Environmental variability off NE Greenland (western Fram Strait) during the past 10,600 years

Abstract

To reconstruct the climatic and paleoceanographic variability offshore Northeast Greenland during the last ~10 ka with multidecadal resolution, sediment core PS93/025 from the outermost North-East Greenland continental shelf (80.5°N) was studied by a variety of micropaleontological, sedimentological and isotopic methods. High foraminiferal fluxes, together with high proportions of ice-rafted debris and high Ca/Fe ratios, indicate a maximum in bioproductivity until ~8 ka related to a low sea-ice coverage. Sortable silt values, planktic foraminifer associations, and stable isotope data of planktic and benthic foraminifers suggest a strong westward advection of relatively warm Atlantic Water by the Return Atlantic Current during this time, with a noticeable bottom current activity. This advection may have been facilitated by a greater water depth at our site, resulting from postglacial isostatic depression. For the following mid-Holocene interval (ca. 8–5 ka), isotope data, lower foraminiferal fluxes and a shift in grain size maxima point to a lasting but successively decreasing Atlantic Water inflow, a weakening productivity, and a growing sea-ice coverage which is also revealed by the PIIIIP25 index. A final stage in the environmental development was reached at ~5 ka with the establishment of pre-industrial conditions. Low Ca/Fe ratios, low foraminiferal fluxes, low sortable silt values and the sea-ice indicating PIIIIP25 index point to a limited productivity and a weak Atlantic Water inflow by the Return Atlantic Current to our research area, as well as a higher and/or seasonally more extended sea-ice coverage during the Late Holocene. Two intervals with somewhat enhanced Atlantic Water advection around 2.0 and 1.0 ka are indicated by slightly increased foraminiferal fluxes and the reoccurrence of subpolar foraminifers. These intervals may correlate with the Roman Warm Period and the Medieval Climate Anomaly, as defined in the North Atlantic region.

Holocene Interactions Between Glacier Retreat, Sea Ice Formation, and Atlantic Water Advection at the Inner Northeast Greenland Continental Shelf

“…Together with the disintegration of NØIB, it is assumed that the reduced buttressing effect on the ice shelf would have encouraged increased ice discharge due to the speed up of 79NG and ZI, facilitating rapid ice margin disintegration and glacier retreat. Results of Core PS100/270 correspond well to model simulations by Dyck et al (2010) and other paleoclimate reconstructions from the outer NEG continental shelf (PS93/025) which infer a general decrease of sea ice concentrations during the early HTM, driven by the combination of an atmospheric and ocean forcing (Figure 11; Syring et al, 2020; Zehnich et al, 2020).…”

“…However, the presence of Stetsonia horvathi and Glomulina oculus through this interval also supports the interpretation of more extensive sea ice during this interval (both species commonly found in regions influenced by a high concentration of sea ice, for example, Jennings et al, 2020; Wollenburg & Mackensen, 1998). Continuing high but variable AW advection toward the NEG continental shelf until about 8 ka is also recorded in the assemblages and isotope data of foraminifers at Core PS93/25 (Zehnich et al, 2020) as well as Core PS1230 (Bauch et al, 2001). This would potentially encourage relatively high rates of basal melting of the floating ice tongue of 79NG glacier and at the grounding line.…”

“…Rising air temperatures (~8°C warmer than preindustrial level, NEEM ice core record) and sea surface temperatures (2–5°C), may have forced an earlier nearly complete seasonal breakup of the local NØIB probably starting already in April/May (which is comparable to the present‐day situation at the end of July) (Figure 1c; Andersen et al, 2004; Bauch et al, 2001; Bendle & Rosell‐Melé, 2007; Buizert et al, 2018; Rimbu et al, 2003; Zehnich et al, 2020). This is evidenced by high IP 25 concentrations and accumulation rates, suggesting increased sea ice breakup, thinning, and local drifting of NØIB ice floes.…”

“…A strong westward advection of AW onto the NEG continental shelf at that time is also reflected in the assemblages and isotope data of planktic and benthic foraminifers determined at the nearby Core PS93/025 (Zehnich et al, 2020). The increased AW influence probably caused relatively high levels of basal melting at the grounding line or of any ice shelf present within Norske or Westwind Troughs.…”

“…Meanwhile, rising air temperatures resulted in intensified surface melt of the GIS (MacGregor et al, 2016), while regional records show a strengthened West Spitsbergen Current at this time (Jennings et al, 2011), potentially increasing the flux of recirculating AW onto the NEG continental shelf within the Return Atlantic Current (RAC) (Bauch et al, 2001; Evans et al, 2009; Schaffer et al, 2020; Zehnich et al, 2020). Indeed, this is supported by the dominance of the benthic foraminifera, Cassidulina neoteretis (Figures 7 and 8), typically indicating presence of AW (e.g., Hald & Korsun, 1997) , within the lower section of the laminated unit immediately after the transition from the subglacial till.…”