Trinitynlahden paleo-oseanografinen kehitys lounaisella Labradorinmerellä keski- ja myöhäisholoseenin aikana

The purpose of this study was to investigate sea surface temperatures in Trinity Bay, eastern Newfoundland during the mid- and late Holosene c. 7200–1200 years ago. The core drilling location was selected because the area is an important deep water formation area. The cold water pulses might have influenced the deep water formation in the Labrador Sea and further to the circulation of the Gulf Stream. The diatom analysis has been done from marine sediment core with high resolution (35-100 years). The impact of the Atlantic and Arctic water masses during different times were analysed. Diatom analysis and transfer function method were used to reconstruct sea surface temperature in the area being the first quantitative reconstruction from the southwestern Labrador Sea. The sea surface temperature reconstruction shows the gradient between c. 9,7 °C (6,79 ka) and c. 4,4 °C (1,29 ka). The reconstruction can be divided into three periods: the warm Holocene Climate Optimum 7.18–5.1 ka, Holocene Transition period 5.1–3.5 ka and the Cool Late Holocene 3,5–1.18 ka. The results indicate both strong and more moderate changes. As a whole, the reconstruction shows the cooling trend that is associated with the diminishing insolation during the early Holocene. The observed cycles of c. 800 years are related to variations in the Arctic water outflow, and possibly to the AMOC. In Trinity Bay the beginning of the Holocene (c. 7,2–5,1 ka) corresponds with the beginning of the Labrador Sea deep water formation and the intensification of the termohaline circulation in the North Atlantic. The Gulf Stream transported warm sea water to Trinity Bay but the melting glaciers, producing cold fresher water, limited the thermohaline circulation. The strong changes in the sea surface temperatures during the Climate Optimum may also have been influenced by the changes in solar activity. The first c. 1000-years-long interval of the Holocene transition period (c. 5,1–3.5 ka) was cold. The c. 800 years cyclicity in Trinity Bay is possibly the same cyclicity seen in the areas influenced by the North Atlantic current (e.g. the British Isles) and this may indicate the influence of the Labrador Sea on the Gulf Stream. The temperature rise in Trinity Bay (c. 4–3,5 ka) is possibly the 4,2 ka-event, which was due to a short-term global warming at this time. The Cool Late Holocene in Trinity Bay started by cooling c. 3,5 ka ago. The record ends on warming c. 1,2 ka interrupting the cooling trend may indicate the beginning of the Medieval Climate Anomaly. The results from the NGRIP-ice core as well as the results from several previous studies support the results of this study from Trinity Bay for the mid- to late Holocene.