Iceland Sea Research Articles

Lateral redistribution of heat and salt in the Nordic Seas

The locations, times, and mechanisms by which heat and salt are transported through and within the Nordic Seas are discussed. The analysis is based on a regional, high resolution coupled sea ice-ocean numerical model, a climatological hydrographic data set, and atmospheric reanalysis. The model and climatology are broadly consistent in terms of heat loss, water masses, and mean geostrophic currents. The model fields are used to demonstrate that the dominant exchange between basins is an export of warm, salty water from the Norwegian Sea into the Greenland and Iceland Seas, with both the mean cyclonic boundary current system and eddy fluxes playing important roles. In both the model and the climatology, approximately 2/3 of the heat loss to the atmosphere over the Nordic Seas is found over the mean cyclonic flow and 1/3 takes place within the closed recirculations in the interior of each of the basin gyres, with the Norwegian Sea having the largest heat loss. The seasonal cycle is dominated by local air-sea heat flux within the gyres while it is dominated by lateral advection in the cyclonic boundary current, particularly in the northern Norwegian and Greenland Seas. The freshwater flux off the east Greenland shelf is correlated with the local winds such that in winter, when winds are generally towards the southwest, freshwater is advected onto the shelf and in summer, when winds are weak or towards the northeast, freshwater is advected into the Greenland Sea, which leads to salinification in winter and freshening in summer.

Heat Balance in the Nordic Seas in a Global 1/12° Coupled Model

AbstractThe Nordic seas are a gateway to the Arctic Ocean, where Atlantic water undergoes a strong cooling during its transit. Here we investigate the heat balance of these regions in the high-resolution Met Office Global Coupled Model GC3 with a 1/12° grid. The GC3 model reproduces the contrasted ice conditions and ocean heat loss between the eastern and western regions of the Nordic seas. In the west (Greenland and Iceland seas), the heat loss experienced by the ocean is stronger than the atmospheric heat gain, because of the cooling by ice melt. The latter is a major contribution to the heat loss over the path of the East Greenland Current and west of Svalbard. In the model, surface fluxes balance the convergence of heat in each of the eastern and western regions. The net east–west heat exchange, integrated from Fram Strait to Iceland, is relatively small: the westward heat transport of the Return Atlantic Current over Knipovich Ridge balances the eastward heat transport by the East Icelandic Current. Time fluctuations, including eddies, are a significant contribution to the net heat transports. The eddy flux represents about 20% of the total heat transport in Denmark Strait and across Knipovich Ridge. The coupled ocean–atmosphere–ice model may overestimate the heat imported from the Atlantic and exported to the Arctic by 10% or 15%. This confirms the tendency toward higher northward heat transports as model resolution is refined, which will impact scenarios of future climate.

Sharing wintering grounds does not synchronize annual survival in a high Arctic seabird, the little auk

Sharing the same wintering grounds by avian populations breeding in various areas may synchronize fluctuations in vital rates, which could increase the risk of extinction. Here, by combining multi-colony tracking with long-term capture-recapture data, we studied the winter distribution and annual survival of the most numerous Arctic seabird, the little aukAlle alle. We assessed whether little auks from different breeding populations in Svalbard and Franz Josef Land use the same wintering grounds and if this leads to synchronized survival. Our results indicate that birds from the Svalbard colonies shared similar wintering grounds, although differences existed in the proportion of birds from each colony using the different areas. Little auks from Franz Josef Land generally spent the winter in a separate area, but some individuals wintered in the Iceland Sea with Svalbard populations. Survival data from 3 Svalbard colonies collected in 2005-2018 indicated that sharing wintering grounds did not synchronize little auk annual survival rates. However, it is clear that the Iceland Sea is an important wintering area for little auks, and environmental changes in this area could have widespread impacts on many populations.

A multi-decadal record of oceanographic changes of the past ~165 years (1850-2015 AD) from Northwest of Iceland.

Extending oceanographic data beyond the instrumental period is highly needed to better characterize and understand multi-decadal to centennial natural ocean variability. Here, a stable isotope record at unprecedented temporal resolution (1 to 2 years) from a new marine core retrieved off western North Iceland is presented. We aim to better constrain the variability of subsurface, Atlantic-derived Subpolar Mode Water (SPMW), using near surface-dwelling planktic foraminifera and Arctic Intermediate Water (AIW) mass changes using benthic foraminifera over the last ~165 years. The reconstruction overlaps in time with instrumental observations and a direct comparison reveals that the δ18O record of Neogloboquadrina pachyderma is reliably representing temperature fluctuations in the SPMWs. Trends in the N. pachyderma δ13C record match the measured phosphate concentration in the upper 200 m on the North Icelandic Shelf well. Near surface-dwelling foraminifera trace anthropogenic CO2 in the Iceland Sea by ~ 1950 ± 8, however, a reduced amplitude shift in the Marine Suess effect is identified. We argue that this is caused by a contemporary ongoing increase in marine primary productivity in the upper ocean due to enhanced Greenland’s freshwater discharge that has contributed to a nutrient-driven fertilization since the 1940s/50s (Perner et al., 2019). Multi-decadal variability is detected. We find that the 16-year periodicity evident in SPMW and AIWs based on the δ18O of N. pachyderma and M. barleeanum is a signal of SST anomalies propagated into the Nordic Seas via the Atlantic inflow branches around Iceland. Spectral analyses of the planktic foraminiferal δ13C signal indicate intermittent 30-year cycles that are likely reflecting the ocean response to atmospheric variability, presumably the East Atlantic Pattern. A long-term trend in benthic δ18O suggests that Atlantic-derived waters are expanding their core within the water column from the subsurface into deeper intermediate depths towards the present day. This is a result of increased transport by the North Icelandic Irminger Current to the North Iceland Shelf over the historical era.

Fine-scale observations of physical and biological environment along a herring feeding migration route

We observed herring horizontal and vertical distribution during feeding migration along a 128 km transect across the Arctic front of the Norwegian and Iceland seas, in early June, in relation to its physical, chemical and biological environment, distribution of prey organisms and pelagic and mesopelagic competitors. The Norwegian Spring Spawning herring is one of the largest and economically most important stocks of pelagic fish in the world and understanding what controls its feeding migration is, and has been for centuries, a major research question that also has major implications for management. High resolution ecosystem data were obtained by hull mounted multi-frequency acoustics and a towed platform undulating between 10 and 400 m equipped with multi-frequency acoustics, temperature, salinity and fluorescence sensors, an Optical Plankton Counter and a Video Plankton Recorder. Additional sampling was done by MOCNESS, Macroplankton trawl, and CTD equipped with water bottles for temperature, salinity, nutrients and chlorophyll at discrete stations along the transect. Biological characteristics and stomach content of the herring were obtained from samples at discrete trawl stations. The Arctic front proved to be an important transitional zone in zooplankton biomass, abundance and diversity. Phenology of phyto- and zooplankton also changed across the front, being somewhat delayed on the cold side. The herring were distributed all along the transect showing a shallow distribution on the warm side and both deep and shallow on the cold side, not clearly related to light and time of the day. The herring stomach content was higher on the cold side. There was no significant pattern in average age, weight, or body length of the herring along the transect. The herring were present and fed in the area of the transect during the time when the overwintering generation of Calanus finmarchicus dominated, before the development of the new generation of the year. We suggest that the phenology of C. finmarchicus can be an important driver of the herring feeding migration. While prey-availability was higher on the Arctic side of the front, light conditions for visual feeding at depth were probably better on the Atlantic side. The herring did not show classical dial vertical migration, but its prey did, and the herring's prey were probably available within the upper 100 m during the course of a 24 h cycle. With a general westward direction of migration, the herring along the transect moved towards lower temperatures and temperature did not seem to be a probable driver for migration. We conclude that fine-scale studies of herring migration and feeding can increase our understanding of the migratory processes and add to our understanding of large-scale distributional patterns, changes therein, and herring trophodynamics and ecological role. The fine-resolution parameters can also be important as input to ecosystem models.

Ecology of mesozooplankton across four North Atlantic basins

A comparative study of the mesozooplankton in four North Atlantic basins is presented. During a trans-Atlantic expedition with R/V G.O. Sars in May and June 2013, the Norwegian Sea, Iceland Sea, Irminger Sea and Labrador Sea was surveyed twice on a round trip from Bergen, Norway to Nuuk, Greenland. Mesozooplankton samples of biomass, species composition and vertical distribution were obtained with WP2 and MOCNESS plankton nets, in addition to in situ data obtained from a Video Plankton Recorder (VPR) and Optical Plankton Counter (OPC) mounted on a submersible towed vehicle. Size-fractionated biomass samples showed that the Norwegian Sea had the highest biomass of small mesozooplankton (180–1000 μm), while Irminger and Iceland Seas had the highest biomass of the medium (1000–2000 μm) and largest (>2000 μm) size fractions, respectively. The Icelandic Sea large fraction biomass was dominated by Amphipods, Chaetognaths, Krill and Calanus hyperboreus. The Labrador Sea had the lowest total mesozooplankton biomass. A total of 9 different species/groups were found to comprise the 5 most numerically dominant species/groups across all basins, with Oithona spp. being the most common genus in all basins. C. finmarchicus was, as expected, found to be the most numerically common species of the Calanus complex in all basins, but the stage composition varied markedly between basins with young copepodite stages dominating only in the Labrador and central Norwegian Seas. In terms of both abundance and biomass, the Iceland Sea had a higher fraction of dominating mesozooplankton distributed below 200 m. The highest average particle density per 25 m interval was registered in the Norwegian Sea during daytime between 25-50 m (OPC data). In the Labrador and Irminger Seas, total estimated particle densities in the upper 50 m were lower and the particle densities peaked at intermediate sizes (1–3 mm). In all basins there were differences in the particle densities estimated between day and night. Based on VPR data, the Irminger and Iceland Seas had the highest density of copepods registered in the upper 200 m, whereas in the Labrador Sea, the highest average copepod densities were registered at depth. Densities of gelatinous organisms were at least an order of magnitude higher in the Labrador and Irminger Seas than in the Iceland Sea.

Vertical distribution and migration of mesopelagic scatterers in four north Atlantic basins

We studied vertical distribution and diel vertical migration (DVM) behaviour of mesopelagic acoustic scattering layers in relation to environmental conditions in the Norwegian Sea, the Iceland Sea, the Irminger Sea, and the Labrador Sea. Distinct mesopelagic scattering layers were found in all basins, but the daytime depth of the layers varied between basins. The results suggested that daytime vertical distribution across the four basins are strongly influenced by optical conditions. DVM occurred in all basins, and since daytime vertical distribution was influenced by optical conditions, it affected the amplitude of vertical connectivity. We used the proportion of the acoustic backscatter that migrated vertically into the epipelagic zone as a proxy for active vertical flux to the mesopelagic. The proportion of micronekton backscatter participating in the vertical migrations varied between the basins, with the highest and lowest vertical connectivity in the Norwegian Sea and the Iceland Sea respectively. We conclude that a more than 8-fold reduction in backscatter flux in the Iceland Sea was primarily attributable to optical conditions there, as high nighttime light levels appeared to exclude the micronekton from the epipelagic zone.

Spatial distributions and seasonality of four Calanus species in the Northeast Atlantic

This paper analyses spatial and seasonal patterns for near-surface abundances of four Calanus species in the Northeast Atlantic based on monthly Continuous Plankton Recorder (CPR) Survey data collected during 2008–2016. C. finmarchicus, C. helgolandicus, C. hyperboreus and C. glacialis represent different ecosystems, and water masses with differing oceanographic properties and origins. Hence, these are considered as indicator species in climate change studies. A southern transect between Norway and the United Kingdom represented the northern North Sea, a central transect crossed the Norwegian and Iceland Seas, while a northern transect between Norway and Svalbard crossed the entrance to the Barents Sea. C. finmarchicus was prevalent everywhere, while C. helgolandicus was mainly confined to the northern North Sea though also documented downstream in the Norwegian Sea as far north as the entrance to the Barents Sea. The ratio of C. helgolandicus to C. finmarchicus abundances is expected to increase in the northern North Sea and southern Norwegian Sea given continued increases in seawater temperature. C. hyperboreus and C. glacialis were mainly associated with regions influenced by Arctic waters in the Iceland and Norwegian Seas, and south of Svalbard, respectively. Within Atlantic water masses in the central Norwegian Sea, a distinct second generation of C. finmarchicus with surprisingly high late-autumn concentrations of older stages were found. In Coastal water, two or more generations of C. finmarchicus occurred, while only one generation was evident in Arctic waters. Young C. finmarchicus of the first annual generation showed an earlier timing in Coastal than Atlantic and Arctic waters. The upper range of the temperature niche for both C. hyperboreus and C. glacialis was found to be around 7 °C. However, the peak occurrence within the study area was in 1–2 °C in Arctic water in the Iceland Sea in April for C. hyperboreus, while around 5 °C in Barents Sea Arctic water in July for C. glacialis. C. finmarchicus was present in all water masses with a peak occurrence in June at around 6 °C. C. finmarchicus generally dominated the Calanus-biomass, but C. hyperboreus in Arctic water in the Iceland and Norwegian Seas in spring, and C. helgolandicus in the northern North Sea, could match or exceed the biomass of C. finmarchicus.

Quantifying two-way influences between the Arctic and mid-latitudes through regionally increased CO2 concentrations in coupled climate simulations

In which direction is the influence larger: from the Arctic to the mid-latitudes or vice versa? To answer this question, CO2 concentrations have been regionally increased in different latitudinal belts, namely in the Arctic, in the northern mid-latitudes, everywhere outside of the Arctic and globally, in a series of 150 year coupled model experiments with the AWI Climate Model. This method is applied to allow a decomposition of the response to increasing CO2 concentrations in different regions. It turns out that CO2 increase applied in the Arctic only is very efficient in heating the Arctic and that the energy largely remains in the Arctic. In the first 30 years after switching on the CO2 forcing some robust atmospheric circulation changes, which are associated with the surface temperature anomalies including local cooling of up to 1 °C in parts of North America, are simulated. The synoptic activity is decreased in the mid-latitudes. Further into the simulation, surface temperature and atmospheric circulation anomalies become less robust. When quadrupling the CO2 concentration south of 60° N, the March Arctic sea ice volume is reduced by about two thirds in the 150 years of simulation time. When quadrupling the CO2 concentration between 30 and 60° N, the March Arctic sea ice volume is reduced by around one third, the same amount as if quadrupling CO2 north of 60° N. Both atmospheric and oceanic northward energy transport across 60° N are enhanced by up to 0.1 PW and 0.03 PW, respectively, and winter synoptic activity is increased over the Greenland, Norwegian, Iceland (GIN) seas. To a lesser extent the same happens when the CO2 concentration between 30 and 60° N is only increased to 1.65 times the reference value in order to consider the different size of the forcing areas. The increased northward energy transport, leads to Arctic sea ice reduction, and consequently Arctic amplification is present without Arctic CO2 forcing in all seasons but summer, independent of where the forcing is applied south of 60° N. South of the forcing area, both in the Arctic and northern mid-latitude forcing simulations, the warming is generally limited to less than 0.5 °C. In contrast, north of the forcing area in the northern mid-latitude forcing experiments, the warming amounts to generally more than 1 °C close to the surface, except for summer. This is a strong indication that the influence of warming outside of the Arctic on the Arctic is substantial, while forcing applied only in the Arctic mainly materializes in a warming Arctic, with relatively small implications for non-Arctic regions.

Origin and Accumulation of an Anthropogenic CO2 and 13C Suess Effect in the Arctic Ocean

AbstractWe determined the impact of anthropogenic CO2 (Cant) accumulation on the δ13C of dissolved inorganic carbon in the Arctic Ocean (i.e., the 13C Suess effect) based on δ13C measurements during a GEOTRACES cruise in 2015. The δ13C decrease was estimated from the amount of Cant change derived by the transit time distribution approach and the ratio of the anthropogenic δ13C/dissolved inorganic carbon change (RC). A significant Cant increase (up to 45 μmol kg−1) and δ13C decrease (up to −0.9‰) extends to ~2,000 m in the Canada and Makarov Basin. We find distinctly different RC values for the intermediate water (300–2,000 m) and upper halocline water (<200 m) of −0.020 and −0.012‰ (μmol kg−1)−1, respectively, which identifies two sources of Cant accumulation from North Atlantic and North Pacific. Furthermore, estimated RC for intermediate waters is the same as the RC observed in the Greenland Sea and the rate of anthropogenic dissolved inorganic carbon increase estimated for intermediate waters at 0.9 μmol kg−1 yr−1 is identical to the estimated rate in the Iceland Sea. These observations indicate that the high rate of Cant accumulation and δ13C decrease in the Arctic Ocean is primarily a result of the input of Cant, via ventilation of intermediate waters, from the Nordic Sea rather than local anthropogenic CO2 uptake within the Arctic Basin. We determine the preindustrial δ13C (δ13CPI) distributions and find distinct δ13CPI signatures of the intermediate and upper halocline waters that reflect the difference in δ13CPI–PO4 relationship of Atlantic and Pacific source water.

The impact of wintertime sea-ice anomalies on high surface heat flux events in the Iceland and Greenland Seas

The gyres of the Iceland and Greenland Seas are regions of deep-water formation, driven by large ocean-to-atmosphere heat fluxes that have local maxima adjacent to the sea-ice edge. Recently these regions have experienced a dramatic loss of sea ice, including in winter, which begs the question have surface heat fluxes in the adjacent ocean gyres been affected? To address this a set of regional atmospheric climate model simulations has been run with prescribed sea ice and sea surface temperature fields. Three 20-year model experiments have been examined: Icemax, Icemed and Icemin, where the surface fields are set as the year with maximum, median and minimum sea-ice extents respectively. Under conditions of reduced sea-ice extent there is a 15% (19 W m−2) decrease in total wintertime heat fluxes in the Iceland Sea. In contrast, there is an 8% (9 W m−2) increase in heat fluxes in the Greenland Sea primarily due to higher local SSTs. These differences are manifest as changes in the magnitude of high heat flux events (such as cold air outbreaks). In the Iceland Sea, 76% of these events are lower in magnitude during reduced sea-ice conditions. In the Greenland Sea, 93% of these events are higher in magnitude during reduced sea-ice conditions as a result of higher SSTs coincident with retreating sea ice. So, in these experiments, the reduced wintertime sea-ice conditions force a different response in the two seas. In both gyres, large-scale atmospheric circulation patterns are key drivers of high heat flux events.

Micronekton biomass distribution, improved estimates across four north Atlantic basins

Distribution of micronekton was investigated during early summer of 2013, using data from a cruise covering the central parts of four north Atlantic basins, the Norwegian Sea (NS), Iceland Sea (ICS), Irminger Sea (IRS), and Labrador Sea (LS). Continuous underway acoustics mapped vertical and horizontal distributions, and trawl sampling provided data on biomass and taxonomic composition. The hull mounted acoustics and trawl catches suggested that, among the four basins, biomass of epipelagic, larger nektonic species (>20 cm length) during the cruise was highest in the NS and ICS basins, while mesopelagic non-gelatinous micronekton biomass peaked in the IRS and LS basins. Biomass of Scyphozoa was also about 1 order of magnitude higher in IRS and LS compared to ICS and NS. In ICS and NS, crustaceans made up about 50% of total non-gelatinous micronekton biomass, with fish making up less than 20% of total biomass. In contrast, fish constituted more than 60% of non-gelatinous biomass of catches in IRS and LS. In catches from ICS and NS the myctophid Benthosema glaciale dominated the catches, whereas bathylagids, gonostomatids, barracudinas and stomiids contributed to the high biomass densities of fish in IRS and LS. In addition to the differences in biomass between the basins, the acoustic measurements suggested gradients within the north-eastern basins, and large differences in vertical distribution of biomass between the basins during the cruise.

The Iceland Greenland Seas Project

AbstractThe Iceland Greenland Seas Project (IGP) is a coordinated atmosphere–ocean research program investigating climate processes in the source region of the densest waters of the Atlantic meridional overturning circulation. During February and March 2018, a field campaign was executed over the Iceland and southern Greenland Seas that utilized a range of observing platforms to investigate critical processes in the region, including a research vessel, a research aircraft, moorings, sea gliders, floats, and a meteorological buoy. A remarkable feature of the field campaign was the highly coordinated deployment of the observing platforms, whereby the research vessel and aircraft tracks were planned in concert to allow simultaneous sampling of the atmosphere, the ocean, and their interactions. This joint planning was supported by tailor-made convection-permitting weather forecasts and novel diagnostics from an ensemble prediction system. The scientific aims of the IGP are to characterize the atmospheric forcing and the ocean response of coupled processes; in particular, cold-air outbreaks in the vicinity of the marginal ice zone and their triggering of oceanic heat loss, and the role of freshwater in the generation of dense water masses. The campaign observed the life cycle of a long-lasting cold-air outbreak over the Iceland Sea and the development of a cold-air outbreak over the Greenland Sea. Repeated profiling revealed the immediate impact on the ocean, while a comprehensive hydrographic survey provided a rare picture of these subpolar seas in winter. A joint atmosphere–ocean approach is also being used in the analysis phase, with coupled observational analysis and coordinated numerical modeling activities underway.

RMetS National Meeting – Arctic prediction in a changing climate: understanding key processes and challenges

RMetS National Meeting – Arctic prediction in a changing climate: understanding key processes and challenges

On the causes of Arctic sea ice in the warm Early Pliocene

Scattered and indirect evidence suggests that sea ice occurred as far south as the Iceland Sea during the Early Pliocene, when the global climate was warmer than present. However, conclusive evidence as well as potential mechanisms governing sea ice occurrence outside the Arctic Ocean during a time with elevated greenhouse gas concentrations are still elusive. Here we present a suite of organic biomarkers and palynological records from the Iceland Sea and Yermak Plateau. We show that sea ice appeared as early as ~4.5 Ma in the Iceland Sea. The sea ice either occurred seasonally or was transported southward with the East Greenland Current. The Yermak Plateau mostly remained free of sea ice and was influenced dominantly by Atlantic water. From ~4.0 Ma, occurrence of extended sea ice conditions at both the Yermak Plateau and Iceland Sea document a substantial expansion of sea ice in the Arctic. The expansion occurred contemporaneous with increased northward heat and moisture transport in the North Atlantic region, which likely led to a fresher Arctic Ocean that favors sea ice formation. This extensive sea ice cover along the pathway of the East Greenland Current gradually isolated Greenland from warmer Atlantic water in the Late Pliocene, providing a positive feedback for ice sheet expansion in Greenland.

Geomagnetic paleosecular variation record spanning from 40 to 20 ka – implications for the Mono Lake excursion from Black Sea sediments

The Mono Lake geomagnetic excursion, characterized by low paleointensity and excursional virtual geomagnetic pole (VGP) positions at about 35 ka, has been cumulatively documented from global sites. However, the geomagnetic field geometry during this short-lived excursion is not conclusively described, since excursional directions are only sporadically reported. A full-vector paleosecular variation (PSV) record between 20 and 40 ka could be reconstructed from seven Black Sea sediment cores. The age models of these cores are based on radiocarbon dating and tephrochronology. Further age constrains were achieved by tuning ice rafted debris (IRD) counts and XRF logs (mainly Ca/Ti ratio) as climate proxies for Dansgaard–Oeschger (D–O) warming events, to the oxygen isotope record from Greenland ice cores (NGRIP). The PSV records of individual Black Sea cores were stacked by using 100-yr bins. At about 34.5 cal. ka BP, the Mono Lake excursion is evidenced in the stacked Black Sea PSV record by both a relative paleointensity (rPI) minimum and directional shifts. Associated VGPs from stacked Black Sea data migrated from Alaska, via the Tibetan Plateau and central Asia, to Greenland, performing a clockwise loop. This agrees with data recorded in the Wilson Creek Formation, USA., and Arctic core PS2644-5 from the Iceland Sea, suggesting a dominant dipole field. On the other hand, the Auckland lava flows, New Zealand, the Summer Lake, USA., and Arctic core ODP-919 yield distinct VGPs located in the central Pacific Ocean due to presumably non-dipole field. Finally, Black Sea sediments younger than the Mono Lake excursion recorded only normal secular variations.

Life cycles and seasonal vertical distributions of copepods in the Iceland Sea

The sub-Arctic Iceland Sea is an important feeding area for the Icelandic capelin stock with copepods as a major food item. Information on the life history of copepods in the area is limited, and therefore the major aim of the present paper is to describe the population development and ontogenetic vertical migrations of dominant copepods in the area. Depth stratified samples were collected on six cruises covering all seasons of the year from 2006 to 2008. Calanus hyperboreus dominated the biomass (~ 45% of copepods), with C. finmarchicus ranking second (~ 28%) and Metridia longa third (~ 17%). The copepods differed in their life history strategies. C. hyperboreus is unique in that it has the deepest winter distribution (~ 800–1000 m), reproduces at depth in February–March in the absence of phytoplankton food, and spends relatively short time in the surface layers during summer. C. finmarchicus also hibernates at depth, however much shallower (~ 200-600 m), and the reproduction at the surface in May–June is timed to the productive period of phytoplankton. A 2- to 3-year life cycle is proposed for C. hyperboreus and a 1 year for C. finmarchicus. Pseudocalanus spp. appear to have a similar life history as C. finmarchicus, while occupying intermediate depths (~ 400–1000 m) during the overwintering period. The life history of the omnivorous species M. longa appears relatively decoupled from the phytoplankton spring bloom. The same applies to the omnivorous species Oithona spp. and Oncaea spp. The information presented adds to the comparative description and understanding of copepods in sub-Arctic areas in general.

The subsurface circulation of the Iceland Sea observed with RAFOS floats

The pathways of dense waters located above the sill depth of Denmark Strait were investigated in the Iceland Sea using 52 acoustically tracked RAFOS floats. These floats were deployed in summer 2013 and 2014, with a target depth of 500 m, resulting in a total of 40.9 float-years of track data covering the Iceland Sea basin. In the interior Iceland Sea basin, the float tracks showed a double gyre circulation, out of which floats eventually escaped towards the Norwegian Sea in the East Icelandic Current, with some appearing to be en route to the Faroe Bank Channel. Four floats exited through Denmark Strait and surfaced in the Labrador and Irminger Seas. Four other floats deployed west of the Kolbeinsey Ridge at 70°N show the connection between the East Greenland Current and the East Icelandic Current. Floats deployed east of the Kolbeinsey Ridge along the Icelandic slope were captured in a region with no clear main flow. Eddy motions, mainly small scale (radii of 0.5–3 km), are seen throughout the Iceland Sea. Several floats were grounded on the Icelandic slope both east and west of the Kolbeinsey Ridge due to upslope currents, which created a rim of cold water along the slope. While this water was indicative of the presence of the North Icelandic Jet, no connection between the eastern Iceland Sea and Denmark Strait sill was found. Our investigation of wind stress curl fields from atmospheric reanalysis data suggests that high wind stress curl conditions may have been unfavorable for a westward connection by the North Icelandic Jet at the time of the float observations.

Ocean convection linked to the recent ice edge retreat along east Greenland

Warm subtropical-origin Atlantic water flows northward across the Greenland-Scotland Ridge into the Nordic Seas, where it relinquishes heat to the atmosphere and gradually transforms into dense Atlantic-origin water. Returning southward along east Greenland, this water mass is situated beneath a layer of cold, fresh surface water and sea ice. Here we show, using measurements from autonomous ocean gliders, that the Atlantic-origin water was re-ventilated while transiting the western Iceland Sea during winter. This re-ventilation is a recent phenomenon made possible by the retreat of the ice edge toward Greenland. The fresh surface layer that characterises this region in summer is diverted onto the Greenland shelf by enhanced onshore Ekman transport induced by stronger northerly winds in fall and winter. Severe heat loss from the ocean offshore of the ice edge subsequently triggers convection, which further transforms the Atlantic-origin water. This re-ventilation is a counterintuitive occurrence in a warming climate, and highlights the difficulties inherent in predicting the behaviour of the complex coupled climate system.

Mid‐Piacenzian Variability of Nordic Seas Surface Circulation Linked to Terrestrial Climatic Change in Norway

AbstractDuring the mid‐Piacenzian, Nordic Seas sea surface temperatures (SSTs) were higher than today. While SSTs provide crucial climatic information, on their own they do not allow a reconstruction of potential underlying changes in water masses and currents. A new dinoflagellate cyst record for Ocean Drilling Program (ODP) Site 642 is presented to evaluate changes in northward heat transport via the Norwegian Atlantic Current (NwAC) between 3.320 and 3.137 Ma. The record is compared with vegetation and SST reconstructions from Site 642 and SSTs from Iceland Sea ODP Site 907 to identify links between SSTs, ocean currents, and vegetation changes. The dinocyst record shows that strong Atlantic water influence via the NwAC corresponds to higher‐than‐present SSTs and cool temperate vegetation during Marine Isotope Stage (MIS) transition M2–M1 and KM5. Reduced Atlantic water inflow relative to the warm stages coincides with near‐modern SSTs and boreal vegetation during MIS M2, KM6, and KM4–KM2. During most of the studied interval, a strong SST gradient between Sites 642 and 907 indicates the presence of a proto‐Arctic Front (AF). An absent gradient during the first half of MIS KM6, due to reduced Atlantic water influence at Site 642 and warm, presumably Atlantic water reaching Site 907, is indicative of a weakened NwAC and East Greenland Current. We conclude that repeated changes in Atlantic water influence directly affect terrestrial climate and that an active NwAC is needed for an AF to develop. Obliquity forcing may have played a role, but the correlation is not consistent.