Peer review of: 3D sedimentary architecture showing the inception of an Ice Age (2020)

Reviewers' comments: 
 
Reviewer #1 (Remarks to the Author): 
 
This is an interesting paper utilizing a unique 3D seismic data set acquired due to the intense oil and gas 
exploration in the North Sea. It is nice to see this data set being used for paleoclimatic and 
sedimentological studies of this kind, and this study brings a more classical geological approach to 
supplement and improve the more general and standard approaches to derive the ice age history based 
on deep sea sediment records. The ability to draw on the unique seismic data brings different novel 
aspects of the development and inception of large-scale Northern Hemisphere glaciation to the table. It is 
therefore a unique and new contribution and despite elements of the story having been available before 
in various studies, this is a much more comprehensive and potentially important study. From this point of 
view I am positive to the paper being published, but have some reservations concerning the contents and 
its ability to communicate to a wide readership which leads me to suggest a relatively major revision 
before it can be published. 
 
More specifically: 
 
1. I am not happy with the use of greenhouse/icehouse jargon in this case. Undoubtedly there was a 
major expansion of NH ice sheets 2.7-2.6Ma, but to call the late Pliocene period immediately before this a 
greenhouse world is not very accurate, for several reasons: Since there are lots of evidence for and 
active NH cryosphere long before this time: e.g. the existence of a Greenland Ice Sheet for several 
million years, and IRD records that point to NH glaciation in the Arctic and Nordic Seas well back into the 
late Miocene. One may argue that a final step in the emergence of bipolar major glaciations happened 
around 2.6Ma, but the world had clearly evolved into an icehouse world long before this event. Existing 
CO2-records also indicate relatively low atmospheric concentrations leading into the glacial expansion, 
hence the greenhouse gas forcing had already been driving climate into a world of active cryospheric 
influence in both hemispheres. 
 
2. The paper deals with the Northern European and Eastern margin of the North Atlantic. Hence, to refer 
to this as the North Atlantic is misleading, in particular since the timing of glacial expansion may have 
been different across the North Atlantic, at least with respect to Greenland. The paper should be more 
precise in referring to the NE North Atlantic or NW European margin. 
 
3. The main weakness of the paper, which also impacts on its readability is the lack of discussion of 
timing and age control. There is a general lacking discussion of the age of the different units and the 
underlying age control and its uncertainties. To be published, this needs to be in place including giving 
numeric values of the time of the events and uncertainties (despite a few dates are indicated in Fig. 3). 
 
It would also help for the general readability if these events were placed into the global and regional deep 
sea evidence from O-isotopes and IRD-records. A discussion on the possible mechanisms behind the 
continued expansion of ice sheets/ice streams onto the shelves, e.g. general climatic and oceanographic 
causes vs changes in ice sheet dynamics due to the changing topography of the mountains and coastal 
regions due to glacial erosion. Here a mentioning of eustatic and isostatic influences would also be 
appropriate. I think the paper misses an opportunity to have a wider impact due to these deficiencies. 
4. The caption of fig. 3 includes discussion and arguments which should have appeared in the main text. I 
wonder why increased glaciation (line 385) would lead to more river flow. Build up of glaciers would 
normally lead to snow accumulation and less net freshwater flux. 
 
5. All in all I believe there is much in the paper and the evidence, and that the paper could be suitable 
after a revision following these suggestions. 
 

Reviewer #2 (Remarks to the Author): 
 
3D sedimentary architecture showing the inception of an Ice Age by Løseth, H., Dowdeswell, J.A., 
Batchelor, C.L. and Ottesen, D. 
 
The manuscript presents a study of the change in depositional setting at the transition from the Pliocene 
“greenhouse climate” to the Quaternary “icehouse” climate. The study is based mainly on high-resolution 
seismic data and access to I assume cutting samples from wells. There is no doubt that the study reveals 
morphological features in the North Sea that indicate a dramatic change. The Neogene succession 
fringing Scandinavia is generally characterized by shoreface-delta progradation each unit rarely exceed 
more than 200 m thickness. A pattern that have lasted since the initial uplift of Scandinavia in the early 
Miocene. Also, during this time frame, the sediment flux from Scandinavian were directed southward into 
the southeastern part of the North Sea. The study by Løseth and colleagues presents new morphological 
features, i.e., the submarine channel and debris-flow deposits. The size of the features presents in the 
study is not known from the Neogene succession in the North Sea. Furthermore, the marked westward 
progradation from Scandinavia as shown by the progradation of the Naust Formation indicate a totally 
new sediment routing system in the area. The height of the clinoformal package (>500 m) above the 
Base Naust Formation also indicate a remarkable change in the overall depositional setting of the North 
Sea Basin. 
 
Therefore, the interpretation presented in the manuscript is likely. The high quality of the seismic data 
reveals features that must be diagnostic for “green-icehouse” changes and consequently, of interest for a 
broader audience. 
 
I have attached my comments on the manuscript. There are a few sentences that needs rewriting in 
order to fulfil a high quality of the manuscript. 
 
 
Erik Skovbjerg Rasmussen