Abstract
The abrupt 8.2 ka cold event has been widely described from Greenland and North Atlantic records. However, its expression in shelf seas is poorly documented, and the temporal resolution of most marine records is inadequate to precisely determine the chronology of major events. A robust hydrographical reconstruction can provide an insight on climatic reaction times to perturbations to the Atlantic Meridional Overturning Circulation. Here we present an annually-resolved temperature and water column stratification reconstruction based on stable isotope geochemistry of Arctica islandica shells from the Fladen Ground (northern North Sea) temporally coherent with Greenland ice core records. Our age model is based on a growth increment chronology obtained from four radiometrically-dated shells covering the 8290–8100 cal BP interval. Our results indicate that a sudden sea level rise (SSLR) event-driven column stratification occurred between ages 8320–8220 cal BP. Thirty years later, cold conditions inhibited water column stratification but an eventual incursion of sub-Arctic waters into the North Sea re-established density-driven stratification. The water temperatures reached their minimum of ~3.7 °C 55 years after the SSLR. Intermittently-mixed conditions were later established when the sub-Arctic waters receded.
Highlights
The 8.2 ka cold event is usually defined by lower stable oxygen isotope values and a reduced ice accumulation rate in Greenland ice cores[1]
The lowest expressed population signal (EPS) score occurred when multiple specimens settled within a short time span combined with times of extended lower than average increment growth in other shells already contained in the chronology
The low EPS values shown in 8.2kC are likely due to the erratic juvenile growth of two specimens that make up its mid-section combined with lower than average shell growth in the other specimens
Summary
The 8.2 ka (before 1950 CE) cold event is usually defined by lower stable oxygen isotope values and a reduced ice accumulation rate in Greenland ice cores[1] This event has been extensively described in the context of the Greenland ice cores and across the wider North Atlantic[1,2,3,4,5], its expression in the Atlantic shelf seas is less well documented[6,7]. We present an annually-resolved reconstruction of the environmental conditions prevalent in the northern North Sea (Fig. 1) based on stable isotope geochemistry from radiocarbon-dated ocean quahog (Arctica islandica) shells centred around the 8.2 ka event. The lowest EPS score occurred when multiple specimens settled within a short time span combined with times of extended lower than average increment growth in other shells already contained in the chronology
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