Sunart, Loch

No previous studies have investigated isotopic composition in modem benthic foraminifera from NW Scottish coastal or fjordic environments. This study therefore aims to (1) compare the temporal pattern of calculated equilibrium calcite at sites from NW Scotland (Loch Sunart, Fig. 1) to 8 Oforaui measured from different species of modern and live benthic foraminifera collected from the same sites and (2) comment on potential seasonal effects in the stable oxygen isotopic composition of the tests. 

Fig. 1. Location of Loch Sunart, a fjord on theNW coast of Scotland (highlighted rectangle). Also shown are the major surface ocean currents (arrows) to the west of Scotland and Ireland, together with a simplified regional bathymetry. Figure modified after Cage (2005).

Surface sediment samples were collected from Loch Sunart, a sea loch (fjord) on the NW coast of Scotland, during cruises aboard the R. V. Clupea (April 1999) and the R. V. Envoy (July 2001 and June 2002). Bottom water temperature and salinity measurements were recorded using a STD Plus 646 conductivity, temperature and depth (CTD) probe at each sample site (Table 1). No data were collected on pH and carbonate ion concentration. Two stationary Anderaa RCM-7 current meters complete with temperature and conductivity sensors and a data logger were deployed in the inner basin (56.6842°N, -5.6211°W) between 21 June 2001 and the 18 June 2002, and the main... 

Fig. 3. The seasonal evolution of calculated monthly averaged equilibrium calcite (S OEq.caidte) fot Loch Sunart (black line), a fjord in NW Scotland, and the Celtic Sea (mixed water column - grey line, stratified water column - dashed grey line).

Mooring data from Loch Sunart show a strong seasonal heating cycle, with temperatures at 40 m... 

Table 1. Measured stable oxygen (8 Ofojaj ) and carbon (8 Cfojaj ) isotopic compositions of modem benthic foraminiferal samples taken from Loch Sunart surface sediments (0-1 cm). Bottom water temperature (BWT) and bottom water salinity (BWS) data are provided for each sample and these data are used to predict the theoretical equilibrium calcite (8 OEq.caicite)- Isotopic disequilibrium (A8i 0) is the difference between 8 OEq.caicite < nd 8 Ofojaj . Analytical accuracy on the measurements was < +0.08%c... 

C. Water temperature profiles from Loch Sunart show that temperatures at 40 m water depth are similar to water temperatures at deeper depths, thus BWTs are likely to record similar interannual variability to the Millport SSTs, albeit with a damped signal. 

Oxygen isotopic disequilibria in Loch Sunart benthic foraminifera... 

The oxygen isotopic disequilibria for benthic foraminifera from Loch Sunart are summarized in Figure 6. Live A. beccarii typically show enriched 81 Oforam ValueS with respect to 8 OEq.caldte with... 

Discrepancies between the observed B WTs recorded during the collection of the mostly live benthic foraminiferal specimens and predicted BWTs (calculated using equations 6 and 7) point to the possibility that a seasonal isotope effect influences the S Oforam values of benthic foraminifera in Loch Sunart (Fig. 7). In particular, the similarity of the predicted BWT for samples collected in April to the observed BWT of samples collected in June/July suggests that live tests collected in the cool BWTs of April actually calcified during the warmer BWTs of the previous summer (Fig. 7). For example, the measured 8 Oforam of C. lobatulus collected from a BWT of 7.88 °C in April, 2001, 3delds a predicted BWT of 13.45 °C and is similar to the... 

Cage, A. G. 2005. The modem and late Holocene marine environments of Loch Sunart, N.W. Scotland. Ph.D thesis. University of St Andrews. 

Gillibrand, P. A., Turrell, W. R. Elliott, A. J. 1995. Deep-water renewal in the upper basin of Loch Sunart, a Scottish fjord. Journal of Physical Oceanography, 25, 1488-1503. 

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