Combining the Mg/Ca of the ostracod Cyprideis torosa with its ontogenic development for reconstructing a 28 kyr temperature record for Lake Banyoles (NE Spain)

Cyprideis torosa is a ubiquitous ostracod found in fresh to hypersaline waters, and commonly in large numbers across the Mediterranean region. Single valves of 51 adult specimens of C. torosa were separated from carapaces that were collected from Lake Banyoles in NE Spain at a depth of 5 m. The Mg/Ca of the valves was compared with known temperatures necessary for successive instar valve calcification, the latter being based on a four-year ecological study of C. torosa collected at Dievengat in northern Belgium by Carlo Heip in 1968–72. Hence, we were able to link the Mg/Ca of fossil valves of C. torosa recovered for a 28 kyr sequence at La Draga, cored on the fringe of Lake Banyoles, with the ontogenic observations of Heip, and reconstruct mean summer temperatures as well as optimal calcification temperature for C. torosa. Principal findings are: (1) the Holocene registered the highest temperatures with also very broad fluctuations; (2) three cold phases are clearly identified at 26.7–23.2, 21.6–20.3 and 16.2–14.3 ka BP; and (3) a prolonged warm phase that lasted about two millennia commenced at 19.5 ka BP and was followed by a progressive temperature decline well over three millennia. Surprisingly the Last Glacial Maximum was not the coldest phase. We finally compare our results with sea-surface temperature (SST) reconstructions from cores from the western Mediterranean Sea. Our record from La Draga clearly matches events recorded in the Alboran Sea that display SST changes obtained from the UK'37 index. The Heinrich 1 and 2 events around 16 and 28 ka BP coincide with significant low temperature excursions at Banyoles, and palynological records in the marine cores which define semi-arid conditions on land match the low temperature record in our core.The coring and analyses were funded by the European Euromaar Project and the Belgian Services fédéraux des affaires scientifiques, techniques et culturelles (SSTC)

Quantification of paleotemperature changes during isotopic stage 2 in the La Draga continental sequence (NE Spain) based on the Mg/Ca ratio of freshwater ostracods

Past summer temperature changes are quantified from the La Draga sequence (Banyoles, NE Spain) during Stage 2 (24-10 ka BP), using trace-element content in lacustrine ostracod valves. The high resolution results from this new method are compared to summer paleotemperature reconstructions from sequences from the North Atlantic area, providing a discussion about the magnitudes of some temperature changes. In NE Spain and offshore Portugal, the coldest part of Stage 2 is not documented at the classical date of similar to 18 C-14 ka BP (similar to 21.5 calendar ka BP) but rather occurred later date of ca. 17-15 ka cal. BP In the North Atlantic area, the onset of the Bolling/Allerod interstadials was relatively synchroneous at similar to 14.6 ka cal. BP, although the magnitude of the Bolling/Allerod improvement was more important in the southern area than in the northern area. The duration of the Younger Dryas is discussed. Even if different durations are reported from calendar ages, it seems that the summer temperature cooling of the Younger Dryas was similar around the North Atlantic area. (C) 1996 Elsevier Science Lt

The response of ostracod shell chemistry to seasonal change in a Mediterranean freshwater spring environment

We established the relationships between water chemistry changes in a pool fed by a permanent spring and seasonal variations in trace-element contents (Sr & Mg) in the shells of the ostracod species Herpetocypris intermedia, based on monthly collections of ostracod and water samples. The water chemistry of the investigated pool (Maiques, Valencia, Spain) was dominated by calcium and bicarbonate, and showed marked seasonal variation in alkalinity, Ca2+ content, Sr/Ca and Mg/Ca ratios. Although the variability in the water chemistry was relatively low (similar to 10% relative standard deviation over the entire period), the trace-clement contents: in the ostracod shells tracked the seasonal change in the water chemistry of Maiques pool. Moreover, due to the rapid renewal of H. intermedia population, this species is able to record in its shells the evolution of the water chemistry at a monthly time scale. Our results also showed that, in the Maiques pool system, ostracod Sr/Ca and Mg/Ca ratios increased with the decrease in water salinity. To our knowledge, this is the first geochemical study of ostracods dwelling in spring environments. The results of this study may be applied to paleohydrological reconstruction using ostracods preserved in sediments deposited around springs (i.e., travertine and tufa deposits)

Temperature influence on development and calcification of Herpetocypris brevicaudata Kaufmann, 1900 (Crustacea: Ostracoda) under experimental conditions

Cultures of the freshwater ostracod Herpetocypris brevicaudata were kept under laboratory conditions in order to study effects of water temperature on development time and calcification process. Four culture temperatures were used: 22.4, 14.6, 19.8 and 23.3 degrees C. H. brevicaudata cultured at 19.8 and 23.3 degrees C showed higher survival rate and faster development than those cultured at 12.4 and 14.6 degrees C. Water temperature also has a clear influence on the degree of calcification of the ostracod shells. For H. brevicaudata, the 15-19 degrees C temperature range constitutes a threshold below which Ca content of valves significantly decreases. Time required to calcify is also longer below this threshold. The increase of the calcification time due to lower water temperatures seems to induce low survival rates

Experimental determination of strontium and magnesium partitioning in calcite of the freshwater ostracod Herpetocypris intermedia

Cultures of the freshwater ostracod Herpetocypris intermedia (Crustacea) were kept under controlled conditions in order to study the influence of the chemistry and the temperature of the water, as well as the influence of the calcification process, on the incorporation of strontium and magnesium in their calcite carapaces. These experiments pointed out to three factors that induced variations in the partition coefficients D(Sr) and D(Mg): (1) the calcification process: light-weight shells were usually depleted in Sr content when compared to well calcified valves; (2) a high water Sr/Ca ratio: in this case an increase of D(Sr) with ostracod Mg content was observed; (3) the water Mg/Ca ratio: above a water Mg/Ca ratio of similar to 1, D(Mg) was nearly constant (0.0042 +/- 0.0007). In low water Mg/Ca ratios (<0.4), D(Mg) increased. Our results also show that temperature does not influence the D(Mg) value for Herpetocypris. We hypothesise that freshwater taxa such as Herpetocypris have developed mechanisms to control the temperature effect on calcite Mg content, because they do not have to exert a control on Mg content during calcification to avoid high-Mg calcite formation

Combining the Mg/Ca of the ostracod Cyprideis torosa with its ontogenic development for reconstructing a 28 kyr temperature record for Lake Banyoles (NE Spain)

Cyprideis torosa is a ubiquitous ostracod found in fresh to hypersaline waters, and commonly in large numbers across the Mediterranean region. Single valves of 51 adult specimens of C. torosa were separated from carapaces that were collected from Lake Banyoles in NE Spain at a depth of 5 m. The Mg/Ca of the valves was compared with known temperatures necessary for successive instar valve calcification, the latter being based on a four-year ecological study of C. torosa collected at Dievengat in northern Belgium by Carlo Heip in 1968-72. Hence, we were able to link the Mg/Ca of fossil valves of C. torosa recovered for a 28 kyr sequence at La Draga, cored on the fringe of Lake Banyoles, with the ontogenic observations of Heip, and reconstruct mean summer temperatures as well as optimal calcification temperature for C. torosa. Principal findings are: (1) the Holocene registered the highest temperatures with also very broad fluctuations; (2) three cold phases are clearly identified at 26.7-23.2, 21.6-20.3 and 16.2-14.3 ka BP; and (3) a prolonged warm phase that lasted about two millennia commenced at 19.5 ka BP and was followed by a progressive temperature decline well over three millennia. Surprisingly the Last Glacial Maximum was not the coldest phase. We finally compare our results with sea-surface temperature (SST) reconstructions from cores from the western Mediterranean Sea. Our record from La Draga clearly matches events recorded in the Alboran Sea that display SST changes obtained from the U-37(K') index. The Heinrich 1 and 2 events around 16 and 28 ka BP coincide with significant low temperature excursions at Banyoles, and palynological records in the marine cores which define semi-arid conditions on land match the low temperature record in our core

Habitat preferences and population dynamics of Ostracoda in a helocrene spring system

Habitat features and ostracod populations were monitored monthly between December 1995 and September 1996 in three contiguous pools of a Mediterranean helocrene spring. Principal-components analysis (PCA) of the physical and chemical properties of the water showed that seasonal variations were minor in the site closest to the source (pool 1). Conversely, the site the most distant from the source (pool 3) had the greatest variation in temperature and oxygen and calcium contents. Differences in limnological factors, especially the equilibrium system of carbonates, among sites were also clear from the results obtained with PCA. The cosmopolitan ostracod Cypridopsis vidua predominated in pool 1, where variations in oxygen content and temperature were minimal, and showed a univoltine reproductive pattern. The crenophilous species Potamocypris villosa and Herpetocypris intermedia were the most abundant ostracods at the other two sites, where the development of filamentous algae and Characeae produced a high oxygen concentration and an increase in calcium carbonate precipitation. The latter two species both produced two generations per year. The small size of springs and their position between interstitial and surface waters make them excellent systems for the study of ostracod ecology and the influences of environmental factors upon their life-history traits

Moulting, survival and calcification: the effects of temperature and water chemistry on an ostracod crustacean (Herpetocypris intermedia) under experimental conditions

Temperature and water chemistry are usually considered as being the two main factors to influence the development and survival of non-marine ostracods. These factors may act upon a wide range of biological parameters, among which, those directly linked to the moulting process are of great importance. In this work, we study the effects of water temperature and ionic composition on survival, moulting success and calcification in the freshwater ostracod Herpetocypris intermedia; we propose a hypothesis on the basis of our general understanding of crustacean physiology to derive a tentative explanation of the ecology and distribution of non-marine ostracods. Several temperatures and water chemistries were used for experimental cultures of the adult and juvenile stages of H. intermedia, in which survival, moulting and shell Ca-uptake were monitored. Water temperatures between 15 degrees C and 20 degrees C resulted in the longest survival times, but high water temperatures (20-24 degrees C) provided the highest rates of moulting and calcification and shortest intermoult times. Despite this, the highest water temperature (24 degrees C) was associated with the shortest survival times, whilst survival time and calcification were low at the lowest temperature examined (13 degrees C). The different effects of ionic composition upon the biological parameters studied show that H. intermedia develops "better" in bicarbonate-rich than in chloride-rich waters. These experimental findings are in general agreement with field data and allow us to establish different tolerance limits and niche preferences for various congeneric taxa. Taking into account previously published data on calcium incorpora tion and ionic regulation in freshwater Crustacea, our results suggest that there is a trade-off between calcification and ionic regulation in non-marine ostracods; these animals need to precipitate calcite and also to pump bicarbonate ions outwards to maintain internal chloride concentrations. In recent times, water ionic ratios, and particularly bicarbonate/chloride ratios, have been considered to be major factors influencing non-marine ostracod distributions. In this sense, the physiological mechanisms cited in this study to explain our experimental results would also illustrate the major biogeographic and ecological patterns observed in non-marine Ostracoda, i.e. that some species are restricted to brackish waters whilst others dwell only in freshwaters

Variability in ostracod partition coefficients D(Sr) and D(Mg) implications for lacustrine palaeoenvironmental reconstructions

Living and sub-recent ostracods were collected from four lakes and foul springs, located in Belgium, France and Spain, characterized by low water Mg/Ca ratios (from 0.08 to 0.65). Valves of ostracods belonging to Cyprideis torosa, Candona neglecta, C. marchica and C. candida have been extensively analysed for their magnesium and strontium contents with respect to calcium. Comparisons of these results are made using the same elements from the waters in which the ostracod valves calcified. Our results offer new and somewhat different interpretations with respect to the uptake of Mg and Sr in the calcitic ostracod valves. These findings include the following. (1) The partition coefficient L)(Sr for ostracods belonging to the same genus (Candona) is not a constant. The observed variability in D(Sr) values could be due to the rare of biological calcification, although more investigations are necessary to assess the influence of this factor; it is possible that some taxa grouped under the genus Candona belong to a different genus. (2) Even at the species level (Cyprideis torosa), the ostracod D(Sr) cannot be considered to be constant. At low water Mg/Ca ratio (0.65), our D(Sr) value for C. torosa is higher than those determined by others for C. torosa calcified in evolved marine water. (3) The Mg/Ca ratio of the water appears as a major factor influencing D(Mg) for ostracods. For low water Mg/Ca values (< similar to 2), D(Mg) drastically increases. This phenomenon is also effective for inorganic calcite; implying a non-biologic effect that could be linked to Mg2+ adsorption. Consequently, large variations in ME content of fossil ostracod valves from selected lacustrine sequences, with expected low water Mg/Ca(< similar to 2), can be due to small variations in water Mg/Ca. (C) 1998 Elsevier Science B.V. All rights reserved