Nathalie Van Der Putten

The onset of deglaciation of Cumberland Bay and Stromness Bay, South Georgia

Carbon dating of basal peat deposits in Cumberland Bay and Stromness Bay and sediments from a lake in Stromness Bay, South Georgia indicates deglaciation at the very beginning of the Holocene before c. 9500 14C yr BP. This post-dates the deglaciation of one local lake which has been ice-free since at least 15 700 14C yr BP on account of its atypical geomorphological location. The latter indicates the likely presence of floristic refugia on South Georgia during the Last Glacial Maximum from which newly exposed terrestrial and aquatic habitats were rapidly colonized.

Late-Holocene expansion of a south Swedish peatland and its impact on marginal ecosystems: Evidence from dendrochronology, peat stratigraphy and palaeobotanical data

In this study, a reconstruction of the long-term development and lateral expansion of a south Swedish peat bog was performed using a multi-proxy approach, including dendrochronology, peat stratigraphy and macrofossil and pollen analyses. By combining mapping of cross-dated subfossil trees with radiocarbon-dated peat sequences, an improved approach to reconstruction of lateral peat expansion was applied. Apart from providing approximate ages of tree burial episodes, the ring-width records offer information on hydrological variations prior to the bog expansion. New bog oak, pine and alder chronologies are presented and their potential as a dating tool for peatland expansion as well as for local to regional environmental interpretations is examined. Our tree-replication records show that increased amounts of bog trees in the central parts can be linked to drier bog-surface conditions, whereas an increase in wood remains in the marginal zone is related to enhanced preservation due to lateral bog expansion. Our reconstructions of the development of the peat deposit and associated changes in the distribution of vegetation communities provide new insight into peatland responses to climate change at the end of the ‘Holocene Thermal Maximum’ (5000–4000 cal. yr BP).

Is palynology a credible climate proxy in the Subantarctic

Pollen and spore analysis is the most successfully used palaeobotanical discipline for reconstructing Holocene vegetation and climate history throughout the world. Subantarctic islands are very specific areas. They are located in the circum-Antarctic Southern Ocean in latitudes that are under strong influence of the southern westerly winds, and are characterised by a treeless, phanerogam-poor flora. Palynological research on many of these islands has resulted in diverging conclusions about how to infer climate history from pollen data. In this study we compare pollen data with macrofossil data on the one hand, and the palaeoenvironmental history based on a multiproxy record on the other hand, of two peat sequences from two different subantarctic islands, South Georgia and Île de la Possession (Îles Crozet). We conclude that palynology must be used with caution as a proxy for climate change on these islands, especially when no other proxy data are available. The upland–lowland principle, as it has been applied in pollen studies in the South Indian Ocean islands, results in erroneous conclusions about climate change on Île de la Possession. More palaeoclimatic multiproxy and pollen studies, in combination with pollen–vegetation relationship studies, can, however, contribute to a more reliable model of how to interpret pollen data in the Subantarctic. We want to stress that our conclusions are only based on Holocene records. Consequently, the question remains if palynology can be used as a palaeoclimatic proxy when climatic changes were more pronounced such as during the last glacial–interglacial transition.

A Holocene peat record in the central South Atlantic: an archive of precipitation changes

Peat deposits from the littoral part of the wetland 2nd Pond on Nightingale Island in the central South Atlantic have been analysed to investigate the Holocene climate development on the island and to test a hypothesis about regionally persistent humidity variations. A variety of proxies were analysed – total carbon and nitrogen, biogenic silica, diatoms, amount of organic matter, macrofossils and magnetic susceptibility – and together with the lithology they are interpreted as a record reflecting changes in humidity/precipitation. Early Holocene (10,000–8500 cal. BP) was possibly significantly drier than today, probably caused by a southerly displacement of the Southern Hemisphere Westerlies (SHW) during the Antarctic climate optimum. From 8500 cal. BP and onwards, the climate became generally more humid and surface run-off increased due to higher precipitation, possibly as an effect of increased influence from the SHW as it moved north. During this generally humid period, our data disclose a distinct pattern of recurrent centennial- to millennial-long events of increased precipitation and the results corroborate the only other study in the region with a similar humidity record. The events might represent large-scale climate oscillations in the Southern Hemisphere, such as latitudinal shifts of the SHW, but may also be related to changes in sea surface temperatures.

Postglacial sedimentary and geomorphological evolution of a small sub-Antarctic fjord landscape, Stromness Bay, South Georgia

Abstract A detailed stratigraphical, palaeoecological and geomorphological reconstruction of a fjord head on South Georgia (Husvik, Stromness Bay) is presented. Six sites were chosen to reconstruct the lithostratigraphy of the area by means of coring. A maximum depth of 11 m was attained and the sediments encountered vary from coarse gravel over sands to fine silts with, in some cases, intercalated peat layers. Diatom analysis allowed determination of whether the sedimentological units were deposited in a marine or freshwater environment. Six radiocarbon dates constrain the chronology. Deglaciation of the area was completed in the early Holocene and the postglacial geomorphological evolution of Husdal (unofficial name) was controlled by fluvio-deltaic deposition and sea level changes. Relative sea level rise was faster than, or kept pace with the isostatic rebound of the land. Our results challenge the presence of Late Glacial and Holocene raised beach deposits in the area as reported in earlier geomorphological studies.

Pachnobium dreuxi, n. g., n. sp discovered as a fossil and still living in the Crozet Islands (Coleoptera: Curculionidae: Ectemnorrhininae)

Résumé Pachnobium dreuxi, nouvelle espèce et nouveau genre de Curculionidae Ectemnorrhininae des îles Crozet, dans l’Océan Indien sud, a été découvert sous forme fossile dans une séquence sédimentaire holocène. Deux spécimens modernes ont ensuite été trouvés parmi le matériel conservé au Muséum national d’Histoire naturelle de Paris. Il diffère très nettement de toutes les autres espèces connues de la sous-famille par son rostre profondément émarginé au sommet, sa tête massive, sa sclérotinisation réduite, ses tibias antérieurs droits et aplatis, etc. Sa biologie et son écologie sont presque entièrement inconnues, bien que certains aspects de sa morphologie comme sa faible sclérotinisation et ses yeux relativement petits soient en faveur d’une vie cachée, voire hypogée, par exemple dans la litière végétale ou dans les nids de pétrels. Les reconstructions paléoenvironnementales suggèrent qu’il fréquente des habitats à végétation dense. L’absence de captures modernes à l’île de la Possession pose la question de sa présence actuelle dans cette localité.