Reduced sea ice concentrations in the Arctic Ocean during the last interglacial period revealed by sediment cores off northern Greenland

Abstract

We present a record encompassing marine isotope stages 7‐1 from a hitherto unexplored and heavily ice‐covered area of the Arctic Ocean, the Lomonosov Ridge off the northern Greenland‐Canada continental margin, using nannofossil and benthic foraminifera stratigraphy. Planktic foraminifera assemblages are used as a key paleoceanographic proxy, and a surprisingly large variability is found for an interior Arctic Ocean site. Abundant small (63–125 μm) subpolar Turborotalita quinqueloba occur in two sections, possibly representing substages 5e (last interglacial) and 5a (warm interstadial). However, the present‐day circulation pattern and the very distant location of high productive regions cannot explain such high abundances of subpolar specimens in the interior, perennially sea ice–covered Arctic Ocean. Hence our proxy record indicates that last interglacial sea ice concentrations were reduced off some areas of northern Greenland‐Canada. Whether this was part of a larger regional pattern or it represents the influence of polynya areas with locally increased productivity remains to be solved. With respect to glacial conditions, increased ice‐rafted debris (IRD) deposition in the area appears to be associated with glacial stages 6, 4, and late 3. Stage 2 sediments (including the Last Glacial Maximum) are condensed with a sparse IRD content only.

Differences between the last two glacial maxima and implications for ice-sheet, δ18O, and sea-level reconstructions

“…However, ice-grounding features (e.g., parallel streamlined submarine landforms and ploughmarks) may be preserved in seafloor sediments, and their occurrence on bathymetric highs, in conjunction with regions devoid of glaciogenic seabed disturbance, has been used to suggest evidence of past floating ice (e.g., Polyak et al, 2001;Jakobsson et al, 2008). In the Arctic, erosional features have been found at depths of~1 km on the Lomonosov Ridge, Chukchi Borderlands, Yermak Plateau, East Siberian Margin, Baffin Bay, and Hovgaard Ridge (Fram Strait) (e.g., Polyak et al, 2001;Kuijpers et al, 2007;Dowdeswell et al, 2010;Gebhardt et al, 2011;Niessen et al, 2013;Arndt et al, 2014), while other portions of the Lomonosov and Mendeleev Ridges are largely devoid of glaciogenic features, which may suggest ice-free conditions . Bathymetric highs in the Arctic may have acted as pinning points, allowing ice-rise formation that stabilised and facilitated ice-shelf thickening (Vogt et al, 1994;Grosswald and Hughes, 1999;Jakobsson et al, 2016).…”

“…Other impacts on the storm track relate to sea-ice and sea-surface temperature distributions (Kageyama and Valdes, 2000): during the LGM, for example, extensive Arctic/North Atlantic sea-ice cover is thought to have caused considerable southward storm-track displacement (e.g., Kageyama et al, 1999). These various influences likely account for the significant difference in EIS distributions between the PGM and LGM (e.g., Liakka et al, 2016), given that (i) the PGM had less extensive and seasonally open sea-ice conditions, relative to extensive and severe sea-ice conditions during the LGM (e.g., Spielhagen et al, 2004;Nørgaard-Pedersen et al, 2007;Polyak et al, 2010;de Vernal et al, 2013;Arndt et al, 2014;L€ owemark et al, 2016), and (ii) the NAIS was smaller/lower during the PGM than during the LGM (e.g., Ehlers et al, 2011a).…”

“…For example, pore-water d sw measurements are different in the deep Pacific, and northern and southern Atlantic between the LGM and today ; the inferred changes suggest a large freshwater imbalance in the northern convecting regions during the LGM, with an important role for increased sea-ice formation and export. Given the great difference in Arctic sea-ice conditions that has been inferred between the PGM (less extensive and seasonally open) and LGM (extensive and severe sea-ice conditions) (Knies et al, 2000;Polyak et al, 2010;de Vernal et al, 2013;Niessen et al, 2013;Arndt et al, 2014;Jakobsson et al, 2010Jakobsson et al, , 2014bL€ owemark et al, 2016), a difference in both the isotopic composition and volumetric contribution of northern-sourced deep waters might be expected between the two glacial periods. There are some hints of local d sw differences between the two glacial intervals (e.g., Skinner and Shackleton, 2005), with a shoaled hydrographic gradient separating northern-and southern-sourced deep waters and a potentially weaker North Atlantic overturning cell during the PGM.…”

“…If PGM and LGM deep-sea temperatures were similar (within about 0.5 C), then a fundamental PGMeLGM offset is implied in the relationships between mean global-ocean d sw and sea level or ice volume. This might arise from: (a) ocean circulation differences among glacial cycles, filling different volumes of the deep sea with waters of different mean d sw values, although such contrasts are thought to be averaged over multi-millennial periods (e.g., Siddall et al, 2010); (b) different moisture pathways feeding contrasting glacial configurations (e.g., Ullman et al, 2014;Colleoni et al, 2016), with impacts on atmospheric vapour isotopic fractionation and, hence, ice d 18 O; or (c) potential development of massive, largely floating Arctic ice shelves during certain glacials (e.g., PGM), and not during others (e.g., LGM) e these would cause negligible sea level change, but considerable mean ocean d 18 O change (Niessen et al, 2013;Jakobsson et al, 2016). Below, we discuss these three options in turn.…”

“…The input of ice-rafted debris (IRD) allows reconstruction of ice sheet dynamics, ice source, and iceberg-melt location (Ruddiman, 1977;Bond and Lotti, 1995;Hemming, 2004). The marine record of Eurasian glacial episodes (e.g., Spielhagen et al, 2004;Sejrup et al, 2005;Toucanne et al, 2009;Obrochta et al, 2014;L€ owemark et al, 2016) and geophysical mapping (e.g., Polyak et al, 2001Polyak et al, , 2004Jakobsson et al, 2010;Niessen et al, 2013;Dove et al, 2014), indicate differences between the LGM and PGM glaciations, with suggestions that the PGM/MIS 6 glaciation was one of the more extensive glacial episodes. Conversely, IRD from North America (Hudson Strait) does not seem to have reached the North Atlantic IRD belt during the penultimate glacial cycle (Obrochta et al, 2014), while it still occurred in the Labrador Sea, in close proximity to the eastern North American margin (Channell et al, 2012).…”