Greenland tidewater glacier advanced rapidly during era of Norse settlement

Abstract

Our ability to improve prognostic modeling of the Greenland Ice Sheet relies on understanding the long-term relationships between climate and mass flux (via iceberg calving) from marine-terminating tidewater glaciers (TWGs). Observations of recent TWG behavior are widely available, but long-term records of TWG advance are currently lacking. We present glacial geomorphological, sedimentological, archaeological, and modeling data to reconstruct the ~20 km advance of Kangiata Nunaata Sermia (KNS; the largest tidewater glacier in southwest Greenland) during the first half of the past millennium. The data show that KNS advanced ~15 km during the 12th and 13th centuries CE at a rate of ~115 m a–1, contemporaneous with regional climate cooling toward the Little Ice Age and comparable to rates of TWG retreat witnessed over the past ~200 years. Presence of Norse farmsteads proximal to KNS demonstrates their resilience to climate change, manifest as a rapidly advancing TWG in a cooling climate. The results place limits on the magnitude of ice-margin advance and demonstrate TWG sensitivity to climate cooling as well as warming. These data combined with our grounding-line stability analysis provide a long-term record that validates approaches to numerical modeling aiming to link calving to climate.

Climate Variability and Glacier Dynamics Linked to Fjord Productivity Changes Over the Last ca. 3300 Years in Nuup Kangerlua, Southwest Greenland

“…During this phase, KNS is known to have retreated over 22 km (Figures 6 and 7) from its LIA maximum extent to close to its modern‐day position (Lea, Mair, Nick, Rea, As, et al., 2014; Weidick et al., 2012). Half of this retreat occurred between 1808 and 1859 CE (Lea, Mair, Nick, Rea, As, et al., 2014; Lea, Mair, Nick, Rea, Weidick, et al., 2014; Pearce et al., 2022; Weidick et al., 2012) when our records suggest the lowest productivity levels of the Neoglacial record (Figures 5 and 6). These low TOC and BSi values in the sediment cores postdate the atmospheric temperature minima (Figure 6) and the period of low fjord productivity occurred under slowly warming climate conditions when glacial melt rates and subglacial discharge were likely increasing, which in turn based on modern observations should have a positive impact on fjord production (Hopwood et al., 2018; Meire et al., 2017).…”

“…The diatom sample scores for the first CA axis show important shifts at this point in both sediment records (Figure 6) suggesting a significant turnover in the assemblage composition and, by inference, in the environmental conditions. Previous studies have proposed that the KNS margin reached its LIA maximum extent by the sill (Figure 7) latest at 1761 CE (Lea, Mair, Nick, Rea, Weidick, et al., 2014; Pearce et al., 2022; Weidick et al., 2012). Based on the change in the diatom assemblage composition and fjord productivity (Figures 4 and 6), it seems plausible that KNS might have advanced to its maximum extent already at ca.…”

“…Not taking the MCA or modern warming into account, atmospheric conditions in Greenland gradually became dryer and cooler over the past millennium (Lasher & Axford, 2019; Zhao et al., 2022), and marine records from south and west Greenland indicate cooling sea‐surface temperatures and increased sea‐ice concentrations (Roncaglia & Kuijpers, 2004; Seidenkrantz et al., 2007; Sha et al., 2011, 2016). Moreover, multiple studies report glacier margin advances in Nuup Kangerlua during the LIA (Lea, Mair, Nick, Rea, As, et al., 2014; Lea, Mair, Nick, Rea, Weidick, et al., 2014; Levy et al., 2017; Pearce et al., 2022; Weidick et al., 2012). All productivity proxies (TOC, BSi, and diatoms) in our two sediment records show large fluctuations during the past millennium (Figure 6).…”

“…The KNS frontline position is one of the best constrained in terms of historical glacier frontline changes in Greenland (Lea, Mair, Nick, Rea, As, et al., 2014; Lea, Mair, Nick, Rea, Weidick, et al., 2014; Pearce et al., 2018, 2022; Weidick et al., 2012; Young et al., 2021). The neighboring AS (Figures 1 and 7) is known to be confluent with KNS for most of the past millennium, whereas NS has been stable after the LIA and remained close to its maximum extent until 2009 (Figure 7; Motyka et al., 2017).…”

Sea-level rise in Southwest Greenland as a contributor to Viking abandonment

“…As we demonstrate, a readvance of the Greenland Ice Sheet (GrIS), which peaked during the Little Ice Age [LIA; 1250-1900 CE; ( 15 – 18 )], would have driven a contemporaneous sea-level rise near the ice margin due to crustal subsidence and load self-gravitation, the latter referring to the increased gravitational attraction of the ocean toward the growing ice sheet ( 19 ). This component of rise, which encompassed the entire Eastern Settlement and which has not been previously considered, would have had a peak amplitude nearly three orders of magnitude greater than the global mean sea-level fall associated with the ice volume increase ( 19 ) and can be larger than the regional sea-level rise associated with ongoing effects of the Pleistocene ice age ( 20 ).…”