Quantifying climate change in Huelmo mire (Chile, Northwestern Patagonia) during the Last Glacial Termination using a newly developed chironomid-based temperature model

Highlights

• A chironomid-based transfer function to reconstruct the temperature was developed.

• This transfer function was applied to a lateglacial sequence from Huelmo mire in Patagonia.

• The reconstruction showed colder spells during the YD, ACR and HMCR chronozones.

• The reconstruction confirms interhemispheric climate coupling mechanisms.

Abstract

The development of quantitative temperature reconstructions in regions of paleoclimate interest is an important step for providing reliable temperature estimates in that region. Fossil chironomid assemblages have been studied in Patagonia showing great promise for reconstructing paleotemperatures; however there is still a lack of robust temperature inference models in that area.

To contribute to the understanding of climate change, a transfer function using chironomids preserved in 46 lakes in Chile and Argentina was developed. The best performing model to infer the mean air temperature of the warmest month was a 3-component WA-PLS model with a coefficient of correlation (r²_jack) of 0.56, a root mean square error of prediction (RMSEP) of 1.69 °C and a maximum bias of 2.07 °C. This model was applied to the chironomids preserved in the sediment of the Huelmo mire (41°31′ S, 73°00′ W), in the lake district of northwestern Patagonia. The reconstruction showed several cold spells (one at 13,200 to 13,000 cal yr BP and a cooling trend between 12,600 and 11,500 cal yr BP) associated with the Younger Dryas and/or Huelmo–Mascardi Cold Reversal (HMCR). Our findings support climate models proposing fast acting inter-hemispheric coupling mechanisms including the recently proposed bipolar atmospheric and/or bipolar ocean teleconnections rather than a bipolar see-saw model.

Introduction

Patagonia is an important area for paleoclimate studies in southern South America because it is significant in understanding climate synchronization between the North and South Hemispheres. However, views are still polarized concerning climate dynamics during key periods of large-scale climate fluctuations (e.g. the Lateglacial/Holocene transition) (Whitlock et al., 2006, Rojas et al., 2009, Killian and Lamy, 2012). Despite efforts to identify climate fluctuations after the Last Glacial Maximum (LGM), the timing and extent of a cold reversal contemporaneous to the Younger Dryas (YD) is still in unresolved. Divergent evidence comes from paleoclimate studies based mainly on terrestrial records from the Andean Patagonian forest of Chile and Argentina. These studies show either i) a cooling pattern synchronous with the YD (12,500 to 11,200 cal yr BP) (Heusser et al., 1996, Ariztegui et al., 1997, Moreno, 1997, Moreno, 2004, Moreno et al., 2001, Massaferro and Brooks, 2002); ii) a cooling pattern synchronous with the Antarctic Cold Reversal (ACR, 14,500 to 13,000 cal yr BP) (Lamy et al., 2004, Moreno et al., 2009); or iii) an intermediate YD/ACR climate signal called Huelmo–Mascardi Cold Reversal (HMCR, 13,500 to 11,600 cal yr BP) (Hajdas et al., 2003, Bertrand et al., 2008b Massaferro et al., 2009). Differences between these records may be attributed to the individual response of proxies, chronological control, sampling resolution, individual site characteristics, the differential influence of the Southern Westerly Winds (SWW) on the east or west side of the Andes or merely because the signature of the cold event in the southern hemisphere is weak. In New Zealand, similar discrepancies were apparent during the Late Glacial/Holocene transition (Denton and Hendy, 1994, Newnham et al., 2003, Turney et al., 2003, McGlone et al., 2004). Resolving this problem is important for understanding the intra- and inter-hemispheric modes of millennial-scale climate changes during the Last Glacial Termination, and for determining the climatic mechanisms involved in their initiation and propagation. Production of quantitative, high resolution reconstructions of summer temperature will be particularly important in this respect. To contribute to the resolution of this problem we have used chironomids to obtain a summer temperature reconstruction, the first of its kind in northern Patagonia, from a Late Glacial lake sediment sequence.

Summer temperature is one of the major controls over the chironomid life cycle (Rossaro, 1991, Brodersen and Lindegaard, 1999) and many models (transfer functions) have been developed in the Northern Hemisphere to quantify summer temperature (e.g. Walker et al., 1991, Olander et al., 1999, Brooks and Birks, 2001, Larocque et al., 2001, Larocque et al., 2006, Self et al., 2011, Eggermont and Heiri, 2012). In the southern Hemisphere, transfer functions have been developed for southern Patagonia (Massaferro and Larocque, 2013), northern Chile (Araneda et al., in prep), Tasmania (Rees et al., 2008) and New Zealand (Dieffenbacher-Krall et al., 2007, Woodward and Shulmeister, 2007) showing the potential of using chironomids in this region for temperature reconstruction. Even though northern Patagonian paleoenvironmental investigations using chironomids are not numerous, there are several qualitative and semiquantitative records indicating that changes have occurred in this faunal community during the Late Glacial period (Massaferro and Brooks, 2002, Massaferro et al., 2009). A recent quantitative reconstruction at Potrok Aike, in southern Patagonia, confirms the potential of chironomids to help in understanding the complex climate fluctuations in southern South America (Massaferro and Larocque, 2013).

In this paper, we present the first quantitative chironomid-inferred temperature model for Northern Patagonia (Argentina and Chile) and use it to reconstruct temperatures during the Late Glacial from a fossil chironomid record from Huelmo mire, located in Chilean Patagonia at 41° S. An earlier qualitative analysis of chironomids and pollen from Huelmo indicated temperature and precipitation changes between ca. 20 and 10 cal kyr BP (Massaferro et al., 2009). The chironomid and pollen records from Huelmo indicated step-wise deglacial warming beginning at ca. 18,000 cal yr BP, in agreement with other paleoclimate records from northwestern Patagonia, and ice core records from Antarctica (Pedro et al., 2011). Isotopic signals from Antarctic ice cores indicate relatively warm conditions between ~ 15,000 and 14,000 cal yr BP, followed by a reversal in trend with cooling pulses at ~ 14,000 and 13,500 cal yr BP, and warming at the beginning of the Holocene (Jouzel et al., 2003) Peak warmth during the Last Glacial Termination was achieved during ~ 14,500 cal yr BP, followed by a cooling trend that commenced during the ACR (~ 14,000 cal yr BP), which later intensified and persisted during the so-called Huelmo–Mascardi Cold Reversal (HMCR) (Hajdas et al., 2003, Massaferro et al., 2009). A reconstruction of temperature using chironomids will quantify the warmer and colder periods suggested by the previous pollen and chironomid records.