EGU2020-18990
https://doi.org/10.5194/egusphere-egu2020-18990
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

A high-resolution ostracod-derived δ18O record of early Holocene abrupt climatic change from N. Scotland.

Joanna Tindall1,2, Jonathan Holmes1, Ian Candy2, Melanie Leng3, Rhys Timms2, Christopher Francis2, Daniel Petts2, Simon Blockley2, Ian Matthews2, and Adrian Palmer2
Joanna Tindall et al.
  • 1University College London , Department of Geography, London, United Kingdom (joanna.tindall.15@ucl.ac.uk)
  • 2Royal Holloway, University of London, Department of Geography, Egham, United Kingdom
  • 3British Geological Survey, Keyworth, Nottingham, United Kingdom

Oxygen-isotope ratios can be measured on a range of materials (e.g. ostracods, bulk carbonates, diatom silica) and this, alongside their sensitivity to changes in temperature and precipitation has resulted in oxygen-isotope analyses becoming a well-established tool for investigating palaeoclimatic change. We use δ18O of calcite from ostracod shells to reconstruct palaeotemperature and palaeo-precipitation variability during an early Holocene abrupt climatic event in Crudale Meadow, SW Orkney Mainland, Scotland, UK. The research ultimately aims to further our understanding of the driving mechanisms of palaeoclimatic change during the early Holocene by producing a high-resolution palaeoclimate record from Crudale Meadow and comparing this to the existing data of NW Europe. 

Crudale Meadow is an ideal study site for this research. Spatially, it completes a transect of published early Holocene δ18O records that span Western Ireland1, NW England2 and into Scandinavia3. It has a ~3m thick early Holocene carbonate sequence which offers a multi-decadal or multi-centennial scale study resolution and its proximity to the N. Atlantic makes it highly likely to have been influenced by any climatic changes in the region. A previous study4 presented a bulk carbonate δ18O record for Crudale Meadow but the skeletal chronology limits its usefulness for comparing with regional trends. Here, we present an improved chronology using  tephra and pollen stratigraphy, in addition to the ostracod-derived δ18O record. The studied sequence is anchored by the previously identified Saksunarvatn visible tephra layer dated to 10,210 ± 70 cal. years BP5.

Ostracods are micro-crustaceans with low-Mg calcite shells which take on the isotopic signal of the water body they are in, at the time of shell calcification. In this study, we use winter calcifying Candona spp. for isotopic analysis. These were abundant and well preserved throughout the sequence. Members of this genus have a well-characterised vital offset6 so the δ18O curve can be reliably corrected for vital effects. Moreover, the species analysed are probable winter calcifers, thus reducing the impact of isotopic enrichment through lake water evaporation during summer months. The high-resolution study allows us to identify structure within the identified isotopic excursion and suggest palaeotemperature estimates from the ostracod- and chironomid-inferred temperatures.

The new data presents a clear climatic event with internal structure, which with the current chronology, we hypothesise to be the 9.3ka event. The 9.3ka event has fewer detailed records in comparison to other early Holocene abrupt climatic events (e.g. 8.2ka). Consequently, to identify a structured isotopic signal of the 9.3ka event in NW Europe is an important contribution to our early Holocene records. It emphasises the need for high-resolution δ18O studies during the early Holocene across NW Europe in order to be able to fully identify subtle abrupt climatic events. 

References: 1Holmes, J.H. et al. (2016) QSR, p.341-349; 2Marshall, J.D. et al. (2007) Geology, 35, p.639–642; 3Hammarlund, D. et al. (2002) The Holocene, 12, p.339–351; 4Whittington, G. et al. (2015) QSR, 122, p.112–130; 5Timms, R.G.O. et al. (2018) Quat. Geochron. 46, p.28–44; 6Holmes, J.H & Chivas, A. (2002) AGU Geophysical Monograph, p.118-204.

How to cite: Tindall, J., Holmes, J., Candy, I., Leng, M., Timms, R., Francis, C., Petts, D., Blockley, S., Matthews, I., and Palmer, A.: A high-resolution ostracod-derived δ18O record of early Holocene abrupt climatic change from N. Scotland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18990, https://doi.org/10.5194/egusphere-egu2020-18990, 2020

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