Chironomids Record Terrestrial Temperature Changes Throughout Arctic Interglacials of the Past 200,000 Yr
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Downloaded from gsabulletin.gsapubs.org on June 23, 2011 Chironomids record terrestrial temperature changes throughout Arctic interglacials of the past 200,000 yr Yarrow Axford1,2,†, Jason P. Briner3, Donna R. Francis4, Gifford H. Miller2,5, Ian R. Walker6, and Alexander P. Wolfe7 1Department of Earth and Planetary Sciences, Northwestern University, 1850 Campus Drive, Evanston, Illinois 60208, USA 2Institute of Arctic and Alpine Research, University of Colorado, UCB 450, Boulder, Colorado 80309, USA 3Department of Geology, University at Buffalo, 411 Cooke Hall, Buffalo, New York 14260, USA 4Department of Geosciences, University of Massachusetts, 233 Morrill Science Center, Amherst, Massachusetts 01003, USA 5Department of Geological Sciences, University of Colorado, UCB 399, Boulder, Colorado 80309, USA 6Palaeoecology Laboratory, University of British Columbia–Okanagan, Kelowna, BC V1V1V7, Canada 7Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB T6G 2E3, Canada ABSTRACT dence for a period of regional deglaciation Marcel, 2008; Brigham-Grette, 2009). Ice cores between MIS 5e and the Holocene (most from Greenland provide invaluable continuous Quaternary interglacial periods provide likely MIS 5a). To our knowledge, the data records of past climate and atmospheric com- glimpses of a warmer Arctic and useful per- presented here represent the longest paleo- position, but the longest continuous ice-core spectives on possible future conditions, but temperature record thus far generated using records from the Northern Hemisphere extend records of Arctic terrestrial conditions over chironomids. The existence of close modern only partway through MIS 5e (Johnsen et al., multiple interglacial periods are rare. Here, analogs for ancient chironomid assemblages 2001; NGRIP Project Members, 2004). we take advantage of a site in the Canadian at Lake CF8 suggests that this method can Recent work has demonstrated that lake Arctic where lacustrine sediments represent- provide useful paleotemperature estimates sediment sequences representing multiple inter- ing the past three interglacial periods are extending back hundreds of millennia. glacials have been preserved on Baffi n Island preserved in an extant lake. We use subfos- despite repeated overriding advances of the Lau- sil insects (chironomids) preserved in this INTRODUCTION rentide Ice Sheet (Briner et al., 2007), present- exceptional sedimentary archive to derive ing a new opportunity for long-term terrestrial temperature reconstructions through the Biological remains preserved in terrestrial environmental reconstruction from a glaciated Holocene up to A.D. 2005, through the Last and marine sediments have made major contri- part of the Arctic. This discovery has allowed Interglacial sensu stricto (marine isotope butions to our understanding of the Quaternary for the recovery of pre–Last Glacial Maxi- stage or MIS 5e), and a portion of the pen- climate history of the Arctic. For example, the mum (pre–MIS 2) sediments and correspond- ultimate interglacial (MIS 7). Chironomid- majority of existing proxy-based estimates of ing paleoecological records from several extant inferred temperatures are warmest for the Arctic temperatures during the last intergla- Baffi n Island lakes (Miller et al., 1999; Wolfe et early Holocene and MIS 5e, two periods with cial period (Last Interglacial sensu stricto, i.e., al., 2000, 2004). The longest of these archives enhanced Northern Hemisphere insolation marine isotope stage [MIS] 5e, ca. 130–115 ka; comes from Lake CF8, which contains sedi- forcing relative to today. Twentieth-century ka = thousands of yr B.P.; Fig. 1) are derived ments recording interglacial periods of at least warming at this site apparently caused the from biological assemblages, including vegeta- the past 200,000 yr (Briner et al., 2007). A brief recent extirpation of cold stenothermous chi- tion, insects, marine mollusks, and foraminifera overview of major conclusions from the multi- ronomid taxa. Assemblages from MIS 5e have (CAPE Last Interglacial Project Members, proxy 200,000 yr record has been presented pre- close analogs in modern training set data as 2006). Unfortunately, there are relatively few viously (Axford et al., 2009a). Here, we present determined by squared-chord distance, and records from the Arctic that quantify tempera- details of the 200,000 yr subfossil chironomid MIS 5e species assemblages are very similar ture changes throughout MIS 5e (Berger and (nonbiting midge; Insecta: Diptera: Chironomi- to Holocene assemblages at this site. MIS Anderson, 2000; Johnsen et al., 2001; NGRIP dae) record and chironomid-inferred paleotem- 7 sediments record summer temperatures Project Members, 2004; CAPE Last Interglacial perature reconstructions from Lake CF8. similar to those of the mid- to late Holocene, Project Members, 2006), and archives record- followed by a descent into glacial conditions. ing changing terrestrial conditions throughout STUDY SITE Even MIS 7 chironomid assemblages, dating earlier interglacial periods in the Arctic are 2 back ~200,000 yr, have close modern analogs. extremely rare (Lozhkin et al., 2007; Brigham- Lake CF8 (zmax = 10 m; surface area = 0.3 km ; These lake sediments also provide direct evi- Grette et al., 2007; de Vernal and Hillaire- elevation = 195 m asl; 70°33.42′N, 68°57.12′W) †E-mail: [email protected] GSA Bulletin; July/August 2011; v. 123; no. 7/8; p. 1275–1287; doi: 10.1130/B30329.1; 6 fi gures; 1 table; Data Repository item 201144. For permission to copy, contact [email protected] 1275 © 2011 Geological Society of America Downloaded from gsabulletin.gsapubs.org on June 23, 2011 Axford et al. -2 δ δ18 (‰) (Wm ) Dice (ppmv) benthic O CF8 380 480 EPICA 175 275 SPECMAP -47 -40 -33 MIS unit 0 1 I 50 5a III 100 5e V 150 Age (ka) 200 7 VII 250 July insolation -425 -375 CO -303 δ18 2 Oice 65°N (‰)Vostok (‰) NGRIP Figure 1. Quaternary context of Lake CF8 stratigraphy, compared with climate indicators for the past 450 ka: July insolation at 65°N (in Wm–2; Berger and Loutre, 1991); δD of ice from Dome C, Antarc- tica (‰; EPICA Community Members, 2004); atmospheric CO2 concentration over Vostok, Antarctica (ppmv; Petit et al., 1999); SPECMAP benthic foraminifera δ18O stack (‰; Imbrie et al., 1984, 1989); smoothed δ18O of ice from NorthGRIP, Greenland (‰; NGRIP Project Members, 2004), marine oxygen isotope stage (MIS) designations, and roman numeral designations assigned to Lake CF8 organic sedi- ment units (Briner et al., 2007; estimated ages of organic sediment units are shown as gray bands). sits on the low-relief Clyde Foreland on north- the only evidence of late Pleistocene ice-sheet sediments in detail, so only a general summary eastern Baffi n Island (Fig. 2) in Nunavut, Arctic advances around Lake CF8 (Fig. 2; Briner et al., is provided here. Cores contain multiple strati- Canada. Lake CF8 is a small through-fl owing 2003, 2006a). The recovery of intact stratifi ed fi ed organic lake mud units (gyttja) alternating lake fed primarily by summer snowmelt. There lacustrine sediments predating the Last Glacial with inorganic sand (Fig. 3) and penetrate to a are no extant glaciers in the lake catchment. At Maximum from Lake CF8 has provided sup- total depth of 3.3 m below the sediment-water the nearby village of Clyde River, modern mean porting evidence for the nonerosive nature of interface. Depth of penetration was limited by annual temperature (for the period A.D. 1961– overriding late Pleistocene ice (Briner et al., the stiffness of the oldest sediments, which are 1990) is −12.8 °C, and mean July temperature 2007), as well as a new opportunity to recon- very dense (1.9 g cm–3), compact dewatered is +4.4 °C (Environment Canada, http://www. struct Arctic paleoenvironments predating the organic sediments. Preliminary geophysical climate.weatheroffi ce.gc.ca). Clyde River’s Last Glacial Maximum. surveys using ground-penetrating radar sug- climate is mid-Arctic. Prostrate dwarf-shrub Although pre-Holocene lake sediment records gest that there are older sediments yet to be tundra vegetation surrounds the lake, which is from the Canadian Arctic are rare, several such recovered (G.S. Baker 2005, personal com- generally ice covered for at least 9 mo each year occurrences are known; their greatest density mun.), but these have thus far eluded our cor- (October–June). The local bedrock is Precam- occurs along the east coast of Baffi n Island ing technology. brian granite and gneiss. (Wolfe and Smith, 2004). Last Interglacial sedi- Briner et al. (2007) assigned Roman numeral Lake CF8 was overridden during the last ments from Fog and Brother of Fog Lakes on designations I–VII to each of the major glacial cycle by the Laurentide Ice Sheet, but east-central Baffi n Island (Fig. 2) have been ana- lithostratigraphic units in the Lake CF8 stra- previous work has demonstrated that this over- lyzed for pollen (Fréchette et al., 2006, 2008), tigraphy; we use the same designations here. riding ice was cold-based (i.e., frozen-bedded) diatoms (Wolfe et al., 2000), and chironomids Units I, III, V, and VII are gyttja; units II, IV, and nonerosive (Briner et al., 2005, 2006a). In (Francis et al., 2006). These lakes have yielded and VI are crudely stratifi ed sands. Gyttja units locations covered by cold-based ice during the superposed sequences of Last Interglacial and are brown to gray-brown in color, weakly strati- last glaciation (Kleman and Hättestrand, 1999), Holocene age only; thus far, only Lake CF8 has fi ed to laminated,