Greenland Side Research Articles

Fresh Water and Atmospheric Cooling Control on Density-Compensated Overturning in the Labrador Sea

Abstract As they rim the basin from the southern tip of Greenland to the southern Labrador coast, the waters in the Labrador Sea boundary current undergo a significant transformation in salinity and temperature, but much less so in density. Motivated by these observations, a previously developed simple three-layer model is adapted to understand the processes responsible for this density-compensated overturning in the Labrador Sea. From our model simulations, we find that the density-compensating water mass transformation in the boundary current can be largely attributed to the combined effect of 1) direct atmospheric cooling of the relatively warm boundary current and 2) freshening due to mixing with the shallower and fresh waters derived from Greenland meltwater discharge and Arctic Ocean inflow. Freshening of the boundary current waters due to the excess of precipitation over evaporation in the basin has an important, but less impactful, role in the density compensation. Studies examining the sensitivity of the density compensation to the freshwater entry location reveal a larger impact when the freshwater enters the boundary current on the Greenland side of the basin, compared to the Labrador side. These results yield insights into how increasing meltwater in the subpolar North Atlantic will affect the overturning.

Um dýpdarboringina í Vestmanna og í Lopra

A 1:50.000 geological map of the Faeroe Islands was published in 1969 with a shortened English edition in 1970. It was based on strictly chronostratigraphic principles. A total sequence of 3 km of tholeiitic basalt lavas was divided into a lower basalt series (about 900 m); a coal bearing sediment series (alout 10—15 m); a middle basalt series (about 1250 m) initiated by explosive volcanism producing agglomerates and tuffs, the tuffagglomerate zone; and an upper basalt series (about 675 m). Minor intrusions occur in form of dikes, sills and irregular intrusive bodies. The plateau has a low-angle easterly dip and the lavas of the lower basalt series are updomed in two areas, Vágar—Mykines and Suðuroy.
 Geological and geophysical investigations were continued out on the shelf around the islands and on the Faeroe bank, Bill Baily bank and Lousy bank to the west.
 Further geological information was obtained from two bore holes, one drilled in the summer 1980 at Vestmanna on Streymoy and the second in the summer and autumn of 1981 near the village of Lopra on Suðuroy (Fig- !)•
 The faeroese government organized, and was economically responsible for the drill project, which was carried out in collaboration with the Geological Survey of Denmark. The drilling work was entrusted to the icelandic »National Energy Authority« (Orkustofnun). The drilling project was supported by the Carlsberg Foundation because of its scientific significance,The bore hole at Vestmanna was drilled to determine if the lower basalt series and the coal bearing sediment series from Vágar could be traced down dip below sea level as far east as Streymoy, and to get information on the regional thermal gradient.
 The bore hoie at Vestmanna (Fig. 2) was drilled from just above sea level with full core to a depth of 660 m (Fig. 3). The coal bearing sedimentary series from Vágar was found at 556 m. Here it was 3 m thick and contained basaltic sand and pebbles, but not coal. The tuff-agglomerate zone did not occur at the drill site in Vestmanna. The drilling continued 101 m into the upper part of the lower basalt series. The thermal gradíent was 40°C/km.
 The Lopra bore hole was planned to penetrate at least 2 km into the unknown sequence below the known part of the lower basalt series and to obtain further thermal gradient data. The drill site was located west of the village Lopra a few m above sealevel, as low in the known part of the lower basalt series as possible (Fig. 4). A section through the bore hole reaching 2178 m below sea level is shown on Fig. 5. Six cores were taken (one core lost) at different levels and cuttings collected for each two m drilled. The drilled sequence consist of about 120 subaerially erupted lava flows indicating a subsidence of more than 2000 m. The lava flows average about 20 m in thickness while the intercalated sediments are up to 5 m. The drilled sequence consists ofaphyric to feldsparphyric tholeiitic basalts and must be considered as a continuation af the lower basalt series. The thickness of the total lava pile on the Faeroes is therefore at least 5 km and the early Tertiary basalt plateau on the European side of the North Atlantic, the Faeroe Islands, then reaches a thickness which is directly comparable with that on the East Greenland side of that ocean. The thermal gradient was about the samt as in Vestmanna.
 Final scientific results will be published in Fróðskaparrit (supplementa) in 2 years.

The Annual Salinity Cycle of the Denmark Strait Overflow

AbstractThe Denmark Strait Overflow (DSO) is an important source of dense water input to the deep limb of the Atlantic Meridional Overturning Circulation (AMOC). It is fed by separate currents from the north that advect dense water masses formed in the Nordic Seas and Arctic Ocean which then converge at Denmark Strait. Here we identify an annual salinity cycle of the DSO, characterized by freshening in winter and spring. The freshening is linked to freshening of the Shelfbreak East Greenland Current in the Blosseville Basin north of the Denmark Strait. We demonstrate that the East Greenland Current advects fresh pycnocline water above the recirculating Atlantic Water, which forms a low salinity lid for the overflow in Denmark Strait and in the Irminger Basin. This concept is supported by intensified freshening of the DSO in lighter density classes on the Greenland side of the overflow. The salinity of the DSO in the Irminger Basin is significantly correlated with northerly/northeasterly winds in the Blosseville Basin at a lag of 3–4 months, consistent with estimated transit times. This suggests that wind driven variability of DSO source water exerts an important influence on the salinity variability of the downstream DSO, and hence the composition of the deep limb of the AMOC.

Deciphering ∼45.000 years of Arctic Ocean lithostratigraphic variability through multivariate statistical analysis

Our understanding of past climate conditions in the Arctic Ocean has been hampered by poor age control caused in part by low sedimentation rates (<1 cm/kyr), hiatuses during glacial intervals as well as the scarcity and poor preservation of calcareous nanno- and microfossils in the sediments. Although recent advances using variations in single element (e.g. Mn) content or physical sediment properties (e.g. bulk density, grain size, colour) of the recovered sediments have aided Arctic core-to-core correlations, unique depositional events and post-depositional changes can complicate stratigraphic interpretations based on individual or even multiple, physical or chemical parameters. Furthermore, clear correlations between cores using physical and chemical parameters are not always possible to establish. To tackle this issue, we developed an algorithm that combines clustering and multivariate ordination to test the interrelation of multiple input parameters (e.g. an array of individual XRF elemental contents), and subsequently identifies statistically significant stratigraphic units on centimetre to decimetre scales. Our preliminary results show that a distinct sedimentological pattern during the past 45,000 years characterizes cores from the region of the Morris Jesup Rise and the Greenland side of the Lomonosov Ridge. Stratigraphic patterns of the Siberian Side of the Lomonosov Ridge yield distinct differences, thus allowing for novel insights into sedimentary processes shaping the different regions within the Arctic Ocean. We also argue that our approach can compensate for some of the weakness of single element or proxy applications, and hence aid the construction of a robust stratigraphic framework for a wide geographical range of Arctic Ocean sediments.

Need for focus on microbial species following ice melt and changing freshwater regimes in a Janus Arctic Gateway

Oceanic gateways are sensitive to climate driven processes. By connecting oceans, they have a global influence on marine biological production and biogeochemical cycles. The furthest north of these gateways is Nares Strait at the top of the North Water between Greenland and Ellesmere Island (Canada). This gateway is globally beneficial, first by supporting high local mammal and bird populations and second with the outflow of phosphate-rich Arctic waters fueling the North Atlantic spring bloom. Both sides of the North Water are hydrologically distinct with counter currents that make this Arctic portal a Janus gateway, after Janus, the Roman god of duality. We examined oceanographic properties and differences in phytoplankton and other protist communities from the eastern and western sides of the North Water (latitude 76.5°N) and found that species differed markedly due to salinity stratification regimes and local hydrography. Typical Arctic communities were associated with south flowing currents along the Canadian side, while potentially noxious Pseudo-nitzschia spp. were dominant on the Greenland side and associated with greater surface freshening from ice melt. This susceptibility of the Greenland side to Pseudo-nitzschia spp. blooms suggest that monitoring species responses to climate mediated changes is needed.

Lower crustal high-velocity bodies along North Atlantic passive margins, and their link to Caledonian suture zone eclogites and Early Cenozoic magmatism

In this study we use crustal-scale Ocean Bottom Seismic models to infer the presence of two types of lower crustal bodies at North Atlantic passive margins; Type I, primarily interpreted as Early Eocene magmatic intrusions, and Type II, interpreted as Caledonian eclogites. We discuss how these eclogites might be related to the main Caledonian Suture Zone and other tectonic features in a conjugate North Atlantic setting. Based on the first-order approximation that P-wave velocities can be related to rock strength, the narrower continental margin at the southern (Møre) transect may be explained by stronger lower crust there, compared with the northern (Vøring) transect. This difference in strength, possibly resulting in a steeper dip in the subducting Baltica Plate south of the proto-Jan Mayen Lineament, may explain the asymmetry in extensional style observed across this lineament. Our interpretation locates the main suture off mid-Norway close to the Møre Trøndelag Fault Zone on the Møre Margin, along the western boundary of the Trøndelag Platform on the Vøring Margin, and further northwards beneath the Lofoten Ridge. The Lower Crustal Body Type I is about 60% thicker on the Greenland side, for both transects, and its thickness along the northern transect is more than twice that of the southern transect. These differences are consistent with sub-lithospheric interaction between the Icelandic hotspot and the continental rift/oceanic accretion system around the time of continental break-up.

Western and central North Atlantic fin whale (Balaenoptera physalus) stock structure assessed using geographic song variations

Variations in calls or songs between areas are increasingly acknowledged as a way to assess stock structure. We present the results of an analysis of 163 fin whale (FW) songs recorded in seven areas of the North Atlantic (NA): Irminger Sea, Davis Strait, Grand Banks of Newfoundland, Southern Newfoundland, Gulf of St. Lawrence, eastern Scotian Shelf, and the waters off Delaware Bay. Song measurements included inter-note intervals (INI), notes' peak frequency and bandwidth and note type (classic, backbeat, and high-frequency) proportion. Seasonal patterns of classic-classic INI provided the highest level of differentiation between areas and revealed the existence of six acoustic stocks. Classification trees revealed that other parameters distinguished between regions over larger spatial scales, grouping some of the recording areas together. These results suggest that (1) there are four distinct stocks in the western NA; (2) the range of a presumed central NA stock includes southwestern Iceland, both sides of Greenland and appears to extend south along the Mid-Atlantic Ridge, at least in recent years; (3) two stocks are present off West Greenland. These results bring new information on potential FW stock delineations in the NA. The latter will be compared to those derived using other stock assessment metrics.

Magmatism and Eurekan deformation in the High Arctic Large Igneous Province: 40Ar–39Ar age of Kap Washington Group volcanics, North Greenland

The High Arctic Large Igneous Province is unusual on two counts: first, magmatism was prolonged and has been suggested to include an initial tholeiitic phase (130–80Ma) and a second alkaline phase (85–60Ma); second, it was subsequently deformed during the Eurekan Orogeny. New 40Ar–39Ar dating of alkaline volcanics from Kap Kane, part of the Kap Washington Group volcanics at the northern tip of Greenland, provides an emplacement age of 71.2±0.5Ma obtained from amphibole in lapilli tuffs, and a thermal resetting age of 49–47Ma obtained in feldspar and whole-rocks from trachyte flows. Patch perthite feldspars and coeval resetting of Rb–Sr isotopes by hydrothermal fluids provide further support for thermal overprinting. This thermal event is interpreted as a result of compressional tectonism of the Kap Cannon Thrust Zone in which older Palaeozoic metasediments were thrusted northwards over the Kap Washington Group volcanics.The formation of the tholeiitic suite (130–80Ma) is linked to the opening of the Canada Basin and may involve mantle plume action. Formation of the alkaline suite (85–60Ma) is attributed to continental rifting in the Lincoln Sea area linked to seafloor spreading in the Labrador Sea and the Baffin Bay, and to eastwards displacement of Greenland relative to North America. The alkaline suite, therefore, may be unrelated to the main tholeiitic phase of the High Arctic Large Igneous Province. The subsequent initiation of continental rifting and ensuing seafloor spreading in the Northeast Atlantic resulted in spreading and volcanism (61–25Ma) on both sides of Greenland, pushing Greenland northwards relative to North America. The tectonic setting in the High Arctic thus changed from extensional to compressional and volcanic activity was terminated. Evaluation of plate kinematic models shows that the relative northwards movement of Greenland culminated in the Eocene, coinciding with thermal resetting. We conclude that compression in North Greenland peaked at 49–47Ma and coincided with the Eurekan Orogeny in a belt across the Canadian Arctic Islands and western Svalbard.

Lycodes adolfi Nielsen and Fosså, 1993 (Teleostei: Zoarcidae) found in the Arctic Ocean

Adolf’s eelpout, Lycodes adolfi, was found at five bottom trawl stations in 2007–2009, on the slope towards the Sofia Deep north of Spitsbergen, at depths of 970–1,220 m and water temperatures below 0°C. Previously, the species has been known from cold and deep waters south of 74°N to both sides of Greenland and in the Norwegian Sea. The present material represents the first records from the Arctic Ocean and may indicate a wider arctic distribution of this species.

Nares Strait hydrography and salinity field from a 3‐year moored array

Nares Strait to the west of Greenland facilitates the exchange of heat and freshwater between the Arctic and Atlantic Oceans. This study focuses on salinity, temperature, and density measurements from Nares Strait from a mooring array deployed from 2003 to 2006. Innovative moorings requiring novel analysis methods measured seawater properties near 80.5°N, at spacing sufficient to resolve the internal Rossby deformation radius. The 3‐year mean geostrophic velocity has a surface‐intensified southward flow of 0.20 m s−1 against the western side of the strait and a secondary core flowing southward at 0.14 m s−1 in the middle of the strait. Data show warm salty water on the Greenland side and cold fresher water on the Ellesmere Island side, especially in the top layers. There was a clear difference in hydrographic structure between times when sea ice was drifting and when it was land fast. Ice was drifting in late summer, fall, and early winter with a strong surface‐intensified geostrophic flow in the middle of the strait. Ice was land fast in late winter, spring, and early summer, when there was a subsurface core of strong geostrophic flow adjacent to the western side of the strait. Salinity variations of about 2 psu in time and space reflect a variable freshwater outflow from the Arctic Ocean. One particularly strong pulse occurred at the end of July 2005. For several days, steeply sloping isohalines indicated strong geostrophic flow down the middle of the strait coinciding with an amplified ice export from the Arctic due to strong southward winds.

On the origins of water masses exported along both sides of Greenland: A Lagrangian model analysis

The origin of the water masses exported from the Arctic to the North Atlantic along both sides of Greenland is investigated using an original numerical method. A quantitative Lagrangian analysis is applied to the monthly climatological 3‐D output of a global ocean/sea ice high‐resolution model. It allows quantification of the different branches of the export to the North Atlantic, as well as related timescales and water mass transformations. In the model, the outflow through Davis Strait consists in equal parts of Pacific and Atlantic water, whilst the export through Fram Strait consists almost fully of Atlantic water (contrary to observations). Pacific water is transferred quickly (O(10 years)) to the North Atlantic through the Beaufort Gyre, where gradual warming and salinification occur. Atlantic water exiting in the surface layer along both sides of Greenland remains about 10 years in the Arctic Basin and undergoes cooling and significant freshening. Below the surface water, Atlantic water exiting through the intermediate and deep layers in Fram Strait follows different pathways in the Arctic, with trajectories being subject to topography constraints. The travel time depends strongly on the pathway (from 1 to 1000 years). The intermediate outflow consists mainly of water entering the Arctic at Fram Strait, while half the deep outflow is composed of water from the Barents Sea. We find that the Barents Sea Branch, which contributes to both the outflows at Fram and Davis straits, is almost fully transformed after a year due to heat exchanges with the very cold atmosphere (in the Barents Sea).

A model-based study of ice and freshwater transport variability along both sides of Greenland

We investigate some aspects of the variability of the Arctic freshwater content during the 1965–2002 period using the DRAKKAR eddy admitting global ocean/sea-ice model (12 km resolution in the Arctic). A comparison with recent mooring sections shows that the model realistically represents the major advective exchanges with the Arctic basin, through Bering, Fram and Davis Straits, and the Barents Sea. This allows the separate contributions of the inflows and outflows across each section to be quantified. In the model, the Arctic freshwater content variability is explained by the sea-ice flux at Fram and the combined variations of ocean freshwater inflow (at Bering) and outflow (at Fram and Davis). At all routes, except trough Fram Strait, the freshwater transport variability is mainly accounted for by the liquid component, with small contributions from the sea-ice flux. The ocean freshwater transport variability through both Davis and Fram is controlled by the variability of the export branch (Baffin Island Current and East Greenland Current, respectively), the variability of the inflow branches playing a minor role. We examine the respective role of velocity and salinity fluctuations in the variability of the ocean freshwater transport. Fram and Davis Straits offer a striking contrast in this regard. Freshwater transport variations across Davis Strait are completely determined by the variations of the total volume flux (0.91 correlation). On the other hand, the freshwater transport through Fram Strait depends both on variations of volume transport and salinity. As a result, there is no significant correlation between the variability of freshwater flux at Fram and Davis, although the volume transports on each side of Greenland are strongly anti-correlated (−0.84). Contrary to Davis Strait, the salinity of water carried by the East Greenland Current through Fram Strait varies strongly due to the ice-ocean flux north of Greenland.

Hydrographic changes in the Labrador Sea, 1960–2005

The Labrador Sea has exhibited significant temperature and salinity variations over the past five decades. The whole basin was extremely warm and salty between the mid-1960s and early 1970s, and fresh and cold between the late 1980s and mid-1990s. The full column salinity change observed between these periods is equivalent to mixing a 6 m thick freshwater layer into the water column of the early 1970s. The freshening and cooling trends reversed in 1994 starting a new phase of heat and salt accumulation in the Labrador Sea sustained throughout the subsequent years. It took only a decade for the whole water column to lose most of its excessive freshwater, reinstate stratification and accumulate enough salt and heat to approach its record high salt and heat contents observed between the late 1960s and the early 1970s. If the recent tendencies persist, the basin’s storages of salt and heat will fairly soon, likely by 2008, exceed their historic highs. The main process responsible for the net cooling and freshening of the Labrador Sea between 1987 and 1994 was deep winter convection, which during this period progressively developed to its record depths. It was caused by the recurrence of severe winters during these years and in its turn produced the deepest, densest and most voluminous Labrador Sea Water (LSW 1987–1994) ever observed. The estimated annual production of this water during the period of 1987–1994 is equivalent to the average volume flux of about 4.5 Sv with some individual annual rates exceeding 7.0 Sv. Once winter convection had lost its strength in the winter of 1994–1995, the deep LSW 1987–1994 layer lost “communication” with the mixed layer above, consequently losing its volume, while gaining heat and salt from the intermediate waters outside the Labrador Sea. While the 1000–2000 m layer was steadily becoming warmer and saltier between 1994 and 2005, the upper 1000 m layer experienced another episode of cooling caused by an abrupt increase in the air-sea heat fluxes in the winter of 1999–2000. This change in the atmospheric forcing resulted in fairly intense convective mixing sufficient to produce a new prominent LSW class (LSW 2000) penetrating deeper than 1300 m. This layer was steadily sinking or deepening over the years following its production and is presently overlain by even warmer and apparently less dense water mass, implying that LSW 2000 is likely to follow the fate of its deeper precursor, LSW 1987–1994. The increasing stratification of the intermediate layer implies intensification in the baroclinic component of the boundary currents around the mid-depth perimeter of the Labrador Sea. The near-bottom waters, originating from the Denmark Strait overflow, exhibit strong interannual variability featuring distinct short-term basin-scale events or pulses of anomalously cold and fresh water, separated by warm and salty overflow modifications. Regardless of their sign these anomalies pass through the abyss of the Labrador Sea, first appearing at the Greenland side and then, about a year later, at the Labrador side and in the central Labrador Basin. The Northeast Atlantic Deep Water (2500–3200 m), originating from the Iceland–Scotland Overflow Water, reached its historically freshest state in the 2000–2001 period and has been steadily becoming saltier since then. It is argued that LSW 1987–1994 significantly contributed to the freshening, density decrease and volume loss experienced by this water mass between the late 1960s and the mid 1990s via the increased entrainment of freshening LSW, the hydrostatic adjustment to expanding LSW, or both.

Understanding basin sedimentary provenance: evidence from allied phytogeographic and heavy mineral analysis of the Palaeocene of the NE Atlantic

The drilling of hydrocarbon exploration wells in the Faroe–Shetland Basin has provided an expanding sample resource that provides material for testing recently developed palynology-based sediment transport analysis. This technique has been verified by comparison with heavy mineral analysis; both approaches have been used to identify sediment sources and input points along the strike of the Palaeocene West Shetland Platform. Integration of heavy mineral and palynological data has provided a basis for understanding arenaceous and argillaceous sediment distribution and sourcing. In addition to a source from the western, Greenland side of the basin, four argillaceous and four arenaceous sedimentary sources have been identified along the strike of the West Shetland Platform. These vary in temporal and spatial distribution, and thus provide a history of sediment source evolution. This analysis supports a persistent difference in source between the Corona Basin and the Flett and Judd Sub-basins. Although source variation and overlap between basins is evident, transfer zones represent both conduits for and barriers to effective sediment transport. Both palynological and heavy mineral evidence identifies the former presence of Late Namurian–Westphalian strata on the West Shetland Platform, which were removed by subsequent erosion.

Habitat Use of Ringed Seals, &lt;i&gt;Phoca hispida&lt;/i&gt;, in the North Water Area (North Baffin Bay)

In conjunction with the International North Water Polynya Study in Smith Sound (northern Baffin Bay) in 1997-99, we examined the area use and diving activity of 23 ringed seals (Phoca hispida) that had been equipped with satellite transmitters on the Greenland side of the North Water (NOW) area. The study covered the period 12 August 1996-30 June 1999. Contact with the seals was maintained for an average of 108 days (range: 8-332 days). Four seals emigrated from the NOW area. During all seasons, the seals that remained in the area spent about 90% of the time in coastal (&lt; 100 m deep) waters in the eastern parts of the NOW area. The total area visited by the seals during the open-water season ranged between 10 300 km² (1996) and 18 500 km² (1998), corresponding to about 15% to 25% of the entire NOW area. In winter, the total area visited by the seals varied between 2500 km² (1996-97) and 7000 km² (1998-99), and in spring, between 800 km² (1999) and 2100 km² (1997). Individual movement was significantly greater during the open-water season than during winter and spring. Maximum dive depths recorded were over 500 m (maximum for the instrument) outside and 376 m inside the NOW, for a 96 kg male seal. Non-adult seals spent about 99% of the time in waters less than 100 m deep, and more than 92% of the time in the upper 50 m. In contrast, adults tended to spend more time at greater depths. The study indicated that (1) the ringed seals took advantage of the generally lighter ice conditions in the eastern NOW, and (2) that non-adults likely exploited ice-associated amphipods and young polar cod (Boreogadus saida), and adults, mainly older polar cod and cephalopods taken at greater depths.

Resuspension and particle transport in the benthic nepheloid layer in and near Fram Strait in relation to faunal abundances and 234Th depletion

The West Spitsbergen Current, flowing northward through Fram Strait, causes a benthic nepheloid layer (BNL) on the western slope of the Yermak Plateau. This BNL is weaker on the eastern side of the Plateau and absent on the Greenland side of the Fram Strait, where the East Greenland Current flows south. In this BNL we find throughout a depletion of 234Th relative to its parent 238U, and we use this to study the particle dynamics in the BNL. The export flux from the ice-covered surface ocean and from a young bloom found in the ice-free waters off NE Greenland is shown to be negligible, allowing us to explain the 234Th depletion by interaction with the sediment alone. The depletion, balanced by a similar excess in the surface layer of the sediment, implies the existence of a settling-resuspension loop with an average particle residence time of 1–2 months. The asymmetry with a stronger resuspension loop on the western (80–120 mg m −2 d −1) than on the eastern side of the Yermak Plateau (1–15 mg m −2 d −1) is reflected in the numbers of species and individuals of suspension feeders in box core samples, and in epifauna densities estimated from video observations. The suspension feeders thus contribute to deposition of particles that are advected from more productive ice-free regions. This explanation is in agreement with the east–west asymmetry in the input of organic material to the sediments of the Yermak Plateau, which has been concluded from the distribution of pigments, bacterial activity and meiofauna abundances, observed in a concurrent study at the same stations. On the West Spitsbergen shelf, a very intensive BNL was monitored over 1 month with a moored filtration system. A part of the sustained high suspended load may be advected over long distances. This study illustrates how the tracer 234Th can help to determine the extent to which suspended particles are in continuous exchange with the seafloor, and where biological mediation and chemical modification can be expected.

Temporal and spatial patterns in the surface-water biomass of phytoplankton in the North Water

Abstract Temperature, salinity, and in vivo fluorescence of surface seawater in the North Water were recorded continuously, using a CTD+fluorometer, in August 1997, April–July 1998 and August–October 1999. The phytoplankton bloom started in the polynya on the Greenland side in April. In April and May, high phytoplankton biomass coincided with saline water on the Greenland side, while biomass was low on the Ellesmere Island (Canada) side where a deep mixed layer prevailed. High phytoplankton biomass extended over the whole polynya in June, when surface temperature increased due to solar heating and salinity decreased due to freshwater input. The initiation of the bloom was about 2 months earlier on the Greenland than the Canadian side. In July and August, phytoplankton biomass became low in the southern survey area, indicating that the phytoplankton bloom had ended. In September, relatively saline and warm water occurred in the southeastern part of the study area where, consistent with the change in water properties, high concentrations of chlorophyll a were observed again. These results imply that both the earlier start of the algal bloom in spring and the eventual increase in phytoplankton biomass in summer contribute to the high annual primary production along the Greenland side, thus influencing the structure and biological productivity of the entire North Water ecosystem.

Physical control of spring–summer phytoplankton dynamics in the North Water, April–July 1998

Abstract A 4-month multidisciplinary expedition, beginning at the end of winter to track the spring phytoplankton bloom to its termination in summer, was conducted from April to July 1998. The aim of the expedition was to investigate possible mechanisms responsible for the high biological productivity of the North Water, the most productive and largest polynya in the Northern Hemisphere. The aims of the present study were to investigate: (1) the effects of the physical forces, driving the formation of the polynya, on the dynamics of the phytoplankton stock in the polynya over the spring–summer period; and (2) the factors that limit the maximum biomass of phytoplankton. Contrasting physical characteristics, including ice concentration, surface mixed-layer depth (MLD), salinity and temperature in the surface mixed layer (SML), were observed between the east and west sides of the polynya. The Greenland (eastern) side of the polynya was characterized by a shallow SML, warm temperature, and high salinity relative to the Ellesmere Island, Canada (western) side. Chlorophyll a (Chl)>1 mg m −3 was observed in late April on the eastern side, and in late May on the western side. The peak phytoplankton bloom occurred in the southeastern part of the polynya, with average Chl of 15 mg m −3 (240–300 mg m −2 ) in the euphotic zone during the end of May and beginning of June. The increased phytoplankton biomass was associated with higher salinity and warmer temperature on the eastern side of the polynya. Low temperature in April and May decoupled the increase of Chl biomass from the shallowed SML, as predicted by Sverdrup's model. As Chl in the euphotic zone increased to 5 mg m −3 , the proportion of light absorption by phytoplankton could not increase further with Chl biomass, which might have limited the increase of primary production in the water column. Although the initial nutrient inventories largely determined the maximum biomass of phytoplankton, self-shading occurred in the build-up phytoplankton biomass to ∼5 mg m −3 , which retarded the timing of the peak bloom. Both sensible heat due to deep warm water entrainment into the SML and the biological heating effect via phytoplankton light absorption appear to contribute to the pattern of phytoplankton distribution in the North Water.

An overview of physical processes in the North Water

The presence of a polynya strongly affects biological processes by influencing underwater light levels, water-column stratification, the upwelling of nutrients, and the timing of production cycles. An overview of the existing literature on the oceanography, meteorology and sea-ice conditions of the North Water, a large recurring polynya in northern Baffin Bay, is presented. The North Water is influenced by a cold inflow of Arctic Ocean water from the north and, in some areas, a warmer inflow of Atlantic water from the south. Earlier observations and modeling studies suggested that both wind and ocean advection of sea ice, as well as heat input to the surface waters by either upwelling or mixing, were responsible for the formation and maintenance of the polynya. Recent data indicate the North Water to be primarily generated by the southward drift of ice by winds and currents, as opposed to melting ice by sensible heat input over large areas. Localized sensible heat effects occur in fall, winter and spring along the Greenland side of the polynya.

Trans-Atlantic correlation of the Palaeogene volcanic successions in the Faeroe Islands and East Greenland

Before continental break-up in the NE Atlantic, the Faeroe Islands and central East Greenland were within a distance of 100–120 km. Chemical and lithological data for complete sections through the 5 km thick piles of contemporaneous Palaeogene flood basalts in the Faeroe Islands and in the Nansen Fjord area in East Greenland show very similar basalt compositions and evolution patterns with time. The Faeroes lower basalt formation and the equivalent Nansen Fjord Formation in East Greenland form a pre-break-up succession overlain by a sediment horizon. A syn-break-up succession consists of the Faeroes middle and upper basalt formations and the equivalent Milne Land Formation in East Greenland in which five intervals can be correlated with a compositional evolution from Ti-rich magnesian basalts and picrites at the base to a dominance of MORB -like low-Ti basalts at the top. The successions were generated in the same mantle melting column beneath a thinning continent with a rift zone that eventually ruptured the continent. The evolution pattern is very similar to that seen on the SE Greenland margin, but spreading according to the Palmason model of 1973 was not yet established. The pre- and syn-break-up successions formed volcanic megasystems stretching across the rift zone with areal extents of 70 000 and 220 000 km 2 and volumes of 120 000 and 250 000 km 3 . Rocks from the pre- and syn-break-up successions can be discriminated based on a simple major-element plot. The overlying succession was 3–3.5 km thick in E Greenland but was thin or absent in the Faeroes; the energy source for the melting appears to have been concentrated on the Greenland side.