Abstract
Abstract. The mass loss from the Greenland Ice Sheet has increased over the past 2 decades. Marine-terminating glaciers contribute significantly to this mass loss due to increased melting and ice discharge. Periods of rapid retreat of these tidewater glaciers have been linked to the concurrent inflow of warm Atlantic-sourced waters. However, little is known about the variability of these Atlantic-derived waters within the fjords, due to a lack of multi-annual in situ measurements. Thus, to better understand the potential role of ocean warming on glacier retreat, reconstructions that characterize the variability of Atlantic water inflow to the fjords are required. Here, we investigate foraminiferal assemblages in a sediment core from Upernavik Fjord, West Greenland, in which the major ice stream Upernavik Isstrøm terminates. We conclude that the foraminiferal assemblage is predominantly controlled by changes in bottom water composition and provide a reconstruction of Atlantic water inflow to Upernavik Fjord, spanning the period 1925–2012. This reconstruction reveals peak Atlantic water influx during the 1930s and again after 2000, a pattern that is comparable to the Atlantic Multidecadal Oscillation (AMO). The comparison of these results to historical observations of front positions of Upernavik Isstrøm reveals that inflow of warm Atlantic-derived waters likely contributed to high retreat rates in the 1930s and after 2000. However, moderate retreat rates of Upernavik Isstrøm also prevailed in the 1960s and 1970s, showing that glacier retreat continued despite a reduced Atlantic water inflow, albeit at a lower rate. Considering the link between bottom water variability and the AMO in Upernavik Fjord, and the fact that a persistent negative phase of the AMO is expected for the next decade, Atlantic water inflow into the fjord may decrease in the coming decade, potentially minimizing or stabilizing the retreat of Upernavik Isstrøm during this time interval.
Highlights
Mass loss from the Greenland Ice Sheet (GrIS) has accelerated over the two most recent decades, raising its contribution to the ongoing global sea-level rise
Terns are high and that randomness inherent to ice-rafting largely overprints the glaciological signal within this fjord. Their use as an indicator of glacier stability was improved by producing a composite record based on multiple cores, but due to the complexities associated with the interpretation of the ice-rafted debris (IRD) record we focus on comparing the results of the benthic foraminifera analysis with historical observations of glacier margins in this study
We show that the abundance and diversity of foraminiferal species in the outer region of Upernavik Fjord is predominantly controlled by the preservation potential of calcareous species, depending on the alkalinity of the prevailing bottom water mass, which is in turn related to variations in water temperature
Summary
Mass loss from the Greenland Ice Sheet (GrIS) has accelerated over the two most recent decades, raising its contribution to the ongoing global sea-level rise. During the early 2000s a rapid retreat of tidewater glaciers along the southeastern (SE) sector (Rignot et al, 2004), central west sector (Holland et al, 2008), and northwest (NW) sector (Bjørk et al, 2012; Joughin et al, 2013; Khan et al, 2010) was observed. This retreat coincided with a warming of the ocean waters in southeastern and western Greenland and led to the hypothesis that shifting ocean currents exert a major control. Benthic foraminiferal communities are sensitive to environmental conditions, and shifts in species composition can be used to reconstruct relative changes of bottom water masses (Murray, 2006)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
