Chironomids as indicators of the Holocene climatic and environmental history of two lakes in Northeast Greenland

Much of Greenland experienced summers warmer than present in parts of the early to middle Holocene, during a precession-driven positive anomaly in summer insolation. However, the magnitude of that warmth remains poorly known, and its timing and spatial pattern are uncertain. Here we describe the first quantitative Holocene palaeotemperature reconstruction from central East Greenland based upon insect (chironomid) assemblages preserved in lake sediments. We postulate that landscapes like our study site, characterized by minimal soil and vegetation development through the Holocene and thus little influenced by some important secondary gradients, are especially well suited to the use of chironomids to reconstruct Holocene temperatures. The inferred timing of warmth at our study site near Scoresby Sund agrees well with other nearby evidence, including glacial geological reconstructions and temperatures inferred from precipitation isotopes at Renland ice cap, supporting the use of chironomids to reconstruct temperatures at this site. We infer highest temperatures from c. 10 to 5.5 ka, followed by gradual cooling after 5.5 ka and progressively colder and less productive conditions after 3.5 ka. Models based upon two independent training sets yield similar inferred temperature trends, and suggest an average summer temperature anomaly from c. 10 to 5.5 ka of 3 to 4°C relative to the preindustrial last millennium. The estimated overall rate of Neoglacial cooling averaged over the period from 5.5 to 0.5 ka was 0.6 to 0.8°C per thousand years, more than twice the rate previously estimated for the Arctic as a whole. Given strong apparent spatial variability in Holocene climate around the Arctic, and the utility of palaeoclimate data for improving climate and ice-sheet models, it should be a priority to further quantify past temperature changes around the margins of the Greenland Ice Sheet, where few quantitative reconstructions exist and future warming will affect global sea level.Yarrow Axford (axford@northwestern.edu),

Section: Discussionsupporting

confidence: 87%

Section: Palaeoenvironmental Proxy Datamentioning

confidence: 97%

mentioning

confidence: 99%

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Timing and magnitude of early to middle Holocene warming in East Greenland inferred from chironomids

Axford

Levy

Kelly

et al. 2017

“…The timing of retracted outlet glaciers from Flade Isblink coincides with a local chironomid‐based temperature maximum ~8–5 ka from Store Koldeway in Northeast Greenland (Schmidt et al . ) and the general pattern of Early to Middle Holocene warming in Greenland (Kaufman et al . ; Briner et al .…”

Section: Discussionmentioning

confidence: 99%

Local ice caps in Finderup Land, North Greenland, survived the Holocene Thermal Maximum

Larsen

Levy

Strunk

et al. 2019

Local glaciers and ice caps (GICs) comprise only ~5.4% of the total ice volume, but account for ~14–20% of the current ice loss in Greenland. The glacial history of GICs is not well constrained, however, and little is known about how they reacted to Holocene climate changes. Specifically, in North Greenland, there is limited knowledge about past GIC fluctuations and whether they survived the Holocene Thermal Maximum (HTM, ~8 to 5 ka). In this study, we use proglacial lake records to constrain the ice‐marginal fluctuations of three local ice caps in North Greenland including Flade Isblink, the largest ice cap in Greenland. Additionally, we have radiocarbon dated reworked marine molluscs in Little Ice Age (LIA) moraines adjacent to the Flade Isblink, which reveal when the ice cap was smaller than present. We found that outlet glaciers from Flade Isblink retreated inland of their present extent from ~9.4 to 0.2 cal. ka BP. The proglacial lake records, however, demonstrate that the lakes continued to receive glacial meltwater throughout the entire Holocene. This implies that GICs in Finderup Land survived the HTM. Our results are consistent with other observations from North Greenland but differ from locations in southern Greenland where all records show that the local ice caps at low and intermediate elevations disappeared completely during the HTM. We explain the north–south gradient in glacier response as a result of sensitivity to increased temperature and precipitation. While the increased temperatures during the HTM led to a complete melting of GICs in southern Greenland, GICs remained in North Greenland probably because the melting was counterbalanced by increased precipitation due to a reduction in Arctic sea‐ice extent and/or increased poleward moisture transport.

“…, b, in press; Schmidt et al . ; Bennike & Wagner , ). Only a few lacustrine records from North Greenland have been studied and most of them have poorly constrained chronologies, which complicate robust palaeoenvironmental reconstructions (Fredskild , ; Funder & Abrahamsen ; Olsen et al .…”

mentioning

confidence: 99%

Holocene environmental change in theSkallingen area, easternNorthGreenland, based on a lacustrine record

Wagner

Bennike

2014

Self Cite

A lacustrine record from a small lake, Lille Sneha Sø, in the Skallingen area indicates that the region was deglaciated in the early Holocene, prior to 8000 cal. a BP. Deglaciation was probably triggered by high temperatures, but it took more than 1000 years for the lake and the catchment to stabilize. Chironomids were amongst the first invertebrates to colonize the lake. The fossil chironomid assemblage is fairly rich and comparable to other records from further south in Greenland. The pioneer vegetation in the area consisted of mosses and herbaceous plants. The oldest remains of woody plants (Salix arctica) are dated to c. 7700 cal. a BP, and remains of Dryas integrifolia appear at around 6700 cal. a BP; these are the only woody plants recorded. Maximum concentrations of chironomids, maximum occurrence of ephippia of the water flea Daphnia pulex, highest organic matter contents and lowest minerogenic input from c. 7700 to 4400 cal. a BP probably reflect the Holocene thermal maximum (HTM). The highest temperatures during the HTM are indicated around 7000 cal. a BP, when Salix arctica, which is considered a warmth‐loving plant, had a maximum. Comparisons with Holocene records from East and North Greenland show similar immigration histories and similar trends, with the Little Ice Age as the coldest period during the Holocene, culminating about 150 years ago. Subsequent warming does not indicate environmental conditions comparable to the HTM yet at this stage. The occurrence of several warmth‐demanding species particularly in the early Holocene sediments indicates redeposition and implies that temperatures in the past, most likely during an interglacial period, were significantly higher than during the HTM.