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Abstract The Cretaceous is often thought of as a warm version of the modern Earth. There was no ice on the poles and, except for the Sevier Highlands of western North America, no high mountains to divert the zonal flow of the winds. As a result the overall climate was more equable. Forced by steady equatorial trade winds, mid-latitude westerlies, and high-latitude easterly winds, the circulation in the Panthalassic Ocean would have been similar to the that of the modern Pacific, A low-latitude circumglobalseaway, the Tethys, separated the northern Laurasian continents from the Gondwanan continents of the south. Past studies of the Cretaceous Ocean have assumed a direct analogy with the modern Earth and its climatology. Only the widespread deposition of organic-carbon-rich black shales in the deep sea has caused paleoceanographers to suspect that something was very different. Here, I propose that the Cretaceous was very different from the modern world. The ice–free condition caused seasonal variations of atmospheric pressure in the polar regions and destabilized the windsat mid– and high latitudes. Without steady westerly winds the subtropical and polar frontal systems in the ocean and the sharp stratification of the low–latitude ocean disappeared. There were no barriers to meridional ocean heat transport. Not only was there flooding of the continental blocks, but there was a doubling of the area of deep marginal seas and a quadrupling of the area of shallow seas. In particular, the area of shallow shelf seas of the arid zone along the northern Tethyan margin was an order of magnitude larger than those in similar latitudes today. Evaporation would have provided many sources of saline waters of different density to the Tethys and Atlantic regions. The overall aspect of the Tethyan circumglobal seaway was similar to the modern North Atlantic, with many competing sources of interior waters.
Postglacial coastal evolution: Ice–ocean–solid Earth interactions in a period of rapid climate change
The most recent glacial-interglacial transition of the late Pleistocene ice age was accompanied by an increase in globally averaged ice-equivalent eustatic sea level of ∼120 m. This increase in sea level occurred over a period of ∼10,000 yr and was accompanied by highly significant regional inundations of the land by the sea as well as by significant regional emergence of the land from the sea in the initially ice-covered regions. These migrations of the coastline can be accurately predicted given only an assumed known history of the deglaciation of the continents. An especially interesting aspect of the suite of physical interactions involved in the global process of glacial isostatic adjustment concerns the influence of variations in the Earth's rotation on the local histories of relative sea level, which may be inferred on the basis of radiocarbon dating of suitable sea-level index points. The observed variability in sea level may be interpreted in terms of fundamentally important climatological and solid Earth geophysical properties of Earth System processes that govern system evolution.
Simulation of the Eemian interglacial and possible mechanisms for the glacial inception
A coupled ocean-atmosphere general circulation model was used to perform multi-centennial climate simulations of the Eemian interglacial and the subsequent glacial inception. The simulations were performed as equilibrium experiments with orbital parameters and greenhouse gas concentrations set to values of 125,000 and 115,000 yr before present (B.P.). These dates represent periods with enhanced and weakened seasonal cycles of insolation in the Northern Hemisphere. A consistent reaction of seasonal temperatures is simulated for most continental regions. Comparisons with pollen-based reconstructions of European temperatures show that the model simulates realistic spatial temperature patterns for the warm phase of the Eemian. In the case of the simulation for 115,000 yr B.P., the model reacts with a long-term cooling trend. This trend is associated with a continuous increase in Northern Hemisphere sea-ice volume and an expansion of the permanently snow-covered areas over North America. Although summer precipitation is reduced in this region, the changes in seasonality of temperature lead to significant higher amounts of summer snowfall. The strengthened North Atlantic circulation does not compensate the cooling of the Northern Hemisphere. The snow accumulation starts in northeastern Canada where southward winds transport cold Arctic air into the continent. The accumulated snow volume on the North American continent is equivalent to a reduction of sea level at a rate of ∼10 cm per century at the end of the simulation.
Predicting seabed change as a function of climate change over the next 50 yr in the Australian southeast
The Australian seabed is influenced by extreme weather conditions of various types, including cyclones, high tidal ranges, offshore currents, and storm waves. Over the past two centuries, substantial progress in our understanding of the seabed and environmental conditions has been made by studies of seabed sedimentology, hydrodynamics, and habitat mapping. As part of the Commonwealth Scientific and Industrial Research Organisation (CSIRO) “Wealth from Oceans” flagship program, we have been involved in a five year study to investigate and predict the effect of possible climate change scenarios on the seabed over the next 50 yr. As an initial phase of this project we have taken the southeast region of the Australian seabed as our study area. The seabed responses to current climate and possible future climatic conditions over the next 50 yr have been simulated for the first time by a state-of-the-art numerical model, Sedsim. We found: (1) that the contribution of river-carried sediment (redistributed by marine processes) to the region's seabed, even with the wettest predicted climate change, is limited. In general, the fluvial sediment in the southeast region cannot keep pace with the action of strong marine forces, such as waves and currents. Therefore, most of the seabed suffers from erosion due to lack of sediment to distribute. This situation would get worse if the local climate swings toward the high-energy side. (2) The generally high wave energy, significant tidal currents, and frequent surges of wind-driven currents make the local seabed highly mobile and sensitive to hydrodynamic change. (3) The change of turbidite activity among different climate scenarios is insignificant with regard to the number of submarine slope failures, the areas affected, and the seabed median grain size.
In sand-shale sequences, subsidence due to compaction may be as important as eustatic and tectonic effects in controlling relative sea-level variations that determine sediment accommodation space and extent of marine transgressions. Furthermore, stratigraphic configuration in coastal settings is more sensitive to relative sea-level changes than either continental or deeper marine environments. Thus, the contribution to local sea-level variations due to compaction and its effect on coastal stratigraphy merit special attention. Compaction in turn is determined by the control of stratigraphic architecture on dewatering, by depositional timing, and by the physical properties of the compacting sediments. In modeling contemporary hydrogeology in these settings, compaction plays a double role: (1) it affects aquifer geometry by way of changes in sediment accommodation space and depositional environment, and (2) it determines petrophysical properties that control water extraction and the ensuing subsidence. We have explored this interaction by using a numerical sedimentary process model coupled with a single-phase flow simulator to study the interaction of sedimentation, dewatering, and compaction in coastal environments. The results explain several features of the sedimentary record and present-day morphology observed in data from the Gulf of Mexico. Although compaction may be hard to separate from other causes of relative sea-level change in ancient environments, careful interpretation of sedimentation timing and quantitative modeling can identify the effect of each. The identification of sedimentation-compaction regimes in coastal settings provides a useful conceptual tool for the geologic interpretation of ancient coastal deposits identified in seismic and well-log data. Hydrogeologic modeling performed on deposits that are simulated by sedimentary process models benefits from a richness of detail that can enhance hydrogeologic predictions. Additionally, the values of petrophysical properties required for hydrogeologic modeling (such as porosity, permeability, and compaction coefficient) can be better constrained by this dual modeling approach, because they result from the prior geologic sedimentation and compaction model, which limits their range of possible values.
The Laptev Sea system since the last glacial
There is growing concern about the rapidity and extent of climate change in recent decades in the Arctic. The changes already evident in the Arctic, such as the cyclonic shift in the distribution of Atlantic and Pacific water masses, atmospheric pressure and winds, as well as the thinning and retreat of the sea ice, will be felt first and most dramatically around the circum-Arctic shelves, which comprise nearly 50% of the area of the Arctic Ocean. In this context, the Laptev Sea and its Siberian hinterland are of particular interest because of their distance both from the Atlantic and Pacific Oceans. River discharge into the Laptev Sea constitutes a key source for the Arctic freshwater input, and it generates a shallow brackish layer on top of the halocline. The shallow Laptev Sea shelf is a major area of sea-ice production that links the Siberian shelves of the Arctic Ocean with the Nordic seas. During the Last Glacial Maximum, most of these shelves were above sea level and developed thick permafrost sequences; today they are submarine, after having experienced the postglacial late Pleistocene and Holocene transgression. The history of the submarine permafrost and its modern state of decay are largely unknown.
We investigate the fate of permafrost since the Last Glacial Maximum in the Laptev and East Siberian Seas, a submergent coastal environment. The shelf here is up to 700 km wide and less than 80 m deep, a large area highly sensitive to changes in environmental conditions. Climate and sea-level histories and the terrestrial and coastal geomorphology of the region are combined with direct observations from drilling campaigns to review existing notions on the distribution, thickness, physical state, and history of the development of terrestrial and offshore permafrost since the Last Glacial Maximum. Drilling transects running perpendicular to the coast in the nearshore zone show that the interface between unfrozen and frozen sediments varies in its angle of inclination as a result of a number of factors, primarily coastal retreat rate. A conceptual model of permafrost development prior to submergence suggests that thermokarst and nearshore processes are critical in altering the development of permafrost in the submarine environment.
This chapter reviews key elements of the last glacial cycle climate change and related geological processes and environmental impacts relative to current theories regarding the peopling of the Americas. Migration routes into the Americas during the last glacial cycle must necessarily have been feasible and landing sites habitable. Climate change and the consequential geological processes experienced during the last glacial cycle, and most particularly during and subsequent to the Last Glacial Maximum (LGM), have made understanding the peopling of the Americas a challenge. Proposed land-based, coastal, and transoceanic migration routes are analyzed in the context of climate and geological processes. A case study from Canada's northwest Pacific margin, which lies along the coastal migration route, exemplifies the influence of climate and geologic processes on coastal habitation and migration and indicates that the region was potentially habitable during and definitely shortly after the LGM. Recent research demonstrates the value of using earth system climate modeling to provide constraints for ocean-based human migration theories. This interdisciplinary perspective elucidates the importance of geological processes and inevitably of climate as influencing factors in the migration of early peoples into the Americas.
The Baltic Sea coast—A model of interrelations among geosphere, climate, and anthroposphere
Coastline changes are the result of the interaction between geosystems and climate. Vertical isostatic movement of Earth's crust competes with the eustatic sea-level variation controlled by changing climatic conditions. The resulting relative sea-level variation has a vital impact on the anthroposphere along the sea coast. This interrelation can be studied in an exceptional manner on the southern Baltic Sea. Here, isostasy and eustasy have shaped the picture of the coastal areas since the last glaciation. The northern Scandinavian part has been uplifting constantly since the last deglaciation, causing a regression of the sea. In contrast, in the south, the Littorina transgression has initiated land loss due to the glacio-isostatically sinking coast. Human populations living along the coast since Mesolithic time have reacted by relocating settlements. This migration is well documented and preserved at the Wismar Bight, Germany, by submarine archaeological remnants. Dates of samples from ancient coastlines, supported by geostatistical methods to estimate sediment transport processes, allow us to model the paleogeographic settings on a local scale using maps. By projecting the investigated processes into the future, scenarios of predicted coastline evolution can be modeled. Extrapolated isostatic measurements and sea-level data derived from IPCC (Intergovernmental Panel on Climate Change) scenario A for the next 800 yr are superimposed in order to estimate areas that may sink below the sea level.
Southern Baltic sea-level oscillations: New radiocarbon, pollen and diatom proof of the Puck Lagoon (Poland)
The Baltic sea-level oscillations in the Atlantic and Subboreal periods are known from sedimentary records on slightly uplifting coasts in Denmark and southern Sweden (e.g., Berglund, 1971 ; Digerfeldt, 1975 ). The periodicity of those oscillations is in close correlation with recent data on climatic cycles with a periodicity of 1500, 1000, and 550 yr (e.g., Stuiver et al., 1995 ; Chapman and Shackleton, 2000 ). The effects of regional eustatic oscillations in the coastal area of the Southern Baltic are poorly known because of the slightly subsiding coast and the magnitude of barographic and storm surges, which are larger than those of eustatic oscillations. To solve these problems, sediment sequences on the western coasts of the Puck Lagoon (northwestern part of the Gulf of Gdańsk) were investigated. Recent vertical movements of Earth's crust are ∼0.0 to −0.5 mm/yr. According to 14 C datings, pollen and diatom analyses, the earliest marine influences occurred in the Middle Atlantic period, while at the end of the Atlantic period almost all of the area was occupied by brackish waters ( Kramarska et al., 1995 ; Uścinowicz and Miotk-Szpiganowicz, 2003 ). Several sediment cores were taken along the western coast of the Puck Lagoon. Ordinates of the collected cores were geodetically determined to ± 1 cm relative to the mean sea level. Peat, plant remains, and marine shells (64 samples) were dated using the classic 14 C and AMS (accelerator mass spectrometry) methods. The plot showing the altitude of peat and marine mollusk shells versus their radiocarbon age shows that during the Subboreal and Subatlantic periods water levels in the Puck Lagoon were as follows: 5 ka B.P.—2.8 m, 4 ka B.P.—1.8–1.9 m, 3 ka B.P.—1.3–1.4 m, 2 ka B.P.—0.8–0.9 m, and 1 ka B.P.—0.4–0.5 m b.s.l. The rises in sea level during the Subboreal and Subatlantic periods may have been cyclical and related to climatic oscillations. The periodicity of water-level changes was ca. 1000 yr and their amplitude was ∼0.3–0.5 m. This is also confirmed by pollen and diatom analyses.
Estimating postglacial coastal sediment budgets is difficult as erosion has removed the landscape drowned by marine transgression and coastal positions through time are rarely known. In the Natural Environment Research Council (NERC)–funded Land Ocean Interaction Study, a model was built, based on detailed characterization of onshore-offshore bathymetric profiles (created by Holocene wave-base migration). Modeling of the pre-Holocene western North Sea land surface (west of 1°E and south of 54°N) and sea-level curves allow determination of the likely position of wave base and coast at any time during the late Holocene. The volumes of materials eroded from cliffs, wave action on the shoreface, and tidal scour associated with erosion of pits (e.g., Inner Silver Pit) from different coastal areas have been estimated. The average annual contribution of sediment per meter length of coast is higher than some recent erosion rates would suggest, but appears consistent with the volumetric difference between the modeled end-Pleistocene surface and the present topographic-bathymetric surface. With other models, outputs would suggest that less than 5% of the Humber Holocene is likely to be of fluvial origin—a percentage corroborated by detailed geochemical and mineralogical provenance studies of the estuarine fill. The model suggests that more sediment has been released from the shoreface than from cliffs per unit length of coastline throughout the Holocene; this is an important finding for coastal managers, as this pattern is likely to continue and because the shore-face cannot be effectively protected from erosion.
A Black Sea lowstand at 8500 yr B.P. indicated by a relict coastal dune system at a depth of 90 m below sea level
Oceanographic surveys in the Black Sea during 1998, 2002, and 2004 in the framework of a French-Romanian joint project, and recently in the framework of the European project ASSEMBLAGE, complement previous seabed mapping and subsurface sampling studies undertaken in the Black Sea by various international expeditions. Until the Ryan and Pitman flood theory and prior to this project, it was proposed that the Black Sea was predominantly a fresh-water lake interrupted by possible marine invasions coincident with high sea level during the Quaternary. From the recent surveys carried out on the western part of the Black Sea it is evident that the Black Sea's lake level rose on the shelf to at least the isobath −40 to −30 m as ascertained by the landward limit of extent of the Dreissena layer characteristic of brackish to fresh-water conditions. This rise in the lake level could coincide with the answer of the Black Sea catchment's basin to the meltwater drained from the thawing of the ice cap ensuing Melt Water Pulse 1A ( Bard et al., 1996 ). It is possible that at that time the lake level filled by fresh water reached the level of its outlet and spilled into the Mediterranean Sea. Later, in the mid-Holocene at 7.5 k.y. B.P., the onset of salt-water conditions is clearly evident in the Black Sea. From these observations Ryan et al. (1997) came to the conclusion that the Black Sea could have been filled by salt water cascading from the Mediterranean. Even though this hypothesis has been challenged ( Aksu et al., 2002b , 1999b ), the recent confirmation of the excellent preservation of drowned beaches, sand dunes, and soils during Ifremer (Institut français de recherche pour l'exploitation de la mer) surveys seems to support the Ryan and Pitman hypothesis ( Ryan and Pitman, 1999 ). The multibeam echo-sounding and the seismic reflection profiles acquired on the Romanian margin during our surveys revealed wave-cut terraces at an average water depth of 100 m. More evidence of seawater penetration is marked at the Bosphorus outlet by the presence of recent canyon heads mapped during the last cruise in 2002. The cores recovered on the Romanian continental shelf penetrated an erosion surface, indicating subaerial exposure well below the level of the modern Bosphorus outlet. The 14 C ages documented a simultaneous colonization of the terrestrial surface by marine mollusks at 7.1 k.y. B.P. The most recent palynology analysis and studies of the dynocyst population ( Popescu, 2004 ) document a real onset of fresh-water arrival during the Younger Dryas and abrupt replacement of Black Sea dynocyst by Mediterranean population, coincident with the onset of the marine mollusks.
Sinis Peninsula (Western Sardinia, Italy) coastal system analysis through hydrodynamic and remote-sensing techniques
The present study describes the coastal land and seafloor morphology of the Sinis Peninsula (West Sardinia, Italy). Based on the analysis of the wave motion hydrodynamic, the 7500 yr B.P. shoreline is outlined. The potential causes of the transportation of deposits, which have been reworked from aplitic dykes from the Mal di Ventre Islet to the central-southern coast of the peninsula, are investigated on the basis of 7500 yr B.P. seafloor wave motion transformations and relative field of velocity analysis.
The Pearl River Delta with its network system and estuarine bays is unique and one of the most complicated large-scale estuarine systems in China. In this paper, a long-term morphodynamic model is developed to simulate the long-term morphological evolution of the Pearl River Delta. The concepts of long-term model calibration and verification are discussed. The paleo–estuary bay topography formed in the last interglacial period is reconstructed and serves as an initial and boundary condition of this model with time steps of 100 yr. Events of shorter duration are ignored. The driving forces and control factors considered in the long-term delta evolution include representative tides, sediment supply from the Pearl River system, sea-level variation, sediment condensation rates, and neotectonic movement. Deposition rates and total deposition volume are investigated and determined and then used to calibrate the model. Core data with 14 C dating at 30 locations are used to verify the model output with satisfactory results. Approximately 1700 collected cores are carefully analyzed to justify the model-simulated evolution processes. Morphodynamic analysis is conducted to justify and explain the output of the model on delta evolution and deposition modes. The study also provides more temporal and spatial details to the delta development originated from the effects of the morphodynamic structures, such as bidirectional jets and the “men” system. The model confirms that the complicated morphology, e.g., the rocky islands in the shallow estuarine bays, is one of the important factors affecting the long-term evolution of the Pearl River Delta.
Abstract Upper Cretaceous reefs were concentrated in low- to mid-latitude regions in the Northern Hemisphere between the Americas and the Arabian Peninsula. Rudist bivalves, scleractinian corals, sponges, stromatoporoids, and algae were the dominant biota. Most Late Cenomanian through Santonian reefs occurred in low paleolatitudes (0–30° N) and were dominated by rudist bivalves. North of 30°, reefs constructed of corals, stromatoporoids, and siliceous sponges outnumbered those of bivalves. Campanian through Maastrichtian reefs occurred between the equator and 30° N and were also dominated by bivalves, whereas corals and bryozoans dominated the northern occurrences. The distribution of Upper Cretaceous reefs was analyzed with respect to paleogeography, surface current circulation patterns, sea level, and sea-water chemistry. Considering the paleogeographic setting of the Late Cretaceous, westward-flowing surface currents accounted for the low- to mid-latitude distribution patterns of reefs, whereas northward surface currents could account for northern occurrences in the European and North American regions, especially during sea-level highstands when shelfal areas were flooded. There is a global correspondence between the development of Upper Cretaceous reefs and the first-order sea-level highstand of Haq et al. (1987) , but there is only a regional, not global, correlation between reefs and second-order sea-level fluctuations; some reefs were associated with third-order and fourth-order fluctuations. We found no direct correspondence between the global distribution of Upper Cretaceous reefs and oceanic anoxic events, salinity, aragonite-calcite seas, or sea-surface temperature, although links still need to be investigated for geographic regions and subdivisions of the Late Cretaceous. Numerical analyses of the PaleoReef database allowed for an assessment of the biological and physical attributes of reefs. From this database, Upper Cretaceous reefs representing the Upper Zuni 111 supersequence (Late Cenomanian-Santonian) can be characterized by rudists of the constructor guild. Other biota are also prominent. Biostromes and reef mounds in shallow intraplatform or platform-margin settings have large amounts of micrite and a moderate debris potential. Reefs representing the Upper Zuni IV supersequence (Campanian-Maastrichtian) can be characterized by rudists and oysters of the constructor guild. Other biota areprominent. Biostromes and reef mounds in a marginal marine setting have large to moderate amounts of micrite and a moderate debris potential.