A preliminary investigation of basin water response to climate forcing in a Scottish fjord: Evaluating the influence of the NAO

School of Geography and Geosciences, University of St. Andrews, St. Andrews KY16 9AL, UK
Continental Shelf Research (Impact Factor: 1.89). 01/2013; 25:571-587. DOI: 10.1016/j.csr.2004.10.011


The sea lochs (fjords) of NW Scotland bridge the land–ocean interface in a region of Europe which is particularly well situated to monitor changes in westerly air streams. Inter-annual atmospheric circulation changes at this latitude are largely governed by the North Atlantic Oscillation (NAO). Comparing two recent extreme NAO years, a two-dimensional model of Loch Sunart, NW Scotland, is used to examine the potential effects of climate oscillations on the magnitude and frequency of deep-water renewal events and the resulting water properties in the fjord basins. In the upper basin of the fjord, meteorological forcing during the high NAO index year (1988–89) resulted in less-frequent deep-water renewal, greater variability in basin salinity and a lower annual-mean salinity (by 0.52) than that predicted for the low NAO index year (1995–96). In the main basin, variations in meteorological forcing had much less effect on basin water properties. In both basins, predicted deep water inflow was significantly greater during the negative phase NAO, with annual inflow to the upper and main basins being respectively 50% and 300% greater during 1995–96 relative to 1988–99. Through a sensitivity analysis, the NAO is shown to affect upper basin water properties through the influence of low-frequency anomalies in the meteorological forcing, particularly the enhanced westerly wind stress associated with positive phases, which inhibits deep water renewal over the winter months. The salinity of the main and upper basins respond differently to the boundary forcing due to differential tidal mixing above the respectively sub- and super-critical entrance sills. Predictions of basin water isotope ratios are made by applying the salinity:δ18Owater mixing line for the region to the salinity results; the combination of the weak dependence of δ18Owater on salinity and the stable salinity predicted for the main basin suggests that some fjord basins may provide ideal sites for palaeotemperature studies.

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Available from: Philip A. Gillibrand, Sep 30, 2015
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    • "A 270 % net increase in precipitation-derived freshwater input into the North Atlantic was observed during the 1960–1990s (Josey and Marsh 2005; Bindoff et al. 2007), stimulating a debate into the future evolution of marine salinity given atmospheric CO 2 projections. By the year 2100, atmospheric temperature is projected to rise by up to 6 °C (IPCC 2013), increasing the 'moisture-holding capacity' of the atmosphere (Trenberth et al. 2007), and thus the potential for precipitation events, enhancing freshwater run-off into the coastal zone (Gillibrand et al. 2005), particularly in the mid/high latitudes (IPCC 2013). A rise in atmospheric temperatures may also lead to more pronounced seasonal ice melt (Hanna et al. 2008); run-off from the Greenland Ice Sheet into the Kangerlussaq drainage basin has increased by 113 km 3 over the last 50 years (Hanna et al. 2008). "
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    ABSTRACT: Mid- to high-latitude fjordic coastal environments experience naturally variable salinity regimes. Climate projections suggest that freshwater input into the coastal ocean will increase in the future, exposing coastal organisms to further periods of reduced salinity. This study investigated the effect of low salinity on Lithothamnion glaciale, a red coralline alga found in mid- to high-latitude fjordic regions, during a 21-day experiment. Specific measurements included: the intracellular concentration of dimethylsulphoniopropionate (DMSP, an algal secondary metabolite and major precursor to the climatically active gas dimethylsulphide), pigment composition and photosynthetic characteristics. No significant difference in intracellular DMSP concentrations was observed between treatments, suggesting that the primary function for DMSP in L. glaciale is not as a compatible solute, perhaps favouring an antioxidant role . Photosynthetic parameters (including pigment composition) exhibited a mixed response, suggesting some degree of photosynthetic resilience to reduced salinity. This study provides evidence of intracellular mechanisms adopted by L. glaciale in response to reduced salinity. This has significant implications for the survival of L. glaciale under a projected freshening scenario and provides organism-level detail to ecosystem-level projected changes should lower-salinity conditions become more frequent and more intense in the future.
    Marine Biology 05/2015; 162(5). DOI:10.1007/s00227-015-2650-8 · 2.39 Impact Factor
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    • "Loch Sunart is located approximately 15 km to the east of the Tiree Passage and has a largely unrestricted exchange with the adjacent coastal waters of the Sound of Mull, notably into the main basin of Loch Sunart where sub-halocline salinity remains stable and tracks the coastal ocean (e.g. Gillibrand et al., 2005). Benthic foraminiferal oxygen isotopes from this record have been interpreted as a record of summer temperature (Cage and Austin, 2010). "
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    ABSTRACT: There is currently a deficiency of annually-resolved temperature series from the marine environment. We present a multiproxy reconstruction of Hebridean shelf sea (Tiree Passage; NW Scotland) spring sea surface temperatures (SSTs) for the period AD 1805-2010. The reconstruction is based on the growth increment series from the first absolutely dated annually-resolved multi-centennial Glycymeris glycymeris bivalve mollusc sclerochronology coupled with previously published stable oxygen isotope data (δ18O) from benthic foraminifera sampled from a dated sediment core from nearby Loch Sunart. The independent series contain significant correlations with SSTs across complementary frequency domains. The low frequency component of the sedimentary archive was combined with the mid and high frequency components of the G. glycymeris chronology indices to create a single multiproxy series. Split calibration-verification statistics (reduction of error, RE, coefficient of efficiency, CE, and R2) indicate that the multiproxy record, calibrated to local instrumental sea surface temperatures, contains significant precision and skill at reconstructing spring SSTs (RE = 0.59, CE = 0.26, R2 = 0.54). These data demonstrate that bivalve sclerochronologies, when combined with low frequency proxies such as sediment archives, can facilitate statistically robust reconstructions of palaeoceanographic variability during the late Holocene for hydrographically-significant regions of the temperate marine system previously void of annually-resolved archives. The reconstructed SSTs contain a general warming trend of 0.60 ± 0.14 °C per century. Only four years in the reconstructed period (1999, 2000, 2002 and 2003) exceed temperatures greater than two standard deviations higher than the reconstructed mean SST (9.03 °C), whilst just three years in the first half of the 19th century (1835, 1838 and 1840) fall more than 2σ below the reconstructed mean (6.80 °C).
    Palaeogeography Palaeoclimatology Palaeoecology 05/2013; 386:275. DOI:10.1016/j.palaeo.2013.05.029 · 2.34 Impact Factor
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    • "nd sustained changes in main basin salinity which are not seen in the recent coastal ocean instrumental records ( Inall et al . , 2009 ) . Additionally , 2 - D circulation modeling of this fjord ( with a constant coastal salinity boundary condition ) has shown that the main basin BWS changed by no more than 0 . 02 during recent extreme NAO years ( Gillibrand et al . , 2005 ) , sug - gesting that any long - term changes in the main basin reflect the coastal ocean salinity . Finally , the present day BWS gradient between the inner basin ( which has a very restricted exchange with main basin waters along with very high freshwater inputs and infrequent DWREs ) and the main basin of Loch Sunart is <2 ( Cage , "
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    ABSTRACT: The first decadal-scale reconstruction of British coastal temperature anomalies spanning the last millennium is presented from a sea loch (fjord) basin, Loch Sunart, NW Scotland. Based on modern observation and the results of previous numerical modeling of fjord circulation, benthic foraminiferal oxygen isotope records are interpreted as a record of summer temperature. A significant climate transition, apparently driven by large-scale reorganization of northern Hemisphere atmospheric circulation, occurs in the record around AD 1400. An abrupt, but relatively short-lived climate warming occurs between AD 1540–1610, when the bottom water temperature anomalies are 1.1 °C above the long-term average, which is warmer than most of the 20th century and the late Medieval Warm Period. A long-term cooling occurs throughout the Little Ice Age culminating in the coldest recorded temperature anomalies between the late 1920s and 1940s. The warmest reconstructed temperatures of the past millennium occurred in the last 5 years of the record, which ends in 2006. A replicated post-AD 1900 shift in benthic foraminiferal δ13C of ca −0.6‰ provides evidence of the Oceanic δ13C Suess Effect; this feature provides an independent test of the age model and demonstrates the value of benthic foraminifera as palaeo-proxies in the Loch Sunart record.
    Quaternary Science Reviews 02/2013; DOI:10.1016/j.quascirev.2010.01.014 · 4.57 Impact Factor
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