Precessional drivers of late Miocene Mediterranean sedimentary sequences: African summer monsoon and Atlantic winter storm tracks

Cyclic sedimentary patterns in the marine record of the Mediterranean Sea have been consistently correlated with orbitally‐driven shifts in climate. Freshwater input driven by the African summer monsoon is thought to be the main control of such hydrological changes, where the runoff signal is transferred from the eastern to the western Mediterranean. The geological record from the Atlantic margin also contains precession‐driven dilution cycles that have been correlated with the sedimentary sequences in the western and eastern Mediterranean despite the lack of a direct connection with the basin. In these regions, Atlantic winter storms have also been invoked to explain the wet phases. In the absence of seasonally‐resolved proxy data, climate simulations at high temporal resolution can be used to investigate the drivers of Mediterranean hydrologic changes both on precessional and seasonal timescales. Here, we use the results of 22 ocean‐atmosphere‐vegetation simulations through an entire late Miocene precession cycle. These show that the African summer monsoon drives the hydrologic budget in the Eastern Mediterranean during precession minima, while the western marginal basins are generally dominated by local net evaporative loss. During precession minima, the western Mediterranean and the Atlantic margin are also influenced by enhanced winter precipitation from the Atlantic storm tracks. We can, therefore, identify two different moisture sources affecting the circum‐Mediterranean area, characterized by the same phasing with respect to precession, but with opposite seasonality. This supports the interregional correlation of geological sections in these areas, as we show for the Messinian and speculate for other time periods

What, if anything, is Quaternary?

The formal recognition of Quaternary as a Period/ System was approved by IUGS in June 2009, in accordance with a proposal originated by INQUA. There are reasons to believe that this will have destabilizing consequences for the geological time scale. Until now, the primary divisions of the stratigraphic record, at the Period level and above, have been based on the progressive change of Earth’s biota. The Quaternary, on the other hand, is a paleoclimatic concept based on glacial-interglacial variability, expressed in lithological change. The IUGS vote holds that this paradigm now supersedes the biochronological identity of the Neogene Period/System. Furthermore, to accommodate the most recent INQUA opinion about “when the Ice Ages began”, the ICS agreed to relocate the base of the Pleistocene to 2.59 Ma from 1.81 Ma, enlarging the epoch by 43% and again without regard for its original paleontological definition, or for the vast literature in other fields of Pleistocene research. If history is a guide, the resulting disruption in late Cenozoic marine and vertebrate paleontology, human evolution, paleoceanography and paleoclimatology will be widely resisted, with potential impact on the authority of IUGS. The consequence of abandoning basic principles in order to satisfy the interest of a special group deserves a wider consideration than it has so far received

Ипотека морского судна в контексте восстановление отечественного торгового флота в Украине

Торговельне мореплавство – одна з тих галузей світової економіки, яка має найбільш швидкий розвиток у наш час. Перш за все, це пов’язано із прискоренням міжнародного товарообміну. Наростання обсягів міжнародної торгівлі, у якій прагне приймати участь також Україна, обумовлює необхідність адекватно швидкого зростання її транспортної галузі. Попри значний транспортний потенціал, що має Україна, багато в чому завдячуючи її географічному положенню, стан вітчизняного транспортного комплексу й, особливо, його морської ланки, потребує покращення. Це, в свою чергу, безпосередньо залежить від правового регулювання, що впорядковує такі процеси

The Gibraltar Corridor:Watergate of the Messinian Salinity Crisis

The existence and evolution of a Messinian salt giant in the Mediterranean Sea has caused much debate in the marine science community. Especially the suggestion that the Mediterranean was a deep desiccated basin during the Messinian Salinity Crisis (MSC, 5.97–5.33 Ma), triggered by a temporal disconnection from the global ocean, made it a well-known crisis beyond the scientific boundaries. Approximately ~50 years after this provocative statement, it remained unknown which Mediterranean–Atlantic seaway delivered the 5–6% of the global ocean's salt into the Mediterranean basin. Here, we review the changes in Mediterranean-Atlantic connectivity throughout the late Miocene in order to locate, date and quantify the missing Messinian gateway that provided the salt water inflow during the MSC. We conclude that all the known pre-MSC gateways through southern Spain and northern Morocco were closed, leaving the “Gibraltar Corridor” at its Messinian configuration as the sole candidate. We consider the possibility of longer and narrower straits existing at depth below the present Gibraltar region, and using strait dynamic theory we calculate its dimensions during the Messinian based on the salinity changes in the Mediterranean. A marine Messinian gateway through the Gibraltar Corridor is in agreement with growing evidence that Atlantic waters reached the Mediterranean Sea during all three stages of the MSC

Astronomically tuned age model for the early Eocene carbon isotope events:A new high-resolution benthic δ13C benthic record of ODP Site 1263 between ~49 and ~54 Ma

The early Eocene represents a time of major changes in the global carbon cycle and fluctuations in global temperatures on both short-and long-time scales. These perturbations of the ocean-atmosphere system have been linked to orbital forcing and changes in net organic carbon burial, but accurate age models are required to disentangle the various forcing mechanisms and assess causal relationships. Discrepancies between the employed astrochronological and radioisotopic dating techniques prevent the construction of a robust time frame between ~ 49 and ~ 54 Ma. Here we present an astronomically tuned age model for this critical time period based on a new high-resolution benthic δ13C record of ODP Site 1263, SE Atlantic. First, we assess three possible tuning options to the stable long-eccentricity cycle (405-kyr), starting from Eocene Thermal Maximum 2 (ETM2, ~ 54 Ma). Next we compare our record to the existing bulk carbonate δ13C record from the equatorial Atlantic (Demerara Rise, ODP Site 1258) to evaluate our three initial age models and compare them with alternative age models previously established for this site. Finally, we refine our preferred age model by expanding our tuning to the 100-kyr eccentricity cycle of the La2010d solution. This solution appears to accurately reflect the long-and short-term eccentricity-related patterns in our benthic δ13C record of ODP Site 1263 back to at least 52 Ma and possibly to 54 Ma. Our time scale not only aims to provide a new detailed age model for this period, but it may also serve to enhance our understanding of the response of the climate system to orbital forcing during this super greenhouse period as well as trends in its background state

Quantifying the Mediterranean freshwater budget throughout the late Miocene : New implications for sapropel formation and the Messinian Salinity Crisis

The cyclic sedimentary record of the late Miocene Mediterranean shows a clear transition from open marine to restricted conditions and finally to evaporitic environments associated with the Messinian Salinity Crisis. This evolution has been attributed to changes in Mediterranean–Atlantic connectivity and regional climate, which has a strong precessional pulse. 31 Coupled climate simulations with different orbital configurations have been combined in a regression model that estimates the evolution of the freshwater budget of the Mediterranean throughout the late Miocene. The study suggests that wetter conditions occur at precession minima and are enhanced at eccentricity maxima. We use the wetter peaks to predict synthetic sapropel records. Using these to retune two Mediterranean sediment successions indicates that the overall net freshwater budget is the most likely mechanism driving sapropel formation in the late Miocene. Our sapropel timing is offset from precession minima and boreal summer insolation maxima during low eccentricity if the present-day drainage configuration across North Africa is used. This phase offset is removed if at least 50% more water drained into the Mediterranean during the late Miocene, capturing additional North African monsoon precipitation, for example via the Chad-Eosahabi catchment in Libya. In contrast with the clear expression of precession and eccentricity in the model results, obliquity, which is visible in the sapropel record during minimum eccentricity, does not have a strong signal in our model. By exploring the freshwater evolution curve in a box model that also includes Mediterranean–Atlantic exchange, we are able, for the first time, to estimate the Mediterranean's salinity evolution, which is quantitatively consistent with precessional control. Additionally, we separate and quantify the distinct contributions regional climate and tectonic restriction make to the lithological changes associated with the Messinian Salinity Crisis. The novel methodology and results of this study have numerous potential applications to other regions and geological scenarios, as well as to astronomical tuning

Quantifying the Mediterranean freshwater budget throughout the late Miocene: New implications for sapropel formation and the Messinian Salinity Crisis

The cyclic sedimentary record of the late Miocene Mediterranean shows a clear transition from open marine to restricted conditions and finally to evaporitic environments associated with the Messinian Salinity Crisis. This evolution has been attributed to changes in Mediterranean–Atlantic connectivity and regional climate, which has a strong precessional pulse. 31 Coupled climate simulations with different orbital configurations have been combined in a regression model that estimates the evolution of the freshwater budget of the Mediterranean throughout the late Miocene. The study suggests that wetter conditions occur at precession minima and are enhanced at eccentricity maxima. We use the wetter peaks to predict synthetic sapropel records. Using these to retune two Mediterranean sediment successions indicates that the overall net freshwater budget is the most likely mechanism driving sapropel formation in the late Miocene. Our sapropel timing is offset from precession minima and boreal summer insolation maxima during low eccentricity if the present-day drainage configuration across North Africa is used. This phase offset is removed if at least 50% more water drained into the Mediterranean during the late Miocene, capturing additional North African monsoon precipitation, for example via the Chad-Eosahabi catchment in Libya. In contrast with the clear expression of precession and eccentricity in the model results, obliquity, which is visible in the sapropel record during minimum eccentricity, does not have a strong signal in our model. By exploring the freshwater evolution curve in a box model that also includes Mediterranean–Atlantic exchange, we are able, for the first time, to estimate the Mediterranean's salinity evolution, which is quantitatively consistent with precessional control. Additionally, we separate and quantify the distinct contributions regional climate and tectonic restriction make to the lithological changes associated with the Messinian Salinity Crisis. The novel methodology and results of this study have numerous potential applications to other regions and geological scenarios, as well as to astronomical tuning

Precession phasing offset between Indian summer monsoon and Arabian Sea productivity linked to changes in Atlantic overturning circulation

Results from transient climate modeling experiments indicate an in-phase relationship between insolation forcing and Indian summer monsoonal precipitation. This is in contrast to high-resolution radioisotopically dated speleothem oxygen isotope (delta O-18) records of China, which showed that East Asian Monsoon maxima lag Northern Hemisphere peak summer insolation by similar to 2,700 years, while an approximately 8,000-year time lag was derived from late Pleistocene records of Arabian Sea sediments. Here, we evaluate the precession phase of the Arabian Sea signal by comparing a new high-resolution productivity and oxygen minimum zone (OMZ) intensity record from the Arabian Sea over the past 450,000 years with the results of a transient climate modeling experiment that includes glacial-bound ice volume variations. The well established tuning technique between radioisotopically dated North Atlantic cold events and the occurrence of deep-dwelling planktonic foraminifera in the Arabian Sea for the last glacial cycle was used to extend the Arabian Sea chronology, independent of orbital tuning. Cross-spectral analysis over the last 224,000 years reveals that Arabian Sea productivity maxima lag precession minima by similar to 6,900 +/- 200 years, i.e., in close agreement with previous reconstructions. Also our climate modeling simulations are in accord with previous studies indicating an in-phase relationship between precession minima and maximum summer monsoon intensity. We argue that the summer monsoon is most likely not the main driver of changes in Arabian Sea biological productivity and OMZ intensity at the precession frequency band, but that changes in the intensity of the Atlantic meridional overturning circulation (AMOC) have played the prominent role in controlling the nutrient delivery into the euphotic layer of the northern Indian Ocean, and hence the amount of primary productivity and intensity of the oxygen minimum zone in the Arabian Sea. Such a mechanism explains the large precession-related time lag between minimum precession and maximum productivity and OMZ conditions in the Arabian Sea, since intensified AMOC occurred during precession maxima