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During my PhD, I was applying the clumped isotope technique to modern brachiopods and fossil belemnites, and I conducted methodological work. Carbonate clumped isotope thermometry is a tool to reconstruct carbonate precipitation temperatures. In contrast to oxygen isotope thermometry, i.e., the δ18O-thermometer, the carbonate clumped isotope thermometer does not require an estimate for the oxygen isotope composition of the seawater, as it considers the fractionation of isotopes exclusively amongst carbonate isotopologues. The ∆47 value of a carbonate expresses the abundance of the 13C–18O bond bearing carbonate isotopologue, within the carbonate, relative to its random distribution. In thermodynamic equilibrium, the ∆47 value of a given carbonate is solely a function of the carbonate precipitation temperature. However, kinetic isotope fractionations, i.e., vital effects, driven by diffusion, pH or incomplete oxygen isotope exchange between water and dissolved inorganic carbonate species can cause the carbonate to be precipitated with isotopic compositions that are offset from those predicted for thermodynamic equilibrium.
Brachiopods serve as important geochemical archives of past climate conditions. To investigate the nature and significance of kinetic controls on brachiopod shell δ18O and ∆47 values, in collaboration with the BASE-LiNE Earth ITN, I analysed the bulk and clumped isotope compositions of eighteen modern brachiopod shells, collected from different geographic locations and water depths that cover a substantial range of growth temperatures. Growth temperatures and seawater δ18O values for each brachiopod were independently determined. Most of the analysed brachiopods exhibit combined offsets from clumped and oxygen isotope equilibrium, and there is a significant negative correlation between the offset values. The observed correlation slope between offset ∆47 and offset δ18O point to the importance of kinetic effects associated with Knudsen diffusion and incomplete hydration and hydroxylation of CO2 (aq), occurring during biomineralisation. The correlations between the growth rates of the analysed brachiopods and both the offset ∆47 and the offset δ18O values provide further arguments for the presence of kinetic effects. In conclusion, the oxygen and clumped isotope composition of modern brachiopod shells are affected by growth rate-induced kinetic effects that hinder their use for palaeoceanography.
To reconstruct ocean circulation changes during specific periods of Earth history, benthic and planktic foraminifera were used as proxies in the different parts of this thesis. Both studied time periods, the Late Cretaceous and the early Pleistocene, are characterized by long-term climate cooling and major changes in ocean circulation. The first part of this thesis concentrated in the Late Cretaceous. During the Late Cretaceous long-term cooling phase, benthic foraminiferal δ18O values show a positive shift lasting about 1.5 Myr (71.5–70 Ma). This shift can be observed on a global scale and has become known as the Campanian-Maastrichtian Boundary Event (CMBE). It is proposed that this δ18O excursion is influenced either by changing intermediate- to deep-water circulation or by temporal build-up of Antarctic ice sheets. Benthic foraminiferal assemblage counts from a southern high-latitudinal site near Antarctica (ODP Site 690) are analyzed to test if the influence of the CMBE on the benthic species composition. One of the two discussed hypotheses for the causation of the δ18O transition is a change in intermediate- to deep-water circulation from low-latitude to high-latitude water masses. This change would result in cooler temperatures, higher oxygen concentration, and possibly lower organic-matter flux at the seafloor, causing a major benthic foraminiferal assemblage change. Another possible explanation of the δ18O transition of the CMBE is significant ice formation on Antarctica. However no major benthic foraminiferal assemblage change would be expected in this case. The benthic foraminiferal assemblage of Site 690 shows a separation of the studied succession into two parts with significantly different species composition. The older part (73.0–70.5 Ma) is dominated by species, which are typical for lower bottom water oxygen concentration and more common in low-latitude assemblages. Species dominating the younger part (70.0–68.0 Ma) are indicators for well-oxygenated bottom waters and more common in high-latitude assemblages. This change in the benthic foraminiferal assemblages is interpreted to represent a shift of low-latitude toward high-latitude dominated intermediateto deep-water sources. A change in oceanic circulation was therefore at least a major component of the CMBE. The Pacific Ocean contributed significantly to the climatic development during the Late Cretaceous cooling period. The contribution of ocean circulation changes in the Pacific Ocean to the Late Cretaceous climatic development in general and the CMBE and Mid-Maastrichtian Event (MME) in particular, however, is poorly understood. Previously measured high resolution planktic and benthic stable isotope data and a neodymium (Nd) isotope record from the Pacific ODP Site 1210 (Shatsky Rise, tropical Pacific Ocean) for the Campanian to Maastrichtian (69.5 to 72.5 Ma) are used to reconstruct changes in surface- and bottom water temperatures as well as changes in the source region of deep- to intermediate waters [see Appendix 4; Jung et al. 2013]. The results of the benthic foraminiferal δ18O and Nd isotope records in combination with Nd isotope records from other studies indicate changes in the intensity of intermediate- to deep ocean circulation in the tropical Pacific across the Campanian-Maastrichtian interval [see Appendix 4; Jung et al. 2013]. During the early Maastrichtian (72.5 to 69.5 Ma), a three-million-year-long period of cooler conditions and a simultaneous change towards less radiogenic Nd isotope signatures is interpreted to represent a period of increased admixture and northward flow of deep waters from the Southern Ocean (Southern Component Water, SCW). This change was probably caused by an intensified formation of deep waters in the Southern Ocean. This was reduced again during the MME (69.5 to 68.5 Ma). This early Maastrichtian cold interval is similar to the CMBEδ13C fall and succeeding δ13C rise towards the MME and is therefore also interpreted to represent tectonically forced, long-term changes in the global carbon cycle and thus a tectonic forcing of the early Maastrichtian climate cooling. Overall, the Campanian-Maastrichtian Nd and stable isotope records of Shatsky Rise indicate changes in ocean circulation that are paralleled by global warming and cooling periods. The fluctuating strength of SCW contribution in the tropical Pacific points towards an increased respectively weakened ocean circulation, which is probably related to the strength of deep-water formation in the Southern Ocean [see Appendix 4; Jung et al. 2013]. For this study, the analysis of benthic foraminiferal assemblages of Site 1210 is carried out for the same time interval (69.5 to 72.5 Ma) as Nd and stable isotopes to evaluate the influence of intermediate- to deep ocean circulation changes on the benthic foraminiferal community. The possible reaction of benthic foraminiferal assemblages is compared to the results of stable isotope and neodymium isotopes. The observed changes in species abundances only partly reflect the circulation changes reconstructed with Nd and stable oxygen istopes. For example, Stensioina spp., Aragonia spp. and Lenticulina spp., cold-water preferring species, start to be increasingly abundant at the beginning of enhanced influence of SCW. However, their abundance pattern does not follow the varying strength of the cold SCW influence at Shatsky Rise. Other species prefer lesser oxygen concentrations and warmer bottom water, e.g. Paralabamina spp. and Globorotalites spp. Paralabamina spp. has its highest relativ abundance at the beginning of the studied succession, where the influence of SCW is small. However, this taxa occurs throughout the record, even though the influence of SCW increases. Globorotalites spp. is even most abundance after the CMBE, where bottom waters are till cold and influenced by SCW. This leads to the conclusion that the varying strength of SCW in the tropical Pacific at Shatsky Rise through the studied interval is not facilitating a significant faunal turnover as has been observed at the South Atlantic Site 690 (Chapter 3). These results of the benthic foraminiferal assemblage analysis suggest a rather minor influence of the SCW on the major environmental factors that are generally influencing benthic foraminiferal communities (e.g., oxygen concentration, organic matter flux to the sea floor, bottom-water temperature). The second major part of this thesis focused on the late Pliocene-earliest Pleistocene. The late Pliocene is characterized by a long-term global cooling trend resulting in a major increase of Arctic ice sheets from around 3 Ma onwards, culminating in the Plio-Pleistocene intensification of the Northern Hemisphere glaciation. At around 2.7 Ma, large amplitude glacial-interglacial excursions (~1‰ δ18O in benthic foraminiferal calcite) in benthic oxygen isotopes can be observed. Marine isotope stage (MIS) 100 at around 2.55 Ma is the first glacial, when widespread ice rafted debris has been found in sediments in the North Atlantic Ocean. To gain a deeper understanding of the climatic evolution of the latest Pliocene-early Pleistocene, it is necessary to improve the reconstructions of North Atlantic paleohydrography, as the North Atlantic provides a key region for global climate. The consequences of the intensification of Northern Hemisphere on the early Pleistocene North Atlantic thermocline stratification and intermediate waters are still poorly understood. However, surface hydrography, the history of the thermocline and development of North Atlantic intermediate waters are well-studied for the Last Glacial Maximum (LGM). These well-known mechanisms responsible for the LGM in comparison with the present-day interglacial North Atlantic are used as an analogue for te early Pleistocene glacialinterglacials cycles. In this study, suborbitally resolved stable oxygen and carbon isotope and Mg/Ca records are measured from a deep-dwelling planktic foraminifera (Globorotaliacrassaformis) from Integrated Ocean Drilling Program Site U1313 (North Atlantic, 41°N) covering marine oxygen isotope stages MIS 103 to 95 (early Pleistocene, 2.6 to 2.4 Ma). The results are interpreted to represent a change in intermediate-water masses on glacialinterglacial timescales. During glacials geochemical records in G. crassaformis (~500–1000 m) bear the imprint of Glacial North Atlantic Intermediate Water (GNAIW), while during interglacials this species reflects the signature of the influence of Mediterranean Outflow Water (MOW) in combination with the subtropical gyre. The comparison of this data with the published records from G. ruber from the same samples facilitates the reconstruction of glacial-interglacial stratification changes of the upper water column at Site U1313. The results show that larger gradients of temperature, salinity and δ13C prevailed during glacials, suggesting a stronger stratification of the upper water column. This can be seen to indicate glacial-interglacial changes in ntermediate water masses in the North Atlantic similar to those reconstructed for the latest Pleistocene. As an additional proxy, the clumped isotope paleothermometer is applied for the Late Cretaceous study as well as for the early Pleistocene. This proxy is commonly assumed to be independent of other factors than temperature. Clumped isotopes are measured for the Late Cretaceous Site 690 on the planktic foraminiferal species Archaeoglobigerina australis and compared to already existing stable oxygen isotopes of this species. This is assumed to enable the reconstruction of paleotemperature independent of ice volume and therefore contribute to the long-lasting discussion whether there was a temporal ice build-up on Antarctic during the Campanian-Maastrichtian cooling period. For the early Pleistocene, the planktic foraminiferal species G. crassaformis is used from Site U1313 from MIS 99 (interglacial) and MIS 98 (glacial). This provides the opportunity to separate ice volume, salinity and temperature effects on the measured δ18O record of G. crassaformis. The results of the clumped isotope measurements reveal comparatively large standard errors. For the Late Cretaceous the standard error of the clumped isotope measurements proved too large to allow any conclusions on the temperature component on the δ18O record of A. australis. For the early Pleistocene, the temperature difference is also too small to be reconstructed with the standard error of the clumped isotope measurements in this study. Measuring many replicates of one sample would minimize the standard error considerably. However, the amount necessary to measure replicates cannot be gained for either time period, as almost all foraminifera were picked from the respective samples. It is concluded that the respective questions may be solved with a different method of clumped isotope analysis requiring less sample material. This method is, for example, available at the ETH Zurich.
As part of two drilling campaigns of the International Continental Scientific Drilling Program (ICDP), several geophysical borehole measurements were carried out by the Leibniz Institute for Applied Geophysics (LIAG) in two lakes. The acquired data was used to answer stratigraphic and paleoclimatic research questions, including the establishment of robust age-depth models and the construction of continuous lithological profiles.
Lake Towuti is located on Sulawesi (Indonesia), within the "Indo-Pacific Warm Pool" (IPWP), a globally important region for atmospheric heat and moisture budgets. The lake exists for approximately one million years, but its exact age is uncertain. We present the first agedepth model for the approximately 100 m continuous sediment sequence from the central part of the lake. The basis for this model is the magnetic susceptibility measured in the borehole and a tephra layer with an age of about 797 ka at 72 m depth. Our age-depth model is inferred from cyclostratigraphic analysis of borehole data and covers a period from 903 ± 11 to 131 ± 67 ka. We suggest that orbital eccentricity and/or changes between global cold and warm periods are responsible for hydroclimatic changes in the IPWP, that these changes affect sedimentation processes in Lake Towuti, and that we can measure and observe this effect in the sediment properties today. Additionally, we created a continuous artificial lithological profile from a series of different borehole data using cluster analysis. This provides information from parts of the borehole where no sediment is available due to core loss.
Lake Ohrid is 1.36 million years old and is located on the Balkan Peninsula on the border between Albania and North Macedonia. The primary hole 'DEEP' in the central part of the lake has been the subject of several investigations, but information about sediments of the marginal locations 'Pestani' and 'Cerava' have not been published yet. In our study, we use natural gamma radiation (GR) measured in the borehole to generate an age-depth model for DEEP. This is performed using the correlation of GR to the global LR04 reference record of Lisiecki and Raymo (2005).
The age information is then transferred via prominent seismic marker horizons to the other two sites, Pestani and Cerava, where it provides the first age-control points for the construction of age-depth models from correlation of GR to LR04. The generated age-depth models are tested using cyclostratigraphic methods, but the limits of this approach are revealed. At DEEP, sedimentation rates (SR) from the cyclostratigraphic method and the correlative approach differ by 2.8 %, at Pestani this difference is 16.7 %, and at Cerava the quality of the data does not allow a reliable evaluation of SR using the cyclostratigraphic approach. We used cluster analysis to construct artificial lithological profiles at all three sites and integrated them into the respective age-depth models. This enables us to determine which sediment types were deposited at what time, and we recognize the change between warm and cold periods in the sediment properties at all three locations. The analyses in this study were all performed on borehole and seismic data and thus do not involve sediment core data. Especially at Pestani and Cerava, new insights into the sedimentological history of Lake Ohrid could be obtained.
In the last part we discuss the occurrence of the half-precession (HP) signal in the European region during the last one million years. The focus is on Lake Ohrid, but a range of other proxies, from the eastern Mediterranean, across the European continent, up to Greenland are analyzed in regards to HP. Applying filters, we focus on the frequency range with a period of 13-8.5 ka and only HP remains in the records. We use correlative methods to determine the clarity of the HP signal in proxies distributed across the European realm. Additionally, we determined the development of HP over time. The HP signal is clearest in the southeast and decreases toward the north. It is further more pronounced in interglacial periods and in the younger part (<621 ka) of most proxies. We suggest that there are mechanisms that transmit the HP signal from its origin near the equator to higher latitudes via different processes. In this context, for instance, the African monsoon, the Nile River and the Mediterranean outflow via the Strait of Gibraltar can be important factors.
Enhanced aridification of Central Asia driven by the combined effects of orogenic surface uplift, Paratethys retreat, changes in atmospheric moisture transport and global cooling is one of the most prominent Cenozoic climate change events of the Northern Hemisphere. Deciphering regional long-term patterns of Central Asian hydrology is, therefore, a key element in understanding the role of Northern Hemisphere mid-latitude drying in the global hydrological system. Pedogenic carbonates record information of the paleoecosystem, the paleogeography, hydrology, tectonic and climatic conditions as well as the sedimentary regime during the time in which they formed. The calcrete-bearing paleosols in continental sedimentary basins yield the possibility for understanding these processes, mechanisms and controlling factors. This study characterizes long-term paleoenvironmental conditions between the late Oligocene and early Miocene in SE Kazakhstan based on stable isotopes, elemental geochemistry and laser ablation U-Pb geochronology from alluvial, fluvial and pedogenic deposits. The main topics addressed in this thesis are paleosol and calcrete formation processes in the light of geochemistry, tectonic and climatic influences on both, as well as the paleoenvironmental and hydrological conditions which led to these processes.
The sedimentological succession of the 14 km-long Kendyrlisai Valley in the Ili Basin, SE Kazakhstan in Central Asia, yields exceptional well-developed paleosols which provide an insight into the relationship between tectonics and sedimentation as well as soil formation processes. The valley accommodates more than 600 m of siliciclastic sediments deposited in a fluvial to alluvial environment in the lower part which grade into lacustrine to fluvial deposition with minor gypsum accumulation in the upper part. The yet undated sediments of Kendyrlisai Valley are compared with a biostratigraphically dated and well described succession in an adjacent location. The correlation of the two successions revealed a proximal-distal relation with the Kendyrlisai Valley succession represents the basin margin position with coarse alluvial-fluvial sediments. The calcrete nodules in Kendyrlisai Valley paleosols give the opportunity of U-Pb dating with LA-ICP-MS which uses the variation in both U and Pb to directly date the calcite. The U-Pb dating revealed a late Oligocene-early Miocene age for the investigated section. The analysis of facies and geochemistry of the paleosol profiles in Kendyrlisai Valley gives insight into calcretization stages, pedogenic processes and landscape stability. Kendyrlisai Valley paleosols show a low to moderate weathering intensity with the highest weathering intensity between 0.5 and 0.8 m depth in the paleosol profile. The comparison between acid leachable and non-acid leachable fraction indicate an incorporation of Ca and Ba in incipient calcrete calcite, whereas clay minerals adsorb Mg and Sr. During the evolution from early to more mature calcrete stages, i.e. calcrete nodules, Ba is lost by dissolution and subsequently adsorbed on clay minerals. The nodules consist almost exclusively of pure calcium carbonate with rare substitution of Ca by Mg indicating a constant supply of Ca by weathering and solution during calcrete formation. The occurrence of Mg-bearing clay minerals indicates high evaporative conditions with alkaline waters (pH >9).
Sampled calcrete nodule cross sections reveal more than one weathering and calcrete formation phase with a higher supply of Ca, Mg and Fe during early phases. The organic and inorganic carbon isotope composition of the calcrete nodules reflects C3 metabolism under occasionally moisture stress, resulting in higher δ13C values and lower respiration rates. This study also presents calculated atmospheric pCO2 values from the calcrete nodules with the equation from Cerling et al. (1999). The average calculated CO2 concentration for Kendyrlisai Valley paleosols is 313 ± 110 ppmv. The comparison with data from other studies during the late Oligocene–early Miocene reveal lower values for Kendyrlisai Valley paleosols, which may stem from an underestimation of the plant-respired CO2.
The knowledge of the variability within the paleosols and calcrete nodules enables a reliable paleoclimatic interpretation for the Kendyrlisai Valley and beyond the Ili Basin. Sedimentary facies and geochemical weathering indices suggest an increased surface and groundwater discharge fed by orographically-enhanced precipitation in the Tien Shan hinterland. In contrast, pedogenic stable isotope data and elevated rates of Mg fixation in clay minerals mirror enhanced rates of evaporation in the vadose zone due to protracted aridification. This study posits that pronounced surface uplift of the Tien Shan Mountains during the Oligocene–Miocene transition promoted regionally increased orographic precipitation and the development of fluvial discharge systems.
The comparison with other studies in adjacent basins creates a precipitation pattern for Central Asia during the late Oligocene to early Miocene. The westerlies supplied Central Asia with atmospheric moisture from the West, possibly from the Eastern Paratethys. The uplifting Tien Shan Mountain ranges captured this moisture on their luv-side, resulting in a pronounced orographic rainfall in the adjacent Ili and Issyk Kul Basins. The Tarim Basin and the Valley of Lakes experienced drier conditions due to the rain shadow effect on the lee-side of the Tien Shan and Altai Mountains. In course of this findings, the thesis highlights the crucial role the Tien Shan Mountains play and had been playing in former times as an orographic barrier for the distribution of atmospheric moisture across Central Asia.
Geochemical investigations on biogenic carbonates are commonly conducted to reconstruct the environmental conditions of the past. However, different carbonate producers incorporate elements to varying degrees, due to biological vital effects. Detecting and quantifying these effects is crucial to produce reliable reconstructions. These paleoreconstructions are of great importance to evaluate the consequences of our recent climate change and identify control mechanisms on the distribution of endangered species such as Desmophyllum pertusum. In chapter three we tested Mg/Ca, Sr/Ca and Na/Ca ratios on this species, among other coldwater scleractinians, to test if they provide reliable proxy information. The results reveal no apparent control of Mg/Ca or Sr/Ca ratios through seawater temperature, salinity or pH. Na/Ca ratios appear to be partly controlled by the seawater temperature, which is also true for other aragonitic organisms such as warm-water corals and the bivalve Mytilus edulis. However, a large variability complicates possible reconstructions by means of Na/Ca. In addition, we explore different models to explain the apparent temperature effect on Na/Ca ratios based on temperature sensitive Na and Ca pumping enzymes.
The bivalve Acesta excavata is commonly found in cold-water coral reefs among the North Atlantic, together with D. pertusum. Multiple linear regression analysis, presented in chapter four, indicates that up to 79% of the elemental variability in Mg/Ca, Sr/Ca and Na/Ca is explainable with temperature and salinity as independent predictor variables. Vital effects, for instance growth rate effects, are evident and make paleoreconstructions not feasible. Furthermore, organic material embedded in the shell, as well as possible stress effects can drastically change the elemental composition. Removal of these organic matrices from bulk samples for LA-ICP-MS (laser ablation inductively coupled mass spectrometer) measurements by means of oxidative cleaning is not possible, but Na/Ca ratios decrease after this cleaning. This is presumably an effect of leaching and not caused by the removal of organic matrices.
Interesting biogeochemical relations were found in the parasitic foraminifera H. sarcophaga. We report Mg/Ca, Sr/Ca, Na/Ca and Mn/Ca ratios measured in H. sarcophaga from two different host species (A. excavata and D. pertusum) in chapter five. Sr/Ca ratios are significantly higher in foraminifera that lived on D. pertusum. This could indicate that dissolved host material is utilized in shell calcification of H. sarcophaga, given the naturally higher strontium concentration in the aragonite of D. pertusum. Mn/Ca ratios are highest in foraminifera that lived on A. excavata but did not fully penetrate the host’s shell. Most likely, this represents a juvenile stadium of the foraminifera during which it feeds on the organic
periostracum of the bivalve, which is enriched in Mn and Fe. The isotopic compositions are similarly affected, both δ18O and δ13C values are significantly lower in foraminifera that lived 23on D. pertusum compared to specimen that lived on A. excavata. Again, this might represent the uptake of dissolved host material or different pH regimes in the calcifying fluid of the hosts (bivalve < 8, coral > 8) that control the extent of hydration/hydroxylation reactions. Temperature reconstructions are possible using stable oxygen isotopes on this foraminifera species; however, the results are only reliable if the foraminifera lived on A. excavata. Samples of H. sarcophaga from D. pertusum would lead to overestimations of the seawater temperature due to the lower δ18O values.
Apart from biological vital effects, storage and preservation methods can significantly change the geochemical composition of different marine biogenic carbonates. In chapter six this is presented on the example of ethanol preservation, a common technique to allow extended storage of biogenic samples. The investigation reveals a significant decrease of Mg/Ca and Na/Ca ratios even after only 45 days storage in ultrapure ethanol. Sr/Ca ratios on the other hand are not influenced.
Besides temperature, salinity and pH further environmental parameters are important such as nutrient availability, especially for the distribution of cold-water corals. In chapter seven we extend the investigations on A. excavata by including the elemental ratios Ba/Ca, Mn/Ca and P/Ca. We expected P/Ca to be helpful in the otherwise difficult process of dentifying growth increments. Based on our observations we had to refute this theory. P/Ca ratios are not systematically enriched in the vicinity of growth lines. Instead, we found a regular sequence of peaks of Ba/Ca, P/Ca and Mn/Ca. This sequence as well as the peaks in general are potentially caused by equential blooms of different algae, diatoms and other planktonic organisms ...
The Late Cretaceous is known to be mostly affected by warm periods interrupted temporarily by a number of cooling events. The reconstruction of the paleoclimatic conditions during a period of high concentration of CO2 in the atmosphere is of great importance for the creation of future climate models. We applied the recently developed method reconstructing the SST from the TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms).
The sample material used for the present study was obtained from the tropical Late Cretaceous southern Tethys upwelling system (Negev/Israel), lasting from the Late Santonian to the Early Maastrichtian (~ 85 to 68 Ma). On the core samples from the Shefela basin, representing the outer belt of the upwelling system and the outcrop profile from the open mine Mishor Rotem (Efe Syncline), representing the inner belt, various bulk geochemical and biomarker studies were performed in this thesis.
Derived from TEX86 data, a significant long-term SST cooling trend from 36.0 to 29.3 °C is recognized during the Late Santonian and the Early Campanian in the southern Tethys margin. This is consistent with the opening and deepening of the Equatorial Atlantic Gateway (EAG) and the intrusion of cooler deep water from the southern Atlantic Ocean influencing the global SSTs and also the Tethys Ocean. Furthermore, the cooler near shore SST usually found in modern upwelling systems could be verified in case of the ancient upwelling system investigated in the present study. The calculated mean SST in the inner belt (27.7 °C) represented in the Efe Syncline was 1.5 °C cooler in comparison to the more seaward located outer belt (Shefela basin).
Moreover, geochemical and biomarker analyses were used to identify both the accumulation of high amounts of phosphate in the PM and good preservation of organic matter (OM) in the lower part of the OSM section. Total organic carbon (TOC) contents are highly variable over the whole profile reaching from 0.6 % in the MM, to 24.5 % in the OSM. Total iron (TFe) varies from 0.1 % in the PM to 3.3 % in the OSM and total sulfur (TS) varies between 0.1 % in the MM and 3.4 % in the OSM. Different correlations of TS, TOC and TFe were used to identify the conditions during the deposition of the different facies types. Natural sulfurization was found to play a key role in the preservation of the OM particularly in the lower part of the OSM. Samples from the OSM and the PM were deposited under dysoxic to anoxic conditions and iron limitation lasted during the deposition of the OSM and the PM, which effected the incorporation of sulfur into OM.
Phosphorus is highly accumulated in the sediments of the PM with a mean proportion of 11.5 % total phosphorus (TP), which is drastically reduced to a mean value of 0.9 % in the OSM and the MM. From the correlation of the bulk geochemical parameters TOC/TOCOR ratio and TP a major contribution of sulfate reducing bacteria to the phosphate deposition is concluded. This interrelation has previously been investigated in recent coastal upwelling systems off Peru, Chile, California and Namibia. This was further supported by the analysis of branched and monounsaturated fatty acids indicating the occurrence of sulfate reducing and sulfide oxidizing bacteria during the deposition.
According to the results from the analysis of n-alkanes and C27- to C29-steranes up to 95 % of the OM was of marine origin.
Organic sulfur compounds (OSC) were a major compound class in the aromatic hydrocarbon fraction and n-Alkyl and isoprenoid thiophenes were the most abundant, with highest amounts found for 2-methyl-5-tridecyl-thiophene (28 µg/g TOC). The relatively high abundance of ββ-C35 hopanoid thiophenes and epithiosteranes is equivalent to an incorporation of sulfur during the early stages of diagenesis.
Moreover, the geochemical parameters δ13Corg, δ15Norg, C/N and the pristane/phytane (Pr/Ph) ratio, were studied for reconstruction of seafloor and water column depositional environments. The high C/N ratio along with relatively low values of δ15Norg (4 ‰ to 6 ‰) and δ13Corg (-29 ‰ to -28 ‰) are consistent with a significant preferential loss of nitrogen-rich organic compounds during diagenesis. Oxygen-depleted conditions lasted during the deposition of the PM and the bottom of the OSM, reflected by the low Pr/Ph ratio of 0.11–0.7. In the upper part of the OSM and the MM the conditions changed from anoxic to dysoxic or oxic conditions. This environmental trend is consistent with co-occurring foraminiferal assemblages in the studied succession and implies that the benthic species in the Negev sequence were adapted to persistent minimum oxygen conditions by performing complete denitrification as recently found in many modern benthic foraminifera.
Furthermore, the anammox process could have influenced the nitrogen composition of the sediments. In this anaerobically process nitrite and ammonia are converted to molecular nitrogen.
Terrestrial climate and ecosystem evolution during ‘Greenhouse Earth’ phases of the early Paleogene remain incompletely known. Particularly, paleobotanical records from high southern latitudes are giving only limited insights into the Paleocene and early Eocene vegetation of the region. Hence, data from continuous well-calibrated sequences are required to make progress with the reconstruction of terrestrial climate and ecosystem dynamics from the southern latitudes during the early Paleogene.
In order to elucidate the terrestrial conditions from the high southern latitudes during the early Paleogene, terrestrial palynology was applied in the present study to two well-dated deep-marine sediment cores located at the Australo-Antarctic region: (i) IODP Site U1356 (Wilkes Land margin, East Antarctica) and (ii) ODP Site 1172 (East Tasman Plateau, southwest Pacific Ocean). The studied sequence from IODP Site U1356 comprises mid-shelfal sediments from the early to middle Eocene (53.9 – 46 million years ago [Ma]). For the ODP Site 1172, the studied succession is characterized by sediments deposited in shallow marine environments of the middle Paleocene to the early Eocene (60.7 – 54.2 Ma).
Based on the obtained pollen and spores (sporomorphs) results from the studied sequences of Site U1356 and Site 1172, this study aims to: (1) decipher the terrestrial climate conditions along the Australo-Antarctic region from the middle Paleocene to the middle Eocene; (2) evaluate the structure, diversity and compositional patterns of forests that throve in the Australo-Antarctic region during the early Paleogene; (3) understand the response of forests from the high southern latitudes to the climate dynamics from the early Paleogene; (4) establish a connection between the generated terrestrial palynomorph data and published Sea Surface Temperatures (SSTs) from the same cores.
To decipher the terrestrial climatic conditions on the Australo-Antarctic region, this study relies on the nearest living relative (NLR) concept that assumes that fossil taxa have similar climate requirements as their modern counterparts. This approach was applied to the sporomorph results of Site U1356 and Site 1172, following mainly the bioclimatic analysis. With regard to the structure and diversity patterns of the vegetation from the same region, the present study presents combined qualitative (i.e., reconstruction of the vegetation based mainly on the habitats of the known living relatives) and quantitative (i.e., application of ordination techniques, rarefaction and diversity indices) analyses of the fossil sporomorphs results.
The overall results from the paleoclimatic and vegetation reconstruction approaches applied in the present study, indicate that temperate and paratropical forests during the early Paleogene throve under different climatic conditions on the Wilkes Land margin and on Tasmania, at paleolatitudes of ∼70°S and ∼65°S, respectively.
Specifically, the sporomorph results from Site U1356, suggest that a highly diverse forest similar to present-day forests from New Caledonia was thriving on Antarctica during the early Eocene (53.9 – 51.9 Ma). These forests were characterized by the presence of termophilous taxa that are restricted today to tropical and subtropical settings, notably Bombacoideae, Strasburgeria, Beauprea, Spathiphyllum, Anacolosa and Lygodium. In combination with MBT/CBT paleotemperature results, they provide strong evidence for near-tropical warmth at least in the coastal lowlands along the Wilkes Land margin. The coeval presence of frost tolerant taxa such as Nothofagus, Araucariaceae and Podocarpaceae during the early Eocene on the same record suggests that paratropical forests were thriving along the Wilkes Land margin. Due to the presence of this kind of vegetation, it is possible to suggest that forests in this region were subject to a climatic gradient related to differences in elevation and/or the proximity to the coastline.
By the middle Eocene, the paratropical forests that characterized the vegetation of the early Eocene on the Wilkes Land margin were replaced by low diversity temperate forests dominated by Nothofagus, and similar to present-day cool-temperate forests from New Zealand. The dominance of these forests and the absence of thermophilous elements together with the lower temperatures suggested by the MBT/CBT and the sporomorph-based temperatures indicate consistently cooler conditions during this time interval.
With regard to the sporomorph results of Site 1172, this study suggests that three vegetation types were thriving on Tasmania from the middle Paleocene to the early Eocene under different climatic conditions. During the middle to late Paleocene, warm-temperate forests dominated by Podocarpaceae and Araucariaceae were the prevailing vegetation on Tasmania. The dominance of these forests was interrupted by the transient predominance of cool-temperate forests dominated by Nothofagus and Araucariaceae across the middle/late Paleocene transition interval (~59.5 to ~59.0 Ma). This cool-temperate forest was characterized by a lack of frost-sensitive elements (i.e., palms and cycads) indicating cooler conditions with harsher winters on Tasmania during this time interval. By the early Eocene, and linked with the Paleocene Eocene Thermal Maximum (PETM), Paleocene temperate forests dominated by gymnosperms were replaced by paratropical rainforests with the remarkable presence of the tropical mangrove palm Nypa during the PETM and the earliest Eocene. The overall results from Site U1356 and Site 1172, provide a new assessment of the terrestrial climatic conditions in the Australo-Antarctic region for validating climate models and understanding the response of high-latitude terrestrial ecosystems to the climate dynamics of the early Paleogene on southern latitudes.
The climatic conditions in the higher latitudes during the early Paleogene were further unravelled by comparing the obtained terrestrial and marine results. The integration of the obtained sporomorph data with previously published TEX86-based SSTs from Site 1172 documents that the vegetation dynamics were closely linked with the temperature evolution from the Australo-Antarctic region. Moreover, the comparison of TEX86-based SSTs and sporomorph-based climatic estimations from Site 1172 suggests a warm-season bias of both calibrations of TEX86 (i.e., TEX86Hand TEX86H), when this proxy is applied to high southern latitudes records of the early Paleogene.