Potential imprint of changes in multidecadal climate variability on temperature reconstructions of the past millennium

PAGES News • Vol.17 • No 2 • June 2009 Sc ie nc e H ig hl ig ht s: O pe n Se ct io n to the late early Miocene (~18.2 Ma) (Figs. 1 and 2; Sangiorgi et al., 2008a; 2008c). The hiatus is marked by a sharp change in sediment color, a few meters above the last abundant occurrence of the middle Eocene marker dinocyst species Phthanoperidinium clithridium. Sediments above the hiatus contain a new dinocyst genus, Arcticacysta, likely of Miocene (Burdigalian) age (Sangiorgi et al., 2008c). The two species found, Arcticacysta backmanii and A. moraniae, co-occur and dominate the interval, where sparse reworked dinocysts of Cretaceous to Oligocene age are also found (Fig. 2). Palynological analyses suggest that the hiatus marks the transition from an anoxic environment with a fresh-brackish water lid, to an estuary-like environment, where high freshwater input co-occurred with oxygenated bottom waters. When the sediments become palynologically barren (Fig. 2; Sangiorgi et al., 2008a), a fully ventilated oxic marine environment develops, likely as result of the opening and the deepening of the Fram Strait (Jakobsson et al., 2007). High abundance of fern and fungal spores in the sediments around the hiatus indicate that sediment deposition occurred either close to shore or on land, suggesting that unexpectedly, the Lomonosov Ridge remained at or near sea level for the duration of the gap, likely as a consequence of tectonic activity (O’Regan et al., 2008).