| dc.description.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. | en |
