Randi Ingvaldsen

Quantifying the Influence of Atlantic Heat on Barents Sea Ice Variability and Retreat

AbstractThe recent Arctic winter sea ice retreat is most pronounced in the Barents Sea. Using available observations of the Atlantic inflow to the Barents Sea and results from a regional ice–ocean model the authors assess and quantify the role of inflowing heat anomalies on sea ice variability. The interannual variability and longer-term decrease in sea ice area reflect the variability of the Atlantic inflow, both in observations and model simulations. During the last decade (1998–2008) the reduction in annual (July–June) sea ice area was 218 × 103 km2, or close to 50%. This reduction has occurred concurrent with an increase in observed Atlantic heat transport due to both strengthening and warming of the inflow. Modeled interannual variations in sea ice area between 1948 and 2007 are associated with anomalous heat transport (r = −0.63) with a 70 × 103 km2 decrease per 10 TW input of heat. Based on the simulated ocean heat budget it is found that the heat transport into the western Barents Sea sets the bou...

Volume and Heat Transports to the Arctic Ocean Via the Norwegian and Barents Seas

The main aim of this paper has been to present a holistic view of the Atlantic water flow along the Norwegian Coast and into the Barents Sea. It has focused on the period starting in the mid-1990s, with simultaneous arrays of moored current meters in the Svinoy section and the Barents Sea Opening. These detailed measurements have provided the bases for improved estimates of means and variations in fluxes, and their forcing mechanisms. Mean volume and heat fluxes associated with Atlantic water in the Norwegian Atlantic Slope Current (NwASC) are 4.3 Sv and 126 TW respectively for the Svinoy section, showing no significant trends, and 1.8 Sv and 48 TW for the Barents Sea Opening, where positive trends have been found in both measures. These estimates are probably higher than the long-tem mean, since hydrographic data along the Norwegian Coast show that the periods of direct current measurements are the prolongations of a period that started in the late 1970s, since when Atlantic water has become warmer and saltier. The close resemblance, throughout the record, between temperature variations in the Kola section and the AMO-index back to the early 20 century illustrates the importance of large-scale longterm variations in the Barents Sea system. Although the magnitudes of these variations are relatively small in comparison with inter-annual variations, other studies have shown them to be of major importance for ecosystem changes (ACIA, 2005). 2 The different forcing effects of the NwASC and the Atlantic inflow to the Barents Sea to similar atmospheric systems are noted. The results strongly suggest that the relative distribution of the Norwegian Atlantic Current entering the Barents Sea and passing through the Fram Strait is very sensitive to storm tracks. Thus, changes in the predominant storm tracks may trigger major changes, including feedback mechanisms, for the Barents Sea climate and the heat budget of the Arctic Ocean.

Loss of sea ice during winter north of Svalbard

Sea ice loss in the Arctic Ocean has up to now been strongest during summer. In contrast, the sea ice concentration north of Svalbard has experienced a larger decline during winter since 1979. The trend in winter ice area loss is close to 10% per decade, and concurrent with a 0.3°C per decade warming of the Atlantic Water entering the Arctic Ocean in this region. Simultaneously, there has been a 2°C per decade warming of winter mean surface air temperature north of Svalbard, which is 20–45% higher than observations on the west coast. Generally, the ice edge north of Svalbard has retreated towards the northeast, along the Atlantic Water pathway. By making reasonable assumptions about the Atlantic Water volume and associated heat transport, we show that the extra oceanic heat brought into the region is likely to have caused the sea ice loss. The reduced sea ice cover leads to more oceanic heat transferred to the atmosphere, suggesting that part of the atmospheric warming is driven by larger open water area. In contrast to significant trends in sea ice concentration, Atlantic Water temperature and air temperature, there is no significant temporal trend in the local winds. Thus, winds have not caused the long-term warming or sea ice loss. However, the dominant winds transport sea ice from the Arctic Ocean into the region north of Svalbard, and the local wind has influence on the year-to-year variability of the ice concentration, which correlates with surface air temperatures, ocean temperatures, as well as the local wind.

Synergies between climate and management for Atlantic cod fisheries at high latitudes

Significance Currently many exploited fish populations, including many of the Atlantic cod stocks, are at historically low levels with widespread concern about whether contemporary management is capable of facilitating population recovery. In contrast, the spawning stock biomass of Barents Sea cod is now at an historic high. Here we demonstrate that successful management actions interacting synergistically with prevailing climate caused this increase. Warming of water masses in the Barents Sea over the last decade positively reinforced management actions. A unique and possibly generic mechanism of climate affecting marine animals at high latitudes, especially when at the polar extreme of their distribution, is identified: adjustment of the suitable feeding area. This adjustment is linked closely to community dynamics and increased stock productivity. The widespread depletion of commercially exploited marine living resources is often seen as a general failure of management and results in criticism of contemporary management procedures. When populations show dramatic and positive changes in population size, this invariably leads to questions about whether favorable climatic conditions or good management (or both) were responsible. The Barents Sea cod (Gadus morhua) stock has recently increased markedly and the spawning stock biomass is now at an unprecedented high. We identify the crucial social and environmental factors that made this unique growth possible. The relationship between vital rates of Barents Sea cod stock productivity (recruitment, growth, and mortality) and environment is investigated, followed by simulations of population size under different management scenarios. We show that the recent sustained reduction in fishing mortality, facilitated by the implementation of a “harvest control rule,” was essential to the increase in population size. Simulations show that a drastic reduction in fishing mortality has resulted in a doubling of the total population biomass compared with that expected under the former management regime. However, management alone was not solely responsible. We document that prevailing climate, operating through several mechanistic links, positively reinforced management actions. Heightened temperature resulted in an increase in the extent of the suitable feeding area for Barents Sea cod, likely offering a release from density-dependent effects (for example, food competition and cannibalism) through prolonged overlap with prey and improved adult stock productivity. Management and climate may thus interact to give a positive outlook for exploited high-latitude marine resources.

The Arctic Ocean in summer: a quasi-synoptic inverse estimate of boundary fluxes and water mass transformation

The first quasi-synoptic estimates of Arctic Ocean and sea ice net fluxes of volume, heat and freshwater are calculated by application of an inverse model to data around the ocean boundary. Hydrographic measurements from four gateways to the Arctic (Bering, Davis and Fram Straits, and the Barents Sea Opening) completely enclose the ocean, and were made within the same 32-day period in summer 2005. The inverse model is formulated as a set of full-depth and density-layer-specific volume and salinity transport conservation equations, with conservation constraints also applied to temperature, but only in non-outcropping layers. The model includes representations of Fram Strait sea ice export and of interior Arctic Ocean diapycnal fluxes. The results show that in summer 2005 the transport-weighted mean properties are, for water entering the Arctic: potential temperature 4.53?C, salinity 34.50 and potential density (?0) 27.33 kg m-3; and for water leaving the Arctic, including sea ice: 0.25?C, 33.81 and 27.14 kg m-3, respectively. The net effect of the Arctic in summer is to freshen and cool the inflows by 0.69 in salinity and 4.28 ?C, respectively, and to decrease density by 0.19 kg m-3. The volume transport into the Arctic of waters above ~1000 m depth is 9.2 Sv (1 Sv = 106 m3 s-1), and the export (similarly) is 9.3 Sv. The net oceanic and sea ice freshwater flux is 186 {plus minus} 48 mSv. The net heat flux (including sea ice) is 192 {plus minus} 37 TW, representing loss from the ocean to the atmosphere.

Skillful prediction of Barents Sea ice cover

A main concern of present climate change is the Arctic sea ice cover. In wintertime, its observed variability is largely carried by the Barents Sea. Here we propose and evaluate a simple quantitative and prognostic framework based on first principles and rooted in observations to predict the annual mean Barents Sea ice cover, which variance is carried by the winter ice (96%). By using observed ocean heat transport and sea ice area, the proposed framework appears skillful and explains 50% of the observed sea ice variance up to 2 years in advance. The qualitative prediction of increase versus decrease in ice cover is correct 88% of the time. Model imperfections can largely be diagnosed from simultaneous meridional winds. The framework and skill are supported by a 60 year simulation from a regional ice-ocean model. We particularly predict that the winter sea ice cover for 2016 will be slightly less than 2015.

Productivity in the Barents Sea - Response to Recent Climate Variability

The temporal and spatial dynamics of primary and secondary biomass/production in the Barents Sea since the late 1990s are examined using remote sensing data, observations and a coupled physical-biological model. Field observations of mesozooplankton biomass, and chlorophyll a data from transects (different seasons) and large-scale surveys (autumn) were used for validation of the remote sensing products and modeling results. The validation showed that satellite data are well suited to study temporal and spatial dynamics of chlorophyll a in the Barents Sea and that the model is an essential tool for secondary production estimates. Temperature, open water area, chlorophyll a, and zooplankton biomass show large interannual variations in the Barents Sea. The climatic variability is strongest in the northern and eastern parts. The moderate increase in net primary production evident in this study is likely an ecosystem response to changes in climate during the same period. Increased open water area and duration of open water season, which are related to elevated temperatures, appear to be the key drivers of the changes in annual net primary production that has occurred in the northern and eastern areas of this ecosystem. The temporal and spatial variability in zooplankton biomass appears to be controlled largely by predation pressure. In the southeastern Barents Sea, statistically significant linkages were observed between chlorophyll a and zooplankton biomass, as well as between net primary production and fish biomass, indicating bottom-up trophic interactions in this region.

Marine living resources of the Barents Sea Ecosystem understanding and monitoring in a climate change perspective

Abstract The Arctic is of special importance to the world, and it is changing rapidly. Uncovering the relationship between drivers of change and biological responses in the Barents Sea is therefore crucial for understanding the potential effects of climate change on the ecosystem in general and on commercially important species in particular. This thematic review provides an overview of the discussions related to long- and short-term variations in climate in the Barents Sea, what these physical changes really are, and how they may develop in the future. Furthermore, questions related to how these predicted climate-driven physical changes may alter ecosystems and the implications and future challenges that this represents for the management of resources in the area are raised. There is no doubt that to better understand the structure and function of an ecosystem, as well as to investigate the possible effects of climate changes, there is a need for thorough monitoring and data collection. The Barents Sea Ecosystem Survey (BESS) is used in several of the studies highlighted in this review. Therefore, we can provide a detailed description of the BESS and relate BESS research activities to other research initiatives in a thematic context.

Responses in spatial distribution of Barents Sea capelin to changes in stock size, ocean temperature and ice cover

Abstract Using data for the period 1972–2010, we relate the variations in the Barents Sea capelin distribution to stock size, ocean temperatures and the area available for dispersal during summer. We find a strong relation between distribution area and stock size, which is most likely caused by a large stock extending the feeding area to meet the higher food demand. However, during the last decade there has been a general expansion of the distribution area and a northward shift of the high-concentration areas, which we relate to the high temperatures and low ice cover observed in the northern Barents Sea during the period. The study shows that ocean temperature and ice cover set the large-scale terms for the capelin distribution, while the stock size determines how capelin uses the available area. Changes of 4 million tonnes in stock size or 1°C in temperature give comparable impacts on the distribution.

Changes in the relationship between sea temperature and recruitment of cod, haddock and herring in the Barents Sea

Abstract Cod, haddock and herring in the Barents Sea have strongly variable recruitment. For these three stocks, earlier studies have suggested a high correlation between their recruitment and a positive relationship between high temperatures and good recruitment. These hypotheses were revisited using stock assessment and temperature data for the period 1913–present. The cod–haddock and herring–haddock recruitment correlations were both significant and positive in some periods, but became insignificant towards the end of the period. Cod and herring recruitment was not significantly correlated. Recruitment variability was found to decline towards the end of the period for all species, in particular for cod. For all three stocks there is a significant positive relationship between recruitment and temperature; this relationship is strongest for haddock and weakest for herring. Recruitment was found to be low at low temperatures and variable at medium/high temperatures during the first year of life for all three species. Temperature during the first winter of life correlates positively with haddock and cod recruitment residuals. This correlation is weakened towards the end of the period for cod, but stays high for haddock. Temperature during the first summer of life correlates positively with herring recruitment during some parts of the period, but also this correlation is weakened towards the end of the period.