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Holocene paleoceanographic development in the Petermann Fjord and growth of the Petermann Ice Tongue based on analysis of lithofacies, grain size properties and foraminifers in OD1507 cores

Jennings, Anne E. 1 ; Reilly, Brendan T. 2 ; Andrews, John T. 3 ; Bailey, Ethan 4 ; Mix, Alan 5 ; Stoner, Joseph 6 ; Walczak, Maureen 7 ; Dyke, Laurence 8

1 INSTAAR, University of Colorado
2 COAS, Oregon State University
3 INSTAAR, University of Colorado
4 INSTAAR, University of Colorado
5 COAS, Oregon State University
6 COAS, Oregon State University
7 COAS, Oregon State University
8GEUS

During marine research expedition OD1507 with Swedish icebreaker Oden in summer 2015, a.k.a. Petermann 2015 Expedition, we collected sediment cores and surface samples from Petermann Fjord, including cores obtained from beneath the modern ice tongue. The Petermann Ice Tongue had extended to the outer fjord since at least 1876, as observed during the Nares Expedition. However, large calving events in 2010 and 2012 reduced the ice tongue to c. 50 km, highlighting its vulnerability to changing ocean and sea-ice conditions (Münchow et al., 2016; Shroyer et al., 2017). The calving events also made it possible to take geophysical data and sediment cores in the middle to outer fjord. In addition, the British Antarctic Survey hot water drill was used to access the seabed beneath the ice tongue allowing sediment cores to be taken at two sub ice tongue sites. We use CT (computed tomography) imaging, sediment grain size, and foraminiferal assemblage analysis of core OD1507-03UW from beneath the modern ice tongue, on a sill at 570 m wd and 25 km from the grounding line of Petermann Glacier, and composite core OD1507-3TC/41GC/3PC from the outer fjord, 991 m wd, near the edge of the ice tongue pre 2010, to assess the environmental changes in the fjord from the early middle Holocene to the present. We ask in particular, ‘when did the Petermann ice tongue form and when did it extend to the outer fjord’; and ‘what sea ice and ocean conditions were associated with the ice tongue history and in the position of the grounding line of the Petermann Glacier?’ Three radiocarbon dates on benthic foraminifers from the outer fjord core confirm that it contains at least the last c. 7180 radiocarbon years; two radiocarbon date samples have been submitted from core 03UW and two additional dates have been submitted from the outer fjord core. Marine reservoir corrections are under study and no reservoir corrections have been applied to the radiocarbon dates presented here.
Modern sub-ice tongue sediments from the sill (core 03UW) are bioturbated and characterized as very poorly sorted, very fine to medium silt with rare or absent material >100 µm, whereas sediments in core 05UW, from a basin 15 km in front of the grounding line lack coarse material (IRD) and are strongly laminated. Grain size analysis of specific laminae show particle size distributions ranging from fine sand to fine silt. Foraminifers in the upper 2 cm of sediments beneath the ice tongue occur in low abundances and are very small, but living specimens of many species suggest that fauna beneath the ice tongue are sustained by food advected beneath the ice tongue by ocean currents. Multicore tops distributed in the fjord have abundant, diverse fauna with Stetsonia horvathi (a perennial sea-ice indicator) being the most abundant species near the modern ice tongue front while Elphidium excavatum (glacial marine indicator) and Cassidulina neoteretis (chilled Atlantic Water/stratified water column indicator) dominate the assemblages in the outer fjord. The outer fjord core has 4 main units defined on lithofacies and foraminifera. The deepest unit comprises glacial marine diamicton and laminated sandy mud with faunal assemblages dominated by C. neoteretis, E. excavatum and Epistominella arctica indicating glacial marine conditions arising from ice retreat by calving through the deep outer fjord during the early part of the middle Holocene. An overlying unit of fine to medium silt with IRD and abundant benthic and planktic foraminifers is interpreted to represent a period of a tidewater glacier (no ice tongue) grounded behind the inner fjord sill, and high productivity in the fjord associated with seasonal sea ice between c. 7180 and 4080 radiocarbon years BP. Based upon the lithofacies and foraminiferal stratigraphy, the inner fjord core, O3UW, captures the end of this high productivity interval in its basal 20 cm. Shortly after 4080 radiocarbon years BP, grain size characteristics reflect growth of the ice tongue but the consistent presence of rare ice rafted clasts suggests that the ice tongue had not extended over the core sites. Planktic foraminiferal abundances decline and benthic foraminfers are dominated by S. horvathi suggesting expanded sea ice and cooling after 4080 radiocarbon years BP. The uppermost unit of laminated mud devoid of IRD begins after c. 2580 radiocarbon years BP and continues to the present. This unit intersects the modern environment of an extensive ice tongue near the mouth of Petermann Fjord and associated low marine productivity. A radiocarbon date in 03UW immediately below the boundary will help to refine the timing of ice tongue expansion.

This research is funded by National Science Foundation PLR-ANS 1417784.

Münchow, A., Washam A.P., Padman L, Nicholls K., 2016, The ice shelf of Petermann Gletscher, North Greenland and its connection to Arctic and Atlantic oceans: Oceanography, v. 29(4), p. 34-45. doi: 10.1017/jog.2016.140

Shroyer, E.L., Padman, L., Samelson, R.M., Münchow, A., Stearns, L.A., 2017, Seasonal control of Petermann Gletscher ice-shelf melt by the ocean’s response to sea-ice cover in Nares Strait: Journal of Glaciology, v. 63(238), p. 324–330.

 

 

 

 

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