East Iceland Current Research Articles

Along‐Stream, Seasonal, and Interannual Variability of the North Icelandic Irminger Current and East Icelandic Current Around Iceland

AbstractData from repeat hydrographic surveys over the 25‐year period 1993 to 2017, together with satellite altimetry data, are used to quantify the temporal and spatial variability of the North Icelandic Irminger Current (NIIC), East Icelandic Current (EIC), and the water masses they advect around northern Iceland. We focus on the warm, salty Atlantic Water (AW) flowing northward through Denmark Strait and the cooler, fresher, denser Atlantic‐origin Overflow Water (AtOW) which has circulated cyclonically around the rim of the Nordic Seas before being advected to the Iceland slope via the EIC. The absolute geostrophic velocities reveal that approximately half of the NIIC recirculates just north of Denmark Strait, while the remaining half merges with the EIC to form a single current that extends to the northeast of Iceland, with no further loss in transport of either component. The AW percentage decreases by 75% over this distance, while the AtOW percentage is higher than that of the AW in the merged current. The NIIC and merged NIIC‐EIC are found to be baroclinically unstable, which causes the flow to become increasingly barotropic as it progresses around Iceland. A seasonal accounting of the water masses within the currents indicates that only in springtime is the NIIC dominated by AW inflow north of Denmark Strait. Overall, there is considerably more seasonal and along‐stream variability in the properties of the flow prior to the merging of the NIIC and EIC. Over the 25‐year time period, the NIIC became warmer, saltier, and increased in volume transport.

Decreased influx of Calanus spp. into the south-western Norwegian Sea since 2003

The copepods Calanus hyperboreus and C. finmarchicus are the ecologically most important copepod species in the Nordic Seas. The larger C. hyperboreus, of polar origin, is advected into the south-western Norwegian Sea with the East Icelandic Current (EIC), and can therefore be considered an indicator species of these waters. Using large spatio-temporal hydrographic and zooplankton data sets, we show that an abrupt reduction in abundance of C. hyperboreus around the year 2003 in the south-western Norwegian Sea coincided with a reduction in the volume of Modified East Icelandic Water (MEIW) in the intermediate layers (R = 0.64, lagged one year). Abundance of C. hyperboreus and the volume of MEIW have since remained lower compared to the previous years (Mann-Whitney U tests, p < 0.05). The total zooplankton biomass in spring within the EIC, east of Iceland, was also much reduced around 2003 and has also since remained low. A comparable post-2003 reduction is observed in the abundance of overwintered stages of C. finmarchicus in May. Our results suggest that the reduction of zooplankton in the south-western Norwegian Sea around 2003 was caused by reduced influence of subarctic waters from the western region. This may in turn impact the extensive feeding migration of herring to this region.

Improved transport estimate of the East Icelandic Current 2002–2012

AbstractThe East Icelandic Current (EIC) is one of the major export pathways from the Iceland Sea north of Iceland, carrying mostly cold and fresh waters of Arctic origin. In this study, volume and freshwater transports are estimated using current profiles and salinity time series from a mooring deployed from 2011 to 2012 over the insular slope northeast of Iceland. These data are extended by hydrographic sections spanning the entire EIC four times per year. In combination with altimetry, geostrophic current profiles of the whole section are obtained for the period 2002–2012. The data are analyzed with respect to volume and freshwater transport variability and their relation to atmospheric forcing. The observations show a mean transport of 0.75 ± 0.08 Sv, and a mean freshwater transport of 3.4 ± 0.3 mSv in the upper 170 m. There is large interannual variability which appears to depend more on local conditions rather than large‐scale atmospheric forcing. The freshwater transport is small compared to the export in the East Greenland Current.

Multidecadal to millennial marine climate oscillations across the Denmark Strait (~ 66° N) over the last 2000 cal yr BP

Abstract. In the area of Denmark Strait (~66° N), the two modes of the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) are expressed in changes of the northward flux of Atlantic water and the southward advection of polar water in the East Iceland current. Proxies from marine cores along an environmental gradient from extensive to little or no drift ice, capture low frequency variations over the last 2000 cal yr BP. Key proxies are the weight% of calcite, a measure of surface water stratification and nutrient supply, the weight% of quartz, a measure of drift ice transport, and grain size. Records from Nansen and Kangerlussuaq fjords show variable ice-rafted debris (IRD) records but have distinct mineralogy associated with differences in the fjord catchment bedrock. A comparison between cores on either side of the Denmark Strait (MD99-2322 and MD99-2269) show a remarkable millennial-scale similarity in the trends of the weight% of calcite with a trough reached during the Little Ice Age. However, the quartz records from these two sites are quite different. The calcite records from the Denmark Strait parallel the 2000 yr Arctic summer-temperature reconstructions; analysis of the detrended calcite and quartz data reveal significant multi-decadal–century periodicities superimposed on a major environmental shift occurring ca. 1450 AD.

Spring production of Calanus finmarchicus at the Iceland–Scotland Ridge

Distribution and reproduction activity of the calanoid copepod Calanus finmarchicus were studied in the waters between Scotland and Iceland in April 1997 during the expected time of the animals’ ascent to surface waters following diapause. Ascent was taking place on both sides of the Iceland–Scotland Ridge, apparently from two separate overwintering centers. The population on the Faroe Shelf (FS) most likely came from the overwintering population in the Faroe Shetland Channel (FSC). Per capita egg production was highest on the FS (>30 eggs female −1 d −1) and lowest in the Iceland Basin (10 eggs female −1 d −1). The maximum clutch size recorded was on the FS (145 eggs). As the maximum clutch sizes that females produced were between 40% and 77% (area averages of the station maximum rates) of their size-specific reproduction potential, it is argued that egg production rates were generally food-limited. Chlorophyll a concentrations were, at all but one station, under 1 μg L −1. Chlorophyll-based ingestion could, theoretically, support the observed average egg production rates in the Iceland Basin and on the FS but only about 30% of the observed production at the stations in the East Icelandic Current (EIC). The carbon assimilated through ingestion of phytoplankton, Calanus own eggs and nauplii in the EIC was estimated to be too low to support the frequently observed production of clutches consisting of over 100 eggs. Cannibalism on eggs and nauplii was not likely to have constituted a significant component of dietary carbon intake. However, a combination of feeding and assimilation of reserved lipid remaining from overwintering could be sufficient to explain the observed per capita egg production rates. C. finmarchicus copepod stages 1–3 were only recorded in considerable numbers only on the FS. This suggests higher survival rates of eggs in the shelf waters.

Volume flux and fresh water transport associated with the East Icelandic Current

The importance of the circulation of fresh water within the Nordic Seas has frequently been pointed out, especially its effect on deep water formation and therefore possibly on the thermohaline circulation. The main source of fresh water is the East Greenland Current entering the Nordic Seas through Fram Strait. The Jan Mayen Polar Current and the East Icelandic Current (EIC) carry a part of the fresh water into the Greenland and Iceland Seas respectively. As a part of the EU project VEINS, Aanderaa current meters were deployed on two moorings within the EIC from June 1997 to June 1998 on a standard CTD section from Langanes, Northeast Iceland, to the central Iceland Sea in the direction towards Jan Mayen. The current was mainly concentrated along the slope where it was baroclinic, while over the deeper part a weak barotropic flow was observed. Geostrophic calculations, referenced to the current meter data, were used for estimating the volume flux and fresh water transport with the current. The total transport over the section towards the east was found to be 2.5 Sv. The fresh water transport relative to a salinity of 34.93, above 170 m, amounted to 5.5 mSv. This is roughly 4% of the fresh water transport through Fram Strait. This transport is put into a long-term perspective using hydrographic data from the Langanes section.

Diatom response to the Holocene climatic optimum on the North Icelandic shelf

A diatom record from core MD992275 on the North Icelandic shelf reveals palaeoclimatic and palaeoceanographic changes during the time interval 9000 to 5600 cal. year BP. The study period includes the Holocene Climate Optimum (HCO), as widely known in the North Atlantic region. A comparison with data for the last 2000 years and with the present-day surface sediment diatom assemblages shows that there was considerably stronger influence of Atlantic water masses in the area during the HCO than in the late Holocene and today. The results of cluster analysis and principal component analysis divide the studied period into three intervals, each characterised by a specific diatom assemblage. The assemblages indicate changes in the interaction of the relatively warm Irminger Current (IC) and the cold East Greenland Current (EGC) and East Icelandic Current (EIC). The North Icelandic shelf was strongly affected by the IC during the interval 8000–6800 cal. year BP, which may be the warmest period of the Holocene. During the intervals 9000–8000 and 6800–5600 cal. year BP, the influence of the IC was relatively weak and that of the EGC and EIC increased correspondingly. The well-known 8200 cal. year BP cooling event, shown in many records from the North Atlantic, is reflected by a relatively strong influence of the EGC and EIC between about 8300 and 8100 cal. year BP in our record. However, the diatom assemblages show that the inferred circulation change did not bring the strength of the IC down to the levels seen at present and during the last two millennia.

Distribution of dinoflagellate cyst assemblages in surface sediments from the northern and western shelf of Iceland

In order to provide calibration for palaeoceanographic investigations, 54 surface sediment samples from the northern and western margin of Iceland and Greenland have been analysed for their dinoflagellate cyst assemblages. Relatively high diversity was observed with a total of 28 taxa. Cysts of Pentapharsodinium dalei are dominant accompanied by Operculodinium centrocarpum and Nematosphaeropsis labyrinthus. Three groups of assemblages have been recognised based on multivariate statistical analyses and these are related to surface water masses and currents. The first association, Group I, located west of Iceland, is characterised by high abundance of O. centrocarpum and N. labyrinthus accompanied by significant occurrence of the heterotrophic taxa Brigantedinium spp., Selenopemphix quanta, cysts of Polykrikos schwartzii and cysts of Protoperidinium americanum. This region is under the influence of the Irminger Current (IC) and contains the most productive waters around Iceland. The second association, Group II, comprising high relative abundance of cysts of P. dalei accompanied by significant occurrence of O. centrocarpum and a very high concentration (up to 256 920 cysts/g), is situated in the northern Icelandic shelf, in the Polar Front realm, i.e. the marginal zone between the East Icelandic Current (EIC) and the northern branch of the IC. The third group (Group III) is in the region influenced by the East Greenland Current and the EIC and characterised by the co-dominance of cysts of P. dalei and O. centrocarpum, relatively high representation of Impagidinium pallidum and low concentrations (from 370 to 56 220 cysts/g). This investigation demonstrates that dinocyst distribution is clearly related to upper water mass physical factors. Advection of temperate species around Iceland suggests significant transport by surface currents, especially the IC; however, the apparent boundaries between the associations and decreasing percentages related to environmental gradients indicate that dispersal by surface transport is limited by the ecological requirements of the dinoflagellate cells. Bottom currents may play a role in the accumulation rate of cysts.

Diatom surface sediment assemblages around Iceland and their relationships to oceanic environmental variables

Canonical correspondence analysis of diatoms from surface sediment samples and oceanographic environmental variables shows that summer and winter sea-surface temperatures, water depth and winter sea-surface salinity are the main environmental factors affecting diatom distribution around Iceland. Of these, summer sea-surface temperature is the most important. Five diatom assemblages are distinguished and the distribution of these assemblages is clearly correlated with oceanic current patterns in the region. The sea-ice diatom assemblage is limited to the area where the East Greenland Current (Polar Water) has its strongest influence, and the cold diatom assemblage is basically controlled by the less cold East Icelandic Current (Modified Polar Water). The mixing diatom assemblage results from the interaction between the cold East Greenland and East Icelandic Currents and the warm Irminger Current. The warm diatom assemblage is located in the area dominated by the Irminger Current and may be used as an indicator of warm-water masses (Atlantic Water). The coastal diatom assemblage is the only one strongly influenced by both water depth and summer water temperatures.

A fine resolution numerical model of the Iceland‐Farœ front with open boundary conditions

An eddy‐resolving limited area primitive equation model of the Iceland‐Farœ frontal region is developed. The spatial and temporal evolution of the front is examined on time‐scales of up to 2 months. Experiments are performed changing the open boundary conditions at the lateral boundaries, using passive and active open boundary conditions. The experiment with the passive open boundary conditions reproduces many observed features of the Iceland‐Farœ frontal region. Discrepancies between these results and observations in the area are noted. In particular, the western end of the front drifts too far north. The model is then forced at the lateral boundaries using two contrasting barotropic velocity fields. Improvements in the results are noted. Comparison of the results illustrate to what extent and how, far‐field currents can affect the dynamics of this frontal region. The East Icelandic current is found to have the following important effect on the front: maintaining its vertical structure and confining the western end of the front to more southerly latitudes.