Some aspects of possible long-term future changes

Some aspects of possible long-term future changes in the ecosystem (introduction)

Thu, 03 Dec 2009 18:02:08 +0000

As discussed in other chapters of this report, several aspects of the impact that human activities have on the ecosystem are clearly manifested and visible or will likely become so in the near future (see chapters General background description of the ecosystem - Ecosystem interactions - Human impact; Current and expected state of the ecosystem - Human activities /impact and Current and expected state of the ecosystem - Conclusions about state of the ecosystem). Other aspects may become visible longer time into the future, and this is the topic of the present chapter.

Future climate change and its effects on the ecosystem and human activities

Thu, 03 Dec 2009 18:02:59 +0000

Air temperatures have increased almost twice as fast in the Arctic than the global average over the last 50 years. Models predict that air temperatures will continue to increase considerably, and summer sea ice in the Arctic will disappear before the middle of this century and winter sea ice by the end of the current century. Because of the complex dynamics of the Barents Sea ecosystem, and because the effects of climate change will interact with other major factors, such as acidification and the impact of fisheries, it is difficult to predict what the total effect on the ecosystem will be.

Effects of fisheries

Thu, 03 Dec 2009 17:55:34 +0000

According to the ICES criteria (ICES 2008b) the stocks of NEA cod, NEA haddock, northern shrimp (Pandalus borealis) and capelin have full reproductive capacity and are harvested within sustainable limits. The stocks of NEA Greenland halibut (Reinhardtius hippoglossoides), golden redfish (Sebastes marinus) and deep-sea redfish (Sebastes mentella) have been fished down to very low levels. These threatened species are long-lived and have low potential growth rates. Although the fisheries at present are strongly regulated, the rebuilding of these stocks will take many years.

Future climate change and its effects on the ecosystem and human activities - Projections of future climate change

Thu, 03 Dec 2009 18:04:12 +0000

The IPCC Fourth Assessment Report (AR4) undertook an evaluation of the evidence for and impacts of anthropogenic change worldwide where they concluded that human-induced climate change was occurring (IPCC, 2007). As part of the IPCC process, the results from several Ocean-Atmosphere Global Circulation Models were presented. The performance of 20 models for different Arctic regions, including the Barents Sea, was evaluated by Overland and Wang (2007).

Their assessment was based upon each model’s ability to simulate observed seasonal changes in ice concentrations for the period 1979-1999. For the Barents Sea, a limit of within 30% was used to determine acceptable models and those exceeding 30% were considered unacceptable. The reasoning was that the models should be able to hindcast the present day conditions if they are to do a good job on future projections. Most of the models produced too much ice in the Barents, as only 7 models met the acceptable criteria.

Future climate change and its effects on the ecosystem and human activities - Projections of ecosystem responses to climate change

Thu, 03 Dec 2009 18:06:07 +0000

Primary production and zooplankton

The disappearance of seasonal sea ice will result in increased primary production in the Barents Sea (Øiestad, 1990; Loeng et al. 2005, Ellingsen et al., 2008). The disappearance of seasonal sea ice would eliminate the ice-edge blooms, which would be replaced by blooms resembling those in the more productive Atlantic waters and their timing would be determined by the onset of seasonal stratification.

Loeng et al. (2005) suggested the spring bloom would occur earlier and this would enhance annual primary production by extending the growing season. They also stated that regions where the seabed or the depth of mixing is <40 m are likely to favour diatom blooms, whereas if mixing extended to about 80 m it would likely favour Phaeocystis. Thus, projected stronger winds are likely to result in Phaeocystis becoming more common than at present in the northern and eastern regions of the Barents Sea. If the surface mixed layer extends beyond about 80 m, it is possible that a low-productive community dominated by nanoflagellates would be favoured.

Possible effects of ocean acidification

Thu, 03 Dec 2009 18:08:18 +0000

Emissions of CO2 from the burning of fossil fuels have increased with more than 1200 % over the last 100 years. Increasing levels of CO2 in the atmosphere do not only contribute to warmer climate, but CO2 is also taken up by the oceans and changes their chemistry. The oceans have absorbed approximately 50% (ca. 525 billion tons) of the carbon dioxide (CO2) released to the atmosphere since the beginning of the industrial revolution. When carbon dioxide is absorbed by the oceans it reacts with seawater to form carbonic acid.

Evolutionary effect of fishing on maturity in cod

Thu, 03 Dec 2009 18:10:08 +0000

Age at first reproduction has declined markedly in cod the last decades (Figure 4.6.6). This may have considerable consequences for cod recruitment and the role of cod as a top predator in the ecosystem. In the 1940s, a cod typically reproduced for the first time when it was between 9 or 10 years old. In the 1990s, average age at first reproduction had declined to between 6 and 7 years.

Re-reading of old cod-otholits suggests that age had been over estimated in the beginning of the time series in the above figure, and that the decline in age at maturity therefore has been less pronounced than suggested here (Zuykova et al 2009).

Effects of climate change on pollution

Thu, 03 Dec 2009 18:11:17 +0000

Climate change may have consequences for the pollution situation in the Barents Sea. The routes and mechanisms by which persistent organic pollutants, heavy metals and radionucleides are delivered to the area are strongly influenced by climate variability and global climate change. Increased precipitation could cause faster washing out of hazardous substances that are currently combined in the environment.