Upper layer cooling and freshening in the Norwegian Sea in relation to atmospheric forcing

Blindheim, Johan; Borovkov, Vladimir; Hansen, Bogi; Malmberg, Svend‐Aage; Turrell, W.R.; Østerhus, Svein

doi:10.1016/s0967-0637(99)00070-9

Cited by 195 publications

(201 citation statements)

References 30 publications

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“…At present the most prominent pattern of atmospheric variability in the North Atlantic region is known as the NAO, itself depending on the Northern Hemisphere annular mode, the Arctic Oscillation (e.g., Marshall et al, 2001). The NAO is defined as the wintertime difference in atmospheric pressure (sea level) between the Icelandic low and the Azores high, controlling the strength and direction of westerly winds, storm tracks across the North Atlantic, temperature and precipitation over western Europe, and the strength of the poleward NAC and equatorward EGC (East Greenland Current; Blindheim et al, 2000;Hurrell et al, 2003). A low NAO index (reduced westerly flow across the Atlantic) induces a reduced flow of the NAC, less precipitation in northern Europe and a more southern direction of the storm tracks .…”

Section: V Dylmer Et Al: Northward Advection Of Atlantic Water Imentioning

confidence: 99%

Northward advection of Atlantic water in the eastern Nordic Seas over the last 3000 yr

et al. 2013

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Three marine sediment cores distributed along the Norwegian (MD95-2011), Barents Sea (JM09-KA11-GC), and Svalbard (HH11-134-BC) continental margins have been investigated in order to reconstruct changes in the poleward flow of Atlantic waters (AW) and in the nature of upper surface water masses within the eastern Nordic Seas over the last 3000 yr. These reconstructions are based on a limited set of coccolith proxies: the abundance ratio between Emiliania huxleyi and Coccolithus pelagicus, an index of Atlantic vs. Polar/Arctic surface water masses; and Gephyrocapsa muellerae, a drifted coccolith species from the temperate North Atlantic, whose abundance changes are related to variations in the strength of the North Atlantic Current.

The entire investigated area, from 66 to 77° N, was affected by an overall increase in AW flow from 3000 cal yr BP (before present) to the present. The long-term modulation of westerlies' strength and location, which are essentially driven by the dominant mode of the North Atlantic Oscillation (NAO), is thought to explain the observed dynamics of poleward AW flow. The same mechanism also reconciles the recorded opposite zonal shifts in the location of the Arctic front between the area off western Norway and the western Barents Sea–eastern Fram Strait region.

The Little Ice Age (LIA) was governed by deteriorating conditions, with Arctic/Polar waters dominating in the surface off western Svalbard and western Barents Sea, possibly associated with both severe sea ice conditions and a strongly reduced AW strength. A sudden short pulse of resumed high WSC (West Spitsbergen Current) flow interrupted this cold spell in eastern Fram Strait from 330 to 410 cal yr BP. Our dataset not only confirms the high amplitude warming of surface waters at the turn of the 19th century off western Svalbard, it also shows that such a warming was primarily induced by an excess flow of AW which stands as unprecedented over the last 3000 yr

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Section: V Dylmer Et Al: Northward Advection Of Atlantic Water Imentioning

confidence: 99%

Northward advection of Atlantic water in the eastern Nordic Seas over the last 3000 yr

et al. 2013

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“…Secondly, high relative abundances of G. quinqueloba, a species strongly related to the Arctic Front (Johannessen et al, 1994), between 8-4 ka also indicate a more eastward location of the boundary between Arctic and Atlantic waters before 4 ka. During recent decades, subsurface eastward migration of Arctic waters has been caused by an increase in the strength of the westerlies (Blindheim et al, 2000). Stronger influence of sub-surface Arctic water could possibly also explain the observed difference between SSTs derived from phytoplankton and zooplankton at the Vøring Plateau.…”

Section: Holocene Ssts In the Norwegian Seamentioning

confidence: 99%

Holocene trends in the foraminifer record from the Norwegian Sea and the North Atlantic Ocean

et al. 2010

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Abstract. The early to mid-Holocene thermal optimum is a well-known feature in a wide variety of paleoclimate archives from the Northern Hemisphere. Reconstructed summer temperature anomalies from across northern Europe show a clear maximum around 6000 years before present (6 ka). For the marine realm, Holocene trends in sea-surface temperature reconstructions for the North Atlantic and Norwegian Sea do not exhibit a consistent pattern of early to midHolocene warmth. Sea-surface temperature records based on alkenones and diatoms generally show the existence of a warm early to mid-Holocene optimum. In contrast, several foraminifer and radiolarian based temperature records from the North Atlantic and Norwegian Sea show a cool midHolocene anomaly and a trend towards warmer temperatures in the late Holocene. In this paper, we revisit the foraminifer record from the Vøring Plateau in the Norwegian Sea. We also compare this record with published foraminifer based temperature reconstructions from the North Atlantic and with modelled (CCSM3) upper ocean temperatures. Model results indicate that while the seasonal summer warming of the seasurface was stronger during the mid-Holocene, sub-surface depths experienced a cooling. This hydrographic setting can explain the discrepancies between the Holocene trends exhibited by phytoplankton and zooplankton based temperature proxy records.

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“…A decoupling due to baroclinic effects is discussed by Hátún et al (2009) ;Lohmann et al (2009b). Direct measurements reveal a strong freshening of the region during the last four decades of the 20th century (Reverdin, 2010;Yashayaev, 2007;Häkkinen and Rhines, 2009;Curry and Mauritzen, 2005;Dickson et al, 2002;Blindheim et al, 2000) with a reversal towards higher salinities in the Eastern North Atlantic after 2001 (Holliday et al, 2008). Satellite observation of sea surface elevation suggest a rapid decline in SPG strength between 1992 and 2003 (Häkkinen and Rhines, 2004).…”

Section: Introductionmentioning

confidence: 99%

Enhanced Atlantic subpolar gyre variability through baroclinic threshold in a coarse resolution model

et al. 2012

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Abstract. Direct observations, satellite measurements and paleo records reveal strong variability in the Atlantic subpolar gyre on various time scales. Here we show that variations of comparable amplitude can only be simulated in a coupled climate model in the proximity of a dynamical threshold. The threshold and the associated dynamic response is due to a positive feedback involving increased salt transport in the subpolar gyre and enhanced deep convection in its centre. A series of sensitivity experiments is performed with a coarse resolution ocean general circulation model coupled to a statistical-dynamical atmosphere model which in itself does not produce atmospheric variability. To simulate the impact of atmospheric variability, the model system is perturbed with freshwater forcing of varying, but small amplitude and multi-decadal to centennial periodicities and observational variations in wind stress. While both freshwater and wind-stress-forcing have a small direct effect on the strength of the subpolar gyre, the magnitude of the gyre's response is strongly increased in the vicinity of the threshold. Our results indicate that baroclinic self-amplification in the North Atlantic ocean can play an important role in presently observed SPG variability and thereby North Atlantic climate variability on multi-decadal scales.

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Upper layer cooling and freshening in the Norwegian Sea in relation to atmospheric forcing

Cited by 195 publications

References 30 publications

Northward advection of Atlantic water in the eastern Nordic Seas over the last 3000 yr

Northward advection of Atlantic water in the eastern Nordic Seas over the last 3000 yr

Holocene trends in the foraminifer record from the Norwegian Sea and the North Atlantic Ocean

Enhanced Atlantic subpolar gyre variability through baroclinic threshold in a coarse resolution model

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