Future CO2-induced climate change scenarios from Global Circulation Models (GCMs) indicate increasing air temperatures, with the greatest warming in the Arctic and Subarctic. Changes to the wind ...fields and precipitation patterns are also suggested. These will lead to changes in the hydrographic properties of the ocean, as well as the vertical stratification and circulation patterns. Of particular note is the expected increase in ocean temperature. Based upon the observed responses of cod to temperature variability, the expected responses of cod stocks throughout the North Atlantic to the future temperature scenarios are reviewed and discussed here. Stocks in the Celtic and Irish Seas are expected to disappear under predicted temperature changes by the year 2100, while those in the southern North Sea and Georges Bank will decline. Cod will likely spread northwards along the coasts of Greenland and Labrador, occupy larger areas of the Barents Sea, and may even extend onto some of the continental shelves of the Arctic Ocean. In addition, spawning sites will be established further north than currently. It is likely that spring migrations will occur earlier, and fall returns will be later. There is the distinct possibility that, where seasonal sea ice disappears altogether, cod will cease their migration. Individual growth rates for many of the cod stocks will increase, leading to an overall increase in the total production of Atlantic cod in the North Atlantic. These responses of cod to future climate changes are highly uncertain, however, as they will also depend on the changes to climate and oceanographic variables besides temperature, such as plankton production, the prey and predator fields, and industrial fishing.
The shift in marine resource management from a compartmentalized approach of dealing with resources on a species basis to an approach based on management of spatially defined ecosystems requires an ...accurate accounting of energy flow. The flow of energy from primary production through the food web will ultimately limit upper trophic-level fishery yields. In this work, we examine the relationship between yield and several metrics including net primary production, chlorophyll concentration, particle-export ratio, and the ratio of secondary to primary production. We also evaluate the relationship between yield and two additional rate measures that describe the export of energy from the pelagic food web, particle export flux and mesozooplankton productivity. We found primary production is a poor predictor of global fishery yields for a sample of 52 large marine ecosystems. However, chlorophyll concentration, particle-export ratio, and the ratio of secondary to primary production were positively associated with yields. The latter two measures provide greater mechanistic insight into factors controlling fishery production than chlorophyll concentration alone. Particle export flux and mesozooplankton productivity were also significantly related to yield on a global basis. Collectively, our analyses suggest that factors related to the export of energy from pelagic food webs are critical to defining patterns of fishery yields. Such trophic patterns are associated with temperature and latitude and hence greater yields are associated with colder, high latitude ecosystems.
Using end-to-end models for ecosystem-based management requires knowledge of the structure, uncertainty and sensitivity of the model. The Norwegian and Barents Seas (NoBa) Atlantis model was ...implemented for use in 'what if' scenarios, combining fisheries management strategies with the influences of climate change and climate variability. Before being used for this purpose, we wanted to evaluate and identify sensitive parameters and whether the species position in the foodweb influenced their sensitivity to parameter perturbation. Perturbing recruitment, mortality, prey consumption and growth by +/- 25% for nine biomass-dominating key species in the Barents Sea, while keeping the physical climate constant, proved the growth rate to be the most sensitive parameter in the model. Their trophic position in the ecosystem (lower trophic level, mid trophic level, top predators) influenced their responses to the perturbations. Top-predators, being generalists, responded mostly to perturbations on their individual life-history parameters. Mid-level species were the most vulnerable to perturbations, not only to their own individual life-history parameters, but also to perturbations on other trophic levels (higher or lower). Perturbations on the lower trophic levels had by far the strongest impact on the system, resulting in biomass changes for nearly all components in the system. Combined perturbations often resulted in non-additive model responses, including both dampened effects and increased impact of combined perturbations. Identifying sensitive parameters and species in end-to-end models will not only provide insights about the structure and functioning of the ecosystem in the model, but also highlight areas where more information and research would be useful-both for model parameterization, but also for constraining or quantifying model uncertainty.
Fisheries exploitation, habitat destruction, and climate are important drivers of variability in recruitment success. Understanding variability in recruitment can reveal mechanisms behind widespread ...decline in the abundance of key species in marine and terrestrial ecosystems. For fish populations, the match-mismatch theory hypothesizes that successful recruitment is a function of the timing and duration of larval fish abundance and prey availability. However, the underlying mechanisms of match-mismatch dynamics and the factors driving spatial differences between high and low recruitment remain poorly understood.
We used empirical observations of larval fish abundance, a mechanistic individual-based model, and a reanalysis of ocean temperature data from 1960 to 2002 to estimate the survival of larval cod (Gadus morhua). From the model, we quantified how survival rates changed during the warmest and coldest years at four important cod spawning sites in the North Atlantic. The modeled difference in survival probability was not large for any given month between cold or warm years. However, the cumulative effect of higher growth rates and survival through the entire spawning season in warm years was substantial with 308%, 385%, 154%, and 175% increases in survival for Georges Bank, Iceland, North Sea, and Lofoten cod stocks, respectively. We also found that the importance of match-mismatch dynamics generally increased with latitude.
Our analyses indicate that a key factor for enhancing survival is the duration of the overlap between larval and prey abundance and not the actual timing of the peak abundance. During warm years, the duration of the overlap between larval fish and their prey is prolonged due to an early onset of the spring bloom. This prolonged season enhances cumulative growth and survival, leading to a greater number of large individuals with enhanced potential for survival to recruitment.
During the 1920s and 1930s, there was a dramatic warming of the northern North Atlantic Ocean. Warmer-than-normal sea temperatures, reduced sea ice conditions and enhanced Atlantic inflow in northern ...regions continued through to the 1950s and 1960s, with the timing of the decline to colder temperatures varying with location. Ecosystem changes associated with the warm period included a general northward movement of fish. Boreal species of fish such as cod, haddock and herring expanded farther north while colder-water species such as capelin and polar cod retreated northward. The maximum recorded movement involved cod, which spread approximately 1200 km northward along West Greenland. Migration patterns of "warmer water" species also changed with earlier arrivals and later departures. New spawning sites were observed farther north for several species or stocks while for others the relative contribution from northern spawning sites increased. Some southern species of fish that were unknown in northern areas prior to the warming event became occasional, and in some cases, frequent visitors. Higher recruitment and growth led to increased biomass of important commercial species such as cod and herring in many regions of the northern North Atlantic. Benthos associated with Atlantic waters spread northward off Western Svalbard and eastward into the eastern Barents Sea. Based on increased phytoplankton and zooplankton production in several areas, it is argued that bottom-up processes were the primary cause of these changes. The warming in the 1920s and 1930s is considered to constitute the most significant regime shift experienced in the North Atlantic in the 20th century.
The focus of this study is on the fluxes and forcing of the Norwegian Coastal Current (NCC) at the entrance to the Barents Sea. The structure and dynamics of the NCC, which consists of a slope branch ...and an offshore branch, are investigated using (1) a recent 1 year full depth current meter record in the core of the slope region; (2) repeated hydrographic data at an inshore monitoring station; (3) broader regional hydrographic surveys; and (4) atmospheric reanalysis data. The total fluxes are estimated to 1.8 Sv for volume and 26 mSv for freshwater relative to a reference salinity of 34.8, with the largest contributions from baroclinic offshore branch. The heat flux calculated for the slope branch only is 34 TW. These estimates are higher compared to earlier estimates but are based on more comprehensive data. The major mode of variability in the slope branch is consistent with a continental shelf wave on time scales in the range of 3–16 days forced by the along‐coast component of the wind stress. Maximum along‐slope currents during fall/winter, corresponding to the stronger wind forcing during these seasons, suggest that the observed seasonality in the NCC can be attributed to a similar mechanism.
Key Points
Fluxes of the Norwegian Coastal Current are larger than previously reported
The major mode of variability in the slope branch is a CSW
Buoyancy forcing of the NCC is the largest contribution with respect to fluxes
The Norwegian Component of the Ecosystem Studies of Sub-Arctic Seas (NESSAS) was funded by the Research Council of Norway from 2005 to 2008. Its aim was to quantify the impact of climate variability ...on the structure and function of the marine ecosystem of the Barents Sea and adjacent waters in order to predict the ecosystem responses to possible future climate change and their possible economic impact. This paper reviews research highlights dealing with climate forcing and its influence. New insights were provided on the role of large-scale atmospheric forcing on the physical oceanography including the effect of Arctic and Atlantic cyclones on the variability of the ice extent in the Barents Sea and the non-linear response of the sub-polar gyre to North Atlantic Oscillation (NAO) forcing. In addition, the NAO was also shown to influence the biology, for example shrimp recruitment in the Barents Sea and primary production in the Nordic Seas, with the strength and sign of the correlations being spatially dependent. The importance of longer term climate variability in the form of the Atlantic Multidecadal Oscillation (60–80years period) was stressed, as it leads to significant changes in fish production, shifts in distribution and changes in spawning sites in the Barents Sea as well as other northern Atlantic ecosystems. Results from comparative studies between several US ecosystems and those of the Norwegian and Barents Seas are presented, including evidence of increased primary productivity in the Barents Sea in recent years and the poleward movement of zooplankton and fish. In addition recruitment patterns of major demersal and pelagic species in the Barents Sea generally show synchrony with those in the Gulf of Maine indicating a common external forcing. Possible ecosystem scenarios for the Barents Sea under anthropogenic-induced future climate change were developed including expectations of structural and functional changes due to distributional changes of many species. Of particular note is the likelihood of increases in the productivity of several fish species, including cod and herring, which potentially could result in higher fisheries yields.
The North Atlantic with its spring-bloom ecosystem has its particular responses to climate change, many of them different from the other parts of the world’s oceans. The system is strongly influenced ...by anthropogenic climate change as well as to strong decadal to multidecadal natural climate variability. In particular, the northernmost part of the system and the Arctic is exposed to higher increase in temperature than any other ocean region. The most pronounced examples of poleward migration of marine species are found in the North Atlantic, and comprise the recent warming phase after the 1970s. The latitudinal asymmetric position of the Arctic Front and its nature of change result in a considerably larger migration distance and migration speed of species in the Northeast Atlantic part of the system. However, we here hypothesize that there is a limit to the future extent of poleward migration of species constrained by the latitudinal region adjacent the Polar Circle. We define this region the critical latitudes. This is because the seasonal light cycle at high latitudes sets particular demands on the life cycle of planktivore species. Presently, boreal planktivore species at high latitudes deposit lipids during the short spring bloom period and overwinter when phytoplankton production is insufficient for feeding. Unless invading temperate species from farther south are able to adapt by developing a similar life cycle future poleward migration of such species will be unlikely.
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