Benthic isopod species in the Ross Sea and their distribution in the Southern Ocean

In this study isopod species of the Ross Sea were investigated. Literature until May 2008 was checked to provide an overview of all known and described species in the Ross Sea. This species checklist was then enlarged through material of the 19th Italica expedition in 2004. During this expedition for the first time a small mesh net (500 µm) was used. Nine thousand four hundred and eighty one isopod specimens were collected during this expedition. Through this material the number of isopod species in the Ross Sea increased from 42 to 117 species, which belong to 20 families and 49 genera. Fifty-six percentage of the isopods species collected during the Italica expedition are new to science. The zoogeography of the 117 species was investigated. A non-transformed binary presence-absence data matrix was constructed using the Bray-Curtis coefficient. The results were displayed in a cluster analysis and by nonmetric multidimensional scaling (MDS). This paper gives a first insight into the occurrence and distribution of the isopod species of the Ross Sea.

Standardized rainfall indices for the West and Central Sahel, and the Guinea Coast

For years, various indices of seasonal West African precipitation have served as useful predictors of the overall tropical cyclone activity in the Atlantic Ocean. Since the mid-1990s, the correlation unexpectedly deteriorated. In the present study, statistical techniques are developed to describe the nonstationary nature of the correlations between annual measures of Atlantic tropical cyclone activity and three selected West African precipitation indices (namely, western Sahelian precipitation in June-September, central Sahelian precipitation in June-September, and Guinean coastal precipitation in the preceding year's August-November period). The correlations between these parameters are found to vary over the period from 1921 to 2007 on a range of time scales. Additionally, considerable year-to-year variability in the strength of these correlations is documented by selecting subsamples of years with respect to various meteorological factors. Broadly, in years when the environment in the main development region is generally favorable for enhanced tropical cyclogenesis (e.g., when sea surface temperatures are high, when there is relatively little wind shear through the depth of the troposphere, or when the relative vorticity in the midtroposphere is anomalously high), the correlations between indices of West African monsoon precipitation and Atlantic tropical cyclone activity are considerably weaker than in years when the overall conditions in the region are less conducive. Other more remote climate parameters, such as the phase of the Southern Oscillation, are less effective at modulating the nature of these interactions.

Sr/Ca ratios of Cenozoic benthic foraminifera

A Cenozoic multi-species record of benthic foraminiferal calcite Sr/Ca has been produced and is corrected for interspecific offsets (typically less than 0.3 mmol/mol) and for the linear relationship between decreasing benthic foraminiferal Sr/Ca and increasing water depth. The water depth correction, determined from Holocene, Late Glacial Maximum and Eocene paleowater-depth transects, is ~0.1 mmol/mol/km. The corrected Cenozoic benthic foraminiferal Sr/Ca record ranges from 1.2 to 2.0 mmol/mol, and has been interpreted in terms of long-term changes in seawater Sr/Ca, enabling issues related to higher-resolution variability in Sr/Ca to be ignored. We estimate that seawater Sr/Ca was ~1.5 times modern values in the late Cretaceous, but declined rapidly into the Paleogene. Following a minimum in the Eocene, seawater Sr/Ca increased gradually through to the present day with a minimum superimposed on this trend centered in the late Miocene. By assuming scenarios for changing seawater calcium concentration, and using published carbonate accumulation rate data combined with suitable values for Sr partition coefficients into carbonates, the seawater Sr/Ca record is used to estimate global average river Sr fluxes. These fluxes are used in conjunction with the seawater strontium isotope curve and estimates of hydrothermal activity/tectonic outgassing to calculate changes in global average river 87Sr/86Sr through the Cenozoic. The absolute magnitude of Sr fluxes and isotopic compositions calculated in this way are subject to relatively large uncertainties. Nevertheless, our results suggest that river Sr flux increased from 35 Ma to the present day (roughly two-fold) accompanied by an overall increase in 87Sr/86Sr (by ~0 to 0.001). Between 75 and 35 Ma, river 87Sr/86Sr also increased (by ~0.001 to 0.002) but was accompanied by a decrease (two- to three-fold) in river Sr flux.

Os isotope ratios of sediments from the Eocene-Oligocene boundary

Osmium (Os) isotope analyses of bulk sediments from the South Atlantic, Equatorial Pacific, and the Italian Apennines yield a well-dated and coherent pattern of 187Os/188Os variation from the late Eocene to the early Oligocene. The resulting composite record demonstrates the global character of two prominent features of the low-resolution LL44-GPC3 Os isotope record (Pegram and Turekian, 1999, doi:10.1016/S0016-7037(99)00308-7). These are: (1) a pronounced minimum in 187Os/188Os (0.22-0.27) in the late Eocene, between 34 and 34.5 Ma, and (2) a subsequent rapid increase in 187Os/188Os, to approximately 0.6 by 32 Ma. An ultramafic weathering event and an increased influx of extraterrestrial particles to the Earth are discussed as alternative explanations for the late Eocene 187Os/188Os minimum. Comparison of the 187Os/188Os to benthic foraminiferal oxygen isotope records demonstrates that the nearly three-fold increase in 187Os/188Os from the late Eocene minimum coincides with the growth and decay of the first large ice sheet of the Oligocene (Oi1 (Miller et al., 1991, doi:10.1029/90JB02015)). The fine structure of the Os isotope record indicates that enhanced release of radiogenic Os, unrelated to the recovery from late Eocene minimum, lagged the initiation of the Oi1 event by roughly 0.5 Myr. This record, in conjunction with weathering studies in modern glacial soils (Blum, in: W.F. Ruddiman (Ed.), Tectonic Uplift and Climate Change, Plenum Press, New York, 1997, pp. 259-288; Peucker-Ehrenbrink and Blum, 1998, doi:10.1016/S0016-7037(98)00227-0), suggests that exposure of freshly eroded material during deglaciation following Oi1 enhanced chemical weathering rates, and may have contributed to ice sheet stabilization by drawing down atmospheric carbon dioxide. The improved temporal resolution and age control of the refined Eocene-Oligocene Os isotope record also makes it possible to illustrate the late Eocene Os isotope excursion as a tool for global correlation of marine sediments.

(Table 1) Heavy fraction minerals in bottom sediments of the Markov Deep, Mid-Atlantic Ridge

An additional ore field in the central part of the MARhas been discovered. Together with previously discovered Logachev (14°45'N) and Ashadze (12°58'N) ore fields, the new ore field constitutes a cluster with preliminarily estimated total ore reserve of >10 Mt, which is comparable with large continental massive sulfide deposits.

North Atlantic late Miocene stable-isotope stratigraphy, biostratigraphy, and magnetostratigraphy

Upper Miocene foraminiferal nannofossil ooze and chalk from DSDP Hole 552A in the northeast Atlantic Ocean have been closely sampled for biostratigraphic, paleomagnetic, and stable-isotopic studies. Sampling at 10-cm intervals resulted in an uppermost Miocene isotope stratigraphy with a 1000- to 3000-yr. resolution. Covariance in benthic (Planulina wuellerstorfi) and planktonic (Globigerina bulloides) foraminiferal d18O records is taken as evidence for variability in continental ice volume. Our best estimate is that glacial maxima occurred at -5.0 and ~ 5.5 Ma and lasted no more than 20,000 yrs. These events probably lowered sea level by 60 m below the latest Miocene average. There is little oxygen-isotope evidence, however, for a prolonged glaciation during the last 2 m.y. of the late Miocene. High- and low-frequency variability in the d13C record of foraminifers is useful for correlation among North Atlantic DSDP Sites 408, 410, 522, 610, and 611, and for correlation with sites in other oceans. Similar d13C changes are seen in P. wuellerstorfi and G. bulloides, but the amplitude of the signal is always greater in G. bulloides. Variability in d13C common to both species probably reflects variability in the d13C of total CO2 in seawater. Major long-term features in the d13C record include a latest Miocene maximum (P. wuellerstorfi = 1.5 per mil ) in paleomagnetic Chron 7, an abrupt decrease in d13C at -6.2 Ma, and a slight increase at -5.5 Ma. The decrease in d13C at -6.2 Ma, which has been paleomagnetically dated only twice before, occurs in the upper reversed part of Chronozone 6 at Holes 552A and 611C, in excellent agreement with earlier studies. Cycles in d13C with a period of ~ 10 4 yrs. are interpreted as changes in seawater chemistry, which may have resulted from orbitally induced variability in continental biomass. Samples of P. wuellerstorfi younger than 6 Ma from throughout the North Atlantic have d13C near lo, on average ~ l per mil greater than samples of the same age in the Pacific Ocean. Thus, there is no evidence for cessation of North Atlantic Deep Water production resulting from the Messinian "salinity crisis." Biostratigraphic results indicate continuous sedimentation during the late Miocene after about -6.5 Ma at Hole 552A. Nannofossil biostratigraphy is complicated by the scarcity of low-latitude marker species, but middle and late Miocene Zones NN7 through NN11 are recognized. A hiatus is present at -6.5 Ma, on the basis of simultaneous first occurrences of Amaurolithusprimus, Amaurolithus delicatus, Amaurolithus amplificus, and Scyphosphaera globulata. The frequency and duration of older hiatuses increase downsection in Hole 552A, as suggested by calcareous nannofossil biostratigraphy and magnetostratigraphy. Paleomagnetic results at Hole 552A indicate a systematic pattern of inclination changes. Chronozone 6 was readily identified because of its characteristic nannoflora (sequential occurrences of species assigned to the genus Amaurolithus) and the d13C decrease in foraminifers, but its lower reversed interval is condensed. Only the lower normal interval of Chronozone 5 was recognized at Hole 552A; the upper normal interval and the lowest Gilbert sediment are not recognized, owing to low intensity of magnetization and to coring disturbance. Interpreting magnetic reversals below Chronozone 6 was difficult because of hiatuses, but a lower normally magnetized interval is probably Chronozone 7. Correlation between DSDP Hole 552A and other North Atlantic sites is demonstrated using coiling direction changes in the planktonic foraminifer Neogloboquadrina. At most sites this genus changed its coiling preference from dominantly right to dominantly left during the late Miocene. At Hole 552A this event probably occurred about 7 m.y. ago. At the same time, P. wuellerstorfi had maximum d13C values. A similar d13C maximum and coiling change occurred together in Chron 7 at Hole 611C, and at Hole 610E. In sediment younger than -5.5 Ma, the coiling of small Neogloboquadrina species is random, but the larger species N. atlantica retains preferential left coiling.

Os isotope ratios of Late Eocene sediments from the tropical Pacific

High resolution records (ca. 100 kyr) of Os isotope composition (187Os/188Os) in bulk sediments from two tropical Pacific sites (ODP Sites 1218 and 1219) capture the complete Late Eocene 187Os/188Os excursion and confirm that the Late Eocene 187Os/ 188Os minimum, earlier reported by Ravizza and Peucker-Ehrenbrink (2003, doi:10.1016/S0012-821X(03)00137-7), is a global feature. Using the astronomically tuned age models available for these sites, it is suggested that the Late Eocene 187Os/188Os minimum can be placed at 34.5 +/- 0.1 Ma in the marine records. In addition, two other distinct features of the 187Os/188Os excursion that are correlatable among sections are proposed as chemostratigraphic markers which can serve as age control points with a precision of ca. +/-0.1 Myr. We propose a speculative hypothesis that higher cosmic dust flux in the Late Eocene may have contributed to global cooling and Early Oligocene glaciation (Oi-1) by supplying bio-essential trace elements to the oceans and thereby resulting in higher ocean productivity, enhanced burial of organic carbon and draw down of atmospheric CO2. To determine if the hypothesis that enhanced cosmic dust flux in the Late Eocene was a cause for the 187Os/188Os excursion can be tested by using the paired bulk sediment and leachate Os isotope composition; 187Os/188Os were also measured in sediment leachates. Results of analyses of leachates are inconsistent between the south Atlantic and the Pacific sites, and therefore do not yield a robust test of this hypothesis. Comparison of 187Os/188Os records with high resolution benthic foraminiferal delta18O records across the Eocene-Oligocene transition suggests that 187Os flux to the oceans decreased during cooling and ice growth leading to the Oi-1 glaciation, whereas subsequent decay of ice-sheets and deglacial weathering drove seawater 187Os/188Os to higher values. Although the precise timing and magnitude of these changes in weathering fluxes and their effects on the marine 187Os/188Os records are obscured by recovery from the Late Eocene 187Os/188Os excursion, evidence of the global influence of glaciation on supply of Os to the ocean is robust as it has now been documented in both Pacific and Atlantic records.