Commentary: Glacial history and depositional environments in little Storfjorden and Hambergbukta of Arctic Svalbard since the younger dryas
Riko Noormets
Nina Kirchner- 1Department of Arctic Geology, University Centre in Svalbard, Longyearbyen, Norway
- 2Department of Physical Geography and Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
A Commentary on
Glacial history and depositional environments in little Storfjorden and Hambergbukta of Arctic Svalbard since the younger dryas
by Joe YJ, Jang K, Forwick M, Laberg JS, Kong GS, Kang M-H, Yoon S-H and Nam S-I (2022). Front. Earth Sci. 10:1017594. doi: 10.3389/feart.2022.1017594
Introduction
In their paper “Glacial history and depositional environments in the Little Storfjorden and Hambergbukta of Arctic Svalbard since the younger dryas”, Joe et al. (2022) suggest that the Terminal Moraine Complex (TMC) at the mouth of the Hambergbukta was formed during the Little Ice Age (LIA). This conclusion is based on analysis of a sediment core from the Little Storfjorden approximately 4 km east of the crest of the TMC and a few multibeam bathymetric and subbottom acoustic profiles in the central part of the TMC. We agree with Joe et al. (2022) that the age range of the TMC formation is poorly constrained. This comment highlights prominent features of the TMC which, in our opinion, are incongruous with formation during LIA advances. The analysis of these features by Joe et al. (2022) has resulted in an incomplete assessment of the morphology and structure, and consequently the formation of the part or the whole of the TMC during the LIA.
Discussion
Important features in this context are the debris flows on the distal flank of the TMC. The sedimentary architecture of the distal flank of the TMC and the total number of debris flows stacked there is unknown because of the limited coverage and insufficient penetration depth of the subbottom acoustic data. However, at least three sets of partially overlapping and cross-cutting debris flow lobes suggest that the Hambergbreen glacier has reached the TMC several times since the initial formation (Figure 1). Based on acoustic data from one debris flow lobe and associated sediment core analyses, Joe et al. (2022) suggest that the formation of the entire TMC took place during a LIA advance of the Hambergbreen glacier. A LIA advance alone, however, does not explain the complex architecture of the multiple large debris flow lobes, let alone the formation of the entire TMC.
FIGURE 1. Oblique view of the Hambergbukta Terminal Moraine Complex (TMC) from southeast based on data in Noormets et al. (2016; Noormets et al. (2021). Possible debris flow lobe on the distal flank of the LIA end moraine is marked with red dotted line. Asterisks (*) mark the flattened crest areas and terraces at multiple depth levels on the distal flank of the TMC. DFL-1, DFL-2 and DFL-3 mark the different generations of debris flow lobes (from oldest to youngest) displaying their overlapping and cross-cutting relationship.
Furthermore, based on subbottom acoustic profile linking the core 905 to one of the debris flow lobes, Joe et al. (2022) suggest that the Facies F-4C is superimposed by the debris flow lobe Facies F-1B (Figure 4 in Joe et al., 2022). However, this subbottom acoustic profile shows change from undisturbed, basin in-fill type of layering at the core site in the Little Storfjorden to clearly disturbed sediments near the TMC. These sediments possibly reflect debris flow and iceberg scour processes, as evidenced by iceberg ploughmarks highlighted by Joe et al. (2022). The criteria for tracking seismic reflectors through the disturbed sediments of the TMC remains unjustified, nor is this correlation permissive, with likely palimpsesting arrangement of stacked deposits, from multiple glacier advances and retreats.
We also indicate the insufficient vertical resolution of the subbottom acoustic data that do not permit reliably linking the key lithological units to seismic facies. For example, the lithological unit corresponding to Facies F-4C at the top of the core 905 is a 12 cm thick layer of glaciomarine deposits with suggested age of ca. 0.4 ka (Figure 7 in Joe et al., 2022). Due to the vertical resolution limitations of the subbottom acoustic data, the authors acknowledge that “The strong surficial reflector of F-4C presumably includes the Facies 4 and uppermost parts of Facies 3, which might have been deposited since approximately 1 ka”. This age uncertainty is inconsistent with the conclusion by Joe et al. (2022) regarding the LIA formation of the TMC and the debris flow lobe. Moreover, considering that the suggested ages in the upper half of the core are interpolated ages based on single radiocarbon date of ca. 0.6 ka from a shell fragment at 19–20 cm core depth, the age of the seismic reflector marking the base of the debris lobe has large uncertainty. This implies that the debris flow lobe could be considerably older than approximately 1 ka, pre-LIA in age, counter to Joe et al. (2022). It is also noteworthy that an increasing number of such terminal moraines in Svalbard, generally assumed to be from LIA (cf. Lefauconnier and Hagen, 1991), have been shown to be significantly older than LIA by later studies (Kempf et al., 2013; Farnsworth et al., 2018; Flink et al., 2018; Flink and Noormets, 2018; Dowdeswell et al., 2020 and references therein). However, local reshaping of these moraines by later glacier advances, including during LIA, cannot be excluded.
Another feature, which is incongruent with the LIA formation of the TMC and the debris flow lobes on its distal flank, is the prominent flattened crest areas and multiple terraces (Figure 1). These features can also be seen in Joe et al. (2022) in their Figures 3–5 and in the first panel of table 2. Previous analysis suggests that these features were eroded by large tabular icebergs with plane bases originating outside of Hambergbukta because there are no similar features in the fjord or proximal flank of the TMC (Noormets et al., 2016). It is noteworthy that Hambergbukta TMC is the only one among several tens of similar terminal moraines identified offshore of Svalbard (cf. Ottesen et al., 2017; Dowdeswell et al., 2020) that exhibits clear flattened crests and terraces, hence implying a nearby source of large tabular icebergs with minimum drafts of 70 m. This keel depth, required to rework the TMC, is far too deep for a nearby LIA source considering that the glacio-isostatic rebound has been marginal since the LIA and only approximately 2 m during the last c. 2,700 years in southern Spitsbergen (Ziaja and Salvigsen, 1995). The limiting shallow depth of the inner Storfjorden and of the submarine Mid-ridge between the Storfjorden and Little Storfjorden (Nielsen and Rasmussen, 2018; Svalbard Navigational Charts, 2020) would have prevented the icebergs with keel depths greater than approximately 50–60 m reaching the Hambergbukta TMC during the LIA. Thus, there was no obvious source for tabular icebergs with keel depth reaching approximately 70 m to explain the formation of terraces at Hambergbukta TMC during and post LIA. However, considering the northwards increasing gradient of glacio-isostatic response of the Storfjorden area (Salvigsen and Mangerud, 1991; Bondevik et al., 1995; Forman et al., 2004 and references therein), the glaciers would have been able to produce icebergs with required keel depth to rework the TMC earlier in the Holocene. Also, the large Storfjorden ice stream (or potentially ice shelf) during the deglaciation (cf. Nielsen and Rasmussen, 2018) within a short distance from the Hambergbukta TMC could well have produced such icebergs suggesting considerably earlier time than the LIA for formation of the TMC.
Joe et al. (2022) also state that the lack of debris flow lobes on the distal flank of the LIA end moraines suggested by Noormets et al. (2021) indicates their non-terminal morainal structure. This assertion does not acknowledge that surge end moraines have been documented without associated debris flow lobes (cf. Flink et al., 2015). Moreover, a closer inspection of bathymetric data indicates presence of a sediment lobe emanating from southern part of a clear moraine form and may be a debris flow lobe associated with the formation of the surge end moraine (Figure 1).
The increased content of IRD in the top 10–12 cm of the sediment core in the Little Storfjorden may reflect the increased glacier (surge) activity in Hambergbukta and in the other fjords in the area as Joe et al. (2022) suggest. Numerous studies have also linked IRD content variations in fjord sediments to ice sheet dynamics, glacier activity, ocean circulation as well as sea ice and iceberg processes (cf. Szczucinski et al., 2009; Fransner et el., 2017; Allaart et al., 2020; Rasmussen and Thomsen, 2021). However, Joe et al. (2022) conclusion that the increase in IRD is evidence for the broader formation of the TMC during LIA, has according to our knowledge not been supported by studies across Svalbard.
In summary, considering the oversight of the complex structure of the multiple debris flow lobes and flattened crest and terraces of the TMC, the insufficient resolution for seismic stratigraphic correlations within debris flow deposits, particularly with subsequent disturbance with iceberg scouring, and the uncertainties arising from the age interpolation of the top part of the sediment core, the conclusions about the processes and age of the TMC formation are premature. The complexity of the Hambergbukta TMC suggests that it was probably formed and modified during multiple glacier advances and retreats post the Younger Dryas chronozone similarly to many other terminal moraines in Svalbard (cf. Kempf et al., 2013; Farnsworth et al., 2018; Flink et al., 2018; Flink and Noormets, 2018; Dowdeswell et al., 2020 and references therein). The number and timing of advances of Hambergbreen (and other glaciers in Svalbard) since the deglaciation after the LGM requires detailed morphological and sedimentological studies of the terminal moraine complexes, and better age control of individual features within them.
Author contributions
RN and NK have contributed equally to the analysis and writing of this commentary. All authors contributed to the article and approved the submitted version.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Keywords: Svalbard, Hambergbukta, deglaciation, Holocene, terminal moraine, glacier surge, multibeam bathymetry, shallow seismic stratigraphy
Citation: Noormets R and Kirchner N (2023) Commentary: Glacial history and depositional environments in little Storfjorden and Hambergbukta of Arctic Svalbard since the younger dryas. Front. Earth Sci. 11:1186972. doi: 10.3389/feart.2023.1186972
Received: 15 March 2023; Accepted: 22 May 2023;
Published: 01 June 2023.
Edited by:
Xingqi Liu, Capital Normal University, ChinaReviewed by:
Steven L. Forman, Baylor University, United StatesCopyright © 2023 Noormets and Kirchner. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Riko Noormets, Riko.Noormets@unis.no