Quantitative climate reconstructions

The period 60,000 to 8000 years ago is dominated by significant climatological contrasts; from the highly variable climate of the Dansgaard-Oeschger (D-O) events and the consistently cold millennia of the Last Glacial Maximum (LGM), through to dramatic climatic changes at the glacial termination followed by mild and stable interglacial conditions in the Holocene.

INTIMATE scientists are studying multifarious archives of past climate, e.g. ice cores, tree rings, marine and lacustrine sediments, using a range of different quantitative palaeoclimate reconstruction techniques. This diversity is well illustrated by the papers in the four special INTIMATE issues of Quaternary Science Reviews and examples include temperature estimates derived from ice cores (Dahl-Jensen et al., 1998), ocean sediment cores (Sanchez-Goni et al., 2008; Rasmussen and Thomsen, 2008), terrestrial palaeoecological proxies (e.g. Bohnke et al., 2008; Heiri et al., 2014), as well as continental climate conditions derived from varved lake sediments (e.g. Neugebauer et al., 2012), loess and speleothems (e.g. Feurden et al., 2014) and past sea level estimates (Siddall et al., 2008).

Each record provides valuable information on how local or regional climate conditions changed and – in some cases – how local ecosystems responded to the changes. Palaeoclimate reconstructions have until recently been based on proxy data (in particular pollen) described on a qualitative basis. Although such an approach has some value in providing a general scheme of events, there are inherent problems including the interpretation of proxy data, disentangling different climate signals, temporal sensitivity of proxies to climatic change and the value of qualitative terms. In the North Atlantic region quantified estimates of climate parameters have been obtained from proxies such as Chironomidae (non-biting midges) (Brooks and Birks, 2000), pollen (Nakagawa et al., 2002), Coleoptera (beetles) (Coope et al., 1998) and biomarker isotopic analyses (Rach et al., 2014). The mission of INTIMATE is to facilitate the integration of these kinds of climate records so that they can be studied together and the contemporaneity of events evaluated. One of the main activities to support this is the establishment of protocols for comparing records based upon precise chronologies and visualising temporal uncertainties in these correlations (Brauer et al., 2014; Bronk Ramsey et al., 2014).

Regional compilations of palaeoclimate datasets have been compiled and published by INTIMATE scientists (e.g. Iberia, by Moreno et al., 2012; Central and Eastern Europe, by Feurdean et al., 2014; the Austrian and Swiss Alps, by Heiri et al., 2014). These collaborative studies are incorporated within the INTIMATE database, which provides a statistical tool for comparing records on related timescales and encourages evaluation of the temporal uncertainties involved in inter-site correlations (Bronk Ramsey et al., 2014). The study of integrated records paves the way for a deeper understanding of the processes and feedbacks active in the climate system. For example, when records from neighbouring locations are precisely compared it is possible to identify possible leads and lags between the records and to set up time lines of events for past periods of climate change (Steffensen et al., 2008). Time lines like these are of paramount importance for the understanding of the dynamics of the climate system because they are the starting points for making hypotheses about not only the dynamics, but the mechanisms, of past climate change, adding to our understanding of the ice-sea-atmosphere interactions and feedbacks during periods of abrupt and extreme change.

References:

Bohncke, S.J.P., Bos, J.A.A., Engels, S., Heiri, O., Kasse, C., 2008. Rapid climatic events as recorded in Middle Weichselian thermokarst lake sediments. Quaternary Science Reviews 27, 162.
Brauer, A., Hajdas, I., Blockley, S.P., Ramsey, C.B., Christl, M., Ivy-Ochs, S., Moseley, G.E., Nowaczyk, N.N., Rasmussen, S.O., Roberts, H.M., 2014. The importance of independent chronology in integrating records of past climate change for the 60–8 ka INTIMATE time interval. Quaternary Science Reviews.
Brooks, S.J., Birks, H.J.B., 2000. Chironomid-inferred Late-glacial air temperatures at WhitrigBog, Southeast Scotland. Journal of Quaternary Science 15, 760.

Coope, G.R., Lemdahl, G., Lowe, J.J., Walkling, A., 1998. Temperature gradients in northern Europe during the last glacial–Holocene transition (14-9 14C kyr BP) interpreted from coleopteran assemblages. Journal of Quaternary Science 13, 419-433.
Dahl-Jensen, D., Mosegaard, K., Gundestrup, N., Clow, G.D., Johnsen, S.J., Hansen, A.W., Balling, N., 1998. Past temperatures directly from the Greenland ice sheet. Science 282, 268-271.
Feurdean, A., Perşoiu, A., Tanţău, I., Stevens, T., Magyari, E., Onac, B., Marković, S., Andrič, M., Connor, S., Fărcaş, S., 2014. Climate variability and associated vegetation response throughout Central and Eastern Europe (CEE) between 60 and 8 ka. Quaternary Science Reviews.
Heiri, O., Brooks, S.J., Renssen, H., Bedford, A., Hazekamp, M., Ilyashuk, B., Jeffers, E.S., Lang, B., Kirilova, E., Kuiper, S., 2014. Validation of climate model-inferred regional temperature change for late-glacial Europe. Nature Communications 5.
Moreno, A., González-Sampériz, P., Morellón, M., Valero-Garcés, B.L., Fletcher, W.J., 2012. Northern Iberian abrupt climate change dynamics during the last glacial cycle: A view from lacustrine sediments. Quaternary Science Reviews 36, 139-153.