North Atlantic

We present palaeoenvironmental, geomorphological, archaeological, and place-name data which allow a holistic assessment of the history of landscape change on Sandoy, Faroe Islands, especially in terms of the changes that occurred in response to the colonization of the island by humans. In contrast to other situations in the North Atlantic region, there is considerable continuity in the patterns and processes of landscape evolution across the initial

For the first time in the Faroe Islands, the paleoecological content of an early Norse farm has been sampled comprehensively in an effort to understand how it functioned and its relationship to the landscape in which it was located. Organic deposits indicate an increase in species diversity at the time of settlement, including the introduction of several new species. Plant resources from various areas of the treeless landscape were exploited and farm buildings contained suites of synanthropic insects dominated by those associated with accumulations of decaying plant debris. Potential fuels included wood, peat, dung, and seaweed. Insect faunas lacked both ectoparasites and a significant foul beetle component. This may be a reflection of animal husbandry, with stock not being stalled over winter in the farm buildings examined, or an absence of wool-processing in the buildings. Results compare well with other sites in the North Atlantic and argue for the consistent nature of the Norse farming economy across the region.

For the first time in the Faroe Islands, the paleoecological content of an early Norse farm has been sampled comprehensively in an effort to understand how it functioned and its relationship to the landscape in which it was located. Organic deposits indicate an increase in species diversity at the time of settlement, including the introduction of several new species. Plant resources from various areas of the treeless landscape were exploited and farm buildings contained suites of synanthropic insects dominated by those associated with accumulations of decaying plant debris. Potential fuels included wood, peat, dung, and seaweed. Insect faunas lacked both ectoparasites and a significant foul beetle component. This may be a reflection of animal husbandry, with stock not being stalled over winter in the farm buildings examined, or an absence of wool-processing in the buildings. Results compare well with other sites in the North Atlantic and argue for the consistent nature of the Norse farming economy across the region.

Oxygen-18 (18O) values of sediment from the Wilson Creek Formation, Mono Basin, California, indicate three scales of temporal variation (Dansgaard–Oeschger, Heinrich, and Milankovitch) in the hydrologic balance of Mono Lake between 35,400 and 12,90014C yr B.P. During this interval, Mono Lake experienced four lowstands each lasting from 1000 to 2000 yr. The youngest lowstand, which occurred between 15,500 and 14,00014C yr B.P., was nearly synchronous with a desiccation of Owens Lake, California. Paleomagnetic secular variation (PSV) data indicate that three of four persistent lowstands occurred at the same times as Heinrich events H1, H2, and H4.18O data indicate the two highest lake levels occurred ∼18,000 and ∼13,10014C yr B.P., corresponding to passages of the mean position of the polar jet stream over the Mono Basin. Extremely low values of total inorganic carbon between 26,000 and 14,00014C yr B.P. indicate glacial activity, corresponding to a time when summer insolation was much reduced.

Variations in the Atlantic meridional overturning circulation (AMOC) between 1979 and 2008 are documented using the operational ocean analysis, the Global Ocean Data Assimilation System (GODAS), at the National Centers for Climate Prediction (NCEP). The maximum AMOC at 40°N is about 16 Sv in average with peak-to-peak variability of 3-4 Sv. The AMOC variations are dominated by an upward trend from 1980 to 1995, and a downward trend from 1995 to 2008. The maximum AMOC at 26.5°N is slightly weaker than hydrographic estimates and observations from mooring array. The dominant variability of the AMOC in 20°-65°N (the first EOF, 51% variance) is highly correlated with that in the subsurface temperature (the first EOF, 33% variance), and therefore, with density (the first EOF, 25% variance) in the North Atlantic, and is consistent with the observational estimates based on the World Ocean Database 2005. The dominant variabilities of AMOC and subsurface temperature are also analyzed in the context of possible links with the net surface heat flux, deep convection, western boundary current, and subpolar gyre. Variation in the net surface heat flux is further linked to the North Atlantic Oscillation (NAO) index which is found to lead AMOC variations by about 5 years. Our results indicate that AMOC variations can be documented based on an ocean analysis system such as GODAS.

The algal-derived compound dimethylsulfoniopropionate (DMSP), which is the precursor of the climatically active gas dimethylsulfide, is potentially an important source of carbon and sulfur to marine bacterioplankton. Currently, bacteria of the Roseobacter clade, a subgroup of ␣-proteobacteria, are hypothesized to be the key participants in the metabolism of DMSP. To test this hypothesis, we used a combination of microautoradiography and fluorescence in situ hybridization (Micro-FISH) to identify the bacteria assimilating 35 S DMSP in the Gulf of Mexico, the Gulf of Maine, and the Sargasso Sea. On average, half of the bacterial community assimilated DMSP in these environments. Members of the ␣-proteobacteria dominated DMSP assimilation, accounting for 35-40% of bacteria assimilating DMSP. Cytophaga-like bacteria and ␥-proteobacteria each accounted for 15-30% of DMSP-assimilating cells. The ␣-proteobacteria accounted for a greater fraction of the DMSP-assimilating community than expected based on their overall abundance, whereas Cytophaga-like bacteria were typically underrepresented in the DMSP-assimilating community. Members of the Roseobacter clade assimilated more DMSP on a per-cell basis than any other group, but they did not account for most of the DMSP assimilation, nor were they always present even when DMSP turnover was high. These results indicate that the biogeochemical flux of dissolved DMSP is mediated by a large and diverse group of heterotrophic bacteria.

The late Quaternary sedimentary history of the continental margin off Portugal was reconstructed from sediment gravity cores. Hemipelagic sedimentation (lithofacies A) was dominant during glacial times. It was interrupted periodically by deposition of shelf-and upper-slope-derived silty and sandy terrigenous material by dilute turbidity currents (lithofacies B and C), ice-rafted debris during distinct periods of breakdown of North Atlantic ice sheets (Heinrich events, lithofacies D) and large amounts of pteropods (lithofacies F). Settling of biogenic particulate material (lithofacies E) prevailed during the Holocene, when sea level and sea surface temperatures were high and terrigenous shelf-input was low.

The Iceland-Scotland Overflow Water (ISOW) is one of the two main dense overflows entering the subpolar North Atlantic across the Greenland-Scotland Ridge. The downstream modification of ISOW as it spreads west and transforms into the Northeast Atlantic Deep Water (NEADW) has not been fully described in either space or time. The figure addresses both issues by showing the salinity of the ISOW/NEADW (salinity maximum) core from the Iceland Basin to the Labrador Sea for two extreme time periods: warm and saline 1964-1972 (Panel A) and cold and fresh 1995 -1997. The complexity of the watermass interactions that modify the spreading plume en route is clear from this figure. NEADW rapidly increases in thickness (not shown) and freshens by $0.03 as its spreading plume rounds the snout of the Reykjanes Ridge to enter the Irminger Sea. This provides a clear indication of an increase in the entrainment and influence of the Labrador Sea Water (LSW) west of the Ridge. The decline in the NEADW salinity (by $0.02) continues along the western boundary where a thinning NEADW plume passes south between the low-salinity LSW and Denmark Strait Overflow Water (DSOW); the freshening influence of DSOW is now adding to that of LSW. Some renewed salinification of NEADW evidently takes place in the Newfoundland Basin. This can be attributed to a fraction of saltier NEADW traveling directly from the Reykjanes Ridge to the Newfoundland Basin without entering the Labrador Sea, and then mixing with the fresher NEADW plume arriving from the Labrador Sea. This mixing process is facilitated by the Newfoundland Basin anticyclonic gyre, known as the Mann Eddy. The Mann Eddy spins both NEADW and DSOW (which resides below NEADW), forming a local recirculation of these waters in the Basin.

Although the Last Interglacial (LIG) is often considered as a possible analogue for future climate in high latitudes, its precise climate evolution and associated causes remain uncertain. Here we compile high-resolution marine sediment records from the North Atlantic, Labrador Sea, Norwegian Sea and the Southern Ocean. We document a delay in the establishment of peak interglacial conditions in the North Atlantic, Labrador and Norwegian Seas as compared to the Southern Ocean. In particular, we observe a persistent iceberg melting at high northern latitudes at the beginning of the LIG. It is associated with (1) colder and fresher surfacewater conditions in the North Atlantic, Labrador and Norwegian Seas, and (2) a weaker ventilation of North Atlantic deep waters during the early LIG (129-125 ka) compared to the late LIG. Results from an ocean-atmosphere coupled model with insolation as a sole forcing for three key periods of the LIG show warmer North Atlantic surface waters and stronger Atlantic overturning during the early LIG (126 ka) than the late LIG (122 ka). Hence, insolation variations alone do not explain the delay in peak interglacial conditions observed at high northern latitudes. Additionally, we consider an idealized meltwater scenario at 126 ka where the freshwater input is interactively computed in response to the high boreal summer insolation. The model simulates colder, fresher North Atlantic surface waters and weaker Atlantic overturning during the early LIG (126 ka) compared to the late LIG (122 ka). This result suggests that both insolation and ice sheet melting have to be considered to reproduce the climatic pattern that we identify during the early LIG. Our modeldata comparison also reveals a number of limitations and reinforces the need for further detailed investigations using coupled climate-ice sheet models and transient simulations.

We present the results of a seismic survey performed around the Kolbeinsey Ridge, North Atlantic. The seismic data were acquired along three profiles: on the ridge axis (L1), 12 km off-ridge (L2), and perpendicular to the ridge axis (L3). The models indicate lower velocity beneath the ridge axis than in the off-ridge area. Along L3, we obtain velocities of 2.6-3.6 km/s (upper crust), 4.8-6.0 km/s (middle crust), and 6.6-6.9 km/s (lower crust) beneath the ridge axis, while at more than 12 km off-ridge, the model shows velocities of 3.6-4.6 km/s (upper crust), 5.6-6.4 km/s (middle crust), and 6.9-7.2 km/s (lower crust). The model of L1 also shows significant lateral variation along the axis in the lower crust. The velocity in the lower crust decreases to 6.3 km/s in the southwestern part of LI, where the Moho depth decreases to 7.2 km. The low-velocity structure beneath the ridge axis is interpreted to be due to high porosity in the upper crust •ind to higher temperatures, as well as a few percent porosity, in the middle and lower crustal material. According to this interpretation, the crustal model of L3 implies that the cracks have been sealed and the temperatures have decreased to normal in 1.2-m.y-o!d crust. The anomalous low velocity structure along L1 can be interpreted as related to the most recent injection processes or a thermal influence of the Spar Fracture Zone situated 50 km south of the profile. 1976; Rosendahl et al., 1976; Lewis and Gatmany, 1982; Bratt and Solomon, 1984; McClain et al., 1985; Burnett et al., 1989; Harding et al., 1989; Toomey et al., 1990; Vera et al., 1990] and the Mid-Atlantic Ridge (MAR) [e.g., Whirmarsh, 1975; Fowler, 1976, 1978; Steinmetz et aL, !977; Fowler and Keen, 1979; Purdy and Detrick, 1986], which are classified as a fast and slow spreading ridge, respectively [e.g., Macdonald, 1982]. These seismic studies found both significant differences and similarities between fast and slow spreading Paper number 96JB03487. 0!48.0227/97/96JB.03487509.00 ridges. For example, at fast spreading ridges, evidence of a crustal velocity inversion with depth ilow-velocity layer), implying the presence of a magma chamber is found, while most studies show no evidence of a velocity inversion with depth at slow spreading ridges [Macdonald, !982]. As an example of similarity, White et al. [1992] showed no resolvable difference in crustal thickness between crust

This paper describes the methods employed in a pilot archival tagging study on albacore tuna onboard an Irish trolling vessel in North Bay of Biscay during July 2005. The study aims to obtain an estimate of recovery rates for fish tagged with 'dummy' archival tags in order to assess the feasibility of conducting an archival tagging study for albacore tuna in the North Atlantic. A total of 199 fish were tagged and released during the first phase of this study.

We here report the discovery of unusual distributions of long-chain alkenones (C,,+) in two Cretaceous black shales from the Blake-Bahama Basin, western North Atlantic. These sediments are Cenomanian (c. 95 Ma) and mid-Albian (c. 105 Ma) in age, thus significantly extending the geological range of these compounds. The precise source of these lipids is, as yet, unknown, although they may derive from an ancient ancestor of Emiliania huxleyi.

... C. Mark Moore 1, 2 , Matthew M. Mills 3 , Eric P. Achterberg 2 , Richard J. Geider 1 , Julie LaRoche 4 , Mike I. Lucas 5 , Elaine L. McDonagh 2 , Xi Pan 2 , Alex J. Poulton 2 , Micha JA Rijkenberg 2 ... Figure 1: Cruise tracks and maps of annual mean excess nutrient distributions. ...

Altimeter measurements of sea level from the Topex/Poseidon mission are used to explore the relationship of sea level to the North Atlantic Oscillation (NAO) in the Mediterranean and the Black Sea. The secular trend in these areas is also calculated, and the confusing effect of the NAO discussed. Sea level throughout the Mediterranean is sensitive to the NAO during the winter months. No clear effect on the Black Sea is discovered. In the period considered (1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001), the NAO has a major effect on inter-annual variability of sea level in the Mediterranean but is unlikely to have affected the apparent secular trend.

Seagrasses, marine flowering plants, are widely distributed along temperate and tropical coastlines of the world. Seagrasses have key ecological roles in coastal ecosystems and can form extensive meadows supporting high biodiversity. The global species diversity of seagrasses is low (< 60 species), but species can have ranges that extend for thousands of kilometers of coastline. Seagrass bioregions are defined here, based on species assemblages, species distributional ranges, and tropical and temperate influences. Six global bioregions are presented: four temperate and two tropical. The temperate bioregions include the Temperate North Atlantic, the Temperate North Pacific, the Mediterranean, and the Temperate Southern Oceans. The Temperate North Atlantic has low seagrass diversity, the major species being Zostera marina, typically occurring in estuaries and lagoons. The Temperate North Pacific has high seagrass diversity with Zostera spp. in estuaries and lagoons as well as Phyllospadix spp. in the surf zone. The Mediterranean region has clear water with vast meadows of moderate diversity of both temperate and tropical seagrasses, dominated by deep-growing Posidonia oceanica. The Temperate Southern Oceans bioregion includes the temperate southern coastlines of Australia, Africa and South America. Extensive meadows of low-to-high diversity temperate seagrasses are found in this bioregion, dominated by various species of Posidonia and Zostera. The tropical bioregions are the Tropical Atlantic and the Tropical Indo-Pacific, both supporting mega-herbivore grazers, including sea turtles and sirenia. The Tropical Atlantic bioregion has clear water with a high diversity of seagrasses on reefs and shallow banks, dominated by Thalassia testudinum. The vast Tropical Indo-Pacific has the highest seagrass diversity in the world, with as many as 14 species growing together on reef flats although seagrasses also occur in very deep waters. The global distribution of seagrass genera is remarkably consistent north and south of the equator; the northern and southern hemispheres share ten seagrass genera and only have one unique genus each. Some genera are much more speciose than others, with the genus Halophila having the most seagrass species. There are roughly the same number of temperate and tropical seagrass genera as well as species. The most widely distributed seagrass is Ruppia maritima, which occurs in tropical and temperate zones in a wide variety of habitats. Seagrass bioregions at the scale of ocean basins are identified based on species distributions which are supported by genetic patterns of diversity. Seagrass bioregions provide a useful framework for interpreting ecological, physiological and genetic results collected in specific locations or from particular species.

The sources and source variations for aerosol at Mace Head, Ireland, were studied by applying positive matrix factorization (PMF), a variant of factor analysis, to a 5-yr data set for bulk aerosol. Signals for the following six sources were evident year round: (1) mineral dust, (2) sea salt, (3) general pollution, (4) a secondary SO\ }Se signal that is composed of both natural (marine) and pollution (coal) components, (5) ferrous industries, (6) and a second marine (possibly biogenic) source. Analyses of seasonally strati"ed data suggested additional sources for iodine and oil emissions but these were present only in certain seasons, respectively. The marine signal is particularly strong in winter. The main pollution transport from Europe to Mace Head occurs in May, but the in#uence of continental European emissions is evident throughout the year. Mineral aerosol evidently follows a transport pathway similar to that of pollution aerosol, i.e., recirculation via the westerlies brings pollutants mixed with dust to the site from nearby land, i.e., Ireland, the United Kingdom, and the Belgium, Netherlands, and Luxemburg (Benelux) region, with some inputs from Scandinavia, Western Europe, Eastern Europe, and even the Mediterranean region. Compared with Bermuda, aerosol at Mace Head has stronger marine sources (especially marine-derived secondary SO\ and Se) but weaker crustal and oil signals. Transport across the North Atlantic, especially in winter, cannot be ruled out.

This article discusses the rôle of the THC in climate, based upon the results of several numerical experiments which use a coupled ocean-atmosphere model developed at the Geophysical Fluid Dynamics Laboratory of NOAA, USA. The first part of the article explores the mechanism which is responsible for the abrupt climate change such as the Younger Dryas event using the coupled model. In response to the freshwater discharge into high north Atlantic latitudes over a period of 500 years, the THC in the Atlantic Ocean weakens, reducing surface air temperature over the northern north Atlantic Ocean, the Scandinavian Peninsula, and the circumpolar ocean and Antarctic Continent of the southern hemisphere. Upon the termination of the water discharge at the 500th year, the THC begins to intensify, regaining its original intensity in a few hundred years. In addition, the sudden onset and the termination of the discharge of freshwater induces the multidecadal fluctuation in the intensity of the THC, which generates the almost abrupt change of climate. It is noted that similar but much weaker oscillation of the THC is also evident in the control integration of the coupled model without freshwater forcing. The irregular oscillation of the THC mentioned above appears to be related to the fluctuation of the Subarctic Gyre and associated east Greenland current, yielding the evolution of the surface salinity anomaly which resembles that of ''great salinity anomaly''. The second part of this article describes the response of a coupled ocean-atmosphere model to the doubling and quadrupling of atmospheric carbon dioxide over centuries timescale. In one integration, the CO 2 concentration increases by 1%/year (compounded) until it reaches 4× the initial value at the 140th year and remains unchanged thereafter. In another integration, the CO 2 concentration also incleases at the rate of 1%/year until it reaches 2× the initial value at the 70th year and remains unchanged thereafter. One of the most notable features of the CO 2-quadrupling integration is the gradual disappearance of thermohaline circulation in most of the model oceans during the first 250-year period, leaving behind wind-driven cells. For example, thermohaline circulation nearly vanishes in the north Atlantic by the 250 years of the integration and remains very weak until the 900th year. However, it begins to restore the original intensity by the 1600th year. In the CO 2-doubling integration, the thermohaline circulation weakens by a factor of more than 2 in the North Atlantic during the first 150 years, but almost recovers its original intensity by the 500th year. The weakening of the THC moderates temporarily the greenhouse warming over the north Atlantic Ocean and its vicinity. In both numerical experiments described above, the initial weakening of the THC results from the capping of oceanic surface by relatively fresh, low-density water, which surpresses the convective cooling of water in the sinking region of the THC.

The first results of the UVic Earth System Model coupled to a land surface scheme and a dynamic global vegetation model are presented in this study. In the first part the present day climate simulation is discussed and compared to observations. We then compare a simulation of an ice age inception (forced with 116 ka BP orbital parameters and an atmospheric CO 2 concentration of 240 ppm) with a preindustrial run (present day orbital parameters, atmospheric [CO 2 ] = 280 ppm). Emphasis is placed on the vegetationÕs response to the combined changes in solar radiation and atmospheric CO 2 level. A southward shift of the northern treeline as well as a global decrease in vegetation carbon is observed in the ice age inception run. In tropical regions, up to 88% of broadleaf trees are replaced by shrubs and C 4 grasses. These changes in vegetation cover have a remarkable effect on the global climate: land related feedbacks double the atmospheric cooling during the ice age inception as well as the reduction of the meridional overturning in the North Atlantic. The introduction of vegetation related feedbacks also increases the surface area with perennial snow significantly.

We review current knowledge and understanding of the biology and ecology of the calanoid copepod Calanus helgolandicus in European waters, as well as provide a collaborative synthesis of data from 18 laboratories and 26 sampling stations in areas distributed from the northern North Sea to the Aegean and Levantine Seas. This network of zooplankton time-series stations has enabled us to collect and synthesise seasonal and multi-annual data on abundance, body size, fecundity, hatching success and vertical distribution of C. helgolandicus. An aim was to enable comparison with its congener Calanus finmarchicus, which has been studied intensively as a key component of European and north east Atlantic marine ecosystems. C. finmarchicus is known to over-winter at depth, whereas the life-cycle of C. helgolandicus is less well understood. Overwintering populations of C. helgolandicus have been observed off the Atlantic coast between 400 and 800 m, while in the Mediterranean there is evidence of significant deep-water populations at depths as great as 4200 m. The biogeographical distribution of C. helgolandicus in European coastal waters covers a wide range of habitats, from open ocean to coastal environments, and its contribution to mesozooplankton biomass ranges from 6% to 93%. Highest abundances were recorded in the Adriatic and off the west coast of Spain. C. helgolandicus is generally found in 9-20°C water, with maximum abundances from 13-17°C. In contrast, C. finmarchicus is found in cooler water between 0 and 15°C, with peak abundances from 0 to 9°C. As water has warmed in the North Atlantic over recent decades, the range of C. helgolandicus and its abundance on the fringes of its expanding range have increased. This review will facilitate development of population models of C. helgolandicus. This will not only help answer remaining questions but will improve our ability to forecast future changes, in response to a warming climate, in the abundance and distribution of this important species.

1 Laboratorio de Observación e Investigación Espacial, Universidad de Quintana Roo; Avenida Andrés Quintana Roo, S/N, Frente a colonia San Gervasio, Cozumel 77600, Quintana Roo, Mexico 2 Colegio de Geografía, Facultad de Filosofía y Letras, Universidad Nacional Autónoma de México, Ciudad Universitaria, Coyoacán 04510, Ciudad de Mexico, Mexico 3 Centro Interdisciplinario de Investigaciones y Estudios sobre Medio Ambiente y Desarrollo, Instituto Politécnico Nacional (CIIEMAD-IPN), Departamento de Territorio y Ambiente, 30 de Junio de 1520 s/n, La Laguna Ticomán, Gustavo A. Madero, 07340, Ciudad de México, Mexico 4 Centro de Estudios Meteorológicos de la Costa, Departamento de Ciencias Exactas, Centro Universitario de la Costa, Universidad de Guadalajara, Av. Juárez No. 976, Colonia Centro, Guadalajara 44100, Jalisco, Mexico 5 Red de Desastres Asociados a Fenómenos Hidrometeorológicos y Climáticos (REDESClim), CONACYT, Av. Insurgentes Sur 1582, Col. Crédito Constructor, Alcaldía Benito...

Geochemical variations in mid-ocean ridge basalts have been attributed to differing proportions of compositionally distinct mantle components in their sources, some of which may be recycled crust. Oxygen isotopes are strongly fractionated by near-surface interactions of rocks with the hydrosphere, and thus provide a tracer of near-surface materials that have been recycled into the mantle. We present here oxygen isotope analyses of basaltic glasses from the mid-Atlantic ridge south of and across the Azores platform. Variations in N 18 O in these samples are subtle (range of 0.47x) and may partly reflect shallow fractional crystallization; we present a method to correct for these effects. Relatively high fractionation-corrected N 18 O in these samples is associated with geochemical indices of enrichment, including high La/Sm, Ce/Pb, and 87 Sr/ 86 Sr and low 143 Nd/ 144 Nd. Our results suggest two first-order conclusions about these enriched materials: (1) they are derived (directly or indirectly) from recycled upper oceanic crustal rocks and/or sediments; and (2) these materials are present in the north Atlantic MORB sources in abundances of less than 10% (average 2^5%). Modeling of variations of N 18 O with other geochemical variables further indicates that the enriched component is not derived from incorporation of sediment or bulk altered oceanic crust, from metasomatism of the mantle by hydrous or carbonate-rich fluids, or from partial melting of subducted sediment. Instead, the data appear to require a model in which the enriched component is depleted mantle that has been metasomatized by smalldegree partial melts of subducted, dehydrated, altered oceanic crust. The age of this partial melting is broadly constrained to V250 Ma. Reconstructed plate motions suggest that the enriched component in the north Atlantic mantle may have originated by subduction along the western margin of Pangea. ß 2004 Elsevier B.V. All rights reserved.

1] Marine sediments recorded a series of Heinrich events during the last glacial period, massive ice surges that deposited prominent layers of ice-rafted debris in the North Atlantic. Here we explore oceanic mechanisms that can potentially trigger and amplify the observed ice calving events. Simulations of abrupt glacial climate change with a coupled ocean-atmosphere-sea ice model show a substantial regional sea level rise in the North Atlantic in response to a collapse of the Atlantic meridional overturning circulation (MOC). The increased heat uptake of the global ocean after the MOC collapse leads to an additional rise in global sea level. We hypothesize that these sea level changes have the potential to destabilize Northern Hemisphere ice shelves and ice sheets and to trigger ice surges. Sea level rise due to ice calving and subsurface ocean warming provides two positive feedback mechanisms contributing to further destabilization of ice shelves and ice sheets.

Interannual sea surface height variations in the Atlantic Ocean are examined from 10 years of highprecision altimeter data in light of simple mechanisms that describe the ocean response to atmospheric forcing: 1) local steric changes due to surface buoyancy forcing and a local response to wind stress via Ekman pumping and 2) baroclinic and barotropic oceanic adjustment via propagating Rossby waves and quasi-steady Sverdrup balance, respectively. The relevance of these simple mechanisms in explaining interannual sea level variability in the whole Atlantic Ocean is investigated. It is shown that, in various regions, a large part of the interannual sea level variability is related to local response to heat flux changes (more than 50% in the eastern North Atlantic). Except in a few places, a local response to wind stress forcing is less successful in explaining sea surface height observations. In this case, it is necessary to consider large-scale oceanic adjustments: the first baroclinic mode forced by wind stress explains about 70% of interannual sea level variations in the latitude band 18°-20°N. A quasi-steady barotropic Sverdrup response is observed between 40°and 50°N.

A generalized coccolithophore bloom classifier has been developed for use with ocean color imagery. The bloom classifier was developed using extracted satellite reflectance data from SeaWiFS images screened by the default bloom detection mask. In the current application, we extend the optical water type (OWT) classification scheme by adding a new coccolithophore bloom class formed from these extracted reflectances. Based on an in situ coccolithophore data set from the North Atlantic, the detection levels with the new scheme were between 1,500 and 1,800 coccolithophore cells/mL and 43,000 and 78,000 liths/mL. The detected bloom area using the OWT method was an average of 1.75 times greater than the default bloom detector based on a collection of SeaWiFS 1 km imagery. The versatility of the scheme is shown with SeaWiFS, MODIS Aqua, CZCS and MERIS imagery at the 1 km scale. The OWT scheme was applied to the daily global SeaWiFS imagery mission data set (years 1997-2010). Based on our results, average annual coccolithophore bloom area was more than two times greater in the southern hemisphere compared to the northern hemisphere with values of 2.00 × 10 6 km 2 and 0.75 × 10 6 km 2 , respectively. The new algorithm detects larger bloom areas in the Southern Ocean compared to the default algorithm, and our revised global annual average of 2.75 × 10 6 km 2 is dominated by contributions from the Southern Ocean.

Infrared satellite images and two ensembles of satellite-tracked buoys have been used to analyze eddy scales in the central and eastern North Atlantic between 35øN and 60øN. Both data sets yield eddy scales which decrease northward from the subtropical Atlantic and can be closely related to the Rossby radius of the first baroclinic mode.

A dynamic model of extension in the Baltimore Canyon trough region of the central North Atlantic indicates that rifting proceeded in two stages and was controlled by laterally offset preexisting weaknesses within the middle crust and upper mantle beneath the Appalachian orogen. The crustal weakness is hypothesized to result from thin-skinned thrust faulting in the Appalachian foreland, and the upper mantle weakness results from crustal thickening beneath the Appalachian hinterland. During the early stages of rifting (225-185 Ma), the loci of extension in the crust and mantle lie within the respective preweakened regions and are connected by a shear zone in the lower crust in a manner similar to whole lithosphere simple shear. Extension and thinning of the upper crust at this time results in the formation of Late Triassic-Early Jurassic rift basins in the Appalachian Piedmont and in the development of a horizontal pressure gradient which drives widespread ductile flow in the lower crust. The pressure gradient may also have influenced magma transport, moving melt generated beneath the eastern Baltimore Canyon trough into the more westerly Triassic basin province. During the late stages of rifting (185-175 Ma), extension in the crust shifts to a position overlying the preexisting upper mantle weakness as a result of thermal weakening by the upwelling asthenosphere in this region. The loci of extension in the crust and mantle are then coincident, and the style of rifting becomes similar to whole lithosphere pure shear. The shift in the locus of crustal extension is accompanied by the cessation of subsidence and volcanism in the Triassic basins, the onset of rapid subsidence in the Baltimore Canyon trough, and the formation of a basement hinge zone separating the highly thinned crust beneath the Baltimore Canyon trough from moderately thinned crust beneath the Triassic basin province. Extension becomes increasingly focused beneath the eastern edge of the Baltimore Canyon trough until the onset of seafloor spreading, approximately 50 m.y. after rifting began. The resulting conjugate margins are asymmetric, with most of the region encompassing the Triassic basins stranded on the North American plate. This paper presents a dynamic model of rifting in the Baltimore Canyon trough region of the central North Atlantic, focusing on the processes that controlled the timing of events and the formation of the structural, stratigraphic, and volcanic Paper number 91TC03012. 0278-7407/92/91TC-03012510.00 features of the margin. Because the Baltimore Canyon trough is one of the best studied rifted margins in the world, the model is well constrained by observations. The Baltimore Canyon trough region has many features common to the neighboring Carolina trough and Georges Bank basins, and in fact to many other rifted margins, so the model is generally applicable to much of the U.S. Atlantic margin and provides important constraints on the dynamics of rifting processes in general. Previous papers have examined the postrift subsidence of the Baltimore Canyon trough [Sawyer et al., 1982; Watts et al., 1982]. This paper examines the synrift development of the margin, emphasizing the role that preexisting weaknesses within the lithosphere played in determining the style of rifting. Preexisting weaknesses have previously been recognized as a controlling factor in the evolution of rifts [Braun and Beaumont, 1987; Bassi and Bonin, 1988a, b; Dunbar and Sawyer, 1988, 1989a], and the tendency of rifts to develop along orogenic zones indicates that orogeny is a major cause of lithospheric weakening. For example, extension in the North Atlantic focused within the Caledonian and Acadian orogens [Ziegler, 1989], the Iberian and Moroccan margins exploited preexisting Hercynian trends [Manspeizer, 1988], and the Rio Grande rift developed within the Laramide belt [Eaton, 1979, 1980]. At the U.S. Atlantic margin, extension focused within the Paleozoic Appalachian orogen. A finite element model presented below demonstrates that preexisting weaknesses within the orogen controlled the development of major structural features of the margin in the Baltimore Canyon trough region, including the early development of onshore Triassic basins, later formation of the deep offshore trough and basement hinge zone, coastal onlap, and crustal thickness variations across the margin. The model also accounts for the distribution of volcanism, the location of seafloor spreading initiation, and the duration of rifting. Features of the model that are broadly applicable to other rifted margins include asymmetric conjugate margins, abrupt seaward thinning of the crust beneath the basement hinge zone, a change in the locus of extension with time, and a transition from a simple shear style of deformation in the early stages of rifting to pure shear in the later stages. THE U.S. ATLANTIC MARGIN The prerift structure of the U.S. Atlantic margin was dominated by the Appalachian orogen as a consequence of intermittent orogenic activity throughout the Paleozoic. The most recent event was the Alleghanian orogeny, which resulted from the collision of North America and Africa during the late Carbonifereous to Early Permian [Hatcher, 1989; Taylor, 1989; Williams and Hatcher, 1982]. The Alleghanian foreland is characterized by thin-skinned thrusting, and encompasses the present Inner Piedmont, Blue Ridge, and Valley and Ridge provinces [Cooke et al., 1979; Harris and Bayer, 1979; Hatcher and Odom, 1980]. The hinterland encompasses the more easterly Avalon terrane and extends beneath the coastal plain and continental margin. Deep-seated thrusting within the hinterland is inferred from high-grade metamorphic facies in the easternmost Avalon exposures [Dallmeyer, 1989; Hatcher, 1989]. Rifting began 225-230 Ma with the formation of Triassic basins in the Appalachian Piedmont and beneath the present

Earthquakes and tsunamis along Morocco's coasts have been reported since historical times. The threat posed by tsunamis must be included in coastal risk studies. This study focuses on the tsunami impact and vulnerability assessment of the Casablanca harbour and surrounding area using a combination of tsunami inundation numerical modelling, field survey data and geographic information system. The tsunami scenario used here is compatible with the 1755 Lisbon event that we considered to be the worst case tsunami scenario. Hydrodynamic modelling was performed with an adapted version of the Cornell Multigrid Coupled Tsunami Model from Cornell University. The simulation covers the eastern domain of the Azores-Gibraltar fracture zone corresponding to the largest tsunamigenic area in the North Atlantic. The proposed vulnerability model attempts to provide an insight into the tsunami vulnerability of building stock. Results in the form of a vulnerability map will be useful for decision makers and local authorities in preventing the community resiliency for tsunami hazards.

Ocean Drilling Program (ODP) Leg 171B recovered continuous sequences that yield evidence for a suite of`critical' events in the Earth's history. The main events include the late Eocene radiolarian extinction, the late Palaeocene benthic foraminiferal extinction associated with the Late Palaeocene Thermal Maximum (LPTM), the Cretaceous± Palaeogene (K±P) extinction, the mid-Maastrichtian event, and several episodes of sapropel deposition documenting the late Cenomanian, late Albian and early Albian warm periods. A compilation of stable isotope results for foraminifera from Leg 171B sites and previously published records shows a series of large-scale cycles in temperature and d 13 C trends from Albian to late Eocene time. Evolution of d 18 O gradients between planktic and benthic foraminifera suggests that the North Atlantic evolved from a circulation system similar to the modern Mediterranean during early Albian time to a more open ocean circulation by late Albian±early Cenomanian time. Sea surface temperatures peaked during the mid-Cretaceous climatic optimum from the Albian±Cenomanian boundary to Coniacian time and then show a tendency to fall o toward the cool climates of the mid-Maastrichtian. The Albian± Coniacian period is characterized by light benthic oxygen isotope values showing generally warm deep waters. Lightest benthic oxygen isotopes occurred around the Cenomanian± Turonian boundary, and suggest middle bathyal waters with temperatures up to 20 8C in the North Atlantic. The disappearance of widespread sapropel deposition in Turonian time suggests that sills separating the North Atlantic from the rest of the global ocean were ®nally breached to sucient depth to permit ventilation by deep waters¯owing in from elsewhere. The Maastrichtian and Palaeogene records show two intervals of large-scale carbon burial and exhumation in the late Maastrichtian±Danian and late Palaeocene±early Eocene. Carbon burial peaked in early Danian time, perhaps in response to the withdrawal of large epicontinental seas from Europe and North America. Much of the succeeding Danian period was spent unroo®ng previously deposited carbon and repairing the damage to carbon export systems in the deep ocean caused by the K±P mass extinction. The youngest episode of carbon exhumation coincided with the onset of the early Eocene Warm Period and the LPTM, and has been attributed to the tectonic closure of the eastern Tethys and initiation of the Himalayan Orogeny.

Geochemical identification of a tephra layer found in two cores from the NE Atlantic Ocean and the SE Norwegian Sea, respectively, and dated to 127 ka BP has enabled us to obtain a precise correlation across the Iceland-Scotland Ridge at the Marine Isotope Stage (MIS) 6/5 transition. The direct distance between the two cores is only about 200 km: South of the Iceland-Scotland Ridge, sea surface temperatures rose abruptly at 130 ka BP at the onset of MIS 5e and at least 2-3000 years earlier than north of the ridge. Maximum sea surface temperatures south of the ridge occurred during this initial phase of MIS 5e, when temperatures in the Nordic Seas were still low. North of the ridge, the sea surface warmed rapidly at 127 ka BP. Correlations between the North Atlantic records and the Eemian of Northwest Europe tentatively indicate that the initial phase of MIS 5e correlates with the early part of the Eemian characterised by a warm, continental type of climate. The period after the warming of the Nordic seas corresponds to the slightly cooler and more oceanic middle Eemian interval in Europe. The sea surface temperatures fell gradually north of the ridge during the later part of MIS 5e and they were low during MIS 5d-5a. South of the ridge the temperatures remained relatively high. The data shows that there was no outflow of deep water from the Norwegian Sea during the later part of MIS 6. Outflow began at the MIS 6/5 transition simultaneous with the sea surface warming south of the ridge. r

The Jurassic succession of Denmark is largely confined to the subsurface with the exception of exposures on the island of Bornholm in the Baltic Sea. In East Greenland, in contrast, the Jurassic is extensively exposed. Comparison of basin evolution in the two regions, which now occur on two separate plates, thus relies on highly different datasets. It is possible nevertheless to con- struct an integrated picture allowing testing of hypotheses concerning basin evolution, regional uplift, onset and climax of rifting, relative versus eustatic sea-level changes and sequence strati- graphic subdivision and correlation. On a smaller scale, it is possible to compare the signatures of sequence stratigraphic surfaces as seen on well logs, in cores and at outcrop and of sequences recognised and defined on the basis of very different data types. Breakdown of the successions into tectonostratigraphic megasequences highlights the high degree of similarity in overall basin evolution and tectonic ...

Earlier studies have indicated that the gross nearshore wave energy resource is significantly smaller than the gross offshore wave energy resource implying that the deployment of wave energy converters in the nearshore is unlikely to be economic. However, it is argued that the gross wave energy resource is not an appropriate measure for determining the productivity of a wave farm and an alternative measure, the exploitable wave energy resource, is proposed. Calculation of a site's potential using the exploitable wave energy resource is considered superior because it accounts for the directional distribution of the incident waves and the wave energy plant rating that limits the power capture in highly energetic sea-states. A third-generation spectral wave model is used to model the wave transformation from deep water to a nearshore site in a water depth of 10 m. It is shown that energy losses result in a reduction of less than 10% of the net incident wave power. Annual wave data for the North Atlantic coast of Scotland is analysed and indicates that whilst the gross wave energy resource has reduced significantly by the 10 m depth contour, the exploitable wave energy resource is reduced by 7 and 22% for the two sites analysed. This limited reduction in exploitable wave energy resource means that for many exposed coasts, nearshore sites offer similar potential for exploitation of the wave energy resource as offshore sites.

We characterized the seamount distribution of the economic exclusive zone (EEZ) of the Azores (Portugal) using 2 bathymetry datasets. Our algorithm showed that peaks and seamounts are common features in this region of the North Atlantic. The density obtained of 3.3 peaks of all sizes per 1000 km 2 is in the same order of magnitude as that obtained on the Mid-Atlantic Ridge by a few other studies. A total of 63 large and 398 small seamount-like features are mapped and described in the Azorean EEZ. Our distribution of seamounts predicts that about 57% of the potential Azores seamounts lie in the zone protected from deep-water trawling by European Commission Council Regulation No. 1568/2005.

1] We measured the absorption properties of phytoplankton, nonalgal particles (NAP), and colored dissolved organic matter (CDOM) at about 350 stations in various coastal waters around Europe including the English Channel, Adriatic Sea, Baltic Sea, Mediterranean Sea, and North Sea. For comparison, we also collected data in the open ocean waters of North Atlantic. The exponential slope of the CDOM absorption spectrum varied within a narrow range around 0.0176 nm À1 (SD = 0.0020 nm À1 ). When data from all the regions were considered altogether, the relationship between phytoplankton absorption and chlorophyll concentration was generally similar to the one previously established for open oceanic waters. Our coastal data, however, show that significant departures from the general trend may occur due to peculiar pigment composition and cell size. In some coastal areas, high phaeopigment concentrations gave rise to especially high blue-to-red ratio of phytoplankton absorption. The NAP absorption covaried with the particle dry weight. Most absorption spectra of these particles were well described by an exponential function with a slope averaging 0.0123 nm À1 (SD = 0.0013 nm À1 ). In some highly turbid waters, the spectra exhibited a signature possibly associated with iron oxides. In the Baltic Sea, NAP absorption systematically showed lower values at wavelengths shorter than 440 nm than predicted from the fitted exponential function. Overall, the variability in the absorption properties of European coastal waters showed some consistent patterns despite the high diversity of the examined waters. Distinct features were identified in the phytoplankton and NAP components. An absorption budget is presented and parameterizations are proposed.

One model for marine migration of Atlantic salmon Salmo salar proposes that North American and southern European stocks (<62 • N) move directly to feeding grounds off west Greenland, then overwinter in the Labrador Sea, whereas northern European stocks (>62 • N) utilize the Norwegian Sea. An alternate model proposes that both North American and European stocks migrate in the North Atlantic Subpolar Gyre (NASpG) where S. salar enter the NASpG on their respective sides of the Atlantic, and travel counterclockwise within the NASpG until returning to natal rivers. A review of data accumulated during the last 50 years suggests a gyre model is most probable. Freshwater parr metamorphose into smolts which have morphological, physiological and behavioural adaptations of epipelagic, marine fishes. Former high-seas fisheries were seasonally sequential and moved in the direction of NASpG currents, and catches were highest along the main axis of the NASpG. Marking and discrimination studies indicate mixed continental origin feeding aggregations on both sides of the Atlantic. Marked North American smolts were captured off Norway, the Faroe Islands, east and west Greenland, and adults tagged at the Faroes were recovered in Canadian rivers. Marked European smolts were recovered off Newfoundland and Labrador, west and east Greenland, and adults tagged in the Labrador Sea were captured in European rivers. High Caesium-137 ( 137 Cs) levels in S. salar returning to a Quebec river suggested 62·3% had fed at or east of Iceland, whereas levels in 1 sea-winter (SW) Atlantic Canada returnees indicated 24·7% had fed east of the Faroes. Lower levels of 137 Cs in returning 1SW Irish fish suggest much of their growth occurred in the western Atlantic. These data suggest marine migration of S. salar follows a gyre model and is similar to other open-ocean migrations of epipelagic fishes.

Geologic studies indicate that prior to --40 Ma the Drake Passage was closed and the Central American Isthmus was open. The effect of these changes has been examined in an ocean general circulation model. Several sensitivity experiments were conducted, all with atmospheric forcing and other boundary conditions from the present climate, but with different combinations of closed and open gateways. In the first experiment, the only change involved closure of the Drake Passage. In agreement with earlier studies the barrier modified the geostrophic balance that now maintains the circumpolar flow in the southern ocean, with the net effect being decreased transport of the Antarctic Current and an approximate fourfold increase in outflow of Antarctic deep-bottom waters. The very large increase in Antarctic outflow suppresses North Atlantic Deep Water (NADW) formation. In addition to corroboration of results from earlier studies, our simulations provide several new insights into the role of a closed Drake Passage. A more geologically realistic closed Drake/open central American isthmus experiment produces essentially the same pattern of deepwater circulation from the first experiment, except that Antarctic outflow is about 20% less than the first experiment. The resultant unipolar deepwater circulation pattern for the second experiment is consistent with paleoceanographic observations from the early Cenozoic. A third Copyright 1993 by the American Geophysical Union. Paper number 93PA00893. 0883-8305/93/93PA-00893510.00 experiment involved an open Drake and open central American isthmus. In this experiment, Antarctic outflow is diminished to slightly above present levels but NADW production is still low due to free exchange of low-salinity surface water between the North Pacific and North Atlantic. The low level of thermohaline overturn should have reduced oceanic productivity in the Oligocene (.--30 Ma), a result in agreement with geologic observations. Finally, simulations with an energy balance model demonstrate that the changes in surface heat flux south of 60øS due to breaching of the Drake barrier do not result in temperature changes large enough to have triggered Antarctic glaciation. This last result suggests that some other factor (CO27) may be required for Antarctic ice sheet expansion in the Oligocene (-•30-34 Ma). Our results lend further support to the concept that even in the absence of changing boundary conditions due to ice sheet growth, variations in the geometry of the ocean basins can significantly influence ocean circulation patterns and the sediment record. The results also suggest that the primary polarities of the Cenozoic deepwater circulation may have been controlled by opening and closing of these two gateways. Cox, M.D., An idealized model of the world ocean, Part I, The global-scale water masses, J. Phys. Climate model comparison of Gondwanan and Laurentide glaciations, J. Geophys. Res., 96, 9217-9226, 1991.