The major states, in which Earth's climate operates, i.e., icehouse, greenhouse and hothouse, are epochs of tens of millions of years. These states set long-term boundary conditions that need to be ...considered for climate and sea-level interpretations. This paper summarizes the conceptual models for hydrological cycling derived from the characteristics of these three climate states. While glacio-eustatic forcing of sea-level changes under icehouse climate conditions is fairly well understood, the drivers of eustatic sea-level fluctuations under greenhouse conditions remain enigmatic. This lack of understanding may be related to incoherencies in the current ideas about the impact of accelerated hydrological cycling on sea level under greenhouse climate conditions.
As an example for a greenhouse climate, we review evidences that link proxies for climate and sea level for the intensely studied, but controversially discussed, mid-Cretaceous sea-level history. Based on sequence stratigraphy and a recently published high-precision timescale, we demonstrate that the late Middle Turonian Pewsey δ13C isotope maximum represents a major transgression, not a regression as previously stated, which conflicts with the interpretation of a co-occurring δ18O maximum to reflect a short glacial episode. This contradiction can be solved by the concept, presented here, that dominance of aquifer-eustasy characterized sea-level forcing during the Turonian greenhouse climate, despite a possible, though contentious, sporadic presence of minor ice sheets. The effects of temperature and ice volume both lead to a pronounced δ18Ocarb maximum during glacio-eustatic regressions. In contrast, the opposing effects of temperature and groundwater volume on oxygen-isotope fractionation lead to a δ18Ocarb maximum during aquifer-eustatic transgressions. We suggest that, throughout Earth history, both aquifer-eustatic and glacio-eustatic forcing formed a combined sea-level response, with dominance of aquifer-eustasy being typical for the greenhouse climate mode. During the icehouse mode, aquifer-eustasy apparently remains active as a background process, but is outpaced by the glacio-eustatic effect.
•Turonian climate cooling corresponds to transgressions not lowstands.•Combined cooling and high sea-level are incompatible with glacio-eustasy.•Aquifer-eustasy dominates in greenhouse modes.
This review provides a synopsis of ongoing research and our understanding of the fundamentals of sea-level change today and in the geologic record, especially as illustrated by conditions and ...processes during the Cretaceous greenhouse climate episode. We give an overview of the state of the art of our understanding on eustatic (global) versus relative (regional) sea level, as well as long-term versus short-term fluctuations and their drivers. In the context of the focus of UNESCO-IUGS/IGCP project 609 on Cretaceous eustatic, short-term sea-level and climate changes, we evaluate the possible evidence for glacio-eustasy versus alternative or additional mechanisms for continental water storage and release for the Cretaceous greenhouse and hothouse phases during which the presence of larger continental ice shields is considered unlikely. Increasing evidence in the literature suggests a correlation between long-period orbital cycles and depositional cycles that reflect sea-level fluctuations, implying a globally synchronized forcing of (eustatic) sea level. Fourth-order depositional sequences seem to be related to a ~405ka periodicity, which most likely represents long-period orbital eccentricity control on sea level and depositional cycles. Third-order cyclicity, expressed as time-synchronous sea level falls of ~20 to 110m on ~0.5 to 3.0Ma timescales in the Cretaceous, are increasingly recognized as connected to climate cycles triggered by long-term astronomical cycles that have periodicity ranging from ~1.0 to 2.4Ma. Future perspectives of research on greenhouse sea-level changes comprise a high-precision time-scale for sequence stratigraphy and eustatic sea-level changes and high-resolution marine to non-marine stratigraphic correlation.
•Up-to-date synopsis of sea-level change fundamentals today and in the geologic record•Eustatic (global) vs. eurybatic (relative) sea level and long-term vs. short term sea-level fluctuations and their drivers•Review of Cretaceous short-term climate and sea-level changes (IGCP 609)•Evaluation and quantification of glacio-eustasy versus aquifer eustasy during the Cretaceous greenhouse
New stable carbon and oxygen isotope data from an Upper Cretaceous section in Tibet are presented, and compared to carbon isotope records from England, Italy, and Germany. Together with a ...stratigraphic re-interpretation of published carbon isotope data from a nearby section in Tibet, our data can surprisingly well be correlated with the European sections. This indicates that, similar to the distinct positive carbon isotope excursion at the Cenomanian-Turonian boundary, also the broad positive carbon isotope shift in the middle-late Coniacian and early Santonian reflects a major perturbation of the carbon cycle on a global scale, even though organic-rich sediments related to the OAE3 appear to be mainly restricted to the Atlantic Ocean and adjacent basins. The data further show that, apart from the broad Coniacian-Santonian carbon isotope excursion, also isotopic shifts on a smaller scale in the Turonian and Coniacian, such as the Round Down, Pewsey, and Hitchwood Events, can be correlated over both hemispheres. This demonstrates that the development of global oceanic anoxic conditions and associated burial of large amounts of organic carbon do not constitute a prerequisite for globally reflected carbon isotopic shifts. The data from Tibet support the concept of a relation between main carbon isotope excursions and major sea-level variations. Cyclic fluctuations of geochemical and lithological parameters are likely to be orbitally driven. These cycles appear to be preferably reflected in the sediments during periods of lower or variable sea-level, whereas the ocean-atmosphere system seems to have operated in a different mode during long phases of high, stable sea-level, as during the Coniacian-Santonian OAE3.
An analytical method has been established to determine the concentration of antimony (Sb), bismuth (Bi), lead (Pb), cadmium (Cd), mercury (Hg), Palladium (Pd), platinum (Pt), tellurium (Te), tin ...(Sn), thallium (Tl) and tungsten (W) in urine. The aim was to develop a method which is equally suitable for the determination of environmentally as well as occupationally caused metal excretion.
Inductively coupled plasma-mass spectroscopy (ICP-MS) was used for the determination of metals. Calibration was done using aqueous solutions and standard addition respectively.
Urine samples of 14 persons occupationally non-exposed to metals were analysed. With the exception of Pt and Bi all the metals were found in these urine samples. The detection limits for these metals lie between 5 and 50 ng/l.
For some metals, which are important from an occupational as well as an environmental viewpoint, ICP-MS is more sensitive than atomic absorption spectrometry (AAS). ICP-MS, moreover, is welcome as a reference method for AAS with the additional advantage of multi-element measurement.
Inductively coupled plasma mass spectrometry (ICP-MS) has been used for the determination of
232Th and
238U in urine of unexposed Jordanian subjects living in six cities. The range of
232Th excretion ...in all subjects was found to be 1.4–640 μBq d
−1 with an average of 34.8 μBq d
−1 (geometric mean 15.8 μBq d
−1). Results showed no statistically significant correlation with age and residential area. The average value obtained is in agreement with levels considered normal in some recent publications. The average value of
238U in all samples was found to be 3955 μBq d
−1 (geometric mean 1107 μBq d
−1), which is higher than reported figures from Germany and India, but in agreement with those figures given in ICRP publication, number 23. The mean values of the different groups were found to be proportional to age up to 60 years. A noticeable drop is observed for subjects greater than 60 years old.
In oceanic regions with high primary production, such as the Arabian Sea, the primary signals of proxies are often altered by diagenetic processes. The present study aims at assessing the effects of ...early diagenesis on calcareous dinoflagellate cysts, which represent a relatively new tool for reconstructing the paleoenvironmental conditions within the photic zone. For this purpose, surface sediment samples from within and below the oxygen minimum zone (OMZ) of the northeastern and southwestern Arabian Sea have been analysed quantitatively for their calcareous dinoflagellate cyst content. The calculated cyst accumulation rates (ARs), the relative abundances and cyst fragmentation values were compared to bottom water oxygen (BWO) content and ARs of organic carbon at the sample positions. Different patterns were found in the northeastern and southwestern part of the Arabian Sea. In the SW, no relationship between cyst ARs and BWO is distinguishable, and the distribution of cyst ARs is thought to largely reflect primary cyst production. In the NE, much higher ARs of all species are found in samples from within the OMZ in comparison to samples from below it. This is interpreted to result from better calcite preservation within the OMZ, presumably due to reduced oxic degradation of organic matter. The differential drop of cyst ARs of the individual species at the lower boundary of the OMZ in the NE Arabian Sea, as well as the species-specific change in relative abundance and fragmentation, indicate different sensitivity to calcite dissolution of the different species. These results show that early diagenetic calcite dissolution can change both relative and absolute abundances of calcareous dinoflagellate cysts, which has to be considered if using them for paleoenvironmental reconstructions. Furthermore, it is shown that considerable calcite dissolution can occur above the carbonate saturation horizon in high productive areas. However, calcite preservation can be substantially increased, as soon as oxygen concentrations are too low for oxic degradation of OM. Under low oxic conditions (within and near the OMZ), the main factor controlling organic matter (OM) preservation appears to be BWO concentrations. Under higher oxygen levels (below ∼1500 m depth in the NE Arabian Sea) there seems to be an increasing influence of bioturbation and sedimentation rate on the preservation of OM by controlling its oxygen exposure time. This study presents an example of a highly productive basin in which differences in early diagenetic processes can lead to the preservation of a signal that is either dominated by primary production (off Somalia) or by secondary alteration (off Pakistan), although in both areas, an oxygen depleted zone is present. For estimating the effects of early diagenetic calcite dissolution in a sediment by metabolic CO
2 (and probably by H
2S oxidation), not only the content of organic carbon but also other geochemical proxies for paleoredox-conditions have to be included for paleoenvironmental reconstructions.
The 2007 drilling season by the Tanzania drilling project (TDP) reveals a much more expanded Upper Cretaceous sequence than was recognized previously in the Lindi region of southern Tanzania. This ...TDP expedition targeted recovery of excellently preserved microfossils (foraminifera and calcareous nannofossils) for Late Cretaceous paleoclimatic, paleoceanographic and biostratigraphic studies. A total of 501.17
m of core was drilled at six Upper Cretaceous sites (TDP Sites 21, 22, 23, 24, 24B and 26) and a thin Miocene–Pleistocene section (TDP Site 25). Microfossil preservation at all these sites is good to excellent, with foraminifera often showing glassy shells and consistently good preservation of small and delicate nannofossil taxa. In addition to adding to our knowledge of the subsurface geology, new surface exposures were mapped and the geological map of the region is revised herein.
TDP Sites 24, 24B and 26 collectively span the upper Albian to lower-middle Turonian (planktonic foraminiferal
Planomalina buxtorfi–
Whiteinella archaeocretacea Zones and calcareous nannofossil zones UC0a–UC8a). The bottom of TDP Site 21 is barren, but the rest of the section represents the uppermost Cenomanian–Coniacian (
W. archaeocretacea–
Dicarinella concavata Zones and nannofossil zones UC5c–UC10). Bulk organic δ
13C data suggest recovery of part of Ocean Anoxic Event 2 (OAE2) from these four sites. In the upper part of this interval, the lower Turonian nannofossil zones UC6a–7 are characterized by a low-diversity nannoflora that may be related to OAE2 surface-water conditions. TDP Site 22 presents a 122-m-thick, lower-middle Turonian (
W. archaeocretacea–
Helvetoglobotruncana helvetica Zones) sequence that includes the nannofossil zones UC6a(-7?), but invariable isotopic curves. Further, a lower to upper Campanian (
Globotruncana ventricosa–
Radotruncana calcarata Zones and nannofossil subzones UC15b
TP–UC15d
TP) succession was drilled at TDP Site 23. Lithologies of the new sites include thin units of gray, medium to coarse sandstones, separating much thicker intervals of dark claystones with organic-rich laminated parts, irregular silty to fine sandstone partings, and rare inoceramid and ammonite debris. These lithofacies are interpreted to have been deposited in outer shelf and upper slope settings and indicate relatively stable sedimentary conditions during most of the Late Cretaceous on the Tanzanian margin.
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