Holocene environmental changes on Nightingale Island, South Atlantic, based on diatom floristic changes in an infilled pond

A Holocene diatom stratigraphy of 2nd Pond, a small, filled pond on Nightingale Island (37° 25 S, 12° 29 W) was analyzed and interpreted to infer paleolimnological changes on Tristan da Cunha, South Atlantic. The diatom assemblage of 2nd Pond has the character of an acidic, oligotrophic wetland and the diatom record suggests that 2nd Pond most likely has been a bog/wetland throughout most of the Holocene. The flora is largely dominated by Pinnularia viridis, a species typically found in peat bogs. The flora also includes benthic and epiphytic Gomphonema sp, Achnanthes saxonica, Frustulia cf. rhomboides, Staurosira venter as well as Pinnularia cf. divergens var. decrescens and Eunotia paludosa var. paludosa. Peaks of aerophytic diatom (i.e. mostly Diadesmis spp. and Luticola spp.) abundances and concentrations correspond to increased magnetic susceptibility and slightly higher C/N ratios and are interpreted to be the result of increased catchment erosion due to precipitation and following increased in-wash of terrestrial diatoms. The diatom record suggests dry conditions in the early Holocene, followed by recurrent periods of increased precipitation in the region at 8600–5600 cal a BP and at 2200–1700 cal a BP. The main causes for these hydrological changes are probably changes in intensity and/or position of the Southern hemisphere west wind belt.