Climate variability and the Icelandic marine ecosystem

Astthorsson, Olafur S.; Gíslason, Ástþór; Jónsson, Steingrímur

doi:10.1016/j.dsr2.2007.07.030

Cited by 121 publications

(120 citation statements)

References 35 publications

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“…Here, a counter-directed, intense north-eastward boundary current of Atlantic Water not only erodes the coastal freshwater signature but also counteracts the development of a south-westward flow. Hence, our model results offer a solution to the ICC quandary, which is defined by two opposing schemes of the coastal circulation around Iceland: (a) the classical view of a freshwater-induced current flowing clockwise around the island (e.g., Stefánsson and Ólafsson, 1991;Halldórsdóttir, 2006); and (b) the assumption that freshwater-induced nearshore dynamics do not form a separate current, with the coastal circulation instead thought to derive from the offshoots of the larger ocean currents further off-shore (e.g., Astþórsson et al, 2007). Our findings point to the possibility that both views are correct when applied to different coastal sections.…”

Section: Resultsmentioning

confidence: 99%

The circulation of Icelandic waters – a modelling study

et al. 2013

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Abstract. The three-dimensional flow, temperature and salinity fields of the North Atlantic, including the Arctic Ocean, covering the time period 1992 to 2006 are simulated with the numerical ocean model CODE. The simulation reveals several new insights and previously unknown structures which help us to clarify open questions on the regional oceanography of Icelandic waters. These relate to the structure and geographical distribution of the coastal current, the primary forcing of the North Icelandic Irminger Current (NIIC) and the path of the Atlantic Water south-east of Iceland. The model's adaptively refined computational mesh has a maximum resolution of 1 km horizontal and 2.5 m vertical in Icelandic waters. CTD profiles from this region and the river discharge of 46 Icelandic watersheds, computed by the hydrological model WaSiM, are assimilated into the simulation. The model realistically reproduces the established elements of the circulation around Iceland. However, analysis of the simulated mean flow field also provides further insights. It suggests a distinct freshwater-induced coastal current that only exists along the south-west and west coasts, which is accompanied by a counter-directed undercurrent. The simulated transport of Atlantic Water over the Icelandic shelf takes place in a symmetrical system of two currents, with the established NIIC over the north-western and northern shelf, and a hitherto unnamed current over the southern and southeastern shelf, which is simulated to be an upstream precursor of the Faroe Current (FC). Both currents are driven by barotropic pressure gradients induced by a sea level slope across the Greenland-Scotland Ridge. The recently discovered North Icelandic Jet (NIJ) also features in the model predictions and is found to be forced by the baroclinic pressure field of the Arctic Front, to originate east of the Kolbeinsey Ridge and to have a volume transport of around 1.5 Sv within northern Denmark Strait. The simulated multi-annual mean Atlantic Water transport of the NIIC increased by 85 % during 1992 to 2006, whereas the corresponding NIJ transport decreased by 27 %. Based on our model results we propose a new and further differentiated circulation scheme of Icelandic waters whose details may inspire future observational oceanography studies.

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Section: Resultsmentioning

confidence: 99%

The circulation of Icelandic waters – a modelling study

et al. 2013

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“…Large colonies exist in several other Arctic and subarctic areas (Gaston & Jones 1998), yet colony sizes in these regions are influenced by different production regimes and divergent oceanographic forcing on prey composition. Large thick-billed murre colonies in north and northwest Iceland (estimated to 1.3 million individuals including nonbreeders) rely heavily on the large stocks of subarctic and north Atlantic fish species, prey whose occurrence and abundance is entirely independent of sea ice dynamics (Lilliendahl & Solmundson 1997;Vilhjalmsson 2002;Astthorsson et al 2007).…”

Section: Discussionmentioning

confidence: 99%

Latitudinal gradients in sea ice and primary production determine Arctic seabird colony size in Greenland

et al. 2008

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Sea ice loss will indirectly alter energy transfer through the pelagic food web and ultimately impact apex predators. We quantified spring-time trends in sea ice recession around each of 46 thick-billed murre (Uria lomvia) colonies in west Greenland across 208 of latitude and investigated the magnitude and timing of the associated spring-time primary production. A geographical information system was used to extract satellite-based observations of sea ice concentration from the Nimbus-7 scanning multichannel microwave radiometer (SMMR, 1979(SMMR, -1987 and the Defence Meteorological Satellite Programs Special Sensor Microwave/Imager (SSMI, 1987(SSMI, -2004, and satellite-based observations of chlorophyll a from the moderate resolution imaging spectroradiometer (MODIS: EOS-Terra satellite) in weekly intervals in circular buffers around each colony site (150 km in radius). Rapid recession of high Arctic seasonal ice cover created a temporally predictable primary production bloom and associated trophic cascade in water gradually exposed to solar radiation. This pattern was largely absent from lower latitudes where little to no sea ice resulted in a temporally variable primary production bloom driven by nutrient cycling and upwelling uncoupled to ice. The relationship between the rate and variability of sea ice recession and colony size of thick-billed murres shows that periodical confinement of the trophic cascade at high latitudes determines the carrying capacity for Arctic seabirds during the breeding period.

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“…The position of the Polar Front is closely linked to North Atlantic Deep Water convection sites and the North Atlantic meridional overturning circulation (e.g. Austin et al 1995;Astthorsson et al 2007;Jónsson 2007), and these strong oceanic and atmospheric gradients make this region particularly sensitive to climate change (Eiríksson et al 2004;Astthorsson et al 2007 and references therein). Because the Irminger and East Greenland currents have distinctly different physical properties (temperature and salinity) and radiocarbon reservoir ages (Tauber and Funder 1975;Larsen et al 2002;Eiríksson et al 2004), biogenic archives that calcify in these waters reflect the dominant water mass present during biomineralization.…”

Section: Introductionmentioning

confidence: 99%

Very Long-Lived Mollusks Confirm 17th Century AD Tephra-Based Radiocarbon Reservoir Ages for North Icelandic Shelf Waters

et al. 2008

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ABSTRACT. Marine sediment records from the north Icelandic shelf, which rely on tephrochronological age models, reveal an average ΔR (regional deviation from the modeled global surface ocean reservoir age) of approximately 150 yr for the last millennium. These tephra-based age models have not hitherto been independently verified. Here, we provide data that corroborate ΔR values derived from these sediment archives. We sampled the youngest portion (ontogenetic age) of a bivalve shell, Arctica islandica (L.), for radiocarbon analysis, which was collected alive in 2006 from the north Icelandic shelf iñ 80 m water depth. Annual band counting from the sectioned shell revealed that this clam lived for more than 405 yr, making it the longest-lived mollusk and possibly the oldest non-colonial animal yet documented. The 14 C age derived from the umbo region of the shell is 951 ± 27 yr BP. Assuming that the bivalve settled onto the seabed at AD 1600, the corresponding local value of ΔR is found to be 237 ± 35 yr by comparison of the 14 C age with the Marine04 calibration curve (Hughen et al. 2004) at this time. Furthermore, we cross-matched a 287-yr-old, dead-collected, A. islandica shell from AD 1601 to 1656 from the same site with the live-caught individual. 14 C analysis from the ventral margin of this shell revealed a ΔR of 186 ± 50 yr at AD 1650. These values compare favorably with each other and with the tephra-based ΔR values during this period, illustrating that 14 C from A. islandica can effectively record 14 C reservoir changes in the shelf seas.

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Climate variability and the Icelandic marine ecosystem

Cited by 121 publications

References 35 publications

The circulation of Icelandic waters – a modelling study

The circulation of Icelandic waters – a modelling study

Latitudinal gradients in sea ice and primary production determine Arctic seabird colony size in Greenland

Very Long-Lived Mollusks Confirm 17th Century AD Tephra-Based Radiocarbon Reservoir Ages for North Icelandic Shelf Waters

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