Holocene sea-ice dynamics in Petermann Fjord in relation to ice tongue stability and Nares Strait ice arch formation

Abstract

Abstract. The Petermann 2015 expedition to Petermann Fjord and adjacent Hall Basin recovered a transect of cores, extending from Nares Strait to underneath the 48 km long ice tongue of Petermann glacier, offering a unique opportunity to study ice–ocean–sea ice interactions at the interface of these realms. First results suggest that no ice tongue existed in Petermann Fjord for large parts of the Holocene, raising the question of the role of the ocean and the marine cryosphere in the collapse and re-establishment of the ice tongue. Here we use a multi-proxy approach (sea-ice-related biomarkers, total organic carbon and its carbon isotopic composition, and benthic and planktonic foraminiferal abundances) to explore Holocene sea ice dynamics at OD1507-03TC-41GC-03PC in outer Petermann Fjord. Our results are in line with a tight coupling of the marine and terrestrial cryosphere in this region and, in connection with other regional sea ice reconstructions, give insights into the Holocene evolution of ice arches and associated landfast ice in Nares Strait. The late stages of the regional Holocene Thermal Maximum (6900–5500 cal yr BP) were marked by reduced seasonal sea ice concentrations in Nares Strait and the lack of ice arch formation. This was followed by a transitional period towards Neoglacial cooling from 5500–3500 cal yr BP, where a southern ice arch might have formed, but an early seasonal breakup and late formation likely caused a prolonged open water season and enhanced pelagic productivity in Nares Strait. Between 3500 and 1400 cal yr BP, regional records suggest the formation of a stable northern ice arch only, with a short period from 2500–2100 cal yr BP where a southern ice arch might have formed intermittently in response to atmospheric cooling spikes. A stable southern ice arch, or even double arching, is also inferred for the period after 1400 cal yr BP. Thus, both the inception of a small Petermann ice tongue at ∼ 2200 cal yr BP and its rapid expansion at ∼ 600 cal yr BP are preceded by a transition towards a southern ice arch regime with landfast ice formation in Nares Strait, suggesting a stabilizing effect of landfast sea ice on Petermann Glacier.

Petermann ice shelf may not recover after a future breakup

“…Our simulations imply that a plausible explanation for the historic re-establishment of Petermann Glacier Ice Shelf was an ocean cooling combined with reduced calving. In light of empirical reconstructions 16 , 41 and our modelling results, the following scenario seems plausible: (1a) Before 2100 yrs BP, a relatively warm ocean and vigorous calving regime prevented ice-shelf growth in Petermann Fjord; (1b) after 2100 yrs BP, an ocean cooling occurs, which in theory allows for an extensive ice shelf. Due to the difficulty to trigger recovery with an ocean cooling alone (Figs.…”

“…These changes may have been accompanied by an ocean cooling similar to what we impose in our experiments. This connection between ocean and sea ice is seen also under modern conditions, as sea ice modifies the ocean circulation in Nares Strait 41 , 42 . Specifically, landfast sea ice weakens the inflow of warm Atlantic Water into Petermann Fjord 42 , while more mobile sea ice is associated with increased warm-water inflow.…”

“…Due to the difficulty to trigger recovery with an ocean cooling alone (Figs. 1 c and 2 a, b), regrowth of the ice shelf is, however, marginal; (2) at 1400 years BP a regime shift towards modern conditions occurs, with landfast sea ice in Nares Strait (see Section “Sea-ice induced advance of ice shelves” 41 ); (3) a sustained weakened oceanic heat flux 42 favours sea-ice growth, dampens calving and allows for regrowth of the ice shelf to present-day conditions at c. 600 years BP (cf. Fig.…”

“…This hypothesis is supported by reconstructions of sea-ice and ocean conditions over the Holocene. Based on marine sediment cores and multiple sea-ice proxies, Detlef et al 41 suggest that changes in sea-ice conditions in the Nares Strait offshore of Petermann Fjord coincide with the reconstructed regrowth of Petermann Glacier Ice Shelf during the late Holocene (see Section “Geological support for past Petermann regime transitions” above; ref. 16 ).…”

Impact of freshwater runoff from the southwest Greenland Ice Sheet on fjord productivity since the late 19th century

“…340 3). In general, TOC and BSi values point to a relatively high productivity in Nuup Kangerlua throughout the 20 th century, when compared to modern values from other coastal Arctic sites (e.g., Ribeiro et al, 2017;Limoges et al, 2018a;Kumar et al, 2016, Detlef et al, 2021. Similarly, high values have been observed on the northwest Greenland shelf during the Holocene when climate conditions were favorable for high primary production (Limoges et al, 2020;Saini et al, 2020;Ribeiro et al, 2021).…”