| 1. |
- Darelius, E., et al.
(författare)
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Downward flow of dense water leaning on a submarine ridge
- 2007
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Ingår i: Deep Sea Research Part I. - : Elsevier BV. - 0967-0637 .- 1879-0119. ; 54:7, s. 1173-1188
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Tidskriftsartikel (refereegranskat)abstract
- Large-scale dense bottom currents are geostrophic to leading order, with the main flow direction along the continental slope. Bottom friction makes the water descend to greater depths, but only at a small angle to the horizontal. Here the effect of a submarine ridge that intersects the slope is considered. It is shown that the presence of a submarine ridge greatly enhances the downward transport. By leaning against the ridge it is possible for the dense water to flow downhill, perpendicular to the depth contours, even though the first-order dynamics are geostrophic. The requirement for downward flow next to the ridge is that the frictional transport that it induces is sufficiently large to counteract geostrophic advection along the isobaths and out of the ridge region. The dynamics are similar to those of downward flow in submarine canyons, but ridges appear to be more effective in channeling the dense water downhill, in particular for narrow ridges/canyons with small seaward slope of the ridge/canyon axis. The downward flow is analyzed using a simplified analytical model and the results are compared to data from the Filchner Overflow, which agree qualitatively with the model.
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| 2. |
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| 3. |
- Andersson, Helén C., 1968, et al.
(författare)
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Regulation of the Indonesian throughflow by baroclinic draining of the North Australian Basin
- 2005
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Ingår i: Deep-Sea Research Part I-Oceanographic Research Papers. - : Elsevier BV. - 0967-0637. ; 52:12, s. 2214-2233
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Tidskriftsartikel (refereegranskat)abstract
- The Indonesian throughflow (ITF) is studied using historic hydrographical data with purpose of obtaining a description of the characteristics of the large-scale flow and an understanding of both the forcing and control of the flow. The investigation makes use of the steric sea level and the contents of freshwater and heat in the water Column integrated down to the depth of the deepest connection (effective sill depth) between the Pacific and Indian Oceans within the Indonesian seas. It is shown that it is mainly low-saline water of North Pacific origin that fills the upper part of both the Indonesian seas and a downstream buoyant (surface) pool (DBP) that stretches horizontally over a large part of the North Australian Basin. The long-term mean steric sea level in the Indonesian seas is approximately horizontal and equal to the sea level in the neighboring part of the Pacific Ocean. This indicates small frictional losses against the mean throughflow, which is verified using a coupled multiple basin model of the Indonesian seas. The chan e of the steric sea level, from the Pacific Ocean level to the Indian Ocean level, Occurs essentially at the border between the DBP and the adjacent Indian Ocean. It is found that Darwin is situated inside the DBP, indicating that the sea level recorded in this place is a poor representative of mean and low frequency parts of the sea level variability of the Indian Ocean. It is argued that the control of ITF is set by the baroclinic transport capacity of the DBP relative to the adjacent (Indian Ocean) water. The mean ITF, estimated as the Outflow from the DBP to the South Equatorial Current, is about 10 Sv. The integrated ITF imprint is fresh and cold and the net heat transport is estimated to be 0.3 PW. The buffering capacity of the DBP is about 5 years, so variations in the circulation should be modest on shorter time-scales. It is suggested that the atmospheric transfer of freshwater to the North Pacific and vertical mixing in the North Pacific provide the driving of the mean ITF and that ITF is a major branch of the estuarine-type vertical circulation of the North Pacific. (c) 2005 Elsevier Ltd. All rights reserved.
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| 4. |
- Björk, Göran, 1956, et al.
(författare)
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Bathymetry and deep-water exchange across the central Lomonosov Ridge at 88°-89°N
- 2007
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Ingår i: Deep-Sea Research I. - : Elsevier BV. ; 54, s. 1197-1208
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Tidskriftsartikel (refereegranskat)abstract
- Seafloor mapping of the central Lomonosov Ridge using a multibeam echo-sounder during the Beringia/Healy–Oden Trans-Arctic Expedition (HOTRAX) 2005 shows that a channel across the ridge has a substantially shallower sill depth than the 2500 m indicated in present bathymetric maps. The multibeam survey along the ridge crest shows a maximum sill depth of about 1870 m. A previously hypothesized exchange of deep water from the Amundsen Basin to the Makarov Basin in this area is not confirmed. On the contrary, evidence of a deep-water flow from the Makarov to the Amundsen Basin was observed, indicating the existence of a new pathway for Canadian Basin Deep Water toward the Atlantic Ocean. Sediment data show extensive current activity along the ridge crest and along the rim of a local Intra Basin within the ridge structure.
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| 5. |
- Björk, Göran, 1956, et al.
(författare)
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The deep waters of the Eurasian Basin, Arctic Ocean: Geothermal heat flow, mixing and renewal
- 2006
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Ingår i: Deep-Sea Research Part I-Oceanographic Research Papers. - : Elsevier BV. - 0967-0637. ; 53:7, s. 1253-1271
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Tidskriftsartikel (refereegranskat)abstract
- Hydrographic observations from four separate expeditions to the Eurasian Basin of the Arctic Ocean between 1991 and 2001 show a 300-700 m thick homogenous bottom layer. The layer is characterized by slightly warmer temperature compared to ambient, overlying water masses, with a mean layer thickness of 500 +/- 100 m and a temperature surplus of 7.0 +/- 2 x 10(-3) degrees C. The layer is present in the deep central parts of the Nansen and Amundsen Basins away from continental slopes and ocean ridges and is spatially coherent across the interior parts of the deep basins. Here we show that the layer is most likely formed by convection induced by geothermal heat supplied from Earth's interior. Data from 1991 to 1996 indicate that the layer was in a quasi steady state where the geothermal heat supply was balanced by heat exchange with a colder boundary. After 1996 there is evidence of a reformation of the layer in the Amundsen Basin after a water exchange. Simple numerical calculations show that it is possible to generate a layer similar to the one observed in 2001 in 4-5 years, starting from initial profiles with no warm homogeneous bottom layer. Limited hydrographic observations from 2001 indicate that the entire deep-water column in the Amundsen Basin is warmer compared to earlier years. We argue that this is due to a major deep-water renewal that occurred between 1996 and 2001. (c) 2006 Elsevier Ltd. All rights reserved.
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| 6. |
- Glud, R. N., et al.
(författare)
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Distribution of oxygen in surface sediments from central Sagami Bay, Japan: In situ measurements by microelectrodes and planar optodes
- 2005
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Ingår i: Deep Sea Research Part I: Oceanographic Research Papers. - 0967-0637. ; 51:10, s. 1974-1987
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Tidskriftsartikel (refereegranskat)abstract
- Distributions of oxygen in surface sediments from central Sagami Bay were quantified using an autonomous vehicle carrying both a profiling microelectrode instrument and a planar optode module. Measurements were performed at 16 sites (either by microelectrodes or optodes) along a 175 m long transect and in total 45 electrode microprofiles and 6 O2 images (each covering 6.9×5.1 cm of surface sediment) were obtained. The data revealed an extensive small-scale variation of the in situ O2 distribution. The diffusive O2 uptake (DOU) as derived from the microelectrode data varied by a factor >10 with an average value of 2.6±1.6 mmol m−2 d−1 (n=45) corresponding to 8% of the estimated average primary production for the area. There was no significant difference in the average O2 penetration depth as quantified from the microprofiles and the planar optode images (P<0.05). The O2 penetration depth of the combined dataset varied between 0.5 and 9.2 mm with an average value of 3.9±1.5 mm (n=347). Even though the organic carbon rich sediments of central Sagami Bay may exhibit higher horizontal heterogeneity than normally encountered in deep-sea sediments, the data document that extrapolation from a few in situ data points should be done with caution. A detailed statistical analysis of the spatial autocorrelation in the O2 penetration depth documented that measurements performed less than 2 cm apart were autocorrelated. This implies that the aerobic benthic activity at the investigated site varied in patches with a characteristic size of a few cm. The presented data represent a detailed in situ study on small-scale spatial variability in sediment O2 distribution and document that planar O2 optode images provide a tool to access spatial heterogeneity of natural sediments.
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| 7. |
- Havenhand, Jonathan N., 1959, et al.
(författare)
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Megalodicopia hians in the Monterey submarine canyon: Distribution, larval development, and culture
- 2006
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Ingår i: Deep-Sea Research Part I-Oceanographic Research Papers. - : Elsevier BV. - 0967-0637. ; 53:2, s. 215-222
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Tidskriftsartikel (refereegranskat)abstract
- The exclusively deep-sea ascidian family Octacnemidae comprises several genera in which the oral siphon has hypertrophied to form two large lips which create an "oral hood" capable of capturing motile prey. Megalodicopia hians is typical of this carnivorous family and has been reported to prey upon small epibenthic crustaceans. Distribution of M. hians in the Monterey Canyon system (36 degrees 45'N, 122 degrees 00'W) (California) was determined with remotely operated vehicles. M hians was found sparsely to depths of at least 3800m throughout the canyon; however, abundance was greatest within the oxygen-minimum zone (400-800m). Eggs, sperm, and recently fertilized embryos were obtained repeatedly from adults returned to the laboratory in vivo, indicating that this species free-spawns routinely. Overall egg diameter (ovum plus chorion, plus follicle cells) was 175-190 mu m-considerably smaller than previously reported for this species. Embryonic development at temperature and oxygen concentrations equivalent to the oxygen-minimum zone was 2-4d and. embryos gave rise to typical phlebobranch "simple" tadpole larvae. Larval period was extremely variable, and settlement/metamorphosis occurred up to 3 months post-hatching. These results are discussed within the context of settlement-site selection and fertilization ecology of the species. (c) 2005 Elsevier Ltd. All rights reserved.
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| 8. |
- Olsson, Anders, 1970, et al.
(författare)
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Intermediate water from the Greenland Sea in the Faroe Bank Channel: spreading of released sulphur hexafluoride
- 2005
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Ingår i: Deep-Sea Research Part I: Oceanographic Research Papers. - : Elsevier BV. - 0967-0637. ; 52:2, s. 279-294
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Tidskriftsartikel (refereegranskat)abstract
- The Faroe Bank Channel is the deepest passage for dense water leaving the Nordic Seas into the North Atlantic. The contribution to this part of the Greenland-Scotland Overflow by intermediate water from the Greenland Sea is investigated by the tracer sulphur hexafluoride (SF6) that was released into the central Greenland Sea in summer 1996. Continuous monitoring has since traced it around the Nordic Seas and into the connecting areas. It was observed for the first time close to the Faroe Islands in early 1999, indicating a transport time from the Greenland Sea of around 2.5 years. This study estimates that approximately 16 kg of SF6 had passed the Faroe Bank Channel by the end of 2002, that is 5% of the total amount released. Both the arrival time and the amount of exported SF6 deduced from the observations are consistent with the results from a numerical ocean model simulating the tracer release and spreading.
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| 9. |
- Turnewitsch, Robert, et al.
(författare)
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Internal tides and sediment dynamics in the deep sea : Evidence from radioactive 234Th/238U disequilibria
- 2008
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Ingår i: Deep-Sea Research. Part I: Oceanographic Research Papers. - : Elsevier BV. - 0967-0637. ; 55:12, s. 1727-1747
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Tidskriftsartikel (refereegranskat)abstract
- Residual flow, barotropic tides and internal (baroclinic) tides interact in a number of ways with kilometer-scale seafloor topography such as abyssal hills and seamounts. Because of their likely impact on vertical mixing such interactions are potentially important for ocean circulation and the mechanisms and the geometry of these interactions are a matter of ongoing studies. In addition, very little is known about how these interactions are reflected in the sedimentary record. This multi-year study investigates if flow / topography interactions are reflected in distributional patterns of the natural short-lived (half life: 24.1 d) particulate-matter tracer 234Th relative to its conservative (non-particle-reactive) and very long-lived parent nuclide 238U. The sampling sites were downstream of, or surrounded by, fields of short seamounts and, therefore, very likely to be influenced by nearby flow / topography interactions. Between about 200 m and 1000 m above the seafloor at the sampling sites recurrent ‘fossil’ disequilibria were detected. ‘Fossil’ disequilibria are defined by clearly detectable 234Th/238U disequilibria (total 234Th radioactivity < 238U radioactivity, indicating a history of intense particulate 234Th scavenging and particulate-matter settling from the sampled parcel of water) and conspicuously low particle-associated 234Th activities. ‘Fossil’ disequilibria were centered around levels in the water column which correspond to the average height of the short seamounts near the sampling sites. This suggests the ‘fossil’ disequilibria are formed on the seamount slopes. Moreover, the magnitude of the ‘fossil’ disequilibria suggests that the slopes of the short seamounts in the study region are characterized by particularly vigorous fluid dynamics. Since ‘fossil’ disequilibria already occurred at ~ O(1 – 10 km) away from the seamount slopes it is likely that these vigorous fluid dynamics rapidly decay away from the slopes on scales of O(1 ? 10 km). These conclusions are supported by the horizontal distribution and magnitude of the modeled total (barotropic + baroclinic) tidal current velocities of the predominating tidal M2 constituent: On (near?)critical seamount slopes baroclinic tides lead to localized [~ O(1 km)] increases of the overall tidal current velocity by a factor of ~ 2, thereby pushing the total current velocity well above the threshold for sediment erosion. The results of this and a previous study (Turnewitsch et al. 2004, Earth and Planetary Science Letters 222, 1023-1036) show that kilometer-scale flow / topography interactions leave a marine geochemical imprint which may help to develop sediment proxies for the reconstruction of past changes of fluid dynamics in the deep sea, particularly the internal wave field. Sites with (near?)critical seafloor slopes are the most promising sites to study paleo-changes of internal tides. To reconstruct the paleo-flow of residual currents and barotropic tides, sediments covering isolated topography of comparable breadth and width, and with sub-critical slopes, seem to be more appropriate. For the sediment-based reconstruction of paleo-parameters other than physical oceanographic ones kilometer-scale topography should be avoided altogether.Residual flow, barotropic tides and internal (baroclinic) tides interact in a number of ways with kilometer-scale seafloor topography such as abyssal hills and seamounts. Because of their likely impact on vertical mixing such interactions are potentially important for ocean circulation and the mechanisms and the geometry of these interactions are a matter of ongoing studies. In addition, very little is known about how these interactions are reflected in the sedimentary record. This multi-year study investigates if flow / topography interactions are reflected in distributional patterns of the natural short-lived (half life: 24.1 d) particulate-matter tracer 234Th relative to its conservative (non-particle-reactive) and very long-lived parent nuclide 238U. The sampling sites were downstream of, or surrounded by, fields of short seamounts and, therefore, very likely to be influenced by nearby flow / topography interactions. Between about 200 m and 1000 m above the seafloor at the sampling sites recurrent ‘fossil’ disequilibria were detected. ‘Fossil’ disequilibria are defined by clearly detectable 234Th/238U disequilibria (total 234Th radioactivity < 238U radioactivity, indicating a history of intense particulate 234Th scavenging and particulate-matter settling from the sampled parcel of water) and conspicuously low particle-associated 234Th activities. ‘Fossil’ disequilibria were centered around levels in the water column which correspond to the average height of the short seamounts near the sampling sites. This suggests the ‘fossil’ disequilibria are formed on the seamount slopes. Moreover, the magnitude of the ‘fossil’ disequilibria suggests that the slopes of the short seamounts in the study region are characterized by particularly vigorous fluid dynamics. Since ‘fossil’ disequilibria already occurred at ~ O(1 – 10 km) away from the seamount slopes it is likely that these vigorous fluid dynamics rapidly decay away from the slopes on scales of O(1 ? 10 km). These conclusions are supported by the horizontal distribution and magnitude of the modeled total (barotropic + baroclinic) tidal current velocities of the predominating tidal M2 constituent: On (near?)critical seamount slopes baroclinic tides lead to localized [~ O(1 km)] increases of the overall tidal current velocity by a factor of ~ 2, thereby pushing the total current velocity well above the threshold for sediment erosion. The results of this and a previous study (Turnewitsch et al. 2004, Earth and Planetary Science Letters 222, 1023-1036) show that kilometer-scale flow / topography interactions leave a marine geochemical imprint which may help to develop sediment proxies for the reconstruction of past changes of fluid dynamics in the deep sea, particularly the internal wave field. Sites with (near?)critical seafloor slopes are the most promising sites to study paleo-changes of internal tides. To reconstruct the paleo-flow of residual currents and barotropic tides, sediments covering isolated topography of comparable breadth and width, and with sub-critical slopes, seem to be more appropriate. For the sediment-based reconstruction of paleo-parameters other than physical oceanographic ones kilometer-scale topography should be avoided altogether.
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| 10. |
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