DOI: 10.5061/dryad.p5hqbzkx8
title: Data from: Sea ice choke points reduce the length of the shipping season in the Northwest Passage

description: Arctic sea ice has shifted from a perennial (older, thicker ice) to a
 seasonal (younger, thinner) ice regime, leading to the increasingly common
 belief that shipping through Canada’s Northwest Passage is becoming more
 viable. Here, we use the Risk Index Outcome values derived from the Polar
 Operational Limit Assessment Risk Indexing System and analyze recent
 changes to shipping season lengths along individual sections of the
 Northwest Passage routes from 2007 to 2021. Results show that multi-year
 ice flushed southward from high-latitude regions maintains the so-called
 choke points along certain route sections, reducing overall shipping
 season length. There is considerable spatiotemporal variability in
 shipping season lengths along the southern and northern routes.
 Specifically, parts of the northern route exhibit a decrease of up to 14
 weeks over the 15 years. The variability of shipping season and, in
 particular, the shortening of the season will impact not only
 international shipping but also resupply and the cost of food in many
 Arctic communities, which require a prompt policy response.
description: # Data from: Sea ice choke points reduce the length of the shipping season
 in the Northwest Passage
 [https://doi.org/10.5061/dryad.p5hqbzkx8](https://doi.org/10.5061/dryad.p5hqbzkx8) These files are the data we generated, analysed, and used resulting in the figures in the Nature Communications Earth & Environment manuscript associated with these files. The datasets contain shipping season lengths in weeks (2007-2021) at 10 km intervals along the four Northwest Passage shipping routes (route locations are shown in the manuscript Figure 2a). The values were derived from weekly Canadian Ice Charts that we converted to Risk Index Outcome (RIO) values using The International Maritime Organization’s Polar Operational Limit Assessment Risk Indexing System (POLARIS), and derived annual shipping season lengths in weeks where RIO &gt;=0, for ships across a range of different ice strengths. The files are spreadsheets of shipping season lengths along the four shipping routes: NWP-S, NWP-N1, NWP-N2, and Prince Regent Inlet. They include the mean shipping length at three 5-year time intervals for ships with four ice strengths; early, mid, and late season length at three 5-year time intervals; annual season lengths along all four shipping routes for PC7 ships; annual season lengths for 4 sections of the routes that have statistically significant changes, for ships of four different ice strengths. ## Description of the data and file structure File details: ### 1\_NWP\_FullSeasonLength\_5YrMeans.xls: Each worksheet in this spreadsheet is for ships of different ice strengths: PC3 (high strength), PC7 (medium strength), 1B (low ice strength), and NonIS (Not Ice Strengthened). Each worksheet contains the mean shipping full season length across three 5-year intervals: 2007-2011 (Column E), 2012-2016 (Column F), 2017-2021 (Column G), at every 10 km (Column C) along the Northwest Passage ship routes. The ship route names (Column B) refer to the labelled routes in Figure 2a. These data are used for the graphs in Figure 2b in our published manuscript. ### 2\_NWP\_EarlySeasonLength\_5YrMeans.xls Each worksheet in this spreadsheet is for ships of different ice strengths: PC3 (high strength), PC7 (medium strength), 1B (low ice strength), and NonIS (Not Ice Strengthened). Each worksheet contains the mean shipping early season length across three 5-year intervals: 2007-2011 (Column E), 2012-2016 (Column F), 2017-2021 (Column G), at every 10 km (Column C) along the Northwest Passage ship routes. The ship route names (Column B) refer to the labelled routes in Figure 2a. Early season refers to the 8 weeks over June and July. These data are used for the graphs in Figure 3a in our published manuscript. ### 3\_NWP\_MidSeasonLength\_5YrMeans.xls Each worksheet in this spreadsheet is for ships of different ice strengths: PC3 (high strength), PC7 (medium strength), 1B (low ice strength), and NonIS (Not Ice Strengthened). Each worksheet contains the mean shipping mid-season length across three 5-year intervals: 2007-2011 (Column E), 2012-2016 (Column F), 2017-2021 (Column G), at every 10 km (Column C) along the Northwest Passage ship routes. The ship route names (Column B) refer to the labelled routes in Figure 2a. Mid-season refers to the 8 weeks in August and September. These data are used for the graphs in Figure 3b in our published manuscript. ### 4\_NWP\_LateSeasonLength\_5YrMeans.xls Each worksheet in this spreadsheet is for ships of different ice strengths: PC3 (high strength), PC7 (medium strength), 1B (low ice strength), and NonIS (Not Ice Strengthened). Each worksheet contains the mean shipping late season length across three 5-year intervals: 2007-2011 (Column E), 2012-2016 (Column F), 2017-2021 (Column G), at every 10 km (Column C) along the Northwest Passage ship routes. The ship route names (Column B) refer to the labelled routes in Figure 2a. Late season refers to the 8 weeks of October and November. These data are used for the graphs in Figure 3c in our published manuscript. ### 5\_NWP\_PC7\_4Sections\_AnnualSeasonLengths.xls This workbook contains data for PC7 (medium ice strength) ships. The data for the four individual sections of the route that are statistically significant and used to produce graphs in Figure 4 in our published manuscript are shown in individual worksheets. Each worksheet contains the annual full shipping season, early season (June-July), mid-season (August-September), and late season (October-November) shipping season lengths along individual sections of the Northwest Passage ship routes, at every 10 km interval. The ship route names (Column B) refer to the labelled routes in Figure 2a. The season lengths in weeks are listed for each year in columns E (2007) to S (2021). ### 6\_NWP\_NonIS\_4Sections\_AnnualSeasonLengths.xls This workbook contains data for NonIS (non ice-strengthened) ships. The data for the four individual sections of the route that are statistically significant and used to produce graphs in Figure 5 in our published manuscript are shown in individual worksheets. Each worksheet contains the annual full shipping season, early season (June-July), mid-season (August-September), and late season (October-November) shipping season lengths along individual sections of the Northwest Passage ship routes, at every 10 km interval. The ship route names (Column B) refer to the labelled routes in Figure 2a. The season lengths in weeks are listed for each year in columns E (2007) to S (2021). ### 7\_NWP\_PC7\_AllRoutes\_AnnualSeasonLengths.xls This workbook contains data for PC7 (medium ice strength) ships. This dataset is the annual full shipping season length in weeks, at every 10 km interval along the Northwest Passage ship routes. The ship route names (Column B) refer to the labelled routes in Figure 2a. The season lengths are listed for each year in columns E (2007) to S (2021). These data are used for the graph in Supplementary Figure 1 in our published manuscript. ### 8\_NWP\_1B\_4Sections\_AnnualSeasonLengths.xls This workbook contains data for 1B (low ice strength) ships. The data for the four individual sections of the route that are statistically significant and used to produce graphs in Supplementary Figure 5 in our published manuscript are shown in individual worksheets. Each worksheet contains the annual full shipping season, early season (June-July), mid-season (August-September), and late season (October-November) shipping season lengths along individual sections of the Northwest Passage ship routes, at every 10 km interval. The ship route names (Column B) refer to the labelled routes in Figure 2a. The season lengths in weeks are listed for each year in columns E (2007) to S (2021). ### 9\_NWP\_PC3\_4Sections\_AnnualSeasonLengths.xls This workbook contains data for PC3 (high ice strength) ships. The data for the four individual sections of the route that are statistically significant and used to produce graphs in Supplementary Figure 6 in our published manuscript are shown in individual worksheets. Each worksheet contains the annual full shipping season, early season (June-July), mid-season (August-September), and late season (October-November) shipping season lengths along individual sections of the Northwest Passage ship routes, at every 10 km interval. The ship route names (Column B) refer to the labelled routes in Figure 2a. The season lengths in weeks are listed for each year in columns E (2007) to S (2021). ## Sharing/Access information Data was derived from the following sources: Historical Canadian Ice Service weekly ice charts which are freely available on [https://iceweb1.cis.ec.gc.ca/Archive/](https://iceweb1.cis.ec.gc.ca/Archive/). The POLARIS RIO data (2007-2021) generated from these charts for our research study is accessible on the Environment and Climate Change Canada data server: [https://crd-data-donnees-rdc.ec.gc.ca/CPS/products/CIS_POLARIS_RIO/](https://crd-data-donnees-rdc.ec.gc.ca/CPS/products/CIS_POLARIS_RIO/) Contact Alison Cook with questions on usage or additional details about the data ([alison.cook@sams.ac.uk](mailto:alison.cook@sams.ac.uk)). The authors kindly ask that you use the following citation: Cook, A. J., *et al*. Sea ice choke points reduce the length of the shipping season in the Northwest Passage, *Nature Comms Earth and Environ.* (2024)