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A synthesis of the ecosystem responses to the late 20th century cold period in the northern North Atlantic
Abstract
Following rapid cooling in the 1960s, much of the North Atlantic Ocean was characterized by a cold period during the 1970s and 1980s. This cold period was part of the multidecadal variability in sea surface temperatures known as the Atlantic Multidecadal Oscillation or AMO, which has a period of 60–80 years. During this cold period, below average air and sea temperatures predominated, increased ice cover was observed in those northern regions with seasonal sea ice, and evidence was found of reduced Atlantic inflow into the Northeast Atlantic Ocean. The ecological responses included a reduction in primary production and geographic shifts in zooplankton species. Also, there was a general southward expansion of arctic and boreal fish species and a retreat of the temperate species. Major fish stocks such as Atlantic cod off Greenland and Labrador/northern Newfoundland, as well as the Norwegian spring-spawning herring, collapsed commercially. These collapses were partly driven by climate-induced declines in growth rates and recruitment survival, as well as fishing. In contrast, in the more southern range of Atlantic cod, such as the North Sea, the opposite response occurred as the cool conditions led to improved growth rates and higher abundance. Long-term measurements in the English Channel documented the replacement of several warm-water species with more northern cold-water species. Benthic and nearshore species also underwent distributional shifts and changing abundances. Comparisons with the responses to the warm periods suggest that following the cold period of the 1970s and 1980s, the ecosystem in the 1990s and 2000s returned to conditions akin to what they were in the previous warm period of the 1930s–1950s. However, there were some notable exceptions, such as the continued low abundance of Atlantic cod off West Greenland and Labrador/northern Newfoundland. © International Council for the Exploration of the Sea 2018. All rights reserved.
... Such biological impacts may manifest not only at an individual species level but also at fish community and marine ecosystem levels (e.g. Alheit & Bakun, 2010;Attrill & Power, 2002;Beaugrand et al., 2015;Drinkwater & Kristiansen, 2018;Faillettaz et al., 2019;Ma et al., 2019;Noakes & Beamish, 2009;Pang et al., 2018;Tian et al., 2003Tian et al., , 2004Tian et al., , 2008Tian et al., , 2014Wooster & Zhang, 2004). Hence, identifying biological responses to physical processes is of crucial importance for the sustainable management of fish populations and ecosystems (Blöcker et al., 2023;Scheffer et al., 2009;Wooster & Zhang, 2004). ...
... regime shift was also identified in the ecosystems of the North Atlantic, suggesting the global impact of the regime shift (Beaugrand et al., 2015;Reid et al., 2016). Increasing evidences demonstrate that the Atlantic Multidecadal Oscillation (AMO), a proxy of water temperature of the North Atlantic, drives the spatio-temporal dynamics of the distribution and abundance of small pelagic fishes and tunas, as well as the North Atlantic ecosystems (Alheit et al., 2014;Drinkwater & Kristiansen, 2018;Faillettaz et al., 2019). A recently updated study indicates that the AMO drives the variability of the Pacific subtropical mode water (STMW) with potential effects on fishes such as skipjack tuna (Hou et al., 2022;Wu et al., 2020). ...
... Increasing evidence demonstrated that the AMO largely impacted not only small pelagic fishes, but also tunas and ecosystems in the North Atlantic (Alheit et al., 2014;Drinkwater & Kristiansen, 2018;Faillettaz et al., 2019). Small pelagic fish populations in the eastern North and Central Atlantic, including those in the Mediterranean Sea, responded quickly to the AMO variability by changing their abundance and migration ranges (Alheit et al., 2014). ...
The marine ecosystems around Japan are very productive and have typical wasp‐waist structure dominated by small pelagic fishes such as sardine, exhibiting large low‐frequency fluctuations in biomass. Whereas studies on the variability in abundance of individual species such as sardine and anchovy are popular, only a few studies focused on the long‐term variability of fish assemblage around Japan. In this study, 13 species/taxa ranging from small forage to large predatory species and from warm‐ to cold‐water species were selected to indicate essential characteristics of the fish assemblage and their drivers were analysed based on fishery, oceanographic and climatic data sets from 1901 to 2018. Results show that two outstanding peaks during the 1930s and 1980s were characterized by abundant sardine. Additionally, species composition showed high similarities during similar temperature regimes while exhibiting contrasts during different temperature regimes. Variations and regime shifts in dominant patterns and fish community indices coincided well with the Atlantic Multidecadal Oscillation (AMO) and regional sea surface temperature (SST). Furthermore, gradient forest analysis identified AMO and regional SSTs as most important predictors of dominant patterns and fish community indices, suggesting that the decadal and multidecadal variability in the fish assemblage around Japan was forced by basin‐scale climate variability as inherent in the AMO through its connections with regional SSTs. Autocorrelation coefficient demonstrated that the ecological indicators have the potential to be early warning signals of regime shifts, which suggests the possibility of coming cold regime since around 2015 and has important implications for fisheries management.
... In the northern hemisphere, nutrient flow and thus species abundance and migration was shown to be linked to the Atlantic Multidecadal Oscillation index (Alvarez-Fernandez, 2012;Hátún et al., 2016), which is the de-trended mean of North Atlantic (0-60° N) SST anomalies (Alheit et al., 2014). The AMO has implications for a trophic cascade through plankton to crustaceans and molluscs to seabirds (Drinkwater & Kristiansen, 2018). Conversely, predation pressure can act as a top-down driver on nest numbers and distribution of seabirds (Barros et al., 2016;Gerell, 1985;Nordström & Korpimäki, 2004), and the impacts of native and introduced predators can differ vastly (Salo et al., 2007). ...
... The AMO is used to capture cyclic changes that can have profound effects on ecosystems (Trenberth & Zhang, 2021), and we found evidence for the Bottom-up control hypothesis of eiders, as climate-driven resource availability partly drives eider nest dynamics in Brokey over the 123 years of study. While there are effects on algal blooms, zooplankton and fish abundance (Drinkwater & Kristiansen, 2018), the population effects on bird species need to be better understood (Nye et al., 2014). The increased oceanic productivity in warm AMO regimes could be projected to translate into higher bird numbers, but this has, for example, not been found in great cormorant (Phalacrocorax carbo) abundance in Iceland (Gardarsson & Jónsson, 2019). ...
Bird species on islands are strongly impacted by biological invasions, with the Icelandic common eider (Somateria mollissima borealis) being particularly threatened. Down collection by local families in Breiðafjörður, West Iceland, provided long‐term datasets of nests from two archipelagos, covering 95 islands over 123 years and 39 islands over 27 years, respectively. Using these exceptional datasets, we found that the arrival of the invasive semi‐aquatic American mink (Neogale vison) was a more impactful driver of population dynamics than climate. This invasive predator heavily reduced eider nest numbers by ca. 60% in the Brokey archipelago. In contrast, we detected an apparently adaptive response to the return of the native fox in the Purkey archipelago, with dense nests on islands inaccessible to the fox and no apparent impact on eider populations. This difference might be due to the eiders lacking a joint evolutionary history with the mink and therefore lacking appropriate antipredator responses.
... Molinero et al., 2005). The dominant influence of NAO on the climate of the North Atlantic, mostly due to the regional asymmetry in wind patterns and its quasi-decadal variability (Hurrell and Dickson, 2004), supports its major role in determining the environmental conditions in marine ecosystems, with measurable effects on many organisms (Nye et al., 2014;Drinkwater and Kristiansen, 2018). The NAO was the dominant cause of shifts reported in the central North Atlantic zone (Figure 3b). ...
Recent changes in oceanic plankton are being reported at unprecedented rates. Most changes are related to environmental factors, and many were identified as driven by climate, either through natural cycles or by anthropogenic effects. However, the separation of both effects is difficult because of the short length of most observational series. Moreover, some changes are related to trends and cycles, while others were perceived as system shifts, often synchronized over large spatial scales. Here, studies on observational series of plankton, with the focus in the North Atlantic, are reviewed. Two main periods of shifts in plankton assemblages were identified: one in the late 1980s and a more recent one at the beginning of the new millennium. While the origin and extent of most shifts varied locally, their synchronization seems to confirm the response of plankton to changes in warming and in large-scale climatic factors. Changes in species abundance and distribution patterns were generally related to hydrographic factors, but also to non-linear effects of warming, the latter particularly affecting species in regions near the limits of their thermal niches. Indeed, most of the changes were attributed to trade-offs between different biological strategies. Taken together, the reviewed case studies indicate a lagged biological response to variations in the local environment driven by large-scale climate forcing. The challenges for interpreting future shifts include considering local changes within a larger geographical area, variations in species life traits, and potential top-down effects of plankton predators.
... The NEA cod stock abundance has been in synchrony with multidecadal climate oscillations, e.g. the Atlantic Multidecadal Oscillation, as have its distribution and spawning habitats (Sundby and Nakken, 2008;Drinkwater and Kristiansen, 2018). Previous studies have shown that the NEA cod stock distribution expands northeast in the feeding habitat in the Barents Sea with increased temperatures and a corresponding smaller ice coverage (Ottersen et al., 1998;Kjesbu et al., 2014). ...
Climate change and harvesting result in temporal and spatial changes and variability in spawning, and thus in offspring ambient drift conditions. As a result, variable survival of offspring and thereby in recruitment are expected. This is especially true for species with long reproduction migration as is the case for some Atlantic cod stocks. We utilize biophysical model simulations to analyze survival from spawning until age 1 resulting from different scenarios of spatial and temporal changes in spawning. We find that survival is 1.5–2 times higher when spawning is shifted southwards as compared to northerly shifts. In general, survival is more sensitive to shifts in spawning location than in spawning time. Early spawning is only favourable if spawning is concurrently shifted farther north. A future spawning scenario with a northward shift in spawning grounds beyond what has been observed historically suggests reduced offspring survival and increased sensitivity to the timing of spawning.
... In the Norwegian and Barents Seas, recent warming and increased Atlantic water inflow events have been recorded, with a decline in sea-ice cover in the northern Barents Sea (19)(20)(21). As a consequence, profound effects on the geographical distribution and productivity of commercial fishing stocks are expected (22)(23)(24). In fact, species turnover was projected to increase in the area in the next decades, resulting from some local species extirpations and the arrival of warmer-water species (17,25,26). ...
Observed range shifts of numerous species support predictions of climate change models that species will shift their distribution northward into the Arctic and sub-Arctic seas due to ocean warming. However, how this is affecting overall species richness is unclear. Here we analyze 20,670 scientific research trawls from the North Sea to the Arctic Ocean collected from 1994 to 2020, including 193 fish species. We found that demersal fish species richness at the local scale has doubled in some Arctic regions, including the Barents Sea, and increased at a lower rate at adjacent regions in the last three decades, followed by an increase in species richness and turnover at a regional scale. These changes in biodiversity correlated with an increase in sea bottom temperature. Within the study area, Arctic species’ probability of occurrence generally declined over time. However, the increase in species from southern latitudes, together with an increase in some Arctic species, ultimately led to an enrichment of the Arctic and sub-Arctic marine fauna due to increasing water temperature consistent with climate change.
... Investigations of 64 herring populations detected the importance of local drivers in formation of R and suggested that generally complex and uncertain processes are responsible for the relationship between SSB and R (Trochta et al. 2020). One of the important drivers behind herring dynamics is climate change-warming, operating via modifications in ecosystem conditions, which may affect larval drift or cause changes in growth rates and recruitment survival (Drinkwater and Kristiansen 2018;Tiedemann et al. 2021). ...
Scientific interest in the dynamics of fish recruitment dates back to the beginning of the 20th century. Since then, several studies have shown that the environment may have a stronger effect on recruitment (R) compared to that of the spawning stock biomass (SSB). By combining a suite of methods designed to detect the nonlinear, nonstationary and interactive relationships, we have re-evaluated the potential drivers and their interactions responsible for the multiannual dynamics of the recruitment dynamics of the Gulf of Riga (Baltic Sea) spring spawning herring (Clupea harengus membras) population at the longest time-span to date (1958–2015) allowing coverage of variable ecosystem conditions. R was affected significantly by prey density and the severity of the first winter. Although SSB was not a good predictor of R, adding interaction with SSB significantly improved the model, hence the effect of the two environmental variables on R was modulated by SSB. While temporal changes in the environment–R relationship were generally gradual, several abrupt changes were evident in the strength of these relationships. In addition, nonstationary, linear and nonlinear relationships were observed.
... For the majority of non-target species in Greenland waters and in contrast with other arctic-boreal ecosystems, such as the Barents Sea, sensitivity to temperature has not been quantitatively tested and recent reviews must still rely on information based on observations from the early 20th century (Drinkwater, 2006;Drinkwater & Kristiansen, 2018). Yet, information about how fish abundance responds to environmental change is necessary to lay the foundation to predict fish distribution in the future and draw conclusions on socio-ecological implications of rising temperatures. ...
As result of ocean warming, marine boreal species have shifted their distribution poleward, with increases in abundance at higher latitudes, and declines in abundance at lower latitudes. A key to predict future changes in fish communities is to understand how fish stocks respond to climate variability. Scattered field observations in the first half of the 20th century suggested that boreal fish may coherently invade Greenland waters when temperatures rise, but this hypothesis has remained untested. Therefore, we studied how local temperature variability and the dynamics of the subpolar gyre, a large‐scale driver of oceanic conditions in the North Atlantic, affect abundance of boreal fishes in a region that sharply defines their lower thermal boundary. We analysed information from demersal trawl surveys from 1981 to 2017, for species distributed from shallow shelf to depths of 1,500 m, collected at over 10,000 stations along ~3,000 km of Greenland. Our results show that local temperature and variability of Labrador and Irminger Sea water in the subpolar gyre region drive interdecadal variability of boreal fish abundance in Greenland waters. Although temperature fluctuations were higher in shallow than deep regions, fish abundance changed as quickly in great depths as in shallow depths. This link between physics and biology provides an opportunity for prediction of future trends, which is of utility in Greenland, where fisheries constitute more than 90% of the national export value.
... While the retraction of ice northwards results in a well-known poleward shift in species distribution [25][26][27], and much is known about the functional role of boreal and arctic benthic fauna [28][29][30], uncertainties remain about how concurrent adjustments in biodiversity and food supply affect benthic biogeochemical responses. One source of ambiguity is that changes in sea ice extent, and all of its correlates, exhibit considerable inter-annual variability [31,32] that can appear to manifest as alternative ecosystem responses [33], making it difficult to distinguish natural variability within a period of gradual change from the onset of an abrupt regime shift [34]. Furthermore, the transition or borealization of arctic fauna [35] can positively affect local levels of biodiversity [36,37] and/or provide a functional buffer by maintaining ecological processes [38], depending on local context [39,40] and how post-borealization species interactions and compensatory responses are realized [41,42]. ...
Arctic marine ecosystems are undergoing rapid correction in response to multiple expressions of climate change, but the consequences of altered biodiversity for the sequestration, transformation and storage of nutrients are poorly constrained. Here, we determine the bioturbation activity of sediment-dwelling invertebrate communities over two consecutive summers that contrasted in sea-ice extent along a transect intersecting the polar front. We find a clear separation in community composition at the polar front that marks a transition in the type and amount of bioturbation activity, and associated nutrient concentrations, sufficient to distinguish a southern high from a northern low. While patterns in community structure reflect proximity to arctic versus boreal conditions, our observations strongly suggest that faunal activity is moderated by seasonal variations in sea ice extent that influence food supply to the benthos. Our observations help visualize how a climate-driven reorganization of the Barents Sea benthic ecosystem may be expressed, and emphasize the rapidity with which an entire region could experience a functional transformation. As strong benthic-pelagic coupling is typical across most parts of the Arctic shelf, the response of these ecosystems to a changing climate will have important ramifications for ecosystem functioning and the trophic structure of the entire food web.
This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.
... Challenges: when relations between fish abundance and climate are examined, the additional impact of fisheries is always a challenge. Most aquatic species will have an unimodal response to temperature, too low and too high temperatures decrease their abundance, e.g., [51] and [52] respectively. For fish species the match-mismatch effects between fish and its food source are important [53]. ...
I address 12 issues related to the study of ocean dynamics and its impact on global temperature change, regional and local climate change, and on the North Atlantic ecosystem. I outline the present achievements and challenges that lie ahead. I start with observations and methods to extend the observations of ocean oscillations over time and end with challenges to find connections between ocean dynamics in the North Atlantic and dynamics in other parts of the globe.
... The observed shifts in spawning sites, may also be linked to temperature through the shifts of sea ice edge in the Barents Sea in cold and warm periods (Figure 4). Such shifts in the sea ice edge change the area available for predation (Sundby and Nakken, 2008;Drinkwater and Kristiansen, 2018). To find the mean position or center of geographic distribution for the spawning sites along the coast in March and April, we use the masks satisfying the spawning mass criteria for this study given in Table 1. ...
In this study we investigate both historical and potential future changes in the spatial distribution of spawning habitats for Northeast Arctic cod (NEA cod) based on a literature study on spawning habitats and different physical factors from a downscaled climate model. The approach to use a high resolution regional ocean model to analyze spawning sites is new and provides more details about crucial physical factors than a global low resolution model can. The model is evaluated with respect to temperature and salinity along the Norwegian coast during the last decades and shows acceptable agreement with observations. However, the model does not take into consideration biological or evolutionary factors which also have impact on choice of spawning sites. Our results from the downscaled RCP4.5 scenario suggest that the spawning sites will be shifted further northeastwards, with new locations at the Russian coast close to Murmansk over the next 50 years, where low temperatures for many decades in the last century were a limiting factor on spawning during spring. The regional model gives future temperatures above the chosen lower critical minimum value in larger areas than today and indicates that spawning will be more extensive there. Dependent on the chosen upper temperature boundary, future temperatures may become a limiting factor for spawning habitats at traditional spawning sites south of Lofoten. Finally, the observed long-term latitudinal shifts in spawning habitats along the Norwegian coast the recent decades may be indirectly linked to temperature through the latitudinal shift of the sea ice edge and the corresponding shift in available ice-free predation habitats, which control the average migration distance to the spawning sites. We therefore acknowledge that physical limitations for defining the spawning sites might be proxies for other biophysically related factors.
... Several studies have documented the ecosystem responses to the mid-20th Century warm period in the North Atlantic associated with the AMO and the recent warming. Drinkwater and Kristiansen (2018) provide a synthesis of the ecosystem responses to the AMO-linked cold period of the 1970s and 1980s following the rapid cooling in the 1960s. This and other cold periods have received much less attention in the scientific literature. ...
An international Open Science Meeting entitled Moving in, out, and across the Subarctic and Arctic marine ecosystems: shifting boundaries of water, ice, flora, fauna, people, and institutions, took place 11–15 June 2017 in Tromsø, Norway. Organized by the Ecosystem Studies of Subarctic and Arctic Seas programme and cosponsored by the International Council for the Exploration of the Sea and the North Pacific Marine Science Organization, the primary aim of the meeting was to examine past, present, and future ecosystem responses to climate variability and ocean acidification (OA) and their effect on fishing communities, the fishing industry and fisheries management in the northern Pacific and Atlantic oceans and the Arctic. This symposium issue contains several papers from the meeting covering topics from climate and OA, ecosystem responses to environmental change, and fisheries management including:
• a synthesis of the ecosystem responses to the AMO-linked cold period of the 1970s and 1980s;
• a novel approach to understand responses to OA in northern climes using natural carbonate chemistry gradients, such as CO2 vents, methane cold seeps, and upwelling area;
• the possibility that warm temperatures are allowing two generations of Calanus finmarchicus per year to be produced;
• a new hypothesis suggesting that in areas where sea ice disappears there could be an increase of fish species with swim bladders;
• results from laboratory experiments on the effects of temperature and food on Arctic and boreal fish larvae;
• the application of ecosystem-based management in northern regions; and
• a description of the United States National Oceanic and Atmospheric Administration approach to marine conservation and how it affects fish populations and fisheries.
As climate change intensifies, there is a pressing concern regarding how ecological communities respond to disturbances occurring at different intensities and time scales. We explored how the type of disturbance influences the dynamics of a marine community. A pulse disturbance is an abrupt, high-magnitude shift in conditions that can cause immediate and significant impacts to an ecological community. Alternatively, press disturbances are long-term, multi-generational pressures acting on communities over time. The Northeast US Continental Shelf Large Marine Ecosystem (NES LME) is one of the fastest-warming regions in the world and has experienced historic overfishing. Assemblage shifts in the NES LME have previously been characterized; however, these were prior to an unprecedented pulse disturbance marine heatwave (MHW) event in 2012 followed by punctuated MHWs over the last decade. We quantified community change across the NES LME using a community trajectory analysis, a multivariate tool that utilizes geometric analyses and comparisons of community trajectories, to quantify shifts in dynamic beta diversity. We hypothesized that the pulse MHWs would strongly influence ecosystem structure; however, no significant impact was detected. Our analysis indicates that the NES LME continues to tropicalize. However, it was not the pulse MHW events that seemed to drive change but rather ecosystem overfishing and rising temperatures. We quantified beta diversity over time in marine communities undergoing abrupt environmental changes and press disturbances. When expanded globally, this analysis can compare how variable disturbance pressures may result in different manifestations of beta diversity change within marine assemblages.
The Barents Sea is one of the Polar regions where current climate and ecosystem change is most pronounced. Here we review the current state of knowledge of the physical, chemical and biological systems in the Barents Sea. Physical conditions in this area are characterized by large seasonal contrasts between partial sea-ice cover in winter and spring versus predominantly open water in summer and autumn. Observations over recent decades show that surface air and ocean temperatures have increased, sea-ice extent has decreased, ocean stratification has weakened, and water chemistry and ecosystem components have changed, the latter in a direction often described as “Atlantification” or “borealisation,” with a less “Arctic” appearance. Temporal and spatial changes in the Barents Sea have a wider relevance, both in the context of large-scale climatic (air, water mass and sea-ice) transport processes and in comparison to other Arctic regions. These observed changes also have socioeconomic consequences, including for fisheries and other human activities. While several of the ongoing changes are monitored and quantified, observation and knowledge gaps remain, especially for winter months when field observations and sample collections are still sparse. Knowledge of the interplay of physical and biogeochemical drivers and ecosystem responses, including complex feedback processes, needs further development.
Observed range shifts of numerous species support predictions of climate change models that species will shift their distribution northwards into the Arctic and sub-Arctic seas due to ocean warming. However, how this is affecting overall species richness is unclear. Here we analyse scientific research trawl surveys from the North Sea to the Arctic Ocean collected from 1994 to 2020, including 193 fish species. We found that demersal fish species richness at the local scale has doubled in some Arctic regions, including the Barents Sea, and increased at a lower rate at adjacent regions in the last three decades, followed by an increase in species richness and turnover at a regional scale. These changes in biodiversity paralleled an increase in sea bottom temperature. Within the study area, Arctic species’ probability of occurrence generally declined over time. However, the increase of species from southern latitudes, together with an increase of some Arctic species, ultimately led to an enrichment of the Arctic and sub-Arctic marine fauna due to increasing water temperature consistent with climate change.
Significance Statement
Global modelling studies suggest increased species arrivals from lower latitudes and local expirations at high latitudes due to global warming. Our analysis of 20,670 standardized scientific trawl surveys with 193 fish species from the north-east Atlantic and Arctic Oceans found an increase in species richness in the region parallel to an increase in sea bottom temperature. Some Arctic species declined in probability of occurrence over time, but some increased. This, together with the increase of southern-latitude species led to an enrichment of the Arctic and sub-Arctic marine fauna attributed to climate change.
This report aims to accelerate climate change adaptation implementation in fisheries management throughout the world. It showcases how flexibility can be introduced in the fisheries management cycle in order to foster adaptation, strengthen the resilience of fisheries, reduce their vulnerability to climate change, and enable managers to respond in a timely manner to the projected changes in the dynamics of marine resources and ecosystems. The publication includes a set of good practices for climate-adaptive fisheries management that have proven their effectiveness and can be adapted to different contexts, providing a range of options for stakeholders including the fishing industry, fishery managers, policymakers and others involved in decision-making. These good practices were linked to one or more of the three common climate-related impacts on fisheries resources: distributional change; productivity change; and species composition change. Therefore, these three impacts can serve as practical entry points to guide decision-makers in identifying good practice adaptation measures suitable for their local contexts. These good practices are based upon transferable experiences and lessons learned from the thirteen case studies across the globe and hopefully will contribute to greater uptake and implementation of climate-adaptive fisheries management measures on the ground.
A twenty-five year (1994–2018) survey at 10 rocky sites within Lough Hyne Marine Reserve (SW Ireland) showed that, despite considerable spatial and temporal patchiness, three barnacle species (Chthamalus stellatus, Semibalanus balanoides, and Austrominius modestus) declined in overall abundance in the early 2000s, particularly at three sites. There was no clear response of A. modestus or C. stellatus to the cold winters of 2010 and 2011. In 2004, however, S. balanoides declined suddenly, but showed a slight recovery after the cold winter of 2010 to maintain sparse populations in the lough, but remained abundant outside the lough. A fourth species, Chthamalus montagui, showed a different pattern, with wide fluctuations in abundance but no overall decline. Changes in the Atlantic Multidecadal Oscillation may have influenced the overall composition of barnacle populations. Rising maximum air temperatures, resulting in high body temperatures recorded for A. modestus even during mild days, are suggested to have impacted the barnacle populations as a result of the prolonged aerial exposure times caused by the lough's asymmetric tidal pattern.
The introduction of 200 n.m. exclusive economic zones (EEZs) in the late 1970s required increased collaboration among neighbouring coastal states to manage transboundary and straddling fish stocks. The established agreements ranged from bilateral to multilateral, including high‐seas components, as appropriate. However, the 1982 United Nations Convention on the Law of the Sea does not specify how quotas of stocks crossing EEZs should be allocated, nor was it written for topical scenarios, such as climate change with poleward distribution shifts that differ across species. The productive Northeast Atlantic is a hot spot for such shifts, implying that scientific knowledge about zonal distribution is crucial in quota negotiations. This diverges from earlier, although still valid, agreements that were predominately based on political decisions or historical distribution of catches. The bilateral allocations for Barents Sea and North Sea cod remain robust after 40 years, but the management situation for widely distributed stocks, as Northeast Atlantic mackerel and Norwegian spring‐spawning herring, appears challenging, with no recent overall agreements. Contrarily, quotas of Northern hake are, so far, unilaterally set by the EU despite the stock's expansion beyond EU waters into the northern North Sea. Negotiations following the introduction of EEZs were undertaken at the end of the last cooler Atlantic Multidecadal Oscillation (AMO) period, that is, with stock distributions generally in a southerly mode. Hence, today's lack of management consensus for several widely distributed fish stocks typically relates to more northerly distributions attributed to the global anthropogenic signal accelerating the spatial effect of the current warmer AMO.
Drinkwater and Kristiansen (hereafter D&K) (2018, A synthesis of the ecosystem responses to the late 20th century cold period in the northern North Atlantic, ICES Journal of Marine Science, 75: 2325–2341) examined multi-trophic level biological responses in relation to a 1960s–1980s “cold period” that they associated with the Atlantic Multidecadal Oscillation (AMO). They concluded that ocean temperature was a major driver of ecosystem changes throughout the North Atlantic during this interval and adversely affected the abundance, spawning stock biomass (SSB), recruitment, survival success of several species including cod in four North Atlantic ecosystems (NE Arctic, Iceland, West Greenland, and Labrador–northern Newfoundland). D&K further suggested that negative ocean temperature anomalies during this cold period occurred first in the Eastern Arctic and Barents Sea, propagated westward across the North Atlantic to the Labrador Sea and were potentially related to a sequential E–W collapse of the four cod stocks. We take issue with these conclusions and suggest that a more quantitative discussion of fisheries exploitation was in order.
Consequences of shifting species distributions
Climate change is causing geographical redistribution of plant and animal species globally. These distributional shifts are leading to new ecosystems and ecological communities, changes that will affect human society. Pecl et al. review these current and future impacts and assess their implications for sustainable development goals.
Science , this issue p. eaai9214
In the decades since World War II, large-scale ecological changes have affected fishing communities across the northern Atlantic. Substantial declines hit their historically important resources, most notably the Atlantic cod. Such declines were often accompanied by increases in other, previously less exploited, species. Interactions between fishing pressure and environmental variation have driven ecological change. Ecological changes in turn reshaped the fisheries, contributing to altered demographic profiles of fisheries-dependent communities. Many places lost population, especially through out-migration of young adults. Broad social forces also contributed to these trends, but the timing and geographical details of population changes often correspond to specific fisheries/ecological events.
Sparse stations and serious measuring problems hamper analyses of climatic conditions in the Arctic. This paper presents a discussion of measuring problems in the Arctic and gives an overview of observed past and projected future climate variations in Svalbard and Jan Mayen. Novel analyses of temperature conditions during precipitation and trends in fractions of solid/liquid precipitation at the Arctic weather stations are also outlined. Analyses based on combined and homogenized series from the regular weather stations in the region indicate that the measured annual precipitation has increased by more than 2.5% per decade since the measurements started in the beginning of the 20th century. The annual temperature has increased in Svalbard and Jan Mayen during the latest decades, but the present level is still lower than in the 1930s. Downscaled scenarios for Svalbard Airport indicate a further increase in temperature and precipitation. Analyses based on observations of precipitation types at the regular weather stations demonstrate that the annual fraction of solid precipitation has decreased at all stations during the latest decades. The reduced fraction of solid precipitation implies that the undercatch of the precipitation gauges is reduced. Consequently, part of the observed increase in the annual precipitation is fictitious and is due to a larger part of the “true” precipitation being caught by the gauges. With continued warming in the region, this virtual increase will be measured in addition to an eventual real increase.
After 1950 traditional herring fisheries were revolutionized by a new technique: sonar, power block, larger nets and bigger boats. As a result all major herring stocks in the North East Atlantic Ocean collapsed. The most dramatic decline was that of the Atlanto-Scandian stock between Iceland and Norway from millions of tons to the border of extinction in a decade. It was one of the largest fish stocks in the world until the fishery crashed in the late 1960s. The catch in 1971 was only 20 thousand metric tons in contrast with the record of 2 million tons in 1966 and the spawning stock declined from 10 million tons to 10 thousand tons in 20 years. After more than 20 years of very restricted catches the stock finally recovered. With hindsight the cause of this disaster was a combination of biological, technological, economical and ecological factors, but the most important ones were over-fishing, recruitment failure and the cooling of the East-Icelandic current which was one aspect of a global climate change in this part of the world during the period 1965-2000. At that time there was no fisheries management authority to limit either catch or effort. The sudden closure of the fishery was a shock to many communities in Norway and Iceland. The small Icelandic economy was especially vulnerable because salting and reduction of herring was for many years the most important export industry in the country, sometimes exceeding 40% of the total value, and a source of wealth around the country that trickled down the society. After describing the simultaneously waning stock and waxing effort by mathematical models we will first demonstrate some macroeconomic quantities before and after the collapse and then take a closer microeconomic look at some of the communities that based their existence on the herring fishery. Finally we will outline the recovery when other species replaced the herring and new industries gradually diversified the economy.
In the 1990s the northern cod Gadus morhua stock off southern Labrador and northeastern Newfoundland declined to such low levels that the Canadian government imposed a fishing moratorium. A decade later, with the moratorium still largely in place, there is little evidence of a recovery. While overfishing is believed to be the major cause of the collapse, this paper provides evidence that severe climate conditions, in particular cold temperatures, also played an important role in the decline of the cod. They contributed to slower growth rates and reduced size-at-age. Approximately 30-50% of the decline in the biomass of the northern cod during the 1980s to the early 1990s was due solely to changes in weight. The presence of large numbers of smaller size fish led to illegal dumping by fisherman, thereby adding to the fishing mortality. Colder temperatures also led to increased mortality of cod eggs and likely lower recruitment. An environmentally-induced southward displacement of the cod may also have resulted in lower recruitment.
The purpose of this review is to describe the global scope of the multidecadal climate oscillations that go back at least, through several hundred years. Literature, historic data, satellite data and global circulation model output have been used to provide evidence for the zonal and meridional jet stream patterns. These patterns were predominantly zonal from the 1970s to 1990s and switched since the 1990s to a meridional wind phase, with weakening jet streams forming Rossby waves in the northern and southern hemispheres. A weakened northern jet stream has allowed northerly winds to flow down over the continents in the northern hemisphere during the winter period, causing some harsh winters and slowing anthropogenic climate warming regionally. Wind oscillations impact ocean gyre circulation affecting upwelling strength and pelagic fish abundance with synchronous behavior in sub Arctic gyres during phases of the oscillation and asynchronous behavior in subtropical gyres between the Atlantic and Pacific oceans.
Oceanographic, meteorological, and ice data were examined to establish the average
conditions that prevailed on the Newfoundland and Labrador continental shelves
during recent decades, and to describe the variability on seasonal and interannual
scales. The results indicate that the below-normal air temperatures established in 1989
persisted over much of eastern Canada, resulting in increased ice growth and reduced
ice melt during the early 1990s. Since 1990, ice conditions have been more severe and
have lasted longer, with 1991 being the worst in 30 years. The net effect of these
conditions was a delayed and reduced heat input into the ocean, which resulted in a
thinner and fresher mixed layer and a lower heat content in the water column.
Conditions during similar anomalous periods of the early 1970s and mid-1980s were
also examined. In general, the large negative temperature and salinity (fresher than
normal) anomalies of the early 1990s were found to be similar to events of the early
1970s and to a lesser extent of the mid-1980s and were associated with colder than
normal winter air temperature and heavier than normal ice conditions in the coastal
region of the Northwest Atlantic.
Possible changes in Atlantic meridional overturning circulation (AMOC) provide a key source of uncertainty regarding future climate change. Maps of temperature trends over the twentieth century show a conspicuous region of cooling in the northern Atlantic. Here we present multiple lines of evidence suggesting that this cooling may be due to a reduction in the AMOC over the twentieth century and particularly after 1970. Since 1990 the AMOC seems to have partly recovered. This time evolution is consistently suggested by an AMOC index based on sea surface temperatures, by the hemispheric temperature difference, by coral-based proxies and by oceanic measurements. We discuss a possible contribution of the melting of the Greenland Ice Sheet to the slowdown. Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event in the past millennium (p > 0.99). Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC.
The Atlantic Meridional Overturning Circulation (AMOC), a major current system in the Atlantic Ocean, is thought to be an important driver of climate variability, both regionally and globally and on a large range of time scales from decadal to centennial and even longer. Measurements to monitor the AMOC strength have only started in 2004, which is too short to investigate its link to long-term climate variability. Here the surface heat flux-driven part of the AMOC during 1900–2010 is reconstructed from the history of the North Atlantic Oscillation, the most energetic mode of internal atmospheric variability in the Atlantic sector. The decadal variations of the AMOC obtained in that way are shown to precede the observed decadal variations in basin-wide North Atlantic sea surface temperature (SST), known as the Atlantic Multidecadal Oscillation (AMO) which strongly impacts societally important quantities such as Atlantic hurricane activity and Sahel rainfall. The future evolution of the AMO is forecast using the AMOC reconstructed up to 2010. The present warm phase of the AMO is predicted to continue until the end of the next decade, but with a negative tendency.
We investigated long-term variability of the calycophoran siphonophores Muggiaea atlantica and Muggiaea kochi in the Western English Channel (WEC) between 1930 and 2011. Our aims were to describe long-term changes in abundance and temporal distribution in relation to local environmental dynamics. In order to better understand mechanisms that regulate the species’ populations, we identified periods that were characteristic of in situ population growth and the environmental optima associated with these events. Our results show that between 1930 and the 1960s both M. atlantica and M. kochi were transient components of the WEC ecosystem. In the late 1960s M. atlantica, successfully established a resident population in the WEC, while the occurrence of M. kochi became increasingly sporadic. Once established as a resident species, the seasonal abundance and distribution of M. atlantica increased. Analysis of environmental conditions associated with in situ population growth revealed that temperature and prey were key determinants of the seasonal distribution and abundance of M. atlantica. Salinity was shown to have an indirect effect, likely representing a proxy for water circulation in the WEC. Anomalies in the seasonal cycle of salinity, indicating deviation from the usual circulation pattern in the WEC, were negatively associated with in situ growth, suggesting dispersal of the locally developing M. atlantica population. However, our findings identified complexity in the relationship between characteristics of the environment and M. atlantica variability. The transition from a period of transiency (1930–1968) to residency (1969–2011) was tentatively attributed to structural changes in the WEC ecosystem that occurred under the forcing of wider-scale hydroclimatic changes
The temperature of the upper 300 m of the North Atlantic increased by about 0.57°C between 1984 and 1999. but this underlying trend was overlain with substantial geographic and interannual variability. Northward shifts occurred in the distribution of many commercial and non-commercial fish species in the NE Atlantic during the 1990s. New records were established for a number of Mediterranean and NW African species on the south coast of Portugal. Red mullet (Mullus surmuletus) and bass (Dicentrarchus labrax) extended their ranges northward to western Norway and catches of the former increased throughout the 1990s in the North Sea. Abundance or relative abundance of warm-water commercial species of gadoids and flatfish generally increased during the 1990s, but like the warming trend the changes in distribution and abundance were by no means uniform and there was considerable interannual variability. There were also examples of southward shifts for some species, which can be related to local hydrographic conditions, such as upwelling. Information on distribution and abundance of Greenland cod (Gadus morhua L.) and Norwegian spring spawning herring (Clupea harengus) during a previous warming period in the late 1920s and 1930s is also presented and compared with changes in the 1990s.
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 physical and ecological 'fingerprints' of anthropogenic climate change over the past century are now well documented in many environments and taxa. We reviewed the evidence for phenotypic responses to recent climate change in fish. Changes in the timing of migration and reproduction, age at maturity, age at juvenile migration, growth, survival and fecundity were associated primarily with changes in temperature. Although these traits can evolve rapidly, only two studies attributed phenotypic changes formally to evolutionary mechanisms. The correlation-based methods most frequently employed point largely to 'fine-grained' population responses to environmental variability (i.e. rapid phenotypic changes relative to generation time), consistent with plastic mechanisms. Ultimately, many species will likely adapt to long-term warming trends overlaid on natural climate oscillations. Considering the strong plasticity in all traits studied, we recommend development and expanded use of methods capable of detecting evolutionary change, such as the long term study of selection coefficients and temporal shifts in reaction norms, and increased attention to forecasting adaptive change in response to the synergistic interactions of the multiple selection pressures likely to be associated with climate change.
Relative to the underlying warming trend during the 20th century the surface waters averaged over the north Atlantic were cool in the period between 1900 and 1930, warm from 1930 to 1960, cool between the late 1960s and 1990 and then warm from 1990 to present. The warming observed in the last three decades has been particularly strong in parts of the north-east Atlantic, with the sea surface around the UK and Ireland warming at rates up to six times greater than the global average. It remains difficult to fully distinguish the natural variations in temperature from those due to anthropogenic influence (including emissions of carbon dioxide, CO 2). Marine Air Temperatures over the Northeast Atlantic and southern North Sea have warmed rapidly over the last 30 years. The observed warming is greatest in the Northeast Atlantic with warming rates of over 0.6 °C decade-1. Similarly, sea-surface temperatures (SST) in UK coastal waters and in the Northeast Atlantic have risen by between 0.1 and 0.5 ?C decade-1 since the 1980s. In UK Coastal Waters the most rapid rises have been observed in the Southern North Sea (Region 2) and off the western coast of Scotland (Region 6 and the southern part of Region 7) at a rate between 0.2 and 0.4 ?C decade-1. Recent cold years have meant that linear trends in Marine Air Temperature in other regions (Regions 1, 3 and much of regions 4 and 5) are not statistically significant. The temperature of the upper ocean (0-800m) to the west and north of the UK has been generally rising since the 1970s (Region 8) and 1980s (Region 7). Superimposed on the underlying upward trend are decadal scale patterns of variability, fluctuating between relative maxima around 1960 and in the 2000s, with relative minima in the 1980s and 1990s. Despite the long-term warming trends in evidence in most regions, whether over the century or last 30 years, temperature evolution at a location has not been linear or smooth with some short periods of rapid change over a few years and others of little change. Since 2008 the SSTs observed in most areas have not risen or have been slightly lower than observed in 2003-2007. The observed temperature variability has been attributed to a combination of global climate change and natural variability, attributed to ‘internal’ variability in the ocean atmosphere system, the Atlantic Multidecadal Oscillation is thought to be a representative pattern of this internal variability, the decadal scale patterns observed in UK waters are similar to that of the AMO. As a result of both of these ‘drivers’, a significant period of rapid warming occurred from 1985 to 2003. West of the UK the water of the deep ocean (>1000m) comes from the Labrador Sea and has generally cooled since 1975. North of the UK, the deep water (800 m) flows from the Nordic Seas and shows no long-term trend since 1950. The deep bottom waters of the Nordic Seas are known to be warming. Over the 21st Century warming in the shelf seas around the UK and Ireland and the upper layers of the North Atlantic is predicted to continue, although perhaps at a lesser average rate to that observed in the last 30 years (which has perhaps been strengthened by natural variability). Natural variability, driven by atmospheric and oceanic processes introduces a level of uncertainty that makes it difficult to predict the direction of temperature change over the next decade. However initial experimental forecasts of ocean temperatures are beginning to be published.
An extended reanalysis, a combination of observations and model output, is used to examine the spatial patterns of physical variables associated with the Atlantic Multidecadal Oscillation (AMO) from 1871 to 2008. The results are presented as anomalies during positive and negative phases of the AMO. As in previous studies, during positive (negative) AMO phases the sea surface temperature (SST) is anomalously warm (cold) over most of the North Atlantic, with the exception of the east coast of the United States. The atmospheric patterns, associated with the positive phase of the AMO, include anomalous low pressure over the Atlantic between 20°S and 50°N, cyclonic surface winds around the low, reduced wind speeds over the tropical Atlantic and enhanced precipitation in the eastern tropical Atlantic, with roughly opposite conditions during negative AMO phases. There are, however, substantial differences in the SST and the atmospheric anomalies between periods of the same phase, especially in the extratropics. Correlations between the AMO and air temperature anomalies are positive over much of the globe between 40°S and 50°N, with correlations exceeding 0.6 (~ 95% significance level) over the Maritime Continent and northern rim of the Pacific Ocean. Most of the sea level pressure (SLP) anomalies beyond the Atlantic are not statistically significant.
Using surface data from 57 UK meteorological stations, a national (BADC-57) and regional wind index for the UK has been calculated for the period 1983 to 2011. For a subset of seven stations, an additional national index (BADC-7) has been calculated for the period 1957 to 2011. The indices show an annual variability of 4% over their respective periods corresponding to a variation in typical wind turbine capacity factor of 7%. These indices are compared with indices calculated from other sources, namely: an index generated using a gridded dataset of observed values interpolated across the UK; an index calculated from an area bounding the UK using the ERA-40 reanalysis dataset; indices calculated from bilinear interpolation of the ERA-40 reanalysis dataset to the 57 and seven stations; and another independent UK wind index. The indices show variation in trends with all showing some level of decline with the exception of that generated using the ERA-40 reanalysis dataset averaged over the UK which shows a significant increase. The various indices show varying degrees of agreement with correlation coefficients, after trends are removed, ranging between 0.611-0.979. The effect of changes in site exposure, instrument bias and measuring height were considered for the BADC-7 and BADC-57 indices. The change in instrument measurement height appears to have a significant biasing effect and it is likely that this along with changes in exposure at urban sites have caused the decline in annual wind speeds observed for some of the indices. There does not appear to be evidence for significant changes in large area (mesoscale) surface roughness. The correlation between annual mean wind speeds at the seven surface station sites used to calculate the BADC-7 index is seen to be quite weak indicating very localised variations in inter-annual variability. When regional differences in the index are investigated, it is seen that wind speeds show a very slight decline across the UK in all regions except the south-east, which shows a slight increase. The greatest decrease is seen in the north-west. These changes are in the same direction as the tentative predictions given by climate models for future changes in wind speed across the UK, though the uncertainty is large given the large degree of inter-annual variation.
It follows from the analysis of observation data that the secular variation of the mean temperature of the Earth can be explained by the variation of short-wave radiation, arriving at the surface of the Earth. In connection with this, the influence of long-term changes of radiation, caused by variations of atmospheric transparency on the thermal regime is being studied. Taking into account the influence of changes of planetary albedo of the Earth under the development of glaciations on the thermal regime, it is found that comparatively small variations of atmospheric transparency could be sufficient for the development of quaternary glaciations. DOI: 10.1111/j.2153-3490.1969.tb00466.x
A review of environmental conditions on the continental shelves and adjacent offshore areas off eastern Canada during 1994 is presented. Wintertime air temperatures over eastern Canada were generally colder-than-normal continuing the trend that has persisted through the 1990s. This was associated with the high positive value of the NAO index caused by the intensification of the Icelandic Low and Azores High. Strong northwesterly, winds over the region brought cold air farther south. The cold air temperatures and stronger northwesterly winds resulted in early ice formation, greater areal extent of ice and a longer presence of ice, both on the Labrador/Newfoundland Shelves and in the Gulf of St. Lawrence/ Scotian Shelf. The cold temperatures, strong winds and heavy ice all contributed to a larger number of icebergs than normal reaching the Grand Bank. Ocean temperatures off Newfoundland at Station 27 were below normal during the winter of 1994. By summer, however, the surface waters had increased upwards of 2°C above normal and to near normal in the deeper waters by fall. The area of the CIL in summer across the northeast Newfoundland Shelf decreased from 1993 and was slightly above or near normal. Large areas of the continental shelf, particularly the Grand Bank, contained cold bottom temperatures (up to 0.5°C below average) continuing a trend that began a decade ago. Temperature anomalies off southern Newfoundland have also been cold since the mid-1980s. Similar cold conditions have been observed within the CIL in both the Gulf of St. Lawrence and on the Scotian Shelf. Large areas of the Magdalen Shallows continue to be covered by bottom waters of less than 1° and less than 0°C during the summer. Temperatures in the CIL layer on the Scotian Shelf appear to be moderating with maximum warming over Emerald Basin due to mixing with warm bottom waters. The latter have occupied the lower layers of the Basin for the past few years and are consistent with warm temperatures in the deep waters of the Laurentian Channel and Cabot Strait to the north and in the Gulf of Maine to the south. The source of these deep waters are the offshore slope waters. Indeed, penetration of the slope water appeared to have lead to significant warming throughout the entire Gulf of Maine during 1994.
We use observed air temperature data series from 14 meteorological stations in coastal Greenland (located all around the Greenland Ice Sheet) for 1960–2010, where long-term records for five of the stations extend back to 1890, to illustrate the annual and monthly temporal and spatial distribution of temperature extremes, with the main focus on the latest decade 2001–2010 (2000s). We find that the 2000s had the highest number of mean annual air temperature (MAAT) warm extremes, and the 1890s the highest number of cold extremes, and that a high (low) positive North Atlantic Oscillation (NAO) Index equals a high number of cold (warm) extreme events. For the 2000s the number of warm extremes was significantly higher by around 50% than the number in the 1940s (the early twentieth century warm period): the latter being the decade with the second highest occurrence of MAAT warm extremes. Since 1960, based on MAAT the number of cold extremes has overall decreased on the decadal timescale, besides a peak in 1980s, while warm extremes have increased, leading to a higher occurrence of extremes (cold plus warm extremes): an almost similar pattern occurred for monthly mean temperatures and monthly mean daily maximum and minimum temperature datasets. Furthermore, a division of Greenland into east and west sectors shows that the occurrence of cold (warm) extremes was more pronounced in the East than in the West in the 1960s and 1970s (mid-1980s to the 2000s).
Few links have been established between the Atlantic Multidecadal Oscillation and long-term dynamics of marine systems due to the scarcity of sustained biological time-series with sufficient multi-decadal coverage. The abundances of co-occurring boreal and Lusitanian species of barnacle have been recorded annually at a rocky shore in Devon, southwest England since 1953. Multidecadal cycles in relative abundances of the cold-water Semibalanus balanoides and warm-water Chthamalus spp. are strongly correlated with both local sea surface temperatures, and a 'Warm Index' of barnacle abundance shows strong links to the basin-scale Atlantic Multidecadal Oscillation. In contrast there are weak or no observed relationships with the North Atlantic Oscillation for either species. The shorter lifecycle of S. balanoides compared to the chthamalids and the increase in spring and summer temperatures to which newly settled S. balanoides recruits have been exposed during the last decade are likely mechanisms by which barnacle densities are responding to low-frequency temperature variability expressed in the Atlantic Multidecadal Oscillation.
twentieth century Northern Hemisphere mean surface temperature (NHT) is
characterized by a multidecadal warming-cooling-warming pattern followed
by a flat trend since about 2000 (recent warming hiatus). Here we
demonstrate that the North Atlantic Oscillation (NAO) is implicated as a
useful predictor of NHT multidecadal variability. Observational analysis
shows that the NAO leads both the detrended NHT and oceanic Atlantic
Multidecadal Oscillation (AMO) by 15-20 years. Theoretical analysis
illuminates that the NAO precedes NHT multidecadal variability through
its delayed effect on the AMO due to the large thermal inertia
associated with slow oceanic processes. An NAO-based linear model is
therefore established to predict the NHT, which gives an excellent
hindcast for NHT in 1971-2011 with the recent flat trend well predicted.
NHT in 2012-2027 is predicted to fall slightly over the next decades,
due to the recent NAO decadal weakening that temporarily offsets the
anthropogenically induced warming.
Understanding the biophysical mechanisms that shape variability in fisheries recruitment is critical for estimating the effects of climate change on fisheries. In this study, we used an Earth System Model (ESM) and a mechanistic individual-based model (IBM) for larval fish to analyze how climate change may impact the growth and survival of larval cod in the North Atlantic. We focused our analysis on five regions that span the current geographical range of cod and are known to contain important spawning populations. Under the SRES A2 (high emissions) scenario, the ESM-projected surface ocean temperatures are expected to increase by >1 °C for 3 of the 5 regions, and stratification is expected to increase at all sites between 1950-1999 and 2050-2099. This enhanced stratification is projected to decrease large (>5 μm ESD) phytoplankton productivity and mesozooplankton biomass at all 5 sites. Higher temperatures are projected to increase larval metabolic costs, which combined with decreased food resources will reduce larval weight, increase the probability of larvae dying from starvation and increase larval exposure to visual and invertebrate predators at most sites. If current concentrations of piscivore and invertebrate predators are maintained, larval survival is projected to decrease at all five sites by 2050-2099. In contrast to past observed responses to climate variability in which warm anomalies led to better recruitment in cold-water stocks, our simulations indicated that reduced prey availability under climate change may cause a reduction in larval survival despite higher temperatures in these regions. In the lower prey environment projected under climate change, higher metabolic costs due to higher temperatures outweigh the advantages of higher growth potential, leading to negative effects on northern cod stocks. Our results provide an important first large-scale assessment of the impacts of climate change on larval cod in the North Atlantic.
Over 32 years of wind data, which are based on surface pressure maps,
from the Hindcast data base that has been developed by the Norwegian
Meteorological Institute have been used to study the wind stress curl
field, over the Nordic Seas. The mean wind stress curl pattern is
characterized by very large values over most of the area, especially
over the Greenland Sea. Within the framework of Sverdrup dynamics this
gives rise to a cyclonic circulation in the area, with a maximum
transport in the western boundary current of about 35 Sv. Only one gyre
is present, and its center is situated between Jan Mayen and Greenland.
The seasonal variation of the wind stress curl is very large, with
almost negligible values during summer, from May through August. During
September the wind stress curl starts to build up and has reached its
full winter strength by November. This maximum is maintained until
April, when it begins to decline to typical summer values. In order to
study the spatial and temporal scales of the wind stress curl, an
empirical orthogonal function analysis was performed on the wind stress
curl after filtering it with a half-power period of 50 days and then
resampling the wind stress curl every 30 days. A Monte Carlo method is
used to estimate the statistical significance of the various modes. The
first 11 modes are found to be significant, and they represent 83.6% of
the total variance of the data set. The first mode clearly shows the
seasonal fluctuations of the mean wind stress curl pattern, representing
the seasonal variation in the intensity of the Icelandic low. The next
two modes show mostly interannual variability, with a decadal time
scale. Most of these variations are happening in the northern part of
the Greenland Sea. The other significant modes are mainly describing
variability that is limited either in space or in time. A large part of
this anomalous variability occurs in the 1980s.
We compare Atlantic cod stocks in the Barents Sea and on the
Newfoundland Shelf.The Barents Sea (BS) cod has remained productive
whereas the NF cod collapsed.Management reduced catches more for BS cod
at a time of crisis in the late 1980s.Intensification of the NAO in the
early 1990s contributed to the differences.
This paper reviews three modes of natural variability that have been
identified in the North Atlantic Ocean, namely, the North Atlantic
Oscillation (NAO), the Atlantic Multidecadal Oscillation (AMO) and the
Atlantic Meridional Mode (AMM). This manuscript focuses on the
multidecadal fluctuations of these three modes. A range of different
mechanisms to initiate phase reversals in these modes on multidecadal
timescales has been suggested previously. We propose a systematic
grouping of these mechanisms into three types that involve,
respectively, (1) the dependency of the Atlantic thermohaline
circulation (THC) on salinity, (2) the sensitivity of the THC to changes
in ocean heat transport and (3) the dependency of the NAO to changes in
the Atlantic meridional temperature gradient. Some new density data is
also provided, demonstrating physical links between the THC and the AMO.
A recent period (1977–1982) of cold climate in the Barents Sea resulted in a greatly reduced feeding area available for the Arctic cod and in consistently low recruitment. With the start of a warmer period in 1982/83, the area and potential for production of cod biomass expanded and recruitment has increased. A hypothesis is presented that through evolutionary processes, the reproduction of the Arctic cod is adjusted to the variations in the feeding area caused by climatic fluctuations. Historical data on sea temperature and ice cover are used to describe the climatic fluctuations for the period 1900–1983 and these are compared with data on fluctuations in year-class strength. It is concluded that conditions favouring high survival rates of cod larvae must be related to the occurrence of high temperatures in the Atlantic component of the Norwegian current. The processes and/or phenomena must have a large time and space scale. This is also confirmed by the high incidence of temporal similarity in survival success of the stocks of cod, haddock and herring in this area.
Stocks of Atlantic cod (Gadus morhua) have been declining over much of the North Atlantic for the past 30 years, owing to a combination of overfishing and adverse changes in their environment. In a previous study, environmental effects were introduced as an extra parameter in the stock-recruit relationship, where they act as a multiplier, independent of the level of spawning-stock biomass (SSB). Using a non-parametric pooled analysis of all cod stocks on the European Shelf south of 62 degrees N, it is shown here that environmental variability (as represented by the North Atlantic Oscillation) only has a significant effect on recruitment when the spawning stock is low. This has implications for fisheries management strategies, and for rates of stock recovery, which will be very dependent on environmental conditions. (c) 2004 International Council for the Exploration of the Sea. Published by Elsevier Ltd. All rights reserved.