Genus Krithe Research Articles

Late Quaternary ostracod and planktonic foraminiferal dissolution signals from the eastern Tasman Sea — palaeoenvironmental implications

Abstract A recently developed ostracod corrosion index is compared (and contrasted) with planktonic foraminiferal fragmentation in latest Quaternary carbonate sediments from the Challenger Plateau, eastern Tasman Sea. Although assemblage data for ostracodal corrosion and planktonic foraminiferal fragmentation are similar (accepting a foraminiferal peak which anticipates the ostracod signal by about 8 kyr in isotopic stage 3, and a second peak which lags that for Ostracoda in isotopic stage 1 by an equivalent amount), plots of carapace corrosion of some ostracod genera show no such relationship. The planktonic foraminiferal fragmentation in core GR 5 4 during the last three isotopic stages duplicates the δ18O signal, suggesting regional surface-water temperature changes had a significant influence on that signal. In contrast, the corrosion index for representatives of the ostracod genus Krithe accurately tracks the δ13C for those 3 isotopic stages. We conclude that the intensity of degradation of those ostracod valves is an accurate reflection of productivity fluctuations in surface-water through time.

Deep-sea ostracode shell chemistry (Mg:Ca ratios) and Late Quaternary Arctic Ocean history

Abstract The magnesium:calcium (Mg:Ca) and strontium:calcium (Sr:Ca) ratios were investigated in shells of the benthic ostracode genus Krithe obtained from 64 core-tops from water depths of 73 to 4411 m in the Arctic Ocean and Nordic seas to determine the potential of ostracode shell chemistry for palaeoceanographic study. Shells from the Polar Surface Water (−1 to −1.5°C) had Mg:Ca molar ratios of about 0.006–0.008; shells from Arctic Intermediate Water (+0.3 to +2.0°C) ranged from 0.09 to 0.013. Shells from the abyssal plain and ridges of the Nansen, Amundsen and Makarov basins and the Norwegian and Greenland seas had a wide scatter of Mg:Ca ratios ranging from 0.007 to 0.012 that may signify post-mortem chemical alteration of the shells from Arctic deep-sea environments below about 1000 m water depth. There is a positive correlation ( r 2 = 0.59) between Mg:Ca ratios and bottom-water temperature in Krithe shells from Arctic and Nordic seas from water depths <900 m. Late Quaternary Krithe Mg:Ca ratios were analysed downcore using material from the Gakkel Ridge (water depths 3047 and 3899 m), the Lomonosov Ridge (water depth 1051 m) and the Amundsen Basin (water depth 4226 m) to test the core-top Mg:Ca temperature calibration. Cores from the Gakkel and Lomonosov ridges display a decrease in Mg:Ca ratios during the interval spanning the last glacial/deglacial transition and the Holocene, perhaps related to a decrease in bottom water temperatures or other changes in benthic environments.

The KRITHE problem — first test of peypouquet's hypothesis, with a redescription of KRITHE PRAETEXTA PRAETEXTA (crustacea, ostracoda)

The ostracode genus Krithe is generally regarded as an index for deeper water but its known depth range is 15–4500 m. Further uncertainty is caused by anterior vestibule variations in otherwise identical specimens. Peypouquet (1977) suggested that interior vestibule-size in Krithe is inversely correlated with the dissolved oxygen content of the ambient seawater. This hypothesis, if true, would enable more precise interpretations of paleodepth by means of fossil Krithe assemblages. We made a partial test of the hypothesis by examining living Krithe praetexta praetexta, collected during May 1988 at 45 m depth in the Gullmar Fjord, on the west coast of Sweden. Our paper includes a description of this taxon and notes some associated ecological factors in Gullmar Fjord. We used a quantitative method to describe their vestibules, based on linear measures obtained by rapid image digitization. A canonical variate analysis of the measures clearly indicates four different groups, one for each valve (right and left) and one for each sex. All our specimens belonged to Peypouquet's B12 morphotype. The actual dissolved oxygen values in Gullmar Fjord during May were very close to those predicted by Peypouquet for the B12 morphotype but values during June were rather less than his prediction. Possibly, the imperfect agreement can be related to variations in food supply and other sources of ostracode shell calcium. Thus, although the test has proved confirmatory as far as it goes, we believe that further study at different depths and latitudes is required. The elements of the ostracode fauna are illustrated.

Bathymetry of Recent Marine Ostracoda in Northwest Gulf of Mexico: ABSTRACT

Holocene bottom samples from the northwest Gulf of Mexico, examined for their Ostracoda faunas, yielded a total of 171 species. A large majority of them have never been described. The number of species per sample varied from 2 to 40; the richest and most diversified faunas occur in middle to outer shelf environments. Numerous species exhibit rather restricted depth ranges, and distinctly different faunal assemblages characterize the various bathymetric environments from shallow freshwater lakes and bayous down to the abyssal depths of the Sigsbee Deep. A bathymetric chart illustrates that at the generic level there exists a marked diversity of faunal composition at different depths. A pronounced relation has been noted between the size of 2 common species of Echinocythereis and the depth at which they were collected. A similar connection was observed in 12 species of the genus Krithe. The results of this study will be of considerable use in evaluating the paleoecologic significance of the rich, ostracod assemblages commonly found in the clastic Tertiary and Upper Cretaceous deposits of the Gulf Coast area. End_of_Article - Last_Page 1904------------