Showing papers on "Continental margin published in 2010"

Submarine canyons: hotspots of benthic biomass and productivity in the deep sea

Abstract: Submarine canyons are dramatic and widespread topographic features crossing continental and island margins in all oceans. Canyons can be sites of enhanced organic-matter flux and deposition through entrainment of coastal detrital export, dense shelf-water cascade, channelling of resuspended particulate material and focusing of sediment deposition. Despite their unusual ecological characteristics and global distribution along oceanic continental margins, only scattered information is available about the influence of submarine canyons on deep-sea ecosystem structure and productivity. Here, we show that deep-sea canyons such as the Kaikoura Canyon on the eastern New Zealand margin (42°01′ S, 173°03′ E) can sustain enormous biomasses of infaunal megabenthic invertebrates over large areas. Our reported biomass values are 100-fold higher than those previously reported for deep-sea (non-chemosynthetic) habitats below 500 m in the ocean. We also present evidence from deep-sea-towed camera images that areas in the canyon that have the extraordinary benthic biomass also harbour high abundances of macrourid (rattail) fishes likely to be feeding on the macro- and megabenthos. Bottom-trawl catch data also indicate that the Kaikoura Canyon has dramatically higher abundances of benthic-feeding fishes than adjacent slopes. Our results demonstrate that the Kaikoura Canyon is one of the most productive habitats described so far in the deep sea. A new global inventory suggests there are at least 660 submarine canyons worldwide, approximately 100 of which could be biomass hotspots similar to the Kaikoura Canyon. The importance of such deep-sea canyons as potential hotspots of production and commercial fisheries yields merits substantial further study.

Geochemical variations in igneous rocks of the Central Andean orocline (13°S to 18°S): Tracing crustal thickening and magma generation through time and space

Abstract: Compositional variations of Central Andean subduction-related igneous rocks reflect the plate-tectonic evolution of this active continental margin through time and space. In order to address the effect on magmatism of changing subduction geometry and crustal evolution of the upper continental plate during the Andean orogeny, we compiled more than 1500 major- and trace-element data points, and 650 Sr-, 610 Nd-, and 570 Pb-isotopic analyses of Mesozoic-Cenozoic (190–0 Ma) magmatic rocks in southern Peru and northern Chile (Central Andean orocline), mostly from new data and the literature. This data set documents compositional variations of magmas since Jurassic time, with a focus on the Neogene period, when major crustal thickening developed and its influence on magma composition was most pronounced. We relate the observed variations in Sr/Y, La/Yb, La/Sm, Sm/Yb, and Dy/Yb ratios, as well as in Sr-, Nd-, and Pb-isotopic ratios, to the crustal structure and evolution of the Central Andean orocline. In particular, the evolution of Dy/Yb and Sm/Yb ratios, which track the presence of the higher-pressure minerals amphibole and garnet, respectively, in the lower crust, documents that crustal thickness has grown through time. Spatial variations in trace elements and isotopic ratios further suggest that crustal domains of distinct composition and age have influenced magma composition through some assimilation. The crustal input in Quaternary magmas is quantified to have been between 7% and 18% by simple two-components mixing. When comparing our geochemical data set to the geological record of uplift and crustal thickening, we observe a correlation between the composition of magmatic rocks and the progression of Andean orogeny. In particular, our results support the interpretation that major crustal thickening and uplift were initiated in the mid-Oligocene (30 Ma) and that crustal thickness has kept increasing until present day. Our data do not support delamination as a general cause for major late Miocene uplift in the Central Andes and instead favor continued crustal thickening.

Paleozoic multiple accretionary and collisional processes of the Beishan orogenic collage

Abstract: The Beishan orogenic collage is located in the southernmost part of the Altaids, and connects the Southern Tien Shan suture to the west with the Solonker suture to the east. The orogen was previously regarded as early Paleozoic in age in contrast to the surrounding southern Altaid collages, which are Late Paleozoic or even Early Mesozoic. This paper reviews the tectonic units of the Beishan orogen, which along a north-south traverse consists of several arcs and ophiolitic melanges. These tectonic units were thrust imbricated and overprinted by strike-slip faulting during Permian-Triassic times, and the youngest strata involved in the deformation are Permian. Stitching plutons are Late Permian in age. Peaks of magmatic-metamorphic-tectonic activity, and paleomagnetic and paleogeographic data indicate that the Beishan orogenic collage evolved by development of several, Early to Mid-Paleozoic arcs in different parts of the Paleoasian Ocean. The Late Paleozoic collage is characterized by three active continental margins or island arcs that are separated by two ophiolitic melanges. The northernmost active margin is represented by the Queershan arc, which may have lasted until the Permian. The Shibanshan unit is the southernmost, subduction-related continental arc along the northern margin of the Dunhuang block. In the Late Carboniferous to Permian the eastern end (promontory) of the Tarim Craton probably collided with the Chinese eastern Tien Shan arc, forming a new active continental margin, which interacted with the Beishan Late Paleozoic archipelago, generating a complicated subduction-accretionary orogen; this is suggested to be one of the last phases in the development of the long-lived Altaid accretionary orogenesis. The new model for this orogen bridges the gap between the western and eastern ends of the southern Altaids. The modern Timor-Australia collision zone with its many surrounding arcs is an appropriate analog for the Altaids in the Late Paleozoic.

Carbon and nutrient fluxes in continental margins : a global synthesis

Abstract: Perspectives and Regional Syntheses.- Biogeochemistry of Continental Margins in a Global Context.- Eastern Boundary Current Systems.- Western Boundary Currents.- Indian Ocean Margins.- Subpolar Margins.- Polar Margins.- Marginal Seas.- Tropical Margins.- Arising Issues and New Approaches.- Examining Human Impacts on Global Biogeochemical Cycling Via the Coastal Zone and Ocean Margins.- Biogeochemical Transformations of Silicon Along the Land-Ocean Continuum and Implications for the Global Carbon Cycle1.- Submarine Groundwater Discharge (SGD) and Associated Nutrient Fluxes to the Coastal Ocean.- Coupled Circulation/Biogeochemical Models to Estimate Carbon Flux1.- Cross-Boundary Fluxes and Global Synthesis.- Cross-Boundary Exchanges of Carbon and Nitrogen in Continental Margins1.- Carbon-Nitrogen-Phosphorus Fluxes in the Coastal Zone: The LOICZ Approach to Global Assessment.- Sediment and Carbon Accumulation on Continental Shelves1.- Global Synthesis1.

Submarine fans at all sea-level stands: Tectono-morphologic and climatic controls on terrigenous sediment delivery to the deep sea

Abstract: Early models of stratigraphic sequence development across continental margins predicted terrigenous sediment delivery to the deep sea principally during periods of sea-level fall and lowstand. However, subsequent models acknowledged caveats to these early predictions. We employ a global database of millennial-scale continental-margin deep-sea deposition rates, activities of canyon-channel systems, and episodes of submarine-fan growth since 35 ka to assess the timing of terrigenous sediment delivery to the deep sea. As predicted by the early models, the majority of continental-margin deep-sea deposition occurred during periods of marine transgression and lowstand of sea level. However, deep-sea deposition is shown to have occurred at all sea-level states, and some deep-sea fans predominantly grew during periods of sea-level highstand. Terrigenous sediment delivery to the deep sea depends on factors such as tectono-morphologic character of the margin (e.g., narrow shelves) and climatic forcings (e.g., subglacial meltwater and monsoonal pulses). A fundamental understanding of the tectonic and climatic forcings inherent to a continental margin and its terrestrial sediment source area is essential to accurately predict timing and magnitude of deep-sea deposition and place it in the context of sequence stratigraphy.

Sinistral to Normal Faulting along the Tan‐Lu Fault Zone: Evidence for Geodynamic Switching of the East China Continental Margin

Abstract: The Tan‐Lu fault zone (TLFZ) along the East China continental margin (ECCM) experienced a change from sinistral to normal faulting in the late Mesozoic. Thirty‐four laser ablation (LA)‐ICPMS zircon U‐Pb dates for plutons and volcanic rocks along the TLFZ indicate that extension‐related magmatism started as early as 136 Ma. The development of pre‐eruption rift basins along the TLFZ during the earliest Early Cretaceous further constrains the onset time of the Tan‐Lu normal faulting to the beginning of Early Cretaceous (ca. 145 Ma). Association of extensive rifts, metamorphic core complexes, and magmatism along the margin with the Tan‐Lu normal faulting suggests an Early Cretaceous extensional regime for the ECCM that also started at the beginning of the Early Cretaceous, about 145 Ma. An undeformed granite dike that intrudes the sinistral ductile shear zone yields an LA‐ICPMS zircon U‐Pb age of 122 Ma. Seven 40Ar/39Ar plateau ages of mica samples from mylonites in the Tan‐Lu sinistral ductile shear...

Large multidecadal salinity trends near the Pacific-Antarctic Continental margin.

Abstract: Ocean temperature and salinity measurements on and near the Antarctic continental shelf in the southwest Pacific sector are evaluated for evidence of temporal change. Shelf water in the southwest Ross Sea has declined in salinity by 0.03 decade−1 from 1958 to 2008, while its temperatures have increased in proportion to the influence of salinity on the sea surface freezing point. Modified deep-water intrusions that reach the central Ross Ice Shelf have freshened at a similar rate and cooled by ∼0.5°C since the late 1970s. Salinity has decreased by 0.08 decade−1 in the westward coastal and slope front currents, consistent with increased melting of continental ice upstream in the Amundsen Sea. Overturning of those near-surface waters during winter sea ice formation and mixing across the slope front is sufficient to account for the 5-decade shelf water salinity change. A strong correlation between the freshening and change in the southern annular mode index suggests a link with the large-scale atmosp...

Yin and yang of continental crust creation and destruction by plate tectonic processes

Abstract: Earth's continental crust today is both created and destroyed by plate tectonic processes, a balance that is encapsulated by the traditional Chinese concept of yin–yang, whereby dualities act in concert as well as in opposition. Yin–yang conceptualizations of crustal growth and destruction are mostly related to plate tectonics; both occur mostly at subduction zones, by arc magmatic creation and by subduction removal. Crust is also created and destroyed by processes unrelated to plate tectonics, including losses by lower crust foundering and additions at hotspots. At present, creation and destruction of continental crust is either in balance (∼3.2 km3/year, or 3.2 AU) or more crust is being destroyed than created; the uncertainty comes from unknown deep losses of continental crust at collision zones and due to lower crustal foundering. The yin–yang creation–destruction balance changes over a supercontinent cycle, with crustal growth being greatest during supercontinent break-up due to high magmatic flux at...

Structural constraints on the evolution of the Central Asian Orogenic Belt in SW Mongolia

Abstract: We provide a detailed description of the structures along a 300 km long and 50 km wide transect across the Central Asian Orogenic Belt (CAOB) in southwestern Mongolia, covering the Precambrian Dzabkhan continental domain with overthrust Neoproterozoic ophiolites in the north (Lake Zone), a Silurian-Devonian passive margin association (Gobi-Altai Zone) and oceanic domain (Trans-Altai Zone) in the center, and a continental area (South Gobi Zone) in the south. Structural analysis suggests late Cambrian collapse of the thickened Lake Zone continental crust, leading to stretching of the lithosphere and followed by Silurian-Devonian formation of oceanic crust in the Trans-Altai domain. Subsequent emplacement of Devonian-Carboniferous and late Carboniferous magmatic arcs occurred on the Gobi-Altai and South Gobi Zone crusts, respectively, during E-W shortening. Finally, the entire system was affected by N-S convergence from the Permian to Jurassic, leading to heterogeneous shortening of the orogenic domain. The model best fitting these observations is one of generalized westward drift of the Tuva-Mongol-Dzabkhan-Baydrag ribbon continents during the Silurian-Devonian, associated with westward-subduction of the Mongol-Okhotsk Ocean and sequential growth of syn-convergent magmatic arcs. Back-arc basins opened during this period in the area of the western Paleoasian Ocean. The present-day shape of the CAOB in southern Mongolia was probably formed during Permian to Mesozoic anticlockwise rotation and folding of the Tuva-Mongol-Dzabkhan-Baydrag continental ribbons, combined with a strike-slip (transpressional) reactivation of ancient transform boundaries in the Paleoasian oceanic domain. All continental and oceanic crustal domains were reactivated and intensely deformed during this convergence in a style controlled by crustal rheology and a heterogeneous Permian magmatic-thermal input. The sequence of tectonic events is tested against published paleomagnetic data, paleogeographic reconstructions and tectonic models, leading to a revised model for the accretion of juvenile crust to a continental margin in the CAOB of southern Mongolia.

Geology of the Norwegian Continental Shelf

Abstract: In the preceding chapters we have included only a few regional examples and case studies because of space limitations. The present chapter will, however, provide some examples. The North Sea and other parts of the Norwegian continental shelf contain several different petroleum provinces which can illustrate some of the general principles of petroleum geology and geophysics. The geological evolution of these sedimentary basins provides a necessary background to understand the distribution of source rocks and the timing of petroleum migration. The structural history of rifted basins, passive margins and also uplifted basins such as the Barents Sea is critical to the trapping of oil and gas. These basins are very well documented by seismic and well data.

India–Asia convergence driven by the subduction of the Greater Indian continent

Abstract: The most spectacular example of plate convergence on Earth was the motion of the Indian plate towards Eurasia, and the subsequent collision. Density estimates of the Greater Indian continent, after its upper crust is scraped off at the Himalayan front, suggest that this continental plate is readily subductable, potentially explaining why the convergence did not halt on collision. The most spectacular example of a plate convergence event on Earth is the motion of the Indian plate towards Eurasia at speeds in excess of 18 cm yr−1 (ref. 1), and the subsequent collision. Continental buoyancy usually stalls subduction shortly after collision, as is seen in most sections of the Alpine–Himalayan chain. However, in the Indian section of this chain, plate velocities were merely reduced by a factor of about three when the Indian continental margin impinged on the Eurasian trench about 50 million years ago. Plate convergence, accompanied by Eurasian indentation, persisted throughout the Cenozoic era1,2,3, suggesting that the driving forces of convergence did not vanish on continental collision. Here we estimate the density of the Greater Indian continent, after its upper crust is scraped off at the Himalayan front, and find that the continental plate is readily subductable. Using numerical models, we show that subduction of such a dense continent reduces convergence by a factor similar to that observed. In addition, an imbalance between ridge push and slab pull can develop and cause trench advance and indentation. We conclude that the subduction of the dense Indian continental slab provides a significant driving force for the current India–Asia convergence and explains the documented evolution of plate velocities following continental collision.

Subduction initiation at passive margins: Numerical modeling

Abstract: [1] Subduction is a key process for terrestrial plate tectonics, but its initiation is still not entirely understood. In particular, despite the abundance of both passive and active continental margins on Earth, no obvious cases of transition between them have been identified so far. It has been shown that at most passive margins, elastic and frictional forces exceed gravitational instability and ridge-push forces, which precludes subduction initiation. Therefore additional factors are needed to start subduction there. We investigated numerically in two dimensions factors controlling passive margins' stability such as age of the oceanic plate, thickness of the continental lithosphere and crust, and density contrast between subcontinental and suboceanic lithospheric mantles. Our numerical experiments show that three subsequent tectonic regimes can develop at a passive margin: (1) stable margin, (2) overthrusting, and (3) subduction. Transition from stable margin to the overthrusting regime is mainly controlled by ductile strength of the lower continental crust. Further transition from overthrusting to the subduction regime is governed by the ductile strength of the subcontinental lithospheric mantle and its chemical density contrast with the suboceanic lithospheric mantle. Our experiments also demonstrate that the age of the oceanic plate is a factor of secondary importance for subduction initiation and only plays a role if other parameters are of critical values. Favorable conditions for subduction initiation thus correspond to passive margins where chemically buoyant (depleted) continental lithosphere becomes thin and hot (Moho temperature >660°C). This situation can be occasionally created by superimposed external processes such as rifting and/or thermal-chemical plume activity.

High‐pressure metasediments in central Turkey: Constraints on the Neotethyan closure history

Abstract: [1] The distribution of oceanic domains and continental blocks in Central Anatolia remains a challenge in understanding the Alpine geodynamic evolution of the Tethys realm. The consumption of a Neotethys oceanic branch at the Mesozoic-Cenozoic boundary welded the Central Anatolian Crystalline Complex in central Turkey and the Anatolide-Tauride Block in western Turkey, with the northerly Eurasian margin. Whether those two regions constituted a single or two distinct continental masses is still matter of debate. High-pressure metamorphism has been locally evidenced in the Afyon Zone, which was, however, defined as a greenschist-facies metamorphic zone of the Anatolide-Tauride Block. Since the Afyon Zone composes a metamorphic equivalent of a continental margin exposed far south of the Izmir-Ankara suture zone, this encouraged us to reevaluate its metamorphic evolution in order to better understand the relation between western and central Turkey. Our investigations reveal that the high-pressure minerals Fe-Mg-carpholite and glaucophane are present in the entire Afyon Zone, which we reconsider as a blueschist-facies zone. We additionally present a tectonic reconstruction, stripping off the postcollisional tectonics. It reveals that today's bending of the high-pressure belt is consistent with an Eocene collision of the Anatolide-Tauride Block around the southern edge of the Central Anatolian Crystalline Complex. We argue that the Central Anatolian Crystalline Complex and the Anatolide-Tauride Block were two distinct continental masses separated by a Neotethyan oceanic stripe, the closure of which engendered subduction-related metamorphism in the latter and arc volcanism and high-grade metamorphism in the former by late Cretaceous to early Cenozoic.

The roles of habitat heterogeneity in generating and maintaining biodiversity on continental margins: an introduction

Abstract: (introduction to Special Issue: The roles of habitat heterogeneity in generating and maintaining biodiversity on continental margins A Contribution to the Census of Marine Life)

Organic matter in sediments of canyons and open slopes of the Portuguese, Catalan, Southern Adriatic and Cretan Sea margins

Abstract: We describe the quantitative and compositional (phytopigment, protein, carbohydrate and lipid) patterns of sedimentary organic matter along bathymetric gradients in seven submarine canyons and adjacent open slopes located at four European regions: one along the NE Atlantic and three along the Mediterranean continental margins. The investigated areas are distributed along a putative longitudinal gradient of decreasing primary production from the Portuguese (northeastern Atlantic Ocean), to the Catalan (western Mediterranean Sea), Southern Adriatic (central Mediterranean Sea) and Southern Cretan (eastern Mediterranean Sea) margins. Sediment concentrations of organic matter differed significantly between the Portuguese margin and the Mediterranean regions and also from one study area to the other within the Mediterranean Sea. Differences in quantity and composition of sediment organic matter between canyons and open slopes were limited and significant only in the eutrophic Portuguese margin, where the differences were as large as those observed between regions (i.e. at the mesoscale). These results suggest that the overall trophic status of deep margin sediments is controlled mostly by the primary productivity of the overlying waters rather than by the local topography. Moreover, we also report that the quantity and nutritional quality of sediment organic matter in canyons and adjacent open slopes do not show any consistent depth-related pattern. Only the Nazare and Cascais canyons in the Portuguese margin, at depths deeper than 500 m, displayed a significant accumulation of labile organic matter. The results of our study underline the need of further investigations of deep margins through sampling strategies accounting for adequate temporal and spatial scales of variability.

Tectonic inheritance and Pliocene‐Pleistocene inversion of the Algerian margin around Algiers: Insights from multibeam and seismic reflection data

Abstract: [1] The Algerian margin has originated from the opening of the Algerian basin about 25–30 Ma ago The central margin provides evidence for large-scale normal faults of Oligo-Miocene age, whereas transcurrent tectonics characterizes the western margin A set of NW–SE oriented dextral transform faults was active during basin opening and divided the 600 km long central margin into segments of ∼120–150 km The upper Miocene, Plio-Quaternary, and present-day tectonic setting is, however, compressional and supports the occurrence of a margin inversion, a process still poorly documented worldwide We show that the central Algerian margin represents a rare example of inverted margin, where the process of subduction inception is particularly well expressed and helps understand how extensional and transtensive structures are involved in margin shortening Using multibeam bathymetry and multichannel seismic reflection sections from the MARADJA 2003 and 2005 cruises, we evidence Pliocene-Pleistocene shortening with contrasting styles along the margin between west (Khayr Al Din bank) and east (Boumerdes-Dellys margin) of Algiers Pre-Miocene structures such as basement highs and transform faults appear to control changes of the deformation pattern along this part of the margin, resulting in different widths, geometries, and relative positions of folds and faults Plio-Quaternary and active blind thrust faults do not reuse Oligo-Miocene normal and transform faults during inversion, but instead grow within the continental margin (as testified for instance by the 21 May 2003 Mw 68 Boumerdes-Zemmouri earthquake), at the foot of the continental slope and at the northern sides of basement highs interpreted as stretched continental blocks of the rifted margin The inherited structures of the margin appear, therefore, to determine this deformation pattern and ultimately the earthquake and tsunami sizes offshore The complex geometry of the fault system along the Algerian margin suggests a process of initiation of subduction in its central and eastern parts

New aeromagnetic and gravity compilations from Norway and adjacent areas: methods and applications

Abstract: The Geological Survey of Norway (NGU) has produced new aeromagnetic and gravity maps from Norway and adjacent areas, compiled from ground, airborne and satellite data. Petrophysical measurements on core samples, hand specimens and on in situ bedrock exposures are essential for the interpretation of these maps. Onshore, the most prominent gravity and magnetic anomalies are attributed to lower crustal rocks that have been brought closer to the surface. The asymmetry of the gravity anomalies along the Lapland Granulite Belt and Kongsberg–Bamble Complex, combined with the steep gradient, points to the overthrusted high-density granulites as being the main source of the observed anomalies. The Kongsberg–Bamble anomaly can be traced southwards through the Kattegat to southern Sweden. This concept of gravity field modelling can also be applied to the Mid-Norwegian continental shelf and could partially explain the observed high-density rocks occurring below the More and Voring basins and in the Lofoten area. Extrapolations of Late-Caledonian detachment structures occurring on the mainland can be traced on aeromagnetic and gravimetric images towards the NW across the continental margin. Subcropping Late Palaeozoic to Cenozoic sedimentary units along the mid-Norwegian coast produce a conspicuous magnetic anomaly pattern. The asymmetry of the low-amplitude anomalies, with a steep gradient and a negative anomaly to the east and a gentler gradient to the west, relates the anomalies to gently westward dipping strata. Recent aeromagnetic surveys in the Barents Sea have revealed negative magnetic anomalies associated with shallow salt diapirs. Buried Quaternary channels partly filled with gravel and boulders of crystalline rocks generate magnetic anomalies in the North Sea. The new maps also show that the opening of the Norwegian–Greenland Sea occurred along stable continental margins without offsets across minor fracture zones, or involving jumps in the spreading axis. A triple junction formed at 48 Ma between the Lofoten and Norway Basins.

Bathymetric zonation of deep-sea macrofauna in relation to export of surface phytoplankton production

Abstract: Macrobenthos of the deep, northern Gulf of Mexico (GoM) was sampled with box cores (0.2 m 2 ) along multiple cross-depth transects extending from depths of 200 m to the maximum depth of the basin at 3700 m. Bathy- metric (depth) zonation of the macrofaunal community was documented for 6 major taxa (a total of 957 species) on the basis of shared species among geographic locations; 4 major depth zones were identified, with the 2 intermediate- depth zones being divided into east and west subzones. Change of faunal composition with depth reflects an underlying continuum of species replacements without dis- tinct boundaries. The zonal patterns correlated with depth and detrital particulate organic carbon (POC) export flux estimated from remotely-sensed phytoplankton pigment concentrations in the surface water. The Mississippi River and its associated mesoscale eddies, submarine canyon, and deep sediment fan appear to influence the horizontal zonation pattern through export of organic carbon from the ocean surface and the adjacent continental margin. On the local scale, near-bottom currents may shape the zonation pattern by altering sediment grain size, food availability, and larval dispersal. This study suggests a macroecological relationship between depth, export POC flux, and zona- tion; parsimonious zonal thresholds need to be tested independently for other continental margin ecosystems.

Plate Tectonics: Continental Drift and Mountain Building

Abstract: 1. Contractional theory, continental drift and plate tectonics,- 2 Plate movements and their geometric relationships,- 3. Continental graben structures,- 4. Passive continental margins and abyssal plains,- 5. Mid-ocean ridges,- 6. Hot spots,- 7. Subduction zones, island arcs and active continental maragins,- 8. Transform faults,- 9. Terranes,- 10. Early Precambrian plate tectonics,- 11. Plate tectonics and mountain building,- 12. Old orogens,- 13. Young orogens - the Earth's loftiest places.

Origin and Extent of Fresh Paleowaters on the Atlantic Continental Shelf, USA

Abstract: While the existence of relatively fresh groundwater sequestered within permeable, porous sediments beneath the Atlantic continental shelf of North and South America has been known for some time, these waters have never been assessed as a potential resource. This fresh water was likely emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and by elevated recharge in areas overrun by the Laurentide ice sheet at high latitudes. To test this hypothesis, we present results from a high-resolution paleohydrologic model of groundwater flow, heat and solute transport, ice sheet loading, and sea level fluctuations for the continental shelf from New Jersey to Maine over the last 2 million years. Our analysis suggests that the presence of fresh to brackish water within shallow Miocene sands more than 100 km offshore of New Jersey was facilitated by discharge of submarine springs along Baltimore and Hudson Canyons where these shallow aquifers crop out. Recharge rates four times modern levels were computed for portions of New England’s continental shelf that were overrun by the Laurentide ice sheet during the last glacial maximum. We estimate the volume of emplaced Pleistocene continental shelf fresh water (less than 1 ppt) to be 1300 km 3 in New England. We also present estimates of continental shelf fresh water resources for the U.S. Atlantic eastern seaboard (10 4 km 3 ) and passive margins globally (3 × 10 5 km 3 ). The simulation results support the hypothesis that offshore fresh water is a potentially valuable, albeit nonrenewable resource for coastal megacities faced with growing water shortages.