Methodological approaches to determining the marine radiocarbon reservoir effect

The marine radiocarbon reservoir effect is an offset in 14C age between contemporaneous organisms from the terrestrial environment and organisms that derive their carbon from the marine environment. Quantification of this effect is of crucial importance for correct calibration of the <sup>14</sup>C ages of marine-influenced samples to the calendrical timescale. This is fundamental to the construction of archaeological and palaeoenvironmental chronologies when such samples are employed in <sup>14</sup>C analysis. Quantitative measurements of temporal variations in regional marine reservoir ages also have the potential to be used as a measure of process changes within Earth surface systems, due to their link with climatic and oceanic changes. The various approaches to quantification of the marine radiocarbon reservoir effect are assessed, focusing particularly on the North Atlantic Ocean. Currently, the global average marine reservoir age of surface waters, R(t), is c. 400 radiocarbon years; however, regional values deviate from this as a function of climate and oceanic circulation systems. These local deviations from R(t) are expressed as +R values. Hence, polar waters exhibit greater reservoir ages (δR = c. +400 to +800 <sup>14</sup>C y) than equatorial waters (δR = c. 0 <sup>14</sup>C y). Observed temporal variations in δR appear to reflect climatic and oceanographic changes. We assess three approaches to quantification of marine reservoir effects using known age samples (from museum collections), tephra isochrones (present onshore/offshore) and paired marine/terrestrial samples (from the same context in, for example, archaeological sites). The strengths and limitations of these approaches are evaluated using examples from the North Atlantic region. It is proposed that, with a suitable protocol, accelerator mass spectrometry (AMS) measurements on paired, short-lived, single entity marine and terrestrial samples from archaeological deposits is the most promising approach to constraining changes over at least the last 5 ky BP

Recycled Cretaceous Belemnites in lower Miocene glacio-marine Sediments (Cape Melville Formation) of King George Island, West Antarctica

Fossiliferous glacio-marine strata of the Cape Melville Formation (Lower Miocene) yielded recycled Cretaceous fossils — coccoliths and belemnites in addition to Tertiary biota. The belemnites here described belong to the family Dimitobelidae Whitehouse, 1924, and are represented by three taxa: Dimitobelus aff. macgregori (Glaessner, 1945), D. cf. superstes (Hector, 1886) and Peralobelus sp. These Cretaceous fossils were brought to King George Island by drifting icebergs during the Lower Miocene Melville Glaciation and redeposited together with other dropstones in outer shelf deposits of the Cape Melville Formation. The provenance of these recycled Cretaceous fossils is unknown: they could have been brought by drifting icebergs either from the area of Alexander Island where Cretaceous strata with analogous belemnites are known, or from another site (or sites) o f the Antarctic Peninsula sector. Relative abundance of recycled belemnites and Cretaceous calcareous nannoplankton suggests rather a source situated at a distance less than that between King George Island and Alexander Island (some 1200 km), either under ice-sheet or Within the shelf area of the Bransfield Strait