Search

Data from a scientific deep-water trawl fisheries survey in the north-east Atlantic were analysed to determine the spatial and bathymetric distribution of elasmobranch species and assess the change in relative abundance over the period 1998-2013. During this period, commercial fisheries for deep-water sharks went from being entirely unregulated, to being briefly managed, to being completely prohibited. A total of 22 species of shark and 10 species of skate were recorded between depths of 300 and 2030 m. All showed strong species-specific depth-related trends in abundance. Out of the 11 more common species, five showed no change in relative abundance over time, two ( Centrophorus squamosus and Centroselachus crepidater) declined significantly and four increased in relative abundance ( Apristurus aphyodes, Apristurus microps, Galeus melastomus and Deania calcea). Assuming these populations were depleted by fisheries in the past, the current data do not suggest there has been an overall recovery. Positive signs for some species in the most recent years suggest movement or recruitment back into the area; however, it is of concern that two species continued to decline. There is a continued need to have precautionary management of these elasmobranch species, and the current ban on landing these species in European waters remains appropriate. [ABSTRACT FROM AUTHOR]

Observations along the southwestern Atlantic WOCE A17 line made during the Dutch GEOTRACES-NL programme (2010-2011) were compared with historical data from 1994 to quantify the changes in the anthropogenic component of the total pool of dissolved inorganic carbon (ΔCant). Application of the extended multi-linear regression (eMLR) method shows that the ΔCant from 1994 to 2011 has largely remained confined to the upper 1000 dbar. The greatest changes occur in the upper 200 dbar in the Subantarctic Zone (SAZ), where a maximum increase of 37 μmol kg-1 is found. South Atlantic Central Water (SACW) experienced the highest rate of increase in Cant, at 0.99 ± 0.14 µmol kg-1 yr-1, resulting in a maximum rate of decrease in pH of 0.0016 yr-1. The highest rates of acidification relative to ΔCant, however, were found in Subantarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW). The low buffering capacity of SAMW and AAIW combined with their relatively high rates of Cant, increase of 0.53 ± 0.11 and 0.36 ± 0.06 μmol kg-1 yr-1, respectively, has lead to rapid acidification in the SAZ, and will continue to do so whilst simultaneously reducing the chemical buffering capacity of this significant CO2 sink. [ABSTRACT FROM AUTHOR]

Water column dissolved inorganic carbon and total alkalinity were measured during five hydrographie sections in the Atlantic Ocean and Drake Passage. The work was funded through the Strategic Funding Initiative of the UK's Oceans2025 programme, which ran from 2007 to 2012. The aims of this programme were to establish the regional budgets of natural and anthropogenic carbon in the North Atlantic, the South Atlantic, and the Atlantic sector of the Southern Ocean, as well as the rates of change of these budgets. This paper describes the dissolved inorganic carbon and total alkalinity data collected along east-west sections at 55-60° N (Arctic Gateway), 24.5° N, and 24° S in the Atlantic and across two Drake Passage sections. Other hydrographic and biogeochemical parameters were measured during these sections, yet are not covered in this paper. Over 95 % of samples taken during the 24.5° N, 24° S, and the Drake Passage sections were analysed onboard and subjected to a 1st level quality control addressing technical and analytical issues. Samples taken during Arctic Gateway were analysed and subjected to quality control back in the laboratory. Complete post-cruise 2nd level quality control was performed using cross-over analysis with historical data in the vicinity of measurements, and data are available through the Carbon Dioxide Information Analysis Center (CDIAC) and are included in the Global Ocean Data Analyses Project, version 2 (GLODAP 2). [ABSTRACT FROM AUTHOR]

Abstract: The presence of thick (∼200 m) carbonaceous shales of Cretaceous age in the deep waters of the eastern Equatorial Atlantic was first revealed by drilling at DSDP sites 367 and 368 near the Cape Verde Islands. More recent seismic investigations show that black shales are widely distributed in this region. In the Gambia Basin they are associated with a group of seismic reflectors lying at depths of 400–600 m below the sea floor. These can be traced southwards from the drill sites into the Sierra Leone Basin and eastwards beneath the African continental rise to depths at which ambient temperatures fall within the oil generation window. In the Gambia Basin the reflectors continue westwards from the Cape Verde Archipelago before terminating on Turonian oceanic basement (∼92 Ma). South of the Guinea Fracture Zone near 10° N extension of the same seismic sequence on to younger oceanic crust indicates that deep-sea carbonaceous deposits formed close to the present equator as late as the early Campanian (∼80 Ma), long after a series of oceanic anoxic events in the Aptian–Albian (OAE1) and over the Cenomanian–Turonian boundary (OAE2) led to widespread accumulation of black shales. This late period of deposition may correspond to the more locally developed OAE3. High surface productivity in equatorial upwelling zones during the late Cretaceous probably played an important role in delivering large amounts of organic carbon to the sea floor when meridional movement of deep water between the South and North Atlantic was restricted by closely-spaced, east–west fracture zones. In some areas seismic data show that the black shales level out rather than drape pre-existing topography, implying significant downslope transport of organic-rich material from upwelling cells near the African margin. [Copyright &y& Elsevier]

Abstract: An extensive study of halocarbon tracers, chlorofluorocarbons (CFCs) and carbon tetrachloride (CCl4), based on over 100 stations in the Labrador Sea, demonstrated water mass structure and ventilation processes. Regional convection and isopycnal mixing of four water masses including newly ventilated Labrador Sea Water (LSWshallow), Labrador Sea Water produced in the winter of 1993–1994 (LSWdeep), North East Atlantic Deep Water (NEADW) and Denmark Strait Overflow Water (DSOW) from the surface to the bottom of the Labrador Sea were resolved from tracer distributions. Saturation levels varied spatially with different tracers and with convection regimes during the production of water masses. Average saturation levels in the LSWshallow for the entire Labrador Sea were 77% for CFC-12, 73% for CFC-11 and 92% for CCl4, respectively. Saturation levels during the time of LSW formation estimated from the area of deep convection were over 84% for CFC-12, 77% for CFC-11 and 99% for CCl4. Regional convection and subsequent horizontal mixing resulted in further reduction in saturation levels to 76%, 70% and 88%, respectively, when LSWshallow exited out to the south at the mouth of the Labrador Sea. LSWdeep was produced during the exceptionally deep convection winter of 1993–1994 and contained lower saturation levels than the Labrador Sea Water produced during weak convection regimes (LSWshallow). CFC-12, CFC-11 and CCl4 saturation levels in the LSWdeep were 66%, 61% and 76%, respectively, indicating that convection regime influenced tracer saturation levels. Estimates of ventilation ages depend strongly on the saturation levels. We calculated ventilation ages using CFC-12 with a range of saturation levels and with the saturation level calibrated tracer ratio, CFC-12/CCl4. The best estimates of ventilation ages for the NEADW and DSOW, obtained using the CFC-12/CCl4 ratio, were 11–13 and 5–8 years, respectively. [Copyright &y& Elsevier]

Data obtained during the last 20 years from selected hydrographic stations throughout the Arctic Ocean basins and at the continental slopes and northern parts of the surrounding shelf seas are examined to estimate the contribution of Atlantic water to the upper part of the Arctic Ocean water column, and to follow the circulation of the Atlantic derived halocline waters around the Arctic Ocean basins. A substantial fraction of the Atlantic water entering the Arctic Ocean in the two inflow branches, the Fram Strait branch and the Barents Sea branch, is transformed into less dense waters. The inflow through Fram Strait encounters and melts sea ice. Its upper part becomes less saline, and in winter, ice formation homogenizes this low salinity upper part into a winter mixed layer, which follows the boundary flow eastward. The inflow over the Barents Sea mainly becomes colder, less saline and denser due to cooling and net precipitation, but melting of sea ice also here creates a less dense upper layer, which is subsequently homogenized by haline convection. Both these components enter the Nansen Basin via the St. Anna Trough and flow eastward along the Siberian continental slope. A third component of the Barents Sea inflow, mainly comprising Norwegian Coastal Current water, remains on the shelf, where it absorbs the runoff from the large Siberian rivers and evolves into low salinity shelf water. This part continues as far east as the Laptev Sea before a major inflow to the deep Arctic Ocean basins occurs. Winter convection, which in most of the Nansen Basin extends to the Atlantic layer, then becomes limited to the injected low salinity shelf water, and the more saline upper layers of the Fram Strait and the Barents Sea branches are transformed into halocline waters. The Fram Strait branch supplies the halocline water of the Amundsen, Makarov and part of the Canada basins, while the upper part of the Barents Sea branch, initially confined to the Siberian continental slope, becomes the main source of the lower halocline below the Pacific water in the Canada Basin beyond the Chukchi Cap. Less dense Pacific water close to the North American continent prevents the Atlantic derived upper layers from fl owing through the Canadian Arctic Archipelago and their main exit is Fram Strait. Only some of the Barents Sea branch halocline water passes through Nares Strait and may occasionally renew the deep and bottom waters of Baffin Bay. [ABSTRACT FROM AUTHOR]

Seismic reflection profiles from the equatorial Atlantic off Africa between 12°N and 1°N reveal remarkably widespread deformation of oceanic sediments in an area lacking teleseismic activity. Uplift of abyssal plain sequences has occurred along the eastern extensions of large-offset fracture zones on the Mid-Atlantic Ridge. Between the major transforms pervasive deformation is imaged in the sedimentary column. Diapirism and faulting may have been associated with extensive fluid migration and sediment mobilization. The deformation occurred during the late Cenozoic and was probably related to reactivation of Cretaceous transforms. [ABSTRACT FROM AUTHOR]