Quaternary environmental and climatic reconstructions using subfossil insects from northern Norway

Abstract

Reconstructing past environmental and climatic conditions allows us to better understand the impact of change on the environment, along with the taxa that inhabit it. This can help with constraining our predictions for future change and focus conservation efforts. As contemporary change is being experienced at an unprecedented rate within the Arctic, investigating past change within this region is of utmost importance. Northern Norway is known to have experienced significant environmental change throughout the Quaternary, alternating between being covered in ice and being ice-free, multiple times. The traditional view that temperate taxa survived periods of glaciation further south, in refugia, is brought into question by the discovery that survival in crypto-refugia on ice-free islands, such as Andøya, was possible. Little work has been undertaken to analyse these Quaternary climatic and environmental changes within northern Norway, despite the effectiveness of insects, especially beetles and chironomids, in reconstructing past environmental and climatic conditions, having been well demonstrated.

Thus, the overall aim of this thesis is to use subfossil insects to reconstruct the environment and climate of northern Norway throughout the Late Quaternary (last 24,000 years), whilst testing their robustness as proxies within the region. In doing so, this study provides the longest high-resolution chironomid study, the earliest, and most complete, Holocene reconstructions using beetles in northern Norway, as well as the first multi-proxy insect study in the region.

Chironomids have been investigated between 24.0 and 8.2 cal ka BP from Øvre Æråsvatnet (Andøya), and quantitative July temperature reconstructions have been made. Beetles were recovered from Ramså (Andøya) from 11.0 to 8.2 cal ka BP and the Hollabåttjønnen Bog (Tønsnes) from 4.3 to 0.7 cal ka BP cal ka BP, and environmental and climatic reconstructions were made from both, based on their modern environmental and climatic preferences. These reconstructions tell a story of fluctuating climatic and environmental conditions throughout the Last Glacial Maximum contrary to previously reported reconstructions of persistent extreme cold. Instead, these results support the side of the debate that the LGM on Andøya was comparatively warm, with chironomid inferred mean July temperatures of 9°C prior to 20.0 cal ka BP. This was followed by a more variable Late Glacial (6.4 - 9.5°C) and a sustained increase in mean July temperatures to between 10 and 11°C during the early Holocene (11.7 - 8.1 cal ka BP), in agreement with other proxies. These reconstructed temperatures do not discount the possibility of other temperate taxa surviving on the island throughout the LGM.

Holocene environmental reconstructions indicate that during the early Holocene (10.9 - 8.2 cal ka BP) Ramså was dominated by Sphagnum moss and aquatic species indicate standing water was nearby. These reconstructions confirm those reported from other proxies, but add further information, for example, that the presence of a wetland environment with standing water indicates that the northwest of Andøya probably experienced higher rainfall than the south. Furthermore, the beetles suggest that trees arrived on Andøya between 10.5 and 9.71 cal ka BP, which compliments and agrees with the evidence from other proxies. During the late Holocene at Tønsnes (4.3 – 0.7 cal ka BP) an oligotrophic bog existed, but this was less homogenous with species indicating drier heathland and small groves of trees present throughout.

These reconstructions have demonstrated the effectiveness of using chironomids and beetles as palaeoecological proxies within northern Norway, as they support, and add detail to, reconstructions made from other proxies. Nonetheless, temperature reconstructions based on beetles are broad and lack the precision of those inferred from chironomids, likely a reflection of the mutual climatic range method working better in reconstructions from lower latitudes, where the number of stenothermic species recovered is significantly higher. Future studies in the region should concentrate on combining the beetle-inferred July temperatures with those inferred from chironomids, giving multiple lines of evidence, which is more likely to reflect the actual air temperature. This study emphasises the need for further methodological development in northern Norway, and likely across high latitudes, to enable beetle reconstructions to be used to their full potential. Moreover, the results demonstrate that the level of detail that can be gained about the environment from beetles cannot be gained from other proxies, including chironomids and, therefore, confirms that beetles should be an integral part of future palaeoenvironmental studies, alongside other proxies. These findings demonstrate that multi-proxy studies should remain a priority in Quaternary reconstructions, particularly at high latitudes. Furthermore, similarities in the beetle assemblages from the early and late Holocene emphasise the importance of peat bogs as an ecosystem within northern Norway, and therefore should be considered key sites for conservation.