A 14,500-year record of landscape change from Okpilak Lake, northeastern Brooks Range, northern Alaska

Abstract

Analyses of lithology, organic-matter content, magnetic susceptibility, and pollen in a sediment core from Okpilak Lake, located in the northeastern Brooks Range, provide new insights into the history of climate, landscape processes, and vegetation in northern Alaska since 14,500 cal year BP. The late-glacial interval ([11,600 cal year BP) featured sparse vegetation cover and the erosion of minerogenic sediment into the lake from nearby hillslopes, as evidenced by Cyperaceae-dominated pollen assemblages and high magnetic susceptibility (MS) values. Betula expanded in the early Holocene (11,600-8,500 cal year BP), reducing mass wasting on the landscape, as reflected by lower MS. Holocene sediments contain a series of silt-and clay-dominated layers, and given their physical characteristics and the topographic setting of the lake on the braided outwash plain of the Okpilak River, the inorganic layers are interpreted as rapidly deposited fluvial sediments, likely associated with intervals of river aggradation, changes in channel planform, and periodic overbank flow via a channel that connects the river and lake. The episodes of fluvial dynamics and aggradation appear to have been related to regional environmental variability, including a period of glacial retreat during the early Holocene, as well as glacial advances in the middle Holocene (5,500-5,200 cal year BP) and during the Little Ice Age (500-400 cal year BP). The rapid deposition of multiple inorganic layers during the early Holocene, including thick layers at 10,900-10,000 and 9,400-9,200 cal year BP, suggests that it was a particularly dynamic interval of fluvial activity and landscape change.

Introduction to the JoPL special issue, “Holocene paleoenvironmental records from Arctic lake sediment”

“…The older parts of these records were interpreted in terms of pronounced climate shifts that took place during the late-glacial period. Oswald et al (2012) report a deglacial age of 14.5 ka at Okpilak Lake in the Brooks Range of northern Alaska, nearly synchronous with the onset of non-glacial sedimentation reported by Kaufman et al (2012) at Lone Spruce Pond in the Ahklun Mountains of southwestern Alaska. Irvine et al (2012) used the midge assemblage from Trout Lake in the northern Yukon to date the onset of abrupt post-glacial warming at around 14.4 ka, with mean July air temperatures exceeding those of the present by 12.8 ka.…”

“…Finney et al (2012) interpreted changes in d 13 C values of organic matter to indicate a low lake level between 6 and 2 ka at Dune Lake in interior Alaska. Oswald et al (2012) interpreted layers of clastic sediment that interrupt organic-rich sediment in Okpilak Lake in northern Alaska as episodes of fluvial aggradation. Wooller et al (2012a) analyzed the d 18 O values of fossil midges to infer changes in the hydrologic balance of Qalluuraq Lake, a shallow tundra pond in northern Alaska.…”

A 16,000-yr-long sedimentary sequence from Lakes Peters and Schrader (Neruokpuk Lakes), northeastern Brooks Range, Alaska

“…Additional evidence suggesting regionally warm conditions during the early Holocene includes the highest rates of thaw-lake initiation and peat formation ages from 11 to 10 cal ka BP (Jones and Yu, 2010; Walter Anthony et al, 2014). Pollen evidence from Okpilak Lake (~40 km east of Lake Peters) suggests early Holocene warming represented by a shift from Cyperaceae- to Betula -dominated pollen assemblages around 12.0–11.6 cal ka BP (Oswald et al, 2012).…”

“…1a) is a large area of considerable interest for paleoclimate research. Sedimentary sequences and geomorphic features in the western and central parts of the 900-km-long range have been studied to reconstruct late Quaternary glacier extent (e.g., Hamilton and Porter, 1975; Calkin, 1988; Hamilton, 2003; Balascio et al, 2005; Pendleton et al, 2015, 2017), vegetation communities (e.g., Anderson, 1988; Anderson and Brubaker, 1994; Oswald et al, 2012), and hydroclimate variability (e.g., Anderson et al, 2001; Mann et al, 2002; Finkenbinder et al, 2015; Gaglioti et al, 2017). Less is known about the remote eastern end of the range, where the highest mountains in the Brooks Range are situated only 70 km from the coast of the Arctic Ocean.…”

Chronology and glass chemistry of tephra and cryptotephra horizons from lake sediments in northern Alaska, USA

“…Ruppert Lake (67°4.28'N 154°14.65'W; see Brubaker et al, 1983; Higuera et al, 2009) and Woody Bottom Pond (informal name), hereafter referred to as “WBP” (67°4.55'N, 154°13.88'W), are in the southern Brooks Range. Several late Quaternary sediment records exist from the Brooks Range (e.g., Brubaker et al, 1983; Edwards et al, 1985; Oswald et al, 2012); however, no tephra beds have yet been reported from the region despite its relative proximity to volcanoes producing intercontinental cryptotephra horizons (Mackay et al, 2016). Ruppert Lake and WBP lie within 750 m of each other; however, because Ruppert Lake is much larger (3.1 km 2 ) than WBP (0.06 km 2 ) and has inflowing streams (Fig.…”