a dilution mechanism to shift the isotopic values. The most likely source of depleted water is from snow entering the lake during the spring thaw. We infer that many authigenic calcite curves from regions with markedly seasonal climates may be temporally limited to a few summer months and that diatom silica provides complementary data on seasonally-specific water isotopic composition rather than a substitute for analyses based on carbonate.

AB - There is increasing interest in the 18O/16O ratio of diatom silica, particularly for lakes where carbonates are absent. Here we compare the 18O/16O ratios preserved in diatom silica and authigenic calcite from an open, spring-fed, freshwater lake core from Turkey which spans marine oxygen isotope stage 3. The two sets of isotope data show contrasting trends in spite of their mutual dependence on the water 18O/16O ratio and lake-water temperature. The most likely explanation for this divergence is difference in seasonality of biological productivity mediated by the strongly continental climate of the Anatolian plateau. Diatom silica and authigenic calcite are precipitated from solutes in the lake-water at different times of the year. Diatom productivity follows a well-defined seasonal cycle, peaking first and most importantly in the spring and then in the autumn. The precipitation of calcite follows productivity by all forms of photosynthetic organisms that deplete CO2 but in most lakes this occurs during the summer months. The 18Ocalcite curve shows mean summer temperature maxima at ca. 30–35 and ca. 58 ka BP while the intervening data represent a period of relatively cool summers. The 18Odiatom curve shows bipolar results (15–20 and 29–33), which suggests that at least two discrete sources or processes contributed to the oxygen composition of the diatoms but probably involved a dilution mechanism to shift the isotopic values. The most likely source of depleted water is from snow entering the lake during the spring thaw. We infer that many authigenic calcite curves from regions with markedly seasonal climates may be temporally limited to a few summer months and that diatom silica provides complementary data on seasonally-specific water isotopic composition rather than a substitute for analyses based on carbonate.

KW - oxygen isotopes

KW - diatom silica

KW - calcite

KW - Turkey

KW - palaeoclimate

U2 - 10.1023/A:1011169832093

DO - 10.1023/A:1011169832093

M3 - Journal article

VL - 25

SP - 343

EP - 349

JO - Journal of Paleolimnology

JF - Journal of Paleolimnology

SN - 0921-2728

IS - 3

ER -