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The late Miocene Messinian salinity crisis was an evaporitic episode that occurred throughout the Mediterranean; it concluded with a transition from hypersaline to fresher-water “lake sea” (Lago Mare) conditions prior to the Pliocene. Whereas numerous researchers propose that Lago Mare sediments accumulated in a Mediterranean-wide lake filled with Paratethyan waters, other workers reject this hypothesis. Here, to test this Paratethyan-overflow model, we develop a novel time-probabilistic approach to evaluate the distribution of precession-related deposits. We apply our methodology to 24 circum-Mediterranean sites, focusing on two previously untested parameters: the probability of preserving intrabasin precession cycles; and the similarities in interbasin preservation. Our results, which show an increase in preservation and similarity in successively younger cycles, display a trend opposite to what is expected from a flooded Mediterranean. Consequently, we conclude that Lago Mare accumulations were deposited in disconnected, shallow lacustrine environments, thereby casting doubt on the widely accepted Paratethyan-supply hypothesis.

Soulet (2018) asserts that the calculation of the 14C reservoir age for the geochronology of the Black Sea sediments suffers from a fundamental flaw. He contends that Yanchilina et al. (2017) obtained reservoir ages by first sorting the δ18O and δ13C values of the mollusks as a function of their corresponding 14C age before aligning the mollusk isotope curves to those of the nearby Sofular Cave. Sorting by 14C age would lead to an incorrect calendar age for each δ18O and δ13C measurement because it does not take into account changing reservoir ages. We reply here that this sorting by 14C age was not the procedure taken. The radiocarbon reservoir ages were derived after tuning the δ18O and δ13C composition of the mollusks, sorted by their δ18O, δ13C, radiocarbon age and stratigraphic location in each core, to the δ18O and δ13C composition of the U/Th dated Sofular Cave stalagmites as a function of calendar age, shown to reflect Black Sea surface water δ18O and δ13C composition. After the calendar age was derived for each mollusk, it was then converted to a corresponding Northern Hemisphere atmospheric 14C age using Reimer et al. (2009). The 14C reservoir age was subsequently calculated from the difference between the measured 14C age of the mollusks and the calculated Northern Hemisphere atmospheric 14C age of the mollusks, R(t) = 14Cshell(t) − 14Catm(t) (e.g., Ryan, 2007; Kwiecien et al., 2009; Jull et al., 2013; Philippsen, 2013; Soulet, 2015; Soulet et al., 2016). The Reimer et al. (2009) calibration used in our original study differs

The illumination of the seafloor through Marie Tharp’s lens was instrumental in the plate tectonics revolution and fundamentally transformed our understanding of earth processes. Rather than creating traditional contour maps from isolated soundings, her work yielded physiographic diagrams based on sparse echo-sounding profiles that were complemented by stylized views based on her interpretation of the trends and texture of the seafloor. These maps showed the fabric of seafloor in ways that could not have been achieved or communicated with traditional contour plots. Despite the sparseness of the input data, Marie Tharp and Bruce Heezen’s early seafloor maps are remarkably consistent with modern bathymetric maps that are based on orders of magnitude more observations.An important part of the legacy of Tharp’s work is codified in the evolution of bathymetric data synthesis efforts led by several of her contemporaries and successors at the Lamont-Doherty Earth Observatory (LDEO). After Tharp’s seminal work transforming bathymetric profiles into the first maps of the global seafloor, efforts were undertaken to digitize echo-sounding profiles creating new opportunities for analysis and integration as well as the development of new software tools and approaches for working with those data. In the 1980s, the availability of multibeam sonars in the academic sector ushered in a new era of mapping by extending the data coverage from profiles to swaths that revealed spatially-continuous areas of the seafloor. The Ridge Multibeam Synthesis (RMBS) Project, which began in the 1990s, built upon Tharp’s early work and sought to advance understanding of the global mid-ocean ridge system by integrating swath data from multiple ships and cruises to create detailed bathymetric grids served online via the early web. Just over a decade later, the Global Multi-Resolution Topography (GMRT) Synthesis emerged as the next generation product under the inspiration of William Haxby. GMRT shifted the focus of effort from the mid-ocean ridges to the global ocean, and presented an efficient scalable solution using a tiled approach for providing access to global bathymetric data at native resolution. GMRT continues today and includes a curated collection of bathymetry data from over 1,100 research expeditions covering more than 9% of the global ocean at 100m spatial resolution. This presentation will describe the legacy of Marie Tharp in the context of the continuity of seabed mapping work at LDEO, including the evolution of bathymetry data synthesis and integration projects and how they connect to complementary efforts in the international arena including the Nippon Foundation – GEBCO Seabed 2030 Project.

Our knowledge of rate and processes in which semi-enclosed environments alternate from lacustrine to marine is commonly limited because of the paucity of specific proxies for sea level and salinity. Here we investigate the timing, rate, and key mechanisms involved in the transformation of the previously isolated Black Sea-Lake to the modern partly-enclosed marine sea using a suite of geophysical, geochemical, and geochronological methods. Cores were collected in transects across shelves of Ukraine, Romania, Bulgaria, and Turkey. Biogenic carbonate from these cores was analyzed for radiocarbon and strontium, oxygen, and carbon isotopes. Strontium results indicate that the submergence of the Black Sea shelf at 9300 calendar years BP was caused by the ingress of Mediterranean water and was abrupt, taking Radiocarbon years are calibrated to calendar years by tuning the oxygen and carbon isotope composition of the mollusk record to that of the U/Th dated Sofular Cave stalagmites. The match shows a reduction of the lake's prior high reservoir age accompanying the inflow of the Mediterranean water. In 900 years the salinity reached a threshold that excluded all previous Black Sea lacustrine fauna. These results imply that any substantial postglacial submergence of the Black Sea shelves did not occur prior to entry of Mediterranean water.

The Marine Isotope Stage 3 (MIS 3) is considered a period of persistent and rapid climate and sea level variabilities during which eustatic sea level is observed to have varied by tens of meters. Constraints on local sea level during this time are critical for further estimates of these variabilities. We here present constraints on relative sea level in the Marmara and Black Sea regions in the northeastern Mediterranean, inferred from reconstructions of the history of the connections and disconnections (partial or total) of these seas together with the global ocean. We use a set of independent data from seismic imaging and core-analyses to infer that the Marmara and Black Seas remained connected persistent freshwater lakes that outflowed to the global ocean during the majority of MIS 3. Marine water intrusion during the early MIS-3 stage may have occurred into the Marmara Sea-Lake but not the Black Sea-Lake. This suggests that the relative sea level was near the paleo-elevation of the Bosporus sill and possibly slightly above the Dardanelles paleo-elevation, ~80 mbsl. The Eustatic sea level may have been even lower, considering the isostatic effects of the Eurasian ice sheet would have locally uplifted the topography of the northeastern Mediterrranean.

Deglaciation of the Eurasian Ice Sheet dispensed vast amounts of meltwater laden with red-brown clay into Black and Caspian Sea's freshwater lakes between 16,350 and 15,400 calendar years BP. The arriving sediment had a mineral composition and strontium-neodymium isotope signatures (87Sr/86Sr, and eNd) consistent with the crystalline bedrock that lay beneath the ice sheet as opposed to sources from landscapes crossed by the rivers that carried meltwater to the lakes. The magnitude and rapidity of the shifts of 87Sr/86Sr and δ18O in shells of ostracods and mollusks, an eight-fold increase in sediment accumulation rate, and a plunge of 1250 14C years in the radiocarbon reservoir age indicate a volume of meltwater sufficient to have replaced most or all of the pre-existing lake water. If the release of >25,000 km3 of water from the Caspian into the Black Sea's New Euxine Lake was abrupt by judging the magnitude of erosion in the floor of the Manych Strait spillway, this event qualifies as a megaflood. Deeply-scoured furrows, channel floor bars, and swaths of mounds 5–20 km in length and 5–20 m in height are reminiscent of scabland landscapes. The meltwater is coincident with Heinrich Stadial 1 when the Alpine and Eurasian ice sheets re-advanced and temperatures of the Black Sea's lake surface remained cold. Sand grains within the red-brown clay indicate they were transported by lake surface ice.

The accumulation of sediments at an Atlantic-type continental margin constitutes a load on the lithosphere which simply sags due to its weight. Studies of the geometry of deformation suggests the lithosphere will respond to these loads either by local loading of an Airy-type crust or flexural loading of a strong rigid crust. Sediment loading models of either type cannot, however, explain the substantial thicknesses of shallow-water sediments observed in commercial boreholes from Atlantic-type margins. Other factors such as thermal contraction, gravitational outflow of crustal material or deep crustal metamorphism may contribute to the subsidence. We have used biostratigraphic data from commercial boreholes from the Gulf of Lion and the East Coast U.S.A. to quantitatively determine the contribution of sediment loading to the subsidence. From these data we determined sea-floor and basement depths for sequential time intervals during margin development. Using the sediment loading models the sediment layers at each margin were progressively “backstripped” and the depth basement would have been without the sediment load calculated. The computed basement depths indicate there is a recognizable component of the subsidence of these margins which is caused by processes other than adjustments to the weight of the sediment. The nature of this subsidence is discussed and comparisons are made with that which would be expected from thermal-contraction models.

There is a growing consensus that the sulfates and halite within the massive evaporite deposits on the shallow margin and deep floor of the Mediterranean sea formed in two steps. Both phases had geodynamic consequences. The current evidence indicates that during the first step when the first cycle “Lower Evaporites” were deposited primarily in marginal settings, the surface of the Mediterranean remained at or very close to the level of the external Atlantic. The geodynamic response resulted from the increasing weight of the brine layer as it concentrated from normal marine salinity to the threshold for sulfate precipitation and then to the threshold for halite precipitation. This weight alone significantly deepened the Mediterranean basins by isostatic loading. Flexure of the lithosphere caused a peripheral bulge to appear that may have been the agent to close off the further entry of Atlantic seawater. Step two began with the subsequent evaporative drawdown and the deposition of the second cycle “Upper Evaporites”. As the basins dried out the loss of weight of the water led to regional isostatic uplift that permanently closed the prior inlets. Sediments removed from the margins by early subaqueous mass-wasting and later subaerial erosion and delivered to the basin floors further accentuated uplift of the margins and subsidence of the depocenters. The principal result has been to progressively tilt the Mediterranean substrate downwards from the margin towards the basin centers. This tilting was enhanced with the flooding of the desiccated sea at the climax of the salinity crisis. Consequently the salt layer rests today out of equilibrium on a surface that is more inclined after precipitation than before. The current mobility and flowage of the salt away from its margins and towards the basin centers is therefore not so much a response to the differential thickness and weight of overlying sediments, but to the combination of geodynamic processes that have produced the seaward tilting. Other giant salt deposits seem to have experienced a similar two-step evolution.

Chirp sub-bottom profiling, multibeam bathymetric mapping and a combination of faunal and isotopic analysis of molluscs and foraminifera in sediment cores on the northern shelf of the Sea of Marmara (SoM) provide evidence of sea-level excursions, water exchanges between the adjacent Mediterranean and Black Seas, and oscillating salinity over the last 160 ka bp. During the marine isotope stages MIS-2, MIS-3, MIS-4 and MIS-6 the SoM disconnected from the Mediterranean Sea and evolved into a lake. During MIS-1, MIS-5 and MIS-7, the SoM reconnected and became salty once again. Sapropels formed shortly after each invasion of Mediterranean saltwater observed in our cores. Concurrent suboxic–dysoxic conditions prevailed over quite shallow substrates on the shelf. Ancient shorelines are pervasive at − 85 m on the northern shelf and in the region of Prince Islands coincident with the elevation of the modern bedrock sill in the Canakkale (Dardanelles) Strait. At times when global (eustatic) sea level dropped below this sill, the surface of the SoM stabilized at its outlet and freshened. Thus this particular shoreline is interpreted as the edge of the most recent SoM lake that existed from about 75 ka bp to 12 ka bp. The freshening is observed in very light (− 6‰) values of δ 18 O measured on freshwater molluscs and the complete absence of foraminifera. Two brief lacustrine episodes during MIS-5 suggest that the level of the Canakkale outlet might have been as shallow as − 50 m in the past, a likelihood supported by submerged terraces along its margins bounding the modern central channel and the presence of an euryhaline biofacies in Unit L4.1 corresponding to MIS-5b. δ 18 O profiles and carbon-14 dating show that salinification of the SoM and the blossoming of bioherms evolved rapidly after the latest connection with the Mediterranean at 12 ka bp. However, freshening proceeded more slowly once the connection was severed.

This historical narrative traces the steps to unravel, over a span of 40 years, an extraordinary event in which 5% of the dissolved salt of the oceans of the world was extracted in a fraction of a million years to form a deposit more than 1 million km 3 in volume. A buried abyssal salt layer was identified with reflection profiling and sampled during the Deep Sea Drilling Project, Leg 13. The dolomite, gypsum, anhydrite and halite in the drill cores paint a surprising picture of a Mediterranean desert lying more than 3 km below the Atlantic Ocean with brine pools that shrank and expanded by the evaporative power of the sun. The desert drowned suddenly when the Gibraltar barrier gave way. The explanation of ‘deep-basin, shallow-water’ desiccation and the notion of a catastrophic Zanclean flood had a mixed reception. However, the hypothesis became broadly accepted following subsequent drilling expeditions. Nevertheless, as experts examined the evaporate facies and sequences of equivalent age in the terrestrial outcrops, weaknesses appeared in the concept of repeated flooding and drying to account for the magnitude of the deposits. The ‘Rosetta Stone’, used to decipher conflicting interpretations, turns out not to be the deposits but the erosion surfaces that enclose them. These surfaces and their detritus ‐ formed in response to the drop in base level during evaporative drawdown ‐ extend to the basin floor. Evaporative drawdown began halfway through the salinity crisis when influx from the Atlantic no longer kept up with evaporation. Prior to that time, a million years passed as a sea of brine concentrated towards halite precipitation. During the later part of this interval, more than 14 cyclic beds of gypsum accumulated along shallow margins, modulated by orbital forcing. The thick salt on the deep seabed precipitated in just the next few cycles when drawdown commenced and the brine volume shrank. Upon closure of the Atlantic spillway, the remnants of the briny sea transformed into salt pans and endorheic lakes fed from watersheds of Eurasia and Africa. The revised model of evaporative concentration now has shallow-margin, shallow-water and deep-basin, deep-water precursors to desiccation.

During the late glacial, marine isotope Stage 2, the Marmara Sea transformed into a brackish lake as global sea-level fell below the sill in the Dardanelles Strait. A record of the basin's reconnection to the global ocean is preserved in its sediments permitting the extraction of the paleoceanographic and paleoclimatic history of the region. The goal of this study is to develop a high-resolution record of the lacustrine to marine transition of Marmara Sea in order to reconstruct regional and global climatic events at a millennial scale. For this purpose, we mapped the paleoshorelines of Marmara Sea along the northern, eastern, and southern shelves at Cekmece, Prince Islands, and Imrali, using data from multibeam bathymetry, high-resolution subbottom profiling (chirp) and ten sediment cores. Detailed sedimentologic, biostratigraphic (foraminifers, mollusk, diatoms), X-ray fluorescence geochemical scanning, and oxygen and carbon stable isotope analyses correlated to a calibrated radiocarbon chronology provided evidence for cold and dry conditions prior to 15 ka BP, warm conditions of the Bolling-Allerod from ∼ 15 to 13 ka BP, a rapid marine incursion at 12 ka BP, still stand of Marmara Sea and sediment reworking of the paleoshorelines during the Younger Dryas at ∼ 11.5 to 10.5 ka BP, and development of strong stratification and influx of nutrients as Black Sea waters spilled into Marmara Sea at 9.2 ka BP. Stable environmental conditions developed in Marmara Sea after 6.0 ka BP as sea-level reached its present shoreline and the basin floors filled with sediments achieving their present configuration.

In their comment Hiscott and co-authors adhere rigidly to ages and sources for sedimentary units in the subsurface of the Marmara shelf that they have previously reported in their publications from 2002 through 2007. This adherence is in spite of a superior age-depth model from our 13 m-long sediment core that penetrated deeply into the deposits under consideration and in disregard to the results of subsequent more-detailed and full-coverage mapping of the region under scrutiny. The age revisions are dismissed by the authors of the comment as representing sediments severely disturbed during coring. We rebut this criticism. The Bosporus source attributed by them to the sedimentary units sampled and dated by us appears to be driven by their conception that the Black Sea had a persistent outflow prior to its two-way connection with Marmara. Irrespective of whether the outflow was persistent, our reply shows that the drawing of the isopachs of the sedimentary units by Hiscott and co-authors was accomplished in a fashion to promote the Bosporus source hypothesis regardless of the geographic limits of their survey. The ages assigned to the units are equally indeterminate because the cores used by them have missing core tops of unknown lengths that are not discussed in their publications. Furthermore, the sub-bottom reflectors at the sites where the reflectors were calibrated to their only core without a missing top are actually hidden by the finite width of the bottom reflecting wavelet.

Flow parameters (velocity and density) for turbidity currents in the Northwest Atlantic Mid-Ocean Channel (NAMOC) have been determined based on two different approaches, channel geometry and grain-size distributions of turbidites. Channel geometry has been obtained by a quantitative morphological analysis of the NAMOC which shows three genetically different segments in the upper 2000 km: (1) an upper 350 km-long ‘equilibrium channel’, (2) a middle 700 km-long ‘modified equilibrium channel’and (3) a lower ‘basement-controlled channel’which is more than 1000 km-long. In contrast to other meandering submarine channels the NAMOC has very low sinuosities and gradients. A consistently higher right-hand levee limits mean flow velocities to 3ms−1 and channel geometry indicates mean flow velocities of 0·86 m s−1 that decrease within the equilibrium channel to 0·05 m s−1. Grain-size distributions on the levees and in the channel suggest strong vertical velocity and density gradients for bank-full flows with velocities of up to 8 m s−1 and excess densities up to 87 kg m−3 at the base, and 0·45 m s−1 and 4 kg m−3 at the top. The internal shear produced by these strong vertical gradients results in a decoupling of the current head and body. Channel geometry appears to be mainly the result of the slowly moving dilute body of the current.

Two distinct series of slumps deform the upper part of the sedimentary sequence along the continental margin of the Levant. One series is found along the base of the continental slope, where it overlies the disrupted eastern edge of the Messinian evaporites. The second series of slumps transects the continental margin from the shelf break to the Levant Basin. It seemed that the two series were triggered by two unrelated, though contemporaneous, processes. The shore-parallel slumps were initiated by basinwards flow of the Messinian salt, that carried along the overlying Plio-Quaternary sediments. Seawater that percolated along the detachment faults dissolved the underlying salt to form distinctly disrupted structures. The slope-normal slumps are located on top of large canyons that cut into the pre-Messinian sedimentary rocks. A layer of salt is found in the canyons, and the Plio-Quaternary sediments were deposited on that layer. The slumps are bounded by large, NW-trending faults where post-Messinian faulted offset was measured. We presume that the flow of the salt in the canyons also drives the slope-normal slumps. Thus thin-skinned halokynetic processes generated the composite post-Tortonian structural patterns of the Levant margin. The Phoenician Structures are a prime example of the collapse of a distal continental margin due to the dissolution of a massive salt layer.

High-resolution reflection seismic profiles with core analyses of sedimentary sequence near the Sea of Marmara (SoM) entrance to the Strait of İstanbul (SoI, Bosphorus) provide detailed record of sealevel changes since the Late Glacial Maximum (LGM). The sequence is deposited over the LGM erosional surface at a maximum depth of -105 m. It includes seven seismic units that can be confidently correlated with 14C-dated sedimentary units in the cores. Unit 6 represents levee deposits of the paleo-SoI channel that was deposited by a Black Sea outflow during 11.2-10.6 kyr BP. The reflection surfaces at base of Unit 5 and 4 correspond to wave-cut terraces at -71and -63 m, respectively, and are estimated to be 10.6 and 9.8 kyr BP. The seismic Unit 2, overlaying a mud drape (Unit 3), comprises deltaic sediments that was deposited during 6.400-3200 yr 14C BP. Isopach map and forset directions of the deltaic unit indicates that the delta was sourced from Kurbağalıdere River. Depositional period of the delta is subdivided into two stages in response to changes in the 49 balance between sealevel change and sediment supply rates: a progradational and an aggradational stages. The progradational stage prevailed during 6.4-4.7 kyr BP when the sealevel rise decelerated and there was a high sediment input from the drainage area of the Kurbağalıdere River. An aggradational stage developed during 4.7-3.2 kyr BP and indicates that the delta grew during faster sealevel rise when the rate of sediment input was relatively decreased. The onset of delta deposition at 6.4 kyr BP is marked in the SoM by termination of the early Holocene Sapropel deposition and the aggradational stage overlaps with the late Holocene Sapropelic unit deposited on the shelf areas. Our finding contradicts the hypothesis of Hiscott et al. (2002) and Aksu et al. (2002) that this delta was sourced from the Black Sea and that it indicates a persistant Black Sea outflow since 10 kyr BP.

The Hudson River Benthic Mapping Project, funded by the New York State Department of Environmental Conservation, resulted in a comprehensive data set consisting of high-resolution multibeam bathymetry, sidescan sonar, and sub-bottom data, as well as over 400 sediment cores and 600 grab samples. This detailed data set made it possible to study the regional pattern and the local variations of the sediment distribution in the Hudson River Estuary. Based on these data we describe the distribution of sediment texture and process-related sedimentary environments for the whole 240-km long estuary together with along-river variations of depth, cross-sectional area, and grain size distribution. We compare these parameters with changes in surrounding geology and tributary input and, as a result, divide the Hudson River Estuary in eight sections with distinct combinations of channel morphology, bedrock type, sediment texture, and sediment dynamics. The regional sediment distribution consists of marine sand-dominated sediments near the ocean end of the estuary, a large, mud-dominated central section, and fluvial sand-dominated sediments in the freshwater section of the Hudson River Estuary. This regional trend is highly modified by small-scale variations in the sediment distribution. These local variations are controlled by changes in morphology, bedrock, and tributary input, as well as by anthropogenic modifications of the estuary. In some areas these local variations are larger than the overall trend in sediment distribution and control the actual sediment type, as well as the condition of erosion and deposition in the estuary.

High-resolution seismic data and sediment cores reveal the late Holocene subsurface stratigraphy of the broad Tappan Zee– Piermont region of the Hudson River Estuary. We identify a series of distinct, extensive horizons beneath the marginal flats, channel banks, and main channel in this area. Physical properties and lithology from sediment cores suggest that these horizons are surfaces of erosion or nondeposition. Radiocarbon dates indicate that they correspond with three distinct time horizons, with maximum ages of 3400, 2200, and 1600 yr BP. We also distinguish two sedimentary facies that occupy the marginal flats and channel banks. The deeper facies forms a deposit 2 km wide and 7 km long that accumulated at rates of 2–4 mm/yr in the vicinity of the Sparkill Creek prior to ∼1700 yr BP, overlying and onlapping the 2200 yr BP seismic surface. Based on its internal geometry, morphology, and proximity to a tributary, we interpret this facies as a delta deposit. The shallower facies accumulated more slowly (1–2 mm/yr), overlying the delta deposit to the south and dominating the marginal flats to the north. Surface sediment samples and geophysical data reveal that the modern marginal flats are no longer actively depositional, but dominated by nondeposition or erosion. Limited accommodation space in the Hudson River Estuary may be the critical factor contributing to the observed sedimentary pattern, characterized by intervals of deposition punctuated by episodes of erosion. An estuarine system that has reached a state of morphological equilibrium will be sensitive to even small fluctuations in sea-level and climate conditions, which may account for the intervals of deposition and erosion we observe. Limited accommodation space and intermittent sediment deposition in the Hudson River Estuary may be due to its evolution from a fjord filled with glacial lake sediments, which distinguishes its infilling behavior from the classic drowned river valley estuary.

The Black Sea was an inland lake during the last ice age and its sediments are an excellent potential source of information on Eurasian climate change, showing linkages between regionally and globally recognized millennial-scale climate events of the last deglaciation. Here, we detail changes from the last glacial maximum (LGM) through the transition to an anoxic marginal sea using isotopic (strontium and oxygen) and trace element (Sr/Ca) ratios in carbonate shells, which record changing input sources and hydrologic conditions in the basin and surrounding region. Sr isotope records show two prominent peaks between ∼18 and 16 ka BP cal, reflecting anomalous sedimentation associated with meltwater from disintegrating Eurasian ice sheets that brought Black Sea level to its spill point. Following a sharp drop in Sr isotope ratios back toward glacial values, two stages of inorganic calcite precipitation accompanied increasing oxygen isotope ratios and steady Sr isotope ratios. These calcite peaks are separated by an interval in which the geochemical proxies trend back toward glacial values. The observed changes reflect negative water balance and lake level decline during relatively warm periods (Bolling–Allerod and Preboreal) and increasing river input/less evaporation, resulting in higher lake levels, during the intervening cold period (the Younger Dryas). A final shift to marine values in Sr and oxygen isotope ratios at 9.4 ka BP cal corresponds to connection with the global ocean, and marks the onset of sedimentation on the Black Sea continental shelf. This date for the marine incursion is earlier than previously suggested based on the appearance of euryhaline fauna and the onset of sapropel formation in the deep basin.

The submerged portions of the North Anatolia Fault system beneath the Marmara Sea were studied with high-resolution multibeam bathymetry, subbottom profiling and sediment cores. The major objectives were to learn about the seismic and tectonic history of the fault from the stratigraphic record at a scale similar to paleoseismic studies on land and to develop tools for submarine earthquake geology that can be applied to fault-controlled basins in general. We focused on Holocene sediment in several Marmara Sea basins of different sizes. The approach was to test whether: (1) the depocenters of the larger basins contain a record of all historic Ms > 7 earthquakes within the Marmara Sea region; (2) the small transform basins record earthquakes that rupture through them; (3) vertical and strike-slip Holocene deformation can be quantified; and (4) the effects of an earthquake generally includes both primary structural features due to rupture of the sea floor, such as strata offset, scarps and tilting, as well as secondary effects due to shaking, such as mass-wasting and gravitational flows. We found evidence of earthquakes that we correlate with historic events in 181 AD, 740 AD, 1063 AD, 1343 AD, 1509 AD, 1766 AD, 1894 AD and 1912 AD. The geologic evidence is primarily from those basins adjacent to the rupture as inferred from historic data. This suggests that coseismic deformation of the sea floor along the rupture is a critical factor in the sedimentary record. We propose a qualitative sedimentation model that relates this coseismic deformation to mass-wasting of the slope, scour of the basin floor, seiche motions and homogenite deposition. Frequent earthquake activity sheds sediments from the flanks, contributes to the much thicker sediment on the basin floor and decreases the likelihood of sediment failures in response to normal marine gravity-driven processes. The surveying techniques and approaches used have therefore the potential of documenting earthquake ruptures of fault segments and to extend the earthquake record far before the known history, thus improving hazard evaluations and the fundamental understanding of earthquake process.

Current interpretation of the Messinian Salinity Crisis (MSC) involves partial “desiccation” of the Mediterranean Sea coupled with the deposition of thick evaporites in the deep basins. New sets of seismic reflection profiles in the western part of the Gulf of Lions confirm the basinward extension of the Messinian erosion and enable the mapping of distinctive seismic markers indicating the Messinian Erosional Surface (or Messinian unconformity), the basin-margin detrital deposits, and the deep evaporite sequence. The geometrical relationship between these three elements and their relationship to the paleogeography of the margin during the MSC provide new information about the evolution of the study area during the Messinian. The Messinian Erosional Surface (MES), commonly correlated with the “desiccation” phase and the deposition of deep evaporites during the apogee of the event, is generally interpreted as a subaerial feature. In the Gulf of Lions, it is a complex diachronic polygenic erosional surface observed at the base of the prograding Plio-Quaternary sequence beneath the shelf and slope; it extends downslope beneath the deep basin Upper Evaporites and the Salt, and possibly correlates conformably with the base of the so-called deep Lower Evaporites. The whole morphology of the MES reflects a buried drainage pattern, supporting the interpretation of fluvial erosion driven by a substantial drop in sea level. Our results also suggest that large submarine gravity flows occurred prior to any significant accumulation of Salt in the basin and prior to the Upper Evaporites. Consequently, interbedded clastic deposits may partly account for the parallel reflectors of the Lower Evaporites. Since river erosion persisted throughout the MSC, the Salt and Upper Evaporite units may also contain a large amount of detrital sediments. The good quality of the new seismic data clearly reveals fan-shaped Messinian deposits in the downstream part of the main Messinian valleys (i.e., the Nile, Var, and Spanish rivers). The depositional scenarios generally involve a substantial sea-level fall coupled with deltaic/prodeltaic accumulations. A chaotic seismic unit (Unit D) filling Messinian lows and extending beneath the Salt within the study area is interpreted as a Messinian clastic unit. We propose a polyphase scenario of detrital fan deposition involving pre-, syn-, and post-Salt deposition in subaqueous/subaerial environments. In the Gulf of Lions, a late Miocene tectonic phase that affected the western shelf also played an important role in controlling (a) the pattern of the Messinian fluvial network, (b) the location of maximum erosion on the shelf, and (c) the location of the detrital fan depocentre downslope.

SUMMARY We report the results of experiments on the initiation of subduction, using stratified analogue models in a large centrifuge, where the experiments are driven only by the enhanced gravity of the centrifuge without the effect of external lateral stresses. The scaled density of the stratified components resembles that of the asthenosphere and the continental and oceanic lithospheres. The experiments demonstrate that under the effect of enhanced gravity, the layers simulating the oceanic lithosphere detach from the front of the ‘continental lithosphere’ and plunge under it, pushing the more pliable asthenosphere downwards. Simultaneously, the ‘continental lithosphere’ is thrust over the downgoing slab; where friction is low, the ‘continental lithosphere’ extends considerably so that the ‘ductile continental lithosphere’ is exposed in some places. The rate of thrusting of the experimental continental slab over the oceanic one, as well as the amount of extension of the overriding slab and the extent of the rollback of the subduction zone that follows the initial lithospheric detachment, are controlled by friction and density differences between the subducting and the overthrust slabs. The analogue experiments emphasize the role of lateral density variations in incipient subduction and the effect of differential seismic friction along the subduction plane on the evolution of subduction zones, their shape and the evolution of their backarc basins. The morphological resemblance of the experimental results to various subduction systems seems to support their applicability to real subduction systems.

The Levant Rift system is an elongated series of structural basins that extends for more than 1000 km from the northern Red Sea to southern Anatolia. The system consists of three major segments, the Jordan Rift in the south, El Gharb–Kara-Su Rift in the north, and the Lebanese Fault splay in between. The rifted parts of this structural system are accompanied by intensively uplifted margins that mirror-image the basinal pattern, namely, the deeper the basin—the higher its margins, and vice versa. Uplifts also occur along the fault splay section. The Jordan Rift comprises axial basins that diminish in size from the south northwards, and are separated from each other by shallow threshold zones along the axis of the rift, where the margins are also subdued. The Lebanese Fault splay consists of five faults that emerge from the northern edge of the Jordan Rift and trend like a fan between the north and the northeast. One of these faults connects the Jordan and El Gharb–Kara-Su rifts. The Levant Rift and its uplifted margins started to develop in the middle-late Miocene, and most of the structural development occurred in the Plio-Pleistocene. The Levant Rift system is characterized by its oblique displacement, and evidence for both dip-slip and strike-slip displacement was measured on its faults. Earthquakes also indicate that same mixed pattern, some of them show strike-slip offset, and others normal. It is generally conceded that the amount of normal offset along the boundary faults of the Rift system reaches 8–10 km, but the lateral displacement is disputed, and offsets ranging from 11 to 107 km were suggested. Assessment of the available data led us to suggest that the sinistral offset along the Levant Rift system is approximately 10–20 km. The similarity between the vertical and the lateral displacements, the basin and threshold structural pattern of the Rift, model experiments in oblique rifting, as well as the significant tectonic resemblance to the Red Sea and the East African rifts, indicate that the Levant Rift is the product of continental breakup, and it is probably an emerging oceanic spreading center.

Acoustic surveying provides valuable information on the distribution of sedimentary environments in subaqueous settings. Frequently, differences in acoustic backscatter strength are used to distinguish sedimentary environments on the basis of their grain size composition. Here, we are presenting acoustic backscatter data from the Haverstraw Bay section of the Hudson River Estuary that has been mapped using sidescan, sub-bottom profiling, and multibeam bathymetry as part of the Benthic Mapping Project of the Hudson River Estuary Program, funded by New York State. In addition, hundreds of gravity cores, and grab samples provide ground truth for a classification of the river bottom into discrete substrate types. Analyses of sedimentary environments reveal patterns in backscatter strength beyond those that can be related to the sediment grain size distribution alone. An integrated interpretation of sidescan, sub-bottom profiling, and high-resolution bathymetry data indicates that the backscatter pattern can be attributed to spatial variations in the modern depositional environments which cause differences in bottom roughness and sediment compaction. Based on an integrated interpretation of the acoustic and sample data sets, we distinguished eight different sedimentary classes. Many of the classes can be linked to dynamic processes including contemporary deposition, erosion, and sediment migration in sand waves. The results provide a better understanding of the dynamic processes of the Hudson River Estuary and improve the interpretation of the acoustic backscatter data from fine grained sedimentary environments.

Geophysical mapping and sampling data provide a record of changing environmental and faunal conditions within the Hudson River estuary during the mid- to late Holocene. On the shallow, broad marginal flats of the mesohaline Hudson, fossil oyster beds (Crassostrea virginica) are found exposed on the river bottom and buried by sediment. The shallowest beds are well imaged in chirp sub-bottom and side-scan sonar data and form discrete flow-perpendicular bands, 0.6–1.0 km wide and up to 3 km long, which cover 30% of the river bottom. Radiocarbon-dated sediment cores indicate oysters thrived within two time periods from ~500–2,400 and ~5,600–6,100 cal. years b.p. Sediment and physical property data indicate a changing depositional regime consistent with the oyster chronology. Similar changes in oyster presence are found in local shell midden sites of the Lower Hudson Valley as well as elsewhere along the Atlantic coast, and may reflect climatic controls associated with warm–cool cycles during the Holocene. Oysters flourished during the mid-Holocene warm period, disappeared with the onset of cooler climate at 4,000–5,000 cal. years b.p., and returned during warmer conditions of the late Holocene. The most recent demise of oysters within the Hudson at 500–900 cal. years b.p. may have accompanied the Little Ice Age.

▪ Abstract Decades of seabed mapping, reflection profiling, and seabed sampling reveal that throughout the past two million years the Black Sea was predominantly a freshwater lake interrupted only briefly by saltwater invasions coincident with global sea level highstand. When the exterior ocean lay below the relatively shallow sill of the Bosporus outlet, the Black Sea operated in two modes. As in the neighboring Caspian Sea, a cold climate mode corresponded with an expanded lake and a warm climate mode with a shrunken lake. Thus, during much of the cold glacial Quaternary, the expanded Black Sea's lake spilled into to the Marmara Sea and from there to the Mediterranean. However, in the warm climate mode, after receiving a vast volume of ice sheet meltwater, the shoreline of the shrinking lake contracted to the outer shelf and on a few occasions even beyond the shelf edge. If the confluence of a falling interior lake and a rising global ocean persisted to the moment when the rising ocean penetrated across the dividing sill, it would set the stage for catastrophic flooding. Although recently challenged, the flood hypothesis for the connecting event best fits the full set of observations.

Overbank flow of turbidity currents sweeping through the entrenched Monterey Fan Channel has generated erosional and depositional features along the channel walls and across the adjacent levees. These features, investigated with side-scan sonar, SeaBeam bathymetry, submersibles, and a towed camera sled include fields of sediment waves, overbank channels, gullied walls and terraces, and slump scars. Overbank flow occurs where the channel path is straight, but is accentuated along sharp outside bends. Along straight channel segments sediment waves trend oblique to the channel and are commonly present on the right-hand (when looking downstream) levee adjacent to the channel. Along curved segments of the channel path, large sediment waves, with crests sub-parallel to the channel and with wavelengths reaching 3 km, are present on the outside levee as far as 15 km from the channel. Commonly, a gully is present on the lee side of the sediment wave, near the mid-point of the wave crest. Gullies are the heads of a tributary system of overbank channels, which feed a larger trunk channel on the fan surface.

Remotely operated vehicle (ROV)-based mapping of tectonic features, zones of anomalous reflectivity, and geomorphic targets in Monterey Bay, California, demonstrates the regional abundance of fluid expulsion along the active transform margin between the Pacific and North American plates. Cold seeps—extant communities characterized by chemosynthetic bivalves, bacterial mats, and rare tubeworms—are the surface manifestations of present-day fluid expulsion of sulfide- and methane-rich fluids, whereas slabs, veins, and chimneys of authigenic carbonate represent regions of either dormant methane-rich fluid expulsion, or areas where the present rate of flow is too low to support chemosynthetic fauna. We have found both active and dormant fluid seepage along fault zones, at the surface expression of mud volcanoes, on organic-rich or permeable substrate, and within headless canyons across a wide range of depths within Monterey Bay. The fluid egress at these sites may be driven by a combination of (1) pore-space reduction caused by rapid sedimentation and/or tectonic compaction related to residual Pacific–North America compression, and (2) increased buoyancy due to a decrease in pore-fluid density related to diagenesis and/or catagenesis at depth. Although provocative, the relationship between topographically driven aquifer discharge and sea-floor fluid expulsion remains speculative for Monterey Bay. The widespread distribution of fluid expulsion features controlled by a variety of conduits in Monterey Bay implies that cold seeps may be common features on translational margins.

Seismic stratigraphic analysis of 40 in3 sleeve-gun profiles from the levees of the proximal Northwest Atlantic Mid-Ocean Channel (NAMOC) of the Labrador Sea reveals seven intervals of levee formation that are characterised by packages of low-amplitude reflections separated by a few high-amplitude reflections, except for the second last interval, which shows high-amplitude reflections throughout. The levees are strongly asymmetric with a maximum thickness of 250 m for the western and 150 m for the eastern levee. Levee asymmetry is greatest for the high-amplitude package and nil for the most recent package. The levees prograde south-eastward and overlie a seismic facies of discontinuous high-amplitude reflections that probably represents channel-fill under the channel and submarine braidplain deposits towards the south. The NAMOC levees, which are very stably positioned with

A side-scan sonar survey was conducted of Monterey Canyon and the San Gregorio fault zone, off shore of Monterey Bay. The acoustic character and morphology of the sonar images, enhanced by SeaBeam bathymetry, show the path of the San Gregorio fault zone across the shelf, upper slope, and Monterey Canyon. High backscatter linear features a few kilometers long and 100 to 200 m wide delineate the sea-floor expression of the fault zone on the shelf. Previous studies have shown that brachiopod pavements and carbonate crusts are the source of the lineations backscatter. In Monterey Canyon, the fault zone occurs where the path of the canyon makes a sharp bend from WNW to SSW (1800 m). Here, the fault is marked by NW–SE-trending, high reflectivity lineations that cross the canyon floor between 1850 m and 1900 m. The lineations can be traced to ridges on the northwestern canyon wall where they have ∼15 m of relief. Above the low-relief ridges, bowl-shaped features have been excavated on the canyon wall contributing to the widening of the canyon. We suggest that shear along the San Gregorio fault has led to the formation of the low-relief ridges near the canyon wall and that carbonate crusts, as along the shelf, may be the source of the high backscatter features on the canyon floor. The path of the fault zone across the upper slope is marked by elongated tributary canyons with high backscatter floors and `U'-shaped cross-sectional profiles. Linear features and stepped scarps suggestive of recent crustal movement and mass-wasting, occur on the walls and floors of these canyons. Three magnitude-4 earthquakes have occurred within the last 30 years in the vicinity of the canyons that may have contributed to the observed features. As shown by others, motion along the fault zone has juxtaposed diverse lithologies that outcrop on the canyon walls. Gully morphology and the canyon's drainage patterns have been influenced by the substrate into which the gullies have formed.

Side-scan sonar and seismic data from the hitherto little-known middle to lower reaches of the giant, north-south–extending Northwest Atlantic Mid-Ocean Channel (NAMOC) between lat 53° and 44°30′N reveal a low- to medium-sinuosity and partly straight channel, the course of which is increasingly basement-controlled toward south. Flow restriction by seamounts locally narrowing the channel in the south caused talweg incision by as much as 80 m below the channel floor. Asymmetric levees, resulting from southward-flowing turbidity currents spilling over the channel walls by a mechanism of continuous flow stripping, are remarkably consistent; there is a 30 to 60 m higher western levee, reflecting the effectiveness of the Coriolis force at mid-latitudes. The levees rise 10 to 30 m above the adjacent ocean floor. Consistently lower seismic penetration and more closely spaced reflectors on 3.5 kHz profiles and higher reflectivity on sleeve-gun profiles indicate a higher proportion of sand in the eastern levee. Wash-over fans on the levees formed at sharp channel bends, where deeper, coarser portions of the flows spilled out. Major portions of the turbidity currents that mostly originated off Hudson Strait, however, passed this intermediate channel segment without sedimentation. The down-channel decrease in the difference in height between the western and eastern levees, channel cross-sectional area, and levee height indicate a possible influence of the decrease in the effect of the Coriolis force, flow volume, and/or current speed; separation of the effects of individual variables, however, is currently not possible.

During latest Quaternary glaciation, the Black Sea became a giant freshwater lake. The surface of this lake drew down to levels more than 100 m below its outlet. When the Mediterranean rose to the Bosporus sill at 7,150 yr BP 1 , saltwater poured through this spillway to refill the lake and submerge, catastrophically, more than 100,000 km2 of its exposed continental shelf. The permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of Europe at that time.

High-resolution mapping and reflection profiling reveal a depositional fan on the Black Sea SW shelf fed from the Strait of Istanbul (Bosporus). The fan is constructed with an initial deposit of pebbles mixed with glacial and post-glacial shell debris. The pebbles are identical in their composition to quartzite and gabbro recovered in drill cores from the Bosporus Strait. Directly above the pebble layer are mollusks and foraminifera of Mediterranean provenance dated at 6.9 ka bp (uncorrected). Synchronicity between the onset of fan construction and arrival of Mediterranean fauna suggests an origin linked to the connection of the Black Sea’s lake with the global ocean. The volume of the chaotic interior of the fan is comparable in magnitude to the volume excavated from the floor of the Bosporus Strait. We propose that when the exterior ocean breached the sill of this inlet, it transformed into an outburst of saltwater that gained energy as it enlarged the inlet. Torrents stripped the glacial and post-glacial covering from its pathway and scattered entrained debris in sheets and mounds as far away as the edge of the shelf. Even in areas where the pre-existing cover survived, its eroded surface attests to the passage of flooding water.

Drainage-extraction algorithms traditionally used for extracting river networks and watersheds from gridded land topography are applied to gridded multibeam bathymetry of the mid-California margin. The algorithms are used to automatically map two regional tributary networks of submarine canyons and deepsea channels draining Monterey Bay, the principal conduits of which are Acension and Monterey Canyons. The algorithms reliably map subaqueous drainage areas, but are prone to error in mapping the extent of submarine canyon and channel thalwegs due to operator subjectivity and algorithm limitations. A geomorphic comparison of the Acension and Monterey Canyon networks, with 12 river networks in the continental U.S., illustrates both the potential and weaknesses of using drainage extraction algorithms to analyze sediment pathways in gridded bathymetry.

Dual-frequency side-looking sonars have the potential to be used as remote sensing tools to characterize subaqueous terrains. In one case study of the carbonate-ooze-coated Blake Plateau off-shore of Georgia, U.S.A., the difference in acoustic attenuation for 50 and 20 mm wavelengths (30 and 72 kHz frequency) permits the discrimination of sub-bottom scatterers from seabed surface textural features to reveal patchy regions where a buried hard ground had been pock-marked by karst-like depressions. In a second study of the Upper Hudson River in New York, U.S.A., related to environmental contaminates, the backscatter response at 15 and 3 mm acoustic wavelengths (100 and 500 kHz frequency) serves as a useful proxy for sediment grain size with coarser detritus distinguished from finer sediments. Sand and gravel regions inferred from the backscatter were confirmed by ground truth sampling.

We present the results of a statistical study on the morphological characteristics of abyssal hills recently mapped along the two adjacent segments of the Pacific-Antarctic Ridge at 65(deg)S.

Multibeam bathymetry and seismic reflection profiles of the New Jersey continental slope reveal a series of abandoned and now-buried submarine canyons that have apparently influenced the development of modern canyons. The buried canyons are infilled along nine slope-wide unconformities separating upper-middle Miocene to Pleistocene sediments that thin downslope. Canyons infilled during the Miocene occur in the southwest part of the study area where Miocene sediments are thickest. Other canyons, infilled during the Pleistocene, occur in the northeast part of the study area where Pleistocene sediments are thickest. When followed downslope, each of the buried canyons arrives at a confluence with a modern canyon, usually where the downslope-tapering sediment cover has failed to smooth over the buried canyon, leaving a sea-floor trough. Sea-ward of the confluences, the modern canyons have exhumed the buried canyons and use the older valleys to reach the base of the slope. Re-use of the lower slope reach of the buried canyons appears to have begun when the sea-floor troughs over the buried canyons captured sediment flows initiated along the upper slope and shelf break and confined them to follow the former path of the buried canyons to the base of the slope. The downslope erosion caused by the sediment.flows is proposed to have initiated the modern canyons, which eventually excavated and deepened the former routes of the buried canyons seaward of the sites of sediment flow capture. The occurrence of buried canyons where strata thickens alongslope suggests that infilling of the buried canyons occurred seaward of shelf-edge depocenters. The heightened sediment input to the slope in these regions may have also led to the initiation and growth of modern-day canyons. The temporal relation between modern canyon formation, sediment supply, and sea level, however, remains to be established.

International audience; This paper presents geophysical and core data obtained from several marine geology surveys carried out in the western Black Sea. These data provide a solid record of water-level fluctuation during the Last Glacial Maximum in the Black Sea. A Last Glacial Maximum lowstand wedge evidenced at the shelf edge in Romania, Bulgaria, and Turkey represents the starting point of this record. Then, a first transgressive system is identified as the Danube prodelta built under ~40 m of water depth. The related rise in water level is interpreted to have been caused by an increase in water provided to the Black Sea by the melting of the ice after 18,000 yr B.P., drained by the largest European rivers (Danube, Dnieper, Dniester). Subsequently, the Black Sea lacustrine shelf deposits formed a significant basinward-prograding wedge system, interpreted as forced regression system tracts. On top of these prograding sequences, there is a set of sand dunes that delineates a wave-cut terrace-like feature around the isobath −100 m. The upper part of the last prograding sequence is incised by anastomosed channels that end in the Danube (Viteaz) canyon, which are also built on the lacustrine prograding wedge. Overlying this succession, there is a shelfwide unconformity visible in very high-resolution seismic-reflection profiles and present all over the shelf. A uniform drape of marine sediment above the unconformity is present all over the continental shelf with practically the same thickness over nearby elevations and depressions. This mud drape represents the last stage of the Black Sea water-level fluctuation and is set after the reconnection of this basin with the Mediterranean Sea.

Closely spaced sampling of basalts around the East Pacific Rise, made possible by a new sampling technique, reveals spatial patterns of change in the composition of the sea floor. The patterns demonstrate the scale and magnitude of temporal variability in the basalt chemistry, and suggest that the characteristic length scale of petrological segmentation can vary over time from 15 to >40 km along a single section of ridge. Patterns of basalt composition on the sea floor reveal the history of the ocean ridge with much finer resolution than do sea-floor spreading magnetic anomalies.

A study of the Monterey Canyon and fan was conducted to investigate contemporary sedimentary activity using a camera sled, Alvin dives and Sea-Beam bathymetry. Physical characteristics and plan view morphology of the walls, terraces, thalweg floor and levees of the Monterey Canyon and fan, as well as the gullied and non-gullied regions of the adjacent continental slope have been studied. The canyon floor and fan valley thalweg channel from 2900 to 3500 m exhibited properties indicative of moderate to low energy conditions (weak currents, smoothed sea-bed, deposits of disintegrated kelp, bioturbated mud substrate, fecal pellets, absence of scour). Chemosynthetic communities consisting of clams and a pogonophoran, were found in the fan valley from 3000 to 3600 m. Local areas of rockfalls and slumps from the canyon and fan valley walls were not fresh (sedimented, abundantly colonized by benthic biota). Terraces and levee crests were mud-draped and bedrock exposures on canyon walls were encrusted by benthic organisms. Freshest disturbances were found in gullies on the adjacent continental slope where bedrock was scoured clean of sediment and loose debris. A major submarine slide detached from escarpments on the lower slope, and extends across the fan. The slide surface was mud-draped, hummocky, and contained bedforms with wavelengths up to 150 m and up to 10 m relief. The survey was conducted shortly before the Loma Prieta earthquake (October 17, 1989) that caused substantial ground motion in on-shore regions of Monterey Bay. Any substantial sub-sea disturbances generated by the ensuing earthquake should be discernable from the pre-earthquake state by comparison with the deep-sea photographs and observations.

[1] The fastest spreading center, the East Pacific Rise (EPR), is consistently deeper than most other spreading centers. Its average depth along the ∼5000 km length is ∼3100 m, while the mean depth along the adjacent, slower spreading Pacific-Antarctic Rise (PAR) is ∼2700 m. The deepest spreading center is the ∼4000 m deep, ∼1000 km long Australian Antarctic Discordance (AAD). Analytic and numerical models show that dynamic thinning of asthenosphere can explain the magnitude and wavelength of the depth anomalies along the EPR and AAD. Previous models did not show such significant depth anomalies along spreading centers because the equations used to describe flow of thin viscous asthenosphere were linearized. At the EPR, fast plate divergence thins the asthenosphere by both sequestering it into diverging lithosphere and dragging it with the plates in contrast to the slower spreading but faster migrating PAR. The AAD asthenosphere is starved because of the restriction of asthenospheric flow due to nearby thick continental lithospheric roots combined with a moderately fast spreading rate. A narrow range of asthenospheric properties explains observed depth anomalies for both the AAD and EPR. If the asthenosphere is ∼100°C hotter, and so ∼10 kg/m3 less dense than the underlying asthenosphere, then the model requires an average asthenospheric thickness of ∼250 km and a viscosity of ∼1019 Pa s. Thinner asthenosphere works in the model if it has a lower density and lower viscosity. Although the source of the asthenosphere is not critical to our models, we assume that it is supplied by upwelling of depleted mantle plumes in contrast to enriched plumes that feed oceanic island basalts.

[1] Seafloor bathymetric data acquired with modern swath echo sounders provide coverage for only a small fraction of the global seabed yet are of high value for studies of the dynamic processes of seafloor volcanism, tectonics, mass wasting, and sediment transport that create and shape the undersea landscape. A new method for compilation of global seafloor bathymetry that preserves the native resolution of swath sonars is presented. The Global Multi-Resolution Topography synthesis consists of a hierarchy of tiles with digital elevations and shaded relief imagery spanning nine magnification doublings from pole to pole (http://www.marine-geo.org/portals/gmrt). The compilation is updated and accessible as surveys are contributed, edited, and added to the tiles. Access to the bathymetry tiles is via Web services and with WMS-enabled client applications such as GeoMapApp®, Virtual Ocean, NASA World Wind®, and Google Earth®.

[1] We present a novel explanation for absolute trench-normal motions of slabs surrounding the Pacific. Rapid subduction-zone retreat on the eastern side of the Pacific and slow advance in the west can result from the large-scale asymmetric plate configuration. We use simple fluid dynamics to explain the mechanical background of this hypothesis, and we use the results of a simple finite difference scheme to estimate the effect on trench motion velocities. The hypothesis is based on two key assumptions. First, we follow the concept of plate-scale horizontal counterflow in the asthenosphere driven by accretion of asthenosphere into lithosphere and by plate motion. Second, we assume that horizontally wide slabs without large slab windows drift passively in the mantle flow field and do not retreat as a result of flow around the slab. If the asthenosphere transfers flow-related horizontal shear stress into deeper levels of the mantle, an asymmetry in the plate configuration leads to different net pressure forces on the two slabs and thus affects the retreat behavior. In an ocean with an asymmetric ridge position, the slab of the smaller plate should retreat faster than the slab of the large plate, which may even advance. Also, the domain of a slower moving plate should collapse faster than the domain of the faster plate. Our model explains the counterintuitive negative correlation between slab age and retreat velocity observed in the Pacific. It also accords with the topographic asymmetry of the ridge flanks along the Pacific rise.

Alvin dives and camera tows within the “meander area” of the Monterey and Ascension Fan Valleys have located nine chemosynthetic communities over depths ranging from 3000 to 3600 m over a distance of 55 km. Most of the observed communities consist largely of Calyptogena phaseoliformis, but Solemya (species unknown) and a pogonophoran (genus Polybrachia), have also been identified. The δ13C values (-35.0 to -33.6 per mil) and the presence of APS reductase and ATP sulfurylase in the C. phaseoliformis tissue is consistent with sulfur chemoautotrophy. Two reduced organic matter sources for the H2S are proposed: (1) older beds exposed by the deep erosion (up to 400 m) of the fan valleys and (2) concentrations of anaerobically decomposd organic matter buried in the valley floor.

A description is given of the acquisition and processing of data collected by a class of high-resolution sonar systems, the SeaMARC (seafloor mapping and remote characterization) swath mapping sonars. The SeaMARC system has two basic configurations: deep-towed, which acquires high-resolution backscatter imagery at slow survey speeds, and shallow-towed, which simultaneously acquires lower resolution backscatter and bathymetric information at higher speeds. Processing techniques applied to the data after acquisition are fairly independent of the initial towing configuration and include: compaction of the original data by decimation; radiometric corrections (noise removal, destriping, beam pattern correction, and contrast enhancement); derivation and merging of vehicle navigation with the sonar data; integration of backscatter and bathymetric information; and geometric corrections for plotting data in geographic coordinates. >

Due to the increasing demand for clean water, recreation areas, and healthy ecosystems the management of watersheds has become an issue of increasing importance. This demand has increased the need for detailed inventories of the present state of watersheds and the understanding of related processes. In 1996, the New York State Department of Environmental Conservation (DEC) initiated an effort to map the benthic habitat of the Hudson River Estuary as part of a larger Hudson River Action Plan. This project includes extensive mapping using sidescan sonar, subbottom profiling, single and multi-beam bathymetry, as well as collecting ground truth data with sediment cores, grab samples, and sediment profiling imagery (SPI). The goal of the project is the creation of a comprehensive data set that includes detailed interpretive maps of sediment distribution, grain size, bed forms, and benthic habitats (Ladd et al., 2002).

The Antarctic Multibeam Bathymetry and Geophysical Data Synthesis (AMBS) is a web-accessible data resource for marine geoscience research in the Southern Ocean. The primary focus is to preserve and provide public access to multibeam bathymetry acquired during expeditions of research vessels supported by the U.S. National Science Foundation. Since its inception in 2003, our primary goal has been to facilitate visualization and exploration of the subsea landscape to the full detail of the original data by both specialists and non-specialists. Visualization across a widerange of map scales at high latitudes is made possible by dynamic access to a gridded synthesis in both Polar and Mercator projections. A second goal is to support multi-disciplinary research needs by offering data discovery and visualization of numerous complementary geoscience datasets. In this report, we describe the design objectives and architecture of the AMBS, as well as recent developments regarding data submission and delivery via Web Services. Citation: Carbotte, S.M., W.B.F. Ryan, S. O’Hara, R. Arko, A. Goodwillie, A. Melkonian, R.A. Weissel, and V.L. Ferrini (2007), Antarctic Multibeam Bathymetry and Geophysical Data Synthesis: An On-Line Digital Data Resource for Marine Geoscience Research in the Southern Ocean, in Antarctica: A Keystone in a Changing WorldOnline Proceedings of the 10 ISAES, edited by A.K. Cooper and C.R.Raymond et al., USGS OpenFile Report 2007-1047, Short Research Paper 002,4 p.; doi:10.3133/of2007-1047.srp002.