Journal of Quaternary Science New ins ights into the late Quaternary evolution of the Bristol Channel, UK Journal: Journal of Quaternary Science Manuscript ID JQS-16-0155.R1 Wiley - Manuscript type: Research Article Date Submitted by the Author: n/a Complete List of Authors: Gibbard, Philip; University of Cambridge, Cambridge Quaternary, Geography Hughes, Philip; The University of Manchester, School of Environment and Development Rolfe, Chris; University of Cambridge, Cambridge Quaternary, Geography Keywords: Glaciation, British Irish Ice Sheet, Fluvial, Glacial, Rivers http://mc.manuscriptcentral.com/jqs Page 1 of 38 Journal of Quaternary Science 1 2 3 4 School of Environment and Development 5 The University of Manchester 6 Oxford Road 7 Manchester M13 9PL 8 9 +44(0)161 306 1220 www.manchester.ac.uk 10 Friday 3rd March, 2017 11 12 13 Dear Professor Duller, 14 15 We have revised our manuscript entitled “New insights into the late Quaternary evolution of 16 the Bristol Channel, UK ” for publication in Journal of Quaternary Science. 17 18 We have revised the manuscript taking into account all comments by the two reviewers and you 19 as Editor. We provide details on these below. We would like to thank you and the reviewers for 20 the very useful comments and these have helped improve the manuscript. 21 22 23 We look forward to seeing this published in Journal of Quaternary Science. 24 25 26 Yours Sincerely 27 28 29 30 31 32 33 Dr. Philip Hughes 34 Reader in Physical Geography 35 36 [email protected] 37 38 39 40 Response to reviewer comments (our comments in red bold font ): 41 42 Reviewer 1 43 44 This is an interesting paper that forms a useful addition to the late Quaternary history of SW 45 England and South Wales and adjoining sea areas. The paper forms a good, general review that 46 47 will be of interest to a wide range of Quaternary scientists working in the area and fills 48 knowledge gaps in our understanding of the Quaternary history of South Wales, Lundy and the 49 SW Peninsula. I think it should be published following some relatively minor changes to the 50 manuscript. These are as follows: 51 52 1. The paper needs better context. It discusses the Quaternary history of land areas adjacent to 53 the Bristol Channel but misses out recent research and publications on these areas. For a start it 54 should cite the paper by Hubbard et al (2009) which produces numerical projections of ice sheet 55 extent from the IIS covering much of the SW. (Hubbard, A.L., Bradwell, T., Golledge, N., Hall, 56 57 A., Patton, H., Sugden, D., Cooper, R., Stoker, M. 2009. Dynamic cycles, ice streams and their 58 impact on the extent, chronology and deglaciation of the British–Irish ice sheet. Quaternary 59 Science Reviews 28 (7-8) pp. 758-776). The implications of these projections should be 60 discussed. http://mc.manuscriptcentral.com/jqs Combining the strengths of UMIST and The Victoria University of Manchester Journal of Quaternary Science Page 2 of 38 1 2 3 4 5 The papers by Evans et al on Dartmoor ice (QSR 2012) and on Exmoor ice by Harrison et al 6 (PGA 1998) should also be cited. 7 8 We have added in these references and also those suggested by the Editor and write: 9 10 “In a recent paper, Smedley et al. (2017) combined cosmogenic and optically stimulated 11 12 luminescence dating (OSL) to confirm the Late Devensian (MIS 2) age of glaciation at the 13 northern edge of the Isles of Scilly. This confirms predictions in a numerical model of 14 glaciation for the Devensian which projects ice over much of the Celtic Sea (Hubbard et 15 al. 2009). The model projections of Hubbard et al. (2009) also project ice into the Bristol 16 Channel and they note (p. 774) that “the experiments presented also indicate significant 17 excursions of wet-based ice into areas of southern England”. Independent ice masses have 18 also been suggested to have existed on Exmoor (Harrison et al. 1998) and Dartmoor 19 (Evans et al. 2012).” 20 21 22 Finally, the paper by Carr and Hiemstra on Lundy (2015 in Quaternary Newsletter) should also 23 be cited as evidence that the glacial story of Lundy is contested (around page 9 line 3), even if 24 you disagree with their views. 25 26 In the Introuduction we now add this “Despite the widely reported evidence of glaciation 27 in the Bristol Channel, Carr and Hiemstra (2015) still questioned the evidence for this in 28 the vicinity of Lundy, although with no basis.” 29 30 2. There are a few typos here and there: p 9 line 42: insert ‘in’ after glaciations. p 15 line 25: 31 32 insert ‘or’ after ‘one’. p 15 line 35: Explain ‘as low as 100m’. p 15 line 43: insert ‘the’ before 33 ‘English’. p 15 line 46: delete ‘in’. 34 35 Done 36 37 3. There could also be mention of the glacial (?) erratic on the south coast of Cornwall (e.g. 38 around Porthleven) in the context of the Quaternary history of the English Channel and Western 39 Approaches. 40 41 42 We have added a range of references to studies of erratic bouldres in the region: “Erratic 43 boulders have been noted in this area (Taylor 1956; Madgett & Inglis 1987) as well as 44 further south on the coast of Cornwall (Flett and Hill 1912; Ealey & James 2001).” 45 46 Reviewer 2 47 48 This manuscript presents a synthesis of newly-released borehole, bathymetric and other data 49 from the Bristol Channel. The study area is at a critical location for understanding British-Irish 50 glacial history as it lies close to the southern limit of at least two phases of ice-sheet advance. 51 52 These glaciations have been mainly documented onshore, so the availability of new offshore 53 data makes this paper a timely contribution to the topic. In general there is a current focus on 54 completing our understanding of the NW European glaciations by including evidence from the 55 shelf, so this is a welcome contribution to this broader focus. The work is well written and 56 includes data from a large number of sources. There are three areas where I suggest 57 improvements: 58 59 a) I would have liked to see a few more technical details about the datasets used, for example 60 the cell size of the EMODNet bathymetry (0.125 arc min or 230m?) and what data types http://mc.manuscriptcentral.com/jqs Combining the strengths of UMIST and The Victoria University of Manchester Page 3 of 38 Journal of Quaternary Science 1 2 3 4 exactly were available via the Atlantic Array Project. Similarly I would be surprised if the 5 EDINA bathymetric grid is at 10 m (I thought it was 30 m), and if so why wasn’t that used for 6 the zoom-ins rather than EMODNet! Similarly I found it difficult to follow the 7 sedimentological argument presented in section 4.2.1 without being able to see the locations of 8 the boreholes relative to the bathymetric moraines on a map. Perhaps all the boreholes could be 9 marked and colour coded according to thickness of glacial deposits? 10 11 12 We have clarified the EMODNet data (0.125 arc min) and changed the caption to Fig. 1 – 13 it is based on EMODNet. We have added an inset map to the borehole figure. We didn’t 14 go for colour coding as the new inset map should help and thickness is indicated on the 15 borehole scales. 16 17 b) I found the main results (section 4) a little dense. I wonder if a few “sign-post sentences” 18 could be added to help guide the more general reader through it and better capture the key 19 points of the argument. Something like what is written at the start of the discussion would be 20 ideal. 21 22 23 We have added text introducing each section now to make it clearer. 24 25 c) At the start of the discussion itself I would have liked to see a slightly clearer 26 acknowledgement of what the new (post 2010 or so) data has contributed. Whilst I understand 27 this study relies on integrating all available data, it would be useful to see what couldn’t have 28 been resolved before and so give encouragement (or otherwise) to re-look at other areas. 29 30 We have added this text: 31 32 33 “The recently available high-resolution bathymetric, borehole and geophysical data from 34 the floor of the Bristol Channel has allowed for new analysis of the seafloor topography 35 and Quaternary geology. This has revealed new information on the fluvial and glacial 36 history of the Bristol Channel, especially evidence for glaciation and the former course of 37 the River Severn.” 38 39 In the comparison between the Bristol and English Channels, I didn’t understand why the 40 additional deepening of the English Channel River was attributed to tidal scouring (Page 15, 41 42 line 43-48), when in the next paragraph the existence of mega-flooding was acknowledged. 43 44 We have added in both to read “In the English Channel the valley extends to depths twice 45 that in the Bristol Channel, possibly a consequence of the tidal scour during 46 transgressions and also catastrophic flooding events.” 47 48 Small points 49 50 We have done all of these. Some edits have comments from us.