Anne Britt Sandø - Academia.edu (original) (raw)

Papers by Anne Britt Sandø

Ocean Dynamics, 2014

Global atmosphere-ocean general circulation models are the tool by which projections for climate ... more Global atmosphere-ocean general circulation models are the tool by which projections for climate changes due to radiative forcing scenarios have been produced. Further, regional atmospheric downscaling of the global models may be applied in order to evaluate the details in, e.g., temperature and precipitation patterns. Similarly, detailed regional information is needed in order to assess the implications of future climate change for the marine ecosystems. However, regional results for climate change in the ocean are sparse. We present the results for the circulation and hydrography of the Barents Sea from the ocean component of two global models and from a corresponding pair of regional model configurations. The global models used are the GISS AOM and the NCAR CCSM3. The ROMS ocean model is used for the regional downscaling of these results (ROMS-G and ROMS-N configurations, respectively). This investigation was undertaken in order to shed light on two questions that are essential in the context of regional ocean projections: (1) How should a regional model be set up in order to take advantage of the results from global projections; (2) What limits to quality in the results of regional models are imposed by the quality of global models? We approached the first question by initializing the ocean model in the control simulation by a realistic ocean analysis and specifying air-sea fluxes according to the results from the global models. For the projection simulation, the global models’ oceanic anomalies from their control simulation results were added upon initialization. Regarding the second question, the present set of simulations includes regional downscalings of the present-day climate as well as projected climate change. Thus, we study separately how downscaling changes the results in the control climate case, and how scenario results are changed. For the present-day climate, we find that downscaling reduces the differences in the Barents Sea between the original global models. Furthermore, the downscaled results are closer to observations. On the other hand, the downscaled results from the scenario simulations are significantly different: while the heat transport into the Barents Sea and the salinity distribution change modestly from control to scenario with ROMS-G, in ROMS-N the heat transport is much larger in the scenario simulation, and the water masses become much less saline. The lack of robustness in the results from the scenario simulations leads us to conclude that the results for the regional oceanic response to changes in the radiative forcing depend on the choice of AOGCM and is not settled. Consequently, the effect of climate change on the marine ecosystem of the Barents Sea is anything but certain.

Climate of the Past

Analyses of observational data (from year 1870 AD) show that sea surface temperature (SST) anomal... more Analyses of observational data (from year 1870 AD) show that sea surface temperature (SST) anomalies along the pathway of Atlantic Water transport in the North Atlantic, the Norwegian Sea and the Iceland Sea are spatially coherent at multidecadal timescales. Spatially coherent SST anomalies are also observed over hundreds of thousands of years during parts of the Pliocene (5.23-5.03, 4.63-4.43, and 4.33-4.03 Ma). However, when investigating CMIP6 (Coupled Model Intercomparison Project 6) SSP126 (Shared Socioeconomic Pathway) future scenario runs (next century) and other Pliocene time intervals, the following three additional SST relations emerge: (1) the Norwegian Sea SST anomaly is dissimilar to the North Atlantic and the Iceland Sea SST anomalies (Pliocene; 4.93-4.73 and 3.93-3.63 Ma), (2) the Iceland Sea SST anomaly is dissimilar to the North Atlantic and the Norwegian Sea SST anomalies (Pliocene; 3.43-3.23 Ma), and (3) the North Atlantic SST anomaly is dissimilar to the SST anomalies of the Norwegian and Iceland seas (future trend). Hence, spatially noncoherent SST anomalies may occur in equilibrium climates (Pliocene), as well as in response to transient forcing (CMIP6 SSP126 low-emission future scenario). Since buoyancy is a key forcing for the inflow of Atlantic Water to the Norwegian Sea, we investigate the impacts of buoyancy forcing on spatial relations between SST anomalies seen in the North Atlantic and the Norwegian and Iceland seas. This is done by performing a range of idealized experiments using the Massachusetts Institute of Technology general circulation model (MITgcm). Through these idealized experiments we can reproduce three out of four of the documented SST anomaly relations: being spatially coherent under weak to intermediate freshwater forcing over the Nordic Seas, the Iceland Sea being dissimilar to the North Atlantic and the Norwegian Sea under weak atmospheric warming over the Nordic Seas, and the North Atlantic being dissimilar to the Norwegian and Iceland seas under strong atmospheric warming over the Nordic Seas. We suggest that the unexplained SST anomaly relation, when the Norwegian Sea is dissimilar to the North Atlantic and the Iceland Sea, may reflect a response to a weakened Norwegian Atlantic Current compensated for by a strong Irminger Current or an expanded East Greenland Current.

The information summarized in Table 2 in the paper is based on information extracted from previou... more The information summarized in Table 2 in the paper is based on information extracted from previously published Pliocene records. To keep consistency and allow for direct comparison when comparing this information to the identified phase relations, these previously published records were resampled every 100 ka between 5.23 and 3.13 Ma, using a linear integration function in AnalySeries (Paillard et al., 1996), and presented as anomalies relative to the mean of their

Journal of Geophysical Research: Oceans, 2022

Pronounced changes in the northeastern Atlantic marine climate and ecosystems have recently been ... more Pronounced changes in the northeastern Atlantic marine climate and ecosystems have recently been attributed to the dynamics of the subpolar gyre, represented by a so-called gyre index. But uncertainty remains about which aspects of the subpolar gyre, strength or shape, the gyre index represents. We first reveal the presence of traceable hydrographic pulses, introduced at the boundary between the subpolar and subtropical gyres every 5-10 years and which propagate to the Greenland-Scotland ridge after 1-2 years. These sub-decadal hydrographic anomalies are here attributed to the shape of the subpolare gyre, more so than the circulation strength, and the gyre shape is in turn linked to meridional shift of the Gulf Stream/North Atlantic Current (NAC) system. When the NAC is in a northerly position, the gyre has an east-west shape, engulfing the Rockall Plateau, and a fresh anomaly ensues in the Rockall Trough. When the NAC shifts south, the northern part of the subpolar gyre follows sui...

Progress in Oceanography, 2009

Pronounced changes in fauna, extending from the English Channel in the south to the Barents Sea i... more Pronounced changes in fauna, extending from the English Channel in the south to the Barents Sea in the northeast and off Greenland in the northwest , have occurred in the late 1920s, the late 1960s and again in the late 1990s. We attribute these events to exchanges of subarctic and subtropical water masses in the northeastern North Atlantic Ocean, associated with changes in the strength and extent of the subpolar gyre. These exchanges lead to variations in the influence exerted by the subarctic or Lusitanian biomes on the intermediate faunistic zone in the northeastern Atlantic. This strong and persistent bottom-up biophysical link is demonstrated using a numerical ocean general circulation model and data on four trophically connected levels in the food chain-phytoplankton, zooplankton, blue whiting, and pilot whales. The plankton data give a unique basin-scale depiction of these changes, and a long pilot whale record from the Faroe Islands offers an exceptional temporal perspective over three centuries. Recent advances in simulating the dynamics of the subpolar gyre suggests a potential for predicting the distribution of the main faunistic zones in the northeastern Atlantic a few years into the future, which might facilitate a more rational management of the commercially important fisheries in this region.

The Greenland Sea is a `hot spot' for open ocean convection. The generation and spreading of... more The Greenland Sea is a `hot spot' for open ocean convection. The generation and spreading of water thus ventilated play a fundamental role in the Nordic Seas' deep-water flow to the North Atlantic, a main constituent of the global thermohaline circulation. In this paper, a recently compiled Russian hydrographical data base and NCEP/NCAR forcing are combined to investigate the location and extent of the late winter Greenland Sea Gyre mixed patch. Separate predictions are made for different phases of the North Atlantic Oscillation (NAO). The patch area is then tagged and introduced as a passive tracer in an advective-diffusive model of the flow of Greenland Sea water. As adequate current data are unavailable, the corresponding flow field of a 20 km resolution general circulation model of the Nordic Seas is used. The evolution of the tracer field provides estimates for the ventilated water's residence time in the Greenland Sea, and its pathways within and through the Nor...

Polar Research

Many areas in the Arctic are vulnerable to the impacts of climate change. We observe large-scale ... more Many areas in the Arctic are vulnerable to the impacts of climate change. We observe large-scale effects on physical, biological, economic and social parameters, including ice cover, species distributions, economic activity and regional governance frameworks. Arctic living marine resources are affected in various ways. A holistic understanding of these effects requires a multidisciplinary enterprise. We synthesize relevant research, from oceanography and ecology, via economics, to political science and international law. We find that multidisciplinary research can enhance our understanding and promote new questions and issues relating to impacts and outcomes of climate change in the Arctic. Such issues include recent insights on changing spawning migrations of the North-east Arctic cod stock that necessitates revisions of socioeconomic estimates of ecosystem wealth in the Barents Sea, better integrated prediction systems that require increased cooperation between experts on climate ...

Analyses of observational data (from year 1870 AD) show that Sea Surface Temperature (SST) anomal... more Analyses of observational data (from year 1870 AD) show that Sea Surface Temperature (SST) anomalies along the pathway of Atlantic Water transport in the North Atlantic, the Norwegian Sea and the Iceland Sea are in-phase at multidecadal time scales. In-phase SST anomaly relationships are also observed over hundreds of thousands of years during parts of the Pliocene (5.23-5.03, 4.63-4.43 and 4.33-4.03 Ma). However, when investigating CMIP6 SSP126 20 future scenario runs (next century) and Pliocene reconstructions (5.23-3.13 Ma), three additional phase relations emerge: 1) The Norwegian Sea is out of phase with the North Atlantic and the Iceland Sea (Pliocene; 4.93-4.73 and 3.93-3.63 Ma); 2) The Iceland Sea is out of phase with the North Atlantic and the Norwegian Sea (Pliocene; 3.43-3.23 Ma); 3) The North Atlantic is out of phase with the Norwegian and Iceland Seas (future trend). Hence, out of phase relationships seem to be possible in equilibrium climates (Pliocene) as well as in response to transient forcing (CMIP6 SSP 126 low-emission 25 future scenario). Since buoyancy is a key forcing for inflow of Atlantic Water to the Norwegian Sea, we investigate the impacts of buoyancy forcing on the phase relation between SST anomalies in the North Atlantic, Norwegian and Iceland Seas. This is done by performing a range of idealized experiments using the Massachusetts Institute of Technology general circulation model (MITgcm). Through these idealized experiments we can reproduce three out of four of the documented phase relations: in-phase relationships under weak to intermediate fresh water forcing over the Nordic Seas; the Iceland 30 Sea out of phase with the North Atlantic and the Norwegian Sea under weak atmospheric warming over the Nordic Seas; and the North Atlantic out of phase with the Norwegian and Iceland Seas under strong atmospheric warming over the Nordic Seas. We suggest that the unexplained phase relation, when the Norwegian Sea SSTs are out of phase with the North Atlantic and the Iceland Sea, may reflect a response to a weakened Norwegian Atlantic Current compensated by a strong Irminger current, or an expanded East Greenland Current.

ICES Journal of Marine Science, 2021

The Barents Sea and its marine ecosystem is exposed to many different processes related to the se... more The Barents Sea and its marine ecosystem is exposed to many different processes related to the seasonal light variability, formation and melting of sea-ice, wind-induced mixing, and exchange of heat and nutrients with neighbouring ocean regions. A global model for the RCP4.5 scenario was downscaled, evaluated, and combined with a biophysical model to study how future variability and trends in temperature, sea-ice concentration, light, and wind-induced mixing potentially affect the lower trophic levels in the Barents Sea marine ecosystem. During the integration period (2010–2070), only a modest change in climate variables and biological production was found, compared to the inter-annual and decadal variability. The most prominent change was projected for the mid-2040s with a sudden decrease in biological production, largely controlled by covarying changes in heat inflow, wind, and sea-ice extent. The northernmost parts exhibited increased access to light during the productive season ...

Frontiers in Marine Science, 2020

In this study we investigate both historical and potential future changes in the spatial distribu... more 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.

PLOS ONE, 2018

Predicting fish stock variations on interannual to decadal time scales is one of the major issues... more Predicting fish stock variations on interannual to decadal time scales is one of the major issues in fisheries science and management. Although the field of marine ecological predictions is still in its infancy, it is understood that a major source of multi-year predictability resides in the ocean. Here we show the first highly skilful long-term predictions of the commercially valuable Barents Sea cod stock. The 7-year predictions are based on the propagation of ocean temperature anomalies from the subpolar North Atlantic toward the Barents Sea, and the strong co-variability between these temperature anomalies and the cod stock. Retrospective predictions for the period 1957-2017 capture well multi-year to decadal variations in cod stock biomass, with cross-validated explained variance of over 60%. For lead times longer than one year the statistical long-term predictions show more skill than operational short-term predictions used in fisheries management and lagged persistence forecasts. Our results thus demonstrate the potential for ecosystem-based fisheries management, which could enable strategic planning on longer time scales. Future predictions show a gradual decline in the cod stock towards 2024.