Deep Norwegian Sea Research Articles

Testing the deep‐sea glacial disturbance hypothesis as a cause of low, present‐day Norwegian Sea diversity and resulting steep latitudinal diversity gradient, using fossil records

AbstractAimWithin the intensively‐studied, well‐documented latitudinal diversity gradient, the deep‐sea biodiversity of the present‐day Norwegian Sea stands out with its notably low diversity, constituting a steep latitudinal diversity gradient in the North Atlantic. The reason behind this has long been a topic of debate and speculation. Most prominently, it is explained by the deep‐sea glacial disturbance hypothesis, which states that harsh environmental glacial conditions negatively impacted Norwegian Sea diversities, which have not yet fully recovered. Our aim is to empirically test this hypothesis. Specific research questions are: (1) Has deep‐sea biodiversity been lower during glacials than during interglacials? (2) Was there any faunal shift at the Mid‐Brunhes Event (MBE) when the mode of glacial–interglacial climatic change was altered?LocationNorwegian Sea, deep sea (1819–2800 m), coring sites MD992277, PS1243, and M23352.Time period620.7–1.4 ka (Middle Pleistocene–Late Holocene).Taxa studiedOstracoda (Crustacea).MethodsWe empirically test the deep‐sea glacial disturbance hypothesis by investigating whether diversity in glacial periods is consistently lower than diversity in interglacial periods. Additionally, we apply comparative analyses to determine a potential faunal shift at the MBE, a Pleistocene event describing a fundamental shift in global climate.ResultsThe deep Norwegian Sea diversity was not lower during glacial periods compared to interglacial periods. Holocene diversity was exceedingly lower than that of the last glacial period. Faunal composition changed substantially between pre‐ and post‐MBE.Main conclusionsThese results reject the glacial disturbance hypothesis, since the low glacial diversity is the important precondition here. The present‐day‐style deep Norwegian Sea ecosystem was established by the MBE, more specifically by MBE‐induced changes in global climate, which has led to more dynamic post‐MBE conditions. In a broader context, this implies that the MBE has played an important role in the establishment of the modern polar deep‐sea ecosystem and biodiversity in general.

Energy transfer from sub-inertial Kelvin waves to continental shelf waves at a transverse bottom escarpment

We consider barotropic coastally-trapped Kelvin waves of tidal origin along a straight coast that propagate from deeper water across a transverse bottom escarpment into a more shallow region. The M2 component, which has a frequency above the inertial frequency f, is modified by crossing the escarpment, but continues basically as a Kelvin wave into the shallow region. For tidal components that have frequencies smaller than f, like K1, some of the energy in the Kelvin wave is converted into a continental shelf wave (CSW) that follows the escarpment with shallow water to the right (in the northern hemisphere). The theory is applied to the shelf north-west of Norway where the deep Norwegian Sea is separated from the much shallower Barents Sea by an escarpment reaching from the north-Norwegian coast towards Spitsbergen. By introducing an idealized bottom topography and coastal geometry, analytical calculations and numerical modeling are used to investigate the energy flux in CSWs towards Spitsbergen caused by sub-inertial Kelvin wave motion along the west coast of Norway. Both analytical and numerical calculations indicate that the CSW energy flux towards Spitsbergen is about eighty percent of the incident sub-inertial Kelvin wave energy flux, and that only twenty percent of the energy flux is transmitted into the Barents Sea in the form of sub-inertial Kelvin waves.

Habitat variability and faunal zonation at the Ægir Ridge, a canyon-like structure in the deep Norwegian Sea.

The Ægir Ridge System (ARS) is an ancient extinct spreading axis in the Nordic seas extending from the upper slope east of Iceland (∼550 m depth), as part of its Exclusive Economic Zone (EEZ), to a depth of ∼3,800 m in the Norwegian basin. Geomorphologically a rift valley, the ARS has a canyon-like structure that may promote increased diversity and faunal density. The main objective of this study was to characterize benthic habitats and related macro- and megabenthic communities along the ARS, and the influence of water mass variables and depth on them. During the IceAGE3 expedition (Icelandic marine Animals: Genetics and Ecology) on RV Sonne in June 2020, benthic communities of the ARS were surveyed by means of a remotely-operated vehicle (ROV) and epibenthic sledge (EBS). For this purpose, two working areas were selected, including abyssal stations in the northeast and bathyal stations in the southwest of the ARS. Video and still images of the seabed were usedtoqualitatively describebenthic habitats based on the presence of habitat-forming taxa and the physical environment. Patterns of diversity and community composition of the soft-sediment macrofauna, retrieved from the EBS, were analyzed in a semiquantitative manner. These biological data were complemented by producing high-resolution bathymetric maps using the vessel’s multi-beam echosounder system. As suspected, we were able to identify differences in species composition and number of macro- and megafaunal communities associated with a depth gradient. A biological canyon effect became evident in dense aggregates of megafaunal filter feeders and elevated macrofaunal densities. Analysis of videos and still images from the ROV transects also led to the discovery of a number ofVulnerable Marine Ecosystems (VMEs) dominated by sponges and soft corals characteristic of the Arctic region. Directions for future research encompass a more detailed, quantitative study of the megafauna and more coherent sampling over the entire depth range in order to fully capture the diversity of the habitats and biota of the region. The presence of sensitive biogenic habitats, alongside seemingly high biodiversity and naturalness are supportive of ongoing considerations of designating part of the ARS as an “Ecologically and Biologically Significant Area” (EBSA).

The Northeast Greenland Shelf as a Potential Habitat for the Northeast Arctic Cod

Observations (1978-1991) of distributions of pelagic juvenile Northeast Arctic cod (Gadus morhua L.) show that up to 1/3 of the year class are dispersed off the continental shelf and into the deep Norwegian Sea while on the way from the spring-spawning areas along the Norwegian coast to the autumn-settlement areas in the Barents Sea. The fate of this variable fraction of pelagic juveniles off-shelf has been an open question ever since Johan Hjort’s (1914) seminal work. We have examined both the mechanisms causing offspring off-shelf transport, and their subsequent destiny using an individual-based biophysical model applied to quantify growth and dispersal. Our results show, consistently with the observations, that total off-shelf transport is highly variable between years and may be up to 27.4 %. Offspring from spawning grounds around Lofoten have a higher chance of being displaced off the shelf. The off-shelf transport is dominated by episodic events where frequencies and dates vary between years. Northeasterly wind conditions over a 3-7-day period prior to the off-shelf events are a good proxy for dispersal of offspring off the shelf. Offspring transported into the open ocean are on average carried along three following routes: back onto the adjacent eastern shelves and into the Barents Sea (36.9 %), recirculating within the Lofoten Basin (60.7 %), or drifting northwest to the northeast Greenland shelf (2.4 %). For the latter fraction the transport may exceed 12 % depending on year. Recent investigations have discovered distributions of young cod on the northeast Greenland shelf indicating that conditions may support survival for NEA cod offspring.

Landform assemblages and sedimentary processes along the Norwegian Channel Ice Stream

Several regional and detailed bathymetric datasets together with 2D and 3D seismic data are compiled to investigate the landform assemblages and sedimentary processes along the former path of the Norwegian Channel Ice Stream (NCIS). At the broad scale, the glacial geomorphology and sedimentary architecture reveals three different zones along the ice-stream path, characterized by: (1) glacial erosion in the onset zone and inner shelf area, (2) sediment transport through the main trunk of the ice stream across the mid-shelf, and (3) a zone of deposition towards the outer continental shelf edge. Along the first 400km of the ice stream bed (outer Oslofjord–Skagerrak–Stavanger) a major overdeepening is associated with suites of crag-and-tail features at the transition from the crystalline bedrock to the sedimentary bedrock, together with evidence of glaciotectonic thrusting in the form of hill-hole pairs. Here we interpret extensive erosion of both sedimentary rocks and Quaternary sediments. This zone is succeeded by an approximately 400km long zone, through which most of the sediments eroded from the inner shelf were transported, rather than being deposited. We infer that sediment was transported subglacially and is likely to have been advected downstream by soft sediment deformation. The thickness of till of inferred Weichselian age generally varies from 0 and 50m and this zone is characterized by mega-scale glacial lineations (MSGLs) which we interpret to be formed in a dynamic sedimentary system dominated by high sediment fluxes, but with some localized sediment accretion associated with lineations. Towards the shelf break, the North Sea Fan extends to the deep Norwegian Sea, and reflects massive sedimentation of glacigenic debris onto the continental slope. Numerous glacigenic debris flows accumulated and constructed a unit up to 400m thick during the Last Glacial Maximum. The presence of these three zones (erosion, transport, deposition) is consistent with observations from other palaeo-ice streams and their significance arises from their potential to feedback and impact on ice stream dynamics.

Leucothoid and Maerid Amphipods (Crustacea) from deep regions of the North Atlantic

From amphipod collections from the deep Norwegian Sea, three species are here redescribed: Maera loveni (Bruzelius 1859) (Maeridae), Leucothoe aff. spinicarpa (Abildgaard, 1789) and L. uschakovi Gurjanova, 1951 (Leucothoidae). A key to all Atlantic and Mediterranean Leucothoe species (males only) is provided.

Ecosystem structure and resilience—A comparison between the Norwegian and the Barents Sea

Abundance and biomass of the most important fish species inhabited the Barents and Norwegian Sea ecosystems have shown considerable fluctuations over the last decades. These fluctuations connected with fishing pressure resulted in the trophic structure alterations of the ecosystems. Resilience and other theoretical concepts (top-down, wasp-waste and bottom-up control, trophic cascades) were viewed to examine different response of the Norwegian and Barents Sea ecosystems on disturbing forces. Differences in the trophic structure and functioning of Barents and Norwegian Sea ecosystems as well as factors that might influence the resilience of the marine ecosystems, including climatic fluctuation, variations in prey and predator species abundance, alterations in their regular migrations, and fishing exploitation were also considered. The trophic chain lengths in the deep Norwegian Sea are shorter, and energy transfer occurs mainly through the pelagic fish/invertebrates communities. The shallow Barents Sea is characterized by longer trophic chains, providing more energy flow into their benthic assemblages. The trophic mechanisms observed in the Norwegian Sea food webs dominated by the top-down control, i.e. the past removal of Norwegian Spring spawning followed by zooplankton development and intrusion of blue whiting and mackerel into the area. The wasp-waist response is shown to be the most pronounced effect in the Barents Sea, related to the position of capelin in the ecosystem; large fluctuations in the capelin abundance have been strengthened by intensive fishery. Closer links between ecological and fisheries sciences are needed to elaborate and test various food webs and multispecies models available.

Distribution of selected anthropogenic radionuclides ( 137Cs, 238Pu, 239,240Pu and 241Am) in marine sediments with emphasis on the Spitsbergen–Bear Island area

Measurements of anthropogenic radionuclides in marine sediments can provide good estimates of past and present radioactive contamination of the marine environment. The Barents Sea is one of the world's richest ocean areas, and it is therefore of major interest for Norwegian fisheries to document the levels of radioactive contamination of this and adjacent ocean areas. In this study, concentrations of 137Cs, 238Pu, 239,240Pu and 241Am were measured in marine sediments collected mainly in the Spitsbergen–Bear Island region. Additional samples collected in the deep Norwegian Sea and near the Greenland ice-edge have been included for comparison. The highest radionuclide levels were found near Spitsbergen, reaching over 50% higher than in adjacent areas. Determinations of the mineral content and particle size distribution indicate a relation between the content of clay minerals and radionuclide levels. The present study confirms earlier observations of elevated levels of 137Cs in sediments in the Spitsbergen–Bear Island area and documents elevated levels of 238Pu, 239,240Pu and 241Am in these sediments. Using an exponential curve fit based on determinations of unsupported 210Pb in sediment cores, sedimentation rates of 0.28, 0.05 and 0.26 cm year −1 were calculated at locations south of Spitsbergen, near the Greenland ice-edge and in the deep Norwegian Sea, respectively.

Quaternary glaciations in southern Fennoscandia: evidence from southwestern Norway and the northern North Sea region

Based on records from the northern North Sea and southern Norway, Quaternary Fennoscandian glaciations are described and discussed. Maximum glaciation, defined as the presence of shelf edge glaciation, an ice stream flowing out of the Norwegian Channel and most likely an ice divide over the central part of Fennoscandia (Sweden, Gulf of Bothnia), occurred for the first time in the late Cenozoic at ca. 1.1 myr (the Fedje Glaciation). This glaciation was followed by a ca. 600 kyr period with at least two glaciations with ice extension somewhat larger than the Younger Dryas event in the region. The first maximum glaciation of the Bruhnes Chron was during isotope stage 12 and was followed by repeated maximum glaciations within each of the light isotopic stages until stage 2. During the Weichselian, the southwestern part of the Fennoscandian ice sheet reached maximum position three times (sometime between 22 and 28, 37 and 50, and 60 and 80 ka). Limited glaciations probably occurred during stadials between the early and middle Weichselian interstadials, between 500 ka and 1.1 Myr, and most likely also prior to 1.1 Myr. Deep Norwegian Sea Ice Rafted Detritus (IRD) records, reflecting contributions from several different ice sheets (Fennoscandian, Barents Sea, Iceland and Greenland), each with large variations in history of ice extent to their respective margins, yet to some degree they reflect the glaciation of the northern North Sea region with an increasing IRD input around 1.1 Myr and a relatively low input of North Sea components, during some cycles around the B/M boundary. Maximum glaciations occurred during insolation minima in the earlier part of the Middle Pleistocene, however, not all such minima are reflected by maximum glaciation in southern parts of Fennoscandia. The relatively poor chronological control and non-continuous character of the data on Weichselian interstadials/stadials precludes a clear relationship to atmospheric changes recorded in Greenland ice cores, as well as to precession and/or obliquity cycles in insolation.

The jæren area, a border zone of the norwegian channel ice stream

The coastal lowlands of Jæren, southwestern Norway, have an extensive cover of Quaternary sediments. Lithological, biostratigraphical and geochronological investigations of a series of boreholes across Jæren have allowed us to combine earlier and new information on these deposits into a temporal model of Quaternary sedimentation. The cores show evidence of at least four ice free episodes with marine deposition, during mainly arctic conditions. The oldest of these is considered to be ca. 200 ka old and the youngest one is the Sandnes interstadial which is 14C AMS dated to 32 ka BP. Interbedded between these units are 10–40 m thick units of till with components of marine material. These findings, together with a re-evaluation of distinct morphological features on Jæren, as well as earlier provenance studies, strongly suggest that Jæren has been a boundary zone between an ice stream following the Norwegian Channel draining a substantial part of the southern region of the Fennoscandian ice sheet, and local ice from south-western Norway. Through multiple periods of glaciation starting ca. 1.1 myr (million years) ago, the Norwegian Channel ice stream has been the main conduit of erosion products from southern Scandinavia to the deep Norwegian Sea. Comparison with ice stream profiles from Antarctica suggests that the deposition of relatively young marine sediments as high as ca. 200 m a.s.l. on Jæren is a result of glacial isostasy, rather than regional tectonic movements.

Variability in deep exchange between the Eurasian and Greenland Basins: Evidence from tritium and helium‐3

Observations of decay corrected tritium in the deep Eurasian Basin and Northern Fram Strait since 1979 indicate a significant decrease in 1993 whereas a box model predicts a steady decline with time. The model simulates the Greenland Sea and Eurasian Basin deep water observations reasonably closely up to the early 1990s. When it is retuned to simulate the 1993 decrease in the deep Eurasian Basin Water tritium, the deep exchange between the Greenland Sea and Eurasian Basin occurs over a shorter time scale. This is likely in response to the reduced deep water formation in the Greenland Sea in the early 1980s. Modeled tritium in the deep Eurasian Basin shows the same trends as in the Greenland Sea and deep Norwegian Sea but with time lags of 8±2 y and 17±2 y, respectively. These lags are in close agreement with values indicated by tritium‐helium3 dating.

Particle mixing processes of Chernobyl fallout in deep Norwegian Sea sediments: Evidence for seasonal effects

A 1430 m deep station in the Norwegian Sea (Voering Plateau) was occupied five times between May 1986 and February 1987 to investigate the seasonal variation in sediment mixing rates. Cherbnbyl-derived radiocesium, identified by its high proportion of short-lived 134Cs, was used as a tracer for mixing. Most of the nuclide input arrived at the sediment within a narrow time span in June/early July during the beginning of the seasonal biogenic sedimentation pulse. Measured 137Cs profiles in the sediment over time were compared with modelled distributions calculated with a finite difference scheme. The input function of radiocesium to the sea floor was evaluated from the increase of the total inventory with time. Time-invariant mixing coefficients did not provide reasonable fits to either summer or winter distributions. The best fit was obtained with a rate of mixing proportional to the radiocesium input flux, with an average enhancement factor of 6.6 during the two summer months. It appears that the benthic macrofauna are more active during the food supply season and rapidly ingest/bury freshly sedimented materials.

Ventilation rates of the Greenland and Norwegian Seas derived from distributions of the chlorofluoromethanes F11 and F12

Distributions of the chlorofluoromethanes (CFM) F11 (CFCl 3) and F12 (CF 2Cl 2) in the Greenland Sea were measured in late winter 1989 as part of the Greenland Sea Project (GSP), where Norwegian Sea Deep Water (NSDW) was also sampled in the Lofoten Basin. In the deep Boreas Basin inflow of NSDW to Greenland Sea Deep Water (GSDW) could be observed. The CFM distributions within the GSDW were homogeneous and not altered compared to 1982. Thus, deep convection in the Greenland Gyre was reduced since 1982 compared to previous years where various tracer measurements (1972, 1979, 1981 and 1982) prove convective turnover of GSDW during that time. In the deep Norwegian Sea, however, the CFM concentrations have increased since 1982. The surfae waters in the Greenland Gyre are saturated to only 79 ± 5% compared to ambient atmospheric CFM concentrations due to previous ice cover and/or rapid cooling of the surface waters. For the first time, CFM measurements have been made in a convection event reaching down to intermediate depths. A comparison of the CFM inventories of this location with those of the mean CFM depth profiles in the Greenland Gyre reveals no difference, showing homogenization of the water column, but no further equilibration between atmosphere and ocean during convection. This may be caused by the short duration of a convection event compared to the equilibration time for gas exchange between air and sea. Although convection did not reach the bottom, the CFM measurements made during convection are applied to construct a CFM boundary condition for the convective renewal of GSDW. With two different five-box models and the boundary conditions developed, ventilation rates of GSDW and NSDW also take into account the reduced turnover rate of GSDW since 1982. For the first time, model ventilation times are presented coincident with the F11 and F12 distribution. In model 1 the reduced convective renewal of GSDW is compensated by an appropriate reduction of the GSDW volume. In model 2, mass balance of the GSDW box is achieved by an upwelling term of the same magnitude than the renewal term. After 1982 both terms are reduced in the same manner. The turnover times of GSDW due to convection prior to 1982 of 19–20 (model 1) and 13–15 years (model 2) are much shorter than reported previously. In the years 1983–1989 the model-derived ventilation time increases to 190–200 years (model 1) and 42–67 years (model 2).

Initiation of Fennoscandian ice-sheet retreat during the last deglaciation

ALTHOUGH the retreat history of the southern margin of the Laurentide ice sheet during the last deglaciation has been well known for several decades1–3 and recently supported by evidence from accelerator mass spectrometer (AMS) radiocarbon dating of meltwater in the Gulf of Mexico4 and the North Atlantic subtropical gyre5, the retreat history of the Fennoscandian ice sheet before 13kyr ago is still poorly documented. From AMS 14C dating and isotopic analysis of a rapidly deposited series of supra-till sediments in the Norwegian Channel (North Sea), we find that the southern margin of the Fennoscandian ice sheet was in retreat by 15 kyr BP (before present), approximately 2,000 yr earlier than previously supposed. Oxygen isotope analyses in the channel sediments confirm earlier evidence from deep Norwegian Sea sediment cores for low salinity due to ice sheet discharge beginning ∼15–14.5 kyr BP (ref. 6). Recent recalibration of the 14C timescale indicates that the onset of deglaciation within the Norwegian Sea occurred during an interval of rapidly increasing summer insolation beginning∼18,000 calendar yr BP (ref. 7), suggesting that ice-sheet retreat may have been caused by increasing insolation acting on a particularly climate-sensitive ice-sheet configuration. Fresh water and icebergs discharged into the Norwegian Sea at this time reached the North Atlantic and may have contributed to a brief interval of extreme oceanic cooling8 and reduced production of North Atlantic Deep Water9,10. These factors may also have helped to briefly reverse the deglaciation trend (Erie Interstade) already underway in North America.

Ventilation of the deep Greenland and Norwegian seas: evidence from krypton-85, tritium, carbon-14 and argon-39

On leg 5 of the TTO expedition, the distributions of 85Kr, tritium, 14C, 39Ar, temperature, salinity, oxygen, carbon dioxide and nutrients were measured in the Greenland and Norwegian seas. These observations support previous observations that Greenland Sea Deep Water is formed by a deep convective process within the Greenland gyre. They also support Aagaard et al.'s (1985, Journal of Geophysical Research, 90, 4833–4846) new hypothesis that Norwegian Sea Deep Water forms from a mixture of Greenland Sea Deep Water and Eurasian Basin Deep Water. Volume transports estimated from the distributions of 85Kr, tritium, 14C and 39Ar range from 0.53 to 0.74 Sv for exchange between the surface and deep Greenland Sea and from 0.9 to 1.47 Sv for exchange between the deep Greenland and deep Norwegian seas. The residence time of water in the deep Greenland Sea with respect to exchange with surface water ranges from 24 to 34 years compared to 26–31 years reported by Peterson and Rooth (1976, Deep-Sea Research, 23, 273–283) and 35–42 years reported by Bullister and Weisss (1983, Science, 221, 265–268). The residence time of water in the deep Norwegian Sea with respect to exchange with the deep Greenland Sea ranges from 19 to 30 years compared to 97–107 years reported by Peterson and Rooth (1976) and 10–28 years reported by Bullister and Weiss (1983). The oxygen consumption rate was estimated to be at most 1.04 μM kg −1 y −1 for the deep Greenland Sea and to be between 0.47 and 0.79 μM kg −1 y −1 for the deep Norwegian Sea.

Anthropogenic Chlorofluoromethanes in the Greenland and Norwegian Seas

The concentrations of two industrially produced chlorofluoromethanes, CCl(3)F(F-11) and CCl(2)F(2)(F-12), have been measured in the water column and in the marine atmosphere of the Greenland and Norwegian seas. Measurable concentrations of these two chlorofluoromethanes have penetrated to the deep basins of both of these regions, and the general characteristics of their vertical distributions are similar to those of the bomb-produced radioisotopes injected into the atmosphere on a similar time scale. The data have been fitted to a time-dependent box model based on deep convective mixing in the Greenland Sea and lateral exchange between the deep basins. The model calculations for the two chlorofluoromethanes in the Greenland Sea give similar results, with a time scale for deep convection of about 40 years. The time scale for lateral mixing between the deep Greenland Sea and the deep Norwegian Sea is estimated to be 20 to 30 years, although the agreement between the calculations for the two chlorofluoromethanes is limited by analytical uncertainties at the low concentrations found in the deep Norwegian Sea and by uncertainties in the model assumptions.

Late Pleistocene Paleo-Oceanography of the Norwegian-Greenland Sea: Benthic Foraminiferal Evidence

AbstractFluctuations in benthic foraminiferal faunas over the last 130,000 yr in four piston cores from the Norwegian Sea are correlated with the standard worldwide oxygen-isotope stratigraphy. One species, Cibicides wuellerstorfi, dominates in the Holocene section of each core, but alternates downcore with Oridorsalis tener, a species dominant today only in the deepest part of the basin. O. tener is the most abundant species throughout the entire basin during periods of particularly cold climate when the Norwegian Sea presumably was ice covered year round and surface productivity lowered. Portions of isotope Stages 6, 3, and 2 are barren of benthic foraminifera; this is probably due to lowered benthic productivity, perhaps combined with dilution by ice-rafted sediment; there is no evidence that the Norwegian Sea became azoic. The Holocene and Substage 5e (the last interglacial) are similar faunally. This similarity, combined with other evidence, supports the presumption that the Norwegian Sea was a source of dense overflows into the North Atlantic during Substage 5e as it is today. Oxygen-isotope analyses of benthic foraminifera indicate that Norwegian Sea bottom waters warmer than they are today from Substage 5d to Stage 2, with the possible exception of Substage 5a. These data show that the glacial Norwegian Sea was not a sink for dense surface water, as it is now, and thus it was not a source of deep-water overflows. The benthic foraminiferal populations of the deep Norwegian Sea seem at least as responsive to near-surface conditions, such as sea-ice cover, as they are to fluctuations in the hydrography of the deep water. Benthic foraminiferal evidence from the Norwegian Sea is insufficient in itself to establish whether or not the basin was a source of overflows into the North Atlantic at any time between the Substage 5e/5d boundary at 115,000 yr B.P. and the Holocene.

Amphipoda Gammaridea from the deep Norwegian Sea. A preliminary report

Abstract The amphipod fauna of the Norwegian abyssal plains has a low diversity. About 30 species have been found and general faunal composition indicates that they represent the majority of species occuring in the area. The number of species would then be 20 % or less than that found in corresponding areas in the North Atlantic. Some of the species occur in great abundance. Endemism at the species level is high. The degree of affinity with the North Atlantic deep basins is low, while, on the other hand, connexions with the High Boreal and Arctic shelf and upper slope faunas are fairly close. The general impression is that the abyssal amphipod fauna is of comparatively recent origin.

Sediment bacteria in the deep Norwegian Sea

During a joint French-Swedish expedition (NORBI) in July-August, 1975, in the deep Norwegian Sea, the density of aerobic, heterotrophic sediment bacteria was determined by viable counts at 9 stations. The numbers rarely exceeded 103 ml-1 wet sediment. ATP measurements, with a limit of detectability of 5 ng ml-1 wet sediment, gave constantly negative results. One third of the strains isolated at 5°C were psychrophiles. The ability to degrade lipids, proteins, starch, and chitin, probably due to maximum biosynthesis of the exoenzymes, was correlated with the optimum temperature for growth. There was a strong positive correlation (P<0.001) between optimum temperature for the isolates and the number of different macromolecules attacked. Lipolytic activity was found to predominate. Differences in the bacterial composition between the Norwegian and Lofoten, Spitsbergen, and Greenland deep basins are discussed in relation to known differences in their faunal density and hydrography.

Formation and exchange of deep water in the Greenland and Norwegian seas

The formation and exchange of deep water in the Greenland and Norwegian seas are modeled by a time-dependent box model. Using tritium and radiocarbon data, primarily from the Geochemical Sections (GEOSECS) 1972 operation, the time scale for deep convective mixing in the Greenland Sea is estimated to be about 30 years, which implies that about 100 m of surface water are mixed down annually. The time scale for exchange between the deep Greenland Sea and the deep Norwegian Sea is estimated to be at least 100 years. It appears, on the basis of tritium data, that the formation and exchange of deep water in the Greenland and Norwegian seas are essentially isolated from the formation of the dense overflow waters of the Denmark Strait and the Iceland-Faroe Passage.