Recent warming and freshening of the Norwegian Sea observed by Argo data

Climate variability in the Norwegian Sea, comprising the Norwegian and Lofoten Basins, was investigated based upon monthly estimates of ocean heat and freshwater contents using data from Argo floats during 2002–18. Both local air–sea exchange and advective processes were examined and quantified for monthly to interannual time scales. In the recent years, 2011–18, the Norwegian Sea experienced a decoupling of the temperature and salinity, with a simultaneous warming and freshening trend. This was mainly explained by two different processes; reduced ocean heat loss to the atmosphere and advection of fresher Atlantic water into the Norwegian Sea. The local air–sea heat fluxes are important in modifying the ocean heat content, although this relationship varied with time scale and basins. On time scales exceeding 4 months in the Lofoten Basin and 6 months in the Norwegian Basin, the air–sea heat flux explained half or even more of the local ocean heat content change. There were both a short-term and long-term response of the wind forcing on the ocean heat content. The monthly to seasonal response of increased southerly wind cooled and freshened the Norwegian Basin, due to eastward surface Ekman transport, and increased the influence of Arctic Water. However, after about a 1-yr delay the ocean warmed and became saltier due to an increased advection of Atlantic Water into the region. Increased westerly winds decreased the ocean heat content in both cases due to increased transport of Arctic Water into the Norwegian Sea.publishedVersio

The mid-depth circulation of the Nordic Seas derived from profiling float observations

Article published in Tellus Series A-Dynamic meterology and oceanography, 62 (4): 516-529 AUG 2010The trajectories of 61 profiling Argo floats deployed at mid-depth in the Nordic Seas—the Greenland, Lofoten and Norwegian Basins and the Iceland Plateau—between 2001 and 2009 are analysed to determine the pattern, strength and variability of the regional circulation. The mid-depth circulation is strongly coupled with the structure of the bottom topography of the four major basins and of the Nordic Seas as a whole. It is cyclonic, both on the large-scale and on the basin scale, with weak flow (<1 cm s−1) in the interior of the basins and somewhat stronger flow (up to 5 cm s−1) at their rims. Only few floats moved from one basin to another, indicating that the internal recirculation within the basins is by far dominating the larger-scale exchanges. The seasonal variability of the mid-depth flow ranges from less than 1 cm s−1 over the Iceland Plateau to more than 4 cm s−1 in the Greenland Basin. These velocities translate into internal gyre transports of up to 15 ± 10 × 106 m3 s−1, several times the overall exchange between the Nordic Seas and the subpolar North Atlantic. The seasonal variability of the Greenland Basin and the Norwegian Basin can be adequately modelled using the barotropic vorticity equation, with the wind and bottom friction as the only forcing mechanisms. For the Lofoten Basin and the Iceland Plateau less than 50% of the variance can be explained by the wind

Numerical models and long term monitoring - How can numerical models be used to support in situ sampling and survey design for long term hydrographic monitoring in standard sections?

As a part of regular monitoring of the marine environment, IMR conducts 10 fixed transects on a multiannual basis during which hydrographical, chemical and plankton data are collected at the same positions several times a year. The transect data sets, which in some cases span up to seven decades, have been vital to the understanding of long-term variability and trends in environmental and climate conditions. As an alternative approach to assemble physical data, numerical circulation models are widely used. There is a large variety of model data archives available, both internally at the IMR and from publicly open data portals, but it is difficult to consider the precision of the different models as they have different properties, resolution, coverage area etc. This report assesses how well existing model products developed and/or intensively used by the Oceanography and Climate Research Group can be utilised to assess and support the shipboard monitoring on the transects. Main focus is on TOPAZ, which is the only fully operational model with a model domain covering all the transects considered here. The results show that TOPAZ reproduces interannual variability and multiannual trends well. However, temperature, salinity and current velocity values, as well as seasonal variability and extreme conditions are less well represented. The operational (internal) Norkyst model show the best skill reproducing current velocities, but do not cover all transects. Using TOPAZ to assess how well the present sampling strategy captures the spatial variability in hydrographic variables suggests that the current sampling strategy is well designed in terms of the horizontal spacing of the fixed transects, although the sections in the northern Norwegian Sea and southern Barents Sea show a significant co-variability of Atlantic Water towards the Arctic Ocean. Assessing the impact of sampling frequency on long-term monitoring efforts in one of the transects, suggests a minimum sampling frequency of 3-4 transects per year to prevent loss of information relating to interannual variability and trends. We note, however, that a full assessment of the impact of sampling frequency on the transects must include also chemical and plankton observations and models, as well as the need of capturing short-term variations like the seasonal cycle.Numerical models and long term monitoring - How can numerical models be used to support in situ sampling and survey design for long term hydrographic monitoring in standard sections?publishedVersio

Arctic and Atlantic waters in the Norwegian Basin, between year variability and potential ecosystem implications

The ocean climate of the southern Norwegian Sea - the Norwegian Basin - is largely set by the relative amount of Atlantic Water in the eastern and Arctic Water in the western region. Here we utilized hydrographic data from repeated sections, together with annually gridded survey data of the upper 1000 m, to resolve the main hydrographic changes over the period 1995-2019. Based on integrated heat -and freshwater content, we divide into three periods. The first period 1995-2005, denoted Arctic, is characterized by relative fresh and cold Atlantic Water overlaying Arctic Intermediate Water that basically covers the whole Norwegian Basin. Differently, the conditions during the period 2006-2016, denoted Atlantic, are warmer and more saline, and the extent and thickness of Arctic Intermediate Water is greatly reduced. During the most recent period denoted Fresh, 2017-2019, there has been a major freshening of the Atlantic waters, the layer of Arctic Intermediate Water has not recovered, but instead a layer of warmer but relative fresh Arctic Water has expanded. We find that increased abundance of the Arctic zooplankton Calanus hyperboreus in the southern and eastern Norwegian Basin coincides with increased extent of Arctic Water. We also note that the overall mesozooplankton biomass in the Norwegian Basin is significantly higher during periods of relative high amount of Arctic Water. Furthermore, we show that both nitrate and silicate winter (pre-bloom) concentrations are significantly higher in the Arctic Water compared to Atlantic Water, and that there is a reduction in nutrients from the Arctic period compared subsequent Atlantic and Fresh periods. Since these nutrients can be interpreted as the potential for new production, changes in the influx of western Arctic waters are expected to have a bottom-up effect on the Norwegian Sea. Hence, this study indicates that the amount of Arctic waters and their concentration of nutrients and zooplankton are more important for the Norwegian Basin ecosystem functioning rather than the temperature of the Atlantic waters.publishedVersio

Acoustic micronektonic distribution and density is structured by macroscale oceanographic processes across 17–48° N latitudes in the North Atlantic Ocean

This study investigates the large-scale distribution patterns of the acoustic scattering layers and micronekton density across the Northeast Atlantic Ocean during daylight hours. A research cruise on board R/V “Kronprins Haakon” was conducted during May 2019 from Cape Verde to Bay of Biscay. Hydrological data were obtained at 20 conductivity-temperature-depth sensor (CTD) stations. To estimate the micronekton densities in front of the trawl, an autonomous echo sounder (120 or 200 kHz) on the headrope of the macroplankton trawl was used. Acoustic data were also collected along the cruise track using ship-mounted multi-frequency echo sounders (backscatter at 18 and 38 kHz was analyzed). Acoustic observations (both at 18, 38 and 120/200 kHz) showed clear patterns in the horizontal distribution of the micronekton during daytime with higher backscatter and echo densities in the south of the study area (from 17 to 37° N), and the absence of high backscatter in the surface from 37 to 45° N. Backscatter and echo densities were found to be significantly influenced by: temperature, salinity, and oxygen, as well as depth and time of the day.publishedVersio

Distribution and composition of mesopelagic macroplankton and micronekton in the North-east Atlantic

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Pelagiske økosystem i De nordiske hav - grunnlagsstudie knyttet til åpningsprosess for utforskning og utvinning av havbunnsmineraler på norsk kontinentalsokkel

Denne rapporten er en leveranse til bestillingen «Grunnlagsstudie: Pelagisk økosystem» fra Oljedirektoratet til Havforskningsinstituttet. Studien er bestilt i forbindelse med at regjeringen har igangsatt en prosess for åpning av norsk sokkel for havbunnsmineralvirksomhet. Rapporten sammenstiller vår nåværende kunnskap om de pelagiske økosystemenes struktur og funksjon og belyser viktige kunnskapshull. Det er lagt særlig vekt på å beskrive økosystemkomponenter og prosesser som er essensielle for arbeidet med planprogram for konsekvensutredning av havbunnsmineralvirksomhet i norske havområder, og fokus vil derfor tidvis være litt annerledes enn det man vil finne i en generell beskrivelse av Norskehavet, Islandshavet og Grønlandshavet. Vi har lagt mer vekt på eksisterende kunnskapshull, og fokusert mer på utredningsområdet og på økologi og prosesser i pelagisk sone i dyphavet, enn det som kan forventes i for eksempel en lærebok om plankton-, fisk eller sjøpattedyrøkologi. Selv om formålet dermed har farget fokuset for beskrivelsene, beskriver kapitlene generell fordeling og økologi i de pelagiske systemene i Norskehavet, Islandshavet og Grønlandshavet.publishedVersio

Fifteen years of ocean observations with the global Argo array

More than 90% of the heat energy accumulation in the climate system between 1971 and the present has been in the ocean. Thus, the ocean plays a crucial role in determining the climate of the planet. Observing the oceans is problematic even under the most favourable of conditions. Historically, shipboard ocean sampling has left vast expanses, particularly in the Southern Ocean, unobserved for long periods of time. Within the past 15 years, with the advent of the global Argo array of pro ling oats, it has become possible to sample the upper 2,000 m of the ocean globally and uniformly in space and time. The primary goal of Argo is to create a systematic global network of pro ling oats that can be integrated with other elements of the Global Ocean Observing System. The network provides freely available temperature and salinity data from the upper 2,000 m of the ocean with global coverage. The data are available within 24 hours of collection for use in a broad range of applications that focus on examining climate-relevant variability on seasonal to decadal timescales, multidecadal climate change, improved initialization of coupled ocean–atmosphere climate models and constraining ocean analysis and forecasting systems.En prens

Innspill til høring - Forslag til program for konsekvensutredning for mineralvirksomhet på norsk sokkel

Rapporten er et høringssvar sendt til Olje- og Energidepartementet i forbindelse med et forslag til konsekvensutredningsprogram for mineralvirksomhet på norsk kontinentalsokkel. I høringssvaret påpeker Havforskningsinstituttet at det er stor mangel på kunnskap, både med hensyn til biomangfold og økologiske forhold, men også når det gjelder teknologien som vil anvendes for utvinning av mineraler og metaller på havbunnen. Denne kunnskapsmangelen representerer en usikkerhet som bør synliggjøres i konsekvensutredningen, blant annet gjennom en risikoanalyse. Havforskningsinstituttet påpeker også at ulike initiativ når det gjelder kunnskapsinnhenting burde vært ferdigstilt før gjennomføringen av høringen. En grundigere oppsummering av rapportens innhold er gitt i første kapittel.publishedVersio